Pt

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Introduction
Several methods to prepare coordination compounds by nucleophilic additions to nitrile ligands have been developed during the last two decades [1].Various types of nucleophiles [2,3] or 1,3-dipoles [4] have been used for the preparation of compounds containing C-N and/or C-O bonds.1,3-Diiminoisoindoline has been used for the synthesis of pthalocyanines [5] and hemiporphyrazine [6], which have a wide range of industrial applications.The iminoisoindoline-1-one, bearing a nucleophilic sp 2 -imino group, has been used as a nucleophile in reaction with various metal-bound isonitriles and nitriles to furnish iminocarbene or triazapentadienato complexes, respectively [7].However, 1,3diiminoisoindoline contains two sp 2 -nitrogen centres which can use both imine moieties for additions to metal-coordinated nitriles, thus furnishing symmetrical triazapentadienate complexes.In contrast to βdiimines, ligands such as triazapentadienes have one extra N donor site, and DFT [8] show that they have a greater capacity of coordination to metal ions than β-diimines.Nevertheless, the coordination chemistry of triazapendiene species is less reported, due to the instability of triazapentadiene complexes, particularly the unsubstituted ones [9].A single-pot synthesis with electron-deficient nitriles has been used to synthetize triazapentadiene complexes [10].Ni(II)-complexes bearing imidoylamidine ligands have been prepared using oximes and nitriles in the presence of Ni(II) ions [11], and this methodology has been used to synthetize a variety of (1,3,5-triazapentadienato)Pd(II) complexes [12].Recently, we have also reported the synthesis of (alkoxy-1,3,5-triazapentadienato)Cu(II) complexes using a template synthesis [13].
On the other hand, Pt(II)-based imidoylamidinate compounds are emissive both in solid state and in solution, at room temperature.UV-visible and luminescence spectroscopies indicate that the lowest excited state of these complexes is 3 MLCT or 3 IL with significant MLCT character, with emission lifetimes of a few µs [14].
In continuation of our research program on the additions to metal-bound nitriles [15], we decided to extend the addition of a sp 2 -nitrogen nucleophile, 1,3-diiminoisoindoline HN=CC and the luminescence emission spectra of some of those complexes.We have thus observed the formation of (1,3,5,7,9-pentaazanona-1,3,6,8-tetraenato)Pt(II) and Pd(II) complexes, 3a-f and 5a, respectively.The photophysical characterization of compounds 3a and 3b permitted the assessment of parameters which, by correlation with other Pt(II) emissive complexes [14], enabled further insight into their electronic structure, namely in terms of optical transitions.The solvents used for photophysical characterization were all of spectroscopic grade.Dichloromethane (99.5% for spectroscopy, Acros Organics), chloroform (≥ 99.8% ACS spectrometric grade, Sigma-Aldrich), ethanol (95%, UV HPLC spectroscopic, Sigma-Aldrich).Deionized water was obtained from a Millipore system Milli-Q ≥ 18 MΩ cm.Polystyrene beads (average M w 35000, Sigma-Aldrich) was used to prepare solid films of compounds 3a and 3b, by dissolving 1 mg of the respective compound in a solution of ca.80 mg of polystyrene in 1 mL chloroform, which was subsequently deposited over a quartz plate, allowing the solvent to evaporate.Luminescence quantum yields were calculated by using Ru(bpy) 3 as reference quantum yield standard for compounds 3a and 3b.The electronic absorption spectra were recorded using a Jasco V-660 spectrophotometer.Fluorescence measurements were carried out in a Horiba-Jobin Yvon Fluorolog-3 spectrofluorimeter.All spectra were recorded with samples in 1 cm optical path length quartz cells, except for the solid films, where the film was placed directly in the optical path, in a 45º angle between the excitation source and the detector.Luminescence lifetime measurements were performed using the single-photon timing method with laser excitation and microchannel plate detection, with the set-up already described [16].), 127.4, 130.5, 135.5, 136.3, 138.9 (C aromatic

Reactions of the nitrile Pt(II) complexes trans-[PtCl
To a solution of 1a, 1b, 1c, 1d, 1e or 1f (0.532 mmol) in chloroform (5 mL) was added at room temperature to 1,3-diiminoisoindoline 2 (77.2 mg, 0.532 mmol), and the mixture was refluxed for 2 h whereupon the solvent was removed in vacuo.The crude residue was purified by column chromatography on silica (chloroform as the eluent), followed by evaporation of the solvent in vacuo to give the final 3a, 3b, 3c, 3d, 3e or 3f products, respectively.
After a careful IR and NMR analyses of each reaction product, it was observed the absence of the products of the addition of 1,3-diiminoisoindoline to nitrile group (N≡C), the resulting mixtures contain a number of unidentified products.Additionally, the reaction of 4e with 2 affords also pnitrophenylacetonitrile (resulting from the decomposition of complex 4e).

