X-ray crystal structure of (eta(5)-pentaphenylcyclopentadienyl)[1-(eta(5/6)-phenyl)-2,3,4,5-tetraphenylcyclopentadienyl]iron(II), [Fe(eta(5)-C(5)Ph(5))[(eta(5/6)-C(6)H(5))C(5)Ph(4)]], a linkage isomer of decaphenylferrocene

Very dark blue prismatic crystals of [Fe(eta(5)-C(5)Ph(5))[(eta(5/6)-C(6)H(5))(C(5)Ph(4))]], the linkage isomer of decaphenylferrocene, were grown from (3:1 v/v) hexane/ethyl acetate and characterized by single-crystal X-ray diffraction (space group P2(1)/n, R1(F) 0.0404). The iron atom is coordinated to two C(5)Ph(5) ligands: one with an eta(5)-C(5)-configuration and the other with a coordinated arene configuration. The phenyl groups of the (eta(5)-C(5)Ph(5)) ligand are oriented in a "paddle-wheel" arrangement about the C(5) ring, with which four of them make an average angle of approximately 53 degrees, the other, an angle of approximately 42 degrees. The coordinated C(6)H(5) ring of the other ligand is inclined at only approximately 5 degrees to the uncoordinated C(5) ring, with which three of the other four phenyl rings make an average angle of approximately 64 degrees, and the other (opposite the coordinated arene ring), an angle of 38 degrees.     

Reaction of nido-7,8-C(2)B(9)H(13) with Dicobalt Octacarbonyl: Crystal Structures of the Complexes [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)], [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)], and [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))

The compounds [Co(2)(CO)(8)] and nido-7,8-C(2)B(9)H(13) react in CH(2)Cl(2) to give a complex mixture of products consisting primarily of two isomers of the dicobalt species [Co(2)(CO)(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (1), together with small amounts of a mononuclear cobalt compound [Co(CO)(2)(eta(5)-10-CO-7,8-C(2)B(9)H(10))] (5) and a charge-compensated carborane nido-9-CO-7,8-C(2)B(9)H(11) (6). In solution, isomers 1a and 1b slowly equilibrate. However, column chromatography allows a clean separation of 1a from the mixture, and a single-crystal X-ray diffraction study revealed that each metal atom is ligated by a terminal CO molecule and in a pentahapto manner by a nido-C(2)B(9)H(11) cage framework. The two Co(CO)(eta(5)-7,8-C(2)B(9)H(11)) units are linked by a Co-Co bond [2.503(2) ?], which is supported by two three-center two-electron B-H right harpoon-up Co bonds. The latter employ B-H vertices in each cage which lie in alpha-sites with respect to the carbons in the CCBBB rings bonded to cobalt. Addition of PMe(2)Ph to a CH(2)Cl(2) solution of a mixture of the isomers 1, enriched in 1b, gave isomers of formulation [Co(2)(CO)(PMe(2)Ph)(eta(5)-7,8-C(2)B(9)H(11))(2)] (2). Crystals of one isomer were suitable for X-ray diffraction. The molecule 2a has a structure similar to that of 1a but differs in that whereas one B-H right harpoon-up Co bridge involves a boron atom in an alpha-site of a CCBBB ring coordinated to cobalt, the other uses a boron atom in the beta-site. Reaction between 1b and an excess of PMe(2)Ph in CH(2)Cl(2) gave the complex [CoCl(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))] (3), the structure of which was established by X-ray diffraction. Experiments indicated that 3 was formed through a paramagnetic Co(II) species of formulation [Co(PMe(2)Ph)(2)(eta(5)-7,8-C(2)B(9)H(11))]. Addition of 2 molar equiv of CNBu(t) to solutions of either 1a or 1b gave a mixture of two isomers of the complex [Co(2)(CNBu(t))(2)(eta(5)-7,8-C(2)B(9)H(11))(2)] (4). NMR data for the new compounds are reported and discussed.     

