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An investigation of the parameters governing both the binding of small molecules to different tungsten complexes and agostic bonding in the W[(CO).sub.3][(P[Cy.sub.3]).sub.2] complex applying ab initio MP2 calculations with and without basis set superposition error (BSSE) correction is described. It is suggested that BSSE correction are a must for quantitative predictions for bimolecular reactions.

The binding of a dihydrogen molecule ([H.sub.2]) to a transition metal center in an organometallic complex was a major discovery because it changed the way chemists think about the reactivity of molecules with chemically 'inert' strong bonds such as H-H and C-H. Before the seminal finding of side-on bonded [H.sub.2] in W[(CO).sub.3][(P[R.sub.3]).sub.2]([H.sub.2]), it was generally believed that [H.sub.2] could not bind to another atom in stable fashion and would split into two separate H atoms to form a metal dihydride before undergoing chemical reaction. Metal-bound saturated molecules such as [H.sub.2], silanes, and alkanes ([sigma]-complexes) have a chemistry of their own, with surprisingly varied structures, bonding, and dynamics. [H.sub.2] complexes are of increased relevance for [H.sub.2] production and storage in the hydrogen economy of the future.

The synthesis and characterization of cationic platinum complexes of the type [(R (sub 2) PC (sub 2) H (sub 4) PR (sub 2)) PtMe (OEt (sub 2))] BAr (sub F) (R =Cy, Et) are reported. A possible mechanism is proposed for the C-C coupling reaction based upon the structures of these bridging biphenyl complexes, which provides a new perspective for the related palladium-catalyzed oxidative coupling of arenes to form analysis.

This review summarizes the deliberations of a workshop colloquium on the 'opportunities for catalysis research in carbon management'. Research progress within the context of greenhouse gas/carbon issues in the areas of hydrogen generation and utilization, carbon dioxide activation, catalysis research to further our search for new and more efficient catalytic processes.

A consolidated characterization of the consequences of the coherent and incoherent dihydrogen exchange on the nuclear magnetic resonance and inelastic neutron scattering spectra of transition metal hydrides is presented. The description is based on the quantum-mechanical density matrix formalism of Alexander-Binsch. The dynamic parameters of the line shape analyses are the exchange couplings or rotational tunnel splittings J of the coherent exchange and the rate constants k of the incoherent exchange.

Vibrational data, including IR, Raman and inelastic neutron scattering, was used to report the complex trans-W(CO)sub3(PCysub3)sub2(etasuper2-Hsub2) (1) and its HD and Dsub2 isotopomers. This supported the established etasuper2-bonding mode for the Hsub2 ligand. The calculated equilibrium isotope effect (EIE) was compared to experimental data for the binding of Hsub2 or Dsub2 to Cr(CO)sub3(PCysub3)sub2.

A comparative analysis of the coordination between hydrogen to hydrogen and silane to hydrogen sigma bonds, as well as their activation on 16e metal centers, was established through NMR spectral studies. The binding behavior of ethylene was determined through the synthesis and x-ray crystallography of ethylene complex W(CO)3(PR3)2(eta2-C2H4). Both hydrogen and silane ligands have similar reaction coordinates for bond cleavage on metal centers except for Mo(CO)(depe)2. Ethylene displayed specificity for P-W-P axial alignment.

The reaction of Pt(PiPr3)3 with SO2 produced (PiPr3)2Pt(SO2) (1), isolated in 93% yield. The addition of (H(OEt(sub 2))2)(super +)(BAr(sub f)=B(3,5-(CF(sub 3)(sub 2)C(sub 6)H(sub 3))(sub 4)) to 1 in ether at -78 degrees C produced the solvent complex trans-((PiPr(sub 3))(sub 2))Pt(H)(OEt(sub 2)))BAr(sub f) (2) in 85% isolated yield. The dichloromethane complex trans-((PiPr(sub 3))(sub 2)Pt(H)(eta(super 1)-ClCH(sub 2)Cl))BAr(sub f) (3) was isolated in 80% yield by the recrystallization of 2 from CH2Cl2/hexane. The reaction of 2 or 3 with iodo- or bromobenzene resulted in the isolation of the haloarene compounds trans-((PiPr(sub 3))(sub 2)Pt(H)(eta(super 1)-XPh))BAr(sub f), where X = I (87% yield) or Br (60% yield).

