On the kinetics and mechanism of the conversion of Cr(CO)5(κ1-P-dppm) to Cr(CO)4(κ2-P,P′-dppm) (dppm = 1,2-diphenylphosphinomethane): an alternative hypothesis

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The data from a previously reported kinetic evaluation dealing with the conversion of Cr(CO)5(κ1-P-dppm) (1: dppm = 1,2-diphenylphosphinomethane) into the corresponding chelated complex Cr(CO)4(κ2-P,P′-dppm) (2), via CO loss, is re-evaluated. The conclusion is that the process is more likely to involve a rate-determining step that is first-order in [Cr(CO)5(κ1-P-dppm)], as opposed to the previously reported zero-order model as proposed. This implies CO loss from 1, by presumably either an I d or more likely a Dissociative (D: S N 1-type) mechanism, leads to 2. This hypothesis is compared and contrasted to reported data and comparisons are made to similar processes involving related Group VI metal carbonyl species. $$ \mathop {{\text{Cr}}\left( {\text{CO}} \right)_{5} (\upkappa^{1} -P-dppm) + \Delta }\limits_{{\mathbf{1}}} \to \mathop {{\text{Cr}}\left( {\text{CO}} \right)_{4} (\upkappa^{2} -P,P^{{\prime }} {\text{-dppm}}) + {\text{CO}}}\limits_{{\mathbf{2}}} $$