Cooperative Bond Activation Reactions with Nickel and Palladium

Article Cite This: Organometallics XXXX, XXX, XXX−XXX

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Cooperative Bond Activation Reactions with Nickel and Palladium Carbene Complexes with a PCcarbeneS Pincer Ligand Lennart T. Scharf, Alexander Kowsari, Thorsten Scherpf, Kai-Stephan Feichtner, and Viktoria H. Gessner* Lehrstuhl für Anorganische Chemie II, Ruhr-Universität Bochum, 44780 Bochum, Germany

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S Supporting Information *

ABSTRACT: A new PCcarbeneS ligand has been designed to stabilize late transition metal carbene complexes with Schrocktype reactivity for bond activations via metal−ligand cooperation. This ligand combines previous approaches to such complexes by stabilizing the carbene moiety through either charge delocalization into adjacent aryl groups or the use of an anion-stabilizing substituent. Nickel and palladium complexes of the PCcarbeneS pincer ligand could be prepared by dehydrohalogenation of the precursors (PCsp3S)NiCl and (PCsp3S)PdCl and were characterized in solution and solid state. X-ray diffraction (XRD) analyses as well as density functional theory (DFT) studies demonstrate that the electronic structure of these complexes can be described by a carbene as well as a zwitterionic complex with a M−C single bond. Due to the strong nucleophilic character at the carbon atom, both complexes are highly reactive and undergo sulfur transfer to form thioketone complexes. The nickel carbene complex is capable of cooperative O−H and N−H bond activations including ammonia activation across the NiC bond.

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INTRODUCTION Metal−ligand cooperation (MLC) has become a powerful tool for bond activation reactions as well as catalysis.1 A typical approach to metal−ligand cooperation is to use cooperating ligands that are able to receive and release protons. Here, some of the most well-known systems are lutidine- and picolinebased PNP- and PNN-pincer-type ligands pioneered by Sacco2 and Milstein3 and further developed by many other groups.4 These ligands make use of an aromatization/dearomatization process in the backbone of the ligand for substrate activation and have been used in catalytic applications, showing impressive results particularly in hydrogenation and dehydrogenation reactions.5 Besides this aromatization/dearomatization mechanism, other modes of MLC have been explored over the past years. Further prominent examples are the Shvotype complexes for transfer hydrogenation6 as well as complexes which undergo bond activations by addition reactions across a metal ligand bond. Here, addition reactions across M−N (above all in PNP pincer ligands),1c,d,7 M−O,8 M−S,9 and M−B10 bonds have been employed. In contrast, carbene complexes have been much less studied in this context.11 Here, substrates are activated by 1,2-addition reactions across the MC bond, i.e., via a transition from a carbene to an alkyl complex. In general, nucleophilic carbene species with late transition metals have so far proven to be best suited for this chemistry, since the usually more ionic early transition metal compounds are too reactive to allow for controlled activations of polar E−H bonds.12 Until now, two different approaches have been employed to stabilize late © XXXX American Chemical Society

transition metal carbene complexes with Schrock-type reactivity: The first approach involves the use of PCsp2P pincer ligands in which the reactive carbene species is stabilized through the rigid ligand complexation. For example, PCP carbene complexes of type A have been used with nickel by Piers13 and palladium by Iluc14 to activate small molecules like ammonia, water, and alcohols (Figure 1).15 Thereby, the

Figure 1. Carbene complexes of type A and B.

delocalization of the π electron density of the metalcarbon bond into the phenylene groups makes these complexes particularly stable. The second approach involved the use of strongly electron withdrawing groups like sulfonyl, thiophosphoryl, or iminophosphoryl moieties, which increase the M C bond polarity by stabilization of the negative charge at the carbenic carbon atom via negative hyperconjugation and Received: June 8, 2019

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DOI: 10.1021/acs.organomet.9b00386 Organometallics XXXX, XXX, XXX−XXX

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Organometallics electrostatic effects.16 As in the case of the PCP complexes, also in these compounds, additional donor sites are used to increase the complex stability. For example, our group has used ruthenium carbene complexes of type B with two anionstabilizing groups including a thiophosphoryl tether to stabilize nucleophilic ruthenium carbene species which were found to be applicable in a wide variety of bond activation reactions (H−H,17 O−H,18 Si−H,19 B−H,20 P−H21). To the best of our knowledge, no combination of these two approaches to synthesize nucleophilic carbene complexes such as C has been employed so far. Thus, we designed ligand 1 with a strongly electron-withdrawing thiophosphoryl moiety and a phosphinophenylene group. We envisioned that also this ligand should give access to carbene complexes that are capable of bond activations via metal−ligand cooperativity.

Figure 2. Molecular structure of ligand 1. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except at the carbon bridgehead are omitted for clarity. Selected bond lengths (Å) and angles (deg): P(1)−C(1) 1.8220(17), C(1)−C(2) 1.498(2), C(2)−C(7) 1.400(2), P(2)−C(7) 1.8454(17), P(1)−S(1) 1.9393(6), C(2)−C(1)−P(1) 112.32(11).

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RESULTS AND DISCUSSION Ligand Synthesis. The synthesis of ligand 1 was achieved via the two-step procedure depicted in Scheme 1. In the first

This strategy was successfully used with other ligands and a variety of different metal precursors. Unfortunately, despite many efforts, this synthetic protocol failed to give access to the corresponding carbene complexes or any other transition metal complex. While the deprotonation of 1 to the alkali metal methanides was facile, as judged by NMR spectroscopy, their isolation was not possible due to repeated reprotonation during workup. Therefore, we addressed a different approach to transition metal complexes of 1, namely, via oxidative addition of a chlorinated analogue of the ligand to metals in low oxidation states with subsequent dehydrohalogenation. The chlorination of 1 was easily accomplished by deprotonation of 1 with n-butyllithium in THF and subsequent addition of 1-Li to hexachloroethane (Scheme 2). Filtration over silica with dichloromethane as solvent and recrystallization from ethanol gave access to the chlorinated ligand 1-Cl in up to 60% yield.

Scheme 1. Two-Step Synthesis of Ligand 1

step, the in situ prepared lithium diphenylphosphide was treated with 2-iodobenyl chloride and subsequently oxidized with elemental sulfur, to give the iodo precursor 2, which could be isolated in 78% yield as a colorless crystalline solid after aqueous workup and recrystallization from ethanol. The precursor 2 is characterized by a low-field shifted signal in the 31P{1H} NMR spectrum at δP = 42.0 ppm. The protons at the carbon bridge appear at δH = 4.11 ppm in the 1H NMR spectrum with a coupling constant of 2JHP = 13.8 Hz. In the next step, the iodo compound was transferred into the final ligand 1 by simple lithiation and trapping with diphenylchlorophosphine. Here, we took advantage of the fact that at low temperatures the lithium halogen exchange of the aryl iodide is faster than the deprotonation at the highly CH acidic benzylic position. To prevent any subsequent intramolecular deprotonation reactions, the chlorophosphine was directly added together with n-butyllithium at −78 °C. Filtration over silica in dichloromethane and repeated recrystallization from ethanol or acetonitrile finally gave 1 in yields of up to 68%. Ligand 1 was characterized by multinuclear NMR spectroscopy, X-ray diffraction, and elemental analysis. Ligand 1 features two singlets in the 31 1 P{ H} NMR spectrum at δP = 42.5 and −15.8 ppm. The protons at the methylene bridge appear as a doublet of doublets at δH = 4.11 ppm with coupling constants of 2JHP = 14.1 Hz and 4JHP = 3.1 Hz in the 1H NMR spectrum. By recrystallization, single crystals suitable for X-ray diffraction analysis could be obtained (Figure 2). In the molecular structure, the P−C1 and C1−C2 bond lengths amount to 1.822(2) and 1.498(2) Å and are thus in the typical range for single bonds.22 With ligand 1 in hand, we next addressed the synthesis of the corresponding alkali metal methanides and methandiides which we intended to use as precursors for the preparation of the metal complexes via simple salt metathesis reactions.16,23

Scheme 2. Synthesis of Chlorinated Ligand 1-Cl

The chlorinated ligand is characterized by two doublets in the 31P{1H} NMR spectrum at δP = 51.3 and −18.5 ppm with a coupling constant of 4JPP = 5.8 Hz. The signal for the protons at the CCP linkage is significantly low-field shifted and appears as a doublet of doublets at δH = 7.14 ppm with coupling constants of 2JHP = 12.8 and 4JHP = 4.1 Hz in the 1H NMR spectrum. During recrystallization, single crystals suitable for XRD analysis could be obtained. The chlorinated ligand 1-Cl crystallizes in the orthorhombic space group Pna21 (Figure 3) with similar bond lengths and angles compared to 1. Synthesis and Characterization of Nickel and Palladium Carbene Complexes. Next, the reactivity of 1-Cl toward group 10 metals in oxidation state zero was tested (Scheme 3). The reaction of 1-Cl with Pd(PPh3)4 or Pd(dba)2 (dba = dibenzylideneacetone) in toluene or THF overnight resulted in the formation of a yellow precipitate that was soluble in DCM and chloroform and characterized by two doublets in the 31P{1H} NMR spectrum at δP = 47.6 and 53.2 ppm with a coupling constant of 4JPP = 12 Hz. The proton at the benzylic carbon atom appears as a doublet of doublets at δH = 3.87 ppm with coupling constants of 2JHP = 8.3 and 3JHP = B


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Organometallics

Figure 3. Molecular structure of chlorinated ligand 1-Cl. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except at the carbon bridgehead are omitted for clarity. Selected bond lengths (Å) and angles (deg): P(1)−C(1) 1.858(2), C(1)−C(2) 1.509(3), C(2)−C(7) 1.408(3), P(2)−C(7) 1.846(2), Cl(1)−C(1) 1.797(2), S(1)−P(1) 1.9465(7), C(2)−C(1)−P(1) 112.94(16).

