Homoleptic organometallic anions of Ti, Zr, Hf, and Nb

Reactions of C(6)H(5)Li and 4-CH(3)C(6)H(4)Li with halides of Ti, Ir, Hf, and Nb lead to the formation of homoleptic organometallic anions of these metals. Owing to their thermal instability and their sensitivity towards H(2) O and O(2) , these compounds are characterized by single-crystal structure determinations at low temperature, whereas other physical data could only be obtained occasionally. Three pentacoordinate complex anions [Ti(C(6)H(5))(5)](-), [Ti(4-CH(3)C(6)H(4))(5)](-), and [Zr(C(6)H(5))(5)](-) have square-pyramidal structures that display only slight deviations from the ideal geometry, in contrast to the already known structures of [Ti(CH(5))(5)](-). The hexacoordinate complex anions [Zr(C(6)H(5))(6)](2-), [Zr(4-CH(3)C(6)H(4))(6)](2-), [Nb(C(6)H(5))(6)](2-), and [Nb(4-CH(3)C(6)H(4))(6)](2-) all have trigonal-prismatic structures, in accord with the known hexamethyl complex dianions. In contrast, the hexacoordinate complex anion [Hf(C(6)H(5))(6)](2)(-) has an octahedral or close to octahedral structure, in contrast to the known trigonal-prismatic structures of [Ta(C(6)H(5))(6)](-) and [Ta(4-CH(3)C(6)H(4))(6) (-). A qualitative explanation for this structural variability is given.     

Reactivity of Mo(PMe3)6 towards benzothiophene and selenophenes: new pathways relevant to hydrodesulfurization

Mo(PMe(3))(6) cleaves a C-S bond of benzothiophene to give (kappa(2)-CHCHC(6)H(4)S)Mo(PMe(3))(4), which rapidly isomerizes to the olefin-thiophenolate and 1-metallacyclopropene-thiophenolate complexes, (kappa(1),eta(2)-CH(2)CHC(6)H(4)S)Mo(PMe(3))(3)(eta(2)-CH(2)PMe(2)) and (kappa(1),eta(2)-CH(2)CC(6)H(4)S)Mo(PMe(3))(4). The latter two molecules result from a series of hydrogen transfers and are differentiated according to whether the termini of the organic fragments coordinate as olefin or eta(2)-vinyl ligands, respectively. The reactions between Mo(PMe(3))(6) and selenophenes proceed differently from those of the corresponding thiophenes. For example, whereas Mo(PMe(3))(6) reacts with thiophene to give eta(5)-thiophene and butadiene-thiolate complexes, (eta(5)-C(4)H(4)S)Mo(PMe(3))(3) and (eta(5)-C(4)H(5)S)Mo(PMe(3))(2)(eta(2)-CH(2)PMe(2)), selenophene affords the metallacyclopentadiene complex [(kappa(2)-C(4)H(4))Mo(PMe(3))(3)(Se)](2)[Mo(PMe(3))(4)] in which the selenium has been completely abstracted from the selenophene moiety. Likewise, in addition to (kappa(1),eta(2)-CH(2)CC(6)H(4)Se)Mo(PMe(3))(4) and (kappa(1),eta(2)-CH(2)CHC(6)H(4)Se)Mo(PMe(3))(3)(eta(2)-CH(2)PMe(2)), which are counterparts of the species observed in the benzothiophene reaction, the reaction of Mo(PMe(3))(6) with benzoselenophene yields products resulting from C-C coupling, namely [kappa(2),eta(4)-Se(C(6)H(4))(CH)(4)(C(6)H(4))Se]Mo(PMe(3))(2) and [mu-Se(C(6)H(4))(CH)C(CH)(2)(C(6)H(4))](mu-Se)[Mo(PMe(3))(2)][Mo(PMe(3))(2)H].     

Syntheses and structural and electrochemical characterizations of vanadatricarbadecaboranyl analogues of vanadocene and the structural characterization of the [Li(CH(3)CN)2+](6-CH(3)-nido-5,6,9-C(3)B(7)H(9-) tricarbadecaboranyl anion.

