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The preparation of the mono-[Tm.sup.R] (where Tm.sup.R= hydrotris(mercaptoimidazolyl)borates) complexes of metal halides that are useful starting materials for various transition metal complex of [Tm.sup.R] are reported. It is indicated that [Tm.sup.R.sub.2]M as well as [Tm.sup.R]MCl is formed at the initial stage of the reaction between M[Cl.sub.2] and the [Tm.sup.R] anion.

A description of the synthesis and characterization of sulfo-bridged dinuclear Mo-Cu complexes related to the active site of [MoCu] carbon monoxide dehydrogenase is presented. The dinuclear Mo-Cu complex, [O(sub2)MoS(sub2)Cu(SPh)](super 2-), is prepared from the reaction of [MoO(sub2)S(sub2)](super 2-) with [Cu(SPh)(sub3)](super 2-).

The elimination-addition mechanism for nucleophilic substitution at the vinylic carbon is established, and the reaction can be employed as a mild method for generation of cyclohexynes. The regioselectivity of the nucleophilic addition to the substituted cyclohexynes is explored.

The heterolytic cleavage of H2 is regarded as a key step in the metalloenzymatic reactions of hydrogenases, the actives sites of which consist of the sulfur-bridged Fe/Fe and Fe/Ni dinuclear centers. Based on the experimental results, the mechanism of the heterocyclic H2 activation and the reverse H2 evolution reactions are discussed.

Half-sandwich iron complexes of N-heterocyclic carbenes are prepared by the reaction of Cp*Fe{N[(Si[Me.sub.3]).sub.2]} with the corresponding imidazolium salts. Coupling reactions between heteroarenes and catecholborane (HBcat) is carried out by treatment of cyclometalated complex with heteroarenes followed by the addition of excess HBcat, giving rise to 2-boryl-heteroarenes and the borohydride complex Cp*Fe([L.sup.[super i][P.sub.r]])([H.sub.2]Bcat).

The 2,6-dimesitylphenyl thiolate (SDmp) complex of iridium has promoted facile [H.sub.2] heterolysis generating [Cp*Ir(P[Me.sub.3])[H.sub.3]](B[Ar.sub.4.sup.F]) and H-SDmp. The kinetic isotope effect has shown that an H-H cleaving process is involved in the rate-determining step and it is compare with the one estimated for the [H.sub.2] activation by the [NiFe] hydrogenase from Allochromatium vinosun.

The simple synthesis and reactions of trithio-chloro molybdate [[MoCl[S.sub.3]].sup.-] from trithiomolybdate [[MoO[S.sub.3]].sup.2-] and trimethylchlorosilane are described. The new complexes could be used as versatile precursor to obtain a series of monomeric trisulfido complexes of molybdenum, Cp*, thiolato, amido, and alkoxo complexes as well as building blocks to prepare a citrate derivative of molybdenum trisulfide and structural and reaction models of the FeMo-cofactor.

The synthesis of 3-(dimethylboryl)pyridine and the effect of substituents at the boron atom on the stability of the oligomer is investigated. The result that both type 1- and 2- nucleophilic substitution mechanisms operate together during the reaction is verified by kinetic studies and calculations with model compounds.

A coordinatively unsaturated dinuclear iron(II) complex of bulky thiolates is synthesized from stepwise reactions of Fe[{N[(Si[Me.sub.3]).sub.2]}.sub.2], HSDmp, HSTip and elemental sulfur (where Tip = 2,4,6-[super i][Pr.sub.3][C.sub.6][H.sub.2] and Dmp = 2,6-[(mesityl).sub.2][C.sub.6][H.sub.3]). The structural relevance of [8Fe-7S] clusters to P-cluster, FeMo-co and FeFe-co of nitrogenases is described.

The structure of the inorganic core of P-cluster which can be generated by a self-assembly reaction of Fe(II) bis-amide, tetramethylthiourea, 2,4,6-triisopropylbenzenethiol, and elemental sulfur (S8) is reported. Oxidation of the P(super 2+) state is reported to produce a cluster with Fe(II)(sub 6) and Fe(III)(sub 2).

The reaction of 4-substituted cyclohex-1 -enyl(phenyl)iodonium tetrafluoroborate with tetrabutyl-ammonium acetate gives both the ipso and cine acetate-substitution products in aprotic solvents. The isomeric 5-substituted iodonium salt also gives the same mixture of the isomeric acetate products. The reaction is best explained by an elimination-addition mechanism with 4-substituted cyclohexyne as a common intermediate. The cyclohexyne formation was confirmed by deuterium labeling and trapping to lead to [4 + 2] cycloadducts and a platinum-cyclohexyne complex. Cyclohexyne can also be generated in the presence of some other mild bases such as fluoride ion, alkoxides, and amines, though amines are less effective bases for the elimination. Kinetic deuterium isotope effects show that the anionic bases induce the E2 elimination (kH/kD > 2), while the amines allow formation of a cyclohexenyl cation in chloroform to lead to E1 as well as SN1 reactions (kH/kD ≈ 1). Bases are much less effective in methanol, and methoxide was the only base to efficiently afford the cyclohexyne intermediate. Nucleophiles react with the cyclohexyne to give regioisomeric products in the ratio dependent on the ring substituent. The observed regioselectivity of nucleophilic addition to substituted cyclohexynes is rationalized from calculated LUMO populations, which are governed by the bond angles at the acetylenic carbons: The less deformed carbon has a higher LUMO population and is preferentially attacked by the nucleophile. [ABSTRACT FROM AUTHOR]