Scheme 3. Synthesis of Oxidative Addition Complexes

Figure 4. (top) Molecular structure of 1-PdCl (left) and side view (right) and (bottom) molecular structure of 1-NiCl. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except at the carbon bridgeheads are omitted for clarity. Selected parameters in Table 1.

one found in the palladium complex A3 of the PCP ligand reported by Iluc et al. (2.0738(19) Å, Figure 1). The fourmembered Pd−C−P−S ring shows a butterfly structure, as can be seen in Figure 4. The molecular structure of 1-NiCl (Figure 3, monoclinic space group P21/c) shows a square planar geometry around the nickel center with a Ni−C bond length of 1.974(2) Å which is identical to the one reported for A by Piers et al. with the PCP ligand (1.973(3) Å).13 The C1−C2 bond length is 1.503(2) Å and in the range of a typical carbon−carbon single bond. Both complexes exhibit a pronounced deviation from a tetrahedral geometry at the central carbon atom due to the ring strain resulting from the coordination of the thiophosphoryl group to the metal center. In the next step, the oxidative addition complexes 1-PdCl and 1-NiCl were dehydrohalogenated to the corresponding carbene complexes by using sodium tert-butoxide as base and an additional coligand for completing the coordination sphere of the metal (Scheme 4). Trimethylphosphine was used for nickel, while triphenylphosphine was employed for palladium. Addition of 1 equiv of trimethylphosphine to a suspension of 1-NiCl in THF resulted in a color change to purple. Subsequent addition of a solution of sodium tert-butoxide (1.2 equiv) in THF gave a dark red solution of the product complex which was isolated as a red solid in 70% yield after

3.2 Hz in the 1H NMR spectrum. Single crystals suitable for XRD analysis could be obtained by slow diffusion of pentane into a saturated solution in DCM. These could be unambiguously identified as the corresponding oxidative addition complex 1-PdCl which could be isolated in excellent yields of 93%. When Pd(PPh3)4 was used for the synthesis of 1-PdCl, the formation of a minor byproduct was observed, which features three signals in the 31P{1H} NMR spectrum at δP = 20.7, 54.3, and 60.3 ppm, which all couple with each other. Presumably, this complex results from the possible coordination of triphenylphosphine to 1-PdCl, which however is disfavored due to steric reasons, as crystallization in the presence of 1 equiv of triphenylphosphine only gave crystals of 1-PdCl. The reaction of Ni(COD)2 and 1-Cl resulted in the selective formation of the corresponding nickel complex 1-NiCl. The complex precipitates from the reaction mixture in acetonitrile and toluene and was isolated as red solid in yields of 74% by filtration and washing with pentane. The nickel complex 1NiCl is characterized by two doublets in the 31P{1H} NMR spectrum at δP = 40.1 and 42.4 ppm with a coupling constant of 3JPP = 6 Hz. The proton at the carbon bridge shows a signal at 3.24 ppm with a coupling constant of 2JHP = 9.5 Hz in the 1 H NMR spectrum. Single crystals suitable for XRD analysis could be obtained for both complexes. The palladium complex 1-PdCl crystallizes in the space group P-1 (Figure 4). It shows a strongly distorted square planar geometry around the palladium center (P−Pd−S angle of 157.51(2)°) with a Pd− C bond length of 2.072(2) Å, which is almost identical to the

Scheme 4. Synthesis of Carbene Complexes

C


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Organometallics filtration and washing with pentane. It is important to note that the use of exactly 1 equiv of PMe3 was found to be crucial for the successful isolation of 1-Ni. The use of an excess of PMe3 resulted in displacement of the ligand and most likely in the formation of nickel(tetrakistrimethylphosphine), as judged by the appearance of a signal in the 31P{1H} NMR spectrum of δP = −23.2 ppm.24 Carbene complex 1-Ni was characterized by multinuclear NMR spectroscopy and XRD analysis. Elemental analysis failed repeatedly, possibly due to the sensitivity of the complex and the formation of elemental nickel. The complex 1-Ni shows three doublets of doublets in the 31P{1H} NMR spectrum at δP = 57.4, 27.9, and −20.2 ppm with coupling constants of 2JPP = 50 Hz and 3JPP = 20 and 27 Hz. The carbenic carbon atom appears as a doublet of doublets of doublets at δC = 55.0 ppm with coupling constants of JCP = 61.5, 57.4, and 26.2 Hz. This is significantly high-field shifted compared to the PCP pincer system A and other methandiidederived ruthenium carbene complexes (e.g., ruthenium carbene complex B: δC = 140.0 ppm), which can be explained by the electronic structure of the complex (see below). Single crystals of 1-Ni could be obtained by slow diffusion of pentane into a benzene solution and were analyzed by X-ray crystallography. The complex 1-Ni crystallizes in the monoclinic space group P21/c and features a square planar geometry around the nickel center (Figure 5). Surprisingly, the Ni−C bond length of 1.927(2) Å is only slightly shorter than the one in 1-NiCl (1.974(2) Å) but still well in the range of similar nickel carbene complexes. For example, the nickel PCP complexes A1 and A2 reported by Piers showed Ni−C distances of 1.927(4) and 1.908(5) Å, respectively.13 Nonetheless, the reduction of the Ni−C bond length is low compared to, e.g., the ruthenium carbene complex B and its corresponding chlorido complex (2.213(4)−1.965(2) Å). In contrast to the oxidative addition complex, the phenylene ring is now in plane with the Ni−C1 bond as well as the phosphine and thiophosphoryl donors. A closer look at the bond lengths provides valuable insights into the bonding situation. The C1− C2 bond length is 1.420(2) Å and is thus significantly shorter in comparison to 1-NiCl and in between a typical carbon− carbon single (1.50 Å) and double bond (1.34 Å).22 Additionally, the bond lengths of C2 to the adjacent carbon atoms of the phenylene ring slightly increase in comparison to 1 (1.417(2) and 1.422(2) Å vs 1.392(2) and 1.403(2) Å). These bond changes in the phenylene ring are similar to the one found in palladium complex A3 reported by Iluc.14 In order to gain further information about the electronic structure of 1-Ni, density functional theory (DFT) calculations were performed. The energy-optimized structure compared well with the experimental data. The HOMO of 1-Ni is mostly located at the carbenic carbon atom but also significantly delocalized into the phenylene ring (Figure 5). The LUMO is delocalized across one of the phenyl rings of the phosphine moiety. The charge at the carbenic carbon atom is only −0.87 which is less negative than that in other methandiide-derived carbene complexes (e.g., −0.98 in ruthenium complex B). However, the WBI of the Ni−C bond amounts to only 0.60, which shows that there is a significant lower double bonding character than that in other carbenes. Interestingly, the WBI of the C1−C2 bond is 1.09, while the WBIs to the adjacent carbon atoms of the phenyl rings are reduced to 1.25 and 1.27, respectively (∼1.5 for normal phenyl rings). The combination of the DFT calculations and the bond length changes observed in the crystallographic studies leads to the conclusion that the

Figure 5. Molecular structure (top), side view (middle), and HOMO (bottom) of 1-Ni. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected parameters in Table 1.