A single-crystal X-ray determination of the [Li(CH(3)CN)(2)(+)](6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-)) salt has shown that the 6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-) tricarbadecaboranyl anion has a nido-cage geometry based on an octadecahedron missing the unique six-coordinate vertex. The resulting six-membered open face is puckered, with two of the cage carbons (C6 and C9) occupying the low-coordinate cage positions above the plane of the four remaining atoms (C5, B7, B8, and B10). The Li(+) ion is centered over the open face and is solvated by two acetonitrile molecules. The reactions of the 6-CH(3)-nido-5,6,9-C(3)B(7)H(9)(-) anion with various vanadium halide salts, including VCl(4), VCl(3), and VBr(2), each resulted in the isolation of the same five paramagnetic products (2-6) of composition V(CH(3)-C(3)B(7)H(9))(2). X-ray crystallographic determinations of 2-5 showed that the complexes consist of two octadecahedral VC(3)B(7) fragments sharing a common vanadium vertex and established their structures as commo-V-(1-V-4'-CH(3)-2',3',4'-C(3)B(7)H(9))(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9)) (2), commo-V-(1-V-5'-CH(3)-2',3',5'-C(3)B(7)H(9))(1-V-4-CH(3)-2,3,4-C(3)B(7)H(9)) (3), commo-V-(1-V-5'-CH(3)-2',3',5'-C(3)B(7)H(9))(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9)) (4), and commo-V-(1-V-2-CH(3)-2,3,4-C(3)B(7)H(9))(2) (5). These complexes can be considered as tricarbadecaboranyl analogues of vanadocene, (eta(5)-C(5)H(5))(2)V. However, unlike vanadocene, these complexes are air- and moisture-stable and have only one unpaired electron. The five complexes differ with respect to one another in that they either (1) contain different enantiomeric forms of the CH(3)-C(3)B(7)H(9) cages, (2) have a different twist orientation of the two cages, or (3) have the methyl group of the CH(3)-C(3)B(7)H(9) cage located in either the 2 or 4 position of the cage. Subsequent attempts to oxidize the compounds with reagents such as Br(2) and Ag(+) were unsuccessful, illustrating the ability of the tricarbadecaboranyl anion to stabilize metals in low oxidation states. Consistent with this, both the electrochemical oxidation and the reduction of 2 were much more positive than those of the same oxidation state changes in vanadocene. The one-electron reduction of 2 is a remarkable 2.9 V positive of that of Cp(2)V.     

P-O donor action from carboxylate anions with phosphorus in the presence of hydrogen bonding. A model for phosphoryl-transfer enzymes

A series of phosphorus compounds (1-3) containing anionic carboxylate groups were synthesized by treatment of the respective neutral precursor acid forms B-D with amines, which also served to introduce hydrogen-bonding interactions. The compounds, subjected to X-ray structure analysis, resulted in hexacoordinated anionic phosphoranates 1A and 1B, a pseudo-trigonal-bipyramidal anionic phosphine (2), and a trigonal-bipyramidal anionic phosphine oxide (3). The structures revealed that P-O donor coordination was present in all members of the anionic series 1-3 and resulted in stronger interactions than existed in the precursor neutral acid forms B-D as measured by the presence of shorter P-O distances. Evaluation of the energies of the donor interactions relative to the energies of the hydrogen bonds that were present showed that the donor energies now exceeded the hydrogen bond strengths. (31)P chemical shifts indicated that the basic coordination geometries were retained in solution. Both 1A and 1B are chiral and exist as racemates. The results suggest that mechanisms of phosphoryl-transfer enzymes should benefit by taking into account donor interactions at phosphorus by residues at active sites in addition to the inclusion of hydrogen bonding. Reference is made to specific phosphoryl-transfer enzymes.     

Influence of hydrogen bonding in competition with lattice interactions on carbonyl coordination at phosphorus. Implications for phosphoryl transfer activated states

A series of phosphorus compounds containing carboxyl groups that serve as mimics for amino acid residues was synthesized. The series was composed of the phosphonium salts 1A, 1B, and 2, the anionic phosphines 3A and 3B, and the anionic phosphine oxide 4. X-ray structural analysis revealed that P-O coordination occurred in the presence of extensive hydrogen bonding and led to pseudo or regular trigonal bipyramidal geometries. (31)P chemical shifts indicated retention of the basic coordination geometries in solution. The two forms observed for 1 and 3 revealed the influence of hydrogen bonding on the P-O donor interactions while 2 and 4 showed the influence of molecular packing effects in competition with hydrogen bonding interactions. The results suggest that phosphoryl transfer enzyme mechanisms should benefit by taking into account P-O donor interactions by residues at active sites that can be manipulated by hydrogen bonding and molecular packing effects in enhancing nucleophilic attack at phosphorus centers.     

