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Two transition‐metal atoms bridged by hydrides may represent a useful structural motif for N2 activation by molecular complexes and the enzyme active site. In this study, dinuclear MoIV‐FeII complexes with bridging hydrides, CpRMo(PMe3)(H)(μ‐H)3FeCp* (2 a; CpR=Cp*=C5Me5, 2 b; CpR=C5Me4H), were synthesized via deprotonation of CpRMo(PMe3)H5 (1 a; CpR=Cp*, 1 b; CpR=C5Me4H) by Cp*FeN(SiMe3)2, and they were characterized by spectroscopy and crystallography. These Mo−Fe complexes reveal the shortest Mo−Fe distances ever reported (2.4005(3) Å for 2 a and 2.3952(3) Å for 2 b), and the Mo−Fe interactions were analyzed by computational studies. Removal of the terminal Mo−H hydride in 2 a–2 b by [Ph3C]+ in THF led to the formation of cationic THF adducts [CpRMo(PMe3)(THF)(μ‐H)3FeCp*]+ (3 a; CpR=Cp*, 3 b; CpR=C5Me4H). Further reaction of 3 a with LiPPh2 gave rise to a phosphido‐bridged complex Cp*Mo(PMe3)(μ‐H)(μ‐PPh2)FeCp* (4). A series of Mo−Fe complexes were subjected to catalytic silylation of N2 in the presence of Na and Me3SiCl, furnishing up to 129±20 equiv of N(SiMe3)3 per molecule of 2 b. Mechanism of the catalytic cycle was analyzed by DFT calculations. [ABSTRACT FROM AUTHOR]

Hydride-bridged transition metal complexes have been found to serve as suitable precursors for the activation of small molecules without the use of reducing agents. In this study, we synthesized a dinuclear Mo2H8 complex supported by bulky C5H2tBu3 (Cp‡) ligands, Cp‡2Mo2H8 (1), from the reaction of Cp‡MoCl4 with KC8 under H2. The hydrides of complex 1 can be replaced with benzene at 60 °C to afford a μ-benzene complex Cp‡2Mo2H2(μ-C6H6) (2). [ABSTRACT FROM AUTHOR]

Transition metal-sulfur (M-S) compounds are an indispensable means for biological systems to convert N2 into NH3 (biological N2 fixation), and these may have emerged by chemical evolution from a prebiotic N2 fixation system. With a main focus on synthetic species, this article provides a comprehensive review of the chemistry of M-S compounds related to the conversion of N2 and the structures/functions of the nitrogenase cofactors. Three classes of M-S compounds are highlighted here: multinuclear M-S clusters structurally or functionally relevant to the nitrogenase cofactors, mono- and dinuclear transition metal complexes supported by sulfur-containing ligands in N2 and N2H x (x = 2, 4) chemistry, and metal sulfide-based solid materials employed in the reduction of N2. Fair assessments on these classes of compounds revealed that our understanding is still limited in N2 reduction and related substrate reductions. Our aims of this review are to compile a collection of studies performed at atomic to mesoscopic scales and to present potential opportunities for elucidating the roles of metal and sulfur atoms in the biological N2 fixation that might be helpful for the development of functional materials. [ABSTRACT FROM AUTHOR]

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.

A synthetic protocol was developed for a series of cubane‐type [Mo3S4M] clusters that incorporate halides of first‐row transition metals (M) from Groups 4–10. This protocol is based on the anionic cluster platform [Cp*3Mo3S4]− ([1]−; Cp*=η5‐C5Me5), which crystallizes when K(18‐crown‐6) is used as the counter cation. Treatment of in situ‐generated [1]− with such transition‐metal halides led to the formation of [Mo3S4M] clusters, in which the M/halide ratio gradually changes from 1:2 to 1:1.5 and to 1:1, when moving from early to late transition metals. This trend suggests a tendency for early transition metals to tolerate higher oxidation states and adopt larger ionic radii relative to late transition metals. The properties of the [Mo3S4Fe] cluster 6 a were investigated in detail by using 57Fe Mössbauer spectroscopy and computational methods. Cubic clusters: A synthetic protocol was developed for a series of cubane‐type [Mo3S4M] clusters, based on the anionic cluster platform [Cp*3Mo3S4]−, which incorporate halides of first‐row transition metals (M) from Group 4–10. The M/halide ratio gradually increases from 1:2 to 1:1.5 and to 1:1 upon moving from early to late transition metals. [ABSTRACT FROM AUTHOR]

