Chemically Non‐Innocent Cyclic (Alkyl)(Amino)Carbenes: Ligand Rearrangement, C−H and C−F Bond Activation

Abstract

A cyclic (alkyl)(amino)carbene (CAAC) was found to undergo unprecedented rearrangements and transformations of its core structure in the presence of Group 1 and 2 metals. Although the carbene was also found to be prone to intramolecular C-H activation, it was competent for intermolecular activation of a variety of sp-, sp(2) -, and sp(3) -hybridized C-H bonds. Double C-F activation of hexafluorobenzene was also observed in this work. These processes all hold relevance to the role of these carbenes in catalysis, as well as to their use in the synthesis of new and unusual main group or transition metal complexes.

Bis(Cyclic Alkyl Amino Carbene) Ruthenium Complexes: A Versatile, Highly Efficient Tool for Olefin Metathesis

“…NMR kinetic studies were undertaken to gain more information about the possible mechanism of initiation of 15 f . The rate of the reaction between 15 f and olefin 13 ([D 8 ]toluene, 60 °C) proved to be independent of the concentration of 13 (see the Supporting Information) and was in good agreement with the stability of 15 f in solution (which appears to be limited by the high lability and low stability of CAAC) 25. Experimental results suggest that a dissociative mechanism operates for 15 f (Scheme 3).…”

“…[28] This results strongly support the classical mechanism in which active,14-electron species are formed via neutral ligand release and also prove that for 15 a dissociation of CAAC is the rate-limiting step.NMR kinetic studies were undertaken to gain more information about the possible mechanism of initiation of 15 f.T he rate of the reaction between 15 f and olefin 13 ([D 8 ]toluene,6 08 8C) proved to be independent of the concentration of 13 (see the Supporting Information) and was in good agreement with the stability of 15 f in solution (which appears to be limited by the high lability and low stability of CAAC). [25] Experimental results suggest that ad issociative mechanism operates for 15 f (Scheme 3). This,h owever,c annot be extrapolated to all complexes 15,a nd further theoretical and kinetic studies are needed to shed more light on the initiation mechanism of these (pre)catalysts.…”

“…Commonly utilized KHMDS or longer times of deprotonation in some cases completely prohibited the formation of products. [25] The product was isolated as ared solid in 70 %yield. Surprisingly, the signal from the phosphorus atom was not present in 31 PNMR spectra, which suggests substitution of both phosphines by CAACs.…”

“…Commonly utilized KHMDS or longer times of deprotonation in some cases completely prohibited the formation of products 25. The product was isolated as a red solid in 70 % yield.…”

Cyclic (Alkyl)(amino)carbenes (CAACs): Recent Developments

“…Ah andful of Group 1a nd Group 2C AACc omplexes have been isolated. [61] Even beryllium has been explored, which has been described by Dutton and Frenking as "the least investigated chemical element of the first octal row of the periodic table except inert neon." [62] Braunschweig et al [63] have shown that the reduction of a( CAAC)BeCl 2 complex in the presence of aC AACafforded the (CAAC) 2 Be adduct 1,inwhich the beryllium atom is in the formal zero oxidation state (Scheme 5).…”