Oxygen/sulfur substitution reactions of tetraoxometalates effected by electrophilic carbon and silicon reagents

Reactions of [MO(4)](2)(-) (M = Mo, W) with certain carbon and silicon electrophiles were investigated in acetonitrile in order to produce species of potential utility in the synthesis of analogues of the sites in the xanthine oxidoreductase enzyme family. Silylation of [MoO(4)](2)(-) affords [MoO(3)(OSiPh(3))](1)(-), which with Ph(3)SiSH is converted to [MoO(2)S(OSiPh(3))](1)(-). Reaction with (Ph(3)C)(PF(6))/HS(-) yields the tetrahedral monosulfido species [MO(3)S](2)(-), previously obtained only from the aqueous system [MO(4)](2)(-)/H(2)S. Dithiolene chelate rings are readily introduced upon reaction with 1,2-C(6)H(4)(SSiMe(3))(2), leading to the square pyramidal trioxo complexes [MO(3)(bdt)](2)(-), a previously unknown dithiolene molecular type. Further ring insertion occurs upon reaction of [WO(3)(bdt)](2)(-) with 1,2-C(6)H(4)(SSiMe(3))(2), giving [WO(2)(bdt)(2)](2)(-). Related reactions occur with [ReO(4)](1)(-). Treatment with 1 equiv of (Me(3)Si)(2)S produces [ReO(3)S](1)(-); with 3 equiv of 1,2-C(6)H(4)(SSiMe(3))(2), [ReO(bdt)(2)](1)(-) is obtained with concomitant Re(VII) --> Re(V) reduction. X-ray structures are reported for [MO(3)S](z)(-) (M = Mo, W, z = 2; M = Re, z = 1), [MO(3)(bdt)](2)(-), and [WO(2)(OSiPh(3))(bdt)](1)(-), a silylation product of [WO(3)(bdt)](2)(-). [MoO(3)(bdt)](2)(-) is related to the site of inactive sulfite oxidase, and [WO(2)(OSiPh(3))(bdt)](1)(-) should closely approximate the metric features of the [(dithiolene)MoO(2)(OH)] site in inactive aldehyde/xanthine oxidoreductase. This work provides convenient syntheses of known and new derivatives of tetraoxometalates, among which is entry to a unique class of oxo-monodithiolene complexes.     

Probing the electronic structure of [MoOS(4)](-) centers using anionic photoelectron spectroscopy

Using photodetachment photoelectron spectroscopy (PES) in the gas phase, we investigated the electronic structure and chemical bonding of six anionic [Mo(V)O](3+) complexes, [MoOX(4)](-) (where X = Cl (1), SPh (2), and SPh-p-Cl (3)), [MoO(edt)(2)](-) (4), [MoO(bdt)(2)](-) (5), and [MoO(bdtCl(2))(2)](-) (6) (where edt = ethane-1,2-dithiolate, bdt = benzene-1,2-dithiolate, and bdtCl(2) = 3,6-dichlorobenzene-1,2-dithiolate). The gas-phase PES data revealed a wealth of new electronic structure information about the [Mo(V)O](3+) complexes. The energy separations between the highest occupied molecular orbital (HOMO) and HOMO-1 were observed to be dependent on the O-Mo-S-C(alpha) dihedral angles and ligand types, being relatively large for the monodentate ligands, 1.32 eV for Cl and 0.78 eV for SPh and SPhCl, compared to those of the bidentate dithiolate complexes, 0.47 eV for edt and 0.44 eV for bdt and bdtCl(2). The threshold PES feature in all six species is shown to have the same origin and is due to detaching the single unpaired electron in the HOMO, mainly of Mo 4d character. This result is consistent with previous theoretical calculations and is verified by comparison with the PES spectra of two d(0) complexes, [VO(bdt)(2)](-) and [VO(bdtCl(2))(2)](-). The observed PES features are interpreted on the basis of theoretical calculations and previous spectroscopic studies in the condensed phase.     

Monodithiolene molybdenum(V, VI) complexes: a structural analogue of the oxidized active site of the sulfite oxidase enzyme family

