title: Mixed Boron(III) and Phosphorous(V) Complexes of meso-Triaryl 25-Oxasmaragdyrins.
abstract: 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 POCl3 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.
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Powai, Mumbai, 400076, India.
authors.forename: Emandi
authors.initials: E
authors.lastname: Ganapathi
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Powai, Mumbai, 400076, India.
authors.forename: Hemanta
authors.initials: H
authors.lastname: Kalita
authors.affiliation: Department of Chemistry and Chemical Biology and, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA.
authors.forename: Gregory G
authors.initials: GG
authors.lastname: Theophall
authors.affiliation: Department of Chemistry and Chemical Biology and, The Baruch '60 Center for Biochemical Solar Energy Research, Rensselaer Polytechnic Institute, Troy, NY, 12180, USA. lakshk@rpi.edu.
authors.forename: K V
authors.initials: KV
authors.lastname: Lakshmi
authors.affiliation: Department of Chemistry, Indian Institute of Technology, Powai, Mumbai, 400076, India. ravikanth@chem.iitb.ac.in.
authors.forename: Mangalampalli
authors.initials: M
authors.lastname: Ravikanth
keywords: bathochromic shift; boron; heterocycles; mixed metal complexes; phosphorous