Chelation Kinetics of Bidentate Phosphine Ligands on Pentacoordinate Ruthenium Carbonyl Complexes

• Published in: Organometallics 2000-09, Vol.19 (18), p.3674-3682
• Main Authors: Bunten, Kevin A, Farrar, David H, Poë, Anthony J, Lough, Alan J
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om000289t

Chelation kinetics of the complexes Ru(CO)4(η1-(P−P)) have been studied in heptane, where P−P = Ph2P(CH2) n PPh2 (n = 1, 2, 3, or 4, i.e., dppm, dppe, dppp, or dppb), Ph2P(NMe)PPh2 (dppma), Ph2P(o-C6H4)PPh2 (dpp-benzene), or R2P(CH2)2PR2 (R = Me or Cy, i.e., dmpe or dcpe). The complexes were prepared in situ by reaction of the bidentate ligands with Ru(CO)4(C2H4), which itself was prepared in situ by photolysis of Ru3(CO)12 under C2H4. The initially formed Ru(CO)4(η1-(P−P)) complexes react cleanly to form axial−equatorial Ru(CO)3(η2-(P−P)), as shown by the crystallographic structures of the products when P−P = dppe, dmpe, and dpp-benzene and the close similarity of their FTIR spectra to those of the other products. The chelated products undergo further reaction in solution or the solid state, and the product when P−P = dppma has been characterized by crystallography as Ru2(CO)3(μ-PPh2)(μ-Ph2PNMePPh2). The kinetics of the displacement of CO from Ru(CO)4(η1-(P−P)) in n-heptane are characterized by ΔH ⧧ values that are lower by up to 9 kcal mol-1 than those of their monodentate P-donor analogues. ΔS ⧧ values range from quite positive to slightly negative and suggest a trend from purely dissociative to appreciably associative mechanisms along the series P−P = dpp-benzene < dcpe < dmpe < dppp ≤ dppm ≈ dppbu ≈ dppe ≪ dppma. This contrasts with the CO-dissociative reactions of analogous Ru(CO)4L complexes when L = monodentate P-donor ligands.