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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.

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.

Research describes a new class of diiron dithiolates, capable of dihydrogen oxidation, diferrous species, exhibiting higher oxidation states and hydrogen binding capabilities. Results reveal that the diferrous species form the basis for the [Fe(sub)2(SR)(sub)2(CNMe)(sub)7](sup)2+ active site of the iron hydrogenases.

Research has been conducted on the ruthenium sulfide clusters. The characterization of these cluster has been carried out crystallographically and the results demonstrate that the clusters ate structurally and stoichiometrically related.

Research was conducted to examine a novel synthesis of tetrathioxalate and its transformation to C3S5(super 2-) and C4S6(super 2-). The objective of the study was to gain insight into the detoxification of organochlorine compounds which may be influenced by the conversion of chlorocarbons to chlorine-free products. Results indicate that the new synthesis is an intermediate in the formation of two essential thioanions, C3S5(super 2-) and C4S6(super 2-).

Reaction of CS2 slurry of ZnS6(TMEDA) with Se2Cl2 at -60 degrees celsius generate 1,2-Se2S6 by tranfering S(sub 6)(super 2-) as an intact unit. Photolysis initiate an intramolecular reaction due to the transient synthesis of rings with excocyclic chalcogen atoms. NMR measurement indicate that CS2 solutions of 1,2-Se2S6 are thermally stable and exhibit a single resonance at 631 ppm. In crown geometry equivalent Se atoms are attached through a C2 rotation axis. The experimental procedure for the synthesis of ZnS6(TMEDA) is discussed.

Several studies are conducted to explain the redox behaviour exhibited by the synthetic models of the [FeFe]-hydrogenase with the amine cofactor and its N-benzyl derivative. The present azadithiolate cofactor is shown to play an extremely significant role in these models.

Phosphine-modified thioester derivatives have served as efficient precursors to phosphine-stabilized ferrous acyl thiolato carbonyls, which has replicated key structural features of the active site of the hydrogenase Hmd. Tricarbonyl Fe(SPh)([Ph.sub.2]P[C.sub.6][H.sub.4]CO)[(CO).sub.3] has reversibly protonated to give a thermally labile derivative, IR measurements of which have shown that the acyl and thiolate ligands are not protonated in Hmd.

The [NiFe]-hydrogenase model complex NiFe(pdt)(dppe)[(CO).sub.3] (pdt = 1,3-propanedithiolate) is prepared. The mechanism of [H.sub.2] evolution has followed an ECEC sequence, where E and C have corresponded to one-electron reductions and protonations.

The iron-nickel dithiolato hydride is characterized crystallographically. The hydride has undergone rapid deprotonation and is an electrocatalyst for hydrogen evolution from trifluoroacetic acid.

The acid-catalyzed hydrogenation of ketones by amido-amine chelates of Ru and Ir are examined by focusing on the hydrogen activation step. The addition of [H.sub.2] to the catalyst Cp*Ir (TsDPEN-H) (TsDPEN = racemic [H.sub.2]NCHPhCHPhN[Ts.sup.-]) is more favorable than for corresponding (cymene)Ru derivatives.

The functional role of oxa- and azadithiolates as proton relays is analyzed. The studies have shown that although both azadithiolate and oxadithiolate display relay-like behavior, only the azadithiolate has enabled hydride formation from weak acids, which is relevant to catalysis at low overpotentials.

A study was conducted to examine the oxidations of [Fe.sub.2]([S.sub.2][C.sub.3][H.sub.6])[(CO).sub.3](L)(dppv) (L = CO, P[Me.sub.3], Pi-[Pr.sub.3]) as models for the [H.sub.ox] state of the [FeFe]-hydrogenases. The results for studied diiron(I) dithiolato carbonyls provide insights into the factors that affect the oxidation state assignments, structures, and reactivity of these low-molecular weight models for the [H.sub.ox] state of the [FeFe]-hydrogenases.

A new synthetic route to iron dithiolato carbonyls that does not require preformed iron carbonyls is described. The method involves the reaction of Fe[Cl.sub.2], Zn and [Q.sub.2][S.sub.2][C.sub.n][H.sub.2n] (Q(+) = Na(+), [Et.sub.3]NH(+)) under an atmosphere of CO to yield [Fe.sub.2]([S.sub.2][C.sub.n][H.sub.2n] (n = 2,3).

A [super 57]Fe nuclear resonance vibrational spectroscopy (NRVS) was used to study the iron site in the iron-sulfur cluster-free hydrogenase Hmd from the methanogenic archaeon Methanothermobacter marburgensis. The data obtained for NRVS provided insights into the dynamics of the Fe site, revealing Fe-CO stretch and Fe-CO bend modes at 494, 562, 590, and 648 [cm.sup.-1], which are consistent with the proposed cis-Fe[(CO).sub.2] ligation.

Protonation of the symmetrical tetraphosphine complexes has afforded the corresponding terminal hydrides, which has established that even symmetrical diiron(I) dithiolates have undergone protonation at terminal sites. The terminal site has catalyzed proton reductional potentials 200 mV milder than the isomeric bridging hydride, thus showing a thermodynamic advantage for catalysis operating via terminal hydride.

Several experiments and studies are conducted to demonstrate the role of a non-innocent ligand in the redox-switched oxidation of dihydrogen. The results prove that redox is an extremely essential part of the hydrogenases.