Thermodynamic and kinetic parameters associated with the fluxional behavior of 2-methyl- and 2,6-dimethyltroponeiron tricarbonyl complexes

Theoretical studies on the protonation behavior of tropone and its metal complexes

“…0.2 kcal/mol lower than that for 5 (20.1 kcal/mol). The barriers obtained from the NMR experiments are 24.1 kcal/ mol for 4 and 27.6 kcal/mol for 5 [2]. Fig.…”

“…These experimental results show that the protonated species of regioisomer 4 0 could be more stable than the protonated species of regioisomer 4 although the neutral regioisomer 4 is more stable than the neutral regioisomer 4 0 . Also, studies on the fluxionality of 2-methyltroponeiron complexes indicated that the barrier to the interconversion between 4 and 4 0 is also different from the barrier to the interconversion between their protonated species [2,4,7]. Similar observations also hold true for 2,6-dimethyltroponeiron complexes having two methyl groups on the tropone ring, i.e., 5 is more stable than 5 0 while the stability order of their protonated species is reversed [2].…”

“…Tropones (1) and troponeiron complexes (2) have received considerable attention because they are important intermediates for cycloaddition reactions and synthesis of heterocyclic compounds [1]. Protonation of such compounds due to their importance in synthesizing other organic compounds has also attracted interest.…”

“…Protonation of such compounds due to their importance in synthesizing other organic compounds has also attracted interest. Studies show that protonation of the tropone complexes (2) followed by reaction with Na 2 CO 3 /ROH yields alkyl ethers (3) [2][3][4].…”

“…These oxygen-protonated complexes upon either standing for several minutes or increasing temperature isomerize to thermodynamically more stable carbon-protonated pentadienyliron cationic complexes (2_CH + ) [7][8][9]. Experimental studies also demonstrated that substituents on the tropone ring influence the relative stability of regioisomers of the protonated troponeiron complexes as well as the barriers to their interconversion [2,4,7]. For example, NMR studies of 2-methyltroponeiron complexes indicated that regioisomer 4 was thermodynamically more stable than regioisomer 4 0 .…”