Chapter Two Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 33 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Chapter Two Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.1 Introduction This chapter describes the synthesis and the coordination chemistry of the pincer complex [PdCl(PCP)] (PCP = -CH(CH2CH2PPh2)2) 2.1. Electrospray Ionisation Mass Spectrometry (ESI-MS) has been used as a tool to investigate the formation and ligand replacement reactions of complex 2.1. An introduction of the application of ESI-MS in coordination chemistry is given here. Electrospray as an ionisation source for mass spectrometry was developed in the late 1960s by Dole and co-workers.84 This ionisation source was coupled to a quadrapole mass spectrometer in 1984 by Fenn and co-workers.85 They have demonstrated the ability of ESI-MS to analyse thermally fragile polar molecules such as proteins.86 Fenn was awarded the 2002 Nobel Prize for chemistry for his contribution.87 ESI-MS has been widely used to study the solution chemistry of coordination compounds.88 It serves as a tool to identify new products,89 to monitor chemical reactions90 and to study the coordination chemistry of metal complexes.91 This technique allows for direct sampling of the solution mixture and therefore in situ studies can be carried out more easily. Apart from that, the 34 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex compounds that are problematic for analysis using NMR spectroscopy, due to the paramagnetism or the lack of NMR active nuclei, can be analysed without any difficulty. However, it is important to note that mass spectrometry has its own limitations.88a The compounds under study are normally charged compounds or compounds that are readily ionised. This technique is also sensitive to the contaminants such as Na+, K+ and Ag+ metal ions or the compounds which have good ionisation efficiency (such as PPh4+ and (PPh3)2N+) that may be present in the capillary system. It also offers less structural information compared to the NMR techniques. The solutions that contain isomers of the same m/z ratio are not easily differentiated. This might lead to confusion in the interpretation of mass spectra. Therefore, a combination of a range of techniques is often required to give a complete picture of the compound under study. This work was motivated by the power of ESI-MS in the study of the coordination complexes. The results will be presented and discussed in the next section. The discussion is focussed on the synthesis of complex 2.1 and its ligand displacement reactions. 2.2 Results and Discussion 2.2.1 Synthesis and Characterisation of [PdCl(PCP)] 2.1 The pincer Pd(II) compound [1,5–bis(di-tert-butylphosphino)pentan-3-ylC,P,P’]chloropalladium(II), [PdCl(PCP-tBu2)] (PCP-tBu2 = -CH(CH2CH2PtBu2)2) was obtained by Trogler and co-worker92 by heating trans-[Pd2Cl4{µt Bu2P(CH2)5PtBu2}2] under a heat lamp, followed by sublimation (Scheme 2-1, 35 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex route 1). The analogous complex 2.1 was obtained in good yield (76%) by refluxing PdCl2(dppt) (2.2a) in DMF (Scheme 2-1, route 2). (CH2)5 PtBu2 PtBu2 Cl photolysis Cl Pd Pd - HCl Cl Cl t t P Bu2 P Bu2 PtBu2 Pd Cl (1) PtBu2 (CH2)5 Ph2 P (H2C)5 Cl DMF, reflux Pd Pd P Ph2 PPh2 Cl - HCl 2.2a Cl (2) PPh2 2.1 Scheme 2-1: Cyclometallation of the Pd(II) diphosphine complexes.92 The crystal structure of complex Pd(O2CCF2CF3 )2(dppt)93 could provide some information on the structure of analogous complex 2.2a (whose crystal structure has not been reported). The crystal structure shows that the PdP2C5 eight-membered ring adopts a boat-chair conformation with one of the methylene groups (Ca) located parallel to the Pd atom (Figure 2-1).93 As a result, the methylene carbon readily undergoes cyclometallation. X-ray quality crystals of complex 2.1 could be obtained despite careful recrystallisation from CH2Cl2/hexane. This method provided a simple and direct route to synthesise a pincer Pd(II) complex with a Pd-C σ bond. 36 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex C C P C Ca P C Pd Figure 2-1: Boat-chair conformation adopted by the PdP2C5 ring in complex Pd(O2CCF2CF3)2(dppt).93 A single-crystal X-ray crystallographic study on complex 2.1 revealed the expected cyclometallation at the centre of the hydrocarbon chain of the diphosphine (Figure 2-2). This results in two fused 5-membered rings sharing the Pd-C bond, which is trans to the chloro ligand. The metal adopts the usual squareplanar geometry but is distorted by the constrained P(1)-Pd(1)-P(2) angle [165.9(7)o], which is smaller but comparable to those of [PdCH3(PCP-tBu2)] [166.2(1)o] and [Pd(OH2)(PCP-tBu2)][BPh4] [167.2(1)o].92 The Pd-Cl bond [2.431(2) Å] is longer, and presumably weaker, than some typical Pd-Cl bonds such as those in K2PdCl4 (2.30 Å)94 and PdCl2(dppf) [average bond length 2.348(1) Å]95 as a result of the trans-influence of the Pd-C bond. The methylene carbons (C2 and C4) could point up or down in their static state. The crystal structure of complex 2.1 shows disorder at C2 and C4 in the phosphine ligand. These two carbon atoms disorder into two positions with the occupancy 60:40. The Pd-C bond length in complex 2.1 [2.111(7) Å] is between that of [PdCH3(PCP-tBu2)] [2.129(4) Å] and [Pd(OH2)(PCP-tBu2)][BPh4] [2.056(6) Å], reflecting the intermediate trans influence of chloro-ligand compared to the methyl and aqua ligands. 