c‒x vs. c‒h activation for the ssynthesis of the cyclometalated complexes [pd(yphbpy)x] (hphbpy = 6-phenyl-2,2’-bipyridine; x/y = (pseudo)halides)

the organometallic pd(ii) complexes [pd(phbpy)x] (x = cl, br, or i) containing the tridentate c^n^n cyclometalating ligand 6-(phen- 2-ide)-2,2’-bipyridine (‒phbpy) were synthesised through oxidative addition using the protoligands x‒phbpy (x = cl, br and i) and [pd2(dba)3] tris(dibenzylideneacetone)dipalladium(0) in yields ranging from 23 to 51%. further complexes [pd(yphbpy)cl] resulted from c‒h palladation of the protoligand derivatives y‒phbpy with y = f, cl, br, h, ho, meo and triflate) with k2pdcl4 in yields ranging from 52 to 98%. all protoligands and pd(ii) complexes were fully characterised using mass spectrometry (ms), nuclear magnetic resonance (nmr) spectroscopy, and single crystal x-ray diffraction (xrd) for y = f, meo. the complexes were studied in detail using electrochemical (cyclic voltammetry) and spectroelectrochemical (uv-vis absorption) methods and uv-vis absorption spectroscopy. relative shifts in the potentials of the ligand centred electrochemical reductions in the range ‒1.7 to ‒2.7 (vs. ferrocene/ferrocenium) or the pd‒x centred oxidations around +1 v are in excellent agreement with variations in the density functional theory (dft) calculated highest occupied molecular orbitals (homo) and lowest unoccupied molecular orbitals (lumo) constitutions. long-wavelength absorption maxima attributable to metal(d)-to-ligand(π*) charge transfer transition observed in the range 350-550 nm were successfully modelled using time-dependent methods (td-dft) showing small contributions from triplet states.