Zinc-rich compounds of iron and cobalt: formation of [Fe2Zn(n)] (n = 2-4) and [Co2Zn3] cores

The reactions of heteroleptic GaCp*/CO containing transition metal complexes of iron and cobalt, namely [(CO)(3)M(μ(2)-GaCp*)(m)M(CO)(3)] (Cp* = pentamethylcyclopentadienyl; M = Fe, m = 3; M = Co, m = 2) and [Fe(CO)(4)(GaCp*)], with ZnMe(2) in toluene and the presence of a coordinating co-solvent were investigated. The reaction of the iron complex [Fe(CO)(4)(GaCp*)] with ZnMe(2) in presence of tetrahydrofurane (thf) leads to the dimeric compound [(CO)(4)Fe{μ(2)-Zn(thf)(2)}(2)Fe(CO)(4)] (1). Reaction of [(CO)(3)Fe(μ(2)-GaCp*(3))Fe(CO)(3)] with ZnMe(2) and stoichiometric amounts of thf leads to the formation of [(CO)(3)Fe{μ(2)-Zn(thf)(2)}(2)(μ(2)-ZnMe)(2)Fe(CO)(3)] (2) containing {Zn(thf)(2)} as well as ZnMe ligands. Using pyridine (py) instead of thf leads to [(CO)(3)Fe{μ(2)-Zn(py)(2)}(3)Fe(CO)(3)] (3) via replacement of all GaCp* ligands by three{Zn(py)(2)} groups. In contrast, reaction of [(CO)(3)Co(μ(2)-GaCp*)(2)Co(CO)(3)] with ZnMe(2) in the presence of py or thf leads in both cases to the formation of [(CO)(3)Co{μ(2)-ZnL(2)}(μ(2)-ZnCp*)(2)Co(CO)(3)] (L = py (4), thf (5)) via replacement of GaCp* with {Zn(L)(2)} units as well as Cp* transfer from the gallium to the zinc centre. All compounds were characterised by NMR spectroscopy, IR spectroscopy, single crystal X-ray diffraction and elemental analysis.     

Linkage and redox isomerism in ruthenium complexes of catecholate, semiquinone, and o-acylphenolate ligands derived from 1,2-dihydroxy-9,10-anthracenedione (alizarin) and related species: syntheses, characterizations, and photophysics

The complexes Ru(CO)2L2(AL-2H) (AL = alizarin; L = PPh3, PCyc3, PBu3, P(m-NaSO3C6H4)3), Ru(CO)(dppe)(PBu3)(AL-2H), and RuH(CO)L2(AL-H) (L = PPh3, PCyc3), and Ru(CO)2L2(AR-2H) (AR = anthrarobin; L = PBu3) were prepared by reactions of Ru3(CO)12, L, and AL, and the complexes RuH(CO)(PPh3)2(AL-H), RuH(CO)(PPh3)2(QN-H) (QN = quinizarin), and RuH(CO)(PPh3)2(LQN-H) (LQN = leucoquinizarin) are prepared by reactions of RuH2(CO)(PPh3)3 with AL or QN. The AL-2H and AR-2H ligands act as 1,2-catecholates, whereas the AL-H, QN-H, LQN-H ligands are 1,9-o-acylphenolate ligands. RuH(CO)(PPh3)2(AL-H) is characterized by X-ray crystallography. The electrochemistry of these complexes is examined, and the semiquinone complexes [Ru(CO)2L2(AL-2H)]+ (L = PPh3, PCyc3, PBu3) and [Ru(CO)(dppe)(PBu3)(AL-2H)]+ are generated by chemical oxidation and were characterized by EPR and IR spectroscopy. The photophysical properties are also reported.     

Enhancement of CO2 sorption uptake on hydrotalcite by impregnation with K2CO3

The awareness of symptoms of global warming and its seriousness urges the development of technologies to reduce greenhouse gas emissions. Carbon dioxide (CO(2)) is a representative greenhouse gas, and numerous methods to capture and storage CO(2) have been considered. Recently, the technology to remove high-temperature CO(2) by sorption has received lots of attention. In this study, hydrotalcite, which has been known to have CO(2) sorption capability at high temperature, was impregnated with K(2)CO(3) to enhance CO(2) sorption uptake, and the mechanism of CO(2) sorption enhancement on K(2)CO(3)-promoted hydrotalcite was investigated. Thermogravimetric analysis was used to measure equilibrium CO(2) sorption uptake and to estimate CO(2) sorption kinetics. The analyses based on N(2) gas physisorption, X-ray diffractometry, Fourier transform infrared spectrometry, Raman spectrometry, transmission electron microscopy, scanning electron microscopy, and energy dispersive X-ray spectroscopy were carried out to elucidate the characteristics of sorbents and the mechanism of enhanced CO(2) sorption. The equilibrium CO(2) sorption uptake on hydrotalcite could be increased up to 10 times by impregnation with K(2)CO(3), and there was an optimal amount of K(2)CO(3) for a maximum equilibrium CO(2) sorption uptake. In the K(2)CO(3)-promoted hydrotalcite, K(2)CO(3) was incorporated without changing the structure of hydrotalcite and it was thermally stabilized, resulting in the enhanced equilibrium CO(2) sorption uptake and fast CO(2) sorption kinetics.     

