Diketones tridentate

Vinylogous amides, which have an enamine function in conjugation with a carbonyl group, constitute tridentate systems and thus open the possibility of alkylation on carbon, nitrogen, or oxygen. It has been found that the pyrrolidine enamine of acetylacetone gives rise to a carbon mcthylation but an oxygen ethylation product 41). The alkylation of cyclic 1,3-diketone-derived enamines has been studied 41,283). O Alkylation was found in alcohol solvents and predominant C alkylation in nonprotonic solvents. 

The monoketone bis(2,2, /V,/V -bipyridyl)ketone forms a [CoinL2]+ complex on reaction with [Co(NH3)4(C03)]+ in water.981 As reported for a quite different Co11 complex, the ketone is hydrated to form the gem diol which binds as a monodeprotonated O-donor along with the two pyridine groups in a tridentate chelate, with very little distortion from octahedral observed in the complex. This appears to represent a facile route for this type of inherently poor donor to achieve coordination. Chelated /3-diketonate anions are long-studied examples of O-donor chelates, and continue to be examined. A simple example is the m-[Co(acac)2(NH 3)2]1 (acac = 2,4-pentane-dionate), structurally characterized and utilized to produce molecular mechanics force field parameters for /3-diketones bound to Co111.982... 

In complex 288 the (3-diketonate fragment behaves as a tridentate ligand, while in 289 and 290 it behaves as a tetradentate ligand, changing in 291 to a pentadentate ligand system [13,546-550]. 

The presence of S-carbonyl groups with at least one proton on the carbon between them allows a keto/enol tautomerism to occur and, under appropriate conditions, the eno-lic proton can be removed. The S-5-tricarbonyl compounds are the higher analogues of the / -diketonates and can take triketone, monoenol and dienol forms in their tautomeric equilibrium (equation 86) accordingly, they can behave as bidentate or tridentate ligands to form metal chelate complexes. ... 

Interesting coordination modes have been discovered in derivatives containing Pd and Pt metal ions or nonmetallic elements, where extra negative charge of the (diketonate)2- arises from removal of one of the methyl protons. In (XIX) the (diketonate)2- is //3-C3-tridentate to Pd through Cl5 C2, and C3, in an allylic fashion, whereas in (XX) the donor is additionally 0,0-bidentate chelating toward another metal. In (XXI) the (diketonate)2- is C,0-bonded to Pt, and in (XXII) is 0,0-bonded to a metal and C-bonded to another metal via a terminal CH2. 

A /3-diketone with a l-(2-hydroxy)-phenyl fragment as R1 and a phenyl as R3 substituent (bzbzOH2) (19) behaves as a dianionic tridentate 0,0,0-donor affording [M2(bzbzO)2] complexes (M = Ni, Cu, and Zn).110... 

Enaminones are compounds containing the system N—C=C—C=0. They are mono enamines of 1,3-diketones (vinylogous amides) or enamines of 3-keto esters (vinylogous urethanes). Their unique properties and the versatility of their applications in organic synthesis follow from the system Na Cb=Cc—Cd=Oe, which is tridentate (sites a, c, and e) toward electrophiles and bidentate (sites b and d) toward nucleophiles. This makes possible a wide variety of reactions, but with such a multiplicity of sites vulnerable to attack, reactions are sometimes unpredictable and can be unexpectedly complex. 

The stability constants of the 1 1 alkali metal picrate complexes of diketone 18. heptacyclic terpyridyl 27 and flexible terpyridine 28 were estimated by hquid-liquid extraction, and the resulting log fj values for Na" " and are also given in Fig. 4. The affinities of 18 and 27 for these alkali metals are remarkably high for hosts containing only five or three ligand atoms, respectively. In water-saturated chloroform, pentadentate host 18 binds Na" and K more strongly than do most crown ethers. Compared to naphtho-18-crown-6 (26), 18 binds Na " 4000 times better, and K 40 times better. Even tridentate host 27 extracts alkali metal picrates into chloroform, whereas flexible model system 28 is ineffective under the same experimental conditions. The potent complexation... 

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