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The paper aims to elucidate the final stages in the biosynthesis of the [2Fe]H active site of the [FeFe]‐hydrogenases. The recently hypothesized intermediate [Fe2(SCH2NH2)2(CN)2(CO)4]2− ([1]2−) was prepared by a multistep route from [Fe2(S2)(CN)(CO)5]−. The following synthetic intermediates were characterized in order: [Fe2(SCH2NHFmoc)2(CNBEt3)(CO)5]−, [Fe2(SCH2NHFmoc)2(CN)−(CO)5]−, and [Fe2(SCH2NHFmoc)2(CN)2(CO)4]2−, where Fmoc is fluorenylmethoxycarbonyl). Derivatives of these anions include [K(18‐crown‐6)]+, PPh4+ and PPN+ salts as well as the 13CD2‐isotopologues. These Fe2 species exist as a mixture of two isomers attributed to diequatorial (ee) and axial‐equatorial (ae) stereochemistry at sulfur. In vitro experiments demonstrate that [1]2− maturates HydA1 in the presence of HydF and a cocktail of reagents. HydA1 can also be maturated using a highly simplified cocktail, omitting HydF and other proteins. This result is consistent with HydA1 participating in the maturation process and refines the roles of HydF. [ABSTRACT FROM AUTHOR]

A cluster‐ligand is disclosed in the form of [Ru3(CN)3(CO)9]3− ([1]3−). Produced by simple reaction of [Ru3(CO)12] with cyanide, [1]3− serves as a precursor to a series of μ‐CN cages. When treated with [Ru3(CO)12], it readily forms the prism [Ru6(μ‐CN)3(CO)18]3−. With 1.5 equiv. of [Cu(MeCN)4]+ [1]3− reacts to give the expanded prism {Cu3[Ru3(μ‐CN)3(CO)9]2}3−, which features three two‐coordinate Cu(I) centers. Sources of Ni2+ and Fe2+ bind two equivalents of [1]3−, giving the double cages {M[Ru3(μ‐CN)3(CO)9]2}4− (M=Ni, Fe) wherein the central metal is octahedral. The 1 : 1 reaction using [Fe(H2O)6]2+ gave the interpenetrated super‐tetrahedrane {Fe4(μ4‐O)[Ru3(μ‐CN)3(CO)9]4}4−. [ABSTRACT FROM AUTHOR]

The degree of substitution that entails the use of chelating ligands is studied which stabilizes the complexes of the type [Fe-Fe]-hydrogenases. It is suggested that the dithiolato complexes with unsymmetrical coordination environments has led to a better understanding of the influence of the dithiolate on the stereochemistry of these complexes.

The acid-base reactivity of MS2(dmpe)2, where M = Mo and W and dmpe = Me2PCH2CH2PMe2 is examined. Consistent with its ready protonation, complex M=Mo is methylated, and the use of excess MeOTf gives [MoS(OTf)(dmpe)2](super +) and Me2S in a rare example of double alkylation at a sulfido ligand.

The first systematic study on the use of tricyanoborates as ligands and also the use of the organoboran tricyanides as precursors to coordination polymers are described. The treatment of [PhB(CN)(sub 3)](super -) with [Cu(PCy3)(sub 2)(NCMe)(sub x)]PF6 has given the one-dimensional polymer [PhB(CN)(sub 3)Cu(PCy3)(Cub 2)], wherein two pf the three BCN substituents are coordinated.

The structural chemistry of cation-containing defect cyanometalate boxes is elucidated. A promising motif for cation receptors is represented by the defect box as these cations are more solvent-accessible and kinetically labile.

Research has been conducted on mixed ligand species [Fe (sub)2 -(S (sub)2 C (sub)3 H (sub)6)(CN)(CO) (sub)4 (PMe (sub)3)] (super)- which catalyzes proton electroreduction to dihydrogen. The description of this compound and its derivatives and analogues as they relate to the proton reduction process, analyzed theoretically and electrochemically, is presented.

