Tautomerism in 3-Substituted-2,4-pentanediones and Their Copper Chelates

Abstract

Seventeen 3-substituted-2,4-pentanediones were synthesized. The effect of substituents in the position 3 on the tautomeric equilibria, i, e., keto-, cis-enol-and trans-enol-forms, has been investigated by nuclear magnetic resonance spectroscopy.It has been found that the percentage of each tautomer depends upon the electronic and steric effects of the substituents.The relative intensity of intramolecular hydrogen bonds in these compounds was evaluated from both the NMR and IR data.It has been found from the half-wave potential data of polarographic reduction and the Cu-O stretching frequencies of 16 copper chelates of 3-substituted-2,4-pentanediones that the relative stability of the chelate decreases with an increase in the electron-withdrawing effect of the substituents.

Probing keto–enol tautomerism using photoelectron spectroscopy

“…[16][17][18] and references therein). [19][20][21][27][28][29][30][31][32][33][34][35][36][37][38][39] The situation is different for the interconversion mechanism. Tautomerism in b-diketone compounds is a particular case since the enolone (also called keto-enol) form of most b-diketones is more stable than the diketo form owing to strong intramolecular hydrogen bonds.…”

“…The stability of different forms in the gas-phase and in different solvents has been extensively investigated. [19][20][21][27][28][29][30][31][32][33][34][35][36][37][38][39] The situation is different for the interconversion mechanism. While the tautomeric mechanism in liquid water in which solvent molecules participate in proton transfer is commonly accepted, 39 the mechanism in the gas-phase has been less studied.…”

Synthesis, Spectroscopic Properties and Structural Studies of Copper(II) Complexes of 2-Substituted-1,3-Diphenyl-1,3-Propanedione, Their 2,2'-Bipyridine and 1,10-Phenanthroline Adducts

“…Upon adduct formation, hypsochromic shifts of the  as (C=O)   as (C=C) in all the adducts relative to the parent complexes were observed except Cu(Me-dbm) 2 bipy, Cu(Me-dbm) 2 phen, and Cu(Et-dbm) 2 phen which had bathochromic shifts. The observed shifts can be used to predict the type of bonds in the adducts (Holtzclaw & Collman, 1957;Tanaka et al, 1969). The hypsochromic shifts probably indicate stronger Cu-N and C-O bonds and weaker Cu-O bonds while the reverse is applicable for bathochromic shifts.…”

Synthesis and Physicochemical Studies of Some 2-substituted-1-phenyl-1,3-butanedionato Nickel(II) and Copper(II) Complexes And Their 2,2?-Bipyridine and 1,10-Phenanthroline Adducts

“…Multiple bands of  s (C-O)C-H were observed in all the compounds except [Ni(Cl-bzac)(bipy)(H 2 O) 2 ](Cl-bzac), [Ni(phen) 2 (H 2 O) 2 ](Cl-bzac) and [Ni(Cl-bzac)(phen)(H 2 O) 2 ](Cl-bzac) which had single band. Studies have shown that methyl deformation band occurred at around 1425 cm -1 in acetylacetone (Holtzclaw and Collman, 1957;Belford et al, 1956) while bands in the 1420-1350 cm -1 region have been assigned as  as (CH 3 )   s (CH 3 ) vibrations (Singh and Sahai, 1967b;Tanaka et al, 1969;Patel and Woods, 1990b;Koshimura et al, 1973;Nakamoto et al, 1961). Furthermore, the M-O+C-N vibrational modes occurred below 700 cm -1 (Patel and Woods, 1990a;Patel and Woods, 1990c).…”

“…Literature is available on the introduction of halogens and nitronium ion at the central carbon atom of -diketones [(R 1 COCH 2 COR 2 ) where R 1 =R 2 =CH 3 ] (Singh and Sahai, 1967a;Singh and Sahai, 1967b;Woods and Patel,1994;Patel and Woods, 1990a;Collman et al, 1962;Ebeid et al, 1966;Tanaka et al, 1969 ) whereas little work has been carried out on the synthesis and characterization of the nickel(II) and copper(II) complexes of 2-substituted-1-phenyl-1,3-butanedione R=Cl,NO 2 ) and their 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen) adducts. In continuation of our work on substituted -diketones (Woods et al, 2009a;Woods et al, 2009b), we report the results of our investigations on the nickel(II) and copper(II) complexes of some 2-substituted-1-phenyl-1,3-butanediones R=Cl,NO 2 ) and their adducts with 2,2′-bipyridine (bipy) and 1,10-phenanthroline (phen).…”