A Readily Accessible Chiral NNN Pincer Ligand with a Pyrrole

Article pubs.acs.org/IC

A Readily Accessible Chiral NNN Pincer Ligand with a Pyrrole Backbone and Its Ni(II) Chemistry: Syntheses, Structural Chemistry, and Bond Activations Jan Wenz, Alexander Kochan, Hubert Wadepohl, and Lutz H. Gade* Anorganisch-Chemisches Institut, Universität Heidelberg, Im Neuenheimer Feld 270, 69120 Heidelberg, Germany S Supporting Information *

ABSTRACT: A new class of chiral C2-symmetric N-donor pincer ligands, 2,5-bis(2-oxazolinyldimethylmethyl)pyrroles (PdmBox)H, was synthesized starting from the readily available ethyl 2,2dimethyl-3-oxobutanoate (1). The synthesis of the ligand backbone was achieved by oxidative enole coupling with CuC12 followed by Paal−Knorr-type pyrrole synthesis. The corresponding protioligands (RPdmBox)H (R = iPr: 5a; Ph: 5b) were obtained by condensation with amino alcohols and subsequent zinc-catalyzed cyclization. Reaction of the lithiated ligands with [NiCl2(dme)] yielded the corresponding square-planar nickel(II) complexes [(RPdmBox)NiCl] (6a/b). Salt metathesis of 6a with the corresponding alkali or cesium salts in acetone led to the formation of air- and moisture-stable [(iPrPdmBox)NiX] (X = F (7), X = Br (8), X = I (9), X = N3 (10), X = OAc (11). Furthermore, the conversion of [(iPrPdmBox)NiF] (7) with hydride transfer reagents such as PhSiH3 led to the stable hydrido species [(iPrPdmBox)NiH] (27), the stoichiometric transformations of which were studied. Treatment of 6a with organometallic reagents such as ZnEt2, PhLi, PhCCLi, NsLi, or (4FBn)2Mg(THF)2 gave the corresponding alkyl, alkynyl, or aryl complexes. The availability of the new nonisomerizable PdmBox pincer ligands allowed the comparative study of their ligation to square-planar complexes as helically twisted spectator ligands as opposed to the enforced planar rigidity of their isoPmBox analogues and the way this influences the reactivity of the Ni complexes.

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INTRODUCTION Compounds containing a chiral oxazoline unit are essential ligands in asymmetric catalysis due to their facile accessibility, modular nature, and applicability in a wide range of metalcatalyzed transformations.1−6 The success of the C2-symmetric bis(oxazolines) (“BOX”) and pyridine-bis(oxazolines) (“Pybox”), which have been used extensively in enantioselective catalysis, established those systems as a “privileged” class of ligands.3,4,7−13 The protioligands bis(oxazolinylmethyl)pyrrole (PmBox)H and bis(oxazolinylmethylidene)isoindole (Boxmi)H have been developed by us as a family of chiral monoanionic pincer ligands (Scheme 1).14−21 In both cases the meridional coordination to the metal center occurs via three nitrogen donor atoms. The central unit containing a deprotonable Nheterocycle is linked by C1 bridges with chiral oxazoline “arms”. The coordination chemistry of the PmBox system with transition metals has been studied extensively by our group (Scheme 2). A characteristic feature of these ligands is their tendency to isomerize upon coordination to a metal center. The resulting formation of a delocalized π-system in isoPmBox leads to a planarization of the ligand in metal complexes.14−16,21 In the presence of oxidants, metal complexes of the corresponding dehydro-PmBox pincers could be obtained by formal H2 elimination.14 © XXXX American Chemical Society

Scheme 1. Anionic Chiral Tridentate N Donor Pincer Box Ligands

Various nonisomerized, isomerized, and oxidized nickel PmBox complexes have been prepared, and their structural properties have been established in comparative studies. The formation of the conjugated π-electron system was found to be essential for the stability of nickel(I) species, which are accessible via H2 elimination from (iso-PmBox)nickel(II) hydrido complexes (Scheme 3).21 The T-shaped iso-PmBox nickel(I) complexes have been used as catalysts to reduce prochiral geminal dichlorides and dibromides enantioselectively to the corresponding secondary Received: January 10, 2017

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4a and 4b was accomplished by melting 3 with the appropriate amino alcohol in the presence of catalytic amounts of NaH. The subsequent conversion to the desired protioligands 5a and 5b was achieved by Mashima’s method using the tetranuclear zinc complex [Zn4O(O2CCF3)6].23 Following this procedure, two derivates of the protioligand (RPdmBox)H (5a R = iPr; 5b R = Ph) were obtained in good yields. Synthesis and Structural Characterization of PdmBox−Nickel(II) Chlorido Complexes. The coordination of the bis(2-oxazolinyldimethylmethyl)pyrrole derivatives (iPrPdmBox)H (5a) and (PhPdmBox)H (5b) to nickel was readily accomplished via deprotonation with lithium bases and subsequent stirring with [(dme)NiCl2] in tetrahydrofuran at room temperature yielding the corresponding nickel(II) complexes (6a) and (6b) as red solids (Scheme 6). The 1H and 13C NMR spectral patterns are consistent with a C2-symmetric molecular species. The characteristic pyrrole NH resonance of the protioligands (5a/b) has disappeared in (6a/ b), and the pyrrole-CMe2-oxazoline proton resonance is characteristically split into two signals (δ = 2.75 ppm, δ = 1.53 ppm) compared to the corresponding signal of protioligands (5a/b) (δ = 1.70 ppm), indicating the coordination of the pyrrolato unit as well as the two oxazoline rings to the nickel atom. Recrystallization from a toluene/ pentane mixture led to analytically pure compounds. The details of the molecular structures of the nickel(II) chlorido complexes (6a) and (6b) were established by X-ray diffraction (Table 1). The solid-state structures of the nickel(II) chlorido complexes containing the iPrPdmBox (6a) and PhPdmBox (6b) ligands are shown in Figure 1. The significant structural parameters in both complexes 6a and 6b are very similar, and the structural discussion will be therefore be restricted to 6a. The coordination geometry at the nickel center in 6a is almost ideally square planar [N(1)−Ni− N(3) 176.05(4)°, N(2)−Ni−Cl 177.07(4)°; sum of interligand angles 360.14(5)°]. The Ni−N bonds involving the two oxazoline units [Ni−N(1) 1.8953(14) Å, Ni−N(3) 1.8962(14) Å] are significantly longer than Ni−N(2) [1.8688(13) Å] of the central pyrrolato unit, whereas the interatomic distances within the pyrrole ring are as expected.15,16 The helical twist (∠helix) between the coordination planes and the planes of the pyrrole rings lies in the range of 30° for 6a and 6b (see Supporting Information) and is a consequence of the structural flexibility of the CMe2 groups that allow the donor functions to adapt to the size of the central metal atom. The bond angles at the linking CMe2 bridges of the meridionally coordinating ligand of C(3)− C(4)−C(5) 106.63(13)°, C(20)−C(4)−C(19) 108.87(14)°, C(8)−C(9)−C(10) 107.84(12)°, and C(22)−C(9)−C(21) 109.97(13)° are close to the ideal tetrahedral angles and indicate the absence of significant intraligand strain.

Scheme 2. Double Bonds in Motion: Key Transformations of the PmBox Nickel System

halides and to activate CF bonds in CF2 groups of appropriate substrates (Scheme 4). Detailed mechanistic studies have shown that in all hydro-dehalogenation reactions the activation of the halogen compound by the nickel(I) species is crucial for the catalysis.17,18,21 Given the interesting reactive behavior of the iso-PmBox nickel complexes, we were interested in the synthesis of a nonisomerized form of the PmBox nickel hydride, to investigate and compare its properties in terms of Ni−H reactivity and stability. However, all efforts to generate such Ni−H complexes resulted in the formation of the isomerized species and subsequent thermal bimolecular H2 elimination. To prevent this isomerization we synthesized 2,5-bis(2oxazolinyldimethylmethyl)pyrroles (PdmBox)H, a new class of monoanionic NNN pincer (protio-) ligands with dimethylmethylidene linkers that cannot undergo the rearrangement in the backbone and studied their coordination chemistry with nickel, which we report in this work.

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RESULTS AND DISCUSSION Synthesis of 2,5-Bis(2-oxazolinyldimethylmethyl)pyrroles. The 2,5-bis(2-oxazolinyldimethylmethyl)pyrroles (RPdmBox)H (5a/b) were obtained on a multigram scale in a five-step synthesis starting from ethyl 2,2-dimethylacetoacetate (1) (Scheme 5). The symmetric dimer 2, constituting the ligand backbone, was prepared by treating ketone 1 with lithium diisopropylamide at −78 °C and subsequent oxidative coupling with CuCl2 in dimethylformamide (DMF) to yield the 1,4-diketone.22 Following a standard protocol for the synthesis of pyrrole derivatives by Paal−Knorr-type16 cyclization from 1,4-diketones, condensation in the melt of 2 with NH4OAc gave compound 3 in high yield. The preparation of bisamides

Scheme 3. Conversion of the (iso-PmBox) Nickelhalogenido Complexes to the Corresponding Hydrido Complexes and Their H2 Pressure-Dependent Equilibrium with the T-Shaped Nickel(I) Species

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Inorganic Chemistry Scheme 4. Hydro-Dehalogenation Reactions

Scheme 5. Synthesis of the (RPdmBox)H Protioligands 5a and 5b

Figure 1. Molecular Structures of the Nickel Complexes 6a (left) and 6b (right).

