Ka. Bunten et al., Chelation kinetics of bidentate phosphine ligands on pentacoordinate ruthenium carbonyl complexes, ORGANOMETAL, 19(18), 2000, pp. 3674-3682
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.