University of Florida, Department of Chemistry, Center for Catalysis, P.O. Box 117200, Gainesville, Florida 32611, USA.
Dalton Trans. 2013 Mar 14;42(10):3326-36. doi: 10.1039/c2dt32653a. Epub 2013 Jan 8.
This report presents the synthesis of the first neutral trianionic ONO pincer-type tungsten alkylidyne complex, [CF(3)-ONO]W≡C((t)Bu)(OEt(2)) (5) {where CF(3)-ONO = (MeC(6)H(3)[C(CF(3))(2)O])(2)N(3-)}. Treating 5 with 1-phenylpropyne, 4,4-dimethyl-2-pentyne, and cyclooctyne yields the corresponding tungstenacyclobutadiene complexes [CF(3)-ONO]W[κ(2)-C((t)Bu)C(Me)C(Ph)] (6), [CF(3)-ONO]W[κ(2)-C((t)Bu)C(Me)C((t)Bu)] (7), and [CF(3)-ONO]W[κ(2)-C((t)Bu)C(CH(2))(6)C] (8). Complexes 6, 7, and 8 do not undergo retro-[2 + 2]-cycloaddition even at 200 °C or in the presence of PMe(3). DFT methods to elucidate the electronic structure of complexes 5 and 6 reveal important electronic factors that contribute to the lack of reactivity for the tungstenacyclobutadienes. An important bonding combination between the pincer N-atom lone pair and the W[triple bond, length as m-dash]C bond within 5, termed an inorganic enamine, provides an explanation for the lack of retro-[2 + 2]-cycloaddition from 6, 7, and 8. (15)N NMR spectroscopy was used to confirm the computational finding of an inorganic enamine bonding combination. Single crystal X-ray analysis of 5, 6, 7, and 8 provides insight into possible steric inadequacies within the CF(3)-ONO(3-) ligand to promote catalytic metathesis.
本报告介绍了首例中性三阴离子 ONO 型钳式钨烷基炔配合物 [CF3-ONO]W≡C((t)Bu)(OEt2) (5) 的合成，其中 CF3-ONO = (MeC6H3[C(CF3)2O])(2)N(3-)。用 1-丙炔、4,4-二甲基-2-戊炔和环辛炔处理 5，得到相应的钨环丁二烯配合物 [CF3-ONO]W[κ2-C((t)Bu)C(Me)C(Ph)] (6)、[CF3-ONO]W[κ2-C((t)Bu)C(Me)C((t)Bu)] (7) 和 [CF3-ONO]W[κ2-C((t)Bu)C(CH2)(6)C] (8)。配合物 6、7 和 8 即使在 200°C 或存在 PMe3 的情况下也不会发生反-[2 + 2]-环加成。阐明配合物 5 和 6 电子结构的 DFT 方法揭示了导致钨环丁二烯缺乏反应性的重要电子因素。在 5 中，钳式 N-原子孤对电子和 W[叁键，长度 as m-dash]C 键之间形成的重要键合组合，称为无机烯胺，为 6、7 和 8 中缺乏反-[2 + 2]-环加成提供了解释。(15)N NMR 光谱用于证实了计算发现的无机烯胺键合组合。5、6、7 和 8 的单晶 X 射线分析提供了有关 CF3-ONO(3-)配体促进催化复分解反应时可能存在的空间位阻不足的见解。