nickel carbene complex can also be described by the mesomeric resonance structure 1-Ni′ with a Ni−C single bond and delocalization of the negative charge into the phenylene ring (Figure 6). This formulation corresponds well with the observed upfield shift of the carbonic carbon atom in the 13C NMR spectrum (see above). The reaction of palladium complex 1-PdCl with sodium tertbutoxide in the presence of triphenylphosphine in THF leads to a color change from yellow to brown and the formation of a new compound that is characterized by three doublets of doublets in the 31P{1H} NMR spectrum with δP = 57.2, 33.7, and 18.2 ppm with coupling constants of 2JPP = 37 Hz and 3JPP = 10 and 28 Hz (see Figure 7). Workup via filtration in toluene, evaporation of the solvent in vacuo, and washing with pentane delivered the complex 1-Pd in 67% yield. The carbene complex could be fully characterized by NMR spectroscopy as well as XRD and elemental analysis. The carbenic carbon atom appears as a doublet of doublets of doublets at δC = 64.5 ppm D


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Organometallics Table 1. Selected Bond Lengths (Å) and Angles (deg) for Chloro and Carbene Complexes 1-MCl and 1-M M−C1 C1−C2 C2−C3 C2−C7 M1−P2 M1−Cl1/P3 M1−S1 S(1)−P(1) C7−P2 C1−P1 P2−M1−S1 C1−M1−Cl1/P3 C2−C1−P1

1-NiCl

1-Ni

1-PdCl

1-Pd

1.9735(2) 1.5025(2) 1.3921(2) 1.4026(2) 2.1378(4) 2.2109(4) 2.2642(4) 2.0016(4) 1.8173(2) 1.7793(2) 166.375(2) 174.00(4) 122.28(9)

1.9270(2) 1.420(2) 1.422(2) 1.417(2) 2.1397(5) 2.2013(5) 2.2762(5) 2.0357(6) 1.8024(2) 1.6901(2) 163.56(2) 175.51(5) 134.00(2)

2.072(2) 1.496(3) 1.401(3) 1.398(3) 2.2207(5) 2.3832(5) 2.4618(5) 2.0031(7) 1.819(2) 1.791(2) 157.505(2) 178.16(5) 120.06(2)

2.052(3) 1.413(5) 1.421(5) 1.424(5) 2.2676(8) 2.3679(8) 2.4106(8) 2.0460(2) 1.800(3) 1.678(3) 159.03(3) 174.73(9) 133.7(3)

Figure 6. Direct comparison of experimentally observed bond lengths of 1-NiCl (left) and 1-Ni (middle); mesomeric resonance structure for 1-Ni (right).

Figure 8. Molecular structure of palladium carbene complex 1-Pd (left) and side view of the metallabicycle (right). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected parameters in Table 1.

and 1-Pd in THF for 1 day, crystals could be recovered from one decomposition product that were analyzed by X-ray crystallography. Both compounds crystallized in the space group P-1 with similar lattice parameters and were revealed to be dimeric thioketone complexes 3Ni and 3Pd in which the sulfur of the thiophosphoryl group was shifted to the carbenic carbon atom (Scheme 5). Such a reactivity of nucleophilic late

Figure 7. 31P{1H} NMR spectrum of palladium carbene complex 1Pd.

Scheme 5. Decomposition of Carbene Complexes in THF to Thioketone Complexes

with coupling constants of 2JPP = 93.2 Hz and 3JPP = 75.0 and 2.7 Hz in the 13C{1H} NMR spectrum. Single crystals suitable for XRD analysis could be obtained by slow diffusion of pentane into a benzene solution. The carbene complex 1-Pd crystallizes in the triclinic space group P-1 (Figure 8). The molecular structure of 1-Pd is very similar to its nickel analogue 1-Ni and shows the same structural changes compared to the palladium chlorido complex 1-PdCl. For example, the Pd−C1 bond length only slightly decreases, while the C1−C2 bond markedly shortens and the C2−C3 and C2−C7 bonds slightly elongate. Furthermore, the geometry around the carbenic carbon atom becomes planar. The negative charge at the carbenic carbon atom calculated by DFT studies amounts to −0.81 and is thus even less negative than in the corresponding nickel carbene complex which might be attributed to triphenylphosphine as a weaker donor. Despite the facile formation of the two carbene complexes, they unfortunately proved to be rather unstable and, for example, decomposed in THF solution. After storage of 1-Ni

transition metal carbene complexes was observed before for other thiophosphoryl-tethered systems25 as well as other reactive carbene species upon treatment with group 16 elements or oxygen sources.26 The complexes 3M are highly insoluble in common organic solvents, thus excluding further characterization. In the molecular structures (Figure 9) of 3Ni and 3Pd, the thioketone moiety coordinates in an η2 fashion to one metal center, while the phosphorus atom of the former thiophosE


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Organometallics Scheme 6. Activation Reactions with 1-Ni

Figure 9. Molecular structures of nickel thioketone complexes 3Ni (see the Supporting Information for 3Pd). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg) for 3Ni: Ni(1)− C(1) 1.9655(15), Ni(1)−S(1) 2.1719(4), Ni(1)−P(2) 2.1725(4), Ni(1)−P(1′) 2.1904(5), Ni(1)−Ni(1′) 2.5468(5), S(1)−C(1) 1.7536(15), C(1)−Ni(1)−S(1) 49.85(4). 3 Pd : Pd(1)−C(1) 2.082(3) Pd(1)−S(1) 2.3776(7), Pd(1)−P(2) 2.2900(7), Pd(1)− P(1′) 2.3272(7), Pd(1)−Pd(1′) 2.7072(4) S(1)−C(1) 1.736(3), C(1)−Pd(1)−S(1) 45.22(8).

phoryl group coordinates to the other metal center. Both compounds show short metal−metal distances of 2.5468(5) and 2.7072(4) Å for nickel and palladium, respectively. The C−S bond lengths of 1.754(2) and 1.736(3) Å, respectively, are in the same range as in similar palladium thioketone complexes. 23a,27 The metal centers adopt a distorted tetrahedral geometry. Bond Activation Reactions. With the targeted carbene complexes in hand, we next addressed bond activations (Scheme 6). Addition of phenol to a solution of 1-Ni in THF instantaneously resulted in a color change from red to violet and the formation of two new species, which showed two doublets at δP = 38.4 and 34.5 ppm with a coupling constant of 3 JPP = 6 Hz and a further set of three doublets of doublets at δP = 49.0, 41.2, and −15.9 ppm with coupling constants of 2JPP = 54 Hz and 3JPP = 18 Hz in the 31P{1H} NMR spectrum. This suggested the successful formation of the O−H activation product 4 (Scheme 6), to which trimethylphosphine still can coordinate in solution. However, upon evaporation of the solvent in vacuo, trimethylphosphine was completely removed from the complex, thus exclusively giving way to the trimethylphosphine-free complex 4. This suggests that similar to the reaction of the palladium complex 1-PdCl with PPh3complex 4 forms an equilibrium with the PMe3 complexed analogue, which can easily be shifted toward the uncoordinated species. Workup by filtration in toluene and washing with diethyl ether and pentane delivered the desired alcoholato complex 4 as a violet solid in a yield of 21%. Albeit the reaction is high yielding according to 31P{1H} NMR, large amounts of the product were lost during the washing process. Single crystals of 4 could be obtained by slow diffusion of pentane into a benzene solution (Figure 10). Activation product 4 crystallizes in the monoclinic space group I2/a and proves the successful OH activation by addition across the

Figure 10. Molecular structure of 4. Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except at the carbon bridgehead are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni(1)−O(1) 1.8865(10), Ni(1)−C(1) 1.9657(13), Ni(1)−P(2) 2.1355(4), Ni(1)−S(1) 2.3072(4), C(1)−C(2) 1.4996(19), C(1)−P(1) 1.7778(14), O(1)−Ni(1)−C(1) 167.79(5), P(2)−Ni(1)−S(1) 161.153(17).

