Complexes catalytic activity

Besides ruthenium porphyrins (vide supra), several other ruthenium complexes were used as catalysts for asymmetric epoxidation and showed unique features 114,115 though enantioselectivity is moderate, some reactions are stereospecific and treats-olefins are better substrates for the epoxidation than are m-olcfins (Scheme 20).115 Epoxidation of conjugated olefins with the Ru (salen) (37) as catalyst was also found to proceed stereospecifically, with high enantioselectivity under photo-irradiation, irrespective of the olefmic substitution pattern (Scheme 21).116-118 Complex (37) itself is coordinatively saturated and catalytically inactive, but photo-irradiation promotes the dissociation of the apical nitrosyl ligand and makes the complex catalytically active. The wide scope of this epoxidation has been attributed to the unique structure of (37). Its salen ligand adopts a deeply folded and distorted conformation that allows the approach of an olefin of any substitution pattern to the intermediary oxo-Ru species.118 2,6-Dichloropyridine IV-oxide (DCPO) and tetramethylpyrazine /V. V -dioxide68 (TMPO) are oxidants of choice for this epoxidation. 

A wide range of catalysts is now known that will bring about B H addition to simple terminal alkenes. For group 9 complexes, catalytic activity follows the order [(dppe)Rh (nbd)]+ > [Rh(PPh3)3Cl] > [(COD)Ir(PCy3)(C5H5N)]+ (where dppe = 2-bis(diphenylphosphino) ethane and nbd = norbornadiene).19 Different facial selectivity is found for catalytic hydroboration reactions of these compounds with chiral alkenes (Equation (1)). Thus, [(dppe)Rh(nbd)]+ gives... 

T. Maruyama, T. Kotani, H. Yamamura, N. Kamiya, M. Goto, Poly(ethylene glycol)-lipase complexes catalytically active in fluorous solvents, Org. Biomol. Chem. 2 (2004) 524-527. 

Industrial heterogeneous catalysts and laboratory-scale model catalysts are commonly prepared by first impregnating a support with simple transition metal complexes. Catalytically active metal nanoparticles (NPs) are subsequently prepared through a series of high temperature calcination and / or reduction steps. These methods are relatively inexpensive and can be readily applied to numerous metals and supports however, the NPs are prepared in-situ on the support via processes that are not necessarily well understood. These inherent problems with standard catalyst preparation techniques are considerable drawbacks to studying and understanding complex organic reaction mechanisms over supported catalysts. (4)... 

In the last decade, there has been a large number of reports on synthetic macro-molecule-metal complexes concerning their complexation, catalytic activities, redox reactions, adsorptions of gaseous molecules and metal ions, photochemical behavior, biochemical effects, modified electrodes, semiconductive and conductive materials, and so on. 

Both kinetic studies and spectroscopic investigations have certain inherent limitations. Kinetic studies are informative about the slowest step, and at best can provide only indirect information about the fast steps. Spectroscopic detection of a complex, catalytically active or not, requires a minimum level of concentration. It is possible that the catalytically active intermediates never attain such concentrations and therefore are not observed. Conversely, the species that are seen by spectroscopy may not necessarily be involved in the catalytic cycle ... 

Other transition metals may be incorporated as carbonyl complexes. Catalytically active complexes of Mn and Fe were prq>ared by synthesizing the complex inside the pores of NaX and NaY zeolites [68,69]. The occluded Mn-bipyridyl and Fe-phthalocyanine complexes catalyze the oxidation of cyciohexene to adipic acid. 

Due to the stability of Ir complexes, catalytic activity of Ir complexes are usually lower than the corresponding Rh ones. Thus, the reported examples of catalytic reactions by Ir complexes are fewer than those of Co and Rh. 

Kiamiya, N., Okazaki, S. Y, and Goto, M., Surfactant-horseradish peroxidase complex catalytically active in anhydrous benzene, Biotechnol. Tech., 11, 375-378, 1997. 

On the example of ethylbenzene oxidation (120°C) the mechanism of control of M(L )2 complexes catalytic activity by additives of electron-donor monodentate ligands (L = HMPA, DMF, MP, MSt) was established [58-61],... 

Pryjomska, L, Bartosz-Bechowski, H., Ciunik, Z. et al. (2006) Chemistry of palladium phos-phinite (PPh2(OR)) and phosphonite (P(OPh)2(OH)) complexes catalytic activity in methoxy-carbonylation and Heck coupling reactions. Dalton Trans., 213-20. 

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