Molecular understanding of the formation of surface zirconium hydrides upon thermal treatment under hydrogen of [([triple bond]SiO)Zr(CH2tBu)3] by using advanced solid-state NMR techniques

The reaction of [([triple bond]SiO)Zr(CH(2)tBu)(3)] with H(2) at 150 degrees C leads to the hydrogenolysis of the zirconium-carbon bonds to form a very reactive hydride intermediate(s), which further reacts with the surrounding siloxane ligands present at the surface of this support to form mainly two different zirconium hydrides: [([triple bond]SiO)(3)Zr-H] (1a, 70-80%) and [([triple bond]SiO)(2)ZrH(2)] (1b, 20-30%) along with silicon hydrides, [([triple bond]SiO)(3)SiH] and [([triple bond]SiO)(2)SiH(2)]. Their structural identities were identified by (1)H DQ solid-state NMR spectroscopy as well as reactivity studies. These two species react with CO(2) and N(2)O to give, respectively, the corresponding formate [([triple bond]SiO)(4-x)Zr(O-C(=O)H)(x)] (2) and hydroxide complexes [([triple bond]SiO)(4-x)Zr(OH)(x)] (x = 1 or 2 for 3a and 3b, respectively) as major surface complexes.     

Supported cationic complexes: selective preparation and characterization of the well-defined electrophilic metallocenium cation [[triple bond]SiO-B(C6F5)3]- [Cp*ZrMe2(Et2NPh)]+ supported on silica

The reaction of Cp*ZrMe3, 1, with the heterogeneous activator [[triple bond]SiO-B(C6F5)3]- [HNEt2Ph]+, 2, has been investigated to generate, by an irreversible process of methane elimination, the well-defined cationic silica-supported metallocenium species [[triple bond]SiO-B(C6F5)3]- [Cp*ZrMe2(NEt2Ph)]+, 3, as an active olefin polymerisation catalyst.     

Cp2V] migration along an octatetrayne chain: from the monometallic complex (Cp2V(2-4eta-tBuC triple bond C2-C triple bond CC triple bond CtBu)] to the dimetallic complex

The oxidative addition of one equivalent of [Cp2V] (4) to the tetrayne ligand tBuC triple bond CC triple bond CC triple bond CC triple bond CtBu (5) gives the monometallic complex [Cp2V(3-4eta-tBuC triple bond C-C2-C triple bond CC triple bond CtBu)] (7). Compound 7 reacts further with a second equivalent of [Cp2V] to give the dimetallic complex [(Cp2V)2(1-2eta:7-8eta-tBuC2-C triple bond CC triple bond C-C2tBu)] (8), which involves a shift of the first coordinated [Cp2V] unit from the internal C3-C4 to the external C1-C2 positions on the alkynyl ligand. Compound 8 is also directly obtained by the addition of two equivalents of [Cp2V] to 5. Reversibly, reaction of 8 with 5 leads to 7. This exchange reaction between 7 and 8 by adding successively 5 and 4 has been monitored by EPR spectroscopy. By contrast, the oxidative addition of one or two equivalents of [Cp2V] to the tetrayne ligand PhC triple bond CC triple bond CC triple bond CC triple bond CPh (6) gives the homodimetallic complex [(Cp2V)2(1-2eta:7-8eta-PhC2-CC triple bond CC triple bond C-C2-Ph)] (9). Both monometallic and dimetallic complexes 7, 8, and 9 have been characterized by X-ray diffraction. Magnetic moment measurements for 8 and 9 from 300 to 4 K indicated a weak antiferromagnetic J exchange coupling of -12.5 and -4.1 cm(-1), respectively.     

