Synthesis, Structure, and Reactivity of Copper(I) Proazaphosphatrane Complexes.

Copper(I) complexes of isobutyl- () and isopropyl-substituted () proazaphosphatranes have been synthesized. Structural and computational studies of a series of monomeric complexes CuX (X = Cl, Br, I) and dimeric [CuCl] provide insight into the transannulation within and steric properties of the proazaphosphatrane ligand. These halide complexes are competent precatalysts in a model borylation reaction, and the silylamido complex CuN(TMS) catalyzes hydrosilylation of benzaldehyde under mild conditions.

Transition Metal as Template: Reversing the Synthesis Logic in the Preparation of Pincer Complexes.

The conventional synthetic approach to transition metal pincer complexes calls for the preparation of the tridentate pincer (pro)ligand first, with subsequent introduction of the transition metal center as the last step. This work demonstrates that the alternative synthetic logic, where the central main group element is introduced last, can be applicable to a number of PEP pincer complexes (E=B, Al, Si, P) derived from phosphinophenols and phosphinopyrroles. This approach obviates the need to isolate well-behaved propincer precursors, and instead relies on the formation of phosphine-metal adducts first, whose nature determines the stoichiometry of the needed main group reagent to complete the synthesis.

Comparative Analysis of the Donor Properties of Isomeric Pyrrolyl Phosphine Ligands.

Understanding the net donor and electronic properties of pyrrole-based phosphines is critical for guiding their use as ligands. In this study, we compare two isomeric 1- and 2-(diphenylphosphino)methylpyrroles ( and , respectively) to determine the degree to which -(phosphino)pyrroles are distinct from aryl- and 2-pyrrolyl phosphines. Ruthenium, rhodium, platinum, and gold complexes as well as selenide derivatives of these ligands are examined using NMR and IR spectroscopy, X-ray crystallography, and cyclic voltammetry.

Synthesis of pyrrole-based PSiP pincer ligands and their palladium, rhodium, and platinum complexes.

The synthesis and coordination chemistry of a new class of silyl pincer ligand featuring pyrrole-based linkers is reported. The steric and electronic properties of these bis(phosphinopyrrole)methylsilane ligands were interrogated using their palladium, rhodium, and platinum complexes. The pyrrole-based linker attenuates the donor ability of the ligand relative to its reported 1,2-phenylene congener while maintaining a similar steric profile.

Study and modular synthesis of unsymmetrical bis(phosphino)pyrrole ligands.

We report the facile and modular synthesis of unsymmetrical 1,2-bis(phosphino)pyrrole ligands and their coordination chemistry. These ligands offer a promising alternative to their 1,2-bis(phosphino)benzene congeners, retaining a similar steric profile with attenuated electron donation. Proof-of-principle application of a bis(phosphino)pyrrole ligand in a nickel-catalyzed C-N cross-coupling reaction under mild conditions is demonstrated.

On Transannulation in Azaphosphatranes: Synthesis and Theoretical Analysis.

A combined synthetic-theoretical study has been undertaken to determine the factors that influence transannulation in azaphosphatranes. The commonly used proazaphosphatrane P(-BuNCHCH)N and several of its oxidized congeners are used as model systems. The haloazaphosphatranes of P(-BuNCHCH)N were synthesized, including a rare fluoroazaphopshatrane, and used as references for computational investigations.

A mechanistic investigation of the photoinduced, copper-mediated cross-coupling of an aryl thiol with an aryl halide.

Photoinduced, copper-catalyzed cross-coupling can offer a complementary approach to thermal (non-photoinduced) methods for generating C-X (X = C, N, O, S, etc.) bonds. In this report, we describe the first detailed mechanistic investigation of one of the processes that we have developed, specifically, the (stoichiometric) coupling of a copper-thiolate with an aryl iodide.

Enantioselective, Stereodivergent Hydroazidation and Hydroamination of Allenes Catalyzed by Acyclic Diaminocarbene (ADC) Gold(I) Complexes.

The gold-catalyzed enantioselective hydroazidation and hydroamination reactions of allenes are presented herein. ADC gold(I) catalysts derived from BINAM were critical for achieving high levels of enantioselectivity in both transformations. The sense of enantioinduction is reversed for the two different nucleophiles, allowing access to both enantiomers of the corresponding allylic amines using the same catalyst enantiomer.

Synthesis of Stable Gold(III) Pincer Complexes with Anionic Heteroatom Donors.

A series of gold(III) complexes supported by pyridine-based bis(amidate), bis(carboxylate), and bis(iminothiolate) substituents is reported. These compounds represent rare examples of pincer-ligated gold(III) centers with multiple anionic heteroaom donors. Reactivity and electrochemical studies demonstrate the stability of these compounds and the marked difference in reduction potentials with varying ligand scaffolds.

Application of fundamental organometallic chemistry to the development of a gold-catalyzed synthesis of sulfinate derivatives.

The development of a gold(I)-catalyzed sulfination of aryl boronic acids is described. This transformation proceeds through an unprecedented mechanism which exploits the reactivity of gold(I)-heteroatom bonds to form sulfinate anions. Further in situ elaboration of the sulfinate intermediates leads to the corresponding sulfones and sulfonamides, two pharmacophores routinely encountered in drug discovery.

High-turnover supramolecular catalysis by a protected ruthenium(II) complex in aqueous solution.

The design of a supramolecular catalyst capable of high-turnover catalysis is reported. A ruthenium(II) catalyst is incorporated into a water-soluble supramolecular assembly, imparting the ability to catalyze allyl alcohol isomerization. The catalyst is protected from decomposition by sequestration inside the host but retains its catalytic activity with scope governed by confinement within the host.

Acetic acid aldol reactions in the presence of trimethylsilyl trifluoromethanesulfonate.

In the presence of TMSOTf and a trialkylamine base, acetic acid undergoes aldol addition to non-enolizable aldehydes under exceptionally mild conditions. Acidic workup yields the beta-hydroxy carboxylic acid. The reaction appears to proceed via a three-step, one-pot process, including in situ trimethylsilyl ester formation, bis-silyl ketene acetal formation, and TMSOTf-catalyzed Mukaiyama aldol addition.

One-pot enol silane formation-Mukaiyama aldol-type addition to dimethyl acetals mediated by TMSOTf.

Various ketones, esters, amides, and thioesters add in high yield to dimethyl acetals in the presence of silyl trifluoromethanesulfonates and an amine base. Acetals derived from aryl, unsaturated, and aliphatic aldehydes are all effective substrates. The reaction proceeds in a single reaction flask, with no purification of the intermediate enol silane necessary.