Acceptor PCP pincer iridium chemistry: (CF3PCP) IrIII coordination properties

Article abstract of DOI:10.1021/om1008633

The syntheses of Ir(I) and Ir(III) complexes incorporating the electron-poor pincer ligand (1,3-C₆H₃(CH ₂P(CF₃)₂)₂) (^CF ₃PCP) are reported. Under mild conditions, the reaction of ^CF₃PCPH with [(cod)Ir(μ-Cl)]₂ in benzene gave polymeric [(cod)IrCl(μ-^CF₃PCPH)]_n, which was structurally characterized. Thermolysis of [(coe)₂Ir(μ- Cl)]₂ or [(cod)Ir(μ-Cl)]₂ with ^CF ₃PCPH in toluene at 120 °C resulted in metalation to give not the anticipated 16-electron (^CF₃PCP)Ir(H)Cl product but rather the coordinatively saturated ^CF₃PCPH-bridged dimer {(^CF₃PCP)Ir(H)Cl}₂(μ-^CF ₃PCPH). The bridging ^CF₃PCPH ligand is readily displaced to afford the monomeric products (^CF₃PCP)Ir(L) (H)Cl (L = CO, MeCN); the direct synthesis of (^CF₃PCP) Ir(L)(H)Cl (L = CO, MeCN, PhCN, C₂H₄, MeP(C ₂F₅)₂) was achieved by reacting [(coe) ₂Ir(μ-Cl)]₂ or [(cod)Ir(μ-Cl)]₂ with 2 equiv of ^CF₃PCPH in the presence of the corresponding trapping ligand. Chloride abstraction from (^CF₃PCP)Ir(CO) (H)Cl was examined: treatment with AgSbF₆ or Et₃Si ⁺B(C₆F₅)₄^- in the presence of 1 atm of CO in CH₂Cl₂ or 1,2-difluorobenzene cleanly afforded cis-(^CF₃PCP)Ir(CO)₂(H) ⁺, and the cis CO coordination geometry was confirmed by X-ray diffraction. Chloride abstraction in the presence of ethylene similarly gave (^CF₃PCP)Ir(CO)(C₂H₄)(H) ⁺, and abstraction with AgSbF₆ in the absence of trapping ligands afforded the Cl-bridged dimer {[(^CF₃PCP)Ir(CO)(H)] ₂(μ-Cl)}⁺, which was structurally characterized. Facile displacement of MeCN from (^CF₃PCP)Ir(MeCN)(H)Cl with PPh₃ was observed to give an 8:1 isomeric mixture of ( ^CF₃PCP)Ir(PPh₃)(H)Cl at-15 °C, with the major species having PPh₃ trans to the hydride.