STUDIES ON THE FORMATION OF BIMETALLIC Rh-CoCLUSTERS FROM MONOMETALLIC RHODIUM ANDCOBALT CLUSTERS

IntroductionFormorethanonedecade,catalyticchemistshavemadenotableachievementsindevelopingthepreparativeapproachestoheterogenizedmolecularcatalystsandhighlydispersedmetalcatalystsfromorganometalliccompoundsandclusters,throughtheexplorationinsurfaceorganome…     

New disulfido molybdenum-manganese complexes exhibit facile addition of small molecules to the sulfur atoms

The reaction of Mn(2)(CO)(7)(mu-S2) (1) with [CpMo(CO)(3)](2) (Cp = C(5)H(5)) and [Cp*Mo(CO)(3)](2) (Cp* = C(5)(CH(3))(5)) yielded the new mixed-metal disulfide complexes CpMoMn(CO)(5)(mu-S2) (2) and Cp*MoMn(CO)(5)(mu-S2) (3) by a metal-metal exchange reaction. Compounds 2 and 3 both contain a bridging disulfido ligand lying perpendicular to the Mo-Mn bond. The bond distances are Mo-Mn = 2.8421(10) and 2.8914(5) A and S-S = 2.042(2) and 1.9973(10) A for 2 and 3, respectively. A tetranuclear metal side product CpMoMn(3)(CO)(13)(mu3-S)(mu4-S) (4) was also isolated from the reaction of 1 with [CpMo(CO)(3)](2). Compounds 2 and 3 react with CO to yield the dithiocarbonato complexes CpMoMn(CO)(5)[mu-SC(=O)S] (5) and Cp*MoMn(CO)(5)[mu-SC(=O)S] (6) by insertion of CO into the S-S bond. Similarly, tert-butylisocyanide was inserted into the S-S bond of 2 and 3 to yield the complexes CpMoMn(CO)(5)[mu-S(C=NBu(t))S] (7) and Cp*MoMn(CO)(5)[mu-S(C=NBu(t))S] (8), respectively. Ethylene and dimethylacetylene dicarboxylate also inserted into the S-S bond of 2 and 3 at room temperature to yield the ethanedithiolato ligand bridged complexes CpMoMn(CO)(5)(mu-SCH(2)CH(2)S) (9), Cp*MoMn(CO)(5)(mu-SCH(2)CH(2)S) (10), CpMoMn(CO)(5)[mu-SC(CO(2)Me)=C(CO(2)Me)S] (11), and Cp*MoMn(CO)(5)[mu-SC(CO(2)Me)=C(CO(2)Me)S] (12). Allene was found to insert into the S-S bond of 2 by using one of its two double bonds to yield the complex CpMoMn(CO)(5)[mu-SCH(2)C(=CH(2))S] (13). The molecular structures of the new complexes 2-7 and 9-13 were established by single-crystal X-ray diffraction analyses.     

Spectroscopic detection and theoretical confirmation of the role of Cr2(CO)5(C5R5)2 and .Cr(CO)2(ketene)(C5R5) as intermediates in carbonylation of N=N=CHSiMe3 to O=C=CHSiMe3 by .Cr(CO)3(C5R5) (R = H, CH3)

Conversion of N=N=CHSiMe3 to O=C=CHSiMe3 by the radical complexes .Cr(CO)3C5R5 (R = H, CH3) derived from dissociation of [Cr(CO)3(C5R5)]2 have been investigated under CO, Ar, and N2 atmospheres. Under an Ar or N2 atmosphere the reaction is stoichiometric and produces the Cr[triple bond]Cr triply bonded complex [Cr(CO)2(C5R5)]2. Under a CO atmosphere regeneration of [Cr(CO)3(C5R5)]2 (R = H, CH3) occurs competitively and conversion of diazo to ketene occurs catalytically as well as stoichiometrically. Two key intermediates in the reaction, .Cr(CO)2(ketene)(C5R5) and Cr2(CO)5(C5R5)2 have been detected spectroscopically. The complex .Cr(13CO)2(O=13C=CHSiMe3)(C5Me5) has been studied by electron spin resonance spectroscopy in toluene solution: g(iso) = 2.007; A(53Cr) = 125 MHz; A(13CO) = 22.5 MHz; A(O=13C=CHSiMe3) = 12.0 MHz. The complex Cr2(CO)5(C5H5)2, generated in situ, does not show a signal in its 1H NMR and reacts relatively slowly with CO. It is proposed to be a ground-state triplet in keeping with predictions based on high level density functional theory (DFT) studies. Computed vibrational frequencies are also in good agreement with experimental data. The rates of CO loss from 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)2(C5H5)]2 and CO addition to 3Cr2(CO)5(C5H5)2 producing 1[Cr(CO)3(C5H5)]2 have been measured by kinetics and show DeltaH approximately equal 23 kcal mol(-1) for both processes. Enthalpies of reduction by Na/Hg under CO atmosphere of [Cr(CO)n(C5H5)]2 (n = 2,3) have been measured by solution calorimetry and provide data for estimation of the Cr[triple bond]Cr bond strength in [Cr(CO)2(C5H5)]2 as 72 kcal mol(-1). The complex [Cr(CO)2(C5H5)]2 does not readily undergo 13CO exchange at room temperature or 50 degrees C implying that 3Cr2(CO)5(C5H5)2 is not readily accessed from the thermodynamically stable complex [Cr(CO)2(C5H5)]2. A detailed mechanism for metalloradical based conversion of diazo and CO to ketene and N2 is proposed on the basis of a combination of experimental and theoretical data.     