37 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Figure 2-2: An ORTEP plot of [PdCl(PCP)] 2.1 with 50% thermal ellipsoids. Carbon atoms C2 and C4 in the phosphine ligand show disorder into positions with occupancies 60: 40 (The disordered component is not shown). Selected bond lengths (Å) and angles (º): Pd(1)-P(1) = 2.313(2), Pd(1)-P(2) = 2.304(2), Pd(1)-Cl(1) = 2.431(2), Pd(1)-C(1) = 2.111(7), C(1)-C(2) = 1.473(6), C(1)-C(4) = 1.475(6); P(2)-Pd(1)-P(1) = 165.9(7), P(1)Pd(1)-Cl(1) = 98.5(7), P(2)-Pd(1)-Cl(1) = 95.5(8), P(1)-Pd(1)-C(1) = 83.2(2), P(2)-Pd(1)C(1) = 82.9(2), Ci(1)-Pd(1)-C(1) = 177.3(2), Pd(1)-C(1)-C(2) = 114.6(6), Pd(1)-C(1)-C(4) = 113.9(6), C(2)-C(1)-C(4) = 117.5(7). A detailed analysis of the 1H, 13C, DEPT 135 and two dimensional COSY, NOESY, γ-HSQC and γ-HMBC data led to the complete assignment of the 1H and 13 C NMR signals of 2.1, which are presented in Table 2-1. Protons are numbered according to the carbon atoms to which they are bonded. These data are consistent with those of the solution form of 2.1 suggesting that there is a vertical plane of symmetry on the plane defined by the H-1 (axial, upper face proton), C-1, Pd and Cl atoms. Thus the H-2a,b/C-2 and H-3a,b/C-3 methylene resonances are equivalent to those of H-4a,b/C-4 and H-5a,b/C-5 respectively (Ha-upper face protons; Hblower face protons). Similarly, two sets of aryl proton and carbon resonances were observed, corresponding to the presence of two pairs of identical phenyl groups, 38 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex one of which is oriented upwards (upper face) and the other downward (lower face) on each of the symmetrically-located P atoms. Each of the aliphatic and aryl carbon resonances, other than the aryl C-4 carbons, appear as well defined virtual triplets (Figure 2-3) due to coupling with the two equivalent P atoms. They are effectively part of the 13C2 - 31P2 (methylene and aryl C-1 and C-4 carbons) or 13 C4 - 31 P2 (aryl C-2/6 and C3/5 carbons) spin systems. Table 2-1: 1H and 13C NMR assignments (in CDCl3) determined for complex 2.1 13 C (ppm) J(C, P) (Hz) H (ppm) Atom Type C 60.8 t, J = 3.18 br, t, J = 12 Hz CH2 36.6 t, J = 1.79 br, t, J = 39 Hz 1.59 m, ν1/2 = 40 Hz CH2 30.2 t, J = 13 2.10 br, t, J = 12 Hz 2.69 m, ν1/2 = 26 Hz 1′ C 133.4 t, J = 20 2′, 6′ CH 133.8 t, J = 7.96 m, ν1/2 = 15 Hz 3′, 5′ CH 128.6 t, J = 7.40 m, ν 1/2 = 15 Hz 4′ CH 130.2 1″ C 131.7 t, J = 19 2'', 6'' CH 133.8 t, J = 8.04 m, ν 1/2 = 15 Hz 3'', 5'' CH 128.7 t, J = 7.40 m, ν 1/2 = 15 Hz 4'' CH 130.5 7.40 m, ν 1/2 = 15 Hz 7.40 m, ν 1/2 = 15 Hz 39 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Figure 2-3: 13C NMR spectrum of complex 2.1 in the 128-134 ppm region. The correlations observed in the COSY spectrum of complex 2.1 help the identification of the H-2a,b and H-3a,b methylene proton signals. The upper and lower face protons are distinguished by correlations observed in the NOESY spectrum of 2.1. In particular, H-1 (3.18 ppm) shows correlations to the upper face H-2a (1.79 ppm) and H-3a (2.10 ppm) signals respectively. The ortho protons of the upper and lower face phenyl groups are distinguished by NOESY correlations observed between the H-2'/H-6' (7.96 ppm, upper face phenyl group) and H-3a (2.10 ppm) and H-3b (2.69 ppm), while the H-2''/H-6'' (8.04 ppm) signals of the lower face phenyl group show correlations to H-3b (2.69 ppm) and H-2b (1.59 ppm). 40 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex The 1H and 13 C NMR chemical shifts are correlated in the HSQC (one- bond) and the HMBC (multiple-bond) experiments performed across both full (20-160 ppm) and narrowed (125-140 ppm) 13C spectral windows. The resolution and the signal-to-noise of the aryl proton region of the narrowed HMBC spectrum (Figure 2-4) enabled the 13 C resonances of the four aryl carbons (C-1, C-6 = C2, C-3 = C5 and C-4) of the upper and lower face phenyl groups to be uniquely identified via the correlations observed for the ortho protons of the upper face (7.96 ppm) and the lower face (8.04 ppm) phenyl groups, respectively. Figure 2-4: γ-HMBC correlations observed for aryl proton and carbon atoms of complex 2.1. 