N‐Heterocyclic Carbene Complexes of Cp*–Aluminum Triflate

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

Indenyl-(Ind) and fluorenyl-(Fl) substituted NHC-stabilized alanes and gallanes (NHC)·EH2R 1-12 (NHC = IiPrMe, IiPr, IMeMe; E = Al, Ga; R = Ind, Fl) were prepared via reaction of the corresponding NHC-iodoalanes and -gallanes with LiInd and LiFl, respectively. Analogously, the alane adducts with two Ind/Fl substituents (NHC)·AlHR213-18 (NHC = IiPrMe, IiPr, IMeMe; R = Ind, Fl) were obtained by using two equivalents of LiInd/LiFl. Elimination of indene and fluorene was induced thermally affording unusual dimeric and trimeric NHC-alane adducts {(NHC)·AlH2}2-μ-Fl 19-20 and {(NHC)·AlH-μ-R}n21-23 (R = Ind, Fl; n = 2, 3) with bridging indenyl and fluorenyl ligands.

Pentamethyl- and 1,2,4-tri(tert-butyl)cyclopentadienyl containing p-block complexes - differences and similarities

The sterically encumbered cyclopentadienyl ligand 1,2,4-(Me₃C)₃C₅H₂ (Cp''') was used to stabilize efficiently the main group metals of Al, Ga, In, Ge and Sn, respectively. The σ-bonded gallium compounds [η¹-Cp'''Ga(μ-X)X]₂ (X = Cl, 2; X = I, 3) and indium compound [η¹-Cp'''In(μ-Br)ⁿBu]₂ (7) exhibit dimers through halogen bridges. Reduction of 2 with 2 equivalents of KC₈ leads almost to the same amount of η¹-Cp'''Ga(THF)Cl₂ (4) and η⁵-Cp'''Ga (5), respectively. The exception is compound 5, which is obtained by reducing 2 or 3 with 4 equivalents of KC₈. Compound 5 as Lewis base reacts with GaI₃ readily forming the Lewis acid-base adduct product η⁵-Cp'''Ga → GaI₃ (6). Moreover, compounds with the Cp''' ligand stabilize heavier low-valent group 14 elements for example [η⁵-Cp'''E^II]⁺[E^IICl₃]^- (E = Ge 8, Sn 9), which are π-bonded ionic compounds that possess a low-valent cation and an anion. In the cation of [η⁵-Cp'''E^II]⁺, the Cp''' ligand adopts an η⁵-coordination mode with germanium and tin, respectively, which present half-sandwich complexes. While the E^II fragment interacts with five π electrons from the Cp''' unit to generate an electron-octet arrangement at the respective element. All new reported structures are comparing well with the corresponding compounds containing the pentamethylcyclopentadienyl (Cp*) ligand.

Donor-Stabilized Monocarba-Bridged Bis(cyclopentadienyl)alanes

Five monocarba-bridged bis(cyclopentadienyl)aluminum halide NHC and thione complexes and one monocarba-bridged bis(cyclopentadienyl)phosphanylalane NHC complex are reported. The former were synthesized by transmetalation of a C[1]magnesocenophane with the corresponding aluminum(III) chloride and aluminum(III) bromide donor adducts. The phosphanylalane complex was obtained by a subsequent functionalization of the corresponding bromoalane with lithium diphenylphosphide. All complexes were characterized in solution by multinuclear NMR spectroscopy and in the solid state by single crystal X-ray diffraction. Bonding energies of the NHC and thione ligands to the aluminum centres were estimated by DFT calculations.

Diverse structure and reactivity of pentamethylcyclopentadienyl antimony(iii) cations

Rare examples of Sb(iii) cations which are not supported by coordinative bonds demonstrate Lewis acidic reactivity.