Synthesis and structure of benzyl substituted derivatives of the dinickel triple-decker complex mu-eta(5)-eta(5)-(2,3-dihydro-1,3-diborolyl)-(eta(3)-allyl)(eta(4)-1,5-hexadiene) dinickel

Hydroboration of phenyl- and mesitylethyne with in situ formed HBCl2 leads to an isomeric mixture of 1,1-bis(dichloroboryl)-2-phenylethane (4a) and 1, 1-bis(dichloroboryl)-1-phenylethane (4b) (ratio 3 : 1) and regioselectively to 1,1-bis(dichloroboryl)-2-mesitylethane (4c). Treatment of 4a/b and 4c w ith BI3 gives the corresponding tetraiodo compounds 5, which undergo redox reactions with butyne-2 to form the 1,3-diiodo-4,5-dimethyl-2,3-dihydro-1,3 -diborole derivatives 6a/b and 6c. Reactions of the diiodo-1,3-diboroles wi th AlMe3 or LiMe result in the formation of the very air-sensitive pentaorg anyl-1,3-diboroles 1a, 1c and the hexaorganyl-1,3-diborole 1b. The mixture of 1a/b as well as 1c react with bis(eta (3)-allyl)nickel to gi ve black products, which are chromatographed on silica with hexane as eluen t. The brown solids were recrystallized from pentane to give the light-brow n crystals of mu-eta (5),eta (5)-[2-benzyl 1,3,4,5-tetramethyl-2,3-dihydro- 1,3-diborolyl](eta (3)-allyl)(eta (4)-1,5-hexadiene) dinickel (2a, 34%) and mu-eta (5),eta (5)-[2-(2,9,6-trimethyl benzyl)-1,3,4,5-tetramethyl-2,3-dih ydro-1,3-diborolyl](eta (3)-allyl)(eta (4)-1,5-hexadiene)dinickel (2c, 43%) . 1b does not react with Ni(C3H5)(2) to form any triple-decker. The composi tions of the new compounds follow from spectroscopic and analytical data, a nd from X-ray structure analyses of 6a and of 2a. The structure of the eta (4)-1,5-hexadiene-eta (3)-allyl-dinickel triple-decker 2a finally disproved the alternative tris(allyl)dinickel arrangement.