LIGAND LABILITY STUDIES IN BRIDGING HYDRIDE COMPLEXES OF GROUP 6B METAL CARBONYLATES
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The reactions of [formula-omitted] with 5A donor ligands have been studied. The predominant if not exclusive product in all cases studied here is L2M(CO)4. The reaction follows a rate law that is first order with respect to the concentration of bridging hydride carbonylate and zero order with respect to the 5A donor ligand concentration when the ligand is in a tenfold or greater excess. Rate constants are dependent on metal (Mo > Cr > W) and on solvent (EtOH > THF). It is proposed that initial substitution occurs on the hydride-bridged dimer, prior to dimer disruption. A complex formulated as [formula-omitted] was isolated as the first-formed product in the [formula-omitted] reaction with [formula-omitted] in THF. Rates of reaction of [formula-omitted] with L to form [formula-omitted] were compared with rates of the nucleophile-facilitated substitution reaction, [formula-omitted] also to form [formula-omitted] or [formula-omitted] The intermediacy of a bridging hydride, [formula-omitted] in the sodium borohydride facilitated substitution reactions of M(CO)6 is consistent with the formation of [formula-omitted] reaction rates, and products. 1978, American Chemical Society. All rights reserved.
