A Stable Seven‐Membered Heterocycle, Containing B, C, N, O, and P Atoms, inside a Smaragdyrin Macrocycle

Abstract

Unprecedented examples of smaragdyrin macrocycles containing seven membered heterocyclic rings were synthesized under simple reaction conditions in high yields. The heterocycle formed inside smaragdyrin macrocycle is rare example of heterocycle containing five different atoms, such as B, C, N, O, and P atoms. The mixed B(III) and P(V) complexes of smaragdyrin macrocycles showed new structural, spectral, and electrochemical properties.

Mixed Boron(III) and Phosphorous(V) Complexes of meso‐Triaryl 25‐Oxasmaragdyrins

“…The DFT‐optimized structure of 8 a (Figure a) indicated that it was a bicyclic spiro compound. Similarly to previous observations for the DFT structure of 6 a , we observed a deviation from planarity in the DFT structure of 8 a . However, in 8 a , the B III ion was very close to the meso ‐carbon plane with a small displacement of 0.049 Å (Table ).…”

“…The average bond angles at the B III ion in 8 a were uniformly tetrahedral (109.5±1°); this ideal geometry led to a more‐stable compound. In contrast, the corresponding angles in 6 a were 109.38±4° . In addition, the B III −N2 and B III −N3 bond lengths were identical in 8 a , whereas a difference of 0.05 Å was observed in 6 a .…”

“…The precursors required for the synthesis of 6 and 8 , B(OH)(Ph)–25‐oxasmaragdyrin complex 5 and B(OH) 2 –25‐oxasmaragdyrin complex 7 , were prepared by previously reported methods . The mixed B III /P V complex of 25‐oxasmaragdyrins 6 a / 6 b were synthesized by reacting 5 a / 5 b with POCl 3 in toluene in the presence of a base at reflux temperature followed by silica gel chromatographic purification afforded the smaragdyrin macrocycle 6 a / 6 b containing an unusual seven‐membered heterocycle consisting B, C, N, O, P atoms as a green solid in 48–52 % yield (Scheme ).…”

“…DFT calculations were used to examine the molecular and electronic structure of meso ‐triaryl‐25‐oxasmaragdyrin 8 a , which contains two seven‐membered B III and P V heterocyclic rings, and these results (Figure a) were compared with those previously obtained for 6 a (Figure b) . The bond angles and dihedral angles and atomic displacements in the DFT structure of 8 a are shown in Tables and , respectively.…”

“…Fluorescence spectra were recorded at 25 °C in a 1 cm quartz fluorescence cuvette. The fluorescence quantum yields ( Φ f ) were estimated from the emission and absorption spectra by a comparative method at λ ex =450 nm by using tetraphenylporphyrrin (H 2 TPP; Φ f =0.11) as a standard . The time‐resolved fluorescence decay measurements were carried out at the magic angle by using a TCSPC fluorescence spectrometer fitted with a picosecond diode laser (IBH, UK).…”