Chapter Four Formation and Decarbonylation of {Ag2Mn4} Clusters 122 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Chapter Four Formation and Decarbonylation of {Ag2Mn4} Clusters 4.1 Introduction The work described in this chapter serves as a platform to gain understanding on the assembly of heterometallic complexes, using a phosphidobridged complex and the phosphine-bridged complexes as precursors. The previous chapter illustrated the use of a pincer model complex, which is Lewis acidic, to construct dinuclear and heteronuclear complexes. In this chapter, a Lewis basic model complex was used to carry out similar constructions. These two chapters in conjunction would demonstrate the diverse strategies used in the dinuclear and the heteronuclear syntheses. The phosphido ligand is another type of bridging ligand that is widely used in supporting the homo- and the heterometallic complexes. However, this anionic, four-electron donor ligand is different from other neutral ligands such as the bipyridine, bisphosphine and the metalloligands as described in Chapter Two and Chapter Three. The background of the homoand heterometallic complexes bridged by the phosphido ligand has been given in Section 1.3. The dinuclear manganese complex [(PPh3)2N)][Mn2(μ-PPh2)(CO)8] 4.1144 was used as a precursor in this study. This complex was previously prepared by Mays et al.144 Heterometallic complexes with different chemical structures were 123 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters obtained from the reactions of 4.1 with various cationic complexes.144, 145 Some of these complexes are shown in Figure 4-1. (CO)4 Mn P Au PPh2 Mn (CO)4 (CO)4 Mn Au P Ph2P Mn (CO)4 (CO)4 (CO)4 Mn Mn Au Ph2P PPh2 Mn Mn (CO)4 (CO) (PPh3)2N P - P = Ph2PCH2PPh2, n = - or Ph2P(C5H4)2FePPh2 (b) Ph2 P (CO)4Mn Au Mn(CO)3 P P P - P = Ph2P(CH2)nPPh2, n = - or Ph2P(C5H4)2FePPh2 (a) (c) Ph2 P Mn(CO)4 (CO)4Mn M L L' M = Rh; L = L' = PPh3 Ph2 P P Pd Mn(CO)4 P P - P = Ph2P(CH2)nPPh2, n = - or Ph2P(C5H4)2FePPh2 (e) M = Ir; L = PPh3; L' = CO (d) Pd PPh2 Cl Pd Ag Ph2P PPh2 Mn (CO)4 Mn (CO)4 P - P = Ph2PCH2PPh2 Ph2 P Ph3P Pd Ph2P H2 C (f) Mn(CO)3 P P P - P = Ph2PCH2PPh2 (g) Figure 4-1: The heterometallic complexes obtained from 4.1.144, 145 Although many heterometallic clusters with a Ag/Mn2 triangular core have been prepared,146 their crystal structures have not been reported. On the other hand, the structures of some of their Au(I) analogues have been reported. The currently known crystal structure of the Ag(I) heterometallic cluster containing a AgMn2 triangle is Mn2(μ-AgClO4)(μ-H)2(CO)6(μ-dppm), which shows a dynamic behaviour in solution (Scheme 4-1).146c 124 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Ph2P OC Mn Hb OC CO OC CO OC Mn Ha OC Ph2P PPh2 [Ag] CO Hb [Ag] Mn Ha CO PPh2 CO Mn CO CO [Ag] = Ph3PAgOClO3 Scheme 4-1: The silver shift of Mn2(μ-AgClO4)(μ-H)2(CO)6(μ-dppm) in solution.146c The Ag(I) dppf)2(TFA)2 4.2b compounds 148 Ag2(µ-dppm)2(OTf)2 4.2a147 and Ag2(µ- were chosen in this study because of their potential application as precursors to the heterometallic complexes. It is interesting to prepare heterometallic clusters containing the Ag/Mn2 core as their structural features are not well understood.146c This chapter describes the synthesis and the structural characterisation of four Ag/Mn heterometallic carbonyl clusters bridged by the phosphido ligand. Their description would complete the series in the previous work on the synthesis of Au/Mn heterometallic clusters.145c, 145d The Ag(I) and Au(I) complexes chemistry can be different due to the relativistic effect.149 The structural differences between Ag(I) and Au(I) in this series of complexes is a focus of this discussion. 125 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.2 Results and Discussion The results on the synthesis of four Ag/Mn heterometallic clusters are presented in Section 4.2.1. The crystal structures (Section 4.2.2) and the formation mechanism (Section 4. 2.3) of the heterometallic clusters will also be discussed. 