Complexes of Pd(II), η⁶-C₆H₆Ru(II), and η⁵-Cp*Rh(III) with Chalcogenated Schiff Bases of Anthracene-9-carbaldehyde and Base-Free Catalytic Transfer Hydrogenation of Aldehydes/Ketones and N-Alkylation of Amines

Abstract

The condensation of 2-(phenylsulfanyl)­ethylamine and 2-(phenylselenyl)­ethylamine with anthracene-9-carbaldehyde resulted in Schiff bases [PhS­(CH2)2CN-9-C14H9]­(L1) and [PhSe­(CH2)2CN-9-C14H9] (L2), respectively. Na2[PdCl4] treatment of L1/L2 in acetone–water mixture for 3 h at room temperature gave palladacycle [PdCl­(C–, N, S/Se)] (1/2; L1/L2–H = (C–, N, S)/(C–, N, Se)). The reaction of [(η6-C6H6)­RuCl­(μ-Cl)]2 with L1/L2 in methanol for 8 h at room temperature (followed by addition of NH4PF6) afforded half-sandwich complex [(η6-C6H6)­Ru­(L)­Cl]­[PF6], 3/4: (L = L1/L2 ≡ (N, E) ligand). The reaction of [(η5-Cp*)­RhCl­(μ-Cl)]2 with L1 /L2 in the presence of CH3COONa at 50 °C (followed by treatment with NH4PF6) resulted in [(η5-Cp*)­Rh­(L-H)]­[PF6], 5/6: (L = L1/L2). On carrying out the reaction of [(η5-Cp*)­RhCl­(μ-Cl)]2 with these ligands at room temperature and in the absence of CH3COONa, complex [(η5-Cp*)­Rh­(L)­Cl]­[PF6], 7/8 (L = L1/L2 ≡ (N, E) ligand), was formed. Complexes 1–8 were authenticated with 1H, 13C­{1H}, and 77Se­{1H} NMR spectroscopy, high-resolution mass spectrometry, elemental analyses, and single-crystal X-ray diffraction. The moisture- and air-insensitive complexes of Pd­(II) (1, 2), Ru­(II) (3, 4) and Rh­(III) (5–8) were thermally stable. Palladium and rhodium (under base-free condition) species efficiently catalyzed transfer hydrogenation (propan-2-ol as H-source). At room temperature conversion was 90% in TH catalyzed with 0.2 mol % of 2. N-Alkylation of aniline with benzyl alcohol under base-free condition was promoted by 3–8. The 7 was most efficient for the two base-free catalytic reactions. For TH optimum loading of 1–2 and 5–8 as catalyst is 0.05–0.2 and 0.2–0.5 mol % respectively. The optimum temperatures are 80 and 100 °C for TH and N-alkylation, respectively. The optimum loading of 3–8 for N-alkylation is 0.5 mol %. Mercury poisoning test supported homogeneous pathway for the two catalytic reactions. The rhodacycles probably gave real catalytic species by losing a Cp* group.

Dichlorido(4-methylaniline-κN)[N-(4-methylphenyl)-1-(thiophen-2-yl)methanimine-κN]palladium(II)

“…Not only does this result contrast with those found for other Schiff base compounds (Dubey et al, 2019), which readily form a stable palladated complex, but this reaction is also a relatively rare example of a mono-amine Pd II complex. A search of the Cambridge Structural Database (CSD, version 5.43, update of November 2021;Groom et al, 2016) for structures containing a Pd(NH 2 -phenyl derivative)Cl 2 fragment gave 51 hits, of which 30 were bis(amine)PdCl 2 moieties and among these was the complex Pd(p-toluidine) 2 Cl 2 (YOYWOB; Tay, 2019) which is relevant for comparison with the title compound.…”

Ultra-small palladium nano-particles synthesized using bulky S/Se and N donor ligands as a stabilizer: application as catalysts for Suzuki–Miyaura coupling

“…[22][23][24][25][26][27][28][29] These have shown good to excellent catalytic activity for the coupling of aryl halides. [22][23][24][25][26][27][28][29] Presence of neutral chalcogen donor in stabilizers affects the catalytic efficiency, composition, size, recyclability, and dispersion of the nanoparticles to a great extent. 30,31 The use of organochalcogen ligands in the development of molecular catalysts has been studied in a variety of cases.…”

“…30,31 The use of organochalcogen ligands in the development of molecular catalysts has been studied in a variety of cases. [22][23][24][25][26][27][28][29] However, the use of such ligands in the stabilization of nanoparticles is limited. 30,31 To the best of our knowledge, no such compound containing a combination of hard-hard or hard-so donors have been reported for this purpose.…”

Catalyst Evolution in Ruthenium-Catalyzed Coupling of Amines and Alcohols

“…Second, some proceed from arene complexes, e.g. [(η 6 -arene)­RuClL 2 ]­X − or [(η 6 -arene)­RuCl 2 L] , (L = PR 3 , NHC, Py, SR 2 , SeR 2 ; X = Cl, PF 6 , OTf). Third, there are several excellent pincer complexes of PNN, PNO/PNS, PNP, and NNC types (Figure ) that typically contain RuH­(CO) fragments and operate through a metal–ligand cooperative mechanism that is enabled by deprotonation of the CH 2 PR 2 group.…”