Cubic cage compounds composed of Co-CN-Ru linkages have been prepared which illustrate the following features: (i) new motifs for alkali metal ion complexation (i.e., cationic receptors for cations), (ii) a new family of triaza-metalloligands, and (iii) a double box-like cage. The cages are synthesized by the condensation of [[CpCo[(CN).sub.3]].sup.-] and [[Cp*Ru[(NCMe).sub.3]].sup.+] (cyclopentadienyl, Cp; pentamethylcyclopentadienyl, Cp*) the presence of [Cs.sup.+]. The species [{Cs[subset]([[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.4]).sup.+] and {Cs[subset][{[[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3][Cp*Rh]).sup.2+] illustrate the box-completion reaction Cs [subset] [Co.sub.4][Ru.sub.3] + M (M = Cp*[Rh.sup.2+], Cp*[Ru.sup.+]). With the naked ion precursors [[Na[(NCMe).sub.6]].sup.+] and [[Fe[(NCMe).sub.6]].sup.2+], the box-completion reactions afforded [{Na[{Cs[subset][[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3]]}.sub.2]}.sup.+] and [{Fe[{Cs[subset] [[CpCo[(CN).sub.3]].sub.4][[Cp*Ru].sub.3]]}.sub.2]}.sup.2+]. These cages provide the first examples, to our knowledge, of the double-box motif.

Research has been conducted on the carbon monoxide, cyanide and ferrous derivatives. Results indicate that the reaction of these derivatives has led to the isolation of the new products characterized via the use of single-crystal X-ray diffraction.

A range of derivatives of the type [Fe2(SR)(Sub 2)(CN)(Sub x)(CO)(Sub 4)] (Super 2-) can be prepared by CN-for -CO substitution reactions. These syntheses occur for alkyl- and arylthiolato derivatives and for alkyldithiolates. The products are stable and have been fully characterized by X-ray diffraction for three derivatives.

A DFT study into the N-H...S hydrogen bond in (TACN)2Fe2S6 and in model systems, was undertaken.

Studies have shown that H(sub 2)S and organic thiols strongly influence the binding of unsaturated substrates to tetrathiorhenate centers. It is stated that in the presence of H(sub 2)S or thiols, one can readily observe the adducts ReS(S(sub 2)C(sub 2)H(sub 3)R)(SH)(SR')(super -) and shown that the addition of thiols to [ReS(sub 2)(S(sub 2)C(sub 2)Rn)](super -) represents an unsual route to SH-containing dithiolene complexes.

Starting from the versatile precursors, (Me3TACN)FeCl2 and [(Me3TACN)FeI(CO)-2](super +), a series of (Me3TACN)Fe(super II) derivatives with soft coligands are investigated. Cyanide and thiolates stabilize the binding of CO at the ferrous center.

An examination of nonlinear absorption and nonlinear refraction of solutions of a series of sulfur-rich molecules and anions confirmed that species containing large amounts of highly polarized sulfur would exhibit refracting properties in the absence of nonlinear absorption. Two structural families were identified, with particularly promising optical properties, including the Zn-S-SpH clusters and condensed dithiocarbonates. Results showed that high figures of merit can be achieved without the undesirable effects of linear absorption.

Electrophilic alkenes were reacted with ZnS(sub x)L(sub n) to yield dithiolenes Zn(S2C2R2)L(sub n). It was found that zinc polysulfido complexes, particularly those bearing triamine coligands, effect the dehydrogenative conversion of alkenes to dithiolenes. The rate-determining step was related to the addition of the alkene to the polysulfide ring to generate an alkanedithiolate. The dehydrogenation of the alkanedithiolate to the dithiolane proceeded at a rate that was independent of the ancillary amine ligand.

Research was conducted to examine the addition of alkenes to ReS4-. The well-behaved reactions were due mainly to the fact that they were cleanly reversible and that single adducts were generated. The reversible binding of alkene is extraordinary for an inorganic complex, particularly when the alkene is not directly bound to the metal. Results demonstrate that inorganic sulfides are fully capable of binding alkenes.

