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[Pt.sup.0] complexes of [[eta].sup.2]-coordinated diarylacetylenes are synthesized and characterized along with the corresponding C-C bond-activated [Pt.sup.II] complexes. It is shown that the C-C cleavage reaction in a substrate containing both electron-donating groups (EDG) and electron-withdrawing groups (EWG) as substituents has produced 55% activation product through the C-C bond adjacent to the EWG-substituted aryl ring and 45% activation product through the one adjacent to the EDG-substituted aryl.

The experimental and density functional theory about the reaction of acetonitrile with a zerovalent nickel bis(dialkylphosphino)ethane fragment showed the C-CN bond activation to be favorable exclusively over C-H bond activation due to the strong thermodynamic driving force and slightly lower kinetic barrier.

The competitive activation of C-H bonds of linear, cyclic, and branched hydrocarbons using the coordinatively 16-electron [Tp'RhL] reactive fragment is studied. Activation of the hydrocarbons leads to the formation of Tp'Rh-(L)(R)(H) alkyl complexes, which were converted to the stable chlorides immediately following the activation of the bonds through photolysis of Tp'Rh(L) in the solvent mixtures.

An example of C-CN bond cleavage that is both efficient and in some cases reversible is described. No C-C or C-N cleavage of the aromatic ring is seen with quinoline or acridine and only n(super 2)- arene complexes are formed.

The report stated that (p(super *)(sub 2)ZrH(sub 2)(Cp(super *)=pentamethylcyclopentadienyl) reacts with vinylic carbon-flourine bonds of (F(sub 2)-CH(sub 2) and 1,1 - difluoromethylenecyclohexane (CF(sub 2)=C(sub 6)H(sub 10) to afford Cp(super *)(sub 2)ZrHF and hydrodefluorinated products. The experimental evidence suggested that an insertion / beta-fluoride elimination mechanism was occurring.

Research has been conducted on the mesocyclic dithioether, 11-dithia[3.3]orthocyclophane. The factors controlling cyclophane conformational preferences upon coordination of this compound have been investigated and are discussed.

It is shown that the reactions of Cp(super *)(sub 2)ZrH(sub 2) with aliphatic fluorocarbons occur through a radical pathway with Cp(super *)(sub 2)Zr(super III)H as the reactive species toward aliphatic C-F bonds. The studies indicate that radicals are not involved in this aromatic C-F activation reaction and that dual hydrodefluorination pathways are operative.

A study was conducted to analyze the formation and activation of catalytic carbon-carbon bonds by platinum and palladium phosphine complexes. The effects of altering the metal was examined by heating Pd(PEt3)3 in the presence of excess biphenylene in C6D6. Results indicated that the ratio of free phosphine to biphenylene correlated with the overall rate and resting state species of the catalytic cycle.

The reactivity of (C5Me5)Rh(PMe3)H2 with different fluoroaromatic compounds was analyzed to determine its performance in thermal selective C-F activation with polyfluoroaromatic compounds. Analysis of the reaction mechanisms involving C-F cleavage in polyfluorinated aromatic substrates indicated the significant contribution of the fluoride ion on the rate of reaction with polyfluoroaromatics. Furthermore, the organometallic complex was capable of thermally and selectively cleaving the C-F bonds of the polyfluoroaromatics.

A series of complexes of the type Tp'Rh(CNCH2CMe3)(R)Cl, where L = CH3, CD3, n-propyl, isopropyl and cyclopropyl were synthesized from the reaction of a Grignard reagent with Tp'Rh(CNCH2CMe3)Cl2. The resulting compounds that were produced via the photolytic reaction process were crystallized in a monoclinic space group. The reaction of KTp' with RhCl3(CHCN)3 also provided an alternative synthesis of Tp'Rh(CH3Cn)Cl2.

Thermolysis of 2-methylbenzothiophene and (C5Me5)Rh(PMe3)(Ar)(H) generates a single C-S insertion product and a C-H activation product due to the insertion of rhodium into S-C bond adjacent to the methyl substituent (2k). Continuous heating of the resulting compounds produces an isomer of 2k, in which metal has inserted into the C-S bond adjacent to the aryl moiety by intramolecular pathway. The insertion occurs through a symmetrical S-bound adduct and the activation of C-H through an eta5-coordination to the thiophene.

An analysis of a binuclear polyhydride system for hydrodesulfurization activity, which involved a study of a homogeneous iridium complex ((C5Me5)IrH3)2, reveals that C-S bonds of thiophene and hydrogenation of the C4 fragment yield butadiene or butane. Cleavage of thiophenic C-S bonds may require two metal centers. A d4 product, where deuterium is evident at all sites of the coordinated butadiene, results from the application of thiophene-d4.

