A New Class of Transition Metal Pincer Ligand: Tantalum Complexes that Feature a [CCC] X_3-Donor Array Derived from a Terphenyl Ligand

摘要

A new class of [CCC] X_3-donor pincer ligand for transitionrnmetals has been constructed via cydometalation of a 2,6-di-p-tolylphenylrn([Ar~(Tol_2)]) derivative. Specifically, addition of Pme_3 to [Ar~(Tol_2)]TaMe3Cl inducesrnelimination of methane and formation of the pincer complex, [k~3-Ar~(To1'_2)]-rnTa(Pme_3)_2MeCl (Tol' = C_6H_3Me), which may also be obtained by treatmentrnof Ta(Pme_3)_2Me_3Cl_2 with [Ar~(Tol_2)]Li. Solutions of [k~3-Ar~(Tol_2)Ta(Pme_3)_2MeClrnundergo ligand redistribution with the formation of [K~3-Ar(Tol2)]Ta(Pme_3)_2Me_2rnand [k-Ar~(Tol_2)]Ta(Pme_3)_2Cl_2, which may also be synthesized by the reactions of [K3-Ar~(Tol_2)]Ta(Pme_3)_2MeCl with MeMgBr andrnZnCl2, respectively. Reduction of [k3-Ar~(Tol_2)]Ta(Pme_3)_2Cl_2 with KC_8 in benzene gives the benzene complex (k3-~(Tol_2)]-rnTa(Pme_3)_2(η6-C_6H_6) that is better described as a 1,4-cyclohexadienediyl derivative. Deuterium labeling employing Ta(Pme_3)_2-rn(CD_3)_3C1_2 demonstrates that the pincer ligand is created by a pair of Ar-H/Ta-Me sigma-bond metathesis transformations, ratherrnthan by a mechanism that involves α-H abstraction by a tantalum methyl ligand.