We have recently used the bulky tris(2-mercapto-1-tert-butylimidazolyl)borate ligand [TmtBu]- to prepare several paramagnetic complexes of cobalt(II), including neutral halo compounds (TmtBu)CoX (X = Cl, Br, I) and cationic triphenylphosphine derivatives [{TmtBu}Co(PPh3)]Y (Y = BPh4, PF6). During the course of these investigations, quite unexpectedly, a single crystal of the Co(I) tris(mercaptoimidazolyl)borane complex [{B(mimtBu)3}Co(PPh3)]BPh4, which is formally the product of ligand B—H bond activation and exhibits a direct cobalt to boron dative bond, was obtained. Although a number of transition metal borane complexes have been isolated in the last 40 years, the first structurally authenticated example, the closely related ruthenaboratrane {B(mimMe)3}Ru(PPh3)(CO), was obtained by Hill and coworkers only in 1999. We report in this presentation the synthesis of hitherto unknown tris(mercaptoimidazolyl)boranes, novel ligands with which the rational syntheses of new metallaboratranes are being pursued in our research group.
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