Richard A. Walton

Multiple bonds between metal atoms

Introduction and Survey.- Complexes of the Group 5 Elements.- Chromium Compounds.- Molybdenum Compounds.- Tungsten Compounds.- X3M=MX3 Compounds of Molybdenum and Tungsten.- Technetium Compounds.- Rhenium Compounds.- Ruthenium Compounds.- Osmium Compounds.- Iron, Cobalt and Iridium Compounds.- Rhodium Compounds.- Chiral Dirhodium (II) Catalysts and Their Applications.- Nickel, Palladium and Platinum Compounds.- Extended Metal Atom Chains.- Physical, Spectroscopic and Theoretical Results.

The X-ray photoelectron spectra of heterogeneous catalysts: II. The chromia-silica catalyst system☆

The X-ray photoelectron spectra of a series of chromia-silica catalysts (containing ~8% Cr) have been recorded. The Cr 2p12, 32 and O 1s binding energies have been monitored as a function of calcination temperature, and the change from Cr(VI) to Cr(III) has been followed as the temperature is increased. A dramatic enhancement in the intensity of the Cr 2p peaks at 500 °C is attributed to a dispersion change in which α-Cr2O3 concentrates on the surface of the silica support. Treatment of the catalysts with CO generates chromium sites which possess Cr 2p binding energies lower than those of Cr(III). This observation is consistent with the formation of Cr(II), a species which is probably the active catalyst site. The concentration of Cr(II) decreases upon exposure of the reduced catalyst to NO at 300 °C. These results are discussed in the light of other studies which have been carried out on these catalysts.

The X-ray photoelectron spectra of inorganic molecules—VIII[1, 2]: Compounds of scandium(III), scandium(III) oxide and complexes with organic oxygen donor molecules

Abstract The X-ray photoelectron spectra of ten compounds of scandium(III) are reported. Spectra were recorded with the samples exposed to a ‘zero’ volt electron flux to reduce to a minimum any surface charging effects. Where appropriate scandium 2 p , oxygen 1 s and carbon 1 s binding energies were measured. The scandium 2 p binding energies were found to be relatively insensitive to the environment about the central scandium atoms. Oxygen 1 s and carbon 1 s binding energies are discussed in terms of the known or presumed structure of the compounds. In the case of Sc 2 O 3 and Sc 2 (C 2 O 4 ) 3 . 6H 2 O, “satellite” peaks were observed on the high binding energy side of the scandium 2 p doublets. The possible origin of these satellites is discussed.

Reactions of quadruply bonded dimolybdenum(II) and dirhenium(III) complexes with 2,6-bis(dicyclohexylphosphinomethyl)pyridine and the related behavior of the mixed P, S, P ligand bis(diphenylphosphinomethyl)sulfide

The first complexes that contain the 2,6-bis(dicyclohexylphosphinomethyl)pyridine ligand (PNP) have been isolated and characterized. The reactions of K4Mo2Cl8, (n-Bu4N)2Re2Cl8 and PdBr2(1,5-COD) afford Mo2Cl4(PNP)(HPCy2) (1), ReCl3(PNP) (2) and PdBr2(PNP) (4), respectively, while from the reaction of PNP with cis-Re2(μ-O2CCH3)2Cl4(H2O)2 the heteromacrocylic dication [Cy2P{CH2pyCH2}2PCy2]2+ has been isolated as its mixed [Cl]−/[ReO4]− salt (3). The reaction of cis-Re2(μ-O2CCH3)2Cl4(H2O)2 with bis(diphenylphosphinomethyl)sulfide (PSP) gives the mononuclear Re(V) complex ReO(OEt)Cl2(PSP) (5) in which the S atom is not coordinated. The structures of 1–5 have been established by X-ray crystallography, that of 5 being the first for a complex of this ligand.

Studies on metal carboxylates. VI. mixed ligand complexes of copper(II) containing pyridine-2,6-dicarboxylic Acid in its monoanionic and dianionic forms

Abstract Starting from the copper(II) complex of pyridine-2,6-dicarboxylic acid (abbreviated dipicH 2 ) Cu dipic)·2H 2 O, a series of mixed ligand complexes of the type Cu(dipic)(L)·xH 2 O (x = 2 for L = 2,2′2,2″-terpyridyl or 2,2′-bipyridyl and x = 0 for L = pyridine or α-picoline) have been isolated. The mixed 2,2′2″-terpyridyl-acetate complexes Cu(terpy)(acetate) X·H 2 O (X = ClO 4 − or PF 6 − ) have also been prepared and were found to react with pyridine-2,6-dicarboxylic acid to afford Cu(dipicH)(terpy)ClO 4 ·H 2 O and Cu(dipicH)(terpy)PF 6 . The latter derivatives contain this acid molecule in its monoanionic form. The spectral and magnetic properties of the above complexes have been studied and the results are discussed. Where possible comparisons are made with the related silver(II) complexes of these types.

Hydrogen-bonding as a tool for building one-dimensional structures based on dimetal building blocks

The ligands isonicotinamide and nicotinamide are used to form assemblies of dimetal (M 2 ) building units via a combination of coordinate bonds and intermolecular hydrogen-bond interactions. Polymeric networks of the linear, zig-zag and sinusoidal varieties are observed in the solid state depending on the ligands and metal precursors involved.

