1,2-eq,eq-[Re-2(CO)(8)(THF)(2)]: A reactive Re-2(CO)(8) fragment that easily activates H-H and C-H bonds

The reaction of [Re-2(mu-H)(2)(CO)(8)] (1) with diazomethane at 193 K in THF-d(8) gives the unstable [Re-2(mu-H)(mu-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-[Re-2(CO)(8)(THF)(2)] (3), which was characterized by NMR spectroscopy and X-ray analysis. In the solid form a staggered conformer of Ca symmetry was found. C-13 NMR analysis revealed the presence, in wet THF, of the aquo complexes [Re-2(CO)(8)(THF)(H2O)] (4) and [Re-2(CO)(8)(H2O)(2)] (5), whose formation is favored at low temperature (Delta H degrees 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" Re-2(CO)(8) fragment, capable of activating different E-H bonds. Reaction with HCl in THF leads to [Re-2(mu-H)(mu-Cl)(CO)(8)], while with H-2 the unsaturated starting material [Re-2(mu-H)(2)(CO)(8)] is obtained. In THF solution, at room temperature, reactions with phenylacetylene, styrene, and acetaldehyde give the derivatives of C-H activation [Re-2(mu-H)(mu-C drop CPh)(CO)(8)], [Re-2(mu-H)(mu-CH=C(H)Ph)(CO)(8)], and [Re-2(mu-H)(mu-eta(2)-C(Me)O)(CO)(8)]. Moreover, the activation of an sp(3) C-H bond in ethyl acetate occurs slowly when 3 is dissolved in the reactant itself, the resultant product being [Re-2(mu-H)(mu-eta(2)-CH2C(O)OEt)(CO)(8)].