Tetrakis(trimethylstannyl) and bis(trimethylstannyl)dimethyl Group 14 element compounds, determination of coupling signs and measurements of isotope induced chemical shifts 1Δ12/13C(119Sn)

Tetrakis(trimethylstannyl) Group 14 element compounds, (Me3Sn)(4)M [M = C (1), Si (2), Ge (3), Sn (4)] and bis(trimethylstannyl)dimethyl Group 14 element compounds (1a-3a) were prepared and studied by H-1-,C-13-, Si-29-, Ge-73-, and Sn-119-NMR spectroscopy. The signs of (1)J((117) Sn-119,M) were determined [M = C-13, Si-29, Ge-73,Sn-119; all reduced coupling constants K-1(Sn,M) > 0]. In the series 1-4, the geminal coupling constants (2)J(Sn,M,Sn) are negative for M = C, Si, Ge, whereas the coupling sign is positive for M = Sn in 4. In the cases of 1a-4a, this geminal coupling constant is always positive, In the same series the reduced coupling constants K-2(Sn,M,C-13) are positive for 2a-4a but negative for 1a. All reduced coupling constants K-3(Sn,M,Sn,C-13) are positive. Isotope induced chemical shifts (1)Delta(12/13)C(Sn-119) cover a fairly large range of ca. 15 ppb. The relationship of this parameter with the magnitude of (1)J(Sn-119,C-13) is not straightforward, and there is also no clear influence of the group electronegativity of substituents. (C) 1999 Elsevier Science S.A. All rights reserved.