Polyfunctional phosphine ligands II. Iridium(I) complexes of the 7-diphenylphosphino-2,4-dimethyl-1,8-naphthyridine (dpnapy) ligand. X-ray crystal structure of [{Ir(cod)Cl}2(μ-dpnapy)]

The coordination chemistry of the polyfunctional phosphine ligand, 7-diphenylphosphino-2,4-dimethyl-1,8- naphthyridine (dpnapy) with iridium(I) complexes has been investigated. Dpnapy reacts with cis-[Ir(CO)2(p- toluidine)Cl] in 1:2 and 1:1 molar ratios giving the P-monodentate containing ligand complexes trans- [Ir(CO)(dpnapy)2Cl] (1) and cis-[Ir(CO)2(dpnapy)Cl] (2), respectively. Complex 2 is unstable in solution; IR and 31P NMR spectroscopic data show at r.t. it transforms into 1 in a short time. The reaction of dpnapy with [{Ir(cod)Cl}2] (cod=cycloocta-1,5-diene) also depends on the metal to ligand ratio used. The mononuclear complex [Ir(cod)(dpnapy)Cl] (3), containing P-coordinated dpnapy, is obtained from the 1:2 dimer:ligand reaction. The 1H and 13C NMR spectra of 3 are temperature dependent. They show that the fluxional behaviour involves the cod ligand and is explained by the formation of a labile five-coordinate intermediate displaying a fast exchange of the non-equivalent cod protons and carbons. Treatment of 3 with AgClO4 leads to a species, formulated on the basis of IR and analytical data, as [{Ir(cod)(dpnapy)}ClO4] (4) in which dpnapy is very likely PN(8) chelated. The binuclear complex [{Ir(cod)Cl}2(μ-dpnapy)] (5), containing a bridging bidentate dpnapy, is obtained from the 1:1 [{Ir(cod)Cl}2]:dpnapy reaction. The bridging function of dpnapy is realized through the phosphorus and the terminal nitrogen binding sites in agreement with the NMR data and as confirmed by an X-ray analysis. Complex 5 crystallizes into the monoclinic space group P21/n with cell parameters a=17.813(4), b=12.339(3), c=18.221(5) Å, β=106.73(2)° and with Z=4. The structure model, with all the non-H atoms anisotropic, was refined up to R=0.040 and Rw=0.050 with the goodness-of-fit=0.91. The asymmetric unit contains one discrete molecule constitued by two independent square-planar iridium moieties, considering each ethylenic system of cycloocta-1,5-diene like a unique coordination site. No interaction exists between the two iridium metal centres.