Metal carbonyls as pharmaceuticals? [Ru(CO)3Cl(glycinate)], a CO-releasing molecule with an extensive aqueous solution chemistry

The pharmacologically active [Ru(CO)(3)Cl(glycinate)] is shown to be in equilibrium with [Ru(CO)(2)(CO(2)H)Cl(glycinate)](-) (isomers) at around pH 3.1 which then at physiological pH reacts with more base to give [Ru(CO)(2)(CO(2))Cl(glycinate)](2-) (isomers) or [Ru(CO)(2)(CO(2)H)(OH)(glycinate)](-) (isomers). The ease with which [Ru(CO)(3)Cl(glycinate)] reacts with hydroxide results in it producing a solution in water with a pH of around 2 to 2.5 depending on concentration and making its solutions more acidic than those of acetic acid at comparable concentrations. Acidification of [Ru(CO)(3)Cl(glycinate)] with HCl gives [Ru(CO)(3)Cl(2)(NH(2)CH(2)CO(2)H)]. The crystal structures of [Ru(CO)(3)Cl(glycinate)] and [Ru(CO)(3)Cl(2)(NH(2)CH(2)CO(2)Me)] are reported.     

Penta- and hexaruthenium carbonyl 'raft' complexes supported by monocarborane cage ligands

Reaction between [PPh4][closo-4-CB8H9] and [Ru3(CO)12] in refluxing toluene affords the unprecedented hexaruthenium metallacarborane salt [PPh4][2,3,7-{Ru(CO)3}-2,6,11-{Ru(CO)3}-7,11,12-{Ru(CO)3}-3,6,12-(micro-H)3-2,2,7,7,11,11-(CO)6-closo-2,7,11,1-Ru3CB8H6] (1a), which contains a planar Ru6 'raft' supported by a {CB8} monocarborane cluster. Addition of [CuCl(PPh3)]4 and Tl[PF6] to a CH2Cl2 solution of 1a results in simple cation replacement, forming the analogous [Cu(PPh3)3]+ salt (1b). The phenyl-substituted monocarborane [NEt4][6-Ph-nido-6-CB9H11] reacts with [Ru3(CO)12] in refluxing 1,2-dimethoxyethane to afford the pentaruthenium cluster species [N(PPh3)2][2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (2), after addition of [N(PPh3)2]Cl. Treatment of 2 with [CuCl(PPh3)]4 and Tl[PF6] in CH2Cl2 forms the zwitterionic complex [10,12-{exo-Cu(PPh3)2}-2,3,7-{Ru(CO)3}-3,4,8-{Ru(CO)3}-7,8,10,12-(micro-H)4-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H4] (3). Substitution of CO by PPh3 with concomitant cation replacement occurs on introduction of [AuCl(PPh3)], Tl[PF6], and PPh3 to a CH2Cl2 solution of 2, forming [Au(PPh3)2][2,3,7-{Ru(CO)2PPh3}-3,4,8-{Ru(CO)2PPh3}-7,8-(micro-H)2-1-Ph-2,2,3,3,4,4-(CO)6-hypercloso-2,3,4,1-Ru3CB8H6] (4). Crystallographic studies confirmed the cluster architectures in 1b, 2, and 3.     

