Structural characterisation of cationic methylallyl, methylindenyl and pentamethylcyclopentadienyl nickel complexes containing the bulky phosphine 1,2-bis(diisopropylphosphino)ethane

A novel high-yield, convenient synthetic method for the complex [Ni(COD)(2) ] has been developed based upon the use of dibutylmagnesium as reducing age nt. The cationic complexes [Ni(eta (3)-CH2C(R)CH2)(dippe)][BPh4] (R=Me 1a o r H 1b; dippe=(Pr2PCH2CH2PPr2i)-P-i) were obtained by reaction of [Ni(COD)( 2)] with BrCH2C(R)=CH2 in diethyl ether, followed by treatment with dippe a nd NaBPh4 in methanol. [Ni(2-MeInd)(dippe)][BPh4] 2 (2-MeInd=2-methylindeny l) and [Ni(C5Me5)(dippe)][BPh4] 3 were respectively prepared by reaction of either [Ni(2-MeInd)Br(PPh3)] or [Ni(C5Me5)Br(PPh3)] with dippe and NaBPh4 in methanol. The crystal structures of 1a, 2 and 3 were determined. All of the compounds show pseudo-square planar "two legged" piano stool structures . The methylallyl ligand in 1a shows eta (3) coordination as expected, wher eas in 2 the occurrence of an allyl-ene distortion in the 2-methylindenyl l igand leads to an intermediate eta (3)/eta (5) coordination mode. An interm ediate allyl-ene/diene distortion is present in the C5Me5 ligand in 3, alth ough in this case a symmetrical eta (5) coordination is observed. All compo unds were also characterised in solution by NMR spectroscopy.