[(iPrPdmBox)NiCl] (6a) by other anionic ligands. Treating a solution of (6a) in acetone with sodium iodide rapidly triggered the halide exchange and the generation of [(iPrPdmBox)NiI] (9) in quantitative yield. Following this protocol a variety of anionic ligands could be introduced by simple one-step reactions (Scheme 7). The conversions in these reactions are quantitative when monitored by NMR, and after recrystallization all compounds 7−18 could be isolated in good yields. We note that late transition-metal complexes bearing anionic heteroatomic ligands such as RO− or RS− are relevant for transition-metal-mediated stoichiometric and catalytic carbon− heteroatom bond-forming reactions.24,25 Metal thiophenolate complexes are attracting increasing interest due to their likely role in biocatalytic systems such as Ni−Fe hydrogenase.26−30 All (iPrPdmBox)Ni(II) complexes 7−18 are square-planar, diamagnetic in solution and in the solid state, were found to be stable toward air, moisture, and elevated temperatures and could therefore be isolated and fully characterized at ambient conditions. The proton spectra of all complexes display the

Scheme 6. Synthesis of [(RPdmBox)NiCl] 6a and 6b

Reactivity of the PdmBox−Nickel(II) Chlorido Complex 6a. Ligand-exchange reactions at the metal center may provide insights into key steps in the reaction mechanisms of stoichiometric and catalytic transformations. To this end, we investigated the substitution of the chlorido ligand of complex Table 1. Selected Bond Lengths [Å] and Angles [deg] selected bond lengths [Å] Ni−Cl Ni−N2 Ni−N1 Ni−N3 a

[(iPrPdmBox)NiCl] 6a

[(PhPdmBox)NiCl] 6ba

2.1968(8) 1.8688(13) 1.8953(14) 1.8962(14)

2.1910(6) [2.1933(6)] 1.8589(19) [1.863(2)] 1.9071(18) [1.887(2)] 1.8907(19) [1.8941(19)]

selected bond angles [deg] N1−Ni−Cl N1−Ni−N2 N1−Ni−N3 N3−Ni−Cl

[(iPrPdmBox)NiCl] 6a

[(PhPdmBox)NiCl] 6ba

90.30(4) 88.64(6) 176.05(4) 92.37(4)

92.62(6) [90.83(6)] 88.98(8) [89.15(9)] 174.18(9) [177.86(9)] 90.33(6) [91.29(6)]

Values in square brackets refer to the second independent molecule. C

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Scheme 7. Halide Exchange Reaction for the Preperation of iPrPdmBox−Nickel(II) (pseudo) Halogenido Complexes (7−10). Salt Methathesis of Chlorido Complex 6a with Heteroanionic Ligands (11−18) and Treatment of 6a with Alkylation/Arylation or Alkinylation Reagents (19−24)

Figure 2. Molecular structures of complexes 20, 21, and 24. Hydrogen atoms are omitted for clarity; thermal ellipsoids displayed at 50% probability. Selected bond lengths [Å] and angles [deg]: (20) Ni−C(23) 1.9577(18), Ni−N(2) 1.9212(16), Ni−N(1) 1.8985(14), Ni−N(3) 1.9005(15), N(1)−Ni−C(23) 92.43(7), N(1)−Ni−N(2) 87.53(6), N(2)−Ni−N(3) 87.51(6), N(3)−Ni−C(23) 92.56(7), N(2)−Ni−C(23) 175.59(8); (21) Ni−C(23) 1.911(2), Ni−N(2) 1.9171(16), Ni−N(1) 1.9059(17), Ni−N(3) 1.9005(17), N(1)−Ni−C(23) 91.75(9), N(1)−Ni−N(2) 89.28(8), N(2)−Ni−N(3) 88.16(8), N(3)−Ni-C(23) 90.74(8), N(2)−Ni−C(23) 178.06(9); (24) Ni−C(23) 1.874(2), Ni−N(2) 1.8875(18), Ni−N(1) 1.8956(17), Ni−N(3) 1.8841(17), N(1)−Ni−C(23) 94.23(8), N(1)−Ni−N(2) 89.99(8) N(2)−Ni−N(3) 88.71(7), N(3)−Ni−C(23) 88.78(8), N(2)−Ni−C(23) 169.88(8).

pyrrole proton signals at δ ≈ 6 ppm; the three oxazoline protons are displayed in the range of 3−5 ppm, and two singlet resonances for the methyl group protons appear between 1 and 3 ppm. The chemical shifts of the 1H NMR resonances were found to be strongly affected by the electronic nature of the fourth anionic ligand. Synthesis and Structural Characterization of Alkyl and Aryl Nickel(II) Complexes. In general, alkyl nickel(II) complexes of late transition metals are interesting as reagents in their own right or intermediate species in catalytic transformations such as cross-coupling reactions. Starting from compound (6a) we synthesized a variety of Ni(II) alkyl and aryl complexes (Scheme 7). The [(iPrPdmBox)NiEt] complex (19) was obtained by reaction of (6a) with diethylzinc in pentane at room temperature and, after workup, was isolated as a yellow crystalline solid in good yield (72%). The nonequivalence of the two diastereopic methylene protons of the Ni−ethyl unit in complex 19 is reflected in higher-order coupling patterns of the proton signals of this group. When heating a solution of 19 in C6D6 at 50 °C over 12 h no β-H elimination was observed, which is consistent with the previously observed thermal stability of other nickel alkyl complexes bearing pincer ligands and is the major reason for their successful application as catalysts in sp3−sp3 coupling reactions. 25,31−39 Upon reaction of (trimethylsilyl)methyllithium with 6a, the complex 20 was isolated as a light

yellow crystalline solid, while treatment with the dibenzylmagnesium THF adduct in toluene gave the benzylnickel complex 21. Following the same protocol as for 19, the phenylsubstituted nickel(II) complexes 22 and 23 as well as the alkynyl complex 24 were prepared and found to be very stable in air and in protic solvents. Purification by chromatography on silica was possible, and thermal decomposition was not observed even when toluene solutions of 22−24 were heated to 110 °C for 16 h. The detailed structures of complexes 19−21 and 24 were established by X-ray diffraction (Figure 2 and Supporting Information). The three N donor atoms of the pincer ligand span the coordination plane around the nickel center. The backbone of the pincer is twisted with respect to this coordination plane to minimize steric intraligand repulsion. The replacement of the chlorido ligand in general leads to no significant change in the structural parameters of the Ni−NNN fragment. This shows that the Ni−N distance and geometry of the metal center is dominated by the structure of the pincer ligand. The benzyl complex (21) was found to display an η1 coordination mode as expected for a 16-electron square-planar compound. Comparison between PmBox-, iso-PmBox, dehydroPmBox, and PdmBox Nickel Complexes. The nonisomerized PmBox ligand possesses high flexibility due to the methylene bridges in the backbone and can adapt to the steric D

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Inorganic Chemistry requirements of the metal and the other ligands through helical twisting. The molecular structures of [(iPrPmBox)NiCl] and [(iPrPdmBox)NiCl] (6a) are very similar (Figure 3): as the steric demand of the anionic fourth ligand is augmented, the twist angle of the pyrrole ring increases accordingly from ∼26° (7) to 36° (9).

Figure 4. Comparison of the molecular structures of the nickel chloro complexes iso-PmBox and dehydro-PmBox. Helical twist (∠helix) between the coordination planes and the planes of the pyrroline rings [deg] for the selected Ni halogenido complexes are given in the Table. a Values in square brackets refer to the second independent molecule. Figure 3. Comparison of the molecular structures of the nickel chloro complexes PmBox and PdmBox. Helical twist angles (∠helix) between the coordination planes and the planes of the pyrrole rings [deg] for the selected Ni halogenido complexes are given in the Table.

Scheme 8. Synthesis of the Nickel Hydride Complex 27

Besides the isomerization, the oxidation of the ligand backbone was sometimes observed as a side reaction. It turned out that these dehydro species can be exclusively made accessible by oxidizing the [(PmBox)NiCl] system with 2,3dichloro-5,6-dicyano-1,4-benzoquinone (DDQ) by formal H2 abstraction. As in case of the iso-PmBox and PbmBox systems the nickelfluorido complex 26 could also be obtained by salt metathesis with CsF (for details see Supporting Information). The isomerization (iso-PmBox) and the oxidation (dehydroPmBox) (25, 26) of the pincer ligand in the coordination sphere of the metal atom leads to the formation of a conjugated, rigid π-electron system, which is reflected in the solid-state structures (Figure 4). This study shows that the PdmBox ligand may thus be viewed as a stable version of the PmBox system, which is nonsusceptible to isomerization and concomitant planarization. Synthesis, Structural Characterization, and Reactivity of (PdmBox)Nickel(II) Hydride 27. Nickel hydride complexes are key intermediates in a variety of nickel-catalyzed transformations.17,21,40−45 Catalytic hydro-dehalogenations involving a Ni(II) hydride complex bearing a NNN pincer ligand have been studied by Hu et al.25 and further developed into an efficient protocol for nickel-catalyzed hydrosilylations of alkenes.46,47 Guan and co-workers have recently shown that pincer nickel hydrides catalyze the hydrosilylation of aldehydes and ketones48 as well as the hydroboration of CO2.49−51 Furthermore, cationic and neutral nickel hydride complexes of aliphatic PNP pincer ligands were found to be active catalysts for nickel-catalyzed alkene hydrogenations under mild conditions.52 The nickel fluorido complex 7 represents a convenient starting point for the synthesis of a nickel(II) hydrido complex via the reaction with silanes such as PhSiH3 or Ph2SiH2 (Scheme 8). The hydrido complex (27), which is immediately formed, was isolated as a yellow solid after crystallization from a concentrated diethyl ether solution at −20 °C. The proton NMR spectrum is consistent with C2 symmetry, and the characteristic Ni−H signal (1H NMR, δ = −25 ppm) lies within

the range expected for nickel hydrido complexes of this type.17,21,25,40−42,44,45,53,54 All efforts to generate 27 directly from [(iPrPdmBox)NiCl] 6a using (strong) hydride transfer reagents, such as LiHBEt3, NaHBOMe3, LiAlH4, or NaBH4, resulted either in low yields, the (re)generation of the protioligand, or unselective decomposition. The molecular structure of complex 27 is depicted in Figure 5 along with selected bond lengths and angles. The structural parameters are very similar to those of the nickel chlorido complex 6a, and the Ni−H bond length of 1.47(3) Å is in good agreement with those reported for related hydrido pincer systems.17,21,25,40−42,44,45,53 It seems that both 7 and 27 appear to have the lowest degree of twisting (∼25°)

Figure 5. Molecular structure of 27. Hydrogen atoms, except for Ni− H, are omitted for clarity; thermal ellipsoids displayed at 50% probability. Selected bond lengths [Å] and angles [deg]: H−Ni 1.47(3), N(1)−Ni 1.877(2), N(2)−Ni 1.910(2), N(3)−Ni 1.870(2), N(1)−Ni−N(2) 91.22(9), N(1)−Ni−H 87.3(12), N(2)−Ni−H 178.0(12), N(3)−Ni−N(1) 176.53(10), N(1)−C(3)−C(4)−C(5) 45.7(3). E

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Scheme 9. Insertion Reactions of Nickel Hydride Complex 27 with Ethylene and Bond-Splitting of PhXXPh (X = S, Se, Te) and RSH Bonds

and characterized. In particular, a nickel hydride complex was isolated and studied in stoichiometric bond activations, including the cleavage of S−S and S−H bonds in thiols and organic disulfides. Generally, the new nickel complexes were found to possess good thermal stability, which also applied to a derivative containing an alkyl ligand with β-hydrogen atoms. Future work will probe the catalytic potential of these nickel(II) complexes and explore the reactivity of other transition complexes bearing the new type of pincers as spectator ligands.

