https://iopscience.iop.org/article/10.1070/RCR4795/pdf

Organofluorine chemistry: promising growth areas and challenges

Anti-Markovnikov additions to alkenes have been a longstanding goal of catalysis, and anti-Markovnikov addition of arenes to alkenes would produce alkylarenes that are distinct from those formed by acid-catalysed processes. Existing hydroarylations are either directed or occur with low reactivity and low regioselectivity for the n-alkylarene. Herein, we report the first undirected hydroarylation of unactivated alkenes with unactivated arenes that occurs with high regioselectivity for the anti-Markovnikov product. The reaction occurs with a nickel catalyst ligated by a highly sterically hindered N-heterocyclic carbene. Catalytically relevant arene- and alkene-bound nickel complexes have been characterized, and the rate-limiting step was shown to be reductive elimination to form the C-C bond. Density functional theory calculations, combined with second-generation absolutely localized molecular orbital energy decomposition analysis, suggest that the difference in activity between catalysts containing large and small carbenes results more from stabilizing intramolecular non-covalent interactions in the secondary coordination sphere than from steric hindrance.

Nickel-catalysed anti-Markovnikov hydroarylation of unactivated alkenes with unactivated arenes facilitated by non-covalent interactions.

Dinitrogen activation by group 4 and group 5 metal complexes supported by phosphine-amido containing ligand manifolds

Cooperative bond activation reactions with carbene complexes.

In this work, the effects of thiolate ligands (-SR, e.g., chain length and functional moiety) on the accessibility and catalytic activity of thiolate-protected gold nanoclusters (e.g., Au25(SR)18) for 4-nitrophenol hydrogenation is reported. The data suggest that Au25(SR)18 bearing a shorter alkyl chain shows a better accessibility to the substrates (shown by shorter induction time, t0) and a higher catalytic activity (shown by higher apparent reaction rate constant, kapp). The functional moiety of the ligands is another determinant factor, which clearly suggests that ligand engineering of Au25(SR)18 would be an efficient platform for fine-tuning its catalytic properties.

Tuning the accessibility and activity of Au25(SR)18 nanocluster catalysts through ligand engineering

A series of Pt(II) complexes of the type (N–N)PtPh(SR2) (N–N = 2,2′-pyridyl-indolate) were prepared, and their performance as catalysts for the hydroarylation of olefins was assessed. Evidence that the catalysis is homogeneous and is Pt-mediated is provided by control experiments with added hindered base (2,6-di-tert-butyl-4-methylpyridine) and Hg(0). Two potential catalytic intermediates, (tBuPyInd)PtPh(C2H4) and (tBuPyInd)Pt(CH2CH2Ph)(C2H4), were synthesized, and their catalytic efficacy was explored. Additionally, decomposition and deactivation pathways, including styrene formation via β-hydride elimination and ligand reductive demetalation, were identified.

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Olefin Hydroarylation Catalyzed by (pyridyl-indolate)Pt(II) Complexes: Catalytic Efficiencies and Mechanistic Aspects

The synthesis and characterization of two 1,2-cyclopentyl-bridged diiminophosphine proligands, CY5[NPN]DMPH2 (CY5 = cyclopentylidene; DMP = 2,6-Me2C6H3) and CY5[NPN]DIPPH2 (DIPP = 2,6-iPr2C6H3), are presented, and tautomerization to the corresponding 1,2-cyclopentenyl-bridged enamineimine phosphine precursors is reported. These two new proligands are obtained by deprotonation of N-DMP- or N-DIPP-cyclopentylideneimine (N-DMP, 2,6-dimethylphenyl; N-DIPP, 2,6-diisopropylphenyl) and the subsequent addition of 0.5 equiv of dichlorophenylphosphine. Each ligand precursor exists as a mixture of isomers that consist of the diimine, enamineimine, and dienamine tautomers and corresponding stereoisomers, each of which could be identified. The bis(dimethylamido)zirconium complexes CY5[NPN]DMPZr(NMe2)2 and CY5[NPN]DIPPZr(NMe2)2 were prepared directly from the neutral proligands and Zr(NMe2)4 via protonolysis. Exchange of the dimethylamido ligands in the latter complexes for chlorides and iodides takes place upon reacti...

