Jack L. Davidson

The mechanistic role of η2-vinyl complexes in metal-promoted alkyne oligomerisations. The crystal and molecular structures of [W{η5-C(CF3)C(CF3)C(CO2Me )C(CO2Me)C(CF3)C(CF3)SPri}(η5-C5H5)], [WF {η5-C(CF2)C(CF3)C( CO2Me)C( CO2Me)C(CF3)C(CF3)SPri}(η5-C5H5)], and [W{η4-C(CF3)C(CF3)C(Me)C(Me)SPri}(η2-CF3CCCF3)(η5-C5H5)]

Reactions of Alkynes RCCR (R = CF3, CO2Me, or Me) with η2-vinyl complexes [W{η2-C(CF3)C(CF3)SR′}(CF3CCCF3)(η5-C5H5)](R′= Et, Prn, or Pri) give isomeric products [W(CF3C2CF3)2(RC2R)SR′(η5-C5H5)] resulting from insertion of the incomingalkyne into the MC bond of the η2-vinyl and thus illustrate that η2-vinyls can act as intermediates in metal-promoted alkyne oligomerisation reactions.

Synthesis and dynamic nuclear magnetic resonance studies of pentafluorobenzenethiolate complexes of molybdenum and tungsten. The crystal and molecular structures of [W(SC6F5)3(CO)(η5-C5H5)]·0.5CH2Cl2and [N(PPh3)2][Mo(SC6F5)4(η5-C5H5)]

The reaction between [WBr3(CO)2(η5-C5H5)] and excess of Tl(SC6F5)(CH2Cl2, 20 °C) affords Tl[W(SC6F5)4(η5-C5H5)](2b) as the major product and [W(SC6F5)3(CO)(η5-C5H5)](3) as the minor product. Complex (3) has been structurally characterised as its 0.5 CH2Cl2 solvate by X-ray diffraction. Chiral molecules of [W(SC6F5)3(CO)(η5-C5H5)] adopt a distorted square-based ‘piano-stool’ geometry with the trans W–S bond [2.443 6(15)A] longer than the cis W–S bonds (mean 2.358 A). The SC6F5 ligands lie with S–C bonds approximately in the plane of the square base and, all C6F5 groups have the same rotational orientation about the central W atom. However, dynamic 19F n.m.r. studies of (3) reveal that two isomeric forms exist at low temperature due to different orientations of the SC6F5 ligands but these undergo exchange at ambient temperature as a result of rotation about the W–SC6F5 bonds or inversion at sulphur. Similar studies of complex (2b) established that apparent rotation of the SC6F5 groups is solvent dependent and occurs in conjunction with ionic dissociation into Tl+ and [W(SC6F5)4(η5-C5H5)]–. The TlI in (2b) and related complexes Tl[Mo(SC6F5)4(η5-C5H5)] and Tl[Mo(SC6F5)2(CO)2(η5-C5H5)] can be replaced by non-co-ordinating cations to give X+[M(SC6F5)4(η5-C5H5)]–[M = Mo, X = NBun4(4a) or N(PPh3)2(4b); M = W, X = NMe4] and N(PPh3)2+[Mo(SC6F5)2(CO)2(η5-C5H5)]– which also exhibit fluxional behaviour according to 19F n.m.r. studies. The structure of complex (4b), determined in the solid state by X-ray diffraction, comprises discrete ions [(Ph3P)N(PPh3)]+ and [Mo(SC6F5)]4[(η5-C5H5)]–. The complex anion has a ‘piano-stool’ geometry with a square base defined by four SC6F5 ligands (mean Mo–S 2.420 A) and the C6F5 groups form a ‘swastika-like’ arrangement about the square plane. Reactions of (2b) with tertiary phosphines (L) in CH2Cl2 at 20 °C afford 1:2 adducts Tl[W(SC6F5)4L2(η5-C5H5)][L = PPh3(6b), PMe2Ph (6c), or PEt3(6d)]. Dynamic 19F n.m.r. studies established a different structure for (6b) in solution compared to (6c) and (6d).

