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Digital simulations of the electrochemical data are used to study the mechanism of [H.sub.2] evolution catalysis. These studies are discussed.

Aspects of the coordination chemistry of mono- and divalent manganese complexes supported by the anionic tris(phosphino)borate ligand, [PhBP.sup.iPr3] (where [PhB(CH2[P.sup.i]Pr2).sub.3].sup.-]), are presented. The present report represents the extended study of the coordination chemistry of first-row mid-to-late transition metals supported by electron-releasing BP3 ligands.

The synthesis and photophysical characterization of a series of (N,C(super 2')-(2-para-tolylpyridyl)2Ir(LL') [tpy)2Ir(LL')] (LL' = 2,4-pentanedionato (acac), bis(pyrazolyl)borate ligands and their analogues, diphosphine chelates and tert-butylisocyanide (CN-t-Bu) are reported. The electrochemical and photophysical properties of the (typ)2Ir(LL') complexes are discussed in detail.

Iminium adducts of palladium supported by a bis(phosphino)borate ligand are generated from beta-hydride elimination of amines at a coordinatively unsaturated Pd-(II) center. The study provides an opportunity for incorporating Pd(II) species in the presence of an oxidant within the broader synthetic context of new methods for the catalytic functionalization of tertiary amines.

A family of tris(phosphino)-borate-supported iron complexes within the context of olefin hydrogenation of chemistry is described. The study reveals a first-order rate dependence on both hydrogen pressure and total iron concentration, consistent with a rate-determining step involving the reaction of H2 with an iron alkyl species.

Research has been conducted on the the bis(8-quinolinyl)amine-type ligands. Results indicate that these ligands can be related to the anionic pincer ligand family which can afford a rich reaction chemistry with metals.

A novel chemical reaction wherein an alkyl radical on the fringes of an NMoO3 or MoO4 tetrahedron is replaced by a titanium-based radical is presented. Some of the basic characteristics of the new reaction are metalloradical attack on an exposed terminal atom, electron transfer across the bridge according to the scheme first outlined by Taube and the retreat of a peripheral substituent to regenerate an exposed terminal and a d(super 0) system.

The proposal of a bimetallic mechanism for dinitrogen cleavage by three-coordinate molybdenum(III) amide complexes is confirmed by the synthesis and characterization of the complexes Mo[N(R)Ar]3 (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2), (mu-N2){Mo[N(R)Ar]3}2, (mu-15N2){Mo[N(R)Ar]3}2, NMo[N(R)Ar]3, 15NMo[N(R)Ar]3, Mo[N(t-Bu)Ph]3, (mu-N2){Mo-[N(t-Bu)Ph]3}2 and NMo[N(t-Bu)Ph]3. Results show the potential usefulness of three-coordinate molybdenum(III) complexes as models for biological nitrogen fixation.

Associated metal hydrido complex and dinitrogen result from deprotonation following the reaction of diazene ligands with amines in isoelectronic cations. Deprotonation of the diazene ligand by NH2R and the formation of hydride trans, trans W(H)(CO)2(NO). (PPh3)2 formation from H migration from the formyl ligands to the metal form part of the reaction process for hydride formation in the tungsten system.

Study is conducted to show that the pincer-type bis(8-quinolinyl)amido).sup.3] (BQA) ligand can accommodate and thermodynamically prefer, a facially coordinated geometry for a mononuclear, octahedral Pt(IV) center. It is concluded that the photoisomerization process described underscores the geometric flexibility accessible to the [BQA.sup.-] ligand.

Research has been conducted on bis(amino)borate ligand. Results demonstrate that this ligand is a bidentate ligand auxiliary used in preparation of a series N-chelated, zwitterionic rhodium(I) complexes.