41 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.2.2 Electrospray Ionisation Mass Spectrometry Studies of [PdCl(PCP)] 2.1 The neutral transition metal halide complexes are widely studied using ESI-MS because these complexes can be ionised easily.88a, 96 The common ionisation pathway for the neutral transition metal halide complexes involves the formation of cations via dissociation of an anionic halide ligand. Addition of small amount of donor ligands results in the displacement of halide ligand(s) by the donor ligand. This approach is useful in enhancing the intensity of the cationic species and simplifying spectra. Cyclometallation of the metal-complexed triphenylphosphine ligands was previously observed by using ESI-MS under high cone voltage conditions.88a, 97 By using ESI-MS, the propensity for a complex to undergo cyclometallation can in theory be ascertained quickly. This can be achieved by using small quantities of sample, and analysed at an appropriate cone voltage. This can then be related to the solution-phase under which the cyclometallated product can be synthesised on a macroscopic scale. Thus, a complex which undergoes cyclometallation at a low cone voltage is likely to be able to be synthesised under relatively mild conditions, and vice versa. It was interesting to study the ligand displacement reactions of complex 2.1 using ESI-MS. This study is significant because the metallated carbon that is trans to the chloro ligand in complex 2.1 has an effect on the reaction. The 42 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex The crystal structure of complex 2.18 contains two pincer Pd(II) fragments bridged solely by a chloro ligand. The two Pd(II) centres are separated by a Pd ··· Pd distance of 3.910(6) Å. This distance is much longer than the commonly observed Pd-Pd bonds, which fall in between 2.701(1) Å and 2.756(5) Å.110 The long Pd-Pd distance suggests that the two atoms are not bonded to each other. The ORTEP plot of complex 2.18 is shown in Figure 2-21. Figure 2-21: An ORTEP plot of complex 2.18 · CH2Cl2 with 50 % thermal ellipsoids. The BF4- anion and the solvent molecule are omitted for clarity. Selected bond lengths (Å) and angles (º): Pd(1)-P(1) = 2.302(9), Pd(1)-P(2) = 2.289(9), Pd(2)-P(3) = 2.292(8), Pd(2)-P(4) = 2.297(1), Pd(1)-Cl(1) = 2.453(8), Pd(2)-Cl(1) = 2.466(9), Pd(1)-C(1) = 2.097(3), Pd(2)-C(6) = 2.086(3), C(1)-C(2) = 1.552(5), C(1)-C(4) = 1.518(5), C(6)-C(7) = 1.518(5), C(6)-C(9) = 1.531(5); Pd(1)-Cl(1)-Pd(2) = 123.8(4), P(1)-Pd(1)-P(2) = 156.4(3), P(3)-Pd(2)-P(4) = 160.5(3), P(1)-Pd(1)-Cl(1) = 100.1(3), P(2)-Pd(1)-Cl(1) = 95.9(3), P(1)-Pd(1)-C(1) = 82.9(1), P(2)-Pd(1)-C(1) = 82.9(1), P(3)-Pd(2)-C(6) = 82.3(1), P(4)Pd(2)-C(6) = 83.1(1), Cl(1)-Pd(1)-C(1) = 174.1(1), Cl(1)-Pd(2)-C(6) = 178.5(1), Pd(2)C(6)-C(7) = 115.0(2), Pd(2)-C(6)-C(9) = 113.9(3), C(2)-C(1)-C(4) = 110.8(3), C(7)-C(6)C(9) = 111.7(3).Dihedral angle (º): P(1)-Pd(1)-P(2)-C(1)-Cl(1)/P(3)-Pd(2)-P(4)-C(6)-Cl(1) = 72.6. There are only a few crystal structures of the monochloro-bridged Pd(II) complexes known. They are [{(η3-C3H5)Pd(C(N(tBu)CH)2)}2(μ-Cl)][PF6],102a (η374 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex C3H5)(Cl)Pd(μ-Cl)Pd(η3-C3H5)(C6H10NOH)102f and the pincer complex [{2, 6((CH3)2NCH2)2C6H3Pd}2(μ-Cl)][BF4].29 These complexes contain a chloro ligand bridged over two Pd(II) centres with a Pd-Cl-Pd angle of 107.3(1)° for (η3C3H5)(Cl)Pd(μ-Cl)Pd(η3-C3H5)(C6H10NOH),102f C3H5Pd(C(N(tBu)CH)2)}2(μ-Cl)][PF6]102a and 119.2(3)° 134.8(1)° [{η3- for for [{2, 6- ((CH3)2NCH2)2C6H3Pd}2(μ-Cl)][BF4].29 Complex 2.18 obtained from the current work gives a Pd(1)-Cl(1)-Pd(2) bond angle of 123.8(4)˚. Such deviation from 90° could be due to the steric effect caused by two bulky pincer moieties, as proposed previously by van Koten et al.29 To overcome the steric repulsion, the two coordination planes are twisted away from each other. The angle made by P(1)Pd(1)-P(2)-C(1)-Cl(1) and P(3)-Pd(2)-P(4)-C(6)-Cl(1) planes is 72.6° (Figure 222). The lengthening of the bridging Pd-Cl bonds [Pd(1)-Cl(1) = 2.453(8) Å; Pd(2)-Cl(1) = 2.466(9) Å] in complex 2.18 as compared to the terminal Pd-Cl bond [Pd(1)-Cl(1) = 2.431(1) Å] in complex 2.1 is expected. The lengthening of this bond was also observed for [{(η3-C3H5)Pd(C(N(tBu)CH)2)}2(μ-Cl)][PF6],102a ((η3-C3H5)(Cl)Pd(μ-Cl)Pd(η3-C3H5)(C6H10NOH)102f and [{2, 6- ((CH3)2NCH2)2C6H3Pd}2(μ-Cl)][BF4].29 Figure 2-22: An ORTEP plot of complex 2.18 · CH2Cl2 with 50 % thermal ellipsoids showing that the Pd(II) coordination planes are twisted away from each other. The phenyl rings, the BF4- anion and the solvent molecule are omitted for clarity. 75 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.2.4 Preliminary Study of the Catalytic Activity of Complexes 2.1 and 2.16a Suzuki–Miyaura reaction is a palladium-catalysed cross-coupling reaction between organic halides or triflates and organoboron compounds (Scheme 212).111 This reaction has been widely used to make C-C bonds.112 R1 X + R2 B(OR)2 Pd R1 R2 + (OR)2B X [Pd] = palladium catalyst; X = halide or triflate Scheme 2-12: A standard Suzuki-Miyaura cross-coupling reaction. Following the successful application of the pincer [PCP] Pd(II) complexes in Heck reactions,113 several research groups have investigated the use of pincer [PCP] Pd(II) complexes as catalysts in the Suzuki–Miyaura reaction.114 It was proposed that the tridentate chelating ligand with support from a strong Pd-C σ bond in the pincer [PCP] Pd(II) complexes would make them more stable than the traditional catalysts. This minimises