Triphenylamine-Based Bis(β-Diketones) for Construction of Supramolecular Copper(II) Complexes

Abstract

Two new bis(β-diketone) ligands based on triphenylamine have been prepared and crystallized. Treatment of 4,4′-diformyltriphenylamine with two phospholenes (2,2,2-trimethoxy-4,5-dimethyl-1,3,2-dioxaphospholene and 2,2,2-trimethoxy-4,5-diethyl-1,3,2-dioxaphospholene) afforded the bis(β-diketones) triphenylaminebis(2,4-pentanedione) (tpbaH₂, 1); and triphenylaminebis(3,5-heptanedione) (tpbprH₂, 2) as white solids. X-ray analysis of 1 and 2 shows that they are in the enol form. Also, their triphenylamine moieties have a chiral “propeller” shape; the centrosymmetric structures contain equal numbers of the two enantiomeric propellers. Reaction of 1 and 2 with [Cu(NH₃)₄]²⁺(aq) yielded dark-green solids. The Cu complex of 1 was insoluble in common solvents, but that of 2, Cu₄(tpbpr)₄ (3), is soluble in dichloromethane and chloroform. 3 is assigned the cyclic tetrameric structure Cu₄(tpbpr)₄ based on ESI–MS and microanalytical data. This is similar to the copper(II) β-diketonate molecular squares reported previously from our group. Molecular modeling indicates that Cu₄(tpbpr)₄ has Cu···Cu distances of ca. 21 Å, as compared to ca. 14 Å in the previous molecular squares.

Graphical Abstract

Crystal structures of two new bis(β-diketones) are reported, which are likely to form large supramolecular structures on reaction with metal ions such as Cu²⁺.