Alkenyl Derivatives of the Unsaturated Dimolybdenum Hydride Complex [Mo2(5-C5H5)2(-H)(-PCy2)(CO)2]

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• 作者：M. Angeles Alvarez ; M. Esther Garc&iacute ; a ; Alberto Ramos ; Miguel A. Ruiz ; Maurizio Lanfranchi ; Antonio Tiripicchio
• 刊名：Organometallics
• 出版年：2007
• 出版时间：November 5, 2007
• 年：2007
• 卷：26
• 期：23
• 页码：5454 - 5467
• 全文大小：233K
• 年卷期：v.26,no.23(November 5, 2007)
• ISSN：1520-6041

文摘

The 30-electron hydride complex [Mo₂Cp₂(-H)(-PCy₂)(CO)₂] reacts at room temperature withp-tolylacetylene to give the unsaturated :-bonded alkenyl derivatives trans-[Mo₂Cp₂(-¹:²-CRCH₂)(-PCy₂)(CO)₂] and trans-[Mo₂Cp₂(-¹:²-CHCHR)(-PCy₂)(CO)₂] (R = ptol; Cp = ⁵-C₅H₅), withthe -substituted alkenyl complex being transformed completely into its -substituted isomer slowly atroom temperature. In solution, both compounds exhibit an isomeric equilibrium (rapid on the NMR timescale) involving the alternate -binding of the alkenyl ligand to each of the metal centers. In addition,the presence of CO allows the partial conversion of the -substituted complex into its cis-dicarbonylisomer cis-[Mo₂Cp₂(-¹:²-CRCH₂)(-PCy₂)(CO)₂], so as to reach a roughly equimolar equilibrium ratio.In contrast, the -substituted alkenyl complex experiences full carbonylation under the same conditionsto give the tricarbonyl complex [Mo₂Cp₂{-¹:²-CHCHR}(-PCy₂)(CO)₃], but similarly displaying acisoid arrangement of the Cp ligands. The title hydride complex also reacts at room temperature withmethyl propiolate, to afford the -alkenyl complexes cis- and trans-[Mo₂Cp₂{-¹:²-C(CO₂Me)CH₂}(-PCy₂)(CO)₂], which are in a solvent-dependent equilibrium and are also involved in further dynamicprocesses derived from the flipping of the alkenyl ligand, but do not undergo - alkenyl isomerization.This reaction also gives smaller amounts of the 30-electron alkenylphosphine complex [Mo₂Cp₂{-¹:²-Cy₂PCHCH(CO₂Me)}(CO)₂] (Mo-Mo = 2.526(2) Å), formed through a reductive elimination betweenthe alkenyl and dicyclohexylphosphide ligands. The title hydride complex also reacts at room temperaturewith an internal alkyne such as dimethylacetylenedicarboxylate to give alkenyl derivatives, but now theunsaturation of the metal center induces the coordination of one of the oxygen atoms of the carboxylategroup in the -position to give three different C,C,O-bonded isomers of the electron-precise [Mo₂Cp₂{-¹,:²-C(CO₂Me)CH(CO₂Me)}(-PCy₂)(CO)₂], all of them characterized through single-crystal X-raydiffraction studies. Two of these isomers, which are in a slow equilibrium in solution, display a similartransoid arrangement of the CO and Cp ligands, but have different relative arrangements of the alkenyland phosphide bridges, implying transoid or cisoid positions of the metal-bound P and O atoms,respectively. The third isomer displays a cisoid arrangement of the Cp and CO ligands, but a transoidposition of the metal-bound P and O atoms. All three isomers exhibit relatively large intermetallicseparations (ca. 2.88-2.96 Å), as expected for molecules having single Mo-Mo bonds.