Abstract
A series of heterometallic coordination clusters (CCs) [Ni(II)2Ln(III)2(L1)4Cl2(CH3CN)2] 2CH3CN [Ln = Y (1Y), Sm (1Sm), Eu (1Eu), Gd (1Gd), or Tb (1Tb)] were synthesized by the reaction of (E)-2-(2-hydroxy-3-methoxybenzylidene-amino)phenol) (H2L1) with NiCl2·6(H2O) and LnCl3·x(H2O) in the presence of Et3N at room temperature. These air-stable CCs can be obtained in very high yields from commercially available materials and are efficient catalysts for the room-temperature domino ring-opening electrocyclization synthesis of trans-4,5-diaminocyclopent-2-enones from 2-furaldehyde and primary or secondary amines under a non-inert atmosphere. Structural modification of the catalyst to achieve immobilization or photosensitivity is possible without deterioration in catalytic activity.
Highlights
The Nazarov cyclization exemplifies such an electrocyclization, providing access to important and useful cyclopentones, and Lewis acids catalyze this cyclization.[37−39] The interest in bifunctionalized cyclopentenones arises from the fact that they are versatile building blocks in the synthesis of natural products such as (+)-Nakadomarin A.40
Batey and Li used a variety of Lewis acids for the synthesis of trans-4,5-diaminocyclopentanones (Scheme 1) from the domino condensation/ringopening/electrocyclization reaction of furfuraldehyde with amines.[41]
The TGA data (Figures S12−S17 in the ESI) for all solid compounds indicated the loss of four CH3CN molecules up to 290 °C and decomposition at higher temperatures
Summary
Polynuclear coordination clusters (CCs),[1,2] assembled from organic ligands, transition-metal elements (3d), and/or lanthanide (4f) elements, are a burgeoning class of functional materials with fascinating structures.[3−8] These materials are already used in areas ranging from molecular magnetism,[9−17] biology,[18−20] molecular imaging,[21] magnetic resonance,[22] and luminescence.[23−27] one of the most common applications for coordination compounds, catalysis, is much less studied for polynuclear 3d/4f heterometallic CCs with classical N,O-donor ligands[28−34] than for organometallic compounds.[35,36] The difference in the growth rates between the two research fields may reflect the fact that organometallic compounds are mainly of low nuclearity, so it is easier to determine a possible mechanism for the catalytic procedure. Cl2(CH3CN)2] 2CH3CN (1Dy) exhibits similar catalytic efficiency, with only 1% loading This CC, unlike Dy(OTf)[3], could catalyze the reaction with secondary and primary amines.[41,47] In our quest to develop these catalytic species further and to (a) seek lower cost materials and (b) investigate its possibility of immobilization, we decided to (i) extend our study to other lanthanides and (ii) to tune the organic periphery of the H2L1 ligand. The brown precipitate that settled as the mixture was allowed to cool was filtered and washed off with cold MeCN (20 mL) and Et2O (10 mL). The filtrate underwent vapor diffusion with Et2O; after 7 days, large brown crystals suitable for XRD study were obtained. The filtrate underwent vapor diffusion with Et2O; after 12 days clear green crystals suitable for XRD study were obtained. The Jmol program was used for visualization purposes.[67]
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