Andrew McCamley

Synthesis and characterisation of (η5-cyclopentadienyl)(η5-ring)titanium alkyl (ring = indenyl or C5H4But) complexes. Crystal and molecular structure of racemic [Ti(η5-C5H5)(η5-C9H7)(CH2SiMe3)Cl]

New, selective and high-yielding preparations of the mixed-ring complexes [Ti(η5-C5H5)(η5-C9H7)C2] and [Ti(η5-C5H5)(η5-C5H4But)Cl2] are reported. These have been used to prepare a range of mono- and di-substituted titanium(IV) alkyl and benzenethiolate complexes of the form [Ti(η5-C5H5)(η5-ring)(CH2SiMe3)Cl] and [Ti(η5-C5H5)(η5-ring)R2](ring = indenyl or C5H4But; R = Me, CH2Ph, CH2SiMe3 or SPh). While the indenyl ligand in the racemic, chiral-at-metal complex [Ti(η5-C5H5)(η5-C9H7)(CH2SiMe3)Cl] is bound in an η5 fashion, X-ray structural data clearly indicate that there is some ‘η3 ring-slip’ character to the bonding. The NMR and nuclear Overhauser effect experiments conducted on [Ti(η5-C5H5)(η5-C5H4But)(CH2SiMe3)Cl] demonstrate hindered rotation around the Ti–C5H4But bond and show the geometry to be fixed such that the But and SiMe3 groups are remote.

C–H activation and nitrile insertion reactions of a cationic niobium alkylidene complex

Oxidation of [Nb(η5-C5H4But)2(CH2Ph)2] yields the stable cationic benzylidene complex [Nb(η5-C5H4But)2(CHPh)(thf)]BPh4, which readily loses thf to form the C–H activation product [Nb(η5-C4H4But)(η5:η1-C5H4CMe2CH2)(η2–CH2Ph)]BPh4 and reacts with acetonitrile to give the double-insertion product [Nb(η5-C5H4But)2{η2-NC(Me)C(Ph)C(Me)NH}]BPh4.

Polymerisation of ethene by the novel titanium complex [Ti(Me3SiNCH2CH2NSiMe3)Cl2]; a metallocene analogue

Reaction of the trimethylsilylated diamine ligand (Me3Si)NHCH2CH2NH(SiMe3) with titanium(IV) precursors affords the novel distorted-tetrahedral complex [Ti(Me3SiNCH2CH2NSiMe3)Cl2] which, when activated by methylaluminoxane, is an active ethene polymerisation catalyst.

Butadiene ‘sandwich compounds’: synthesis of bis(η-1,4-di-tert-butylbuta-1,3-diene) complexes of titanium and vanadium

The vapours of titanium or vanadium react with 1,4-di-tert-butylbuta-1,3-diene to afford the novel, homoleptic diene complexes [M(η-1,4-But2C4H4)2], M = Ti, V.

Photochemistry of Os(η6-arene) complexes in low-temperature matrices: an infrared spectroscopic study of CH bond activation

Abstract The photochemistry of a series of Os(η6-arene) complexes has been investigated in argon, methane and dinitrogen matrices with IR and UV/vis detection. The coordinatively unsaturated complex, Os(η6-C6H3Me3)(CO), may be formed by photolysis of either Os(η6-C6H3Me3)(CO)(H)2 or Os(η6-C6H3Me3)(CO)(H) in argon matrices. Irradiation of Os(η6-C6H3Me3)(CO)(H)2 in nitrogen matrices yields Os(η6-C6H3Me3)(CO)(N2). Activation of methane CH bonds occurs on photolysis of either Os(η6-C6H3Me3)(CO)(H)2 or Os(η6-C6H3Me3)(CO)2 in methane matrices. The formation of Os(η6-C6H3Me3)(CO)(CH3)(rmH) is established by comparison of a complete IR spectrum with that of an authentic sample in the matrix. These studies provide extremely strong evidence that insertion into alkane CH bonds is preceded by the information of the 16-electron intermediate Os(η6-C6H3Me3)(CO). Vinyl hydride complexes Os(η6-C6H3Me3)(L)(C2H3)(H)(rmL= CO, C2H4) and Os(η6-C6H6)(CO)(C2H3)H are formed on photolysis of the ethene complexes, Os(η6-C6H3Me3(L)(C2H4) and Os(η6-C6H6)(CO)(C2H4). The vinyl hydride products are established by comparison of the spectra from C2H4 and C2D4 complexes, and observation of OsH(D) and vinly vibrations, as well as charactersitic v(CO) modes. The photoproducts of Os(η6-C6H3Me3)(CO)(CH2=CHMe) are probably cis and trans isomers of the propenyl hydride Os(η6-C6H3Me3)(CO)(CH=CHMe)H.

