Nitrogen complexes exchange reactions

Zinc dithiocarbamates have been used for many years as antioxidants/antiabrasives in motor oils and as vulcanization accelerators in rubber. The crystal structure of bis[A, A-di- -propyldithio-carbamato]zinc shows identical coordination of the two zinc atoms by five sulfur donors in a trigonal-bipyramidal environment with a zinc-zinc distance of 3.786 A.5 5 The electrochemistry of a range of dialkylthiocarbamate zinc complexes was studied at platinum and mercury electrodes. An exchange reaction was observed with mercury of the electrode.556 Different structural types have been identified by variation of the nitrogen donor in the pyridine and N,N,N, N -tetra-methylenediamine adducts of bis[7V,7V-di- .vo-propyldithiocarbamato]zinc. The pyridine shows a 1 1 complex and the TMEDA gives an unusual bridging coordination mode.557 The anionic complexes of zinc tris( V, V-dialkyldithiocarbamates) can be synthesized and have been spectroscopically characterized.558... 

Species such as XXV, XXVI, or XXVII readily form coordination complexes when treated with AuCl, H20So(C0)j q, Idn(CO)3(r -C5Hj), Fe(C0)3(PhCH=CHC(0)CH3>, or [RhCl(CO)2]2 ( ) Tw results are of special interest. First, the skeletal nitrogen atoms in XXV-XXVII do not participate in the coordination process. Presumably, they are effectively shielded by the aryloxy units and are of low basicity. Second, coordinatlve crosslinking can occur when two phosphine residues bind to one metal atom. Ligand-exchange reactions were detected for the rhodium-bound species. The tri-osmium cluster adducts of XXV, XXVI, and XXVII are catalysts for the isomerization of 1-hexane to 2-hexene. 

The kp values calculated from the experimental data increase with increase of the H+ concentration kp = k +kj [H+] +k2 [H+]2. From this dependence of kp on [H+], it seems probable that the exchange reactions can take place through the dissociation of protonated complexes. The protonated complexes GdHL are formed in equilibrium reactions. The protonation occurs on a carboxylate group, but the proton can be transferred to a nitrogen and the dissociation of this protonated intermediate is much faster than the spontaneous (or H20-assisted) dissociation of the complex GdL. 

The nitrogen atom contained in a neutral pyrrole molecule (184, R = Alk, Ar) is practically deprived of its donor properties [8,302]. In this respect, for nonsubstituted pyrrole (184, R — II). the exchange reactions of the proton of the NH group with a metal (187) are typical, as well as its participation in the complex formation as an anion r 5(ji)-ligand system (see above, Sec. 2.2.4.1) ... 

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