Synthesis,structure, and dissociation equilibrium of [Co(eta5-C5H5)(Se2C6H4)]2, a novel metalladiselenolene complex

A (phenylenediselenolato)cobalt complex dimer, [Co(eta(5)-C(5)H(5))(Se(2)C(6)H(4))](2) (1), was synthesized by a reaction of carbonyl(eta(5)-cyclopentadienyl)diiodocobalt(III) ([Co(eta(5)-C(5)H(5))I(2)(CO)]) with poly(o-diselenobenzene). The structure of 1, determined by single-crystal X-ray crystallography, was found to be located in the space group of P2(1)/c (No. 14), with a = 9.3346(5) A, b = 11.6477(9) A, c = 10.2179(5) A, beta = 111.491(1) degrees, and Z = 2. Covalent Co-Se bonds bridge the metal centers. In solution, dimers and monomers coexist at equilibrium. The dissociation equilibrium constant of 1 in solution was evaluated by (1)H NMR spectra at several temperatures between 20 and 80 degrees C. Dissociation enthalpies/entropies were found to be 50/110, 60/120, and 88 kJ mol(-1)/200 J K(-1) mol(-1) in dimethyl sulfoxide-d(6), benzene-d(6), and chloroform-d(1), respectively.     

Coordination chemistry of a kinetically stabilized germabenzene: syntheses and properties of stable eta6-germabenzene complexes coordinated to transition metals

The first stable eta6-germabenzene complexes, that is, [M(CO)3(eta6-C5H5GeTbt)] {M=Cr (2), Mo (3), and W (4); Tbt=2,4,6-tris[bis(trimethylsilyl)methyl]phenyl}, have been synthesized by ligand-exchange reactions between [M(CO)3(CH3CN)3] (M=Cr, Mo, and W) and the kinetically stabilized germabenzene 1 and characterized by 1H and 13C NMR, IR, and UV/Vis spectroscopy. In the 1H and 13C NMR spectra of 2-4, all of the signals for the germabenzene rings were shifted upfield relative to their counterparts in the free germabenzene 1. X-ray crystallographic analysis of 2 and 4 revealed that the germabenzene ligand was nearly planar and was coordinated to the M(CO)3 group (M=Cr, W) in an eta6 fashion. The formation of complexes 2-4 from germabenzene 1 should be noted as the application of germaaromatics as 6pi-electron ligands toward complexation with Group 6 metals. On the other hand, treatment of 1 with [{RuCp*Cl}4] (Cp*=C5Me5) in THF afforded a novel eta5-germacyclohexadienido complex of ruthenium-[RuCp*{eta5-C5H5GeTbt(Cl)}] (9)-instead of the expected eta6-germabenzene-ruthenium cationic complex [RuCp*{eta6-C5H5GeTbt}]Cl (10). Crystallographic structural analysis of 9 showed that the five carbon atoms of the germacyclohexadienido ligand of 9 were coordinated to the Ru center in an eta5 fashion.     

Structural isomers of aryl-substituted eta(3)-propargyl complexes: eta(2)-1-Metalla(methylene)cyclopropene and eta(3)-benzyl complexes

Hydride abstraction from C(5)Me(5)(CO)(2)Re(eta(2)-PhC triple bond CCH(2)Ph) (1) gave a 3:1 mixture of eta(3)-propargyl complex [C(5)Me(5)(CO)(2)Re(eta(3)-PhCH-C triple bond CPh)][BF(4)] (5) and eta(2)-1-metalla(methylene)cyclopropene complex [C(5)Me(5)(CO)(2)Re(eta(2)-PhC-C=CHPh)][BF(4)] (6). Observation of the eta(2)-isomer requires 1,3-diaryl substitution and is favored by electron-donating substituents on the C(3)-aryl ring. Interconversion of eta(3)-propargyl and eta(2)-1-metalla(methylene)cyclopropene complexes is very rapid and results in coalescence of Cp (1)H NMR resonances at about -50 degrees C. Protonation of the alkynyl carbene complex C(5)Me(5)(CO)(2)Re=C(Ph)C triple bond CPh (22) gave a third isomer, the eta(3)-benzyl complex [C(5)Me(5)(CO)(2)Re[eta(3)(alpha,1,2)-endo,syn-C(6)H(5)CH(C triple bond CC(6)H(5))]][BF(4)] (23) along with small amounts of the isomeric complexes 5 and 6. While 5 and 6 are in rapid equilibrium, there is no equilibration of the eta(3)-benzyl isomer 23 with 5 and 6.     