Synthesis, structure, and thermochemistry of the formation of the metal-metal bonded dimers [Mo(mu-TeAr)(CO)3(PiP3)]2 (Ar = phenyl, naphthyl) by phosphine elimination from *Mo(TePh)(CO)3(PiPr3)2

The complexes (*TeAr)Mo(CO)3(PiPr3)2 (Ar = phenyl, naphthyl; iPr = isopropyl) slowly eliminate PiPr3 at room temperature in a toluene solution to quantitatively form the dinuclear complexes [Mo(mu-TeAr)(CO)3(PiPr3)]2. The crystal structure of [Mo(mu-Te-naphthyl)(CO)3(PiPr3)]2 is reported and has a Mo-Mo distance of 3.2130 A. The enthalpy of dimerization has been measured and is used to estimate a Mo-Mo bond strength on the order of 30 kcal mol-1. Kinetic studies show the rate of formation of the dimeric chalcogen bridged complex is best fit by a rate law first order in (*TeAr)Mo(CO)3(PiPr3)2 and inhibited by added PiPr3. The reaction is proposed to occur by initial dissociation of a phosphine ligand and not by radical recombination of 2 mol of (*TeAr)Mo(CO)3(PiPr3)2. Reaction of (*TePh)Mo(CO)3(PiPr3)2, with L = pyridine (py) or CO, is rapid and quantitative at room temperature to form PhTeTePh and Mo(L)(CO)3(PiPr3)2, in keeping with thermochemical predictions. The rate of reaction of (*TeAr)W(CO)3(PiPr3)2 and CO is first-order in the metal complex and is proposed to proceed by the associative formation of the 19 e- radical complex (*TePh)W(CO)4(PiPr3)2 which extrudes a *TePh radical.     

Reactions of M(CO)5X (M = Mn, Re; X = Cl, Br) with (Ph2PCH2)3CCH3 (P3) and (Ph2P(CH2)2)3P (P3P'): synthetic, spectroscopic, electrochemical, and electrospray mass spectrometric studies

The reactions of M(CO)5X (M = Mn, Re; X = Cl, Br) with (Ph2PCH2)3CCH3 (P3) and (Ph2P(CH2)2)3P (P3P') are investigated, and the products are characterized by IR, NMR (31P and 13C), and electrospray mass spectrometric (ESMS) techniques. With P3, the major products are fac-M(CO)3(eta 2-P3)X (syn and anti isomers) and cis,fac-M(CO)2(eta 3-P3)X, and with P3P', the major product for each metal is cis,mer-M(CO)2(eta 3-P3P')X, but cis-[M(CO)2(eta 4-P3P')]X and fac-[Re(CO)3(eta 3-P3P')]X are also characterized. Addition of MeI to those complexes containing pendant phosphine groups produces the corresponding phosphonium cations without affecting the remainder of the molecule. On the voltammetric time scale, electrochemical oxidation of cis,fac-Mn(CO)2(eta 3-P3)X yields the corresponding 17e cation cis,fac-[Mn(CO)2(eta 3-P3)X]+, but on the longer time scale of exhaustive electrolysis or chemical oxidation, the product is fac-[Mn(CO)3(eta 3-P3)]+. In contrast, the rhenium cation cis,fac-[Re(CO)2(eta 3-P3)X]+ is stable on the synthetic time scale, but upon oxidation of cis,fac-Re(CO)2(eta 3-P3)X with NOBF4, the final product is the 18e [Re(CO)(NO)(eta 3-P3)X]+. cis,mer-Mn(CO)2(eta 3-P3P')X is reversibly oxidized to cis,mer-[Mn(CO)2(eta 3-P3P')X]+ on the voltammetric time scale, but on the longer synthetic time scale, the product isomerizes to trans-[Mn(CO)2(eta 3-P3P')X]+, which can be reduced to trans-Mn(CO)2(eta 3-P3P')X. Upon voltammetric oxidation, the corresponding rhenium complexes show an initial irreversible response associated with the pendant phosphine group prior to the reversible oxidation of the metal on the synthetic time scale; spectroscopic data indicate formation of cis,mer-Re(CO)2(eta 3-P3P'O)X. The complex cis,mer-[Re(CO)2(eta 3-P3P'Me)X]+ shows only the reversible metal oxidation response. ESMS data are obtained directly for the methylated cationic complexes, and neutral complexes are either oxidized or adducted with sodium ions to produce cationic species.     

Binuclear cyclopentadienylcobalt carbonyls: comparison with binuclear iron carbonyls

