SOLUTION BEHAVIOR OF UNSATURATED MOLYBDENUM CARBONYL SPECIES AS EVIDENCED VIA STEREOSPECIFIC CO-13 LABELING STUDIES
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Stereospecific incorporation of 13CO into the triene complex, (bicyclo[6.1.0]nona-2,4,6-triene)molybdenum tricarbonyl, has been found to occur with the axially labeled 13CO tetracarbonyl derivative being formed where the triene ligand is acting as a four-electron donor. A facile, high-yield synthesis of other stereospecific 13CO-labeled cis-disubstituted derivatives of molybdenum has been developed which involves displacement of the olefin with a variety of incoming ligands, namely, nor-bornadiene, diamines, PPh3, P(OPh)3, SbPh3, and diphos. The retention of the axial 13CO label in these cis-Mo(CO)4L2 derivatives is ascribed to a site preference of these ligands(L) for an equatorial position in the square-pyramidal structure of the five-coordinate intermediates involved in this process where the barrier to CO rearrangement is large. On the other hand, when the incoming ligand is the small, relatively good acceptor, P(OMe)3, CO rearrangement was found to readily occur. Similarly, reaction of Mo(CO)4(triene) with 13CO afforded a statistical distribution of cis and trans bis-13CO species, thus indicating that the CO groups in the [Mo(CO)s] intermediate lose their stereochemical integrity at a rate which is rapid relative to their solution lifetime. The infrared spectral details in the v(CO) region of the 13CO labeled derivatives prepared in this investigation are discussed. 1978, American Chemical Society. All rights reserved.