A soluble cubic cyanometalate framework that binds metal cations particularly Cs+ has been synthesized. The box-like cages (M(Cp*Rh(CN)3)4(Mo(CO)3)4)(super 3-) result from the reaction of (Cp*Rh(CN)3)(super -) with (eta(super 6)-C(sub 6)H(sub 3)Me(sub 3))Mo(CO)(sub 3) in the presence of K+ and Cs+. They were isolated as their Et4N+ salts with M = K+ and Cs+. Crystallographic analysis reveal that the M8(mu-CN)12 cages have alkali metal cations. They 12 external CO and 4 external C4Me5 ligands.

A study relating to the development of new routes to transition metal sulfides has resulted in the development of a convenient route that produces a reactive, sulfur-rich form of titanium sulfide that is quasimolecular or extractable into donor solvents. The sulfiding agent ZnS6(TMEDA) was used on solutions of TiCl4. The compound derived from their reaction is amorphous and reactive, which is consistent with a rapid polymerization of the formation of Ti(Sn)2.

Research was conducted to investigate the effect of ancillary ligands on the reactivity and structure of zinc polysulfido complexes. Proton NMR studies reveal that samples of the pentacoordinate complex, ZnS4(PMDETA), react with elemental sulfur to generate a substantial amount of a second polysulfido complex. Variable-temperature proton NMR spectroscopy showed the inversion of the stereochemistry at Zn in ZnS4(PMDETA). Results suggest that the third amine ligand enhanced the nucleophilicity of ZnS4(PMDETA).

The redox behaviour of the S-S bond is significant in several areas of chemistry. Organic disulfides are of interest as an alternative to inorganic sulfur in the cathodes, and they have a similar redox cycle to that involving alkali metal polysulfides. Several new binary carbon sulfide anions and molecules have been prepared, including the tricyclic species C(sub6)S(sub8), which is prepared via thermal decomposition of C(sub3)S(sub5)H(sub2).

Cp4Fe4(CO)4 is primarily produced from the thermolysis of a xylene solution of Cp2Fe2(CO)4 and PPh3, together with smaller amounts of (C5H4Ph)Cp3Fe4(CO)4 and Cp3Fe3(CO)3(PPh2). This was gleaned from a study of the functionalization of performed Cp-metal clusters. The main finding is that Cp4Fe4(CO)4 can be functionalized using various methods, such as alkylation and arylation by using organolithium reagents and deprotonation with lithium diisopropylamide and treatment with electrophiles to afford (C5H4X)Cp3Fe4(CO)4.

Related 52e-M3S4 cluster compounds such as [(C5Me5)3RhRu2S4(MeCN)]2+ (PF6)2 (M = Rh or Ir) were synthesized by the reaction of (C5Me5)2RuS4 with [(C5Me5)M(MeCN)3](PF6)2. The dicationic [(C5Me5)3RhRu2S4(MeCN)](SbF6)2 crystals were composed of an unsymmetrical RhRu2S4 core containing an isosceles triangle of metal atoms and one M-M bond. Furthermore, the (C5Me5)3RhRu2S4(MeCN)2+ cluster was composed of sulfur atoms in cationic clusters containing persulfido ligands which induced high reactivity.

The photoaddition of Fe2S2(CO)5L (L=CO,PPh3) to the fullerenes C60 and C70 was examined. The resulting iron-sulfido derivative C60(S2Fe2(CO)6)n, C60(S2Fe2(CO)5(PPh3))n, and C70(S2Fe2(CO)6)n were isolated by size exclusion chromatography and characterized by high performance liquid chromatography, FAB-MS, IR, and 13C nuclear magnetic resonance spectroscopy, as well as X-ray diffraction.