The binuclear cyclopentadienylcobalt carbonyls Cp2Co2(CO)n (n = 3, 2, 1; Cp = eta5-C5H5) are studied by density functional theory using the B3LYP and BP86 functionals. The experimentally known monobridged isomer Cp2Co2(CO)2(mu-CO) and the tribridged isomer Cp2Co2(mu-CO)3 of Cp2Co2(CO)3 with formal Co-Co single bonds are found to be similar in energy, with the precise relative energies of the two isomers depending on the functional chosen. For Cp2Co2(CO)2, the experimentally known coaxial isomer Cp2Co2(mu-CO)2 with two bridging CO groups and a formal Co=Co double bond (2.360 angstroms by B3LYP or 2.346 angstroms by BP86) is found to lie 38.2 (B3LYP) or 34.9 kcal/mol (BP86) below a perpendicular isomer perpendicular-Cp2Co2(CO)2. Similarly, for Cp2Co2(CO), the coaxial isomer Cp2Co2(mu-CO) with one bridging CO group and a formal CoCo triple bond (2.021 angstroms by B3LYP or 2.050 angstroms by BP86) is found to lie 9.36 (B3LYP) or 9.62 kcal/mol (BP86) below the corresponding perpendicular isomer perpendicular-Cp2Co2(CO). This coaxial isomer Cp2Co2(mu-CO) is a possible intermediate in the known pyrolysis of the trimer (eta5-C5H5)3Co3(mu-CO)3 to give the tetranuclear complex (eta5-C5H5)4Co4(mu3-CO)2. These optimized Cp2Co2(CO)n (n = 3, 2, 1) structures can be compared with the corresponding Fe2(CO)6+n structures since the CpCo and Fe(CO)3 groups are isolobal. In general, the metal-metal bonds are 0.09-0.22 angstroms shorter for the Cp2Co2(CO)n (n = 3, 2, 1) complexes than for the corresponding Fe2(CO)6+n complexes. For Fe2(CO)9, the experimentally well-known Fe2(CO)6(mu-CO)3 isomer is shown to be very close in energy to the unknown Fe2(CO)8(mu-CO) isomer, with the precise relative energies depending on the basis set used.     

Synthesis and properties of fac-Re(dmbpy)(CO)3CHO (dmbpy = 4,4'-dimethyl-2,2'-bipyridine), a possible intermediate in reductions of CO2 catalyzed by fac-Re(dmbpy)(CO)3Cl

Synthesis of fac-Re(dmbpy)(CO)3CHO 2 and its reactions with CO2 in DMF and DMSO have been conducted; 2 transfers hydride to CO2 to give Re(dmbpy)(CO)4+ OCHO- 5 which is rapidly transformed to fac-Re(dmbpy)(CO)3(OCHO) 3 in DMF, thus supporting the viability of 2 in photocatalytic reactions of fac-Re(dmbpy)(CO)3Cl with CO2.     

Forming trifluoromethylmetallates: competition between decarboxylation and C-F bond activation of group 11 trifluoroacetate complexes, [CF3CO2ML]-

A combination of gas-phase 3D quadrupole ion trap mass spectrometry experiments and density functional theory (DFT) calculations have been used to examine the mechanism of thermal decomposition of fluorinated coinage metal carboxylates. The precursor anions, [CF(3)CO(2)MO(2)CCF(3)](-) (M = Cu, Ag and Au), were introduced into the gas-phase via electrospray ionization. Multistage mass spectrometry (MS(n)) experiments were conducted utilizing collision-induced dissociation, yielding a series of trifluoromethylated organometallic species and fluorides via the loss of CO(2), CF(2) or "CF(2)CO(2)". Carboxylate ligand loss was insignificant or absent in all cases. DFT calculations were carried out on a range of potentially competing fragmentation pathways for [CF(3)CO(2)MO(2)CCF(3)](-), [CF(3)CO(2)MCF(3)](-) and [CF(3)CO(2)MF](-). These shed light on possible products and mechanisms for loss of "CF(2)CO(2)", namely, concerted or step-wise loss of CO(2) and CF(2) and a CF(2)CO(2) lactone pathway. The lactone pathway was found to be higher in energy in all cases. In addition, the possibility of forming [CF(3)MCF(3)](-) and [CF(3)MF](-), via decarboxylation is discussed. For the first time the novel fluoride complexes [FMF](-), M = Cu, Ag and Au have been experimentally observed. Finally, the decomposition reactions of [CF(3)CO(2)ML](-) (where L = CF(3) and CF(3)CO(2)) and [CH(3)CO(2)ML](-) (where L = CH(3) and CH(3)CO(2)) are compared.     

Mononuclear and dinuclear complexes with a [Ru(tBu2PCH2CH2PtBu2)(CO)] core

Thermolysis of solid [Ru(d(t)bpe)(CO)2Cl2](2, d(t)bpe =(t)Bu2PCH2CH2P(t)Bu2) under vacuum affords the five-coordinate complex [Ru(d(t)bpe)(CO)Cl2] (4), which was shown by X-ray crystallography to contain a weak remote agostic interaction. In solution, 4 can be readily trapped by CO, CH3CN or water to give [Ru(d(t)bpe)(CO)(L)Cl2](L = CO, 2; L = CH3CN, 6; L = H2O, 7). Reaction of 4 with AgOTf/H2O yields the tris-aqua complex [Ru(d(t)bpe)(CO)(H2O)3](OTf)2 (8), which has been structurally characterised and probed in solution by pulsed-gradient spin echo (PGSE) NMR spectroscopy. The water ligands in 8 are labile and easily substituted to give [Ru(d(t)bpe)(CO)(NCCH3)3](OTf)2 (10) and [Ru(d(t)bpe)(CO)(DMSO)3](OTf)2 (11). In the presence of CO, the tris-aqua complex undergoes water-gas shift chemistry with formation of the cationic hydride species [Ru(d(t)bpe)(CO)3H](OTf) (12) and CO2. X-Ray crystal structures of complexes 2, 4, 6, 8 and 11-12 are reported along with those for [{Ru(d(t)bpe)(CO)}2(mu-Cl)2(mu-OTf)](OTf) (3), [{Ru(d(t)bpe)(CO)}2(mu-Cl)3][Ru(d(t)bpe)(CO)Cl3](5) and [Ru(d(t)bpe)(CO)(H2O)2(OTf)](OTf)(9).     

