Search

A [NiFe] hydrogenase model compound having a distorted trigonal-pyramidal nickel center, [(CO).sub.3]Fe[([mu]-[S.sup.t]Bu).sub.3]Ni(SDmp), 1 (Dmp= [C.sub.6][H.sub.3]-2;6-[(mesityl).sub.2]), was synthesized from the reaction of the tetranudear Fe-Ni-Ni-Fe complex [[[(CO).sub.3]Fe[([mu]-[S.sup.t]Bu).sub.3]Ni].sub.2]([mu]-Br)2, 2 with NaSDmp at -40[degrees]C. The nickel site of complex 1 was found to add CO or CNtBu at -40[degrees]C to give [(CO).sub.3]Fe([S.sup.t]Bu)[([mu]-[S.sup.t]Bu).sub.2]Ni(CO) (SDmp), 3, or [(CO).sub.3]Fe([S.sup.t]Bu)[([mu]-[S.sup.t]Bu).sub.2]Ni([CN.sup.t]Bu)(SDmp), 4, respectively. One of the CO bands of 3, appearing at 2055[cm.sup.-1] in the infrared spectrum, was assigned as the Ni-CO band, and this frequency is comparable to those observed for the CO-inhibited forms of [NiFe] hydrogenase. Like the CO-inhibited forms of [NiFe] hydrogenase, the coordination of CO at the nickel site of I is reversible, while the CNtBu adduct 4 is more robust. iron | nickel | thiolates doi/10.10731pnas.0913399107

The reaction of Ni[Br.sub.2][(EtOH).sub.4] with a 1:2-3 mixture of Fe[Br.sub.2][(CO).sub.4] and Na(SPh) generated a linear trinuclear Fe-Ni-Fe cluster [(CO).sub.3]Fe[([mu]-SPh).sub.3] Ni[([mu]-SPh).sub.3]Fe[(CO).sub.3,], 1, whereas the analogous reaction system Fe[Br.sub.2][(CO).sub.4]/Na ([S.sup.t]Bu)/Ni[Br.sub.2][(EtOH).sub.4] (1:2-3:1) gave rise to a linear tetranuclear Fe-Ni-Ni-Fe cluster [[[(CO).sub.3]Fe[([mu]-[S.sup.t]Bu).sub.3] Ni([mu]-Br)].sub.2], 2. By using this tetranuclear cluster 2 as the precursor, we have developed a new synthetic route to a series of thiolate-bridged dinuclear Fe[(CO).sub.3]-Ni complexes, the structures of which mimic [NiFe] hydrogenase active sites. The reactions of 2 with SC[([NMe.sub.2]).sub.2] (tmtu), Na{S[([CH.sub.2]).sub.2]SMe} and ortho-NaS([C.sub.6][H.sub.4])SR (R = Me, [sup.t]Bu) led to isolation of [(CO).sub.3]Fe[([mu]-[S.sup.t]Bu).sub.3] NiBr(tmtu), 3, [(CO).sub.3]Fe([S.sup.t]Bu)[([mu]-[S.sup.t]Bu).sub.2]Ni{S [([CH.sub.2]).sub.2]SMe}, 4, and [(CO).sub.3]Fe([S.sup.t]Bu) [([mu]-[S.sup.t]Bu).sub.2]Ni{S([C.sub.6][H.sub.4])SR}, 5a (R = Me) and 5b (R = [sup.t]Bu), respectively. On the other hand, treatment of 2 with 2-methylthiophenolate (ortho-O([C.sub.6][H.sub.4])SMe) in methanol resulted in [(CO).sub.3]Fe[([mu]-[S.sup.t]Bu).sub.3] Ni(MeOH){O([C.sub.6][H.sub.4])SMe}, 6a. The methanol molecule bound to Ni is labile and is readily released under reduced pressure to afford [(CO).sub.3]Fe([S.sup.t]Bu)[([mu]-[S.sup.t]Bu).sub.2]Ni{O([C.sub.6] [H.sub.4])SMe}, 6b, and the coordination geometry of nickel changes from octahedral to square planar. Likewise, the reaction of 2 with NaOAc in methanol followed by crystallization from THF gave [(CO).sub.3]Fe[([micro]-[S.sup.t]Bu).sub.3]Ni(THF)(OAc), 7. The dinuclear complexes, 3-7, are thermally unstable, and a key to their successful isolation is to carry out the reactions and manipulations at -40[degrees]C.

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).