Synthesis, Structural Characterization, and Cyclometalation Chemistry of Tantalum Terphenyl Compounds

The κ1-m-terphenyl complex of tantalum, [ArTol2]­Ta­(NMe2)3Cl ([ArTol2] = 2,6-di-p-tolylphenyl), has been synthesized by the reaction of [Ta­(NMe2)3Cl2]2 with two equivalents of [ArTol2]­Li. [ArTol2]­Ta­(NMe2)3Cl provides access to a variety of monoalkyl compounds, [ArTol2]­Ta­(NMe2)3R (R = Me, Et, Prn, Bun, and Np; Np = CH2But), via the reactions with the corresponding RLi. In addition, the reaction of [Ta­(NMe2)3Cl2]2 with excess [ArTol2]Li affords the bis(terphenyl) complex, [ArTol2]2Ta­(NMe2)3, while the reaction of [ArTol2]­Ta­(NMe2)3Cl with LiBH4 gives the borohydride complex, [ArTol2]­Ta­(NMe2)3(κ2-BH4). The dichloride compound, [ArTol2]­Ta­(NMe2)2Cl2, which is obtained via the reaction of [ArTol2]­Ta­(NMe2)3Cl with Me3SiCl, provides access to a series of dialkyl derivatives, [ArTol2]­Ta­(NMe2)2R2 (R = Me, Et, Prn, Bun, and Np), via the reactions with the corresponding RLi. The κ1-m-terphenyl ligands in these complexes are susceptible to metalation. Thus, [ArTol2]­Ta­(NMe2)3R eliminates RH to afford [κ2-ArTol,Tol′]­Ta­(NMe2)3 (Tol′ = C6H3Me), while [ArTol2]­Ta­(NMe2)2Np2 eliminates NpH to form [κ2-ArTol,Tol′]­Ta­(NMe2)2Np.