NiC bond. The complex features a square planar geometry around the nickel center, while C1 pyramidalizes upon protonation. Accordingly, the phenylene group is not in plane with the NiC bond anymore, similar to the corresponding chlorido complex. Accordingly, the C1C2 bond elongates from 1.420(2) Å in the carbene complex to 1.500(2) Å in 4. Comparable to the O−H activation, also amine activation proved to be successful. Addition of 4-toluidine to a solution of 1-Ni in THF at room temperature resulted in precipitation of a bright red solid. Removal of THF, filtration in toluene, and subsequent washing with diethyl ether gave access to 5 in F


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Organometallics yields of 54%. Activation product 5 is characterized by two singlets in the 31P{1H} NMR spectrum at δP = 46.4 and 27.7 ppm, the signal for the benzylic proton at δH = 2.40 ppm, and a nitrogen bound hydrogen at δH = 0.34 ppm in the 1H NMR spectrum. Crystallization by slow diffusion of pentane into a saturated solution of 5 in THF gave access to single crystals that were analyzed by X-ray crystallography. The complex 5 crystallizes in the monoclinic space group P21/c and shows a dimeric structure, in which the two nickel centers are connected via bridging amido ligands (Figure 11). The Ni−

Figure 12. Molecular structure of 62 (left) and the N−Ni−N−Ni butterfly ring structure (right). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except at the carbon bridgehead and the nitrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni(1)−N(2) 1.917(4), Ni(1)− N(1) 1.929(4), Ni(1)−C(1) 1.995(4), Ni(1)−P(2) 2.1145(13), Ni(1)−Ni(2) 2.6552(10), N(2)−Ni(1)−N(1) 78.59(17), N(2)− Ni(1)−C(1) 172.66(18), N(1)−Ni(1)−C(1) 101.11(18).

and confirms the formation of a dimer with two NH2 moieties bridging two nickel centers. Comparable to complex 5, the thiophosphoryl groups are not coordinating anymore. This behavior is similar to the one of the nickel carbene complex A by Piers et al. in which one of the phosphine moieties loses the Ni−P contact upon ammonia activation. Complex 62 shows a short Ni−Ni distance of 2.655(1) Å and Ni−N bond lengths of 1.917(4) and 1.929(4) Å. In contrast to 5, the fourmembered Ni1−N1−Ni2−N2 ring adopts a butterfly structure, thus explaining the two different signals for the hydrogens in the 1H NMR spectrum. The Ni−C1 bond lengths amount to 1.995(4) and 1.992(4) Å and thus are slightly elongated compared to the oxidative addition complex 1-NiCl (1.9735(13) Å) which most likely can be attributed to the decoordination of the thiophosphoryl moiety. In general, the purification of the activation products was found to be difficult. The presence of liberated PMe3 and decomposed nickel species complicated workup and made us unable to access the activation products in a pure form. Besides the activation of the polar O−H and N−H bonds, we also addressed the activation of dihydrogen with 1-Ni. Unfortunately, no selective reaction was observed. Likewise, bond activations with the corresponding palladium carbene complex 1-Pd only resulted in complex product mixtures. This can possibly also be attributed to the presence of the bulkier triphenylphosphine ligand, which prevents or hampers selective addition reactions across the PdC bond.

Figure 11. Molecular structure of 52 (left) and the N−Ni−N−Ni planar ring structure (right). Thermal ellipsoids are drawn at the 50% probability level. Hydrogen atoms except for the benzylic and nitrogen bound hydrogen atoms are omitted for clarity. Selected bond lengths (Å) and angles (deg): Ni(1)−N(1′) 1.9527(13), Ni(1)− N(1) 1.9559(13), Ni(1)−C(1) 1.9797(15), Ni(1)−P(2) 2.1432(4), Ni(1)−Ni(1′) 2.9093(5) N(1′)−Ni(1)−N(1) 83.80(6), N(1′)− Ni(1)−C(1) 175.45(6), N(1)−Ni(1)−C(1) 92.81(6), N(1)− Ni(1)−P(2) 161.83(4).

N−Ni−N four-membered ring is planar with Ni−N bond lengths of 1.953(2) and 1.956(2) Å and a rather long Ni−Ni distance of 2.9093(5) Å. This structural motif is similar to the ammonia activation product observed by Piers.13 After successful activation of the N−H bond in 4-toluidine, we also addressed the more challenging activation of ammonia. While the reaction of 1-Ni with 1 equiv of ammonia in THF at room temperature resulted in the formation of multiple products, the reaction at −78 °C overnight was somewhat more selective and gave way to a species featuring two signals in the 31P{1H} NMR spectrum at δP = 48.3 and 41.1 ppm. Nonetheless, the reaction was accompanied by the concomitant formation of considerable amounts of tetrakistrimethylphosphine nickel(0) formed from the decomposition of the carbene complex and liberated trimethylphosphine. Despite the formation of several byproducts, the N−H activation product 6 could be isolated as a yellow solid in 32% yield by filtration in toluene and repeated washing of the obtained solid with diethyl ether. Activation product 6 is characterized by a doublet for the benzylic proton at δH = 2.60 ppm in the 1H NMR spectrum with a coupling constant of 2JHP = 12 Hz. Surprisingly, the NH protons are not equivalent and appear at δH = −3.84 and −2.66 ppm. This suggests the formation of a rigid dimeric complex analogous to 6 in solution, in which the two NH2 protons differ due to their position either above or below the central Ni−N−Ni−N ring. This is confirmed by XRD analysis (Figure 12). Suitable single crystals of 6 could be obtained by slow diffusion of pentane into a THF solution. Complex 6 crystallizes in the monoclinic space group P21/n

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CONCLUSION In summary, a new PCcarbeneS ligand was developed that combines both stabilization approaches for nucleophilic late transition metal carbenes, i.e., charge stabilization through anion-stabilizing and aromatic substituents and the use of a pincer framework. The corresponding nickel and palladium carbene complexes 1-Ni and 1-Pd were obtained by oxidative addition of the chlorinated PCS ligand to Ni(0) and Pd(0) precursors and subsequent dehydrohalogenation of the chlorido complexes (PCsp3S)NiCl and (PCsp3S)PdCl in the presence of an additional phosphine ligand. The MC bond in the carbene complexes was found to be strongly polarized with a marked contribution of a zwitterionic structure, in which the π-electron density is shifted into the phenylene spacer. Thus, both complexes are highly nucleophilic and undergo G


