Philip P. Power

University of California, Davis, Davis, California, United States

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Publications (551)3515.41 Total impact

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    ABSTRACT: The characterization of the unstable Ni(II) bis(silylamide) Ni{N(SiMe3 )2 }2 (1), its THF complex Ni{N(SiMe3 )2 }2 (THF) (2), and the stable bis(pyridine) derivative trans-Ni{N(SiMe3 )2 }2 (py)2 (3), is described. Both 1 and 2 decompose at ca. 25 °C to a tetrameric Ni(I) species, [Ni{N(SiMe3 )2 }]4 (4), also obtainable from LiN(SiMe3 )2 and NiCl2 (DME). Experimental and computational data indicate that the instability of 1 is likely due to ease of reduction of Ni(II) to Ni(I) and the stabilization of 4 through dispersion forces. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition 09/2015; DOI:10.1002/anie.201505518 · 11.26 Impact Factor
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    ABSTRACT: The bis(μ-oxo) dimeric complexes {Ar(iPr8)OM(μ-O)}2 (Ar(iPr8) = C6H-2,6-(C6H2-2,4,6-(i)Pr3)2-3,5-(i)Pr2; M = Fe (1), Co (2)) were prepared by oxidation of the M(I) half-sandwich complexes {Ar(iPr8)M(η(6)-arene)} (arene = benzene or toluene). Iron species 1 was prepared by reacting {Ar(iPr8)Fe(η(6)-benzene)} with N2O or O2, and cobalt species 2 was prepared by reacting {Ar(iPr8)Co(η(6)-toluene)} with O2. Both 1 and 2 were characterized by X-ray crystallography, UV-vis spectroscopy, magnetic measurements, and, in the case of 1, Mössbauer spectroscopy. The solid-state structures of both compounds reveal unique M2(μ-O)2 (M = Fe (1), Co(2)) cores with formally three-coordinate metal ions. The Fe···Fe separation in 1 bears a resemblance to that in the Fe2(μ-O)2 diamond core proposed for the methane monooxygenase intermediate Q. The structural differences between 1 and 2 are reflected in rather differing magnetic behavior. Compound 2 is thermally unstable, and its decomposition at room temperature resulted in the oxidation of the Ar(iPr8) ligand via oxygen insertion and addition to the central aryl ring of the terphenyl ligand to produce the 5,5'-peroxy-bis[4,6-(i)Pr2-3,7-bis(2,4,6-(i)Pr3-phenyl)oxepin-2(5H)-one] (3). The structure of the oxidized terphenyl species is closely related to that of a key intermediate proposed for the oxidation of benzene.
    Inorganic Chemistry 09/2015; 54(18). DOI:10.1021/acs.inorgchem.5b00930 · 4.76 Impact Factor
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    ABSTRACT: Treatment of the linear, two-coordinate Mn(II) dialkyl complex, Mn{C(SiMe3)3}2, with KC8 and 18-crown-6 or 15-crown-5 afforded the first two-coordinate Mn(I) dialkyl salts, [K2(18-crown-6)3][Mn{C(SiMe3)3}2]2 (1) and [K(15-crown-5)2][Mn{C(SiMe3)3}2] (2), which were characterized by X-ray crystallography, UV-vis spectroscopy, SQUID magnetometry and EPR spectroscopy. The two compounds have similar magnetic properties that are consistent with the presence of 3d6 manganese(I) ions with S = 2 ground states and a quenched orbital magnetic moment, in contrast to the isoelectronic d6 species Fe{C(SiMe3)3}2, which exhibits an ml = ±2 orbital contribution in the ground state. Ab initio multiconfigurational calculations show that this is a result of 4s–3dz2 mixing, resulting in a (3dz2)2(3dxy)1(3dx2–y2)1(3dxz)1(3dyz)1 configuration with no first-order orbital angular momentum.
