A ruthenium cis-dihydride with 2-phosphinophosphinine ligands catalyses the acceptorless dehydrogenation of benzyl alcohol

The first ruthenium dihydride complex featuring a phosphinine ligand cis-[Ru(H)₂(2-PPh₂-3-Me-6-SiMe₃-PC₅H₂)₂] was synthesised exclusively as the cis-isomer. When formed in situ from the reaction of cis-[Ru(Cl)₂(2-PPh₂-3-Me-6-SiMe₃-PC₅H₂)₂] with two equivalents of Na[BHEt₃], as demonstrated by ³¹P and ¹H NMR spectroscopy, the catalysed acceptorless dehydrogenation of benzyl alcohol was observed leading to benzyl benzoate in up to 70% yield.

Electrocatalytic Proton Reduction by a Cobalt(III) Hydride Complex with Phosphinopyridine PN Ligands

Cobalt complexes with 2-(diisopropylphosphinomethyl)pyridine (PN) ligands have been synthesized with the aim of demonstrating electrocatalytic proton reduction to dihydrogen with a well-defined hydride complex of an Earth-abundant metal. Reactions of simple cobalt precursors with 2-(diisopropylphosphino-methyl)pyridine (PN) yield [Co^II(PN)₂(MeCN)][BF₄]₂ 1, [Co^III(PN)₂(H)(MeCN)][PF₆]₂ 2, and [Co^III(PN)₂(H)(Cl)][PF₆] 3. Complexes 1 and 3 have been characterized crystallographically. Unusually for a bidentate PN ligand, all three exhibit geometries with mutually trans phosphorus and nitrogen ligands. Complex 1 exhibits a distorted square-pyramidal geometry with an axial MeCN ligand in a low-spin electronic state. In complexes 2 and 3, the PN ligands lie in a plane leaving the hydride trans to MeCN or chloride, respectively. The redox behavior of the three complexes has been studied by cyclic voltammetry at variable scan rates and by spectroelectrochemistry. A catalytic wave is observed in the presence of trifluoroacetic acid (TFA) at an applied potential close to the Co(II/I) couple of 1. Bulk electrolysis of 1, 2, or 3 at a potential of ca. -1.4 V vs E(Fc⁺/Fc) in the presence of TFA yields H₂ with Faradaic yields close to 100%. A catalytic mechanism is proposed in which the pyridine moiety of a PN ligand acts as a pendant proton donor following opening of the chelate ring. Additional mechanisms may also operate, especially in the presence of high acid concentration where speciation changes.

Synthesis and coordination chemistry of the PPN ligand 2-[bis(diisopropylphosphanyl)methyl]-6-methylpyridine

The synthesis and crystal structure of the multidentate PPN ligand 2-[bis(diisopropylphosphanyl)methyl]-6-methylpyridine (L), C19H35NP2, are described. In the isostructural tetrahedral Fe and Co complexes of type LMCl2 (M = Fe, Co), namely {2-[bis(diisopropylphosphanyl)methyl]-6-methylpyridine-κ2 P,N}dichloridoiron(II), [FeCl2(C19H35NP2)], and {2-[bis(diisopropylphosphanyl)methyl]-6-methylpyridine-κ2 P,N}dichloridocobalt(II), [CoCl2(C19H35NP2)], the ligand adopts a bidentate P,N-coordination, whereas in the case of the octahedral Mn complex {2-[bis(diisopropylphosphanyl)methyl]-6-methylpyridine-κ2 P,P′}bromidotricarbonylmanganese(I), [MnBr(C19H35NP2)(CO)3], the ligand coordinates via both P atoms to the metal centre.

Efficient acceptorless dehydrogenation of secondary alcohols to ketones mediated by a PNN-Ru(ii) catalyst

The ruthenium(ii) complex, [fac-PN_HN]RuCl₂(PPh₃) (C), in combination with t-BuOK proved an effective and versatile catalyst allowing aromatic-, aliphatic- and cycloalkyl-containing alcohols to be efficiently converted to their corresponding ketones with high values of TON achievable.

Phosphine-pyridonate ligands containing octahedral ruthenium complexes: access to esters and formic acid

Selective formation of esters from primary alcohols or formic acid from carbon dioxide was achieved in the presence of phosphine-pyridone containing ruthenium catalysts.

Probing the effect of heterocycle-bonding in PNX-type ruthenium pre-catalysts for reactions involving H2

This study describes a series of ruthenium complexes with PNX-type ligands (X = heterocyclic donor group), and their catalytic activities in hydrogenation and dehydrogenation reactions are compared.