Article

Organometallics

in vacuo and the oily residue redissolved in 30 mL of DCM. The suspension was filtered over silica, and the filtrate was evaporated in vacuo. A 30 mL portion of ethanol was added to the remaining oil and shortly boiled until precipitation set in. Afterward, the precipitate was recrystallized from 175 mL of ethanol to give 1 as colorless crystals (4.61 g, 9.40 mmol, 68%). 1H NMR (400.3 MHz, CDCl3): δ = 4.35 (dd, 2JHP = 14.0 Hz, 4JHP = 3.3 Hz, 2H, CH2), 6.87−6.95 (m, 1H, CHarom), 7.07−7.19 (m, 5H, CHPPh2), 7.19−7.26 (m, 1H, CHarom), 7.26−7.37 (m, 6H, CHPPh2), 7.39−7.47 m, 4H, CHPPh2), 7.47−7.59 (m, 3H, CHPPh2), 7.79−7.90 (m, 4H, CHPPh2). 13C{1H} NMR (100.7 MHz, CD2Cl2): δ = 38.2 (dd, 1JCP = 50.5 Hz, 3JCP = 25.0 Hz, CH2), 127.9 (d, 2JCP = 3.1 Hz, CHarom), 128.7 (s, Cpara), 128.8 (d, 2JCP = 2.8 Hz, CPPh2,ortho), 128.9 (br, Carom), 129.0 (d, 2JCP = 13.0 Hz, CPS,meta), 130.9 (dd, 3JCP = 4.6 Hz, 3JCP = 4.6 Hz, CHarom), 131.9 (d, 4JCP = 2.9 Hz, Cpara), 132.2 (dd, 2JCP = 10.2 Hz, 6JCP = 1.0 Hz, CPS,ortho), 133.0 (d, 1JCP = 80.0 Hz, CPS,ipso), 134.0 (d, 3JCP = 19.4 Hz, CPPh2,meta), 134.8 (d, 4JCP = 1.7 Hz, CHarom), 137.0 (d, 1JCP = 10.9 Hz, CPPh2,ipso), 137.3 (dd, 2JCP = 26.8 Hz, 2JCP = 6.9 Hz, CCH2), 137.8 (dd, 1JCP = 11.7 Hz, 4JCP = 6.7 Hz, CParom). 31P{1H} NMR (162.1 MHz, CDCl3): δ = −16.2 (s, PPPh2), 42.1 (s, PPS). Elemental analysis for C31H26P2S: calculated: C 75.59, H 5.32, S 6.51; found: C 75.29, H 5.40, S 6.41. Synthesis of 1-Cl. Ligand 1 (4.40 g, 8.93 mmol) was dissolved in 40 mL of THF and cooled to −78 °C. n-BuLi (1.54 M in hexane, 6.4 mL, 9.8 mmol) was added, and the resulting red solution was stirred for an hour at room temperature. Hexachloroethane (2.54 g, 10.7 mmol) was dissolved in 40 mL of THF, and the solution of 1-Li was added over 2 h at 0 °C. After warming to room temperature, the solvent was evaporated in vacuo and 30 mL of DCM was added to the oily residue. The suspension was filtered over silica and the solvent evaporated in vacuo. The colorless solid was recrystallized from 60 mL of ethanol to give 1-Cl as colorless crystals (2.83 g, 5.37 mmol, 60%). 1 H NMR (400.3 MHz, CD2Cl2): δ = 6.83−6.89 (m, 1H), 6.91−6.98 (m, 2H), 7.14 (dd, 2JHP = 12.8 Hz, 4JHP = 4.1 Hz, 1H, CHCl), 7.20− 7.46 (m, 13H), 7.52−7.70 (m, 5H), 8.11−8.19 (m, 2H), 8.19−8.24 (m, 1H). 13C{1H} NMR (100.7 MHz, CD2Cl2): δ = 54.1 (dd, 1JCP = 53.3 Hz, 3JCP = 36.0 Hz, CHCl), 128.6 (d, J = 12.3 Hz), 128.9 (d, J = 6.7 Hz), 129.1 (s), 129.2 (s), 129.2 (d, JCP = 2.5 Hz), 129.5 (s), 129.8 (d, JCP = 2.0 Hz), 129.8 (d, 1JCP = 82.0 Hz, CPS,ipso), 129.9 (d, JCP = 2.0 Hz), 130.8 (dd, JCP = 3.8 Hz, JCP = 3.8 Hz), 131.9 (d, 1JCP = 82.0 Hz, CPS,ipso), 132.1 (d, JCP = 3.0 Hz), 132.4 (dd, JCP = 9.9 Hz, JCP = 2.2 Hz), 132.7 (d, JCP = 3.0 Hz), 133.1 (d, JCP = 9.6 Hz), 133.9 (d, JCP = 12.1 Hz), 134.1 (d, JCP = 12.1 Hz), 134.2 (s), 136.0 (d, 1JCP = 61.1 Hz, CPPh2,ipso), 136.1 (d, 1JCP = 61.1 Hz, CPPh2,ipso), 137.8 (dd, 3JCP = 11.6 Hz, 1JCP = 6.4 Hz, Carom), 139.9 (d, 2JCP = 23.9 Hz, CHClCarom). 31 1 P{ H} NMR (162.1 MHz, CD2Cl2): δ = −18.5 (d, 4JPP = 5.8 Hz, PPPh2), 51.3 (d, 4JPP = 5.8 Hz, PPS). Elemental analysis for C31H25P2ClS: calculated: C 70.65, H 4.78, S 6.08; found: C 70.08, H 4.36, S 5.85. HRMS (ESI): calculated for C31H26P2ClS+ ([M + H]+): m/z = 527.0914; found: m/z = 527.0901. Synthesis of 1-PdCl. Chlorinated ligand 1-Cl (1.2 g, 2.3 mmol) and tetrakistriphenylphosphine palladium(0) (2.62 g, 2.27 mmol) were dissolved in 40 mL of toluene and stirred for 72 h. The yellow precipitate was filtered off, washed with 10 mL of toluene, and dried (1.48 g, mixture of 75/25 free and PPh3 coordinated species, Mmix = 699 g/mol, 2.12 mmol, 94%). A sample for characterization was prepared by mixing 1-Cl (100 mg, 0.190 mmol) and Pd(dba)2 (114 mg, 0.198 mmol) in 10 mL of THF. The formed yellow precipitate was washed with THF and pentane to give free 1-PdCl. 1H NMR (400.3 MHz, CD2Cl2): δ = 3.87 (dd, 2JHP = 8.3 Hz, 4JHP = 3.2 Hz, 1H, CH), 7.14−7.25 (m, 4H, CHarom), 7.15−7.39 (m, 6H, CHarom), 7.39− 7.56 (m, 5H, CHarom), 7.59−7.66 (m, 2H, CHarom), 7.66−7.73 (m, 1H, CHarom), 7.75−7.86 (m, 4H, CHarom), 7.90−7.99 (m, 2H, CHPPh2,ortho). 13C{1H} NMR (100.7 MHz, CD2Cl2): δ = 20.1 (dd, 1JCP = 43.3 Hz, 3JCP = 6.8 Hz, CHCl), 128.0 (dd, J = 7.0 Hz, J = 2.1 Hz), 128.7 (d, J = 6.6 Hz), 128.9 (d, J = 6.6 Hz), 129.0 (d, 1JCP = 84.2 Hz), 129.3 (d, JCP = 10.9 Hz), 129.8 (d, JCP = 11.7 Hz), 130.6 (d, JCP =

decomposition via sulfur transfer from the thiophosphoryl tether. Nonetheless, phenol, ammonia, and para-toluidine could be activated with the nickel carbene complex by 1,2addition of the EH bond across the NiC bond. These results demonstrate that the ligand portfolio to access nucleophilic carbene species suitable for metal ligand cooperation is more diverse than explored so far. Further developments in the ligand design are necessary to improve the complex stability and to establish further applications of such carbene species also in bifunctional catalysis.

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EXPERIMENTAL SECTION

General Methods. All experiments were carried out under a dry, oxygen-free argon atmosphere using standard Schlenk techniques. Involved solvents were dried using an MBraun SPS-800 (THF, Toluene, Et2O, DCM, Pentane) or dried in accordance with standard procedures.. H2O is distilled water. 1H, 13C, and 31P NMR spectra were recorded on an Avance-400 spectrometer at 25 °C if not stated otherwise. All values of the chemical shift are in ppm regarding the δscale. All spin−spin coupling constants (J) are printed in Hertz (Hz). To display multiplicities and signal forms correctly, the following abbreviations were used: s = singulet, d = doublet, dd = doublet of doublets, ddd = doublet of doublets of doublets, m = multiplet, br = broad signal. Signal assignment was supported by DEPT and HMQC experiments. Elemental analyses were performed on an Elementar vario MICRO-cube elemental analyzer. High-resolution electrospray ionization mass spectrometry (ESI HRMS) was performed on Bruker Apex IV ESI-FTICR and Bruker ESI timsTOF mass spectrometers. The samples were diluted with spectrum-grade CH3CN (1:10) and then mass spectra recorded. All reagents were purchased from SigmaAldrich, ABCR, Rockwood Lithium, or Acros Organics and used without further purification. Synthesis of 2. Diphenylphosphine (2.70 g, 2.52 mL, 14.5 mmol) was dissolved in 50 mL of THF and cooled to −78 °C. n-BuLi (2.28 M in hexane, 6.04 mL, 13.8 mmol) was added slowly, and the resulting red solution was stirred at room temperature for 2 h. The solution of lithium diphenylphosphide was added to a solution of 2iodobenzyl chloride (3.73 g, 14.0 mmol) in 30 mL of THF at −30 °C upon which the solution turned yellow. The resulting solution was stirred at room temperature overnight; then, elemental sulfur (0.48 g, 15.0 mmol) was added upon which the solution turned dark red. After 20 min, 50 mL of water was added, the phases were separated, and the aqueous phase was extracted three times with 40 mL of DCM each. The resulting brown oil was stirred in pentane until turning solid, and the solid was recrystallized from 150 mL of ethanol to give 2 as colorless crystals (4.73 g, 10.9 mmol, 78%). 1H NMR (400.1 MHz, CDCl3): δ = 4.11 (d, 2H, CH2, 2JHP = 14.0 Hz), 6.88−6.95 (m, 1H, CH arom ), 7.22−7.28 (m, 1H, CH arom ), 7.40−7.47 (m, 4H, CHPPh,meta,para), 7.48−7.58 (m, 2H, CHPPh,meta,para, 1H, CHarom), 7.69−7.73 (m, 1H, CHarom), 7.74−7.83 (m, 4H, CHPPh,ortho). 13 C{1H} NMR (125.8 MHz, CDCl3): δ = 45.1 (d, CH2, 1JCP = 50.5 Hz), 103.3 (d, CIarom, 3JCP = 7.5 Hz), 128.0 (d, CHarom, 3/4/5JCP = 3.1 Hz), 128.6 (d, CHPPh,meta, 2JCP = 12.1 Hz), 129.1 (d, CHarom, 3/4/5 JCP = 3.4 Hz), 121.3 (d, CHarom, 3/4/5JCP = 4.8 Hz), 131.8 (d, CHPPh,para, 4JCP = 3.0 Hz), 131.9 (d, CHPPh,ipso, 1JCP = 81.0 Hz), 132.0 (d, CHPPh,ortho, 2JCP = 10.0 Hz), 134.8 (d, CHarom, 3/4/5JCP = 7.1 Hz), 139.6 (d, CHarom, 3/4/5JCP = 2.7 Hz). 31P{1H} NMR (162.0 MHz, CDCl3): δ = 42.0. Elemental analysis for C19H16PSI: calculated: C 52.55, H 3.71, S 7.38; found: C 52.85, H 3.65, S 7.34. Synthesis of 1. Compound 2 (6.0 g, 13.8 mmol) was dissolved in 150 mL of THF. Diphenylchlorophosphine (3.0 mL, 3.7 g, 16.7 mmol) was dissolved in 7 mL of THF. A 1.8 mL portion of the diphenylchlorophosphine solution were added to the solution of 2, and the resulting solution was cooled to −78 °C. n-BuLi (1.69 M in hexane, 8.2 mL, 13.9 mmol) and the remaining 8.2 mL of the diphenylchlorophosphine solution were added concomitantly via a syringe pump over 1.5 h at −78 °C (5 mL/h, syringe diameter 16 mm). After warming to room temperature, the solvent was evaporated H


