301ChemInform Abstract The title diphosphine (II) is obtained as shown. Its 1:1 molar reaction with PdCl2(NCPh)2 leads to the mononuclear cis-complex (III). Substitution of the 2-(diphenylphosphino)pyridine ligands in the binuclear complex (IV) with one or two equiv. of the diphosphine yields the diphosphine complexes (V) and (VIa) (X: Cl). By metathetic reactions the last is converted into its derivatives (VIa) (X: Br,I, NCO). The analogue (VIb) with two different diphosphines are obtained from (V). Of the dinuclear Pd2Cl2 species, only (VIb) reacts with CO in solution to form reversibly the A-frame complex (VII). Molecular and crystal structures of the mononuclear complex (III) (space group P1, Z=4), and of the dinuclear complex (VIa) (X: Cl; Fdd2, Z=16) are determined by X-ray analysis. The last is onlyobtained in its anti-form.
The kinetic and thermodynamic parameters for the reversible insertion of carbon monoxide into the palladium-palladium bond of Pd2(dpm)2X2 complexes (dpm = Ph2PCH2PPh2; X = Cl, Br, I, NCO) in iVJV-dimethylacetamide solution have been determined by spectrophotometric methods. The forward reaction is first order in both Pd2 and CO and occurs on the stopped-flow time scale at around ambient temperatures, the rate constants being similar for the four systems (3.15-6.60) X 103 M"1 11s-1 at 24 °C. The equilibrium constants, estimated by kinetic and/or static methods, decrease in the order X = NCO > Cl > Br > I (from 3.7 X 105 to 1.3 X 103 M"1 at 24 °C) and are governed largely by the first-order off-rates, which probably depend more on a weakening of the Pd-CO bonds throughout the series than changes in the metal-metal bond strength. A correlation between In for the off-rates and the energy of a high intensity UV band of the Pd2(dpm)2X2 complexes is noted. The CO addition to give Pd2(dpm)2(/u-CO)X2 occurs because of the exothermicity of the reaction that is unfavorable in terms of AS; an approximate value of 90-120 kJ mol"1 is estimated for the Pd-Pd bond strength. The systems show high selectivity for binding of CO in the presence of H2, C2H2, C2H4, C02, 02, or air.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.