The active sites of the xanthine oxidase and sulfite oxidase enzyme families contain one pterin-dithiolene cofactor ligand bound to a molybdenum atom. Consequently, monodithiolene molybdenum complexes have been sought by exploratory synthesis for structural and reactivity studies. Reaction of [MoO(S(2)C(2)Me(2))(2)](1-) or [MoO(bdt)(2)](1-) with PhSeCl results in removal of one dithiolate ligand and formation of [MoOCl(2)(S(2)C(2)Me(2))](1-) (1) or [MoOCl(2)(bdt)](1-) (2), which undergoes ligand substitution reactions to form other monodithiolene complexes [MoO(2-AdS)(2)(S(2)C(2)Me(2))](1-) (3), [MoO(SR)(2)(bdt)](1-) (R = 2-Ad (4), 2,4,6-Pr(i)(3)C(6)H(2) (5)), and [MoOCl(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (6) (Ad = 2-adamantyl, bdt = benzene-1,2-dithiolate). These complexes have square pyramidal structures with apical oxo ligands, exhibit rhombic EPR spectra, and 3-5 are electrochemically reducible to Mo(IV)O species. Complexes 1-6 constitute the first examples of five-coordinate monodithiolene Mo(V)O complexes; 6 approaches the proposed structure of the high-pH form of sulfite oxidase. Treatment of [MoO(2)(OSiPh(3))(2)] with Li(2)(bdt) in THF affords [MoO(2)(OSiPh(3))(bdt)](1-) (8). Reaction of 8 with 2,4,6-Pr(i)(3)C(6)H(2)SH in acetonitrile gives [MoO(2)(SC(6)H(2)-2,4,6-Pr(i)(3))(bdt)](1-) (9, 55%). Complexes 8 and 9 are square pyramidal with apical and basal oxo ligands. With one dithiolene and one thiolate ligand of a square pyramidal Mo(VI)O(2)S(3) coordination unit, 9 closely resembles the oxidized sites in sulfite oxidase and assimilatory nitrate reductase as deduced from crystallography (sulfite oxidase) and Mo EXAFS. The complex is the first structural analogue of the active sites in fully oxidized members of the sulfite oxidase family. This work provides a starting point for the development of both structural and reactivity analogues of members of this family.     

Silylation, sulfidation, and benzene-1,2-dithiolate complexation reactions of oxo- and oxosulfidomolybdates(VI) and -tungstates(VI)

The synthesis and structures of two types of molecules are presented: [MVIO3 - nSn(OSiR2R')]1- (M = Mo, n = 0-3; M = W, n = 3) and [MVIO2(OSiR2R')(bdt)]1- (M = Mo, W; bdt = benzene-1,2-dithiolate). For both types, R2R' are Me3, Pri3, Ph3, Me2But and Ph2But. The complete series of oxo/sulfido/silyloxo molybdenum complexes has been prepared. Complexes with n = 0 are readily prepared by the silylation of Ag2MoO4 and sustain mono- or disulfidation with Ph3SiSH to form a species with n = 1 and n = 2, respectively. Complexes with n = 3 are accessible by the silylation of [MOS3]2-. Structures of the representative series members [MoO3(OSiPh2But)]1-, [MoO2S(OSiPh3)]1-, [MoOS2(OSiPri3)]1-, [MoS3(OSiPh2But)]1-, and also [WS3(OSiMe2But)]1-, all with tetrahedral stereochemistry, are presented. Benzene-1,2-dithiolate complexes are prepared by the reaction of [MoO3(OSiR2R')]1-with the dithiol or by the silylation of previously reported [MO3(bdt)]2-. The structures of [MoO2(OSiPh2But)(bdt)]1- and [WO2(OSiPri3)(bdt)]1- conform to square-pyramidal stereochemistry with an oxo ligand in the apical position. The role of these complexes in the preparation of site analogues of the xanthine oxidoreductase enzyme family is noted. The sulfidation reactions reported here point to the utility of Ph3SiSH and Pri3SiSH as reagents for MoVI-based oxo-for-sulfido conversions.     

A new series of molybdenum-(IV), -(V), and -(VI) dithiolate compounds as active site models of molybdoenzymes: preparation, crystal structures, spectroscopic/electrochemical properties and reactivity in oxygen atom transfer

A new set of molybdenum-(IV), -(V), and -(VI) compounds containing 3,6-dichloro-1,2-benzenedithiolate (bdtCl2) were isolated and characterised by crystallographic and other spectroscopic techniques as active site models of arsenite oxidase, one of the molybdoenzymes. MoO2 compounds were prepared in high yields by reaction of MoO2Cl2 with bdtCl2, related dithiolene and thiocatecholate in methanol at low temperature. The bdtCl2 ligand particularly stabilised the MoO compounds with oxidation numbers of +4 and +5 as well as the MoO2 compound with an oxidation number of +6. The compounds (Et4N)2[MoVIO2(bdtCl2)2], (Et4N)2[MoIVO(bdtCl2)2] and (Et4N)[MoVO(bdtCl2)2] were successfully isolated, whereas (Et3NH)2[MoO2(thiocatecholate)2] gradually decomposed in acetonitrile. A distorted octahedral structure similar to that of was suggested for the structure of the active site of the oxidised form of arsenite oxidase on the basis of a comparison of their bond distances and angles. The bond distances and angles around the molybdenum(IV) atom in were similar to those around the molybdenum(IV) centre in the reduced form of arsenite oxidase. The reversible / couple exhibited a more positive redox potential than common MoO dithiolene compounds. Underwent an irreversible proton-coupled reduction process to yield. An oxygen atom transfer reaction of with triphenylphosphine afforded and triphenylphosphine oxide, and proceeded in second order as v=-d/dt[MoO2]=k[MoO2][PPh3]. The structures and properties of the oxo-bridged dinuclear compound (Et4N)2[MoVIO2(bdtCl2)]2(micro-O), a dimer of bdtCl2 and were also characterised.     

