Chirally
regulated π-conjugated polymers containing platinum
(Pt) complex moieties have great potential as chiroptically functional
materials. In this study, novel platinum-containing conjugated polymers,
poly(1a-2) and poly(1b-2), were synthesized by the dehydrochlorination coupling polymerization
of dichloro(4,4′-tert-butyl-2,2′-bipyridyl)platinum
(1a) and dichloro(4,4′-dinonyl-2,2′-bipyridyl)platinum
(1b) with N-[3,5-bis(4-ethynylphenylethynyl)benzoyl]-l-alanine dodecylamide (2), and their chiral secondary
structures in solutions were investigated. Poly(1a-2) exhibited bisignate circular dichroism (CD) signals assignable
to the main chain chromophore (300–450 nm) in dimethylformamide
(DMF)/MeOH = 50/50 (v/v). The presence of particles of Z-average = 30 nm was confirmed in this solution. These results indicated
that poly(1a-2) formed chirally regulated aggregates.
Single-crystal X-ray analysis of the model compound and density functional
theory (DFT) calculations were carried out to examine the mode of
aggregation of the polymers.
Ring-opening metathesis polymerization (ROMP) of norbornene derivatives is useful for preparing thermally stable and transparent polymeric materials with good moldability. This study deals with ROMP of norbornene monomer 1 bearing...
The functionalization of the chain end of a polymer is gathering increasing attention in the field of synthetic polymer chemistry. The present study is the first example to demonstrate the incorporation of a platinum−acetylide complex at the terminal of a polynorbornene derivative. N-Benzyl-5-norbornene-2-exo,3exo-dicarboxyimide (1) was polymerized with Grubbs 3rdgeneration catalyst (G3). The polymerization was quenched with (Z)-1,4-bis(3-((trimethylsilyl)ethynyl)phenoxy)-2-butene (2) to obtain poly(1)′, followed by the cleavage of trimethylsilyl group and dehydroiodination coupling with trans-bis(tributylphosphine)phenylethynyl iodo platinum (3a) to obtain poly(1a), which was functionalized with a platinum complex at the chain end. Poly(1)′ exhibited no remarkable absorption around 330 nm, while poly(1a) exhibited an intense absorption based on ligand-to-metal chargetransfer transition. Poly(1b) functionalized with a naphthylamide ethynyl platinum complex was synthesized in a similar fashion. The photoluminescene color of a poly(1b) solution in CH 2 Cl 2 changed from green to red with Ar bubbling and rapidly returned to green by ceasing Ar bubbling. A poly(1b)-containing polymethyl methacrylate film exhibited a similar trend, as was observed for the polymer in solution. The weight residues of poly(1a) and poly(1b) at 800 °C were higher than that of poly(1).
Platinum (Pt)-containing novel conjugated polymers, poly(1-2a)− poly(1-2d) having bipyridine ligands were synthesized by the Sonogashira−Hagihara coupling polymerization of [Pt(4,4′-dibromo-2,2′-bipyridine)((R,R)-2,3-bis(tertbutylmethylphosphino)quinoxaline)(trifluoromethanesulfonate) 2 ] (1) coordinated with 4,4′-dibromo-2,2′-bipyridine/(R,R)-2,3-bis(tert-butylmethylphosphino)quinoxaline [(R,R)-QuinoxP*] and 1,4-diethynylbenzene (2a), 1,4-diethynyl-2,5bis(heptyloxy)benzene (2b), 1,4-diethynyl-2,5-bis(2-ethylhexyloxy)benzene (2c), and 1,4-diethynyl-2,5-bis(2-(2-methoxyethoxy)ethoxy)benzene (2d). Poly(1-2d) exhibited circular dichroism signals derived from (R,R)-QuinoxP* and the conjugated main chain around 290 and 440 nm in DMF, respectively. The simulated CD spectroscopic pattern of a low molecular model compound, M1-Pt, agreed well with the observed spectra. The TEM images of poly(1-2d) in the solid state exhibited dispersed patterns with sizes around 10 nm. Concentrated solutions of polymer 1-2d in DMF and CHCl 3 partly exhibited patterns assignable to the formation of lyotropic liquid crystals.
