The donor properties of 1,8-bis(diphenylphosphino)-3,6-dioxaoctane towards cationic rhodium(I) salts revisited. X-Ray structural characterization of a quadridentate mode of bonding

Article abstract of DOI:10.1016/0022-328X(94)80057-X

The <(dppoo)Rh(COD)>⁺ cation (dppoo=(Ph2PCH2CH2OCH2)2) reacts with chloroform at room temperature to give ⁺, whose structure has been established by X-ray structural determination on .The dppoo ligand adopts a planar η⁴ mode of bonding, the two chlorine atoms being in the trans position. <(dppoo)Rh(COD)> (2) reacts with dihydrogen at atmospheric pressure to give <(dppoo)Rh> (4) in which dppoo adopts the same mode of bonding, as deduced from spectroscopic data.The formation of 4 involves the transient formation of unstable <(dppoo)Rh(H)2> which has been detected by nuclear magnetic resonance (NMR) spectroscopy.Under carbon monoxide, <(dppoo)Rh(CO)2> (6) is formed, and is readily decarbonylated to <(dppoo)Rh(CO)> (7) under vacuum.In 6, dppoo is trans bidentate.In 7, low temperature NMR experiments imply an equilibrium between η³ and η⁴ bonding for dppoo. 2 is a poor catalyst for the hydrogenation of alkynes and ketones and shows a low activity towards the hydroformylation of 1-hexene.Key words: Rhodium; Hydrogenation; Hydroformylation; Phosphine ether