N‐Heterocyclic Carbene Complexes of Cp*–Aluminum Triflate

Abstract

To prepare the half-metallocene complex of aluminum strong σ-donating NHC ligands were allowed to react with [Cp*Al(OTf ) 2 ] 2 to afford the corresponding Cp*Al(NHC)(OTf ) 2 compound (3). The neutral Al complexes turned out to be more acidic than B(C 6 F 5 ) 3 on the Gutmann-Beckett scale and highly reactive towards chloroform, acetonitrile and nitromethane.[a]

Syntheses of Square Planar Gallium Complexes and a Proton NMR Correlation Probing Metalloaromaticity

“…In previous reports, four-and three-coordinate Al complex adducts with Et 3 PO have been characterized with 31 P NMR chemical shifts observed at 83.4 and 81.5 ppm, respectively. 30,31 The observations made herein are consistent with significant ligand−metal charge transfer character and an aromatic electronic structure which lowers the Lewis acidity of 1−5 relative to other known three-and four-coordinate Al compounds.…”

“…This data shows that the Lewis acidity does not change much across 1 – 5 , and that the Lewis acidity decreases in the order 2 ≥ 4 > 1 ≥ 5 which does not reflect the expectation that Al­(III) complexes are more Lewis acidic than Ga­(III) complexes. In previous reports, four- and three-coordinate Al complex adducts with Et 3 PO have been characterized with 31 P NMR chemical shifts observed at 83.4 and 81.5 ppm, respectively. , The observations made herein are consistent with significant ligand–metal charge transfer character and an aromatic electronic structure which lowers the Lewis acidity of 1 – 5 relative to other known three- and four-coordinate Al compounds.…”

Subvalent group 13 molecules by carbene-induced hydrogen abstraction

“…Chiu et al recently presented the synthesis of (NHC)·Cp*AlCl 2 from the reaction of (Cp*AlCl 2 ) 2 with the NHC Mes 2 Im H . 18 As we were interested in the reactivity of NHCs and related molecules with group 13 element hydrides, we reacted the NHCs Me 2 Im Me , iPr 2 Im Me and Dipp 2 Im of different steric demands with the Cp* aluminum dihydride trimer (Cp*AlH 2 ) 3 . The reaction of (Cp*AlH 2 ) 3 ( 1 ) with one equivalent of the NHC in hexane at room temperature afforded (NHC)·Cp*AlH 2 (NHC = Me 2 Im Me 5 , iPr 2 Im Me 6 , Dipp 2 Im 7 ), which were isolated as colorless powders in good yields ( 5 : 75%, 6 : 47%, 7 : 55%; see Scheme 2).…”

“…13,19 The M–C Cp* (M = Al, Ga) bond lengths of 2.0699(18) Å ( 5 ) and 2.0900(14) Å ( 7 ) of the alanes are slightly shorter than the bond length of 2.0875(14) Å observed for (Me 2 Im Me )·Cp*GaH 2 ( 8 ), and are also similar to the values reported for carbene-stabilized Cp*-substituted aluminum chlorides and bromides. 17,18…”

NHC-ligated indenyl- and fluorenyl-substituted Alanes and Gallanes: synthons towards indenyl- and fluorenyl-bridged (AlC)n-heterocycles (n = 2,3)

“…8 Lin and Chiu et al reacted [Cp*Al(OTf) 2 ] 2 with strong σ-donating NHCs to prepare the half-sandwich piano-stool aluminum complexes Cp*Al(NHC)(OTf) 2 . 9 For NHC-stabilized alanes with the less demanding Cp ligand we shortly provided easy access via substitution of the corresponding NHC-iodoalanes with NaCp affording the mono - and bis -Cp-substituted derivatives (Fig. 1a).…”