The reactions of several fused polycyclic arenes with (C5Me5)Rh(PMe3)(Ph)H and (C5H5)Rh(PMe3)-(Ph)H, and the thermodynamic preferences for eta2-arene coordination versus C-H bond stimulation have been examined. Phenathrene, anthracene, 2-methoxynaphthalene, 2,6-dimethyoxynaphthalene, pyrene, and fluoranthene yield only eta2-complexes, while equlibrium mixtures of C-H activation and eta2-complexes result from naphthalane, perylene and triphenylene.

The nature of CpRh-(PMe3)(n2-C6F6) and its Cp* analogs, Cp*Rh(PMe3)(n2-C6F6) and CpIr(PMe3)(n2-C6F6) is presented and their reactivities with each other are compared. The photochemical reactions of the compound and its analogs in low temperature matrices are also examined. Findings proved that hexafluorobenzene (C6F6) is a highly reactive compound with effective ligand and oxidation inhibition properties. It was also determined that the said compounds undergo different C-F insertion routes as shown by the resulting product's growth factor patterns.

The results of the reaction of the cyclopentadienyl complex, ReH7(PPh3)2, with indene and indene related derivatives, a discussion on the characterization and reactivity of the complexes obtained from this reaction, along with the mechanism for their formation are presented. The reaction of indene with ReH7(PPh3)2 leads to the formation of organometallic complexes in which the metal is bound on either the five- or six-memebered ring. Metal hydride to facile ring migrations are prevalent in this reaction and these migrations transform metals from five-membered ring to the six-membered ring.

The relative kinetic selectivity of the coordinately unsaturated fragment /Tp'Rh(CN-neopentyl)~ toward various types of alkyl, aryl and benzylic C-H bonds is studied. The photolysis experiments are performed in neat substrate to generate the required products. Results indicate that the kinetic selectivity of /Tp'Rh(CN-neopentyl)~ is not necessarily realted to the thermodynamic stability of the alkylhydridomental products.

The thioallyl complex (n4-C4H5S)ReH2(PPh3)2 derived from the reaction of ReH7(PPh3)2 with excess thiophene in the presence of 3,3-dimethyl-1-butene underwent various thermal and photochemical interactions. Bound thiophene.H substituents were intramolecularly hydrogenated by the complex to produce free tetrahydrothiophene. Moreover, photochemical reactions of the complex with thiophene proceeded via homogenous hydrogenolysis which involved C-S bond scission to form compounds bearing ethylthioketene, 1-butene-1-thiolate and 1-butanethiolate substituents.

A study is made on the mechanism of the C-C bond formation in the ring opening and coupling of thiophene by (C5Me5)Rh(C2H4)2. The insertion of a rhodium complex into the C-S bond of thiophene is investigated. The results indicate that this insertion is quite general and can facilitate the formation of a C-C bond by a new route. Dimer formation through the bridging of sulfur atoms can also induce juxtaposition of two metal carbon bonds with p orbitals properly oriented for C-C bond formation.

The photolysis of the ruthenium(II) complex with bisdimethylphosphinoethane, Ru(dmpe)2H2, in low-temperature matrix and in solution generates the Ru(dmpe)2 species. When dihydrogen is present in the matrix or in the absence of other ligands in solution, selective irradiation regenerates Ru(dmpe)2H2. The reactions of Ru(dmpe)2 with H2 or CO shows that it exists as a singlet. Ru(dmpe)2 is also very reactive with a number of ligands, the presence of which shifts the photoreaction equilibrium. The chemical behavior and spectra of Ru(dmpe)2 differ from those of Fe(dmpe)2 but are closer to those of Ru(CO)2(PMe3)2.

The kinetics of reductive elimination from the thermolysis of Tp'Rh(H)(Ph)(CN-neopentyl) (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate) (1) in benzene in the presence of added neopentyl isocyanide was reported. A proposed pathaway for the formation of Tp'Rh(CN-neopentyl)2 was an irreversible reaction of 1 with isocyanide to yield an intermediate. Another possible pathway was a reversible reductive elimination of benzene followed by a bimolecular displacement of the pi-coordinated benzene by isocyanide from an intermediate.

