Pyridones, complex

Structural chemistry of pyridonate complexes of late 3d metals 97ACR89. 

The first structural information was obtained for an o-pyridone complex [Pt2(NH3)4(pyridone)2]2(N03)5 (Figure 3.36). 

Figure 3.36 Structure of the a-pyridone complex [Pt2(NH3)4(pyridone)2]2(N03)5. (Reprinted with permission from/. Am. Chem. Soc., 1978,100,3785. Copyright (1978) American Chemical Society.)...

Experimental confirmation of this predicted behavior was obtained via the examination of DCLs of trinuclear metallamacrocycles formed from ruthenium pyridonate complexes (Fig. 1.26). After first forming the individual homotrimers (i.e., 52-52-52), these were mixed in various combinations and allowed to undergo exchange. As predicted, the thermodynamically most stable species was not always the most strongly selected. 

FIGURE 19. Variation of 13C chemical shifts with the extent of Si—O bond making in pyridone complexes 125104,138. Reproduced from Reference 138 by permission of The Royal Society of Chemistry... 

Addition of l,3-thiazolium-4-olates to (l-alkynyl)carbene tungsten complexes lb,n affords thiophene and/or pyridone complexes, 64 and 65, by extrusion of sulfur and isocyanate, respectively, from the [3+2] adduct formed initially (Scheme 21).97 [3+2] cycloaddition reactions of azomethine... 

Group 5 pyridonate complexes are also readily prepared by salt metathesis and protonolysis routes to access both mono- and bis(pyridonate) tantalum complexes (Figure 12). [41] Such complexes can be difficult to rigorously characterize in the solid state as they are much more soluble than their group 4 pyridonate, or their group 5 amidate, counterparts. 

In 2013, Schafer s group [22b] reported titanium bis(amidate) and bis(pyridonate) complexes for the homopolymerization of rac-lactide and e-caprolactone, and also the formation of a random copolymer of the two. These complexes form pseudo-octahedral six-coordinate species, which were characterized in the solid state. Complexes were synthesized by first installing 2 equiv. of the ligand on homoleptic TifNMe ) followed by protonolysis of dimethylamido ligands with 2 equiv. of alcohol (Figure 19). 

The efficiency that this set of initiators showed for both types of polymerization reactions, and the displayed influence of the bound A,0-chelating ligand, led to testing for copolymerization of the two monomers. Impressively, the titanium pyridonate complexes led to a random copolymer with a nearly 1 1 ratio of monomers. These random copolymers have average molecular weights of 1.8-2.2X 10 g/mol with PDl values of 1.29-1.41. 

To this end, a titanium bis(2-pyridonate) complex (17) has been developed. [22c] These catalytic systems promote catalyst-controlled selectivity for hydroaminoalkylation over hydroamination and for the first time amine-substituted cyclopentanes can be prepared preferentially over piperidine hydroamination products (Scheme 25). 

Another dissociative process leads to a different sort of isomerization in the bis-N 0 bridged head to head a-pyridonate complex, (19). It isomerizes in... 

The analogous mono complexes with ethylenediamine have also been structurally characterized [35]. The corresponding bis-a-pyridone complex has been obtained from reaction with cw-[PtCl2(NH3)2] [36] in fact this is a neutral 2-hydroxypyridine (a-pyrH) species with cldoride counteranion, the minor tautomer being stabilized in the complex. The iminol form of 1-MeThymine has also been recognized upon protonation of cis-[Pt(NH3)2(l-MeT)2] [33]. The stabilization of tautomeric forms of the unsubstituted pyrimidines has also been noted [31]. 

Scheme 5.1. Formation of dimeric pyrimidine and a pyridone complexes.

Sakurai H, Tamura A, Fugono J, Yasui H, Kiss T. 2003. New antidiabetic vanadyl-pyridone complexes effect of equivalent transformation of coordinating atom in the ligand. Coord Chem Rev 245 31-37. 

Figure 4. Geometrical structure of mono- and dihydrated 2-pyridone complexes. The experimental data are in parentheses.

Unfortunately, the results of the computational studies of the interaction of 2-pyridone molecule with more than two water molecules are unavailable to us. Also note that according to the combined experimental and theoretical study [104] of the different monohydrated forms of oxo- and hydroxopyridines, the monohydrated hydroxo-form is predominating in the Ar matrix, so more careful investigation of the potential surface topology is needed for the hydrated 2-pyridone complexes. 

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