K. Folting

RECENT DEVELOPMENTS IN VANADIUM SULPHUR AND OXYGEN CHEMISTRY

Abstract We survey recent results from our efforts in vanadium sulphur and oxygen chemistry. A unifying theme for most of the discussion is the reactivity characteristics of vanadyl (VO 2+ ) complexes, and it is shown how such complexes are capable of a variety of transformations leading to products with oxidation states in the range III–V and nuclearities in the range 1–5. Also described are mononuclear non-oxo vanadium sulphur complexes, including the structural characterization of both V(SBu t ) 4 and V(SBu t ) 4 − . The relevance of this work to our understanding of the fate of crude oil vanadyl impurities during hydrotreating processes is discussed.

Pyridine, isocyanide, carbodiimide and allene adducts of hexakis (trifluoromethyl t-botoxy) ditungsten. A comparison of ligand binding to W2(OtBu)6 and W2(OCMe2CF3)6

Abstract W2(OR)6 compounds where RtBu and CMe2CF3, both reversibly bind pyridine in hydrocarbon solvents to form adducts W2(OR)6L2. Pyridine binds more strongly to the fluoroalkoxide but the structural parameters of the compounds W2(OCMe2CF3)6(C6H5N)2 and W2(OtBu)6(4-CH3C6H4N)2 reveal an essentially identical W2O6N2 core with W  W = 2.39(1) A ,, W  O = 1.92–1.95 A and W  N = 2.26(1) A . Both compounds were crystallographically characterized in the space group C2/c and each molecule has rigorous C2 symmetry. Allene and 1,3-di-p-tolycarbodiimide form 1:1 adducts with W2(OCMe2CF3)6 in which the substrate is bound parallel to the M-M axis, i.e. μ-η2,η2-C3H4 and μ-η2,η2-ArNCNAr-W2(OCMe2CF3)6. Also W2(OCMe2CF3)6 and W2(OSitBuMe2)6 bind two equivalents of xylylisocyanide to afford W2(OR)6(η1-CNAr)2. For W2(OCMe2CF3)6(η1-CNAr)2, the molecular structure has been determined by X-ray crystallography and shows a nearly eclipsed central W2O6C2 skeleton with W  W = 2.44(1) A , W  O = 1.94(1) A (av.) and W  C = 2.14(1) A , whereas the WWO angles span the range of 105–114°, the WWC angles are 83(1)°. Similarly, W2(OCMe(CF3)2)4(NMe2)2 forms a bis adduct upon reaction with the isocyanide. However, the molecular structure of W2(OCMe(CF3)2)4(NMe2)2(η1-CNAr)2 shows a staggered arrangement of the two ligands about the ditungsten center where W  W = 2.382(1) A , W  O = 2.00(1) A (av.), W  N = 1.93(1) A (av.) and W  C = 2.14(1) A (av.) with a CWWC dihedral angle of 41.9°. These reactions and their products are compared for W2(OR)6 compounds where R  t Bu , t BuMe 2 Si and Cme 2 CF 3 .

The dimolybdenum pentapivalate anion: X-ray crystal structure and dynamic solution behaviour and comments on the substitutional lability of containing compounds

Abstract The reaction between Mo2(O2CBut)4 and [Bun4N]+[ButCO2]− in toluene yields the yellow toluene-soluble salt [Bun4N]+[Mo2(O2CBut)5]− as large yellow plates upon crystallization. The molecular struture of the anion contains the now common paddle-wheel or lantern M2(O2C)4 core, = 2.1035(7) and MoO = 2.12(2) A (av), with a monodentate pivalate ligand coordinated to one metal atom, MoO = 2.298(5) A in the axial position and MoMoO (ηl-pivalate) = 176.6(1)°. In CD2Cl2 and toluene-d8 solutions the anion shows fluxional behaviour such that exchange between all pivalates is rapid on the NMR time-scale at room temperature. At −80°C this fluxional process becomes sufficiently slow to lead to the expected 4:1 ratio for the But protons. In pyridine-d5 the exchange of pivalates is slower but still sufficiently fast to lead to coalescence at elevated temperatures. In pyridine solution the predominant species are Mo2(O2CBut)4(py)2 and [Bun4N]+[ButCO2]−. These findings complement earlier work wherein [Et4N]+[Mo2(O2CCF3)5]− was prepared (Garner and Senior, J. Chem. Soc., Dalton Trans. 1975, 1171) and the exchange of CF3CO−2 groups in the reaction between Mo2(O2CCF3)4 and NaO2CCF3 in CH3CN was studied (Sasaki et al., Bull. Chem. Soc. Japan 1979, 52, 446). The facile intramolecular exchange of pivalate ligands in the Mo2(O2CBut)−5 anion emphasizes that Mo4+2 containing compounds are kinetically labile to associative nucleophilic substitution reactions. Possible reaction pathways leading to exchange of ButCO−2 are discussed.

