Synthesis of Mono <i>β</i>‐Pyrrole Substituted Triphyrin(2.1.1)s
Gurpreet Kaur, Avisikta Sinha, Mangalampalli Ravikanth
Abstract
Abstract A series of ten mono β ‐substituted triphyrin(2.1.1)s were synthesized by coupling mono β ‐bromo triphyrin(2.1.1) with appropriate boronic acid in THF/toluene/water (1 : 1 : 1) in the presence of a catalytic amount of Pd(PPh 3 ) 4 in 17–67% yields. Different boronic acids such as methyl, phenyl, p ‐tolyl, p ‐anisyl, p ‐fluorophenyl, p ‐chlorophenyl, 3‐thienyl, 3‐pyridyl, 4‐pyridyl, p ‐biphenyl boronic acids were used. This synthetic approach to β ‐substituted triphyrin(2.1.1)s was facile. The mono‐ β ‐substituted triphyrin(2.1.1)s were characterized and studied by mass spectrometry, NMR, absorption, electrochemical and DFT/TD‐DFT techniques. The spectral studies indicated slight alterations in their electronic properties due to presence of an alkyl/aryl/heteroaryl substituent at the β ‐pyrrole carbon. DFT studies indicated that the pyrrole ring which was substituted with alkyl group at its β ‐position exhibited more deviation compared to the other two pyrroles of triphyrin(2.1.1) macrocycle from the mean plane. However, the β ‐aryl/heteroaryl substituted pyrrole showed less deviation from the mean plane and overall β ‐aryl/heteroaryl macrocycle was planar. Furthermore, the studies also supported the participation of a β ‐substituent with π ‐delocalization of triphyrin(2.1.1). TD‐DFT studies support the experimental observations.