Coordinated nitrogen, reactions

Fig. 7-2. Potential energy E as a function of the reaction coordinate for reactions of the P-nitrogen of arenediazonium ions with nucleophiles yielding (Z)- and (is)-azo compounds, a) Reactant-like transition states (e. g., reaction with OH) b) product-like transition states (e. g., diazo coupling reaction with phenoxide ions product = cyclohexadienone-type o-complex (see Sec. 12.8).

The mercury atom is four-coordinate, both nitrogen atoms being involved in intramolecular coordination. The reaction of (Cabc,N)SnMe2Br with Na afforded the bis(o-carboranylamino)distannane [(Cabc,N)SnMe2]2 53. The two tin atoms exhibit approximately trigonal-bipyramidal geometry. 

It was argued that the relatively low ee in this case could be attributed to the large separation between the source of chirality and the reactive center, and so the reaction in Scheme 8.10 was investigated [19]. The chirality in the leaving group in compound 9 is closer to the reaction center than in the first studied substrate 8, since the stereocenter in 9 is in the position a to the coordinating nitrogen. 

The success of copper-catalyzed cycloaddition reactions yielding products with up to 99% ee stimulated further investigations in this regard. Both of the key ligand structure types represented by C2-symmetric sulfoximine 60 and Q-symmetric 82 had a two-carbon distance between the two coordination nitrogens. 

Coordinated nitrogen donor atoms can be involved in chelate-forming template reactions by virtue of nucleophilic addition to carbonyl compounds. An early and rather specific example does not allow the possibility of elimination following the addition step (equation 46).171 More recent work on ruthenium(III) and osmium(III) results in the formation of a-diimine chelate rings... 

A number of reactions have been reported which occur at coordinated nitrogen-containing groups and lead to the isolation of nitrosyl complexes these will now be considered. Electrophilic attack at a nitro group, leading to nitrosyl formation, has been reported (see equation 11).M... 

Coordinated ligands, reactions of, 58, 123 Covalent hydration in heteroaromatic compounds, 4, 1, 43 in nitrogen heterocycles, 20, 117 Current views on some physicochemical aspects of purines, 24, 215 Cyclazines and related N-bridged annulenes, 22, 321... 

More investigations of nitrogen reactions with transition metal compounds [162] confirmed the capability of nitrogen to readily enter reactions and reduction by many organometallic and inorganic coordination compounds of transition metals [163],... 

As noted above, the first monomeric pyrazol-l-ylborane was isolated as its trimethyl-amine adduct The compound (CH3)3N—BH2[pz-3,5-(Cp3)2] (Hpz = pyrazoie) was obtained as a distillable material on reaction of (CH3)3N—BH3 with 3,5-bis(tri-fluoromethyl)pyrazole = H[pz-3,5-(Cp3)2] = Hpz. Surprisingly, when THP—BH3 (THF = tetrahydrofuran) was employed as reagent, the dimeric species H2B(p-pz )2BH2, a pyrazabole (see Sect. IV.), was obtained without difficulty Apparently, the two-coordinate nitrogen of the pyrazolyl group in THP—BH2[pz-3,5-(Cp3)2] is sufficiently basic to displace THP but this base displacement cannot occur in the corresponding (CH3)3N—BH2[pz-3,5-(Cp3)j]. 

A variety of reactions can take place with coordinated nitrogen ligands. In many instances, the products are controlled by the template effect see Templating). In other cases, coordination can induce a dramatic increase in the reaction rate. 

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