Unsymmetrical PNP-Pincer Type Phosphaalkene Ligands Protected by a Fused-Ring Bulky Eind Group: Synthesis and Applications to Rh(I) and Ir(I) Complexes

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• 作者：Hiro-omi Taguchi ; Daichi Sasaki ; Katsuhiko Takeuchi ; Shota Tsujimoto ; Tsukasa Matsuo ; Hiromasa Tanaka ; Kazunari Yoshizawa ; Fumiyuki Ozawa
• 刊名：Organometallics
• 出版年：2016
• 出版时间：May 23, 2016
• 年：2016
• 卷：35
• 期：10
• 页码：1526-1533
• 全文大小：442K
• 年卷期：0
• ISSN：1520-6041

文摘

We recently reported that 2-(phospholanylmethyl)-6-(2-phosphaethenyl)pyridine (PPEP) with a 2,4,6-tri-tert-butylphenyl group (Mes*) as steric protection of the P═C bond serves as a noninnocent ligand on Ir(I), leading to extremely high reactivity toward metal–ligand cooperative activation of ammonia and acetonitrile. The high reactivity is largely due to the strong π-accepting properties of the P═C bond. However, PPEP had a stability problem that provokes the loss of the P═C bond on other transition metals, including Rh(I), and restricts its utilization. This paper describes the synthesis of Eind-PPEP protected by an octaethyl-s-hydrindacen-4-yl group (Eind) instead of Mes*. The fused-ring bulky Eind group successfully prevents the loss of the P═C bond and enables us to compare the reactivity of Rh(I) and Ir(I) complexes toward ammonia. The complex K[RhCl(Eind-PPEP*)], bearing a dearomatized Eind-PPEP* ligand, undergoes simple ligand displacement to give [Rh(NH₃)(Eind-PPEP*)], whereas the iridium analogue K[IrCl(Eind-PPEP*)] causes N–H bond cleavage to form [Ir(NH₂)(Eind-PPEP)]. DFT calculations indicate a thermodynamic cause of the metal-dependent product change.