    Chemical Communications 07/2015; 51(68). DOI:10.1039/C5CC05166E · 6.83 Impact Factor
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    ABSTRACT: Metalloradical species [Co2 Fv(CO)4 ](.+) (1(.+) , Fv=fulvalenediyl) and [Co2 Cp2 (CO)4 ](.+) (2(.+) , Cp=η(5) -C5 H5 ), formed by one-electron oxidations of piano-stool cobalt carbonyl complexes, can be stabilized with weakly coordinating polyfluoroaluminate anions in the solid state. They feature a supported and an unsupported (i.e. unbridged) cobalt-cobalt three-electron σ bond, respectively, each with a formal bond order of 0.5 (hemi-bond). When Cp is replaced by bulkier Cp* (Cp*=η(5) -C5 Me5 ), an interchange between an unsupported radical [Co2 Cp*2 (CO)4 ](.+) (anti-3(.+) ) and a supported radical [Co2 Cp*2 (μ-CO)2 (CO)2 ](.+) (trans-3(.+) ) is observed in solution, which cocrystallize and exist in the crystal phase. 2(.+) and anti-3(.+) are the first stable thus isolable examples that feature an unsupported metal-metal hemi-bond, and the coexistence of anti-3(.+) and trans-3(.+) in one crystal is unprecedented in the field of dinuclear metalloradical chemistry. The work suggests that more stable metalloradicals of metal-metal hemi-bonds may be accessible by using metal carbonyls together with large and weakly coordinating polyfluoroaluminate anions. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition 06/2015; 127(31). DOI:10.1002/anie.201503392 · 11.26 Impact Factor
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    ABSTRACT: The synthesis and characterization of a series of heavier group 14 element (Ge, Sn, and Pb) carbene homologues based on the electronically modified, 2,6-dimesityl substituted terphenyl ligands Ar#-3,5-iPr2, Ar#-4-SiMe3, and Ar#-4-Cl (Ar#-3,5-iPr2 = C6H2-2,6-Mes2-3,5-iPr2; Ar#-4-Cl = C6H2-2,6-Mes2-4-Cl; Ar#-4-SiMe3 = C6H2-2,6-Mes2-4-SiMe3; Mes = C6H2-2,4,6-Me3) are presented. The consequences of introducing electron withdrawing and -releasing substituents on the solid state structures of the newly synthesized germylenes, stannylenes, and plumbylenes as well as their Mössbauer, NMR and UV–vis spectroscopic properties are presented and discussed in the context of a second order Jahn–Teller type mixing of frontier orbitals with appropriate symmetry. Experimental findings were supported by DFT calculations. More electron withdrawing ligands lead to a bonding situation with higher contribution of p-orbitals from the central heavier group 14 element in σ-bonding toward the ligands and thus increased s-electron character of the lone pair. Furthermore, this results in an increase in the energy separation between the frontier orbitals. Experimentally, these changes are manifested in narrower bending angles at the heavy tetrel atoms and hypsochromic in their UV–vis spectra. In contrast, derivatives of more electron rich m-terphenyl ligands are characterized by a smaller HOMO–LUMO gap and wider interligand angles.
