Nancy Brodie

Reaction kinetics of some substituted tetrarhodium carbonyl clusters

Abstract Quantitative kinetic data have been obtained for reactions, in 1,2-dichloroethane at 25°C, of the known cluster Rh4(CO)9(etpb)3 (etpb = P(OCH2)3CEt), and of the new cluster Rh4(CO)10(PCy3)2 (Cy = C6H11), with some P-donor nucleophiles and, for the latter cluster, with AsPh3. Both clusters obey the two term rate equation: kobs = k1 + k2[L] although the value of k1 for Rh4(CO)10(PCy3)2 is only observed for reactions with AsPh3 and is relatively very small and quite approximate. The values of k2 can be used to obtain electronic and steric profiles from which it can be concluded that bond-making is very low for reactions of the intrinsically much more reactive Rh4(CO)10(PCy3)2, but significant for reactions of the intrinsically less reactive Rh4(CO)9(etpb)3. Steric effects due to different nucleophile cone angles are consequently much less pronounced for Rh4(CO)10(PCy3)2 than for Rh4(CO)9(etpb)3. Comparison with data reported elsewhere for Rh4(CO)9{HC(PPh2)3} shows that the intrinsic susceptibility of these clusters towards nucleophilic attack increases along the series Rh4(CO)9{HC(PPh2)3}

Photofragmentation kinetics of some triruthenium carbonyl clusters

The photokinetics of fragmentation reactions of [Ru3(CO)12] with L = PPh3, P(OPh)3, AsPh3, CO, 1-octene, and methyl acrylate in a variety of solvents have been studied. Quantum yields increase to limiting values at high [L] but the limiting values vary significantly with the nature of L. The low efficiency of photochlorination in chlorocarbon solvents, the absence of inhibition by CO of reactions with L = PPh3, and the absence of appropriate effects of varying incident light intensity all suggest that the first kinetically significant product is a non-radical reactive isomer of [Ru3(CO)12]. This can revert to [Ru3(CO)12] or react with L to form [Ru3(CO)12L] which itself can revert to [Ru3(CO)12] or undergo fragmentation. The former choice governs the rate of increase with [L] to a limiting quantum yield whereas the latter choice governs the dependence of the values of the limiting quantum yield on the nature of L. This scheme is also applicable to photoreactions of [Os3(CO)12] and the quantitative behaviour of the two clusters is not significantly different. Only lower limits for quantum yields for formation of the reactive isomers can be deduced from the data and it remains possible that the primary photophysical process is the formation of a very short-lived diradical by homolysis of a metal-metal bond. Photokinetic studies of reactions of [Ru3(CO)9L3] with L (L = PPh3 or PBun3) are also reported.

F N 2 reactions of some trinuclear metal carbonyl clusters

The metal carbonyl clusters Me3(CO)12-n(PBun3)n(M = Os, n= 0–1, M = Ru, n= 1–2) react with PBun3 by bimolecular paths that involve fragmentation to mononuclear products, and that can be given the mechanistic.

Photoinduced Radical Chain Bromination of Decarbonyldimanganese

The reaction of bromine with Mn2(CO)10 in tetrachloro methane proceeds quite rapidly and cleanly on exposure to light to form Mn(CO)5Br as the only IR detectable product. The kinetics of this reaction have been studied under a wide variety of conditions, reaction being initiated by photodissociation of bromine with light of wavelength ca. 435nm. It is concluded that the bromine atoms initiate a chain reaction by attacking the Mn2(CO)10 and forming Mn(CO)5Br and an Mn(CO)5 radical. This in turn reacts with bromine to generate Mn(CO)5Br and another bromine atom to continue the chain. The absence of appropriate effects on varying the intensity of absorbed light shows that chain termination does not involve radical recombination. It is probably effected by reaction of bromine atoms and Mn(CO)5 radicals with the solvent or, more effectively, with CBrCl3 when added in small amounts. Reaction in perfluorodecalin proceeds by a similar path but with higher quantum yields. Only bromine atoms, and not Mn(CO)5 radicals, appear to be involved in the termination step.