Synthesis and Characterization of Two Isostructural POCOP Ni(II) Pincer Complexes Containing Fluorothiophenolate Ligands: [Ni(SC 6 F 4 -4-H){C 6 H 2 -3-(C 2 H 3 O)-2,6-(OP i Pr 2 ) 2 }] and [Ni(SC 6 F 5 ){C 6 H 2 -3-(C 2 H 3 O)-2,6-(OP i Pr 2 ) 2 }]

: Among their many applications, metal pincer complexes are of interest for their properties as catalysts in cross-coupling reactions. Pincer ligands exhibit tridentate coordination to the metal center and occupy the meridional positions forming two chelate rings. The two Ni(II) POCOP pincer complexes with a ﬂuorothiophenolate ligand reported herein, with formulas [Ni(SC 6 F 4 -4-H){C 6 H 2 -3-(C 2 H 3 O)-2,6-(OP i Pr 2 ) 2 }] ( 2 ) and [Ni(SC 6 F 5 ){C 6 H 2 -3-(C 2 H 3 O)-2,6-(OP i Pr 2 ) 2 }] ( 3 ), are isostructural. Additionally, they are prepared in a facile manner from the chloride compound [NiCl{C 6 H 2 -3-(C 2 H 3 O)-2-6-(OP i Pr 2 ) 2 }] ( 1 ). The complexes exhibited slightly distorted square planar geometries around the metal. The ﬂuorothiophenolate ligands are responsible of the C—H ··· F, C—F ··· π and C=O ··· π F interactions that contribute to stabilize the crystal structure arrays.


Introduction
In general, pincer complexes are constituted by an anionic chelating tridentate ligand coordinated in a meridional fashion, the anionic position is coordinated to the metal center by a negatively charged atom, typically a carbon atom of the aryl ring [1,2]. While the other positions are occupied by linkers of the same ligand including donor atoms such as N, P, O, S or Se, located in the pendant arms at the ortho positions to the carbon atom [3]. These characteristics provide stability and play a key role on the reactivity of the complexes they form. These properties, in combination with the mere variation of the metal center, are responsible for the wide variety of applications that pincer compounds have found in different areas of chemistry, this being particularly true in the case of catalysis [4,5]. Over the last years, our research group has focused on the design, synthesis and use of pincer-type ligands and their transition metal complexes [6][7][8], mainly due to the versatility of applications that they may have in different areas such as catalysis [9,10], materials [11], and medicine [12,13]. Resorcinol-based POCOP-type pincer complexes of group 10 adopt a square planar geometry [14,15]. Traditionally, complexes of these transition metals have been used as efficient catalysts in C-C cross-coupling reactions, which are one of the most important kinds of catalytic reactions to produce carbon-carbon bonds. These reactions have been traditionally catalyzed by Pd(II) species, however in recent years research has been focused in the potential use of their analogous nickel compounds. Thus, given the aforementioned properties of pincer complexes, Ni(II) pincer compounds have been considered as a suitable alternative for this kind of couplings [16]. Among the pincer complexes, phosphinite POCOP pincer ligands and their complexes have proved to be very valuable, since they exhibit similar and often enhanced reactivity when compared to their phosphine counterparts and are easily synthesized from the direct reaction of resorcinol with a given chlorophosphine. The simplicity of this procedure allows by careful selection of a resorcinol derivative to produce pincer ligands substituted in the 3-position of the aryl ring, giving entrance to the production of non-symmetric pincer ligands and their complexes in a rather simple form [5]. Thus, following our continuous interest in the design of new pincer ligands, their complexes, and potential applications as well as our long-standing interest in the use of fluorothiophenolate moieties to fine tune both electronics and sterics in a given compound [17,18], we would like to present our findings in the synthesis, characterization and structural analysis of the two non-symmetric Ni(II)-POCOP pincer complexes [Ni(

