Stabilization of the tautomers HP(OH)2 and P(OH)3 of hypophosphorous and phosphorous acids as ligands

Abstract

Treatment of [CpRu(PPh₃)₂Cl] 1 with the stoichiometric amount of H₃PO₂ or H₃PO₃ in the presence of chloride scavengers (AgCF₃SO₃ or TlPF₆) yields compounds of formula [CpRu(PPh₃)₂(HP(OH)₂)]Y (Y = CF₃SO₃2a or PF₆2b) and [CpRu(PPh₃)₂(P(OH)₃)]Y (Y = CF₃SO₃3a or PF₆3b) which contain, respectively, the HP(OH)₂ and P(OH)₃ tautomers of hypophosphorous and phosphorous acids bound to ruthenium through the phosphorus atom. The triflate derivatives 2a and 3a react further with hypophosphorous or phosphorous acids to yield, respectively, the complexes [CpRu(PPh₃)(HP(OH)₂)₂]CF₃SO₃4 and [CpRu(PPh₃)(P(OH)₃)₂]CF₃SO₃5 which are formed by substitution of one molecule of the acid for a coordinated triphenylphosphine molecule. The compounds 2 and 3 are quite stable in the solid state and in solutions of common organic solvents, but the hexafluorophosphate derivatives undergo easy transformations in CH₂Cl₂: the hypophosphorous acid complex 2b yields the compound [CpRu(PPh₃)₂(HP(OH)₂)]PF₂O₂6, whose difluorophosphate anion originates from hydrolysis of PF₆⁻; the phosphorous acid complex 3b yields the compound [CpRu(PPh₃)₂(PF(OH)₂)]PF₂O₂7, which is produced by hydrolysis of hexafluorophosphate and substitution of a fluorine for an OH group of the coordinated acid molecule. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structures of 2a, 3a and 7 have been determined by X-ray diffraction methods.