Regioselective and reversible carbon-nitrogen bond formation: synthesis, structure and reactivity of ureato-bridged complexes [Mo2(NAr)2(mu-X){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; X = S, NAr; R = Me, Et, Pr)

Reaction of ArNCO with syn-[MoO(mu-O)(S2CNR2)]2 or syn-[MoO(mu-NAr)(S2CNR2)]2 at 110 degrees C leads to the facile formation of bridging ureato complexes [Mo2(NAr)2(mu-NAr){mu-ArNC(O)NAr}(S2CNR2)2](Ar = Ph, p-tol; R = Me, Et, Pr), formed upon substitution of all oxo ligands and addition of a further equivalent of isocyanate across one of the bridging imido ligands. Related sulfido-bridged complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] have been prepared from syn-[Mo2O2(mu-O)(mu-S)(S2CNR2)2]. When reactions with syn-[MoO(mu-NAr)(S2CNEt2)]2 were followed by NMR, intermediates were observed, being formulated as [Mo2O(NAr)(mu-NAr){mu-ArNC(O)NAr}(S2CNEt2)2], which at higher temperatures convert to the fully substituted products. A crystallographic study of [Mo2(N-p-tol)2(mu-S){mu-p-tolNC(O)N-p-tol}(S2CNPr2)2] reveals that the bridging ureato ligand is bound asymmetrically to the dimolybdenum centre-molybdenum-nitrogen bonds trans to the terminal imido ligands being significantly elongated with respect to those cis-a result of the trans-influence of the terminal imido ligands. This trans-influence also leads to a trans-effect, whereby the exchange of aryl isocyanates can occur in a regioselective manner. This is followed by NMR studies and confirmed by a crystallographic study of [Mo2(N-p-tol)2(mu-N-p-tol){mu-p-tolNC(O)NPh}(S2CNEt2)2]--the PhNCO occupying the site trans to the terminal imido ligands. Ureato complexes also react with PhNCS, initially forming [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2], resulting from exchange of the bridging imido ligand for sulfur, together with small amounts of [Mo2(NAr)2(mu-S)(mu-S2)(S2CNEt2)2], containing bridging sulfide and disulfide ligands. The ureato complexes [Mo2(NAr)2(mu-S){mu-ArNC(O)NAr}(S2CNR2)2] react further with PhNCS to give [Mo2(NAr)2(mu-S)2(S2CNR2)2]n (n = 1, 2), which exist in a dimer-tetramer equilibrium. In order to confirm these results crystallographic studies have been carried out on [Mo2(N-p-tol)2(mu-S)(mu-S2)(S2CNEt2)2] and [Mo2(N-p-tol)2(mu-S)2(S2CNPr2)2]2.     

Tuning of the spin distribution between ligand- and metal-based spin: electron paramagnetic resonance of mixed-ligand molybdenum tris(dithiolene) complex anions

Electron paramagnetic resonance spectra of homoleptic and mixed-ligand molybdenum tris(dithiolene) complex anions [Mo(tfd)(m)(bdt)(n)](-) (n + m = 3; bdt = S(2)C(6)H(4); tfd = S(2)C(2)(CF(3))(2)) reveal that the spin density has mixed metal-ligand character with more ligand-based spin for [Mo(tfd)(3)](-) and a higher degree of metal-based spin for [Mo(bdt)(3)](-): the magnitude of the isotropic (95,97)Mo hyperfine interaction increases continuously, by a factor of 2.5, on going from the former to the latter. The mixed complexes fall in between, and the metal character of the spin increases with the bdt content. The experiments were corroborated by density functional theory computations, which reproduce this steady increase in metal-based character.     

New oxovanadium bis(1,2-dithiolate) compounds that mimic the hydrogen-bonding interactions at the active sites of mononuclear molybdenum enzymes

Reaction of VO(acac)(2) with 1,2-dithiols in the presence of triethylamine gives pentacoordinate oxovanadium complexes [HNEt(3)](2)[VO(bdt)(2)] (1), [HNEt(3)](2)[VO(tdt)(2)] (2), and [HNEt(3)](2)[VO(bdtCl(2))(2)] (3) (where H(2)bdt = 1,2-benzenedithiol, H(2)tdt = 3,4-toluenedithiol, and H(2)bdtCl(2) = 3,6-dichloro-1,2-benzenedithiol). Compounds 1-3 have been characterized by IR, UV/visible, EPR, and mass spectroscopies. The X-ray crystal stuctures of 1 and 2 show hydrogen-bonding interactions between the terminal oxo atom and triethylammonium counterions and between ligand sulfur atoms and the counterions. These interactions are comparable with those found at the active sites of mononuclear molybdenum enzymes.     

