New Azasllatranes: Bldentate and Tridentate Coordination Modes of the Novel Ligand EtOSI(Ph2PNCH2CH2l.(HNCH2CH2)N

The synthesis and characterization of EtOSHPh2PNCH2CHjh(HNCH2CH21N (ethoxy·N,N'·bis(di. phenylphosphinolazasilatrane, the title compound 3b) is reporud. ts reactions with sulfur and Mel proceed easily via quaternization at the phosphorus sites to give the bis(phosphonium) salt and the bis(phosphlne) sulfide, respectively. Synthesis and characterization of the coordination compounds (3b)Ni(COh, (3b)PtCI2, (3b)M(CO). (M "" Mo, W), and (3b)M(COh (M "" Mo, W) give evidence for the existence of two possible coordination modes; one wherein 3b behaves as a bidentate (P,P') ligand and the other as a tridentate (P,P',O) ligand. The latter coordination mode provides a rare example of coordination of a sHyl ether to a transition metal. NMR spectroscopic studies in solution and the solid state establish the presence of transannular Si-N bonding and hypercoordination at silicon. Solid·state SLp NMR spectra give direct evidence for the presence of a twisted, helically chiral conformation of the silatranyl cage, which in solution is lost 85 a consequence of rapid conformational mobility on the NMR time scale. These findings are further corroborated by the results of crystal structure determinations of the bis(phosphine) sulfide and (3b)PtCI2• Crystals of the bis(phosphine) sulfide are monoclinic, space group P2dc, with Z = 4 in a unit cell havin! dimensions a = 11.552 (3) A. b "" 19.661 (3) A, c "" 15.199 (3) A, fj "" 107.35 (W, and dcalod = 1.311 g/ em. Crystals of (3b)PtCI2 are monoclinic, space group C2!m, Z "" 2, dWod "" 1.48 g/cmJ, with unit cell dimensions a = 15.U7 (2) .3.. , b = 17.270 (2) A, c "" 9.791 (2) A, and fj "" 105.20 (2)°.