Polymerization of Terminal Acetylenes by a Bulky Monophosphine-Palladium Catalyst

Abstract

A well-defined palladium complex [(tBuXPhos)Pd(Me)-(BAr f )] bearing a bulky monophosphine ligand was synthesized and fully characterized. X-ray diffraction analysis shows that the 1,3,5triisopropylaryl group of the dialkylbiaryl phosphine ligand exhibits a weak η 6 -interaction with the Pd(II) center. This catalyst exhibits excellent functional group tolerance and polymerizes propargyl esters containing benzoyl and acetyl groups, propargyl methyl ether, propargyl alcohol, benzyl acetylene, and phenyl acetylene to yield polymers with M n values in the range of 5−15 kDa with monomodal molecular weight distributions between ca. 1.4 and 2.1.

Novel Route to Cationic Palladium(II)–Cyclopentadienyl Complexes Containing Phosphine Ligands and Their Catalytic Activities

“…At this point, we decided to test the catalytic activity of compounds 1 – 10 towards another type of substrate, and the addition polymerization of phenylacetylene ( PA ) was examined ( Scheme 6 , Table 5 ). Polyacetylenes are used in applications such as photonics, light-emitting diodes, conductors or semi-conductors, sensors, gas separation membranes, and chiral materials [ 92 , 93 ]. Poly(phenylacetylene) ( PPA ) is mainly produced from catalyzed reactions of phenylacetylene with early- and late-transition metal complexes, driven either via metathesis or insertion polymerization mechanisms [ 92 ].…”

“…Rhodium-based late-transition metal catalysts are commonly used, but they are associated with a high-cost disadvantage [ 94 , 95 , 96 ]. Therefore, there is a need to develop other catalytic systems, with Pd-based catalysts attracting most attention [ 92 , 93 , 97 , 98 , 99 , 100 ]. It has been established [ 92 , 93 , 97 ] that efficient palladium catalysts for the polymerization of phenylacetylene also fall under the category of cationic organometallic compounds bearing bulky phosphine ligands.…”

“…Therefore, there is a need to develop other catalytic systems, with Pd-based catalysts attracting most attention [ 92 , 93 , 97 , 98 , 99 , 100 ]. It has been established [ 92 , 93 , 97 ] that efficient palladium catalysts for the polymerization of phenylacetylene also fall under the category of cationic organometallic compounds bearing bulky phosphine ligands. The most notable examples are [(dppf)Pd(MeCN)(CH 3 )]OTf [ 101 ], developed by Darkwa, Pollack et al, and [(tBuXPhos)Pd(Me)](BAr f ) bearing a Buchwald-type dialkylbiarylphosphine ligand, proposed by Chen, Daugulis, and Brookhart [ 93 ].…”

“…It has been established [ 92 , 93 , 97 ] that efficient palladium catalysts for the polymerization of phenylacetylene also fall under the category of cationic organometallic compounds bearing bulky phosphine ligands. The most notable examples are [(dppf)Pd(MeCN)(CH 3 )]OTf [ 101 ], developed by Darkwa, Pollack et al, and [(tBuXPhos)Pd(Me)](BAr f ) bearing a Buchwald-type dialkylbiarylphosphine ligand, proposed by Chen, Daugulis, and Brookhart [ 93 ]. Therefore, we expected that compounds 1 – 10 would exhibit interesting catalytic properties during screening.…”

“…The thermal stability of compound 3 in the polymerization of phenylacetylene, therefore, was modest. Gel permeation chromatography curves ( Figures S95–S100, SI ) of the obtained PPAs at 25–50 °C displayed bimodal distribution, which is characteristic of Pd initiators [ 93 , 99 , 101 , 107 , 108 ]. The effect of reaction time on conversion, activity, and molecular weight is summarized in the entries in Table 5 .…”