1,2-eq,eq-[Re2(CO)8(THF)2]: A Reactive Re2(CO)8Fragment That Easily Activates H−H and C−H Bonds

Abstract

The reaction of [Re2(μ-H)2(CO)8] (1) with diazomethane at 193 K in THF-d8 gives the unstable [Re2(μ-H)(μ-CH3)(CO)8] derivative (2) containing a methyl group arising from the insertion of CH2 into a Re−H−Re bond. Isotopic perturbation of the equilibria by partial deuteration demonstrated that the methyl bridges the Re−Re bond in an unsymmetrical way, with a fast exchange between one agostic and two terminal C−H bonds. At temperatures higher than 253 K, 2 decomposes, in THF solution, with CH4 elimination to give the novel red complex 1,2-eq,eq-[Re2(CO)8(THF)2] (3), which was characterized by NMR spectroscopy and X-ray analysis. In the solid form a staggered conformer of C2 symmetry was found. 13C NMR analysis revealed the presence, in wet THF, of the aquo complexes [Re2(CO)8(THF)(H2O)] (4) and [Re2(CO)8(H2O)2] (5), whose formation is favored at low temperature (ΔH° for the formation of 5 from 4: −14.4(2) kJ mol-1). In solution, due to the lability of the THF ligands, 3 behaves as a “lightly stabilized” Re2(...