The H-cluster of [Fe–Fe] hydrogenase consists of a [4Fe]H subcluster linked by the sulfur of a cysteine residue to an organometallic [2Fe]H subcluster that utilizes terminal CO and CN ligands to each Fe along with a bridging CO and a bridging SCH2NHCH2S azadithiolate (adt) to catalyze proton reduction or hydrogen oxidation. Three Fe–S "maturase" proteins, HydE, HydF, and HydG, are responsible for the biosynthesis of the [2Fe]H subcluster and its incorporation into the hydrogenase enzyme to form this catalytically active H-cluster. We have proposed that HydG is a bifunctional enzyme that uses S-adenosylmethione (SAM) bound to a [4Fe–4S] cluster to lyse tyrosine via a transient 5′-deoxyadenosyl radical to produce CO and CN ligands to a unique cysteine-chelated Fe(II) that is linked to a second [4Fe–4S] cluster via the cysteine sulfur. In this "synthon model", after two cycles of tyrosine lysis, the product of HydG is completed: a [Fe(CN)(CO)2(cysteinate)]− organometallic unit that is vectored directly into the synthesis of the [2Fe]H sub-cluster. However our HydG-centric synthon model is not universally accepted, so further validation is important. In this Frontiers article, we discuss recent results using a synthetic "Syn-B" complex that donates [Fe(CN)(CO)2(cysteinate)]− units that match our proposed HydG product. Can Syn-B activate hydrogenase in the absence of HydG and its tyrosine substrate? If so, since Syn-B can be synthesized with specific magnetic nuclear isotopes and with chemical substitutions, its use could allow its enzymatic conversions on the route to the H-cluster to be monitored and modeled in fresh detail. [ABSTRACT FROM AUTHOR]

Azadithiolate, a cofactor found in all [FeFe]‐hydrogenases, is shown to undergo acid‐catalyzed rearrangement. Fe2[(SCH2)2NH](CO)6 self‐condenses to give Fe6[(SCH2)3N]2(CO)17. The reaction, which is driven by loss of NH4+, illustrates the exchange of the amine group. X‐ray crystallography reveals that three Fe2(SR)2(CO)x butterfly subunits interconnected by the aminotrithiolate [N(CH2S)3]3−. Mechanistic studies reveal that Fe2[(SCH2)2NR](CO)6 participate in a range of amine exchange reactions, enabling new methodologies for modifying the adt cofactor. Ru2[(SCH2)2NH](CO)6 also rearranges, but proceeds further to give derivatives with Ru‐alkyl bonds Ru6[(SCH2)3N][(SCH2)2NCH2]S(CO)17 and [Ru2[(SCH2)2NCH2](CO)5]2S. [ABSTRACT FROM AUTHOR]

DNMR analysis of Me(C5H4)4Ru4S3(SMe)(super +), produced by the reaction of (MeC5H4)4Ru4S4 with MeO3SCF(MeOTf) reveals that Ru-Ru bonds exhibit mobility. Crystallographic analysis of (1Me)OTf reveals a distorted tetrahedron of Ru atoms with four Ru-Ru nonbonding and two Ru-Ru bonding contacts. NMR studies indicate that this structure is maintained in solution. The compound 1Me+ undergoes a 2e oxidation at 480 mV.

Reaction of ReOCl3(PPH3)2 with thienyllithium reagents in a THF slurry produces thiophene complexes of oxometal centers, Li(THF)(sub n)ReO(thienyl)4 having reduced d-electrons. The oxidation of Re(super V) occurs at moderate potentials. The resulting compound contains square pyramidal Re center with four thienyl ligands located in the equatorial plane at C-Re-O angle of 108-112 degree and C-Re-C angles of 81-85 degree as revealed by crystallographic analysis.

Four types of electrophilic reactions help convert the kinetic isomer of C3S(sub 5)(super 2-) into new carbon sulfides C3S8, C6S8, C6S10, and C6S12. These compounds help prepare new C-S-O compounds that exhibit increased solubility and help complete the characterization of the binary system. Reaction between (Bu4N)2(Zn(C3H5)2) and 4 equiv of SO2Cl2 leads to the formation of C3S5Cl2, which helps prepare nitrogen containing heterocycles. X-ray, NMR, MS and IR experiments help characterize all the synthetic compounds.

