DOI: 10.1002/chem.200501047 Long-Lived Palladium Catalysts for CO/Vinyl Arene Polyketones Synthesis: A Solution to Deactivation Problems JØrôme Durand, [a] Ennio Zangrando, [a] Mauro Stener, [a] Giovanna Fronzoni, [a] Carla Carfagna, [b] Barbara Binotti, [b] Paul C. J. Kamer, [c] Christian Müller, [d] Maria Caporali, [d] Piet W. N. M. van Leeuwen, [d] Dieter Vogt, [d] and Barbara Milani* [a] Introduction The performance of a catalyst in a general sense and of a catalyst for polymerization in particular, results from a com- bination of several factors such as activity, selectivity, life- time, deactivation processes and the properties of the prod- ucts. These factors are related to the components of the cat- alytic system only, such as the ancillary ligands, the comono- mers, the reaction medium, the cocatalysts, the temperature. Catalyst deactivation is a very common phenomenon in ho- mogeneous catalysis and represents a problem that cannot be easily overcome. [1] In particular, the perfectly alternating palladium-catalyzed CO/vinyl arene copolymerization represents a well-known example of a reaction suffering from this problem. [2] In this case, the deactivation is mainly due to the decomposition of the active species to inactive palladium metal thus resulting in the catalyst death and limiting also the possibility of ob- taining high molecular weight polymers. During the last few years, we have studied in detail the factors affecting the catalyst stability and we found that the catalyst lifetime can be greatly enhanced when the copoly- merization reaction is carried out in 2,2,2-trifluoroethanol (TFE) instead of methanol and when the complexes [PdACHTUNGTRENNUNG(N– N) 2 ]ACHTUNGTRENNUNG[PF 6 ] 2 (N–N = 1,10-phenanthroline (phen), 2,2’-bipyri- dine (bpy), their symmetrically and unsymmetrically substi- tuted derivatives), with an N–N to Pd ratio of 2, are used. [3] Abstract: A series of cationic palladi- um complexes of general formula [Pd(Me)ACHTUNGTRENNUNG(MeCN)ACHTUNGTRENNUNG(N–N)]ACHTUNGTRENNUNG[PF 6 ] (N–N = (phen) 1a, 4,7-dichloro-1,10-phenan- throline (4,7-Cl 2 -phen) 2a, 4,7-diphen- yl-1,10-phenanthroline (4,7-Ph 2 -phen) 3a, 4-methyl-1,10-phenanthroline (4- Me-phen) 4a, 4,7-dimethyl-1,10-phe- nanthroline (4,7-Me 2 -phen) 5a, 5,5,6,6- tetrafluoro-5,6-dihydro-1,10-phenan- throline (F 4 -phen) 6a, containing dif- ferent substituted phenanthroline li- gands, have been prepared from the corresponding neutral chloro deriva- tives [Pd(Me)(Cl)ACHTUNGTRENNUNG(N–N)], (1b–6b). The X-ray crystal structure of [Pd(Cl) 2 (4,7-Cl 2 -phen)] (2b’) was deter- mined. DFT calculations show that the electron density on the metal is tuned by the substituents on the ligands. The catalytic behavior of complexes 1a–6a in the CO/styrene and CO/p-Me-styr- ene copolymerizations was studied in detail, showing that the generated cata- lysts are active for at least 90 h, yield- ing 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, yield- ing the syndiotactic CO/styrene copoly- mer with a stereoregularity of 96 % (uu triad) and with an M w value of 1 000 000. Keywords: N ligands · palladium · polyketones · polymerization · stereochemistry [a] Dr. J. Durand, Prof. E. Zangrando, Dr. M. Stener, Prof. G. Fronzoni, Dr. B. Milani Dipartimento di Scienze Chimiche, Università di Trieste Via Licio Giorgieri 1, 34127 Trieste (Italy) Fax: (+ 39) 040-558-3903 E-mail: milani@dsch.units.it [b] Dr. C. Carfagna, Dr. B. Binotti Istituto di Scienze Chimiche, Università di Urbino Piazza Rinascimento 6, Urbino (Italy) [c] Prof. Dr. P. C. J. Kamer The School of Chemistry, University of St. Andrews St. Andrews, Fife, KY16 9ST (UK) [d] Dr. C. Müller, Dr. M. Caporali, Prof. Dr. P. W. N. M. v. Leeuwen, Prof. Dr. D. Vogt Schuit Institute of Catalysis, Laboratory of Homogeneous Catalysis Eindhoven University of Technology, P.O. Box 513 5600 MB Eindhoven (The Netherlands) Chem. Eur. J. 2006, 12, 7639 – 7651 # 2006 Wiley-VCH Verlag GmbH&Co. KGaA, Weinheim 7639 FULL PAPER