Synthesis, structure and electrochemical properties of the organonickel complex [NiBr(Mes)(phen)] (Mes = 2,4,6-trimethylphenyl, phen = 1,10-phenanthroline)

Journal of Organometallic Chemistry 750 (2014) 59e64

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Synthesis, structure and electrochemical properties of the organonickel complex [NiBr(Mes)(phen)] (Mes ¼ 2,4,6trimethylphenyl, phen ¼ 1,10-phenanthroline) Dmitry G. Yakhvarov a, b, *, Andreas Petr c, **, Vladislav Kataev c, Bernd Büchner c, e, Santiago Gómez-Ruiz d, Evamarie Hey-Hawkins d, **, Svetlana V. Kvashennikova a, Yulia S. Ganushevich a, Vladimir I. Morozov a, Oleg G. Sinyashin a a

A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, Kazan 420088, Russian Federation A.M. Butlerov Institute of Chemistry, Kazan (Volga Region) Federal University, Kazan 420008, Russian Federation c Institute for Solid State and Materials Research, IFW-Dresden, Dresden D-01069, Germany d Institut für Anorganische Chemie, Universität Leipzig, Leipzig D-04103, Germany e Institut für Festkörperphysik, Technische Universität Dresden, Dresden D-01062, Germany b

a r t i c l e i n f o

a b s t r a c t

Article history: Received 12 July 2013 Received in revised form 31 October 2013 Accepted 5 November 2013

The organonickel complex [NiBr(Mes)(phen)] (1) (Mes ¼ 2,4,6-trimethylphenyl, phen ¼ 1,10phenanthroline) was synthesized by oxidative addition of MesBr to nickel(0) complexes, obtained from [Ni(COD)2] (COD ¼ 1,5-cyclooctadiene) and phen, or electrochemically generated from [NiBr2(phen)], and by ligand exchange reaction from [NiBr(Mes)(PPh3)2]. The electrochemical properties of [NiBr(Mes)(phen)] were investigated by cyclic voltammetry and in situ EPR spectroelectrochemistry. The cathodic reduction of 1 resulted in formation of the neutral radical complex [Ni(Mes)(phen)] with a 1,10-phenanthroline radical anion bound to a nickel(II) centre. The electrochemical generation of the free 1,10-phenanthroline radical anion from 1,10-phenanthroline is also described. Ó 2013 Elsevier B.V. All rights reserved.

Keywords: Organonickel s-complexes 1,10-Phenanthroline Electrochemistry In situ EPR spectroelectrochemistry Electroreduction Ligand dissociation

1. Introduction Organonickel complexes with a sigma-CeNi-bond (sigmacomplexes) are important intermediates in several catalytic processes involving nickel catalysts [1,2]. These species are very reactive and only a limited number has been isolated and characterized. The first organonickel sigma-complexes were reported in the early 1960s [3], and derivatives containing the bpy ligand were described about twenty years later [4,5]. Chatt and Shaw [3] had shown in the 1960s that ortho-substituents in a s-bonded aryl substituent can stabilize the complex by preventing free rotation about the nickel-carbon s bond. Since then, the synthesis and

* Corresponding author. A.E. Arbuzov Institute of Organic and Physical Chemistry, Kazan Scientific Centre of the Russian Academy of Sciences, Kazan 420088, Russian Federation. ** Corresponding author. E-mail addresses: [email protected] (D.G. Yakhvarov), [email protected] (A. Petr), [email protected] (E. Hey-Hawkins). 0022-328X/$ e see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.jorganchem.2013.11.003

reactivity of s-aryl nickel complexes bearing diimine ligands have been the focus of several reports [6e11]. The major route to organonickel sigma-complexes is the reaction of nickel halide complexes with organomagnesium or organolithium reagents followed by a ligand exchange reaction [1,2]. Alternatively, organonickel sigma-complexes can be obtained by oxidative addition of organic halides to nickel(0) complexes [1,2]. Recently, we have shown that diimine organonickel s-aryl complexes [NiBr(aryl)(bpy)] (bpy ¼ 2,20 -bipyridine) bearing orthosubstituents in the s-bonded aromatic ring can be efficiently synthesized using electrochemical techniques, either in a single electrochemical cell with a sacrificial nickel anode [12], or in an electrochemical cell supplied with a diaphragm for separation of the anodic and cathodic compartments [13]. The first approach, use of a sacrificial anode, proved to be the most efficient procedure. The mechanism of the overall process involves cathodic in situ electrochemical generation of the highly reactive nickel(0) complex [Ni0(bpy)] followed by oxidative addition of ortho-substituted aryl

