Boratatrozircenes: cycloheptatrienyl zirconium boratabenzene sandwich complexes – evaluation of potential η6–η5 hapticity interconversions

Abstract

The salt metathesis reactions of [(η7-C7H7)ZrCl(tmeda)] (1) with various boratabenzene ligands Li(C5H5B–R) (R = H, CH3, CC–SiMe3) afford the 16-electron sandwich complexes [(η7-C7H7)Zr(η6-C5H5B–R)] (2: R = H, 3: R = CH3, 4: R = CC–SiMe3). The molecular structures of 3 and 4 were determined by X-ray diffraction analyses; they display distorted η6-coordinated boratabenzene ligands with short Zr–B bonds of 2.683(2) and 2.649(6) Å. The possibility of an η6–η5 hapticity interconversion, accompanied by B–L bond formation, upon addition of a Lewis base L (L = PMe3, 4-(dimethylamino)-pyridine) to 3 was studied. However, Zr–L bond formation was observed instead, leading to [(η7-C7H7)Zr(η6-C5H5B–CH3)(L)] (5: L = PMe3, 6: L = 4-(dimethylamino)-pyridine), even if a large excess of L was used.