Facile Activation of Triarylboranes by Rhenium(V) Oxo Imido Complexes

We report the synthesis and reactivity studies of a pair of rhenium(V) oxo imido complexes. Oxidation of the rhenium(III) terminal oxo ORe(eta(2) -DHF)(BDI) (DHF = dihydrofulvalene, BDI = N,N'-bis(2,6-diisopropylphenyl)-3,5-dimethyl-beta-diketiminate) with organic azides R-N-3 (R = Bu-t, 2,6-diisopropylphenyl) yields the title complexes. Computational studies confirm that the rhenium oxo moieties of these complexes are polarized and correspondingly nucleophilic, owing to the preferential pi bonding of the imido ligand to the Re center. This asymmetry in the metal- ligand multiple bond electronic structure facilitates the ready activation of B- C bonds in triarylboranes (BPh3 and B(C6F5)(3)), yielding rhenium(V) aryl borinate complexes. In the case of BPh3, subsequent cyclometalation of the 1,2-addition products was found to take place upon heating, ejecting benzene to form bidentate diphenylborinate complexes.