Monoanionic molybdenum and tungsten tris(dithiolene) complexes: a multifrequency EPR study

Numerous Mo and W tris(dithiolene) complexes in varying redox states have been prepared and representative examples characterized crystallographically: [M(S(2)C(2)R(2))(3)](z) [M = Mo, R = Ph, z = 0 (1) or 1- (2); M = W, R = Ph, z = 0 (4) or 1- (5); R = CN, z = 2-, M = Mo (3) or W (6)]. Changes in dithiolene C-S and C-C bond lengths for 1 versus 2 and 4 versus 5 are indicative of ligand reduction. Trigonal twist angles (Θ) and dithiolene fold angles (α) increase and decrease, respectively, for 2 versus 1, 5 versus 4. Cyclic voltammetry reveals generally two reversible couples corresponding to 0/1- and 1-/2- reductions. The electronic structures of monoanionic molybdenum tris(dithiolene) complexes have been analyzed by multifrequency (S-, X-, Q-band) EPR spectroscopy. Spin-Hamiltonian parameters afforded by spectral simulation for each complex demonstrate the existence of two distinctive electronic structure types. The first is [Mo(IV)((A)L(3)(5-?))](1-) ((A)L = olefinic dithiolene, type A), which has the unpaired electron restricted to the tris(dithiolene) unit and is characterized by isotropic g-values and small molybdenum superhyperfine coupling. The second is formulated as [Mo(V)((B)L(3)(6-))](1-) ((B)L = aromatic dithiolene, type B) with spectra distinguished by a prominent g-anisotropy and hyperfine coupling consistent with the (d(z(2)))(1) paramagnet. The electronic structure disparity is also manifested in their electronic absorption spectra. The compound [W(bdt)(3)](1-) exhibits spin-Hamiltonian parameters similar to those of [Mo(bdt)(3)](1-) and thus is formulated as [W(V)((B)L(3)(6-))](1-). The EPR spectra of [W((A)L(3))](1-) display spin-Hamiltonian parameters that suggest their electronic structure is best represented by two resonance forms {[W(IV)((A)L(3)(5-?))](1-) ? [W(V)((A)L(3)(6-))](1-)}. The contrast with the corresponding [Mo(IV)((A)L(3)(5-?))](1-) complexes highlights tungsten's preference for higher oxidation states.     

CpNi(dithiolene)] (and diselenolene) neutral radical complexes

Various preparations of the neutral radical [CpNi(dddt)] complex (dddt = 5,6-dihydro-1,4-dithiin-2,3-dithiolate) were investigated with CpNi sources, [Cp2Ni], [Cp2Ni](BF4), [CpNi(CO)]2, and [CpNi(cod)](BF4), and dithiolene transfer sources, O=C(dddt), the naked dithiolate (dddt(2-)), the monoanion of square-planar Ni dithiolene complex (NBu4)[Ni(dddt)2], and the neutral complex [Ni(dddt)2]. The reaction of [CpNi(cod)](BF4) with (NBu4)[Ni(dddt)2] gave the highest yield for the preparation of [CpNi(dddt)] (86%). [CpNi(ddds)] (ddds = 5,6-dihydro-1,4-dithiin-2,3-diselenolate), [CpNi(dsdt)] (dsdt = 5,6-dihydro-1,4-diselenin-2,3-dithiolate), [CpNi(bdt)] (bdt = 1,2-benzenedithiolate), and [CpNi(bds)] (bds = 1,2-benzenediselenolate) were synthesized by the reactions of [Cp2Ni] with the corresponding neutral Ni dithiolene complexes [Ni(ddds)2]2, [Ni(dsdt)2], [Ni(bdt)2], and [Ni(bds)2], respectively. The five, formally Ni(III), radical complexes oxidize and reduce reversibly. They exhibit, in the neutral state, a strong absorption in the NIR region, from 1000 nm in the dddt/ddds/dsdt series to 720 nm in the bdt/bds series with epsilon values between 2500 and 5000 M(-1) cm(-1). The molecular and solid state structures of the five complexes were determined by X-ray structure analyses. [CpNi(dddt)] and [CpNi(ddds)] are isostructural, while [CpNi(dsdt)] exhibits a closely related structure. Similarly, [CpNi(bdt)] and [CpNi(bds)] are also isostructural. Correlations between structural data and magnetic measurements show the presence of alternated spin chains in [CpNi(dddt)], [CpNi(ddds)], and [CpNi(dsdt)], while a remarkably strong antiferromagnetic interaction in [CpNi(bdt)] and [CpNi(bds)] is attributed to a Cp...Cp face-to-face sigma overlap, an original feature in organometallic radical complexes.     