The characterization of electrophilic, trigonal bipyramidal [{[Si[P.sub.3.sup.R]Pt(L)}.sup.+] cations featuring weakly coordinated ligands including C[H.sub.2][Cl.sub.2], [Et.sub.2]O, toluene and [H.sub.2] is described. Prototypical four-coordinate [d.sup.8] platinum and palladium complexes are square planar and hence the trigonal pyramidal (TP) [d.sup.8] cations are shown to be geometrically distinct.

Variable temperature emission spectroscopy and photoluminescence decay measurement of doped vapor-deposited films are used to demonstrate E-type delayed fluorescence exhibited by a highly emissive bis(phosphine)diarylamido dinuclear copper(I) complex. Several physical methods, including electrically detected EPR, cyclic voltammetry, and photoluminescence in the presence of applied current demonstrated the function of the emissive dopant in OLEDs

Density functional theory methods were utilized to examine the electronic structures and reactivities of the trigonal bipyramidal iron(I) complex [Si[P.sup.iPr.sub.3]]Fe([N.sub.2]) ([Si[P.sup.iPr.sub.3]] = [(2-i[Pr.sub.2]P[C.sub.6][H.sub.4]).sub.3][Si.sup.-]) toward organoazides. Competitive trapping experiments provide strong evidence for the intermediacy of reactive nitrene complexes of the type [Si[P.sup.iPr.sub.3]]Fe(NAr) that couple bimolecularly in the N-N bond forming step.

The characterization of a series of fascinating diiron complexes featuring bridging [N.sub.x][H.sub.y] ligands stabilized by tris(phosphine)borate ([PhB[(C[H.sub.2]P[R.sub.2]).sub.3]] = [PhB[P.sup.R.sub.3]) ligands are reported. The complexes constituted the first example of a diiron [Fe.sub.2][([mu]-NH).sub.2] diamond-shaped core which featured both bridging hydrazine and hydrazido ligands.

A three-coordinate Cu-N[R.sub.2] system (R = p-tolyl) supported by the anionic bis(phosphino) borate ligand is isolated and characterized in both its anionic [Cu.sup.I] and neutral [Cu.sup.II] oxidation states. The studies have shown that the oxidized form is regarded as a [Cu.sup.I]-aminyl radical complex rather than a [Cu.sup.II]-amido species, with about 70% localization of the unpaired electron on the N[R.sub.2] unit.

A combination of Mossbauer spectroscopy, magnetic susceptibility measurements, and X-ray crystallography were used to study the electronic structure of a family comprising tetrahedral ([alpha]-diimine)iron dichloride, and tetrahedral bis([alpha]-diimine)iron compounds. The compounds were found to contain a high-spin ferrous ion ([S.sub.Fe] = 2), which is antiferromagnetically coupled to two [alpha]-diiminate(1-) [pi]-radical anions yielding the observed S = 1 ground state.

A series of dicopper diamond core complexes that can be isolated in three different oxidation states [[[Cu.sub.2]([mu]-X[R.sub.2])].sup.n+] (where X = N or P and n = 0, 1, 2) is discussed. The electronic structure picture that emerges for these inorganic dicopper diamond cores has shared similarities with the [Cu.sub.2][([mu]-SR).sub.2] [Cu.sub.A] sites of cytochrome c oxidases and nitrous oxide reductases.

The synthesis and luminescence properties of a new series of amidophosphine complexes of copper, silver, and zinc which exhibit lifetimes as long as 150 [mu]S in benzene and quantum efficiencies in the range of 0.16 < [phis] < 0.70 is reported.

An unusual iron(I) system is described that reacts readily with C[O.sub.2] at ambient temperature to mediate its reductive cleavage. This iron system can mediate both the reductive cleavage and coupling of CO2.

The mononuclear iron(III) and cobalt(III) imido complexes of the monoanionic tridentate ligand [PhB[P.sub.3]] ([PhB[P.sub.3]] = [[PhB(C[H.sub.2]PP[h.sub.2])[.sub.3]][.sup.-] were examined to clarify the vibrational features for these trivalent metal imides. The degree of coupling to the ancillary organic group appears higher in the aryl imides than in the alkyl imides, but in both cases, isotope labeling was utilized to arrive at the modes with the greatest degree of metal-nitrogen stretching character.

