Kinetics of phosphine substitution in cyclopentadienylruthenium bis(triarylphosphine)chlorides CpRu(PAr3)2Cl (Ar = m-tolyl, m-fluorophenyl, m-anisyl, p-chlorophenyl) and Cp’Ru(PPh3)2Cl (Cp’ = CH3C5H4 and CH3C(O)C5H4)

• Kinetic measurements on six η 5 -RC 5 H 4 Ru(PAr 3 ) 2 Cl compounds reveal that m-substituted Ar groups on the PAr 3 show little rate enhancement over the corresponding p-substituted tertiary phosphine ligands. • Both electron donating and electron withdrawing groups R onn the η 5 -RC 5 H 4 ligands do increase the reaction rate. • Any rate effects of the Ar group in the PAr 3 or R on the η 5 -RC 5 H 4 ligands depends on the σ-donating and π-accepting properties of the tri(aryl)phosphine ligands. Reactions between CpRu(PAr 3 ) 2 Cl (Ar = m -CH 3 C 6 H 4 1a , m -FC 6 H 4 1b , and m -CH 3 OC 6 H 4 1c ) and PMePh 2 yield the corresponding mono-substituted products, CpRu(PAr 3 )(PMePh 2 )Cl ( 2a-c ). Kinetic measurements for the reaction in CDCl 3 under pseudo-first order conditions yield values for k obs ranging from 22.2±0.2 × 10 -6 to 5.41±0.24 × 10 –6 s –1 . Activation parameters, ∆H † and ∆S † , range from 93±7 to 116±12 kJ/mol and –38±56 to 39±40 J/mol-K, respectively. The relative rates follow the order 1a > 1b > 1c . The rate constants for 1a-c are similar to k obs for CpRu(PAr 3 ) 2 Cl where Ar = p -CH 3 C 6 H 4 3a , p -FC 6 H 4 3b , and p -CH 3 OC 6 H 4 3c, suggesting that there is little or no steric effect of the m- vs p- position of the substituent on the Ar group. The rate of phosphine substitution in CpRu[P( p- ClC 6 H 4 ) 3 ] 2 Cl ( 1d ) is slower than for 3a-3c . Despite different electronic properties (E 1/2 ), similar rates are observed for reactions of (MeC 5 H 4 )Ru(PPh 3 ) 2 Cl ( 1e ) and (C 5 H 4 C(O)Me)Ru(PPh 3 ) 2 Cl ( 1f ) with PMePh 2 . Taken together, the data suggest that the rates of phosphine substitution in (η 5 -RC 5 H 4 )Ru(PAr 3 ) 2 Cl complexes depends on a combination of σ-donor and π-acceptor properties of the PAr 3 ligands.