Cyclometalation at carbon adjacent to oxygen in platinum(II) and iridium(I) phosphine complexes

Abstract

Heating trans-PtCl 2(t-Bu 2PCH 2OCH 3) 2 at 125°C in 2-methoxyethanol yields a cyclometalated derivative, P tCl(t-Bu 2PCH 2OCH 2)(t-Bu 2PCH 2OCH 3). Adding excess NaI and 1,8-bis(dimethylamino)naphthalene accelerates the reaction and gives the iodide-substituted analog. Under the same conditions, trans-PtCl 2(t-Bu 2POCH 2CH 3) 2 is also metalated at the methyl carbon atom. However, the slower rate of this reaction indicates that an α-oxygen atom has an electronic accelerating effect on the metalation process. Neither t-Bu 2POCH 3 nor t-Bu 2PCH 2CH 2OCH 3 give platinum(II) cyclometalated complexes; four- or six-membered chelate ring formation appears to be unfavorable. The t-Bu 2PCH(CH 3)OCH 3 ligand also does not yield a platinum(II) metalated derivative. However, [IrCl(COT) 2] 2 (COT = cyclooctene) reacts at 25°C with both t-Bu 2PCH 2OCH 3 and t-Bu 2PCH(CH 3)OCH 3, to form iridium(III) metalated complexes by oxidative addition to the methyl CH bond. These coordinatively unsaturated compounds react with CO, yielding octahedral iridium(III) carbonyl hydride complexes.