compared to the other Pdmbox nickel complexes (30°), which may be due to the reduced steric demand of small anionic ligand such as F or H.55−57 The hydride complex (27) was found to be stable in solution at room temperature over days. When heated in solution to 50 °C it decomposed slowly to yield the protonated ligand (iPrPdmBox)H (5a), which we attribute to N−H reductive elimination. The formation of stable Ni(I) species as in case of the iso-PmBox system (Scheme 3) was not observed. Compound 27 was found to be inert toward CC and CO bond insertion; no appreciable insertion product was detected when a solution of the complex in benzene-d6 was treated with 1-hexene, trans-stilbene, styrene, benzaldehyde, or acetophenone at room temperature. Only the reaction with ethylene (saturated solution in toluene) led to the slow formation of insertion product [(iPrPdmBox)NiEt] (19) over a period of 16 h in quantitative yield. The addition of 0.5 equiv of PhXXPh (X = S, Se, Te) smoothly transformed the nickel hydride to the corresponding phenylchalcogenido complexes [(iPrPdmBox)Ni(XPh)] (X = S, (16); X = Se, (28); X = Te, (29); see Scheme 9). These homolytic bond-splitting reactions were accompanied by the formation of molecular hydrogen. Only in the case of tellurium slow thermal decomposition in solution was subsequently observed. Both the treatment with aryl, benzyl, and alkyl disulfides led to a clean conversion to the corresponding thiolato complexes 16−18 (Scheme 9). An alternative access to complexes 16−18 involved the use of thiols instead of disulfide compounds. All compounds were found to be thermally very stable, and no decomposition was observed when a toluene solution was heated to 100 °C for 12 h. Furthermore, reaction with electrophiles such as PhCH2Br, CH3I, CCl4, PhCl, and Ph3CCl, even at elevated temperatures, failed to induce Ni−S cleavages. Finally, the reaction of elemental sulfur with the nickel hydride complex 27 resulted in an instant change of color from light yellow to dark green, accompanying the formation of the nickel sulfhydrido complex 30 (Scheme 9). The latter was found to be sensitive toward oxygen and moisture and decomposed within 3 h at room temperature in solution.

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EXPERIMENTAL SECTION

Methods and Instrumentation. All manipulations of air- and moisture-sensitive materials were performed under an inert atmosphere of dry argon (Argon 5.0 purchased from Messer Group GmbH and dried over Granusic phosphorpentoxide granulate) using standard Schlenk techniques or by working in a glovebox. The solvents were dried over sodium (toluene), potassium (hexane), or sodium/ potassium alloy (pentane, diethyl ether), distilled, and degassed prior to their use.58 Deuterated solvents were purchased from Deutero GmbH, dried over potassium (C6D6), vacuum-distilled, degassed, and stored in Teflon valve ampules under argon. The 2,5-bis(oxazolinylmethyl)pyrrole protioligand (iPrPmBox)H15 as well as the complex [(iPrPmBox)NiCl] were synthesized according to literature procedures.15 All other reagents were obtained from commercial sources and were used as received unless explicitly stated otherwise. Air-sensitive samples for NMR spectroscopy were prepared under argon in 5 mm Wilmad tubes equipped with J. Young Teflon valves. 1 H and 13C NMR spectra were recorded on a Bruker Avance (200 MHz), a Bruker Avance II (400 MHz), and a Bruker Avance III (600 MHz, equipped with a CryoProbe) NMR spectrometers and were referenced internally using the residual protio solvent (1H) or solvent (13C).59 The appearance of the signals was described using the following abbreviations: s (singlet), d (doublet), dd (doublet of doublets), ddd (doublet of doublets of doublets), dt (doublet of triplets), t (triplet), q (quartet), m (multiplet), b (broad signal). Elemental analyses were recorded by the analytical service of the Heidelberg Chemistry Department using the vario EL and vario MIKRO cube analytical devices. Mass spectra were acquired on Bruker ApexQe hybrid 9.4 T FT-IVR (HR-ESI, HR-DART) and JEOL JMS700 magnetic sector (HR-FAB, HR-EI, LIFDI) spectrometers at the mass spectrometry facility of the Organic Department at the University of Heidelberg. Either 3-nitrobenzyl alcohol (NBA) or o-nitrophenyloctyl ether (NPOE) were used as matrix in the fast atom bombardment mass spectrometry (FAB-MS) measurements. An Agilent Technologies Supernova-E CCD (Cu Kα or Mo Kα Xradiation, microfocus tube, multilayer mirror optics) and a Bruker AXS Smart 1000 CCD diffractometer (Mo Kα radiation, graphite monochromator, λ = 0.710 73 Å) were used for X-ray data acquisition. UV/vis spectra were recorded on a Varian Cary 5000 UV/vis/NIR spectrometer. Ethyl 2,2-dimethylacetoacetate (1),60 (S)-2-amino-3-

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CONCLUSION In this work we have established a new class of chiral C2 symmetric meridionally coordinating N-donor ligands that are ideally adapted to tricoordination in square-planar transitionmetal complexes. A series of nickel complexes containing the (iPrPdmBox) pincer ligand with different anions was prepared F

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Inorganic Chemistry methylbutan-1-ol and (R)-2-amino-2-phenylethan-1-ol,61 tetranuclear zinc complex [Zn4O(O2CCF3)6],23 [(iPriso-PmBox)NiCl],16 and Bn2Mg(THF)262 were prepared as described. All other chemicals were purchased from commercial sources and used without purification unless otherwise stated. Synthetic Procedure. Atom numbering for the assignment of the NMR spectra:

= 410.3015 (M+), 279.2066 (M+-C6H12NO2). 4b: (90%): 1H NMR (CDCl3, 600 MHz, 295 K): δ (ppm) = 9.46 (bs, 1 H, NH), 7.29 (t, 3 JH,H = 7.8 Hz, 4 H, H10), 7.23 (t, 3JH,H = 7.4 Hz, 2 H, H11), 7.12 (d, 3 JH,H = 7,7 Hz, 4 H, H9), 6.27 (d, 4JH,H = 7.9 Hz, 2 H, H1), 6.05 (d, 3 JH,H = 3.0 Hz, 2 H, NH), 5.02 (td, 3JH,H = 8.0 Hz, 4.2 Hz, 2 H, H6), 3.80 (dd, 3JH,H = 11.7 Hz, 4.2 Hz, 2 H, H7), 3.52 (dd, 3JH,H = 12.0 Hz, 8.1 Hz, 4 H, H7′, OH), 1.59 (s, 6 H, H4′), 1.55 (s, 6 H, H4′). 13C NMR (CDCl3, 150 MHz, 295 K): δ (ppm) = 177.5 (C5), 138.8 (C8), 136.1 (C2), 128.9 (C9,10,11), 127.9 (C9,10,11), 126.5 (C9,10,11), 105.2 (C1), 65.0 (C6), 55.5 (C7), 43.4 (C3), 26.2 (C4), 25.7 (C4′). HR-FAB+: m/z = 478.2740 (M++H). GP2. G eneral synthetic procedure for the 2,5-bis(oxazolinyldimethylmethyl)pyrroles (5a and 5b). Compounds 4a and 4b were refluxed for 36 h in 100 mL of dry chlorobenzene in the presence of [Zn4(OCOCF3)6O] (3 mol %). After removal of all volatiles under reduced pressure, the crude product was subjected to column chromatography. 5a: (95%): 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 10.31 (s,1 H, NH), 6.16 (d, 4JH,H = 2.6 Hz, 2 H, H1), 3.78 (dd, 3JH,H = 8.1 Hz, 9.6 Hz, 2 H, H6), 3.70−3.66 (m, 2 H, H7), 3.58 (dd, 3JH,H = 8.0 Hz, 8.0 Hz, 2 H, H6′), 1.70 (s, 12 H, H4) 1.52 (ds, 3 JH,H = 6.6 Hz, 6.5 Hz, 2 H, H8), 0.92 (d, 3JH,H = 6.7 Hz, 6 H, H9), 0.75 (d, 3JH,H = 6.8 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 171.5 (C5), 135.2 (C2), 104.2 (C1), 72.4 (C6), 70.2 (C7), 37.2 (C3), 33.1 (C5), 28.2 (C4′), 27.4 (C4), 18.8 (C9), 18.6 (C9′). HRFAB+: m/z = 374.2817 (M++H), 373.2754 (M+), 358.2488 (M+-CH3). Anal. Calcd for C22H35N3O2: C 70.74, H 9.44, N 11.25. Found C 70.49, H 9.53, N 11.26%. 5b: (61%): 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 10.33 (s, 1 H, NH), 7.10−7.01 (m, 10 H, H9,10,11), 6.21 (d, 4JH,H = 2.7 Hz, 2 H, H1), 4.84 (dd, 3JH,H = 10.1 Hz, 9.1 Hz, 2 H, H7), 3.95 (dd, 3JH,H = 10.0 Hz, 8.2 Hz, 2 H, H6), 3.62 (dd, 3JH,H = 8.3 Hz, 8.3 Hz, 2 H, H6), 1.74 (s, 6 H, H4), 1.72 (s, 6 H, H4). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 172.9 (C5), 143.4 (C8), 135.2 (C2), 128.8 (C9,10,11), 127.5 (C9,10,11), 126.8 (C9,10,11), 104.5 (C1), 74.6 (C6), 69.8 (C7), 37.4 (C3), 28.1 (C4), 27.4 (C4′). HR-FAB+: m/z = 442.2490 (M++H). GP3. General synthetic procedure for (RPdmBox)nickel(II) halogenido complexes (6a and 6b): The protioligand (RPdmBox)H (2.7 mmol) was dissolved in 20 mL of THF and then metalated at room temperature by slow addition of n-buthyllithium (1.8 M in hexane, 2.81 mmol, 1.05 equiv). The solution turned from colorless to yellow and was canulated to a suspension of [(dme)NiCl2] (3 mmol, 1.1 equiv) in 20 mL of THF. The mixture was stirred for 2 h at room temperature. The solvents were removed in vacuo. The residue was treated with a toluene/pentane (1:2) mixture, and the inorganic metal salts were filtered off. After the removal of the solvents, the product was recrystallized from a toluene/pentane mixture at −20 °C to give the product as red crystalline solid. 6a: Yield 85%: 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.06 (s, 2 H, H1), 4.34−4.31 (m, 2 H, H7), 3.51 (dd, 3JH,H = 5.6 Hz, 9.2 Hz, 2 H, H6), 3.38 (dd, 3JH,H = 10.1 Hz, 9.3 Hz, 2 H, H6′), 3.19−3.11 (m, 2 H, H8), 2.75 (s, 6 H, H4), 1.52 (s, 6 H, H4′), 0.66 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.64 (d, 3JH,H = 7.3 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 175.9 (C5), 137.5 (C2), 103.1 (C1), 69.1 (C6), 67.2 (C7), 38.6 (C3), 34.8 (C4), 31.0 (C8), 22.1 (C4′), 18.3 (C9′), 14.7 (C9). HR-FAB+: m/z = 465.1697 (M+). Anal. Calcd for C22H34N3O2NiCl. C 56.62, H 7.34, N: 9.00. Found C 56.85, H 7.29, N 9.15%. 6b: Yield 90%: 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.31−7.10 (m, 10 H, H9−11), 6.11 (s, 2 H, H1), 5.25 (dd, 3JH,H = 5.9 Hz, 10.3 Hz, 2 H, H7), 3.56 (dd, 3JH,H = 8.9 Hz, 10.4 Hz, 2 H, H6), 3.46 (dd, 3JH,H = 8.9 Hz, 6.1 Hz, 2 H, H6′), 2.43 (s, 6 H, H4), 1.53 (s, 6 H, H4′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.0 (C5), 143.9 (C8), 137.5 (C2), 129.1 (C9,10,11), 127.8 (C9,10,11), 126.8 (C9,10,11), 103.3 (C1), 75.9 (C6), 66.2 (C7), 38.7(C3), 34.6 (C4), 22.0 (C4′). HR-FAB+: m/z = 533.1355 (M+). Anal. Calcd for C28H30N3O2NiCl. C 62.90, H 5.66, N 7.86. Found C 63.15, H 5.82, N 7.66%. GP4. General synthetic procedure for ((S)iPrPdmBox) nickel(II) halogenido complexes (7−10): [((S)iPrPdmBox)NiCl] 6a (100 mg, 0.215 mmol) and the corresponding Li, Na, or Cs salt (0.63 mmol, 3 equiv) were suspended in 30 mL of acetone. The reaction mixture was

