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

Abstract

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 1). 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 p-strain [1] 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 groups [2][3][4][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

Rhenium(VII) Oxide/Aluminum Oxide: More Experimental Evidence for an Oxametallacyclobutane Intermediate and a Pseudo‐Wittig Initiation Step in Olefin Metathesis

“…[7] More recent studies have shown that rhenium alkylidene complexes can be generated from the corresponding glycolate through an oxarhenacyclobutane, suggesting that the pseudoWittig pathway can indeed be a viable pathway of initiation. [15][16][17] Here below, a combined reactivity study of various olefins with Re 2 O 7 /Al 2 O 3 shows that this catalyst contains only 2 % of active sites, and the propagating alkylidene does not need to be formed through a p-allyl intermediate, so that the pseudoWittig reaction is a preferred initiation mechanism. , [7] and shows that propene can generate the propagating carbene, while ethene cannot [Eqs.…”

Aldehyde olefination with a ruthenium(II) salen catalyst

“…Furthermore, the use of transition metal complexes as catalysts also opens the possibility of efficient asymmetric olefination [4,5]. Accordingly, several catalytic aldehyde and ketone olefination systems have been reported based on Mo [6,7], Re [8][9][10][11][12][13][14][15], Ru and Rh [16][17][18][19][20][21][22], Fe [20,[23][24][25][26][27] and Co [28] complexes.…”

Unprecedented ROMP Activity of Low‐Valent Rhenium–Nitrosyl Complexes: Mechanistic Evaluation of an Electrophilic Olefin Metathesis System

“…[32] Indeed, the reaction of several strained cyclic olefins, such as norbornene, dicyclopentadiene (DCPD), and cyclooctene, with a 0.1-0.2 % load of the catalysts 2 a or 2 b in chlorobenzene at room temperature, produced polymers of high molecular weight and with a surprisingly high Z content of the olefin groups in the polymer backbone (Table 1). The Z-olefinic content in ROMP polymers is usually low.…”

“…However, defined soluble rhenium complexes have rarely exhibited high activity. A few catalysts are known with rhenium in a high oxidation state; [32] systems with rhenium in a low oxidation state have not been studied, except for a dinuclear rhenium-carbonyl complex activated with iBuAlCl 2 . [33,34] We therefore focused on the development of novel rhenium-based olefin metathesis catalysts.…”