Mechanistic study on the coupling reaction of aryl bromides with arylboronic acids catalyzed by (iminophosphine)palladium(0) complexes. Detection of a palladium(II) intermediate with a coordinated boron anion

The complexes [Pd(eta2-dmfu)(P-N)] [P-N = 2-(PPh2)C6H4-1-CH=NR, R = C(6)H(4)OMe-4; CHMe2; C6H3Me2-2,6; C6H3(CHMe2)-2,6] react with an excess of BrC6H4R1-4 (R1= CF3; Me) yielding the oxidative addition products [PdBr(C6H4R1-4)(P-N)] at different rates depending on R [C6H4OMe-4 > C6H3(CHMe2)-2,6 > CHMe2 approximately C6H3Me2-2,6] and R1 (CF3> Me). In the presence of K2CO3 and activated olefins (ol = dmfu, fn), the latter compounds react with an excess of 4-R2C6H4B(OH)2 (R2= H, Me, OMe, Cl) to give [Pd(eta2-ol)(P-N)] and the corresponding biaryl through transmetallation and fast reductive elimination. The transmetallation proceeds via a palladium(II) intermediate with an O-bonded boron anion, the formation of which is markedly retarded by increasing the bulkiness of R. The intermediate was isolated for R = CHMe2, R1 = CF3 and R2= H. The boron anion is formulated as a diphenylborinate anion associated with phenylboronic acid and/or as a phenylboronate anion associated with diphenylborinic acid. In general, the oxidative addition proceeds at a lower rate than transmetallation and represents the rate-determining-step in the coupling reaction of aryl bromides with arylboronic acids catalyzed by [Pd(eta2-dmfu)(P-N)].     

Carbon-sulfur bond cleavage and hydrodesulfurization of thiophenes by tungsten

The reactions of W(PMe(3))(4)(η(2)-CH(2)PMe(2))H, W(PMe(3))(5)H(2), W(PMe(3))(4)H(4) and W(PMe(3))(3)H(6) towards thiophenes reveal that molecular tungsten compounds are capable of achieving a variety of transformations that are relevant to hydrodesulfurization. For example, sequential treatment of W(PMe(3))(4)(η(2)-CH(2)PMe(2))H with thiophene and H(2) yields the butanethiolate complex, W(PMe(3))(4)(SBu(n))H(3), which eliminates but-1-ene at 100 °C. Likewise, sequential treatment of W(PMe(3))(4)(η(2)-CH(2)PMe(2))H with benzothiophene and H(2) yields W(PMe(3))(4)(SC(6)H(4)Et)H(3), which releases ethylbenzene at 100 °C. Moreover, W(PMe(3))(4)(η(2)-CH(2)PMe(2))H desulfurizes dibenzothiophene to form a dibenzometallacyclopentadiene complex, [(κ(2)-C(12)H(8))W(PMe(3))](μ-S)(μ-CH(2)PMe(2))(μ-PMe(2))[W(PMe(3))(3)].     

Zirconium complexes incorporated with asymmetrical tridentate pincer type mono- and di-anionic pyrrolyl ligands: mechanism and reactivity as catalytic precursors

The reactions of Zr(NR(2))(4) (1, R = Me; 2, R = Et) with an asymmetrical tridentate pincer type pyrrole ligand precursor [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] and treatment of the derivatives with either PhNCS or PhNCO have been carried out and characterized. Reacting Zr(NR(2))(4) (1, R = Me; 2, R = Et) with [C(4)H(2)NH(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))] generates Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NR(2))(2) (3, R = Me; 4, R = Et) in high yield along with the elimination of 2 equiv of dimethylamine or diethylamine, respectively. Interestingly, while changing the solvent from Et(2)O to CH(2)Cl(2), the complex Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))][C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))]Cl (5) is produced by undergoing C-Cl bond cleavage. Furthermore, reaction of either 3 or 4 with 1 or 2 equiv of PhNCS or PhNCO yields Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NMe(2))[PhNC(NMe(2))S] (6), Zr[C(4)H(2)N(2-CH(2)N(t)Bu)(5-CH(2)NMe(2))](NEt(2))[PhNC(NEt(2))O] (7) and Zr[C(4)H(2)N(2-CH(2)NH(t)Bu)(5-CH(2)NMe(2))][PhNC(NEt(2))O](3) (8), respectively. All the aforementioned complexes were characterized by (1)H and (13)C NMR spectrometry and the molecular structures of 5, 6, and 8 have been determined by single-crystal X-ray diffractometry. Complexes 4, 5, and 7 initiated the ethylene polymerization in the presence of MAO as the co-catalyst.     

