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

Abstract

A series of second-generation ruthenium olefin metathesis catalysts was investigated using a combination of reaction kinetics, X-ray crystallography, NMR spectroscopy, and DFT calculations in order to determine the relationship between the structure of the chelating oalkoxybenzylidene and the observed initiation rate. Included in this series were previously reported catalysts containing a variety of benzylidene modifications as well as four new catalysts containing cyclopropoxy, neopentyloxy, 1-adamantyloxy, and 2-adamantyloxy groups. The initiation rates of this series of catalysts were determined using a UV/vis assay. All four new catalysts were observed to be faster-initiating than the corresponding isopropoxy control, and the 2-adamantyloxy catalyst was found to be among the fastest-initiating Hoveyda-type catalysts reported to date. Analysis of the X-ray crystal structures and computed energy-minimized structures of these catalysts revealed no correlation between the Ru−O bond length and Ru−O bond strength. On the other hand, the initiation rate was found to correlate strongly with the computed Ru−O bond strength. This latter finding enables both the rationalization and prediction of catalyst initiation through the calculation of a single thermodynamic parameter in which no assumptions about the mechanism of the initiation step are made.

Reactivity Studies of Alkoxy-Substituted [2.2]Paracyclophane-1,9-dienes and Specific Coordination of the Monomer Repeating Unit during ROMP

“…Both signals most probably originate from coordination of the methoxy substituent's oxygen, as for methoxy-substituted catalysts a multiple carbene signal was reported in the literature. 31,33 Furthermore, the integrals' ratio of hydrogens attached to oxygen located next to a trans double bond compared to those located next to a cis double bond is 6:4 for the polymer obtained from isomer 2b. Therefore, the estimated trans to cis ratio of 1:1 implies a location solely of methoxy substitutents in proximity to trans configurated double bonds (six hydrogens) and 2-ethylhexyloxy substituents in proximity to cis configurated double bonds (four hydrogens from O−CH 2 −R) for the polymer obtained from isomer 2b (see Figure 7).…”

Fast-Initiating, Ruthenium-based Catalysts for Improved Activity in Highly E-Selective Cross Metathesis

“…Solids were collected on a medium frit and washed with methanol (3 × 5 mL) to generate the pure product as a maroon solid (236. 2 …”

An SNAr Approach to Sterically Hinderedortho-Alkoxybenzaldehydes for the Synthesis of Olefin Metathesis Catalysts

“…Analytical data for compounds 18−20 and 22−24 have been reported elsewhere. 21 2-(Cyclohexyloxy)benzaldehyde (13a). The title compound was prepared from 2-fluorobenzaldehyde (1.05 mL, 10.0 mmol) and cyclohexanol (1.10 mL, 10.5 mmol) according to the general three- 2-(((1r,3r,5r,7r)-Adamantan-2-yl)oxy)-5-nitrobenzaldehyde (13u).…”