Two dicationic clusters are prepared and purified by ion exchange chromatography, and crystallographic studies are employed to characterize these compounds. Variable temperature 1H NMR study reveals the fluxional nature of the molecule, and it is due to mobile metal-metal bond. Internal Ir(super IV)/Ir(super III) self-exchange is responsible for this mobility. Cyclovoltammetry is employed to analyze redox properties of the clusters.

The process of internal redox forms cluster dynamics which display various properties such as diamagnetism of the specimens, sizeable conformational alterations in the influenced metals, and the influence of rapid and gradual exchange extents on the clusters. Mobility of metal-metal bonds results in the stereochemical flexibility of a group of RuIV clusters with different valencies. Lack of pairing to other alterations in metal ligation render this geometrical modification as rare. Clusters with similar conformations are examined.

A study was done on the reduction and protonation of eta4-thiophene ligands in (C6R6)Ru(C4R4S)2+. It was shown that the hydrogenolysis of thiophenes by sulfided metal catalysts proceed by thiophene coordination, electron transfer to the heterocycle, proton transfer to the ring and then C-S cleavage. These findings serve as the basis for further studies on the reactivity of partially hydrogenated thiophene ligands.

A study was done on base hydrolysis of (C5Me5)Rh(C4Me4S)2+ and the relationship of the reaction intermediate to the isomers of (C5Me5)Rh(C4Me4SO). It was shown that hydrolysis of the methylthiophene complex involves the use of OH- as the nucleophile. Thiophene accepts up to two equivalents of the hydroxide resulting in the net addition of O2- to the heterocycle. Further studies have demonstrated that nucleophilic attack at thiophene can occur at sulfur and nucleophile additions at sulfur can occur through initial attack at sulfur.

Photoelectron (PE) spectroscopy, cyclic voltammetry and other physical methods were employed in the investigation of the electronic structure of cyclopentadienyl clusters. These clusters included (eta-C5H4 super i Pr MoS)4, (eta-C5H4 super i Pr MoSe)4, (eta-C5H4Me CrS)4, (eta-C5H4Me CrSe)4, (eta-C5H4Me TiS)4, (eta-C5H4Me VS)4, (eta-C5H5 CrO)4 and (eta-C5H4Me CrO)4. Results revealed that all the clusters have the highest molecular orbital metal based. Moreover, a molecular ion state ordering of (super 2)T(sub 2) < (super 2)E < (super 2)A(sub 1) is favored.

Two types of ruthenium selenide Ru2 (Se2)-based core structures are interconverted by reduction/oxidation procedures, and their structures assigned on the basis of spectroscopic and electrochemical investigations. The oxidized product is obtained in ((MeCp)Ru(PPh3))2 (Se2)2+ while the reduced product is ((MeCp)Ru(PPh3)2)Se4, which is comparable to the compound ((Me4)Ru(PPh3))2(mu-S2). Se2-based complexes such as (C5H4R)Ru(PPh3)2 and (CpRu(PPh3))2Se2+ are analyzed for the production process and large range of bonding modes.

The complex ((C5Me5)Rh)3(eta4,eta1-C4Me4S)2 (1) was obtained from the thermal decomposition of (C5Me5)Rh(eta4-C4Me4S) and characterized by elemental analysis and 1H and 13C NMR spectroscopy. Single-crystal X-ray diffraction showed the structure of ((C5Me4Et)Rh(eta4, eta1-C4Me4S))2Rh(C5Me4Et) to consist of a pair of (C5Me4Et)Rh(eta4-C4Me4S) ligands binded by sulfur atoms to a central (C5Me4Et)Rh unit. The decomposition of 1 followed a first-order kinetics.