catalyst decomposition to give metal that could interfere with the product separation and purification. An enhancement in catalytic activity in the Heck reaction was observed previously when the pincer Pd(II) complexes with an sp3-hybridized metallated carbon were used as catalysts.115 Such an increase in catalytic activity was believed to be the result of higher electron density of the metal centre imparted by a sp3-metallated carbon. This feature makes the pincer complexes more catalytically active as compared to those complexes with sp2-hybridized 76 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex metallated carbon. The catalytic study of pincer [PCP] complexes in the Suzuki– Miyaura reaction reported so far were focused on those complexes containing a sp2-hybridized metallated carbon, mainly from a phenyl ring. Therefore it was interesting to study the catalytic activity of the pincer [PCP] complexes containing a sp3-hybridized metallated carbon in the Suzuki–Miyaura reaction. Such studies are important to understand how different electronic properties in the pincer [PCP] complexes affect their catalytic activity. However, the objective of this work was not to compare the different electronic structures of pincer Pd(II) complexes in the Suzuki–Miyaura reaction. Instead, it aimed to introduce more options for future studies. Complexes 2.1 and 2.16a were chosen for this study because they can be obtained in high yield (Scheme 2-13 and Table 2-6). The data showed that the yield of the products was higher for those substrates with an electron-withdrawing group in the para position, as shown in entries 1, 2, and 6. X B(OH)2 [cat] + condition R R Scheme 2-13: A cross-coupling reaction between aryl bromides and phenyl boronic acid catalysed by complexes 2.1 and 2.16a. 77 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Table 2-6: Selected catalytic data of 2.1 and 2.16a towards Suzuki-Miyaura crosscoupling reaction of phenyl boronic acid and aryl bromides a, b Isolated Entry Aryl bromide Time [h] Cat yield [%] 4-Bromoacetophenone 16 2.1 90 4-Bromobenzonitrile 15 2.1 65 Bromobenzene 16 2.1 52 4-Bromoanisole 20 2.1 19 4-Bromoacetophenone 17 2.16a 78 4-Bromobenzonitrile 19 2.16a 80 Bromobenzene 15 2.16a 72 4-Bromoanisole 15 2.16a 32 a Reaction conditions are generally not optimised. b Conditions : aryl bromide (1 mmol), phenylboronic acid (1.5 mmol), catalyst (0.01 mmol), K2CO3 (2 mmol), 1,4-dioxane 110 ºC (10 ml), atmospheric pressure. Further investigations using 4-bromoacetophenone as substrate with catalysts 2.1 and 2.16a revealed that inorganic bases (K2CO3, Cs2CO3 and NaOH) were bases of choice for both catalysts (Table 2-7). Both complexes showed good catalytic activity when the coupling reactions were performed in commonly-used solvents for this type of reaction, being either polar solvent (1, 4-dioxane and DMF) or non-polar (toluene). The conversion remained quantitative for catalyst 2.16a even when the catalyst load was reduced to as low as 0.1 mol % (Entry 19). 78 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Table 2-7: Selected catalytic data of 2.1 and 2.16a towards the Suzuki-Miyaura crosscoupling reaction of phenyl boronic acid and 4-bromoacetophenone under different conditions a,b Entry Cat Base Solvent T (ºC) Catalyst loading c (mol %) 2.1 K2CO3 1,4-dioxane 110 100 2.1 Cs2CO3 1,4-dioxane 110 100 2.1 NaOH 1,4-dioxane 110 100 2.1 NEt3 1,4-dioxane 110 46 2.1 K2CO3 Toluene 110 100 2.1 K2CO3 DMF 110 81 2.1 K2CO3 1,4-dioxane 110 0.5 100 2.1 K2CO3 1,4-dioxane 110 0.1 88 2.1 Cs2CO3 1,4-dioxane RT 45 10 2.1 Cs2CO3 1,4dioxane/H2O (2 : v/v) RT 92e 11 2.1 Cs2CO3 1,4-dioxane 70 86 12 2.16a K2CO3 1,4-dioxane 110 100 13 2.16a Cs2CO3 1,4-dioxane 110 100 14 2.16a NaOH 1,4-dioxane 110 93 15 2.16a NEt3 1,4-dioxane 110 48 16 2.16a K2CO3 Toluene 110 100 17 2.16a K2CO3 DMF 110 99 18 2.16a K2CO3 1,4-dioxane 110 0.5 100 19 2.16a K2CO3 1,4-dioxane 110 0.1 100 20 2.16a Cs2CO3 1,4-dioxane RT 22 21 2.16a Cs2CO3 1,4dioxane/H2O (2 : v/v) RT 72e 22 2.16a Cs2CO3 1,4-dioxane 70 94 Conversion (%) d a Conditions: 4-Bromoacetophenone (1 mmol), phenylboronic acid (1.5 mmol), base (2 mmol), solvent (10 ml), reaction time (16 h). b The reactions were conducted at atmospheric pressure. c Relative to 4-Bromoacetophenone used in the reaction. d Determined using GC-MS based on aryl halide with n-dodecane as internal standard. e Catalyst decomposition observed. 79 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Full conversion could be achieved within four hours for both catalysts albeit at a high temperature. The catalytic activity at room temperature was generally poorer compared to the known catalysts.116 This could be improved by conducting the reaction in the presence of water (Entries 10 vs 9, and 21 vs 20).117 However, some catalyst decomposition (formation of a black solid which is presumably palladium metal) was also observed. The catalytic activity of 2.1 and 2.16a under similar conditions were generally comparable. 