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Peter S. White

Publications and source records attributed to Peter S. White.

12 recordsLinked to original sources
PubMed2001

Isolation and Characterization of the Osmium(V)-Imido Complex [Os(V)(Tp)(Cl)(2)(NH)] We are grateful to the National Science Foundation under Grant number CHE-9503738, the Los Alamos National Laboratory (DOE) under Grant Number 10730-001-00-2C, and the Laboratory Directed Research and Development Program for support of this research. M. H. V. Huynh gratefully acknowledges postdoctoral fellowship support from the Directorapos;s Office of Los Alamos National Laboratory. Los Alamos National Laboratory is operated by the University of California for the U.S. Department of Energy under Contract W-7405-ENG-36. We also thank Dr. Paul R. Sharp (Professor of Chemistry, University of Missouri, Columbia, MO, 65211) for the information on transition metal parent imido complexes.

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PubMed2001

First Catalytic Asymmetric Aldol-Tishchenko Reaction-Insight into the Catalyst Structure and Reaction Mechanism J.P.M. gratefully acknowledges receipt of an NSF Career Award (CHE-9875488), a David and Lucile Packard Fellowship and a DuPont Young Professor Grant. Support from Amoco Chemicals is also appreciated. The authors thank Prof. Joseph Templeton for helpful discussions and Andrew Larsen of the Gagné research group for assistance with vapor pressure osmometry experiments.

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PubMed1999

Intervalence Transfer at the Localized-to-Delocalized, Mixed-Valence Transition in Osmium Polypyridyl Complexes.

The mixed-valence complexes [(bpy)(2)(Cl)Os(III)(BL)Os(II)(Cl)(bpy)(2)](3+) and [(tpy)(bpy)Os(III)(BL)Os(II)(bpy)(tpy)](5+) (bpy is bipyridine; tpy is 2,2':6',2' '-terpyridine; BL is a bridging ligand, either 4,4'-bipyridine (4,4'-bpy) or pyrazine (pz)) have been prepared and studied by infrared and near-infrared measurements in different solvents. For BL = 4,4'-bpy, there is clear evidence for localized Os(II) and Os(III) oxidation states in the appearance of the expected two interconfigurational dpi --> dpi bands at Os(III) and additional, broad absorption features in the near-infrared arising from intervalence transfer (IT) transitions. For [(bpy)(2)(Cl)Os(pz)Os(Cl)(bpy)(2)](3+) and [(tpy)(bpy)Os(pz)Os(bpy)(tpy)](5+), unusually intense nu(pz) bands appear in the infrared at 1599 cm(-)(1) (epsilon = 2600 M(-)(1) cm(-)(1)) for the former and at 1594 cm(-)(1) (epsilon = 2020 M(-)(1) cm(-)(1)) for the latter. They provide an oxidation state marker and evidence for localized oxidation states. A series of bands appear in the near-infrared from 2500 to 8500 cm(-)(1) that can be assigned to a combination of interconfigurational dpi --> dpi and IT transitions. In CD(3)CN, in the mid-infrared, bands arising from nu(bpy) ring stretching modes from 1400 to 1500 cm(-)(1) are averaged for [(bpy)(2)(Cl)Os(pz)Os(Cl)(bpy)(2)](3+) or significantly perturbed for [(tpy)(bpy)Os(pz)Os(bpy)(tpy)](5+) compared to electronically isolated Os(II) and Os(III) complexes. The pyrazine-bridged complexes have properties that place them in a new class of mixed-valence molecules, Class II-III having properties associated with both Class II and Class III in the Robin and Day classification scheme. The characteristic features of this class are that oxidation states are localized because of vibrational coupling but that solvent orientational motions are uncoupled because of rapid intramolecular electron transfer.

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PubMed1999

Acid-Base Adducts of Catalytically Active Titanium(IV) Lewis Acids.

A series of monomeric Lewis acid-base adducts of the Diels-Alder catalyst Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2) have been synthesized from bidentate diphosphines and diamines, Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2)L(2) (L(2) = dmpe, depe, dpeda, and dmeda). X-ray crystal structures of Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2)(dmpe) and Ti(O-2,6-Me(2)C(6)H(3))(2)Cl(2)(dpeda) establish a distorted octahedral coordination environment with trans-chloride ligands. Bidentate ligands that were also studied but did not form isolable complexes with the Ti(IV) Lewis acid include dppe, tmeda, and binam. Through pairwise exchange reactions a qualitative ranking of relative bidentate ligand binding strengths to the Lewis acid were obtained (dmeda >/= dpeda > dmpe >/= depe > tmeda > binam > dppe). The ranking is readily rationalized using hard-soft electronic arguments except for tmeda, which requires that unfavorable steric interactions be invoked.

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PubMed1999

Formation and Redox Reactivity of Osmium(II) Thionitrosyl Complexes.

