N‐tert‐Alkyl‐Substituted N‐Heterocyclic Carbenes with a 1,1’‐Ferrocenediyl Backbone

Abstract

1,1'-Diaminoferrocene (1) was converted to α-aminonitriles fc[NHC(CN)MeR'] 2 (fc = 1,1'-ferrocenediyl; 2 a: R' = Me, 2 b: R' = Ph, 2 c: R' = tBu) by reaction with ketones MeC(O)R' in the presence of NaCN/HOAc or to the diimine fc(N=CPh 2 ) 2 (3) by condensation with Ph 2 CO. Treatment of 2 a-c or 3 with MeLi furnished fc(NHR) 2 (4 a: R = tBu, 4 b: R = CMe 2 Ph, 4 c: R = CMe 2 tBu, 4 d: R = CMePh 2 ) after aqueous work-up. The formylative cyclisation of 4 a-d to fc[(NR) 2 CH][BF 4 ] (5H[BF 4 ]) was possible only for R = CMe 3 (a) and CMe 2 Ph (b). The reaction of these formamidinium compounds with NaN(SiMe 3 ) 2 afforded the N-heterocyclic carbenes fc{[N(CMe 3 )] 2 C:} (5 a) and fc{[N-(CMe 2 Ph)] 2 C:} (5 b). 5 a was converted to the thiourea derivative 5 aS with elemental sulfur. 5 a and 5 b slowly decompose in solution by alkene elimination, affording the respective formamidine fc(NRCH=N) (6 a: R = CMe 3 , 6 b: R = CMe 2 Ph). 6 a was transformed to fc{[N(CMe 3 )][N(CPh 3 )]CH}[BF 4 ] (5eH[BF 4 ]) with Ph 3 C[BF 4 ].

A Stable Crystalline N‐Heterocyclic Carbene with a 1,1’‐Ferrocenylene Backbone and BenzylicN‐Substituents

“…These values are in concert with the C−Se bond lengths discussed above in view of the 0.15 Å difference of the covalent radii of S (1.05 Å) and Se (1.20 Å) [36] . A very similar C−S bond length of 1.685(3) Å has been determined for the tert ‐butyl homologue 1 t Bu S [7a] . In comparison to the C−E distances (E=S, Se) of thioketones (ca.…”

A complete series of N-heterocyclic tetrylenes (Si–Pb) with a 1,1′-ferrocenediyl backbone enabled by 1,3,2-diazaborolyl N-substituents

“…They are tilted by 4.7°due to the bulky N-substituents, which also cause a displacement of the N amino atoms from their respective cyclopentadienyl ring plane, the C ipso -N vector pointing away from the Fe atom (ring centroid-C ipso -N 3.2°). In contrast to several diaminoferrocene derivatives of the type fc(NHR) 2 (R = t Bu, 7l CMe 2 Ph, 20 CMePh 2 , 20 Ph 21 ), the NH units of 1H 2 are not involved in short contacts compatible with weak NH⋯N hydrogen bonds, which is plausibly due to the bulky nature of the {B} groups. Note, however, that such hydrogen bonds may be absent also in the case of less bulky N-substituents such as, for example, CH 2 t Bu 22 or CH 2 -p-C 6 H 4 -X (X = OMe, NMe 2 ).…”

Formation of CNHC∧Calkyl and CNHC∧Caryl κ2-Chelate Complexes through Competitive sp3- and sp2-CH Activations: An Experimental and Computational Study

“…In the past few decades, various N-heterocyclic carbenes (NHCs) have been shown to be valuable ligands for the preparation of organometallic complexes. The interest in NHCs as ligands is based on their broad range of stereoelectronic properties 1 and consequently the use of their complexes as efficient catalysts 2 for various transformations.…”