Nitrogen complexes with transition metals

The works by Volpin and Shur [160] as well as by Shilov [161] on molecular nitrogen fixation via complexing with transition metals indicates nitrogen readily reacting with low-valence organometallic compounds of titanium, chromium, molybdenum, wolfram and iron. 

Alkenyl groups in A-alkenylazoles act as weak or moderate -electron acceptors. Thus, the basic pKa of 1-vinylimi-dazole (5.14) is nearly 2 pK units lower than that of imidazole. Examination of 1SN NMR spectra of 1-vinylimidazoles and -benzimidazoles shows that the nitrogen attached to the vinyl group resonates in at a higher field than N(3). In accord with these results 1-vinylimidazoles form less stable complexes with transition metals than 1-alkylimidazoles. 

Two major areas of complexation have developed over the years with regard to synthehc macrocycles. Those with nitrogen, sulfur, phosphorus, and arsenic tend predominantly to form traditional covalent coordination complexes with transition metal ions. A notable exception to this tendency, however, is the rapidly expanding chemistry of the... 

Sulfur and nitrogen represent a versatile combination in the formulation of binary anions with cyclic, cage, or catenated structures, none of which have counterparts among the known N-0 anions. In addition, several S-N anions are known only in complexes with transition metals (see Section 8.5). 

Macrocyclic Polyamines - Nitrogen-Based Cyclic Hosts Protonated macro-cyclic polyamines can be good hosts for various anions. Macrocyclic polyamines also form complexes with transition metal anions. 

Sonication of 68 or 69 in the presence of transition metal ions produced coordi-natively polymerized bilayer membranes (CPBMs) as schematically illustrated in 70 26.27.130 Upon complexation with the transition metal ions, stability of bilayer membranes was remarkably improved. Amphiphiles 68 and 69 form complexes with transition metal ions with 1 1 stoichiometry. The pronounced enhancement of the stability of bilayer membranes suggests that each metal ion of the resulting CPBM is bound to two nitrogen atoms of the two adjacent azobenzene moieties as indicated by 70. Some metal ions of the CPBMs may be attached to one azobenzene unit. Even if metal ions are singly attached to the azo ligand, a polymeric cluster of metal ions bound to the dihydroxyazobenzene ligand is obtained upon sonication of the amphiphile with transition metal ions. 

The nitrogen atom in ri -pyrrolylmanganesetricarbonyl forms a donor-acceptor bond with transition metals. Complexes in which the pyrrolyl ring behaves as a tt ligand for the manganese atom and n-donor for the other metal were synthesized 12 (M = Mn, Re) [78JOM(157)431]. The binuclear heterobimetallic complexes... 

---