Berthoud Romain, Rendón Nuria, Blanc Frédéric, Solans-Monfort Xavier, Copéret Christophe, Eisenstein Odile
Institut de Chimie de Lyon, C2P2, CNRS-Université Lyon 1-ESCPE Lyon, F-308-43 Boulevard du 11 Novembre 1918, F-69616, Villeurbanne Cedex, France.
Dalton Trans. 2009 Aug 14(30):5879-86. doi: 10.1039/b901669d. Epub 2009 Mar 17.
Grafting of Os bisalkylidene complexes, [Os(=CHtBu)(2)(CH(2)tBu)(2)], on a silica partially dehydroxylated at 700 degrees C selectively yields an alkylidyne complex [([triple bond]SiO)Os([triple bond]CtBu)(CH(2)tBu)(2)] according to mass balance analysis, IR and solid state NMR spectroscopies, but 70% of the silanols remains unreacted. Grafting corresponds to a replacement of one alkyl by a siloxy ligand and induces the isomerisation of the metal fragment from a bis-alkylidene to an alkyl alkylidyne. Molecular (B3PW91) and periodic DFT-calculations show that the bis-alkylidene is the energetically favoured isomer for the perhydrocarbyl complex, while the alkyl alkylidyne isomer is more stable when one of the alkyl ligands is replaced by a siloxy ligand. The change of the nature of the ligand is accompanied with a change of geometry: from a distorted tetrahedral structure for [Os(=CHtBu)(2)(CH(2)tBu)(2)] to a butterfly-geometry with apical siloxy and alkylidyne ligands for [([triple bond]SiO)Os([triple bond]CtBu)(CH(2)tBu)(2)]. Finally, DFT calculations show that grafting occurs via a sigma-bond metathesis between the silanol and a metal-alkyl bond and not through the typical addition of the silanol onto the alkylidene ligand.
在700℃下部分脱羟基的硅胶上接枝双亚烷基锇配合物[Os(=CHtBu)(2)(CH(2)tBu)(2)]，根据质量平衡分析、红外光谱和固态核磁共振光谱，选择性地生成了亚烷基配合物[([三键]SiO)Os([三键]CtBu)(CH(2)tBu)(2)]，但70%的硅醇仍未反应。接枝过程相当于一个烷基被硅氧基配体取代，并导致金属片段从双亚烷基异构化为烷基亚烷基。分子（B3PW91）和周期性DFT计算表明，对于全烃基配合物，双亚烷基是能量上更有利的异构体，而当其中一个烷基配体被硅氧基配体取代时，烷基亚烷基异构体更稳定。配体性质的变化伴随着几何结构的变化：从[Os(=CHtBu)(2)(CH(2)tBu)(2)]的扭曲四面体结构变为[([三键]SiO)Os([三键]CtBu)(CH(2)tBu)(2)]的具有顶端硅氧基和亚烷基配体的蝶形几何结构。最后，DFT计算表明，接枝是通过硅醇与金属-烷基键之间的σ键复分解发生的，而不是通过硅醇典型地加成到亚烷基配体上。
