INTERMEDIATES IN THE REACTION OF TRANS-CR(CO)4(PPH3)2 WITH CO-13 AND FLUXIONALITY IN OCTAHEDRAL GROUP 6B METAL-CARBONYLS VIA A NON-DISSOCIATIVE MECHANISM

The stereoselectivity of the dissociative process involving the reaction of trans-Cr(CO)4(PPh3)2 with 13C-labeled carbon monoxide to afford the pentacarbonylchromium triphenylphosphine derivative is examined. The data presented are consistent with a completely stereoselective process where the incoming 13CO ligand occupies a site in the octahedral complex cis to the PPh3 ligand (i.e., formation of cis-Cr(CO)4(13CO)PPh3). Hence rearrangement of the initially formed [Cr(CO)4PPh3] intermediate of C4v symmetry to that of Cs symmetry occurs faster than the bimolecular reaction of the intermediate with carbon monoxide. A subsequent reaction involving a stereomobility of the ligands in the six-coordinate derivative is observed which takes place in the absence of ligand (CO or PPh3) dissociation. Comparisons with the analogous processes involving the molybdenum derivatives are presented. Similar ligand stereomobility in other phosphine or phosphite complexes of chromium and tungsten are summarized. 1982, American Chemical Society. All rights reserved.

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