Palladium(II) Complexes with Phosphanylferrocene-carboxylate Ligands and their Use as Catalyst Precurors for the Semialternating CO-Ethylene Copolymerization

Neutral [Pd(?P,?O-P~O)(?3C,C,C-carbocycloenyl)] complexes, where P~O is a chiral or achiral chelating phosphanylferrocenecarboxylate ligand, were synthesized and characterized by multinuclear NMR spectroscopy. The crystal structure of a representative complex was determined by single- crystal X-ray diffraction analysis. In all complexes, the palladium(II) ion is located at the centre of a square plane formed by the P and O donor atoms from an anionic P~O- ligand, a ?-carbon atom and a C-C double bond from a carbocycloenyl ligand. Neutral methyl complexes with the formulas [PdCl(Me)(?P,?H-P~OH)] and [Pd(Me)(OTs)(?P,?HP~ OH)] were also synthesized and characterized. On the basis of IR, NMR and MS-FAB data, the methyl complexes are proposed to be formulated with the fourth coordination position occupied by an agostic O-H···Pd interaction from a free carboxylic acid moiety [P~OH = 1-(diphenylphosphanyl)ferrocenecarboxylic acid] or a solvent molecule. Selected complexes were employed as catalyst precursors for CO-ethyl- Introduction The organometallic chemistry of functionalized phosphanes modified with an additional (non-phosphane) donor group is attracting considerable attention, predominantly because of its successful and varied applications in homogeneous catalysis.[1] As a contribution to this area, some of us have designed and synthesized several phoshanylferrocenecarboxylic acid ligands (Scheme 1) and studied their ability to coordinate to transition metals, with the ultimate goal of utilizing the obtained compounds in cataly- [a] Istituto di Chimica dei Composti Organometallici (ICCOMCNR), Area di Ricerca CNR di Firenze, Via Madonna del Piano 10, 50019 Sesto Fiorentino, Italy Fax: +39-0555-225-203 E-mail: werner.oberhauser@iccom.cnr.it [b] ICCOM-CNR, Sezione di Pisa, c/o Dipartimento di Chimica e Chimica Industriale, Via Risorgimento 35, 56126 Pisa, Italy [c] Charles University in Prague, Faculty of Science, Department of Inorganic Chemistry, Hlavova 2030, 12840 Prague, Czech Republic Fax: +420-221951253 E-mail: stepnic@natur.cuni.cz Eur. J. Inorg. Chem. 2008, 441-452 © 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim 441 ene copolymerization in MeOH in the presence of an excess of p-toluenesulfonic acid. In all cases, low molecular weight semialternating polyketones were produced. The catalytic activities were rather low and the extra-ethylene insertion reached a maximum value of 4.3%. An operando high-pressure NMR experiment with [Pd(Me)(S)2(?P-P~OH)]OTs (S = solvent, adventitious water) precursor showed that this monocationic PdII alkyl complex is readily converted into a catalytically inactive binuclear carbonyl-bridged PdI compound, which, however, regenerates catalytically active PdII- H species by reaction with TsOH and that ?-chelates of the formula [Pd(CH2CH2C(O)P)(S)(?P-P~OH)]OTs (P = propagating polyketone chain) are catalyst resting states. For the first time, ?-chelate propagating species have been intercepted in a CO-olefin copolymerization assisted by catalysts devoid of a chelating ligand.