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(tim(Me))(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)(5)Br] or (NEt4)(2)[Re(CO)(3)Br-3] with the stoichiometric amount of Li[H(R)B(tim(Me))(2)] (R = Me (1), Ph (2)) or Na[HB(tim(Me))(3)] gave the tricarbonyl complexes [Re{kappa (3)-R(mu -H)B(tim(Me))(2)}(CO)(3)] (R=Me (1), Ph (2)) or [Re{kappa (3)-HB(tim(Me))(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-(HRe)-Re-... interaction. (C) 2001 Elsevier Science BN. All rights reserved.