ORGANOMETALLIC-SUBSTITUTED ALLENES - DETERMINATION OF COUPLING SIGNS AND MOLECULAR-STRUCTURES OF 2 STANNYLATED ALLENES

The stannylated allenes 1 and 2 were prepared by 1,1-organoboration of two equivalents of bis(trimethylstannyl)ethyne (4) with one equivalen t of triethylborane or ferrocenyl-dimethylborane. The organometallic-s ubstituted alkenes 5 and 6 could be obtained from 1: 1 reactions. -1,1 ,4,4-tetrakis(trimethylstannyl)-1,2-buatadiene (3) was obtained from t he reaction of 4 with dimeric 9-borabicyclo[3.3.1]nonane. The molecula r structures of the allenes 1 and 3 were determined by X-ray analysis. In both cases, the structural parameters of the (Me(3)Sn)(2)C-BR(2) u nit indicate Sn-C hyperconjugation, and this model is supported by the small magnitude of the coupling constants (1)J(Sn-119, C-13), by the increased B-11 nuclear shielding as well as by the unusual changes in the delta(119)Sn values in going from the solution to the solid state. A fairly complete set of signs of coupling constants (n)J(Sn-119, H-1 ), (n)J(Sn-119,C-13) and (n)J(Sn,Sn) was derived for the allene 3 usin g 2D C-13/H-1 and Sn-119/H-1 heteronuclear shift correlations.