Bridging dinitrogen complex {Mo(CO)(Et2PC2H4PEt2)2}2 (mu-N2) is synthesized by reacting trans-Mo(N2)2(Et2PC2H4PEt2)2 with ethyl acetate. X-ray crystallography reveals a agostic Mo...H-C interaction between the molybdenum atom and an aliphatic gamma-C-H bond of the alkyldiphosphine ligand. The observed interaction is stronger in the nitrogen free compound when compared to the compound involving an ortho-aromatic C-H bond of the diphosphine ligand.

Reduction of MoCl5 in THF under suitable conditions with diphosphine ligands gives bis(dinitrogen)molybdenum complexes. 1H NMR spectroscopy of the 16-electron complexes obtained from the reaction between ethylacetate and the bis(dinitrogen) molybdenum complexes show an agostic Mo...H-C interaction between molybdenum and an ortho aryl hydrogen atom. IR, NMR and neutron scattering spectroscopies reveal the existence of eta2-H2 coordination in the adducts, formed between the 16-electron complexes and small molecules such as H2, N2 and SO2, with normal H-H distance. The normal H-H distance reveals the existence of a flat reaction coordinate for H2 cleavage.

Oxidative addition reactions between W(CO)3(phen)(EtCN) and disulfides yield 16-electron complexes of the type W(CO)2(phen)(SR)2, R is Ph, (t)Bu, Me, benzyl. Spectroscopic studies reveal the involvement of coordinate disulfide complexes as intermediates. W(CO)2(phen)(SR)2 complexes undergo addition, substitution and exchange reactions with various ligands. Variable temperature equilibrium studies help determine thermodynamic parameters for reversible binding of CO with the complex. X-ray studies help study the structures of W(CO)2(phen)(SPh)2 and W(CO)(P(OMe)3)(phen)(SPh)2.

Different techniques help in the preparation of various transition metal dihydrogen complexes Cr(CO)(3)(PR3)(2) (eta (super 2)-H(2)) (R=cy, Pr(super i)). X-ray crystallography and several other techniques are used for the characterization of these complexes. Cr(CO)(3) (PPr(3) (super i)(2) CH(2)) is the most unstable separable H(2) complex which has the shortest ligated H-H bond.

The raction coordinate for hydrogen activation by transition metal centers is studied. The synthesis and characterization of derivatives of Mo(Co)(R2PC2H4PR2)2 and their reactions with H2, N2 and SO2 are also investigated. Results reveal that the reaction lacks an elongated H-H bond length with a dihydride tautomer despite the nearness of H2 to the cleavage. This finding indicate that the reaction coordinate for the oxidative addition of H2 is flat until the relatively precipitous cleavage of the H2.

The biactivated SO2 adduct Cp*2Cr2(mu-S)(mu-S2)(mu-SS.SO2).SO2 and the SO3 adduct Cp*2Cr2S4. SO3 were synthesized and characterized. Cp*2Cr2S5 possesses both an eta(super 2)-S2 and an eta(super 1)-S2 metal bridging ligands and was the precursor to the SO2 adduct. The SO2 adduct was found to possess a molecular structure with SO2 binding to the mu-eta(super 1)-S2 ligand. It was also the precursor of the SO3 adduct which may also be considered as a mu-thiosulfate ligand.

The chemistry of the binding and reactivity of dihydrogen ([H.sub.2]) on different transition metals underlying the hydrogenase function and the production and storage of [H.sub.2] is described. These new storage methods can be easily used, as the [H.sub.2] molecules can easily bind with various materials.

The structural, thermochemical and kinetic studies of a mechanism of formation of [[Mo([mu].TeAr)[(CO).sub.3](Pi[P.sub.3])].sub.2] by phosphine elimination from [super .]Mo(TePh)[(CO).sub.3][(Pi[Pr.sub.3]).sub.2] are reported. The rate of reaction of ([super .]TeAr)W-[(CO).sub.3][(Pi[Pr.sub.3]).sub.2] and CO is found to be first-order in the metal complex and is proposed to proceed by the associative formation of the 19 [e.sup.-] radical complex ([super .]TePh)W-[(CO).sub.4][(Pi[Pr.sub.3]).sub.2], which extrudes a [super .]TePh radical.

