Acylation 1,3-diketone metal complexes

The (3-diketonate chelate complexes are very stable and exhibit properties which are rather typical of aromatic systems. Many of their reactions such as halogenation, alkylation and acylation can be compared with those of the P-diketonate anions associated with alkali metal cations. However, complexes of transition and other metals add to the stability of the system, so that quite vigorous reaction conditions can be employed. In most of the work carried out on P-diketonate chelates, the modified ligand has not been removed from the metal ion, but this can usually be effected if desired. 

Derivatives of Sn , Ti Cr , V , Cu, Sm are well-known as reductants [108, 109]. In particular, Kagan s reagent Sml2 reduces acyl chlorides to diketones, aldehydes, and ketones to pinacols in aptotic media and to alcohols in protic media [110], It has also been applied to many other organic reactions [110], Cr salts have been extensively used to reduce alkyl- and aryl halides [109]. These reduced metal complexes have been known as reductants of transition metal ions since Taube s pioneering work [108, 109]. 

Condensation reactions of 3,3-dichlorocyclopropenes [176] or of ethoxycyclopropenium salts [177] with metal complexes of 6-diketones have produced triafulvenes with two acyl groups on the exocyclic carbon atom and reactions of cyclopropenones with malononitrile in the presence of acetic anhydride have provided dicyanotriafulvenes CXIV) [119,178-180] ... 

The term metalla-/3-diketonate refers to an anionic diacyl complex, such as L M(RCO)(R CO) , in which the two acyl ligands occupy adjacent coordination sites of the metal atom. Resonance stabilization of the negative charge by 7r-delocalization onto the two acyl ligands gives Lewis structures 1 and 2. The two acyl ligands acquire an acyl/carbene... 

The nickel acylate complex [Ni( 0)3 = (Bu)OLi ] reacts with mono- and disubstituted alkyne derivatives to afford 1,4-diketones, cyclopentenones or y-lactones, depending on the substitution pattern and the reaction time. " Nickelocene, [Ni(q - 5H5)2], reacts with 1,3-dimesitylimidazolium chloride to afford the carbene complex 63, the chloride ligand of which may be subsituted for a methyl group through further reaction with MeLi. Reduction of nickelocene with metallic sodium in the presence of either 1-pentene or 1-hexene results in alkene activation and formation of trinickel products containing p3-carbyne... 

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