Stereochemical Control and Reactivity of Pd Complexes with Meso and Racemic Ligands in the Isotactic Alternating Propene−Carbon Monoxide Copolymerization

Abstract

We report here that C 2 -and C s -symmetric [(P∧P)Pd(H 2 O) 2 ](SO 3 -CF 3 ) 2 complexes, P∧P being either a rac-or a meso-diphosphine ligand, catalyze the copolymerization of propene and carbon monoxide to isotactic poly(1-methyl-2-oxo-1,3-propanediyl) (1a); the meso ligands are even more stereoselective than the racemic ligands and display much higher catalytic activity.The relationship between the geometric characteristics of the catalytic system and the microstructure of the produced polymer has received much attention in recent years, 1 particularly in the field of the polymerization of olefins by metallocenes. 2 Thus, C 2 -symmetric catalysts, 3,4 in which the alternative coordination sites are homotopic, 5,6 give isotactic polymers, whereas C s -catalysts with enantiotopic coordination sites give syndiotactic polymers. 7 Similarly, C 2 -symmetric palladium catalyst precursors enable the copolymerization of aliphatic or aromatic olefins with carbon monoxide to polyketones 1, 8 which have a highly isotactic microstructure. 9-13 With C 1 -symmetric catalyst precursors, isotacticity in the copolymerization was also achieved, 14-17 as was the case for poly-1-olefins with some C 1 -metallocene systems. 18,19 The role of square planar C s -catalysts in the copolymerization reaction is still unclear with respect to the possible synthesis of materials with an unknown microstructure as well as to the mechanistic implications for the catalysis. A first comparison was made with the [(P∧P)Pd(H 2 O) 2 ](SO 3 -CF 3 ) 2 20 complexes 2a-4a, modified with the corresponding ligands 2-4, for the copolymerization of propene (Table 1). Systems containing 2 and 4 had already been used as catalysts. 21 The results in Table 1 and the 13 C NMR spectra in the region of the carbonyl resonances of the synthesized copolymers ( Figure 1) clearly show that the meso ligand has much better stereochemical control and higher catalytic activity. In the related ethene copolymerization, the activity of the system modified by 3 was only 1.4 times higher than the corresponding system modified by 4. 22 Due to the possible implications of the incomplete regioselectivity exhibited by catalyst precursors 2a to 4a, however, we used systems that show better control of the regiochemistry of the insertion of propene, namely systems related to the recently investigated 5. 23 Ligands 6 and 7 were synthesized from 5 by using a slightly modified form of the procedure reported for their 1,3-isomers; 24 they were stereochemically identified by 31 P NMR (1) Kobayashi, S.

The role of phosphine in cobalt-catalyzed carbonylative polymerization of N-alkylaziridine

“…The lowest frequency CO absorption from acyl-C(O)Co(CO) 3 L does not noticeably shift during the entire reaction, but its absorbance dwindles somewhat as the polymerization proceeds. Assuming that the molar absorbability is not affected by the chain growth, the above observation Table 2 IR data (hexane, RT) of the CH 3 Co(CO) 3 PR 3 complexes (1) 123.44 (11) 122.06 (12) 122.04(17) 120.6 (3) indicates that the concentration of acyl-C(O)Co(CO) 3 L is the highest at the beginning of the polymerization and decreases somewhat as the polymerization proceeds. A direct comparison of the rate constants was impossible because the order of rate dependence on aziridine concentration appeared to be different when different catalysts were used.…”

“…However, the use of carbonylation in polymer synthesis has primarily been focused on polyketone synthesis [8][9][10][11][12][13][14][15][16][17]. A few early reports and patents in the 1960s disclosed that inorganic compounds of group 8-10 metals, some times in the presence of main group organometallic compounds, catalyzed copolymerizations of CO and oxygen containing comonomers [18][19][20][21][22][23].…”

The Control of the Stereochemistry in the Palladium-Catalyzed Alternating Styrene/Carbon Monoxide Copolymerization: Effect of the Chirality of the Ligand and of the Ligand-to-Palladium Ratio, Preliminary Communication

“…We showed that [Pd(PP)(H 2 O) 2 ][OTf] 2 complexes (where PP is either (1R,1'S)-or (1RS,1'RS)-1,2-bis[1,1'-(diphenylphosphino)ethyl]benzene, OTf trifluoromethanesulfonate), when used as catalyst precursors for the copolymerization of propene with CO, produce both isotactic poly(1-methyl-2-oxopropane-1,3-diyl) [8]. The meso-ligand shows higher stereospecificity and much higher catalytic activity than the racemicligand, possibly due to the highly stereo-and regiospecific formation of the olefin intermediate responsible for insertion.…”

Giambattista Consiglio's Passion for Homogeneous Catalysis, CC Bond Formation, and Stereochemistry

“…4, a) turned out to perform much better than the corresponding racemic derivatives in terms of productivity, regioregularity, and stereoregularity in the CO/propene copolymerization, and give the most isotactic CO/propene ever produced [21]. Finally, the steric and electronic optimization of chiral diphosphinoferrocene ligands of the Josiphos family showed that the electronic effects of the donors boost the productivity of the Pd catalyst in the CO/propene copolymerization, with the electronic asymmetry of the P-donors and the 3,5-disubstitution of one Ar 2 P group playing a pivotal role [22].…”