Cationic aluminum hydride complexes: reactions of carbene–alane adducts with trityl-borate

Abstract

Reaction of (Idipp)AlH3 with [Ph3C][B(C6F5)4] in toluene affords the dimeric aluminum dication [((Idipp)AlH(μ-H))2][B(C6F5)4]22. In contrast, the reaction of (IBn)AlH3 with [Ph3C][B(C6F5)4] in bromobenzene gives a redistribution product, the salt of a monomeric dication [(IBn)2AlH][B(C6F5)4]24.

Reactivity of NHC Alane Adducts towards N‐Heterocyclic Carbenes and Cyclic (Alkyl)(amino)carbenes: Ring Expansion, Ring Opening, and Al−H Bond Activation

“…Aluminum hydride cations are relatively scarce and Stephan et al. presented only recently the closely related compounds [{(Dipp 2 Im) ⋅ AlH( μ 2 ‐H)}2] 2+ 2[B(C 6 F 5 ) 4 ] − and [(Bn 2 Im) 2 AlH] 2+ 2[B(C 6 F 5 ) 4 ] − , which are the first examples of NHC‐stabilized aluminum cations . To our knowledge, 8 is the first example of an NHC‐stabilized cationic aluminum center with the coordination number six.…”

“…Molecular structure of (iPr 2 Im)·AlH 3 (3)i nthe solid state (ellipsoids set at the 50 %p robability level). Selectedbondlengths []a nd angles [ 8]: Al1ÀC1 2.0405 (17), Al1ÀH1 1.54(2), Al1ÀH2 1.56(2), Al1ÀH3 1.492 (19), Al2À C112 .0375 (17),Al2ÀH4 1.53(2), Al2ÀH5 1.52(2), Al2ÀH6 1.53(2), C1-Al1-H1 108.5 (7), C1-Al1-H2 104.1 (8), C1-Al1-H3 105.4 (8), H1-Al1-H2 112.1(11), H1-Al1-H3 113.5(10), H2-Al1-H3 112.5(11), C11-Al2-H4 104.5 (8), C11-Al2-H51 09.2(7), C11-Al2-H6 106.5 (8), H4-Al2-H5 112.2(10),H 4-Al2-H61 11.4(11), H5-Al2-H6 112.5(11). Figure 3.…”

“…Besides simple decomposition of the compounds to unidentified molecules, NHC to a NHC ( a NHC=abnormal N‐heterocyclic carbene) rearrangement in the coordination sphere of aluminum and ring‐expansion reaction of an NHC in β‐diketiminatoaluminum dihydrides have been observed . However, the utilization of carbenes in aluminum chemistry also facilitates the isolation of interesting substances with new molecular structures, such as (Dipp 2 Im) ⋅ H 2 Al−AlH 2 ⋅ (Dipp 2 Im), obtained by magnesium(I)‐mediated dehydrogenative coupling of (Dipp 2 Im) ⋅ AlH 3 , or a cAAC‐stabilized neutral aluminum radical and the NHC‐stabilized aluminum cation [{(Dipp 2 Im) ⋅ AlH( μ 2 ‐H)} 2 ] 2+ 2[B(C 6 F 5 ) 4 ] − . Based on our experience of the reactivity of carbenes with phosphines, silanes, tin hydrides, and especially boranes, and the existing reports on the instability of some NHC aluminum compounds, we decided to take a closer look at the behavior of carbenes with different aluminum hydrides and we report the first results here.…”

Three‐Coordinate Boron(III) and Diboron(II) Dications

“…In contrast, the reaction of 6 [SbCl 6 ] 2 with a large excess of Li[AlH 4 ] (14 equiv, THF, 24 h) afforded the bisimino‐substituted aluminum dihydride salt 7 [A] via transmetallation of the ligand (A − =AlB 2 H 8 − , BH 4 − ) . The compound marks an aluminum dihydride cation and a concise overview on the small number of related compounds has been given by Stephan and co‐workers recently . The structural characterization of the [AlB 2 H 8 ] − anion indicates that the bisimino ligand can be detached from the diboron fragment without cleavage of the boron–boron bond.…”

Electronically Unsaturated Three‐Coordinate Aluminum Hydride and Organoaluminum Cations

“…These factors can restrict the commonly observed unwanted processes, such as hydride/alkyl bridge formation and exchange reactions, and therefore, stabilized these cations in three‐coordinate state. Stephan and co‐workers reported aluminum hydride cation ( I ) supported by a bulky N ‐arylimidoylamidine and N‐heterocyclic carbene stabilized aluminum hydride dication ( II ) . Jordan and co‐workers described the structures of organoaluminum cations ( III ) and ( IV ) supported by aminotroponiminate and β‐diketiminate ligands, respectively.…”