P2 addition to terminal phosphide M[triple bond]P triple bonds: a rational synthesis of cyclo-P3 complexes

The diphosphaazide complex (Mes*NPP)Nb(N[Np]Ar)3 (Mes* = 2,4,6-tri-tert-butylphenyl, Np = neopentyl, Ar = 3,5-Me2C6H3), 1, has previously been reported to lose the P2 unit upon gentle heating, to form (Mes*N)Nb(N[Np]Ar)3, 2. The first-order activation parameters for this process have been estimated here using an Eyring analysis to have the values Delta H(double dagger) = 19.6(2) kcal/mol and Delta S(double dagger) = -14.2(5) eu. The eliminated P2 unit can be transferred to the terminal phosphide complexes P[triple bond]M(N[(i)Pr]Ar)3, 3-M (M = Mo, W), and [P[triple bond]Nb(N[Np]Ar)3](-), 3-Nb, to give the cyclo-P3 complexes (P3)M(N[(i)Pr]Ar)3 and [(P3)Nb(N[Np]Ar)3](-). These reactions represent the formal addition of a P[triple bond]P triple bond across a M[triple bond]P triple bond and are the first efficient transfers of the P2 unit to substrates present in stoichiometric quantities. The related complex (OC)5W(Mes*NPP)Nb(N[Np]Ar)3, 1-W(CO)5, was used to transfer the (P2)W(CO)5 unit in an analogous manner to the substrates 3-M (M = Mo, W, Nb) as well as to [(OC)5WP[triple bond]Nb(N[Np]Ar)3](-). The rate constants for the fragmentation of 1 and 1-W(CO)5 were unchanged in the presence of the terminal phosphide 3-Mo, supporting the hypothesis that molecular P2 and (P2)W(CO)5, respectively, are reactive intermediates. In a reaction related to the combination of P[triple bond]P and M[triple bond]P triple bonds, the phosphaalkyne AdC[triple bond]P (Ad = 1-adamantyl) was observed to react with 3-Mo to generate the cyclo-CP2 complex (AdCP2)Mo(N[(i)Pr]Ar)3. Reactions of the electrophiles Ph3SnCl, Mes*NPCl, and AdC(O)Cl with the anionic, nucleophilic complexes [(OC)5W(P3)Nb(N[Np]Ar)3](-) and [{(OC)5W}2(P3)Nb(N[Np]Ar)3](-) yielded coordinated eta(2)-triphosphirene ligands. The Mes*NPW(CO)5 group of one such product engages in a fluxional ring-migration process, according to NMR spectroscopic data. The structures of (OC)5W(P3)W(N[(i)Pr]Ar)3, [(Et2O)Na][{(OC)5W}2(P3)Nb(N[Np]Ar)3], (AdCP2)Mo(N[(i)Pr]Ar)3, (OC)5W(Ph3SnP3)Nb(N[Np]Ar)3, Mes*NP(W(CO)5)P3Nb(N[Np]Ar)3, and {(OC)5W}2AdC(O)P3Nb(N[Np]Ar)3, as determined by X-ray crystallography, are discussed in detail.     

Detailed structural investigation of the grafting of [Ta(=CHtBu)(CH2tBu)3] and [Cp*TaMe4] on silica partially dehydroxylated at 700 degrees C and the activity of the grafted complexes toward alkane metathesis

The reaction of [Ta(=CHtBu)(CH2tBu)3] or [Cp*Ta(CH3)4] with a silica partially dehydroxylated at 700 degrees C gives the corresponding monosiloxy surface complexes [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2] and [([triple bond]SiO)Ta(CH3)3Cp*] by eliminating a sigma-bonded ligand as the corresponding alkane (H-CH2tBu or H-CH3). EXAFS data show that an adjacent siloxane bridge of the surface plays the role of an extra surface ligand, which most likely stabilizes these complexes as in [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') and [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a'). In the case of [(SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])], the structure is further stabilized by an additional interaction: a C-H agostic bond as evidenced by the small J coupling constant for the carbenic C-H (JC-H = 80 Hz), which was measured by J-resolved 2D solid-state NMR spectroscopy. The product selectivity in propane metathesis in the presence of [([triple bond]SiO)Ta(=CHtBu)(CH2tBu)2([triple bond]SiOSi[triple bond])] (1a') as a catalyst precursor and the inactivity of the surface complex [([triple bond]SiO)Ta(CH3)3Cp*([triple bond]SiOSi[triple bond])] (2a') show that the active site is required to be highly electrophilic and probably involves a metallacyclobutane intermediate.     

