ARTICLE DOI: 10.1002/zaac.201100134 Syntheses and Structures of Nitridorhenium(V) and Nitridotechnetium(V) Complexes with N,N-[(Dialkylamino)(thiocarbonyl)]-N'-(2hydroxyphenyl)benzamidines Hung Huy Nguyen,*[a] Thi Nguyet Trieu,[a] and Ulrich Abram*[b] Keywords: Rhenium; Technetium; Tridentate benzamidine; Nitrido complexes; Structure analysis Abstract [MNCl2(PPh3)2] complexes (M = Re, Tc) react with N-[(dialkylamino)(thiocarbonyl)]-N'-(2-hydroxyphenyl)benzamidines (H2L1) with formation of neutral, five-coordinate nitrido complexes of the composition [MN(L1)(PPh3)] The products have distorted squarepyramidal coordination spheres with each a tridentate, double-deprotonated benzamidine and a PPh3 ligand in their basal planes Introduction phenyl)benzamidines (H2L1) has been intensively studied Most of the isolated complexes with these ligands have oxorhenium(V) or oxotechnetium(V) cores Five-coordinate oxorhenium(V) and oxotechnetium (V) complexes,[2] as well as cis methoxo compounds,[5] ‘3+2’ mixed-ligand complexes,[6] and dimeric oxorhenium(V) complexes[5] were isolated and structurally characterized Only one exceptional compound is an octahedral technetium(III) complex.[2] In continuation of our systematic studies on thiocarbamoylbenzamidinato complexes of rhenium and technetium, here we report the synthesis and molecular structures of nitridorhenium(V) and nitridotechnetium(V) complexes with ligands of the type H2L1 Despite the fact that bidentate N-[(dialkylamino)(thiocarbonyl)]benzamidines (I) are well known chelators and a large number of their complexes with many transition metal ions, such as Ni2+, Pd2+, Pt2+, Co3+, Cu2+, Ag+, and Au+ have been extensively studied during the last three decades,[1] surprisingly less is known about tridentate benzamidines Recently, we have reported about such ligands (II), which can be prepared by reactions of benzimidoyl chlorides with functionalized primary amines.[2] These ligand systems allow a variety of modifications in the periphery of their chelating system, which tune their properties and also give access to amino acid derivatives and bioconjugation.[3] Some complexes of the new ligands, preferably derivatives of thiosemicarbazides, reveal promising cytotoxic properties against human MCF-7 breast cancer cells.[4] Particularly the coordination chemistry of rhenium and technetium with N-[(dialkylamino)(thiocarbonyl)]-N'-(2-hydroxy* Dr N H Huy E-Mail: nguyenhunghuy@hus.edu.vn * Prof Dr U Abram Fax: +49-30-838-2676 E-Mail: ulrich.abram@fu-berlin.de [a] Inorganic Chemistry Department Hanoi University of Science 19 Le Thanh Tong Hanoi, Vietnam [b] Institute of Chemistry and Biochemistry Freie Universität Berlin Fabeckstrasse 34–36 14195 Berlin, Germany 1330 Results and Discussion [MNCl2(PPh3)2] compounds (M = Re, Tc) are common starting materials for the synthesis of ReV and TcV nitrido complexes The compounds are sparingly soluble in organic solvents However, they slowly dissolve in stirred solutions of H2L1 in CH2Cl2 at room temperature with formation of deep red solutions, from which red crystalline products of the composition [MN(L1)(PPh3)] (M = Re, Tc) can be isolated in high yields The addition of a supporting base like Et3N accelerates the consumption of [ReNCl2(PPh3)2], whereas [TcNCl2(PPh3)2] is more labile than its analogous rhenium compound and readily reacts with the ligand without the addition of a base (Scheme 1) The complexes are readily soluble in polar organic solvents such as CHCl3 or THF They are stable as solids as well in solution Their structures were studied by common spectroscopic methods Infrared spectra of the complexes exhibit strong bathochromic shifts of the νC=N stretches from the range between 1610 and 1620 cm–1 of the non-coordinated benzamidines to the 1510 cm–1 region This indicates chelate formation with a large degree of π-electron delocalization within the chelate rings and has been observed before for the corresponding oxo complexes.