Cyclometalated Tridentate C-N-N Ligands with an Amine or Amido Donor in Platinum(II) and Palladium(II) Complexes and a Novel Potassium Alkoxide Aggregate

The new ligand 2-phenyl-6-(2-aminoisopropyl)pyridine, papH2, was synthesized and
characterized. The corresponding Pt(II) and Pd(II) complexes Pt(papH)Cl (2) and Pd(papH)Cl (3) were synthesized and fully characterized by NMR spectroscopy and single-crystal X-ray
diffraction. In each complex the κ3N,N,C tridentate papH ligand forms two five-membered
rings with the metal, one of which is created by cyclometalation of the ortho carbon of the
phenyl group. Compound 2 was found to react with KOtBu to afford a Pt(II) amido complex
that was isolated as [Pt(pap)]2(KCl)(KOtBu)8 (4). As revealed by single-crystal X-ray
diffraction, compound 4 has a novel structure, in which two Pt(pap) moieties are attached
to the K9O8Cl “core” of the potassium alkoxide aggregate. A solution of compound 4 does not
react with H2(g), even at 3 atm and 60 °C. A hydride complex that is suspected to be Pt(papH)H was observed by reacting 2 with K[BH(sBu)3]. This hydride does not react with
acetophenone. These properties are in contrast with those of ruthenium hydrido amine/amido catalysts that readily hydrogenate acetophenone. The reaction of compound 3 with
KOtBu yielded a complicated, unidentified mixture that can be reduced to Pd(0) by 3 atm of
dihydrogen at ambient temperature.