Syntheses and 1H-, 13C- and 15N-NMR spectra of ethynyl isocyanide, H-C triple bond C-N triple bond C, D-C triple bond C-N triple bond C and prop-1-ynyl isocyanide, H3C-C triple bond C-N triple bond C, D3C-C triple bond C-N triple bond C: high resolution infrared specturm of prop-1-ynyl isocyanide

Ethynyl isocyanide, H-C triple bond C-N triple bond C (1a), deuteroethynyl isocyanide, D-C triple bond C-N triple bond C (1b), prop-1-ynyl isocyanide, H3C-C triple bond C-N triple bond C (1c), and trideuteroprop-1-ynyl isocyanide, D3C-C triple bond C-N triple bond C (1d) are synthesized by flash vacuum pyrolysis of suitable organometallic precursor molecules (CO)5Cr(CN-CCl triple bond CClH) (5a), (CO)5Cr(CN-CCI=CClD) (5b), (CO)5Cr(CN-CCl=CCl-CH3) (5c) and (CO)5Cr(CN-CCI=CCl-CD3) (5d), respectively. Compounds 5a-d are formed in two steps by radical alkylation of tetraethyl-ammonium pentacarbonyl(cyano)chromate, NEt4[Cr(CO)5(CN)] (2) by 1,1,2,2,-tetrachloroethane (3a), 1,1,2,2-tetrachloro-1,2-dideuteroethane (3b), 1,1,2,2,-tetrachloropropane (3c), and 1,1,2,2-tetrachloro- 1,3,3,3-tetradeutero-propane (3d) yielding [(CO)5Cr(CN-CCl2-CCl2-H)] (4a), [(CO)5Cr(CN-CCl2-CCl2D)] (4b), [(CO)5Cr(CN-CCl2-CCl2-CH3)] (4c), and [(CO)5Cr(CN-CCl2-CCl2-CD3)] (4d). Dehalogenation of 4a-d using zinc in diethylether/acetic acid gives 5a-d, respectively. A multinuclear NMR study revealed the 1H-, 13C- and 15N-NMR data of 1a and 1c. Molecular spectroscopic data of 1c were determined by high resolution infrared spectroscopy. The by-products of the pyrolysis are the E and Z isomers of the halogenated ethenyl isocyanides H(Cl)C=CCl-NC (6a) and H3C(Cl)C=CCl-NC (6c) which have been characterized by IR, MS and NMR spectroscopy.     

Synthesis, characterization, and activity in ethylene polymerization of silica supported cationic cyclopentadienyl zirconium complexes

Cp*ZrMe3 reacts with silica pretreated at 800 degrees C, SiO(2-(800)) through two pathways: (a) protolysis of a Zr-Me group by surface silanols and (b) transfer of a methyl group to the surface by opening of strained siloxane bridges, in a relative proportion of ca. 9/1, respectively, affording a well-defined surface species [([triple bond]SiO)ZrCp*(Me)2], 3, but with two different local environments 3a, [([triple bond]SiO)ZrCp*(Me)2][[triple bond]Si-O-Si[triple bond]], and the other with 3b, [structure: see text]. The reaction of the species 3 with B(C6F5)3 is controlled by this local environment and gives three surface species [([triple bond]SiO)ZrCp*(Me)](+)[MeB(C6F5)3]- [[triple bond]Si-O-Si[triple bond]], 4a (20%), [([triple bond]SiO)ZrCp*(Me)](+)[(Me)B(C6F5)3]- [[triple bond]Si-Me], 4b (10%), and [([triple bond]SiO)2ZrCp*](+)[(Me)B(C6F5)(3)](-)[[triple bond]Si-O-Si[triple bond]], 5 (70%). On the contrary, the reaction of Cp*Zr(Me)3, Cp2Zr(Me)2 with [[triple bond]SiO-B(C6F5)3](-)[HNEt2Ph]+, 6, leads to a unique species [([triple bond]SiO)B(C6F5)3](-)[Cp*Zr(Me)2.NEt2Ph]+, 7, and [([triple bond]SiO)ZrCp2](+)[(Me)B(C6F5)3]-, 9 respectively. The complexes 4 and 7 are active catalysts in ethylene polymerization at room temperature, 93 and 67 kg PE mol Zr1- atm(-1) bar(-1), respectively, indicating that covalently bounded Zr catalyst 4 is slightly more active than the "floating" cationic catalyst 7.     

