Triphenyl(tetrahydrofuran)aluminium(III)

In the title compound, [Al(C6H5)3(C4H8O)], the Al atom has a distorted tetrahedral geometry. The C—Al—C angles range from 113.25 (7) to 116.27 (8)°, much larger than the O—Al—C angles, which range from 103.39 (7) to 103.90 (6)°. The tetrahydrofuran ring adopts an envelope conformation. The crystal packing is stabilized by C—H⋯π interactions.

In the title compound, [Al(C 6 H 5 ) 3 (C 4 H 8 O)], the Al atom has a distorted tetrahedral geometry. The C-Al-C angles range from 113.25 (7) to 116.27 (8) , much larger than the O-Al-C angles, which range from 103.39 (7) to 103.90 (6) . The tetrahydrofuran ring adopts an envelope conformation. The crystal packing is stabilized by C-HÁ Á Á interactions.

Experimental
Crystal data [Al(C 6

S1. Comment
Triphenylaluminium was first reported 40 years ago and the solid-state study revealed a dimeric Al 2 Ph 6 structure bridging through two phenyl groups (Malone & McDonald, 1967). For synthesis of monomeric triarylaluminium complexes, two synthetic strategies were used. The first route employed a reaction of dimesitylmercury with Al/HgCl 2 , furnishing threecoordinate trimesitylaluminium (Jerius et al., 1986) which possesses a trigonal planar structure. The second synthetic route used a strategy of providing an additional neutral ligand, such as tetrahydrofuran (THF) or diethyl ether (OEt 2 ), giving four-coordinate monomeric AlAr 3 (L) complexes (L = THF or OEt 2 ) (Barber et al., 1982;De Mel & Oliver, 1989).
In addition to structural studies, organoaluminium reagents had been demonstrated as excellent nucleophiles in organic synthesis, owing to their higher reactivity and the Lewis acidity of the aluminium center. Recently, we reported applications of AlAr 3 (THF) in asymmetric aryl additions to aldehydes (Wu & Gau, 2006) and to ketones  and in coupling reactions (Ku et al., 2007). Due to their diversified applications in catalysis, we report herein the synthesis and structure of a four-coordinate triphenylaluminium compound, [Al(C 6 H 5 ) 3 (OC 4 H 8 )].

S2. Experimental
A solution of phenylmagnesium bromide (90.0 mmol) in THF (50 ml) was slowly added to a solution of AlCl 3 (4.00 g, 30.0 mmol) in THF (20 ml) at 273 K. The mixture was stirred at room temperature for 12 h and the solvent was removed under reduced pressure to afford a residue which was extracted with toluene (2 × 40 ml

S3. Refinement
All H atoms were fixed geometrically [C-H = 0.93 Å or 0.97 Å] and treated as riding, with U iso (H) = 1.2U eq (C). The C atoms of the tetrahydrofuran ring display large displacement parameters, but no suitable refinement model for disorder was found.

Figure 1
The molecular structure of the title compound with atom-numbering and displacement ellipsoids drawn at the 20% probability level.

Triphenyl(tetrahydrofuran)aluminium(III)
Crystal data Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.