Slippage of η3-allenyl/propargyl to an η1 structure and tautomerization of η1-propargyl to η1-allenyl in ligand addition and substitution reactions of platinum(II) complexes

Reactions of [(PPh3)2Pt(η3-CH2CCPh)]OTf with each of PMe3, CO and Br− result in the addition of these species to the metal and a change in hapticity of the η3-CH2CCPh to η1-CH2CCPh or η1-C(Ph)CCH2. Thus, PMe3 affords [(PMe3)3Pt(η1-C(Ph)CCH2)]+, CO gives both [trans-(PPh3)2Pt(CO)(η1-CH2CCPh)]+ and [trans-(PPh3)2Pt(CO)(η1-C(Ph)CCH2)]+, and LiBr yields cis-(PPh3)2PtBr(η1-CH2CCPh), which undergoes isomerization to trans-(PPh3)2PtBr(η1-CH2CCPh). Substitution reactions of cis- and trans-(PPh3)2PtBr(η1-CH2CCPh) each lead to tautomerization of η1-CH2CCPh to η1-C(Ph)CCH2, with trans-(PPh3)2PtBr(η1-CH2CCPh) affording [(PMe3)3Pt(η1-C(Ph)CCH2)]+ at ambient temperature and the slower reacting cis isomer giving [trans-(PPh3)(PMe3)2Pt(η1-C(Ph)CCH2)]+ at 54 °C . All new complexes were characterized by a combination of elemental analysis, FAB mas spectrometry and IR and NMR (1H, 13C{1H} and 31P{1H}) spectroscopy. The structure of [(PMe3)3Pt(η1-C(Ph)CCH2)]BPh4·0.5MeOH was determined by single-crystal X-ray diffraction analysis.