Syntheses and characterization of binuclear Rh2, Ir2 and RhIr complexes containing dimethyl phosphonate and pyrazolate bridging ligands

Abstract

The reaction of [Ir(η⁵-C₅Me₅)I{PO(OMe)₂}{P(OH)(OMe)₂}] with pyrazole (Hpz) in the presence of AgPF₆ gave [Ir(η⁵-C₅Me₅){PO(OMe)₂}{P(OH)(OMe)₂}(Hpz)]PF₆1. Deprotonation of 1 with sodium carbonate afforded the neutral compound [Ir(η⁵-C₅Me₅){PO(OMe)₂}₂(Hpz)]2 which, in turn, can be deprotonated to [(η⁵-C₅Me₅)Ir{PO(OMe)₂}₂(pz)M′](M′= Tl 3 or Na 4) by Tl(acac)(acac = acetylacetonate) or NaH, respectively. The complex [Ir(η⁵-C₅Me₅)I₂{P(OH)(OMe)₂}]5, prepared by cleaving the iodide bridges in [{Ir(η⁵-C₅Me₅)I}₂(µ-I)₂] with HPO(OMe)₂, reacted with Hpz in the presence of AgPF₆ to give [Ir(η⁵-C₅Me₅){PO(OMe)₂}(Hpz)₂]PF₆6. Complexes of formulae [(η⁵-C₅Me₅)Ir{PO(OMe)₂}₂(pz)M″L₂][M″L₂= Rh(CO)₂7, Rh(cod)8 or Ir(cod)9] were prepared from 2 and [Rh(acac)(CO)₂] or from 3′ and the appropriate [{M″(cod)}₂(µ-Cl)₂] dimer (cod = cycloocta-1,5-diene). Complex 6 reacted with [{Rh(cod)}₂(µ-Cl)₂] in basic medium to give [(η⁵-C₅Me₅)Ir{PO(OMe)₂}(pz)₂Rh(cod)]10. The rhodium–thallium compound [(η⁵-C₅Me₅)Rh{PO(OMe)₂(pz)Tl] or the in situ prepared sodium derivative [(η⁵-C₅Me₅)Rh{PO(OMe)₂}(pz)₂Na] reacted with the dimers [{M″(diolefin)}₂(µ-Cl)₂] affording [(η⁵-C₅Me₅)Rh{PO(OMe)₂}₂(pz)M″(diolefin)][M″(diolefin)= Ir(cod)11 or Rh(nbd)12] or [(η⁵-C₅Me₅){PO(OMe)₂}Rh(pz)₂M″(diolefin)][M″(diolefin)= Rh(cod)13, Ir(cod)14 or Rh(nbd)15], respectively (nbd = bicyclo[2.2.1]hepta-2,5-diene). Related heterovalent complexes of general formula [I(η⁵-C₅Me₅)M{PO(OMe)₂}₂M″(diolefin)][M = Ir, M′(diolefin)= Rh(cod)16 or Ir(cod)17; M = Rh, M″(diolefin)= Rh(cod)18, Ir(cod)19, or Rh(nbd)20] have been prepared starting from the mononuclear complexes [M(η⁵-C₅Me₅I{PO(OMe)₂}{P(OH)(OMe)₂}](M = Ir or Rh). All the complexes have been characterized by spectroscopic means and the fluxional behaviour of 7–9, 11 and 12, in solution, has been studied. The protonation of 8 by toluene-p-sulfonic acid is reported. The structures of 8 and 16 have been determined by X-ray diffraction methods. Both complexes consist of doubly bridged binuclear (C₅Me₅)Ir–Rh(cod) species, where the Ir atoms exhibit pseudo-octahedral coordination and the rhodium square planar. The bridging system in 16 is formed by two identical P,O-bonded phosphonate groups, while in 8 a pyrazolate and a phosphonate ligand are bridging the metals. The intermetallic separations are 4.0445(9)(8) and 4.0928(9)Å(16).