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bromides (arylBr), while the anode material (Mg, Zn, Ni, or Al) is oxidized (Scheme 1). Organonickel sigma-complexes [NiBr(R)(bpy)] are key intermediates in several electrocatalytic homo- and cross-coupling processes with organic halides, dichlorophosphines or white phosphorus (P4) as substrates [14,15]. However, most stable organonickel complexes display very low reactivity. The reactivity can be strongly increased by electron transfer at negative potentials and by performing the electrochemical synthetic process at the potentials of the reduction of these species (i.e. 100e200 mV more negative in comparison with the system NiII/Ni0) [14,15]. We have shown that electrochemical reduction strongly increases the reactivity of the complexes in cross-coupling reactions giving products that contain the aromatic group of the organonickel complex [16]. Although the organonickel complexes bearing a-diimine ligands have been studied [17,18], the mechanism of their activation and the nature of the formed active species are not yet clearly understood. In the present communication we describe the synthesis, X-ray structure and investigation of the electrochemical properties of the organonickel complex [NiBr(Mes)(phen)] (1) by cyclic voltammetry and in situ EPR spectroelectrochemistry.

[NiBr2(PPh3)2] + MgBr(Mes) [NiBr(Mes)(PPh3)2] + phen

[NiBr(Mes)(PPh3)2] + MgBr2 [NiBr(Mes)(phen)] + 2 PPh3 1

Scheme 2. Synthesis of complex 1 by ligand exchange reaction.

ligand in a cis arrangement (Fig. 1). The mesityl ring is perpendicular to the N,N,Ni,Br plane, apparently due to steric interaction of the methyl groups with the bromo ligand and the ortho hydrogen atom of the phen ligand. Bond lengths and angles of 1 0.5 THF are very similar to those reported for related 2,20 -bipyridine complexes [7,13] and other diimine ligands [19]. 2.3. Cyclic voltammetry study

[NiBr(Mes)(phen)] (1) was synthesized electrochemically, using a modified procedure [12] in a single electrochemical cell supplied with a sacrificial nickel anode (Scheme 1). Alternatively, 1 can be synthesized with the Grignard reagent according to a method described by Seidel [4] and modified by Klein et al. [6,7] for the related complex [NiBr(Mes)(bpy)] (Scheme 2), and by reaction of oxidative addition of MesBr to in situ formed from [Ni(COD)2] and 1,10-phenanthroline [Ni(COD)(phen)] complex. Although the yield of organonickel sigma-complex 1 in the electrochemical process is little bit less than in case of the classical ligand exchange reaction, this method seems more convenient, because allows direct access to this specie starting from the binary nickel salt without preparation of flammable Grignard reagents or low stable [Ni(COD)2] complex.

In the cyclic voltammogram of complex 1, two chemically reversible reduction peaks C1 and C2, having anodic re-oxidation peaks A1 and A2, are observed at the first potential scanning from 0.00 V to 2.00 V (Fig. 2). At the anodic potentials a peak of oxidation A3 corresponding to the oxidation of bromide anion in the coordination sphere of nickel complex is present. It is interestingly to note that in case of preliminary cathodic polarization of the working electrode two additional anodic peaks A4 and A5 appeared on the CV-curve (solid curve). However, these peaks are absent when the cyclic voltammogram is recorded to the anodic part (dashed curve). Thus we can conclude that a one electron transfer to the complex 1 leads to the formation of free bromide in solution which is oxidized in a two step process at A4 and A5. This electrochemical behaviour of 1 is very characteristic for the related a-diimine complexes. Thus according to Klein et al., in the related organonickel complex, formed by 2,20 -bipyridine and tetramethylphenanthroline ligands, the first peak of the reduction (C1) corresponds to the formation of a radical anion complex [17,18]. The mechanism of the following stabilization process of the formed radical anion, including the formation of binuclear species, has been proposed on the base of EPR and UV/vis/NIR spectroelectrochemistry. However, the data for the related organonickel sigma-complexes with unsubstituted phen are still missed.

