A family of bis(arylamino)chlorophosphines of the general formula (Ar = 4-MeO-C6H4, 3a; Ar = 2,4,6-Me3-C6H2, 3b; Ar = 2,6-(CHMe2)2-C6H3, 3c) has been prepared from PCl3 and the appropriate diamine. Steric interactions involving the 2,6-aryl substituents in 3b,c result in hindered rotation about the N−CAr bond, as evidenced by 1H NMR spectroscopy. Treatment of halophosphines 3a−c with AgOSO2CF3 (AgOTf) or Tl{B[3,5-(CF3)2-C6H3]4 } (TlBArF) affords the cationic bis(arylamino)phosphenium compounds (4a−e; A = OTf, BArF), in high yield. Phosphenium cations 4a−d reversibly form adducts with trimethylphosphine. The structure of the phosphinophosphenium adduct 5c (Ar = 2,6-(CHMe2)2-C6H3) has been determined by single-crystal X-ray diffraction techniques, revealing both the steric influences of the 2,6-Ar substituents and the electronic nature of the bonding in 5. Treatment of Wilkinson's catalyst, RhCl(PPh3)3, with 1 equiv of 4a gives the first well-defined Rh phosphenium complex, (6), which is isolated in 80% yield. In contrast, treatment of Wilkinson's catalyst with 4c results in quantitative formation of [Rh(PPh3)3](OTf) and chlorophosphine 3c. The influence of the phosphenium N−Ar substituents is further evidenced by the analogous reaction between RhCl(PPh3)3 and mesityl-substituted 4b, which affords products analogous to 4a,c as well as the isomeric Rh phosphenium complex 7a, having cis PPh3 ligands. 31P NMR spectroscopic parameters for 6 and 7a,b are consistent with Rh−P multiple bonding.

A new phase-separable catalysis concept is demonstrated using supercritical carbon dioxide and the room temperature ionic liquid 1-butyl-3-methylimidazolium hexafluorophosphate for hydrogenation of alkenes and carbon dioxide.

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A comprehensive analysis of adsorption strength, average molecular orientation, and absolute molecular direction for p-nitrophenol at solid-air, solid-liquid, and liquid-air interfaces is obtained from the nearresonant optical second harmonic generation (SHG) from the interface. Perturbation theory calculations of the molecular nonlinear polarizability tensor elements using *-electron wave functions are used to identify the dominant tensor elements. The near-resonant SHG from a monolayer of p-nitrophenol is shown to require the use of two molecular nonlinear polarizability tensor elements in the equations relating the experimentally measured SHG to the average molecular orientation in the monolayer and therefore cannot be correctly described with the usual assumption of the complete dominance of a single molecular nonlinear polarizability tensor element. The average molecular orientation within the adsorbed monolayer is then obtained from the polarization dependence of the surface SHG and is described by the orientation parameter, D = (cos3 8 )I (cos e), where 8 is the angle between the molecular symmetry axis and the surface normal. A more realistic description of the molecular orientation is obtained by allowing for a partial Gaussian distribution in the angle 8. Additional measurements of the phase of the surface SHG are used in conjunction with the theoretical calculations of the molecular nonlinear polarizability to ascertain the direction of the transition dipole moment relative to the surface.

Dedicated to Professor M. Frederick Hawthorne on the occasion of his 75th birthdayThe application of electrophilic late-transition-metal complexes in catalysis has enjoyed widespread success in recent years. [1][2][3][4][5][6] We have been investigating electrophilic platinum complexes for catalysis and hydrocarbon CÀH bond activation [7,8] and recently reported a simple strategy for obtaining unsaturated electrophilic metal centers by addition of bulky bis(N-arylamino)phosphenium cations, easily derived from bis(N-aryl)diimines.

This is the final report of a three-year, Laborato~-Directed Research and Development (LDRD) project at the Los Alamos National Laboratory (LANL). Our objectives were to develop a multidisciplinary team and capabilities to develop a fundamental understanding of homogeneous, heterogeneous, and heterogenized catalysts. With the aid of theoretical chemistry approaches we explored and characterized the chemical reactivity and physical properties of a large number of catalytic systems.

Variable-temperature 1H NMR spectroscopy indicates fluxional behavior for a number of group 3 metallocene allyl complexes. Spectral simulations and line shape analyses for the variable-temperature spectra indicate an allyl rearrangement mechanism involving rate-determining carbon−carbon double-bond dissociation from the metal center, i.e. an η3 to η1 change in coordination. Activation barriers to olefin dissociation have been determined for (η5-C5Me5)2Sc(η3-C3H5), meso-Me2Si(η5-3-CMe3-C5H3)2Sc(η3-C3H5), meso-Me2Si[η5-2,4-(CHMe2)2-C5H2]2Sc(η3-C3H5), meso-Me2Si{η5-3-[2-(2-Me)-adamantyl]-C5H3}2Sc(η3-C3H5), meso-Me2Si{η5-3-[2-(2-Me)-adamantyl]-C5H3}2Y(η3-C3H5), rac-Me2Si[η5-2,4-(CHMe2)2-C5H2]2Sc(η3-C3H5)), and R-(C20H12O2)Si(η5-2-SiMe3-4-CMe3-C5H2)2Sc(η3-C3H5):  Δ G ⧧ = 11−16 kcal mol-1 at ca. 300−350 K. Donor solvents do not significantly affect the rate of olefin dissociation. A second rearrangement mechanism that involves 180° rotation of the η3-C3H5 moiety has been found to operate in those metallocenes whose ancillary ligand arrays adopt rigid meso geometries. Line shape analysis indicates that the rate of η3-C3H5 rotation is generally more than 1 order of magnitude faster than olefin dissociation for a given meso metallocene. The data do not allow unambiguous assessments of the mechanism(s) for the fluxional behavior for the allyl derivatives of the racemic metallocenes. An X-ray structure determination for rac-Me2Si[η5-C5H2-2,4-(CHMe2)2]2Sc(η3-C3H5) has been carried out.

Dedicated to Professor M. Frederick Hawthorne on the occasion of his 75th birthdayThe application of electrophilic late-transition-metal complexes in catalysis has enjoyed widespread success in recent years. [1][2][3][4][5][6] We have been investigating electrophilic platinum complexes for catalysis and hydrocarbon CÀH bond activation [7,8] and recently reported a simple strategy for obtaining unsaturated electrophilic metal centers by addition of bulky bis(N-arylamino)phosphenium cations, easily derived from bis(N-aryl)diimines.