A proton NMR investigation of metalmetal bonding in trimethyltin-aluminium, -gallium, -indium and -thallium organometallic compounds

Proton NMR data for the Group III methyl derivatives, MMe₃ and LiMMe₄ are compared with NMR data for the novel tin—Group III-metal bonded species, LiMe₃SnMMe₃] (M  Al, Ga, In and Tl) and for Li(Me₃Sn)_n-TlMe_4?n] (n = 0 to 4), reported here for the first time.The presence of tinmetal bonding in these derivatives is established by the observed tin-across-metal coupling constants and for the thallium derivatives by the additional observation of thallium-across-tin coupling.The variation in the magnitudes of ²J(SnCH), ²J(TlCH), ³J(SnMCH) and ³J(TlSnCH) are reported as a function of M and as a function of the number of Me₃Sn groups bond to thallium in the (Me₃Sn)_nTIME₄?_n]^?anions. Proposals concerning the factors governing the changes in these coupling constants and the chemical shifts are presented.