摘要：

Bis(che1ated) palladium(n) complexes with a diphosphine and a dinitrogenligand: very efficient catalyst precursors in the co- and ter-polymerisation ofCO and olefinstBarbara Milani,*-" Lidia Vicentini," Anna Sommazzi,b Fabio Garbassi,b Elisabetta Chiarparin,"Ennio Zangrando " and Giovanni Mestroni "a Dipartimento di Scienze Chimiche, Universita di Trieste, Via L. Giorgieri 1, 34127 Trieste, ItalyIstituto Guido Donegani - ENICHEM, Via G. Fauser 4, 28100 Novara, ItalyA new series of palladium(1r) complexes of general formula [Pd(dppp)(L-L)][PF,], has been synthesisedand characterised [dppp = Ph,P(CH,),PPh,, L-L = 2,2'-bipyridine (bipy), 4,4'-dimethyl-2,2'-bipyridine,phenanthroline or 3,4,7,8-tetramethyl-l, 1 0-phenanthroline]. The crystal structure of [Pd(dppp)(bipy)][PF61,has been determined.The chemical behaviour of the complexes in solution has been studied by NMRspectroscopy. Depending on the nature of the solvent, the chemical environment of palladium in solution canbe either the same as in the solid state or different. Whereas in CD,Cl, the co-ordination sphere remains intact,partial dissociation of the nitrogen ligand occurs in co-ordinating solvents. The complexes were found to bevery active catalyst precursors in the CO-olefin co- and ter-polymerisation reactions. Detailed investigation oftheir catalytic activity allowed the catalyst precursor to be considered as the result of the assembly of differentparts, each with a well defined role. In particular, the dissociated N-donor modulates the proton concentration,thus affecting the length of the polymeric chain.Carbon monoxide-olefins co- and ter-polymerisation reactions,yielding perfectly alternating polyketones, are of great interest,as demonstrated by the number of patents"' and papers3*4published in recent years.The commercial availability of theCOXthylene-propylene terpolymer with the name of CarilonBhas been announced by Shell.5The catalytic systems are based on palladium(I1) salts withphosphorus- or nitrogen-donor chelating ligands, either as insitu systems or as preformed c~mplexes,~ with a Br~nstedacid as cocatalyst and, frequently, an oxidant such as 1,4-benzoquinone. When aliphatic olefins, in particular ethylene,are involved, catalytic systems based on diphosphines givehigher yields of polyketones than those with dinitrogenligands.2a.6 For some years we have been involved in theinvestigation of palladium(r1) complexes with nitrogen-donorchelating ligands as potential catalyst precursors in theCO-olefins copolymerisation.' 9 ' We mainly focused on twodifferent kinds of complexes: neutral monochelated com-pounds of general formula [Pd(L-L)(RCO,),] [L-L =2,2'-bipyridine (bipy), 1,lO-phenanthroline (phen) and theirsubstituted derivatives; R = Me or CF,] and dicationicbis(che1ate) complexes of formula [Pd(L-L)(L'-L')][X], withL-L either equal or different to L'-L', X = PF,-, CF,CO,-or MeCO, - . The monochelated compounds are very active inCO-styrene copolymerisation under mild conditions. ' Thebis(che1ated) ones also catalyse CO-ethylene copolymerisationunder more drastic conditions.'" In both cases no acidcocatalyst is required.Preliminary results on the carbonmonoxide-ethylene copolymerisation catalysed by [Pd( L-L)-(L'-L')] [PF6I2 complexes allowed us to recognise someimportant features of the catalytic ~ y s t e m : ~ ( i ) the anionshould be non-esterifiable and non-co-ordinating; (ii) theactive species is very likely a monochelated one, thereforean equilibrium involving the dissociation of at least one ofthe two chelating ligands has to occur in solution; (iii) theother nitrogen chelating ligand is important to increase thet Non-SI unit employed: atm = 101 325 Pa.stability of the catalyst toward decomposition to palladiummetal.Based on these considerations and the strong trans effect ofthe phosphine ligands and the lability of the Pd-N bond," wesynthesized a new class of palladium(r1) complexes of generalformula [Pd(dppp)(L-L)] [PF6I2 [dppp = 1,3-bis(diphenyl-phosphino)propane; L-L = bipy 1, 4,4'-dimethyl-2,2'-bi-pyridine (dmbipy) 2, phen 3 or 3,4,7,8-t

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