SUBVALENT GROUP-14 METAL-COMPOUNDS .16. SYNTHESIS, CRYSTAL-STRUCTURE AND CHARACTERIZATION OF SOME BETA-FUNCTIONALIZED-ALKYLTIN(II) COMPLEXES, SNR(X) (R = C5H4N[C(SIME3)2], X = R, CL OR N(SIME3)2)

Crystalline monomeric alkyltin(II) compounds were prepared using the beta-N-functionalised ligand 2-pyridylbis(trimethylsilyl)methyl, C5H4N[C(SiMe3)2]-2 (R): (a) SnR2 1 from (LiR)2 and SnCl2 or Sn(OC6H3But2-2,6)2 (b) SnR(Cl) 2 from SnCl2 and SnR2 or 1/2(LiR)2; and (c) SnR[N(SiMe3)2] 3 from Sn[N(SiMe3)2]2 and 1/2(LiR)2. Single-crystal X-ray diffraction data showed that in each of 1-3 R- behaves as a chelating C,N-centred ligand, and that the lone pair on tin is stereochemically active. The mean Sn-C [and Sn-NC5H4] bond lengths (angstrom) are 2.35(2) [2.42(2)] in 1, 2.32(2) [2.27(3)] in 2, and 2.356(8) [2.299(5)] in 3. Variable-temperature multinuclear (H-1, C-13, Si-29 and Sn-119) NMR spectral data were obtained for 1-3 in [H-2(8)]toluene. These showed that dynamic processes were operative, believed to be Sn-N (C5H4) dissociations, with DELTAG(double-dagger)T(c) = 43.5 +/- 0.8 for 2 or 42.7 +/- 0.8 kJ mol-1 for 3 (the coalescence temperature T(c) being 220 +/- 2 for 2 and 214 +/- 2 K for 3); for 3 a further fluxion with DELTAG(double-dagger)T(c) = 76.1 +/- 0.8 kJ mol-1 (T(c) = 368 +/- 2 K) is attributed to the barrier to rotation about the tin-amide nitrogen bond. Attempts were made to reduce 2 [evidence for (SnR)n], and to prepare analogues of Ge(II) and Pb(II) of 1 and 2. A further beta-functionalised complex, SnCl(OCBut2CH2PMe2) 4, was obtained from SnCl2 and 1/2[Li(OCBut2CH2PMe2)]2; there was no evidence for P-31-Sn-119 coupling, and a plausible structure is [Sn(mu-Cl)(OCBut2CH2PMe2)]2. A similar metathetical reaction between SnCl2 and Sn(OC6H3But2-2,6)2 in tetrahydrofuran (thf) gave 1/m[SnCl(OC6HBut2-2,6)(thf)n]m, whereas SnCl2 + SnR'2 [R' = CH(SiMe3)2] yielded SnR'2Cl2 + Sn.