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Carbene rearrangements in three-coordinate N-heterocyclic carbene complexes of cobalt(II) bis(trimethylsilyl)amide.
- Source :
-
Inorganic chemistry [Inorg Chem] 2014 Oct 06; Vol. 53 (19), pp. 10578-84. Date of Electronic Publication: 2014 Sep 09. - Publication Year :
- 2014
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Abstract
- The synthesis and molecular structures of the cobalt(II) N-heterocyclic carbene (NHC) complexes [(NHC)Co{N(SiMe3)2}2], where NHC = 1,3-bis(diisopropylphenyl)imidazolylidene (IPr) (6), 1,3-bis(mesityl)imidazolylidene (IMes) (7), and 1,3-bis(tert-butyl)imidazol-2-ylidene (I(t)Bu) (8), are reported. Complexes 6-8 are rare examples of three-coordinate cobalt NHC complexes. The steric congestion within the coordination environments of the cobalt(II) centers in 6 and 7 results in the longest Co-C(NHC) distances currently known. Investigating the thermal stability of 6-8, we have found that the steric congestion in 6 is such that heating the complex to reflux in toluene prompts a rearrangement from the normal, C2-bonding mode of the IPr ligand to the corresponding "abnormal" or mesoionic bonding mode. The rearrangement results in formation of [(aIPr)Co{N(SiMe3)2}2] (9), which is the first cobalt complex of an abnormal NHC ligand. The Co-C bond in 9 is 0.06 Å shorter than the analogous bond in 6, suggesting that, although the rearrangement occurs due to the spatial demands of the IPr ligand, there is also a thermodynamic driving force in terms of the Co-C bond. In contrast to the case for 6, complex 7 is stable with respect to the normal-to-abnormal rearrangement. Refluxing complex 8 in toluene results in activation of a tert-butyl substituent, which is eliminated as isobutene, followed by formation of the 1-tert-butylimidazole complex [((t)BuIm)Co{N(SiMe3)2}2] (10).
Details
- Language :
- English
- ISSN :
- 1520-510X
- Volume :
- 53
- Issue :
- 19
- Database :
- MEDLINE
- Journal :
- Inorganic chemistry
- Publication Type :
- Academic Journal
- Accession number :
- 25203858
- Full Text :
- https://doi.org/10.1021/ic501677k