Article

Organometallics

calculated for NiC34H34P3S + ([M + H]+): m/z = 625.0942; found: m/z = 625.0950. Synthesis of 1-Pd. Complex 1-PdCl (1.72 g, 2.47 mmol), triphenylphosphine (0.486 g, 1.85 mmol), and sodium tert-butoxide (0.237 g, 2.47 mmol) were dissolved in 30 mL of THF. After 10 min, the solvent was evaporated in vacuo and the brown residue dissolved in 40 mL of toluene and filtered. The solvent was evaporated in vacuo and the brown residue washed twice with 20 mL of pentane to give 1Pd as a brown solid (1.57 g, 1.82 mmol, 74%). 1H NMR (400.3 MHz, d8-THF): δ = 5.90−5.98 (m, 1H, CHarom), 6.26−6.34 (m, 1H, CHarom), 6.34−6.43 (m, 1H, CHarom), 6.47−6.56 (m, 1H, CHarom), 7.06−7.21 (m, 11H, CHarom,P), 7.21−7.43 (m, 20H, CHarom,P), 7.70− 7.82 (m, 4H, CHarom,P). 13C{1H} NMR (100.7 MHz, d8-THF): δ = 64.5 (ddd, 1JCP = 93.2 Hz, 2JCP = 75.0 Hz, 2JCP = 2.2 Hz, Ccarbene), 113.5 (d, J = 8.4 Hz, CHarom), 117.4 (ddd, JCP = 24.0 Hz, JCP = 8.8 Hz, JCP = 7.0 Hz, Carom), 122.9 (ddd, JCP = 59.3 Hz, JCP = 27.1 Hz, JCP = 11.2 Hz, Carom), 128.5 (d, 3JCP = 11.5 Hz, CHPPh2,meta), 128.6 (d, JCP = 9.4 Hz, CHPPh3), 128.8 (d, 3JCP = 10.3 Hz, CHPS,meta), 130.2 (d, 4JCP = 1.4 Hz, CHPPh2,para), 130.5 (d, 4JCP = 2.2 Hz, CHP,para), 130.7 (d, 4JCP = 2.8 Hz, CHP,para), 131.2 (d, JCP = 11.3 Hz, CHPPh2,meta), 131.5 (br, CHarom), 132.8 (d, JCP = 4.9 Hz, CHarom), 133.4 (d, 2JCP = 12.3 Hz, CHPS,meta), 133.9 (d, 1JCP = 33.3 Hz, CPPh3,ipso), 135.0 (d, 1JCP = 45.0 Hz, CP,ipso), 135.0 (d, JCP = 12.9 Hz, CHPPh3), 140.0 (dd, JCP = 60.5 Hz, JCP = 4.0 Hz, CP,ipso), 160.8 (dd, JCP = 44.6 Hz, JCP = 10.7 Hz, Carom). 31P{1H} NMR (162.1 MHz, d8-THF): δ = 18.2 (dd, 2JPP = 37.0 Hz, 3JPP = 29.0 Hz, PPPh3), 33.7 (dd, 2JPP = 37.0 Hz, 3JPP = 10.0 Hz, PPPh2), 57.2 (dd, 3JPP = 29.0 Hz, 3JPP = 10.0 Hz, PPS). Elemental analysis for PdC49H39P3S: calculated: C 68.49, H 4.58, S 3.73; found: C 68.11, H 4.85, S 3.45. Synthesis of 4. Carbene complex 1-Ni (100 mg, 0.160 mmol) was dissolved in 2 mL of THF. Phenol (15.1 mg, 0.160 mmol) was dissolved in 2 mL of THF and added to the solution of 1-Ni. After 2 h, the solvent was evaporated in vacuo and the violet residue was dissolved in toluene and filtered. The solvent was evaporated in vacuo, and the residue was washed three times with 3 mL of Et2O and once with 5 mL of pentane to give 4 as a violet powder (21.5 mg, 33.4 μmol, 21%). 1H NMR (400.3 MHz, d8-THF): δ = 2.83 (d, 2JHP = 10.4 Hz, 1H, CH), 6.07−6.15 (m, 1H, CHphenol,para), 6.58−6.73 (m, 4H, CHphenol), 7.08−7.15 (m, 1H, CHarom), 7.15−7.47 (m, 13H, CHarom), 7.47−7.65 (m, 4H, CHarom), 7.69−7.79 (m, 2H, CHPS,ortho), 7.79− 7.89 (m, 2H, CHPPh2,ortho), 8.23−8.33 (m, 2H, CHPS,ortho). 13C{1H} NMR (100.7 MHz, d8-THF): δ = 5.7 (dd, 1JCP = 39.1 Hz, 3JCP = 17.3 Hz, CH), 112.7 (s, CHphenol,para), 121.6 (s, CHphenol), 127.5 (dd, J = 6.5 Hz, J = 2.2 Hz, CHarom), 128.2 (s, CHphenol), 128.8 (d, 3JCP = 10.6 Hz, CHPPh2,meta), 128.9 (d, 3JCP = 12.8 Hz, CHPS,meta), 129.1 (d, 3JCP = 10.3 Hz, CHPPh2,meta), 129.7 (d, 3JCP = 11.5 Hz, CHPS,meta), 130.4 (d, 2JCP = 11.8 Hz, CHPS,ortho), 130.5 (d, JCP = 9.0 Hz, CHarom), 130.6 (d, JCP = 5.8 Hz, CHarom), 131.0 (d, 1JCP = 52.3 Hz, CPS,ipso), 131.0 (d, 4JCP = 2.5 Hz, CHPPh2,para), 131.6 (br, CHPPh2,para), 131.7 (d, 1 JCP = 20.7 Hz, CPPh2,ipso), 131.9 (d, 1JCP = 49.2 Hz, CPS,ipso), 132.4 (d, 4JCP = 2.9 Hz, CHPS,para), 132.6 (d, 4JCP = 3.0 Hz, CHPS,para), 133.1 (s, CHarom), 133.6 (d, 2JCP = 8.1 Hz, CHPPh2,ortho), 133.7 (d, 2JCP = 8.2 Hz, CHPPh2,ortho), 134.4 (d, 2JCP = 10.3 Hz, CHPS,ortho), 138.8 (d, JCP = 48.4 Hz, CPPh2,ipso), 140.2 (dd, JCP = 56.5 Hz, JCP = 11.8 Hz, Carom), 150.2 (dd, JCP = 35.8 Hz, JCP = 3.7 Hz, Carom), 169.9 (s, Cphenol,ipso). 31P{1H} NMR (162.1 MHz, d8-THF): δ = 34.5 (d, 3JPP = 6.0 Hz, PPPh2), 38.4 (d, 3JPP = 6.0 Hz, PPS). Synthesis of 52. Carbene complex 1-Ni (100 mg, 0.160 mmol) was dissolved in 2 mL of THF. para-Toluidine (17.1 mg, 0.160 mmol) was dissolved in 2 mL of THF, added to the solution of 1-Ni, and stirred for 2 h at room temperature upon which a red solid precipitated. The solvent was evaporated in vacuo, and the red residue was dissolved in toluene and filtered. The solvent was evaporated in vacuo, and the residue was washed three times with 3 mL of Et2O and once with 5 mL of pentane to give 52 as a bright red powder (56 mg,