2.2. Description of crystal structure

2.4. In situ EPR-spectroelectrochemistry

Complex 1 was characterized by various methods, including Xray crystallography. 1 crystallizes in the orthorhombic space group Pbcn with eight molecules in the unit cell and four THF molecules located on a two-fold axis. The nickel atom in 1 0.5 THF is coordinated in a distorted square-planar fashion by a chelating phen ligand (via N(1) and N(2)), a s-bonded mesityl group and a bromo

We have, therefore, investigated the electroreduction of complex 1 in an electrochemical EPR flat cell supplied with a

2. Results and discussion 2.1. Syntheses

EpC1 Cathode:

[NiBr2(bpy)2] + 2 e - 2 Br[Ni0(bpy)2]

[Ni0(bpy)2]

[Ni0(bpy)]

arylBr [NiBr(aryl)(bpy)]

- bpy

Anode:

M0

Mn+ + n e

Mn+ + n Br-

MBrn

n = 2 (M = Ni, Mg, Zn), 3 (M = Al) Scheme 1. Electrochemical synthesis of organonickel s-aryl complexes.

Fig. 1. Molecular structure of the complex unit of 1 in 1 0.5 THF with 50% thermal ellipsoids. Hydrogen atoms and THF molecules have been omitted for clarity. Selected bond lengths ( A) and angles ( ) for 1 0.5 THF C(1)eNi(1) 1.887(3), N(1)eNi(1) 1.982(2), N(2)eNi(1) 1.917(2), Ni(1)eBr(1) 2.2970(4); C(1)eNi(1)eN(2) 91.2(2), C(1)e Ni(1)eN(1) 172.1(2), N(2)eNi(1)eN(1) 83.72(9), C(1)eNi(1)eBr(1) 89.16(8), N(2)e Ni(1)eBr(1) 176.34(7), N(1)eNi(1)eBr(1) 95.58(6).

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Fig. 2. Cyclic voltammograms of 1 (in DMF, 102 M) in the presence of (Bu4N)BF4 (101 M). CV curves were recorded without IR compensation at the first scan at constant potential scan rate 50 mV s1 from 0.00 V to 2.00 V then to þ0.80 V and back to 0.00 V (solid-curve) and from 0.00 V to þ0.80 V then to 2.00 V and back to 0.00 V (dashed-curve). Peak potentials are referred to Ag/AgNO3, 0.01 M in CH3CN reference electrode.

sacrificial Al anode as an auxiliary electrode and a Pt cathode. Applying a cathodic potential (Ew.e. ¼ 0.65 V vs Ag/Agþ) did not give any colour change of the solution, but resulted in an EPR signal of the 1,10-phenanthroline radical anion phen [20,21] coordinated at nickel (g ¼ 2.000) (Fig. 3) in agreement with previously published data for related a-diimine complexes [17,18]. The simulated spectrum was obtained for a hyperfine coupling of two groups of two hydrogens (aH ¼ 0.27 mT and aH ¼ 0.38 mT) and of two nitrogens (aN ¼ 0.32 mT). In order to confirm the formation of the coordinated phenanthroline radical anion, the free phenanthroline radical anion was also generated electrochemically by applying a constant current to a solution containing 1,10-phenanthroline using the same electrochemical EPR cell (Scheme 3). Tetrabutylammonium cations of supporting electrolyte play a role of the counter ions in the present

T = 300 K

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simulated experimental

3480

3500

case. The colour of the solution changed to violet and an EPR signal (g ¼ 2.003) was observed (Fig. 4). The EPR spectrum was simulated with a hyperfine interaction of two nitrogens (aN ¼ 0.39 mT), two times two hydrogens (aH ¼ 0.275 mT and aH ¼ 0.105 mT) and a line width of 0.05 mT. The experimental spectrum is in good agreement with the simulation, but is less resolved (Fig. 4). Due to the fact, that the radical anions were produced by electrochemical reduction at a rather high current density we do not have a homogenous concentration of the radicals. In the vicinity of the electrode the concentration is higher than at a larger distance to the electrode surface. Therefore the part close to the electrode surface will experience a larger broadening by dipolar interaction and electron spin exchange also the pH can vary in the electrolyte. The coupling constants are different from those given in the literature, where they were obtained for ion pairs with potassium [21]. The spectrum in Ref. [21] was simulated with two aN ¼ 0.28 mT, two aH ¼ 0.041 mT, two aH ¼ 0.360 mT, two aH ¼ 0.280 mT and one aH ¼ 0.041 mT. It was not possible to simulate the spectrum of the coordinated phenanthroline radical anion with the coupling constants of the free radical anion. This indicates that the electroreduction of complex 1 does not yield the free phenanthroline radical anion. It is noteworthy that the radical anion of free phenanthroline is obtained at a potential of about 1.0 V more negative in comparison with the electroreduction potential of complex 1. A comparison of the EPR spectra of electrochemically generated phen, obtained from reduction of complex 1 and 1,10phenanthroline, recorded in frozen solutions (T ¼ 30 K), also showed differences in the free and coordinated state (Fig. 5, gfactors differ by 0.003). The free phen is a p-type organic radical where nearly all spin-orbit contributions are quenched and a gfactor close to the free electron is expected. The spectrum in Fig. 5 can be simulated with an axially symmetric g-tensor of gk ¼ 2.0000 and gt ¼ 2.0035 which is in good agreement with our expectations.

