Rh₄(CO)₁₂-Catalyzed Hydroformylation of Cyclopentene Promoted with HMn(CO)₅. Another Example of Rh₄(CO)₁₂/HMn(CO)₅ Bimetallic Catalytic Binuclear Elimination

Abstract

A detailed in situ high-pressure FTIR spectroscopic study was performed to investigate the bimetallic origins of catalytic synergism in homogeneous catalysis. The reaction chosen was the homogeneous catalyzed hydroformylation of cyclopentene to cyclopentanecarboxaldehyde, starting with unmodified rhodium and manganese carbonyls as catalyst precursors in n-hexane as solvent. The spectra were analyzed by an advanced signal processing and statistical technique. Only four organometallic spectra could be found. These were RCORh-(CO) 4 , Rh 4 (CO) 12 , HMn(CO) 5 , and Mn 2 (CO) 10 . A very significant increase in aldehyde formation was observed in the experiments when both rhodium carbonyl and manganese carbonyl complexes were used simultaneously. The kinetics of product formation shows a distinct linear-bilinear form in observable organometallics; k 1 [RCORh(CO) 4 ][H 2 ][CO] -1 + k 2 [RCORh(CO) 4 ][HMn(CO) 5 ][CO] -1.6 . The determined activation parameters for the bilinear term were ∆H q ) 47 ( 8 kJ/mol and ∆S q ) -88 ( 28 J/(mol K). The results, particularly the bilinear term and the negative entropy of activation, suggest that the origin of synergism is the presence of bimetallic catalytic binuclear elimination: namely, the hydride attack on the acyl species. The present results are consistent with observations and conclusions reached for a previously studied Rh 4 (CO) 12 /HMn(CO) 5 /3,3-dimethylbut-1-ene hydroformylation system.

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

“…In both cases, reaction occurred on the timescale of mixing, and the product was all-terminal RhRe(CO) 9 [61][62][63]. By varying the hydrogen partial pressure, it was possible to show that the reaction is reversible and very rapid, again on the mixing timescale, pushing the organometallics back towards HRe(CO) 5 and Rh 4 (CO) 12 .…”

“…After the advent of the latest generation of signal processing techniques, HRh(CO) 4 was identified at 2,124, 2,072 and 2,042 cm À1 and its deuterated analogue DRh(CO) 4 was identified at 2,124, 2,072 and 2,042 cm À1 under circa 50 bar of syngas [59]. An alkylrhodium tetracarbonyl RRh(CO) 4 (R ¼ C 2 H 5 ) was tentatively reported using high-pressure in situ FTIR [60], but it is now known that the reported bands are due to the acylrhodium tetracarbonyl RCORh(CO) 4 (R ¼ C 2 H 5 ) [61][62][63]. The acylrhodium tetracarbonyl RCORh(CO) 4 was first reported by Garland and Bor [64] and since then a few dozen different R groups have been used and the spectra reported.…”

“…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].…”

Carbonylation of Alkenes and Dienes

“…Only four organometallic species, Rh 4 (CO) 12 , C 5 H 9 CORh(CO) 4 , HMn(CO) 5 , and Mn 2 (CO) 10 were found in the reaction mixture. The kinetics of cyclopentanecarboxaldehyde formation suggest that the origin of synergism is the HMn(CO) 5 attack on the acyl species [80].…”