Synthesis and luminescence behaviour of novel heterodecanuclear silver(I)-rhenium(I) alkynyl complexes. X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2

A novel series of luminescent heterodecanuclear mixed-metal alkynyl complexes, [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(N--N)(CO)3]4](PF6)2, (N--N = tBu2bpy, Me2bpy, phen, Br2phen), have been successfully synthesized; the X-ray crystal structures of [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Me2bpy)(CO)3]4](PF6)2 and [Ag6(mu-dppm)4[mu3-C[triple bond]CC[triple bond]C-Re(Br2phen)(CO)3]4](PF6)2 have also been determined.     

Cross-metathesis between ethane and toluene catalyzed by [([triple bond, length as m-(SiO)(2)TaH]: the first example of a cross-metathesis reaction between an alkane and an aromatic

The silica-supported tantalum hydride [([triple bond, length as m-dash]SiO)(2)TaH] catalyzes at moderate temperature (150-250 degree C) the cross-metathesis reaction between toluene and ethane, to form mainly ethylbenzene and xylenes.     

Carbon-rich molecules: synthesis and isolation of aryl/heteroaryl terminal bis(butadiynes) (HC[triple bond]C-C[triple bond]C-Ar-C[triple bond]C-C[triple bond]CH) and their applications in the synthesis of oligo(arylenebutadiynylene) molecular wires

The synthesis, isolation and characterisation are reported for a series of terminal aryl/heteroaryl bis(butadiynes) (HC[triple bond]C-C[triple bond]C-Ar-C[triple bond]C-C[triple bond]CH) 4a-e including the X-ray molecular structure of the 2,5-pyridylene derivative 4d; compound 4a and the mono-protected analogue [HC[triple bond]C-C[triple bond]C-Ar-C[triple bond]C-C[triple bond]C-C(OH)Me2] 5a serve as convenient precursors for the synthesis of highly-conjugated oligo(arylenebutadiynylene)s.     

Infrared spectra of CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) formed by activation of CH(4) by molybdenum atoms

Reaction of laser-ablated Mo atoms with CH(4) in excess argon forms the CH(3)-MoH, CH(2)=MoH(2), and CH(triple bond)MoH(3) molecules, which are identified from infrared spectra by isotopic substitution and density functional theory frequency calculations. These simple methyl, methylidene, and methylidyne molybdenum hydride molecules are reversibly interconverted by alpha-H transfers upon visible and ultraviolet irradiations. The methylidene dihydride CH(2)=MoH(2) exhibits CH(2) and MoH(2) distortion and agostic interaction to a lesser degree than CH(2)=ZrH(2). Molybdenum methylidyne trihydride CH(triple bond)MoH(3) is a stable C(3v) symmetry molecule.     

Dramatic enhancement of the alkene metathesis activity of Mo imido alkylidene complexes upon replacement of one tBuO by a surface siloxy ligand

[(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(OtBu)], a well-defined silica supported alkene metathesis catalyst precursor, shows a dramatic enhancement of activity and selectivity compared to [Mo(triple bond NAr)(=CHCMe2R)(OtBu)2] and [(triple bond SiO)Mo(triple bond NAr)(=CHCMe2R)(CH2tBu)], respectively.     

B2(BO)2(2-)-diboronyl diborene: a linear molecule with a triple boron-boron bond

We have produced and investigated an unique boron oxide cluster, B4O2(-), using photoelectron spectroscopy and ab initio calculations. Relatively simple and highly vibrationally resolved PES spectra were obtained at two photon energies (355 and 193 nm). The electron affinity of neutral B4O2 was measured to be 3.160 +/- 0.015 eV. Two excited states were observed for B4O2 at excitation energies of 0.48 and 0.83 eV above the ground state. Three vibrational modes were resolved in the 355 nm spectrum for the ground state of B4O2 with frequencies of 350 +/- 40, 1530 +/- 30, and 2040 +/- 30 cm(-1). Ab initio calculations showed that neutral B4O2 (D(infinity h), 3sigma(g)-) and anionic B4O2(-) (D(infinity h), 2pi(u)) both possess highly stable linear structures (O[triple bond]B-B=B-B[triple bond]O), which can be viewed as a B2 dimer bonded to two terminal boronyl groups. The lowest nonlinear structures are at least 1.5 eV higher in energy. The calculated electron detachment energies from the linear B4O2- and the vibrational frequencies agree well with the experimental results. The three observed vibrational modes are due to the B-B, B=B, and B[triple bond]O symmetric stretching vibrations, respectively, in the linear B2(BO)2. Chemical bonding analyses revealed that the HOMO of B2(BO)2, which is half-filled, is a bonding pi orbital in the central B2 unit. Thus, adding two electrons to B2(BO)2 leads to a B[triple bond]B triple bond in [O[triple bond]B-B[triple bond]B-B[triple bond]O]2-. Possibilities for stabilizing B2(BO)2(2-) in the form of B2(BO)2Li2 are considered computationally and compared with other valent isoelectronic, triple bonded species, B2H2Li2, B2H2(2-), and C2H2. The high stability of B2(BO)2(2-) suggests that it may exist as a viable building block in the condensed phase.     

