Chelation Kinetics of Bidentate Phosphine Ligands on Pentacoordinate Ruthenium Carbonyl Complexes

Abstract

Chelation kinetics of the complexes Ru(CO) 4 (η 1 -(P-P)) have been studied in heptane, where P-P ) Ph 2 P(CH 2 ) n PPh 2 (n ) 1, 2, 3, or 4, i.e., dppm, dppe, dppp, or dppb), Ph 2 P(NMe)PPh 2 (dppma), Ph 2 P(o-C 6 H 4 )PPh 2 (dpp-benzene), or R 2 P(CH 2 ) 2 PR 2 (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 (C 2 H 4 ), which itself was prepared in situ by photolysis of Ru 3 (CO) 12 under C 2 H 4 . The initially formed Ru(CO) 4 (η 1 -(P-P)) complexes react cleanly to form axial-equatorial Ru-(CO) 3 (η 2 -(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 Ru 2 -(CO) 3 (µ-PPh 2 )(µ-Ph 2 PNMePPh 2 ). The kinetics of the displacement of CO from Ru(CO) 4 (η 1 -(P-P)) in n-heptane are characterized by ∆H q values that are lower by up to 9 kcal mol -1 than those of their monodentate P-donor analogues. ∆S q 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 e dppm ≈ dppbu ≈ dppe , dppma. This contrasts with the CO-dissociative reactions of analogous Ru(CO) 4 L complexes when L ) monodentate P-donor ligands.

Synthesis and reactivity of silylated tetrathiafulvalenes

“…These data also match well with those reported for [Ru(CO) 4 (g 1 -dppm)] (d 39.8 and −25.7; 2 J P-P = 91 Hz). 37 CV experiments performed in CH 2 Cl 2 at a scan rate of 100 mV s −1 on compounds 14 and 15 evidence the same electrochemical behaviour as previously encountered for [{Pt(PPh 3 ) 2 } 2 {l-(Me 2 Si) 4 TTF}]. For both systems, two reversible oxidation waves are observed.…”

Tetrathiafulvalene–phosphine-based iron and ruthenium carbonyl complexes: Electrochemical and EPR studies

“…The infrared spectrum shows the three characteristic bands of a [Ru(L2)(CO) 3 ] complex, where L2 is a chelating diphosphine. 28,29 The fluxional behavior of the complex in solution is evidenced by the unique resonance in 31 P NMR spectrum and the triplet observed for the carbonyl carbon atoms in 13 C NMR spectrum. As in the case of pentacoordinate iron complexes, 30,31 the corresponding ruthenium complexes show a fast interconversion occurring in solution at the NMR time scale, between a trigonal bipyramidal and a square pyramidal geometry.…”

Mechanistic Studies on the Formation of η2-Diphosphine (η6-p-cymene)ruthenium(II) Compounds

“…While the use of bidentate phosphine ligands is prevalent in the coordination chemistry of the transition metals, it is interesting to note that the actual process of forming these complexes has received relatively little attention. The chelation reactions for a variety of bidentate phosphine ligands on metal carbonyl complexes of group VI (eq 1) and recently in those of ruthenium (eq 2) have previously been investigated and found to proceed with varying degrees of bond breaking and making. For ruthenium, entropies of activation range from 63 to −13 J mol -l K -1 and were taken to imply a mechanism with predominately dissociative to significantly associative character along the series PPh 2 ( o -C 6 H 4 )PPh 2 < Cy 2 P(CH 2 ) 2 PCy 2 < Me 2 P(CH 2 ) 2 PMe 2 < dppp ≤ dppm ≈ dppb ≈ dppe ≪ PPh 2 (NMe)PPh 2 .…”