LReO₃ Epoxidizes, cis-Dihydroxylates, and Cleaves Alkenes as Well as Alkenylates Aldehydes:  Toward an Understanding of Why

Abstract

The relative reaction thermodynamics for the probable pathways leading to alkene epoxidation, cis-dihydroxylation, and C−C cleavage as well as alkenylation of aldehydes have been investigated for the reaction of ethylene with LReO3, L = CH3, Cl, OH, OCH3, O-, C5H5(Cp), and C5(CH3)5 (Cp*). We find the reaction pathway exothermicities to be quite sensitive to the ligand. For ClReO3, CH3ReO3, HOReO3, CH3OReO3, and O-ReO3, reaction with ethylene is endothermic with metallaoxetane preferred over dioxylate formation. For CpReO3 and Cp*ReO3, the reaction with ethylene is exothermic but nearly thermoneutral with dioxylate formation preferred. The π-binding attributes of the ligand are found to correlate with thermodyanmic preference.

Metallaoxetanes and Carbenes from Diolates in High‐Valent Rhenium Oxo Chemistry: The Importance of the Coordination Number

“…The most convincing experimental study, a kinetic isotope effect study by using the method from Singleton, best fits expectations based on a [3+2] mechanism 14. Quantum chemical calculations have been decisive in the entire story,1, 15–17 which have not only provided the basis for interpretation of experimentally determined isotope effects, but moreover predicted, in general, that the metallaoxetane intermediate in the [2+2] mechanism lay too high in energy, typically about 10–30 kcal mol −1 , above the isomeric diolate to be chemically significant. However, observation of the relevant metallaoxetane intermediates or products that could be uniquely associated has been wholly missing from the experimental side of the discussion.…”

“…We report an electrospray ionization tandem mass spectrometric study of the chemistry of Re V diolate complexes in which the intermediacy of the isomeric metallaoxetane complexes is implicated by dissociation of the diolates to rhenium carbene complexes instead of the expected oxo species (Scheme ). Not only is the chemistry unprecedented for well‐defined diolate complexes, but the marked dependence of the preferred reaction path upon coordination number in the original diolate complex supports a qualitative molecular orbital argument based on π‐strain1 that may be able to guide further design of new catalysts.…”

“…The chemistry of Re V diolates and the corresponding Re VII oxo complexes is closely related to that of OsO 4 , and has been examined by other groups2–5 in part as a model for the reactions of the latter complex, especially in connection to the catalytic asymmetric dihydroxylation reaction introduced by Sharpless and coworkers 6. While the original mechanistic hypothesis by Böseken and De Graaft, and by Criegee and co‐workers,7 termed the [3+2] mechanism, had been accepted for decades, the mechanistic possibility of an alternative [2+2] mechanism8 was investigated at length by stereochemical,9, 10 kinetic,11, 12 isotope effect,13, 14 and computational means 1. 15–17 A direct observation, however, of a metallaoxetane intermediate in high‐valent Re or Os chemistry, or products uniquely derived from metallaoxetanes, has remained outstanding.…”

“…It remains to explain why the observation of carbene products has remained outstanding up until now, and why the reactivity of 1 shows such a sharp dichotomy depending on whether one or two pyridine units are coordinated to the metal center. A rationale, which had in fact provided a part of the reasoning behind the experimental design, is inspired by a computational study by Rappé and co‐workers 1. For the reaction of an olefin with a model four‐coordinate complex LReO 3 , in which L ranges from a strong σ donor like CH 3 to strong π donors, such as O or Cp, Rappé and co‐workers proposed that the thermodynamically favored product, either diolate or metallaoxetane, would be determined by release of π strain.…”

A computational study of the addition of ReO3L (L = Cl−, CH3, OCH3 and Cp) to ethenone

“…In contrast to ketenes, experimental and theoretical investigations on the mechanism of addition of transition metal-oxide of the type LMO 3 (M = Mn, Tc and Re) across the C=C double bonds of olefins has been extensively reported (Sharpless and Akashi 1975 ; Wiberg 1965 ; Aniagyei et al 2013a , b , c ; Tia and Adei 2009 , 2011 ; Nelson et al 1997 ; Corey and Noe 1997 ; Haller et al 1997 ; Houk and Strassner 1999 ; Torrent et al 1998 ; Del Monte et al 1997 ; Tia and Adei 2011 ; Pietsch et al 1998 ; Deubel and Frenking 1999 ; Gisdakis and Rösch 2001 ). Ketenes are related to olefins by the presence of the C=C double bonds but ketenes constitute activated double bonds due to the presence of the C=O double bond directly bonded to the C=C double bond.…”