Styrene Cyclopropanation and Ethyl Diazoacetate Dimerization Catalyzed by Ruthenium Complexes Containing Chiral Tridentate Phosphine Ligands

Abstract

Various five-coordinate ruthenium(II) complexes of the general formula RuCl 2 L, where L is a chiral triphosphine ligand, have been tested as catalyst precursors for the cyclopropanation of styrene using ethyl diazoacetate (EDA) as the carbene source. Some of the complexes investigated have been found to catalyze the cyclopropanation reaction, but the conversions to cyclopropanes and the diastereoselectivities were generally poor. With all the catalyst precursors investigated, the dimerization of ethyl diazoacetate to diethyl maleate or diethyl fumarate largely prevailed over cyclopropanation. The best performance was obtained with the complex RuCl 2 (ttp*) (2; ttp* ) (S,S)-PhP(CH 2 CHMeCH 2 PPh 2 ) 2 ) which gave ca. 21% of cyclopropanes, 42% of olefins, and 1% of metathesis products. The highest enantiomeric excess was 35% for the (Z)-2-phenylcyclopropanecarboxylate. In the presence of silver triflate, 2 gave rise to a much more active and selective catalyst system, as the yield in cyclopropanation products increased up to 84%. Neither the regioselectivity nor the diastereoselectivity was appreciably improved, however. The carbene complexes RuCl 2 (ttp*)(dCHCO 2 Et) and RuCl 2 (ttp)(dCHCO 2 Et), where ttp is the achiral ligand PhP(CH 2 CH 2 CH 2 PPh 2 ) 2 , were isolated and characterized by multinuclear NMR spectroscopy. These carbene complexes were found to react with an excess of ethyl diazoacetate to give exclusively diethyl maleate and diethyl fumarate in a 95:5 ratio. The selective formation of cyclopropanation products was conversely observed upon reaction with styrene in the presence of silver triflate. In the absence of a chloride scavenger, cyclopropanes were still formed together with an appreciable amount of the metathesis product PhHCdCHCO 2 Et.

N-Propylphthalimide-Substituted Silver(I) N-Heterocyclic Carbene Complexes and Ruthenium(II) N-Heterocyclic Carbene Complexes: Synthesis and Transfer Hydrogenation of Ketones

“…Recently, the newly synthesized Ru complexes have provided with particularly ligands to maintain a compatible equilibrium between the electronic and steric environment around the metal and to control on their stability, activity and chemoselectivity profiles [19][20][21][22][23][24][25][26][27][28][29][30]. Typically, most of NHC ligands emerge quite suitability with heteroatom including air, moisture and functional groups, thus expanding areas of application [31] in the many organic transformations.…”

Alkane Catalytic Functionalization by Carbene or Nitrene Insertion Reactions

“…A series of Fe, Ru and Os carbene complexes have been reported by the groups of Collman [31], Woo [32][33][34], Che [35][36][37], Simonneaux [38] (Scheme 6.6b). Nishiyama (Scheme 6.6c) [39] and Bianchini (Scheme 6.6d) [40] independently reported the formation of ruthenium and osmium carbene complexes with pybox and triphosphine ligands, respectively. Mezzetti has employed a PNNP ligand to detect a ruthenium-carbene complex (Scheme 6.6e) [41] involved in the imine aziridination reaction.…”

Kupfer‐Carben‐Komplexe: hochentwickelte Katalysatoren, neue Erkenntnisse

“…Aus Metall-Porphyrinen (M = Fe, [7] Ru [8] und Os [9] ) erhielt man jedoch zahlreiche Carben-Komplexe 13, in denen das Carben-Kohlenstoffatom ausschließlich am Metall gebunden ist. Dreizähnige Amin-und Phosphinliganden wurden zur Herstellung der Carben-Komplexe 14 [10] und 15 [11] verwendet. Röntgenstrukturanalysen sichern die Konstitution derartiger Verbindungen.…”