Chiral Ru-Based Complexes for Asymmetric Olefin Metathesis:  Enhancement of Catalyst Activity through Steric and Electronic Modifications

Abstract

Design, synthesis, characterization, and catalytic activity of six enantiomerically pure Ru-based metathesis catalysts are disclosed (3a-3f). The new chiral catalysts were prepared through steric and electronic alterations of the parent catalyst system (3). The present studies indicate that the effect of structural modifications of chiral complex 3 does not always correspond to those of the related achiral complexes. The present findings illustrate that modified Ru complexes (3e and 3f) deliver reactivity levels that are more than 2 orders of magnitude higher than 3. Reactivity and physical data are provided that shed light on the origin of activity differences. Some members of the new generation of chiral Ru catalysts promote asymmetric ring-opening (AROM) and ring-closing (ARCM) metatheses that cannot be effected by the first generation chiral catalyst (3).

Origins of Initiation Rate Differences in Ruthenium Olefin Metathesis Catalysts Containing Chelating Benzylidenes

“…1-Isopropoxy-4-nitro-2-vinylbenzene (S19) 23 was equally effective. Analytical data were in agreement with published data.…”

Synthesis of novel N-heterocyclic carbene-Rh complexes derived from L-proline and their catalysis in the addition of arylboronic acids to aldehydes

“…HRMS also confirmed the proposed structure. 6e was selected for the synthesis of NHC-Rh complex because it has a bulky mesityl group on N-atom which had previously been shown to be superior over other substituents in catalysis 9 . The addition of organometallic reagents to aldehydes has been one of the general methods for the synthesis of secondary alcohols.…”

“…The reaction was sensitive to changes in rhodium source. With 1 mol% of 6e and 0.5 mol% rhodium salt as the catalyst, [Rh(COD)Cl] 2 gave the alcohol in 95% yield ( 8,9). The catalyst loading has also important effect on yield.…”

Asymmetric catalysts for stereocontrolled olefin metathesis reactions

“…This class found wide applications in AROCM processes; a sufficient level of activity was obtained by structural variations within the N-binaphthyl and styrene etherate moiety in 29. 23 As shown in Scheme 6, catalyst 30a promoted the transformation of 38 under ambient conditions with a pronounced E/Z-selectivity (see also Section 3.…”