β-Hydride Elimination from Methoxo vs. Ethyl Ligands: Thermolysis of (DPPE)Pt(OCH3)2, (DPPE)Pt(CH2CH3)(OCH3) and (DPPE)Pt(CH2CH3)2

Article abstract of DOI:10.1021/ja00276a018

Thermolysis of (DPPE)Pt(OCH3)2 (1) (DPPE=1,2-bis(diphenylphosphino)ethane, (C6H5)2PCH2CH2P(C6H5)2) at 25 deg C leads to a mixture of methanol, formaldehyde oligomers, and small amounts of carbon monoxide (CO).Kinetics experiments, labeling studies, and solvent effects suggest this decomposition proceeds by initial preequilibrium β-hydride migration to the metal followed by rate-limiting release of organic products.While 1 decomposes at 25 deg C and (DPPE)Pt(CH2CH3)2 only slowly releases ethylene and ethane at 160 deg C, (DPPE)Pt(CH2CH3)(OCH3) (3) decomposes to a mixture of ethylene, ethane, methanol, and formaldehyde oligomers at 100 deg C.The predominance of ethylene over ethane suggests thermolysis proceeding by β-elimination from the ethyl ligand is energetically easier than the comparable process from the methoxo ligand by 0.3 kcal/mol.Labeling studies confirm the preequilibrium nature of this β-elimination.The relative M-C vs.M-O bond strengths are discussed in light of this information.