The preparation and characterization of M2(OEPh3)2(NMe2)4,where M = Mo and W and E = C and Si. The x-ray crystal structures of gauche-W2(OCPh3)2(NMe2)4, anti-Mo2(OCPh3)2(NMe2)4 and anti-W2(OSiPh3)2(NMe2)4

Abstract Reaction of M 2 (NMe 2 ) 6 (M = Mo, W) with triphenylmethanol in hexane/ether produces M 2 (OCPh 3 ) 2 (NMe 2 ) 4 ( I ) as yellow crystals in high yield (92–97%). M 2 (OCPh 3 ) 2 (NMe 2 ) 4 are air-sensitive, soluble in aromatic solvents and decompose around 160°C. The 1 H NMR of I is temperature dependent and shows a mixture of anti and gauche rotamers. The X-ray crystal structures of I reveal exclusively the gauche isomer for tungsten and the anti isomer for molybdenum. The reactions between M 2 (NMe 2 ) 6 and triphenylsilanol (2 equiv.) yield M 2 (OSiPh 3 ) 2 (NMe 2 ) 4 compounds (M = Mo, W) ( II ) as orange crystals. In the presence of ρ6 equiv. of Ph 3 SiOH the M 2 (NMe 2 ) 6 compounds react further to give yellow crystalline compounds, M 2 (OSiPh 3 ) 4 (NMe 2 ) 2 . In.compound II , where M = W, the W 2 O 2 N 4 skeleton adopted the anti conformation with WW = 2.2954(6) A, W O = 1.925(4) A, WN = 1.935(8) A, WWO = 108.1(1)°, WWN = 102(1)°. The addition of Ph 3 SiOH (6 equiv.) to W 2 (OBu t ) 6 yielded the related compound W 2 (OBu t ) 2 (OSiPh 3 ) 4 .

The molybdenum-molybdenum triple bond. 7. Bis(1,3-di-p-tolyltriazenido)tetrakis(dimethylamido)dimolybdenum

Abstract : Mo2(NMe2)(6) reacts in hydrocarbon solvents with 1,3-di-p-tolyltriazine, C7H8NNNHC7H8, to give the title compound, Mo2(NMe2)4(C7H8N3C7H8)2, as a red, crystalline solid. An X-ray study shows that in the solid state each molybdenum atom is coordinated to four nitrogen atoms which lie in a plane; there is an unbridged molybdenum-to-molybdenum triple bond with a Mo-Mo distance of 2.212(1) angstroms, and the molecule has crystallographically imposed C2 symmetry. Variable temperature 1H nmr spectra recorded at 220 MHz support the view that this form of the molecule is present in solution.

Molybdenum-molybdenum triple bond. 9. Bis(1,3-di-p-tolyltriazenido)bis(dimethylamido)dimethyldimolybdenum

Abstract : 1,2-Mo2Me2(NMe2)4 reacts in hydrocarbon solvents with 1,3-di-p-tolyl-triazine, C7H8NNNHC7H8, to give the title compound as a red crystalline solid. An X-ray study shows that in the solid state, the molecule has a crystallographically imposed C2 axis of symmetry. The Mo=Mo bond, 2.174(1)angstroms, is bridged by a cis-pair of triazenido ligands which afford sufficient flexibility to allow a non-eclipsed geometry. Each molybdenum atom is coordinated to three nitrogen atoms and one carbon atom which roughly lie in a plane. Pertinent bond distances are Mo-C (methyl) = 2.193(4) angstroms, Mo-N (dimethylamido) = 1.948(3) angstroms, Mo-N (triazinido) = 2.157(3) and 2.283(3) angstroms, with the longer distance associated with the Mo-N bond which is trans to the Mo-CH3 bond. These observations are compared with other findings in dimolybdenum and ditungsten chemistry (M=M). Crystal data for Mo2Me2(NMe2)2-(C7H8N3C7H8)2 are a = 21.608(5) angstroms, b = 9.440(2) angstroms, c = 24.076(6) angstroms, = 135.49(1), V = 3442.5(1) angstroms(cubed), Z = 4, d sub calcd = 1.464 g cc and space group C2/c. (Author)