A homogeneous removal of sulfur (hydrodesulfurization or HDS) from thiophene takes place in the hydroprocessing of oil. With such thiofurans as 2- and 3-methylthiophene, 2,5-dimethylthiophene, and benzothiophene, the (C5Me5) Rh(PMe3) fragment reactsby insertion into the unsubstituted C-S bond. This is followed by migration of the alpha-carbon to the metal center. Eta(super 2)-complexation to the C-C double bond also yields C-H activation products. The experimental data also suggest that the alpha-carbon equilibrates between a pi and a sigma bond structure before forming the S-bound complex that leads to the C-S cleavage.

The photolysis of ([C.sub.5][Me.sub.5])Rh(P[Me.sub.3])[H.sub.3] in neat benzonitrile has resulted in C-H activation at the ortho, meta and para positions and thermolysis of the mixture in neat benzonitrile has resulted in clean conversion to the C-C activation product. The reactions of acetonitrile and benzonitrile with the fragment [Tp'Rh(CNneopentyl)] have shown only C-H and no C-C activation and the reactions with rhodium are compared to reactions with [[Ni(dippe)H].sub.2], which has shown only C-CN bond cleavage.

C-H bond activation of fluorinated aromatic hydrocarbons by [Tp'Rh(CNneopentyl)] has resulted in the formation of products of the type Tp'Rh(CNneopentyl)([aryl.sub.F])H. A large change in Rh-[C.sub.aryl] bond strength is measured for small changes in the respective calculated C-H bond strengths and relating M-C to C-N bond strengths has resulted in a line that has matched the theoretically calculated value.

Several kinetic techniques are employed to analyze the different thermodynamic trends that are observed during the carbon-hydrogen bond activation in different nitriles and chloroalkanes. The M-C bonds are shown to be highly strengthened by the presence of different CN and CL substitutents.

The selective C-H bond cleavage reactions of several halogenated substrates with the photochemically generated fragment [Tp'Rh(CNR)] (Tp' = hydrotris(3,5-dimethylpyrazolyl)borate; R = C[H.sub.2]C[Me.sub.3]) is reported. The results provide evidence for the formation of small quantities of C-rhodiumH cleavage products [alpha] to the chloro substituent with 1-chloroalkanes and the reactions of neopentyl chloride also showed evidence for small quantities of [alpha]-chloro C-H activation product.

The reactivity of the nickel(I) dimer [[(dippe)Ni([mu]-H)].sub.2] with biphenyl-2-thiol is analyzed in order to clarify the key step of sulfur during the hydrodesulfurization process by using dibenzothiophene (DBT). The reactivity of the nickel(I) dimer and biphenyl-2-thiol is examined by using different ratios of reactants, which has allowed the synthesis of [(dippe)Ni[([[eta].sup.1]-S-biphenyl-2-thiolate).sub.2]] when using an excess of this substrate.

Bi-, tri-, and tetracyclic isoquinoline salts are prepared at room temperature from readily available starting materials after three reaction steps. The isoquinoline salts are prepared from readily available starting materials by using one-pot procedures, thus providing a novel, efficient method for metal-mediated synthesis of heterocycles.

The various activation parameters taking part in one competitive cleavage of C-CN and C-H bonds in 2-methyl-3-butenenitrile using [[(dippe)NiH].sub.2] are computed. The results prove that the C-H activation is more favorable than the C-C activation, when considered enthalpically.

The reaction of 2-cyanothiophene with a zerovalent Pt bisalkylphosphine fragment which yields two thiaplatinacycles derived from cleavage of the substituted and unsubstituted C-S bonds is demonstrated. The results obtained revealed that the transition state energy leading to the formation of the kinetically favored C-S bond cleavage product is lower by 5.3 kcal [mol.sup.-1] than the barrier leading to the thermodynamically favored product.

2,3-Substituted quinolines are prepared from diallylanilines in good yields under mild conditions by using [Co.sub.2][(CO).sub.8] as catalyst. The results have shown that both steric and electronic effects have influenced the isolated yields.

An overview of the use of pentamethylcyclopentadienyl and trispyrazolylborate rhodium complexes for the activation of arene and alkane C-H bonds is presented. Insights into bond strengths, kinetic and thermodynamic selectivities, and the nature of the intermediates involved are reviewed.

The mechanisms of carbon-fluorine bond activation in various substrates by Cp(sub 2)(super *)ZrH2 are studied for a variety of flurocarbon substrates. The regiochemistry of the exchange is related with the strong asymmetric charge distribution in the perfluoropropene olefin.

