Neil M. Walker

Reactivity of BH3 and 9-BBN towards palladium(II) complexes of diphenylvinyl- and diphenylallyl-phosphine; X-ray structures of [PdCl2(PPh2CH2CH2CH3)]2 and [PdCl2(PPh2CH2CHCH2)]2

Abstract Palladium(II) chloride complexes PdCl 2 L 2 and [PdCl 2 L] 2 have been prepared with the phosphine ligands PPh 2 CHCH 2 and PPh 2 CH 2 CHCH 2 . The reactions of PdCl 2 L 2 complexes with thf·BH 3 afford equilibria in which the components may be identified by 31 P{ 1 H}-NMR spectroscopy. PdCl 2 L 2 and [PdCl 2 L] 2 complexes and phosphine–borane adducts are observed. In addition, analogues of the PdCl 2 L 2 and [PdCl 2 L] 2 complexes are present in which one or both phosphine ligands have undergone alkene hydroboration. The reaction of PdCl 2 (PhCN) 2 and the cyclic adduct formed between 9-BBN and PPh 2 CH 2 CHCH 2 [cyclo-(9-borabicyclo[3.3.1]nonanyl)-propyl(diphenyl)phosphine] has been studied. Opening of the P–B dative bond occurs with the formation of a [PdCl 2 L′] 2 complex in which the phosphine ligand contains a pendant borane moiety. Hydrolysis in air yields the crystallographically characterised dimer [PdCl 2 (PPh 2 CH 2 CH 2 CH 3 )] 2 . The X-ray structure of the unsaturated analogue, [PdCl 2 (PPh 2 CH 2 CHCH 2 )] 2 , has also been obtained. Both compounds exist as symmetrical dimeric structures with terminal and asymmetric bridging halides.

Transition metal mediated homologation of BH3·THF: synthesis and crystal structure of [WH3(PMe3)3B3H8]

Abstract The novel arachno -2-tungstametallaborane, [WH 3 (PMe 3 ) 3 B 3 H 8 [, has been made in high yield (>90%) by the reaction of the monoborane BH 3 ·THF (THF = tetrahydrofuran) with [WH 6 (PMe 3 ) 3 ]. This represents a controlled transition metal mediated synthesis of a higher borane moiety from a mononuclear precursor. The crystal structure of [WH 3 (Pme 3 ) 3 B 3 H 8 ] has been determined.

Reactivity of AlMe3 with titanium(IV) Schiff base complexes: X-ray structure of [Ti{(μ-Br)(AlMe2)}{(μ-Br)(AlMe2X)}(salen)] · C7H8 (X=Me or Br) and reactivity studies of mono-alkylated [Ti(Me)X(L)] complexes

Abstract [TiCl2(salen)] (1) reacts with AlMe3 (1:2) to give the heterometallic Ti(III) and Ti(IV) complexes [Ti{(μ-Cl)(AlMe2)}{(μ-Cl)(AlMe2X)}(salen)] (X=Me or Cl) (2) and [TiMe{(μ-Cl)(AlCl2Me)}(salen)] (3). Addition of diethyl ether to 3 affords [Ti(Me)Cl(salen)] (4). The analogous reaction of [TiBr2(salen)] (5) gives the crystallographically characterised [Ti{(μ-Br)(AlMe2)}{(μ-Br)(AlMe2X)}(salen)] (X=Me or Br) (6) and [Ti(Me)Br(salen)] (7) in a single step, whilst the comparable reaction of [TiCl2{(3-MeO)2salen}] (8) with AlMe3 yields [Ti(Me)Cl{(3-MeO)2salen}] (9) with no evidence of titanium(III) species. Reactivity of both halide and methyl groups of 4 has been probed using magnesium reduction, SbCl5 and AgBF4 halide abstraction and SO2 insertion reactions. Hydrolysis of [Ti(Me)X(L)] complexes affords μ-oxo species [TiX(L)]2(μ-O) [X=Cl, L=salen (13); X=Br, L=salen (14); X=Cl, L=(3-MeO)2salen (15)].

