Abstract
The [Rh(L-alaninate)(cod)] (cod = 1,5-Cyclooctadiene) complex was synthesized and characterized. Asymmetric polymerizations of achiral phenylacetylene with two hydroxyl groups and a dodecyl group (DoDHPA) were performed by using the rhodium complex as the catalyst to provide polymers with a higher molecular weight (>105) than the polymers obtained using the [Rh(cod)Cl]2 initiator systems. The resulting polymers showed circular dichroism (CD) signals at approximately 310 and 470 nm, indicating that they have a preferential one-handed helical structure. The helix sense in the polymer main chain was controlled by the sign of the catalyst chirality. These findings suggest that the rhodium complex with a chiral amine is the true active species for the helix-sense-selective polymerization of DoDHPA. The [Rh(L-alaninate)(cod)] complex also exhibits high catalytic activity in the polymerization of phenylacetylene (PA) to give a high yield and molecular weight. All these results demonstrate that this Rh complex is an excellent catalyst for the polymerization of phenylacetylene monomers.
Highlights
Asymmetric catalysis is one of the best methods for the synthesis of optically active organic compounds [1,2]
The mass spectrum showed that the peak at 299 corresponds to the formation of [Rh(L-alaninate)(cod)] (Figure S13, Supplementary Materials)
These findings indicate that the chiral rhodium complex with L-alaninate as the ligand is effective for helix-sense-selective polymerization (HSSP)
Summary
Asymmetric catalysis is one of the best methods for the synthesis of optically active organic compounds [1,2]. Masuda and coworkers have designed and developed Rh catalyst systems for the authors speculated that (R) or (S)-PEA coordinates to the rhodium catalyst, and the formed complex polymerizations of substituted acetylenes in the past several years [7,9]. (tcb)Rh+[η6-(C6H5)B-(C6H5)3] can induce helix-sense-selective resulting polymers were thought to act as the ligand and cocatalyst of HSSP instead of (R)-and (S)-PEA. Casado polymerized PA by using a rhodium complex with mixed anionic N–O bidentate species of HSSP or SHSSP was desired but was difficult due to the low stability of the Rh-amine ligands. (tfb)Rh [η -(C6 H5 )B (C6 H5 )3 ] and (tcb)Rh [η -(C6 H5 )B (C6 H5 )3 ] can induce helix-sense-selective asymmetric polymerization of DoDHPA.
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