Synthesis, Structure, and Properties of Helical Bis-Cu(II) Complex of Linear Hexapyrrolic Ligand

Abstract

The chemistry of metal helical complexes has attracted wide interest not only because of their resemblance with DNA structure but also due to their unique photophysical and chiroptical properties. Linear hexapyrrolic ligand 1 has been designed and synthesized using 3-pyrrolyl BODIPY as a key precursor. The reactivity of the appended pyrrole group of 3pyrrolyl BODIPY was taken as an advantage to synthesize bis(3pyrrolyl BODIPY) by treating 3-pyrrolyl BODIPY with 10 equiv of acetone in CHCl 3 under acid-catalyzed conditions and afforded bis(3-pyrrolyl BODIPY) 2 in 20% yield. Bis(3-pyrrolyl BODIPY) 2, in which two 3-pyrrolyl BODIPY units were connected via sp 3 meso carbon, was very stable, and its identity was confirmed by HR-MS, NMR, and X-ray crystallographic analysis. The X-ray structure revealed that the 3-pyrrolyl BODIPY moieties in bis(3pyrrolyl BODIPY) 2 remained almost planar and arranged at an angle of 98.4°with each other, leading to a V-shaped conformation. In the next step, bis(3-pyrrolyl BODIPY) 2 was treated with AlCl 3 in acetonitrile/methanol at reflux to afford hexapyrrolic ligand 1. Hexapyrrolic ligand 1 was treated with CuCl 2 in acetonitrile at room temp for 1 h followed by crystallization to afford helical bis-Cu(II) complex 1-Cu. Bis-Cu(II) complex 1-Cu was characterized and studied by HR-MS, X-ray crystallography, ESR, absorption, and DFT/TD-DFT techniques. The X-ray structure revealed that the bis-Cu(II) complex was a double-stranded bimetallic helicate and each Cu(II) ion was coordinated to four nitrogen atoms of two dipyrrin units from two hexapyrrolic ligands in a distorted tetrahedral geometry. The crystal packing diagram showed that the bis-Cu(II) complex formed as a racemic mixture containing both M and P isomers which was unable to isolate. The ESR spectrum of bis-Cu(II) complex 1-Cu indicated the presence of two noninteracting Cu(II) ions in slightly different coordination environments. DFT and TD-DFT studies were in agreement with the experimental observations of bis(3-pyrrolyl BODIPY) 2 complex and bis-Cu(II) complex 1-Cu.

A new bis(thioether)-dipyrrin N2S2 ligand and its coordination behaviors to nickel, copper and zinc

“…, Cu1–N1 = 1.982(5) Å, Cu1–N2 = 1.940(5) Å, and Cu1–Cl1 = 2.285(2) Å in part A and Cu2–N4 = 1.975(5) Å, Cu2–N3 = 1.952(5) Å, and Cu2–Cl2 = 2.2874(18) Å in part B), typical of a copper complex, and in good agreement with those of the previously reported copper complex. 39,63,64 In addition, the Cu–SMe bonds in the axial positions are 2.3027(18) Å and 2.3266(17) Å along with the dihedral angles between 5-methyl-2-(methylthio)phenyl moieties and the mean dipyrrin planes of 35.138 (0.214)° and 38.795 (0.297)°, which is the range of the usual Cu–S(thioether) distances. 65,66 The Cu–SMe bonds at the equatorial positions are 2.662(2) Å and 2.6336(19) Å, accompanied by the dihedral angles between 5-methyl-2-(methylthio)phenyl moieties and the mean dipyrrin planes of 42.798 (0.109)° and 42.180 (0.218)°.…”

“…3) reveals that the copper center is pentacoordinated by two thioether sulfur atoms, two pyrrole nitrogen atoms and a chloride anion 18) Å in part B), typical of a copper complex, and in good agreement with those of the previously reported copper complex. 39,63,64 In addition, the Cu-SMe bonds in the axial positions are 2.3027(18) Å and 65,66 The structure of complex (6DF) 2 Zn was unambiguously determined by X-ray crystallographic analysis and its crystallographic data and selected bond distances and angles are summarized in Table 1 and Tables S1 and S2 in the ESI. † It crystallized in an orthorhombic crystal system with the P2 1 2 1 2 1 space group.…”

Substitution at boron in BODIPYs

“…79 This approach has been key to generating prodigiosene-type complexes whereby a pyrrolide flanks the dipyrrinato unit to create an effective chelation pocket. 80,81 Deprotection of F-BODIPYs via Cl-BODIPYs has proven to be reliable, gaining use such as in the synthesis of some tripyrrolic natural products. For example, a concise metal-free method for the facile synthesis of synthetic and natural prodigiosenes utilized the -BF 2 unit as a protective motif for the dipyrrinato construct 31, enabling isolation of these stable and non-polar synthetic intermediates.…”

“…79 This approach has been key to generating prodigiosene-type complexes whereby a pyrrolide flanks the dipyrrinato unit to create an effective chelation pocket. 80,81…”

Pd(ii), Ni(ii), and Cu(ii) complexes of α,α′-ditolylmethanone dipyrroethene

“…Dipyrrins or dipyrromethenes consisting of two pyrrole rings connected by one meso-carbon (methine carbon) are versatile building blocks for preparing porphyrins, corroles, expanded porphyrinoids and related macrocycles, metal dipyrrin complexes, fluorescent BF 2 -dipyrrin complexes (BODIPYs), metal organic frameworks, and so on. [1][2][3][4][5][6] Dipyrrins 1 (Fig. 1) are monoanionic bidentate ligands and have been extensively investigated in coordination chemistry.…”