Reactions of (H<sub>2</sub>AlMes*)<sub>2</sub> (Mes* = 2,4,6-(<i>t</i>-Bu)<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) with H<sub>2</sub>EAr (E = N, P, or As; Ar = aryl):  Characterization of the Ring Compounds (Mes*AlNPh)<sub>2</sub> and (Mes*AlEPh)<sub>3</sub> (E = P or As)

1996-01-31T00:00:00Z (GMT) by Rudolf J. Wehmschulte Philip P. Power
The reaction between sterically crowded, dimeric, arylalane (H<sub>2</sub>AlMes*)<sub>2</sub> and some aryl amines, phosphines, or arsines are described. Treatment of (H<sub>2</sub>AlMes*)<sub>2</sub> (Mes* = 2,4,6-(<i>t</i>-Bu)<sub>3</sub>C<sub>6</sub>H<sub>2</sub>) with the amines H<sub>2</sub>NPh and H<sub>2</sub>NDipp (Dipp = 2,6-(<i>i</i>-Pr)<sub>2</sub>C<sub>6</sub>H<sub>3</sub>) affords the monomeric bis(amino)alane products Mes*Al(NHPh)<sub>2</sub>·Et<sub>2</sub>O (<b>1</b>·Et<sub>2</sub>O) and Mes*Al(NHDipp)<sub>2</sub> (<b>2</b>) which feature three-coordinate aluminum and nitrogen centers and short Al−N bonds. Heating of a 1:1 mixture of H<sub>2</sub>AlMes* and aniline under carefully controlled conditions affords the dimer (Mes*AlNPh)<sub>2</sub>, <b>3</b>. Reaction of (Mes*AlH<sub>2</sub>)<sub>2</sub> with H<sub>2</sub>PPh or H<sub>2</sub>AsPh at <i>ca. </i>160 °C gives the trimeric, six-membered-ring compounds (Mes*AlPPh)<sub>3</sub>·Et<sub>2</sub>O (<b>4</b>·Et<sub>2</sub>O) and (Mes*AlAsPh)<sub>3</sub>·Et<sub>2</sub>O (<b>5</b>·Et<sub>2</sub>O) which are formal valence analogues of borazine. The structure of <b>3</b> features a planar Al<sub>2</sub>N<sub>2</sub> core, which also extends to the ipso carbons of the aryl rings; the Al−N distance is 1.824(2) Å. The structures of <b>4</b> and <b>5</b> have six-membered rings of alternating aluminum and phosphorus or arsenic atoms arranged in a nonplanar boat conformation. Little or no delocalization of the phosphorus or arsenic lone pairs is evident since the average Al−P and Al−As distances are consistent with single bond lengths. Moreover, pyramidal coordination is observed at all the pnictide centers. The structures of <b>5 </b>and <b>4</b> represent respectively the first and second examples of bonding between three-coordinate aluminum and arsenic or phosphorus, whereas <b>3</b> represents a unique instance of an Al<sub>2</sub>N<sub>2</sub> ring with organic substituents. The compounds were characterized by <sup>1</sup>H, <sup>13</sup>C, and <sup>31</sup>P (<b>4</b>, only) NMR spectroscopy and by X-ray crystallography in the case of <b>1</b>, <b>3</b>, <b>4</b>, and <b>5</b>. Crystal data with Cu Kα (λ = 1.54178 Å) radiation at 130 K:  <b>1</b>, <i>a</i> = 10.255(3) Å, <i>b</i> = 16.733(5) Å, <i>c</i> = 19.267(8) Å, β = 95.09(3)°, <i>V</i> = 3293(2) Å<sup>3</sup>, <i>Z</i> = 4, space group <i>P</i>2<sub>1</sub>/<i>c</i>, 3070 (<i>I</i> > 2σ(<i>I</i>)) data, <i>R</i> = 0.061; <b>3</b>, <i>a</i> = 8.750(1) Å, <i>b</i> = 9.326(2) Å, <i>c</i> = 14.025(3) Å, α = 101.04(2)°, β = 92.90(1)°, γ = 113.11(1)°, <i>V</i> = 1088.7(4) Å<sup>3</sup>, <i>Z</i> = 1, space group <i>P</i>1̄, 2629 (<i>I</i> > 2σ(<i>I</i>)) data, <i>R</i> = 0.053; <b>4</b>, <i>a</i> = 9.383(5) Å, <i>b</i> = 17.719(7) Å, <i>c</i> = 23.603(14) Å, α = 80.86(4)°, β = 82.50(5)°, γ = 75.61°(4), <i>V</i> = 3736(3) Å<sup>3</sup>, <i>Z</i> = 2, space group <i>P</i>1̄, 5626 (<i>I</i> > 2σ(<i>I</i>)) data, <i>R</i> = 0.084; <b>5</b>, <i>a</i> = 9.404(7) Å, <i>b</i> = 17.79(2) Å, <i>c</i> = 23.643(10) Å, α = 81.01(6)°, β = 83.04(5)°, γ = 75.68(7)°, <i>V</i> = 3771(5) Å<sup>3</sup>, <i>Z</i> = 2, space group <i>P</i>1̄, 6363 (<i>I </i>> 2σ(<i>I</i>)) data, <i>R</i> = 0.063.