X-ray structure determinations
For the X-ray structure determination; X-ray-quality single crystal of Pt(II) complex [PtCl{NH=C(Me)N=C(C 6 H 4 )NC=NC(Me)=NH}] 3a was obtained by slow evaporation from chloroform.The crystals of 3a were immersed in cryo-oil, mounted in a MiTeGen loop and measured at 120 K.The X-ray diffraction data were collected on a Bruker KappaApex II or an Agilent Technologies Supernova using Mo Kα radiation (λ = 0.70173 Å).The CrysAlisPro [17] program packages were used for cell refinements and data reductions.The structure was solved by charge flipping method using the SUPERFLIP [18] program.A multi-scan absorption correction based on equivalent reflections (CrysAlisPro) was applied to the data.Structural refinement was carried out using SHELXL2014 [19].
The N-H hydrogen atom (H1) was located from the difference Fourier map and refined isotropically.
Other hydrogen atoms were positioned geometrically and constrained to ride on their parent atoms, with C---H = 0.95-0.98Å and U iso = 1.2-1.5 U eq (parent atom).
The crystallographic details are summarized in Table 1.Detailed structural parameters are given in supplementary material.CCDC number 1518110 contains the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
The stability of the 1,3-diiminoisoindoline and of the products of its addition to nitrile ligands Herein, we describe the selective synthesis of new symmetrical (1,3,5,7,9-pentaazanona-1,3,6,8tetraenato)Pt(II) complexes by using various aliphatic and aromatic nitriles as starting bis(nitrile) Pt(II) complexes and 1,3-diiminoisoindoline as the reacting sp 2 -nitrogen nucleophile.In a blank experiment, a prolonged reflux (24 h) of a mixture of one equivalent of acetonitrile and two equivalents of 1,3-diiminoisoindoline in chloroform showed no addition to cyanocarbon of acetonitrile and only the starting materials were recovered, indicating the Pt(II)-assisted character of the coupling.
The IR spectrum of complex 5a do not exhibit the typical υ(N≡C) values (2350-2300 cm -1 range), while new bands due to υ(NH) and υ(N=C) are detected at 3440 and 1639 cm -1 , respectively.In

UV-vis absorption spectra
The absorption spectra of the Pt(II) complexes 3a and 3b exhibit a band at 400-430 nm typical of a metal-to-ligand charge transfer (MLCT) low energy transition, and intrinsic of the d 8 platinum complexes.The bands located around 330 nm are more ligand-centered and, due to the solvent cut-off, it was not possible to observe the highest energy absorption bands, which should be located below 250 nm for this type of complexes [14], and correspond to 1 (π−π*) IL (intraligand) transitions.
The absorption data (maximum absorption wavelengths and corresponding molar absorption coefficients) are summarized in Table 3. a in chloroform; b in dichloromethane.

Luminescence emission spectra
Both compounds are emissive in dichloromethane solution, and exhibit very similar emission spectra, luminescence quantum yields and lifetimes.This might be due to the structural similarity between the two compounds, which only differ by one carbon atom in two of the imine substituents.
The emission data are collected in Table 3. Absorption, emission and excitation spectra of both complexes are represented in Figures 4 and 5.By comparison of the luminescence lifetimes assessed for these compounds with those collected for Pt(II) imidoylamidinates [14], it is possible to observe that the former are several orders of magnitude lower.This might be due to the fact that Pt(II) complexes 3a and 3b exhibit a smaller degree of electronic delocalization, which ultimately governs the lifetime of the emissive triplet state.It is worth mentioning that degassing produced no effect on their lifetimes and quantum yields.

Solid state luminescence
Compounds 3a and 3b also exhibited luminescence in solid state.The characterization was performed following the procedure described in section 2.1, and the resulting emission spectra are depicted in Figure 6.The spectra are very similar to the ones obtained in solution for both compounds, except for the slight elevation of the baseline, which is common for solid samples, owing to scattering.Regarding luminescence lifetimes, a significant increase occurs in the solid state, a common lifetime of 160 ns being measured for both 3a and 3b.Immobilization of the compounds in the solid matrix significantly reduces collisional quenching, hence increasing the excited state lifetime.

Table 1 .
Crystal data and structure refinement for complex 3a.

Table 3 .
Wavelengths of the absorption maxima, respective molar absorption coefficients, luminescence quantum yields and lifetimes for Pt(II) complexes 3a and 3b.