A microwave spectroscopic and quantum chemical study of propa-1,2-dienyl selenocyanate (H(2)==C==CHSeC[triple bond]N) and cyclopropyl selenocyanate (C(3)H(5)SeC[triple bond]N)

The microwave spectra of propa-1,2-dienyl selenocyanate, H(2)C==C==CHSeC[triple bond]N, and cyclopropyl selenocyanate, C(3)H(5)SeC[triple bond]N, are reported. The spectra of the ground and two vibrationally excited states of the (80)Se isotopologue and the spectrum of the ground state of the (78)Se isotopologue were assigned for one rotameric form of H(2)C==C[double bond, length as m-dash]CHSeC[triple bond]N. This conformer is characterized by a C-C-Se-C dihedral angle of 129(5) degrees from synperiplanar (0 degrees ) and is shown to be the global minimum of H(2)C[double bond, length as m-dash]C[double bond, length as m-dash]CHSeC[triple bond]N. The spectra of the ground and of three vibrationally excited states of the (80)Se isotopologue, as well as of the ground state of the (78)Se isotopologue of one rotamer of C(3)H(5)SeC[triple bond]N were assigned. This conformer has a H-C-Se-C dihedral angle of 80(4) degrees from synperiplanar and is at least 3 kJ mol(-1) more stable than any other form of the molecule. The microwave study has been augmented by quantum chemical calculations at the B3LYP/6-311+ +G(3df,3pd) and MP2/6-311+ +G(3df,3pd) levels of theory.     

Structural consequences of the one-electron reduction of d4 [Mo(CO)2(eta-PhC[triple bond]CPh)Tp']+ and the electronic structure of the d5 radicals [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {L = CO and P(OCH2)3CEt}

Reduction of [M(CO)2(eta-RC[triple bond]CR')Tp']X {Tp' = hydrotris(3,5-dimethylpyrazolyl)borate, M = Mo, X = [PF6]-, R = R' = Ph, C6H4OMe-4 or Me; R = Ph, R' = H; M = W, X = [BF4]-, R = R' = Ph or Me; R = Ph, R' = H} with [Co(eta-C5H5)2] gave paramagnetic [M(CO)2(eta-RC[triple bond]CR')Tp'], characterised by IR and ESR spectroscopy. X-Ray structural studies on the redox pair [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'] and [Mo(CO)2(eta-PhC[triple bond]CPh)Tp'][PF6] showed that oxidation is accompanied by a lengthening of the C[triple bond]C bond and shortening of the Mo-C(alkyne) bonds, consistent with removal of an electron from an orbital antibonding with respect to the Mo-alkyne bond, and with conversion of the alkyne from a three- to a four-electron donor. Reduction of [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'][PF6] with [Co(eta-C5H5)2] in CH2Cl2 gives [MoCl(CO)(eta-MeC[triple bond]CMe)Tp'], via nitrile substitution in [Mo(CO)(NCMe)(eta-MeC[triple bond]CMe)Tp'], whereas a similar reaction with [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']+ (M = Mo or W) gives the phosphite-containing radicals [M(CO){P(OCH2)3CEt}(eta-MeC[triple bond]CMe)Tp']. ESR spectroscopic studies and DFT calculations on [M(CO)L(eta-MeC[triple bond]CMe)Tp'] {M = Mo or W, L = CO or P(OCH2)3CEt} show the SOMO of the neutral d5 species (the LUMO of the d4 cations) to be largely d(yz) in character although much more delocalised in the W complexes. Non-coincidence effects between the g and metal hyperfine matrices in the Mo spectra indicate hybridisation of the metal d-orbitals in the SOMO, consistent with a rotation of the coordinated alkyne about the M-C2 axis.     

