Synthesis and structures of the dinuclear tin(II) complexes [R = Ph, X(Z) = CPh; R = SiMe3, X(Z) = PPh2] and of related compounds

Tin(II) compounds containing the ligands [CH(C6H3Me2-2,5)C(But)NSiMe3]− (≡ L1), [CH(Ph)C(Ph)NSiMe3]− (≡L2), [CH(SiMe3)P(Ph)2NSiMe3]− (≡ L3), (≡ L4), [C(Ph)C(Ph)NSiMe3]2− (≡ L5), and [C(SiMe3)P(Ph)2NSiMe3]2− (≡ L6) are reported: the transient SnBr(L1) (1) and SnBr(L2) (2), Sn(L1)2 (3) [P.B. Hitchcock, J. Hu, M.F. Lappert, M. Layh, J.R. Severn, J. Chem. Soc., Chem. Commun. (1997) 1189], the labile Sn(L2)2 (4), [Sn(L5)]2 (5), SnCl(L3) (6), Sn(L3)2 (7), [Sn(L6)]2 (8), Sn(L4)2 (9) and Pb(L4)2 (10). They were prepared from (i) SnBr2 and K(L1) (1, 3) or K(L2) (2, 4, 5); (ii) SnCl2 and Li(L3) (6–9); or (iii) PbCl2 and Li(L4) (10). Each of 1, 3 and 5–10 has been characterised by multinuclear NMR spectra; 3, 5, 6, 8, 9 and 10 by EI-mass spectra, but only 3, 5, 8, 9 and 10 were isolated pure and furnished X-ray quality crystals. Of greatest novelty are the title binuclear fused tricyclic ladder-like compounds 5 and 8. Quantum chemical calculations, on alternative pathways to 5 from 2 and to 8 from 7, are reported.