The reactivity of the phenyl dichalcogenides (PhE-EPh, E = S, Se, Te) with three metal complexes M[(CO).sub.3][(P[R.sub.3]).sub.2], W(CO)3(PR3)2 and Mo[(N[[t.sub.Bu]]Ar).sub.3] is investigated. The calculations of electron densities of the SOMO have shown the increasing electron density on the chalcogen atom on going from S to Se to Te.

A new series of Fe(II), FeCl2{N(R)=C(Me)=N(R)} containing diimine ligands with hemiliable sidearms R (R=CH2(CH2)2NMe(sub 2), CH2(CH2)2OMe, CH2(CH2)2SMe) were synthesized. It was found that interaction of Co with high-spin 5-coordinate Fe model complex is thermoneutral but favored to low-spin diphosphine fragments.

The first structurally characterized Re diethyl ether and CH2Cl2 complexes and the first H2 adduct of the M(CO)4(PR3) fragment are presented, with the (cis-Re(CO)4(PR3)(L))(BAr(sub f)) system. The cationic Re fragment is found to bind and heterolytically activate H2, which indicates that it may be used in reactions in which ionic hydrogenation of hindered substrates from a metal catalyst and H2 is desired. It is also found to coordinate weak bases. The occurrence of heterolytic cleavage of R3Si-H bonds is also supported by initial evidence.

A new 16-electron precursor (Mn(CO)(dppe)2)BAr'4 (1) which can bind small molecules was synthesized to study the reaction coordinate for addition of H2 to metals. This species has yielded the first well-characterized cationic manganese-H2 complex, (Mn-(H2)(CO)(dppe)2)BAr'4. The complexes MnH3(R2PC2H4PR2)2(R = Me (dmpe), Et (depe)) were suggested to contain H2 ligands and CpMn(Co)2(H2) was previously isolated. The N2 reaction with 1 provides an extremely labile N2 complex characterized by 15N NMR.

Synthesis of the first transition metal eta2-SiH4 complexes Cis-Mo(eta2-SiH4)(CO)(R2PC2H4PR2)2 (R = Ph, Bu(i)) involves a reaction of 1 equiv of SiH4 with Mo(CO)(R2PC2H4PR2)2. X-ray crystallography enables the determination of an eta2-SiH4 (R = Bu(i)) complex. A tautomeric equilibrium is observed between an eta2-SiH4 complex and a hydridosilyl species. Formation of hydridosilyl species, by the eta2 coordination of SiH4 followed by Si-H bond cleavage, functions as a model for methane coordination and activation.

The synthesis of eta2-silane complexes having eta2-coordination of Si-H sigma bonds to transition metal Mo, which also binds eta2-dihydrogen ligands and agostic C-H bonds, involves an addition reaction of 16-electron complexes Mo(CO)-(R2PC2H4PR2)2 with primary or secondary silane. Spectroscopic studies establish the eta2-silane coordination and single-crystal x-ray diffraction studies help determine the molecular structure of various eta2-silane complexes.

The reaction between organic disulfides and W(CO)3(P(i)Pr3)2 yields an intensely colored solution of stable 17-electron tungsten thiolate radicals. Iodination of the tungsten complex yields an analogous radical product that is characterized by X-ray analysis. Thiols undergo oxidative addition with the W complex to yield thiolate hydrides that have weak W-H bonds. A chromium radical abstracts the hydrogen from the thiolate hydride, producing stable radicals.

A group 6 dihydrogen complex, Cr(CO)3(PCy3)2(Eta squared-H2)3, that completely dissociates the H2 molecule in a metal solution, has its rotational carrier's potential measured by inelastic neutron scattering. This is calculated to be 1.3 kilocalories per minute and 2.2 kilocalories per minute for the Mo and W analogues, respectively. The W analogue had bond strengths nus(M-H2) of 951 per centimeter and of 1568 per centimeter, while the nus(M-H2) for Mo was 885 per centimeter. This is comparable to the nus(M-H2) and nuas(M-H2) values of 950 per centimeter and 1540 per centimeter, respectively, for (Cr-H2) compound. This indicates a lesser bond strength for the Mo complex.