4,4'-(4,5-dimethyl-1,2-phenylene)bis(2-methylbut-3-yn-2-ol): structural variation in vicinal dialkynols.

The structure of the title compound, C(18)H(22)O(2), contains two non-equivalent molecules which differ primarily in the location of the -OH groups on opposite sides or on the same side of the molecular plane. Inversion-symmetric pairs of molecules form intermolecular O-H..

Studies of a series of [Ni(P(R)2N(Ph)2)2(CH3CN)]2+ complexes as electrocatalysts for H2 production: substituent variation at the phosphorus atom of the P2N2 ligand.

A series of [Ni(P(R)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) complexes containing the cyclic diphosphine ligands [P(R)(2)N(Ph)(2) = 1,5-diaza-3,7-diphosphacyclooctane; R = benzyl (Bn), n-butyl (n-Bu), 2-phenylethyl (PE), 2,4,4-trimethylpentyl (TP), and cyclohexyl (Cy)] have been synthesized and characterized. X-ray diffraction studies reveal that the cations of [Ni(P(Bn)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) and [Ni(P(n-Bu)(2)N(Ph)(2))(2)(CH(3)CN)](BF(4))(2) have distorted trigonal bipyramidal geometries. The Ni(0) complex [Ni(P(Bn)(2)N(Ph)(2))(2)] was also synthesized and characterized by X-ray diffraction studies and shown to have a distorted tetrahedral structure.

Electrocatalytic oxidation of formate by [Ni(P(R)2N(R')2)2(CH3CN)]2+ complexes.

[Ni(P(R)(2)N(R')(2))(2)(CH(3)CN)](2+) complexes with R = Ph, R' = 4-MeOPh or R = Cy, R' = Ph , and a mixed-ligand [Ni(P(R)(2)N(R')(2))(P(R''(2))N(R'(2)))(CH(3)CN)](2+) with R = Cy, R' = Ph, R'' = Ph, have been synthesized and characterized by single-crystal X-ray crystallography. These and previously reported complexes are shown to be electrocatalysts for the oxidation of formate in solution to produce CO(2), protons, and electrons, with rates that are first-order in catalyst and formate at formate concentrations below ∼0.04 M (34 equiv).

Moving protons with pendant amines: proton mobility in a nickel catalyst for oxidation of hydrogen.

Proton transport is ubiquitous in chemical and biological processes, including the reduction of dioxygen to water, the reduction of CO(2) to formate, and the production/oxidation of hydrogen. In this work we describe intramolecular proton transfer between Ni and positioned pendant amines for the hydrogen oxidation electrocatalyst [Ni(P(Cy)(2)N(Bn)(2)H)(2)](2+) (P(Cy)(2)N(Bn)(2) = 1,5-dibenzyl-3,7-dicyclohexyl-1,5-diaza-3,7-diphosphacyclooctane). Rate constants are determined by variable-temperature one-dimensional NMR techniques and two-dimensional EXSY experiments.

[Ni(P(Ph)2N(C6H4X)2)2]2+ complexes as electrocatalysts for H2 production: effect of substituents, acids, and water on catalytic rates.

A series of mononuclear nickel(II) bis(diphosphine) complexes [Ni(P(Ph)(2)N(C6H4X)(2))(2)](BF(4))(2) (P(Ph)(2)N(C6H4X)(2) = 1,5-di(para-X-phenyl)-3,7-diphenyl-1,5-diaza-3,7-diphosphacyclooctane; X = OMe, Me, CH(2)P(O)(OEt)(2), Br, and CF(3)) have been synthesized and characterized. X-ray diffraction studies reveal that [Ni(P(Ph)(2)N(C6H4Me)(2))(2)](BF(4))(2) and [Ni(P(Ph)(2)N(C6H4OMe)(2))(2)](BF(4))(2) are tetracoordinate with distorted square planar geometries. The Ni(II/I) and Ni(I/0) redox couples of each complex are electrochemically reversible in acetonitrile with potentials that are increasingly cathodic as the electron-donating character of X is increased.

Phosphinidene group-transfer with a phospha-Wittig reagent: a new entry to transition metal phosphorus multiple bonds.

The phosphanylidene-sigma(4)-phosphorane reagents Me(3)P[double bond, length as m-dash]PAr (Ar = 2,4,6-(t)Bu(3)C(6)H(2) and 2,6-Mes(2)C(6)H(3)) are good delivery vehicles of the terminal phosphinidene moiety, PAr, to early-transition metals composed of zirconium and vanadium.

Tellus in, tellus out: the chemistry of the vanadium bis(telluride) functionality.

The vanadium-bis(telluride) complex, [(PNP)V(Te)(2)] (see picture), in which the terminal telluride units can act as leaving groups or protecting groups, is prepared by activation of elemental Te by V. The complex masks {(PNP)V(I)} or {(PNP)V(III)} sources when exposed to oxidants such as azides and diphenyldiazomethane. Isocyanides promote elimination of one Te ligand to furnish a V(III) complex with a terminal telluride ligand.