Weakly coordinating anions HA2-generated from oxoanions A- and their conjugate acids. Coordination equilibria,ionic conductivities,and the structures of [Cu2(H(CH3SO3)2)4]n and [Cu(CO)(H(CF3CO2)2)]2

The coordination or ion pairing of the hydrogen-bonded anions H(CF3CO2)2- and H(CH3SO3)2- to NEt4+, Li+, Cu+, and/or Cu2+ was investigated. The structure of [Cu2(H(CH3SO3)2)4]n consists of centrosymmetric dimeric moieties that contain two homoconjugated (CH3SO2O-H...OSO2CH3)- anions per Cu2+ ion, forming typical Jahn-Teller tetragonally elongated CuO6 coordination spheres. The oxygen atoms involved in the nearly linear O-H...O hydrogen bonds (O...O approximately 2.62 A) are not coordinated to the Cu2+ ions. The structure of Cu2(CO)2(H(CF3-CO2)2)2 consists of pseudo-C2-symmetric dimers that contain one homoconjugated (CF3COO-H...OCOCF3)- anion per Cu+ ion, forming highly distorted tetrahedral Cu(CO)O3 coordination spheres. Three of the four oxygen atoms in each hydrogen-bonded H(CF3CO2)2- anion are coordinated to the Cu+ ions, including one of the oxygen atoms in each O-H...O hydrogen bond (O...O approximately 2.62 A). Infrared spectra (v(CO) values) of Cu(CO)(CF3CO2) or Cu(CO)(CH3SO3) dissolved in acetonitrile or benzene, with and without added CF3COOH or CH3SO3H, respectively, demonstrate that HA2- anions involving carboxylates or sulfonates are more weakly coordinating than the parent anions RCO2- and RSO3-. Direct current conductivities of THF solutions of Li(CF3CO2) containing varying concentrations of added CF3COOH further demonstrate that Li+ and NEt4+ ion pair much more weakly with H(CF3CO2)2- than with CF3CO2-.     

Chelate control of diiron(I) dithiolates relevant to the [Fe-Fe]- hydrogenase active site

The reaction of Fe2(S2C2H4)(CO)6 with cis-Ph2PCH=CHPPh2 (dppv) yields Fe2(S2C2H4)(CO)4(dppv), 1(CO)4, wherein the dppv ligand is chelated to a single iron center. NMR analysis indicates that in 1(CO)4, the dppv ligand spans axial and basal coordination sites. In addition to the axial-basal isomer, the 1,3-propanedithiolate and azadithiolate derivatives exist as dibasal isomers. Density functional theory (DFT) calculations indicate that the axial-basal isomer is destabilized by nonbonding interactions between the dppv and the central NH or CH2 of the larger dithiolates. The Fe(CO)3 subunit in 1(CO)4 undergoes substitution with PMe3 and cyanide to afford 1(CO)3(PMe3) and (Et4N)[1(CN)(CO)3], respectively. Kinetic studies show that 1(CO)4 reacts faster with donor ligands than does its parent Fe2(S2C2H4)(CO)6. The rate of reaction of 1(CO)4 with PMe3 was first order in each reactant, k = 3.1 x 10(-4) M(-1) s(-1). The activation parameters for this substitution reaction, DeltaH = 5.8(5) kcal/mol and DeltaS = -48(2) cal/deg.mol, indicate an associative pathway. DFT calculations suggest that, relative to Fe2(S2C2H4)(CO)6, the enhanced electrophilicity of 1(CO)4 arises from the stabilization of a "rotated" transition state, which is favored by the unsymmetrically disposed donor ligands. Oxidation of MeCN solutions of 1(CO)3(PMe3) with Cp2FePF6 yielded [Fe2(S2C2H4)(mu-CO)(CO)2(dppv)(PMe3)(NCMe)](PF6)2. Reaction of this compound with PMe3 yielded [Fe2(S2C2H4)(mu-CO)(CO)(dppv)(PMe3)2(NCMe)](PF6)2.     

