Metal complexes of anionic 3-borane-1-alkylimidazol-2-ylidene derivatives

Addition of BH3·thf to 1-alkylimidazoles (alkyl=methyl, butyl) and 1-methylbenzimidazole leads to BH3 adducts, which are deprotonated by BuLi to yield the organolithium compounds (L)Li+(1b–d)−. In the solid state (thf)Li+1b− is dimeric. The acyl–iron complexes (thf)3Li+(3b,d)− are formed from (thf)Li+(1b,d)− and Fe(CO)5. (L)Li+(1a–c)− react with [CpFe(CO)2X], however, the only complex obtained is [CpFe(CO)21a] (5a). The analogous reaction of (L)Li+1a− with the pentadienyl complex [(C7H11)Fe(CO)2Br] yields the corresponding iron compound 6a. Their compositions follow from spectroscopic data. Treatment of Cp2TiCl with (L)Li+1a− leads to [Cp2Ti1a] (7a), which could not be oxidized with PbCl2 to give the corresponding Ti(IV) complex. The compounds [Li(py)4]+9a− and [Li(L)4]+(10b–d)− are obtained when (L)Li+1− are reacted with VCl3 and ScCl3. The X-ray structure analysis of the vanadium complex reveals a distorted tetrahedron of the anion [V(1a)4]− with two smaller and four larger CVC angles. The scandium compound [Li(dme)2+10c−] has a different structure: the distorted tetrahedron of the anion [Sc(1c)4]− contains two larger (140.2 and 142.9°) and four smaller CScC angles (93.9–98.7°). This arrangement allows the formation of four bridging BHSc 3c,2e bonds to give an eight-fold coordination. The anion 10c− is formally a 16e complex.