Preparation and Reactions of 3-C4H7)(Ph2PCH2CH2PPh2-κ2P)(Ph2PCH2CH2PPh2-κP)>: the Intramolecular Interconversion between η3-2-Methylallyl and η4-Trimethylenemethane Ligands

Article abstract of DOI:10.1039/DT9940000767

The complex 3-C4H7)(dppe-κ²P)(dppe-κP)> (dppe = Ph2PCH2CH2PPh2) has been prepared.Variable-temperature 1H, 13C and 31P NMR spectroscopy demonstrates that this 16-electron, η³-2-methylallyl species (the dominant form at 25 deg C) rapidly interconverts, intramolecularly, to the 18-electron, η⁴-trimethylenemethane species, 4-C4H6)(dppe-κ²P)(dppe-κP)> (the dominant form at -80 deg C).Protonation of 3-C4H7)(dppe-κ²P)(dppe-κP)> with HCl at 25 deg C gives stoichiometric yields of 2P)2> and t-BuCH2C(Me)CH2.Stopped-flow spectrophotometric studies of the protonation reaction indicate that the alkene formation involves rapid protonation of the molybdenum to give 3-C4H7)(dppe-κ²P)(dppe-κP)>(+), which undergoes rate-limiting intramolecular hydrogen migration to form 2-Me2C=CH2)(dppe-κ²P)2>(+).Subsequent formation of t-BuCH2C(Me)=CH2 occurs rapidly and is not amenable to kinetic analysis.However, the dimerisation is too fast to be catalysed by the excess of HCl alone, and a mechanism involving formation of t-BuCH2C(Me)=CH2 at the molybdenum centre is proposed.

Full text of DOI:10.1039/DT9940000767

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