Ruthenium Alkylidene Complexes of Chelating Amine Ligands

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• 作者：Giovanni Occhipinti ; Hans-Ren&eacute ; Bjrsvik ; Karl Wilhelm Tö ; rnroos ; Vidar R. Jensen
• 刊名：Organometallics
• 出版年：2007
• 出版时间：November 19, 2007
• 年：2007
• 卷：26
• 期：24
• 页码：5803 - 5814
• 全文大小：304K
• 年卷期：v.26,no.24(November 19, 2007)
• ISSN：1520-6041

文摘

A density functional theory-based computational comparison of various [Ru]-L bonds in L(PCy₃)Cl₂Ru=CH₂ complexes, where L is a dative ligand, shows that similar bond strengths can be expected forruthenium-imine and ruthenium-amine bonds. The similarity remains when comparing the correspondingbond strengths in ruthenium olefin metathesis catalysts coordinated by bidentate Schiff-base ligands withthose of ruthenium complexes of corresponding chelating amino-benzyloxy ligands. This observationprompted us to synthesize two bidentate amino-benzyloxy ligands and one tridentate amino-bis(benzyloxy)ligand. Ruthenium alkylidene complexes coordinated by the bidentate ligands proved to be unstable andeluded isolation. Reaction of the potassium salt of the tridentate ligand with (PCy₃)₂Cl₂Ru=CHPh and(PCy₃)₂Cl₂Ru(=CH-o-OⁱPrC₆H₄) resulted in two complexes, 10 and 11, respectively, that represent thefirst examples of ruthenium alkylidenes (arylidenes) coordinated by an amine. 10 and 11 contain anessentially symmetrically coordinated tridentate ligand and both are also coordinated by a tri-cyclohexyl-phosphine ligand. The isopropyloxy function of the alkylidene group in 11 is not coordinated to themetal. Complexes 10 and 11 are fairly stable to air, moisture, and protic solvents, but display low thermalstability. Only very low catalytic activity has been obtained in ring-closing metathesis of diethyldiallylmalonate using 10 or 11 dissolved in acid-free solvents. The presence of a Brnsted acid increasesthe activity dramatically, although at the expense of an increased decomposition rate of the catalyst.