1.2- Diimines, reaction with

FIGURE 22.33 Reaction between phenylhydrazine and the ketone form of the substituted enol leads to a phenylhydrazone different from the one formed in the reaction of Figure 22.32. Aniline is now eliminated to give a diimine. Reaction with a third equivalent of phenylhydrazine leads to the osazone. 

An interesting extrapolation of this synthesis deals with the preparation of the bispyridinium salt 62 from 1,2-phthalic dicarboxaldehyde and its subsequent reaction with primary amines (92BSB509).Tlie expected diimines 63 readily cyclize so that 2-aryl-l-arylimino-2,3-dihydro-l//-isoindoles 64 can be isolated in excellent yields (90-95%). Contrary to the reactions performed by employing the dialdehyde and amines directly, the syntheses involving the azinium salts do not produce those typical dark-colored complex mixtures of products (77JOC4217 85JHC449) (Scheme 20). 

Peroxides oxidize N,N-DPDD to Wurster s red, a semiquinone diimine derivative [4]. Similarly Wurster s red is also produced from N,N-DPDD by reaction with halogen-containing substances in the presence of sodium ethylate and UV light and by reaction with the chlorinated triazines produced by reaction with chlorine [7]. 

Peroxides oxidize TPDD to Wurster s blue, a product with a semiquinone diimine structure [1]. Similarly Wurster s blue is also produced from TPDD by reaction with halogen-containing substances produced by the reaction of aromatic amines and triazines with chlorine gas. 

C-H insertion also occurs in the reactions with acetone and acetophenone, presumably through the rearrangement of transient OH-substituted phosphi-ranes [87]. C-C insertions occur for diketones to give 45 and have been postulated to occur via initial 1,2-addition to the conjugated enol 44 [87]. Diimines 46 also undergo C-C insertions [88]. Based on a theoretical evaluation, the products 47 are considered to result from a 2,3-sigmatropic rearrangement of initial formed P,N-ylids. 

An NMR and structural study characterized the intermediates generated from diimine catalysts on reaction with diazodiphenylmethane.193 The dominant species in solution is dinuclear, but a monomeric metallocarbene species can be detected. 

In a series of studies of the spectroscopy and photochemistry of nickel(O) -a-diimine complexes, the structural differences among the complexes NiL2 and Ni(CO)2L (L Q-diimine) have been examined by means of molecular orbital calculations and electronic absorption Raman resonance studies.2471, 472 Summing up earlier work, the noninnocence of a-diimine ligands with a flat — N=C—C=N— skeleton in low-valent Ni chemistry and the course of substitution reactions of Ni° complexes with 1,4-diaza-1,3-dienes or a,a -bipyridine have been reviewed.2473... 

The most widely applied precursors for the synthesis of monocyclic NHPs are a-diimines which can be converted to the target heterocycles either in a two-step reaction sequence involving two-electron reduction of the diimine to an enediamide, enediamine, or a-aminoamine and subsequent condensation with PC13 [18-20] or a dichlorophosphine RPC12 [21], or via direct base-promoted reaction with PC13 [20, 22], The latter reaction involves addition of a P-Cl bond to each imine moiety followed by base-promoted elimination of hydrogen chloride leading to 2,4-dichloro-... 

The two-electron reduction of a-diimines to prepare the required starting materials for a subsequent condensation is usually achieved by reaction with lithium but other alkaline (Na) or alkaline earth (Mg) metals should be useful as well. The synthesis of the heterocycles 10 is either accomplished by direct metathesis of the formed metal enediamide with PC132 [19] or, alternatively, by quenching the diamide with a suitable acid to produce an enediamine or a-aminoimine, respectively, and subsequent base-induced condensation with PC13 or RPC12 [18, 20] (Scheme 3). 1,3-l )i-/e/t-butyl-2-chloro-1,3,2-diazaphospholene was also prepared from the reaction... 

Several combinatorial approaches to the discovery of transition metal based catalysts for olefin polymerization have been described. In one study Brookhart-type polymer-bound Ni- and Pd-(l,2-diimine) complexes were prepared and used in ethylene polymerization (Scheme 3).60,61 A resin-bound diketone was condensed with 48 commercially available aminoarenes having different steric properties. The library was then split into 48 nickel and 48 palladium complexes by reaction with [NiBr2(dme)] and [PdClMe(COD)], respectively, all 96 pre-catalysts being spatially addressable. 

Jacobsen, Panek and co-workers (86) investigated the intermolecular Si-H bond insertion of diazoesters. Bis(oxazolines) and diimines were found to be effective in this reaction, with diimine enf-88a providing optimal selectivities. As expected, enantioselectivity is a function of silane structure, with bulkier silanes providing higher selectivities but lower reactivity. Both CuOTf and Cu(OTf)2 catalyze this reaction but the Cu(II) precursors leads to much lower enantioselectivity (44% vs 83% at -40°C). 

Similar results were obtained for the redox reactions of a series of cobalt diimine complexes with cytochrome c (156, 157). In general a good agreement exists between the kinetically and thermodynami-... 

