1,1-Organoboration of silylethynyltin compounds studied by multinuclear magnetic resonance spectroscopy:isomerization at the C=C bonds and electron-deficient Si-H-B bridges

摘要

1,1-Organoboration,using triethyl-,triallyl-and triphenyl-borane(BEt_3,BAll_3,BPh_3),of dimethysilylethynyl(trimethyl)stannane,Me_3Sn-C ident to C-Si(H)Me_2(1),affords alkenes bearing three different organometallic groups at the C=C bond.For BEt_3 and BPh_3,the first products are the alkenes 4 with boryl and stannyl groups in cis-positions.These rearrange by consecutive 1,1-deorganoboration and 1,1-organoboration into the isomers 5 as the final products,where boryl and silyl groups are in cis-positions linked by an electron-deficient Si-H-B bridge.1,1-Ethylboration of bis(dimethylsilylethynyl)dimethylstannane,Me_2Sn[C ident to C-Si(H)Me_2]_2(2),leads to the stannacyclopentadiene 6 along with non-cyclic di(alkenyl)tin compounds 7 and 8.1,1-Ethylboration of ethynyl(trimethylstannylethynyl)methylsilane,Me(H)Si(C ident to C-SnMe_3)C ident to C-H(3),leads selectively to a new silacyclopentadiene 13 as the final product.The reactions were monitored and the products were characterized by multinuclear magnetic resonance spectroscopy(~1H,~(11)B,~(13)C,~(29)Si and ~(119)Sn NMR).