Ferrocene-Functionalized Dithiocarbamate Zinc(II) Complexes as Efficient Bifunctional Catalysts for the One-Pot Synthesis of Chromene and Imidazopyrimidine Derivatives via Knoevenagel Condensation Reaction

Abstract

Four new mononuclear/coordination polymeric (CP) zinc(II) complexes (1−4) of ferrocenyl/pyridyl-functionalized dithiocarbamate ligands, N-ferrocenylmethyl-N-butyl dithiocarbamate (L1), N-ferrocenylmethyl-N-ethylmorpholine dithiocarbamate (L2), N-ferrocenylmethyl-N-2-(diethylamino)ethylamine dithiocarbamate (L3), and N-4-methoxybenzyl-N-3-methylpyridyl dithiocarbamate (L4), have been synthesized and characterized by elemental analyses, IR, UV−vis, and 1 H and 13 C{ 1 H} NMR spectroscopic techniques. The solid-state structures of complexes 1, 3, and 4 have been determined by single-crystal X-ray crystallography as well as powder X-ray diffraction. Single-crystal X-ray crystallography revealed a monomeric structure for complex 1 but 1D polymeric structures for complexes 3 and 4. In all complexes, dithiocarbamate ligands are bonded to the Zn(II) metal ion in a S^S chelating mode, and in the CPs, N atoms on the 2-(diethylamino)ethylamine and 3-pyridyl functionalities in the ligands on the neighboring molecules are also bonded to metal centers, leading to the formation of either a discrete tetrahedral molecule in 1 or 1D CP structures in 3 and 4. The Zn(II) metal centers in the polymeric structures exhibited either square-pyramidal or octahedral geometries. The supramolecular structures in these complexes are sustained via C−H•••π (ZnCS 2 , chelate; 3 and 4), C−H•••π, and H•••H interactions. The catalytic performances of complexes have also been assessed in the Knoevenagel condensation and one-pot multicomponent reactions. Catalysis results showed that the CP 3 acts as a heterogeneous bifunctional catalyst with excellent transformation efficiency at low catalyst loading.

Highly Active Cyclic Zinc(II) Thione Catalyst for C−C and C−N Bond Formation Reactions

“…For instance, catalyst 1 is much better than the resorcine[4]arene‐based two‐dimensional Zn(II) supramolecular catalyst (0.01 mmol/acetone/40 min/60 °C) which requires a higher temperature with a longer reaction time [22] . The catalytic efficiency of 1 is nearly comparable, except for the reaction time, with ferrocene‐factionalized dithiocarbamate zinc(II) catalysts (H 2 O/ 1 h/RT) [12] …”

“…Based on the previous literature, [2–4,11–18] a plausible catalytic mechanism for the Knoevenagel condensation reaction is illustrated in scheme 7. We presume that zinc(II) in 1 can act as a Lewis acidic site to lead to catalytic activities.…”

“…[22] The catalytic efficiency of 1 is nearly comparable, except for the reaction time, with ferrocenefactionalized dithiocarbamate zinc(II) catalysts (H 2 O/ 1 h/RT). [12] Synthesis of 2,3-dihydro-1H-perimidine derivatives by catalyst 1: The catalytic scope of 1 was further extended to the synthesis of perimidine derivatives. Perimidines are tricyclic heterocyclics, where the dihydroperimidine ring is ortho-and peri-fused to naphthalene fragments.…”

“…Notably, the majority of these catalysts have been developed for the Knoevenagel condensation reactions. Zinc(II) clusters and metal‐organic frameworks have been used as the active catalysts for the Knoevenagel condensation reactions [11–17] . We presume that the unsaturated open metal sited of zinc(II) can act as Lewis acid sites while ligand can act as Lewis base sites to promote the catalytic application in Knoevenagel condensation reactions.…”

“…Zinc(II) clusters and metal-organic frameworks have been used as the active catalysts for the Knoevenagel condensation reactions. [11][12][13][14][15][16][17] We presume that the unsaturated open metal sited of zinc(II) can act as Lewis acid sites while ligand can act as Lewis base sites to promote the catalytic application in Knoevenagel condensation reactions. On account of earlier literature, the four coordinated zinc(II) complexes have been considered to be the coordinatively unsaturated open catalytically active metal sites.…”