Ronald G. Cavell

Early transition metal and lanthanide bis(iminophosphorano)methandiide complexes; ‘pincer’ and bridging bis(phosphorus) metal carbenes

Abstract The spontaneous double deprotonation of bis(iminophosphorano)methane ligands with alkyl or bis(trimethylsilyl)amido metal precursors yields ‘pincer’ carbenes of Group 4 and lanthanide metals. The generality of the system is extended with the dilithiumbis(iminophosphorano)methandiide salt which is obtained by lithiating bis(trimethylsilylimino(diphenylphosphorano))methane with two moles of lithium alkyl. This dilithium salt reacts with metal halides with metathetical elimination of LiCl to access the same types of pincer complexes. Herein the synthesis of a complete triad of Group 4 ‘pincer’ complexes is reviewed and their reaction chemistry demonstrating (a) nucleophilic alkylation, (b) the Lewis Acidity of the metal, (c) 1,2 addition across the MC carbene bond and (d) [2+2] cycloaddition across this MC bond is surveyed. The structural data for the ‘pincer’ complexes suggests strongly that there is a MC carbene double bond. The addition reactions also support this interpretation because a MC bond persists after the addition. The reactivity pattern also strongly suggests that the chemistry of this carbene center is similar to the metal alkylidene complexes, and not the Fischer heteroatom carbene complexes. The chemistry extends to many other elements. The extension to Sm as a representative lanthanide is described. This species adopts a structure very similar to the Group 4 ‘pincers’. Chromium(II) gave a novel bridging carbene dimer instead of the monomeric pincer. This bridging structure is developing as another structural motif in this system.

PH2P(NSIME3)2CLI2 : A DILITHIUM DIANIONIC METHANIDE SALT WITH AN UNUSUAL LI4C2 CLUSTER STRUCTURE

Four lithium atoms in a square-planar arrangement are capped by two carbon atoms and encapsulated by NSiMe3 chelation in the dilithium methanide salt 1. This air- and moisture-sensitive complex is formed by the reaction of CH2 (Ph2 P=NSiMe3 )2 with alkyl- or aryllithium reagents.

Actinide Metals with Multiple Bonds to Carbon: Synthesis, Characterization, and Reactivity of U(IV) and Th(IV) Bis(iminophosphorano)methandiide Pincer Carbene Complexes

Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P═NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P═NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P═NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P═NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P═NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P═NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)═carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M═C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both π and σ character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C≡N to the U═carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.

Photoelectron spectra of acetylene with HeI, HeII, Zr Mζ, and Mg Kα radiation sources

Valence level photoelectron spectra of gaseous acetylene excited by HeI (21.217 eV), HeII (40.8 eV), Zr Mζ (151.4 eV) with Mg Kα (1253.6 eV) radiations have been obtained. With one exception, the 3σg band under Mg Kα excitation, all of the expected valence level excitations are observed in each case. The best measured orbital ionization potentials are 1πu (11.41 eV), 3σg (16.76 eV), 2σu (18.71 eV), and 2σg (23.65 eV). All values except that for 1πu are adiabatic values. Relative photoionization probabilities (cross sections) have been determined for each of the radiations and compared to those estimated theoretically. The low calculated cross sections for 3σg excitation with Mg Kα radiation provides an explanation for the lack of an observable band due to this ionization in the photoelectron spectrum. A prominent ’’shake‐up’’ peak is observed at 27.6 eV in both the Mg Kα and Zr Mζ excited valence shell photoelectron spectra although it is more pronounced in the former. Similarly the C1s core spectrum show...

Photoelectron spectroscopy with Zr Mζ (151 eV) radiation. A study of the variation of relative photoionization cross sections of molecules containing first row atoms (C, N, O) with exciting radiation from HeI to Mg Kα limits

Relative perpendicular photoionization intensities for the noble gases Ne and Ar and the molecules CH4, NH3, H2O, CO, N2, and CO2 have been measured with HeI (21.2 eV), HeII (α, 40.8 eV and β, 48.4 eV) resonance lines and Zr Mζ (151 eV) and Mg Kα (1253.6 eV) soft x rays using the same instrument for all measurements. New valence shell spectra of NH3, CO, and CO2 obtained with Zr Mζ radiation are illustrated. The experimental values are compared to values calculated for each radiation by the method of Ellison [J. Chem. Phys. 61, 507 (1974)]. Reasonable success was achieved by the theory which appears to falter most seriously with the inner valence orbitals of dominant 2s atomic character. This failure is most likely due to the improper treatment of the Cooper minimum. Attempts to improve the agreement between observed and calculated relative intensities by inclusion of multiple electron processes (’’shake up’’ transitions) are discussed.

X-ray photoelectron spectroscopy study of the skutterudites La Fe 4 Sb 12 , Ce Fe 4 Sb 12 , Co Sb 3 , and Co P 3

The electronic structure of the skutterudites

Effects of metal substitution in transition-metal phosphides (Ni1−xM′x)2P (M′ = Cr, Fe, Co) studied by X-ray photoelectron and absorption spectroscopy

\mathrm{Co}{\mathrm{Sb}}_{3}

[Ph2P(NSiMe3)]2CLi2: ein dianionisches Dilithiummethanidsalz mit einer ungewöhnlichen Li4C2-Clusterstruktur

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Spectroscopy of the cation distribution in the schorlomite species of garnet

\mathrm{Co}{\mathrm{P}}_{3}

High resolution molecular gas phase photoelectron spectra of core levels using synchrotron radiation - vibrational and ligand field splittings

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