Iridium-PPh₃ Catalysts for Conversion of Amides to Enamines

Abstract

Studies on the deactivation mechanism of the reaction of N,N-dialkylamides with TMDS catalyzed by Vaska’s complex, IrCl­(CO)­(PPh3)2 (1a), triggered the discovery of highly active Ir-PPh3 catalysts: photochemically activated 1a and thermally activated IrCl­(PPh3)3 (8). Both catalysts showed excellent activity toward the selective conversion of a variety of N,N-dialkyl-, N-alkyl-N-aryl-, and N,N-diarylamides to the corresponding enamines with low catalyst loadings. The 14-electron species “ClIr­(PPh3)2”, which is stabilized by solvents or reactants in the actual catalytic reactions, could be involved in the catalysis, which produces “HIr­(PPh3)2” and “SiIr­(PPh3)2” (Si = Me2HSiOMe2Si−) species in the catalytic cycle. An in situ generation method for the “ClIrL2” species was established by simply mixing [IrCl­(η4-COD)]2 with PPh3 or other phosphorus ligands, which realized the facile large-scale syntheses of enamines.

The Enones as New Alkenyl Reagents via Ligand Promoted C–C Bonds Activation

“…methyl (2E,4E)-5-(m-tolyl)penta-2,4-dienoate 9 3n: 12.1 mg, 60% yield; 1 H NMR (500 MHz, CDCl3) δ 7.45 (ddd,J = 15.3,6.4,3.9 Hz,1H),3H) 24,143.98,138.52,136.78,131.34 (q,J = 32.4 Hz),130.20,129.32,127.91,125.41 (q,J = 3.8 Hz), 123.92 (q, J = 272. 4 methyl (2E,4E)-5-(naphthalen-1-yl)penta-2,4-dienoate 9 3s: 12.4 mg, 52% yield; 1 H NMR (500 MHz, CDCl3) δ 8.13 (d,J = 8.4 Hz,1H),7.87 (d,J = 7.4,1H),7.84 (d,J = 8.2,1H),2H),3H),7.48 (t,J = 7.8 Hz,1H),6.96 (dd,J = 15.8,11.2 Hz,1H),6.06 (d,J = 15.3 Hz,1H) 67, 150.17, 149.20, 145.15, 140.53, 129.11, 124.31, 121.27, 119.69, 111.14, 109.08, 55.97, 55.90, 51. 60, 144.82, 144.16, 142.72, 130.26, 126.14, 123.94, 119.90, 107.32, 51.55. HRMS-EI calcd for C10H10O3 [M] + , 178.0625; found 178.0624. methyl (2E,4E)-5-(thiophen-3-yl)penta-2,4-dienoate 11 3x: 10.7 mg, 55% yield; 1 H NMR (500 MHz, CDCl3) δ 7.41 (dd,J = 15.3,11.1 Hz,1H),2H),1H),6.90 (d,J = 15.5 Hz,1H),…”

“…The residue was subjected to column chromatography for isolation (gradient eluent: hexane/ethyl acetate) to give products 7 and 4. 74 : 8.4 mg, 31% yield; 1 H NMR (500 MHz, CDCl3) δ 7.42 -7.35 (m, 5H), 7.28 -7.21 (m, 5H), 7.17 -7.07 (m, 6H),5.64 (d, J = 14.0 Hz, 1H).…”

Reduction of Carboxylic Acids to Alcohols via Manganese(I) Catalyzed Hydrosilylation

“…This scarcity results inter alia from the Brønsted acidity and coordinative ability of carboxylic acids, which can deactivate the catalysts by interfering with the metal, the ligand, and possible metal–ligand cooperative pathways. − An alternative route to the use of traditional stoichiometric metal hydrides is offered by easy-to-handle and safe silane reagents . There are many examples reported for the hydrosilylation of esters and recently also for amides. − However, only very few examples exist for free carboxylic acids: they require a large excess of the silane reagent; make use of noble metal catalysts like Ru, , Rh, and Ir; are performed in halogenated solvents like chloroform; or require a specific experimental apparatus. , Therefore, the development of a direct catalytic reduction from free carboxylic acids to their corresponding alcohols still seems highly desirable. , …”