Group 13 organometallic chemistry
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The syntheses and molecular structures of several organometallic group 13 compounds and complexes are presented herein. The organometallic chemistry of RLi (R = 2,6-(4-t-BuC6H4)2C6H3-) and R´Li (R´ = 2,6-(4-Me-C6H4)2C6H3-) was examined on group 13 halides to yield a number of new compounds 1-8: RGaCl2(OEt2) (1), R2GaCl (2), RAlBr2(OEt2) (3), [RAlCl(OEt2)]2O (4), R3In (5), [R′GaCl3][Li(OEt2)2] (6), [R′InCl3][Li(OEt2)(THF)] (7), R′3In. Compounds 5 and 8 are notable as the first tris-m-terphenyl-group 13 compounds, while 4 is an interesting oxo-bridged-di(m-terphenyl-aluminum chloride) complex with exceptionally long Al−Cl bonds. Sodium metal reduction of 1 provides a rare catenated tri-gallium complex, [R3Ga3][Na(OEt2)]3 (9). Additionally, the organometallic chemistry at the group 13−group 4 interface was explored, wherein three new compounds were isolated: Cp2Hf(ER)2 (10, E = Ga; 11, E = In; R = 2,6-(2,4,6-i-Pr3C6H2)2C6H3-) and (C10H8)(ZrCp)2(μ−H)(μ−Cl)(μ−GaR) (R = 2,6-(4-t-BuC6H4)2C6H3-) (12). Compounds 10 and 11 contain the first reported group 13−Hf bonds, while compound 12 is the only compound with gallium engaged in bonding with two zirconium atoms. Extending the organometallic chemistry of m-terphenyl ligands to the group 4 metallocenes gave the first m-terphenyl−titanium(III) radical Cp2TiR´ (13) and the first m-terphenyl−zirconocene(IV) compound, Cp2ZrR(Cl) (14) (R = 2,6-(4-t-BuC6H4)2C6H3-). This research project also involved the study of heterometallic aromaticity, which ultimately produced the first gallepin, bis(gallepin)2·TMEDA (18), by the reaction of 2,2′-dilithio-Z-stilbene(TMEDA)2 (16) and GaCl3. The aromatic nature of the gallepin was evaluated using Nucleus-Independent Chemical Shifts (NICS) and compared to that of borepins. Additionally, the σ-donor properties of N-heterocyclic carbenes were evaluated on mesityl-group 13 dihalides, wherein several new carbene-mesityl-group 13 dihalide adducts were prepared: MesGaCl2(:L) (19), MesAlBr2(:L) (20), MesInBr2(:L) (21) (Mes = 2,4,6-Me3C6H2-; :L = :C 2). Potassium graphite reduction of 19 yielded a rare meso-digallane, [MesGaCl(:L)]2 (22), with four-coordinate gallium atoms, while reduction with potassium metal unexpectedly produced an unprecedented neutral Ga6-octahedron cluster, Mes4Ga6(:L)2 (23). NICS calculations were used to support its aromatic properties and compared with that of the thoroughly studied dianionic hexaborate octahedron, [B6H6]-2. In conjunction with these studies a new detailed synthetic protocol to prepare Arduengo’s carbene (26) from adamantylammonium chloride was established and full single crystal X-ray structural analysis reported.