Reaction of Alkynes with Rh4(CO)12. A Mid-Infrared Vibrational and Kinetic Study of (μ4-η2-alkyne)Rh4(CO)8(μ-CO)2

Specificity of Sites within Eight-Membered Ring Zeolite Channels for Carbonylation of Methyls to Acetyls

The acid-catalyzed formation of carbon-carbon bonds from C1 precursors via CO insertion into chemisorbed methyl groups occurs selectively within eight-membered ring (8-MR) zeolite channels. This elementary step controls catalytic carbonylation rates of dimethyl ether (DME) to methyl acetate. The number of O-H groups within 8-MR channels was measured by rigorous deconvolution of the infrared bands for O-H groups in cation-exchanged and acid forms of mordenite (M,H-MOR) and ferrierite (H-FER) after adsorption of basic probe molecules of varying size. DME carbonylation rates are proportional to the number of O-H groups within 8-MR channels. Na+ cations selectively replaced protons within 8-MR channels and led to a disproportionate decrease in carbonylation turnover rates (per total H+). These conclusions are consistent with the low or undetectable rates of carbonylation on zeolites without 8-MR channels (H-BEA, H-FAU, H-MFI). Such specificity of methyl reactivity upon confinement within small channels appears to be unprecedented in catalysis by microporous solids, which typically select reactions by size exclusion of bulkier transition states.

Experimental Raman spectra of dilute and laser-light-sensitive [Rh4(CO)9(µ-CO)3] and [(µ4-η2-3-hexyne)Rh4(CO)8(µ-CO)2]. Comparison with theoretically predicted spectra

The reaction of [Rh(4)(CO)(9)(mu-CO)(3)] with 3-hexyne to form the butterfly cluster [(mu(4)-eta(2)-3-hexyne)Rh(4)(CO)(8)(mu-CO)(2)] was monitored viain-situ Raman spectroscopy using an NIR laser source, at room temperature and under atmospheric argon using n-hexane as solvent. The collected raw spectra were deconvoluted using band-target entropy minimization (BTEM). The pure component mid-Raman spectra of the [Rh(4)(CO)(9)(mu-CO)(3)] and the butterfly cluster [(mu(4)-eta(2)-3-hexyne)Rh(4)(CO)(8)(mu-CO)(2)], were reconstructed with a high signal-to-noise ratio. Full geometric optimization and Raman vibrational prediction were carried out using DFT. The experimental and predicted Raman spectra were in good agreement. In particular, the far-Raman vibrational modes in the region 100-280 cm(-1) provided characterization of the metal-metal bonds and direct confirmation of the structural integrity of the polynuclear frameworks in solution.