The bicyclic quinone diimine 10a exhibits the same product pattern in the reaction with excess GSH as the monocyclic quinonimine 9a. Reduction results in slow formation of... 

Ru(CN)jNO reactions with OH , SH and SOj" resemble those of the nitroprusside ion, with attack at the coordinated nitrosyl to give analogous transients and similar second-order rate constants. Ruthenium(II) complexes of the general type Ru(N2), Nj = biden-tate hgands, are important reactants. The relative inertness of Ru(NH3) + and Ru(diimine)f+ towards substitution makes these complexes definite, although weak, outer-sphere reductants (Tables 5.4, 5.5, 5.6 and 5.1). Ruthenium(ll) complexes of the general type Ru(diimine)f +, and particularly the complex Ru(bpy)j+, have unique excited state properties. They can be used as photosensitizers in the photochemical conversion of solar energy. Scheme 8.1 ... 

Several cyclopropylimines have been synthesized and their reactions with a range of nucleophiles have been investigated. Mild hydrolysis of diimine (16) produces, amongst other products, the /3-ketoimine (17), stabilized by intramolecular hydrogen bonding. 

Other aspects of solvation have included the use of surfactants (SDS, CTAB, Triton X-100), sometimes in pyridine-containing solution, to solubilize and de-aggregate hemes, i.e., to dissolve them in water (see porphyrin complexes, Section 5.4.3.7.2). An example is provided by the solubilization of an iron-copper diporphyrin to permit a study of its reactions with dioxygen and with carbon monoxide in an aqueous environment. Iron complexes have provided the lipophilic and hydrophilic components in the bifunctional phase transfer catalysts [Fe(diimine)2Cl2]Cl and [EtsBzNJpeCU], respectively. 

Oxidation of [Fe(phen)3] + by concentrated nitric acid is autocatalytic. " T e hen)3] + reacts with bromate by rate-determining oxidation at high bromate concentration, [Fe(bipy)3] + and ligand-substituted [Fe(phen)3] + cations react with perbromate by rate-limiting dissocia-587 Reactions of [Fe(diimine)3] + with peroxodiphosphate also involve rate-limiting dissocia-... 

Ammine ligands complexed to platinum(IV) will undergo condensation reactions with acetylacetone. Thus Pt(NH3) + and acetylacetone react rapidly to give the diimine complex (equation 332).1032... 

The hexahydropyrimidine (58), formed from l-phenylpropane-l,2-dione and propane-1,3-diamine, is an excellent precursor for the a-diimine macrocyclic complexes (60), presumably via the amino ketone (59) (Scheme 36).126 In this case, intramolecular cyclization of (59) to (58) is reversible, so that the metal ion can exert a thermodynamic template effect in formation of the complex (60). This represents a further example of a long-known phenomenon in which a metal ion can stabilize an a-diimine structure by virtue of the formation of stable five-membered chelate rings. Many 2-hydroxy- or 2-mercapto-amines undergo reaction with a-dicarbonyl compounds to yield heterocyclic compounds rather than a-diimines. However, in the presence of suitable metal... 

Simple a-diimines are hydrolytically unstable, but can be stabilized as metal complexes by virtue of the formation of stable five-membered chelate rings.68 69 a-Diketones and glyoxal undergo metal template reactions with amines to yield complexes of multidentate ligands such as (34),70 (35)71 and (36).72>73 In the last case, the metal exerts its stabilizing influence on the a-diimine partner in an equilibrium process (Scheme 5). The same phenomenon occurs with amino alcohols74 75 in addition to amino thiols. The thiolate complexes (37) can be converted to macrocyclic complexes by alkylation in a kinetic template reaction (Scheme 5).76 77... 

In similar but more complicated processes, chelated a-diimines can be formed by reaction of ruthenium(III) and osmium(III) ammine complexes with biacetyl however, reduction of the metal also occurs (Scheme 49).220 A 0-diimine complex is obtained when acetylacetone undergoes reaction with hexaammineplatinum(TV) ions in basic solution (equation 39).220... 

Figure 5-15. The bromination of a 1,2-diimine. Although the ligand is neutral, co-ordination to the metal centre allows a smooth reaction with the electrophile.

Leland and Powell also studied ECL obtained from reaction of [(bpy)3Ru]3+ with trialkylamines [47], Since the mechanism involves an electron transfer from the amine to Ru3+, there exists an inverse relationship between the first ionization potential of the amine and ECL intensity. The relative intensity of [(bpy)3Ru]2+ ECL was found to be ordered tertiary > secondary > primary. Quaternary ammonium ions and aromatic amines do not produce ECL with Ru(II) diimine complexes. Brune and Bobbitt subsequently reported the detection of amino acids by [(bpy)3Ru]2+ ECL [28,29], Employing capillary electrophoresis for separation, the presence of various amino acids can be detected directly by reaction with [(bpy)3Ru]3+ generated in situ with up to femtomo-lar sensitivity and with a selectivity for proline and leucine over other amino acids. The formation of an amine radical cation intermediate is characteristic of proposed mechanisms of both aliphatic amines and amino acids. 

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