Generation and coupling of [Mn(dmpe)2(C triple bond CR)(C triple bond C)]* radicals producing redox-active C4-bridged rigid-rod complexes

The symmetric d(5) trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)] (R = Me, 1 a; Et, 1 b; Ph, 1 c) (dmpe = 1,2-bis(dimethylphosphino)ethane) have been prepared by the reaction of [Mn(dmpe)(2)Br(2)] with two equivalents of the corresponding acetylide LiC triple bond CSiR(3). The reactions of species 1 with [Cp(2)Fe][PF(6)] yield the corresponding d(4) complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(2)][PF(6)] (R = Me, 2 a; Et, 2 b; Ph, 2 c). These complexes react with NBu(4)F (TBAF) at -10 degrees C to give the desilylated parent acetylide compound [Mn(dmpe)(2)(C triple bond CH)(2)][PF(6)] (6), which is stable only in solution at below 0 degrees C. The asymmetrically substituted trans-bis-alkynyl complexes [Mn(dmpe)(2)(C triple bond CSiR(3))(C triple bond CH)][PF(6)] (R = Me, 7 a; Et, 7 b) related to 6 have been prepared by the reaction of the vinylidene compounds [Mn(dmpe)(2)(C triple bond CSiR(3))(C=CH(2))] (R = Me, 5 a; Et, 5 b) with two equivalents of [Cp(2)Fe][PF(6)] and one equivalent of quinuclidine. The conversion of [Mn(C(5)H(4)Me)(dmpe)I] with Me(3)SiC triple bond CSnMe(3) and dmpe afforded the trans-iodide-alkynyl d(5) complex [Mn(dmpe)(2)(C triple bond CSiMe(3))I] (9). Complex 9 proved to be unstable with regard to ligand disproportionation reactions and could therefore not be oxidized to a unique Mn(III) product, which prevented its further use in acetylide coupling reactions. Compounds 2 react at room temperature with one equivalent of TBAF to form the mixed-valent species [[Mn(dmpe)(2)(C triple bond CH)](2)(micro-C(4))][PF(6)] (11) by C-C coupling of [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] radicals generated by deprotonation of 6. In a similar way, the mixed-valent complex [[Mn(dmpe)(2)(C triple bond CSiMe(3))](2)(micro-C(4))][PF(6)] [12](+) is obtained by the reaction of 7 a with one equivalent of DBU (1,8-diazabicyclo[5.4.0]undec-7-ene). The relatively long-lived radical intermediate [Mn(dmpe)(2)(C triple bond CH)(C triple bond C*)] could be trapped as the Mn(I) complex [Mn(dmpe)(2)(C triple bond CH)(triple bond C-CO(2))] (14) by addition of an excess of TEMPO (2,2,6,6-tetramethyl-1-piperidinyloxy) to the reaction mixtures of species 2 and TBAF. The neutral dinuclear Mn(II)/Mn(II) compounds [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))] (R = H, 11; R = SiMe(3), 12) are produced by the reduction of [11](+) and [12](+), respectively, with [FeCp(C(6)Me(6))]. [11](+) and [12](+) can also be oxidized with [Cp(2)Fe][PF(6)] to produce the dicationic Mn(III)/Mn(III) species [[Mn(dmpe)(2)(C triple bond CR(3))](2)(micro-C(4))][PF(6)](2) (R = H, [11](2+); R = SiMe(3), [12](2+)). Both redox processes are fully reversible. The dinuclear compounds have been characterized by NMR, IR, UV/Vis, and Raman spectroscopies, CV, and magnetic susceptibilities, as well as elemental analyses. X-ray diffraction studies have been performed on complexes 4 b, 7 b, 9, [12](+), [12](2+), and 14.     

Aliphatic and aromatic carbon-fluorine bond activation with Cp*(2)ZrH(2): mechanisms of hydrodefluorination.

