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.