Rhodium hydride formation in the presence of a bulky monophosphite ligand: a spectroscopic and solid-state investigation

Abstract

A study has been carried out on rhodium catalyst preforming when modified with the bulky tris(2,4-di-tert-butylphenyl) phosphite, P(Obtbp)(3). X-Ray crystal structure determinations of a tropolone-type precursor complex [Rh(TropBr(3))(CO){P(Obtbp)(3)}].P(Obtbp)(3).CH(3)COCH(3)(TropBr(3)= 3,5,7-tribromotropolonate) and the free P(Obtbp)(3) ligand are reported. Systematic in situ IR and NMR studies of the particular rhodium phosphite modified catalyst and its precursors have led to the identification of two distinct rhodium hydride species. A {(1)H,(31)P} HMBC NMR experiment afforded clarity on the (31)P NMR spectra observed under hydroformylation conditions. The species were identified as [HRh(CO)(3){P(Obtbp)(3)}] and [HRh(CO)(2){P(Obtbp)(3)}(2)]. Attention was also given to the rate of catalyst formation when starting from different rhodium precursors.

New Ligands for Rh‐Catalysed Hydroformylation of 1‐Octene in Supercritical Carbon Dioxide – X‐ray Structure of [Rh{PPh2(OC9H19)}4]PF6

“…The slow reaction rate of similar precursors containing phosphite ligands with CO/H 2 has been reported. [24] The broad doublet at δ = 144.1 (J Rh,P = 168.7 Hz) ppm is better resolved at -60°C and could correspond to dimeric Rh 0 complexes [Rh 2 (CO) 6 (2) 2 ] or [Rh 2 (CO) 4 (2) 4 ], as has been observed for other P-donor-rhodium systems. [25] The broad multiplets at δ = 120 and 82 ppm were attributed to mixed phosphonite/ phosphonate species.…”

Carbon Monoxide as a Chemical Feedstock: Carbonylation Catalysis

“…The latter were thought to lead to mono-ligand complexes under hydroformylation conditions. A recent spectroscopic study has also shown that a bis-ligand complex is involved [33]. Ligand 1 gives a l/b ratio of 24 and a low percentage of isomerization can be obtained; at low phosphite concentrations it is also a good isomerization catalyst and internal heptenes give linearities as high as 60%.…”

Understanding chemistry from combined X-ray and quantum mechanical studies

“…In pioneering studies we could demonstrate that these CCs not only influence the geometry of coordination compounds [3] and solids but also serve as controlling parameters for important chemical reactions like the activation of chemical bonds in catalytic reactions [4]. Furthermore, in covalent solids such as transition metal oxides and carbides they appear to signal electron localization phenomena which are reflected by metal-to-insulator transitions or the suppression of superconductivity [5].…”

“…This is the case of the early metal activation of the alkanes C-H bonds ("agostic" interaction), whose features we catalogued [2]. As another topic, the systematic study of series of structures allowed revising the parameters for the redox coupling/uncoupling between sulphido anions, namely the dichotomies 2S 2 4-/S 4 2-or 2S 2-/S 2 2-over one or more metal centers [3] The lecture will also illustrate how some key structures can be used as milestones along complicate patterns of reactivity also in processes of bio-catalytic relevance, such as the modeling of hydrogenases [4].[1] Ienco, A.; Caporali, ;M.; Zanobini, F.; Mealli, C. Inorg. Chem.…”