11.5 Hz), 130.7 (d, JCP = 51.7 Hz), 130.8 (dd, JCP = 5.4 Hz, JCP = 20.3 Hz), 131.2 (d, JCP = 55.8 Hz), 131.3 (d, JCP = 2.8 Hz), 131.6 (d, JCP = 2.6 Hz), 132.2 (dd, JCP = 1.7 Hz, JCP = 1.7 Hz), 132.6 (d, JCP = 3.0 Hz), 133.1 (d, JCP = 3.0 Hz), 133.4 (s), 133.5 (d, JCP = 4.8 Hz), 133.7 (d, JCP = 4.6 Hz), 134.0 (d, JCP = 10.4 Hz), 138.1 (d, JCP = 55.0 Hz), 139.8 (dd, JCP = 53.7 Hz, JCP = 10.3 Hz), 148.3 (dd, JCP = 32.0 Hz, JCP = 4.0 Hz). 31P{1H} NMR (162.1 MHz, CD2Cl2): δ = 47.6 (d, 3JPP = 11.6 Hz, PPPh2), 53.2 (d, 3JPP = 11.6 Hz, PPS). Elemental analysis for PdC31H25P2ClS: calculated: C 58.78, H 3.98, S 5.06; found: C 59.08, H 3.74, S 3.60. HRMS (ESI): calculated for PdC31H25P2S+ ([M − Cl]−): m/z = 597.0182; found: m/z = 597.0183; calculated for PdC49H40P3S+ ([M + PPh3 − Cl]−: m/z = 859.1093; found: m/z = 859.1110. Synthesis of 1-NiCl. Chlorinated ligand 1-Cl (0.20 g, 0.38 mmol) and Ni(COD)2 (0.13 g, 0.47 mmol) were dissolved in 5 mL of acetonitrile and were stirred overnight. The red solid which precipitated was separated from the solution and dissolved in DCM. The red solution was filtered, and the solvent was removed in vacuo to give 1-NiCl as a red solid (0.18 g, 0.30 mmol, 80%). 1H NMR (400.3 MHz, CD2Cl2): δ = 3.24 (d, 2JHP = 9.6 Hz, 1H, CH), 7.10−7.17 (m, 2H, CHarom), 7.17−7.26 (m, 2H, CHarom), 7.26−7.35 (m, 4H, CHarom), 7.35−7.42 (m, 2H, CHarom), 7.42−7.49 (m, 3H, CHarom), 7.49−7.68 (m, 5H, CHarom), 7.68−7.77 (m, 2H, CHarom), 7.83−7.91 (m, 2H, CHarom), 8.18−8.28 (m, 2H, CHarom). 13C{1H} NMR (100.7 MHz, CD2Cl2): δ = 11.3 (dd, 1JCP = 40.3 Hz, 3JCP = 16.1 Hz, CHCl), 128.7 (dd, J = 6.5 Hz, J = 2.2 Hz), 128.7 (d, J = 10.8 Hz), 128.9 (d, J = 12.6 Hz), 129.0 (d, JCP = 10.3 Hz), 129.3 (s), 129.7 (d, JCP = 11.6 Hz), 129.8 (dd, JCP = 10.3 Hz, JCP = 6.0 Hz), 130.1 (d, JCP = 11.9 Hz), 130.7 (d, JCP = 12.4 Hz), 130.9 (d, JCP = 2.8 Hz), 131.2 (d, JCP = 18.8 Hz), 131.3 (d, JCP = 2.5 Hz), 131.8 (dd, JCP = 2.5 Hz, JCP = 2.5 Hz), 132.6 (d, JCP = 2.9 Hz), 132.7 (s), 132.8 (d, JCP = 3.1 Hz), 133.4 (d, JCP = 10.6 Hz), 133.6 (d, JCP = 10.7 Hz), 134.1 (d, JCP = 10.6 Hz), 137.6 (d, JCP = 49.5 Hz), 140.6 (dd, JCP = 55.6 Hz, JCP = 11.8 Hz), 148.5 (dd, JCP = 35.5 Hz, JCP = 3.5 Hz). 31P{1H} NMR (162.1 MHz, CD2Cl2): δ = 40.1 (d, 3JPP = 6.1 Hz, PPPh2), 42.3 (d, 3JPP = 6.1 Hz, PPS). Elemental analysis for NiC31H25P2ClS: calculated: C 63.57, H 4.30, S 5.41; found: C 63.07, H 4.31, S 4.97. HRMS (EI): calculated for NiC31H25P2ClS+ ([M − e]−): m/z = 584.0189; found: m/z = 584.01368. Synthesis of 1-Ni. Complex 1-NiCl (1.25 g, 2.13 mmol) was suspended in 20 mL of THF, and trimethylphosphine (0.22 mL, 0.16 g, 2.1 mmol) was added. Sodium tert-butoxide (0.215 g, 2.24 mmol) was dissolved in 8 mL of THF and added to the 1-NiCl·PMe3 solution. Instantly afterward, the solvent was evaporated in vacuo and the red residue dissolved in 30 mL of toluene and filtered. The solvent was evaporated in vacuo, and the red solid was washed twice with 20 mL of pentane to give 1-Ni as a dark red solid (0.85 g, 1.36 mmol, 64%). 1H NMR (400.3 MHz, d8-THF): δ = 0.90 (d, 2JPH = 7.6 Hz, PCH3), 5.90−5.99 (m, 1H, CHarom), 6.15−6.23 (m, 1H, CHarom), 6.46−6.54 (m, 1H, CHarom), 6.54−6.62 (m, 1H, CHarom), 7.28−7.49 (m, 12H, CHarom,P), 7.67−7.79 (m, 4H, CHPPh2,ortho), 7.90−8.01 (m, 4H, CHPS,ortho). 13C{1H} NMR (100.7 MHz, d8-THF): δ = 14.7 (d, 1 JCP = 23.5 Hz, PCH3), 55.0 (ddd, 1JCP = 61.5 Hz, 2JCP = 57.4 Hz, 2JCP = 26.2 Hz, Ccarbene), 113.4 (d, J = 8.6 Hz, CHarom), 116.8 (ddd, JCP = 18.6 Hz, JCP = 6.5 Hz, JCP = 6.5 Hz, Carom), 127.7 (ddd, JCP = 68.0 Hz, JCP = 31.4 Hz, JCP = 13.5 Hz, Carom), 128.4 (d, 3JCP = 11.1 Hz, CHPPh2,meta), 129.0 (d, 3JCP = 9.6 Hz, CHPS,meta), 130.5 (d, 4JCP = 2.8 Hz, CHPPh2,para), 130.8 (d, 4JCP = 2.2 Hz, CHPS,para), 130.9 (d, 2JCP = 11.3 Hz, CHPPh2,ortho), 131.0 (br, Carom), 131.7 (br, Carom), 133.8 (d, JCP = 11.5 Hz, CHPS,ortho), 134.7 (d, JCP = 39.1 Hz, CHPS,ipso), 140.1 (dd, JCP = 56.1 Hz, JCP = 4.5 Hz, CPPh2,ipso), 160.6 (dd, JCP = 44.5 Hz, JCP = 12.1 Hz, Carom). 31P{1H} NMR (162.1 MHz, d8-THF): δ = −20.2 (dd, 2JPP = 50.4 Hz, 3JPP = 27.9 Hz, PPMe3), 27.9 (dd, 2JPP = 50.4 Hz, 3JPP = 20.5 Hz, PPPh2), 57.4 (dd, 3JPP = 27.9 Hz, 3JPP = 20.5 Hz, PPS). Elemental analysis for NiC34H33P3S: calculated: C 65.31, H 5.32, S 5.13; found: C 64.69, H 5.05, S 5.01. HRMS (ESI): I