2.3 Summary The pincer [PCP] complex Pd(II) 2.1 was synthesised. Its formation and ligand displacement reactions were studied using ESI-MS. The pincer [PCP] Pd(II) complexes with triflato 2.16a, nitrato 2.16b and aqua 2.17a ligands were also prepared. The dinuclear complex 2.18 was isolated in an attempt to synthesise complex 2.17a. Preliminary catalytic study of complexes 2.1 and 2.16a suggested that they are active in the Suzuki-Miyaura coupling reaction. However their high activity under relatively harsh conditions (high temperature and highly alkaline solution) may also be interpreted as assistance from heterogeneous particulates.118 Therefore, it is important to investigate this reaction further to identify the true identity of the active catalyst. 80 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.4 Experimental Section 2.4.1 General Procedures and Materials Complex 2.2a119 was prepared from PdCl2(CH3CN)2 with the diphosphine ligand by stirring the reactants in an CH3CN solution while 2.2b was prepared from PtCl2(COD) with an equivalent of the Ph2P(CH2)5PPh2 ligand in CH2Cl2. The latter was analysed directly after addition of pyridine and dilution with CH3OH. Au(4-Spy)PPh3,120 Hg(4-Spy)Ph and Pt(4-Spy)2(dppe)121 were prepared from literature methods by reacting AuClPPh3, HgClPh and PtCl2(dppe) with 4pyridinethiol ligand in CH3OH with Et3N. All solvents were freshly dried using 3Ǻ molecular sieves. All reagents were commercial products and were used as received. Elemental analyses were performed by the Chemical, Molecular and Materials Analysis Centre (CMMAC) NUS. 2.4.2 NMR Spectroscopy One- and two-dimensional 1H and 13 C{1H}NMR spectra of complex 2.1 were determined at 27oC using a Bruker DRX400 spectrometer fitted with Z-axis pulse field gradient hardware and an inverse mm probehead. Bruker supplied pulse programs were used to acquire 1H, 13 C{1H}, DEPT135, COSY, TOCSY, SELTOCSY, NOEDIFF, NOESY, SELNOESY, γ-HSQC and γ-HMBC spectral data. Other NMR spectra were recorded at 25oC on a Bruker ACF 300MHz FTNMR spectrometer. Chemical shifts are reported relative to TMS where δ CHCl3 = 7.26 ppm (1H) or δ CDCl3 = 77.1 ppm (13C). The 31P{1H} NMR spectra were 81 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex externally referenced to 85 % H3PO4 at 121.39 MHz. The 19 F{1H} NMR spectra were referenced to CF3COOH at 282.38 MHz. 2.4.3 Electrospray Ionisation Mass Spectrometry Mass spectra were recorded in the positive ion mode using a VG Platfrom II mass spectrometer. CH3OH was used as the mobile phase in the reactivity study due to its less coordinating properties compared to CH3CN. The spectrometer employed a quadrupole mass filter with a maximum m/z of 3000. The compounds were dissolved in CH2Cl2 or pyridine due its good solubility and were diluted using mobile phase. The spectra were recorded on freshly prepared solutions. The dilute sample solution was injected into the spectrometer via a Rheodyne injector fitted with a 10 µL sample loop. A Thermo Separation Products Spectra System P1000 LC pump delivered the solution to the mass spectrometer source. The source temperature was maintained at 60oC. The cone voltage was usually maintained at V-20 V for observation of clean molecular ions, and at higher voltages (up to 80 V) to observe cyclometallation processes. Peaks were assigned from the m/z values and confirmation of species was aided by comparison of the observed and predicted isotope distribution patterns. Theoretical isotope distribution patterns were calculated using the ISOTOPE122 or the MS/MS IsoPro123 computer program. The species were identified for the most intense peak in each case. The mass spectra of the authentic samples were recorded in positive ion mode using a Thermo Finningan LCQ spectrometer. 82 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.4.4 X-Ray Crystallography The diffraction was carried out on a Bruker AXS CCD diffractometer with Mo Kα radiation (λ= 0.71073 Å). The software SMART124 was used for data frame collection, indexing reflections, and determining lattice parameters. The integration of intensity of reflections and scaling was done by using SAINT;124 SADABS125 was used for empirical absorption correction and SHELXTL126 for space group determination, refinements, graphics and structure reporting. The structures were solved by direct methods to locate the heavy atoms, followed by difference maps for the light non-hydrogen atoms. Anisotropic thermal parameters were defined for the rest of the non-hydrogen atoms. The hydrogen atoms were placed in their ideal positions. Carbon atoms C2 and C4 in the phosphine ligand of complex 2.1 show disorder into two positions with occupancies 60: 40. The asymmetric unit of complex 2.16a contains one molecule of the titled compound. For complex 2.16b, the crystal is orthorhombic, space group P212121. The asymmetric unit contains one molecule of complex which is the nitrate of the palladium complex cation. Carbon atoms of the methylene backbone are disordered into two positions with occupancies 50:50. Final R values are: R1 = 0.0487 and wR2 = 0.1255. The Flack parameter is x = 0.0066(esd 0.0403). The crystal of complex 2.17a is orthorhombic, space group Pnma. In the asymmetric unit of the crystal there is half a titled cation, half BF4 - anion, half diethyl ether and half dichloromethane. The palladium, boron, oxygen and chorine atoms are on the mirror. The hydrogen atoms of the water coordinated to the palladium were located from difference. Hydrogen bonding existed between the water and the oxygen atom of the diethyl ether as well as the fluorine atom of the BF4 - anion. 