Electronic structure, spin-state, and geometrical relationships for a series of pseudotetrahedral Co(II) aryloxide, siloxide, and silylthiolate complexes supported by the tris(phosphino)borate [BP3] ligands [PhBP3] and [PhBP(super iPr)(sub 3)]([PhB(CH2PPh2)3](super -) and [PhB(CH2P{super i}Pr2)3]{super -}, respectively) are described. Magnetic and spectroscopic data demonstrate that both S-1/2 and S=3/2 ground-state electronic configurations are accessible for the umbrella distorted structure type.

An amido-bridged bimetallic copper system, {(PNP)Cu(super 1)}(sub 2) is described, derived from a chelating bis(phosphine)amide ligand ([PNP](super -) = bis(2-(diisobutylphosphino)phenyl)amide). This species is an exceptional luminophore in its own right.

The pseudotetrahedral iron(II) coordination complexes that contain bridged nitride and terminal imide linkages, and exihibit singlet ground-state electronic configurations, are described. It is suggested that dinuclear [{[PhBP3]Fe}2(mu-N][Na(THF)5] is best described as containing two high-spin iron(II) centers that are strongly antiferromagentically coupled to give rise to a singlet ground-state at room temperature.

The synthesis and characterization of a host of nickel complexes supported by BP3 ligands is focused along with the theoretical and reactivity issues pertinent to the possible construction of L3Ni=E and L3Ni triple bond E linkages. The stabilization of the lower oxidation states of nickel by tris(phosphino)borate scaffolds is demonstrated while maintaining a four-coordinate tetrahedral geometry.

High-oxidation state iron complexes that features metal-to-ligand multiple bonds are proposed as key intermediates in numerous biocatalytic transformations. The maiden observation of the terminal iron (IV) nitride, [PhBP(sub 3)(super iPr)]Fe(super IV) triple bond N ([PhBP(sub 3)(super iPr)]= [PhB(Ch2P(super i)Pr2)(sub 3)](super -)), is described.

A study was conducted to examine the reactivity patterns of hydrogen with molecular iron complexes featuring Fe-N multiple bond linkages. But this is difficult to undertake due to the historical absence of well-defined Fe = NR and Fe triple-bond N species.

A Cu2N2 diamond core structure supported by a [SNS](super -) ligand is prepared. The dicopper system exhibits a fully reversible one-electron redox process between a reduced Cu(super 1)Cu(super 1) complex, and a class III delocalized Cu(super 1.5)Cu(super 1.5) state.

The synthesis of a new kind of monodentate tertiary phosphines is described. Reports show that they are highly stable, strong electron-releasing and coordinated metals.

Research has been conducted on strong-field tris(diisopropylphosphino)borate ligand. The authors report the study of ligand's conformational and electonic characteristics within host complexes.

Research has been conducted on dimethyldiaryltin reagents. The reaction of these reagents with BCl (sub)3 leads to the corresponding diarylchloroboranes.

A mechanistic outline of the benzene solution chemistries for the Zwitterionic and the cationic systems that highlights their key similarities and differences is described. The relative electronic impact of each ligands with respect to a coordinated metal center's electron-richness is examined sing comparative molybdenum and platinum model carbonyl and alkyl complexes.

A series of divalent cobalt(II) complexes is prepared supported by the [PhBP3] ligand [PhBP3] = ([PhB(CH2PPh2)(sub 3)](super -)) to probe certain structural and electronic phenomena that arise from this strong field, anionic tris(phosphine) donor ligand. The solid-state structure of the complex [PhBP3] accompanied by SQUID, EPR and optical data, indicates that it is a pseudotetrahedral cobalt(II) species with a doublet ground state-the first of its type.

