Cyclic Trimeric Hydroxy, Amido, Phosphido, and Arsenido Derivatives of Aluminum and Gallium. X-ray Structures of [t-Bu₂Ga(µ-OH)]₃ and [t-Bu₂Ga(µ-NH₂)]₃

Reaction of t-Bu₃Al with PH₃ or AsH₃ produces cyclic trimeric complexes of formula [t-Bu₂Al(µ-EH₂)]₃ (E = P (1), As (2), which were identified by their IR, NMR, and mass spectra. From infrared data the ∠H-P-H and ∠H-As-H angles are calculated to be 97 (3) and 105 (3)°, respectively. The adduct t-Bu₃GaNH₃ (3) may be isolated from mixtures of t-Bu₃Ga and NH₃ at room temperature. Heating 3 to 160 °C results in the formation of [t-Bu₂Ga(µ-NH₂)]₃ (4), whose cyclic trimeric structure was confirmed in the solid state by X-ray crystallography. The analogous µ-ND₂ complex 5 can be prepared by substituting ND₃ for NH₃. Reaction of t-Bu₃Ga with H₂O in pentane solution at 25 °C gives the cyclic trimer [t-Bu₂Ga(µ-OH)]₃ (6) in 90% yield. The deuterium-labeled compound [t-Bu₂Ga(µ-OD)]₃ (7) may be prepared in a similar fashion using D₂O. Compound 6 is also formed by the hydrolysis of [t-Bu₂Ga(µ-PH₂)]₃, [t-Bu₂Ga(µ-AsH₂)]₃, and [t-Bu₂Ga(µ-As(t-Bu)H)]₃. The cyclic trimeric structure of 6 was confirmed by X-ray crystallography, which showed a planar Ga₃O₃ ring with t-Bu groups extending above and below the plane. Crystal data for 4: C₂₄H₆₀N₃Ga₃; M_n = 600.03; rhombohedral space group R3̅c; a = 10.443 (2) Å; c = 50.836 (13) Å; V = 4801 (5) ų; Z = 6, D_calc = 1.250 g cm⁻³; µ(Cu Kε) = 11.26 cm⁻¹; 932 unique reflections over the range of 2 < 2θ < 110° (ω/2θ scan mode) were measured; 652 unique observed reflections were used in the refinement with I > 3σ(I); R and R_w = 0.0310 and 0.0329, respectively. Crystal data for 6: C₂₄H₅₇Ga₃; M_n = 602.17; rhombohedral space group R3̅c; a = 10.362 (2) Å; c = 50.927 (10) Å; V = 4735.89 (15) ų; Z = 6, D_calc = 1.262 g cm⁻³; µ(Mo Kα) = 13.4 cm⁻¹, 1117 reflections over the range 3.0 < 2θ < 50.0° (θ/2θ scan mode) were measured; 610 reflections with I > 3σ(I) were used in the refinement; R and R_w = 0.044 and 0.0548, respectively.