Cp*(2)ZrH(2) (1) (Cp* = pentamethylcyclopentadienyl) reacts with primary, secondary, and tertiary monofluorinated aliphatic hydrocarbons to give Cp*(2)ZrHF (2) and/or Cp*(2)ZrF(2) and alkane quantitatively through a radical chain mechanism. The reactivity of monofluorinated aliphatic C-F bonds decreases in the order 1 degrees > 2 degrees > 3 degrees. The rate of hydrodefluorination was also greatly reduced with -CF(2)H and -CF(3) groups attached to the hydrocarbon. An atmosphere of H(2) is required to stabilize 1 against C-H activation of the Cp*-methyl groups and subsequent dimerization under the thermal conditions employed in these reactions. Reaction of 1 with fluorobenzene cleanly forms a mixture of Cp*(2)ZrHF, benzene, and Cp*(2)Zr(C(6)H(5))F. Detailed studies indicate that radicals are not involved in this aromatic C-F activation reaction and that dual hydrodefluorination pathways are operative. In one mechanism, hydridic attack by Cp*(2)ZrH(2) on the aromatic ring and fluoride abstraction is involved. In the second mechanism, an initial ortho C-H activation occurs, followed by beta-fluoride elimination to generate a benzyne complex, which then inserts into the zirconium-hydride bond.     

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.     

Ancillary ligands and spectator cations as controlling factors in the construction of coordination and hydrogen-bonded networks with the tert-Bu-C triple bond C superset Ag(n) (n=4, 5) supramolecular synthon

Supramolecular networks constructed with the tBu--C[triple bond]C superset Ag(n) (n=4 or 5) metal-ligand synthon and trifluoroacetate have been transformed through the introduction of ancillary terminal nitrile ligands, from acetonitrile through propionitrile to tert-butyronitrile, giving rise to a 2D coordination network in AgC[triple chemical bond]CtBu3 AgCF(3)CO(2)H(2)O (1), a 2D hydrogen-bonded network in AgC[triple chemical bond]CtBu5 AgCF(3)CO(2)4 CH(3)CNH(2)O (2), a 2D hybrid coordination/hydrogen-bonded network in AgC[triple chemical bond]CtBu3 AgCF(3)CO(2)CH(3)CH(2)CN2 H(2)O (3), and another 2D coordination network in AgC[triple chemical bond]CtBu4 AgCF(3)CO(2) (CH(3))(3)CCN2 H(2)O (4). Concomitantly, the linkage modes between adjacent ethynide-bound Ag(n) aggregates in these compounds are also changed. A layer-type hydrogen-bonded host lattice in isostructural AgC[triple chemical bond]CtBu4 AgCF(3)CO(2)(R(4)N)(CF(3)CO(2)) 2 H(2)O (R(4)=BnMe(3), 5; R(4)=Et(4), 6; R(4)=nPr(4), 7) is obtained by introducing quaternary ammonium cations as guest templates, which occupy the interstices and thereby mediate the interlayer separation. Use of the bulky nBu(4)N(+) cation leads to disruption of the host network in AgC[triple bond]CtBu4 AgCF(3)CO(2)3[(nBu(4)N)(CF(3)CO(2))]H(2)O (8) with generation of a discrete dense nido-Ag(5) cluster.     

Defluorination of perfluoropropene using Cp*2ZrH2 and Cp2ZrHF: a mechanism investigation from a joint experimental-theoretical perspective

Cp*(2)ZrH(2) (1) (Cp* = pentamethylcyclopentadienyl) reacts with perfluoropropene (2) to give Cp*(2)ZrHF (3) and hydrodefluorinated products under very mild conditions. Initial C-F bond activation occurs selectively at the vinylic terminal position of the olefin to exchange fluorine for hydrogen. Subsequent hydrodefluorination leads to the formation of the n-propylhydride complex Cp*(2)ZrH(CH(2)CH(2)CH(3)), which can be cleaved with dihydrogen to give propane and 1. A theoretical study of the reaction of Cp*(2)ZrH(2) (Cp* = cyclopentadienyl) and CF(2)[double bond]CF(CF(3)) has been undertaken. Several mechanisms have been examined in detail using DFT(B3PW91) calculations and are discussed for this H/F exchange: (a) internal olefin insertion/beta-fluoride elimination, (b) external olefin insertion/beta-fluoride elimination, and (c) F/H metathesis from either an inside or outside approach. Of these, the first case is found to be energetically preferred. Selective defluorination at the terminal carbon has been shown to be favored over defluorination at the substituted and allylic carbons.