    Organometallics 06/2015; 34(11):2222-2232. DOI:10.1021/om500946e · 4.13 Impact Factor
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    ABSTRACT: The 2 to 300 K magnetic susceptibilities of Fe{N(SiMe2Ph)2}2, 1, Fe{N(SiMePh2)2}2, 2, and the diaryl complex Fe(ArPri4)2, 3, where ArPri4 is C6H3-2,6(C6H3-2,6-Pri2)2 have been measured. Initial fits of these properties in the absence of an independent knowledge of their ligand field splitting have proven problematic. Ab initio calculations of the CASSCF/RASSI/SINGLE-ANISO type have indicated that the orbital energies of the complexes, as well as those of Fe(ArMe6)2, 4, where ArMe6 is C6H3-2,6(C6H2-2,4,6-Me3)2), are in the order dxy ≈ dx2–y2 < dxz ≈ dyz < dz2, and the iron(II) complexes in this ligand field have the (dxy, dx2–y2)3(dxz, dyz)2(dz2)1 ground electronic configuration with a substantial orbital contribution to their effective magnetic moments. An ab initio-derived ligand field and spin-orbit model is found to yield an excellent simulation of the observed magnetic properties of 1 – 3. The calculated ligand field strengths of these ligands are placed in the broader context of common coordination ligands in hypothetical two-coordinate linear iron(II) complexes. This yields the ordering I− < H− < Br− ≈ PMe3 < CH3− < Cl− ≈ C(SiMe3)3− < CN− ≈ SArPri6− < ArPri4− < ArMe6− ≈ N3− < NCS− ≈ NCSe− ≈ NCBH3− ≈ MeCN ≈ H2O ≈ NH3 < NO3− ≈ THF ≈ CO ≈ N(SiMe2Ph)2− ≈ N(SiMePh2)2− < F− ≈ N(H)ArPri6− ≈ N(SiMe3)Dipp− < OArPri4−. The magnetic susceptibility of the bridged dimer, [Fe{N(SiMe3)2}2]2, 5, has also been measured between 2 and 300 K and a fit of χMT with the isotropic Heisenberg Hamiltonian, H =-2JS1∙S2 yields an antiferromagnetic exchange coupling constant, J, of –131(2) cm–1.
    Dalton Transactions 05/2015; 44(24). DOI:10.1039/C5DT01589H · 4.20 Impact Factor
  • Jing-Dong Guo · Shigeru Nagase · Philip P. Power
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    ABSTRACT: The dissociation of the sterically encumbered diphosphanes and diarsanes [:E{CH(SiMe3)2}2]2 (E = P or As) and [:E{N(SiMe3)2}2]2 (E = P or As) into :Ė{CH(SiMe3)2}2 or :Ė{N(SiMe3)2}2 radical monomers was studied computationally using hybrid density functional theory (DFT) at the B3PW91 with the 6-311+G(d) basis set for P and As, and the 6-31G(d,p) basis set for other atoms. The structures were reoptimized with the dispersion corrected B3PW91-D3 method to estimate dispersion force effects. The calculations reproduced the experimental structural data for the tetraalkyls with good accuracy. Without the dispersion correction, negative dissociation energies of −10.3 and −6.5 kcal mol-1 were calculated for the phosphorus and arsenic tetraalkyls, indicating that the radical monomers are more stable. In contrast, the incorporation of dispersion force effects afforded high, positive dissociation energies of +37.6 and +37.1 kcal mol-1 that favored dimeric structures. The dissociation energies (without dispersion) calculated for the tetraamido-substituted dimer are also negative, but changed to positive values of +29.3 and +32.5 kcal mol-1 upon optimization with the D3 dispersion term. In contrast to earlier calculations, which indicated that the release of accumulated strain energy within the tetraalkyl dimers was the driving force for dissociation to monomers (i.e., the “Jack-in-the-Box” molecular model), the current calculations show that dispersion force attractive interactions exceed those of ligand relaxation and stabilize the dimeric structures. Single-point MP2 (second-order Møller-Plesset perturbation theory) calculations including dispersion effects afforded dissociation energies of 30.4 and 30.8 kcal mol-1 for the tetraalkyl species, suggesting that the addition of the D3 dispersion term to the B3PW91 functional may overestimate such forces by 7-8 kcal mol-1. It is concluded that the balance of dispersion forces and entropic effects are the major determinants of the dissociation equilibria.
