Molecular Group 13 Metallaborates Derived from M-O-M Cleavage Promoted by BH 3 .

The reaction of metalloxanes [{Me LM(OH)}2 (μ-O)] [M = Al (1), Ga (2);Me L = CH{CMe(NAr)}2 - , Ar = 2,4,6-Me3 C6 H2 , Me = methyl] with an excess of BH3 ·D (D = tetrahydrofuran (THF), SMe2 ) affords annular metallaborate systems achieved through M-O-M cleavage. Compound 1 led exclusively to the formation of eight-membered ring systems [{Me LAl(μ-O){B(On Bu)}(μ-O)}2 ] (3) and [{Me LAl(μ-O)(BH)(μ-O)}2 ] (6), while for 2 the unprecedented six-membered ring systems [{(Me LGa)2 (μ-O)}(μ-O)2 {B(On Bu)}] (4) and [(Me LGa)(μ-O)2 {(BOn Bu)2 (μ-O)}] (5) were observed. The use of BH3 ·THF with 1 and 2 led to the concomitant THF ring-opening reaction, while with BH3 ·SMe2 in THF no such reaction was observed. The metallaborates [Me LAl{OB(pinacol)}(OH)] (7) and [{Me LGa(OB(pinacol))}2 (μ-O)] (8) were synthesized from pinacolborane and the corresponding metalloxane, providing structural evidence that supports the reaction pathways proposed for the formation of 3-6. Density functional theory studies were performed on 3-5 to assess the effect of the metal exchange between aluminum and gallium atoms on the energy of the general ring structures.