Kinetics and mechanism of arene displacement in (eta-arene)dicarbonyl(chalcocarbonyl)chromium(0) complexes, (eta-arene)Cr(CO)/sub 2/(CX) (X = S, Se), by tertiary phosphites
The kinetics and mechanism of the arene substitution reactions of the chalcocarbonyl complexes (eta-arene)Cr(CO)/sub 2/(CX) (X = S, arene = C/sub 6/H/sub 6/, PhMe, PhNMe/sub 2/, PhCO/sub 2/Me, o-C/sub 6/H/sub 4/Me/sub 2/, m-C/sub 6/H/sub 4/(CO/sub 2/Me)Me, p-C/sub 6/H/sub 4/(CO/sub 2/Me)/sub 2/, p-C/sub 6/H/sub 4/(OMe)/sub 2/, 1,3,5-C/sub 6/H/sub 3/Me/sub 3/; X = Se, arene = C/sub 6/H/sub 6/) by tertiary phosphites (L = (MeO)/sub 3/P, (PhO)/sub 3/P, (C/sub 6/H/sub 11/O)/sub 3/P) in methylcyclohexane to form mer-Cr(CO)/sub 2/(CX)L/sub 3/ have been investigated. The reactions are significantly faster than those for the corresponding tricarbonyl complexes and are first-order in both substrate and entering ligand L. Activation parameters for arene = C/sub 6/H/sub 6/ and L = (MeO)/sub 3/P: X = S, ..delta..H/sup double dagger/ = 74.1 kJ mol/sup -1/, ..delta..S/sup double dagger/ = -117 J mol/sup -1/ deg/sup -1/; X = Se, ..delta..H/sup double dagger/ = 74.9 kJ mol/sup -1/, ..delta..S/sup double dagger/ = -100 J mol/sup -1/ deg/sup -1/. A mechanism involving the slight slippage of the arene ring from eta/sup 6/- to eta/sup x/-coordination (6 > x > 4) prior to entry of the first L ligand in the rate-determining step is proposed. The greater reactivity of the thio- and selenocarbonyl derivatives compared to that of the tricarbonyl analogues is attributed to the better ..pi..-acceptor capacities of CS and CSe compared to that of CO, resulting in weaker bonding between the Cr metal and the arene. Also, on the basis of this kinetic study, it appears likely that the thio- and selenocarbonyl complexes will not be as good catalysts as the (eta-arene)chromium tricarbonyl complexes for the hydrogenation of dienes.
- Research Organization:
- McGill Univ., Montreal, Quebec
- OSTI ID:
- 6996753
- Journal Information:
- Inorg. Chem.; (United States), Vol. 25:22
- Country of Publication:
- United States
- Language:
- English
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