Thomas G. Richmond

Mechanism of carbon monoxide substitution in metal carbonyl radicals: vanadium hexacarbonyl and its phosphine-substituted derivatives

La substitution de CO dans V (CO) 6 a lieu a, ou au-dessous de la temperature ordinaire pour former des composes V (CO) 5 L (L=phosphine ou phosphite). La substitution a lieu par un processus du 2eme ordre selon une loi de vitesse du 1er ordre par rapport a V (CO) 6 et au nucleophile phosphore

Hydrogen bonding in transition metal fluorides

Abstract Hydrogen bonding often plays a crucial role in the chemistry of metal complexes and is of particular importance in the interactions of coordination compounds with biological systems. This account will discuss the role of hydrogen bonding in transition metal compounds with particular emphasis on utilizing this aspect of their chemistry to develop new metal based reagents for molecular recognition. After a brief introduction to the role of metal reagents in biochemistry and the influence of hydrogen bonding in the chemistry of organometallic compounds, recent results concerning the hydrogen bonding properties of metal fluorides prepared in my laboratory will be described. Synthetic and mechanistic chemistry relevant to chelate assisted carbon-halogen (Cl, Br, I) activation at tungsten(0) will be discussed along with structural studies of seven coordinate tungsten(II) metallacycles containing either single or double C-N bonds. The synthesis of metal carbonyl fluorides by chelate assisted oxidative addition of C-F bonds to tungsten(O) will be described including recent extensions of this chemistry to difluoro-rather than pentafluoro-substituted aromatics. Alternative synthetic routes to tungsten(II) fluorides by metathesis reactions and the reactivity of the halide in these systems will be noted. Spectroscopic (IR and 19 F NMR) and crystallographic characterization of hydrogen bonds involving tungsten(II) and titanium(IV) fluorides, and quantitative assessments of the base strength of fluoride bound to these metals will be included. Remarkably, fluoride bound to tungsten(II) forms 1:1 adducts with 4-chlorophenol with equilibrium association constants that rival that of the organic base pyridine. This work provides the foundation required for the design of more sophisticated receptors for target substrates.

Metal Reagents for Activation and Functionalization of Carbon-Fluorine Bonds

The distinctive physical properties of fluorocarbons derived from the great strength of the C-F bond often result in chemical compounds with unique properties and technologically useful applications. However, this same factor conspires to make fluorocarbons unreactive under most conditions. In the past decade it has become clear that metal reagents provide a unique tool for activation and functionalization of the C-F bond under mild conditions. Fundamental approaches toward the activation of C-F bonds are discussed with an emphasis on transition metal reagents. Intramolecular systems provided the intellectual foundation for the development of intermolecular C-F bond activation chemistry. Mechanistic studies of model systems give an indication of the scope of this process. Exciting recent advances in the catalytic chemistry of the C-F bond in fluorinated aromatic and aliphatic systems will be described. Selective C-F bond activation is a key requirement for the application of these reagents in organic synthesis. Theoretical and gas phase studies which provide insight into the mechanisms of these reactions will be discussed.

Synthesis and reactivity of 1,2- and 1,4-dihydroxyarene complexes of chromium tricarbonyl

Abstract Direct reaction of Me3Si protected 1,2- or 1,4-dihydroxyarenes with Cr(CO)6 affords fair to good yields of the corresponding Cr(CO)3 complexes (1a–4a) which were characterized by 1H and 13C NMR and IR spectroscopic measurements. Removal of the Me3Si protecting groups with KF·2H2O or HBF4·Et2O afforded the 1,2- or 1,4-dihydroxyarene complexes 1b–4b which were characterized in solution but their instability and air-sensitivity precluded their isolation. Proton transfer reactions were monitored by IR spectroscopy. The crystal structure of 2,3-(Me3Si)2C10H6Cr(CO)3 was determined in the space group P21/c with a = 11.019(4), b = 17.613(9), c = 11.843(4) A, β = 105.11(3)°, V = 2219.0 A3, Z = 4. This synthetic route provides access to the π-coordination chemistry of 1,2-dihydroxyarenes which cannot be prepared by direct interaction of the arene with Cr(CO)6.

