Synthesis, characterization and reactivity of tetranuclear ruthenium hydrido clusters containing chiral phosphineligands

Abstract

The chiral clusters [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] have been synthesized by derivatizing the parent carbonyl cluster [H(4)Ru(4)(CO)(12)] with the appropriate mono- or didentate chiral phosphine ligand. The phosphine-substituted clusters were found to be able to catalyze the (asymmetric) hydrogenation of tiglic acid albeit with relatively low selectivity (enantiomeric excesses varying from 0 to 23%). It was found that the stability of the chiral ruthenium hydride clusters and the product distribution obtained in the catalytic reactions are dependent on the nature of the chiral phosphine. The crystal structures of [H(4)Ru(4)(CO)(12-n)(L)(n)] (n = 1, 2; L = NMDPP), 1,1-[H(4)Ru(4)(CO)(10)(L-L)] (L-L = DUPHOS, O-DUPHOS (partially oxygenated ligand), DIPAMP), 1,2-[H(4)Ru(4)(CO)(10)(DIOP)] and [{H(4)Ru(4)(CO)(10)(DIOP)}(2)] are presented.

Chiral and achiral phosphine derivatives of alkylidyne tricobalt carbonyl clusters as catalyst precursors for (asymmetric) inter- and intramolecular Pauson–Khand reactions

“…2) was reacted with [Co 3 (l 3 -CH)(CO) 9 ] at elevated temperature for 4 h. Only one product was isolated and identified as the mono-substituted cluster [Co 3 (l 3 -CH)(CO) 8 (NMDPP)] ( 7) in 51% yield. The spectroscopic data from IR, 1 H and 31 P NMR measurements, the mass spectrum and the microanalysis are in full agreement with the suggested formula. In addition to the typical IR bands found in monosubstituted alkylidyne tricobalt clusters, the spectrum reveals a signal at 1858 cm −1 similar to that found in clusters 2 and 4.…”

“…The FAB mass spectrum confirmed the proposed molecular formula. However, 1 H and 31 P NMR as well as IR spectra indicate the presence of isomers in solution. The peak areas in the 1 H NMR spectra show some inconsistency.…”

Homogeneous Catalysis by Organometallic Polynuclear Clusters

“…Continued work by Nordlander investigated the changes in cluster stability and activity in the asymmetric hydrogenation of 29a induced by various chiral phosphine ligands [85]. While improvement was observed over the parent hydrido cluster, (µ-H)4Ru4(CO)12, the authors noted varying conversion (70 -95%), with poor increase in enantioselectivity (up to 23% ee), along with thermal decomposition.…”

Asymmetric hydrogenation of an α-unsaturated carboxylic acid catalyzed by intact chiral transition metal carbonyl clusters – diastereomeric control of enantioselectivity

“…In previous studies, we have shown that the chiral diphosphine ligands play an important role in asymmetric hydrogenation 21,22,26 and that the chiral configurations of the hydrogenated products are dependent on the chiral ligand used. 27 The ability of the new clusters 3-22 to function as catalysts for asymmetric hydrogenation was investigated.…”

“…27 The ability of the new clusters 3-22 to function as catalysts for asymmetric hydrogenation was investigated. Tiglic acid [trans-2-methyl-2-butenoic acid] was chosen as a substrate because (i) it has been used as a benchmark substrate in earlier assessments of asymmetric hydrogenation effected by transition metal carbonyl clusters, facilitating comparison with other work, 21,26,[28][29][30][31] (ii) there is a well-established and reliable protocol for the evaluation of enantiomeric excess, and (iii) asymmetric hydrogenation of α-unsaturated carboxylic acids and their substituted derivatives, which are essential pharmaceuticals or chiral building blocks for the synthesis of biologically active compounds, is of considerable importance. 32,33 Instead of the high hydrogen pressure that has been commonly used in previous cluster-based catalysis investigations (130 bar), 34 a hydrogen pressure of 50 bar was used.…”