Conversion of a Hydrido鈥揃utenylcarbyne Complex to 畏2-Allene-Coordinated Complexes and Metallabenzenes

详细信息    查看全文

• 作者：Jinxiang Chen ; Chunhong Zhang ; Tingwan Xie ; Ting Bin Wen ; Hong Zhang ; Haiping Xia
• 刊名：Organometallics
• 出版年：2013
• 出版时间：July 22, 2013
• 年：2013
• 卷：32
• 期：14
• 页码：3993-4001
• 全文大小：508K
• 年卷期：v.32,no.14(July 22, 2013)
• ISSN：1520-6041

文摘

Treatment of OsCl₂(PPh₃)₃ with HC鈮CH(OH)Et produces the cyclic complex Os(PPh₃)₂Cl₂(CHC(PPh₃)CH(OH)CH₂CH₃) (1), which can undergo dehydration to give the hydrido鈥揳lkenylvinylidene complex Os(PPh₃)₂HCl₂(鈺怌鈺怌(PPh₃)CH鈺怌HCH₃) (2). Reaction of 2 with HBF₄ generates the hydrido鈥揵utenylcarbyne complex [OsHCl₂(鈮C(PPh₃)鈺怌H(Et))(PPh₃)₂]BF₄ (3). The complex 3 evolves into the unstable metallabenzene [(PPh₃)₂(RCN)ClOs(CHC(PPh₃)CHCHCH)]BF₄ (4; RCN = benzonitrile, 2-cyanobenzaldehyde, 3-methoxyacrylonitrile, 2-cyanoacetamide) via triple hydrogen eliminations in the presence of excess nitriles in refluxing CHCl₃ in an air atmosphere. The ligand substitution reaction of 4 with excess CO affords the stable metallabenzene product [(PPh₃)₂(CO)ClOs(CHC(PPh₃)CHCHCH)]BF₄ (5). The key intermediates, 畏²-allene-coordinated osmium complexes [(PPh₃)₂(RCN)ClOs(CH鈺怌(PPh₃)CH鈺怌鈺怌H₂)]BF₄ (6; RCN = benzonitrile, 2-cyanobenzaldehyde, 3-methoxyacrylonitrile, 2-cyanoacetamide) can be captured by performing the conversion at room temperature. Remarkably, in the absence of nitriles, reaction of 3 with excess CO only generates the vinylethenyl complex [(PPh₃)₂(CO)₂ClOs(CH鈺怌(PPh₃)CH鈺怌HCH₃)]BF₄ (7). The complexes 1鈥?b>3, 5, 6a, and 7 have been structurally characterized by single-crystal X-ray diffraction. Detailed mechanisms of the conversions have been investigated with the aid of density functional theory (DFT) calculations. DFT calculations suggest that the high stablility of the carbonyl coordinated complexes in the conversion inhibits the further transformation to metallabenzene product. However, the transformation is both kinetically and thermodynamically favorable in the presence of the relatively weaker nitrile ligand, which is consistent with the experimental conversion of 3 to 5 via unstable metallabenzenes 4 observed for in situ NMR experiments.