Synthesis and Characterization of Sterically Encumbered Derivatives of Aluminum Hydrides and Halides:  Assessment of Steric Properties of Bulky Terphenyl Ligands

Abstract

The synthesis and characterization of several sterically encumbered monoterphenyl derivatives of aluminum halides and aluminum hydrides are described. These compounds are [2,6-Mes(2)C(6)H(3)AlH(3)LiOEt(2)](n)() (1), (Mes = 2,4,6-Me(3)C(6)H(2)-), 2,6-Mes(2)C(6)H(3)AlH(2)OEt(2) (2), [2,6-Mes(2)C(6)H(3)AlH(2)](2) (3), 2,6-Mes(2)C(6)H(3)AlCl(2)OEt(2) (4), [2,6-Mes(2)C(6)H(3)AlCl(3)LiOEt(2)](n)() (5), [2,6-Mes(2)C(6)H(3)AlCl(2)](2) (6), TriphAlBr(2)OEt(2) (7), (Triph = 2,4,6-Ph(3)C(6)H(2)-), [2,6-Trip(2)C(6)H(3)AlH(3)LiOEt(2)](2) (8) (Trip = 2,4,6-i-Pr(3)C(6)H(2)-), 2,6-Trip(2)C(6)H(3)AlH(2)OEt(2) (9), [2,6-Trip(2)C(6)H(3)AlH(2)](2) (10), 2,6-Trip(2)C(6)H(3)AlCl(2)OEt(2) (11), and the partially hydrolyzed derivative [2,6-Trip(2)C(6)H(3)Al(Cl)(0.68)(H)(0.32)(&mgr;-OH)](2).2C(6)H(6) (12). The structures of 2, 3a, 4, 6, 7, 9a, 10a, 10b, 11, and 12 were determined by X-ray crystallography. The structures of 3a, 9a, 10a, and 10b, are related to 3, 9, and 10, respectively, by partial occupation of chloride or hydride by hydroxide. The compounds were also characterized by (1)H, (13)C, (7)Li, and (27)Al NMR and IR spectroscopy. The major conclusions from the experimental data are that a single ortho terphenyl substituent of the kind reported here are not as effective as the ligand Mes (Mes = 2,4,6-t-Bu(3)C(6)H(2)-) in preventing further coordination and/or aggregation involving the aluminum centers. In effect, one terphenyl ligand is not as successful as a Mes substituent in masking the metal through agostic and/or steric effects.

Bis(tetramethylpiperidino)aluminum Halide Adducts tmp2AlX · Do and Tetrahaloaluminates of Tricoordinated Aluminum Cations [tmp2Al(Do)]AlX4

“…Thus, AlϪCl bond lengths shorter than those in the adducts 2a, b have been observed even for usually longer bridging AlϪClϪAl distances, e.g. in the centrosymmetric organoaluminum dichloride Ar(Cl)Al(µ-Cl) 2 Al(Cl)Ar (Ar ϭ 2,6-Mes 2 C 6 H 3 ), where the AlϪCl bond lengths amount to 2.195(2) Å , terminal: 2.125(2) Å ] [24] . This is also true for 3؊4, which exhibit long AlϪX distances in the range typical of bridging AlϪXϪAl units, e.g.…”

Aluminium Atoms at High Connectivity Sites in Polyhedral Polyborane Analogous Clusters: From Aluminaboranes to Carbaalanes

“…However, only alkyl or aryl cluster is analogous to that of closo- [B 11 H 11 ] 2Ϫ [3] and has a six-membered heterocycle in a boat conformation bridged aluminium dihydrides with very bulky substituents are available. [70] Dihydrides bearing smaller substituents may be by an Al atom as a very characteristic structural motif. With the exception of the distances to the unique Al atom formed in trace amounts by the dismutation equilibrium of dialkylaluminium hydrides, and we suppose that they are Al7, short AlϪAl separations were observed, which are between 258.1 and 259.4 pm for the unsupported AlϪAl intermediates in the hydroalumination reactions described here.…”

The First Structurally Characterized Diorganoaluminate

“…The 27 Al resonance (δ ϭ 137 ppm) is at higher frequencies than those in 1a and 1b (δ ϭ 113Ϫ115); similar shifts (δ ϭ 132Ϫ141) have been reported in 2 [19] and other diorganoaluminates. [11] The organoaluminates 1a؊1e are versatile starting materials for the synthesis of a range of organoaluminum derivatives bearing bulky groups, [20,28,29] since the AlϪH bonds are considerably more reactive than the more protected AlϪC bonds towards a variety of reagents. The reactions of the diorganoaluminates 2 and 3 can be expected to lead to a similar range of products containing AlR 2 or AlRRЈ fragments, in which R and RЈ are bulky or fairly bulky organic groups.…”

“…Treatment of LiAlH 4 with LiR (R ϭ C 6 H 2 iPr 3 -2,4,6) followed by SiMe 3 Cl gave AlR 2 H, again suggesting that a diarylaluminate intermediate was formed from the monoaryl species. [20] We have not been able to obtain crystals of 2 suitable for an X-ray structure determination, but we report the synthesis of the related compound [{Li(THF)} (AltBu{C(SiMe 3 ) 3 }H 2 )] 2 (3) and its crystal structure. The iodide AltBu 2 I·THF (4) and the compounds Li(TMEN) n -[AltBu 2 H 2 ] (n ϭ 2, 5; n ϭ 1, 6; TMEN ϭ tetramethylethylenediamine), are also described.…”