4.2.1 Synthesis and Characterisation of Clusters Ag2Mn4(µPPh2)2(CO)16(µ-P-P) (P–P = dppm 4.3a; dppf 4.3b) and AgMn2(μ-PPh2)(CO)7(μ-P-P) (P-P = dppm 4.4a; dppf 4.4b) Reactions of two equivalents of complex 4.1 with complexes 4.2a and 4.2b in CH2Cl2 produced the hexanuclear cluster complexes [Ag2Mn4(CO)16(μPPh2)2]2(μ-P-P) (P-P = dppm 4.3a; P-P = dppf 4.3b) (Scheme 4-2). This condensation reaction was promoted by the displacement of one of the diphosphine bridges by chelation of an [Mn2(µ-PPh2)(CO)8]- fragment at each of the Ag(I) centre. This resulted in an open cluster network with a diphosphine bridging two AgMn2 heterometallic triangles. The Au(I) analogues have been similarly prepared from [AuCl]2(μ-P-P) (P-P = dppm, dppf) and 4.1.145d 126 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Ph2 P (PPh3)2N (OC)4Mn + Mn(CO)4 4.1 2+ P P Ag Ag 2[X'] P P P-P =dppm, X' =OTf 4.2a P-P =dppf, X' = TFA 4.2b RT , CH2Cl2 (CO)4 Mn Ph2P Ag P Mn (CO)4 [(PPh3)2N]X' + P P P (CO)4 Mn PPh2 Ag Mn (CO)4 P - P = dppm 4.3a, 55% P - P = dppf 4.3b, 43% Scheme 4-2: Condensation reaction of 4.1 with 4.2a and 4.2b to give complexes 4.3a and 4.3b. Similar reactions under thermal (reflux in toluene) or chemical [(CH3)3NO] decarbonylative conditions led to AgMn2(CO)7(μ-PPh2)(μ-P-P) (P-P = dppm, 4.4a, 11%; P-P = dppf, 4.4b, 2%) as additional products to 4.3a and 4.3b. The yields of 4.4a (8%) and 4.4b (9%) were not improved by the presence of molar equivalents of diphosphine ligand and a higher amount of (CH3)3NO ∙ 2H2O in the decarbonylation reaction (Scheme 4-3). 127 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters (CO)4 Mn Ag Ph2P (CO)4 Mn Ag P Ph2P Mn (CO)4 P (CO)4 Mn Ag PPh2 Mn (CO)4 (CH3)3NO 2H2O P -P THF P P Mn (CO)4 + CO2 Ph2 P (OC)4Mn P - P =dppm 4.3a P - P = dppf 4.3b (CO)4 Mn Ag PPh2 Mn (CO)4 Ag Mn(CO)3 P P P - P =dppm 4.4a P - P = dppf 4.4b Scheme 4-3: Preparation of the Ag/Mn complexes 4.4a and 4.4b from 4.3a and 4.3b. The signals corresponding to the protons of the methylene group (3.72 ppm) and the phenyl rings (7.21-7.82 ppm) were observed in the 1H NMR spectrum of cluster 4.3a. The 31 P{1H} NMR spectrum of 4.3a (Figure 4-2 and Table 4-1) showed a broad doublet of triplets peak at -5.1 ppm with 107/109 Ag-31P coupling that remained unresolved down to 183 K, corresponding to the P atoms bonded to the two Ag(I) centres. Besides, the signal corresponding to the phosphido ligand was observed in the downfield region (201.2 ppm). Cluster 4.3b gave two sets of signals which correspond to the bridging phosphine (3.2 ppm) and the bridging phosphido ligands (200.3 ppm) with characteristic Ag-P coupling constants (J(107)Ag-P = 368 Hz, J(109)Ag-P = 424 Hz). The presence of the dppf ligand is supported by the observation of the signals corresponding to the Cp protons in its 1H NMR spectrum (4.18 ppm and 4.58 ppm). Coupling to quadrupolar 55 Mn nuclei (I = 5/2) resulted in the broadening of the phosphido ligand signal in all clusters. The 31 P{1H} NMR spectra of 4.4a and 4.4b showed three resonances 128 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters corresponding to the three chemically inequivalent P atoms (P1, P2 and P3), as shown in the 31 P{1H} NMR spectrum of 4.4b (Figure 4-3 and Table 4-1). The signal of Mn bound phosphine (P3) was observed at 72.8 ppm (doublet) and 65.7 ppm (singlet) for clusters 4.4a and 4.4b respectively. The signal of P3 in 4.4a is split by the Ag bound phosphine (P1) with a coupling constant of 139 Hz. A threebond coupling between P1 and Mn bound phosphido ligand (P2) contributed to the splitting observed in 4.4a (3JP-P = 23 Hz). The observed coupling constant is similar to that of Mn2Au{μ-P(OEt)2}(CO)6(μ-dppm)(PR3) (R = Ph, p-tol) (3JP-P = 33 Hz).146a The 1H NMR and 31 P{1H} NMR analyses of 4.4a and 4.4b (notably 4.4a) suggested that the clusters slowly decomposed in solution upon prolonged atmospheric exposure. The presence of the carbonyl ligands in clusters 4.3a, 4.3b, 4.4a and 4.4b is supported by their FT-IR spectra. The carbonyl stretching bands were observed in the range of 1897cm-1 – 2027 cm-1. 129 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Table 4-1: 31P chemical shifts (in ppm) of clusters 4.3a, 4.3b, 4.4a and 4.4b (CO)4 Mn P2 Ag P1 Mn (CO)4 (CO)4 Mn P2 Ag (OC)3Mn (CO)4 Mn P1 Ag P2 Mn (CO)4 P3 4.3 4.3aa P1 4.4 P1 (ppm) P2 (ppm) -5.1 (dt, br) 201.2 (s, br) P3 (ppm) J(107)Ag-P = 313 Hz J(109)Ag-P = 439 Hz 4.3ba 3.2 (dd, br) 200.3 (s, br) J(107)Ag-P = 368 Hz J(109)Ag-P = 424 Hz 4.4ab -1.6 (ddd) 195.3 (s, br) JAg-P = 335 Hz JP-P = 139 Hz JP-P = 147 Hz 4.4bb 72.8 (d, br) JP-P = 23 Hz 4.0 (dd) 199. (s, br). 65.7 (s, br), J(107)Ag-P = 327 Hz J(109)Ag-P = 375 Hz a = recorded in CDCl3, b = recorded in C4D8O 130 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 210 208 206 204 202 200 198 196 194 192 -1 -2 -3 -4 -5 (a) 200 175 150 -7 -8 -9 -10 -11 (ppm) (ppm) P2 -6 P1 (b) 125 100 75 50 25 -25 (ppm) Figure 4-2: 31P{1H} NMR spectrum of cluster 4.3a recorded in CDCl3. The inserts show enlarged (a) P2 and (b) P1 regions. 