Ligand diimine

Oxidation of Coordinated Diimine Ligands in Basic Solutions of Tris( diimine )iron(III),-ruthenium(III), and -osmium(III)... 

The general structure of bidentate a-diimine ligands used in this study was shown in Scheme... 

Examination of the HOMO and LUMO orbitals in these TSs indicates that the electronic effect operates mainly through the LUMO. The EWG cyano tends to localize the LUMO on the (3-carbon, whereas ERG substituents have the opposite effect. Similar trends were found for Pd coordinated by diimine ligands.150 These results indicate that the Markovnikov rule applies with the more electrophilic Pd complexes. When steric effects become dominant, the Pd adds to the less hindered position. 

Complexes with pyridine-2,6-diimine ligands, five-coordinate [NiX2(174)] (X = C1, Br) or six-coordinate [Ni(174)2]X2, were usually assumed to have innocent neutral ligands. The X-ray structure and spectroscopic characteristics of [Ni(174)2](PF6) confirm that the complex contains the neutral ligand ([174] ) and a divalent nickel ion.579 The cyclic voltamogram of this complex in CH2C12 shows three reversible one-electron-transfer processes at = 1.19 V, —1.30 V, and — 1.82V (vs. Fc+/Fc), of which the first is a one-electron oxidation, while the other two correspond to two successive one-electron reductions. The spectroscopic data allow one to assign these processes as follows ([174]1 is a one-electron reduced radical form of [174] ) [Nini(174)°2]3+ [NiII(174)02]21 - " [NiI(174)°2]+ = " [NiI(174)°(174)1 ]°. 

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 reaction of AgOTf with a flexible diimine ligand in 1 2 and 1 1 ratio leads to the mono- or dinuclear complex, respectively. They further react with AgOTf to give coordination polymers. These complexes are models for the chain-growth process required in the formation of coordination polymers (see Scheme 2).642,643 Similar complexes are obtained with the 1,4-di-t-butyldia-zabut- 1,3-diene derivative.644... 

The first examples of highly active olefin polymerization catalysts based on late transition metals were nickel and palladium complexes containing bulky diimine ligands.310 312 For example, complex (120) was found to polymerize ethylene with an activity of ll,000gmmol h bar A range of PE materials with molecular weights up to 106 and... 

The introduction of cyano groups in the 3-position of diketimiminate ligands greatly increased the crystallinity of their complexes (Figure 49, 95), due to the formation of one-dimensional coordination polymers. A new f3-oxo-<5-diimine ligand, in turn, allowed the synthesis of a bimetallic organozinc complex 96, by the same methods that had been used for the syntheses of the mononuclear species 92-94.154... 

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. 

Catalysts Derived from Cyclic a-Diimine Ligands. 206... 

Numerous modifications to the bis(aryl)-a-diimine ligand motif have been reported, especially in the patent literature. The review by Ittel includes an index of diimine and related ligands in proprietary publications up to the year 2000 [26]. Instead, this discussion will focus on academic reports of Ni(II) and Pd(II) polymerization catalysts bearing a-diimine or other closely related chelating neutral nitrogen ligands. 

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

A specific goal we have in mind is to design cyclophane-based a-diimine ligands for overcoming the low thermal stability of the regular a-diimine catalyst systems. 

Fig. 11 Late transition metal polymerization catalysts from cyclic a-diimine ligands...

Scheme 12 Concept of hemilabile axial donor a-diimine ligand...

---