Tertiary phosphines with pendant arenes R2PR' (R = Cy, Ph; R' = CH2CH2Ph or CH2CHPh2) (1-4) were synthesized and converted to the corresponding chelating ruthenium(II) complexes [RuCl2(eta(1):eta(6)-R2PR')] (1a-4a). Halide exchange yielded [RuI2(eta(1):eta(6)-R2PR')] (1b,3b), which were structurally characterized by single crystal X-ray diffraction. The systems (la,2a,4a) were activated for ROMP of norbornene by addition of a diazo compound (trimethylsilyldiazomethane) and AgBF4 (A), by a diazo compound alone (B) or by a combination of the sodium salt NaB(Ar-f)(4)(Ar-f = 3,5-(CF3)(2)C6H3) and methanol (C). The influence of the thereby created differing number of accessible coordination sites on the polymerization activity and the polymer microstructure (cis/trans ratio) was investigated. The nucleophilicity of the counter ion was found to play a crucial role in terms of catalytic activity.