Reactivity of molybdenum and rhenium hydroxo-carbonyl complexes toward organic electrophiles

The hydroxo compounds [Re(OH)(CO)(3)(N-N)] (N-N=bipy, 2 a; Me(2)-bipy, 2 b) were prepared in a biphasic H(2)O/CH(2)Cl(2) medium by reaction of [Re(OTf)(CO)(3)(N-N)] with KOH. In contrast, when anhydrous CH(2)Cl(2) was used, the binuclear hydroxo-bridged compound [[Re(CO)(3)(bipy)](2)(mu-OH)]OTf (3-OTf) was obtained. Compound [Re(OH)(CO)(3)(Me(2)-bipy)] (2 b) reacted with phenyl acetate or vinyl acetate to afford [Re(OAc)(CO)(3)(Me(2)-bipy)] (4) and phenol or acetaldehyde, respectively. The reactions of [Mo(OH)(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (1), 2 a, and 2 b toward several unsaturated organic electrophiles were studied. The reaction of 1 with (p-tolyl)isocyanate afforded an adduct of N,N'-di(p-tolyl)urea and the carbonato-bridged compound [[Mo(eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)](2)(mu-eta(1)(O),eta(1)(O)-CO(3))] (5). In contrast, the reaction of 2 a with phenylisocyanate afforded [Re(OC(O)NHPh)(CO)(3)(bipy)] (6); this results from formal PhNCO insertion into the O-H bond. On the other hand, compounds [Mo[SC(O)NH(p-tolyl)](eta(3)-C(3)H(4)-Me-2)(CO)(2)(phen)] (7), [Re[SC(O)NH(p-tolyl)](CO)(3)(Me(2)-bipy)] (8 a), and [Re[SC(O)NHEt](CO)(3)(Me(2)-bipy)] (8 b) were obtained by reaction of 1 or 2 b with the corresponding alkyl or aryl isothiocyanates. In those cases, RNCS was inserted into the M-O bond. The reactions of 1, 2 a, and 2 b with dimethylacetylenedicarboxylate (DMAD) gave the complexes [Mo[C(OH)-C(CO(2)Me)C(CO(2)Me)-O](eta(3)-C(3)H(4)-Me-2)(CO)(phen)] (9) and [Re[C(OH)C(CO(2)Me)C(CO(2)Me)O](CO)(2)(N-N)] (N-N=bipy, 10 a; Me(2)-bipy, 10 b). The molecules of these compounds contain five-membered metallacycles that are the result of coupling between the hydroxo ligand, DMAD, and one of the CO ligands. The new compounds were characterized by a combination of IR and NMR spectroscopy, and for [[Re(CO)(3)(bipy)(2)(mu-OH)]BF(4) (3-BF(4)), 4, 5, 6, 7, 8 b, 9, and 10 b, also by means of single-crystal X-ray diffraction.     

Nickel-manganese sulfido carbonyl cluster complexes. synthesis, structure, and properties of the unusual paramagnetic complexes Cp2Ni2Mn(CO)3(mu 3-E)2, E = S, Se

The reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) yielded the paramagnetic new compound Cp(2)Ni(2)Mn(CO)(3)(mu(3)-S)(2) (1) and a new hexanuclear metal product Cp(2)Ni(2)Mn(4)(CO)(14)(mu(6)-S(2))(mu(3)-S)(2) (2). Structurally, compound 1 contains two triply bridging sulfido ligands on opposite sides of an open Ni(2)Mn triangular cluster. EPR and temperature-dependent magnetic susceptibility measurements of 1 show that it contains one unpaired electron. The electronic structure of 1 was determined by Fenske-Hall molecular orbital calculations which show that the unpaired electron occupies a low lying antibonding orbital delocalized unequally across the three metal atoms. The selenium homologue Cp(2)Ni(2)Mn(CO)(3)(mu(3)-Se)(2) (3) was obtained from the reaction of a mixture of Mn(2)(CO)(10) and [CpNi(CO)](2) with elemental selenium and Me(3)NO.2H(2)O. It also has one unpaired electron. Compound 1 reacted with elemental sulfur to yield the dinickeldimanganese compound, Cp(2)Ni(2)Mn(2)(CO)(6)(mu(4)-S(2))(mu(4)-S(5)), 4, which can also be made from the reaction of Mn(2)(CO)(7)(mu-S(2)) with [CpNi(CO)](2) and sulfur. Compound 4 was converted back to 1 by sulfur abstraction using PPh(3). The reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) in the presence of thiirane yielded the ethanedithiolato compound CpNiMn(CO)(3)(mu-SCH(2)CH(2)S) (5), which was also obtained from the reaction of Mn(4)(CO)(15)(mu(3)-S(2))(mu(4)-S(2)) with [CpNi(CO)](2) in the presence of thiirane. Compound 5 reacted with additional quantities of thiirane to yield the new compound CpNiMn(CO)(3)[mu-S(CH(2)CH(2)S)(2)], 6, which contains a 3-thiapentanedithiolato ligand that bridges the two metal atoms. Compound 6 was also obtained from the reaction of Mn(2)(CO)(10) with [CpNi(CO)](2) and thiirane. The molecular structures of the new compounds 1-6 were established by single-crystal X-ray diffraction analyses.     

Synthetic and structural studies on [Fe2(SR)2(CN)x(CO)6-x](x-) as active site models for Fe-only hydrogenases.

