Synthesis of poly(1,10-phenanthroline-5,6-diyl)s having a π-stacked, helical conformation

Abstract

a 5,6-Diboromo-1,10-phenanthroline and 2,9-di-n-butyl-5,6-dibromo-1,10-phenanthroline were polymerized using a Ni catalyst to afford helical polymers in which the phenanthroline moieties are densely stacked on top of each other. Polymerization of the latter monomer using a chiral catalyst led to a preferredhanded helix. This is the first Ni-catalyzed helix-sense-selective polymerization of aromatic compound.Helical polymers are an important class of material that finds a wide range of applications such as chiral recognition, nonlinear optics, and chiral catalysis.1 Such a conformation has been realized for various types of synthetic polymers including vinyl polymers, conjugated polymers and polymers containing hetero atoms in the main chain. 2 Among main-chain conjugated polymers, poly(ophenylene) and its derivatives may be expected to form a helical conformation due to restricted rotation around single bonds connecting aromatic groups arising from steric hindrance and π-stacking between aromatic groups. However, examples of synthesis and structural analysis of poly(o-phenylene) and its derivatives are far more limited compared with poly(para-phenylene) and its derivatives. The first synthesis of poly(o-phenylene) was attempted by Wittig 3 through coupling of o-dilithiobenzene in the presence of transition metal salt resulting in products that seem to be cyclic compounds. Later, Ullmann reaction 4 , Kumada coupling 5 and electrochemical polymerization 6 aiming at poly(o-phenylene) were also reported. Conventional step-by-step methods such as Suzuki coupling 7 and copper-mediated oxidative coupling 8 were also used.Recently, polymerizations of aryne and oxabicyclic alkene with copper and palladium catalysis, respectively, were developed. 9 As one of the most noticeable achievements, uniform poly(ophenylene) derivatives up to 48-mer were synthesized through copper-mediated oxidative reaction of lithiated precursors starting from a 2,2'-biphenyl derivative and n-BuLi, and a tight helical conformation was clarified through X-ray crystal analysis. 8 In this case, single-handed helix was obtained through resolution by triage of conglomerate crystals 8a as well as chiral HPLC.

Panchromatic Copper Complexes for Visible Light Photopolymerization

“…All photoinitiators were prepared with analytical purity up to accepted standards for new organic compounds (>98%); this was checked by high field NMR analysis. 2,9-Diphenyl-1,10-phenanthroline [20], 2,9-dibutyl-1,10-phenanthroline [21], 2-tert-butyl-1,10-phenanthroline [22] and complex G1 [3] were synthesized as previously reported in the literature, without modification and in similar yields.…”

Free-Radical Copolymerization of Dibenzofulvene with (Meth)acrylates Leading to π-Stacked Copolymers

“…Poly(DBF) can be prepared by anionic, radical, and cationic polymerization of DBF [7,8,9,10,11,12,13] (Scheme 1A). The examples of π-stacked polymers include poly(DBF) and derivatives [6,7,8,9,10,11,12,13,14,15], poly(benzofulvene) and derivatives [16,17], polymers consisting of cyclophane-based monomeric units [18,19,20], polyurethanes [21], polyphenanthrolines [22], polyethers [23], and side-chain aromatic vinyl polymers [24,25]. Poly(DBF) indicates intriguing photo-electronic properties including characteristic photo-absorbance and emission profiles and rather high charge mobility due to the π-stacked side-chain fluorene moieties, and its derivatives with substituents on the fluorene backbone of the DBF unit have been synthesized.…”

Recent developments in the synthesis of regioregular thiophene-based conjugated polymers for electronic and optoelectronic applications using nickel and palladium-based catalytic systems

“…224 Strong repulsion originating from highly angled connections made this synthesis quite challenging, and very few examples of the synthesis of poly(o-arylene)s via direct polymerizations have been reported so far. [225][226][227][228][229] Commercially available thiophene was used to synthesize 2-bromo-5alkylthiophen-3-ylboronic acid pinacol ester 110 through three steps, consisting of alkylation using n-butyl lithium, bromination with NBS and then boronation in gram scale quantities. In situ quenching strategy was used to prevent halogen dance rearrangement during the borylation step (Scheme 35).…”