[2] The absence of absorptions in the regions around © 2011 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Z Anorg Allg Chem 2011, 637, 1330–1333 Nitridorhenium(V) and Nitridotechnetium(V) Complexes The structure of [TcN(L1b)(PPh3)] is virtually identical Thus, no extra Figure is presented for the technetium compound The corresponding bond lengths and angles, however, are also contained in Table Scheme Reactions of [MNCl2(PPh3)2] (M = Re, Tc) with H2L1 The addition of NEt3 is only required for the rhenium compound (see text) 3350 cm–1 and 3150 cm–1, in which the νNH and νOH stretches are detected in the spectra of the uncoordinated H2L1, indicates the expected double deprotonation of the ligands during complex formation Absorption bands of medium intensity around 1065 cm–1 are assigned to Re≡N and Tc≡N stretches.[7] The NMR spectra of the complexes provide additional evidence for the proposed composition and the molecular structures of the complexes A hindered rotation around the C–NR2 bonds results in magnetic inequivalence of the two residues R Thus, two triplet signals of the methyl groups in the –NEt2 residues are observed in the 1H NMR spectra of [ReN(L1a)(PPh3)] and [TcN(L1a)(PPh3)] at room temperature However, the proton signals of the two methylene groups, which should consequently be two quartet signals, appear as four multiplet resonances including two overlapping signals at 3.80 ppm and two well separated signals at 3.68 ppm and 4.17 ppm in the spectrum of the rhenium compound This pattern of the methylene signals can be explained by the rigid structure of the tertiary amine group, which makes the methylene protons magnetically inequivalent with respect to their axial and equatorial positions The rigidity of morpholinyl moiety of {L1b}2– in [ReN(L1b)(PPh3)] results in four broad singlet signals at 3.59, 3.81, 3.96, and 4.32 ppm, which correspond to two CH2–N protons and two CH2–O protons The signals of four other protons appear as two overlapping broad singlet signals at 3.70 and 4.16 ppm Similar coupling patterns are observed in the spectra of the corresponding technetium complexes The 13C NMR spectra of the complexes are easier to explain, since their patterns are only influenced by hindered rotation around the C–NR2 bonds Consequently, two separated signals for each CH2 and CH3 carbon atoms in the NEt2 groups and/ or CH2–N and CH2–O atoms in the morpholinyl units appear The presence of triphenylphosphine ligands in the coordination sphere of the products is confirmed by each one singlet signal in their 31P NMR spectra, appearing around 30.0 ppm for the rhenium compounds and around 45 ppm for the technetium complexes ESI+ mass spectra of the rhenium complexes show intense signals corresponding to the expected [M + Na]+ and [M + H]+ ions X-ray structure analyses were performed for [ReN(L1b)(PPh3)] and [TcN(L1b)(PPh3)] Suitable single crystals were obtained by slow evaporation of CH2Cl2/MeOH solutions of the