On the origin of dinitrogen hydrogenation promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2)

The origin of the hydrogenation of the dinitrogen ligand in [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) has been investigated by a combined computational and experimental study. Density functional theory calculations on the zirconocene dinitrogen complex demonstrate significant imido character in the zirconium nitrogen bonds, arising from effective pi-back-bonding from the low-valent zirconium and the side-on bound N2 ligand. The twisted ground-state structure of the N2 complex is a key requirement for nitrogen hydrogenation, as calculations on the model complex [(eta5-C5H5)2Zr]2(mu2,eta2,eta2-N2) reveal reduced overlap as the dihedral angle between the zirconocene wedges approaches 0 degrees . Experimentally, isotopic labeling studies on the microscopic reverse are consistent with a 1,2-addition mechanism for nitrogen hydrogenation.     

Unexpected coupling between an eta5-indenyl ligand and alkenyl-vinylidene fragments: synthesis of unprecedented (eta6-indene)ruthenium(II) metallacycles

Vinylidene complexes [Ru[=C=C(H)CR1R2CH2C(Me)=CH2](eta5-C9H7)(PPh3)2][BF4] undergo an intramolecular coupling between the alkenyl-vinylidene fragment and the eta5-indenyl ligand to afford indene-metallacyclic compounds (6a,b) in which the resulting functionalised indene group is eta6-coordinated to the metal.     

Dinitrogen functionalization with terminal alkynes, amines, and hydrazines promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2): observation of side-on and end-on diazenido complexes in the reduction of N2 to hydrazine

Functionalization of the N2 ligand in the side-on bound dinitrogen complex, [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2), has been accomplished by addition of terminal alkynes to furnish acetylide zirconocene diazenido complexes, [(eta5-C5Me4H)2Zr(C[triple bond]CR)]2(mu2,eta2,eta2-N2H2) (R = nBu, tBu, Ph). Characterization of [(eta5-C5Me4H)2Zr(C[triple bond]CCMe3)]2(mu2,eta2,eta2-N2H2) by X-ray diffraction revealed a side-on bound diazenido ligand in the solid state, while variable-temperature 1H and 15N NMR studies established rapid interconversion between eta1,eta1 and eta2,eta2 hapticity of the [N2H2]2- ligand in solution. Synthesis of alkyl, halide, and triflato zirconocene diazenido complexes, [(eta5-C5Me4H)2ZrX]2(mu2,eta1,eta1-N2H2) (X = Cl, I, OTf, CH2Ph, CH2SiMe3), afforded eta1,eta1 coordination of the [N2H2]2- fragment both in the solid state and in solution, demonstrating that sterically demanding, in some cases pi-donating, ligands can overcome the electronically preferred side-on bonding mode. Unlike [(eta5-C5Me4H)2ZrH]2(mu2,eta2,eta2-N2H2), the acetylide and alkyl zirconocene diazenido complexes are thermally robust, resisting alpha-migration and N2 cleavage up to temperatures of 115 degrees C. Dinitrogen functionalization with [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) was also accomplished by addition of proton donors. Weak Br?nsted acids such as water and ethanol yield hydrazine and (eta5-C5Me4H)2Zr(OH)2 and (eta5-C5Me4H)2Zr(OEt)2, respectively. Treatment of [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) with HNMe2 or H2NNMe2 furnished amido or hydrazido zirconocene diazenido complexes that ultimately produce hydrazine upon protonation with ethanol. These results contrast previous observations with [(eta5-C5Me5)2Zr(eta1-N2)]2(mu2,eta1,eta1-N2) where loss of free dinitrogen is observed upon treatment with weak acids. These studies highlight the importance of cyclopentadienyl substituents on transformations involving coordinated dinitrogen.     

