Philip P. Power

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

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Publications (491)3228.23 Total impact

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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; DOI:10.1039/C5DT01589H · 4.10 Impact Factor
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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: 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 · 4.79 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; DOI:10.1021/ic501925e · 4.79 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 · 4.25 Impact Factor
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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 · 2.05 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 · 4.79 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 · 11.44 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 · 5.70 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 · 4.25 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 · 6.72 Impact Factor
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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 · 4.79 Impact Factor
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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 · 4.79 Impact Factor
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    ABSTRACT: Treatment of toluene solutions of the silylenes Si(SArMe6)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3), 1) or Si(SArPri4)2 (ArPri4 = C6H3-2,6(C6H3-2,6-Pri2), 2) with excess ethylene gas affords the siliranes (ArMe6S)2SiCH2CH2 (3) and (ArPri4S)2SiCH2CH2 (4). Silirane 4 evolves ethylene spontaneously at room temperature. A Van't Hoff analysis by variable temperature 1H NMR spectroscopy showed that ΔGassn is -24.9 (2.5) kJ mol-1 for 4. A computational study of the reaction mechanism using a model silylene Si(SPh)2 (Ph = C6H5) was in harmony with the Van't Hoff analysis and yields ΔGassn = -24 kJ mol-1 and an activation energy ΔG‡ of 54 kJ mol-1.
    Journal of the American Chemical Society 12/2013; 136(2). DOI:10.1021/ja411951y · 11.44 Impact Factor
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    ABSTRACT: The synthesis and characterization of the sterically crowded primary alanes (AriPr4AlH2)2 (AriPr4 = C6H3-2,6(C6H3-2,6-iPr2)2) and (AriPr8AlH2)2 (AriPr8 = C6H-2,6(C6H2-2,4,6-iPr6)2-3,5-iPr2) are described. They, along with their previously reported less-hindered analogue (ArMe6AlH2)2 (ArMe6 = C6H3-2,6(C6H2-2,4,6-Me3)2), were reacted with ammonia to give the parent amido alanes {ArxAl(H)NH2}2 (Arx = ArMe6, 1; AriPr4, 2; AriPr8, 3), which are the first well-characterized hydride amido derivatives of aluminum and are relatively rare examples of parent aluminum amides. In contrast, the reaction of (ArMe6AlH2)2 with phosphine yielded the structurally unique Al/P cage species {(ArMe6Al)3(μ-PH2)3(μ-PH)PH2} (4) as the major product and a smaller amount of {(ArMe6Al)4(μ-PH2)4(μ-PH)} (5) as a minor product. All compounds were characterized by NMR and IR spectroscopy, while compounds 2–5 were also characterized by X-ray crystallography.
    Organometallics 12/2013; 33(1):329–337. DOI:10.1021/om4010675 · 4.25 Impact Factor
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    ABSTRACT: The reaction of phosphine gas with a low coordinate diaryl germylene or diarylstannylene results in both oxidative addition and arene elimination at the group 14 atom. The products were characterised by (31)P NMR spectroscopy and X-ray crystallography, and represent the first P-H bond activation by a heavy group 14 element compound.
    Chemical Communications 12/2013; 50(16). DOI:10.1039/c3cc48933g · 6.72 Impact Factor
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    ABSTRACT: The titanium bisamido complex Ti{N(H)Ar(iPr6)}2 (Ar(iPr6) = C6H3-2,6-(C6H2-2,4,6-(i)Pr3)2 (2), along with its three-coordinate titanium(III) precursor, TiCl{N(H)Ar(iPr6)}2 (1), have been synthesized and characterized. Compound 1 was obtained via the stoichiometric reaction of LiN(H)Ar(iPr6) with the Ti(III) complex TiCl3·2NMe3 in trimethylamine. Reduction of 1 with 1 equiv of KC8 afforded Ti{N(H)Ar(iPr6)}2 (2) in moderate yield. Both 1 and 2 were characterized by X-ray crystallography, NMR, and IR spectroscopy, magnetic studies, and by density functional theory (DFT) computations. The precursor 1 has quasi-four-coordinate coordination at the titanium atom, with bonding to two amido nitrogens and a chlorine as well as a secondary interaction to a flanking aryl ring of a terphenyl substituent. Compound 2 displays a very distorted four-coordinate metal environment in which the titanium atom is bound to two amido nitrogens and to two carbons from a terphenyl aryl ring. This structure is in sharp contrast to the expected two-coordinate linear structure that was observed in its first row metal (V-Ni) analogues. Magnetic studies confirm a d(1) electron configuration for 1 but indicate that Ti{N(H)Ar(iPr6)}2 (2) is diamagnetic at ambient temperature consistent with the oxidation of titanium to Ti(IV). The different structure of 2 is attributed to the high reducing tendency of the Ti(II) in comparison to the other metals.
