Rhenium(I) organometallic complexes with novel bis(mercaptoimidazolyl)borates and with hydrotris(mercaptoimidazolyl)borate: chemical and structural studies

Lithium salts of novel poly(mercaptoimidazolyl)borate anions [H(R)B(timMe)2]− have been synthesised under mild conditions by reaction of the corresponding lithium organoborohydrides with 2-mercapto-1-methylimidazole. Treatment of the Re(I) starting materials [Re(CO)5Br] or (NEt4)2[Re(CO)3Br3] with the stoichiometric amount of Li[H(R)B(timMe)2] (R=Me (1), Ph (2)) or Na[HB(timMe)3] gave the tricarbonyl complexes [Re{κ3-R(μ-H)B(timMe)2}(CO)3] (R=Me (3), Ph (4)) and [Re{κ3-HB(timMe)3}(CO)3] (5). These complexes were also prepared under aqueous and aerobic conditions, in almost quantitative yield, using (NEt4)2[ReBr3(CO)3] as starting material. Compounds 1–5 have been characterised by the usual analytical techniques and by X-ray crystallographic analysis in the case of 3–5. The X-ray diffraction analysis of 3–5 showed that the rhenium atom adopts a slightly distorted octahedral coordination with a facial arrangement of the carbonyl ligands. In complex 5 the three remaining coordination positions are occupied by the three thione sulphur atoms from the tripodal hydrotris(2-mercapto-1-methylimidazolyl)borate, and in 3 and 4 these positions are occupied by the two thione sulphur atoms and by one hydrogen atom, which is involved in a strong agostic BH⋯Re interaction.