Novel organometallic building blocks for molecular crystal engineering. Part 4. Synthesis and characterization of mono- and bis-amido derivatives of [Co(III)(eta5-C5H4COOH)2]+ and their utilization as ligands

The synthesis and structural characterization of the hexafluorophosphate salts of the substituted bis-amido molecular complexes [Co(III)(eta5-C5H4CONHC4H3N2)2]+ (1), [Co(III)(eta5-C5H4CONHCH2C5H4N)2]+ (2), [Co(III)(eta5-C5H4CON(C5H4N)2)2]+ (3), and of the amido-carboxyl complexes [Co(III)(eta5-C5H4CON(C5H4N)2)(eta5-C5H4COOH)]+ (4), and [Co(III)(eta5-C5H4CONHC2N3(C5H4N)2)(eta5-C5H4COOH)]+ (5) are reported. The pyridyl and pyrazine substituted amido ligands on the sandwich cores have been chosen because they allow both coordination to metal centres and participation in hydrogen bonding. The hydrogen bonding interactions established by the family of complexes in the solid state has been investigated. The utilization of complex 5 for the preparation of the complex of complexes[Cd(NO3)2{Co(III)(eta5-C5H4CONHC2N3(C5H4N)(C5H4NH))(eta5-C5H4COOH)}2]6+ (6) is reported as a first example of the potential of the substituted mono-and bis-amides as ligands. The isolation and structural characterization of the carbonyl chloride cation [Co(III)(eta5-C5H4COCl)2]+ (7) as its tetrachloro cobaltate anion salt is also described.     

Multifunctional behavior by a Bis-(phosphinimino)methanide ligand: eta 2- vs eta 3-coordination vs Bronsted basicity

The reaction of [(Cymene)RuCl2]2 with the chelate LiHC(PPh2NPh)2 occurs to remove both chloride ligands, to furnish a cationic Ru(II) complex with the monoanionic ligand bound eta3, through two N and an sp3 carbon. This cation is also produced from the conjugate acid of the ligand H2C(PPh2NPh)2 because this molecule can serve as a Br?nsted base, to deprotonate the acidic carbon of another molecule of H2C(PPh2NPh)2. DFT calculations show an energy surface where (Cymene)RuHC(PPh2NPh)2L is more stable with a Ru-CH(PPh2NPh)2 bond and with L = Cl- or MeCN not coordinated to Ru, than to an eta2-HC(PPh2NPh)2 structure with coordinated L; this is tested experimentally. The greater tendency for this ligand to be coordinated eta3 vs analogous diketiminates is discussed. The nucleophilicity of Cgamma in structure 1, vs that of donors L = Cl- or MeCN, is evaluated to understand the preference of the bis(phosphinimino)methanide to be bidentate or tridentate.     

Synthesis and selectivity in the formation of cyclophosphazene-derived 1,3-cyclohexadienes from reactions of RCpCo(COD) [R = MeOC(O)] with alkynes and alkenes

