Rhodium carbonyl complexes, reactive intermediates

Forster, D. (1976) Mechanism of a rhodium-complex-catalyzed carbonylation of melhanol to acetic add. Journal of the American Chemical Society, 98, 846 Adamson, G.W., Daly, J.J. and Forster, D. (1974) Reaction of iodocarbonylrhodium ions with melhyl-iodide - structure of rhodium acetyl complex -[Me3PhN+]2[Rh2l6(MeCO)2(CO)2]2-. Journal of Organometallic Chemistry, 71, Cl7 Haynes, A., Mann, B.E., Gulliver, D.J., Morris, D.E. and Maillis, P.M. (1991) Direct observation of MeRh(CO)2l3 the key intermediate in rhodium catalyzed methanol carbonylation. Journal of the American Chemical Society 113, 8567 Haynes, A., Mann, B.E., Morris, G.E. and Maidis, P.M. (1993) Mechanistic studies on rhodium-catalyzed carbonylation reactions — spectroscopic detection and reactivity of a key intermediate, [MeRh(CO)2l3]. Journal of the American Chemical Society, 115, 4093. 

The studies of Wilkinson et al. included IR and H-l NMR spectroscopy of the intermediate species of this catalyst system (7). This led to recognizing tris(triphenylphosphine)rhodium(I) carbonyl hydride (D) as the key stable rhodium complex. The reactive trans-bis-(triphenylphosphine)rhodium(I) carbonyl hydride (E) resulting via the dissociation of this complex... 

Thus, as is the case for the st pincer derivatives with nickel, Moulton and Shaw also reported the first PCP pincer rhodium and iridium derivatives and studied their reactivity toward carbon monoxide [4]. Hence, the (PCP) rhodium derivative (38) affords complex (40), as a product of the decomposition of the unstable hydrido chloro carbonyl intermediate (39) via a hydrodechlorination process, although this compound is obtained impure. To favor the hydrodechlorination process, an alternative route was attempted employing EtONa as base. This approach afforded exclusively compound (40) (Scheme 2.21). It is noteworthy that analogous reactions with the iridium analogous to complex (38) only afford impure samples of the carbonyl species analogous to complex (40). 

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