145332-52-1Relevant 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 (2009/02/03)
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.
Self-assembly and anion encapsulation properties of cavitand-based coordination cages
Fochi,Jacopozzi,Wegelius,Rissanen,Cozzini,Marastoni,Fisicaro,Manini,Fokkens,Dalcanale
, p. 7539 - 7552 (2007/10/03)
Two novel classes of cavitand-based coordination cages 7a-j and 8a-d have been synthesized via self-assembly procedures. The main factors controlling cage self-assembly (CSA) have been identified in (i) a P-M-P angle close to 90° between the chelating ligand and the metal precursor, (ii) Pd and Pt as metal centers, (iii) a weakly coordinated counterion, and (iv) preorganization of the tetradentate cavitand ligand. Calorimetric measurements and dynamic 1H and 19F NMR experiments indicated that CSA is entropy driven. The temperature range of the equilibrium cage-oligomers is determined by the level of preorganization of the cavitand component. The crystal structure of cage 7d revealed the presence of a single triflate anion encapsulated. Guest competition experiments revealed that the encapsulation preference of cages 7b,d follows the order BF4- > CF3SO3- ? PF6- at 300 K. ES-MS experiments coupled to molecular modeling provided a rationale for the observed encapsulation selectivities. The basic selectivity pattern, which follows the solvation enthalpy of the guests, is altered by size and shape of the cavity, allowing the entrance of an ancillary solvent molecule only in the case of BF4-.
