Synthesis and Properties of two CuI Complexes Involving Tetrathia-fulvalene-Fused Phenanthroline Ligand

Two Cu complexes based on the π-conjugated tetrathiafulvalene-annulated phenanthroline ligands (TTF-Phen, L1 and L2), [Cu(Xantphos)(L1)]BF4 (1, Xantphos = 9,9-dimethyl-4,5-bis(diphenylphosphino)xanthene) and [Cu (Binap)(L2)]BF4 (2, Binap = 2,2’-bis(diphenylphosphino)-1,1’-binaphthyl), have been synthesized. They have been fully characterized, and their photophysical and electrochemical properties are reported together with those of L1 and L2 for comparison. Both Cu I complexes show metal-to-ligand charge transfer (MLCT) absorption bands, whereas the MLCT luminescence is strongly quenched.


Introduction
][10][11] Following this strategy, we recently reported two TTF-based Cu I complexes, [Cu I (Binap)(TTF-TzPy)]BF 4 and [Cu I (Xantphos)(TTF-Tz-Py)]BF 4 , which exhibit interesting electrochemical and photophysical properties. 13owever, TTF-TzPy is a non-conjugated system with σ-bonded molecular bridge.Thus, in this paper, we use more π-conjugated TTF-Phen ligand instead of TTF-TzPy ligand to form two Cu I complexes, The photophysical and electrochemical properties of these complexes are investigated.

1. Materials and Measurements
All air-sensitive and/or water-sensitive reactions were carried out under a dry nitrogen atmosphere.All commercial chemicals were used without further purification unless otherwise stated.Solvents were dried and degassed following standard procedures.Column chromatography was carried out using 200-300 μm mesh silica.were synthesized according to the literature. 14 1  NMR spectra were recorded on a Bruker AM 400 MHz instrument.Chemical shifts were reported in ppm relative to Me 4 Si as internal standard.ESIMS spectra were recorded on an Esquire HCT-Agilent 1200 LC/MS spectrometer.FT-IR spectra were taken on a Nicolet 6700 FTIR spectrometer (400-4000 cm -1 ) with KBr pellets.The thermoanalytical anaysis (TG) was performed with a simultaneous NETZSCH STA 449C thermal analyzer.The elemental analyses were performed on a Vario EL Cube Analyzer system.UV-Vis spectra were recorded on a Hitachi U3900/3900H spectrophotometer.Fluorescence spectra were carried out on a Hitachi F-7000 spectrophotometer.

3. Cyclic Voltammetry
Cyclic voltammetry (CV) was performed on a CHI 1210B electrochemical workstation, with a glassy carbon electrode as the working electrode, a platinum wire as the counter electrode, an aqueous saturated calomel electrode (SCE) as the reference electrode, and 0.1 M n-Bu 4 NClO 4 as the supporting electrolyte.

Results and Discussion
The synthetic routes to complexes 1-2 are shown in Scheme 1.The TTF-fused ligands, copper(I) salt and P^P ligands were added in dry DCM and MeOH, and coordinated to afford corresponding Cu I complexes 1-2.The crude product was recrystallized from dichloromethane and diethyl ether.Complexes 1-2 were characterized by IR, ESI-MS, elemental analysis, 1 H NMR, UV-vis, FL spectra and cyclic voltammetry.

1. IR and ESI Spectra
In the IR spectrum of complexes 1 and 2 (Fig. S1 and Fig. S2), their spectra have almost the same tendency.The peaks at 3056, 2922, 1405 cm -1 for 1 and 3056, 2925, 1433 cm -1 for 2 are ν C-H of CH 3 group and ν Ar-H , and the strong absorption peak at 1058 cm -1 for 1 and 1060 cm -1 for 2 are attributed to B-F stretches of BF 4 -group.Moreover, the strong absorption peaks at 746 and 696 cm -1 for 1 and 746, 696 cm -1 for 2 are δ C-CH .Particularly, the strong absorption peaks at 1727 cm -1 for 2 are attributed to C=O stretches of CO 2 Me group.
The structure of complexes 1 and 2 was also studied by electrospray ionization mass spectrometry (ESI-MS).A positive ion ESI-MS of complexes 1 and 2 (Fig. S3 and Fig. S4) were measured in methanol solution.The main peak at m/z 1089.1 of 1 is [Cu I (Xantphos)(L 1 )] + ion and m/z 1157.1 of 2 is [Cu I (Binap)(L 2 )] + ion, respectively.