Structural and characterization of novel copper(II) azodye complexes

The synthetic methods of novel Cu(II) and adduct complexes, with selective azodyes containing nitrogen and oxygen donor ligands have been developed, characterized and presented. The prepared complexes fall into the stoichiometric formulae of [Cu(L(n))(2)](A) and [Cu(L(n))(2)(Py)(2)](B), where two types of complexes were expected and described. In type [(A) (1:2)] the chelate rings are six-membered/four coordinate, whereas in type [(B) (1:2:2)] they are six-membered/six coordinate. The important bands in the IR spectra and main (1)H NMR signals are tentatively assigned and discussed in relation to the predicted assembly of the molecular structure. The IR data of the azodye ligands suggested the existing of a bidentate binding involving azodye nitrogen and C-O oxygen atom of enolic group. They also showed the presence of Py coordinating with the metal ion. The coordination geometries and electronic structures are determined from the framework of the proposed modeling of the formed novel complexes. The complexes (1-5) exist in trans-isomeric [N,O] solid form, while adduct complexes (6-10) exist in trans isomeric (Py) form. The square planar/octahedral coordination geometry of Cu(II)/adduct is made up of an N-atom of azodye, the deprotonated enolic O-atom and two Py. The azo group was involved in chelation for all the prepared complexes. ESR spectra show the simultaneous presence of a planar trans and a nearly planar cis isomers in the 1:2 ratio for all N,O complexes [Cu(L(n))(2)]. The ligands in the dimmer are stacked over one another. In the solid state of azo-rhodanine, the dimmers have inter- and intramolecular hydrogen bonds. Interactions between the ligands and Cu(II) are also discussed.     

Re(III)Cl(3)] core complexes with bifunctional single amino acid chelates

The reactions of the Re(V) starting material [ReO(PPh(3))(2)Cl(3)] with ligands of the type XN(Y)Z [X = Y = 2-pyridylmethyl, Z = -CH(2)CO(2)Et (L(1)Et), -CH(2)CH(2)CO(2)Et (L(2)Et), -CH(2)CH(2)CH(2)CH(2)CH(NHCO(2)Bu(t))CO(2)H (L(3)H); X = 2-pyridylmethyl, Y = 2-(1-methylimidazolyl)methyl, Z = -CH(2)CO(2)Et (L(4)Et)] yielded the Re(III) trichloride complexes of the type [ReCl(3)(L(n)R)]. The complexes are mononuclear, paramagnetic species with a facial geometry of the chloride ligands. The nitrogen donors of the tridentate L(n)()R ligands complete the distorted octahedral coordination spheres of the complexes. Crystal data: [ReCl(3)(L(1)Et)] (1), monoclinic, C2/m, a = 16.088(3) A, b = 9.980(2) A, c = 12.829(2) A, beta = 91.384(3) degrees, Z = 4, D(calc) = 1.967 g/cm(-)(3); [ReCl(3)(L(4)Et)] (4), monoclinic, C2/c, a = 22.880(1) A, b = 7.4926(4) A, c = 22.560(1) A, beta = 94.186(1) degrees, Z = 8, D(calc) = 2.001 g/cm(-3).     

Cyclotriphosphazene hydrazides as efficient multisite coordination ligands. eta(3)-fac-non-geminal-N(3) coordination of spiro-N(3)P(3)[O(2)C(12)H(8)][N(Me)NH(2)](4) (L) in L(2)CoCl(3) and L(2)M(NO(3))(2) (M = Ni, Zn, Cd)

The cyclophosphazene tetrahydrazide spiro-N(3)P(3)[O(2)C(12)H(8)][N(Me)NH(2)](4) (L) functions as a multisite coordination ligand and affords L(2)CoCl(3).2CH(3)OH (4), L(2)Ni(NO(3))(2).2CHCl(3).2.5H(2)O (5), L(2)Zn(NO(3))(2).2CH(3)CN.2H(2)O (6), and L(2)Cd(NO(3))(2) (7). Each of the cyclophosphazene ligands that is involved in coordination to the metal functions as a non-geminal-N(3) donor coordinating through one ring nitrogen atom and two non-geminal-NH(2) nitrogen atoms. The coordination geometry around the metal ion in 4-6 is approximately octahedral while it is severely distorted in the case of 7.     