    Organometallics 05/2015; 34(10):150513115037004. DOI:10.1021/acs.organomet.5b00254 · 4.13 Impact Factor
  • Jeremy D Erickson · James C Fettinger · Philip P Power
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    ABSTRACT: The reaction of the tetrylenes Ge(Ar((Me)6))2, Sn(Ar((Me)6))2, and Pb(Ar((Me)6))2 [Ar((Me)6) = C6H3-2,6-(C6H2-2,4,6-(CH3)3)2] with the group 13 metal alkyls trimethylaluminum and trimethylgallium afforded (Ar((Me)6))2Ge(Me)AlMe2 (1), (Ar((Me)6))2Ge(Me)GaMe2 (2), and (Ar(Me6))2Sn(Me)GaMe2 (3) in good yields via insertion reaction routes. In contrast, the reaction of AlMe3 with Sn(Ar((Me)6))2 afforded the [1.1.1]propellane analogue Sn2{Sn(Me)Ar((Me)6)}3 (5) in low yield, and the reaction of AlMe3 or GaMe3 with Pb(Ar((Me)6))2 resulted in the formation of the diplumbene {Pb(Me)Ar((Me)6)}2 (6) and AlAr((Me)6)Me2 (7) or GaAr((Me)6)Me2 (8) via metathesis. The reaction of Sn(Ar((Me)6))2 with gallium trialkyls was found to be reversible under ambient conditions and analyzed through the reaction of Sn(Ar((Me)6))2 with GaEt3 to form (Ar((Me)6))2Sn(Et)GaEt2 (4), which displayed a dissociation constant Kdiss and ΔGdiss of 8.09(6) × 10(-3) and 11.8(9) kJ mol(-1) at 296 °C. The new compounds were characterized by X-ray crystallography, NMR ((1)H, (13)C, (119)Sn, and (207)Pb), IR, and UV-vis spectroscopies.
    Inorganic Chemistry 01/2015; 54(4). DOI:10.1021/ic502824w · 4.76 Impact Factor
  • Petra Vasko · Shuai Wang · Heikki M Tuononen · Philip P Power
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    ABSTRACT: Reaction of the tin cluster Sn8 (Ar Me 6)4 (Ar Me 6=C6 H2 -2,6-(C6 H3 -2,4,6-Me3 )2 ) with excess ethylene or dihydrogen at 25 °C/1 atmosphere yielded two new clusters that incorporated ethylene or hydrogen. The reaction with ethylene yielded Sn4 (Ar Me 6)4 (C2 H2 )5 that contained five ethylene moieties bridging four aryl substituted tin atoms and one tin-tin bond. Reaction with H2 produced a cyclic tin species of formula (Sn(H)Ar Me 6)4 , which could also be synthesized by the reaction of {(Ar Me 6)Sn(μ-Cl)}2 with DIBAL-H. These reactions represent the first instances of direct reactions of isolable main-group clusters with ethylene or hydrogen under mild conditions. The products were characterized in the solid state by X-ray diffraction and IR spectroscopy and in solution by multinuclear NMR and UV/Vis spectroscopies. Density functional theory calculations were performed to explain the reactivity of the cluster. © 2015 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.
    Angewandte Chemie International Edition in English 01/2015; 127(12). DOI:10.1002/anie.201411595 · 13.45 Impact Factor
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    ABSTRACT: Cycloaddition reactions of the acyclic silylene Si(SAriPr4)2 (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) with a variety of alkenes and alkynes were investigated. Its reactions with the alkynes phenylacetylene and diphenylacetylene and the diene 2,3-dimethyl-1,3-butadiene yielded silacycles (AriPr4S)2Si(CH═CPh) (1), (AriPr4S)2Si(PhC═CPh) (2), and (AriPr4S)2SiCH2CMeCMeCH2 (3) at ambient temperature. The compounds were characterized by X-ray crystallography, 1H, 13C, and 29Si NMR spectroscopy, and IR spectroscopy. No reaction was observed with more substituted alkenes such as propene, (Z)-2-butene, tert-butylethylene, cyclopentene, 1-hexene, or the alkyne bis(trimethylsilyl)acetylene under the same reaction conditions. The germylene Ge(SArMe6)2 and stannylene Sn(SArMe6)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2) analogues of Si(SArMe6)2 displayed no reaction with ethylene. Quantum chemical calculations using model tetrylenes E(SPh)2 (E = Si, Ge, Sn; Ph = C6H5) show that cyclization reactions are endothermic in the case of germanium and tin derivatives but energetically favored for the silicon species.