Monocyclopentadienyl pentafluorothiophenolate complexes of molybdenum and their interactions with thallium(I) ions; dynamic nuclear magnetic resonance studies and crystal and molecular structures of [TlMo(SC6F5)2L2(cp)](L = CO or SC6F5; cp =η5-C5H5)

Reactions between [MoCl(CO)3(cp)](cp =η5-C5H5) and Tl(SC6F5) afford the fully characterised complexes [TlMo(SC6F5)2L2(cp)][L = CO (1) or SC6F5(2)]. Complex (2) is formed by an oxidative substitution process and can also be obtained by reactions of Tl(SC6F5) with other molybdenum-(II), -(III), or -(IV) precursors. Molecular structures of crystalline complexes (1) and (2) have been determined by X-ray diffraction. Complex (1) contains units of [(cp)(OC)2Mo(µ-SC6F5)2Tl] in which TlI is co-ordinated by two S atoms (mean Tl–S 3.015 A) and is close to one ortho-F atom of each C6F5ring (mean Tl ⋯ F 3.095 A); intermolecular Tl ⋯ S interactions between individual units of (1) give this material an extended-chain structure in the solid state. Crystalline (2) contains discrete molecular units of [(cp) Mo(µ-SC6F5)4Tl] in which TlI is co-ordinated by four S atoms (mean Tl–S 3.272 A); these four S atoms, four closely associated o-F atoms, one from each C6F5ring (mean Tl ⋯ F 3.062 A), and the Mo atom [Mo ⋯ Tl 3.402(3)A] define a cavity in which the TlI is situated. The anion [Mo(SC6F5)4(cp)]– in (2) is acting as a polydentate ligand to Tl+. Variable-temperature 19F n.m.r. studies on complexes (1) and (2) in toluene, dichloromethane, and acetone solutions establish the occurrence both of restricted rotation of the C6F5 groups and of solvent-dependent ionic dissociation into Tl+ and [Mo(SC6F5)2L2(cp)]–. Significant ionisation occurs in the polar solvent acetone, and this is supported by conductivity measurements. Reactions of complex (1) with tertiary phosphines give products [Mo(SC6F5)(CO)2L(cp)][L = PMe2Ph (3), PMePh2(4), or PPh3(5)] with ‘four-legged piano-stool’ geometry; these complexes are principally cis isomers although minor amounts of trans isomers were detected by 1H n.m.r. spectroscopy in solutions of (3) and (5). Reaction of complex (2) with PPh3 affords a species [TlMo(SC6F5)4(PPh3)2(cp)] which variable-temperature 1H, 19F, and 31P n.m.r. studies show to exist as a mixture of two interchanging forms in solution.

Metal-promoted alkyne trimerisation leading to novel metallacycles. The molecular structures of [Mo{η3-C(CF3)C(CF3)C(Me)C(Ph)SPri}(CF3CCCF3)(η5-C5H5)], [WSPri{η5-C(CF3)C(CF3)C(CF3)C(CF3)C(Me)C(Ph)}(η5-C5H5)], and [W(SC6H4Me-4){η4-C(CF3)C(CF3)C(CO2Me)C(CO2Me)C(CF3)C(CF3)}(η5-C5H5)]

Addition of alkynes to isomeric η2-C,C-vinyl [M{η3-C(CF3)C(CF3)SR′}(CF3CCCF3)(η5-C5H5)](M = Mo, W; R′= Pri) and bis-alkyne complexes [MSR′(CF3CCCF3)2(η5- C5H5)](M = W, R′= 4-MeC6H4) gives new metallacycles formed by linking of two or three alkynes; X-ray analyses reveal two modes of bonding for the tris alkyne (CR)6 ligands.

Synthesis, reactions, and dynamic nuclear magnetic resonance studies of η2-vinyl complexes of tungsten, [W{η3-C(CF3)C(CF3)(SR)}(CF3cCCF3)(η5-C5H5)](R = Me, Et, Prn, Pri, or But)

Reactions of the hexafluorobut-2-yne complex [WCl(CF3CCCF3)2(η5-C5H5)] with thallium(I) thiolates TI(SR) give the bis-alkyne derivative [W(SR)(CF3CCCF3)2(η5-C5H5)] when R = C6H4Me-4 whereas an isomeric η2-vinyl form [W{η3-C(CF3)C(CF3)(SR)(CF3CCCF3)(η5C5H5)], resulting from migration of the SR ligand to a bridging mode between the metal and a fluorocarbon ligand, is obtained when R = Me, Et, Prn, Pri, or But. When R = Pri or But one isomeric form is observed which undergoes fluxional behaviour involving total CF3 group scrambling, indicating reversible fission of the C–S bond of the η2-vinyl ligand. With R = Me, Et, or Prn two isomeric η2-vinyl forms are observed, both of which undergo CF3 group exchange in addition to isomer exchange, according to 19F n.m.r. studies. Reactions of both bis-alkyne (R = C6H4Me-4) and η2-vinyl complexes (R = Pri or But) with tertiary phosphines and phosphites (L) give η2-vinyl complexes [W(SR){η2-C(CF3)C(CF3)(L)}(CF3CCCF3)(η5-C5H5)] the stability of which increases with the nucleophilic character of the phosphorus ligand. 19F N.m.r. studies have established that in some cases the reactions proceed via two unstable kinetic isomers which undergo thermal rearrangement to a thermodynamically more stable form.