compounds Figure illustrates the molecular structure of the rhenium complex Selected bond lengths and angles are presented in Table Z Anorg Allg Chem 2011, 1330–1333 Figure Ellipsoid representation of the molecular structure of [ReN(L1b)(PPh3)] Hydrogen atoms are omitted for clarity Thermal ellipsoids represent 50 per cent probability Table Selected bond lengths /Å and angles /° in [MN(L1b)(PPh3)] (M = Re, Tc) complexes The atomic labeling scheme of Figure is also applied for the technetium complex M–N10 M–P M–S1 M–N5 M–O57 S1–C2 C2–N3 N3–C4 C4–N5 C2–N6 N10–M–P N10–M–S1 N10–M–N5 N10–M–O57 P–M–N5 O57–M–S1 [ReN(L1b)(PPh3)] [TcN(L1b)(PPh3)] 1.645(6) 2.418(1) 2.316(1) 2.084(4) 2.026(4) 1.764(6) 1.338(8) 1.310(8) 1.354(7) 1.336(8) 92.6(2) 104.7(2) 107.8(2) 111.5(2) 158.0(1) 143.8(1) 1.619(5) 2.436(1) 2.330(1) 2.091(4) 2.029(4) 1.758(6) 1.341(7) 1.335(8) 1.327(8) 1.330(8) 93.3(2) 104.9(2) 107.7(2) 112.0(2) 157.9(1) 143.0(1) The metal atoms show distorted square-pyramidal coordination spheres with the nitrido ligands in apical positions Such an assignment of the molecular geometry is supported by the corresponding τ values of 0.25 (technetium compound) and 0.24 (rhenium complex) They clearly indicate that the complexes under study are better described with a square-pyramidal coordination sphere (τ = 0) than as trigonal bipyramids (τ = 1) The thiocarbamoylbenzamidines coordinate meridional to the metal atoms as tridentate dianionic ligands as in their previously reported oxo complexes The remaining positions in the basal planes of the square pyramids are occupied each by a triphenylphosphine ligand The metal atoms lie above the equatorial planes towards the nitrido ligands by 0.528(2) Å for © 2011 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim www.zaac.wiley-vch.de 1331 ARTICLE H H Nguyen, T N Trieu, U Abram the rhenium complex and 0.544(2) Å for the technetium compound The N10–Re–X angles (X = equatorial donor atom) fall in the range between 92.6 and 111.5°, the corresponding N10– Tc–X angles are between 93.3 and 112.0° These values are in complete agreement with the typical bonding situation of square-pyramidal ReVN and TcVN complexes.[8] The Re–N10 and Tc–N10 distances of 1.645(6) and 1.619(5) Å are within the expected range of rhenium or technetium–nitrogen triple bonds.[9] The six-membered chelate rings are strongly distorted for both complexes, with main deviations of 0.413(4) Å (rhenium complex) and 0.419(4) Å (technetium complex) from the mean least-square planes each for the nitrogen atoms N5 Nevertheless, a considerable delocalization of π-electron density is observed This is indicated by the C–S and C–N bond lengths inside the chelate rings, which all fall within the range between carbon–sulfur and carbon–nitrogen single and double bonds This bond length equalization is even extended to the C2–N6 bonds, which are significantly shorter than expected for single bonds All the MO, MN and M–S bonds are slightly longer than those in the corresponding oxo complexes.[2,5] This can be understood by the larger steric bulk of the M≡N triple bond, which results in larger N≡MX(equatorial) angles and consequently in a somewhat less effective overlap between the ligand and the d orbitals of the metal ions Details have been discussed previously on a series of oxo, nitrido and phenylimido compounds of technetium and rhenium with 1,2-dicyanoethene-1,2-dithiolate.