    Organometallics 11/2014; 33(21):6253-6258. DOI:10.1021/om500947x · 4.13 Impact Factor
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    ABSTRACT: Mössbauer studies of three two-coordinate linear high-spin Fe(2+) compounds, namely, Fe{N(SiMe3)(Dipp)}2 (1) (Dipp = C6H3-2,6-(i)Pr2), Fe(OAr')2 (2) [Ar' = C6H3-2,6-(C6H3-2,6-(i)Pr2)2], and Fe{C(SiMe3)3}2 (3), are presented. The complexes were characterized by zero- and applied-field Mössbauer spectroscopy (1-3), as well as zero- and applied-field heat-capacity measurements (3). As 1-3 are rigorously linear, the distortion(s) that might normally be expected in view of the Jahn-Teller theorem need not necessarily apply. We find that the resulting very large unquenched orbital angular momentum leads to what we believe to be the largest observed internal magnetic field to date in a high-spin iron(II) compound, specifically +162 T in 1. The latter field is strongly polarized along the directions of the external field for both longitudinal and transverse field applications. For the longitudinal case, the applied field increases the overall hyperfine splitting consistent with a dominant orbital contribution to the effective internal field. By contrast, 2 has an internal field that is not as strongly polarized along a longitudinally applied field and is smaller in magnitude at ca. 116 T. Complex 3 behaves similarly to complex 1. They are sufficiently self-dilute (e.g., Fe···Fe distances of ca. 9-10 Å) to exhibit varying degrees of slow paramagnetic relaxation in zero field for the neat solid form. In the absence of EPR signals for 1-3, we show that heat-capacity measurements for one of the complexes (3) establish a geff value near 12, in agreement with the principal component of the ligand electric field gradient being coincident with the z axis.
    Inorganic Chemistry 11/2014; 53(22). DOI:10.1021/ic501925e · 4.76 Impact Factor
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    ABSTRACT: The reactions of the sterically crowded primary alane (Ar(Pr)i(8)AlH(2))(2) (Ar(Pr)i(8) = C6H-2,6(C6H2-2,4,6-Pr-3(i))(2)-3,5-Pr-2(i)) with alkynes and alkenes are described. It is shown that hydroalumination of the terminal alkynes HCCSiMe3 and HCCPh readily occurs under mild conditions via the cis-addition of the AlH moiety across the CC triple bond with no evidence of hydrogen elimination. Hydroalumination was observed also with a range of terminal olefins, but no reactivity was observed with internal alkenes or alkynes. The relatively high reactivity of (Ar(Pr)i(8)AlH(2))(2) was attributed to the steric crowding of the large terphenyl substituent, which favors dissociation of the alane and increases the availability of the more reactive three-coordinate aluminum site in the monomer. In keeping with this view, studies of the reactions of the three primary alanes (Ar(Pr)i(8)AlH(2))(2), (Ar(Pr)i(4)AlH(2))(2) (Ar(Pr)i(4) = C6H3-2,6(C6H3-2,6-Pr-2(i))(2)), and ((Ar6AlH2)-Al-Me)(2) (Ar-6(Me) = C6H3-2,6(C6H2-2,4,6-Me-3)(2)) with alkenes showed that the reaction rates are inversely proportional to the size of the terphenyl substituent, consistent with higher reactivity of the aluminum monomer. The structures of the alkenyl insertion products, Ar(Pr)i(8)Al(CHCHPh)2 and Ar(Pr)i(8)Al(CHCHSiMe3)(2), the alkylated derivative, Ar(Pr)i(8)Al(CH2CH2SiMe3)(2), and the precursor aluminates {Li(OEt2)H(3)AlAr(Pr)i(8).Li(OEt2)(2)H(3)AlAr(Pr)i(8)}, (LiH3AlAr(Pr)i(8))(2), and alanes (Ar(Pr)i(8)AlH(2))(2), and (Ar(Pr)i(4)AlH(2))(2) were determined by X-ray crystallography.