Reaction between [Os(VI)(tpm)(Cl)(2)(N)](PF(6)) (tpm = tris(1-pyrazolyl)methane) (1) or Os(VI)(Tp)(Cl)(2)(N) (Tp = hydrotris(1-pyrazolyl)borate anion) (2) and CS(2) + N(3)(-) in acetone gives the corresponding thionitrosyl complexes, (-)SCN, and N(2). There is an extensive reactivity chemistry of the thionitrosyl group in [Os(II)(tpm)(Cl)(2)(NS)](PF(6)) (3b). Reaction between 3b and PPh(3) occurs with S-atom transfer to give [Os(IV)(tpm)(Cl)(2)(NPPh(3))](+) and S=PPh(3). 3b undergoes chemical or electrochemical reduction to give the corresponding Os(II) ammine complex and H(2)S. O-atom transfer from O=NMe(3) to 3b occurs to give Os(III)(tpm)(Cl)(2)(NSO). Competitive NO(+)/NS(+) exchange and S(2)(-) transfer occur in the reaction between [Os(II)(tpm)(Cl)(2)(NS)](BF(4)) (3c) and NO(+) to give a mixture of [Os(VI)(tpm)(Cl)(2)(N)](+) and [Os(II)(tpm)(Cl)(2)(NO)](+).

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PubMed1999

Synthesis and Characterization of Chiral Platinum(II) Sulfonamides: (dppe)Pt(NN) and (dppe)Pt(NO) Complexes.

Reaction of (dppe)Pt(CO(3)) with (1S,2S)-HN(R)CHPhCHPhNH(R) (R = SO(2)CF(3), 1a; SO(2)-4-(t)BuC(6)H(4), 1b) and (1S,2R)-HN(R)CHPhCHPhOH (R = SO(2)CF(3), 3a; SO(2)-4-(t)BuC(6)H(4), 3b) leads to well-behaved chiral (dppe)Pt[N(R)CHPhCHPhN(R)] (R = SO(2)CF(3), 2a; SO(2)-4-(t)BuC(6)H(4), 2b) and (dppe)Pt[N(R)CHPhCHPhO] (R = SO(2)CF(3), 4a; SO(2)-4-(t)BuC(6)H(4), 4b) complexes. X-ray structural analysis of 2a and 4b reveal that the Pt-N bond lengths are long with the triflamide bond lengths being slightly longer than the aryl sulfonamide bond lengths ( approximately 2.12 and 2.06 Å, respectively). Solid-state (X-ray) and solution ((1)H NMR) structural analysis indicates that the phenyl groups alpha to the sulfonamide nitrogen adopt an axial conformation, as characteristic (3)J(Pt)(-)(H) coupling constants are observed for equatorial, but not axially disposed hydrogens in the heterocycle. Relative binding affinities of 1a/b and 3a/b to the (dppe)Pt fragment were determined through pairwise ligand exchange reactions: Tf > SO(2)Ar and NN > NO.

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PubMed1998

Reactivity of Osmium(VI) Nitrides with the Azide Ion. A New Synthetic Route to Osmium(II) Polypyridyl Complexes.

There is an extensive reactivity chemistry between trans-[Os(VI)(tpy)(Cl)(2)(N)](+) (1) (tpy = 2,2':6',2"-terpyridine) and N(3)(-). Reaction of 1 with N(3)(-) in CH(2)Cl(2) or acetone occurs by electron transfer to give trans,trans-(tpy)(Cl)(2)Os(II)(N(2))Os(II)(Cl)(2)(tpy). In CH(3)CN, trans-Os(II)(tpy)(Cl)(2)(N(2)) forms but undergoes solvolysis to give trans-Os(II)(tpy)(Cl)(2)(CH(3)CN). 1 reacts with excess N(3)(-) in CH(3)CN to give Os(III)(tpy)(Cl)(2)(5-CH(3)-tetrazolate), which has been characterized by X-ray crystallography. This is the first known Os-tetrazolato complex. 1 reacts with N(3)(-) in the presence of CS(2) to give trans-[Os(II)(tpy)(Cl)(2)(NS)](+), SCN(-), and N(2).

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PubMed1998

Reactions of H(3)Al.NMe(3) with E(SiMe(3))(3) (E = P, As). Structural Characterization of the Trimer [H(2)AlP(SiMe(3))(2)](3) and Base-Stabilized Adduct [H(2)AlAs(SiMe(3))(2)].NMe(3) and Their Thermal Decomposition toward Nanocrystalline AlP and AlAs, Respectively.

Dehydrosilylation reactions in diethyl ether between H(3)Al.NMe(3) and E(SiMe(3))(3) afforded for E = P a high yield of the trimer [H(2)AlP(SiMe(3))(2)](3) (1), while for E = As a monomeric base-stabilized adduct [H(2)AlAs(SiMe(3))(2)].NMe(3) (2) as well as its degradation solid product were obtained. No reaction occurred for E = N. The single-crystal X-ray structure determination for 1 yielded a planar six-membered ring of alternating four-coordinated Al and P centers. The structural solution for 2 revealed the monomeric unit [H(2)AlAs(SiMe(3))(2)] stabilized by coordination of NMe(3) at the Al site. Pyrolysis of 1 at 450 degrees C promoted further dehydrosilylation and yielded a product which by XRD spectroscopy showed the onset of AlP crystallinity while at 950 degrees C afforded nanocrystalline AlP with 5 nm average particle size. Pyrolysis of 2 at 450 degrees C resulted in the formation of nanocrystalline AlAs with 2 nm average particle size. Under applied pyrolysis conditions for 1 and 2, the target elimination-condensation pathway via dehydrosilylation was accompanied by other decomposition side reactions and retention of some contaminant residues.