Synthesis and reactions of η-cycloheptatriene and η-cycloheptatrienyl derivatives of zirconium and hafnium

The new compounds [M(η-C7H8)L2Cl2](M = Zr, L = PMe31; M = Hf, L = PMe32; M = Zr, L = PMe2Ph 3; M = Hf, L = PMe2Ph 4; M = Zr, L = PMePh25) have been synthesised by reduction of MCl4 using sodium amalgam in the presence of the tertiary phosphine and cycloheptatriene. Lithium indenide reacts with the triene compounds to give [M(η-C7H7)(η5-C9H7)](M = Zr 6 or Hf 8) which react with trimethylphosphine or 1,2-bis(dimethylphosphino)ethane (dmpe) to form [M(η-C7H7)(η5-C9H7)(PMe3)](M = Zr 7 or Hf 9) and [{Hf(η-C7H7)(η5-C9H7)}2(µ-dmpe)]10 respectively. Treatment of 1 or 2 with sodium cyclopentadienide gives [M(η-C5H5)2{η2-1,2-(or -3,4-) C7H8}(PMe3)][M = Zr 11 or Hf 12). The X-ray crystal structures of 1, 10 and [Zr(η-C5H5)2(η2-3,4-C7H8)(PMe3)]11a have been determined.

Half-sandwich η-cycloheptatri-ene and -enyl derivatives of titanium and zirconium

Treatment of [Zr(η6-C7H8)2]1 in tetrahydrofuran with iodine gives [Zr(η-C7H7)(thf)2I]2 which reacts with PMe3 forming [Zr(η-C7H7)(PMe3)2I]3. The latter reacts with iodotrimethylsilane to give the exo-trimethylsilylcycloheptatriene compound [Zr{exo-η6-C7H7(SiMe3)}(PMe3)2I2]4. Thermolysis of 4 gives [Zr(η6-C7H8)(PMe3)2I2]5. The compounds [M(η-C7H7)L2Cl][M = Ti, L2=(PMe3)26, Me2NCH2CH2NMe27 or Me2PCH2CH2PMe28; M = Zr, L2= Me2NCH2CH2NMe29] have been prepared in one-pot reactions.

Half-sandwich compounds of zirconium(II): the synthesis of [Zr(η6-C7H8)(PMe3)2Cl2]

Reduction of [ZrCI4] in the presence of cycloheptatriene and PMe3 forms [Zr(η6-C7H8)(PMe3)2Cl 2](1), and reaction of iodotrimethylsilane with [Zr(η7-C7H7)(PMe3)2](2), produced from [Zr(η6-C7H8)2](4)via[Zr(η7-C7H7)(tetrahydrofuran)2l](5), forms [Zr(exo-η6-C7H7SiMe3)(PMe3)2l2](3); the crystal structures of (1),(3),and (5) have been determined.

Formation of titanium-aluminium Schiff base complexes: X-ray structure of [Ti(μ-Cl)(AlMe2) (μ-Cl)(AlMe2X)(salen)] (X = Me OR Cl)

Abstract Reaction of [TiCl 2 (salen)] [salen = N, N′-ethylene bis (salicylideneiminate)] and AlMe 3 in toluene/hexane afforded the hetero-bimetallic [Ti{(μ-Cl)(AlMe 2 )}{(μ-Cl)(AlMe 2 X)} (salen)] (X = Me or Cl), 1 and [TiMe{(μ-Cl)(AlCl 2 Me)} (salen)], 2 ; the crystal structure of the titanium(III) complex ( 1 ) has been determined. In tetrahydrofuran 2 forms the stable monoalkylated titanium(IV) complex [Ti(Me)Cl(salen)] ( 3 ).