    Organometallics 10/2014; DOI:10.1021/om500911f · 4.13 Impact Factor
  • Felicitas Lips · James C. Fettinger · Philip P. Power
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    ABSTRACT: The reaction of the bulky lithium terphenyl thiolates LISArMe6 (Ar-Me6 = C6H3-2,6-(C6H2-2,4,6-Me-3)(2)) and LiSAriPr4 (AriPr4 = C8H3-2,6-(C8H3-2,6-iPr2)2) with AlBr3 in PhMe or Et20 resulted in the formation of two new lithium aluminum thiolate salts LiAl(SArme6)2Br2.PhMe 1, [LiAl(SArme6)Br312 2, and the etherate Al(SAriPr4)13r2(OEt2) 3. Compounds 1-3 were structurally characterized and analyzed by 1H, 13C NMR and IR spectroscopy. In further investigations the reduction of 1 and 2 with KC8 or Rieke's magnesium in different solvent systems afforded the compounds KAI(SArme6)3H.2PhMe 4 and LiAl(SArme6)Bro3811.84(2THF).PhMe 5. All of the compounds described herein contain four-coordinate aluminum atoms with distorted tetrahedral geometries.
    Polyhedron 09/2014; 79:207–212. DOI:10.1016/j.poly.2014.04.056 · 2.01 Impact Factor
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    ABSTRACT: Three potassium crown ether salts, [K(Et2O)2(18-crown-6)][Fe{N(SiMe3)Dipp}2] (1a; Dipp = C6H3-2,6-Pr(i)2), [K(18-crown-6)][Fe{N(SiMe3)Dipp}2]·0.5PhMe (1b), and [K(18-crown-6)][M{N(SiMe3)Dipp}2] (M = Co, 2; M = Ni, 3), of the two-coordinate linear or near-linear bis-amido monoanions [M{N(SiMe3)Dipp}2](-) (M = Fe, Co, Ni) were synthesized by one-electron reduction of the neutral precursors M{N(SiMe3)Dipp}2 with KC8 in the presence of 18-crown-6. They were characterized by X-ray crystallography, UV-vis spectroscopy, cyclic voltammetry, and magnetic measurements. The anions feature lengthened M-N bonds in comparison with their neutral precursors, with slightly bent coordination (N-Fe-N = ca. 172°) for the iron(I) complex, but linear coordination for the cobalt(I) and nickel(I) complexes. Fits of the temperature dependence of χMT of 1 and 2 reveal that the iron(I) and cobalt(I) complexes have large negative D zero-field splittings and a substantial orbital contribution to their magnetic moments with L = 2, whereas the nickel(I) complex has at most a small orbital contribution to its magnetic moment. The magnetic results have been used to propose an ordering of the 3d orbitals in each of the complexes.
    Inorganic Chemistry 08/2014; 53(17). DOI:10.1021/ic501534f · 4.76 Impact Factor
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    ABSTRACT: Mono- and bis-terphenyl complexes of molybdenum and tungsten with general composition M2(Ar')(O2CR)3 and M2(Ar')2(O2CR)2, respectively (Ar' = terphenyl ligand), that contain carboxylate groups bridging the quadruply bonded metal atoms, have been prepared and structurally characterized. The new compounds stem from the reactions of the dimetal tetracarboxylates, M2(O2CR)4 (M = Mo, R = H, Me, CF3; M = W, R = CF3) with the lithium salts of the appropriate terphenyl groups (Ar' = ArXyl2, ArMes2, ArDipp2 and ArTrip2). Substitution of one bidentate carboxylate by a monodentate terphenyl forms a M-C σ bond and creates a coordination unsaturation at the other metal atom. Hence in M2(Ar')2(O2CR)2 complexes the two metal atoms have a low coordination number and an also low electron count (fourteen). The unsaturation seems to be compensated by a weak M-Carene interaction that implicates one of the aryl substituents of the terphenyl central aryl ring, as revealed by X-ray studies performed with some of these complexes. Notwithstanding, the long M-Carene distances of ca. 2.78 Å found in some of these complexes suggest that the flanking aryl ring, whose spatial distribution is imposed by the topology of the Ar' ligand, may simply provide steric protection to the low-coordinate metal centre.
