Dinuclear platinum(II) complexes with bridging twofold deprotonated 2,2′:6′,2″-terpyridine. New molecules with a 3,5-diplatinated-pyridyl inner core: [Pt 2(terpy-2H)(Me) 2(L) 2], [Pt 2(terpy-2H)(X) 2(L) 2] and [Pt 2(terpy-2H)(H) 2(L) 2] (L = neutral ligand; X = halide) – Crystal and molecular structure of [Pt 2(terpy-2H)(Cl) 2(PPh 3) 2

Abstract

A series of dinuclear platinum complexes where the metal ions are linked by a twofold deprotonated 2,2′:6′,2″-terpyridine (terpy) has been synthesized. Reaction of cis-[Pt(Me) 2(DMSO) 2] with terpy in toluene at 90 °C (molar ratio Pt:terpy 2:1) results in activation of the C(3)- and C(5)–H bonds of the inner pyridinic ring to give the cyclometalated dinuclear derivative [Pt 2(terpy-2H)(Me) 2(DMSO) 2] ( 1a), ( trans Me–Pt–N). From complex 1a, substitution of DMSO with neutral two-electron donors, L, allows isolation of a number of new species [Pt 2(terpy-2H)(Me) 2(L) 2] with the same N,C ∧C,N bridging ligand. The “Pt 2(terpy-2H)” fragment is very robust: it is not affected by alkylating reagents such as MeI or acids such as HPF 6 or even HCl. Nevertheless the latter acid cleaves the Pt–Me bond affording another series of complexes having a chloride in place of a methyl, [Pt 2(terpy-2H)(Cl) 2(L) 2], ( trans-Cl–Pt–C). The structure of complex 7, [Pt 2(terpy-2H)(Cl) 2(PPh 3) 2], has been solved by X-ray analysis: the platinum atoms are in a tetrahedrally distorted square planar coordination. The inner framework of the molecule is not flat: the dihedral angle between the best planes of the metal ions is 37.2(1)°. The coordinated chlorides can be abstracted to give cationic solvento derivatives or exchanged with other anions such as iodides. Exchange with [BH 4] − allows to obtain the corresponding hydrides, examples of very rare C,N cyclometalated platinum(II) hydrides. Finally a two step approach allows the synthesis of unsymmetric derivatives, [Pt 2(terpy-2H)(Cl) 2(L)(L′)], with different ligands around each platinum atom. The surprising deprotonation of terpy, typically a neutral ligand, points to the potential of the “Pt(Me) 2” fragment in the intramolecular C–H bond activation.