The first examples of mono and bisfluorophosphazene derived [eta (5)-cyclopentadienyl] [eta (4)-1,3-cyclohexadiene] cobalt complexes have been prepared along with the sandwich compound [eta (5)-carbomethoxycyclopentadienyl] [eta (4)-1,3-bis(pentafluorocyclotriphosphazenyl)-2,4-diphenylcyclobutadiene] cobalt and acetylene trimerized products from the reactions of [eta (5)-MeOC(O)C 5H 4]Co[COD], PhCCP 3N 3F 5 and phenylacetylene in the presence or absence of an additional cycloalkene or indene. Formation of these mono and bis fluorophosphazene derived cobalt cyclohexadiene complexes provide experimental evidence for a metallacyclopentadiene pathway for cyclohexadiene formation in CpCo catalyzed reactions. Selectivity is also observed in the formation of bisfluorophosphazene derived cyclohexadienes which stems from the fact that two P 3N 3F 5 units cannot be accommodated on vicinal carbon atoms of a carbacycle or metallacycle. Interestingly, reactions of (beta-phenylethynyl)pentafluorobenzene with [eta (5)-MeOC(O)C 5H 4]Co[COD] in the presence and absence of external cycloalkene under identical reaction conditions yielded only the cis and trans isomers of the metallocene [eta (5)-MeOC(O)C 5H 4]Co[eta (4)-C 4Ph 2(C 6F 5) 2] along with alkyne trimerized product indicating that the selectivity in cyclohexadiene formation is governed more by steric than electronic factors. All the new compounds were characterized by (1)H, (13)C, (31)P, and (19)F NMR as well as mass spectrometry and elemental analysis. Mono and bispentafluorocyclotriphosphazene derived [eta (5)-cyclopentadienyl] [eta (4)-1,3-cyclohexadiene] cobalt complexes and [eta (5)-carbomethoxycyclopentadienyl] [eta (4)-bis(1,3-pentafluorophenyl)-2,4-diphenylcyclobutadiene] cobalt have also been structurally characterized by single crystal X-ray analysis.     

Syntheses,reactivity, and crystal structures of molybdenum complexes with pyridine-2-thionate (pyS)-containing ligands: crystal structures of [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2), exo-[Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-dppe)], [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)], and [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)

The doubly bridged pyridine-2-thionate (pyS) dimolybdenum complex [Mo(eta(3)-C(3)H(5))(CO)(2)](2)(mu-eta(1),eta(2)-pyS)(2) (1) is accessible by the reaction of [Mo(eta(3)-C(3)H(5))(CO)(2)(CH(3)CN)(2)Br] with pySK in methanol at room temperature. Complex 1 reacts with piperidine in acetonitrile to give the complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(2)-pyS)(C(5)H(10)NH)] (2). Treatment of 1 with 1,10-phenanthroline (phen) results in the formation of complex [Mo(eta(3)-C(3)H(5))(CO)(2)(eta(1)-pyS)(phen)] (3), in which the pyS ligand is coordinated to Mo through the sulfur atom. Four conformational isomers, endo,exo-complexes [Mo(eta(3)-C(3)H(5))(CO)(eta(2)-pyS)(eta(2)-diphos)] (diphos = dppm, 4a-4d; dppe, 5a-5d), are accessible by the reactions of 1 with dppm and dppe in refluxing acetonitrile. Homonuclear shift-correlated 2-D (31)P((1)H)-(31)P((1)H) NMR experiments of the mixtures 4a-4d have been employed to elucidate the four stereoisomers. The reaction of 4 and pySK or [Mo(CO)(3)(eta(1)-SC(5)H(4)NH)(eta(2)-dppm)] (6) and O(2) affords allyl-displaced seven-coordinate bis(pyridine-2-thionate) complex [Mo(CO)(eta(2)-pyS)(2)(eta(2)-dppm)] (7). All of the complexes are identified by spectroscopic methods, and complexes 1, 5d, 6, and 7 are determined by single-crystal X-ray diffraction. Complexes 1 and 5d crystallize in the orthorhombic space groups Pbcn and Pbca with Z = 4 and 8, respectively, whereas 6 belongs to the monoclinic space group C2/c with Z = 8 and 7 belongs to the triclinic space group Ponemacr; with Z = 2. The cell dimensions are as follows: for 1, a = 8.3128(1) A, b = 16.1704(2) A, c = 16.6140(2) A; for 5d, a = 17.8309(10) A, b = 17.3324(10) A, c = 20.3716(11) A; for 6, a = 18.618(4) A, b = 16.062(2) A, c = 27.456(6) A, beta = 96.31(3) degrees; for 7, a = 9.1660(2) A, b = 12.0854(3) A, c = 15.9478(4) A, alpha = 78.4811(10) degrees, beta = 80.3894(10) degrees, gamma = 68.7089(11) degrees.     