83 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Final R values are: R1 = 0.0513 and wR2 = 0.1429. For complex 2.18, the crystal is monoclinic, space group P21/c. The asymmetric unit contains one [{Pd(PCP)}2(μ-Cl)]+ cation, one BF4 - anion and one disordered dichloromethane. Final R values are: R1 = 0.0420 and wR2 = 0.1136. The data collection parameters of complexes 2.1, 2.16a, 2.16b, 2.17a · (C2H5)2O · CH2Cl2 and 2.18 · CH2Cl2 are listed in Table 2-8. Table 2-8: Data collection parameters of pincer [PCP] Pd(II) complexes 2.1, 2.16a, 2.16b, 2.17a · (C2H5)2O · CH2Cl2 and 2.18 · CH2Cl2 2.1a C29H29ClP2Pd 581.31 Orthorhombic P212121 8.560(2) 15.276(4) 20.019(5), 90 90 90 2617.8(1) 1.475 0.949 223(2) 8888 Chemical formula FW, g mol-1 Crystal system Space group a, Å b, Å c, Å α, o β, o γ, o Volume, Å3 Z ρcalcd, Mg m-3 µ, mm-1 T (K) No of reflections collected No of independent 4532 reflections [R(int) = 0.0612] No of parameters 304 GooF 0.962 R1 and wR2 R1 = 0.0569 [I> sigma(I)] wR2 =0.1194 R1 and wR2 R1 = 0.1034 (all data) wR2 =0.1339 Large diff. peak and 0.846 and -0.778 hole (e.Å-3) a Absolute structure parameter = 0.11(8) b Absolute structure parameter = 0.01(4) 2.16a C30H29F3O3P2PdS 694.93 Triclinic Pī 9.427(7) 10.678(8) 15.861(1) 98.489(2) 93.482(2) 114.897(1) 1418.9(2) 1.627 0.892 223(2) 18705 2.16bb C29H29NO3P2Pd 607.87 Orthorhombic P212121 8.651(5) 15.599(9) 19.626(1) 90 90 90 2648.4(3) 1.525 0.853 223(2) 18705 6515 [R(int) = 0.0272] 361 1.066 R1 = 0.0313, wR2 = 0.0726 R1 = 0.0356, wR2 = 0.0780 0.924 and -0.362 6067 [R(int)= 0.0472] 343 1.045 R1 = 0.0488 wR2 = 0.1120 R1 = 0.0563 wR2 = 0.1158 1.563 and -0.505 84 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex Table 2-8: Data collection parameters of pincer [PCP] Pd(II) complexes 2.1, 2.16a, 2.16b, 2.17a · (C2H5)2O · CH2Cl2 and 2.18 · CH2Cl2 (continued) Chemical formula FW, g mol-1 Crystal system Space group a, Å b, Å c, Å α, o β, o γ, o Volume, Å3 Z ρcalcd, Mg m-3 µ, mm-1 T (K) No of reflections collected No of independent reflections No of parameters GooF R1 and wR2 [I> sigma(I)] R1 and wR2 (all data) Large diff. peak and hole (e.Å-3) 2.17a · (C2H5)2O · CH2Cl2 C33.50H42B ClF4O2P2Pd 767.27 Orthorhombic Pnma 10.155(5) 16.307(8) 21.988(1) 90 90 90 3641.1(3) 1.400 0.719 293(2) 24811 2.18 · CH2Cl2 C59H60BCl3F4P4Pd2 1298.91 Monoclinic P21/c 12.551(5) 23.504(1) 20.037(9) 90 105.486(1) 90 5696.4(4) 1.515 0.936 223(2) 74579 4317 [R(int) = 0.0428] 240 1.084 R1 = 0.0512, wR2 =0.1353 R1 = 0.0620, wR2 = 0.1416 1.099 and -0.719 13085 [R(int) = 0.0294] 675 1.054 R1 = 0.0420 wR2 = 0.1074 R1 = 0.0420 wR2 = 0.1133 1.208 and -0.738 2.4.5 Preparation of [PdCl(PCP)] 2.1 Complex 2.2a (0.21 g, 0.33 mmol) was refluxed in DMF (100 ml) under nitrogen for 8h during which time the solution turned from yellow to pale yellow. The solution was filtered to remove a trace amount of metallic decomposition product. Upon evaporation, the crude product was recrystallised twice from CH2Cl2/Et2O to give pale yellow crystals of 2.1 (0.15 g, 76 %). The crystals of 2.1 were grown by layering hexane to a CH2Cl2 solution of complex 2.1. Analytical 85 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex data for 2.1: (Found: C, 59.98 H, 5.26. Anal. Calcd. for C29H29P2PdCl : C, 59.94 H, 4.99.) 31P{1H} NMR (CDCl3) (δ): 41.8 (s).The 1H and 13 C NMR assignments of 2.1 in CDCl3 are listed in Table 2-1. 2.4.6 Preparation of [Pd(OTf)(PCP)] 2.16a Complex 2.1 (0.43g, 0.74 mmol) was dissolved in degassed CH2Cl2 (20 ml). To the solution was added a solution of excess AgOTf (0.77g, 3.00 mmol) in deionised water (5 ml). The mixture was stirred overnight shielded from light. The resultant solution was filtered through Celite to remove the AgCl formed. The product was extracted into CH2Cl2 and the organic fraction was dried using anhydrous MgSO4. After filtration, the filtrate was concentrated to a small volume under reduced pressure. Addition of Et2O (10 ml) gave a milky white powder of 2.16a (0.41g, 79 %). The X-ray quality crystals of complex 2.16a were grown by layering Et2O onto a concentrated CH2Cl2 solution of 2.16a. Analytical data for 2.16a: (Found: C, 51.85 H, 4.19. Anal. Calcd. for C30H29P2PdF3SO3: C, 51.85 H, 4.17). 1H NMR (CDCl3) (δ): 1.58-1.71 (m, 4H, PCH2CH2), 2.10 (br, t, 2H, PCH2CH2), 2.58 (m, 2H, PCH2CH2), 3.45 (br, t, 1H, PdCH), 7.43-7.93 (m, 20H, Ph). 13 C{1H} NMR (CDCl3) (δ): 29.2 (vt, PCH2CH2, JC-P = 13 Hz), 36.9 (vt, PCH2CH2, 2JC-P = Hz), 58.3 (s, br, PdC), 119.8 (q, CF3SO3-, JC-F = 319 Hz), 128.7 (vt, Ph, 3JC-P = Hz), 128.9 (vt, Ph, 3JC-P = Hz), 129.9 (vt, Ph, JC-P = 20 Hz), 130.6 (s, Ph), 131.0 (s, Ph) , 131.8 (vt, Ph, JC-P = 20 Hz), 132.5 (vt, Ph, 2JC-P = Hz), 133.7 (vt, Ph, 2JC-P = Hz). 