[10] Conclusions The ready synthesis and the stability of the nitrido complexes under study and the promising biological properties of the related oxo compounds[2–4] recommend transition metal complexes with ligands of the thiocarbamoylbenzamidine family for further consideration with regard to medical and nuclear medical applications Ongoing studies with tri- to pentadentate ligands with peripheral coupling positions for biomolecules are presently underway in our laboratories They also include nitrido complexes with the ligands discussed in this paper as well as tetradentate systems derived from diamines Experimental Section Materials and Measurements All reagents used in this study were reagent grade and used without further purification Solvents were dried and used freshly distilled unless otherwise stated [ReNCl2(PPh3)2][11] and [TcNCl2(PPh3)2][12] were prepared by standard procedures The synthesis of H2L1 ligands were described in a previous paper.[2] Infrared spectra were recorded from KBr pellets with a Shimadzu FT instrument in the range 400–4000 cm–1 Positive electrospray ionization mass spectra (ESI+ MS) were measured with an Agilent 6210 ESITOF (Agilent Technologies) (results are given in the form: m/z, % based peak, assignment) Elemental analyses were determined using a Heraeus vario EL elemental analyzer The technetium content was determined by liquid scintillation measurements NMR spectra were taken at 25 °C with a JEOL 400 MHz multinuclear spectrometer 1332 www.zaac.wiley-vch.de Radiation Precautions 99 Tc is a weak β- emitter All manipulations with this isotope were performed in a laboratory approved for the handling of radioactive materials Normal glassware provides adequate protection against the low-energy β- emission of the technetium compounds Secondary Xrays (bremsstrahlung) play an important role only when larger amounts of 99Tc are used Synthesis of [ReN(L1)(PPh3)] Solid [ReNCl2(PPh3)2] (80 mg, 0.1 mmol) was added to a stirred solution of H2L1 (0.1 mmol) in CH2Cl2 (5 mL) The mixture was stirred at room temperature for 15 and then drops of Et3N were added This resulted in a complete dissolution of [ReNCl2(PPh3)2] and the formation of a red solution The solvent was removed under vacuum, and the residue was crystallized by slow evaporation of a CH2Cl2/ MeOH solution as red blocks The side products (HNEt3)Cl and PPh3 remain in the residual MeOH Alternatively, the crude reaction product can be washed twice with methanol before re-dissolution in CH2Cl2 for crystallization Data for [ReN(L1a)(PPh3)] (R1 = R2 = Et): Yield: 60 mg, 76 % Elemental analysis Calcd for C36H34N4OPSRe: C, 54.88; H, 4.35; N, 7.11; S, 4.07 % Found: C, 54.78; H, 4.30; N, 7.07; S, 4.15 % IR: ν = 3059 (w), 2978 (w), 2932 (w), 1512 (vs), 1492 (vs), 1477 (vs), 1439 (s), 1393 (m), 1354 (m), 1254 (vs), 1096 (m), 1065 (m), 1026 (w), 744 (m), 686 (s), 528 (s), 505 (m) 1H NMR (CDCl3): δ = 1.08 (t, J = 7.0 Hz, H, CH3), 1.26 (t, J = 7.1 Hz, H, CH3), 3.68 (m, H, CH2), 3.80 (m, H, CH2), 4.17 (m, H, CH2), 6.27 (t, J = 7.6 Hz, H, PhOH), 6.47 (d, J = 7.8 Hz, H, PhOH), 6.62 (t, J = 7.0 Hz, H, PhOH), 6.83 (d, J = 7.8 Hz, H, PhOH), 7.26 (t, J = 7.3 Hz, H, Ph), 7.35 (m, 10 H, Ph + PPh3), 7.79 (m, H, Ph + PPh3) 13C NMR (CDCl3): δ = 12.8, 13.2 (CH3), 46.3, 47.7 (CH2), 117.0–135.8 (Caromatic), 141.3 (Caromatic–N), 162.1 (Caromatic–O), 166.8 (C=N), 171.6 (C = S) 31P NMR (CDCl3): δ = 29.6 (s) ESI+ MS (m/z): 811, 100 %, [M + Na]+; 789, 40 %, [M + H]+ Data for [ReN(L1b)(PPh3)] (NR1R2 = morph): Yield: 64 mg, 80 % Elemental