[Co_3(1,2-S2C6H4)_3(PPh_3)_3]+, A basic triangle unit of some polynuclear molecules

[Co3(1,2-S2C6H4)3(PPh3)3][CoBr3(DMF)].sol (1, sol=CHCl3,O(C2H5)2,H2O) was obtained from the reaction of CoBr(PPh3)3 with Na2(S2C6H4) in chloroform. The Co3 core in the cation of 1 exhibits a metal-metal bonded isosceles triangle, in which the two longer Co-Co bonds are both bridged by S2C6H4 ligands on two sides of the triangle plane respectively, while the bottom short Co-Co bond is bridged by the third bidentate S2C6H4 ligand. A series of polynu-clear cobalt cluster compounds with phosphine, thiolate and/or sulphur ligands were prepared by low oxidation state Co+ with thiolates in organic solvents. These tri-, tetra-, hexa-, heptanuclear cluster compounds 1-8 with various types of crystal structures can be viewed as the condensed polynuclear cobalt complexes that the cobalt atom frameworks with sulphur bridged were built through the small triangular units of [Co3S3nL3] (n=1,2) with or without [CoL] (L=PR3, Br, Cl, 5-C5H5) fragments.     

Bridging mu-eta(5):eta(4)-coordination of an indenyl ligand and reductive coupling of diazabutadienes in the assembly of di- and tetranuclear mixed-valent ytterbium indenyldiazabutadiene complexes

The redox reaction of [Yb(C(9)H(7))(2)(thf)(2)] with the diazabutadiene PhN==C(Me)--C(Me)==NPh (DAD) has been found to depend on the molar ratio of the reactants. Reaction in a 1:2 molar ratio affords the dinuclear mixed-valent complex [Yb(2)(mu-eta(5):eta(4)-C(9)H(7))(eta(5)-C(9)H(7))(2){mu-eta(4):eta(4)-PhNC(Me)==C(Me)NPh}] containing an indenyl ligand with an unusual mu-eta(5):eta(4) bridging coordination. Reaction of equimolar amounts of these compounds results in an organolanthanide-mediated reductive coupling of the DAD ligands and formation of the tetranuclear mixed-valent complex [Yb(2)(mu-eta(5):eta(4)-C(9)H(7))(eta(5)-C(9)H(7))(2){mu-eta(4):eta(4)-PhNC(CH(2))==C(Me)NPh}](2) with a novel tetradentate tetraimine ligand.     

Carbene- and carbyne-like behavior of the Mo-P multiple bond in a dimolybdenum complex inducing trigonal-pyramidal coordination of a phosphinidene ligand

The phosphinidene complex [Mo2Cp(micro-kappa1:kappa1,eta5-PC5H4)(CO)2(eta6-R*H)] (2; Cp = eta5-C5H5; R* = 2,4,6-C6H2tBu3) has substantially different Mo-P bonds and displays a high reactivity located at the short Mo-P bond. Sideways cycloaddition or addition processes are observed toward RCCR, HCl, and [Fe2(CO)9], to give respectively metallacyclobutene and arylphosphide-bridged and heterometallic phosphinidene-bridged derivatives, a behavior reminiscent of the nucleophilic mononuclear phosphinidene complexes (carbene-like behavior), which is in good agreement with the ground-state electronic structure of 2 derived from density functional theory calculations. However, the reaction of 2 with [Co2(CO)8] implies the addition of two cobalt fragments to its short Mo-P bond and thus reveals a carbyne-like behavior of compound 2. In most of the new products, the P atom displays an unprecedented trigonal-pyramidal-like environment, instead of the expected tetrahedral distribution of bonds.     