Conversion of azomethine moiety to carboxamido group at cobalt(III) center in model complexes of Co-containing nitrile hydratase

The Co(III) complex of the Schiff base ligand N-2-mercaptophenyl-2'-pyridylmethyl-enimine (PyASH), namely, [Co(PyAS)(2)]Cl (1), has been synthesized via an improved method and its structure has been determined by X-ray crystallography. The two deprotonated ligands are arranged in mer configuration around the Co(III) center and the overall coordination geometry is octahedral. The coordinated azomethine function in 1 is rapidly converted into carboxamido group upon reaction with OH(-). The product is the bis carboxamido complex (Et(4)N)[Co(PyPepS)(2)] (2), reported by us previously. Reaction of H(2)O(2) with 1 in DMF affords [Co(PyASO(2))(PyPepSO(2))] (3), a species with mixed imine and carboxamido-N donor centers as well as S-bound sulfinates. Further reaction with H(2)O(2) in the presence of NaClO(4) converts 3 into the previously reported bis carboxamido/sulfinato complex Na[Co(PyPepSO(2))(2)] (4). The reaction conditions for the various transformation reactions for complexes 1-4 and the structure of 3 are also reported. The mechanism of the -CH=NR + [O] --> -C(=O)NHR transformation has been discussed. The reactions reported here provide convenient alternate routes for the syntheses of Co(III) complexes with coordinated carboxamide, thiolate, and/or sulfinate donors as models for the Co-site in the Co-containing nitrile hydratase(s).     

Self-assembled metallo-macrocycle based coordination polymers with unsymmetrical amide ligands

A series of metallo-macrocyclic based coordination polymers has been prepared from flexible amide ligands N-6-[(3-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic acid (L1-CH(3)) and N-6-[(4-pyridylmethylamino)carbonyl]-pyridine-2-carboxylic acid (L2-CH(3)). In all but one case, self-assembled dinuclear metallo-macrocyclic units form the basis of the polymeric structures, whereby discrete metal centres, and dinuclear or trinuclear clusters, are linked by the self-assembled macrocycles to give 1D and 2D coordination polymers. In one instance, a 1D coordination polymer is formed in a reaction carried out under ambient conditions; when the same reaction is conducted under solvothermal conditions a 2D structure is formed. In all but two of these structures, the polymeric chains and nets are close-packed within the crystals. In the case of a 6,3-connected 2D coordination polymer {[Cd(3)(L2-CH(3))(3)(NO(3))(L2)(CH(3)OH)](NO(3))(2)·12?H(2)O}(n) (9), small oval channels percolate down the a-axis of the unit cell.     

Preparation, structure, and ethylene (co)polymerization behavior of Group IV metal complexes with an [OSSO]-carborane ligand

The synthesis of Group IV metal complexes that contain a tetradentate dianionic [OSSO]-carborane ligand [(HOC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2 (B(10)H(10))] (1a) is described. Reactions of TiCl(4) and Ti(OiPr)(4) with the [OSSO]-type ligand 1a afford six-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2a) and four-coordinated titanium complex [Ti(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))(OiPr)(2)] (2b), respectively. ZrCl(4) and HfCl(4) were treated with 1a to give six-coordinated zirconium complex [Zr(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2) (thf)(2)] (2c) and six-coordinated hafnium complex [Hf(OC(6)H(2)tBu(2)-4,6)(2)(CH(2))(2)S(2)C(2)(B(10)H(10))Cl(2)] (2d). All the complexes were fully characterized by IR, NMR spectroscopy, and elemental analysis. In addition, X-ray structure analyses were performed on complexes 2a and 2b and reveal the expected different coordination geometry due to steric hindrance effects. Extended X-ray absorption fine structure (EXAFS) spectroscopy was performed on complexes 2c and 2d to describe the coordination chemistry of this ligand around Zr and Hf. Six-coordinated titanium complex 2a showed good activity toward ethylene polymerization as well as toward copolymerization of ethylene with 1-hexene in the presence of methylaluminoxane (MAO) as cocatalyst (up to 1060 kg[mol(Ti)](-1) h(-1) in the case of 10 atm of ethylene pressure).     