analysis Calcd for C36H32N4O2PSRe: C, 53.92; H, 4.02; N, 6.99; S, 4.00 % Found: C, 53.87; H, 4.15; N, 7.10; S, 4.09 % IR: ν = 3051 (w), 2970 (w), 2905 (w), 2858 (w), 1507 (vs), 1477 (vs), 1435 (s), 1388 (s), 1357 (w), 1257 (s), 1219 (m), 1096 (m), 1068 (m), 1026 (m), 745 (m), 690 (s), 528 (s), 505 (m) 1H NMR (CDCl3): δ = 3.59 (br s, H, NCH2), 3.70 (br s, H, NCH2), 3.81 (br s, H, NCH2), 3.96 (br s, H, OCH2), 4.16 (br s, H, OCH2), 4.32 (br s, H, OCH2), 6.27 (t, J = 7.6 Hz, H, PhOH), 6.49 (d, J = 7.8 Hz, H, PhOH), 6.64 (t, J = 7.6 Hz, H, PhOH), 6.84 (d, J = 7.9 Hz, H, PhOH), 7.27 (t, J = 7.3 Hz, H, Ph), 7.37 (m, 10 H, Ph + PPh3), 7.77 (m, H, Ph +PPh3) 13C NMR (CDCl3): δ = 48.8, 49.7 (NCH2), 66.7, 66.9 (OCH2), 117.2–135.7 (Caromatic), 140.9 (Caromatic–N), 163.0 (Caromatic–O), 167.1 (C=N), 171.3 (C = S) 31P NMR (CDCl3): δ = 28.8 (s) ESI+ MS (m/z): 825, 100 %, [M + Na]+; 803, 40 %, [M + H]+ Synthesis of [TcN(L1)(PPh3)] The technetium complexes were prepared following the procedure described for their analogous rhenium complexes except that the precursor [TcNCl2(PPh3)2] was used and no NEt3 was added Data for [TcN(L1a)(PPh3)] (R1 = R2 = Et): Yield: 59 mg, 84 % Elemental analysis Calcd for C36H34N4OPSTc: Tc, 14.1 % Found: Tc, 14.1 % IR: ν = 3051 (w), 2970 (w), 2924 (w), 1504 (vs), 1477 (vs), © 2011 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Z Anorg Allg Chem 2011, 1330–1333 Nitridorhenium(V) and Nitridotechnetium(V) Complexes 1434 (s), 1396 (m), 1350 (m), 1307 (m), 1258 (vs), 1095 (m), 1057 (m), 1026 (w), 798 (m), 741 (m), 690 (s), 528 (s), 497 (m) cm–1 1H NMR (CDCl3): δ = 1.09 (t, J = 7.1 Hz, H, CH3), 1.26 (t, J = 7.1 Hz, H, CH3), 3.67 (m, H, CH2), 3.75 (m, H, CH2), 4.00 (m, H, CH2), 6.23 (t, J = 7.5 Hz, H, PhOH), 6.37 (d, J = 7.7 Hz, H, PhOH), 6.63 (t, J = 7.1 Hz, H, PhOH), 6.79 (d, J = 7.8 Hz, H, PhOH), 7.26 (t, J = 7.4 Hz, H, Ph), 7.30 (m, 10 H, Ph + PPh3), 7.73 (m, H, Ph + PPh3) 31P NMR (CDCl3): δ = 45.4 (s) Data for [TcN(L1b)(PPh3)] (NR1R2 = morph): Yield: 63 mg, 89 % Elemental analysis Calcd for C36H32N4O2PSTc: Tc, 13.8 % Found: Tc, 13.9 % IR: ν = 3051 (w), 2970 (w), 2909 (w), 2843 (w), 1498 (vs), 1477 (vs), 1431 (s), 1400 (s), 1357 (w), 1312 (m), 1265 (s), 1215 (m), 1095 (m), 1060 (m), 1026 (m), 844 (m), 748 (s), 691 (s), 524 (s), 505 (m) cm–1 1H NMR (400 MHz, CDCl3): δ = 3.61 (br s, H, NCH2), 3.70 (m, H, NCH2), 3.76 (br s, H, NCH2), 3.98 (br s, H, OCH2), 4.05 (br m, H, OCH2), 4.20 (br s, H, OCH2), 6.22 (t, J = 7.5 Hz, H, PhOH), 6.38 (d, J = 7.8 Hz, H, PhOH), 6.65 (t, J = 7.6 Hz, H, PhOH), 6.79 (d, J = 7.8 Hz, H, PhOH), 7.22 (t, J = 7.4 Hz, H, Ph), 7.34 (m, 10 H, Ph + PPh3), 7.71 (m, H, Ph + PPh3) 31P NMR (CDCl): δ = 44.6 (s) X-ray Crystallography The X-ray diffraction data were collected with a STOE IPDS diffractometer with Mo-Kα radiation The structures were solved by the Patterson method using SHELXS-97.[13] Subsequent Fourier-difference map analyses yielded the positions of the non-hydrogen atoms Refinement was performed using SHELXL-97.