31P{1H} NMR (CDCl3) (δ): 44.8 (s, PPh2). 19 F{1H} NMR(CDCl3) (δ): -1.7 (s, OTf-). ESI-MS (m/z, %): [Pd(PCP)]+ (545, 100), [Pd(PCP)(CH3CN)]+ (587, 8). 86 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.4.7 Preparation of [Pd(NO3)(PCP)] 2.16b Complex 2.1 (0.10g, 0.17 mmol) was dissolved in degassed (CH3)2CO (30 ml). To this solution was added a solution of AgNO3 (0.15g, 0.86 mmol) in deionised H2O (10 ml). The mixture was stirred for h shielded from light, giving a colourless solution with brown residue. It was filtered through a Celite column to remove AgCl. The filtrate was evaporated under reduced pressure. The milky white solid obtained was washed with deionised H2O (2 x ml) followed by Et2O (2 x ml). The solid was then dissolved in (CH3)2CO and dried with anhydrous MgSO4. The solution was then filtered and dried under vacuum. The milky white powder was washed with Et2O (2 x ml) to give complex 2.16b (0.02g, 20 %). The X-ray quality crystals of complex 2.16b were grown by layering Et2O onto a concentrated CH2Cl2 solution of 2.16b. Analytical data for 2.16b: (Found: C, 57.12 H, 4.55 N, 2.01. Anal. Calcd. for C29H29P2PdNO3: C, 57.29 H, 4.82 N, 2.30). H NMR (CDCl3) (δ): 1.52-1.79 (m, 4H, PCH2CH2, overlapped with H2O peak), 2.09 (br, t, 2H, PCH2CH2), 2.58 (m, 2H, PCH2CH2), 3.35 (br, t, 1H, PdCH), 7.397.90 (m, 20H, Ph). 13C{1H} NMR (CDCl3) (δ): 29.5 (vt, PCH2CH2, JC-P = 13 Hz), 36.7 (vt, PCH2CH2, 2JC-P = Hz), 56.0 (vt, PdC, 3JC-P = Hz), 128.9 (vt, Ph, 3JC-P = Hz), 130.6 (s, Ph, overlapped with phenyl ring C1 signal), 130.7 (vt, Ph, JC-P = 19 Hz, overlapped with phenyl ring C4 signal), 130.9 (s, Ph, overlapped with phenyl ring C1 signal), 132.1 (vt, Ph, 2JC-P = Hz), 132.5 (vt, Ph, JC-P = 20 Hz), 133.6 (vt, 4C, Ph, 2JC-P = Hz). 31P{1H} NMR (CDCl3) (δ): 44.6 (s, PPh2) . ESIMS (m/z, %): [Pd(PCP)]+ (545, 100), [Pd(PCP)(CH3CN)]+ (586, 23). 87 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2.4.8 Preparation of [Pd(OH2)(PCP)][BF4] · H2O · (CH3CH2)2O [2. 17a · H2O · (CH3CH2)2O] Complex 2.17a was prepared similarly to complex 2.16b using complex 2.1 (0.05g, 0.09 mmol) and AgBF4 (0.08g, 0.43 mmol). The final product was obtained by adding Et2O into CH2Cl2 solution of 2.17a giving yellow crystals (0.03g, 50 %). Yellow crystals of 2.17a · (C2H5)2O · CH2Cl2 were obtained by diffusing Et2O into a CH2Cl2 solution of 2.17a. The presence of H2O and Et2O solvent was confirmed by elemental analysis and NMR spectroscopy. Analytical data for [2.17a · H2O · (CH3CH2)2O]: (Found: C, 53.17 H, 5.35 Anal. Calcd. for C33H43P2PdO3BF4: C, 53.35 H, 5.85). 1H NMR (CDCl3) (δ): 1.19 (t, 6H, CH3, diethyl ether), 1.38-1.78 (m, 4H, PCH2CH2), 2.12 (br, t, 2H, PCH2CH2), 2.62 (m, br, 4H, PCH2CH2 + H2O), 3.53 (q, br, 5H, PdCH + diethyl ether), 7.45 – 7.83 (m, 20H, Ph). 13 C{1H} NMR (CDCl3) (δ): 15.3 (s, CH3, diethyl ether), 29.1 (vt, PCH2CH2, JC-P = 13 Hz), 36.7 (vt, PCH2CH2, 2JC-P = Hz), 58.6 (s, br, PdC,), 65.9 (s, CH2, diethyl ether), 129.1 (vt, Ph, JC-P = 20 Hz), 129.4 (vt, Ph, 3JC-P = Hz), 129.5 (vt, Ph, 3JC-P = Hz), 131.2 (s, Ph), 131.4 (vt, Ph, JC-P = 20 Hz), 131.6 (s, Ph), 132.2 (vt, Ph, 2JC-P = Hz), 133.5 (vt, Ph, 2JC-P = Hz). (CDCl3) (δ): 46.0 (s, PPh2). bonded to 10 19 31 P{1H} NMR F{1H} NMR (CDCl3) (δ): -76.0 (s, br, fluorine B nuclei), -76.1 (s, br, fluorine bonded to 11 B nuclei). ESI-MS (m/z, %): [Pd(PCP)]+ (545, 100), [Pd(PCP)(CH3CN)]+ (586, 35). 2.4.9 Preparation of [{Pd(PCP)}2(μ-Cl)][BF4] 2.18 Complex 2.1 (0.05g, 0.09 mmol) was dissolved in degassed CH2Cl2 (30 ml). To this solution was added 2.17a (0.05g, 0.08 mmol). The pale orange 88 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex solution was stirred overnight and filtered. The filtrate was concentrated under reduced pressure. Addition of Et2O (10 ml) gave pale orange powder, which was crystallised twice from CH2Cl2/Et2O to give complex 2.18 as pale yellow crystals (0.02g, 22%). Analytical data for 2.18: (Found: C, 57.16 H, 4.71. Anal. Calcd. for C58H58P4Pd2ClBF4: C, 57.35 H, 4.82). 31P{1H} NMR (CDCl3) (δ): 44.9 (s, br, PPh2, ν1/2 = 10 Hz). 19F{1H} NMR(CDCl3) (δ): -77.3 (s, br, fluorine bonded to 10B nuclei), -77.4 (s, br, fluorine bonded to 11B nuclei). ESI-MS (m/z, %): [Pd(PCP)]+ (547, 25), [Pd(PCP)(CH3CN)]+ (585, 60), [{Pd(PCP)}2(μ-Cl)]+ (1127, 100). 2.4.10 General Procedure for Suzuki-Miyaura Reaction Aryl bromide (1 mmol) and phenylboronic acid (1.5 mmol) were added to degassed 1,4-dioxane (10 ml). K2CO3 (2 mmol) and the Pd(II) complex (0.01 mmol) were introduced. The mixture was refluxed under N2 flow. Upon cooling, the solvent was removed under vacuum. Water was added to the residue, followed by Et2O (2 x 10 ml) and the product extracted. The organic fractions were combined, dried with anhydrous MgSO4, filtered, and the solvent removed under vacuum. The crude product was purified by column chromatography using hexane and ethyl acetate (95:5 v/v) as eluent. The final product was weighed before GCMS analysis. The conversion was determined by GC-MS based on 4bromoacetophenone in the crude product with n-dodecane as an internal standard. 