183W NMR Data (δ(183W), nJ(W,H), and 1J(W,F)) for tungsten(II) metallacycles via two-dimensional indirect (1H, 183W) NMR spectroscopy

Abstract The 183 W data for the tungsten(II) metallacycles (Me) 2 N(CH 2 ) 2 N(CHC 6 H 4 )-W(CO) 3 X ( 1 : X = F; 2 : X = Cl; 3 : X = Br; 4 : X = I), (C 6 H 4 XCH)N(CH 2 ) 2 N(CHC 6 -H 4 )W(CO) 3 X ( 5 : X = Cl; 6 : X = Br; 7 : X = I), H 2 N(CH 2 ) 2 N(CHC 6 H 4 )W(CO) 3 F ( 8 ), H 2 N(C 6 H 4 )N(CHC 6 F 4 )W(CO) 3 F ( 9 ), and H 2 N(C 6 H 4 )N(CHC 6 H 4 )W(CO) 3 Cl ( 10 ) have been obtained by using n J (W,H) ( n – 3) couplings and the indirect two-dimensional ( 1 H, 183 W) detection scheme. The chemical shifts δ( 183 W), 3 J (H,W), together with its dihedral angle dependence, and the values 1 J (F,W) for these complexes are discussed.

Origin of the exceptional reactivity of vanadium pentacarbonyl nitrosyl

Le complexe V (CO) 5 (NO) subit une substitution de CO par PMe 3 , PPh 3 , P (OMe) 3 et NEt 3 (L) pour donner V (CO) 4 L (NO). Etude de stabilite thermique

The effect of solvent type on the infrared spectrum of carbon monoxide adsorbed at platinum electrodes

Abstract The infrared spectrum of CO adsorbed on a platinum electrode from several solvents was investigated. In N-methylformamide, acetonitrile, and 1,2-dichloroethane, the infrared band attributed to linearly bonded CO had experimental Stark tuning rates of 20 cm−1/V, 22 cm−1/V, and 19 cm−1/V, respectively. For each of these solvents, the potential dependence of the band position was found to be linear for the entire potential range investigated. When methanol was the solvent, the plot of the band position versus potential had three distinctly linear portions, each with a different value for the slope. The behavior is explained in terms of the ability of the solvent molecules to approach the electrode surface closely, the polarity of the solvent, and the orientation of solvent molecules with respect to the polarization of the electrode.

Tungsten(0) inserts into a carbon–fluorine bond in the presence of a carbon–hydrogen bond

The first examples of chelate assisted insertion of a transition metal centre into a C–F bond of mono- and di-fluoro substituted aromatic rings resulting in chelate stabilized aryl fluoride oxidative addition complexes are reported.

Preparation of molybdenum(II) η2-vinyl complexes via sequential CCl activation and alkyne insertion

Abstract Reaction of the Schiff base ligand 1, prepared by the condensation of 2-chlorobenzaldehyde and N,N-dimethylethylenediamine with (η6-C6H5CH3)Mo(CO)3 2 resulted in the formation of the seven-coordinate molybdenum(II) metallacycle, 3, by oxidative addition of the strong aromatic CCl bond at molybdenum(0). The metallacycle 3 undergoes migratory insertion with electron-deficient internal acetylenes to afford novel η2-vinyl complexes 4, resulting in net replacement of a CCl bond by a CC bond.

Coordination chemistry of chelating nitrogen ligands with tungsten carbonyl nitriles

Abstract The reactions of a series of Schiff base ligands (1–4) prepared by condensation of pyridine-2-carboxaldehyde and 2-X-anilines (X = F, Cl, Br, OMe) with W(CO)3(RCN)3 results in the formation of deeply coloured complexes W(CO)3(1–4)(NCR) which readily react with carbon monoxide to afford W(CO)4(1–4). The ligand 5, prepared from pyridine-2-carboxaldehyde and N,N-dimethylethylenediamine, coordinates to W(CO)3 through the conjugated pyridine—imine chelate to afford complexes with a pendant dimethylamino group which reacts with electrophiles. Of the ligands studied, only the bis-amine, pyridine ligand 8, coordinates to W(CO)3 in a tridentate manner. These reactions provide insight into the geometric and electronic factors which influence coordination of nitrogen containing ligands at a fac-tricarbonyl metal centre.