N-Heterocyclic carbene stabilized adducts of alkyl magnesium amide, bisalkyl magnesium and Grignard reagents: trapping oligomeric organo s-block fragments with NHCs

Abstract

Developing N-heterocyclic carbene (NHC) chemistry of simple organomagnesium compounds, this study reports the synthesis, X-ray crystallographic, and NMR spectroscopic characterization of three such new carbene complexes. The 1 : 1 alkyl magnesium amide : carbene complexes nBuMg(TMP)·IPr 1 and nBuMg(HMDS)·IPr 2 both exist as mononuclear complexes in the crystal but differ in solution as 2 remains intact whereas 1 undergoes a dynamic exchange involving partial decoordination of IPr [TMP is 2,2,6,6-tetramethylpiperidide; IPr is 1,3-bis-(2,6-diisopropylphenyl)imidazol-2-ylidene); HMDS is 1,1,1,3,3,3-hexamethyldisilazide]. Reaction of commercial nBu(2)Mg with IPr surprisingly produced the organoaluminium carbene complex nBu(3)Al·IPr, 3, which also forms a simple mononuclear structure in the crystal. The presence of the Al could be traced to the deliberate addition of a small quantity of Et(3)Al as a stabilizing agent in the commercial nBu(2)Mg reagent. Repeating this reaction with Al-free nBu(2)Mg afforded the hemisolvated carbene complex nBu(8)Mg(4)·2IPr, 4, the stoichiometry of which is dictated by its structure rather than by that used in the initial reaction mixture. The molecular structure of 4 is tetranuclear with a linear chain of 4 Mg centres bridged by nBu ligands and capped at each end by terminal nBu and IPr ligands. Synthesized by treating the Grignard reagent nBuMgCl with IPr, nBuMgCl·IPr, 5, forms a cyclodimer structure with chloro bridges and terminal nBu and IPr ligands.

N‐Heterocyclic‐Carbene‐Induced Monomerization of Sterically Encumbered Dialkylmagnesium and Dialkylmanganese Polymers

“…The Mg-C carbene distances of 1 [2.267(3) Å] and 3 [2.288(5) Å] are consistent with those previously reported for monomeric, three-coordinate alkylamido, [7] dialkyl [7,14] and diamido [15] Mg-NHC complexes (2.254-2.285 Å), while the Mn-C carbene distances of 2 [2.236(2) Å] and 4 [2.277(4) Å] are marginally longer than those of a series of The coordination spheres of the metal centres are all clearly trigonal-planar (Σ(ЄM) = 359.99, 360.00, 359.99 and 360.00°for 1, 2, 3 4, respectively). All complexes show a distortion from planarity with respect to the dihedral angle between the two planes defined by N-C carbene -N and C alkyl -M-C alkyl , the less bulky alkyl groups of complexes 1 and 2 [16.64(6) and 16.15(4)°for 1 and 2, respectively] almost certainly causing an appreciably lower movement away from planarity than the bulkier ligands in 3 and 4 [46.17(10) and 45.42(7)°for 3 and 4, respectively].…”

“…[6] Part of our recent studies have involved the preparation of N-heterocyclic-carbenestabilized alkyl/amido magnesium complexes, such as nBuMg(TMP)·IPr, nBuMg(HMDS)·IPr and [nBu 2 Mg] 4 · 2IPr (TMP = 2,2,6,6-tetramethylpiperidide and HMDS = 1,1,1,3,3,3-hexamethyldisilazane). [7] We now extend this concept to bulky Mg and Mn dialkyl species and present herein the new complexes [(Me 3 Si) 3 = Mg (1) and Mn (2); x = 1, M = Mg (3) and Mn (4); IPr = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene], which are novel because they are monomeric and each contains a trigonal-planar three-coordinate MC 3 centre.…”

Lewis base adducts of diisobutylaluminum azide: synthesis and thermal stability

“…The 1 H NMR spectra of 1 and 2 clearly confirm the 1 : 1 stoichiometry, and the IR spectra display strong azide absorptions around 2100 cm −1 . The 13 C chemical shifts of the coordinated carbene carbons are a bit more upfield (2a: 172.4 ppm, 2b: 175.2 ppm) than those of the related carbene complexes IMes·AlMe 3 (178.2) [26] and IDipp·Al(n-Bu) 3 (191.0 ppm) [27]. The reaction of the diimine B with i-Bu 2 AlN 3 afforded the iminoamide complex 3.…”

Coordination chemistry of ditopic carbanionic N-heterocyclic carbenes

“…The availability of the free carbene to do further chemistry was demonstrated by the reaction of the complexes with various Lewis acids such as BH 3 , AlMe 3 and CO 2 (Fig. 20), in a similar manner to the Lewis acid-base adducts which are already known for free NHCs [95][96][97][98][99][100][101][102][103][104][105][106][107][108][109][110][111][112]. …”