89 [...]... Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex 2 PPh2 Pd Cl PPh2 Ph2P R PPh2 2 2.1 Ph2P R PPh2 excess Ph2P R PPh2 PPh2 Pd PPh2 PPh2 + R PPh2 Cl- R = CH2 2. 9a, R = (CH2)5 2. 9b, R = (CH2)6 2. 9c, R = Fe(η5-C5H4 )2 2.9d 2+ PPh2 Pd PPh2 PPh2 R PPh2 PPh2 Pd 2Cl- PPh2 R = CH2 2. 10a (negligible), R = (CH2)5 2. 10b, R = (CH2)6 2. 10c, R = Fe(η5-C5H4 )2 2.10d Scheme 2- 6: Reactivity... 11 32 11 32. 6 1 122 .6 11 32. 6 1133.6 1 122 .6 1133.6 1134 1 122 1 120 1 121 .7 1 121 .7 0 1 121 1 123 1 121 1 122 1 123 1 124 1 125 1 126 1 127 1 128 1 129 1131 11331133 1 125 1 127 1 129 1130 1131 11 32 (a) Da/e 1134 1 120 1 123 1136 1 126 1 129 11 32 1135 1138 (b) Figure 2- 9: The isotope distribution patterns of [2. 6a - Cl-]+ cation (a) observed and (b) calculated 49 Chapter Two: Synthesis and Ligand Displacement Reactions of A Mononuclear... 5 42 550.4 543 0 5 42 5 42 545 544 544 546 543 546 547 548 548 550 549 550 5 52 Da/e 5 52 551 5 42 5 52 544 546 548 550 5 52 (b) (a) Figure 2- 8: The isotope distribution patterns of [2. 1 - Cl-]+ cation (a) observed and (b) calculated 100 1 128 1 127 .6 1 127 .6 1 126 .6 1 128 .6 1 129 .6 1 125 .6 1 126 .6 1 129 .6 1 125 .6 1130 1 126 1 128 .6 1 124 .6 % 1 124 .6 1130.6 1 123 .6 1131.6 1 124 1130.6 1131.6 1 123 .6 11 32 11 32. 6 1 122 .6 11 32. 6... 1 120 1117.6 11 17.6 10 0 1119 1116.7 1115.7 1119.7 1114.6 1118.6 11 16 7 11 15.7 11 1 4.6 11 1 9.7 1114 1 1 18.6 1113.6 1 1 13.6 1 121 1 122 1 120 .7 1 121 .6 % 1 1 20 .7 11 2 1.6 % 11 12. 7 1 122 .6 1 123 .6 1 124 .6 11 1 2. 7 1113 11 22 .6 1 1 23 .6 11 12 1111 11 2 4.6 1 1 25 .6 11 2 6.6 11 1 1.8 0 Da/ e 11 1 1 11 12 11 13 11 14 1 1 15 11 1 6 11 17 11 18 11 19 1 1 20 11 2 1 1 1 22 11 2 3 11 24 11 25 11 26 1 1 27 11 12. .. (20 %) excess AgX PPh2 Pd Solvent/ H2O (3:1 v/v) r.t Cl Pd X PPh2 PPh2 2. 1 PPh2 AgCl X= OTf, 2. 16a; NO3, 2. 16b Scheme 2- 8: Preparation of complexes 2. 16a and 2. 16b from 2. 1 [2. 16a, Solvent = CH2Cl2; 2. 16b, Solvent = (CH3)2CO] A mixture of aqua complex [Pd(OH2)(PCP)][BF4] 2. 17a and chlorobridged dimer [{Pd(PCP) }2( μ-Cl)][BF4] 2. 18 was obtained from a reaction between AgBF4 and complex 2. 1 in a CH2Cl2/H2... Pd(II) Complex Ph2 P Cl N (H2C)5 M P Cl Ph2 M = Pd 2. 2a M = Pt 2. 2b Ph2 N P (H2C)5 M P Cl Ph2 + Cl- M = Pd 2. 3a, m/z = 6 62, CV = 5 V M = Pt 2. 3b, m/z = 750, CV = 20 V -N Ph2 + P (H2C)5 M ClP Cl Ph2 M = Pd 2. 4a, m/z = 581, CV = 20 V M = Pt 2. 4b, m/z = 671, CV = 40 V -HCl + PPh2 M Cl- PPh2 M = Pd 2. 5a, m/z = 545, CV = 40 V M = Pt 2. 5b, m/z = 634, CV = 80 V Scheme 2- 2: Cyclometallation of 2. 2 studied by ESI-MS... 1116 1 120 1111 1 124 1 125 1114 1117 1 120 1 123 1108 1109 1110 1111 11 12 1113 1114 1115 1116 1117 1118 1119 1 120 1 121 1 122 1 123 1 124 1 125 1 126 1 127 1 124 (a) 1 123 (b) 1188.6 616 .2 204.5 593.1 6 72. 3 0 Da/e 20 0 400 600 800 1000 120 0 1400 1600 1800 20 00 Figure 2- 11: Positive-ion ESI mass spectrum of 2. 1 with one drop of aqueous NaCN solution added The sample was dissolved in a small quantity of CH2Cl2, and then... Two: Synthesis and Ligand Displacement Reactions of A Mononuclear Pincer [PCP] Pd(II) Complex + PPh2 Pd Cl + PPh2 + PPh2 Pd OH2 BF4 PPh2 Ph2P CH2Cl2 Pd r.t BF4 Pd PPh2 Ph2P PPh2 2. 17a 2. 1 Cl 2. 18 Scheme 2- 10: A proposed formation pathway of complex 2. 18 from complexes 2. 1 and 2. 17a Complexes 2. 16 and 2. 17a gave characteristic 1H, 13 C and 31 P chemical shifts in their NMR spectra (Table 2- 4) The signals... Pd PPh2 (i) 2 Cl Pd BF4 OH2 PPh2 PPh2 2. 1 2. 17a (i) (i) (ii) (ii) Ph2P PPh2 Pd PPh2 Cl BF4 Pd Ph2P 2. 18 Scheme 2- 11: Interconversion of complexes 2. 1, 2. 17a and 2. 18 (i) aqueous AgBF4 (ii) aqueous NaCl solution Table 2- 5: The 19F{1H} NMR chemical shifts of complexes 2. 16a, 2. 17a and 2. 18 2. 16a δF (ppm) 2. 17a 2. 18 -1.7 -76.0, -76.1 -77.3, -77.4 The presence of the triflato ligand in complex 2. 16a was... Cl- ]2+ (773, 40) Ph2P(CH2)6PPh2 [Fe(η5-C5H4PPh2 )2] (dppf) [Pd(PCP)(dppf)]+ [2. 9d – Cl-]+ (1099, 100), [{Pd(PCP) }2( μ-dppf) ]2+ [2. 10d – Cl- ]2+ ( 823 , 5) 4, 4’-(C5H4N )2 (4,4’-bpy) [Pd(PCP)(4,4’-bpy)]+ [2. 11a – Cl-]+ (701, 100) 2, 2 -(C5H4N )2 (2, 2’-bpy) [Pd(PCP) (2, 2’-bpy)]+ [2. 11b – Cl-]+ (701, 100) Phen [Pd(PCP)(Phen)]+ [2. 11c – Cl-]+ ( 725 , 100) The reactivity of 2. 1 towards metalloligands Au(4-Spy)PPh3 . 1 127 1 128 1 129 1130 1131 11 32 1133 1134 Da/e 0 100 % 1 127 .6 1 126 .6 1 125 .6 1 124 .6 1 123 .6 1 122 .6 1 121 .7 1 129 .6 1 128 .6 1130.6 1131.6 11 32. 6 1133.6 1 121 1 123 1 125 1 127 1 129 1131 1133 1 121 .7 1 122 .6. 1 120 1 121 1 122 1 123 1 124 1 125 1 126 1 127 Da/e 0 100 % 1117.6 1116.7 1115.7 1114.6 1113.6 11 12. 7 1111.8 1119.7 1118.6 1 120 .71 121 .6 1 122 .6 1 123 .6 1 125 .6 1 124 .6 1 126 .6 20 0 400 600 800 1000 120 0 1400. 5 51 5 52 (b) 1 120 1 123 1 126 1 129 11 32 1135 1138 (b) 1 120 1 122 1 124 1 126 1 128 1130 11 32 1134 1136 Chapter Two: Synthesis and Ligand Displacement