Philip E. Fanwick

An Efficient Method for the Preparation of Oxo Molybdenum Salalen Complexes and Their Unusual Use as Hydrosilylation Catalysts

A number of molybdenum(VI) dioxo salalen complexes were prepared from the reaction of Mo(CO)(6) and salen ligands containing bulky substituents, providing a novel and facile entry to Mo-salalen compounds. Two of the complexes were characterized by single-crystal X-ray diffraction. Reduction with organic phosphines or silanes afforded the monooxo molybdenum(IV) complexes, along with dinuclear molybdenum(V) species featuring a bridged oxo ligand (mu-O). One of the dinuclear complexes as well as a molybdenum(VI) dioxo salan complex was characterized structurally. All of the molybdenum compounds except the monooxo molybdenum(IV) were fully characterized by NMR, mass spectrometry, and elemental analyses. Investigations of acetophenone and 4-Ph-2-butanone reduction with PhSiH(3) showed that all of these molybdenum oxo complexes could serve as catalysts at reasonably low loading (1 mol % Mo) and approximately 110 degrees C. The time profiles and efficacy of catalysis varied depending on the precursor form of the catalyst, Mo(VI)(O)(2) vs (O)Mo(V)-O-Mo(V)(O) vs Mo(IV)(O). Solvent effects, radical scavenger probes, and other mechanistic considerations reveal that the monooxo molybdenum(IV) is the most likely active form of the catalyst.

Reactions of the electron-rich triply bonded dirhenium(II) complexes Re2X4(μ-dppm)2 (X=Cl, Br) with dioxygen Part III. The isolation and structural characterization of the dirhenium(V) complex Re2(μ-O)2(O)2Cl2(μ-dppm)2

Abstract The complex Re2(μ-O)(O)2Cl4(μ-dppm)2 converts to the closely related tetraoxo dirhenium(V) species Re2(μ- O)2(O)2Cl2(μ-dppm)2 in dichloromethane in the presence of amines such as NEt3 and pyridine. This reaction can be reversed upon reacting Re2(μ-O)2(O)2Cl2(μ-dppm)2 with thionyl chloride. A structural analysis of Re2(μ- O)2(O)2Cl2(μ-dppm)2 shows it to have an edge-sharing bioctahedral structure with a very long Re⋯Re distance (3.1237(7) A). This is the first example of a structurally characterized (Re2O4]2+ species in which there is a planar centrosymmetric ORe(μ-O)2ReO unit. Crystal data for Re2(μ-O)2(O)2Cl2(μ-dppm)2·4CH2Cl2 at −70 °C: triclinic space group P 1 (No. 2), a=9.769(3), b=12.269(4), c=13.128(6) A, α=96.59(4), β=107.92(4), γ=93.09(3)°, V=1480(2) A3, Z=1. The structure was refined to R=0.040 (Rw=O.050) for 3388 data with I > 3σ(I).

Di-μ-hydroxido-bis-[aqua-(pyridine-2,6-dicarboxyl-ato)iron(III)] monohydrate.

In the dinuclear title complex, [Fe2(OH)2(C7H3NO4)2(H2O)2]·H2O, the two Fe atoms are separated by 3.063 (1) Å. Intermolecular O—H⋯O hydrogen bonds form an extensive three-dimensional hydrogen-bonding network, which consolidates the crystal packing.

Synthesis, and Structural Characterization of [{CH3(C5H4N)}Ga(SCH2(CO)O)2] −[(4-MepyH)]+, A Novel Ga(III) Five-Coordinate Complex

The synthesis and structural characterization of a novel ionic Ga(III) five-coordinate complex [{CH3(C5H4N)}Ga(SCH2(CO)O)2]−[(4-MepyH)]+, (4-Mepy=CH3(C5H5N)) from the reaction between Ga2Cl4 with sodium mercapto-acetic acid in 4-methylpyridine is described. Under basic reaction conditions the mercapto ligand is found to behave as a 2e− bidentate ligand. Single crystal X-ray diffraction studies show the complex to have a distorted square-pyramidal geometry with the [(−SCH2(CO)CO−)] ligands trans. The compound crystallizes in the P21/c (No. 14) space group with a=7.7413(6)Å, b=16.744(2)Å, c=14.459(2)Å, V,=1987.1(6)&Aringsup3;, R(F, o)=0.032 and RW =0.038.

Synthesis and Structural Characterization of a Novel Indium Mercapto Derivative [ClIn(SCH2(CO)O)2]2-[(4-MepyH)2]2+

The synthesis and structural characterization of a novel In(III) complex is described. The reaction between InCl3 with sodium mercapto-acetic acid (NaSCH2(CO)OH) in 4-methylpyridine (CH3(C5H5N), (4-Mepy)) at 25°C affords [ClIn(SCH2(CO)O)2]2-[(4-MepyH)2]2+ (1). X-ray diffraction studies of (1) show it to have a distorted square-pyramidal geometry with the [(-SCH2(CO)CO-)] ligands in a trans conformation. The compound crystallizes in the P1(No. 2) space group with a = 7.8624(6) Å, b = 9.950(1) Å, c = 13.793(2) Å, α = 107.60(1)°, β = 90.336(8)°, γ = 98.983(9)°, V = 1014.3(4) Å3, R(F°) = 0.037 and Rw = 0.048.

Isolation of a new series of η2-olefin complexes of tungsten(IV) containing cyclometallated 2,6-diphenylphenoxide ligation

Addition of ethylene to solutions of the bis(cyclometallated) compounds [W(OC6H3PhC6H4)2(L)2] (1, LPMe2Ph; 2, LPMePh2; OC6H3PhC6H4 = cyclometallated 2,6-diphenylphenoxide) produces the η2-ethylene complexes [W(OC6H3PhC6H4)2(L)(η2-C2H4)] (3, LPMe2Ph; 4a, LPMePh2). Addition of α-olefins, RCHCH2 (RPh, SiMe3, CF3) to solutions of 2 produced an equilibrium mixture of 2, free PMePh2 and the corresponding η2-olefin complexes [W(OC6H3PhHC6H4)2(PMePh2)(η2-RCHCH2)] (4b, RPh; 4c, RSiMe3; 4d, RCF3). The solid state structure of the ethylene complex 3 shows a pseudo-octahedral environment about the tungsten metal centre, with mutually trans aryloxide oxygen atoms and mutually cis metallated phenyl rings. The olefin ligand is aligned co-planar with the WP bond, i.e. perpendicular to the OWO axis. The WC (olefin) distances of 2.275(8) and 2.229(8) A are longer than the WC(phenyl) distances of 2.162(7) and 2.127(8) A. This, combined with an olefin CC distance of 1.39(1) A, shows a lack of strong π-backbonding from the tungsten metal centre. In solution, however, restricted rotation about the tungsten-ethylene bond in 3a is observed in the 1H NMR spectrum. The bonding of the olefin ligands in these complexes is discussed.

Crystal and molecular structure of [Ta(H)2(OC6H3Pri2-2,6)3(PMe2Ph)]: a distorted six-coordinate tantalum dihydride

Reaction of [Ta(OC6H3Pri2-2,6)3R2](R = CH2C6H4-4-Me) with H2 in the presence of phosphine ligands (L) leads to the dihydride compounds [Ta(H)2(OC6H3Pri2-2,6)3(L)], the solid-state structure of the PMe2Ph derivative shows a geometry about the metal centre that is severely distorted from octahedral; hydrogenation of aryl-phosphines and other aromatic substrates is catalysed by these dihydride compounds.