Synthesis and structure of benzyl substituted derivatives of the dinickel triple-decker complex μ-η5,η5-(2,3-dihydro-1,3-diborolyl)-(η 3-allyl)(η4-1,5-hexadiene)dinickel

Article abstract of DOI:10.1515/znb-2001-0112

Hydroboration of phenyl- and mesitylethyne with in situ formed HBCl₂ leads to an isome-ric 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 with 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 with AlMe₃ or LiMe result in the formation of the very air-sensitive pentaorganyl-1,3-diboroles 1a, 1c and the hexaorganyl-1,3-diborole 1b. The mixture of 1a/b as well as 1c react with bis(η³-allyl)nickel to give black products, which are chromatographed on silica with hexane as eluent. The brown solids were recrystallized from pentane to give the light-brown crystals of μ-η⁵,η ⁵-[2-benzyl-1,3,4,5-tetramethyl-2,3-dihydro-1,3-diborolyl](η ³-allyl)(η⁴-1,5-hexadiene)dinickel (2a, 34%) and μ-η⁵,η ⁵-[2-(2,4,6-trimethyl-benzyl)-1,3,4,5-tetramethyl-2,3-dihydro-1,3- diborolyl](η³-allyl)(η⁴-1,5-hexadiene)dinickel (2c, 43%). 1b does not react with Ni(C₃H₅)₂ to form any triple-decker. The compositions of the new compounds follow from spectroscopic and analytical data, and from X-ray structure analyses of 6a and of 2a. The structure of the η⁴-1,5-hexadiene-j;3-allyl-dinickel triple-decker 2a finally disproved the alternative tris(allyl)dinickel arrangement.