Silicon hydrides and nickel complexes : I. Phosphine-nickel(II) complexes as hydrosilylation catalysts

A variety of dihalodiphosphinenickel(II) complexes have been found to be effective catalysts for hydrosilylation of olefins and acetylenes. Reactions with nickel(II) catalysts, at least those containing a bidentate phosphine ligand, scarcely proceed below 90°. At 120° the reaction proceeds smoothly to form, in many cases, an unexpected (“abnormal”) adduct which has arisen from an interchange of hydrogen and chlorine on silicon in addition to the expected (“normal”) one. Both total yields, and the ratios of the “abnormal” to the “normal” adduct increase, in general, with increasing electron-donating ability of both the phosphine ligands and the substituents on the olefins. Isomerization of olefins occurs during the course of hydrosilylation. cis-Addition occurs preferentially. The reactivity of the silicon hydrides decreases in the order HSiCl₃ ? HSiMeCl₂ ? HSiMe₂Cl ? HSiMe₃.     

Alkyl complexes of palladium(II) with trimethylphosphine and 1,2-bis-(dimethylphosphino)ethane ligands

A number of neutral, mononuclear dialkylpalladium(II) tertiary phosphine complexes of geneal formula cis or trans-PdR₂(PMe₃)₂ and cis-PdR₂ (dmpe) [dmpe = 1,2-bis(dimethylphosphino)ethane], R = Me, CH₂Ph, CH₂CMe₂Ph, CH₂SiMe₃ have been obtained by interaction of magnesium reagents with palladium(II) acetate or trans-Pd(O₂CMe)₂(PMe₃)₂.     

Silicon hydrides and nickel complexes : II. Mechanism of the hydrosilylation catalyzed by nickel-phosphine complexes

Two ethylene-nickel(0) complexes, viz., [1,2-bis(diphenylphosphino)ethane]-(ethylene)nickel(0) and bis(triphenylphosphine)(ethylene)nickel(0) have been used in a comparison of their catalytic activities in hydrosilylation reactions with those of the corresponding nickel(II) complexes, viz., dichloro [1,2-bis(diphenylphosphino)-ethane]nickel(II) and dichlorobis(triphenylphosphine)nickel(II). The reaction profiles are similar, apart from a significant difference in the induction period; the nickel(II) catalysts requiring a substantially longer time. A mechanism involving a nickel(0) species is proposed for the hydrosilylation.The interchange of hydrogen and chlorine on silicon accompanying the hydrosilylation is related to a high electron density at the nickel atom bearing the phosphine, olefin, and silicon hydride ligands.     

1,2-Dialkoxyacenaphthylenes and 2,3,11,12-bis-(1,2-acenaphtho)-[18]crown-6

A general synthesis of 1,2-dialkoxyacenaphthylenes by dehydrogenation of the corresponding acenaphthene derivatives with high potential quinones is described. The new crown ether, 2,3,11,12-bis(1,2-acenaphtho)-[18]crown-6, 1, is obtained by this route. The surprisingly poor complexing ability of 1 is ascribed to electronic and geometrical effects of the acenaphthylene rings as shown by spectroscopic and voltammetric data and the crystal structure of the free ligand 1.     

Di[2-(4-substituted-phenyl)-3-mercapto-propenato]-nickel(II) complexes. Metallo-mesogens exhibiting broad nematic ranges

Di[2-(4-substituted-phenyl)-3-mercapto-propenato]-nickel(II) complexes have been synthesized and investigated. All of them are mesomorphic; they have nematic phases with wide ranges and typical Schlieren textures.     

Di[2-(4-substituted-phenyl)-3-mercapto-propenato]-nickel(II) complexes. Metallo-mesogens exhibiting broad nematic ranges

Abstract

Di[2-(4-substituted-phenyl)-3-mercapto-propenato]-nickel(II) complexes have been synthesized and investigated. All of them are mesomorphic; they have nematic phases with wide ranges and typical Schlieren textures.     

Aqueous rhodium(III) hydrides and mononuclear rhodium(II) complexes

In aqueous solutions, as in organic solvents, rhodium hydrides display the chemistry of one of the three limiting forms, i.e. {Rh(I)+ H+}, {Rh(II)+ H.}, and {Rh(III)+ H-}. A number of intermediates and oxidation states have been generated and explored in kinetic and mechanistic studies. Monomeric macrocyclic rhodium(II) complexes, such as L(H2O)Rh2+ (L = L1 = [14]aneN4, or L2 = meso-Me6[14]aneN4) can be generated from the hydride precursors by photochemical means or in reactions with hydrogen atom abstracting agents. These rhodium(II) complexes are oxidized rapidly with alkyl hydroperoxides to give alkylrhodium(III) complexes. Reactions of Rh(II) with organic and inorganic radicals and with molecular oxygen are fast and produce long-lived intermediates, such as alkyl, superoxo and hydroperoxo complexes, all of which display rich and complex chemistry of their own. In alkaline solutions of rhodium hydrides, the existence of Rh(I) complexes is implied by rapid hydrogen exchange between the hydride and solvent water. The acidity of the hydrides is too low, however, to allow the build-up of observable quantities of Rh(I). Deuterium kinetic isotope effects for hydride transfer to a macrocyclic Cr(v) complex are comparable to those for hydrogen atom transfer to various substrates.     