It is proved that the reaction of [(dippe)Ni(mu-H)]2 with allyl cyanide at low temperature cleanly produces the eta2-olefin complex (dippe)Ni(CH2=CHCH2CN). Also, the rates for the competitive C-H cleavage, C-C cleavage, and C-C bond formation reactions that occur in the system were determined as a function of temperature and showed that the rate constant for the C-CN bond formation step demonstrated a much stronger temperature dependence than rate constants of C-H and C-C cleavage.

Research has been conducted on diallylanilines. The authors demonstrate that these compounds have undergone cobalt-carbonyl catalyzed rearrangement to quinolines.

Research shows that the inverse kinetic isotope effect for alkane reductive elimination in transient sigma-alkane complexes occurs because of an inverse equilibrium isotope effect that separates the alkyl hydride complex from the sigma-alkane complex. Data indicate that such isotope effects originate from two opposing normal kinetic isotope effects.

Research into the synthesis of a range of Pt(O)-diphenylacetylene complexes with chelating P,N- or P,P-ligands and into the cleavage of the C(sp2) bond in diphenylacetylene is presented. It was established that the thermal accessibility of the reverse reaction shows that the oxidative addition of sp2-sp C-C bonds is uphill thermodynamically.

The use of (C5ME5)2ZrH2 for aliphatic carbon-fluorine bond activation is described.

Kinetic and structural evidence suggests the existence of a late-metal terminal sulfido compound. This was gleaned from a study of the mechanism of desulfurizations and the intermediacy of the three possible binding modes of a sulfur atom to nickel. The chemical feasibility of binding modes of a sulfur atom to supported nickel may present significant mechanistic implications in both homogeneous and heterogeneous desulfurization reactions as well as in the reaction chemistry of sulfided clusters as a whole.

Research was conducted to study the synthesis of an organometallic nickel complex which could activate the C-S bond of dibenzothiophenes. The desulfurization of dibenzothiophenes did not require a hydride, a proton, or a hydrogen atom source. Results indicated that the complex was able to mediate activation of both C-S bonds of dibenzothiophenes at room temperature, and produced structurally characterized organometallic compounds.

The mechanism of cleavage in aryl-aryl C-C bond is investigated by making strong metal-aryl bonds. Rhodium complex provides a thermodynamically favorable C-C cleaved complex. The cleavage of C-C bond in biphenylene is due to the formation of a stable pentametallacycle and on a strained form membrane ring.

Alkane delta-complexes are thought to be involved in oxidative addition/reductive elimination reactions of Tp'Rh(L)(R)H compounds.

The nickel hydride dimer ((dippe)NiH)2 was observed to react with a number of organosulfur substrates under mild conditions leading to C-S bond insertion adducts. The transition-metal insertions into the C-S bonds of thiophene, benzothiophene and dibenzothiophene are all reversible, and lead to new organometallic complexes when dissolved in hydrocarbon solvent. Independent synthetic routes to the desulfurization products have also afforded an entry into the preparation of a number of nickel-sulfur complexes.

Results of two sets of experiments provide indirect evidence that alkane sigma-complexes are involved in oxidative addition/reductive elimination reactions of Tp'Rh(L)(R)H complexes. The methyl deuteride complex Tp'Rh(L)(CH3)D is observed to rearrange to Tp'Rh(L)(CH2D)H prior to loss of CH3D. In the same manner, Tp'Rh(L)(CD3)H rearranges to Tp'Rh(L)(Cd2H)D prior to loss of CD3H. The rate of elimination of methane from Tp'Rh(L)(CH3)H in benzene/perfluorobenzene solvent mixtures is found to be dependent upon the concentration of benzene. Both processes and their rates are accommodated by the reversible formation of alkane sigma-complexes prior to dissociation of alkane.

Bi-, tn-, and tetracyclic isoquinoline salts were readily synthesized in excellent yields at room temperature from readily available starting materials after three reaction steps. Aromatic C-H activation was first promoted by sodium acetate with [Cp*MCI[sub2]][sub2] (M = Rh, Ir) at room temperature to form cyclometalated compounds. Dimethylacetylenedicarboxylate was then found to insert into the metal-carbon bonds of the cyclometalated compounds. Finally, the insertion compounds underwent oxidative coupling to form the desired isoquinoline salts and regenerate [Cp*MCI[sub2]][sub2]. All of the intermediate compounds following C-H activation, alkyne insertion, and oxidative coupling were fully characterized, including the determination of X-ray structures in several cases, and the results shed light on the overall mechanism. Moreover, it was possible to synthesize the isoquinoline salts from readily available starting materials using one-pot procedures; thus, this work provides a novel, efficient method for metal-mediated synthesis of heterocycles. [ABSTRACT FROM AUTHOR]