This study reports chirality transfer from optically active diphosphine ligands to optically inactive platinum-containing polymers. Cis-platinum complex 1 smoothly reacted with optically active diphosphine ligands L1 and L2 to give cis-platinum complex 1-L1 and trans dimeric platinum complex 1-L2, respectively. Cyclic trans dimeric complex 1-L2 gradually isomerized to cismonomeric complex 1-L2′. Polymer 4-L2 was insoluble in common organic solvents, even though the reaction was carried out under highly dilute conditions (c = 0.1 mM). On the other hand, polymer 5-L2 was CH 2 Cl 2 -soluble when the reaction was carried out at 1 and 0.1 mM concentrations, in which intramolecular bridging predominated over intermolecular crosslinking. CD spectroscopic measurements suggested that 5-L2 adopts a folded helical conformation, which was supported by DFT calculations.
The Sonogashira–Hagihara coupling polymerization of ferrocene‐containing l‐phenylalanine‐derived optically active o‐, m‐, p‐substituted bis(iodophenylene) monomers 1o
, 1m
, 1p
with 1,4‐diethynylbenzene (2) and 1,4‐diethynyl‐2,5‐bis[2‐(2‐methoxyethoxy)ethoxy]benzene (3) is carried out to obtain the corresponding polymers consisting of ferrocene, amino acid, and phenyleneethynylene moieties. In the solution state, poly(1o
‐2), poly(1o‐3), and poly(1m
‐2) exhibit no circular dichroism (CD) signals in N,N‐dimethylformamide (DMF), while poly(1m‐3), poly(1p
‐2), and poly(1p
‐3) exhibit CD signals assignable to the main chain chromophore, indicating the formation of certain chiral structures. In the solid state, poly(1o
‐2), poly(1o‐3), poly(1m
‐2), and poly(1m‐3) exhibit CD signals in the solid state, while poly(1p
‐2), poly(1p
‐3) does not, indicating the different aggregation manners of the polymers in the solution and solid states. The monomer and the polymers exhibit redox properties assignable to the ferrocene moieties. Thermal gravimetry analysis (TGA) measurements reveal that a 30% weight reduction occurs at 500 °C yielding black ferromagnetic solids.
L-Alanine-derived optically active trans-platinum complexes bearing azobenzene moieties, L-trans-Pt[P(Ph) 2 -1,4-C 6 H 4 -CONH-C*H(CH 3 )-CONH-1,4- (L-2a-5c) were synthesized by the ligand exchange reaction of trans-Pt(PPh 3 ) 2 (CCPh) 2 and cis-Pt(cod)(CCPh) 2 , respectively, with L-P(Ph) 2 -1,4-C 6 H 4 -CONH-C*H(CH 2 Ph)-CONH-1,4-C 6 H 4 -NN-Ph. The trans-azobenzene moieties of the complexes isomerized to the cis form upon UV-light irradiation and returned to the trans form upon visible-light irradiation. L-2a-5t displayed weak circular dichroism (CD) signals irrespective of the trans and cis forms of the azobenzene moieties. On the other hand, L-2a-5c with trans-azobenzene moieties displayed strong CD signals, whose intensity decreased upon UV-light irradiation, accompanied by an increase in CD signals based on cis-azobenzene moieties. DFT calculations of the complexes indicated that intramolecular hydrogen bonds form between the amide moieties of two ligands in the cis-platinum complexes, resulting in retention of conformation. A noncovalent interaction plot analysis also indicated that the π−π interaction between the benzene rings of the ligands also contributes to conformational maintenance. The D-alanine-derived counterparts, D-2a-5t and D-2a-5c, exhibited mirror-image CD spectroscopic patterns in comparison to those of L-2a-5t and L-2a-5c. Solution-state IR absorption spectroscopic peaks of CO stretching and N−H bending vibrations of L-2a-5c were observed broadly at ca. 10 cm −1 lower and higher than those of P(Ph) 2 -1,4-C 6 H 4 -CONH-C*H(CH 3 )-CONH-1,4-C 6 H 4 -NN-Ph (L-2a), respectively, thus supporting the formation of intramolecular hydrogen bonding at the amide groups.
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