220 210 200 190 180 74 72 70 68 66 64 62 60 58 56 (ppm) (ppm) (a) (b) -1 (ppm) (c) P3 P1 P2 200 175 150 125 100 75 50 25 (ppm) Figure 4-3: 31P{1H} NMR spectrum of cluster 4.4b recorded in C4D8O using a Bruker AMX 500MHz FT-NMR spectrometer. The inserts show enlarged (a) P2 and (b) P3 (c) P2 regions. 131 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.2.2 Crystal Structures of Clusters 4.3a, 4.3b, 4.4a and 4.4b The crystal structures of clusters 4.3a (as CH2Cl2 solvate) (Figure 4-4) and 4.3b (Figure 4-5) show two isostructural open-clusters with a diphosphine bridging the two heterometallic triangles. In cluster 4.3b, an anti conformation of the dppf ligand allows the two metal triangles to move away from each other to minimise the steric hindrance.150 Each Mn atom is coordinated by four carbonyl ligands. They are bonded to each other and bridged by the phosphido ligand Figure 4-4: An ORTEP plot of cluster 4.3a · CH2Cl2 with 50% thermal ellipsoids. Only the ipso carbons of the phenyl rings are shown. The CH2Cl2 molecule is omitted for clarity. Selected bond lengths (Å) and bond angles (º): Ag(1)-Mn(1) = 2.676(9), Ag(1)Mn(2) = 2.757(9), Ag(2)-Mn(3) = 2.731(1), Ag(2)-Mn(4) = 2.676(1), Mn(1)-Mn(2) = 3.044(1), Mn(3)-Mn(4) = 3.055(1), Ag(1)-P(2) = 2.442(2), Ag(2)-P(3) = 2.431(2), Mn(1)P(1) = 2.274(2), Mn(2)-P(1) = 2.282(2), Mn(3)-P(4) = 2.284(2), Mn(4)-P(4) = 2.275(2); Mn(1)-Ag(1)-Mn(2) = 68.1(3), Mn(3)-Ag(2)-Mn(4) = 68.8(3), Ag(1)-Mn(1)-Mn(2) = 57.2(2), Ag(1)-Mn(2)-Mn(1) = 54.7(2), Ag(2)-Mn(3)-Mn(4) = 54.8(2), Ag(2)-Mn(4)Mn(3) = 56.5(3), Mn(1)-P(1)-Mn(2) = 83.8(6), Mn(3)-P(2)-Mn(4) = 84.1(6), Mn(1)Mn(2)-P(1) = 48.0(4), Mn(2)-Mn(1)-P(1) = 48.2(4), Mn(3)-Mn(4)-P(4) = 48.1(5), Mn(4)Mn(3)-P(4) = 47.8(5), Mn(1)-Ag(1)-P(2) = 153.0(4), Mn(2)-Ag(1)-P(2) = 130.7(4), Mn(3)-Ag(2)-P(3) = 127.4(4), Mn(4)-Ag(2)-P(3) = 150.2(4), Ag(1)-Mn(1)-P(1) = 105.0(5), Ag(1)-Mn(2)-P(1) = 102.3(5), Ag(2)-Mn(3)-P(4) = 102.0(5), Ag(2)-Mn(4)-P(4) = 103.9(5). 132 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Figure 4-5: An ORTEP plot of cluster 4.3b with 50% thermal ellipsoids. Only the ipso carbons of the phenyl rings are shown. Selected bond lengths(Å) and angles (º): Ag(1)Mn(1) = 2.773(1), Ag(1)-Mn(2) = 2.667(1), Mn(1)-Mn(2) = 3.048(2), Ag(1)-P(2) = 2.426(2), Mn(1)-P(1) = 2.279(2), Mn(2)-P(1) = 2.276(2); Mn(1)-Ag(1)-Mn(2) = 68.1(4), Ag(1)-Mn(1)-Mn(2) = 54.3(3), Ag(1)-Mn(2)-Mn(1) = 57.6(3), Mn(1)-P(1)-Mn(2) = 84.0(7), Mn(1)-Mn(2)-P(1) = 48.1(5), Mn(2)-Mn(1)-P(1) = 48.0(6), Mn(1)-Ag(1)-P(2) = 143.6(6), Mn(2)-Ag(1)-P(2) = 148.1(6), Ag(1)-Mn(1)-P(1) = 101.3(6), Ag(1)-Mn(2)-P(1) = 104.7(7). The use of different phosphine ligands resulted in small differences of the Ag-P bond lengths in clusters 4.3a · CH2Cl2 [Ag(1)-P(2) = 2.442(2) Å, Ag(2)-P(3) = 2.431(2) Å] and 4.3b [Ag(1)–P(2) = 2.426(2) Å] (Table 4-2). The Ag-P bond lengths in both clusters are longer than that of the Au–P bond in the analogous cluster [Au2Mn4(CO)16(μ-PPh2)2]2(μ-dppf) [2.318(2) Å],145d This observation is consistent with the expected relativistic contraction of Au.151 133 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters However, no significant differences were observed in the Mn-Mn and MMn (M = Ag, Au) bond lengths between cluster [Au2Mn4(CO)16(μ-PPh2)2]2(μdppf) [Mn-Mn = 3.049(2) Å; Au-Mn = 2.660(1) Å, 2.776(1) Å] and 4.3b [Mn(1)– Mn(2) = 3.048(2) Å, Ag(1) – Mn(1) =2.773(1) Å, Ag(1) – Mn(2) = 2.667(1) Å]. These bond lengths are comparable to 4.3a · CH2Cl2 [Mn(1)–Mn(2) = 3.044(1) Å, Mn(3)-Mn(4) = 3.055(1) Å, Ag(1)–Mn(1) = 2.676(9) Å, Ag(1)–Mn(2) = 2.757(9) Å, Ag(2)-Mn(3) = 2.731(1) Å, Ag(2)-Mn(4) = 2.676(1) Å]. It has shown that the Mn–Mn bonds are longer than that in complex 4.1 [2.867(2) Å]. This finding is consistent with a three-centre-two-electron (3c-2e) bond involving the Ag and Mn atoms.145d X-ray structural analyses of clusters 4.4a and 4.4b revealed a metal triangle with the phosphido ligand bridging the Mn-Mn bond and a phosphine ligand bridging one of the Ag-Mn bonds. A similar metal framework was observed in the Au/Mn2 system.145c The crystal data of cluster 4.4a shows two molecules and three THF solvent molecules per asymmetric unit. The ORTEP diagram of one of the molecules of cluster 4.4a is shown in Figure 4–6. The ORTEP plot of cluster 4.4b is shown in Figure 4-7. 