Roger J. Mawby

Preparation, mechanism of formation, structure, and reactions of η-allyl complexes of ruthenium(II)

Reaction of either of two isomers of [Ru(CO)2Cl2(PMe2Ph)2] or either of two isomers of [{Ru(CO)Cl2(PMe2Ph)2}2] with SnBu3(C3H5) yields a single isomer of [Ru(CO)Cl(η-C3H5)(PMe2Ph)2]. A mechanism involving the intermediate formation of the five-co-ordinate species [Ru(CO)Cl2(PMe2Ph)2] and [Ru(CO)Cl(σ-C3H5)(PMe2Ph)2] is proposed for the reactions. Treatment of complexes [{Ru(Co)2Cl2L}2](L = phosphorus or arsenic ligand) with SnBu3(C3H5) yields the related complexes [Ru(CO)2Cl(η-C3H5)L], and the method can be extended to the preparation of 1-methylallyl and 2-methylallyl complexes. Simulation of the complex 1H n.m.r. spectra of [Ru(CO)2Cl(η-C3H5)(PMe2Ph)] and its AsMe2Ph analogue provides detailed information about the coupling between the protons in the allyl ligand. Treatment of [Ru(CO)2Cl(η-C3H5)(PMe2Ph)] with excess of PMe2Ph results in the formation of [Ru(CO)Cl(COC3H5)(PMe2Ph)3], which is very slowly converted in solution into [Ru(CO)Cl(η-C3H5)(PMe2Ph)2]: the key intermediate in the system appears to be [Ru(CO)2Cl(σ-C3H5)(PMe2Ph)2].

Consecutive substitution in, and reduction of, η-allyl molybdenum(II) complexes, and a study of ligand exchange in a molybdenum(0) product

Reactions of the allyl and 2-methylallyl complexes[Mo(CO)2Cl(η-C3H4R)(NCMe)2](R = H or Me) with ligands L = PMe2Ph or PMePh2 involve initial substitution to give [Mo(CO)2Cl(η-C3H4R)L2] followed by reduction to cis-[Mo(CO)2L4] or [Mo(CO)2(NCMe)(PMePh2)3]. The reduction, which is first order in the concentrations of both molybdenum complex and L, is thought to involve initial nucleophilic attack on the allyl ligand. Two of the PMe2Ph ligands in cis-[Mo(CO)2(PMe2Ph)4], believed to be the mutually cis pair, undergo rapid dissociative exchange with free PMe2Ph in solution at high temperatures: the exchange occurs without scramblig the cis pair of ligands with the trans pair. In the absence of free PMe2Ph, slow decomposition at 353 K yields specifically the mer isomer of [Mo(CO)3(PMe2Ph)3]. It is shown that this is the expected result if the labile Mo–P bonds are those to the cis pair of PMe2Ph ligands.

Intramolecular rearrangement in η-allyl complexes of molybdenum(II) containing unidentate amine ligands

Allyl and 2-methylallyl complexes [Mo(CO)2X(η-C3H4R)L2](X = Cl, Br, or I; R = H or Me; L = NC5H5, NC5H4 Me-4, or NC5H3Me2-3,5) exist in solution at low temperatures in a single isomeric form in which the two carbonyl ligands, the two amine ligands, and the two ends of the allyl ligand are inequivalent. At higher temperatures, rearrangement (shown to be an intramolecular process) has the effect of removing all these inequivalences from the 1H and 13C n.m.r spectra of the complexes. At a given temperature, the rearrangement rate is essentially independent of the nature of L, decreases with increase in the size of the halogen ligand, and is greater for the 2-methylallyl than for the allyl complexes. At the lowest temperatures studied, rotation of one amine ligand about the metal–nitrogen bond is restricted for the 2-methylallyl complexes only. Two structures are suggested for the complexes in solution: in one case (viewed as the more probable of the two) the variation in spectra can be attributed to a trigonal twist of the halogen and amine ligands relative to the remainder of the complex, and in the other to an oscillation of the allyl ligand about the metal–allyl axis.

Mechanism of light- and heat-induced rearrangements of complexes of ruthenium(II)

Comolexes cis-[Ru(CO)2L2X2](L = ligand with phosphorus or arsenic donor atom. X = haloaen) are converted to their all-trans-isomers by u.v. radiation; the process can be reversed by heating. Similar rearrangements occur with complexes [Ru(CO)2LL′Cl2] containing Two different phosphorus ligands L and L′. Studies of the thermal rearrangements of complexes all-trans-[Ru(CO)2(PMe2Ph)2X2] and all-trans-[Ru(CO)2(PMePh2)2X2] show that they occur by two competing routes, one direct and one by way of a third isomer, the all-cis-isomer. Evidence from these studies and from the stereochemistry of carbonyl-substitution reactions of the various isomers of [Ru(CO)2(PMe2Ph)2Cl2] is presented to support mechanisms for the photochemical and thermal isomerizations which involve dissociation of a carbonvl liaand as a first step During the isomerizations, partial loss of CO from solution causes the formation of complexes [{Ru(CO)L2X2}2] as by-products.