Synthesis and structure of amido- and imido(pentafluorophenyl)borane zirconocene and hafnocene complexes: N-H and B-H activation

Treatment of Me(2)S·B(C(6)F(5))(n) H(3-n) (n=1 or 2) with ammonia yields the corresponding adducts. H(3)N·B(C(6)F(5))H(2) dimerises in the solid state through N-H···H-B dihydrogen interactions. The adducts can be deprotonated to give lithium amidoboranes Li[NH(2)B(C(6)F(5))(n)H(3-n)]. Reaction of the n=2 reagent with [Cp(2)ZrCl(2)] leads to disubstitution, but [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)] is in equilibrium with the product of β-hydride elimination [Cp(2)Zr(H){NH(2)B(C(6)F(5))(2)H}], which proves to be the major isolated solid. The analogous reaction with [Cp(2)HfCl(2)] gives a mixture of [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)] and the N-H activation product [Cp(2)Hf{NHB(C(6)F(5 )(2)H}]. [Cp(2)Zr{NH(2)B(C(6)F(5))(2)H}(2)]·PhMe and [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]·4(thf) exhibit β-B-agostic chelate bonding of one of the two amidoborane ligands in the solid state. The agostic hydride is invariably coordinated to the outside of the metallocene wedge. Exceptionally, [Cp(2)Hf{NH(2)B(C(6)F(5))(2)H}(2)]?PhMe has a structure in which the two amidoborane ligands adopt an intermediate coordination mode, in which neither is definitively agostic. [Cp(2)Hf{NHB(C(6)F(5))(2)H}] has a formally dianionic imidoborane ligand chelating through an agostic interaction, but the bond-length distribution suggests a contribution from a zwitterionic amidoborane resonance structure. Treatment of the zwitterions [Cp(2)MMe(μ-Me)B(C(6)F(5))(3)] (M=Zr, Hf) with Li[NH(2)B(C(6)F(5))(n)H(3-n)] (n=2) results in [Cp(2) MMe{NH(2)B(C(6)F(5))(2)H}] complexes, for which the spectroscopic data, particularly (1)J(B,H), again suggest β-B-agostic interactions. The reactions proceed similarly for the structurally encumbered [Cp'(2)ZrMe(μ-Me)B(C(6)F(5))(3)] precursor (Cp'=1,3-C(5)H(3)(SiMe(3))(2) , n=1 or 2) to give [Cp'(2)ZrMe{NH(2)B(C(6)F(5))(n)H(3-n)}], both of which have been structurally characterised and show chelating, agostic amidoborane coordination. In contrast, the analogous hafnium chemistry leads to the recovery of [Cp'(2)HfMe(2)] and the formation of Li[HB(C(6)F(5))(3)] through hydride abstraction.     

Imine-assisted C-F bond activation by electron-rich iron complexes supported by trimethylphosphine

C-F bond activation of ortho-fluorinated benzalimines 2,6-F(2)C(6)R1R2R3-CH=N-R (1-3) using the electron-rich complex Fe(PMe(3))(4) is reported. With the assistance of the imine group as the anchoring group, bis-chelated iron(II) complexes (C(6)FR1R2R3-CH=N-R)(2)Fe(PMe(3))(2) (4-6) were formed. The reaction of 2,6-difluorobenzylidenenaphthalen-1-amine 2,6-F(2)C(6)H(3)-CH=N-C(10)H(7) (9) with Fe(PMe(3))(4) affords [CNC]-pincer iron(II) complex (C(6)H(3)F-CH=N-C(10)H(6))Fe(PMe(3))(3) (10) through both C-F and C-H bond activation and π-(C=N) coordinate iron(0) complex (C(6)H(3)F-CH=N-C(10)H(7))(2)Fe(PMe(3))(2) (11) with C,C-coupling, while a similar reaction with perfluorobenzylidenenaphthalen-1-amine C(6)F(5)-CH=N-C(10)H(7) (14) gave rise to only [CNC]-pincer iron(II) complex (C(6)F(4)-CH=N-C(10)H(6))Fe(PMe(3))(3) (15). The proposed formation mechanisms of these complexes are discussed. The structures of complexes 5, 6, 10 and 11 were confirmed by X-ray single crystal diffraction.     