A study of the photochemical reaction between W2(OCH2 tBu) 6P4. Characterization of the phosphidocluster W4 (P) 2 (OCH2 tBu) 10

Abstract The photochemical reaction between W2 (OCH2 tBu) 6 and P4 has been studied by NMRspectroscopy in toluene-d8 and those reactions have been complemented by studies on the benchtop. A complex sequence of reactions is implicated by the formation of a variety of products, oneof which has been observed previously in the thermal reaction between W2 (OCH2 tBu) 6L2 whereL = py and HNMe2 and P4, namely W3 (μ3-P) (OCH2 tBu) 9, while others must arise fromdegradation of OR ligands. A new compound W4 (μ3-P) 2 (μ-OCH2 tBu) 4 (OCH2 tBu) 6 has beenisolated and characterized. Crystal data at −165°C : a = 19.955 (4) , b = 25.222 (3) , c = 12.775 (2) A, Z = 4 and space group Pcab. The centrosymmetric structure consists of adistorted rhombus of metal atoms having two different W — W edge distances 2.6938 (8) and2.7981 (8) A and a bonding W — W distance of 2.692 (1) A between the back-bone W atomsof the planar W4 butterfly. The outer or wing-tip tungsten atoms are in a square based pyramidalenvironment with respect to the PWO4 moiety with the W — P bond in the apical position. The O4 basal plane involves two terminal and two bridging OR groups. The internal or back-bonetungsten atoms are also five coordinate, P2WO3, where two bridging OR groups occupy axial andthe two W — P bonds and one W — OR terminal group occupy equatorial sites of a trigonalbipyramid. The cluster geometry is compared with those seen for W3 (μ3-X) (OR) 9, where X = CCH3 and P, W4 (OiPr) 12 and W4 (OEt) 16. The latter contains a central centrosymmetric W16+ 4cluster as does the present compound and the presence of the distorted rhomboidal geometryobserved in both is proposed to arise from a second order Jahn-Teller distortion.

The tungsten-tungsten triple bond. XV. Synthesis, structure and reactivity of 1,2-W2[CH(SiMe3)2]2(NMe2)4: the remarkable inertness of a sterically-encumbered tungsten-amido complex

Abstract Addition of 1,2-W 2 Cl 2 (NMe 2 ) 4 (W≡W) to a toluene slurry of LiCH(SiMe 3 ) 2 (2 equiv) results in the formation of 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (NMe 2 ) 4 (W≡W) ( I ) in 79% isolated yield. Compound I has been characterized by 1 H and 13 C NMR, IR, elemental analysis and single-crystal X-ray diffraction. The molecule exists exclusively in the gauche conformation in solution and in the solid state with WW = 2.320(1) A. Compound I is very sterically encumbered as evidenced by: (1) large WWC angles, 110°, at the disyl ligand; (2) skewing of the NC 2 planes of the NMe 2 ligands off the WW vector; (3) anomalously large barriers to WNM 2 bond rotation in solution; (4) the inertness of I towards CO 2 and alcohols. However, compound I reacts with acetic anhydride to form 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (O 2 CMe) 4 (W≡W) ( II ) in 31% isolated yield. Compound II has been characterized by 1 H and 13 C NMR, IR, and elemental analysis. The mechanistic implications of these studies with regard to alcoholysis and CO 2 insertion reactions of other 1,2-W 2 R 2 (NMe 2 ) 4 compounds are discussed. Crystal data for 1,2-W 2 [CH(SiMe 3 ) 2 ] 2 (NMe 2 ) 4 at −140°C: space group P 2 1 / n , a = 12.555(3), b = 18.699(5), c = 15.214(4) A, β = 95.24(1)° and Z = 4.