Synthesis and structural characterization of a new class of organoborato ligands containing imidazolyl functional groups [MeB(Im(N-Me))(2)(X)](-)

A series of alkylborate compounds containing imidazolyl functional groups [ MeB(Im(N-Me))(2)(X)](-) (X = OPri 1, Cl 2, Pz 3 or Ph 4) has been synthesiz ed and characterized. Reaction of di(isopropoxy)methylborane with 2 equival ents of 2-lithio-1-methylimidazole yielded the lithium isopropoxymethylbis( 2-methyl-1-imidazolyl)borate, Li[1]. The chlorobis(imidazolyl)methylborate 2, which was obtained by treatment of 1 with HCl, could be transformed to t he pyrazolyl and phenyl derivatives 3 and 4, respectively, by nucleophilic substitution of the B-bound chlorine atom. The molecular structures of {H-2 [2]}Cl, H[3] and Ni[4](2) have been successfully determined by X-ray crysta llography. In {H-2[2]}Cl both the imidazolyl groups are protonated, forming an intermolecular hydrogen bonding interaction with the chloride anion and giving a dimeric structure. In H[3] an intramolecular hydrogen bond betwee n the the non-co-ordinated nitrogen atoms of the two imidazolyl groups is f ormed. Structural properties of the protonated imidazole rings in {H-2[2]}( +) and H[3] indicate delocalization of positive charge over the rings, whic h results in strong interaction with the negatively charged boron center. F ormation of Ni[4](2) clearly indicates the chelation ability of the bis(imi dazolyl)borate framework. Therefore, the imidazolyl groups in [MeB(Im(N-Me) )(2)(X)](-) act as a proton acceptor and metal-binding site as found for po ly(pyrazolyl)borates.