1066880-32-7Relevant academic research and scientific papers
Palladium catalysed alkyne hydrogenation and oligomerisation: A parahydrogen based NMR investigation
Lopez-Serrano, Joaquin,Duckett, Simon B.,Dunne, John P.,Godard, Cyril,Whitwood, Adrian C.
, p. 4270 - 4281 (2008)
The role phosphine ligands play in the palladium(ii)-bis-phosphine-hydride cation catalysed hydrogenation of diphenylacetylene is explored through a PHIP (parahydrogen induced polarization) NMR study. The precursors Pd(LL′)(OTf)2 (1a-e) [LL′ = dcpe (PCy2CH 2CH2PCy2), dppe, dppm, dppp, cppe (PCy 2CH2CH2PPh2)] are used. Alkyl palladium intermediates of the type [Pd(LL′)(CHPhCH2Ph)](OTf) (2 and 3) are detected and demonstrated to play an active role in hydrogenation catalysis. Magnetization transfer experiments reveal chemical exchange from the α-H of the alkyl ligand of 2a (LL′ = dcpe) and linkage isomer 2e′ (LL′ = cppe) into trans-stilbene on the NMR timescale. Activation parameters (ΔH≠ and ΔS≠) for this transformation have been determined. These experiments, coupled with GC/MS data, indicate that the catalytic activity is greater in methanol, where it follows the order: dcpe > cppe > dppp > dppe > dppm, than in CD 2Cl2. All five of the phosphine systems described are less active than those based on bcope [where bcope is (C8H 14)PCH2-CH2P(C8H14)] and tbucope [where tbucope is (C8H 14)PC6H4CH2P(tBu) 2]. cis, cis-1,2,3,4-Tetraphenyl-buta-1,3-diene is detected as a minor reaction product with Pd(LL′)(PhCH-CHPh-CPh=CHPh)+ (4) also being shown to play a role in the alkyne dimerisation step.
