Long‐Lived Palladium Catalysts for CO/Vinyl Arene Polyketones Synthesis: A Solution to Deactivation Problems

Abstract

A series of cationic palladium complexes of general formula [Pd(Me)(MeCN)(N-N)][PF(6)] (N-N = (phen) 1 a, 4,7-dichloro-1,10-phenanthroline (4,7-Cl(2)-phen) 2 a, 4,7-diphenyl-1,10-phenanthroline (4,7-Ph(2)-phen) 3 a, 4-methyl-1,10-phenanthroline (4-Me-phen) 4 a, 4,7-dimethyl-1,10-phenanthroline (4,7-Me(2)-phen) 5 a, 5,5,6,6-tetrafluoro-5,6-dihydro-1,10-phenanthroline (F(4)-phen) 6 a, containing different substituted phenanthroline ligands, have been prepared from the corresponding neutral chloro derivatives [Pd(Me)(Cl)(N-N)], (1 b-6 b). The X-ray crystal structure of [Pd(Cl)(2)(4,7-Cl(2)-phen)] (2 b') was determined. DFT calculations show that the electron density on the metal is tuned by the substituents on the ligands. The catalytic behavior of complexes 1 a-6 a in the CO/styrene and CO/p-Me-styrene copolymerizations was studied in detail, showing that the generated catalysts are active for at least 90 h, yielding copolymers of high molecular weight. A firm correlation between the electron density on palladium on the one hand and the catalytic activity of the complexes and the molecular weight and the stereochemistry of the polyketones synthesized on the other hand has been established: the catalyst containing the F(4)-phen is thus far the most active among those tested, yielding the syndiotactic CO/styrene copolymer with a stereoregularity of 96 % (uu triad) and with an M(w) value of 1 000 000.

Catalyst activity or stability: the dilemma in Pd-catalyzed polyketone synthesis

“…This catalytic behavior is different from that found by us for analogous palladium complexes with ligands belonging to the family of 1,10-phenanthroline 21 that over a range of 90 h showed a linear dependence of CO uptake with time, in agreement with the stronger coordinating capability of phenanthroline ligands with respect to that of Ar-BIANs. 20 The comparison of the CO uptake curves of precatalyst 1b with those of complexes 4b and 5b…”

“…This trend is in agreement with the productivity data obtained in the batch copolymerization reactions, 17 but is the opposite of that found in the case of the phenanthroline-containing catalysts. 21,43 The kinetic analysis shows that the higher activity of the present catalysts in the CO/styrene copolymerization is also associated with a faster deactivation, since not only k 1 , but also k 3 values are consistently higher than in the case of 4-Me-styrene (Tables 2 and 3). The values of the kinetic constants highlight that in the series of the catalysts with the symmetric Ar-BIANs, those with electron-donating substituents show the lowest propagation and decomposition rate, while the ligands symmetrically substituted with CF 3 or F yield the most active catalysts, but also show the highest deactivation rate, in particular in the CO/4-Mestyrene copolymerization.…”

“…21,[25][26][27][28] and with the general trend that the weakest ligand (here the nitrogen atom bearing the fluorine substituted aryl ring) is found trans to the stronger trans-labilizing ligand (here the methyl group). The opposite preference towards the cis isomer was observed in case of high steric hindrance around the palladium centre.…”

Unprecedented Comonomer Dependence of the Stereochemistry Control in Pd‐Catalyzed CO/Vinyl Arene Polyketone Synthesis

“…[16,43] Complexes 1a and 2a,o btainedasyellowororange solids in yields rangingf rom4 0to90%,werefully characterized both in solids tate,b ye lemental analysis,a nd in solution,b y NMRs pectroscopy( seet he Supporting Information).I nt he 1 HNMR spectrar ecordeda tr oomt emperature in CD 2 Cl 2 solution,t he number of signalsa nd theiri ntegration revealed that only oneofthe twopossibleisomers waspresent (Figure2). The value of the chemical shift of the Pd-Me group,a t0 .36 and 0.08 ppm for 1a and 2a,r espectively,r emarkably lower than 1.00 ppm, clearly indicated that in the observed species the Pd-Me group was cis to the pyrene fragment.…”

“…[12] The phosphino-phosphite BINAPHOSl igand was found to be able to promote the copolymerization of carbon monoxide with both propene and styrene. [13,14] Focusingt he discussion on aromatic alkenes, the researches published up to now allowed establishing ar elationship between the symmetry of the bidentate N-donor ligand in the palladium catalyst andt he copolymer stereochemistry.P d complexes with C 2v symmetric ligands, such as 2,2'-bipyridine [15] and 1,10-phenanthroline, [16] afforded syndiotactic polyketones,w hereas Pd derivatives with enantiomerically pure C 2 symmetric ligands, such as bi-or bis-oxazolines, [17][18][19] aza bisoxazolines, [20] and diketimines [21] led to the formationo fisotatic copolymers. C s ligands have been reported to yield both syndio-and atacticp olyketones, [22] whereas all the possible microstructures can be obtained by using C 1 ligands.…”