Isomerism and fluxional behaviour in η2 -vinyl complexes resulting in inversion of configuration at an asymmetric carbon atom. The crystal and molecular structures of two isomeric forms of [MoCl{η2 -C(CF3)C(CF3)(PEt3)} (CF3CCCF3)(η5 -C5H5)]

Abstract η 2 -Vinyl complexes [MCl{η 2 -C(CF 3 )C(CF 3 )L} (CF 3 CCCF 3 )(η 5 -C 5 H 5 )] (M = Mo, W: L = tertiary phosphine or phosphite or pyridine) have been shown by NMR and X-ray diffraction studies to exist in two distinct isomeric forms which exhibit (a) different orientations of the η 2 -vinyl ligand (b) different configurations at the asymmetric carbon atom of the η 2 -vinyl ligand: variable temperature NMR studies reveal fluxional behaviour thought to involve reversible inversion of configuration at this carbon atom.

Preparation and studies of paramagnetic diene complexes of molybdenum(III); molecular and electronic structures of [MoCl2(η-C4H6)(η-C5H5)] and [Mo3(µ-Cl)(µ3-O){µ3-σ,σ:η2:η2-C4(CF3)4}(η-C5H5)3]

Reactions of complexes [MoX{η-C2(CF3)2}2(η-C5H5)] with certain dienes give the paramagnetic complexes [MoX2(η-diene)(η-C5H5)][diene = 1,3-butadiene, X = Cl (la), Br (1b), or I (1c); diene = isoprene, X = Cl (2); diene =trans-1,3-pentadiene, X = Cl (3)] characterised by elemental analysis, i.r. spectroscopy, and mass spectrometry. The structure of (1a), determined from 2 716 observed reflections measured at 185 K and refined to R= 0.0367 (R′= 0.0532), shows a molecule of near Cs symmetry. The cyclopentadienyl ligand is distorted from regular η5 bonding by slippage of the Mo atom across the ring by 0.12 A towards η3 co-ordination. The 1,3-butadiene adopts a cis-endo configuration with internal C–C bonds shorter by 0.045 A than terminal C–C bonds; the Mo–C bonds are shorter to terminal than to internal C atoms, and the butadiene is tilted away from a parallel geometry to assume a configuration with Mo which approaches a metallacyclopentene unit. Extended-Huckel molecular orbital (EHMO) calculations on complex (1a) are presented and confirm the stability of the endo conformation relative to the exo form (85 kJ mol–1). A by-product in the formation of complex (1a) is [Mo3(µ-Cl)(µ3-O){µ3-σ,σ:η2:η2-C4(CF3)4}(η-C5H5)3], (4), which has been structurally characterised as its 0.5C4H6 solvate by X-ray diffraction. The structure has been refined to R= 0.0377 (R′= 0.0488) using 4 215 data recorded at 185 K. A flattened isosceles triangle of metal atoms, base ca. 2.90 A, base–apex ca. 2.58 A, is face-capped by O and (open) edge-bridged by Cl. The C4(CF3)4 unit is symmetrically bonded to the opposite Mo3 face to the capping O atom, in a 2σ+ 4π bonding mode. EHMO calculations suggest some multiple character for the base–apex Mo–Mo bonds, but little direct bonding between the basal atoms. Complex (1a) is interconverted with Tl(SR) into [Mo(SR)2(η-C4H6)(η-C5H5)][R = C6H4Me-4 (5a)(72%) or C6F5(5b)(15%)], characterised by analysis and spectroscopy. Cyclic voltammetric studies on complexes (1a), (5a), and (5b) establish a reversible reduction process in both tetrahydrofuran and dichloromethane, and also more complex oxidations. The most easily reduced complex is (5b), whereas (5a) is most readily oxidised. Complexes (1) and (5) all show e.s.r. spectra in solution with hyperfine coupling to 95,97Mo and to ligand nuclei of 35,37Cl, 79,81Br, and diene terminal 1H atoms. E.s.r. spectra of these complexes in frozen 2-methyltetrahydrofuran are also presented. The e.s.r. results are discussed in relation to the electronic structures of the complexes, especially the nature of the singly occupied molecular orbital, as determined by EHMO calculations on complex (1a).

