A hexanuclear iridium complex with a novel binding mode of a PCP-pincer ligand

The hexanuclear iridium complex [η⁴-(COD)Ir] ₂{η⁶-[κ⁴-C₆H ₂(CH₂P^tBu₂)₂]Ir ₂H₂Cl₃} (1) has been prepared by the reaction of [Ir(COD)Cl]₂ with the "PCP" ligand precursor, 1,3-C ₆H₄(CH₂P^tBu₂) ₂ (PCP-H). Characterization by X-ray diffraction reveals that complex 1 has an unusual structure in which metalation (C-H addition) of the ligand has occurred at the 4- and 6-positions of the PCP aryl ring. This is in contrast to the widespread reactivity of this ligand precursor in which a single metalation typically occurs at the 2-position, thereby allowing coordination of both phosphino groups to a single metal center to give the κ³- meridional pincer coordination. The complex can be viewed as being composed of a dimer of two bis-metalated (Ir(III)) PCP units, held together by two bridges of three chlorides each; the aryl ring of each of the PCP ligands of this hypothetical tetra-iridium dianion is then bound to a cationic [Ir(I)(COD)] ⁺ unit. The structure discussed here crystallizes as the tetra(acetone) solvate in the monoclinic space group P2₁/n with lattice parameters a=14.4154(11) Å, b=15.4435(12) Å, c=19.5181(15) Å, b=99.996(1)°and V=4279.31(6) ų. Convergence to conventional R values of R(F)=0.041 and R_w(F)=0.092 was obtained for 445 variable parameters and 8085 reflections with F>4σ(F). Complex 1 also crystallizes as the octabenzene solvate in the orthorhombic space group Pbca, with lattice parameters a=16.4247(14) Å, b=24.1695(21) Å, c=28.0460(24) Å and V=11134(1) ų. Convergence of the orthorhombic phase to R(F)=0.038 and R_w(F)=0.084 was obtained for 595 variable parameters and 12885 reflections with F>4σ(F).