Steric factors affecting the additions of acids to complexes of type trans-[IrCl(CO)(PButR2)2] and trans-[IrCl(CO)(PBut2R)2](R = Me, Et, or Prn)

Abstract

New complexes of the types [IrHX₂(CO)L₂] and trans-[IrX(CO)L₂]{X = Cl or Br, L = PBu^tR₂ or PBu^t₂R (R = Me, Et, or Prⁿ)} have been prepared. With L = PBu^tR₂ or PBu^t₂Me the complexes [IrHCl₂(CO)L₂] were readily converted into trans-[IrCl(CO)L₂] by treatment with sodium methoxide in methanol. The complexes [IrHCl₂(CO)L₂](L = PBu^t₂Et or PBu^t₂Prⁿ) lose hydrogen chloride in ethanol to give trans-[IrCl(CO)L₂]. Although trans-[IrCl(CO)(PBu^tMe₂)₂] undergoes metathesis readily with sodium iodide to give trans-[Irl(CO)(PBu^tMe₂)₂], other complexes of this type require much longer treatment to affect metathesis, e.g. trans-[IrCl(CO)(PBu^t₂Prⁿ)₂] requires 18 h in boiling acetone. Treatment of trans-[IrX(CO)L₂](X = Cl or Br, L = PBu^tPrⁿ₂ or PBu^t₂Prⁿ) with sodium isopropoxide in propan-2-ol, followed by water, gives the corresponding hydroxo-complexes, trans-[Ir(OH)(CO)L₂]. These hydroxo-complexes readily undergo metathesis when treated with a variety of sodium salts, NaX, to give trans-[IrX(CO)L₂](X = Cl, Br, I, N₃, NCO, NCS, NO₂ or NO₃). Complexes of the type trans-[IrCl(CO)L₂] are protonated reversibly by benzoic acid (L = PBu^tR₂) or hydrochloric acid (L = PBu^t₂R) and the position of equilibrium measured spectrophotometrically. The relative order of the extent of protonation is L = PMe₂Ph > PBu^tMe₂ > PBu^tEt₂ > PBu^tPrⁿ₂ > PBu^t₂Me > PBu^t₂Prⁿ > PBu^t₂Et, i.e. the bulky t-butyl group has a marked effect. The extent of addition of hydrogen chloride to trans-[IrCl(CO)(PBu^t₂Et)₂] in ethanol–benzene solution is increased by increasing the chloride ion concentration (with lithium chloride). In contrast, nitrate ion inhibits the addition and trans-[IrCl(CO)(PBu^t₂Et)₂] shows much less affinity for nitric acid than for hydrochloric acid. I.r. and ¹H n.m.r. data are given and discussed.