Cooperativity in Bimetallic Dihydroalkoxylation Catalysts Built on Aromatic Scaffolds: Significant Rate Enhancements with a Rigid Anthracene Scaffold

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• 作者：Joanne H. H. Ho ; Sandra W. S. Choy ; Stuart A. Macgregor ; Barbara A. Messerle
• 刊名：Organometallics
• 出版年：2011
• 出版时间：November 14, 2011
• 年：2011
• 卷：30
• 期：21
• 页码：5978-5984
• 全文大小：377K
• 年卷期：v.30,no.21(November 14, 2011)
• ISSN：1520-6041

文摘

This work describes investigations into metal-catalyzed sequential reactions using a series of single metal and bimetallic Rh(I) and/or Ir(I) pyrazolyl complexes. Monometallic complexes with bis(1-pyrazolyl)methane (bpm) ligands [M(CO)₂(bpm)]BAr^F₄ (1), bimetallic complexes [M₂(CO)₂(L_scaffold)][BAr^F₄]₂ (2鈥?b>4) where M = Rh(I) or Ir(I) bearing bitopic ligands L_scaffold = bis(1-pyrazolyl)methane-derived ligands, p-C₆H₄[CH(pz)₂]₂ (L_p), m-C₆H₄[CH(pz)₂]₂ (L_m), and anthracene-bridged 1,8-C₁₄H₈[CH(pz)₂]₂ (L_Ant), [M₂(CO)₄(L_p)][BAr^F₄]₂ (2), [M₂(CO)₄(L_m)][BAr^F₄]₂ (3), and [M₂(CO)₄(L_Ant)][BAr^F₄]₂ (4) were used as catalysts. The efficiency of the complexes as catalysts was tested for the dihydroalkoxylation of a series of alkyne diol substrates, 2-(6-hydroxyhex-1-ynyl)benzyl alcohol (5), 1-methyl-3-heptyne-1,7-diol (6), 2-(5-hydroxypent-1-ynyl)benzyl alcohol (7), and 2-(4-hydroxybut-1-ynyl)benzyl alcohol (8), forming spiroketals. All complexes tested were highly effective catalysts for the intramolecular dihydroalkoxylation reaction. The homobimetallic complexes 2鈥?b>4 showed significant enhancement in activity and selectivity relative to the single metal catalysts (1). The order of catalytic activity of the bimetallic complexes was found to be [M₂(CO)₄(L_Ant)][BAr^F₄]₂ > [M₂(CO)₄(L_m)][BAr^F₄]₂ > [M₂(CO)₄(L_p)][BAr^F₄]₂ for all substrates, and the bimetallic cooperativity index was established for each reaction.