Photochemical reactions of allyl and crotyl halides with cyclopentadienyl-chromium, -molybdenum and -tungsten complexes

Abstract [MoCl(CO) 3 (η 5 -C 5 H 5 )] on photolysis with allyl or crotyl halides C 5 H 4 RX gives Mo IV complexes [MoX 2 (CO)(η 3 -C 3 H 4 R)(η 5 -C 5 H 5 )] (R = H, X = Cl, Br, I; R = Me, X = Cl, Br). [WCl(CO) 3 (η 5 -C 5 H 5 )] under similar conditions gives trihalides [WX 3 (CO) 2 (η 5 -C 5 H 5 )] (X = Cl, Br) on reaction with C 3 H 5 Cl and C 3 H 5 Br while [WCl(CO) 3 (η 5 -C 5 H 4 SiMe 3 )] and [CrI(CO) 3 (η 5 -C 5 H 5 )] react with allyl chloride to give [WCl 3 (CO) 2 (η 5 -C 5 H 4 SiMe 3 )] and [CrCl 2 (η 5 -C 5 H 5 )] respectively.

Synthetic, spectroscopic and structural studies of metallacyclopentadiene complexes of tungsten; the crystal structure of [WC(CF3)C(CF3)C(CF3)C(CF3)(SPri)-(4-MeC6H4NC)2(η5-C5H5)]

Abstract Reactions of the η2-vinyl complex [W {η3-C(CF3)C(CF3)SPri}(CF3CCCF3)(η5C5H5)] with isocyanides RNC give metallacyclopentadiene derivatives [ WC(CF 3 )C(CF 3 )C(CF 3 )C (CF3)(SPri)(CNR)2 (η5-C5H5)] (R = Me, Ph or 4-MeC6H4) via coordinatively unsaturated intermediates [ WC(CF 3 )C(CF 3 )C(CF 3 )C (CF3)(SPri)(CNR)(η5-C5H5)] isolated and characterised in the case R = 4-MeC6H4. The crystal structure of the d2 complex [ WC(CF 3 )C(CF 3 )C(CF 3 )C (CF3)(SPri)-4-MeC6H4NC)2(η5-C5H5)] has been determined by X-ray methods. The WC4(CF3)4 ring system is approximately planar, with single WC bonds, mean length 2.210(4) A, and localised CC double bonds.

Cyclo-oligomerisation reactions of bis(alkyne) and η2-vinyl complexes of molybdenum and tungsten with t-butyl isocyanide leading to iminocyclopentadiene derivatives

Reactions of t-butyl isocyanide with bis(alkyne) complexes [M(SR)(CF3CCCF3)2(η5-C5H5)](M = Mo, R = C6F5; M = W, R = C6H4Me-4) and isomeric η2-vinyl complexes [W{C(CF3)C(CF3)SR}(CF3CCCF3)(η5-C5H5)](R = Me, Pri, or But) give bis(isocyanide)-metallacyclic derivatives [[graphic omitted](CF3)}(SR)(CNBut)2(η5-C5H5)](7), viaη2-vinyl, [M{η2-C(CF3)C(CF3)CNBut}(SR)(CF3CCCF3)(η5-C5H5)](M = Mo, R = C6F5), or 16-electron monoisocyanide complexes, [[graphic omitted](CF3)}(SR)(CNBut)(η5-C5H5)](6), isolated for M = W, R = But. Metallacyclic complexes (6)(R = But) and (7)(M = W; R = C6H4Me-4, Pri, or But) can be hydrolysed to the iminoacyl oxo complex [W{η3-C(NBut)C(CF3)C(CF3)C(CF3)C(CF3)H}(O)(η5-C5H5)] whereas thermolysis of (7)(M = Mo, R = C6F5; M = W, R = Pri) gives complexes [M(SR)(CNBut){η2-C4(CF3)4CNBut}(η5-C5H5)] containing an iminocyclopentadiene ligand bonded in a novel η2 manner via the exocyclic C–N bond to the metal.