C–C Bond formation and C–H bond cleavage in redox reactions of ruthenium complexes

Complexes [Ru(CO)2R1R2(PMe2Ph)2]decompose intramolecularly in CHCl3to yield ketines R1R2CO; the complex[Ru(Co)2(C6H4Me-4)2(PMe2Ph)2](1a) also yields [[graphic omitted])C6H4Me}Cl(PMe2Ph)2](4).

Insertion of dioxygen between organic ligands in a rhodium complex

Atmospheric oxidation of [Rh(dpf)2]+(dpf = 6,6-diphenylfulvene) in propanone solution results in the linking of the exocyclic carbon atoms in the two fulvene ligands by a peroxide bridge.

Isomerism in carbonyldihalogenotris(phosphine)ruthenium(II) complexes: photochemical and thermal rearrangements

Four isomers of the complexes [Ru(CO)Cl2(PMe2Ph)2L′][(I), (II), (IV), and (VI); L′= P(OMe)3 or PPh(OMe)2] can be isolated and characterized. Isomer (II) is obtained, directly or indirectly, by heating any of the otherthree isomers, but irradiation of (II) leads specificallyto isomer (I). A separate equilibrium exists between (I) and (VI). Isomers (I) and (II) of complexes [Ru(CO)X2(PMe2Ph)3](X = Cl, Br, or I) can be similarly interconverted. Kinetic study of the rearrangement (I)→(II) for [Ru(CO)Cl2(PMe2Ph)3] indicates that the initial step involves loss of a PMe2Ph ligand: the five-co-ordinate intermediate obtained can either react directly with PMe2Ph to form isomer (II) or rearrange prior to reaction with PMe2Ph. Evidence of the lability of the bonds to both types of phosphorus ligand in the various isomers of the complexes [Ru(CO)Cl2(PMe2Ph)2L′][L′= P(OMe)3 or PPh(OMe)2] suggests that mechanisms involving initial dissociation of a phosphorus ligand may also be involved in their interconversions.

Preparation, and mechanism of formation, of alkyl and phenyl complexes of ruthenium(II)

New alkyl and phenyl complexes [Ru(CO)2L2ClR](L = PMe2Ph or PMePh2: R = Me, Et, or Ph) have been prepared by reaction of the all-trans- or all-cis-isomers of [Ru(CO)2L2Cl2] with HgR2 or SnMe4: the cis-isomers of [Ru(CO)2L2Cl2] do not react with these reagents. Mechanisms for the reactions, involving initial dissociation of a carbonyl ligand, are proposed on the basis of information about their stereochemistry and kinetics, and studies of halide-exchange reactions of all-trans-[Ru(CO)2(PMe2Ph)2Cl2] with bromide and iodtde ion. In the case of reactions between [Ru(CO)(PMe2Ph)3Cl2] and HgR2, in which complexes [Ru(CO)(PMe2Ph)3ClR] are formed as intermediates, the transfer of alkyl or phsnyl ligand between mercury and ruthenium has been found to be reversible.

Preparation and reactions of alkyl carbonyl complexes of platinum(II)

One-step reduction of PtCl2 to platinum(0) cluster complexes [Pt4(CO)5L4], followed by oxidative addition with Mel, provides a route to new platinum(II) complexes [Pt(CO)L(I)Me](where L is a phosphorus ligand). These react with uncharged ligands L′ to give carbonyl substitution or insertion products or a mixture of both. Both electronic and steric effects help to determine the type of product obtained and, in the case of the insertion reactions, the position of equilibrium between the complexes [Pt(CO)L(I)Me] and [PtLL′I(COMe)].

Combination of aryl and carbonyl ligands in ruthenium(II) complexes: a kinetic study

Reactions of diaryl complexes [Ru(CO)2RR′(PMe2Ph)2] with Me3CNC yield the acyl complexes [Ru(CO)(CNCMe3)(COR)R′(PMe2Ph)2]. Rate-determining combination of aryl and carbonyl ligands is followed by rapid attack by isonitrile trans to the acyl ligand. In symmetrical diaryl complexes, rates are increased by electron-releasing substituents in the para position of the aryl ring. A methyl substituent in the meta position has a rather large accelerating effect, presumably for steric reasons. In unsymmetrical diaryl complexes, the aryl ligand bearing the more electron-releasing substituent becomes incorporated in the acyl ligand. Variations in the aryl ligand not directly involved in the reaction have little effect on rate, and solvent effects are relatively small. The fairly large negative entropies of activation are attributed to the formation in the transition state of a three-membered metal–carbonyl–aryl ring, in which the aryl ring has presumably lost its freedom of rotation.