Insertion of CO and Alkenes into the (methyl)Pd Complexes of the Bidentate Porphyrin Ligand

The (methyl)Pd complex of a bidentate N,21N22-1,2-diphenyletheno-bridged porphyrin
ligand, PdII(Me)(Cl)(N21,N22-(PhCCPh)(TPP)), gave the (acetyl)Pd complex PdII(C(O)Me)(Cl)(N21,N22-(PhCCPh)(TPP)) in 85% yield under atmospheric CO pressure. The acetyl−chloro site exchange in the (acetyl)Pd complex was monitored by variable-temperature NMR,
and the ΔG⧧323 value was estimated as 68 kJ mol-1. The reaction of the cationic (methyl)Pd
complex [PdII(Me)(N21,N22-(PhCCPh)(TPP))(MeCN)]ClO4 with CO gave a cationic (acetyl)(carbonyl)Pd complex which readily lost CO to give the (carbonyl)(methyl)Pd complex
[PdII(Me)(N21,N22-(PhCCPh)(TPP))(CO)]ClO4. These Pd complexes were easily characterized
by the 1H NMR spectra. The X-ray crystal structures of the (acetyl)Pd complex and the
(carbonyl)(methyl)Pd complexes were determined. Insertion of norbornadiene and norbornene
into the cationic (carbonyl)(methyl)Pd complex occurred on the exo side. Two isomers with
different orientations of the norbornenyl moiety relative to the bidentate porphyrin ligand
were observed at low temperature, and isomerization by a ligand rotation mechanism
occurred at room temperature to give a single isomer.