Iridium Olefin Complexes Bearing Dialkylamino/amido PNP Pincer Ligands: Synthesis, Reactivity, and Solution Dynamics

The reaction of [IrCl(COE)2]2 (1, COE = cyclooctene) with pincer ligand HN(CH2CH2PiPr2)2 ((PNP)H) and AgPF6 gives iridium(I) amino olefin complex [Ir(COE)(PNP)H]PF6 (3COE-PF6). Without anion exchange, the stability of 3COE-Cl is highly solvent dependent. In benzene or THF a mixture of amido complex [Ir(COE)(PNP)] (4COE), [IrHCl2(PNP)H] (5), and [IrHCl(C8H13)(PNP)H] (6) with a vinylic cyclooctenyl ligand is obtained. A pathway is proposed that includes concurrent trapping of intramolecular C−H versus intermolecular N−H activation products. 3L-PF6 (L = C2H4, C3H6, CO) are prepared by olefin substitution. Deprotonation with KOtBu gives the corresponding amido complexes [IrL(PNP)] (4L; L = COE, C2H4, CO). Reversible COE C−H activation is proposed to account for the fluxional behavior of 3COE-PF6 in solution as compared with the structural rigidity of 4COE, which points toward strong N→Ir π-donation in the amido complexes.

二(环辛烯氯化铱(I))二聚体（[IrCl(COE)₂]₂，其中COE为环辛烯（cyclooctene））与钳形配体（pincer ligand）双(2-二异丙基膦乙基)胺（(PNP)H）以及六氟磷酸银（AgPF₆）反应，得到一价铱氨基烯烃配合物[Ir(环辛烯)(PNP)H]六氟磷酸盐（3COE-PF₆）。若不进行阴离子交换，3COE-Cl的稳定性高度依赖溶剂。在苯或四氢呋喃中，可得到酰胺基配合物（amido complex）[Ir(环辛烯)(PNP)]（4COE）、[IrHCl₂(PNP)H]（5）以及带有乙烯基环辛烯基配体（vinylic cyclooctenyl ligand）的[IrHCl(C₈H₁₃)(PNP)H]（6）的混合物。研究提出了一条同时捕获分子内C-H键活化与分子间N-H键活化产物的反应路径。通过烯烃取代反应可制备3L-六氟磷酸盐（3L-PF₆，L=乙烯（C₂H₄）、丙烯（C₃H₆）、一氧化碳（CO））。用叔丁醇钾（KOᵗBu）去质子化，可得到对应的酰胺基配合物[IrL(PNP)]（4L；L=环辛烯、乙烯、一氧化碳）。相较于4COE的结构刚性，3COE-PF₆在溶液中的流变行为（fluxional behavior）可通过可逆的环辛烯C-H键活化来解释，这表明该类酰胺基配合物中存在较强的N→Ir π给电子作用（π-donation）。