Syntheses, structural, photophysical and theoretical studies of heteroleptic cycloplatinated guanidinate(1−) complexes bearing acetylacetonate and picolinate ancillary ligands

Abstract

Cycloplatination of symmetrical N,N′,N′′-triarylguanidines, (ArNH)₂CNAr with cis-[Pt(TFA)₂(S(O)Me₂)₂] in toluene afforded cis-[Pt(TAG)(TFA)(S(O)Me₂)] (TAG = triarylguanidinate(1−)-κC,κN; TFA = OC(O)CF₃; 6–9) in 75–82% yields. The reactions of 6–9 and the previously known cis-[Pt(TAG)X(S(O)Me₂)] (X = Cl (1) and TFA (2–5)) with acetylacetone (acacH) or 2-picolinic acid (picH) in the presence of a base afforded [Pt(TAG)(acac)] (acac = acetylacetonate-κ²O,O′; 10–18) and [Pt(TAG)(pic)] (pic = 2-picolinate-κN,κO; 19) in high yields. The new complexes were characterised by analytical, IR and multinuclear NMR spectroscopies. Further, molecular structures of 11, 12, 13·0.5 toluene and 14–19 were determined by single crystal X-ray diffraction. Absorption spectra of 10–19 in solution and their emission spectra in crystalline form were measured. Platinacycles 10–19 are bluish green light emitter in the crystalline form, and emit in the λ_PL = 488–529 nm range (11 and 13–19) while 12 emits at λ_PL = 570 nm. Unlike other platinacycles, the emission band of 12 is broad, red shifted, and this pattern is ascribed to the presence of an intermolecular N–H⋯Pt interaction involving the endocyclic amino unit of the six-membered [Pt(TAG)] ring and the Pt(II) atom in the adjacent molecule in an asymmetric unit of the crystal lattice. Lifetime measurements were carried out for all platinacycles in crystalline form, which revealed lifetime in the order of nanoseconds. The origin of absorption and emission properties of 11, 15, 18 and 19 were studied by TD-DFT calculations.