Isonicotinamide as entering ligand on trans-[Ru(NH 3) 4P(OR) 3(H 2O)]2 2+, (R = Me, Pr, iPr and Bu)

Abstract

trans-[Ru(NH 3) 4P(OR) 3(H 2O)] 2+ (R = Me, Pr, iPr, and Bu) reacts with isonicotinamide at second-order- specific rates k 1 of 1.2, 2.3, 7.4 and 8.1 M −1 s −(25 °C, μ = 0.10 NaCF 3COO/CH 3COOH), respectively, for R = Me, Pr, iPr and Bu. The products trans- [Ru(NH 3) 4P(OR) 3isn](PF 6) 2 have been isolated and characterized by micro analysis, cyclic voltammetry, and electronic spectral data. The aquation rates k −1 for the isonicotinamide (isn) derivatives are 5.2 × 10 −2, 5.9 × 10 −2, 2.0 × 10 −1 and 3.4 × 10 −1 s −1 for R= Me, Pf, Bu and iPr, respectively. The activation parameters for the forward and backward reactions indicate the same mechanism for all of them. The substitution proceeds by a dissociative mechanism with a significant outer-sphere association of trans-[Ru(NH 3) 4P(OR) 3(H 2O)] 2+ complexes with isn. Assuming k 1 as indicative of the lability of the coordinated water molecule on the monophosphite complexes, the following sequence of increasing trans-effect mav be proposed: P(OMe) 3 <P(OEt) 3 <P(OPr) 3 <P(O iPr) 3 <P(OBu) 3. The affinity of the monophosphite complexes for isn increases according to P(OMe) 3 ⋍ P(O iPr) 3 < P(OEt) 3 < P(OPr) 3 ⋍ P(OBu) 3.