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

Abstract

Addition of BH 3·thf to 1-alkylimidazoles (alkyl=methyl, butyl) and 1-methylbenzimidazole leads to BH 3 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) 2 1a] (5a). The analogous reaction of (L)Li + 1a − with the pentadienyl complex [(C 7H 11)Fe(CO) 2Br] yields the corresponding iron compound 6a. Their compositions follow from spectroscopic data. Treatment of Cp 2TiCl with (L)Li + 1a − leads to [Cp 2Ti 1a] ( 7a), which could not be oxidized with PbCl 2 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 VCl 3 and ScCl 3. 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.