Metals Nitrogen—carbon bonds

The cobalt-nitrogen double bond in VI may be assumed to arise from interaction between the 2p orbital of nitrogen and one of the 3d orbitals of cobalt. Such a double bond may be compared with the metal-carbon and metal-nitrogen double bonds proposed for cyano and nitro complexes (p. 359), but in a structure such as VI, the ligand atom, rather than the metal ion, assumes the role of r-electron donor. 

This latter reaction only occurs when there is at least one monodentate phosphine coordinated to the metal. For the purpose of discussion, the remainder of this section will be divided into reactions that (i) form nitrogen-carbon bonds (ii) form nitrogen-hydrogen bonds and (iii) reactions of polynuclear complexes. 

A third alternative simply uses ferrocenes as walls in cyclophane-like structures.The ferrocenyl units typically are linked via flexible hydrocarbon chains appended to cyclopentadiene ligands. In other words, covalent carbon-carbon bonds rather than coordinate-covalent metal-nitrogen, - carbon, -oxygen, or -phosphorous bonds are used. 

Carbonylation with aUcenylation is one of the most important reactions in the application of intramolecular five-membered ring compounds. Heterocyclic ketones are synthesized by the insertion of carbon monoxide into a metal-carbon bond followed by demetalation reactions. Because metal-carbon or metal-nitrogen a-bonds are... 

A few final comments should be made on the insertions of substrates containing C-C multiple bonds into the bonds between a transition metal and an electronegative heteroatom. First, insertions of olefins into related thiolate and phosphide complexes are as rare as insertions into alkoxo and amido complexes. Reactions of acrylonitrile into the metal-phosphorus bonds of palladium- and platinum-phosphido complexes to give products from formal insertions have been observed, and one example is showm in Equation 9.90. However, these reactions are more likely to occur by direct attack of the phosphorus on the electrophilic carbon of acrylonitrile than by migratory insertion. Second, the insertions of alkynes into metal-oxygen or metal-nitrogen covalent bonds are rare, even though the C-C ir-bond in an alkyne is weaker than the ir-bond in an alkene. 

In the octahedral cation (55) of tran -[IrCl(CO)(PPh3)2(FC,H8NNH]-IBF4] the arylazo-ligand is co-ordinated to the metal atom through one nitrogen atom and also via a metal-o-carbon bond. The Ir-C(arylazo),... 

Chisolm MH, Extine M (1975) Carbon dioxide exchange reactions involving transition-metal N,N-dimethylcarbamato compounds reversible insertion of carbon dioxide into transition-metal-nitrogen o bonds. J Chem Soc Chem Commun 438-439... 

Chisolm MH, Extine M (1977) Reactions of transition metal-nitrogen a bonds. 4. Mechanistic studies of carbon dioxide insertion and carbon dioxide exchange reactions involving early transition-metal drmethylamido and N, N-dimethylcarbamato compounds. J Am Chem Soc 99 792-802... 

Nitriles. Nitriles can be prepared by a number of methods, including ( /) the reaction of alkyl haHdes with alkaH metal cyanides, (2) addition of hydrogen cyanide to a carbon—carbon, carbon—oxygen, or carbon—nitrogen multiple bond, (2) reaction of hydrogen cyanide with a carboxyHc acid over a dehydration catalyst, and (4) ammoxidation of hydrocarbons containing an activated methyl group. For reviews on the preparation of nitriles see references 14 and 15. 

If it is assumed that 2,2 -bipyridine is bonded to the catalyst by both nitrogen atoms, then the position of the chemisorbed molecule on the metal is rigidly fixed. Unless two molecules of this base can be adsorbed at the required distance from each other and in an arrangement which is close to linear, overlap of the uncoupled electrons at the a-position cannot occur. The failure to detect any quaterpyridine would then indicate that nickel atoms of the required orientation are rarely, if ever, available. Clearly the probability of carbon-carbon bond formation is greater between one chemisorbed molecule of 2,2 -bipyridine and one of pyridine, as the latter can correct its orientation relative to the fixed 2,2 -bipyridine by rotation around the nitrogen-nickel bond, at least within certain limits. 

For a review, see Harada, K. in Patai The Chemistry of the Carbon-Nitrogen Double Bond, Ref. 40, p. 276. For a review with respect to catalytic hydrogenation, see Rylander, P.N. Catalytic Hydrogenation over Platinum Metals, Ref. 165, p. 123. 

One-electron oxidation of the vinylidene complex transforms it from an Fe=C axially symmetric Fe(ll) carbene to an Fe(lll) complex where the vinylidene carbon bridges between iron and a pyrrole nitrogen. Cobalt and nickel porphyrin carbene complexes adopt this latter structure, with the carbene fragment formally inserted into the metal-nitrogen bond. The difference between the two types of metalloporphyrin carbene, and the conversion of one type to the other by oxidation in the case of iron, has been considered in a theoretical study. The comparison is especially interesting for the iron(ll) and cobalt(lll) carbene complexes Fe(Por)CR2 and Co(Por)(CR2) which both contain metal centers yet adopt... 

In addition to activation of sihcon bonds by fluoride ions as discussed in Section 2.4, silicon-silicon, silicon-carbon, silicon-hydrogen, and silicon-nitrogen bonds are activated by transition metal salts and transition metal complexes. Thus, hydrolysis of silicon-carbon bonds such as in phenyltrimethylsilane 81 can be induced by... 

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