Article pubs.acs.org/IC Synthesis and Characterization of Ferrocene-Chelating Heteroscorpionate Complexes of Nickel(II) and Zinc(II) Mark Abubekerov and Paula L. Diaconescu* Department of Chemistry and Biochemistry, University of California, Los Angeles, California 90095, United States *S Supporting Information ABSTRACT: The first example of a ferrocene-chelating heteroscorpionate, [Li(THF)2][fc(PPh2)(BH[(3,5- P,B ′ Me)2pz]2)] ((fc )Li(THF)2,fc=1,1-ferrocenediyl) is described. Starting from a previously reported compound, fcBr(PPh2), a series of ferrocene derivatives, fc(PPh2)(B- [OMe]2), [Li(OEt2)][fc(PPh2)(BH3)], [Li(THF)2][fc(PPh2)- (BH[(3,5-Me)2pz]2)] (pz = pyrazole), was isolated and P,B P,B characterized. Compound (fc )Li(THF)2 allowed the synthesis of the corresponding nickel and zinc complexes, (fc )NiCl, (fcP,B)NiMe, (fcP,B)ZnCl, and (fcP,B)ZnMe. All compounds were characterized by NMR spectroscopy, while the zinc and nickel complexes were also characterized by X-ray crystallography. The redox behavior of (fcP,B)NiCl, (fcP,B)NiMe, (fcP,B)ZnCl, and (fcP,B)ZnMe was studied by cyclic voltammetry and supported by density functional theory calculations. ■ INTRODUCTION without exposure to air. NMR solvents were obtained from Cambridge − Isotope Laboratories, degassed, and stored over activated molecular Poly(pyrazolyl)borates, also known as “scorpionates”,1 3 have 4−6 sieves prior to use. NMR spectra were recorded at ambient versatile electronic and steric properties. Due to the ease of temperature on Bruker AV-300, AV-400, AV-500, and DRX-500 introducing new substituents on the three carbon atoms of the spectrometers unless otherwise noted. Proton and carbon chemical pyrazolyl ring, such ligands have found widespread applications shifts are given relative to residual solvent peaks. Phosphorus and 2,7−14 in coordination chemistry and catalysis. However, despite boron chemical shifts are given relative to external standards, H3PO4 · their advantages, poly(pyrazolyl)borates lack the potential for and Et2O BF3, respectively. Magnetic susceptibility measurements 28,29 were performed in C6D6 using the Evans method. fc(PPh2)Br (1) redox activity. Given the increasing interest in redox active 30 ligands and their applications in catalysis,15 several examples of was prepared using a literature procedure, and, unless otherwise ferrocene-substituted poly(pyrazolyl)borates have been synthe- noted, all reagents were acquired from commercial sources and used as 16−21 received. Elemental analyses were performed on an Exeter Analytical, sized, but metal complexes containing chelating versions Inc. CE-440 Elemental Analyzer with the exception of the analysis for are unknown; these motifs are particularly interesting since they compound 6 that was carried out by Midwest Microlab, LLC, impart special steric and electronic properties to the resulting − Indianapolis, IN. 22 25 2 metal complexes. Therefore, a new type of a hetero- fc(PPh2)(B[OMe]2)(). Compound 1 (1.00 g, 2.23 mmol) was P,B P,B scorpionate ligand, fc (fc = fc(PPh2)(BH[(3,5-Me)2pz]2)], dissolved in 100 mL of THF and cooled to −78 °C. n-Butyl lithium fc =1,1′-ferrocenediyl) was designed in order to combine the (2.5 M in hexanes, 1.07 mL, 2.68 mmol) was added dropwise over a stereoelectronic versatility of poly(pyrazolyl)borates and the period of 10 min. The resulting yellow slurry was stirred at −78 °C for redox properties of a ferrocene-chelating moiety. Based on the 15 min. The reaction mixture was removed from the cold well, interest of the Diaconescu group in redox active ferrocene- immediately quenched with B(OMe)3 (1.27 mL, 11.2 mmol) and based chelating ligands,23,24,26 we set out to investigate the stirred for 1 h at ambient temperature. Volatile substances were P,B removed under reduced pressure. The resulting yellow-orange oil was activity of the fc ligand in combination with nickel for extracted in 15 mL of toluene and filtered through Celite. Toluene was potential use in redox-switchable catalysis for the synthesis of removed under reduced pressure, and the remaining orange oil was fi P,B ole nic copolymers. The redox properties of fc were probed redissolved in 8 mL of n-pentane, filtered through Celite, and stored at by characterizing two nickel(II) complexes. In order to provide −40 °C overnight to afford a bright yellow solid (0.898 g, 91.1%). X- an unambiguous interpretation of their redox properties, the ray quality crystals were obtained from n-pentane at −40 °C upon 1 δ analogous, redox inactive zinc(II) complexes were also prolonged standing. H NMR (C6D6, 500 MHz, 298 K): (ppm) 3.61 − − − prepared and characterized. (s, 6H, OCH3), 4.09 (t, 2H, Cp H), 4.23 (m, 4H, Cp H), 4.50 (t, 2H, Cp−H), 7.05 (m, 6H, m-Ph, p-Ph), 7.49 (m, 4H, o-Ph). 