A POCO type pincer complex of iridium: Synthesis, characterization, and catalysis

Guerbet upgrading of ethanol to n-butanol using Ru(iii) catalysts under air

“…Reaction time also plays an important role in deciding the selectivity of the Guerbet reaction. 4–6 In order to investigate the effect of reaction time on the yield and selectivity, we performed the standard catalytic reaction (0.1 mol% catalyst, 10 mol% base) at different time intervals. We found that extending the reaction time to 48 h (entry 12, Table 1) resulted in an increase in the formation of higher alcohols (23%), while the amount of n -butanol formed remained mostly the same (28%), thus decreasing the selectivity of n -butanol formation to 55%.…”

“…Since the first stage of the Guerbet reaction (the dehydrogenation step) is thermodynamically uphill, this catalytic reaction is normally conducted at high temperatures, with 120–150 °C being the most common temperature used in the earlier reports. 4–6 Lowering the temperature often led to reduced reactivity, except in the case of the Jones’ catalyst 8 which was found to function well even at 80 °C. In the current system, when the reaction temperature was lowered to 100 °C (entry 15, Table 1), a moderate conversion of ethanol to n -butanol (23%) was observed with a 70% selectivity after 24 h. Although this is a decent conversion, a decrease in the reactivity as compared to the reactions executed at 150 °C was evident.…”

“…11 The cooperativity between the metal center and the amino functionality of the ligands has been a key factor in Guerbet catalysis. 4–6 In the current study, the efficacy of the NNN donor pincer-type ligand L1 was compared with the other three ligands (L2–L4) of tridentate NNN (L2) and bidentate NN (L3 and L4) ligation pattern and dissimilar backbone structures (Fig. 1).…”

“…Several homogeneous catalyst systems have been employed for the Guerbet upgrading of ethanol to n -butanol to date. Most of them contain ruthenium 4 or iridium 5 centers, but lately systems containing manganese 6 centers are also gaining attention. However, most of these catalysts work at elevated temperatures and are sensitive to air and water, leading to catalyst decomposition after a prolonged period.…”

P,N-type phosphaalkene-based Ir(i) complexes: synthesis, coordination chemistry, and catalytic applications

“…Ruthenium complexes are active for the Guerbet-type synthesis of both nand iso-butanol, [33][34][35][36][37][38][39] Homogeneous iridium systems have been previously reported for the Guerbet reaction of ethanol to n-butanol. [40][41][42][43] The only example of an iridium system for the upgrading of ethanol/methanol to iso-butanol was reported by Xu and Mu using iridium complexes immobilised on N-functionalised carbon materials. 44 Therefore, we turned our attention to investigate the efficacy of our iridium complex 5 in the co-condensation of ethanol and methanol to produce isobutanol.…”