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Mixed Boron(III) and Phosphorous(V) Complexes of meso ‐Triaryl 25‐Oxasmaragdyrins
Author(s) -
Ganapathi Emandi,
Kalita Hemanta,
Theophall Gregory G.,
Lakshmi K. V.,
Ravikanth Mangalampalli
Publication year - 2016
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201600131
Subject(s) - bathochromic shift , chemistry , toluene , conformational isomerism , ring (chemistry) , free base , base (topology) , absorption spectroscopy , crystallography , absorption (acoustics) , singlet state , boron , medicinal chemistry , molecule , organic chemistry , fluorescence , materials science , mathematical analysis , physics , salt (chemistry) , mathematics , quantum mechanics , nuclear physics , excited state , composite material
Two unprecedented mixed B III /P V complexes of meso ‐triaryl 25‐oxasmaragdyrins were synthesized in appreciable yields under mild reaction conditions. These unusual 25‐oxasmaragdyrin complexes containing one or two seven‐membered heterocyclic rings comprised of five different atoms (B, C, N, O, and P) were prepared by reacting B(OH)(Ph)‐smaragdyrin and B(OH) 2 ‐smaragdyrin complexes, respectively, with POCl 3 in toluene at reflux temperature. The products were characterized by HRMS and 1D‐ and 2D‐NMR spectroscopy. X‐ray crystallography of one of the mixed B III /P V smaragdyrin complexes indicated that the macrocycle is significantly distorted and contains a stable seven‐membered heterocyclic ring within the macrocycle. The bands in the absorption and emission spectra were bathochromically shifted with reduced quantum yields and singlet‐state lifetimes relative to the free base, meso ‐triaryl 25‐oxasmaragdyrin. The mixed B III /P V complexes were difficult to oxidize but easier to reduce than the free base. The DFT‐optimized structure of the 25‐oxasmaragdyrin complex with two seven‐membered heterocycles indicated that it was a bicyclic spiro compound with two half‐chair‐like conformers. This was in contrast to the chair‐like conformation of the complex with a single seven‐membered heterocyclic ring. Moreover, incorporation of a second phosphate group in the former case stabilized the bonding geometry and resulted in higher stability, which was reflected in the bathochromic shift of the absorption spectra, more‐positive oxidation potential, and less‐negative reduction potential.