Selective Ethylene Dimerization by Palladium(II) Complexes Bearing a Phosphinoferrocene Sulfonate Ligand

• Published in: Organometallics 2019-04, Vol.38 (7), p.1534-1543
• Main Authors: Zábranský, Martin, Oberhauser, Werner, Manca, Gabriele, Císařová, Ivana, Štěpnička, Petr
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/acs.organomet.9b00015

Palladium­(II) complexes featuring the hybrid anionic ligand 1′-(diphenylphosphino)­ferrocene-1-sulfonate (L –), viz., trans-(Et3NH)2[Pd­(μ-Cl)­Me­(L-κP)]2 (1), [Pd­(Me)­(dmap-κN 1)­(L-κ2 O,P)]­(2; dmap = 4-(dimethylamino)­pyridine), and [Pd­(η3-allyl)­(L-κ2 O,P)] (6), were synthesized and together with the previously reported compounds trans-(Et3NH)2[PdCl2(L-κP)2] and [Pd­(LCY)­(L-κ2 O,P)] (LCY = 2-[(dimethylamino-κN)­methyl]­phenyl-κC 1 and 2-[(methylthio-κS)­methyl]­phenyl-κC 1) tested as precatalysts for Pd-catalyzed ethylene dimerization. Only compound 1 gave rise to an active catalyst after activation by sequential halogen removal with Tl­[PF6] and Na­[BAr′4] (Ar′ = 3,5-bis­(trifluoromethyl)­phenyl) in chloroform. Thus, the formed catalyst efficiently mediated the dimerization of ethylene showing both good activity (TOF ≈ 95 h–1) and high selectivity for 1-butene (95%) at 21 °C and 30 bar of ethylene pressure. DFT calculations have shown that the dimerization reaction is thermodynamically preferred over the formation of higher oligomers and that O,P-chelate coordination of the phosphinosulfonate ligand in all Pd­(II) reaction intermediates is vital for the catalytic process. In particular, the O,P-chelating phosphinoferrocene sulfonate ligand stabilizes and electronically differentiates the reaction intermediates and favors concerted ethyl migration to coordinated ethylene giving rise to 1-butene.