134 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Figure 4-6: An ORTEP plot showing one of the molecules of cluster 4.4a · 1.5 THF with 50% thermal ellipsoids. Only the ipso carbons of the phenyl rings are shown. The tetrahydrofuran solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (º): Ag(1)-Mn(1) = 2.806(7), Ag(1)-Mn(2) = 2.595(7), Ag(1)-P(1) = 2.420(1), Ag(1)-C(7) = 2.626(5), Mn(1)-Mn(2) = 3.165(9), Mn(1)-P(3) = 2.251(1), Mn(2)-P(3) = 2.292(1), Mn(1)-P(2) = 2.303(1), Mn(2)-C(7) = 1.806(5), C(7)-O(7) = 1.170(6); Mn(1)Ag(1)-Mn(2) = 71.6(2), Ag(1)-Mn(1)-Mn(2) = 51.1(2), Ag(1)-Mn(2)-Mn(1) = 57.3(2), Mn(1)-P(3)-Mn(2) = 88.3(5), Mn(1)-Mn(2)-P(3) = 45.3(3), Mn(2)-Mn(1)-P(3) = 46.4(3), P(2)-Mn(1)-P(3) = 166.8(5), P(2)-Mn(1)-Mn(2) = 120.9(4), Mn(1)-Ag(1)-P(1) = 106.3(3), Mn(2)-Ag(1)-P(1) = 170.7(3), Ag(1)-Mn(1)-P(3) = 96.1(4), Ag(1)-Mn(1)-P(3) = 101.1(4), Ag(1)-Mn(1)-P(2) = 72.6(3), Ag(1)-Mn(2)-C(7) = 70.7(2), Mn(2)-C(7)-O(7) = 172.8(5). 135 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Figure 4-7: An ORTEP plot of cluster 4.4b · THF with 50% thermal ellipsoids. Only the ipso carbons of the phenyl rings are shown. The tetrahydrofuran solvent molecules are omitted for clarity. Selected bond lengths (Å) and angles (º) : Ag(1)-Mn(1) = 2.696(2), Ag(1)-Mn(2) = 2.717(2), Ag(1)-P(1) = 2.454(2), Mn(1)-Mn(2) = 3.140(2), Mn(1)- P(3) = 2.247(3), Mn(2)-P(3) = 2.285(3), Mn(1)-P(2) = 2.318(2), Mn(2)-C(7) = 1.811(1), C(7)O(7) = 1.166(1); Mn(1)-Ag(1)-Mn(2) = 70.9(4), Ag(1)-Mn(1)-Mn(2) = 54.9(4), Ag(1)Mn(2)-Mn(1) = 54.2(4), Mn(1)-P(3)-Mn(2) =87.7(9), Mn(1)-Mn(2)-P(3) = 45.7(6), Mn(2)-Mn(1)-P(3) = 46.6(7), P(2)-Mn(1)-P(3) = 173.5(1), P(2)-Mn(1)-Mn(2) = 128.8(8), Mn(1)-Ag(1)-P(1) = 151.3(7), Mn(2)-Ag(1)-P(1) = 134.8(7), Ag(1)-Mn(1)-P(3) = 101.0(8), Ag(1)-Mn(2)-P(3) = 99.4(7), Ag(1)-Mn(1)-P(2) = 75.3(7), Ag(1)-Mn(2)-C(7) = 70.5(3), Mn(2)-C(7)-O(7) = 173.4(9). Attempts to obtain the crystal of cluster 4.4b which is isomorphous to AuMn2(CO)7(µ-PPh2)(µ-dppf)145c was unsuccessful. The crystallographic data shows that there are two THF solvent molecules in the crystal lattice (Figure 4-7). The Mn-Mn bond lengths in clusters 4.4a and 4.4b are comparable to each other (4.4a · 1.5 THF [Mn(1)-Mn(2) = 3.165(9) Å] and 4.4b · THF [Mn(1)-Mn(2) = 136 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 3.140(2) Å]). They are slightly longer as compared to 4.3a and 4.3b. This is consistent with the nature of phosphine ligand being a better σ donor compared to the carbonyl ligand.152 However, the Ag-Mn bond lengths are significantly different between the two clusters (4.4a · 1.5 THF [Ag(1)-Mn(1) = 2.806(7) Å, Ag(1)-Mn(2) = 2.595(7) Å]; 4.4b · THF [Ag(1)-Mn(1) = 2.696(2) Å, Ag(1)-Mn(2) = 2.717(2) Å]). One of the Ag-Mn bonds bridged by the sterically hindered dppf ligand in 4.4b is significantly longer than that in the dppm supported cluster 4.4a. Accordingly, the other Ag-Mn bond in 4.4b is significantly shorter than that in 4.4a. This suggests that the metal triangle could adjust itself in such a way that the longer and presumably weaker Ag-Mn bond is balanced by the other short Ag-Mn bond.145c Such adjustment would allow the metal triangle to adapt to the diphosphine ligands with different backbone. It could also explain why the same metal triangle could be formed when moving from Au(I) and Ag(I). Semi-bridging of one of the carbonyl ligands previously observed in AuMn2(CO)7(µ-PPh2)(µ-P-P) (P-P = dppe and dppp)145c is again observed in 4.4a · 1.5 THF [Ag(1)-C(7) = 2.626(5) Å, Mn(2)-C(7)-O(7) =172.8(5)º]. The Ag–C bond length falls in the range of Ag-C bond lengths of [Ag3(µ-dppm)3(µ3-η1-C≡C-C6H4-NO2-p)2][PF6] [2.257(7) Å 2.981(8) Å]153 and Ag2C2.8CF3SO3Ag.2EtCN · 3H2O [2.153(9)Å - 2.69(1) Å].154 The asymmetric parameter α (α = (d2-d1)/d1 = 0.31; d1 = Mn(2)-C(7) = 1.805(5) Å; d2 = Ag(1)-C(7) = 2.626(5) Å) falls in the range of the α value defined by Curtis as semibridging carbonyl (0.1≤ α ≤ 0.6).155 The semi-bridging of the carbonyl ligand was supported by the observation of peaks at low wave-number in the FTIR spectrum [1897 cm-1 (s), 1939 cm-1 (s), 1981 cm-1 (s) and 2025 cm-1 (s)]. 137 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.2.3 Mechanistic Consideration The Formation of clusters 4.3a and 4.3b was driven by a condensation reaction of 4.1 with 4.2a and 4.2b, as well as by eliminating one of the phosphine ligands from the Ag(I) complex. The formation of clusters 4.4a and 4.4b was promoted by a decarbonylation reaction thus creating a vacant site for phosphine coordination. The latter process thus provided sufficient driving force for the dppf to change from its usually favoured bridging coordination mode (bridging two metal triangles) to the coordination mode bridging across the Ag-Mn bond (Scheme 4-4). [(PPh3)2N] Ph2 P (OC)4Mn Mn(CO)4 + P P Ag Ag P P Ph2 P (OC)4Mn Mn(CO)3 Ag P 2+ [X'] P 4.4 4.1 4.2 (CO)4 P Mn Ag Ph2P Mn (CO)4 P P Ag P (CO)4 Mn + [(PPh3)2N] [X'] PPh2 Mn (CO)4 P Proposed intermediate P (CO)4 Mn Ph2P Ag P Mn (CO)4 4.3 P (CO)4 Mn P Ag PPh2 Mn (CO)4 (CO)4 Mn Ph2P Ag (OC)4Mn (CO)4 Mn P Ag PPh2 Mn (CO)3 Proposed intermediate THF CO (CO)4 Mn Ag Ph2P Mn (CO)4 P (CO)4 Mn P Ag PPh2 Mn(CO)3 OC Proposed intermediate Scheme 4-4: A proposed mechanism for the formation of complexes 4.3 and 4.4. 