Structure, Spectroscopy, and Electrochemistry of Manganese(I) and Rhenium(I) Quinoline Oximes

Abstract

Reactions of α- and β-diimine quinoline aldoximes with Mn­(I) and Re­(I) tricarbonyl halides afford quinoline oxime complexes. Both Mn­(I) and Re­(I) complexes experience severe geometric strain due to ligand steric interactions: 6-membered metallocycles exhibit more pronounced distortions than 5-membered ones, consistent with density functional theory structural analyses. Such distortions likely also affect reactivity patterns, as evidenced by Re­(I)-induced deoximation of a quinoline variant containing a CF3-ketoxime.

Manganese and Rhenium Tricarbonyl Complexes Equipped with Proton Relays in the Electrochemical CO2 Reduction Reaction

“…16 and 18. [39,46,47] Two other complexes with acidic protons in equatorial positions of the ligand have been investigated (Figure 4, Figure 5). 19, with an α-diimine quinoline aldoxime ligand, was inactive.…”

“…20 (Figure 4), in which a α-diimine quinoline aldoxime ligand was utilised, causes an current increase in MeCN with TFE in an CO 2 atmosphere under reductive conditions with regard to the measurement under Ar, but the authors did not suggest any catalytic activity. [47] Proton relays in axial position of α-diimine-Mn(CO) 3 complexes could have an dramatic impact not only on the electronic structure and overpotential for the CO 2 reduction, but also on the reaction products. In contrast to the Re derivatives, in Mn complexes the protonation of the doubly reduced metal centre forming the hydride species could be competitive to the reaction with CO 2 , when a suitable proton relay is introduced.…”

“…19 , with an α‐diimine quinoline aldoxime ligand, was inactive. [ 47 ] We utilised the dinuclear complex 21 with an pyridine‐pyrazole unit and it was only moderately active and stable (Figure 5). [ 48 ] Initial reduction of 21 at –2.24 V in dmf is a 2e – reduction as proven by coulometry, and leads to a homolytic N–H‐bond rupture similar to that observed in 3 .…”

“…20 (Figure 4), in which a α ‐diimine quinoline aldoxime ligand was utilised, causes an current increase in MeCN with TFE in an CO 2 atmosphere under reductive conditions with regard to the measurement under Ar, but the authors did not suggest any catalytic activity. [ 47 ]…”

One‐Pot and Reducible‐Functional‐Group‐Tolerant Synthesis of α‐Aryl‐ and α‐Heteroaryl‐α‐Trifluoromethyl Alcohols via Tandem Trifluoroacetylation and MPV Type Reduction

“…However, these methodologies are not suitable for the preparation of α‐aryl‐α‐trifluoromethyl alcohols carrying electron‐withdrawing groups on the phenyl ring, such as ester, cyano, and nitro groups or α‐electron‐deficient heteroaryl groups , since trifluoroacetylation of electron‐withdrawing group‐substituted arenes or electron‐deficient heteroarenes is quite difficult even at a high reaction temperature and with the addition of Lewis acids. Therefore, another route that involves trifluoromethylation of the corresponding aldehydes using various nucleophilic trifluoromethylating agents, such as Ruppert–Prakash reagent, iodotrifluoromethane,[7j], [7k] trifluoromethane,[7l] borazine,[7m] and other compounds,[7n], [7o] has been developed for this purpose, as shown in Scheme .…”