Diimines substitution

In 1995 Brookhart and co-workers reported that cationic diimine-substituted palladium complexes of type 5 [Eq. (5)] can polymerize ethylene to high molecular-weight, highly branched material in organic solvents such as methylene chloride. 

TV-Substituted l,4-dihydro-l,4-diazocines 6 can be obtained by [TC2S + 2S + 2S] cycloreversion from. mi-benzene diimine (cA-bisazirinofa. c]benzene, diaza-c-bishomobenzene) derivatives 5 at room temperature or slightly elevated temperatures.2 - 5 The syn-benzene diimines (3,8-dia-zatricyclo[5.1.0.02,4]oet-5-enes), which are required for the valence isomerization, are available by two methods from benzene oxide derivatives. 

The products from cyclization reactions of 5-substituted isoindolinediimirtes are 2,9,16,23-tetrasubstituted phthalocyanines, e.g. 2.110121,4lf Again, a mixture of four structural isomers is obtained (see p 737). It should be emphasized that reaction conditions employing isoindoline-diimines are mild in comparison to the use of phthalonitriles. 

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. 

Scheme 40 Diastereoselective addition of y-substituted allyllithium and allylzinc reagents to a chiral diimine...

Scott et al. [45] prepared diimine derivatives of 2,2 -diamino-6,6 -dimethyl-biphenyl (as structure 37 in Scheme 19) as copper chelates for the catalyzed cyclopropanation reaction. All catalysts were active in this reaction but enan-tioselectivities varied importantly according to the substitution pattern of the imine aryl group only ortho-substituted ligands (by chloride or methyl groups) led to products with measurable enantioselectivity for the model test reaction (up to 57% ee with 37). 

The methodologies described above lead to NHC precnrsors rather limited in terms of substitution at the four- and five-positions as their access is restricted to the accessibility of the appropriate diimine. As snch snbstitntions are of great interest in particular for the design of asymmetric catalysts, rontes to the synthesis of the NHC precursors have more recently been developed. Some of these approaches are described in Scheme 1.4. 

The synthesis of [Ircp Cl(bpy-cd)]Cl, where bpy-cd is a /3-cyclo-dextrin attached at the 6 position to a bpy ligand, is detailed.138 The complexes [Ircp (diimine)X]+, X = C1, H, diimine = bpy, phen, are active catalysts for the light-driven water-gas-shift reaction.139 The hydride complexes luminesce at 77 K and room temperature, whereas the chloride complexes do not.140 The three-legged piano-stool arrangement of the ligands in [Ircp (bpy)Cl]+ and [Ircp (4,4 -COOFl-bpy)Cl]+ is confirmed by X-ray crystallography.141,142 Further mechanistic studies on the catalytic cycle shown in reaction Scheme 11 indicate that Cl- is substituted by CO and the rate-determining step involves loss of C02 and H+ to leave the Ir1 species, which readily binds Fl+ to yield the lrIH hydride species.143... 

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... 

There has been considerable interest in the study of multinuclear metal complexes with bridging sulfide ligands.381 The first examples of triangulo palladium(II) are the complexes containing substituted 2,2 -bipyridine and triply bridging sulfide ligands, namely [Pd3(diimine)3(M3-S)2][C104]2382... 

Several reports have also considered the quadratic NLO properties of DT complexes.458-461 Chen et al. have used NIR absorption data and SC A//12 values to estimate f30 according to the TSM for various Ni11 or Pt11 mixed a-diimine/DT complexes,458,459 and also for several asymmetrically substituted bis(DT)s (e.g., (175) and (176)).460 Dipole analyses indicate that the NIR transition in (175) is primarily LLCT in nature, whereas that of (176) has only limited CT character.460 The complex (177) has a red-shifted LLCT absorption and a considerably larger fa value than (175).461 The // 2 for the NIR band of (177) is also somewhat larger than that of (175), but the two complexes have very similar A//12 values.461... 

The reactions of methanol-coordinated triruthenium complex 2 with diimine ligands such as 2,2 -bipyridine and 1,10-phenanthroline at ambient temperature induced isolation of a series of oxo-centered triruthenium derivatives [Ru30(0Ac)s p.-T 1(C),T 2(N,N)-bipyridine (py)2]+ (bipyridine = dbbpy 31 dmbpy 32 bpy 33 Br2bpy 34 phen 35) containing an ort/zo-metallated bipyridine [8]. Formation of triruthenium derivatives 31-35 is involved in substitution of the coordinated methanol as well as one of the six bridging acetates in the precursor complex 2 by an orf/jo-metallated bipyridine in a p.-r 1(C),r 2(N,N) bonding fashion. 

Fig. 8 Teraryl-substituted a-diimine ligand-based Ni(II) polymerization catalysts...

Table 5 Ethylene polymerizations by teraryl-substituted a-diimine Ni(II) catalysts8...

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