X-ray photoelectron spectra of inorganic molecules: XXX1. Organometallic derivatives of tungsten(O) and tungsten(II)

Abstract The W 4f binding energies of various carbonyl-containing complexes of tungsten are reported. Comparisons between WII complexes containing the [(η3-allyl)W(CO)2] moiety and neutral derivatives of the type W(CO)6-xLx are made. The absence of a clear-cut correlation between the W 4f binding energies and the value of x in W(CO)6-xLx is discussed and these results compared with those obtained for the analogous molybdenum complexes.

Studies directed towards the isolation and characterization of the paramagnetic cations [Re2X4(LL)2]+ (X = CL or Br; LL = Ph2PCH2PPh2, Ph2AsCH2AsPh2 or Ph2PNHPPh2), and the crystal structure of Re2Cl4(Ph2PNHPPh2)2·(Ch3)2CO

Abstract The synthesis of the triply bonded dirhenium(II) complexes Re2X4(dpam)2 (X = Cl or Br; dpam = Ph2AsCH2AsPh2) has been accomplished through the reactions of Re2(O2CCH3)2X4(H2O)2 with dpam in hot methanol. Solutions of these complexes, and of Re2X4(dppm)2 (X = Cl or Br; dppm = Ph2PCH2PPh2) and Re2Cl4(dppa)2 (dppa = Ph2PNHPPh2), in n-Bu4NPF 6/CH2Cl2 have been oxidized electrochemically (at ca + 0.5 V vs Ag/AgCl) to generate solutions of the paramagnetic, ESR-active monocations. The salts [Re2X4(dppm)2]PF6 have been prepared by the reaction of Re2X4(dppm)2 with [(η5-C5H5)2Fe]PF6 in acetone. Cyclic voltammetric data for solutions of all these complexes in 0.1 M n-Bu4NPF6/CH2Cl2 are reported. The crystal structure of Re2Cl4(dppa)2·(CH3)2CO has been determined and shown to resemble that of Re2Cl4(dppm)2. The crystallographic data are as follows: monoclinic space group P21/n, a = 11.382(2), b = 23.273(5), c 19.212(3) A, β = 92.429(8)°, V = 5084(3) A3 and Z = 4. The structure was refined to R 0.031 (Rw = 0.036) for 4490 data with I > 3.0σ(I). The complex has a ReRe bond distance of 2.2417(5) A, and contains intramolecular dppa ligand bridges. A staggered rotational geometry is characterized by average ClReReCl and PReReP torsional angles of 51.7[2] and 41.8[5]°, respectively.

The triply-bonded complex tetrachlorobis[bis(diphenylphosphino)methane] dirhenium(II) and related species, and their use as reagents in dirhenium chemistry

Abstract The complex Re 2 Cl 4 (μ-dppm) 2 (dppm = Ph 2 PCH 2 PPh 2 ) and its bromide analogue serve as important precursors to many other dirhenium complexes because of the ability of the bridging dppm ligands to stabilize the dimetal unit. Reactions of these complexes with π-acceptors such as CO and RNC lead to the incorporation of up to three of these ligands, as exemplified by the conversion of Re 2 Cl 4 (dppm) 2 to Re 2 Cl 4 (dppm) 2 (CO), then Re 2 Cl 4 (dppm) 2 (CO) 2 , and finally [Re 2 Cl 3 (dppm) 2 (CO) 3 ] + . The redox activity of Re 2 X 4 (μ-dppm) 2 (X = Cl or Br) has been utilized in the reductive coupling of nitrile ligands (RCN) to give [Re 2 X 3 (μ-HN 2 C 2 R 2 )(μ-dppm) 2 (NCR)]PF 6 . When a non-bridging phosphine ligand is used, then the reaction course can be quite different. Thus, α-Re 2 Cl 4 (dppbe) 2 (dppbe = 1,2-bis(diphenylphosphino)benzene) reacts with EtCN in the presence of conc. HCl to give the rhenium(V) imido complex, Re(NCH 2 Et)Cl 3 (dppbe), in good yield. A different aspect of the redox activity of Re 2 Cl 4 (μ-dppm) 2 is encountered in its reactions with LiAlH 4 in THF to give Re 2 (μ-H) 2 H 6 (μ-dppm) 2 .

Some recent developments in the chemistry of multiply bonded dimetal complexes that contain the intramolecular bridging phosphine ligands R2P(CH2)nPR2

Abstract Recent synthetic and structural studies on multiply bonded complexes of stoichiometry M2X4[μ-R2P(CH2)nPR2]2 (M = Mo, W or Re; X = Cl, Br or I; R = Me, Et or Ph; n = 1 or 2), the ditungsten(III) hydride W2(μ-H)(μ-Cl)Cl4(μ-dppm)2 (dppm = Ph2PCH2PPh2), Re2Cl4(μ-dmpm)3 (dmpm = Me2PCH2PMe2), and M2(μ-Cl)2 Cl4(μ-R2PCH2PR2)2 (R = Me or Ph) are surveyed. The first examples of multiply bonded complexes that contain the Ph2PCH  CHPPh2 ligand (abbreviated dppee) are described, viz. the α- and β-isomers of M2X4(dppee)2 (M = Mo or Re, X = Cl or Br). The reactions of Re2X4(dppm)2 (X = Cl or Br) with RNC, RCN and CO ligands that yield complexes in which a metal-metal multiple bond is preserved are reviewed.