1,2-Diiodo-4,5-dimethyl-benzene.

The structure of the title compound, C(8)H(8)I(2), conforms closely to the mm2 symmetry expected for the free mol-ecule and is the first reported structure of a diiodo-dimethyl-benzene. Repulsion by neighboring I atoms and the neighboring methyl groups opposite to them results in a slight elongation of the mol-ecule along the approximate twofold rotation axis that bis-ects the ring between the two I atoms. In the extended structure, the mol-ecules form inversion-related pairs which are organized in approximately hexa-gonal close-packed layers and the layers then stacked so that mol-ecules in neighboring layers abut head-to-tail in a manner that optimizes dipole-dipole inter-actions.

1-Ethyl 2,2-dimethyl 3-(1,3-benzodioxol-5-yl)propane-1,2,2-tricarboxylate.

The molecular structure of the title triester compound, C(17)H(20)O(8), consists of a benzodioxole fused-ring system, an ethoxycarbonylmethyl group and two methoxycarbonyl groups arranged around a tetrahedral carbon center. Unlike similar triesters, which are oils, the title compound crystallizes at room temperature as interdigitated bilayers of triester molecules, with short O..

The progression of synthetic strategies to assemble titanium complexes bearing the terminal imide group.

The synthesis of terminal titanium imides is described in this account. The incorporation of this functional group has evolved from more simplistic approaches to more complex or unusual methods. Past and current synthetic strategies to incorporate the terminal imide functionality are explained with particular emphasis on low-coordinate titanium environments bearing this ubiquitous but vital type of motif.

Silver(I) and thallium(I) complexes of a PNP ligand and their utility as PNP transfer reagents.

Silver(I) and thallium(I) complexes of a diarylamido-based PNP pincer ligand have been prepared and characterized. The silver complex [(PNP)Ag]2 exists as a dimer both in solution and in the solid state and is stable under an ambient atmosphere. Thallium complex (PNP)Tl is, however, monomeric and acutely sensitive to moisture and air.

Activation of atmospheric nitrogen and azobenzene N=N bond cleavage by a transient Nb(III) complex.

Atmospheric N2 is activated by two transient Nb(III) "(PNP)NbCl2" (PNP- = N[2-P(CHMe2)2-4-methylphenyl]2) fragments to form the bridging diimido [(PNP)NbCl2]2(mu-N2) (1). Complex 1 can also be independently synthesized from Nb(IV) and Nb(V) precursors via one-electron and transmetalation reactions, respectively. In the presence of azobenzene, the transient Nb(III) intermediate, prepared from Li(PNP) and NbCl3(DME) (DME = dimethoxyethane) under Ar, cleaves the N=N bond via a metal-ligand cooperative four-electron reduction to form niobium imide and phosphoranimine functionalities.

Neutral and zwitterionic low-coordinate titanium complexes bearing the terminal phosphinidene functionality. Structural, spectroscopic, theoretical, and catalytic studies addressing the Ti-P multiple bond.

Alpha-hydrogen abstraction and alpha-hydrogen migration reactions yield novel titanium(IV) complexes bearing terminal phosphinidene ligands. Via an alpha-H migration reaction, the phosphinidene ((tBu)nacnac)Ti=P[Trip](CH(2)(tBu) ((tBu)nacnac(-) = [Ar]NC((t)Bu)CHC((t)Bu)N[Ar], Ar = 2,6-(CHMe2)(2C6H3, Trip = 2,4,6-(i)Pr3C6H2) was prepared by the addition of the primary phosphide LiPH[Trip] to the nucleophilic alkylidene triflato complex ((tBu)nacnac)Ti=CH(t)Bu(OTf), while alpha-H abstraction was promoted by the addition of LiPH[Trip] to the dimethyl triflato precursor ((tBu)nacnac)Ti(CH)(2)(OTf) to afford ((tBu)nacnac)Ti=P[Trip](CH3). Treatment of ((tBu)nacnac)Ti=P[Trip](CH3) with B(C6F5)(3) induces methide abstraction concurrent with formation of the first titanium(IV) phosphinidene zwitterion complex ((tBu)nacnac)Ti=P[Trip]{CH3B(C6F5)(3)}.

Aryl isocyanate, carbodiimide, and isocyanide prepared from carbon dioxide. A metathetical group-transfer tale involving a titanium-imide zwitterion.

Carbon dioxide can be readily converted quantitatively and under mild conditions into the aryl isocyanate and symmetrical carbodiimide via a metathetical reaction involving a zwitterionic titanium imide (nacnac)Ti=NAr(CH(3)B(C(6)F(5))(3)) (nacnac(-) = [ArNC((t)Bu)](2)CH, Ar = 2,6-(i)Pr(2)C(6)H(3)). The metathetical process to generate isocyanates allows also for facile formation of sterically demanding aryl isocyanide, by a deoxygenation route. Labeling studies using enriched (13)CO(2) are also described.