Heteronuclear tin(IV)–silver(I) complexes with phosphinothiolate ligands. X-ray structure of [AgSn(μ-SC6H4PPh2)2Me2(PPh2Me)]CF3SO3·CH2Cl2
Introduction
Much of the current interest in metallic thiolate complexes stems from the discovery that some metallic derivatives with sulphur atoms in the co-ordination sphere form the active centres of enzymes [1] such as hydrogenases and CO-dehydrogenases [2].
In the same way, the chemistry of asymmetric multidentate ligands have attracted a great deal of attention, in particular towards the phenomenon of hemilability [3]. Thiolate phosphine ligands are a good example of asymmetric multidentate ligands. Both phosphorus and sulphur are excellent ligand donor atoms for a wide range of metals, while the low ionisation energy of sulphur and the presence of several lone pairs of electrons offer the possibility of a rich sulphur-based chemistry of the complexes. The best known are R2PCH2CH2S− and R2PC6H4S− ligands [4], [5], [6], but in recent years there has been and increasing interest in the ligands RP(C6H4S−)2 and P(C6H4S−)3 [4], [6], [7], [8], which are considered as potentially tri- and tetra-dentate ligands.
In a recent paper [9] we described the synthesis of tin (IV) complexes with phosphinethiolate ligands with the general formula [SnR2(SC6H4PPh2)2] as well as their reactivity towards gold (I) and silver (I) derivatives, mainly with the former. With continuied interest in the formation of heteronuclear tin–silver complexes, we report the reaction between [Ag(CF3SO3)(PR3)] (PR3=PPh3 and PPh2Me) and [SnR2(SC6H4PPh2)2]. In addition, we have prepared similar tin derivatives with the phosphine PPh(C6H4SH)2, [SnR2{(SC6H4)2PPh}], and performed the subsequent formation of the heterometallic complexes. The X-ray structure of [AgSn(μ-SC6H4PPh2)2Me2(PPh2Me)]CF3SO3 confirms the heteronuclear nature of these complexes and the role of phosphinothiolate as bridging ligand.
Section snippets
Results and discussion
The reaction of [SnR2(SC6H4PPh2)2] (R=Me and Ph) with [AgCF3SO3(PR3)] (PR3=PPh3 and PPh2Me) affords complexes 1–4 with the general formula [AgSn(μ-SC6H4PPh2)2R2(PR3)]CF3SO3 (R=Me, PR3=PPh3 (1); PPh2Me (2); R=Ph, PR3=PPh3 (3); PPh2Me (4)) in good yields as a result of the co-ordination of [AgPR3]+ units to the starting material (Scheme 1, i, ii).
The 1H-NMR spectra at room temperature of methyl compounds 1–2 show, among other resonances, a singlet for methyl protons. At −80°C each singlet splits
Conclusion
In conclusion we describe some heteronuclear Sn–Ag complexes with the phosphino–thiolate ligands SC6H4PPh2 and (SC6H4)2PPh. Although the coordination of the ligands in the starting tin derivatives [SnR2(SC6H4PPh2)2] and [SnR2{(SC6H4)2PPh}] (R=Me and Ph) are mainly through the sulphur atoms, the formation of heteronuclear complexes involves the coordination of the phosphorus atoms to the silver centre. In addition, the silver centre is bonded to some of the thiolate end of the ligands;
General procedures
IR spectra were recorded on a Perkin Elmer 883 spectrophotometer, over the range 4000–200 cm−1, by using Nujol mulls between polyethylene sheets. 1H- and 31P-NMR spectra were recorded on a Varian UNITY 300 or BRUKER 300 in CDCl3 or CD2Cl2 solutions; chemical shifts are quoted relative to SiMe4 (1H) and H3PO4 (external 31P). The C, H, N and S analyses were performed with a Perkin–Elmer 2400 microanalyser. Mass spectra were recorded on a VG Autospec, by liquid secondary ion mass spectrometry
Supplementary material
Crystallographic data for the structural analysis have been deposited with the Cambridge Crystallographic Data Centre, CCDC no. 149862. Copies of this information may be obtained from The Director, CCDC, 12 Union Road, Cambridge, CB2 1EZ, UK (fax: +44-1233-336033; e-mail: [email protected] or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
The Spanish authors thank the Dirección General de Enseñanza Superior (PB98-0542) for financial support and M.B.H. thanks the Engineering and Physical Sciences Research Committee for support of the X-ray facilities.
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