Ruthenium-Catalyzed Bond Cleavage Reactions

DCyPE l,2-bis(dicydohexylphosphino)ethane (Cy2PC2H4PCy2) DCyPP l,2-bis(dicydohexylphosphino)propane (Cy2PC3H6PCy2) DEPE l,2-bis(diethylphosphino)ethane (Et2PC2H4PEt2) 

Ruthenium in Organic Synthesis. Shun-Ichi Murahashi (Ed.) 

Copyright 2004 WILEY-VCH Verlag GmbH Co. KGaA, Weinheim ISBN 3-527-30692-7 

C-Si bonds are also described, but only briefly. Thus, the additional examination of reference materials and books describing general comprehensive descriptions of transition metal-mediated bond cleavage reactions would be advantageous to the reader [1], 

This section details selected catalytic C-H bond cleavage reactions, in addition to strategies for cleaving sp and sp C-H bonds. The activation of polar C-H bonds is also described. 

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Transition-metal-mediated C-O bond cleavage reactions are interesting in view of environmentally benign halogen-free chemical processes [59]. Zerovalent ruthenium complexes are also active toward C-O bond-deavage reactions, and a number of catalytic processes have been developed in this respect. For example, Ru(l,5-COD)(l,3,5-COT) catalyzes allylic alkylation of carbon nucleophiles with allylic carbonates in basic solvent (Scheme 14.24) [60]. 

The alkylation of the sp3 C-H bonds adjacent to a heteroatom becomes more practical when the chelation assistance exists in the reaction system. The ruthenium-catalyzed alkylation of the sp3, C-H bond occurs in the reaction of benzyl(3-methylpyridin-2-yl)amine with 1-hexene (Equation (30)).35 The coordination of the pyridine nitrogen to the ruthenium complex assists the C-H bond cleavage. The ruthenium-catalyzed alkylation is much improved by use of 2-propanol as a solvent 36 The reaction of 2-(2-pyrrolidyl)pyridine with ethene affords the double alkylation product (Equation (31)). 

In (C5Me5)Rh(C2H3SiMe3)2-catalyzed C-H/olefin coupling the effect of the coordination of the ketone carbonyl is different from that in the ruthenium-catalyzed reaction [10], In the rhodium-catalyzed reaction all C-H bonds on the aromatic ring are cleaved by the rhodium complex without coordination of the ketone carbonyl. Thus, C-H bond cleavage and addition of Rh-H to olefins proceed without coordination of the ketone carbonyl. After addition of the Rh-H species to the olefin, a coordinatively unsaturated Rh(aryl) (alkyl) species should be formed. Coordination of the ketone carbonyl group to the vacant site on the rhodium atom leads... 

In 2001, Oi et al. [54] reported on the ruthenium(II) phosphine catalyzed re-gioselective arylation of 2-arylpyridines using aryl halides (Eq. 29). C-C bond formation occurs predominantly at the position ortho to the pyridyl group. The same catalyst system is also effective for the arylation of aromatic imines (Eq. 30) [55]. Although the reaction mechanism has not been elucidated, it was proposed that a tetravalent arylruthenium complex,for example,Ru(Ph)(Br)(Cl)2(I) ,reacts electrophilically with the arylimines. Therefore, C-H bond cleavage is believed to proceed via an electrophilic substitution pathway. 

Catalytic C-C bond formation via sp- C-H bond cleavage represents the ultimate reaction in organic synthesis. A relatively ideal catalytic reaction system involves the use of sp3 C-H bonds adjacent to a heteroatom such as nitrogen and oxygen atoms. Recently, Jim et al. [69] succeeded in the Ru3(CO)12-catalyzed alkylation of an sp3 C-H bond a to the nitrogen atom in benzyl-(3-methyl-2-pyridinyl)amine by means of chelation assistance (Eq. 43). In this case, the coordination of the pyridine nitrogen to the ruthenium complex followed by C-H... 

When ruthenium dioxide or ruthenium trichloride is used to catalyze periodate cleavages, it is likely that Ru04 is first formed (equation 33) and then reacts with the double bond as depicted in equations (31) and (32). Sharpless and coworkers have demonstrated that the best solvent system for this reaction is a mixture of carbon tetrachloride, acetonitrile and water, in a volume ratio of 2 2 3. 

The chapter will broadly survey the literature dealing with ruthenium-catalyzed reactions involving the cleavage of an otherwise unreactive carbon-hydrogen and carbon-halogen bonds in organic synthesis up to the early stages of 2003. Only limited... 

In place of carbon monoxide, isocyanides are often used as the isoelectronic compound. In 1986, Jones et al. reported that the low-valent ruthenium phosphine complex catalyzed intramolecular insertion of isocyanide into the sp3 C-H bond under thermal conditions (Eq. 33) [60,61 ]. Their finding provided a new route for synthesis of indole. An interesting feature of their reaction is that C-H bond cleavage occurs even in the presence of an excess of the trapping ligand, i.e., isocyanide. 

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