Group 13 Heavier Carbene Analogues Stabilized by the Bulky Bis(4-benzhydryl-benzoxazol-2-yl)methanide Ligand.

Abstract

On the basis of the bulky bis(4-benzhydryl-benzoxazyl-2-yl)methane ligand (4-BzhH2Box2CH2), neutral monovalent group 13 complexes [M13(4-BzhH2Box2CH)] [M13 = Tl (1), In (2), or Ga (3)] have been synthesized by salt metathesis reaction of the corresponding potassium or sodium precursor and TlOTf, InOTf, or "GaI". The diiodido gallium species [GaI2(4-BzhH2Box2CH)] (3a) was realized as a byproduct once the synthesis of 3 was carried out at higher temperatures. The synthesis of [AlI2(4-BzhH2Box2CH)] (6) as a potential precursor for an aluminum(I) congener was accomplished by two alternative synthetic routes. During one of those procedures, [AlMe2(4-BzhH2Box2CH)] (4) was synthesized in good yields by deprotonation with an AlMe3 solution (method A). Subsequently, 4 was converted to the monoiodinated species [AlMeI(4-BzhH2Box2CH2)] (5) using 1 equiv of I2 or to 6 by iodination with 2 equiv of I2 at 70 °C for 4 days. As an alternative, complex 6 could be prepared by iodination of 1 equiv of I2 and [AlH2(4-BzhH2Box2CH)] (7), which was previously obtained by facile reaction of 4-BzhH2Box2CH2 and AlH3NMe2Et. All main products 1-7 were completely characterized by nuclear magnetic resonance spectroscopy, mass spectrometry, elemental analysis, and single-crystal X-ray structure determination. Alane 7 was additionally analyzed by solid-state fluorescence spectroscopy. Density functional theory calculations on [M13(4-BzhH2Box2CH)] [M13 = Tl (1), In (2), Ga (3), or Al] revealed that the complexes consist of monovalent group 13 cations coordinated by an anionic (4-BzhH2Box2CH) ligand similar to metallacycles incorporating a NacNac ligand.