Expedient Access to Normal‐ and Abnormal‐ N‐Heterocyclic Carbene (NHC) Magnesium Compounds from Imidazolium Salts

Abstract

Treatment of imidazolium salts (IPrH)Cl (1) and (IPrH)I (2) with MeMgI leads to the formation of normal N-heterocyclic carbene (nNHC) compounds (IPr)MgCl(I) (3) and (IPr)MgI 2 (4) [IPr = 1,3bis(2,6-diisopropylphenyl)imidazol-2-ylidene], respectively. By employing a similar strategy, the first magnesium compound (aIPr Ph )MgI 2 (OEt 2 ) (6) featuring an abnormal-NHC [aIPr Ph = 1,3bis(2,6-diisopropylphenyl)-2-phenyl-imidazol-4-ylidene] is prepared by the treatment of a C2-arylated imidazolium salt (IPrPh)I (5) with MeMgI. While the deprotonation of 1 and 2 can be accomplished at * Priv.-Doz. Dr. R. S. Ghadwal E-Mail: rghadwal@uni-bielefeld.de [a] Anorganische Molekülchemie und Katalyse am Lehrstuhl für Anorganische Chemie und Strukturchemie

Molecular Manipulations of a Utility Nitrogen–Heterocyclic Carbene by Sodium Magnesiate Complexes and Transmetallation Chemistry with Gold Complexes

“…In addition, the resonance assigned to the carbenic C2 is at 200.2 ppm supporting the C2 coordination of the anionic NHC to Na. [27] This methodr elies on the deprotonationo faC2-functionalised imidazoliums alt using aG rignardr eagent which affords [aIPr Ph MgI 2 ·OEt 2 ] (aIPr Ph = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazol-4-ylidene) which can then further undergo salt-metathesis and give the [aIPr Ph ·Mg(HMDS) 2 ]c omplex. [14] Accessing an abnormalNHC-Mgcomplex via electrophilic interception Withinm ain group chemistry,t he number of complexesc ontaininga bnormal (or mesoionic) carbenes remains very limited, and for Mg the first examples containing this type of ligands were only reported in 2016 by Ghadwall.…”

“…[14] Accessing an abnormalNHC-Mgcomplex via electrophilic interception Withinm ain group chemistry,t he number of complexesc ontaininga bnormal (or mesoionic) carbenes remains very limited, and for Mg the first examples containing this type of ligands were only reported in 2016 by Ghadwall. Having successfully isolated anionic NHC complex 2 we next pondered, if it could undergo selective electrophilic interception to render the relevant neutral aNHC-Mg complex, as this approach has already shown promising potentialf or other main group elements including B, [31] Ga [22,27,32] andZ n. [33] To explore this possibility sodiumm agnesiate 2 was treated with amolar equivalent of Me 3 SiCl in toluene at À30 8C. Our previous attemptt o access aIPr·MgR 2 by employing thermally induced isomerization of its normal analogue (i.e.…”

“…[14] Accessing an abnormalNHC-Mgcomplex via electrophilic interception Withinm ain group chemistry,t he number of complexesc ontaininga bnormal (or mesoionic) carbenes remains very limited, and for Mg the first examples containing this type of ligands were only reported in 2016 by Ghadwall. [27] This methodr elies on the deprotonationo faC2-functionalised imidazoliums alt using aG rignardr eagent which affords [aIPr Ph MgI 2 ·OEt 2 ] (aIPr Ph = 1,3-bis(2,6-diisopropylphenyl)-2-phenyl-imidazol-4-ylidene) which can then further undergo salt-metathesis and give the [aIPr Ph ·Mg(HMDS) 2 ]c omplex. Our previous attemptt o access aIPr·MgR 2 by employing thermally induced isomerization of its normal analogue (i.e.…”

“…IPr·MgR 2 ), [28] am ethodology that has been successful for complexes of Ga, [28] Fe, [29] B [2a] or Al [30] and seems to be driven by the steric relief around the metal centre, did not work even under forcing reactionc onditions (72 ha t1 00 8C). Having successfully isolated anionic NHC complex 2 we next pondered, if it could undergo selective electrophilic interception to render the relevant neutral aNHC-Mg complex, as this approach has already shown promising potentialf or other main group elements including B, [31] Ga [22,27,32] andZ n. [33] To explore this possibility sodiumm agnesiate 2 was treated with amolar equivalent of Me 3 SiCl in toluene at À30 8C. Exchange of toluene in vacuo to aT HF/hexane mixture led to isolation of free carbene IPr TMS in 61 %y ield (Scheme 2a), identified by comparison of its 1 Ha nd 13 CNMR data to literature data.…”

Transmetalation from Magnesium–NHCs—Convenient Synthesis of Chelating π-Acidic NHC Complexes

“…This is also true for magnesium, although the first example of an NHC-magnesium complex dates back to 1993 [56]. Subsequent investigations with s-block metals focused [57][58][59][60][61][62][63][64][65][66][67][68] largely on anionic ligands because of the weak magnesium-NHC bond [69][70][71][72][73][74]. For magnesium-NHC complexes, examples of saturated [75] and benzannulated [76,77] NHCs remain extraordinarily scarce.…”