Synthesis and magnetic properties of new nickel(II)-copper(II)-nickel(II) trinuclear complexes with irregular spin-state structure

Summary Four novel heterotrinuclear complexes were prepared, namely {[Ni(L)₂]₂[Cu(pba)]}(ClO₄)₂, where pba = pro-pylene-1,3-bis(oxamato) and L = 1,10-phenanthroline (phen), 5-nitro-1,10-phenanthroline (NO₂-phen), 2,2-bipyridyl (bpy), 4,4-dimethyl-2,2-bipyridyl (Me₂bpy). Based on i.r., elemental analyses, conductivity measurements and electronic spectra oxamato-bridged structures are proposed for these complexes, consisting of two nickel(II) ions, each in a distorted octahedral environment, and a copper(II) ion in a square planar environment, respectively. The temperature dependence of the magnetic susceptibility of {[Ni(phen)₂]₂[Cu(pba)]}(ClO₄)₂·H₂O was studied in the 4–300 K range, giving the exchange integral J = - 106 cm^–1. TheX _scm T versusT plot exhibited a minimum at ca. 98 K, characteristic of this kind of coupled polymetallic complex with an irregular spin-state structure. E.s.r. spectra of these complexes clearly indicated a strong rhombicity withg ₁ = 5.20,g ₂ = 2.29 andg ₃ = 2.02 (approximately), which agrees with an anisotropicS = ±1/2 Kramer doublet in the ground state.     

Mononuclear nickel(III) and nickel(II) thiolate complexes with intramolecular S-H proton interacting with both sulfur and nickel: relevance to the [NiFe]/[NiFeSe] hydrogenases

Mononuclear, distorted square planar [Ni(II)(ER)(P(o-C(6)H(4)S)(2)(o-C(6)H(4)SH))](-) (ER = SePh (1), 2-S-C(4)H(3)S (2)) with a S-H proton directly interacting with both nickel and sulfur atoms were prepared by reaction of [Ni(CO)(SePh)(3)](-)/[Ni(CO)(2-S-C(4)H(3)S)(3)](-) and P(o-C(6)H(4)SH)(3), individually. The presence of combinations of intramolecular [Ni-S...H-SR]/[Ni...H-SR] interactions was verified in the solid state by the observation of an IR nu(SH) stretching band (2273 and 2283 cm(-)(1) (KBr) for complexes 1 and 2, individually) and (1)H NMR spectra (delta 8.079 (d) (CD(2)Cl(2)) and 8.39 (d) (C(4)D(8)O) ppm (-SH) for complexes 1 and 2, respectively) and subsequently confirmed by X-ray diffraction study. The exo-thiol proton (o-C(6)H(4)SH) in complexes 1 and 2 was identified as a D(2)O exchangeable proton from NMR and IR studies and was quantitatively removed by Lewis base Et(3)N to yield Ni(II) dimer [Ni(II)(P(o-C(6)H(4)S)(3))](2)(2)(-) (5). Instead of the ligand-based oxidation to form dinuclear Ni(II) complexes and dichalcogenide, oxidation of THF-CH(3)CN solution of complexes 1 and 2 by O(2) resulted in the formation of the mononuclear, distorted trigonal bipyramidal [Ni(III)(ER)(P(o-C(6)H(4)S)(3))](-) (ER = SePh (3), 2-S-C(4)H(3)S (4)) accompanied by byproduct H(2)O identified by (1)H NMR, respectively. The 4.2 K EPR spectra of complexes 3 and 4 exhibiting high rhombicities with three principal g values of 2.304, 2.091, and 2.0 are consonant with Ni(III) with the odd electron in the d(z)(2) orbital. Complex 3 undergoes a reversible Ni(III/II) process at E(1/2) = -0.67 V vs Ag/AgCl in MeCN.     

Thiolato-technetium complexes. 4(1): Synthesis,characterization and electrochemical properties of bis(1,2-bis(dimethylphosphino)-ethane)technetium(III) complexes with arene-thiolato ligands

Summary The reaction of trans-[Tc^v(OH)(O)(DMPE)₂]²⁺ (DMPE = 1,2-bis(dimethylphosphino)ethane) with a series of arenethiols in base produces the novel complexes cis-[Tc^III-(SC₆H₄X-p)₂ (DMPE)₂]⁺ for X = H, Cl, Me, OMe, t-Bu. One of the complexes has been characterized by X-ray crystallography: cis-[Tc(SPh)₂(DMPE)₂]PF₆, chemical formula Tc₁S₂P₅F₆C₂₄H₄₂, crystallizes in the orthorhombic space group P2₁nb with Z = 4 and lattice parameters a = 9.311(1) Å, b=11.190(2) Å, c = 31.936(4) Å, Vol = 3327.3(8) ų. The final weighted R-value was 0.033. Averaged structural parameters are Tc—S = 2.29(2) Å, Tc—P (trans to P) = 2.42(1) Å, Tc—P (trans to S) = 2.49(3) Å, Tc—S—C = 118.5(5)°. The complexes have been characterized by FAB mass spectrometry and u.v.-vis. spectroscopy. The visible region charge transfer bands are diagnostic for cis geometry in the [Tc(SR)₂(DMPE)₂]⁺ complexes. Electrochemical and spectroelectrochemical measurements show reversible Tc^III/II redox couples in the range -0.19V to -0.38V versus Ag/AgCl (3 M NaCl). Irreversible couples are exhibited at ca. -1.1 V to -1.2 V for Tc^II/I and +0.7V to +0.9V for Tc^IV/III. Variation in redox potential is discussed in terms of sulphur nucleophilicity.On leave from the Department of Chemistry, The University of Tsukuba, Tsukuba, Ibaraki 305, Japan.On leave from Dipartimento di Chimica dell'Universita' di Sassari, Via Vienna, 2-Sassari, Italy.     

Synthesis,characterization and electrical conductivities of 1,2-bis-(2-pyridyl)methyleneiminobenzene cyano complexes of nickel(II), copper(II) and cobalt(II)

Transition Metal Chemistry -