Chelates 3-polyketonate

Polyisothiouronium group chelating resins mineral processing, 6,826 Polyketones metal complexes, 2, 399 Poly(L-lysine) metal complexes, 2, 764 Polymerization solid state, 1, 470 Polymers... 

The active species in the catalytic cycles are square-planar Pd complexes of the formula [Pd (X)(S)(L-L)]Y where L-L is a chelating ligand with the same or different donor atoms among P, N, O and S X is the growing polyketone chain or hydride S may be a solvent molecule, a co-monomer, or a keto group from the chain. Finally, Y is a counter-anion of weak nucleophilicity in order to avoid competition with the co-monomer for coordination to palladium (Scheme 7.1). 

Besides proving the formation of p-chelates [Pd(CH7CH7C(0)Me)(P-P)] at room temperature, the spectra showed the occurrence of chain-transfer by protonolysis with adventitious water to give the p-hydroxo compounds cis/trans [Pd(p-OH)(P-P)]2 as well as the conversion of the latter compounds into cis/trans bis-chelates [Pd(P-P)2] (Chart 7.2) [5f]. Independent experiments with isolated compounds showed that the p-OH and bis-chelate complexes are not dead ends, and can reenter the catalysis cycle to give alternating polyketones. 

In anhydrous organic solvents, ethene/CO copolymerisation termination occurs exclusively by P-H transfer to give vinyl terminated polyketone and Pd-H (Scheme 7.15c). On the other hand, traces of water are very difficult to eliminate and consequently chain transfer by protonolysis is often observed, together with p-H transfer. Experimental evidence in this sense has been straightforwardly obtained by an in situ NMR study of the chemical stability of the p-chelate [Pd(CH7CH7C(0)-Me)(dppe)]PF5 (7) in wet and anhydrous CD2CI2 [5ej. Figure 7.13 reports a sequence of P H NMR spectra taken after dissolution of the p-chelate in the wet solvent already the first spectrum at room temperature showed the formation of the p-hydroxo binuclear complex [Pd(OH)(dppe)]2(PF )2 (8), that was the only detectable species after 15 h. 

Another area of considerable interest in polynuclear metal complex chemistry for which the -polyketones seem well suited is that of mixed metal and mixed valence complexes. When one is seeking fundamental data on how the molecular structure and properties of such compounds relate to bulk properties, it is not sufficient to be content with uncertainties concerning purity and the positions of the different ions. In this paper we report on a systematic approach to the preparation of some heteronuclear, molecular chelates, i,e, molecules containing two or more... 

Since this finding, a large variety of transition-metal-based catalysts have been reported for the production of perfectly alternating aliphatic polyketones (17-27). Particularly suitable systems include palladium(II)- or nickel(II)-based complexes modified with a neutral or anionic bidentate chelating ligand and weakly coordinating anions X (such as OTs, OTf, TEA, BF4 and tetra-arylborates) (2,3,13). 

Dossett, S.J., GiDon, A., Orpen, A.G., Fleming, J.S., Pringle, P.G., Wass, D.F, and Jones, M.D. (2001) Steric activation of chelate catalysts efficient polyketone catalysts based on four-membered palladium(II) diphosphine chelates,/oumal of the Chemical Society, Chemical Communications, 699. 

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