Syntheses, structures and fluxional behaviour of η4-1,4-di-tert-butylbuta-1,3-diene complexes of iron and ruthenium

The complexes [M(CO)3(η4-diene)](M = Fe or Ru; diene = 1,4-di-tert-butylbuta-1,3-diene) have been synthesised and their crystal structures and solution fluxional behaviour determined. While they adopt square-pyramidal geometries in the solid state, the carbonyl ligands show fluxional behaviour in solution (Ea= 44.6, ΔH‡= 42.2 kJ mol–1, ΔS‡=–29.8 J K–1 mol–1 where M = Fe; 52.6, 50.0 kJ mol–1 and –30.5 J K–1 mol–1 where M = Ru). These activation parameters are the largest reported for simple [M(CO)3(diene)] complexes. An inverse correlation between Ea and the diene ‘bite’ angle θ1 for a range of [M(CO)3(diene)] complexes is described and used to account for variations in activation barriers.

Synthesis and reactivity of bis(η-1,4-di-tert-butylbuta-1,3-diene)cobalt; the X-ray crystal structure of the anionic butadiene sandwich complex [K(18-crown-6)(thf)2][Co(η-C4H4But2)2]

Cocondensation of cobalt atoms with 1,4-di-tert-butylbuta-1,3-diene affords the stable, paramagnetic butadiene sandwich compound [Co(η-C4H4But2)2], which is a reactive source of Co0 fragments; reduction of [Co(η-C4H4But2)2] with potassium affords the first crystallographically characterised homoleptic butadiene sandwich complex, [Co(η-C4H4But2)2]–, in which the bonding is that of a genuine diene rather than a metallacyclopentene.

Photochemical generation of 16-electron [Rh(η5)-C5H5)-(PMe3)] and [Ir(η5-C5H5)(PMe3)] in low-temperature matrices: evidence for methane activation

The photochemical reactions of [Rh(η5-C5H5)(PMe3)(H)2] and [Ir(η5-C5H5)(PMe3)(H)2] have been studied in Ar, CH4, N2 and CO-doped argon matrices by IR and UV/VIS spectroscopy. The UV photolysis in argon matrices results in the formation of the 16-electron complexes [M(η5-C5H5)(PMe3)] with characteristic visible absorption maxima (M = Rh, λmax 399 and 488 nm; M = Ir, λmax, 436 and 526 nm). The reaction is partially reversed by long-wavelength photolysis. The conversion of [Rh(η5-C5H5)(PMe3)(H)2] to [Rh(η5-C5H5)(PMe3)(Me)H] on photolysis in methane matrices is confirmed by extensive isotopie labelling studies and by the use of alternative precursors for the methyl hydride, viz.[Rh(η5-C5H5)(PMe3)(η2-C6F6)] and [Rh(η5-C5H5)(PMe3)(C2H4)], Evidence has also been obtained to show that irradiation of [Ir(η5-C5H5)(PMe3)(H)2] in methane yields [Ir(η5-C5H5)(PMe3)(Me)H]. Photolysis of [M(η5-C5H5)(PMe3)(H)2]in N2 and CO-doped Ar matrices generates [M(η5-C5H5)-(PMe3)L](M = Rh or Ir, L = N2 or CO).

Laser spectroscopy of open-shell sandwich complexes

Abstract Emission and excitation spectra of the metallocenes, Cp2M (M = Re, Mo, W) and Cp*2Re (Cp = η5-C5H5 Cp* = η5-C5Me5) isolated in N2and Ar matrices at 12 K have been excited by low-power irradiation with a tunable pulsed laser into their lowest LMCT bands. This method generates vibrationally resolved spectra which are much sharper than their absorption counterparts because the laser selects individual conformers or matrix trapping sites of the guest molecule. Emission lifetimes of 72 and 3.6 ns have been measured for Cp2Re and Cp*2Re respectively. The arene sandwich complexes, V(η6-C6H6)2 and V(η6-1,3,5-C6H3Me3)2, respond differently to laser irradiation yielding resonance Raman spectra with long vibrational progressions.

C-H activation by organometallics: the role of matrix isolation studies

Advances are reported in the application of matrix isolation in combina- tion with solution techniques to the study of C-H activation reactions of organo- metallics. Laser-induced fluorescence proves applicable to all the open-shell metallocenes studied, (75-CsHs) M (M = Mo, W, Re) and (75-C5Me5),Re. Studies with pulsed dye-lasers allow the determination of excitation spectra and the emission lifetimes. Three types of situation are encountered when the behaviour of photoproducts in matrices is compared with that in solution. In the type 1 situation, a coordinatively unsaturated intermediate is stabilised by the matrix. It may be observed in solution using time-resolved spectroscopy if the matrix and solution studies share a common spectroscopic technique (e.g. Ru(Me,PCH,CH,PMe,),). In type 2 reactions, photolysis leads to an unstable isomer of the precursor. Such species may often be observed by NMR following photolysis of solutions or frozen solutions at low temperature. The cage formed by the matrix or viscous solvent may play a significant role in this type of reaction as, for instance, in the isomerisation of some metal-ethene complexes. Type 3 reactions involve intermolecular reaction in the matrix (e.g. (75.-C5H )Rh(CO), with methane), but the products of reaction may be very labile. ?he corresponding reactions with alkanes may be observed by laser flash photolysis with the aid of a common spectroscopic method.