    Journal of the American Chemical Society 05/2014; 136(25). DOI:10.1021/ja503750a · 12.11 Impact Factor
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    ABSTRACT: Two unique systems based on low-coordinate main group elements that activate P4 are shown to quantitatively release the phosphorus cage upon short exposure to UV light. This reactivity marks the first reversible reactivity of P4, and the germanium system can be cycled 5 times without appreciable loss in activity. Theoretical calculations reveal that the LUMO is antibonding with respect to the main group element–phosphorus bonds and bonding with respect to reforming the P4 tetrahedron, providing a rationale for this unprecedented activity, and suggesting that the process is tunable based on the substituents.
    Chemistry - A European Journal 05/2014; 20(22). DOI:10.1002/chem.201402031 · 5.73 Impact Factor
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    ABSTRACT: The homoleptic cobalt(I) alkyl [Co{C(SiMe2Ph)3}]2 (1) was prepared by reacting CoCl2 with [Li{C(SiMe2Ph)3}(THF)] in a 1:2 ratio. Attempts to synthesize the corresponding iron(I) species led to the iron(II) salt [Li(THF)4][Fe2(μ-Cl)3{C(SiMe2Ph)3}2] (2). Both 1 and 2 were characterized by X-ray crystallography, UV–vis spectroscopy, and magnetic measurements. The structure of 1 consists of dimeric units in which each cobalt(I) ion is σ-bonded to the central carbon of the alkyl group −C(SiMe2Ph)3 and π-bonded to one of the phenyl rings of the −C(SiMe2Ph)3 ligand attached to the other cobalt(I) ion in the dimer. The structure of 2 features three chlorides bridging two iron(II) ions. Each iron(II) ion is also σ-bonded to the central carbon of a terminal −C(SiMe2Ph)3 anionic ligand. The magnetic properties of 1 reveal the presence of two independent cobalt(I) ions with S = 1 and a significant zero-field splitting of D = 38.0(2) cm–1. The magnetic properties of 2 reveal extensive antiferromagnetic exchange coupling with J = −149(4) cm–1 and a large second-order Zeeman contribution to its molar magnetic susceptibility. Formation of the alkyl 1 and the halide complex 2 under similar conditions is probably due in part to the fact that Co(II) is more readily reduced than Fe(II).
    Organometallics 04/2014; 33(8):1917–1920. DOI:10.1021/om500180u · 4.13 Impact Factor
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    ABSTRACT: Reactions of the tetrylenes Ge(SAr(Me6))2 () (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2), and Sn(SAr(Me6))2 () with (Mo(CO)4(NBD) (NBD = bicyclo[2.2.1]hepta-2,5-diene) gave three new, unusual complexes [Mo(THF)(CO)3{Ge(SAr(Me6))2}] (), [Mo(THF)(CO)3{Ge(SAr(Me6))2}] () and [Mo(CO)4{Sn(SAr(Me6))2}] () which display no significant Ge/Sn-Mo bonding. Instead the ligands are coordinated to molybdenum in a bidentate fashion via the thiolato sulfurs.