13C NMR δ − − ■ EXPERIMENTAL SECTION (C6D6, 126 MHz, 298 K): (ppm) 52.3 (d, OCH3), 72.0 (d, Cp C), 73.8 (s, Cp−C), 73.9 (s, Cp−C), 76.3 (s, Cp−C), 77.5 (d, Cp−C), General Considerations. All reactions were performed using 11 134.3 (d, aromatic), 140.3 (d, aromatic). B NMR (C6D6, 161 MHz, standard Schlenk techniques or in an MBraun drybox (<1 ppm of O2/ δ 31 δ 298 K): (ppm) 28.8 (br s). P NMR (C6D6, 121 MHz, 298 K): H2O) unless noted otherwise. All glassware, cannulae, and Celite were stored in an oven at >425 K before being brought into the drybox. Solvents were purified using a two-column solid-state purification Received: November 10, 2014 system by the method of Grubbs27 and transferred to the glovebox © XXXX American Chemical Society A DOI: 10.1021/ic502691b Inorg. Chem. XXXX, XXX, XXX−XXX Inorganic Chemistry Article − − − − (ppm) 15.53 (s). Anal. calcd: fc(PPh2)(B[OMe]2)(C24H24BFeO2P) CCH3), 4.06 (br s, 2H, Cp H), 4.24 (t, 2H, Cp H), 4.32 (t, 2H, Cp C, 65.21; H, 5.47. Found: C, 65.19; H, 5.26. H), 4.34 (t, 2H, Cp−H), 5.52 (s, 2H, CH), 6.96 (br s, 4H, m-Ph), 7.05 3 13 [Li(OEt2)] [fc(PPh2)(BH3)] ( ). Compound 2 (0.839 g, 1.90 mmol) (m, 2H, p-Ph), 7.30 (m, 4H, o-Ph). C NMR (C6D6, 126 MHz, 298 − ° δ − was dissolved in 50 mL of diethyl ether and cooled to 78 C. Lithium K): (ppm) 5.1 (d, NiCH3), 13.8 (br s, CCH3), 14.0 (br s, CCH3), − − aluminum hydride (0.072 g, 1.90 mmol) in 5 mL of diethyl ether was 14.6 (br s, CCH3), 15.3 (br s, CCH3), 69.2 (br s, Cp C), 69.6 (s, Cp added dropwise over a period of 5 min. The reaction mixture was C), 70.0 (s, Cp−C), 70.4 (br s, Cp−C), 70.6 (br s, Cp−C), 72.7 (br s, stirred at −78 °C for 30 min followed by 1 h at ambient temperature. Cp−C), 72.9 (br s, Cp−C), 73.7 (s, Cp−C), 73.8 (s, Cp−C), 106.9 (br The reaction solution was filtered through a glass frit and volatiles s, CH), 107.3 (br s, CH), 129.4 (br s, aromatic), 130.4 (br s, aromatic), removed under reduced pressure. The resulting yellow-orange solid 133.3 (br s, aromatic), 133.6 (br s, aromatic), 146.2 (s, CCH3), 148.8 11 was washed with 30 mL of hexanes, redissolved in diethyl ether, and (br s, CCH3), 149.2 (br s, CCH3). B NMR (C6D6, 161 MHz, 298 fi δ − 31 δ ltered through Celite. Reduction in volume of the solution and K): (ppm) 7.8 (br s). P NMR (C6D6, 121 MHz, 298 K): − ° ff P,B storage at 40 Caorded orange crystalline material in two crops (ppm) 30.33 (s). Anal. calcd: (fc )NiMe (C33H36BFeN4NiP) C, (0.746 g, 84.6%). X-ray quality crystals were obtained from THF/ 61.45; H, 5.63; N, 8.69. Found: C, 60.54; H, 5.91; N, 8.37. − ° 1 δ P,B hexanes layering at 40 C. H NMR (C6D6, 300 MHz, 298 K): (fc )ZnCl (7). To ZnCl (18.5 mg, 0.136 mmol) in 2 mL of THF 4 1 − 2 (ppm) 1.92 (br m, JHB = 75.2 Hz, 3H, BH3), 4.08 (t, 4H, Cp H), (98.3 mg, 0.136 mmol) in 2 mL of THF was added dropwise. The − − 4.29 (t, 2H, Cp H), 4.35 (t, 2H, Cp H), 7.02 (m, 6H, m-Ph, p-Ph), reaction solution was stirred for 1 h. Volatile substances were removed 7.62 (m, 4H, o-Ph). The complex was not soluble enough in C6D6 to under reduced pressure and the desired product was extracted into 4 13 11 δ obtain a C NMR spectrum. B NMR (C6D6, 161 MHz, 298 K): mL of toluene and filtered through Celite. Reduction in volume of the − 1 31 (ppm) 27.1 (q, JHB = 75.2 Hz). P NMR (C6D6, 121 MHz, 298 K): toluene solution to 1 mL and layering of 3 mL of hexanes afforded δ − · (ppm) 17.1 (s). Anal. calcd: [fc(PPh2)(BH3)]Li (Et2O) orange crystalline material after 24 h at −40 °C (90.0 mg, 86.4%). (C26H31BFeLiOP) C, 67.29; H, 6.73. Found: C, 66.96; H, 6.54. 4 Crystals of 7 always contain a molecule of toluene per molecule of [Li(THF)2][fc(PPh2)(BH[(3,5-Me)2pz]2)] ( ). Compound 3 (0.439 g, compound as supported by NMR data.