138 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Reaction of 4.3a with (CH3)3NO ∙ 2H2O in the presence of dppf (Scheme 4-5) gave a mixture of products containing clusters 4.3a, 4.3b, 4.4a and 4.4b. The clusters 4.3b and 4.4a were obtained as major products, as indicated in their 31 P{1H} NMR spectra (Figure 4-8 and Figure 4-9). This observation is consistent with the nature of dppf ligand which allowed for the bridging of two separate fragments156 as compared to the dppm ligand which preferred to act as a supporting bridge.157 A similar formation pathway has been described for the Au/Mn analogues.145c (CO)4 Mn Ph2P Ag (OC)4Mn H2 C P Ph2 P Ph2 (CO)4 Mn Ag PPh2 4.3a Mn (CO)4 PPh2 Fe + Ph2P equivalent of (CH3)3NO 2H2O THF, 65oC (CO)4 H2 Mn C Ph2P P Ag Ag P Ph2 Ph2 (OC)4Mn (CO)4 Mn PPh2 Mn (CO)4 Ph2 P (OC)4Mn (minor) 4.3a Mn(CO)3 PPh2 (major) Ag P CH2 Ph2 4.4a + (CO)4 Mn Ph2P (OC)4Mn Fe Ag P Ph2 4.3b + (CO)4 Ph2 Mn P Ag PPh2 Mn (CO)4 Ph2 P (major) (OC)4Mn Mn(CO)3 (minor) PPh2 Ag PPh2 Fe 4.4b Scheme 4-5: A reaction of cluster 4.3a with dppf ligand. 139 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.3b 4.3b 4.3a 4.3a P1 P2 205 200 (ppm) (ppm) (a) 200 -5 (b) 160 120 80 40 (ppm) Figure 4-8: 31P{1H} NMR spectrum of the product isolated from the first chromatographic band (yellow) of the of reaction between 4.3a and dppf in the presence of (CH3)3NO ∙ 2H2O. The inserts are the enlarged (a) P2 and (b) P1 region. 4.4a 4.4a 4.4a 4.4b 200 195 (ppm) P2 200 4.4b 4.4b (a) 160 75 (ppm) -5 P1 (ppm) (b) P3 120 80 (c) 40 (ppm) Figure 4-9: 31P{1H} NMR spectrum of the product isolated from the second chromatographic band (red) of the reaction between 4.3a and dppf in the presence of (CH3)3NO ∙ 2H2O.The insets are the enlarged (a) P2 , (b) P3 and (c) P1 region. 140 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Despite the use of a di-silver precursor, there was no evidence for the formation of a Ag2Mn2 cluster. This suggested the high stability of the AgMn2 moieties in these clusters. The use of mono-silver sources such as AgX’ (X’ = OTf, TFA) with the anionic Mn2 complex, the diphosphine and the amine oxide did not lead to higher yield of 4.4a and 4.4b. It still gave rise to the highnuclearity clusters 4.3a and 4.3b which then led to 4.4a, 4.4b and other decomposition products. 4.3 Summary The heterometallic clusters 4.3a and 4.3b were obtained from condensation reactions of 4.1 with 4.2a and 4.2b. When the reactions were carried out under reflux or in the presence of (CH3)3NO∙ 2H2O, clusters 4.3a and 4.3b underwent phosphine migration to give clusters 4.4a and 4.4b. All clusters have been characterised by NMR and FTIR spectroscopy, elemental analysis and X-ray crystallography. Clusters 4.3b and 4.4b were found to isostructural to the previously reported Au(I) clusters.145c, 145d Comparison of crystal data of 4.3b and 4.4b with their gold analogue showed longer Ag-P bonds as compared to the Au-P bonds. The possible reason could be the relativistic effect of the Au atoms. A mechanism of formation of the clusters was proposed based on the previous study on the Au-Mn clusters.145c, 145d The Au(I) analogue of 4.4b was previously reported to be stable toward CO and PPh3 but could be destroyed by PPhMe2.145c However, the low yield and the instability of clusters 4.4a and 4.4b, and in particular 4.4a precluded the performance of such a comparative reactivity study. This remains to be a challenge for further investigation. 141 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.4 Experimental Section 4.4.1 General Procedures and Materials The syntheses were carried out under nitrogen using standard Schlenk techniques. All reagent are commercial products and used without further purification. Tetrahydrofuran used for synthesis was distilled using Na/benzophenone and degassed before used. Complexes 4.1,144 4.2a147 and 4.2b148 were prepared according to literature methods. TLC plates used were precoated TLC plates ADAMANT UV254 (layer 0.25mm and 20 x 20 cm). Elemental analyses were performed by the Chemical, Molecular and Materials Analysis Centre (CMMAC), NUS. 4.4.2 NMR and FTIR Spectroscopy NMR spectra were measured on a Bruker ACF 300MHz FT-NMR spectrometer at 300.14 MHz (1H) and 121.49 MHz (31P{1H}) unless otherwise stated. Variable temperature 31 P{1H} NMR spectra of 4.3 were measured in CD2Cl2 on a Bruker AMX 500MHz FT-NMR spectrometer at 202.46 MHz. 1H chemical shifts was quoted downfield of TMS and referenced to residual CHCl3 in CDCl3 and C4H8O in C4D8O. 31 P{1H} chemical shifts were externally referenced to 85% H3PO4 and are listed in Table 4-1. FTIR spectra in KBr pellet were measured in the range of 4000-400 cm-1 on a Biorad FTS-165 FTIR instrument. 