Pyridines homogeneous catalysis

Bonnemann, H. (1985) Organocobalt compounds in pyridine syntheses - an example for structure-activity relations in homogeneous catalysis. Angew. Chem. Int. Ed. Engl, 24, 248. 

Another tedious issue is to position an axial ligand like pyridine on the zeolite encapsulated Me(salen). It is known from homogeneous catalysis that epoxide... 

The search for new reactivity and new reactions is an important target in homogeneous catalysis. A declared goal is the selective activation of C-H bonds under mild conditions. Although there are numerous examples of stoichiometric C-H bond oxidative additions to transition metal centers, successful examples regarding catalytic functionalization of C-H bonds have been made only during the last five years. Notable advances have been achieved by Moore and coworkers who described in 1992 the ortAo-acylation of pyridine with olefins and carbon monoxide. The cluster compound triruthenium dodecacarbonyl has been used as catalyst (Scheme 10). 

A. J. Pardey, P. C. Ford, Homogeneous catalysis of the water-gas shift reaction by rhodium complexes in aqueous substituted pyridine solutions, J. Mol. Catal. 53 (1989) 247-263. 

H. Bonnemann, Organocobalt Compounds in the Synthesis of Pyridines - An Example of Structure-Effectivity Relationships in Homogenous Catalysis, Angew. Chim. Int. Eng. Edn., 1985, 248. 

Hence, carbon dioxide can be reduced to methanol on hydrogenated Pd electrodes, in the presence of pyridinium ions, which enable homogeneous catalysis. This reduction takes place at a modest overpotential of -200 mV. Although the reduction of protons to H2 competes with methanol formation, methanol Faradaic yields of up to 30% have been reached. Methanol formation proceeds both directly at the electrode surface, and indirectly, by the reduction of pyridinium species to form methanol, pyridine and hydrogen [150]. 

The first application of a phosphinine-based catalyst in homogeneous catalysis was reported in 1996 by Zenneck et al. The f/ -phosphinine-iron complex 33 was used in the catalytic [2 -h 2 -h 2] cyclotrimerization of the electron-poor alkyne dimethyl acetylenedicarboxylate to give C6(C02Me)6 and in the co-cyclotrimer-ization of methyl propargylether with butyronitrile affording functionalized pyridine derivatives (Scheme 6.8) [60]. Turnover-numbers of up to 160 for the pyridine derivatives and chemoselectivities of up to 1.4 1 (pyridinesiarenes) were observed. Nevertheless, the efficiency of 33 is significantly lower compared to classical CpCo catalysts [61, 62]. 

Bbnnemann H (1985) Organocobalt compounds in the synthesis of pyridines— an example of structuie-effectivity relationships in homogeneous catalysis. Angew Chem Int Ed 24 248-262... 

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