Esteruelas Miguel A, Leon Félix, Moreno-Blázquez Sonia, Oliván Montserrat, Oñate Enrique
Departamento de Química Inorgánica - Instituto de Síntesis Química y Catálisis Homogénea (ISQCH) - Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza - CSIC, 50009 Zaragoza, Spain.
Inorg Chem. 2023 Oct 16;62(41):16810-16824. doi: 10.1021/acs.inorgchem.3c02228. Epub 2023 Oct 2.
Iridium centers of [Ir(μ-Cl)(CH)] () activate the C(sp)-H bond of benzylideneacetone to give [Ir(μ-Cl){κ--[C(Ph)CHC(Me)O]}] (), which is the starting point for the preparation of the spiro iridafurans IrCl{κ--[C(Ph)CHC(Me)O]}(PPr) (), [Ir{κ--[C(Ph)CHC(Me)O]}(MeCN)]BF (), [Ir(μ-OH){κ--[C(Ph)CHC(Me)O]}] (), Ir{κ--[C(Ph)CHC(Me)O]}{κ--[CMeH-py]} (), and Ir{κ--[C(Ph)CHC(Me)O]}{κ--[acac]} (). The five-membered rings are orthogonally arranged with the oxygen atoms in in an octahedral environment of the iridium atom. Spiro iridafurans are aromatic. The degree of aromaticity and the negative charge of the CH-carbon of the rings depend on ligand to the carbon directly attached to the metal. Aromaticity has been experimentally confirmed by bromination of iridafurans with -bromosuccinimide (NBS). Reactions are sensitive to the degree of aromaticity of the ring and the negative charge of the attacked CH-carbon. Iridafurans can be selectively brominated, when different ligands lie to metalated carbons. Bromination of occurs in the ring with the metalated carbon to chloride, whereas the bromination of takes place in the ring with the metalated carbon to pyridyl. The first gives IrCl{κ--[C(Ph)CBrC(Me)O]}{κ--[C(Ph)CHC(Me)O]}(PPr) (), which reacts with more NBS to form IrCl{κ--[C(Ph)CBrC(Me)O]}(PPr) (). The second yields Ir{κ--[C(Ph)CBrC(Me)O]}{κ--[C(Ph)CHC(Me)O]}{κ--[CMeH-py]} (). The origin of the selectivity is kinetic, with the rate-determining step of the reaction being the NBS attack. The activation energy depends on the negative charge of the attacked atom; a higher negative charge allows for a lower activation energy. Accordingly, complex undergoes bromination in the acetylacetonate ligand, giving Ir{κ--[C(Ph)CHC(Me)O]}{κ--[acacBr]} ().
[Ir(μ-Cl)(CH)]（）的铱中心激活亚苄基丙酮的C(sp)-H键，生成[Ir(μ-Cl){κ--[C(Ph)CHC(Me)O]}]（），这是制备螺铱呋喃IrCl{κ--[C(Ph)CHC(Me)O]}(PPr)（）、[Ir{κ--[C(Ph)CHC(Me)O]}(MeCN)]BF（）、[Ir(μ-OH){κ--[C(Ph)CHC(Me)O]}]（）、Ir{κ--[C(Ph)CHC(Me)O]}{κ--[CMeH-py]}（）和Ir{κ--[C(Ph)CHC(Me)O]}{κ--[acac]}（）的起始点。在铱原子的八面体环境中，五元环与中的氧原子正交排列。螺铱呋喃具有芳香性。环的芳香性程度和环中CH-碳的负电荷取决于与直接连接到金属的碳相连的配体。通过用N-溴代琥珀酰亚胺（NBS）对铱呋喃进行溴化反应，已通过实验证实了芳香性。反应对环的芳香性程度和被攻击的CH-碳的负电荷敏感。当不同的配体与金属化碳相邻时，铱呋喃可以被选择性溴化。对的溴化发生在与氯相邻的金属化碳所在的环中，而对的溴化发生在与吡啶基相邻的金属化碳所在的环中。前者生成IrCl{κ--[C(Ph)CBrC(Me)O]}{κ--[C(Ph)CHC(Me)O]}(PPr)（），它与更多的NBS反应形成IrCl{κ--[C(Ph)CBrC(Me)O]}(PPr)（）。后者生成Ir{κ--[C(Ph)CBrC(Me)O]}{κ--[C(Ph)CHC(Me)O]}{κ--[CMeH-py]}（）。选择性的起源是动力学的，反应的速率决定步骤是NBS的攻击。活化能取决于被攻击原子的负电荷；较高的负电荷允许较低的活化能。因此，配合物在乙酰丙酮配体中发生溴化反应，生成Ir{κ--[C(Ph)CHC(Me)O]}{κ--[acacBr]}（）。