142 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.4.3 X-Ray Crystallography Crystals of 4.3a · CH2Cl2 and 4.3b were grown by layering hexane onto concentrated solutions of the compounds in CH2 Cl2. Crystals of 4.4a · 1.5 THF and 4.4b · THF were grown by layering hexane onto concentrated solutions of the compounds in THF. Crystals of 4.4a · 1.5 THF were grown in air. The solution slowly undergoes decomposition during crystal growing. Therefore the crystals of 4.4b · THF were grown under N2 atmosphere by assuming that the solution is not stable in air. Analyses of crystals of clusters 4.3a, 4.3b, 4.4a and 4.4b were carried out using the instrument, softwares124-126 and methods as described in Section 2.4.4. The crystal of complex 4.3a is triclinic, space group Pī. There is one molecule of the titled compound per asymmetric unit. There is also one solvent molecule of CH2Cl2 which disordered into three positions. The titled molecule consists of two trinuclear Mn2Ag moieties linked through a dppm bridge. It has an approximately two-fold rotational axis through the methylene carbon of the dppm bridge (C17). However, this symmetry element was not utilised in the crystal packing. The asymmetric unit of the crystal of complex 4.3b consists of half of the titled molecule. For complex 4.4a, the crystal is monoclinic, space group P21. There are two molecules of the compound and three THF solvent molecules per asymmetric unit. Final refinement gave R1 = 0.047 and wR2 = 0.118. There are two residual peaks greater than 1.0 eÅ-3. These probably arise out of crystal imperfection. The crystal of complex 4.4b is triclinic, space group Pī. The asymmetric unit contains one titled molecule and two THF molecules. The two THF molecules have larger thermal parameters. The crystal was observed to be not stable probably due to 143 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters losing of solvent. The data set was not good with R(int) of 0.133 at 2θ of 50 º. Final R values are: R1 = 0.087 and wR2 = 0.209. The parameters for crystal structures determination of clusters 4.3a · CH2Cl2, 4.3b, 4.4a · 1.5 THF and 4.4b · THF are listed in Table 4-2. Table 4-2: Crystallographic data collection parameters for clusters 4.3a · CH2Cl2, 4.3b, 4.4a · 1.5 THF and 4.4b · THF Chemical formula 4.3a ·CH2Cl2 C66H44Ag2Cl2 Mn4O16P4 FW, g/mol 1723.29 Crystal system Triclinic Space group Pī a, Å 13.849(7) b, Å 15.651(8) c, Å 19.513(1) o α, 78.107(1) o β, 87.502(1) o γ, 65.102(1) Volume, Å 4860.0(4) Z -3 ρcacld, Mgm 1.526 -1 µ, mm 1.382 T (K) 223(2) No of reflections 49232 collected No of 17184 independent [R(int)= 0.0616] reflections No of parameters 895 Goodness-of –fit 1.084 R1 and wR2 R1 = 0.0644 [I>2 sigma(I)] wR2 = 0.1578 a 4.3b C74H48Ag2Fe Mn4O16P4 4.4a·1.5 THFa C50H44Ag Mn2O8.5P3 C61H54AgFe Mn2O9P3 1808.35 Monoclinic P21/c 14.613(8) 14.595(8) 16.568(9) 90 92.084(2) 90 3749.4(3) 1.701 1.593 223(2) 20360 1091.51 Monoclinic P21 11.011(6) 35.069(7) 13.306(7) 90 108.930(1) 90 3531.0(3) 1.492 1.062 223(2) 34735 1297.55 Triclinic Pī 12.679(4) 13.039(4) 17.811(5) 106.867(6) 93.757(6) 90.162(6) 2811.1(1) 1.533 1.177 223(2) 29154 6201 [R(int)= 0.0975] 457 0.945 R1 = 0.0584 wR2 = 0.1115 20788 [R(int)= 0.0371] 1163 1.014 R1 = 0.0472 wR2 = 0.1140 9906 [R(int)= 0.01335] 694 1.021 R1 = 0.0870 wR2 = 0.1802 4.4b· 2THF R1 and wR2 (all data) R1 = 0.0978 wR2 = 0.1736 R1 = 0.1184 wR2 = 0.1309 R1 = 0.0549 wR2 = 0.1188 R1 = 0.1512 wR2 = 0.2073 Largest diff. peak and hole (eÅ-3) 1.436 and -0.580 0.954 and -0.507 1.635 and -0.494 1.459 and -1.173 Absolute structure parameter = 0.00(3) 144 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.4.4 Synthesis of Ag2Mn4(µ-PPh2)2(CO)16(µ-dppm) 4.3a 4.2a (0.0608g, 0.05 mmol) was added to a stirring CH2Cl2 solution (20ml) of 4.1 (0.1000g, 0.10 mmol). The orange solution changed to golden orange at the end of addition. The mixture was allowed to stir for hours. The resulting cloudy brown solution was dried under reduced pressure. The crude product was separated using TLC using CH2Cl2/Hexane (ratio = 1: 2.5 v/v). Major yellow band (Rf = 0.54) was collected and extracted using CH2Cl2. The solvent was removed under reduced pressure to give an orange powder of complex 4.3a (0.0453g, 55%). A minor brown band was observed (Rf = 0.11). However, attempts to extract the product from silica gel were unsuccessful. Analytical data for 4.3a: (Found: C, 48.32; H, 2.67. Anal. Calcd. for C65H42Ag2Mn4O16P4: C, 47.65; H, 2.56.) 