[13] The positions of hydrogen atoms were calculated for idealized positions and treated with the ‘rid- Table Crystal data and refinement results Formula Mw /g·mol–1 Crystal system a /Å b /Å c /Å α /° β /° γ /° V /Å3 Space group Z Dcalcd /g·cm–3 μ /mm–1 No of reflections No of independent /Rint No parameters R1/wR2 GOF Deposit reference number [ReN(L1b)(PPh3)] [TcN(L1b)(PPh3)] C36H32N4O2PReS 801.89 triclinic 9.473(1) 11.650(1) 15.423(1) 95.04(1) 95.96(1) 108.32(1) 1593.9(2) P1¯ 1.671 3.968 17391 8499 / 0.1023 406 0.0422 / 0.0901 0.937 816874 C36H32N4O2PSTc 713.69 triclinic 9.454(1) 11.656(1) 15.451(1) 94.76(1) 95.41(1) 108.45(1) 1596.3(2) P1¯ 1.485 0.606 17115 8518 / 0.1245 407 0.0711 / 0.1378 0.988 816875 Z Anorg Allg Chem 2011, 1330–1333 ing model’ option of SHELXL-97 Crystal data and more details of the data collections and refinements are contained in Table Additional information on the structure determinations have been deposited at the Cambridge Crystallographic Data Centre Acknowledgement We thank the Deutscher Akademischer Austauschdienst (DAAD) for generous support H H Nguyen is additionally grateful to Vietnam’s National Foundation for Science and Technology Development for the financial support through project 104.02–2010.31 References [1] a) J Hartung, G Weber, L Beyer, R Szargan, Z Anorg Allg Chem 1985, 523, 153; b) R del Campo, J J Criado, E Garcia, M R Hermosa, A Jimenez-Sanchez, J L Manzano, E Monte, E Rodriguez-Fernandez, F Sanz, J Inorg Biochem 2002, 89, 74; c) W Hernandez, E Spodine, R Richter, K H Hallmeier, U Schröder, L Beyer, Z Anorg Allg Chem 2003, 629, 2559; d) U Schröder, R Richter, L Beyer, J Angulo-Cornejo, M Lino-Pacheco, A Guillen, Z Anorg Allg Chem 2003, 629, 1051; e) E Guillon, I Dechamps-Olivier, A Mohamadou, J.-P Barbier, Inorg Chim Acta 1998, 268, 13; f) R Richter, U Schröder, M Kampf, J Hartung, L Beyer, Z Anorg Allg Chem 1997, 623, 1021 [2] H H Nguyen, J Grewe, J Schroer, B Kuhn, U Abram, Inorg Chem 2008, 47, 5136 [3] a) H H Nguyen, U Abram, Polyhedron 2009, 28, 3945; b) J Schroer, U Abram, Polyhedron 2009, 28, 2277 [4] H H Nguyen, J J Jegathesh, P I da S Maia, V M Deflon, R Gust, S Bergemann, U Abram, Inorg Chem 2009, 48, 9356 [5] H H Nguyen, K Hazin, U Abram, Eur J Inorg Chem 2011, 78 [6] H H Nguyen, V M Deflon, U Abram, Eur J Inorg Chem 2009, 3179 [7] C Bolzati, M Cavazza-Ceccato, S Agostini, F Tisato, G Bandoli, Inorg Chem 2008, 47, 11972 [8] C Bolzati, F Refosco, A Cagnolini, F Tisato, A Boschi, A Duatti, L Uccelli, A Dolmella, E Marotta, M Tubaro, Eur J Inorg Chem 2004, 1902 [9] a) U Abram, Rhenium, in: Comprehensive Coordination Chemistry II (Eds.: J A McCleverty, T J Mayer), Elsevier, Amsterdam, The Netherlands, 2003;Vol 5, p 271; b) R Alberto, Technetium, in: Comprehensive Coordination Chemistry II (Eds.: J A McCleverty, T J Mayer), Elsevier, Amsterdam, The Netherlands, 2003;Vol 5, p 127 [10] B Kuhn, U Abram, Z Anorg Allg Chem 2011, 637, 242 [11] J Chatt, J D Garforth, N P Johnson, G A Rowe, J Chem Soc 1964, 1012 [12] U Abram, B Lorenz, L Kaden, D Scheller, Polyhedron 1988, 7, 285 [13] G M Sheldrick, SHELXS-97 and SHELXL97, Programs for the Solution and Refinement of Crystal Structures, University of Gưttingen, Germany, 1997 © 2011 WILEY-VCH Verlag GmbH & Co KGaA, Weinheim Received: March 21, 2011 Published Online: June 6, 2011 www.zaac.wiley-vch.de 1333 ... metal complexes with ligands of the thiocarbamoylbenzamidine family for further consideration with regard to medical and nuclear medical applications Ongoing studies with tri- to pentadentate ligands... agreement with the typical bonding situation of square-pyramidal ReVN and TcVN complexes. [8] The Re–N10 and Tc–N10 distances of 1.645(6) and 1.619(5) Å are within the expected range of rhenium... of the non-hydrogen atoms Refinement was performed using SHELXL-97.[13] The positions of hydrogen atoms were calculated for idealized positions and treated with the ‘rid- Table Crystal data and