Diimine complexes 3-diketonates

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. 

Several series of macrocyclic p-diimine complexes have been shown to undergo reactions similar to those of the p-diketonates. Reversible protonation of the complexes (27) (equation 15) has been... 

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 ... 

The observed pattern of C—C and C—N distances indicates delocalization of n-electrons within the six-membered P-diiminate rings. Open-chain tetraaza ligand complexes [AuL j, in which condensation of only one P-diketonate has occurred. 

Schiff bases having two nitrogen atoms as donors may be derived either from condensation of dialdehydes and diketones with two molecules of an amine, or from reaction of diamines with aldehydes or ketones. In Section 20.1.2.1, it has been pointed out that coordination through the N atom may occur only under particular circumstances. However, in the case of diimines the formation of chelate rings stabilizes the metal-nitrogen bond. Thus, they can form both mono-41 and bis-chelate42 complexes. 

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... 

With complete exclusion of air, fra i -[FeCl2(H20)4] reacts with acetylacetone to form hydrated bis(2,4-pentanedionato)iron(II). The complex is coordinatively unsaturated and forms an interesting tetrameric structure [Fe4(acac)g] in which two asymmetric triply oxygen bridged dimers (32) are linked by rather long Fe-C bonds (2.785 A, 33). [Fe(acac)2] forms simple hexacoordinate adducts in reaction with a variety of bases, for example, heterocyclic diimines snch as bipyridines. Complexes formed by iron(II) with other /3-diketonates are polymeric and highly air sensitive. Iron(III), however, forms a series of stable highly colored... 

When a metal ion such as nickel (II) is absent, thiazoles and mercaptals are formed. Such reactions have been carried out in which the diketone was biacetyl, 2,3-pentanedione, 2,3-octanedione, l-phenyl-l,2-propane-dione, and 1,2-cyclohexanedione (51). In like manner, the tris complexes of W,W -dimethyl-2,3-butane diimine with iron(II), cobalt(II), and nickel(II) may be prepared from methylamine and biacetyl when the appropriate metal ion (27j 28j 41) is present. Replacing methylamine with hydroxylamine causes the formation of a-dioximes (13). 

The template condensation of a-diketones with 1,3-propanediamine in the presence of divalent iron, cobalt, nickel, or copper leads to 14-membered-ring macrocyclic complexes containing two a-diimines. A number of complexes of this class, derived from 2,3-butanedione,1-3 1-phenyl-1,2-propanedione,4,5 benzil,6 and substituted benzils,5 have been prepared. Preparation of the Ni(II)... 

Catalyst libraries for combinatorial screening of diimine-based nickel and palladium catalysts can be developed by attaching a diketone to a Merrifield resin, reacting with a variety of anilines in the presence of a dehydrating catalyst, and complexing with the metal (Scheme 25). After each variant is activated with MAO or borate salt, the 96-well microtiter plate is exposed to ethylene and polymerization activity is qualitatively determined by infrared imaging. 

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