Fac versus mer coordination for a tridentate diethylene glycloiate ligand in tantalum complexes: A combined experimental and theoretical study

A series of new tantalum-digol (digol = diethylene glycolate) complexes TaCp*Cl2(κ3-digol) (1), TaCp*Me2(κ3-digol) (2), TaCp*ClMe(κ3-digol) (3), and TaCp*Me(OTf)(κ3-digol) (OTf = triflate) (4) have been synthesized. Treatment of 2 with 1 equiv of H2O·B(C6F5)3 enabled the synthesis of a tantalum-oxo borane-stabilized complex, TaCp*{O·B(C6F5)3}(κ3-digol) (5). Insertion processes into the methyl groups of complexes 2, 3, and 4 were not observed upon reaction with CO or isocyanides. In contrast, complex 4 reacted slowly with 1 equiv of xylylisocyanide (xylyl = 2,6-dimethylphenyl) to yield the dicationic aminocarbene complex [TaCp*{C(Me)NH(xylyl)}(OH2)(κ3-digol)][OTf]2 (6). All products were characterized by NMR spectroscopy and elemental analysis. The single-crystal structures of 1, 5, and 6 were determined. The molecular structures of 1, 2, 3, and 6 were also determined by means of DFT-based methods.Some of us (R.F.,C.H.,A.O.,A.R., M.J.R.) gratefully acknowledge financial support from the Ministerio de Educacion y Ciencia, Spain (Grant No.BQU200204638-CO2-02) and the Junta de Comunidades de Castilla-La Mancha (Grant Nos.PAC-02-003andGC-02-010). C.B.and M.F. are indebted to the ICIQ Foundation for financial support.Peer reviewe