From simple to complex: topological evolution and luminescence variation in a copper(I) pyridylpyrazolate system tuned via second ligating spacers

By systematically varying the geometric length and electronic properties of the second ligating ligands of halogen (Cl(-), Br(-), and I(-)) and pseudohalogen (CN(-), SCN(-), and N(3)(-)) anions, we synthesized 11 isomeric/isostructural copper(I) complexes: [Cu(2)(L3-3)I](n) (1), [Cu(2)(L4-4)Br](n) (2-Br), [Cu(2)(L4-4)Cl](n) (2-Cl), [Cu(2)(L3-4)(CN)](n) (3), [Cu(2)(L3-3)(CN)](n) (4), [Cu(3)(L4-4)(CN)(2)](n) (5), {[Cu(2)(L4-4)Br](2)·CuBr}(n) (6-Br), {[Cu(2)(L4-4)Cl](2)·CuCl}(n) (6-Cl), [Cu(2)(L4-4)(SCN)](n) (7α-SCN), [Cu(2)(L4-4)(SCN)](n) (7β-SCN), and [Cu(2)(L4-4)(N(3))](n) (7α-N(3)). These structures are based on a series of isomeric pyridylpyrazole ligands, namely, 3,5-bis(3-pyridyl)-1H-pyrazole (HL3-3), 3-(3-pyridyl)-5-(4-pyridyl)-1H-pyrazole (HL3-4), and 3,5-bis(4-pyridyl)-1H-pyrazole (HL4-4), and their structural features range from 1-D (1), 2-D (2), and 3-D noninterpenetration (3), to 3-D 2-fold interpenetration (4 and 5), to 3-D self-catenation (6 and 7), exhibiting a trend from simple to complex with dimension expansion and an interpenetrating degree increase. The five most complex structures (6 and 7) with self-catenated networks are based on 2-fold interpenetrated networks linked via appropriate second ligating spacers (Cl(-), Br(-), SCN(-), and N(3)(-)), representing a strategy to construct self-catenated coordination polymers through cross-linking interpenetrated frameworks. Moreover, these complexes exhibit strong photoluminescence, which is mainly ascribed to Cu(I)-related charge transfers (MLCT, MC, and MMLCT) regulated by the electronic properties of halogen or pseudohalogen. The topological evolution and luminescence variation presented in this work open an avenue to understanding the luminescence origin and the structure-property relationship of luminescent coordination polymers.     

Mechanistic studies on the reactions of PhS(-) or [MoS(4)](2)(-) with [M(4)(SPh)(10)](2)(-) (M = Fe or Co)

Kinetic studies, using stopped-flow spectrophotometry, on the reactions of [M(4)(SPh)(10)](2)(-) (M = Fe or Co) with PhS(-) to form [M(SPh)(4)](2)(-) are described, as are the reactions between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) to form [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). The kinetics of the reactions with PhS(-) are consistent with an initial associative substitution mechanism involving attack of PhS(-) at one of the tetrahedral M sites of [M(4)(SPh)(10)](2)(-) to form [M(4)(SPh)(11)](3)(-). Subsequent or concomitant cleavage of a micro-SPh ligand, at the same M, initiates a cascade of rapid reactions which result ultimately in the complete rupture of the cluster and formation of [M(SPh)(4)](2)(-). The kinetics of the reaction between [M(4)(SPh)(10)](2)(-) and [MoS(4)](2)(-) indicate an initial dissociative substitution mechanism at low concentrations of [MoS(4)](2)(-), in which rate-limiting dissociation of a terminal thiolate from [M(4)(SPh)(10)](2)(-) produces [M(4)(SPh)(9)](-) and the coordinatively unsaturated M site is rapidly attacked by a sulfido group of [MoS(4)](2)(-). It is proposed that subsequent chelation of the MoS(4) ligand results in cleavage of an M-micro-SPh bond, initiating a cascade of reactions which lead to the ultimate break-up of the cluster and formation of the products, [S(2)MoS(2)Fe(SPh)(2)](2)(-) or [S(2)MoS(2)CoS(2)MoS(2)](2)(-). With [Co(4)(SPh)(10)](2)(-), at higher concentrations of [MoS(4)](2)(-), a further substitution pathway is evident which exhibits a second order dependence on the concentration of [MoS(4)](2)(-). The mechanistic picture of cluster disruption which emerges from these studies rationalizes the "all or nothing" reactivity of [M(4)(SPh)(10)](2)(-).     

Reactivity studies of oxo-Mo(IV) complexes containing potential hydrogen-bond acceptor/donor phenolate ligands

Reactivity studies of oxo-Mo(IV) complexes, Tp(iPr)MoO{2-OC(6)H(4)C(O)R-κ(2)O,O'} (R = Me, Et, OMe, OEt, OPh, NHPh), containing chelated hydrogen-bond donor/acceptor phenolate ligands are reported. Hydrolysis/oxidation of Tp(iPr)MoO(2-OC(6)H(4)CO(2)Ph-κ(2)O,O') in the presence of methanol yields tetranuclear [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2) (1), while condensation of Tp(iPr)MoO{2-OC(6)H(4)C(O)Me-κ(2)O,O'} and methylamine gives the chelated iminophenolate complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κ(2)O,N} (2), rather than the aqua complex, Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe-κO}(OH(2)). The oxo-Mo(IV) complexes are readily oxidized by dioxygen or hydrogen peroxide to the corresponding cis-dioxo-Mo(VI) complexes, Tp(iPr)MoO(2){2-OC(6)H(4)C(O)R}; in addition, suitable one-electron oxidants, e.g., [FeCp(2)]BF(4) and [N(C(6)H(4)Br)(3)][SbCl(6)], oxidize the complexes to their EPR-active (g(iso) ≈ 1.942) molybdenyl counterparts (3, 4). Molybdenyl complexes such as Tp(iPr)MoOCl{2-OC(6)H(4)C(O)R} (5) and Tp(iPr)MoOCl(2) also form when the complexes react with chlorinated solvents. The ester derivatives (R = OMe, OEt, OPh) react with propylene sulfide to form cis-oxosulfido-Mo(VI) complexes, Tp(iPr)MoOS{2-OC(6)H(4)C(O)R}, that crystallize as dimeric μ-disulfido-Mo(V) species, [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (6-8). The crystal structures of [Tp(iPr)MoO(μ-O)(2)MoO](2)(μ-OMe)(2), Tp(iPr)MoO{2-OC(6)H(4)C(Me)NMe}, Tp(iPr)MoOCl{2-OC(6)H(4)C(O)NHPh}·{2-HOC(6)H(4)C(O)NHPh}, and [Tp(iPr)MoO{2-OC(6)H(4)C(O)R}](2)(μ-S(2)) (R = OMe, OEt) are reported.     

