C-N bond activation

The reactivity of the carbene transfer agent ImMes2.AgCl towards a variety of osmium clusters (Os3(p-H)2(CO)i0, Os3(CO)i0(NCMe)2, Os4(p-H)4(CO)i2) and Ru4(p-H)4(CO)i2 has been examined, and a number of new NHC complexes resulting from C-H and C-N bond activation reported (29 -34), including examples containing coordinated silver and chloride atoms.31... 

Electron-rich metal fragments can react with 2-substituted In yielding either the kinetic C-H or the thermodynamic N-H insertion products. C-N bond activation, on the other hand, is not observed, in contrast with C-S bond breaking, which is readily promoted by electron-rich metal centers, as described in Chapter 4. 

Despite the fact that the bonding modes of pyridines hitherto described in this Section represent reasonable models for a variety of forms of adsorption of Py onto HDN catalyst surfaces, none of them has been found to be adequate for C-N bond scission to occur in solution. In contrast, the curious ri (N,C) coordination mode effectively activates the Py ring toward C-N bond activation, as discussed in the following section. The first r (N,C)-Py complex, (silox)3Ta(T (N,C)-NC5H5) (silox = BusSiO ), was prepared by Wolczanski and coworkers in 1988 [54] through the direct reaction of Ta(silox)3 with the appropriate pyridine, as illustrated in Eq. 6.15. 

In this Section examples of other reactions, representative of the some of the elementary steps that are known or believed to occur during HDN after hydrogenation, are described. Of particular interest are the rather uncommon reactions leading to C-N bond activation and denitrogenation. 

The concept of chemistry beyond functional group transformation concerns mainly reaction participants, and this chapter is aimed at providing a summary of some recent development in that respect. The contents of this chapter include (1) sp3 C—H and sp2 C—H bond activation, (2) C—C bond activation, (3) C—O bond activation, (4) C—F bond activation, (5) C—N bond activation, and (6) small molecule activation (H2, 02, and CH4). More detailed information can be found in the cited references. 

Metal-mediated C-N bond-activation reactions relevant to HDN... 

The bonding modes of pyridines described so far represent reasonable models for the adsorption and activation of pyridines, quinolines, and acridines on HDN catalysts, but none of them promotes C-N bond activation, which ultimately leads to nitrogen removal. In contrast, a curious t7 (N,G) coordination mode has been discovered, w hich... 

Burling S, Mahon MF, PoweU B-E, Whittlesey MK, WUhams JMJ. Ruthenium induced C—N bond activation of an N-heterocyclic carbene isolation of C- and N-bound tautomers. J Am Chem Soc. 2006 128 13702-13703. 

Haller LJL, Page MJ, Erhardt S, Macgregor SA, Mahon MF, Naser MA, Velez A, Whittlesey MK (2010) Experimental and computational investigation of C-N bond activation in ruthenium N-heterocyclic carbene complexes. J Am Chem Soc 132 18408-18416... 

Besides cyclizations of hetaryl acetonitriles, the reactions of isocyanate 845 with anilines were studied. In presence of base the reaction leads to N-aUcylidene-N-arylureas 879. The compounds 879 bearing the C=N bond activated by trifluoromethyl group undergo thermal intramolecular cyclization to give 4-trifluoromethyl-l,2,3,4-tetrahydroquinazolin-2-ones 880 in good yields. A wide range of anilines... 

---