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 hydride-supported [Mo2Fe2] cluster complex {Cp*Mo(PMe3)}2{FeN(SiMe3)2}2(H)8 ( 2 a; Cp*=η5-C5Me5) and its [Mo2Mn2] congener 2 b were synthesized from the reactions of Cp*Mo(PMe3)(H)5 ( 1) with M{N(SiMe3)2}2 (M=Fe, Mn). The amide-to-thiolate ligand-exchange reactions of complex 2 a with bulky thiol reagents (HSR; R=2,4,6- iPr3C6H2 (Tip), 2,6-(SiMe3)2C6H3 (Btp)) furnished the corresponding hydride-supported [Mo2Fe2](SR)2 cluster complexes. The [Mo2Fe2] clusters served as catalyst precursors for the reductive silylation of N2 and yielded ≈65-69 equivalents of N(SiMe3)3 relative to the [Mo2Fe2] clusters. Treatment of complexes 2 a and b with an excess of CN tBu resulted in the formation of dinuclear Mo−Fe and Mo−Mn complexes, which indicated that the [Mo2M2] cores (M=Fe, Mn) split into two dinuclear species upon accommodation of substrates. [ABSTRACT FROM AUTHOR]

The hydride-supported [Mo2Fe2] cluster complex {Cp*Mo(PMe3)}2{FeN(SiMe3)2}2(H)8 ( 2 a; Cp*=η5-C5Me5) and its [Mo2Mn2] congener 2 b were synthesized from the reactions of Cp*Mo(PMe3)(H)5 ( 1) with M{N(SiMe3)2}2 (M=Fe, Mn). The amide-to-thiolate ligand-exchange reactions of complex 2 a with bulky thiol reagents (HSR; R=2,4,6- iPr3C6H2 (Tip), 2,6-(SiMe3)2C6H3 (Btp)) furnished the corresponding hydride-supported [Mo2Fe2](SR)2 cluster complexes. The [Mo2Fe2] clusters served as catalyst precursors for the reductive silylation of N2 and yielded ≈65-69 equivalents of N(SiMe3)3 relative to the [Mo2Fe2] clusters. Treatment of complexes 2 a and b with an excess of CN tBu resulted in the formation of dinuclear Mo−Fe and Mo−Mn complexes, which indicated that the [Mo2M2] cores (M=Fe, Mn) split into two dinuclear species upon accommodation of substrates. [ABSTRACT FROM AUTHOR]

A square-planar Co4 amide cluster, Co4{N(SiMe3)2}4 ( 2), and an octahedral Co6 hydride cluster, Co6H8(P iPr3)6 ( 4), were obtained from metathesis-type amide to hydride exchange reactions of a CoII amide complex with pinacolborane (HBpin) in the absence/presence of P iPr3. The crystal structure of 4 revealed face-capping hydrides on each triangular [Co3] face, while the formal CoII2CoI4 oxidation state of 4 indicated a reduction of the cobalt centers during the assembly process. Cluster 4 catalyzes the hydrosilylation of 2-cyclohexen-1-one favoring the conjugate reduction. Generation of the catalytically reactive Co cluster species was indicated by a trapping experiment with a chiral chelating agent. [ABSTRACT FROM AUTHOR]

Recent developments have substantially expanded the scope of N-heterocyclic carbenes (NHCs) as ancillary ligands in coordination chemistry and homogeneous catalysis. This review provides a short overview of the emerging field of NHC-supported transition metal complexes of N2 and the possibilities to catalytically activate N2 in these complexes. [ABSTRACT FROM AUTHOR]

Recent developments have substantially expanded the scope of N-heterocyclic carbenes (NHCs) as ancillary ligands in coordination chemistry and homogeneous catalysis. This review provides a short overview of the emerging field of NHC-supported transition metal complexes of N2 and the possibilities to catalytically activate N2 in these complexes. [ABSTRACT FROM AUTHOR]