Metal-dependent and redox-selective coordination behaviors of metalloligand [MoV(1,2-benzenedithiolato)3]- with CuI/AgI ions

The synthesis and characterization of two coordination polymers, {Cu(I)[Mo(V)(bdt)(3)]·0.5Et(2)O}(n) (1·0.5Et(2)O, bdt: o-benzenedithiolato) and {Ag(I)[Mo(V)(bdt)(3)]}(n) (2), composed of redox-active [Mo(V)(bdt)(3)](-) metalloligand with Cu(I) and Ag(I) ions are reported. The complexation reactions of [Mo(V)(bdt)(3)](-) with Cu(II)(ClO(4))(2) or Ag(I)ClO(4) commonly lead to the formation of one-dimensional (1-D) coordination polymers. The presence of Cu(I) in 1·0.5Et(2)O strongly indicates that the Cu(II) ion is reduced during the complexation reaction with [Mo(V)(bdt)(3)](-), which acts as an electron donor. The total dimensionalities of the assembled structures of 1·0.5Et(2)O and 2 are significantly different and related to the type of additional metal ions, Cu(I) and Ag(I). In contrast to the isolated 1-D chain structure of 1·0.5Et(2)O, complex 2 has a three-dimensional (3-D) assembled structure constructed from additional π-π stacking interactions between adjacent [Mo(V)(bdt)(3)](-) moieties. These structural differences influence the solubility of the complexes in organic solvents; complex 1·0.5Et(2)O is soluble as origomeric species in highly polar solvents, while 2 is insoluble in organic solvents and water. Coordination polymers 1·0.5Et(2)O and 2 were investigated by UV-vis spectroscopy in the solid state, and that in solution together with their electrochemical properties were also investigated for 1 because of its higher solubility in polar organic solvents. Complex 1·0.5Et(2)O dissolved in CH(3)CN demonstrates concentration-dependent UV-vis spectra supporting the presence of coordinative interactions between [Mo(V)(bdt)(3)](-) moieties and Cu(I) ions to create the origomeric species even in solutions, an observation that is supported also by electrochemical experiments.     

Novel Mo(V)-dithiolene compounds: characterization of nonsymmetric dithiolene complexes by electrospray ionization mass spectrometry

Three new Mo(V) dithiolene compounds have been synthesized by addition of alkynes ((Me(3)Si)(2)C(2) (TMSA), (Me(3)Si)(2)C(4), and (Ph)(2)C(4) to MoO(2)S(2)(2-) in a MeOH/NH(3) mixture: [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(2))](2)(-) 1, [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(C(2)Ph))](2-) 2 (X = O or S), and [Mo(2)(O)(2)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)H(C(2)H))](2-) 3. The structure of 1 as determined by single-crystal X-ray diffraction study (space group Pbca, a = 13.3148(1) A, b = 15.7467(4) A, c = 28.4108(7) A, V = 5956.7(2) A(3)) is discussed. 2 and 3 have been identified by ESMS (electrospray mass spectrometry), (1)H NMR, (13)C NMR, and infrared spectroscopies. This investigation completes our previous study devoted to the addition of DPA (C(2)Ph(2)) to MoO(2)S(2)(2-) which led to [Mo(2)(O)(X)(mu-S)(2)(eta(2)-S(2))(eta(2)-S(2)C(2)Ph(2))](2-) 4 (X = O or S). A reaction scheme is proposed to explain the formation of the different species present in solution. The reactivity of the remaining nucleophilic site of these complexes (eta(2)-S(2)) toward dicarbomethoxyacetylene (DMA) is also discussed.     