Synthesis, crystal structure and reactions of zerovalent 16-electron bis(η-cycloheptatriene)zirconium

Reduction of ZrCl4 with sodium amalgam in the presence of cycloheptatriene gives the crystallographically identified [Zr(η6-C7H8)2]1 which exhibits a non-parallel arrangement of the cycloheptatrienyl ligands. This reacts with PMe3 or 1,2-bis(dimethylphosphino)ethane (dmpe) to yield [Zr(η7-C7H7)(η5-C7H9)(PMe3)]2 and [{Zr(η7-C7H7)(η5-C7H9)}2(dmpe)]3 respectively. Treatment of compound 1 with (AlEt2Cl)2 in tetrahydrofuran (thf) yields [{Zr(η7-C7H7)(thf)(µ-Cl)}2]4 which reacts with N,N,N′,N′-tetramethylethylenediamine, PMe3, dmpe and 1,2-dimethoxyethane to produce [Zr(η7-C7H7)(Me2NCH2CH2NMe2)Cl]5, [Zr(η7-C7H7)(PMe3)2Cl]6, [Zr(η7-C7H7)(dmpe)Cl]7 and [Zr(η7-C7H7)(MeOCH2CH2OMe)Cl]8, respectively. The electronic structures of 1 and [Zr(η7-C7H7)(η5-C7H9)]11 have been investigated by photoelectron spectroscopy and extended-Huckel molecular-orbital calculations.

Stereochemical non-rigidity in rhodium–triruthenium clusters studied by nuclear magnetic resonance spectroscopy

Variable-temperature (v.t.)1H and 13C n.m.r. studies on tetranuclear clusters [RhRu3(µ-H)2(µ-CO)(CO)9(η-C5H5)](1), [RhRu3(µ-H)2(η-CO)(CO)9(η-C5Me5)](2), and [RhRu3(µ-H)4(CO)9(µ-C5Me5)](3) establish various types of stereochemical non-rigidity in solution. Cluster (1) exhibits at least three distinct CO exchange processes: the lowest-energy intramolecular interchange, with ΔG195‡= 35.2 ± 0.3 kJ mol–1, monitored by v.t. 1H and 13C n.m.r., including 13C-{1H} two-dimensional exchange correlated spectra at 163 K (NOESY sequence), involves a pairwise exchange of eight CO groups resulting from a ‘rocking motion’ of CO ligands around a single RhRu2 triangular face. Three isomers of cluster (2) are in dynamic equilibrium in solution: one isomer is relatively rigid stereochemically whereas the other two are fluxional and undergo rapid interconversion at all but the lowest temperatures [e.g. 146 K 1H (200 MHz)]. Two distinct exchange processes are observed for cluster (3): localised site exchange of CO ligands at Ru(CO)3 centres, with ΔG223‡= 47.5 ± 1.5 kJ mol–1, and µ-H mobility, with ΔG164‡= 29.4 ± 0.2 kJ mol–1. Reactions of (1) with phosphines produce clusters [RhRu3(µ-H)2(µ-CO)(CO)9–n(η-C5H5)(PPh3)n][n= 1 (4) or 2 (5)] and [RhRu3(µ-H)2(µ-CO)(CO)7(η-C5H5)(dppe)](6)(dppe = Ph2PCH2CH2PPh2), accompanied by cleavage products including [Ru3(CO)8(dppe)2]. Varaible-temperature 1H, 13C, and 31P n.m.r. studies indicate that (4) exists in solution in two isomeric forms undergoing slow interconversion at low temperatures: the major isomer is more fluoxional with a lowest-energy exchange related to that in (1) with ΔG203‡= 38.0 ± 0.3 kJ mol–1. Clusters (5) and (6) show n.m.r. spectra of stereochemically rigid species in solution at ambient temperature and structures of these complexes are discussed.

Divalent diene and triene compounds of zirconium and hafnium; X-ray crystal structures of [Hf(η4-CH2CMe–CMeCH2)(PMe3)2Cl2], [Zr(η5-C5H5)2(PMe3)(η2-C7H8)], and {[Hf(η7-C7H7)(η5-C9H7)]2(µ-Me2PCH2CH2PMe2)}

The synthesis and reactions of divalent compounds [Hf(η4-CH2CMe–CMeCH2)(PMe3)2Cl2] and [M(η6-C7H8)(PMe3)2Cl2](M = Zr, Hf) are described.