    Inorganic Chemistry 11/2013; 52(24). DOI:10.1021/ic4021355 · 4.79 Impact Factor
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    Philip P Power
    Inorganic Chemistry 11/2013; 52(22):12855-9. DOI:10.1021/ic402721e · 4.79 Impact Factor
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    ABSTRACT: A series of high spin, two-coordinate first row transition metal-amido complexes, M{N(SiMe3)Dipp}2 {M = Fe (1), Co (2), or Ni (3); Dipp = C6H3-2,6-Pr(i)2} and a tetranuclear C-H activated chromium amide, [Cr{N(SiMe2CH2)Dipp}2Cr]2(THF) (4), were synthesized by reaction of their respective metal dihalides with 2 equiv of the lithium amide salt. They were characterized by X-ray crystallography, electronic and infrared spectroscopy, SQUID magnetic measurements, and computational methods. Contrary to steric considerations, the structures of 1-3 display planar eclipsed M{NSiC(ipso)}2 arrays and short M-N distances. DFT calculations, corrected for dispersion effects, show that dispersion interactions involving C-H-H-C moieties likely stabilize the structures by 21.1-29.4 kcal mol(-1), depending on the level of the calculations employed. SQUID measurements confirm high spin electron configurations for all the complexes and substantial orbital contributions for 1 and 2.
    Inorganic Chemistry 11/2013; 52(23). DOI:10.1021/ic402105m · 4.79 Impact Factor
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    ABSTRACT: The synthesis, magnetic, and spectroscopic characteristics of the synthetically useful dimeric cobalt(II) silylamide complex [Co{N(SiMe3)2}2]2 (1) and several of its Lewis base complexes have been investigated. Variable-temperature nuclear magnetic resonance (NMR) spectroscopy of 1 showed that it exists in a monomer-dimer equilibrium in benzene solution and has an association energy (ΔGreacn) of -0.30(20) kcal mol(-1) at 300 K. Magnetic data for the polycrystalline, red-brown [Co{N(SiMe3)2}2]2 (1) showed that it displays strong antiferromagnetic exchange coupling, expressed as -2JexS1S2, between the two S = (3)/2 cobalt(II) centers with a Jex value of -215(5) cm(-1), which is consistent with its bridged dimeric structure in the solid state. The electronic spectrum of 1 in solution is reported for the first time, and it is shown that earlier reports of the melting point, synthesis, electronic spectrum, and magnetic studies of the monomer "Co{N(SiMe3)2}2" are consistent with those of the bright green-colored tetrahydrofuran (THF) complex [Co{N(SiMe3)2}2(THF)] (4). Treatment of 1 with various Lewis bases yielded monomeric three-coordinated species-[Co{N(SiMe3)2}2(PMe3)] (2), and [Co{N(SiMe3)2}2(THF)] (4), as well as the previously reported [Co{N(SiMe3)2}2(py)] (3)-and the four-coordinated species [Co{N(SiMe3)2}2(py)2] (5) in good yields. The paramagnetic complexes 2-4 were characterized by electronic and (1)H NMR spectroscopy, and by X-ray crystallography in the case of 2 and 4. Magnetic studies of 2-5 and of the known three-coordinated cobalt(II) species [Na(12-crown-4)2][Co{N(SiMe3)2}3] (6) showed that they have considerably larger χMT products and, hence, magnetic moments, than the spin-only values of 1.875 emu K mol(-1) and 3.87 μB, which is indicative of a significant zero-field splitting and g-tensor anisotropy resulting from the pseudo-trigonal crystal field. A fit of χMT for 2-6 yields a large g-tensor anisotropy, large negative D-values (between -62 cm(-1) and -82 cm(-1)), and E-values between ±10 cm(-1) and ±21 cm(-1).
    Inorganic Chemistry 10/2013; 52(20). DOI:10.1021/ic402019w · 4.79 Impact Factor

Publication Stats

13k Citations
3,228.23 Total Impact Points

Institutions

  • 1983–2014
    • University of California, Davis
      • Department of Chemistry
      Davis, California, United States
  • 2006
    • California State University, Dominguez Hills
      • Department of Chemistry and Biochemistry
      Carson, California, United States
  • 2005–2006
    • Hebrew University of Jerusalem
      Yerushalayim, Jerusalem, Israel
  • 2002
    • Harvard University
      Cambridge, Massachusetts, United States
    • University of California, Irvine
      • Department of Chemistry
      Irvine, California, United States
  • 2001
    • University of Oslo
      • Department of Chemistry
      Kristiania (historical), Oslo, Norway
  • 1999
    • University of California, Berkeley
      • Department of Chemistry
      Berkeley, California, United States
  • 1976–1985
    • University of Sussex
      • Department of Chemistry
      Brighton, England, United Kingdom
  • 1978
    • California State University, Los Angeles
      Los Angeles, California, United States