Dangling thiyl radical: stabilized in [PPh4]2[(bdt)W(VI)(O)(μ-S)2Cu(I)(SC6H4S•)

The synthesis, crystal structure, and spectroscopic characterization of [PPh(4)](2)[(bdt)W(O)(S(2))Cu(SC(6)H(4)S(?))] (3; bdt = benzenedithiolate) relevant to the active site of carbon monoxide dehydrogenase are presented. Curiously, in 3, the copper(I) benzenemonothiolate subcenter possesses a dangling thiyl radical that is stabilized by a disulfido-bridged oxo tungsten dithiolene core. The benzenedithiolate ligand, which is generally bidentate in nature, acts as a bidentate and also as a monodentate in 3. The formation of an unusual dangling thiyl radical has been magnetically and spectroscopically identified and has been supported by the density functional theory level of calculation.     

Coordination complexes of molybdenum with 3,6-di-tert-butylcatechol. Addition products of DMSO, pyridine N-oxide, and triphenylarsine oxide to the putative [MoVIO(3,6-DBCat)2] monomer and self-assembly of the chiral [(MoVIO(3,6-DBCat)2)4] square

Molybdenum complexes of 3,6-di-tert-butylcatechol have been prepared from the reaction between [Mo(CO)(6)] and 3,6-di-tert-butyl-1,2-benzoquinone. A putative "[MoO(3,6-DBCat)(2)]" monomer is assumed to form initially by reaction with trace quantities of oxygen. Condensation of the reaction mixture leads to the formation of oligomeric products, including the [(MoO(3,6-DBCat)(2))(4)] chiral square isolated by chromatographic separation. Molybdenum centers at the corner of the square are bridged by oxo ligands centered along edges. Four-fold and inversion crystallographic symmetry gives tetramers as either LambdaLambdaLambdaLambda or DeltaDeltaDeltaDelta isomers, and the crystal structure consists of parallel columns of squares with the same chirality. Addition of O-Subst (O-Subst = dmso, pyridine N-oxide, triphenylarsine oxide) ligands to [MoO(3,6-DBCat)(2)] occurs selectively to give cis-[MoO(O-Subst)(3,6-DBCat)(2)] products. All three addition complexes are fluxional in solution. The temperature-dependent stereodymanic behavior of [MoO(dmso)(3,6-DBCat)(2)] has been shown to occur via a trigonal prismatic intermediate (Bailar twist) that conserves the cis disposition of oxo and dmso ligands. Electrochemical and chemical reduction reactions have been investigated for [MoO(dmso)(3,6-DBCat)(2)] with interest in displacement of SMe(2) with formation of cis-[MoO(2)(3,6-DBCat)(2)](2-). Cyclic voltammetry shows an irreversible two-electron reduction for the complex at -0.852 V (vs Fc/Fc(+)). Chemical reduction using CoCp(2) was observed to give a product with an electronic spectrum that is generally associated with cis-[MoO(2)(Cat)(2)](2-) complexes. Structural characterization revealed that the product was [CoCp(2)][MoO(3,6-DBCat)(2)], possibly formed as the product of dmso displacement upon one-electron reduction of [MoO(dmso)(3,6-DBCat)(2)].     

Double-stranded W/Ag/S chain structure generated from [syn-(WO(NCS)(2))(2)(mu-S)(2)] building blocks

The dimeric W(V) complex [Et(4)N](4)[syn-(O=W(NCS)(3))(2)(mu-S)(2)], 1, prepared from [Et(4)N](2)[WS(4)], SCN(-), and Cd(2+), shows interesting reactivity patterns in that the thiocyanate trans to the oxo group can in part be replaced, initiated by Mn(2+), by dimethylformamide (DMF) to form [Et(4)N](2.5)[(O=W(NCS)(2.25)(DMF)(1.25))(2)(mu-S)(2)], 2. With Ag(+), 1 undergoes partial replacement of SCN(-) by DMF and coordinates to the silver ions to generate ([Et(4)N](2.5)[(W(2)O(2)(NCS)(2)(mu-S)(2))(mu-NCS)(2)(DMF)(Ag(0.5)(SCN))])(n), 3. Compound 3 constitutes a polymeric double-stranded chain, with normal bonding interactions [via W-(mu-NCS)-Ag] between the two strands, and moderate intrastrand [W-(mu-NCS).Ag] bonding. The crystal and molecular structures of the three compounds are described.     

Sulfur-bridged Co(III)Pt(II)Co(III) trinuclear complexes with mixed aliphatic and aromatic thiolate ligands: effect of nonbridging ligands on the homochiral linkage of cobalt(III) octahedrons by platinum(II)