    Chemical Communications 04/2014; 50(42). DOI:10.1039/c4cc00999a · 6.83 Impact Factor
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    Aimee M Bryan · Gary J Long · Fernande Grandjean · Philip P Power
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    ABSTRACT: Treatment of the cobalt(II) amide, [Co{N(SiMe3)2}2]2, with four equivalents of the sterically crowded terphenyl phenols, HOAr(Me6) (Ar(Me6) = C6H3-2,6(C6H2-2,4,6-Me3)2) or HOAr(iPr4) (Ar(iPr4) = C6H3-2,6(C6H3-2,6-Pr(i)2)2), produced the first well-characterized, monomeric two-coordinate cobalt(II) bisaryloxides, Co(OAr(Me6))2 (1) and Co(OAr(iPr4))2 (2a and 2b), as red solids in good yields with elimination of HN(SiMe3)2. The compounds were characterized by electronic spectroscopy, X-ray crystallography, and direct current magnetization measurements. The O-Co-O interligand angles in 2a and 2b are 180°, whereas the O-Co-O angle in 1 is bent at 130.12(8)° and its cobalt(II) ion has a highly distorted pseudotetrahedral geometry with close interactions to the ipso-carbons of the two flanking aryl rings. The Co-O distances in 1, 2a, and 2b are 1.858(2), 1.841(1), and 1.836(2) Å respectively. Structural refinement revealed that 1, 2a, and 2b have different fractional occupations of the cobalt site in their crystal structures: 1, 95.0%, 2a, 93.5%, and 2b, 84.6%. Correction of the magnetic data for the different cobalt(II) occupancies showed that the magnetization of 2a and 2b was virtually identical. The effective magnetic moments for 1, 2a, and 2b, 5.646(5), 5.754(5), and 5.636(3) μB respectively, were indicative of significant spin-orbit coupling. The differences in magnetic properties between 1 and 2a/2b are attributed to their different cobalt coordination geometries.
    Inorganic Chemistry 02/2014; 53(5). DOI:10.1021/ic403098p · 4.76 Impact Factor
  • Mateusz Brela · Artur Michalak · Philip P Power · Tom Ziegler
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    ABSTRACT: The nature of the bonding between the two M(μ-NAr(#)) imido monomers [M = Si, Ge, Sn, Pb; Ar(#) = C6H3-2,6-(C6H2-2,4,6-R3)2; R = Me, iPr] in the {M(μ-NAr(#))}2 dimer is investigated with the help of a newly developed energy and density decomposition scheme as well as molecular dynamics. The approach combines the extended transition state energy decomposition method with the natural orbitals for chemical valence density decomposition scheme within the same theoretical framework. The dimers are kept together by two σ bonds and two π bonds. The σ bonding has two major contributions. The first is a dative transfer of charge from nitrogen to M. It amounts to -188 kcal/mol for {Si(μ-NAr(#))}2, -152 kcal/mol for {Ge(μ-NAr(#))}2 with -105 kcal/mol for {Sn(μ-NAr(#))}2, and -79 kcal/mol for {Pb(μ-NAr(#))}2. The second is a charge buildup within the ring made up of the two dimers. It amounts to -82 kcal/mol for M = Si with -61 kcal/mol for M = Ge and ∼-50 kcal/mol for M = Sn and Pb. We finally have π bonding with a donation of charge from M to nitrogen. It has a modest contribution of ∼-30 kcal/mol. The presence of isopropyl (iPr) groups is further shown to stabilize{M(μ-NAr(#))}2 [M = Si, Ge, Sn, Pb; Ar(#) = C6H3-2,6-(C6H2-2,4,6-iPr3)2] compared to the methylated derivatives (R = Me) through attractive van der Waals dispersion interactions.
    Inorganic Chemistry 02/2014; 53(4). DOI:10.1021/ic403108z · 4.76 Impact Factor

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  • 1983–2015
    • University of California, Davis
      • Department of Chemistry
      Davis, California, United States
  • 2006
    • Hebrew University of Jerusalem
      Yerushalayim, Jerusalem, Israel
    • California State University, Dominguez Hills
      • Department of Chemistry and Biochemistry
      Carson, California, United States
  • 1991
    • University of California, San Diego
      • Department of Chemistry and Biochemistry
      San Diego, California, United States
  • 1987
    • University of California, Irvine
      • Department of Chemistry
      Irvine, California, United States
  • 1976–1987
    • University of Sussex
      • Department of Chemistry
      Brighton, England, United Kingdom
  • 1978
    • California State University, Los Angeles
      Los Angeles, California, United States