Reaction of the Phenoxide Ion with Trimethylaluminum. Isolation and Crystal Structure of [K•dibenzo-18-crown-6][Al₂Me₆OPh] and K[AlMe₂(OPh)₂]

Potassium phenoxide reacts cleanly with trimethylaluminum in toluene in the presence of a 1:1 ratio of crown ether to salt. The product [K·dibenzo-18-crown-6][Al₂Me₆OPh], 1, was crystallized by cooling from 70 °C to room temperature. In a 1:2 ratio of crown ether to salt, the temperature must be raised to ca. 160 °C for complete reaction. Slow cooling afforded K[AlMe₂(OPh)₂], 2, as the possible decomposition product of [Al₂Me₆OPh]^-1 belongs to the monoclinic space group P2₁/n with a = 19.763 (6) Å, b = 9.830 (3) Å, c = 20.661 (6) Å, β = 116.00 (2)°, and ρ_calcd = 1.18 g/cm³ for Z = 4. The structure was refined to R = 0.088 with 1756 observed reflections. 2 crystallizes in the orthorhombic space group Pbcn with a = 20.487 (6) Å, b = 10.129 (4) Å, c = 7.259 (3) Å, and ρ_calcd=1.24 g/cm³ for Z = 4. The refinement based on 483 observed reflections led to R = 0.031. The anion of 1 has a Y-shaped structure with Al-O-Al = 128.3 (7)° and Al-O = 1.86 (1) Å. The plane of the phenyl ring makes a 77° angle with the Al-O-Al plane. The anion of 2 resides on a crystallographic twofold axis with the Al-O length a short 1.800 (3) Å.