Concurrent Synergism and Inhibition in Bimetallic Catalysis: Catalytic Binuclear Elimination, Solute−Solute Interactions and a Hetero-Bimetallic Hydrogen-Bonded Complex in Rh−Mo Hydroformylations

Abstract

Hydroformylations of cyclopentene and 3,3-dimethylbut-1-ene were performed using both Rh(4)(CO)(12) and (eta(5)-C(5)H(5))Mo(CO)(3)H as precursors in n-hexane at 298 K. Both stoichiometric and catalytic hydroformylations were conducted as well as isotopic labeling experiments. Six organometallic pure component spectra were recovered from the high-pressure FTIR experiments, namely the known species Rh(4)(CO)(12), (eta(5)-C(5)H(5))Mo(CO)(3)H, RCORh(CO)(4), and the new heterobimetallic complexes RhMo(CO)(7)(eta(5)-C(5)H(5)), a weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4), and a substituted RhMo(CO)(7-y)(eta(5)-C(5)H(5))L(y), where y = 1 or 2 and L = (pi-C(5)H(8)). The main findings were (1) catalytic binuclear elimination (CBER) occurs between (eta(5)-C(5)H(5))Mo(CO)(3)H and RCORh(CO)(4) resulting in aldehyde and RhMo(CO)(7)(eta(5)-C(5)H(5)), and this mechanism is responsible for ca. 10% of the product formation; (2) molecular hydrogen is readily activated by the new heterobimetallic complex(es); (3) FTIR and DFT spectroscopic evidence suggests that the weak hydrogen bonded species (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) has an interaction of the type eta(5)-C(5)H(4)-H...O=C; and (4) independent physicochemical experiments for volumes of interaction confirm that significant solute-solute interactions are present. With respect to the efficiency of the catalytic cycle, the formation of a weak (eta(5)-C(5)H(5))Mo(CO)(3)H-C(5)H(9)CORh(CO)(4) complex results in a significant decrease in the measured turnover frequency (TOF) and is the primary reason for the inhibition observed in the bimetallic catalytic hydroformylation. Such hydrogen bonding through the eta(5)-C(5)H(5) ring might have relevance to inhibition observed in other catalytic metallocene systems. The present catalytic system is an example of concurrent synergism and inhibition in bimetallic homogeneous catalysis.

Hydrogen and Dihydrogen Bonds in the Reactions of Metal Hydrides

“…The “acidic” hydrides CpMH­(CO) 3 (M = Mo, W) and HM­(CO) 5 (M = Mn, Re) have been used as parts of bimetallic catalytic systems for the hydroformylation of alkenes. − The Rh 4 (CO) 12 precatalyst was shown to transform into unsaturated Rh­(CO) 4 (RCO), which forms weak hydrogen bonds with the acidic hydrides CpMH­(CO) 3 . Interestingly, in this case, the hydrogen-bonded complex is also stabilized by CO···HM and CO···HC Cp interactions, , but in our view, only the more reactive MH bonds are relevant to the reaction.…”

Detailed spectroscopic analysis of complex multi‐component materials using a combination of Raman mapping with BTEM

“…Comparisons between BTEM analysis and other self‐modelling curve resolution methods, in the context of vibrational spectroscopies has appeared elsewhere . Even in the case of very similar pure component spectra and a high degree of spectral overlap, BTEM is able to recover outstanding spectral estimates, and the structure of the new non‐isolatable species can be subsequently verified by comparison of the BTEM spectral estimates and density functional theory predicted spectra . In the following, a number of case studies are presented for the successful application of BTEM analysis to Raman microscopic mapping measurements of various materials.…”

Amino‐methyl coumarin as a potential SERS@Ag probe for the evaluation of protease activity and inhibition

“…BTEM analyses large sets of multi‐component spectra and provides a set of ‘pure component’ spectral estimates for the constituents present, without recourse to any a priori information. Furthermore, these spectral estimates often have outstanding signal‐to‐noise ratios, even for the minor or trace constituents present . BTEM has been successfully applied to Fourier transform infrared,Raman,nuclear magnetic resonance, mass spectrometry, UV–vis, Spatially Offset Raman Spectroscopy,Reflection Absorption Infra Red Spectroscopy (RAIRS) etc.…”