The Rh₄(CO)₁₂-Catalyzed Hydroformylation of 3,3-Dimethylbut-1-ene Promoted with HMn(CO)₅. Bimetallic Catalytic Binuclear Elimination as an Origin for Synergism in Homogeneous Catalysis

Abstract

The bimetallic origins of catalytic synergism were studied using unmodified rhodium and manganese carbonyls as catalyst precursors during the low-temperature hydroformylation of 3,3-dimethylbut-1-ene to 4,4-dimethylpentanal in n-hexane solvent (T approximately 298 K, P(CO) = 1.0-4.0 MPa, P(H2) = 0.5-2.0 MPa). A dramatic increase in the catalytic rate was observed in the experiments conducted when both metals were used simultaneously. Detailed in-situ FTIR measurements indicated the observable presence of only homometallic complexes during catalysis, e.g., RCORh(CO)(4), Rh(4)(CO)(12), Rh(6)(CO)(16), HMn(CO)(5), and Mn(2)(CO)(10). The kinetics of product formation show a distinct linear-bilinear form in observables: k(1)[RCORh(CO)(4)][CO](-1)[H(2)] + k(2)[RCORh(CO)(4)][HMn(CO)(5)][CO](-1.5). The first term represents the classic unicyclic rhodium catalysis, while the second indicates a hydride attack on an acyl species. These spectroscopic and kinetic results strongly suggest that the origin of synergism is the presence of bimetallic catalytic binuclear elimination and not cluster catalysis. This appears to be the first detailed evidence for such a catalytic mechanism, and its implications for selectivity and nonlinear catalytic activity are accordingly discussed.

The Catalytic Binuclear Elimination Reaction: Importance of Non-linear Kinetic Effects and Increased Synthetic Efficiency

“…In situ spectroscopic analysis was not available/reported. In a series of studies, HMn(CO) 5 [61][62][63]74], HRe(CO) 5 [75][76][77][78], HMoCp(CO) 3 [77,78] and HWCp(CO) 3 [79] the complexes were added individually to unmodified rhodium-catalysed alkene hydroformylations. In situ FTIR spectroscopy was performed on all systems, and detailed modelling was performed on the more well-behaved systems containing HMn(CO) 5 and HRe(CO) 5 .…”

A Review of BTEM Analysis for Catalytic Studies and a Recent Homogeneous Catalytic Example

“…Recently, BTEM was used to identify a new homogeneous catalytic reaction mechanism that involves both mononuclear and dinuclear intermediates simultaneously. This mechanism is now called ''catalytic binuclear elimination'' [26][27][28][29][30]. In the following example, some unpublished details from a recent study are presented [30].…”

On the Determination of Partial Molar Polarizations and Dipole Moments of Solutes from Multicomponent Solutions Alone: Experimental and Model Development Using Deutero-Labeled Organic Compounds

“…The later is frequently encountered in the study of kinetically labile systems, possessing spectroscopically observable and quantifiable intermediates, such as in organometallic chemistry and homogeneous catalysis. 11 The determination of higher order interactions in complex systems and the determination of the physicochemical properties of non-isolatable intermediates provide rich opportunities for further understanding solution chemistries.…”