Sulfoxide carbon-sulfur bond activation

The alkynylsulfoxide, TMSCCSO(p-tolyl) (TMS = trimethylsilyl, tolyl = C6H4Me), undergoes reaction with (eta5-C5H5)Co(PPh3)2 at room temperature to give the cobaltosulfoxide complex, (C5H5)Co(PPh3)(eta1-CCTMS)[eta1-(S)-SO(p-tolyl)], which was characterized by X-ray crystallography. Exposure of this cobaltosulfoxide complex to oxygen gas leads to the formation of the corresponding metallosulfone complex, (C5H5)Co(PPh3)(eta1-CCTMS)[eta1-(S)-SO2(p-tolyl)], which was characterized by X-ray crystallography. Alternatively, in solution at room temperature, the metallosulfoxide is converted to a 1:4 mixture of the equatorial-equatorial and equatorial-axial bridging cobalt-thiolato dimers, {(C5H5)Co[mu-S(p-tolyl)]}2, respectively. The equatorial-equatorial isomer was characterized by X-ray crystallography.     

Synthesis and structural characterization of Be(eta 5-C5Me5)(eta 1-C5Me4H). Evidence for ring-inversion leading to Be(eta 5-C5Me4H)(eta 1-C5Me5)

The mixed-ring beryllocene Be(C5Me5)(C5Me4H), that contains eta 5-C5Me5 and eta 1-C5Me4H rings, the latter bonded to the metal through the CH carbon atom (X-ray crystal structure) reacts at room temperature with CNXyl (Xyl = C6H3-2,6-Me2) to give an iminoacyl product, Be(eta 5-C5Me4H)[C(NXyl)C5Me5] derived from the inverted beryllocene structure Be (eta 5-C5Me4H)(eta 1-C5Me5).     

(C5H5)Co(P(O)(OH)2)3H]: a novel organometallic tris-phosphonic acid that dissolves glass to form a six-coordinate silicon complex

The sodium salt of the tripodal oxygen ligand Na[(C5H5)Co(P(O)(OMe)2)3] (1) reacts with gaseous hydrogen chloride in dichloromethane to give sodium chloride and [(C5H5)Co(P(O)(OMe)2)3H2]Cl (2). Addition of an equimolar amount of 1 leads to precipitation of sodium chloride again to yield the acid form of the ligand [(C5H5)Co(P(O)(OMe)2)3H] (3). Its solid-state structure contains a very short intramolecular OH.O hydrogen bond. The compound hydrolyses in boiling water to give methanol and the title complex [(C5H5)Co(P(O)(OH)2)3H] (4). This complex is a rather strong tris-phosphonic acid (pK(a1) 2.0, pK(a2) 4.0, pK(a3) 6.3, and pK(a4) 9.6). Attempts to grow single crystals of this highly water-soluble yellow crystalline compound lead to the silicon complex [((C5H5)Co[P(O)(OH)2]2[P(O)2(OH)])(2)Si].8 H2O (5). The crystal structure determination shows that it is a molecular complex of two tris-phosphonic acids that each act as a tris-chelating ligand. Additional water molecules form a complex net of hydrogen bonds between the complexes of 5. The SiO6 octahedron is only insignificantly distorted with Si-O bond lengths of 1.78 A. Complex 4 reacts with stoichiometric amounts of potassium carbonate to yield the potassium salt K[(C5H5)Co(P(O)(OH)2)3] (6). The crystal structure of 6 has also been determined. In the solid state it is a two-dimensional coordination polymer with each potassium ion being coordinated by twelve oxygen atoms of six tris-phosphonic acids.     

A favorable case where an experimental electron density analysis offers a lead for understanding a specific fluxional process observed in solution

A topological analysis of the electron density in the ketene complex (eta(5)-MeC(5)H(4))(CO)(2)Mn[eta(2)-O=C=C((mu-eta(2)-CCPh)Co(2)(CO)(6))Ph] indicates a predisposition for the carbene component of the ketene ligand to bind the neighboring C atom of the adjacent CO ligand.     

First planar chiral bidentate ligand based on a (eta5-cyclopentadienyl)(eta4-cyclobutadiene) cobalt backbone: high efficiency in enantioselective palladium-catalyzed allylic substitutions

The synthesis of the planar chiral (R)-[eta5-(1-diphenylphosphino-2-tert-butylsulfenyl)cyclopentadienyl](eta4-tetraphenylcyclobutadiene) cobalt and its high efficiency as P,S-bidentate ligand in Pd-catalyzed allylic substitutions is described.