Modified Synthetic Procedure for 2.22 Lithium diisopropylamide (LDA) (7.35 g, 68 mmol) was dissolved in 75 mL of dry THF and cooled to −78 °C. A solution of ethyl 2,2-dimethyl-3-oxobutanoate (10.0 g, 63 mmol) in 30 mL of THF was slowly added by means of a cannula. Anhydrous CuCl2 (9.05 g, 67 mmol) was slowly dissolved in 75 mL of DMF under ice-cooling and then added by cannula to the THF solution of lithium enolate. The dark green solution was stirred for an additional 30 min and then allowed to warm to room temperature. The reaction mixture became dark brown and homogeneous. The reaction mixture was treated with 3% aqueous HCl and extracted with ether. The ether extract was washed twice with brine and dried over Na2SO4. The ether solution was evaporated to give 10.0 g of crude product 2,7-dicarbethoxy-2,7-dimethyloctane-3,6dion. 1H NMR (CDCl3, 600 MHz, 295 K): δ (ppm) = 4.16 (q, 3JH,H = 7.1 Hz, 4 H, H2), 2.75 (s, 4 H, H7), 1.37 (s, 12 H, H6), 1.24 (t, 3JH,H = 7.1 Hz, 6 H, H1). 13C NMR (CDCl3, 150 MHz, 295 K): δ (ppm) = 206.9 (C5), 173.7 (C3),61.5 (C2), 55.5 (C4), 31.9(C7), 22.3 (C6), 14.2 (C1). Electron ionization (EI+): m/z = 223, 199, 171, 125, 97, 87, 59. Synthetic Procedure for 3. Compound 2 (10 g, 31.8 mmol) was used without purification and, with ammonium acetate (10 g, 129 mmol, 4.1 equiv), was placed in a Schlenk flask and melted at 85 °C. The reaction was monitored by gas chromatography-mass spectrometry (GC-MS) analysis. After 3 h conversion was complete. After removal of all volatiles under reduced pressure, the crude product was purified by column chromatography on silica (eluent: petroleether/ ethyl acetate 9:1). The pure product was obtained as a yellow oil (5.7 g, 60%). 1H NMR (CDCl3, 600 MHz, 295 K): δ (ppm) = 8.95 (bs, 1 H, NH), 5.91 (d, 4JH,H = 2.9 Hz, 2 H, H1), 4.14 (q, 3JH,H = 7.1 Hz, 4 H, H6), 1.54 (s, 12 H, H4), 1.26 (t, 3JH,H = 7.1 Hz, 6 H, H7). 13C NMR (CDCl3, 150 MHz, 295 K): δ (ppm) = 175.8 (C5), 134.3 (C2), 104.0 (C1), 61.1 (C6), 42.2 (C3), 25.9 (C4), 14.1 (C7). High-resolution electron ionization (HR-EI+): m/z = 295.1782 (M+), 222.1488(M+(C3O2H5)), 148.1158 (M+-(C3O2H5)2). GP1. General synthetic procedure for the 2,5-[bis((N-1-hydroxyethyl)acetamido)isopropyl]pyrroles (4a and 4b). Compound 3 and the respective amino alcohol (2.1 equiv) were mixed and melted in a Schlenk tube under argon. The solid mixture was then rapidly heated to 120 °C (in a preheated oil bath). To the resulting melt 100 mg of solid NaH was added, and the reaction mixture was stirred under a dynamic vacuum for 3 h. During this period, the reaction mixture turned brown and became highly viscous, and after subsequent cooling to ambient temperature gave a brown amorphous solid. The crude product was subjected to column chromatography on silica (eluent: dichloromethane/methanol). The pure product was isolated as a colorless hygroscopic solid (yields 80−90%). 4a: (84%): 1H NMR (CDCl3, 600 MHz, 295 K): δ (ppm) = 9.58 (bs, 1 H, NH), 6.00 (d, 4 JH,H = 2.6 Hz, 2 H, H1), 5.71 (d, 3JH,H = 9.0 Hz, 2 H, H6), 4.04 (bs, 2 H, NH/OH), 3.74−3.69 (m, 4 H, H7, NH/OH), 3.41 (dd, 3JH,H = 9.0 Hz, 12.0 Hz, 2 H, H7′), 1.74−1.67 (m, 2 H, H8), 1.56 (s, 6 H, H4), 1.55 (s, 6 H, H4′), 0.87 (d, 3JH,H = 6.7 Hz, 6 H, H9), 0.80 (d, 3JH,H = 6.8 Hz, 6 H, H9′). 13C NMR (CDCl3, 150 MHz, 295 K): δ (ppm) = 178.0 (C5), 136.3 (C2), 104.9 (C1), 63.6 (C7), 56.9 (C6), 43.5 (C3), 29.4 (C8), 26.4 (C4), 25.6 (C4′), 19.7 (C9), 18.6 (C9′). HR-FAB+: m/z G

DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

H16), 8.22 (dt, 3JH,H = 7.8 Hz, 4JH,H = 1.1 Hz, 1 H, H12), 7.16 (ddd, 3 JH,H = 7.8 Hz, 4JH,H = 2.2 Hz, 4JH,H = 1.0 Hz, 1 H, H14), 6.93 (t, 3JH,H = 7.8 Hz, 1 H, H13), 6.04 (s, 2 H, H1), 3.49 (dd, 3JH,H= 9.0 Hz, 5.4 Hz, 2 H, H6), 3.37 (dd, 3JH,H = 10.0 Hz, 9.3 Hz, 2 H, H6′), 3.28−3.24 (m, 2 H, H7), 3.02 (ds, 3JH,H= 6.8 Hz, 3.4 Hz, 2 H, H8), 2.79 (s, 6 H, H4), 1.53 (s, 6 H, H4′), 0.70 (d, 3JH,H = 6.12 Hz, 6 H, H9), 0.54 (d, 3JH,H = 6.1 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.9 (C5), 170.4 (C10), 138.5 (C15), 137.8 (C2), 134.3 (C11), 130.7 (C14), 129.9 (C16), 129.6 (C12), 127.8 (C13), 103.5 (C1), 69.3 (C6), 66.7 (C7), 38.8 (C3), 35.1 (C4), 30.8 (C8), 22.4 (C4′), 18.3 (C9′), 14.9 (C 9 ). DART + : m/z = 586.1988 (M + +H). Anal. Calcd for C29H38N3O4NiCl. C 59.36, H 6.53, N 7.16. Found C 59.32, H 6.55, N 7.18%. 13: Yield 73%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.40 (dd, 3JH,H = 9.0 Hz, 3JH,F = 4.2 Hz, 2 H, H11), 7.00 (dd, 3JH,H = 8.5 Hz, 3JH,F = 8.5 Hz, 2 H, H12), 6.07 (s, 2 H, H1), 3.51−3.46 (m, 4 H, H6,7), 3.37−3.31(m, 2 H, H6′), 2.75 (ds, 3JH,H = 6.9 Hz, 3JH,H = 3.2 Hz, 2 H, H8), 2.58 (s, 6 H, H4), 1.52 (s, 6 H, H4′), 0.68 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.53 (d, 3JH,H = 7.2 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.6 (C5), 163.7 (4JC,F = 1.0 Hz, C10), 154.1 (d, 1JC,F = 229.7 Hz, C13), 137.8 (C2), 119.2 (d, 3JC,F = 7.3 Hz, C11), 115.6 (d, 2JC,F = 22.0 Hz, C12), 103.6 (C1), 69.4 (C7), 65.8 (C6), 38.5 (C3), 35.0 (C4), 31.3 (C8), 22.5 (C4′), 18.3 (C9′), 14.9 (C9). 19F NMR (C6D6, 376 MHz, 295 K): δ (ppm) = −132.5 (s). DART+: m/z = 542.2381 (M++H). Anal. Calcd for C28H38N3O3NiF C 62.01, H 7.06, N 7.75. Found C 62.16, H 7.30, N 7.35%. 14: Yield 89%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.54 (d, 3JH,H = 9.0 Hz, 2 H, H11), 6.97 (d, 3JH,H = 8.8 Hz, 2 H, H12), 6.10 (s, 2 H, H1), 3.62 (ddd, 3JH,H = 9.7 Hz, 4.9 Hz, 3.7 Hz, 2 H, H7), 3.52 (s, 3 H, H14), 3.50 (dd, 3JH,H = 9.1 Hz, 5.1 Hz, 2 H, H6), 3.37 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.83 (ds, 3JH,H = 6.9 Hz, 3JH,H = 3.6 Hz, 2 H, H8), 2.63 (s, 6 H, H4), 1.54 (s, 6 H, H4′), 0.71 (d, 3JH,H = 6.8 Hz, 6 H, H9), 0.56 (d, 3 JH,H = 7.2 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.4 (C5), 161.5 (C10), 150.0 (C13), 137.9 (C2), 119.5 (C11), 115.3 (C12), 103.4 (C1), 69.4 (C7), 65.8 (C6), 55.7 (C14), 38.6 (C3), 35.0 (C4), 31.3 (C8), 22.5 (C4′), 18.4 (C9′), 15.0 (C9). DART+: m/z = 554.2530 (M++H). Anal. Calcd for C29H41N3O4Ni. C 62.83, H 7.46, N 7.58. Found C 62.66, H 7.35, N 7.63%. 15: Yield 77%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.07 (d, 3JH,H = 7.3 Hz, 2 H, H12), 6.74 (t, 3JH,H = 7.3 Hz, 1 H, H13), 6.03 (s, 2 H, H1), 3.51 (dd, 3 JH,H = 9.2 Hz, 4.5 Hz, 2 H, H6), 3.36 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 3.23−3.18 (m, 2 H, H7), 2.99 (ds, 3JH,H = 7.1 Hz, 3JH,H = 3.5 Hz, 2 H, H8), 2.81 (s, 6 H, H14), 2.74 (s, 6 H, H4), 1.53 (s, 6 H, H4′), 0.54 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.51 (d, 3JH,H = 7.3 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.1 (C5), 164.6 (C10), 138.0 (C2), 129.3 (C11), 128.5 (C12), 115.4 (C13), 103.2 (C1), 68.9(C7), 64.5 (C6), 38.6 (C3), 34.5 (C4), 31.1 (C8), 22.3 (C4′), 18.8 (C14), 18.3 (C9′), 14.2 (C9). DART+: m/z = 552.2737 (M++H). Anal. Calcd for C30H43N3O3Ni. C 65.23, H 7.85, N 7.61. Found C 65.21, H 7.94, N 7.38%. GP6. General synthetic procedure for diphenyldisulfid or sulfid activation. To a solution of [((S)iPrPdmBox)NiH] 27 (120 mg, 0.28 mmol) in 2 mL of benzene the corresponding organic disulfide (0.14 mmol, 0.5 equiv) or sulfide (0.28 mmol, 1.0 equiv) was added in 2 mL of benzene. After complete conversion the solvent was removed in vacuo. 16: Yield 99%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 8.17 (dd, 3JH,H = 8.1 Hz, 1.1 Hz, 2 H, H11), 7.03 (t, 3JH,H = 7.7 Hz, 2 H, H12), 6.94 (tt, 3JH,H = 7.3 Hz, 1.1 Hz, 1 H, H13), 6.13 (s, 2 H, H1), 4.08 (ddd, 3JH,H = 9.8 Hz, 4.4 Hz, 3.5 Hz, 2 H, H7), 3.48 (dd, 3JH,H = 9.1 Hz, 4.4 Hz, 2 H, H6), 3.26 (ds, 3JH,H = 7.0 Hz, 3JH,H = 3.5 Hz, 2 H, H8), 3.16 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.72 (s, 6 H, H4), 1.57 (s, 6 H, H4′), 0.54 (d, 3JH,H = 6.9 Hz, 6 H, H9), 0.53 (d, 3JH,H = 6.8 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.7 (C5), 147.1 (C10), 137.3 (C2), 133.4 (C11), 128.0 (C12), 122.7 (C13), 102.7 (C1), 68.6 (C7), 68.5 (C6), 38.8 (C3), 34.6 (C4), 31.5 (C8), 22.2 (C4′), 18.3 (C9′), 14.2 (C9). HR-MS FAB+: m/z = 540.2192. (M++H). Anal. Calcd for C28H39N3O2NiS C 62.23, H 7.27, N 7.78. Found C 62.21, H 7.47, N 7.57%. 17: Yield 99%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.62 (dm, 3JH,H = 6.9 Hz, 2 H, H12), 7.24 (t, 3JH,H = 7.8 Hz, 2 H, H13), 7.10 (tt, 3JH,H = 7.4 Hz, 4JH,H = 1.1 Hz, 1 H, H14), 6.13 (s, 2 H, H1), 4.33 (ddd, 3JH,H = 10.0 Hz, 4.7 Hz, 3.5 Hz, 2 H, H7), 3.61 (dd,

