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

Improved syntheses of the monophosphites L-a and L-b derived from calix[4]arene and p-tert-butylcalix[4]arene respectively are reported. Both L-a and L-b 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-a)] and [AuCl(L-b)] are readily made from [AuCl(tht)] (tht = tetrahydrothiophene). Treatment of K[PtCl3(C2H4)] with L-a gives the mononuclear cis-[PtCl2(L-a)(2)] whereas L-b gives the binuclear trans-[Pt2Cl2(mu-Cl)(2)(L-b)(2)]. The platinum(0) complexes [Pt(L)(nor)(2)] and [Pt(L)(2)(nor)] (L = L-a or L-b, nor = norbornene) have been characterised in solution by P-31 and Pt-195 NMR spectroscopy. Treatment of [PdCl2(NCPh)(2)] with L-a gives a poorly soluble complex assigned the structure [PdCl2(L-a)(2)]. Treatment of [PdCl2(NCPh)(2)] with L-b gives the binuclear [Pd2Cl2(mu-Cl)(2)(L-b)(2)] which reacts with Y to give bridge-cleaved products [PdCl2(Y)(L-b)] (Y = CO, CNBut or CNMe). The iridium complexes [IrCl(L-a)(cod)] and [IrCl(L-b)(cod)] are made by the additions of L-a or L-b to [Ir-2(mu-Cl)(2)(cod)(2)]. The crystal structures of [Pt2Cl2(mu-Cl)(2)(L-b)(2)], [Pd2Cl2(mu-Cl)(2)(L-b)(2)], [PdCl2(CNBut)(L-b)] and [IrCl(L-a)(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 degrees for L-a and 176 degrees for L-b. The bulkiness of the ligand is such as to preclude octahedral geometry at the metal. The trans influence of the ligands L-a and L-b appear to be greater than either chloride or isocyanide. The P-O distances and the O-P-O angles imply that L-a and L-b are less pi-acidic than most triarylphosphite ligands.