Results and Discussion
The title complexes were obtained in good yields through metathetical reaction between the parent Ni(II)-POCOP pincer complex and the corresponding thiolate lead salt according to Scheme 1. The POCOP ligand L1 was produced from the direct reaction of 2,4-dihydroxyacetophenone with ClP i Pr 2 in a 1:2 molar ratio using and slight excess of triethylamine as base. Further, the Ni(II)-POCOP pincer compound [NiCl{C 6 H 2 -3-(C 2 H 3 O)-2-6-(OP i Pr 2 ) 2 }] (1) was obtained from the reaction of NiCl 2 ·6 H 2 O in refluxing toluene [7].  (Table 1), intermolecular interactions and packing patterns, these characteristics suggesting isostructurality among the crystal structures. The asymmetric units are consistent of one molecule of the complex and four by unit cell. The coordination geometry around the metal centers Ni(II) in compounds 2 and 3 can be described as a slightly distorted square planar, as shown by the angles around the central atom that are different to 90 • (Tables 2 and 3). The deviation from the best plane formed by coordination sphere (Ni1, S3, P1, C2 and P2 atoms) are of r.m.s. = 0.054 and 0.062 Å for complexes 2 and 3, respectively. The bond lengths and angles are similar in both complexes and the molecular structures including atom labels are shown in Figure 1. As expected, the POCOP ligands coordinate to the nickel center in a tridentate fashion via two phosphorus atoms (P1, P2) and one carbon (C2) atom, the ligand forming two chelating five-member rings (Ni-P-O-C-C) with bite angles P1-Ni1-C2 and P2-Ni1-C2 with values of 81.96 (14) and 82.12 (14) • for complex 2, and 81.98 (8) and 82.13 (8) • for complex 3. The chelate rings are near to coplanarity with the phenyl ring since the dihedral angles between the mean planes of the rings present values of 2.75 and 2.32 • in complex 2, and of 1.84 and 1.48 • in complex 3. The bond lengths of the coordinated pincer ligand are similar to other previously reported POCOP pincer complexes [19,20] (Tables 2 and 3).

General
All chemical reagents were obtained commercially and used as received without further purification. Melting points were recorded on a Mel-Temp II apparatus and are reported without correction. NMR spectra were recorded on a Bruker-Avance 300 MHz spectrometer, the 1 H, 13

Synthesis of the Ligand [C 6 H 2 -4-(C 2 H 3 O)-1-3-(OP i Pr 2 ) 2 ] (L1)
A Schlenk flask was charged with 2,4-dihydroxyacetophenone (1.3 mmol), Et 3 N (3.3 mmol) and 20 mL of dry THF. The resulting mixture was stirred for 30 min at room temperature and then a solution of ClP i Pr 2 (2.6 mmol) in 5 mL of THF was added dropwise. The mixture was then set to reflux for 12 h and allowed to cool down to room temperature before filtered via cannula. The solvent was removed from the filtrate under vacuum to afford ligand L1 as a colorless viscous oil. Identity and purity of the ligand was assessed by 31 P{ 1 H} NMR. Thus, this compound was used in the next step without further purification. Yield: 80%. 31

General Procedure for Synthesis of Complexes 2 and 3
To a solution of complex 1 (0.088 mmol) in CH 2 Cl 2 (10 mL), a solution of either [Pb(SC 6 F 4 -4H) 2 ] or [Pb(SC 6 F 5 ) 2 ] (0.044 mmol) in acetone (20 mL) was added dropwise under stirring. The resulting red-brick solution was stirred overnight. After this time the resulting reaction mixture was filtered through a short plug of Celite ® to remove the PbCl 2 and the solvent was removed under vacuum and the residue recrystallized from CH 2 Cl 2 affording in both cases yellow crystals, that were suitable for the X-ray diffraction analysis.

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. Carbon-bound H atoms were positioned geometrically and included as riding atoms, with C-H = 0.98 Å with U iso (H) values of 1.5U eq (C) for methyl H, and C-H = 0.95 Å and 1.00 Å with U iso (H) values of 1.2 U eq (C) for methine. For more information about the structures of compounds 2 and 3, please refer to Supplementary Materials, as the picture shows

Conclusions
Thus, in conclusion, we have provided a facile procedure for the synthesis of two Ni(II) pincer complexes including fluorinated thiolates on their structures. The complexes were fully characterized both in solution and solid state. Further analysis in the solid state revealed some interesting features that can be useful for the further development of these species and potential uses in catalysis, medicinal chemistry and materials sciences, some of these possibilities being currently explored in our laboratories.
Supplementary Materials: The following supporting information can be downloaded. Supplementary data for complexes (2) and (3)