Reductive coupling of diisopropylcarbodiimide by a dirhenium carbonyl complex

Abstract

The reaction of Re2(CO)8(μ-H)[μ-η2-C(H) = C(H)Bun] with N,N′-diisopropylcarbodiimide yielded the new rhenium diamidinate complex [Re(CO)4]2[(μ-C2(N{iPr})4], 2, in 59% yield that was formed by the reductive coupling of two of carbodiimide molecules at the central carbon atom. The diamidinate ligand is nonplanar and four iminyl nitrogen atoms are coordinated to two Re(CO)4 groups in two chelating groups that have formed five-membered rings. Density functional molecular orbital analyses were used to explain the bonding of the diamidinate ligand to the two rhenium atoms. A second product Re2(CO)8(μ-OH)(μ-H), 3 was obtained from the reaction of N,N′-diisopropylcarbodiimide and Re2(CO)8(μ-C6H5)(μ-H), 1. Compound 3 was subsequently found to be a product of the reaction of 1 with traces of H2O in the original reaction and was independently obtained in 60% yield from the reaction of 1 with H2O. Compound 3 contains a bridging hydroxo ligand and a bridging hydrido ligand across the Re–Re bond between two mutually bonded Re(CO)4 groups. Both new compounds were characterized structurally by single-crystal X-ray diffraction analysis.