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PubMed1997

Osmium Hydrazido and Dinitrogen Complexes.

[Os(tpy)(bpy)(NH(3))](PF(6))(2) (1) was oxidized electrochemically in the presence of a series of amines in aqueous solutions buffered to pH 7. With secondary aliphatic amines, electrolysis gave [Os(tpy)(bpy)(NNR(2))](PF(6))(3) (3); number of electrons n = 4.6-5.0. 3 was reduced to [Os(tpy)(bpy)(NNR(2))](PF(6))(2) (2) in aqueous and nonaqueous solutions with n = 1.0. The structures of 2 were determined by X-ray crystallography for NR(2) = diethylamide (2a) and morpholide (2c) and were found to exhibit bent hydrazido(2-) coordination (Os-N-N = 137 degrees ). The salts crystallized in the triclinic system, space group P&onemacr;. For 2a, a = 9.004(1) Å, b = 9.796(1) Å, c = 20.710(2) Å, alpha = 88.78(2) degrees, beta = 85.43(2) degrees, gamma = 86.22(2) degrees, and Z = 2. For 2c, a = 9.632(8) Å, b = 21.229(9) Å, c = 9.039(5) Å, alpha = 97.41(4) degrees, beta = 94.28(5) degrees, gamma = 85.07(5) degrees, and Z = 2. Solutions of 2 were protonated in strongly acidic media to give hydrazido(1-) complexes. The pK(a) of the protonated form of 2a is 0.90 +/- 0.01. Reduction of 2 in aqueous solutions of pH <1 gave 1 and NH(2)R(2)(+) with n = 4.0. At higher pH, there is evidence for an Os(II) hydrazine intermediate. Oxidation of 3 by one electron afforded transiently stable species which decomposed to give [Os(tpy)(bpy)(NCCH(3))](3+) in acetonitrile solution. Pseudo-first-order rate constants of 8.1 +/- 0.9 s(-)(1) and 0.200 +/-.005 s(-)(1) were estimated by cyclic voltammetry on solutions of 2a and 2b(NR(2) = piperidide), respectively. Oxidation of 1 at pH 7, in the presence of primary aliphatic amines or ammonia, occurred with n = 5.9-6.2, and generated [Os(II)(tpy)(bpy)(N(2))](PF(6))(2) (4).

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PubMed1996

Preparation and Characterization of Halogen-Boron-Phosphorus Compounds. X-ray Crystal Structures of X(3)B.P(SiMe(3))(3) and [X(2)BP(SiMe(3))(2)](2) (X = Cl, Br).

The 1:1 mole ratio reactions of boron trihalides (BX(3)) with tris(trimethylsilyl)phosphine [P(SiMe(3))(3)] produced 1:1 Lewis acid/base adducts [X(3)B.P(SiMe(3))(3), X = Cl (1), Br (2), I (5)]. Analogous 1:1 mole ratio reactions of these boron trihalides with lithium bis(trimethylsilyl)phosphide [LiP(SiMe(3))(2)] produced dimeric boron-phosphorus ring compounds {[X(2)BP(SiMe(3))(2)](2), X = Br (3), Cl (4)}. X-ray crystallographic studies were successfully conducted on compounds 1-4. Compound 1 crystallized in the orthorhombic space group Pbca, with a = 13.420(3) Å, b = 17.044(5) Å, c = 21.731(7) Å, V = 4970.6(25) Å(3), and D(calc) = 1.229 g cm(-3) for Z = 8; the B-P bond length was 2.022(9) Å, Compound 2 crystallized in the orthorhombic space group Pbca, with a = 13.581(6) Å, b = 17.106(7) Å, c = 22.021(9) Å, V = 5116(4) Å(3), and D(calc) = 1.540 g cm(-3) for Z = 8; the B-P bond length was 2.00(2) Å. Compound 3 crystallized in the monoclinic space group P2(1)/n, with a = 9.063(5) Å, b = 16.391(8) Å, c = 9.331(4) Å, V = 1379.2(12) Å(3), and D(calc) = 1.676 g cm(-3) for Z = 2; the B-P bond length was 2.023(10) Å. Compound 4 crystallized in the monoclinic space group P2(1)/n, with a = 9.143(5) Å, b = 16.021(8) Å, c = 9.170(4) Å, V = 1342.2(11) Å(3), and D(calc) = 1.282 g cm(-3) for Z = 2; the B-P bond length was 2.025(3) Å. Thermal decomposition studies were performed on compounds 1-4, yielding colored powders with boron:phosphorus ratios greater than 1:1 and significant C and H contamination indicated by elemental analyses.

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