1H NMR (CDCl3) (δ): 3.72 (s, br, 2H, CH2), 7.21-7.82 (m, 40H, Ph). IR(CO, cm-1): 1910s , 1941s,1978s, 2013s (KBr). 4.4.5 Synthesis of Ag2Mn4(µ-PPh2)2(CO)16(µ-dppf) 4.3b A similar procedure was performed using 4.1 (0.1005g, 0.10 mmol) and 4.2b (0.0705 g, 0.05 mmol) in CH2Cl2 (20ml) for hours. TLC was performed using CH2Cl2/Hexane (ratio = 1: v/v) as solvent. Major yellow band (Rf = 0.50) was collected, extracted and dried to give 4.3b as an orange solid (0.0386 g, 43%). Analytical data for 4.3b: (Found: C, 48.78; H, 2.53. Anal. Calcd. for C74H48Ag2Mn4O16P4Fe: C, 49.16; H, 2.65.) 1H NMR (CDCl3) (δ): 4.18 (s, br, 4H, Cp), 4.58 (s, br, 4H, Cp), 7.32-7.90 (m, 40H, Ph). IR(CO, cm-1):1917s, 1949s, 1976s, 2012s (KBr). 145 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4.4.6 Preparation of AgMn2(µ-PPh2)(CO)7(µ-dppm) 4.4a from 4.3a 4.3a (0.1000 g, 0.06 mmol), dppm (0.0234g, 0.06 mmol) and (CH3)3NO · H2O (0.0136 g, 0.12 mmol) were filled in a Schlenk flask. THF (20 ml) was injected into the flask using a syringe. The golden orange solution turned red after ca 30 minutes of stirring. The solution was allowed to stir at 65oC and monitored using TLC. The red spot slowly increased in intensity and the reaction was stopped when the TLC did not give any significant change (ca. hours). A brown residue was observed at the end of the reaction. The red cloudy solution was then pumped dry. The crude product was separated using TLC. Slow decomposition was observed during the chromatographic separation. Elution using CH2Cl2/Hexane (1: 2.5 v/v) gave 4.3a (0.0176 g, 36%) and 4.4a (0.0068g, 11%). The Rf value of complex 4.4a is 0.37. Using excess (CH3)3NO · 2H2O (0.0339 g, 0.31 mmol) in the reaction gave 4.3a (0.0127g, 26%) and 4.4a (0.0050g, 8%). The yield % was calculated based on the amount of cluster 4.3a used as shown in Scheme 4-3. Attempts to purify cluster 4.4a using TLC did not improve the purity of the product as slow decomposition was observed. Therefore satisfactory microanalytical data was unable to be obtained. Analytical data for 4.4a: 1H NMR (C4D8O) (δ): 3.86 (dt, br, 2H, CH2), 7.16-7.92 (m, 30H, Ph). IR (CO, cm-1):1897s, 1939s, 1981s, 2025s (KBr). 4.4.7 Preparation of AgMn2(µ-PPh2)(CO)7(µ-dppf) 4.4b from 4.3b A similar procedure was applied using 4.3b (0.1000 g, 0.06mmol), dppf (0.0307g, 0.06 mmol) and (CH3)3NO · H2O (0.0123 g, 0.11 mmol). The solution 146 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters was allowed to stir overnight. Elution using CH2Cl2/Hexane (1:2 v/v) gave 4.3b (0.0299 g, 55%) and 4.4b (Rf = 0.36) (0.0013 g, 2%). Using excess of (CH3)3NO ∙ H2O (0.0307 g, 0.28 mmol) gave 4.3b (0.0353g, 65%) and 4.4b (0.0064g, 9%). The yield % was calculated based on complex 4.3b used as shown in Scheme 4-3. Analytical data for 4.4b: (Found: C, 55.42; H, 4.00. Anal. Calcd. for C53H38AgMn2O7P3Fe: C, 55.20; H, 3.30). 1H NMR (C4D8O) (δ): 4.15 (s, br, 4H, Cp), 4.46 (s, br, 4H, Cp), 7.13-7.89 (m, 30H, Ph). IR(CO, cm-1): 1901s, 1948s, 1980s, 2027s (KBr). 4.4.8 Reaction of 4.3a with Dppf in the Presence of (CH3)3NO · 2H2O 4.3a (0.1000 g, 0.06mmol), dppf (0.0333, 0.06 mmol) and (CH3)3NO · 2H2O (0.0136 g, 0.12 mmol) were filled in a Schlenk flask. THF (20 ml) was injected into the flask using a syringe. The golden orange solution turned red after ca 30 minutes stirring. The solution was allowed to stir at 65oC and monitored using TLC. The red spot slowly increased in intensity and the reaction was stopped when the TLC did not give any significant change (ca. hours). The red cloudy solution was then pumped dry. The crude product was separated using TLC. Elution using CH2Cl2/ Hexane (1: 2.5 v/v) gave a mixture of 4.3a and 4.3b at 1st major yellow band (0.0784g). Clusters 4.4a and 4.4b were obtained at the 2nd minor band (0.0080g). 31 P {1H} NMR spectrum of 1st band (in CDCl3) suggest 4.3b as major product while 31 P {1H} NMR spectrum (in C4D8O) of 2nd band suggest 4.4a as major product. 147 [...]... with the anionic Mn2 complex, the diphosphine and the amine oxide did not lead to higher yield of 4. 4a and 4. 4b It still gave rise to the highnuclearity clusters 4. 3a and 4. 3b which then led to 4. 4a, 4. 4b and other decomposition products 4. 