An anomalous low-spin cobalt(II) complex, [PhBP3]Col, exhibiting a distorted tetrahedral geometry is prepared. A synthetic strategy concerning a two-electron 'NR' group-transfer reaction to a suitable cobalt(I) derivative is described. Maintaining approximate 3-fold symmetry is believed to be a promising design strategy for further developments in this area of synthesis.

A zwitterionic palladium II (Pd(II)) alkyl complex supported by the anionic ligand [Ph2BP2], acting as a very active catalyst for the copolymerization of CO and ethylene at ambient temperature is reported. Analysis suggests that a more electron-rich, zwitterionic [Ph2BP2] system is essentially as active as the conventional bis-diphenyl(phosphino)propane (dppp) system, which is based upon cationic palladium.

A new hybrid pyrazolyl/phosphinoborate ligand that could support pseudotetrahedral iron in the +1, +2, +3 and +4 oxidation states are described. The results indicate that imides in the +3 and +4 oxidation states are accessible using [PhBP(super tBu)(sub 2)(pz')]Fe systems.

The characterization of a phosphido-bridged dicopper system, {(PPP)Cu}(sub 2) ([PPP](super -) = bis(2-di-iso-propylphosphinophenyl)phosphide), in which each Cu center maintains a highly distorted tetrahedral geometry across these three oxidation states, is described. The results show that synthetic dicopper centers bridged in the diamond-core structural motif become unusually redox active, in this case sampling the oxidation states Cu(super I)Cu(super I), Cu(super 1.5)Cu(super 1.5), and Cu(super II)Cu(super II).

Low valent and low-coordinate bridging iron nitrides stabilized by [PHBP(sub 3)] ligands mediate facile H(sub 2) activation under mild conditions (room temperature, 1 atm H(sub 2)). In contrast to previous work from the lab concerning the hydrogenation of low spin Fe(III) imides, complete scission of the Fe-N linkage is not observed which is presumably due to the presence of an additional metal center that traps the imide-hydride as a bimetallic species.

A pseudotetrahedral d(super 7) complex, [PhBP3]Co(OSiPh3) that exhibits thermally induced spin-crossover is analyzed. The study shows that an equilibrium mixture of low and high spin forms for a distorted tetrahedral d(super 7) ion, and the cobalt(II) system described underscores the close electronic structure relationship that can arise between four-coordinate, pseudotetrahedral systems and their six-coordinate, octahedral counterparts.

The [PhBP(sub 3)(super iPr)] ligand is used to isolate a single iron center in a pseudo-tetrahedral environment in which a single binding site is compatible with coordination of N2 diazenido (N2Me) imide (NR). Other such salient features are described that collectively motivate further development of the present first-row systems into possible models for functional nitrogen fixation.

The synthesis of 4-coordinate Fe(I) complex, [PhBP3]Fe(PPh3) ([PhBP3] = [PhB(CH2PPh2)3]- is presented. It is shown that this complex undergoes rapid oxidation by aryl azide to produce terminally bonded Fe(III) imide, [PhBP3]Fe(N-p-tolyl).

The C-H activation of benzene at a charge neutral zwitterionic platinum(II) compound is reported.

Research is presented describing the activation of both Si-H bonds in a secondary silane to provide a synthetic pathway to complexes of iridium silylene. The process is relevant to a postulated mechanism for the dehydrogenative coupling of silanes to polysilanes using metal catalysts.

A carbidomolybdenum anion was studied and the solid-state 13C NMR data and proton-transfer self exchange kinetics examined.

Research is presented demonstrating dinitrogen (1 atm, THF, 25 degrees centigrade) splitting by Mo(N[R]Ar)3 (R = C(CD3)2CH3, Ar = 3,5-C6H3Me2) to give 2 equiv of nitrite N(triple bond)Mo(N[R]Ar)3.

Focuses on solution and solid-state spin-crossover behavior in a pseudotetrahedral d[sup 7] ion. Displacement ellipsoid; Electronic structure relationship between four-coordinate, pseudotetrahedral systems and their six-coordinate, octahedral counterparts.