A series of models for the active site (H-cluster) of the iron-only hydrogenase enzymes (Fe-only H2-ases) were prepared. Treatment of MeCN solutions of Fe2(SR)2(CO)6 with 2 equiv of Et4NCN gave [Fe2(SR)2(CN)2(CO)4](2-) compounds. IR spectra of the dicyanides feature four nu(CO) bands between 1965 and 1870 cm(-1) and two nu(CN) bands at 2077 and 2033 cm(-1). For alkyl derivatives, both diequatorial and axial-equatorial isomers were observed by NMR analysis. Also prepared were a series of dithiolate derivatives (Et4N)2[Fe2(SR)2(CN)2(CO)4], where (SR)2 = S(CH2)2S, S(CH2)3S. Reaction of Et4NCN with Fe2(S-t-Bu)2(CO)6 gave initially [Fe2(S-t-Bu)2(CN)2(CO)4](2-), which comproportionated to give [Fe2(S-t-Bu)2(CN)(CO)5](-). The mechanism of the CN(-)-for-CO substitution was probed as follows: (i) excess CN(-) with a 1:1 mixture of Fe2(SMe)2(CO)6 and Fe2(SC6H4Me)2(CO)6 gave no mixed thiolates, (ii) treatment of Fe2(S2C3H6)(CO)6 with Me3NO followed by Et4NCN gave (Et4N)[Fe2(S2C3H6)(CN)(CO)5], which is a well-behaved salt, (iii) treatment of Fe2(S2C3H6)(CO)6 with Et4NCN in the presence of excess PMe3 gave (Et4N)[Fe2(S2C3H6)(CN)(CO)4(PMe3)] much more rapidly than the reaction of PMe3 with (Et4N)[Fe2(S2C3H6)(CN)(CO)5], and (iv) a competition experiment showed that Et4NCN reacts with Fe2(S2C3H6)(CO)6 more rapidly than with (Et4N)[Fe2(S2C3H6)(CN)(CO)5]. Salts of [Fe2(SR)2(CN)2(CO)4](2-) (for (SR)2 = (SMe)2 and S2C2H4) and the monocyanides [Fe2(S2C3H6)(CN)(CO)5](-) and [Fe2(S-t-Bu)2(CN)(CO)5](-) were characterized crystallographically; in each case, the Fe-CO distances were approximately 10% shorter than the Fe-CN distances. The oxidation potentials for Fe2(S2C3H6)(CO)4L2 become milder for L = CO, followed by MeNC, PMe3, and CN(-); the range is approximately 1.3 V. In water,oxidation of [Fe2(S2C3H6)(CN)2(CO)4](2-) occurs irreversibly at -0.12 V (Ag/AgCl) and is coupled to a second oxidation.     

Rhenium-mediated coupling of acetonitrile and pyrazoles. New molecular clefts for anion binding

The reaction of fac-[ReBr(CO)3(NCMe)2] (1) with either pyrazole (Hpz) or 3,5-dimethylpyrazole (Hdmpz) in a 1:2 Re/pyrazole ratio affords the known complexes fac-[ReBr(CO)3(Hpz)2] (2) and [ReBr(CO)3(Hdmpz)2] (3). Using a 1:1 ratio, MeCN as solvent, and longer reaction times led to a mixture in which the major components are the pyrazolylamidino complexes fac-[ReBr(CO)3(HN=C(CH3)pz-kappa2N,N)] (4) and fac-[ReBr(CO)3(HN=C(CH3)dmpz-kappa2N,N)] (5). The complexes fac-[ReBr(CO)3(Hpz)(NCMe)] (6) and fac-[ReBr(CO)3(Hdmpz)(NCMe)] (7) (along with 2 and 3) were found to be minor components of these reactions. Analogous reactions of fac-[Re(OClO3)(CO)3(NCMe)2] yielded fac-[Re(NCCH3)(CO)3(HN=C(CH3)pz-kappa2N,N)]ClO4 (8), fac-[Re(NCCH3)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]ClO4 (9), fac-[Re(Hpz)(CO)3(HN=C(CH3)pz-kappa2N,N)]ClO4 (10), and fac-[Re(Hdmpz)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]ClO4 (11). The X-ray structure of 11 showed the perchlorate anion to be hydrogen-bonded by the N-H groups of the pyrazole and pyrazolylamidino ligands. The behavior of the compound fac-[Re(Hdmpz)(CO)3(HN=C(CH3)dmpz-kappa2N,N)]BAr'4 (13) (synthesized by reaction of [ReBr(CO)3(Hdmpz)2] (3) with (i) AgOTf and (ii) NaBAr'(4)/MeCN) as an anion receptor has been studied in CD3CN solution. In addition, the structure of the supramolecular adduct fac-[Re(CO)3(Hdmpz)(HN=C(CH3)dmpz-kappa2N,N)].Cl (14), featuring chloride binding by the two N-H groups, was determined by X-ray diffraction.