Conversion of trans-Diboran(4)yl Platinum Complexes into Their cis-Bisboryl Analogues

摘要

The diboran(4)yl trans- [(iPr_3P)_2Pt(Br)(NMe_2)B(NMe_2)Br}] (1) is readily converted into its cis-bisboryl analogues 2 and 3 by reaction with the chelating bisphosphines 1,2- bis(dicyclohexylphosphino)ethane (dcpe) and 1,1-bis(dicyclohexylphosphino) methane (dcpm), respectively. A plausible mechanism of this transformation consists of a sequence of reductive diborane(4) elimination and subsequent reoxidative addition of its B-B bond to the low-valent platinum centers. Thus, the forced cis configuration of the phosphine ligands induces a change in the preferred reaction site of the diborane(4) with respect to oxidative addition. The reactions proceed with high selectivities, and the cis-bisboryl complexes 2 and 3 were isolated in moderate yields (55 and 46%). Moreover, their identity was clearly verified by NMR spectroscopy and Xray diffraction studies.