The cationic Ru−H complex [(C 6 H 6 )(PCy 3 )(CO)-RuH] + BF 4 − (1) was found to be an effective catalyst for the dehydrative C−H coupling reaction of phenols and aldehydes to form 2-alkylphenol products. The coupling reaction of phenols with branched aldehydes selectively formed 1,1-disubstituted benzofurans, while the coupling reaction with salicylaldehydes yielded xanthene derivatives. A normal deuterium isotope effect was observed from the coupling reaction of 3-methoxyphenol with benzaldehyde and 2-propanol/2-propanol-d 8 (k H /k D = 2.3 ± 0.3). The carbon isotope effect was observed on the benzylic carbon of the alkylation product from the coupling reaction of 3-methoxyphenol with 4-methoxybenzaldehyde (C(3) 1.021(3)) and on both benzylic and ortho-arene carbons from the coupling reaction with 4-trifluorobenzaldehdye (C(2) 1.017(3), C(3) 1.011(2)). The Hammett plot from the coupling reaction of 3-methoxyphenol with para-substituted benzaldehydes p-X-C 6 H 4 CHO (X = OMe, Me, H, F, Cl, CF 3 ) displayed a V-shaped linear slope. Catalytically relevant Ru−H complexes were observed by NMR from a stoichiometric reaction mixture of 1, 3-methoxyphenol, benzaldehyde, and 2-propanol in CD 2 Cl 2 . The DFT calculations provided a detailed catalysis mechanism featuring an electrophilic aromatic substitution of the aldehyde followed by the hydrogenolysis of the hydroxy group. The calculations also revealed a mechanistic rationale for the strong electronic effect of the benzaldehdye substrates p-X-C 6 H 4 CHO (X = OMe, CF 3 ) in controlling the turnover-limiting step. The catalytic C−H coupling method provides an efficient synthetic protocol for 2-alkylphenols, 1,1-disubstituted benzofurans, and xanthene derivatives without employing any reactive reagents or forming wasteful byproducts.

The ruthenium-hydride catalyst has been successfully used for the tandem sp3 C–H dehydrogenation–alkylation reaction of saturated hydrocarbon substrates with alcohols to form the alkyl-substituted alkene and arene products. The analogous one-pot dehydrogenation–insertion of saturated ketones with alkenes and dienes directly yielded synthetically useful 2-alkylphenol and benzopyran products in a highly regio- and stereoselective manner without forming any wasteful byproducts.

The chelate assistance strategy was devised to promote a highly regioselective catalytic C–C bond activation reaction of saturated and unsaturated carbonyl compounds. The cationic Ru–H complex 1 was found to be an effective catalyst for mediating the coupling reaction of 1,2-disubstituted indoles with α,β-unsaturated aldehydes and ketones, in which the regioselective Cα–Cβ activation of the carbonyl substrates has been achieved in forming the 3-alkylindole products. The analogous coupling reaction of indoles with saturated aldehydes and ketones directly led to the Cα–Cβ cleavage of the carbonyl substrates in forming the 3-alkylindole products. The coupling reaction of 1,2-dimethylinole with (E)-3-nonen-2-one and 2-propanol-d 8 showed 20–22% of deuterium incorporation to both α- and β-CH2 of the 3-alkylindole product. The coupling reaction of 1,2-dimethylinole with (E)-3-nonen-2-one exhibited the most significant carbon kinetic isotope effect on the α-carbon of the product (Cα = 1.046). The Hammett plot constructed from the reaction of 1,2-dimethylinole with a series of para-substituted enones p-X-C6H4CHCHCOCH3 (X = OMe, Me, H, Cl, CF3) showed a modest promotional effect by an electron-donating group (ρ = −0.2 ± 0.1). Several catalytically relevant Ru–H species were detected by NMR from a stoichiometric reaction mixture of the Ru–H complex 1 with 1,2-dimethylindole and (E)-3-nonen-2-one in CD2Cl2. These results support a mechanism of the catalytic coupling reaction via conjugate addition of indoles to enones followed by the C–C bond activation and hydrogenolysis steps.

A GREEN METHOD TO PRODUCE BIODIESEL FROM PALM OLEIN OIL INTRODUCTIONBiodiesel is considered as a greener alternative to petrodiesel. This is because it is renewable and biodegradable. Unlike petrodiesel, biodiesel emissions are not harmful to the environment. It consists of a mixture of monoalkyl esters of long-chain fatty acids produced from the transesterification of triglycerides in vegetable oils, animal fats or waste cooking oil in the presence of alcohol as a catalyst. The by-product of the transesterification reaction is glycerol. In order to use biodiesel as an alternative fuel, the quality of biodiesel should comply with the recommended standards, while the cost of production should be less than or comparable with that of petrodiesel. In the transesterification process, methanol is normally used as the alcohol and either NaOH or KOH is used as the homogeneous base catalyst. There are certain challenges associated with this procedure; NaOH is a corrosive chemical which cannot be reused, a large volume of wastewater is released when separating NaOH from biodiesel, treatment of the effluent is expensive and procedure is time-consuming (Granados et al., 2010; Alba Rubio et al., 2012, Lee et al. 2015. A promising solution to mitigate such challenges is to develop and use a greener catalyst which can be easily recovered and make possible the use of minimum amounts of chemicals.Heterogeneous catalysts have been identified as a potential solution for problems associated with the homogeneous catalyst NaOH. This is because, separation of the solid catalyst is easier, generation Journal of Oil Palm Research Vol. 29 (2) June 2017 p. 267 -277 DOI: https://doi.org/10.21894/jopr.2017.2902

The in situ generated catalytic system from the tetranuclear Ru−H complex [(PCy 3 )(CO)RuH] 4 (O)(OH) 2 (1) with 3,4,5,6-tetrachloro-1,2-benzoquinone (L1) has been found to mediate a multicomponent deaminative coupling reaction of phenols with aldehydes and enamines to form xanthene products. The multicomponent C−H coupling reaction of phenols with 2hydroxybenzaldehydes and cyclic enamines efficiently installed the tricyclic 1,3-dioxacin derivatives, while the analogous coupling reaction of phenols with 2-hydroxybenzaldehydes and triethylamine selectively formed bicyclic 1,5-dioxacyclic derivatives. The density functional theory (DFT) calculations established two energetically viable mechanistic pathways for the formation of xanthene products, in which both pathways identified the C−O bond cleavage step as the turnover limiting step. A Hammett plot from the coupling reaction of 3,5-dimethoxyphenol with an enamine and para-substituted benzaldehydes p-X-C 6 H 4 CHO (X = OMe, Me, H, Cl, CF 3 ) showed a negative slope (ρ = −0.98). The calculated energy analysis showed a similar trend (ρ = −0.59) for the mechanism via the C−O cleavage rate-limiting step. The combined experimental and DFT computational results support a mechanistic path that involves the dehydrative C−H coupling of phenol with aldehyde, followed by the deaminative coupling reaction with an enamine in forming the xanthene product.