3520

Magnetic induction/Gauss Fig. 3. Experimental (solid-curve) and simulated (dashed-curve) EPR spectra of the electrochemically generated phen coordinated at nickel.

Scheme 3. Electrochemical formation of radical anion of 1,10-phenanthroline.

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experimental simulated

phenanthroline radical anion a symmetric line pattern was observed, whereas the pattern obtained from the complex was clearly asymmetric due to the above discussed g-factor anisotropy. The formation of such a coordinatively unsaturated complex may explain the increased reactivity of organonickel sigmacomplexes in electrocatalytic processes. The free coordination site at the nickel centre allows coordination of a substrate initiating a new catalytic cycle leading to the coupling product. 2.5. Conclusions

3470

3480

3490

3500

3510

Magnetic induction/Gauss Fig. 4. EPR spectrum of electrochemically generated free phen (solid-curve) (at 293 K). Dashed curve: simulated EPR spectrum.

The situation with the bound phen can be quite different. Here a contribution of an orbital momentum which is not completely quenched at the central Ni atom can change the g-factor significantly. The larger the spin density at the central metal atom is the larger the deviation from the free electron value can be expected. Such a binding of phen can possibly enhance also the anisotropy of the g-factor. The low temperature spectrum from the reduction of complex 1 can be simulated with an axially symmetric g-tensor of gk ¼ 1.980 and gt ¼ 2.005. The anisotropy Dg ¼ 0.025 is larger than for the free phen Dg ¼ 0.0035 but not as large as is expected for a strong metal contribution [17]. Therefore the spin density is located mainly in the phenanthroline ligand with only a small leakage to the central metal ion. Such a weak but experimentally well detectable coupling is visible even in the raw EPR data: For the free

3300

3400

3500

Magnetic induction/Gauss

Electrochemical generation of the highly reactive [Ni0(phen)] complex in the presence of 2,4,6-trimethylbromobenzene results in formation of organonickel complex [NiBr(Mes)(phen)]. This new organonickel sigma-complex also can be successfully prepared by oxidative addition of MesBr to [Ni(COD)(phen)] or by ligand exchange reaction from [NiBr(Mes)(PPh3)2]. A one-electron reduction of [NiBr(Mes)(phen)] leads to elimination of bromide and formation of coordinatively unsaturated neutral complex [Ni(Mes)(phen)] bearing a 1,10-phenanthroline radical anion (phen) in the coordination sphere of nickel (Scheme 4). The obtained results are nicely fit with previous discussion concerning electrochemical properties of the related organonickel complexes formed by 2,20 -bipyridine and some tetramethylphenanthroline ligands [17,18] and, very probably, can be applied for increasing of the reactivity of sigma-complexes in electrocatalytic coupling processes. 3. Experimental 3.1. General procedures All manipulations and reactions were carried out under an atmosphere of dry nitrogen. All solvents were purified and dried prior to use. DMF was dried with calcium hydride and purified by distillation. [NiBr2(phen)] [22] and [Ni(COD)2] [23] were synthesized according to literature procedures; (NBu4)BF4 (Acros Organics), 1,10-phenanthroline (Alfa Aesar) and MesBr (Sigmae

3300

3400

3500

Magnetic induction/Gauss

Fig. 5. Electrochemically generated radical anions measured in frozen solution at 30 K. Left side: generated from reduction of free phenanthroline. Right side: generated from reduction of complex 1.

