Ruthenium-catalysed hydrogenation of esters using tripodal phosphine ligands

Abstract

24/09/12 meb. Author version attached, OK to publish

Hydrogenation of nitrophenols catalyzed by carbon black-supported nickel nanoparticles under mild conditions

“…Undoubtedly, the precious metal-based catalysts are still remain the leading catalysts for hydrogenation such as palladium [25][26][27], platinum [28][29][30], rhodium [31,32], ruthenium [33,34] and aurum-based [35][36][37] systems, even though their widespread applications are limited by their low earth-abundance and high cost. In order to solve these problems, various non-precious metal catalysts [38][39][40], especially nickel-based catalysts [3,[39][40][41] have been developed as economical alternatives in hydrogenation reactions.…”

Beyond Triphos – New hinges for a classical chelating ligand

“…Consequently derivatives with less sterically demanding phosphines, or more forcing conditions were implemented to enforce a κ 3 -coordination mode. NP 3 R derivatives bearing ethyl (N(CH 2 PEt 2 ) 3 , NP 3 Et , 132) [53], isopropyl (N(CH 2 P i Pr 2 ) 3 , NP 3 iPr , 133) [54] and cyclopentyl (N(CH 2 PCyp 2 ) 3 , NP 3…”

“…The diphenyl-(NP 3 Ph , 113) and diethyl-phosphino nitrogen-centered ligands (NP 3 Et , 132) were evaluated for their ability to hydrogenate the industrially relevant ester dimethyl oxalate (DMO) to ethane-1,2-diol (ED) via methyl glycolate (MG) (Scheme 31), but it was found that both of these ligands underperformed when compared to Ph [53]. The catalysts were formed in situ from [Ru(acac) 3 ] (acac = acetylacetone) and triphosphine, and N-centered ligands all displayed longer induction periods, where hydrogen was being consumed but no DMO conversion was observed by analysis of sampled aliquots and headspace gas.…”

“…This discrepancy in kinetic profile suggests DMO binding to ruthenium is facile during the carbon-centered regime, but becomes rate determining when nitrogen-centered ligands are employed [53]. Further differences between the two ligand regimes were identified, in that the MeCP 3…”

“…Ph )] (179) as a well-defined molecular catalyst did not enhance catalyst efficacy, presumably as the carbonyl-stabilized ruthenium(0) center could not undergo the prerequisite oxidative process to afford the proposed 16-electron ruthenium(II) active species [RuH 2 (NP 3 R )] [53]. The 14-electron ruthenium(0) species [Ru(P 3 R )] (P 3 R = MeCP 3 Ph , NP 3 Ph , NP 3 Et ) is proposed to exist prior to oxidative addition of hydrogen to reproduce the catalytically active 16-electron ruthenium dihydride.…”