Activation of Ethylene by N‐Heterocyclic Carbene Coordinated Magnesium(I) Compounds

Abstract

Reactions of as eries of magnesium(I) compounds with ethylene, in the presenceo fa nN-heterocyclic carbene (NHC), have been explored. Treating [{(Mes Nacnac)Mg} 2 ] (Mes Nacnac = [HC(MeCNMes) 2 ] À ,M es = mesityl) with an excess of ethylene in the presence of two equivalents of :C{(MeNCMe) 2 }(TMC) leads to the formal reductivec oupling of ethylene, and formationo ft he 1,2-dimagnesiobutane complex, [{(Mes Nacnac)(TMC)Mg} 2 (m-C 4 H 8)].I nc ontrast, when the reactioni sr epeated in the presence of three equivalents of TMC, am ixture of the b-diketiminato magnesium ethyl, [(Mes Nacnac)(TMC)MgEt],a nd the NHC coordinated magnesium diamide, [(Mes Nacnac-H)Mg(TMC) 2 ], results. Four related products,[ (Ar Nacnac)(TMC)MgEt] (Ar = 2,6-dimethylphenyl (Xyl) or 2,6-diisopropylphenyl (Dip)) and [(Ar Nacnac-H)Mg-(TMC) 2 ](Ar = Xyl or Dip), were similarly synthesised and crystallographically characterized. Computational studies have been employed to investigate the mechanisms of the two observed reaction types, whicha ppear dependent on the substitution pattern of the magnesium(I) compound, and the stoichiometrice quivalents of TMC used in the reactions.

Generation of organo-alkaline earth metal complexes from non-polar unsaturated molecules and their synthetic applications

“…In the presence of an N -heterocyclic carbene ligand that can coordinate with Mg( i ) centers as a Lewis base, the magnesium( i ) dimer 20 could reductively activate even inert ethylene, forming 1,4-dimagnesiobutane 29 in 43% yield ( Scheme 7 ). 28 …”

Stereoselective Insertion of Cyclopropenes into Mg–Mg Bonds

“…This type of reactivity has already been reported by Jones and co-workers for reaction of 1b with ethylene in the presence of an N-heterocyclic carbene ligand. 15 In the case of 2c, an intermediate 3d could be spectroscopically observed. Addition of a further equiv.…”

“…Very recently the scope of main group reagents that can be used to functionalise alkenes has been expanded to compounds that contain reactive Mg-Mg bonds. [10][11][12] Both Jones and coworkers, [13][14][15] and our group, 16 have demonstrated the 1,2-dimagnesiation of alkenes. In specific cases the reaction has been shown to be reversible.…”

“…20 Prior DFT studies have modelled the addition of ethylene to a derivative of 1b, but stereochemistry was not a consideration in this case. 15 The reaction of 1b with cyclopropene 2a is calculated to proceed by an initial formation of a weak van der Waals complex Int-1 followed by a stereoselective syn-addition transition state TS-1 that connects directly to the product Int-2 (Figure 2). Int-2 (R 1 = Me, R 2 = Ph) is a direct analogue of the spectroscopically observed intermediate 3d (R 1 = R 2 = Ph).…”

Stereoselective insertion of cyclopropenes into Mg–Mg bonds

“…Very recently the scope of main group reagents that can be used to functionalise alkenes has been expanded to compounds that contain reactive Mg-Mg bonds. [9][10][11] Both Jones and coworkers, [12][13][14] and our group, 15 have demonstrated the 1,2dimagnesiation of alkenes. In specific cases the reaction has been shown to be reversible.…”