Stepwise degradation of the unsaturated cluster tetrakis(μ-hydrido)decacarbonyltrirhenate(1-) by reaction with iodine. Crystal and molecular structures of the tetraethylammonium salts of the new anions bis(μ-hydrido)bis(μ-iodo)decacarbonyltrirhenate(1-) and (μ-hydrido)bis(μ-iodo)hexacarbonyldirhenate(1-)

The reactions of the unsaturated anion [Re3(M-H)4(CO)10] with iodine have been investigated in various solvents. While in donor solvents, such as ethanol, the only product obtained is the anion [Re3(μ-H)3(μ-I)(CO)10]-, in dichloromethane and similar solvents the reaction proceeds with evolution of H2, giving mixtures of products of variable composition, depending on the amounts of iodine. The process implies stepwise degradation, with progressive substitution of (Chemical Equation Presented) bonds by Re-I-Re ones, leading, as a final result, to the dimeric species [Re2(μ-I)3(CO)6]- and Re2(μ-I)2(CO)8. The intermediate products have been isolated and characterized as [Re3(μ-H)3(μ-I)(CO)10]- (first step), [Re3(μ-H)2(μ-I)2(CO)10]- (second step), and [Re2(μ-H)(μ-I)2(CO)6]- plus Re2(μ-H)(μ-I)(CO)8 (third step). All the compounds have been spectroscopically characterized, and the crystal structures of the novel anions [Re3(μ-H)2(μ-I)2(CO)10] - and [Re2(μ-H)(μ-I)2(CO)6]-, as their tetraethylammonium salts, have been investigated by single-crystal X-ray analysis. The former species gives monoclinic crystals, space group P21/n, with a = 9.685 (2) Å, b = 12.679 (3) Å, c = 24.439 (5) Å, β = 98.18 (1)°, and Z = 4. The structure solution and refinements were based on 2646 significant counter data, the final R value being 0.025. The second species is monoclinic, space group C2/c, with a = 14.601 (1) Å, b = 11.794 (1) Å, c = 14.548 (1) Å, β = 110.88 (1)°, and Z = 4. Refinements, performed with 1353 significant counter intensities, led to a final R value of 0.030. The anion [Re3(μ-H)2(μ-I)2(CO)10] - contains an open trimetal array, derived from a triangle with one broken edge bridged by an iodine atom. It shows one long hydrogen-bridged Re-Re interaction with 3.321 (1) Å, while the other Re-Re bond, double-bridged by one hydride and one iodide ligand, is shorter, 3.107 (1) Å. The values of the Re-I interactions are in the range 2.797 (1)-2.841 (1) Å. In the dinuclear anion [Re2(μ-H)(μ-I)2(CO)6]-, of idealized C2v, symmetry, the rhenium atoms display an almost octahedral coordination with three CO groups and the bridging I and H atoms. Differently from other known Re(μ-X)3Re systems, where X is a three-electron donor group, in this anion a formal direct metal-metal bond is required and this is reflected in the value of the Re-Re distance of 2.954 (1) Å. Also in the dinuclear compound Re2(μ-H)(μ-I)(CO)8, mainly characterized by mass spectroscopy, a Re-Re bond is considered to be present, representing a situation intermediate between those of Re2(μ-H)2(CO)8 and of Re2(μ-I)2(CO)8. © 1983 American Chemical Society.