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

The hexanuclear iridiurn complex [eta(4)-(COD)Ir](2) {eta(6)-[kappa(4)-C6H2(CH2P'Bu-2)(2)]Ir2H2Cl3} (1) has been prepared by the reaction of [Ir(COD)Cl](2) with the "PCP" ligand precursor, 1,3-C6H4(CH2P'Bu-2)(2) (PCP-H). Characterization by X-ray diffraction reveals that complex I 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 kappa(3)-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 P2(1)/n with lattice parameters a = 14.4154(11) Angstrom, b = 15.4435(12) Angstrom, c = 19.5181(15) Angstrom, b = 99.996(1)degrees and V = 4279.31(6) Angstrom(3). 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 > 4sigma(F). Complex I also crystallizes as the octabenzene solvate in the orthorhombic space group Pbca, with lattice parameters a = 16.4247(14) Angstrom, b = 24.1695(21) Angstrom, c = 28.0460(24) Angstrom and V = 11134(1) Angstrom(3). Convergence of the orthorhombic phase to R(F) = 0.038 and R-w(F) = 0.084 was obtained for 595 variable parameters and 12 885 reflections with F > 4sigma(F). (C) 2004 Elsevier B.V. All rights reserved.