Research Output
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Publication
Synthesis of a sterically modulated pyridine-NHC palladium complex and its reactivity towards ethylene
2012-08-01, Khlebnikov, Vsevolod, Meduri, Angelo, Müller-Bunz, Helge, Milani, Barbara, Albrecht, Martin
A new cationic pyridine-carbene palladium complex has been prepared that features a C,N-bidentate coordinating ligand with a shielded pyridine and a sterically less protected carbene moiety; evaluation of this complex in ethylene polymerization revealed competitive reductive elimination processes and provides guidelines for further catalyst design.
Publication
Palladium carbene complexes for selective alkene di- and oligomerization
2012-01-13, Khlebnikov, Vsevolod, Meduri, Angelo, Müller-Bunz, Helge, Montini, Tiziano, Fornasiero, Paolo, Zangrando, Ennio, Milani, Barbara, Albrecht, Martin
A series of palladium complexes were synthesized that comprise three sterically different C,N-bidentate coordinating NHC-pyridine ligands (NHC = N-heterocyclic carbene). In one set, the pyridine and the carbene are linked by a flexible CH2 group (a), in the other two sets, the two ligand units are directly linked and feature a shielding mesityl substituent on the carbene and either an unsubstituted pyridine (b) or a xylyl-substituted pyridine unit (c). Investigation of the reactivity of cationic complexes [Pd(C^N)Me(NCMe)]+, 6, analogues to Brookhart’s α-diimine system, towards alkenes showed a strong correlation between the catalytic activity and selectivity and the ligand setting. While 6a was inactive in ethylene conversion, 6b afforded low-molecular weight olefins (oligomerization), and 6c produced exclusively butene (dimerization). With styrene as substrate, exclusive dimerization occurred with all three complexes. Steric and electronic factors were identified that govern the disparate activity and selectivity, and that allow for efficient tailoring of the catalytic performance.