stirred and monitored by NMR spectroscopy. After complete conversion (2 to 48 h) the solvents were removed in vacuo. The residue was treated with a toluene/pentane (1:3) mixture, and the inorganic metal salts were filtered off. After the removal of the solvents, the product was recrystallized from a toluene/pentane mixture at room temperature. 7: Salt metathesis reaction with CsF, 24 h. Yield 83%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.08 (s, 2 H, H1), 3.90−3.84 (m, 2 H, H7), 3.61−3.54 (m, 4 H, H6/6′), 2.66− 2.52 (m, 2 H, H8), 2.46 (s, 6 H, H4′), 1.53 (s, 6 H, H4′), 0.93 (d, 3JH,H = 6.8 Hz, 6 H, H9), 0.90 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.7 (C5), 137.9 (C2), 103.8 (C1), 70.2 (C6), 65.1 (C7), 38.6 (C3), 35.2 (C4), 31.3 (C8), 22.7 (C4′), 18.5 (C9′), 16.1 (C9). 19F NMR (C6D6, 376 MHz, 295 K): δ (ppm)= −448.6 (s). HR-FAB+: m/z 430.2003 (M+-F). Anal. Calcd for C22H34N3O2NiF. C 58.69, H 7.61, N 9.33. Found C 58.77, H 7.44, N 9.36%. 8: Salt metathesis reaction with LiBr, 12 h. Yield 85%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.05 (s, 2 H, H1), 4.47 (ddd, 3JH,H = 10.2 Hz, 5.2 Hz, 3.6 Hz, 2 H, H7), 3.50 (dd, 3JH,H = 9.3 Hz, 5.5 Hz, 2 H, H6), 3.32 (dd, 3JH,H = 9.7 Hz, 9.7 Hz, 2 H, H6′), 3.28 (ds, 3JH,H = 6.9 Hz, 3.5 Hz, 2 H, H8), 2.81 (s, 6 H, H4), 1.52 (s, 6 H, H4′), 0.59 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.57 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.1 (C5), 137.5 (C2), 103.1 (C1), 69.0(C7), 68.9 (C6), 38.6 (C3), 34.7 (C4), 30.9 (C8), 21.9 (C4′), 18.2 (C9′), 14.2 (C9). HR-FAB+: m/z = 513.1110 (M+), 430.1996 (M+-Br). Anal. Calcd for C22H34N3O2NiBr. C 51.70, H 6.71, N 8.22. Found C 51.36, H 6.73, N 8.11%. 9: Salt metathesis reaction with NaI, 2 h. Yield 92%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.06 (s, 2 H, H1), 4.62 (ddd, 3JH,H = 10.1 Hz, 5.2 Hz, 3.4 Hz, 2 H, H7), 3.47 (dd, 3JH,H = 9.1 Hz, 5.1 Hz, 2 H, H6), 3.37 (ds, 3JH,H = 7.0 Hz, 3.4 Hz, 2 H, H8), 3.23 (dd, 3JH,H = 10.1 Hz, 9.0 Hz, 2 H, H6′), 2.86 (s, 6 H, H4), 1.51 (s, 6 H, H4′), 0.54 (d, 3JH,H = 6.7 Hz, 6 H, H9), 0.46 (d, 3JH,H = 6.9 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.6 (C5), 137.4 (C2), 103.1 (C1), 72.3 (C6), 68.7 (C7), 38.8 (C3), 34.8 (C4), 30.8 (C8), 21.8 (C4′), 18.1 (C9′), 13.6 (C 9 ). HR-FAB + : m/z = 533.1355 (M + ). Anal. Calcd for C22H34N3O2NiI C 47.34, H 6.14, N 7.53. Found C 47.79, H 6.27, N 7.68%. 10: Salt metathesis reaction with CsN3, 24 h. Yield 76%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.03 (s, 2 H, H1), 3.90− 3.85 (m, 2 H, H7), 3.52 (dd, 2 H, 3JH,H = 9.1 Hz, 5.1 Hz, 2 H, H6), 3.47 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.74 (ds, 3JH,H = 7.8 Hz, 3.7 Hz, 2 H, H8), 2.54 (s, 6 H, H4), 1.49 (s, 6 H, H4′), 0.74 (d, 3JH,H = 6.7 Hz, 6 H, H9), 0.69 (d, 3JH,H = 6.9 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.2 (C5), 137.5 (C2), 103.3 (C1), 69.8 (C7), 66.9 (C6), 38.6 (C3), 35.0 (C4), 31.8 (C8), 22.1 (C4′), 18.1 (C9′), 15.3 (C9). HR-FAB+: m/z = 474.2100 (M+), 430.2028 (M+-N3). Anal. Calcd for C22H34N6O2Ni. C 55.84, H 7.24, N 17.76. Found: C 55.92, H 7.38, N, 18.06%. GP5. General synthetic procedure for ((S)iPrPdmBox) nickel(II) (ER, E = O, S) complexes (11−18): To a suspension of NaH (0.32 mmol, 1.5 equiv) in 10 mL of THF was added the corresponding carboxylic acid, phenol, or thiol (0.268 mmol, 1.25 equiv) at room temperature. The resulting mixture was stirred for 10 min, [((S)iPrPdmBox)NiCl] 6a (100 mg, 0.215 mmol) was subsequently added, and the reaction mixture was stirred for additional 2 h. The volatiles were removed under vacuum, and the residue was extracted with pentane and filtered through a pad of diatomaceous earth. After the removal of the solvents, the products were recrystallized from pentane at −20 °C. 11: Yield 79%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.08 (s, 2 H, H1), 3.55 (dd, 3JH,H = 8.9 Hz, 5.5 Hz, 2 H, H6), 3.49 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 3.36 (ddd, 3JH,H = 9.7 Hz, 5.6 Hz, 3.9 Hz, 2 H, H7), 2.99 (ds, 3JH,H = 7.0 Hz, 3.4 Hz, 2 H, H8), 2.77 (s, 6 H, H4), 2.03 (s, 3 H, H10), 1.55 (s, 6 H, H4′), 0.69 (d, 3 JH,H = 6.8 Hz, 6 H, H9), 0.65 (d, 3JH,H = 6.9 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.6 (C5), 176.2 (C11), 137.8 (C2), 103.4 (C1), 69.3 (C6), 66.8 (C7), 38.7 (C3), 35.0 (C4), 30.7 (C8), 23.8 (C10), 22.3 (C4′), 18.5 (C9′), 14.9 (C9). Direct analysis in real time (DART+): m/z = 490.2217 (M++H). Anal. Calcd for C24H37N3O4Ni. C 58.80, H 7.61, N 8.57. Found C 58.93, H 7.51, N 8.53%. 12: Yield 82%. 1H NMR (C6D6, 600 MHz, 295 K): 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 8.43 (t, 3JH,H = 2.0 Hz, 1 H, H

DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

H6,7), 3.38 (dd, 3JH,H = 8.7 Hz, 8.7 Hz, 2 H, H6′), 2.67−2.60 (m, 2 H, H8), 2.62 (s, 6 H, H4), 1.85 (d, 2JH,H = 9.8 Hz, 1 H, H14), 1.67 (s, 6 H, H4′), 1.38 (d, 2JH,H = 9.8 Hz, 1 H, H14′), 0.40 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.38 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.2 (C5), 160.5 (d, 1JC,F = 238.5 Hz, C13), 148.3 (d, 4JC,F = 3.0 Hz, C10), 137.0 (C2), 129.3 (d, 3JC,F = 6.8 Hz, C11), 115.2 (d, 2JC,F = 20.4 Hz, C12), 101.7 (C1), 67.7 (C7), 67.5 (C6), 39.1 (C3), 34.6 (C4), 31.4 (C8), 22.2 (C4′), 18.1 (C9′), 13.7 (C9), 7.9 (C14). 19 F NMR (C6D6, 376 MHz, 295 K): δ (ppm) = −121.6 (s). DART+: m/z = 540.2584 (M++H). Anal. Calcd for C29H40N3O2NiF. C 64.46, H 7.46, N 7.78. Found C 64.83, H 7.60, N 7.94%. Synthetic Procedure for 22. To a solution of [((S)iPrPdmBox)NiCl] 6a (230 mg, 0.49 mmol) in 200 mL of toluene, PhLi (1.8 M in dibutyl ether 1.1 equiv) was added in 100 mL of toluene at room temperature. The reaction was stirred for another 30 min at ambient temperature. After all volatiles were removed, the product could be isolated by column chromatography (petroleum ether/ethyl acetate 10:1) followed by crystallization from pentane at −20 °C to give 22 as a yellow solid (56%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.83 (d, 3JH,H = 6.6 Hz, 2 H, H11), 7.09 (t, 3JH,H = 7.3 Hz, 2 H, H12), 7.00 (t, 3JH,H = 7.2 Hz, 1 H, H13), 6.17 (s, 2 H, H1), 3.44 (dd, 3JH,H = 9.1 Hz, 4.8 Hz, 2 H, H6), 3.21 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.80−2.70 (m, 4 H, H7,8), 2.55 (s, 6 H, H4), 1.65 (s, 6 H, H4′), 0.47 (d, 3 JH,H = 7.0 Hz, 6 H, H9), 0.25 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.2 (C5), 159.1 (C10), 138.2 (C11), 137.3 (C2), 126.1 (C12), 122.8 (C12), 101.8 (C1), 69.4 (C7), 68.1 (C6), 39.1 (C3), 35.3 (C4), 30.8 (C8), 22.3 (C4′), 18.1 (C9′), 13.9 (C 9 ). DART + : m/z = 508.2478 (M + +H). Anal. Calcd for C28H39N3O2Ni C 66.16, H 7.73, N 8.27. Found C 66.44, H 7.91, N 8.25%. Synthetic Procedure for 23. To a solution of [((S)iPrPdmBox)NiCl] 6a (200 mg, 0.43 mmol) in 10 mL of pentane, Zn(p-Tol)2 (110 mg, 0.44 mmol, 1.02 equiv) was added in 10 mL of pentane at 0 °C. The reaction was stirred for another 30 min at ambient temperature. After all volatiles were removed the product could be isolated by column chromatography (PE/EE 10:1) to give 23 as a yellow solid (35%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.81 (dd, 3JH,H = 7.8 Hz, 2 H, H11), 7.07 (dd, 3JH,H = 7.1 Hz, 2 H, H12), 6.26 (s, 2 H, H1), 3.49 (dd, 3JH,H = 9.2 Hz, 4.8 Hz, 2 H, H6), 3.28 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.91 (dsd, 3JH,H = 9.8 Hz, 4.7 Hz, 3.3 Hz, 2 H, H7), 2.86−2.80 (m, 2 H, H8), 2.62 (s, 6 H, H4), 2.32 (s, 3 H, H14), 1.71 (s, 6 H, H4′), 0.54 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.31 (d, 3JH,H = 7.4 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.2 (C5), 153.5 (C10), 138.0 (C13), 137.3 (C11), 131.4 (C2), 127.2 (C12), 101.8 (C1), 69.3 (C7), 68.0 (C6), 39.1 (C3), 35.3 (C4), 30.8 (C8), 22.3 (C14), 21.2 (C4′), 18.1 (C9′), 13.9 (C9).DART+: m/z = 522.2645 (M++H). Anal. Calcd for C29H41N3O2Ni. C 66.68, H 7.91, N 8.04. Found C 66.32, H 7.87, N 8.05%. Synthetic Procedure for 24. To a solution of complex [((S)iPrPdmBox)NiCl] 6a (200 mg, 0.43 mmol) in 50 mL of toluene, PhCCLi (92 mg, 0.86 mmol, 2 equiv) was added in 100 mL of toluene at room temperature. The reaction was stirred for another 60 min at ambient temperature. After all volatiles were removed, the product could be isolated by column chromatography (PE/EE 10:1) followed by crystallization from diethyl ether−pentane mixture to give 24 as a brown solid (70%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.56 (d, 3JH,H = 8.1 Hz, 2 H, H11), 7.14 (t, 3JH,H = 7.6 Hz, 2 H, H12), 7.00 (t, 3JH,H = 7.5 Hz, 1 H, H13), 6.20 (s, 2 H, H1), 4.46 (ddd, 3JH,H = 10.1 Hz, 6.1 Hz, 4.0 Hz, 2 H, H7), 3.58 (dd, 3JH,H = 9.2 Hz, 6.0 Hz, 2 H, H6), 3.47 (dd, 3JH,H = 9.6 Hz, 9.6 Hz, 2 H, H6′), 3.15 (ds, 3JH,H = 7.0 Hz, 3.5 Hz, 2 H, H8), 2.43 (s, 6 H, H4), 1.62 (s, 6 H, H4′), 0.71 (d, 3 JH,H = 7.0 Hz, 12 H, H9,9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.5 (C5), 137.2 (C2), 131.3 (C11), 128.4 (C12), 127.6 (C10), 125.6 (C13), 108.6 (C14), 102.0 (C1), 98.9 (C15), 70.4 (C7), 69.0 (C6), 38.8 (C3), 35.3 (C4), 31.3 (C8), 22.3 (C4′), 18.5 (C9′), 14.8 (C 9 ). DART + : m/z = 532.2472 (M + +H). Anal. Calcd for C30H39N3ONi. C 67.69, H 7.38, N 7.89. Found C 67.53, H 7.42, N 7.94%. Synthetic Procedure for 25. Complex 26 (296 mg, 0.724 mmol) and CsF (170 mg, 1.12 mmol) were suspended in 50 mL of acetone

3

JH,H = 9.0 Hz, 4.5 Hz, 2 H, H6), 3.46 (d, 1JH,H = 13.0 Hz, 1 H, H10), 3.40 (d, 1JH,H = 13.0 Hz, 1 H, H10′), 3.37 (dd, 3JH,H = 18.7 Hz, 9.5 Hz, 2 H, H6′), 3.29 (ds, 3JH,H = 7.0 Hz, 3JH,H = 3.4 Hz, 2 H, H8), 2.61 (s, 6 H, H4), 1.59 (s, 6 H, H4′), 0.58 (d, 3JH,H = 7.1 Hz, 6 H, H9), 0.50 (d, 3 JH,H = 6.8 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.7 (C5), 145.8 (C11), 137.3 (C2), 128.9 (C12), 128.5 (C13), 125.9 (C14), 102.4 (C1), 68.1 (C7), 68.5 (C6), 38.8 (C3), 34.7 (C4), 33.7 (C10) 31.3 (C8), 22.0 (C4′), 18.4 (C9′), 13.9 (C9). DART+: m/z = 554.2377 (M++H). Anal. Calcd for C 29H41N3O2NiS C 62.83, H 7.45, N 7.58. Found C 62.82, H 7.33, N 7.76%. 18: Yield 99%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.15 (s, 2 H, H1), 4.41 (ddd, 3JH,H = 9.9 Hz, 4.3 Hz, 3.5 Hz, 2 H, H7), 3.64 (dd, 3JH,H = 9.1 Hz, 4.5 Hz, 2 H, H6), 3.46−3.40 (m, 4 H, H6′,8), 2.62 (s, 6 H, H4), 2.40 (ddd, 1JH,H = 12.3 Hz, 3JH,H = 7.6 Hz, 6.5 Hz, 1 H, H10), 2.15 (ddd, 1JH,H = 12.1 Hz, 3JH,H = 7.1 Hz, 7.1 Hz, 1 H, H10′), 2.08−1.99 (m, 1 H, H11), 1.99−1.90 (m, 1 H, H11′), 1.77−1.62 (m, 2 H, H12), 1.59 (s, 6 H, H4′), 1.05 (t, 3JH,H = 7.5 Hz, 3 H, H13), 0.67 (d, 3JH,H = 7.1 Hz, 6 H, H9), 0.53 (d, 3JH,H = 7.1 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.5 (C5), 137.3 (C2), 102.3 (C1), 69.1 (C7), 68.5 (C6), 38.7 (C3), 37.8 (C11), 34.5 (C4), 31.4 (C8), 28.9 (C10), 23.0 (C12), 22.1 (C4′), 18.4 (C9′), 14.3 (C13), 14.0 (C9). HRMS DART + : m/z = 520.2520 (M + +H). Anal. Calcd for C26H43N3O2NiS. C 60.01, H, 8.33, N, 8.07. Found C 60.01, H 7.93, N 8.03%. Synthetic Procedure for 19. To a solution of [((S)iPrPdmBox)NiCl] 6a (90 mg, 0.19 mmol) in 20 mL of pentane, ZnEt2 (1.6 M in hexane, 200 μL 1.1 equiv) was added in 10 mL of pentane at room temperature. The reaction was stirred for another 30 min. After filtration and removal of the solvents, the crude product was recrystallized from a diethyl ether/pentane mixture at −40 °C to give a yellow crystalline solid in 72% yield. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.24 (s, 2 H, H1), 3.74−3.70 (m, 2 H, H7), 3.66 (dd, 3JH,H = 9.1 Hz, 4.4 Hz, 2 H, H6), 3.42 (dd, 3JH,H = 9.4 Hz, 9.4 Hz, 2 H, H6′), 2.96 (ds, 3JH,H = 7.0 Hz, 2.9 Hz, 2 H, H7), 2.58 (s, 6 H, H4), 1.72 (s, 6 H, H4′), 1.12 (t, 3JH,H = 7.8 Hz, 3 H, H11), 0.55 (d, 3JH,H = 7.3 Hz, 6 H, H9), 0.52 (d, 3JH,H = 6.7 Hz, 6 H, H9′), 0.38−0.32 (m, 1 H, H10), 0.28−0.24 (m, 1 H, H10′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.0 (C5), 137.0 (C2), 101.3 (C1), 68.0 (C7), 67.7 (C6), 39.1 (C3), 34.8 (C4), 31.9 (C8), 22.3 (C4′), 18.4 (C9′), 16.4 (C11), 13.9 (C9), −2.3 (C10). Anal. Calcd for C24H39N3O2Ni. C 62.63, H 8.54, N 9.13. Found C 62.43, H 8.42, N 9.28%. Synthetic Procedure for 20. To a solution of [((S)iPrPdmBox)NiCl] 6a (125 mg, 0.27 mmol) in 50 mL of pentane, NsLi (25 mg, 0.28 mmol, 1.01 equiv) was added at room temperature. The mixture was stirred for 2 h at room temperature. The solvents were removed in vacuo. The residue was treated with a toluene/pentane (1:10) mixture, and the inorganic metal salts were filtered off. After the removal of the solvents, the product was recrystallized from diethyl ether at −40 °C to give the product 20 as a orange solid (72%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.19 (s, 2 H, H1), 3.61 (dd, 3JH,H = 9.0 Hz, 3.9 Hz, 2 H, H6), 3.54 (ddd, 3JH,H = 9.4 Hz, 3.5 Hz, 3.5 Hz, 2 H, H7), 3.40 (dd, 3JH,H = 9.3 Hz, 9.3 Hz, 2 H, H6′), 2.98 (ds, 3JH,H = 7.0 Hz, 3.2 Hz, 2 H, H8), 2.67 (s, 6 H, H4), 1.66 (s, 6 H, H4′), 0.52 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.37 (d, 3JH,H = 6.8 Hz, 6 H, H9′), 0.32 (s, 9 H, H11), −0.69 (d, 1JH,H = 12.0 Hz, 1 H, H10), −1.03 (d, 1JH,H = 12.0 Hz, 1 H, H10′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.3 (C5), 137.0 (C2), 101.5 (C1), 68.6 (C7), 67.3 (C6), 39.0 (C3), 34.3 (C4), 31.3 (C8), 22.2 (C4′), 18.3 (C9′), 13.4 (C9), 3.3 (C11), −14.5 (C10). DART+: m/z = 518.2717 (M++H). Anal. Calcd for C26H45N3O2NiSi. C 60.24, H 8.75, N 8.11. Found C 59.91, H 8.68, N 7.88%. Synthetic Procedure for 21. To a solution of [((S)iPrPdmBox)NiCl] 6a (200 mg, 0.43 mmol) in 50 mL of toluene, Mg(4FBn)2·2THF (332 mg, 0.86 mmol, 2 equiv) was added in 100 mL of toluene at room temperature. The reaction was stirred for another 60 min at ambient temperature and filtered through a pad of aluminum oxide. After all volatiles were removed, the product could be isolated after crystallization from a diethyl ether−pentane mixture to give 21 as a yellow solid (67%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 7.22 (dd, 3JH,H = 8.3 Hz, 3JH,F = 5.4 Hz, 2 H, H11), 6.89 (dd, 3JH,H = 8.7 Hz, 3JH,F = 8.7 Hz, 2 H, H12), 6.19 (s, 2 H, H1), 3.62−3.54 (m, 4 H, I

DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

= 9.8 Hz, 4.1 Hz, 3.4 Hz, 2 H, H7), 3.59 (ds, 3JH,H = 6.9 Hz, 3.2 Hz, 2 H, H8), 3.46 (dd, 3JH,H = 8.8 Hz, 3JH,H = 4.1 Hz, 2 H, H6), 2.94 (dd, 3 JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.77 (s, 6 H, H4), 1.58 (s, 6 H, H4′), 0.56 (d, 3JH,H = 7.2 Hz, 6 H, H9), 0.43 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13 C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.2 (C5), 141.4 (C11), 137.8(C2), 137.2 (C10), 129.5(C12), 125.6 (C13), 102.4 (C1), 73.3 (C7), 68.5 (C6), 39.1 (C3), 34.1 (C4), 31.7 (C8), 22.0 (C4′), 18.2 (C9′), 13.6 (C9). Rapid thermal decomposition of 29 precluded a correct elemental analysis. Synthetic Procedure for 30. Sulfur (11 mg, 0.35 mmol, 1 equiv) was added as a solid to a solution of [((S)iPrPdmBox)NiH] 27 (150 mg, 0.35 mmol) in 2 mL of benzene. After 15 min at room temperature the solvent was removed in vacuo yielding 30 as a green solid. Yield 99%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.13 (s, 2 H, H1), 4.01 (ddd, 3JH,H = 9.9 Hz, 5.0 Hz, 3.5 Hz, 2 H, H7), 3.53 (dd, 3JH,H = 9.1 Hz, 5.0 Hz, 2 H, H6), 3.44 (ds, 3JH, = 7.0 Hz, 3.0 Hz, 2 H, H8), 3.28 (dd, 3JH,H = 9.6 Hz, 9.6 Hz, 2 H, H6), 2.73 (s, 6 H, H4), 1.58 (s, 6 H, H4′), 0.56 (d, 3JH,H = 7.1 Hz, 6 H, H9), 0.52 (d, 3JH,H = 6.9 Hz, 6 H, H9′), −2.48 (s, 1 H, SH). 13C NMR (C6D6, 150 MHz, 295 K): δ = 176.4 (C5), 137.1 (C2), 102.4 (C1), 68.7 (C7), 68.2 (C6), 38.8 (C3), 34.3 (C4), 30.8 (C8), 22.0 (C4′), 18.3 (C9′), 13.9 (C9). HRMS FAB+: m/z = 464.1876 [M++H]. Anal. Calcd for C22H35N3O2NiS. C 56.91, H 7.60, N 9.05. Found C 56.53, H 7.28, N 9.00%. Cystallographic Data. Crystal data and details of the structure determinations are compiled in Tables S2−S5. Full shells of intensity data were collected at low temperature with a Bruker AXS Smart 1000 CCD diffractometer (Mo Kα radiation, sealed X-ray tube, graphite monochromator) or an Agilent Technologies Supernova-E CCD diffractometer (Mo or Cu Kα radiation, microfocus X-ray tube, multilayer mirror optics). Detector frames (typically ω-, occasionally φ-scans, scan width 0.4···1°) were integrated by profile fitting.63−66 Data were corrected for air and detector absorption and Lorentz and polarization effects64−66 and scaled essentially by application of appropriate spherical harmonic functions.66−70 Absorption by the crystal was treated with a semiempirical multiscan method (as part of the scaling process) and augmented by a spherical correction,66−70 analytically66,69,71 or numerically (Gaussian grid).66,69,72 For data sets collected with the microfocus tubes an illumination correction was performed as part of the numerical absorption correction.66,69 The structures were solved by “modern” direct methods73,74 (compounds 6b·0.5 toluene, 7, 8, and 9) or by the charge flip procedure75,76 and refined by full-matrix least-squares methods based on F2 against all unique reflections.77−79 All non-hydrogen atoms were given anisotropic displacement parameters. Hydrogen atoms were generally placed at calculated positions and refined with a riding model. When justified by the quality of the data the positions of some hydrogen atoms were taken from difference Fourier syntheses and refined. The hydride ligand in 27 was also located and fully refined. When found necessary, disordered groups and/or solvent molecules were subjected to suitable geometry restraints or constraints as well as atomic displacement parameters (adp) restraints. Absolute configuration was verified in all cases by conventional refinement of both enantiomorphs as a racemic twin,12 Parsons′ quotient (based on [I+ − I−]/[I+ + I−]) methods,80,81 or Bayesian statistics analysis of the Friedel differences.82 Crystals of 21 were found to be twinned by merohedry (twin law: twofold rotation around [1−10]). Twin fractions refined to 0.61 and 0.39, respectively. Because of severe disorder and fractional occupancy, electron density attributed to solvent of crystallization (n-pentane) was removed from the structure of 25 0.5 H2O·x n-pentane with the BYPASS procedure, 8 3 , 8 4 as implemented in PLATON (SQUEEZE).85,86 Partial structure factors from the solvent masks were included in the refinement as separate contributions to Fcalc. The shape of the anisotropic displacement ellipsoids of the azide ligand in 10 indicates librational effects. Analysis of the anisotropic displacement parameters with the assumption of a liberation axis going treatment87−90 with the libration axis going through Ni and N(4) resulted in attached rigid group corrections for the bonds N(4)−N(5) and N(5)−N(6) of +0.008 and +0.007 Å, respectively, in the order of 3

