Some complexes of rhodium(I), rhodium(II), and rhodium(III) containing tertiary t-butylphosphines as ligands

Abstract

Paramagnetic rhodium(II) complexes of the type trans-[RhCl₂(PBu^t₂R)₂](R = Me, Et, or Prⁿ) are formed rapidly by treating ethanolic rhodium(III) chloride trihydrate with the tertiary phosphine at 25 °C. The complexes have low magnetic moments in the solid state (<1·4 B.M.) but in solution trans-[RhCl₂(PBu^t₂Me)₂] has the expected moment of ca. 2·12 B.M. Treatment of rhodium trichloride trihydrate with some t-butylphosphines (L = PBu^tPrⁿ₂, PBu^t₂Me, PBu^t₂Et, or PBu^t₂Prⁿ) in refluxing propan-2-ol gives square pyramidal hydridorhodium(III) complexes [RhHCl₂L₂]. [RhHCl₂(PBu^tPrⁿ₂)₂] reacts with some ligands Q [Q = MeNC, MeCN, pyridine, or P(OMe)₃] to give complexes of type [RhHCl₂(PBu^tPrⁿ₂)₂Q]. [RhHCl₂(PBu^t₂Me)₂] reacts with hydrogen gas to give [RhH₂Cl(PBu^t₂Me)₂], and trans-[RhCl₂(PBu^t₂Me)₂] with hydrogen gas gives a ca. 1 : 1 mixture of [RhHCl₂(PBu^t₂Me)₂] and [Rh₂Cl(PBu^t₂Me)₂]. Treatment of rhodium chloride in propan-2-ol with tri-t-butylphosphine gives the five-co-ordinate dihydride [RhH₂Cl(PBu^t₃)₂]. [RhH₂Cl(PBu^tMePh)₃] was formed similarly as a mixture of enantiomers. Prolonged (7 days) treatment of hydrated rhodium trichloride in ethanol at 20 °C with di-t-butylalkylphosphines gives rhodium(I) carbonyl complexes trans-[RhCl(CO)(PBu^t₂R)₂](R = Me, Et, or Prⁿ) in ca. 75% yield. Addition of a strong base (e.g., NaOMe) to solutions of complexes of the type [RhHCl₂L₂] in ethanol or methanol gives trans-[RhCl(CO)L₂] within a few seconds. Ethanolic rhodium trichloride reacts with PHBu^t₂ to give [RhCl(PHBu^t₂)₃]. ¹H and ³¹P N.m.r., i.r., and electronic absorption spectral data are reported and discussed as are magnetic susceptibility data for the rhodium(II) complexes.