3 Summary The heterometallic clusters 4. 3a and 4. 3b were obtained from condensation reactions of 4. 1 with 4. 2a and 4. 2b When the reactions were carried out under... (CO )4 H2 Mn C Ph2P P Ag Ag P Ph2 Ph2 (OC)4Mn (CO )4 Mn PPh2 Mn (CO )4 Ph2 P (OC)4Mn (minor) 4. 3a Mn(CO)3 PPh2 (major) Ag P CH2 Ph2 4. 4a + (CO )4 Mn Ph2P (OC)4Mn Fe Ag P Ph2 4. 3b + (CO )4 Ph2 Mn P Ag PPh2 Mn (CO )4 Ph2 P (major) (OC)4Mn Mn(CO)3 (minor) PPh2 Ag PPh2 Fe 4. 4b Scheme 4- 5: A reaction of cluster 4. 3a with dppf ligand 139 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4. 3b 4. 3b 4. 3a... (0.0386 g, 43 %) Analytical data for 4. 3b: (Found: C, 48 .78; H, 2.53 Anal Calcd for C74H48Ag2Mn4O16P4Fe: C, 49 .16; H, 2.65.) 1H NMR (CDCl3) (δ): 4. 18 (s, br, 4H, Cp), 4. 58 (s, br, 4H, Cp), 7.32-7.90 (m, 40 H, Ph) IR(CO, cm-1):1917s, 1 949 s, 1976s, 2012s (KBr) 145 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4. 4.6 Preparation of AgMn2(µ-PPh2)(CO)7(µ-dppm) 4. 4a from 4. 3a 4. 3a (0.1000... = 48 .0 (4) , Mn(2)-Mn(1)-P(1) = 48 .2 (4) , Mn(3)-Mn (4) -P (4) = 48 .1(5), Mn (4) Mn(3)-P (4) = 47 .8(5), Mn(1)-Ag(1)-P(2) = 153.0 (4) , Mn(2)-Ag(1)-P(2) = 130.7 (4) , Mn(3)-Ag(2)-P(3) = 127 .4( 4), Mn (4) -Ag(2)-P(3) = 150.2 (4) , Ag(1)-Mn(1)-P(1) = 105.0(5), Ag(1)-Mn(2)-P(1) = 102.3(5), Ag(2)-Mn(3)-P (4) = 102.0(5), Ag(2)-Mn (4) -P (4) = 103.9(5) 132 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Figure 4- 5:... [(PPh3)2N] Ph2 P (OC)4Mn Mn(CO )4 P + P Ag Ag P Ph2 P (OC)4Mn Mn(CO)3 Ag P 2+ P 2 [X'] P 4. 4 4. 1 4. 2 (CO )4 P Mn Ag Ph2P Mn (CO )4 P P Ag P (CO )4 Mn + 2 [(PPh3)2N] [X'] PPh2 Mn (CO )4 P Proposed intermediate 1 P (CO )4 Mn Ph2P Ag P Mn (CO )4 4.3 P (CO )4 Mn P Ag PPh2 Mn (CO )4 (CO )4 Mn 2 Ph2P Ag (OC)4Mn (CO )4 Mn P Ag PPh2 Mn (CO)3 Proposed intermediate 3 THF CO (CO )4 Mn Ag Ph2P Mn (CO )4 P (CO )4 Mn P Ag PPh2 Mn(CO)3... CH2Cl2, 4. 3b, 4. 4a · 1.5 THF and 4. 4b · 2 THF are listed in Table 4- 2 Table 4- 2: Crystallographic data collection parameters for clusters 4. 3a · CH2Cl2, 4. 3b, 4. 4a · 1.5 THF and 4. 4b · 2 THF Chemical formula 4. 3a ·CH2Cl2 C66H44Ag2Cl2 Mn4O16P4 FW, g/mol 1723.29 Crystal system Triclinic Space group Pī a, Å 13. 849 (7) b, Å 15.651(8) c, Å 19.513(1) o α, 78.107(1) o β, 87.502(1) o γ, 65.102(1) 3 Volume, Å 48 60.0 (4) ... 48 60.0 (4) Z 2 -3 ρcacld, Mgm 1.526 -1 µ, mm 1.382 T (K) 223(2) No of reflections 49 232 collected No of 171 84 independent [R(int)= 0.0616] reflections No of parameters 895 Goodness-of –fit 1.0 84 R1 and wR2 R1 = 0.0 644 [I>2 sigma(I)] wR2 = 0.1578 4. 3b C74H48Ag2Fe Mn4O16P4 4. 4a·1.5 THFa C50H44Ag Mn2O8.5P3 C61H54AgFe Mn2O9P3 1808.35 Monoclinic P21/c 14. 613(8) 14. 595(8) 16.568(9) 90 92.0 84( 2) 90 3 749 .4( 3)... Scheme 4- 4: A proposed mechanism for the formation of complexes 4. 3 and 4. 4 138 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters Reaction of 4. 3a with (CH3)3NO ∙ 2H2O in the presence of dppf (Scheme 4- 5) gave a mixture of products containing clusters 4. 3a, 4. 3b, 4. 4a and 4. 4b The clusters 4. 3b and 4. 4a were obtained as major products, as indicated in their 31 P{1H} NMR spectra (Figure 4- 8... = 0.2073 Largest diff peak and hole (eÅ-3) a R1 = 0.0978 wR2 = 0.1736 1 .43 6 and -0.580 0.9 54 and -0.507 1.635 and -0 .49 4 1 .45 9 and -1.173 Absolute structure parameter = 0.00(3) 144 Chapter Four: Formation and Decarbonylation of {Ag2Mn4} Clusters 4. 4 .4 Synthesis of Ag2Mn4(µ-PPh2)2(CO)16(µ-dppm) 4. 3a 4. 2a (0.0608g, 0.05 mmol) was added to a stirring CH2Cl2 solution (20ml) of 4. 1 (0.1000g, 0.10 mmol) The... Formation and Decarbonylation of {Ag2Mn4} Clusters 4. 2.2 Crystal Structures of Clusters 4. 3a, 4. 3b, 4. 4a and 4. 4b The crystal structures of clusters 4. 3a (as CH2Cl2 solvate) (Figure 4- 4) and 4. 3b (Figure 4- 5) show two isostructural open-clusters with a diphosphine bridging the two heterometallic triangles In cluster 4. 3b, an anti conformation of the dppf ligand allows the two metal triangles to move away from . P 2 , (b) P 3 and (c) P 1 region. P 1 P 2 4. 3a 4. 3b 4. 3b 4. 3a 4. 4a 4. 4b 4. 4a 4. 4b 4. 4a 4. 4b P 1 P 2 P 3 (a) (b) (c) (a) (b) Chapter Four: Formation and Decarbonylation. Formation and Decarbonylation of {Ag 2 Mn 4 } Clusters 130 Table 4- 1: 31 P chemical shifts (in ppm) of clusters 4. 3a, 4. 3b, 4. 4a and 4. 4b Ag P 1 AgP 1 (CO) 4 Mn (CO) 4 Mn Mn (CO) 4 Mn (CO) 4 P 2 P 2 4 . 3 Ag ( C O ) 4 Mn (OC) 3 Mn P 2 P 3 P 1 4 . 4 . the diphosphine and the amine oxide did not lead to higher yield of 4. 4a and 4. 4b. It still gave rise to the high- nuclearity clusters 4. 3a and 4. 3b which then led to 4. 4a, 4. 4b and other decomposition