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63

Scheme 4. The proposed mechanism of organonickel complex 1 electroreduction.

Aldrich) were commercial products. The electrolyte (NBu4)BF4 was dried by melting in vacuum and stored under nitrogen.

13.40; found: C, 57.15; H, 4.60; Br, 18.15; N, 6.26; Ni, 13.65. IR: n(Nie Br) 216, 191 cm1 [24]. M.p. 179  C (dec.).

3.2. Electrochemical methods and apparatus

3.4. Synthesis of 1 from [NiBr(Mes)(PPh3)2]

Cyclic voltammograms were recorded with a glassy carbon electrode (working surface 3.14 mm2) in a thermostatically controlled (T ¼ 20  C) three-electrode electrochemical cell under N2 in the presence of (NBu4)BF4 (0.1 M). A silver electrode Ag/ AgNO3 (0.01 mol L1 solution in CH3CN) was used as a reference electrode and a platinum wire served as an auxiliary electrode. Curves were recorded at a constant potential scan rate of 50 mV s1 at T ¼ 20  C using a potentiostat/galvanostat model PI-50-1 (USSR). The electrochemical synthesis of [NiBr(Mes)(phen)] was carried out at room temperature in galvanostatic conditions [the potential of the working electrode was in the region 1.48 to 1.55 V vs Ag/ AgNO3 (0.01 mol L1 solution in CH3CN)]. The electrolysis was performed in a single electrochemical cell (three-electrode cell, 40 mL) without separation of anodic and cathodic compartments supplied with a nickel anode [12]. A glassy carbon or platinum electrode with a surface area of 60 cm2 was used as cathode. Nitrogen was continuously bubbled through the stirred electrolyte during the electrolysis. The glassy flat cell supplied with a platinum cathode (working electrode) and a sacrificial aluminium anode was used for EPR spectroelectrochemical experiments. The silver wire was used as the reference electrode. The EPR measurements were performed with a Bruker EMX spectrometer operational in the X-band. The microwave power used was in the range of 1 mWe4 mW. For the solution spectra we used modulation amplitudes from 0.01 mT up to 0.1 mT. Time constants were chosen properly. For the ESRspectra at low temperature we used a modulation amplitude of 0.5 mT. The NMR spectra were recorded on Bruker Avance 400 spectrometer. Melting points were measured with an Electrothermal IA9000 SERIES Digital Melting Point Apparatus in capillary tubes. The nickel content was determined by atomic absorption spectrometry using a Carl Zeiss AAS1 spectrometer.

A solution of 1,10-phenanthroline (240.0 mg, 1.33 mmol) in 5 mL of benzene was added to a suspension of [NiBr(Mes)(PPh3)2] [4,7] (941.0 mg, 1.2 mmol) in 20 mL of benzene. After stirring for 16 h the solvent was evaporated, the residue was washed with n-hexane (3  7 mL) and dried in vacuum for 6 h. 1 (0.47 g, 89%) was obtained as a dark red powder. M.p. 179  C (dec.). The NMR data were in agreement with those given above.

3.3. Electrochemical synthesis of 1

3.7. Electrochemical generation of the 1,10-phenanthroline radical anion in an EPR cell

A solution for electrolysis was prepared by mixing [NiBr2(phen)] [22] (0.199 g, 0.5 mmol), MesBr (0.076 mL, 0.5 mmol), and (NBu4) BF4 (0.987 g, 3.0 mmol) in DMF (30 mL). A constant current of 26.8 mA was passed through the solution for 1 h (the potential of the working electrode was in the region 1.48 to 1.55 V vs Ag/ AgNO3, 0.01 mol L1 solution in CH3CN). After the electrolysis was completed, the solution was transferred to a flask, the solvent was evaporated in vacuum and the residue was extracted with acetone (three times). The product was recrystallized from hot THF. Cooling to 20  C, gave 0.18 g (82%) of bright red crystals of 1 suitable for Xray analysis. Compound 1 was dried in vacuum at room temperature prior to NMR studies. 1 H NMR (400 MHz, acetone-d6, 25  C): d ¼ 9.49 (d 3J(H2e H3) ¼ 4.8 Hz, 1H, Hphen-2), 8.66 (d, 3J(H4eH3) ¼ 8.0 Hz, 1H, Hphen-4), 8.62 (d, 3J(H7eH8) ¼ 8.0 Hz, 1H, Hphen-7), 8.06 (d, 3J(H5e H6) ¼ 8.8 Hz, 1H, Hphen-5), 8.02 (d, 3J(H6eH5) ¼ 8.8 Hz, 1H, Hphen-6), 7.93 (t, 1H, Hphen-3), 7.58 (t, 1H, Hphen-8), 7.34 (d, 3J(H9e H8) ¼ 5.2 Hz, 1H, Hphen-9), 6.38 (s, 2H, m-H in Mes), 2.97 (s, 6H, oCH3 in Mes), 2.10 (s, 3H, p-CH3 in Mes). C21H19BrN2Ni (M ¼ 437.99 g mol1): calcd: C, 57.59; H, 4.37; Br, 18.24; N, 6.40, Ni,