2. 1. Absorption Properties
The absorption spectra of the ligands L 1 -L 2 and complexes 1-2 were measured in dichloromethane solution at room temperature (Fig. 1), and the data are provided in Table 1.For complexes 1-2, absorption spectra are similar to that of the free ligand L 1 -L 2 .Intense absorption bands from 250 to 350 nm at high energy are observed, which is attributed to spin-allowed intraligand (π-π * ) transitions.Compared with L 1 -L 2 , the absorption bands at low energy (λ > 350 nm) of complexes 1-2 are slightly blue shifted, and the intensities are increased around 400-410 nm, which may be related to metalation of the ligand. 15

2. 2. Emission Properties
The normalized emission spectra of the ligands L 1 -L 2 and complexes 1-2 in CH 2 Cl 2 solution are presented in Fig. 2. The emission data are also included in Table 1.In comparison to the related ligands, the emission spectra of complexes 1-2 exhibit similar emission.The emission maxima at 381-383 nm and a shoulder peak at 406-434 nm are observed resulting from the ligand-centered (LC) π→π* relaxations.However, no obvious emissions with 3 MLCT character are found.

Electrochemical Properties
Electrochemical properties of the complexes 1-2 were investigated by cyclic voltammetry in CH 3 CN/CH 2 Cl 2 as illustrated in Fig. 3, and their electrochemical data are collected in Table  2 for 1 are 0.79 and 0.98 V, and those for 2 are 0.93 and 1.15 V, respectively.Upon coordination, the two oxidation processes of TTF subunits for 1-2 are shifted to more positive potentials in comparison with the respective ligands (Table 2).This is attributed to the electron-withdrawing inductive effect of Cu I core. 12For the previously synthesized Cu I complexes based on TTF-TzPy, redox potentials for the ligand and Cu I complexes have no obvious change. 13These differences result is that we use different types of ligands.TTF-TzPy is a non-conjugated system with σ-bonded molecular bridge, which is unfavorable to the transmission of electrons.However, we use more π-conjugated TTF-Phen ligand and the phen unit is grafted on the TTF core through a conjugated spacer group, which is advantageous to intramolecular electron transfer and communications.Consequently, Cu I complexes 1-2 possess better electron-withdrawing abilities than the free ligands.
with the calculated value of 6.76%.For complex 2, no weight loss was observed up to 250 °C, indicating that it is stable below 250 °C.With the increase of temperature, the organic fragments start to decompose gradually in range of 250 to 640 °C.The residue weight of 6.68% is due to CuO and is in agreement with the calculated value of 6.38%.

4. Thermal Stability
The TG analyses were carried out from 30 °C to 700 °C in N 2 atmosphere with a heating rate of 10 °C min -1 .As shown in Fig. 4, complex 1 began to lose weight at approximately 295 °C and continuous decomposition is observed during 295 to 650 °C with the increase of temperature.The residue weight of 6.94% is due to CuO and is in agreement

Conclusions
In summary, we have synthesized two new Cu I complexes with TTF-Phen as the ligands, [Cu I (Xantphos)(L 1 )]BF 4 (1) and [Cu I (Binap)(L 2 )]BF 4 (2).Their thermal stability, photophysical properties and electrochemical behaviors have been investigated.The two new Cu I complexes are stable below 250 °C.The emission of complexes 1-2 is no longer of 3 MLCT but rather of ligandcentered (LC) nature.The interesting redox-active properties for complexes 1 and 2 have been evidenced by electrochemical studies.The association of the redox-active bridging TTF ligand to a variety of mixed-ligand transition-metal complexes may pave the way to obtain multifunctional materials, which are currently under investigation in our laboratory.

2
. All compounds (L 1 -L 2 , 1-2) exhibit two one-electron oxidation processes, which are associated with the successive oxidation of the Niu et al.: Synthesis and Properties of two Cu I Complexes ... TTF unit to TTF + and TTF 2+ .The redox potentials E 1/2 1 and E 1/2

Table 1 .
Photophysical data for compounds L 1 -L 2 and 1-2 Measured in degassed CH 2 Cl 2 solution at room temperature.b Data from ref. 13. a