Out-of-center distortions in d(0) transition metal oxide fluoride anions

Electronic effects and the bond network are the two factors that cause out-of-center distortions in octahedral d(0) transition metal oxide fluoride anions. Overlap between filled oxide p orbitals and vacant cation d orbitals results in strong, short metal-oxide bonds causing the metal ion to distort toward the oxide ligand. This primary, electronic distortion is not dependent on the extended structure. Smaller, secondary distortions of the anionic octahedra are caused by interactions with the bond network. [HNC(6)H(6)OH](2)[Cu(NC(5)H(5))(4)(NbOF(5))(2)], prepared with 5-hydroxy-2-methylpyridine that provides two coordination contact sites to the anion when protonated, exhibits distortions in the anion reflecting both factors. Crystal data for [HNC(6)H(6)OH](2)[Cu(NC(5)H(5))(4)(NbOF(5))(2)]: monoclinic, space group C2/c (No. 15), with a = 10.9427(8) A, b = 16.204(1) A, c = 21.396(2) A, beta = 93.263(1) degrees, and Z = 4. Conditions for detection of both distortion types are discussed with five additional examples.     

Periodic trends in lanthanide and actinide phosphonates: discontinuity between plutonium and americium

The hydrothermal reactions of trivalent lanthanide and actinide chlorides with 1,2-methylenediphosphonic acid (C1P2) in the presence of NaOH or NaNO(3) result in the crystallization of three structure types: RE[CH(2)(PO(3)H(0.5))(2)] (RE = La, Ce, Pr, Nd, Sm; Pu) (A type), NaRE(H(2)O)[CH(2)(PO(3))(2)] (RE = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy; Am) (B type), or NaLn[CH(2)(PO(3)H(0.5))(2)]·(H(2)O) (Ln = Yb and Lu) (C type). These crystals were analyzed using single crystal X-ray diffraction, and the structures were used directly for detailed bonding calculations. These phases form three-dimensional frameworks. In both A and B, the metal centers are found in REO(8) polyhedra as parts of edge-sharing chains or edge-sharing dimers, respectively. Polyhedron shape calculations reveal that A favors a D(2d) dodecahedron while B adopts a C(2v) geometry. In C, Yb and Lu only form isolated MO(6) octahedra. Such differences in terms of structure topology and coordination geometry are discussed in detail to reveal periodic deviations between the lanthanide and actinide series. Absorption spectra for the Pu(III) and Am(III) compounds are also reported. Electronic structure calculations with multireference methods, CASSCF, and density functional theory, DFT, reveal localization of the An 5f orbitals, but natural bond orbital and natural population analyses at the DFT level illustrate unique occupancy of the An 6d orbitals, as well as larger occupancy of the Pu 5f orbitals compared to the Am 5f orbitals.     

Mononuclear titanium(IV)-citrate complexes from aqueous solutions: pH-specific synthesis and structural and spectroscopic studies in relevance to aqueous titanium(IV)-citrate speciation

