First Example of the Solid-State Thermal Cyclometalation of Ligated Benzophenone Imine Giving Novel Luminescent Platinum(II) Species

Abstract

The (benzophenone imine)platinum(II) compounds trans-[PtCl2(Ph2C=NH)(RR'SO)] [R, R'=Me, Me (2); n-Pr, n-Pr (3); (CH2)4 (4); Me, Ph (5); Me, p-MeC6H4 (6)] were prepared by the reaction of Ph2C=NH with K[PtCl3(RR'SO)], obtained in situ from K2[PtCl4] and the corresponding sulfoxide, giving 2-6 as well as cis-[PtCl2(Ph2C=NH)2] (1) as a minor product. The complexes were characterized by 1H, 13C, and 195Pt NMR and IR spectroscopy, electrospray ionization mass spectrometry, and C, H, and N elemental analysis. The X-ray crystallography of 1 enables confirmation of the cis configuration of the complex, while in 2 and 4.1/2CHCl3, the imine and sulfoxide ligands are mutually trans. The solid-state structure of 4.1/2CHCl3 consists of two dimeric Pt moieties representing a rather weak Pt...Pt interaction. The dimeric architecture of 4.1/2CHCl3 is enhanced by the hydrogen bonding between imine H atoms and O atoms. The orthometalation of 1 and 2-6 proceeds both in the solid phase and in a toluene suspension, leading to the formation of [PtCl{Ph(C6H4)C=NH}(Ph2C=NH)] (7) and [PtCl{Ph(C6H4)C=NH}(RR'SO)] (8-12), respectively, isolated in nearly quantitative yields. Complexes 8-12 are emissive at room temperature both in solution (lambdaemmax approximately 535 nm) and in the solid state (lambdaemmax 560-610 nm), with excited-state lifetimes of ca. 300-600 ns, representing a new family of PtII-based luminescent complexes. Compounds 8 and 10 have been characterized by X-ray analysis, confirming the square-planar coordination geometry of the metal center with the almost planar platinacycles. In 8, the asymmetric unit contains two independent Pt molecules, while in 10, it includes four Pt molecules linked by the intermolecular hydrogen-bonding network between the NH group and Cl atoms.

Luminescent Platinum(II) Complexes Containing Cyclometallated Diaryl Ketimine Ligands: Synthesis, Photophysical and Computational Properties

“…400 nm (Figure S5 in the Supporting Information) can be assigned mixed-ligand and MLCT character based on theoretical calculations (see below) and similarities in the energy and intensity of MLCT transitions in other platinum complexes. [22] The emission bands at λ max ≈ 450 and 550 nm are assigned to mixed-ligand and MLCT states having significant singlet and triplet character, respectively, in agreement with the theoretical calculations (see below).…”

“…[22] However, by varying the ligand structure we have succeeded in increasing the efficiency of phosphorescence almost 500-fold for 15b and 16b (Table 1) in comparison to that of the parent complex 12b. [22] From these observations, we see that for systems with incomplete intersystem crossing (ISC), very poor total emission quantum yields are measured, whereas in the two complexes 15b and 16b, where no obvious fluorescence type emission is observed, there is a concomitant dramatic increase in total emission, which must all arise from phosphorescence. This implies that in this family of complexes there is an efficient non-radiative singlet decay channel, which effectively quenches all the singlets and/or singlet-to-triplet harvesting, [31] and only those states survive that cross to the triplet manifold.…”

“…The optimised ground-state (S 0 ) geometry for 12b at the B3LYP// LANL2DZ/6-311G** level of theory is in reasonable agreement with the experimentally (X-ray) determined geometry of 12b. [22] (See the Supporting Information for the computational and geometric details.) This level of theory was applied to calculations on all cyclometallated systems synthesised here.…”

“…At the outset of our work Scaffidi-Domianello et al reported (benzophenone imine)platinum(II) compounds, trans-[PtCl 2 (Ph 2 C=NH)(RRЈSO)] containing a range of different dialkyl(aryl) sulfoxide ligands. [22] The solution photoluminescence quantum yields of the derived cyclometallated complexes were very low, the maximium being Φ em = 0.019. Solid-state quantum yields and device fabrication studies were not reported, and no other imine derivatives were studied in this work.…”

Site‐Selective Ser‐Hydrolase Labelling with a Luminescent Organometallic NCN–Platinum Complex

“…[21,33] Interestingly, many different coordination complexes with exciting luminescent properties are known from the literature, [34][35][36] but only very few of them have been used in the labelling of biomolecules, [37][38][39][40][41][42][43][44][45][46][47][48][49][50][51][52][53][54] which is mainly caused by the instability (e.g., water or redox sensitivity) of these complexes under biological conditions. Inspired by the high quantum yields of various organoplatinum complexes, as demonstrated by the Williams [25][26][27]55] and other groups [56] and by our own results on the design and applications of novel organometallic phosphonate inhibitors, we embarked on the modification of one of these highly luminescent NCN-platinum complexes [57] (complex 1, Scheme 1) to develop a novel luminescent organometallic NCN-platinum phosphonate inhibitor (6, Figure 1, Scheme 1).…”