The selective N-methylation of bifunctionalized amines with supercritical methanol (scCH(3)OH) promoted by the conventional solid acids (H-mordenite, beta-zeolite, amorphous silica-alumina) and acid-base bifunctional catalysts (Cs-P-Si mixed oxide and gamma-alumina) was investigated in a continuous-flow, fixed-bed reactor. The use of scCH(3)OH in the reaction of 2-aminoethanol with methanol (amine/CH(3)OH = 1/10.8) over the solid catalysts led to a significant improvement in the chemoselectivity of the N-methylation. Among the catalysts examined, the Cs-P-Si mixed oxide provided the most efficient catalyst performance in terms of selectivity and reactivity at 300 degrees C and 8.2 MPa; the N-methylation selectivity in the products reaching up to 94% at 86% conversion. The present selective methylation was successfully applied to the synthesis of N-methylated amino alcohols and diamines as well as O-methylated ethylene glycol. Noticeably, ethoxyethylamine was less reactive, suggesting that the hydroxy group of the amino alcohols is a crucial structural factor in determining high reactivity and selectivity, possibly because of the tethering effect of another terminus, a hydroxo group, to the catalyst surface. The magic-angle-spinning NMR spectroscopy and X-ray diffraction analysis of the Cs-P-Si mixed oxide catalyst revealed that the acidic and basic sites originate from P(2)O(5)/SiO(2) and Cs/SiO(2), respectively, and the weak acid-base paired sites are attributed to three kinds of cesium phosphates on SiO(2). The weak acid-base sites on the catalyst surface might be responsible for the selective dehydrative methylation.

Thermolysis (170 °C, 3 days) of a diruthenium µ-methylene complex, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO) 2 (1), in the presence of HSiMe 3 produces methane along with methylsilane (SiMe 4 ) and mononuclear organometallic products, CpRu(H)(SiR 3 ) 2 (CO) (2) and CpRu(CO) 2 (SiMe 3 ) (3). The reaction mechanism involving initial CO dissociation has been investigated by using a labile µ-methylene species, Cp 2 Ru 2 (µ-CH 2 )(µ-CO)(CO)(MeCN) (4), the MeCN adduct of the coordinatively unsaturated species resulting from decarbonylation of 1. Treatment of 4 with HSiR 3 produces the hydrido-silyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SiR 3 )(CO) 2 (5) and the disilyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SiR 3 ) 2 (CO) 2 (6) successively. Further reaction of 5 and 6 with HSiR 3 affords methane under milder conditions (120 °C, 12 h) compared to the methane formation from 1. Meanwhile complicated exchange processes are observed for the silylated µ-methylene species 5 and 6. The dynamic behavior of the hydrido-silyl species 5 giving a 1 H-NMR spectrum consistent with an apparent C s structure at ambient temperature has been analyzed in terms of a mechanism involving intramolecular H-and R 3 Si-group migration between the two ruthenium centers. It is also revealed that intramolecular exchange reaction of the hydride and µ-CH 2 atoms in 5 proceeds via the coordinatively unsaturated methyl intermediate Cp 2 Ru 2 (CH 3 )(SiR 3 )(CO) 2 (9). In addition to these intramolecular processes, the hydride, µ-CH 2 , and SiR 3 groups in 5 and 6 exchange with external HSiR 3 via replacement of the η 2 -bonded H 2 or HSiR 3 ligand in µ-methylene or µ-silylmethylene intermediates Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(η 2 -H-Y) [X, Y ) H, SiR 3 (7), SiR 3 , H (18), SiR 3 , SiR 3 (16)] as confirmed by trapping experiments of 7 with L (CO, PPh 3 ) giving Cp 2 Ru 2 (µ-CHX)(µ-CO)(CO)(L) [X, L ) H, CO (1), H, PPh 3 (11), SiR 3 , CO (12), SiR 3 , PPh 3 (13)]. Hydrostannanes (HSnR 3 ) also react with 4, in a manner similar to the reaction with HSiR 3 , to give the hydrido-stannyl-µ-methylene intermediate Cp 2 Ru 2 (µ-CH 2 )(H)(SnR 3 )(CO) 2 ( 20) and the distannyl-µ-methylene complex Cp 2 Ru 2 (µ-CH 2 )(SnR 3 ) 2 (CO) 2 ( 21) successively (the stannyl analogues of 5 and 6, respectively). The intramolecular exchange processes (H T SnR 3 , H T µ-CH 2 ) are also observed for 20. But the HSnPh 3 adduct 20c is further converted to a mixture containing the µ-η 1 :η 2 -phenyl complex Cp 2 Ru 2 (µ-Ph)(SnCH 3 Ph 2 )(CO) 2 ( 22) and the bis(µ-stannylene) complex Cp 2 Ru 2 (µ-SnPh 2 ) 2 (CO) 2 ( 23) instead of 21c. The isolation of 22 supports viability of the methyl species (9). These results suggest that methane formation from 1 follows (i) CO dissociation, (ii) H-SiR 3 oxidative addition giving the hydrido-silyl-µ-methylene intermediate 5, (iii) equilibrium with the methyl intermediate 9, (iv) a second oxidative addition of H-SiR 3 , and (v) elimination of methane repeating reductive elimination from mono-and dinuclear hydrido-methyl intermediates 27 and 28. The...

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Hydroxycarbonylation of alkenes using formic acid (HCOOH) is ideal for the synthesis of various carboxylic acids as a means to develop a sustainable reaction system with lower environmental impact. In...