and stirred for 24 h at room temperature. The solvent was removed in vacuo. The residue was treated with a toluene/pentane (1:1) mixture, and the insoluble salts were filtered off. After the removal of the solvents the product could be obtained as a red-brown solid (170 mg, 0.433 mmol, 60%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.26 (s, 2 H, H1), 5.27 (s, 2 H, H3), 4.31 (td, 3JH,H = 3.1 Hz, 3JH,H = 9.0 Hz, 2 H, H6), 3.84 (dd, 3JH,H = 3.5 Hz, 3JH,H = 8.9 Hz, 2 H, H5′) 3.64 (t, 3JH,H = 8.9 Hz, 2 H, H5), 2.92−2.84 (m, 2 H, H7), 0.76 (d, 3JH,H = 7.0 Hz, 6 H, H8), 0.71 (d, 3JH,H = 7.0 Hz, 6 H, H8′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 163.0 (C2), 159.8 (C4), 133.8 (C1), 86.1 (C3), 67.8 (C5), 66.0 (C6), 31.8 (C7), 19.3 (C8′), 14.4 (C8). 19F NMR (C6D6, 376 MHz, 295 K): δ (ppm) = −447.1 (s). HR-FAB+: m/z = 372.1254 (M+-F). Anal. Calcd for C18H24N3O2NiF. C 55.14, H 6.17, N 10.72. Found C 54.78, H 6.30, 10.23%. Synthetic Procedure for 26. [((S)iPrPmBox)NiCl] (459 mg, 1.12 mmol) and 2,3-dichloro-5,6-dicyano-1,4- benzoquinone (ddq; 254 mg, 1.12 mmol) were dissolved in 50 mL of toluene. The reaction mixture turned dark and was stirred for one additional hour. After filtration the solvent was removed in vacuo. The residue was treated with a toluene/ pentane (1:1) mixture, and the insoluble residue was filtered off. After the removal of the solvents, the product was recrystallized from a toluene/pentane mixture at room temperature to give the product as brown crystalline solid (296 mg, 0.725 mmol, 65%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.21 (s, 2 H, H1), 5.16 (s, 2 H, H3), 4.89 (td, 3JH,H = 2.7 Hz, 3JH,H = 8.6 Hz, 2 H, H6), 3.63 (dd, 3JH,H = 2.8 Hz, 3 JH,H = 8.7 Hz, 2 H, H5′), 3.48 (dd, 3JH,H = 8.8 Hz, 3JH,H = 8.8 Hz, 2 H, H5), 2.96 (ds, 3JH,H = 7.0 Hz, 3JH,H = 2.7 Hz, 2 H, H7), 0.69 (d, 3JH,H = 7.0 Hz, 6 H, H8), 0.57 (d, 3JH,H = 7.0 Hz, 6 H, H8′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 162.8 (C2), 160.6 (C4), 134.0 (C1), 86.6 (C3), 69.0 (C5), 67.0 (C6), 32.1 (C7), 18.8 (C8′), 14.3 (C8). HR-FAB+: m/z = 372.1227 (M+-Cl). Anal. Calcd for C18H24N3O2NiCl. C 52.92, H 5.92, 10.29. Found C 53.27, H 5.88, 10.26%. Synthetic Procedure for 27. To a solution of [((S)iPrPdmBox)NiF] 7 (1.06 g, 2.36 mmol) in 50 mL of diethyl ether, phenylsilane (300 mg, 2.5 mmol) in 5 mL of Et2O was added. The color changed from orange to yellow, and the mixture was stirred for 20 min at room temperature. The solvents were removed in vacuo, and the residue was treated with a toluene/pentane (1:10) mixture and filtered through a pad of diatomaceous earth. After the removal of the solvents, the product was recrystallized from a saturated diethyl ether solution at −40 °C. Yield 90%. 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 6.39 (s, 2 H, H1), 3.53−3.49 (m, 2 H, H7), 3.44−3.40 (m, 4 H, H6), 2.17 (s, 6 H, H4), 1.80 (s, 6 H, H4′), 2.84−2.75 (m, 2 H, H8), 0.75 (d, 3 JH,H = 7.1 Hz, 6 H, H9), 0.57 (d, 3JH,H = 6.9 Hz, 6 H, H9′), −24.68 (s, 1 H, Ni−H). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 177.0 (C5), 137.6 (C2), 102.2 (C1), 75.3 (C6), 68.1 (C7), 39.3 (C3), 34.0 (C4), 30.8 (C8), 25.2 (C4′), 18.4 (C9′), 14.8 (C9). IR (KBr) ν (cm−1) = 3105 (w), 2958 (s), 2919 (s), 2871 (m), 1812 (Ni−H) (s), 1633 (s), 1462 (m), 1384 (m), 1366 (m), 957 (m), 730 (m). HR-MS FAB+: m/z = 431.2063 [M+]. Anal. Calcd for C22H35N3O2Ni. C 61.13, H 8.16, N 9.72. Found C 60.76, H 7.85, N 9.38%. GP7. Reaction with Ph-XX-Ph (X = S, Se, Te): To a solution of [((S)iPrPdmBox)NiH] (27) (60 mg, 0.14 mmol) in 1 mL of C6D6 the corresponding diphenyl disulfide/selenide/telluride (0.07 mmol, 0.5 equiv) was added. After complete conversion the solvent was removed in vacuo. 28: (99%). 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 8.24−8.22 (m, 2 H, H11), 7.00−6.93 (m, 3 H, H12/13), 6.14 (s, 2 H, H1), 4.09 (ddd, 3JH,H = 9.8 Hz, 3.7 Hz, 3.7 Hz, 2 H, H7), 3.47 (dd, 3 JH,H = 8.9 Hz, 4.3 Hz, 2 H, H6), 3.42 (ds, 3JH,H = 7.1 Hz, 3JH,H = 3.0 Hz, 2 H, H8), 3.07 (dd, 3JH,H = 9.5 Hz, 9.5 Hz, 2 H, H6′), 2.76 (s, 6 H, H4), 1.57 (s, 6 H, H4′), 0.56 (d, 3JH,H = 7.0 Hz, 6 H, H9), 0.49 (d, 3JH,H = 7.0 Hz, 6 H, H9′). 13C NMR (C6D6, 150 MHz, 295 K): δ (ppm) = 176.9 (C5), 137.3 (C2), 136.6 (C10), 136.1 (C11), 127.8 (C12/13), 124.1 (C12/13), 102.5 (C1), 70.0 (C7), 68.6 (C6), 38.9 (C3), 34.5 (C4), 31.6 (C8), 22.1 (C4′), 18.3 (C9′), 14.0 (C9). DART+: m/z = 588.1651 (M++H). Anal. Calcd for C28H39N3O2NiSe. C 57.26, H 6.69, N 7.16. Found C 57.26, H 6.81, N 6.72%. 29: 99%. 29: 1H NMR (C6D6, 600 MHz, 295 K): δ (ppm) = 8.25 (dd, 3JH,H = 8.1 Hz, 4JH,H = 1.3 Hz, 2 H, H11), 6.99 (tt, 3JH,H = 7.5 Hz, 4JH,H = 1.3 Hz, 1 H, H13), 6.82 (dd, 3JH,H = 7.6 Hz, 3JH,H = 7.6 Hz, 2 H, H12), 6.15 (s, 2 H, H1), 3. 98 (ddd, 3JH,H J

DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

reactions. Catalytic, asymmetric cyclopropanation of olefins. J. Am. Chem. Soc. 1991, 113, 726−728. (9) Corey, E. J.; Imai, N.; Zhang, H. Y. Designed catalyst for enantioselective Diels-Alder addition from a C2-symmetric chiral bis(oxazoline)-iron(III) complex. J. Am. Chem. Soc. 1991, 113, 728− 729. (10) Müller, D.; Umbricht, G.; Weber, B.; Pfaltz, A. C2-Symmetric 4,4′,5,5′-Tetrahydrobi(oxazoles) and 4,4′,5,5′-Tetrahydro-2,2′methylenebis[oxazoles] as Chiral Ligands for Enantioselective Catalysis Preliminary Communication. Helv. Chim. Acta 1991, 74, 232−240. (11) Nishiyama, H.; Sakaguchi, H.; Nakamura, T.; Horihata, M.; Kondo, M.; Itoh, K. Chiral and C2-symmetrical bis(oxazolinylpyridine)rhodium(III) complexes: effective catalysts for asymmetric hydrosilylation of ketones. Organometallics 1989, 8, 846− 848. (12) Flack, H. D.; Bernardinelli, G. J. Reporting and evaluating absolute-structure and absolute-configuration determinations. J. Appl. Crystallogr. 2000, 33, 1143. (13) Deng, Q.-H.; Melen, R. L.; Gade, L. H. Anionic Chiral Tridentate N-Donor Pincer Ligands in Asymmetric Catalysis. Acc. Chem. Res. 2014, 47, 3162−3173. (14) (a) Mazet, C.; Gade, L. H. Double Bonds in Motion: Bis(oxazolinylmethyl)pyrroles and Their Metal-Induced Planarization to a New Class of Rigid Chiral C2-symmetric Complexes. Chem. - Eur. J. 2003, 9, 1759−1767. See also: (b) Mazet, C.; Gade, L. H. A Bis(oxazolinyl)pyrrole as a Tridentate Supporting Ligand in the Catalytic Suzuki-Type C-C Coupling. Organometallics 2001, 20, 4144. (15) Konrad, F.; Lloret Fillol, J.; Wadepohl, H.; Gade, L. H. Bis(oxazolinylmethyl)pyrrole Derivatives and Their Coordination as Chiral “Pincer” Ligands to Rhodium. Inorg. Chem. 2009, 48, 8523− 8535. (16) Konrad, F.; Lloret Fillol, J.; Rettenmeier, C.; Wadepohl, H.; Gade, L. H. Bis(oxazolinylmethyl) Derivatives of C4H4E Heterocycles (E = NH, O, S) as C2-Chiral Meridionally Coordinating Ligands for Nickel and Chromium. Eur. J. Inorg. Chem. 2009, 2009, 4950−4961. (17) Wenz, J.; Rettenmeier, C. A.; Wadepohl, H.; Gade, L. H. Catalytic C-F bond activation of geminal difluorocyclopropanes by nickel(i) complexes via a radical mechanism. Chem. Commun. 2016, 52, 202−205. (18) Rettenmeier, C. A.; Wenz, J.; Wadepohl, H.; Gade, L. H. Activation of Aryl Halides by Nickel(I) Pincer Complexes: Reaction Pathways of Stoichiometric and Catalytic Dehalogenations. Inorg. Chem. 2016, 55, 8214−8224. (19) Rettenmeier, C.; Wadepohl, H.; Gade, L. Electronic Structure and Reactivity of Nickel(I) Pincer Complexes: Their Aerobic Transformation to Peroxo Species and Site Selective C H Oxygenation. Chemical Science 2016, 7, 3533. (20) Rettenmeier, C. A.; Wadepohl, H.; Gade, L. H. Structural Characterization of a Hydroperoxo Nickel Complex and Its Autoxidation: Mechanism of Interconversion between Peroxo, Superoxo, and Hydroperoxo Species. Angew. Chem., Int. Ed. 2015, 54, 4880− 4884. (21) Rettenmeier, C.; Wadepohl, H.; Gade, L. H. Stereoselective Hydrodehalogenation via a Radical-Based Mechanism Involving TShaped Chiral Nickel(I) Pincer Complexes. Chem. - Eur. J. 2014, 20, 9657−9665. (22) Ito, Y.; Konoike, T.; Harada, T.; Saegusa, T. Synthesis of 1,4diketones by oxidative coupling of ketone enolates with copper(II) chloride. J. Am. Chem. Soc. 1977, 99, 1487−1493. (23) Ohshima, T.; Iwasaki, T.; Mashima, K. Direct conversion of esters, lactones, and carboxylic acids to oxazolines catalyzed by a tetranuclear zinc cluster. Chem. Commun. 2006, 2711−2713. (24) Bradley, D. C.; Mehrotra, R. C.; Gaur, D. P. Z. Chem. 1980, 20, 396−396. (25) Breitenfeld, J.; Scopelliti, R.; Hu, X. Synthesis, Reactivity, and Catalytic Application of a Nickel Pincer Hydride Complex. Organometallics 2012, 31, 2128−2136.

times the estimated standard deviation from the least-squares refinement without incorporation of librational effects.91

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.7b00077. Complete experimental procedures and characterization data of organic compounds 1−5 and complexes 6−30, including their atom labeling schemes; listings of the crystal data and structural parameters of all compounds characterized by X-ray diffraction (PDF) X-ray crystallographic information (CIF)

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lutz H. Gade: 0000-0002-7107-8169 Funding

We acknowledge funding by the Deutsche Forschungsgemeinschaft (Ga 488/9−1) as well as the University of Heidelberg. Notes

The authors declare no competing financial interest. CCDC Nos. 1522638−1522653 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via https://www.ccdc.cam.ac.uk/data_request/cif.

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ACKNOWLEDGMENTS We thank I. Gerz and F. S. Menke for expermental support and C. A. Rettenmeier for advice. DEDICATION Dedicated to Professor Walter Siebert on the occasion of his 80th birthday. REFERENCES

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DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.7b00077 Inorg. Chem. XXXX, XXX, XXX−XXX