Cycloruthenation of N‐(Naphthyl)salicylaldimine and Related Ligands: Utilization of the Ru–C Bond in Catalytic Transfer Hydrogenation

Abstract

Upon reaction with [Ru(PPh3)2(CO)2Cl2], N‐(naphthyl)‐4‐R‐salicylaldimines (R = OCH3, H, Cl; H2L1–H2L3) and 2‐hydroxy‐N‐(naphthyl)naphthaldimine (H2L4) readily undergo cycloruthenation by C–H bond activation at the peri position to afford complexes of the type [Ru(PPh3)2(L)(CO)] (L = L1–L4). The crystal structures of the [Ru(PPh3)2(L)(CO)] (L = L1, L2, L4) complexes were determined and the structure of [Ru(PPh3)2(L3)(CO)] optimized by DFT calculations. The thermodynamics for the reaction of [Ru(PPh3)2(CO)2Cl2] with H2L2 to give [Ru(PPh3)2(L2)(CO)] were determined. All the complexes show intense absorptions in the visible and UV regions, which have been analyzed by TDDFT calculations. Cyclic voltammetry of the four cycloruthenated complexes showed two oxidations within the range 0.50–1.35 V versus SCE and a reduction at around –1.75 V versus SCE. The [Ru(PPh3)2(L)(CO)] (L = L1–L4) complexes were found to efficiently catalyze the transfer hydrogenation of carbonyl compounds.

Palladium(0)-mediated C–H bond activation of N-(naphthyl)salicylaldimine and related ligands: utilization of the resulting organopalladium complexes in catalytic C–C and C–N coupling reactions

“…It is relevant to mention here that the ONC-mode of coordination displayed by four aldiminate ligands in [Pd(L)(PPh 3 )] (where L = L 1 -L 4 ) represents a rare bonding mode in fourcoordinate palladium(II) compounds. 5 Typically, such aldimine ligands undergo reaction with transition metals to furnish the more common ON-mode of coordination. 6 The formation of the cyclopalladated [Pd(L)(PPh 3 )] complexes was initially thought to occur via stepwise displacement of chloride ligands in [PdCl 4 ] 2− by the aldimine ligand to give the monoanionic ON-chelated complex cis-[PdCl 2 (ON)] − .…”

“…It is relevant to mention here that the ONC-mode of coordination displayed by four aldiminate ligands in [Pd(L)(PPh 3 )] (where L = L 1 -L 4 ) represents a rare bonding mode in fourcoordinate palladium(II) compounds. 5 Typically, such aldimine…”

Transfer hydrogenation via generation of hydride intermediate and base‐free alcohol oxidation activity studies on designed ruthenium complexes derived from NNN pincer type ligands

“…In the geometry optimization of metal complexes the PPh 3 group wereexchanged with PH 3 derivatives for simplifying the calculations . The optimized geometry of the synthesized complexes 1 , 2 and 3 were shown in ESI Figure S25.…”

“…Herein, we propose a probable mechanism for the transfer hydrogenation reaction catalyzed by complexes 1 – 3 [8c, 21] . The catalytic process starts after the addition of isopropyl alcohol via dehydrochlorination of complexes in the presence of base KOH and the formation of an alkoxide intermediate (I).…”

Catalysis with cycloruthenated complexes

“…In 2014, Bhattacharya and co-workers reported the use of a ruthenium ONC pincer catalyst Ru59 in the transfer hydrogenation of aldehydes and ketones ( Scheme 36 ). 71 These reductions were conducted with low catalyst loadings (0.1 mol%) and a reaction time of 6 hours. Several examples proceeded in comparable yields to the reduction of aromatic ketones and aldehydes.…”