The reaction of [Ni[Co(aet)(2)(pyt)](2)](2+) (aet = 2-aminoethanethiolate, pyt = 2-pyridinethiolate) with [PtCl(4)](2)(-) gave an S-bridged Co(III)Pt(II)Co(III) trinuclear complex composed of two [Co(aet)(2)(pyt)] units, [Pt[Co(aet)(2)(pyt)](2)](2+) ([1](2+)). When a 1:1 mixture of [Ni[Co(aet)(2)(pyt)](2)](2+) and [Ni[Co(aet)(2)(en)](2)](4+) was reacted with [PtCl(4)](2)(-), a mixed-type S-bridged Co(III)Pt(II)Co(III) complex composed of one [Co(aet)(2)(pyt)] and one [Co(aet)(2)(en)](+) units, [Pt[Co(aet)(2)(en)][Co(aet)(2)(pyt)]](3+) ([2](3+)), was produced, together with [1](2+) and [Pt[Co(aet)(2)(en)](2)](4+). The corresponding Co(III)Pt(II)Co(III) trinuclear complexes containing pymt (2-pyrimidinethiolate), [Pt[Co(aet)(2)(pymt)](2)](2+) ([3](2+)) and [Pt[Co(aet)(2)(en)][Co(aet)(2)(pymt)]](3+) ([4](3+)), were also obtained by similar reactions, using [Ni[Co(aet)(2)(pymt)](2)](2+) instead of [Ni[Co(aet)(2)(pyt)](2)](2+). While [Pt[Co(aet)(2)(en)](2)](4+) formed both the deltalambda (meso) and deltadelta/lambdalambda (racemic) forms in a ratio of ca. 1:1, the preferential formation of the deltadelta/lambdalambda form was observed for [1](2+) (ca. deltalambda:deltadelta/lambdalambda = 1:3) and [2](3+) (ca. delta(en)lambda(pyt)/lambda(en)delta(pyt):deltadelta/lambdalambda = 1:2). Furthermore, [3](2+) and [4](3+) predominantly formed the deltadelta/lambdalambda form. These results indicate that the homochiral selectivity for the S-bridged Co(III)Pt(II)Co(III) trinuclear complexes composed of two octahedral [Co(aet)(2)(L)](0 or +) units is enhanced in the order L = en < pyt < pymt. The isomers produced were separated and optically resolved, and the crystal structures of the meso-type deltalambda-[1]Cl(2).4H(2)O and the spontaneously resolved deltadelta-[4](ClO(4))(3).H(2)O were determined by X-ray analyses. In deltalambda-[1](2+), the delta and Lambda configurational mer(S).trans(N(aet))-[Co(aet)(2)(pyt)] units are linked by a square-planar Pt(II) ion through four aet S atoms to form a linear-type S-bridged trinuclear structure. In deltadelta-[4](3+), a similar linear-type trinuclear structure is constructed from the delta-mer(S).trans(N(aet))-[Co(aet)(2)(pymt)] and delta-C(2)-cis(S)-[Co(aet)(2)(en)](+) units that are bound by a Pt(II) ion with a slightly distorted square-planar geometry through four aet S atoms.     

Variation of heterometallic structural motifs based on [W(CN)8]3- anions and Mn(II) ions as a function of synthetic conditions

Reactions of [W(CN)(8)](3-/4-) anions with complexes of Mn(2+) ion with tridentate organic ligand 2,4,6-tris(2-pyridyl)-1,3,5-triazine (tptz) lead to a series of heterobimetallic complexes. The crystal structures of these compounds are derived from the same basic structural fragment, namely a W(2)Mn(2) square constructed of alternating cyanide-bridged W and Mn ions. In [Mn(II)(tptz)(OAc)(H(2)O)(2)](2){[Mn(II)(tptz)(MeOH)(1.58)(H(2)O)(0.42)](2)[W(V)(CN)(8)](2)}.5 MeOH.9.85 H(2)O (3), isolated molecular squares are co-crystallized with mononuclear cationic Mn(II) complexes. The structure of {[Mn(II)(tptz)(MeOH)](2)[W(IV)(CN)(8)].2 MeOH}(infinity) (4) is based on an infinite chain of vertex-sharing squares, while {[Mn(II) (2)(tptz)(2)(MeOH)(3)(OAc)][W(V)(CN)(8)].3.5 MeOH0.25 H(2)O}(infinity) (5) and {[Mn(II) (2)(tptz)(2)(MeOH)(3)W(V)(CN)(8)][Mn(II)(tptz)(MeOH)W(V)(CN)(8)].2 H(2).OMeOH}(8) (7) are derived from such an infinite chain by removing one of the W-C[triple bond]N-Mn linkages in each of the squares. The decanuclear cluster [Mn(II) (6)(tptz)(6)(MeOH)(4)(DMF)(2)W(V) (4)(CN)(32)].8.2 H(2)O.2.3 MeOH (6) is a truncated version of structure 4 and consists of three vertex-sharing W(2)Mn(2) squares. The structure of [Mn(II)(tptz)(MeOH)(NO(3))](2)[Mn(II)(tptz)(MeOH) (DMF)](2)[W(V)(CN)(8)](2).6 MeOH (8) consists of a hexanuclear cluster, in which the central W(2)Mn(2) square is extended by two Mn side-arms attached via CN(-) ligands to the W corners of the square. The magnetic behavior of these heterobimetallic complexes (except for 4) is dominated by antiferromagnetic coupling between Mn(II) and W(V) ions mediated by cyanide bridges. Compounds 3, 6, and 8 exhibit high spin ground states of S=4, 13, and 9, respectively, while 5 and 7 exhibit behavior typical of a ferrimagnetic chain with alternating spin centers. Complex 4 contains diamagnetic W(IV) centers but holds promise as a potential photomagnetic solid.