Atropisomeric PˆN Ligands for the Palladium‐Catalyzed Copolymerization of Styrene with Carbon Monoxide. Preliminary Communication

Abstract

Achiral and chiral cationic palladium catalysts, modified with atropisomeric P N ligands with different steric and electronic properties, can efficiently produce poly(styrene-alt-CO) with essentially complete regioregularity and variable tacticity, depending on the ligand geometry; the electronic effect on catalytic activity depends on the geometry of the ligand.The alternating copolymerization of styrene with carbon monoxide to poly[1-oxo-2-phenylpropane-1,3-diyl] has attracted much attention in recent years [1 ± 10]. The catalyst precursors used to produce stereoregular copolymers were[12] complexes (S solvent molecule; X weakly coordinating anion). N N Ligands such as bipyridine or phenanthroline result in syndiotactically specific copolymerization [13], whereas a bis-oxazoline type of ligand [14] [15] or atropisomeric diketo imines [8] result in isotactically specific copolymerization. Cationic palladium complexes of the type [(P N)Pd(S) 2 ](X) 2 (P N 4-substituted 4,5-dihydro-2-phosphinooxazole ligand) also produce highly isotactic copolymers. In contrast to the above-mentioned N N modified compounds, these complexes can be used under high carbon monoxide pressure to achieve higher polymer yields [16]. However, the substituent at C(4) of the dihydrooxazole moiety is necessary for the isotactic microstructure of the copolymer, but also causes rate reduction [17]. In an attempt to combine the good catalytic activity of the bipyridine systems [10] with the stabilizing effect of the diphosphine, without losing the isotactic steric control, we tried to exploit atropisomeric ligands and to compare them with their achiral counterparts. We, therefore, synthesized, where P N are the corresponding ligands 1' ± 4', and used them as catalyst precursors for the copolymerization of styrene with carbon monoxide.The Table lists the results of the copolymerization experiments. They were carried out at high carbon monoxide pressure (320 bar), after identifying the positive order of the carbon monoxide concentration of catalyst precursor 1a, as found for the other P N ligands [16] [19]. The achiral catalyst precursor 1a has the highest catalytic activity of the ligands with diphenylphosphino substituents. It is noteworthy that system 2, with the planar ligand, is not catalytically active. Analogously, for the N N ligand systems under comparable reaction conditions, the phenanthroline catalyst is less active than

The Effect of Counterion/Ligand Interplay on the Activity and Stereoselectivity of Palladium(II)–Diimine Catalysts for CO/p‐Methylstyrene Copolymerization

“…Catalysts 1-4 afford regioregular polyketones with a "quasi-atactic" microstructure, [14,[43][44][45] (Table 1, entries 1-6), whereas a remarkable increment of the isotactic ll component is observed with complexes 5-7, which bear Me groups in the ortho positions (80 % for complex 7 b). A slight prevalence for the ll triad (that increases with the size of R 2 ) is also observed for the copolymers produced by the orthomonosubstituted compounds 11-13.…”

Unique syndio-selectivity in CO/styrene copolymerization reaction catalyzed by palladium complexes with 2-(2′-oxazolinyl)-1,10-phenanthrolines

“…8,9 Moreover, thanks to the presence of the carbonyl group, the post-functionalization of the polyketone macromolecules is possible with no degradation of the polymeric chain yielding new polymeric materials. [10][11][12][13][14][15][16][17][18] Palladium complexes with bidentate chelating ligands are the catalysts of choice for this process and a wide range of homobidentate P-donor and N-donor ligands, as well as of heterobidentate phosphine-nitrogen (P-N) [19][20][21][22] or phosphinephosphite (P-OP) [23][24][25][26] ligands have been utilized in the preparation of active metal catalysts. From the data available in the literature, P-donor derivatives are the catalysts of choice for the copolymerization of aliphatic α-olefins, whereas Pd complexes based on P-N or P-OP or N-N ligands turn out to be better suited to the copolymerization of vinyl arenes; a process where these catalysts enable the proper control of the reaction leading to good yields of copolymer.…”

Copolymerization of olefins and CO catalyzed by new chiral arsine–oxazoline palladium complexes

“…for C 25 H 27 NOAsPdCl: C,52.29;H,4.74;N,2.44. Found: C,52.18;H,4.64;N,PdMe(NCCH 3 ) þ BF À 4 ] Complex 4 (5.9 mg, 10.3 lmol) and AgBF 4 (2.0 mg, 10.3 lmol) were mixed together in CH 2 Cl 2 (1 mL) with stirring under nitrogen. Fresh-distilled acetonitrile (0.01 ml, 190 lmol) was added.…”