Synthesis and Characterization of Dyes and Macrocycles Derived from Dipyrrin and Modified Dipyrrins

Abstract

The thesis entitled “Synthesis and Characterization of Dyes and Macrocycles Derived from Dipyrrin and Modified Dipyrrins” describes synthesis and characterization of multiple BODIPY chromophores appended on benzene and biphenyl unit. It also describes the reactivity of N-confused dipyrrin, doubly N-confused dipyrrin and their benzo derivatives with various metal salts. In general, regular dipyrrins are known to form square planar, tetrahedral and octahedral metal complexes. Dipyrrin can be derived from dipyrromethane which contains two pyrrole rings are connected at their α-position to the meso-carbon atom. Regular dipyrrins having additional co-ordinating agents at α and meso-position leads to formation of complexes with diverse geometries. There are no reports known on reactivity of singly and doubly N-confused dipyrrin and their benzo derivatives with metal salts. This thesis describes the synthesis of multi-BODIPY appended dyes along with their structural and electronic properties. Subsequent chapters describe the results of the reactions between metal salts with modified dipyrrins that was aimed at the synthesis of metal complexes of N-confused dipyrrins. The first chapter describes the brief literature reports on synthesis, reactivity of regular dipyrrin and their derivatives with various metal salts leading to the formation of different types of metal complexes. It also describes the employability of these metal complexes in the synthesis of porphyrinoids. Overall, this thesis gives an account on the synthesis and characterization of BODIPY derivatives, expanded norroles, planar aza-heptalenes and couple of unusual dimers. Quantum mechanical calculations were also employed for the better understanding aromatic and anti-aromatic characteristics of these molecules. The second chapter describes the detailed synthesis of multi-BODIPY units appended on benzene and biphenyl units. The single crystal X-ray diffraction analysis (SCXRD) of the 1,3-Bis BODIPY benzene confirmed the presence of two BODIPY moieties meta to each other on the benzene ring and in 1,4-Bis BODIPY benzene, para to each other on benzene ring. The location of the BODIPY directs the structural features and the intramolecular interactions of these molecules. This is justified by the two BODIPY moieties oriented in an orthogonal conformation in 1,3-Bis BODIPY and more planar in 1,4-Bis BODIPY. With the help of similar studies, the location of three BODIPY moieties was confirmed at meta to each other in the 1,3,5-Tris BODIPY benzene. The packing diagram of this BODIPY displayed the formation of hydrogen bonded porous organic framework. The molecular structure of tetra BODIPY displayed a symmetrical link between the two 1,3-Bis BOIDPY through benzene rings and the two benzene rings were found to be co-planar suggesting the effective delocalization of π-electrons between them. Chapter 3 consists of sections A and B. Section A starts with the description of the attempts at chelating various metals and non-metals by employing N-confused dipyrrin as a ligand as per the protocol employed for regular dipyrrins. N-confused dipyrromethane was synthesized as a precursor, which contains one pyrrole ring connected through their β-carbon to the meso-carbon atom. It was observed that only the confused pyrrole ring of the N-confused dipyrromethane gets oxidized upon oxidation by DDQ (2,3-dichloro-5,6-dicyano-1,4-benzoquinone). When N-confused dipyrrin reacted with boron trifluoride etherate, mass spectroscopy and SCXRD confirmed the formation of simple N-confused dipyrrin-boron trifluoride adduct instead of the expected boron difluoride complex. Surprisingly, N-confused dipyrrin reacts with copper(II) acetate to cyclomerize into macrocyclic products which are coined as expanded norroles. A similar cyclomerization was also observed with various other metal ions such as Zn2+, Mn2+, Fe2+, Fe3+, Ti4+ and Sn2+. These expanded norroles with 24π and 32π are completely characterized by HMRS, NMR and SCXRD. The 24π anti-aromatic hexapyrrolic macrocycle represents the structural isomer of non-aromatic rosarin, while the 32π anti-aromatic octapyrrolic macrocycle is the apparent structural isomer of non-aromatic octaphyrin. The section B of the third chapter describes the reactivity of doubly N-confused dipyrrins with metal salts. Doubly N-confused dipyrrin was derived from its dipyrromethane, which consists of two pyrrole rings linked to the meso-carbon through on of their β-carbon atoms. Doubly N-confused dipyrrin on reaction with copper(II) acetate undergoes cyclodimerization into pink colored symmerical aza-heptalene. The mode of dimerization depends on metal salt employed in the reaction. Under similar reaction conditions, this dipyrrin undergoes cyclodimerization with iron(III) acetylcetonoate into greenish yellow colored unsymmetrical aza-heptalene. Based on NMR studies, both the aza-heptalenes indicate diatropic ring current effect and hence characterized as aromatic in nature. The aromaticity of these molecules was also supported by calculating NICS(0) at the centre of seven membered rings. Furthermore, UV-Visible absorption spectroscopy and TD-DFT calculations provide evidence for heptalene kind of nature rather than macrocylic products. Chapter 4 describes the reactivity of monobenzo derivative of N-confused dipyrrin and monobenzo and dibenzo derivatives of doubly N-confused dipyrrin with metal salts. Monobenzo derivative of N-confused dipyrrin upon reaction with copper(II) acetate underwent cyclomerization into 24π oxidized expanded norrole. Under dilute reaction conditions, along with 24π oxidized expanded norrole an unexpected dimer was also obtained. This dimer has unsymmetrical connection between two confused dipyrrins leading to one seven membered ring between them. Similar results were observed with other metal salts such as Zn(OAc)2, Co(OAc)2, Mn(OAc)2, Mn(acac)3, Co(acac)3 and Fe(acac)3. A similar synthetic process could be employed for the synthesis of aza-heptalenes. Monobenzo derivative of doubly N-confused dipyrrin on reaction with copper(II) acetate yielded a structural of the above described aromatic aza-heptalenes. A similar derivative of aza-heptalene was expected with dibenzo derivative of doubly N-confused dipyrrin but an unexpected dimer was obtained with copper(II) acetate. SCXRD has confirmed the formation of unusual dimer which was further well supported by NMR studies. This dimer also contains the unsymmetrical linkage of the two confused dipyrrin units leading to formation of one six and one seven membered ring between them.