1.3- diimines, deprotonation

The cubic NLO properties of Ru11 tris-(a-diimine) complexes have been investigated only relatively recently by Ji and co-workers using 540 nm Z-scan all of the complexes studied exhibit both NLO absorption and SDF behavior.135-138 The large and 7 values of complexes such as (73) depend on the position of the -N02 group in the order 4- > 2- > 3-.135 Also, the NLO responses decrease on deprotonation of the imidazolyl nitrogens (although this effect is only... 

Ni(II) by strong oxidants, such as OH, Br and (SCN), produced by pulse radiolysis and flash photolysis. Rate constants are 10 M" s for oxidation by OH and Brf and = 10 M s for (SCN)f Ref. 259. The most popular means of production in both aqueous and nonaqueous solution is electrolytic, jjjg ligands which stabilize Ni(III) are cyanide, deprotonated peptides, amines and aminocarboxylates, a-diimines and tetraaza macrocycles, including porphyrins. Low spin d Ni(III) resembles low spin Co(II). The kinetics of the following types of reactions have been studied ... 

Mechanism 2 requires deprotonation of a ligand, and dissociation of the hydrogen bound to the C(3) atom was suggested to be the slow step for the reaction of tris(2,2 -bipyridine)ruthenium(III) in base (12). This would require a mechanism for the 1,10-phenanthroline complexes different from that of the 2,2 -bipyridine complexes, but, from the data in Table II as illustrated in Figs. 3-5, this seems unlikely. The requirement of a different mechanism is based upon the significant differences in rates of D/H exchange as measured by 1H NMR for the tris(diimine)... 

The mechanism depicted in Scheme 2 involves two main steps. Rupture of the first metal-nitrogen bond accompanied by coordination of a water ligand at the metal center is followed by reversible deprotonation and intramolecular reduction of the metal center. Under the experimental conditions wherein the concentration of base is much larger than the concentration of tris(diimine) complex, and, applying the steady-state approximation to the concentration of the intermediate species with the monodentate diimine ligand, Eq. (6) can be derived as... 

The template condensation of 2,3-butanedione dihydrazone with aldehydes or ketones affords a variety of octaazabis(a-diimine) macrocyclic complexes of nickel(II), according to the Scheme 48.2655 NH deprotonation with py or Et3N of the aforementioned cationic complexes leads to neutral NiL species. 

Aza-analogues of oxygen compounds frequently show related reactivity patterns, and this is certainly seen in a comparison of the chemistry of imines and carbonyl compounds. For example, 1,3-diimines are readily deprotonated to yield the 1,3-diketonate analogues. The most frequent consequence of this is that reactions which are expected to yield 1,3-diimine complexes often lead to those of the deprotonated species. This is seen in the formation of the gold(m) complex of a deprotonated macrocycle in the reaction of 1,2-diaminoethane with 2,4-pentanedione in the presence of Na[AuCl4] (Fig. 5-4). The exact sequence of events in this reaction is not known, but note that the product is a square-planar gold(in) complex of the doubly-deprotonated macrocycle, rather than a gold(i) species ... 

Figure 5-5. The deprotonation of a 1,3-diimine ligand co-ordinated to a copper(n) centre...

In an important step to mimic the natural photosystem, tyrosine residues tethered to a Rubpy sensitizer as in 15 have been shown to reduce the Rum center obtained after oxidative quenching with methylviologen or [Co(NH3)5C1]2+.187 Formation of the resulting tyrosyl radical is a proton coupled process and it has been shown to be a concerted process in which the reorganization energy associated with deprotonation can be tuned by H-bonding and pH.188191 Similar results are observed for tyrosyl residues tethered to Re(I)diimine based chromophores.192... 

Ligands with a carbon anion directly bonded to a metal ion are more common than perhaps supposed. The family of ligands (82) (Figure 14) invariably act as a tridentate N2C donor ligand to Pt, via deprotonation of the carbon marked in the figure. The C-deprotonated N2C pincer ligand (83) forms a totally flat palladacycle with sp hybridization of C and both N donors. A diimine tridentate (84) with the carbanion as a terminal rather than central donor of the N2C ligand has... 

The reactivity of the hetero ring, with electron deficient 2(3)-positions, has been compared to glyoxal diimine." Quinoxalines are deactivated towards electrophilic substitutions, however, substitution is most likely to occur at the equivalent positions 5 and 8, where electron-localization calculations show the highest electron density to be. Electron-donor substituents in the benzenoid ring facilitate electrophilic substitution and, when activating substituents are present in the hetero ring, the site of reaction depends on the reaction conditions. In deprotonated alkyl-substituted quinoxalines an increased number of resonance possibilities exists and mildly basic conditions arc usually required for condensation reactions. 

Recent studies have shown that coordinated ammonia and amine ligands under basic conditions may effect nucleophilic attack at carbonyl centres in organic compounds, " These reactions occur due to formation of deprotonated amido species which can act as nucleophiles. For example, reaction of cobalt(III) and platinum(IV)ammines with ketones gives the corresponding Co and Pt imine complexes. A similar reaction between [Ru(NH3)6] and diones produces the corresponding Ru diimine (108). It has also been found that nitrilepentaammineruthenium(II)... 

---