Sterische Stabilisierung von 20-Eletronen-Halbsandwichkomplexen. Die kristallstruktur von [(C 5H 5)Co{P(OMe) 2O} 3Ni(C 5Ph 5

Abstract

The nickel complexes [(C 5Ph 5)Ni(CO)Br] and [(C 5Ph 5)Ni(CO)(CIO 4)] react with the sodium salts Na[C 5H 5)Co{P(R) 2O} 3] in dichloromethane to yield the compounds [(C 5H 5)Co{P(R) 2O} 3Ni(C 5Ph 5] (R = OMe ( 2a), OEt ( 2b), O i Pr ( 2c)). The crystals of 2a are triclinic, space group Povbar|1 wit a 1226.4(2), b 2014.7(4), c 2047.3(4) pm, α 61.09(3), β 81.33(3), γ 89.56(3)°, Z = 4, and R = 0.042 for 9353 observed reflections. Apart from the cyclopentadienyl ring the molecules approximateto three-fold symmetry. Three OP(OMe) 2-units bridge the two metal with all three phosphoryl oxygen atom-nickel distances being equal. The 20-electron compoundsd 2a-c are stable at room temperature and paramagnetic in solution ad in the solid state. The magnetic moment of 2a and 2b in the solid state has been determined, it correponds to two unpaired electrons. The cyclovoltammograms of 2a-cdemonstrate that they can be oxidised quasi-reversibly at = + 0.26 V (vs SCE). The cations formed coud not be isolated; they decompse with elimination of the stable pentaphenylcyclopentadienyl radical and formation of the nickel (II) complex [{(C 5H 5)Co[P(R) 2] 3}Ni]. The cyclic voltammogram of [{(C 5H 5)Co[P(OEt) 2O] 3} 2Ni] shows a reversible nickel (II/III) wave at + 1.2 V (vs SCE).