David S. Barratt

Upon the mechanism of the homogeneous hydrogenation of carbon monoxide

Abstract Model studies on isolable complexes of ruthenium and osmium suggest that homogeneously catalysed carbon monoxide hydrogenation occurs via successive intermolecular additions of H− and H+ to coordinated carbon monoxide.

A 2,3-naphthoquinodimethane complex of ruthenium

Abstract Treatment of 2,3-dimethylnaphthalene with BuLi·TMED (TMED = tetramethylethylenediamine) gives 2-lithiomethyl-3-methyl-naphthalene·TMED, which in tu

Experimental and theoretical studies of the reactions of electrophiles with cationic formyl complexes; formation of methoxy- and hydroxy-carbene complexes of ruthenium(II) and osmium(II)

Complexes of the form trans-[M(CHO)(CO)(P–P)2][SbF6][M = Ru or Os, P–P = Ph2PCH2CH2PPh2(dppe) or o-(Ph2P)2C6H4(dppb)] react with CF3SO3R (R = Me or H) at –30 °C to give trans-[M(CHOR)(CO)(P–P)2][SbF6][CF3SO3], which have been isolated and spectroscopically characterised. EHMO (extended Huckel molecular orbital) calculations demonstrate that the site of attack for hard or soft electrophiles is expected to be the formyl oxygen atom (as is observed) but that hard nucleophiles will attack the carbonyl carbon atom and soft nucleophiles the formyl carbon atom.

New decomposition pathways for formyl complexes of ruthenium(II)

The preparation of trans-[Ru(CHO)(CO)(dppb)2][SbF6][dppb = 1,2-bis(diphenylphosphino)benzene] from hydridic reduction of trans-[Ru(CO)2(dppb)2][SbF6]2 is described. The formyl complex decomposes with first-order kinetics (t½= 28 min) at 30 °C to give exclusively trans-[RuH(CO)(dppb)2][SbF6]. Detailed studies of the decomposition reaction including the observation of initiation of free-radical polymerization of methyl methacrylate during the reaction lead to the postulation of rate-determining homolytic cleavage of the Ru–CHO bond. The low rate of initiation of polymerization, together with the high isotope effect for the decomposition (kH/kD= 2.3) and the failure to observe cross-over products during co-decomposition of trans-[Ru(13CHO)(13CO)(dppb)2][SbF6] and trans-[Ru(CDO)(CO)(dppb)2][SbF6], lead to the conclusion that another decomposition pathway, involving concerted H migration and CO loss in a six-co-ordinate complex, operates. These results are compared with those obtained for trans-[Ru(CHO)(CO)(dppe)2][SbF6][dppe = 1,2-bis(diphenylphosphino)ethane].

Cationic ruthenium formyl complexes, evidence for a homolytic cleavage of the Ru–formyl bond in trans-[Ru(CHO)(CO)(dp)2][SbF6][dp = 1,2-bis(diphenylphosphino)benzene]

The complex, trans-[Ru(CHO)(CO)(dp)2][SbF6][dp = 1,2-bis(diphenylphosphino)benzene] decomposes with first order kinetics to give trans-[RuH(CO)(dp)2][SbF6], via a free radical mechanism.

Ion pairing effects in the formation of ruthenium formyls vis intermolecular hydride transfer

For M = K, M[HRu3(CO)9(dppe)] reacts with trans-[Ru(CO)2(P–P)2][SbF6]2[P–P = 1,2-dis(diphenylpgosphino)ethane(dppe)or 1,2-dis(diphenylphosphino)benzene(dp)] to give trins-[Ru(CHO)(CO)(P–P)2]+ whereas for M = Na, no reaction is observed; the extent of ion-pairing is shown to be responsible for this difference is reactivity.

The co-ordination of small molecules by manganese(II) phosphine complexes. Part 11. The co-ordination of dioxygen by manganese(II) complexes containing long-chain phosphine ligands

Manganese(II) complexes of long-chain phosphines, [MnX2(phosphine)][X = Cl, Br, or I; phosphine = P(C12H25)3, P(C14H29)3, P(C16H33)3, PPh(C12H25)2, PPh(C14H29)2, or PPh(C16H33)2], have been prepared. They form highly coloured 1 : 1 adducts with dioxygen, [MnX2(phosphine)(O2)], in both toluene and tetrahydrofuran (thf) solution. Infrared and e.s.r. spectra strongly suggest that these [MnX2(phosphine)] complexes are pseudotetrahedral dimers in the solid state and in toluene, contrasting vividly with the previously reported structure of [Mnl2(PPhMe2)]. Some molecular weight data indicate the product of dioxygenation in toluene to be the monomeric [MnX2(phosphine)(O2)] species. Dioxygen-binding curves for toluene and thf solutions have been obtained and equilibrium constants, KO1, for the dioxygenation reaction have been deduced. The general observation that KO2 increases and P50, the partial pressure when 50% of sites are deoxygenated, decreases for changes in halide ligand from Cl to Br to I in both solvents mirrors earlier observations with complexes of short-chain phosphines. The affinity of the complexes for O2 in thf is in the order phenyldialkylphosphines < trialkylphosphines. Hill coefficients, n, are approximately 1 for thf solutions of the chloride and bromide complexes, but for the iodides in thf and all of the complexes in toluene n lies in the range 1.10–1.64 indicating co-operativity for O2 binding, which may be related to the dimeric structure proposed for the complexes in toluene.

The reversible co-ordination of nitric oxide by the manganese(II) phosphine complexes, MnX2(PR3), in the solid state and in tetrahydrofuran solution

The MnX2(PR3), (X = Cl, Br, I; R3= Prn3, Bun3, PhMe2, PhEt2) complexes bind nitric oxide to form MnX2(PR3)(NO) in the Solid State and in tetrahydrofuran; the reaction is reversible, and the affinity for NO is both halide and phosphine dependent.