3.5. Synthesis of 1 from [Ni(COD)2] A solution of 1,10-phenanthroline (450.5 mg, 2.5 mmol) in toluene (5 mL) was added to a cooled (30  C) suspension of [Ni(COD)2] (687.5 mg, 2.5 mmol) in toluene (20 mL). MesBr (3.8 mL, 25.0 mmol) was added to this mixture at 30  C. The reaction mixture was slowly warmed to room temperature (over 3 h) and stirred at r.t. for 6 h. The resulting solution was filtered, the solvent evaporated in vacuum, and the product extracted from the residue with diethyl ether. Evaporation of diethyl ether gave 1 as a dark red powder (0.76 g, 69%). M.p. 177e179  C (dec.). The NMR data were in agreement with those given above. 3.6. Electrochemical reduction of 1 in an EPR cell A solution for electrolysis was prepared by dissolving [NiBr(Mes)(phen)] (10.9 mg, 0.025 mmol) and (NBu4)BF4 (164.5 mg, 0.5 mmol) in DMF (5 mL). Subsequently, this solution was placed in an electrochemical EPR cell, supplied with a Pt cathode and a sacrificial Al anode. A constant current of 5.0 mA was passed through the solution for 15 min (the potential of the working electrode was in the region 0.65 to 0.75 V vs Ag/Agþ); the 1,10phenanthroline radical anion coordinated to nickel was observed. The colour of the solution did not change during experiment.

A solution for electrolysis was prepared by dissolving 1,10phenanthroline (2.7 mg, 0.015 mmol) and (NBu4)BF4 (98.7 mg, 0.3 mmol) in DMF (3 mL). Subsequently, this solution was placed in an electrochemical EPR cell, supplied with a Pt cathode and a sacrificial Al anode, and a constant current of 5.0 mA was passed through the solution for 15 min (the potential of the working electrode was in the region 1.60 to 1.70 V vs Ag/Agþ); the 1,10phenanthroline radical anion was observed. After electrolysis, the cathodic part of the solution was violet. Acknowledgements DGY acknowledges support of the IFW, DFG project PE 771/4-1 and DAAD project A/13/71281 during his stay in Dresden. YSG is thankful to DAAD (A/11/90605) for supporting of her stay in Leipzig. Financial support from the Russian Foundation for Basic Research and Tatarstan Academy of Sciences (RFBR 12-03-97067) and the Ministry of the Education and Sciences of the Russian Federation (state contract N  16.552.11.7083) are also gratefully

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acknowledged. The work has been supported in part by the DFG project FOR 1154 “Towards molecular spintronics”. We thank Dr. N. Hlubek for calibration of the temperature controlling device. Appendix A. Supplementary material CCDC 948868 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. Appendix B. Supplementary data Supplementary data related to this article can be found at http:// dx.doi.org/10.1016/j.jorganchem.2013.11.003. References [1] J. Campora, in: R.H. Crabtree, D.M.P. Mingos (Eds.), Comprehensive Organometallic Chemistry III, Compounds of Group 10, vol. 8, Elsevier, Oxford, 2007, pp. 27e132. [2] Y. Tamaru, Modern Organonickel Chemistry, Wiley-VCH Verlag GmbH & Co., Weinheim, 2005. [3] J. Chatt, B.L. Shaw, J. Chem. Soc. 4 (1960) 1718e1729. [4] W. Seidel, Z. Chem. 25 (1985) 411. [5] J.M. Coronas, G. Muller, M. Rocamora, C. Miravitlles, X. Solans, J. Chem. Soc. Dalton Trans. (1985) 2333e2341.

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