Calix[4]arene derived phosphites: their hydrolytic stability and complexes with gold(I), platinum(II,0), palladium(II) and iridium(I)

Abstract

Improved syntheses of the monophosphites L_aa and L_bb derived from calix[4]arene and p-tert-butylcalix[4]arene respectively are reported. Both L_aa and L_bb are thermally stable and air stable even in refluxing toluene; moreover they are not hydrolysed by aqueous HCl or NaOH. The two-coordinate gold(I) complexes [AuCl(L_aa)] and [AuCl(L_bb)] are readily made from [AuCl(tht)] (tht = tetrahydrothiophene). Treatment of K[PtCl₃(C₂H₄)] with L_aa gives the mononuclear cis-[PtCl₂(L_aa)₂] whereas L_bb gives the binuclear trans-[Pt₂Cl₂(μ-Cl)₂(L_bb)₂]. The platinum(0) complexes [Pt(L)(nor)₂] and [Pt(L)₂(nor)] (L = L_aa or L_bb, nor = norbornene) have been characterised in solution by ³¹P and ¹⁹⁵Pt NMR spectroscopy. Treatment of [PdCl₂(NCPh)₂] with L_aa gives a poorly soluble complex assigned the structure [PdCl₂(L_aa)₂]. Treatment of [PdCl₂(NCPh)₂] with L_bb gives the binuclear [Pd₂Cl₂(μ-Cl)₂(L_bb)₂] which reacts with Y to give bridge-cleaved products [PdCl₂(Y)(L_bb)] (Y = CO, CNBu^t or CNMe). The iridium complexes [IrCl(L_aa)(cod)] and [IrCl(L_bb)(cod)] are made by the additions of L_aa or L_bb to [Ir₂(μ-Cl)₂(cod)₂]. The crystal structures of [Pt₂Cl₂(μ-Cl)₂(L_bb)₂], [Pd₂Cl₂(μ-Cl)₂(L_bb)₂], [PdCl₂(CNBu^t)(L_bb)] and [IrCl(L_aa)(cod)] have been determined. The calixarene conformation in all cases has arenes in {down, out, up, up} orientations with one aryl blocking an axial site at the square planar metal. The cone angles are 160° for L_aa and 176° for L_bb. The bulkiness of the ligand is such as to preclude octahedral geometry at the metal. The trans influence of the ligands L_aa and L_bb appear to be greater than either chloride or isocyanide. The P–O distances and the O–P–O angles imply that L_aa and L_bb are less π-acidic than most triarylphosphite ligands.