Chelation kinetics of bidentate phosphine ligands on pentacoordinate ruthenium carbonyl complexes

Chelation kinetics of the complexes Ru(CO)(4)(eta(1)-(P-P)) have been studi ed 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)(2)PR2 (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 Ru-3(CO)(12) under C2H 4. The initially formed Ru(CO)(4)(eta(1)-(P-P)) complexes react cleanly to form axial-equatorial Ru(CO)(3)(eta(2)-(P-P)), as shown by the crystallogra phic 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 sta te, and the product when P-P = dppma has been characterized by crystallogra phy as Ru-2-(CO)(3)(mu-PPh2)(mu-Ph2PNMePPh2). The kinetics of the displacem ent of CO from Ru(CO)(4)(eta(1)-(P-P)) in n-heptane are characterized by De lta H-double dagger values that are lower by up to 9 kcal mol(-1) than thos e of their monodentate P-donor analogues. Delta S-double dagger values rang e from quite positive to slightly negative and suggest a trend from purely dissociative to appreciably associative mechanisms along the series P-P = d pp-benzene < dcpe < dmpe < dppp less than or equal to dppm approximate to d ppbu approximate to dppe much less than dppma. This contrasts with the GO-d issociative reactions of analogous Ru(CO)(4)L complexes when L = monodentat e P-donor Ligands.