Titanium is a metal frequently employed in a plethora of materials supporting medical applications. In an effort to comprehend the involvement of titanium in requisite biological interactions with physiological ligands, synthetic efforts were launched targeting aqueous soluble species of Ti(IV). To this end, aqueous reactions of TiCl(4) with citric acid afforded expediently, under pH-specific conditions, the colorless crystalline materials Na(6)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].16H(2)O (1) and Na(3)(NH(4))(3)[Ti(C(6)H(4.5)O(7))(2)(C(6)H(5)O(7))].9H(2)O (2). Complexes 1 and 2 were characterized by elemental analysis, FT-IR, (13)C-MAS solid state and solution NMR, cyclic voltammetry, and X-ray crystallography. 1 crystallizes in the triclinic space group P, with a = 15.511(9) A, b = 15.58(1) A, c = 9.848(5) A, alpha = 85.35(2) degrees, beta = 76.53(2) degrees, gamma = 61.97(2) degrees, V = 2042(2) A(3), and Z = 2. 2 crystallizes in the triclinic space group P, with a = 12.437(5) A, b = 12.440(5) A, c = 12.041(5) A, alpha = 83.08(2) degrees, beta = 81.43(2) degrees, gamma = 67.45(2) degrees, V = 1697(2) A(3), and Z = 2. The X-ray structures of 1 and 2 reveal the presence of a mononuclear complex, with Ti(IV) coordinated to three citrate ligands in a distorted octahedral geometry around Ti(IV). The citrates employ their central alkoxide and carboxylate groups to bind Ti(V), while the terminal carboxylates stay away from the Ti(IV)O(6) core. Worth noting in 1 and 2 is the similar mode of coordination but variable degree of protonation of the bound citrates, with the locus of (de)protonation being the noncoordinating terminal carboxylates. As a result, this work suggests the presence of a number of different Ti(IV)-citrate species of the same nuclearity and coordination geometry as a function of pH. This is consistent with the so far existing pool of mononuclear Ti(IV)-citrate species and provides a logical account of the aqueous speciation in the requisite binary system. Such information is vital in trying to delineate the interactions of soluble and bioavailable Ti(IV) forms promoting biological interactions in humans. To this end, chemical properties, structural attributes, and speciation links to potential ensuing biological effects are dwelled on.     

Thermal activation of hydrocarbon C-H bonds initiated by a tungsten allyl complex

Gentle thermolysis of the allyl complex, CpW(NO)(CH(2)CMe(3))(eta(3)-H(2)CCHCMe(2)) (1), at 50 degrees C in neat hydrocarbon solutions results in the loss of neopentane and the generation of transient intermediates that subsequently activate solvent C-H bonds. Thus, thermal reactions of 1 with tetramethylsilane, mesitylene, and benzene effect single C-H activations and lead to the exclusive formation of CpW(NO)(CH(2)SiMe(3))(eta(3)-H(2)CCHCMe(2)) (2), CpW(NO)(CH(2)C(6)H(3)-3,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (3), and CpW(NO)(C(6)H(5))(eta(3)-H(2)CCHCMe(2)) (4), respectively. The products of reactions of 1 with other methyl-substituted arenes indicate an inherent preference of the system for the activation of stronger arene sp(2) C-H bonds. For example, C-H bond activation of p-xylene leads to the formation of CpW(NO)(CH(2)C(6)H(4)-4-Me)(eta(3)-H(2)CCHCMe(2)) (5) (26%) and CpW(NO)(C(6)H(3)-2,5-Me(2))(eta(3)-H(2)CCHCMe(2)) (6) (74%). Mechanistic and labeling studies indicate that the transient C-H-activating intermediates are the allene complex, CpW(NO)(eta(2)-H(2)C=C=CMe(2)) (A), and the eta(2)-diene complex, CpW(NO)(eta(2)-H(2)C=CHC(Me)=CH(2)) (B). Intermediates A and B react with cyclohexene to form CpW(NO)(eta(3)-CH(2)C(2-cyclohexenyl)CMe(2))(H) (18) and CpW(NO)(eta(3)-CH(2)CHC)(Me)CH(2)C(beta)H(C(4)H(8))C(alpha)H (19), respectively, and intermediate A can be isolated as its PMe(3) adduct, CpW(NO)(PMe(3))(eta(2)-H(2)C=C=CMe(2)) (20). Interestingly, thermal reaction of 1 with 2,3-dimethylbut-2-ene results in the formation of a species that undergoes eta(3) --> eta(1) isomerization of the dimethylallyl ligand following the initial C-H bond-activating step to yield CpW(NO)(eta(3)-CMe(2)CMeCH(2))(eta(1)-CH(2)CHCMe(2)) (21). Thermolyses of 1 in alkane solvents afford allyl hydride complexes resulting from three successive C-H bond-activation reactions. For instance, 1 in cyclohexane converts to CpW(NO)(eta(3)-C(6)H(9))(H) (22) with dimethylpropylcyclohexane being formed as a byproduct, and in methylcyclohexane it forms the two isomeric complexes, CpW(NO)(eta(3)-C(7)H(11))(H) (23a,b). All new complexes have been characterized by conventional spectroscopic methods, and the solid-state molecular structures of 2, 3, 4, 18, 19, 20, and 21 have been established by X-ray crystallographic analyses.