NICKEL-COMPLEXES WITH HETEROFUNCTIONALIZED PHOSPHINE-LIGANDS - CATALYTIC OLIGOMERIZATION OF ETHYLENE WITH [NI(C5PH5)(PH2PCH=C(O)PH)]

Reaction of [Ni(C5Ph5)Br(CO)] with Ph2PCH2C(O)Ph in the presence of 1, 8-bis(dimethylamino)naphthalene (proton sponge) gives the chelate comp lex [Ni(C5Ph5){Ph2PCH=C(O)ph}] 1. The complexes [Ni(C5Ph5){Ph2PCH=C(O) (C5H4)Fe(C5H5)}] 2, [Ni(C5Ph5){Ph2PCH=C(O)(1,3-C6H4)C(O)= HCPPh2}Ni(C5 Ph5)] 3, (Ni(C5H5){Ph2PCH=C(O)Ph}] 4 and [Ni(C5H5){Ph2PCH=C(O)(C5H4)Fe (C5H5)}] 5 have been synthesised using the appropriate phosphine ligan d and applying a procedure similar to that for 1. Complex 1, activated with NaBH4, exhibits catalytic activity in the low-pressure oligomeri zation of ethylene. At 130-degrees-C, under 38 bar of ethylene, select ivities of up to 98% towards linear alpha-olefins were achieved. Proto nation of the bimetallic complex 2 with HBF4 gave the cationic complex [Ni(C5Ph5){Ph2PCH2C(O) (C5H4) Fe(C5H5)}] BF4 6. Crystals of 6 belong to the orthorhombic space group Pbca with a = 19.427(6), b = 38.595(11 ), c = 13.001(4) angstrom and Z = 8. The structure was refined to R = 0.049 (R' = 0.067). The bonding of C5Ph5 contrasts with the bonding mo des usually found for cyclopentadienyl ligands. The ring contains two short [1.384(8) and 1.389(8)], two medium [1.444(8) and 1.443(8)], and one long [1.474(8) angstrom] C-C bonds so that the C5Ph5 may be viewe d as an (alkyl, diene) ligand. This unusual bonding is likely to resul t from the 'chemical' dissymmetry of the P,O ligand and the low trans influence of the oxygen atom. The extremely low nu(C=O) frequency of t he co-ordinated ketone (1525 cm-1) reflects the strong electron-withdr awing effect of the Ni(C5Ph5)+ moiety.