New cyclopentenyl-linked [NPN] ligands and their coordination chemistry with zirconium: synthesis of a dinuclear side-on-bound dinitrogen complex.

Four bidentate, hybrid ligands (R(NP)R′H) featuring imine-nitrogen and alkyl-phosphine donors linked by a cyclopentyl ring were synthesized. The ortho position of the aryl group attached to nitrogen is varied such that R is Me or Pri; additionally, the groups decorating phosphorus (R′) are varied between But or Pri. The addition of each ligand to RuHCl(PPri3)2(CO) in the presence of KOBut generates four enamido-phosphine complexes RuH{R(NP)R′}(PPri3)(CO) that were characterized by NMR spectroscopy, elemental analyses, and, in the case of R = Pri and R′ = But or Pri, X-ray crystallography. Depending on R′, the reaction of RuH{R(NP)R′}(PPri3)(CO) with H2 generates varying amounts of the imine-phosphine complex RuH2{R(NP)R′H}(PPri3)(CO). Insights into the mechanism of H2 activation by these enamido derivatives were explored using RuH{Pr(NP)Pri}(PPri3)(CO), for which an intermediate was identified as the dihydrogen–dihydride complex, RuH2(H2){Pri(NP)PriH}(PPri3)(CO), on the basis of the T1,min value of 22 ms ...

Ruthenium Complexes Stabilized by Bidentate Enamido-Phosphine Ligands: Aspects of Cooperative H2 Activation

Use of the Imine–Enamine Equilibrium in Cooperative Ligand Design

In order to generate tridentate enamido diphosphine ligand platforms, we developed procedures for the preparation of tBu2PCH2CH2P(tBu)I, which involve low temperatures, pentane solvent and addition of 4 equiv. of tBuLi to Cl2PCH2CH2PCl2 or 2 equiv. of tBuLi to known Cl(tBu)PCH2CH2P(tBu)Cl also at low temperatures in pentane; an alternate method involves the inverse addition of Cl(tBu)PCH2CH2P(tBu)Cl to 2 equiv. of tBuLi in pentane at 0 °C; all of these methods generate good yields of the tetraphosphine dimer (tBu2PCH2CH2P(tBu))2 contaminated by small amounts of tBu2PCH2CH2PtBu2 (dtbpe), which can be conveniently separated by sublimation. Subsequent oxidative cleavage of the P–P bond with I2 or 1,2-diiodoethane results in the formation of the desired tBu2PCH2CH2P(tBu)I, which undergoes C–P bond formation when added to 1 equiv. of the lithium N-2,6-diisopropylphenylenamide of cyclopentylidene imine to generate the HNPP ligand precursor; this species exists as a tautomeric mixture of the corresponding enamine and imine, the ratio of which depends on workup conditions used. This enamine–imine mixture can be used directly to form Ru(II) species either directly with heating to generate the five-coordinate (NPP)RuCl(CO) via loss of H2 or by inclusion of 1 equiv. of KOtBu to generate (NPP)RuH(CO). X-ray crystallographic studies confirm that the geometry in the solid state matches the solution spectroscopic data. Subsequent studies of (NPP)RuH(CO) indicate that it reacts with benzaldehyde, benzyl alcohol, and H2 in a cooperative manner to generate a series of hydride carbonyls that have been characterized fully by NMR spectroscopy and X-ray crystallography.

Truman C. Wambach

Papers

Olefin Hydroarylation Catalyzed by (pyridyl-indolate)Pt(II) Complexes: Catalytic Efficiencies and Mechanistic Aspects

New cyclopentenyl-linked [NPN] ligands and their coordination chemistry with zirconium: synthesis of a dinuclear side-on-bound dinitrogen complex.

Ruthenium Complexes Stabilized by Bidentate Enamido-Phosphine Ligands: Aspects of Cooperative H2 Activation

Use of the Imine–Enamine Equilibrium in Cooperative Ligand Design

Synthesis of a sterically bulky diphosphine synthon and Ru(II) complexes of a cooperative tridentate enamide-diphosphine ligand platform