Catalyst Behavior in Metal-Catalyzed Carbonyl-Olefin Metathesis

Abstract

Iron(III)-catalyzed carbonyl-olefin ring-closing metathesis employs reactivity not typically observed in Lewis acid-catalyzed reactions. In converting a ketone with a pendant olefin into a cycloalkene and a simple carbonyl byproduct, the reaction requires the Lewis acid catalyst to differentiate between the carbonyl of the substrate and that of the byproduct. It is necessary to determine how this solution interaction imparts the desired reactivity to best employ this method. Herein, we report detailed kinetic, spectroscopic, and colligative measurements applied toward the identification of the solution structures of the active Fe(III) and Ga(III) carbonyl-olefin metathesis catalysts. These data are consistent with formation of Lewis acid-carbonyl pairs for both metal systems under stoichiometric conditions. However, they diverge in the presence of higher equivalents of carbonyl, with Fe(III) forming highly ligated complexes, and no observed change for Ga(III). These findings are consistent with the resting state identity of the Fe(III) metathesis catalyst changing over the course of the reaction.

Investigation of Lewis Acid-Carbonyl Solution Interactions via Infrared-Monitored Titration

“…Further, we have reported a crystal structure for highly ligated complex 41 (Figure 21), where four molecules of 3 coordinate to the Fe(III) center. 16 Because of this result, we analogously propose structure 39 for the addition of 1, 34 for the addition of 2, and 42 for the addition of 4 as likely forming in solution. However, the nonunity slopes observed in Figure 14 may be consistent with a distribution of complexes, and 41 might simply be the structure that crystallized under forcing conditions.…”

Ring-opening carbonyl–olefin metathesis of norbornenes

“…It should be stressed that, even though the cycloadditions proceed via the (E)-hydrazoniums, the energies shown reect the difference between the more stable (Z)hydrazoniums 23-Z and transition state structures 24, which thus represent the full energetic cost of cycloaddition. Interestingly, bicyclic hydrazines 6 and 18, as well as pyrazolidine (19), had lower activation barriers than the [2.2.1]-hydrazine 4, while the barriers for the larger ring monocyclic hydrazines 20 and 21 were noticeably higher.…”

“…At the present time, however, this area is still in its infancy, and the generality of available catalytic platforms falls far short of what would be needed to realize many of the potential applications of this reaction. Recent exciting developments in the use of organocatalysts, 8,9 Lewis acids, [10][11][12][13][14][15][16][17][18][19][20][21] and Brønsted acids 22,23 notwithstanding, this area requires breakthrough advances in catalyst and strategy design if it is to approach the levels of utility realized by other mature catalytic processes.…”

Complementarity in Cyclotricatechylene Assemblies: Symmetric Cages Linked within 3D Cubic Hydrogen Bonded Networks

“…Although examples of alkali metal ions coordinated by six acetone molecules are known, they are part of aggregates involving more than one alkali metal ion e.g., cationic clusters such as [Na3((CH3)2CO)9] 3+ [27]. A search of the Cambridge Crystallographic Database reveals only three discrete M[(CH3)2CO]6 n+ complexes, [Mg((CH3)2CO)6] 2+ which serves as a counter cation for bis((µ2-iodo)-iodo-copper(I)) [28], [Ni[(CH3)2CO]6] 2+ which accompanies a Ni-Cu carbide carbonyl cluster [29] and [Fe((CH3)2CO)6] 2+ which is the countercation for [FeCl4] − [30]. In each of these hexaacetone complexes there is a bend at the carbonyl oxygen atom whereas in III the Cs + -O=C angle is 180° with the carbonyl oxygen group aligned along the unit cell axes.…”