Article

Organometallics 82 μmol, 51%). 1H NMR (400.1 MHz, d8-THF): δ = 0.34 (s, 1H, NH), 2.34 (s, 3H, CH3), 2.40 (d, 2JHP = 17.7 Hz, 1H, CH), 6.30 (br, 1H, CHarom), 6.38 (br, 2H, CHarom), 6.62 (br, 2H, CHarom), 6.30 (br, 1H, CHarom), 6.30 (br, 1H, CHarom), 6.30 (br, 1H, CHarom), 6.72−6.91 (m, 6H, CHarom), 6.92−7.04 (m, 4H, CHarom), 7.04−7.16 (m, 4H, CHarom), 7.16−7.25 (m, 3H, CHarom), 7.26−7.39 (m, 3H, CHarom), 7.39−7.49 (m, 3H, CHarom). 13C{1H} NMR (100.7 MHz, d8-THF): δ = 21.0 (s, CH3), 37.9−38.4 (m, CH), 126.3 (br, CHarom), 127.0 (d, JCP = 11.1 Hz, CHarom), 128.0 (d, JCP = 9.4 Hz, CHarom), 128.0 (d, JCP = 11.4 Hz, CHarom), 128.5−128.8 (m, CHarom), 129.2 (s, CHarom), 129.3 (s, CHarom), 129.3 (s, CHarom), 129.6 (d, JCP = 3.0 Hz, CHarom), 130.1 (br, CHarom), 130.4 (d, JCP = 5.3 Hz, CHarom), 130.8 (d, JCP = 3.0 Hz, CHarom), 130.8 (s, Carom), 131.3 (d, JCP = 9.4 Hz, Carom), 131.5 (s, Carom), 132.5−132.7 (m, CHarom), 133.5−133.7 (m, CHarom), 134.0−134.2 (m, CHarom), 134.7 (d, JCP = 8.6 Hz, CHarom), 134.9 (s, Carom), 141.1 (s, Carom), 141.7 (s, Carom), 141.8−142.7 (m, Carom), 143.5 (s, Carom) 155.3 (s, Carom). 31P{1H} NMR (162.1 MHz, d8THF): δ = 27.7 (s, PPPh2), 46.4 (s, PPS). Elemental analysis for NiC38H33P2SN: calculated: C 69.53, H 5.07, N 2.13, S 4.88; found: C 68.62, H 5.08, N 2.50, S 4.47. Synthesis of 62. Carbene complex 1-Ni (94 mg, 0.150 mmol) was dissolved in 2 mL of THF and cooled to −78 °C. Ammonia in THF (0.5 M, 0.3 mL, 0.15 mmol) was added to the solution of 1-Ni and stirred overnight at room temperature. The solvent was evaporated in vacuo, and the brown residue was dissolved in toluene and filtered. The solvent was evaporated in vacuo, and the residue was washed five times with 3 mL of Et2O and once with 5 mL of pentane to give 62 as a brown powder (27.8 mg, 46.6 μmol, 32%). 1H NMR (400.3 MHz, d8-THF): δ = −3.87−3.79 (m, 1H, NH2), −2.71−2.61 (m, 1H, NH2), 2.61 (d, 2JHP = 12.0 Hz, 1H, CH), 6.56−6.63 (m, 1H, CHarom), 6.83− 6.92 (m, 1H, CHarom), 6.93−7.06 (m, 3H, CHarom), 7.10−7.17 (m, 1H, CHarom), 7.17−7.25 (m, 2H, CHarom), 7.25−7.57 (m, 12H, CHarom), 7.90−8.00 (m, 4H, CHarom). 13C{1H} NMR (100.7 MHz, d8-THF): δ = 36.7−37.4 (m, CH), 126.0 (br, CHarom), 127.5 (d, 3JCP = 10.8 Hz, CHPS,meta), 127.8 (d, 3JCP = 11.1 Hz, CHPS,meta), 128.4− 128.6 (m, CHPPh2,meta), 128.9−129.1 (m, CHPPh2,meta), 129.6 (br, CHPS,para), 129.9 (br, CHarom), 130.1 (br, CH), 130.3 (br, CH), 130.4 (d, 4JCP = 2.6 Hz, CHPS,para), 132.1 (d, 2JCP = 8.9 Hz, CHPS,ortho), 132.2 (d 1JCP = 42.7 Hz, CPPh2,ipso), 132.2−132.4 (br, CH), 132.8 (d, JCP = 3.4 Hz, CHarom), 133.1 (d, 2JCP = 9.0 Hz, CHPS,ortho), 133.7−133.9 (m, CHPPh 2,ortho), 134.0−134.2 (m, CHPPh2,ortho), 137.0 (d, 1JCP = 40.9 Hz, CPPh2,ipso), 137.1 (d, 1JCP = 77.0 Hz, CPS,ipso), 138.2 (d, 1JCP = 63.2 Hz, CPS,ipso), 140.4 (br, Carom), 155.9 (br, Carom). 31P{1H} NMR (162.1 MHz, d8-THF): δ = 43.1 (s, PPPh2), 48.3 (s, PPS). HRMS (ESI): calculated for Ni2C62H52P4S2N+ ([M − NH2]+): m/z = 1116.1153; found: m/z = 1116.1156. Computational Details. All calculations were performed without symmetry restrictions. Starting coordinates were obtained from the crystal structure analyses. The geometry optimization was performed with the Gaussian 09 (revision E.01) program package28 using density functional theory (DFT)29 with the PBE0 functional30 and the LANL2TZ(f) basis set and the corresponding ECP for palladium31 and the def2svp basis32 set for all other atoms with Grimme’s D3 dispersion correction with Becke−Johnson damping.33 The metrical parameters of the energy-optimized geometry compared well with those determined by X-ray diffraction. Harmonic vibrational frequency analysis was performed on the same levels of theory to determine the nature of the structure.34 The vibrational frequency analyses showed no imaginary frequencies for the ground states. NBO analyses35 were performed with the internal NBO3.1 module in Gaussian 09.36 Crystallographic Details. Data collection of all compounds was conducted either with a Bruker X8-APEX II (1), Oxford Synergy (4, 5, 6), or Oxford SuperNova (1-Cl, 1-Ni, 1-NiCl, 1-Pd, 1-PdCl, 3-Ni, 3-Pd). Suitable crystals of all compounds were mounted in an inert oil (perfluoropoly alkylether) and directly transferred into a cold nitrogen stream. Crystal structure determinations were affected at 100 K. The

structures were solved using direct methods, refined using full-matrix least-squares techniques on F2 with the Shelx software package,37 and expanded using Fourier techniques. Data collection parameters are given in Tables S1−S4. Crystallographic data (including structure factors) have been deposited with the Cambridge Crystallographic Data Centre as supplementary publication no. CCDC-1921059− 1921069.

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00386. NMR spectra, crystallographic details, and coordinates of the energy-optimized structures (PDF) Computational XYZ coordinates for 1-Ni and 1-Pd (XYZ) Accession Codes

CCDC 1921059−1921069 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Viktoria H. Gessner: 0000-0001-6557-2366 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS This work was supported by the German Research Foundation (Emmy-Noether grant DA1402/1-1) and the Fonds der Chemischen Industrie (scholarship to L.T.S.). This project has also received funding from the Deutsche Forschungsgemeinschaft (DFG, German Research Foundation) under Germany’s Excellence Strategy − EXC-2033 − Projektnummer 390677874. We thank Prof. Dr. Carsten Strohmann, Felix Langenohl, and Laura Schneider from TU Dortmund for recording the HR-ESI mass spectra.

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REFERENCES

(1) For reviews, see: Khusnutdinova, J. R.; Milstein, D. Metal-Ligand Cooperation. Angew. Chem., Int. Ed. 2015, 54 (42), 12236−12273. (b) Grützmacher, H. Cooperating Ligands in Catalysis. Angew. Chem., Int. Ed. 2008, 47, 1814−1818. (c) van der Vlugt, J. I.; Reek, J. N. H. Neutral Tridentate PNP Ligands and Their Hybrid Analogues: Versatile Non-Innocent Scaffolds for Homogeneous Catalysis. Angew. Chem., Int. Ed. 2009, 48, 8832−8846. (d) Schneider, S.; Meiners, J.; Askevold, B. Cooperative Aliphatic PNP Amido Pincer Ligands − Versatile Building Blocks for Coordination Chemistry and Catalysis. Eur. J. Inorg. Chem. 2012, 2012, 412−429. (2) (a) Sacco, A.; Vasapollo, G.; Nobile, C. F.; Piergiovanni, A.; Pellinghelli, M. A.; Lanfranchi, M. Syntheses and structures of 2diphenylphosphinomethylenide-6-diphenylphosphinomethylenepyridine complexes of palladium(II) and platinum(II); crystal structures of [PtCl2-(CHPPH2)-6-(CH2PPh2)pyridine] and [Pd(COOMe)2(CHPPh2)-6-(CH2PPh2)pyridine]. J. Organomet. Chem. 1988, 356, 397−409. (b) Vasapollo, G.; Giannoccaro, P.; Nobile, C. F.; Sacco, A. Synthesis and reactivity toward gas molecules of chloro 2,6J


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Organometallics di(diphenylphosphinomethyl)pyridine rhodium(I). Inorg. Chim. Acta 1981, 48, 125−128. (3) (a) Gunanathan, C.; Milstein, D. Metal-Ligand Cooperation by Aromatization-Dearomatization: A New Paradigm in Bond Activation and “Green” Catalysis. Acc. Chem. Res. 2011, 44, 588−602. (b) Milstein, D.; Zell, T. Hydrogenation and Dehydrogenation Iron Pincer Catalysts Capable of Metal−Ligand Cooperation by Aromatization/Dearomatization. Acc. Chem. Res. 2015, 48, 1979− 1994. (4) For selected examples, see: (a) Mastalir, M.; Stöger, B.; Pittenauer, E.; Allmaier, G.; Kirchner, K. Air-Stable Triazine-Based Ni(II) PNP Pincer Complexes As Catalysts for the Suzuki−Miyaura Cross-Coupling. Org. Lett. 2016, 18, 3186−3189. (b) Deibl, N.; Ament, K.; Kempe, R. A Sustainable Multicomponent Pyrimidine Synthesis. J. Am. Chem. Soc. 2015, 137, 12804−12807. (c) Deibl, N.; Kempe, R. Manganese-Catalyzed Multicomponent Synthesis of Pyrimidines from Alcohols and Amidines. Angew. Chem., Int. Ed. 2017, 56, 1663−1666. (d) Gorgas, N.; Stöger, B.; Veiros, L. F.; Pittenauer, E.; Allmaier, G.; Kirchner, K. Efficient Hydrogenation of Ketones and Aldehydes Catalyzed by Well-Defined Iron(II) PNP Pincer Complexes: Evidence for an Insertion Mechanism. Organometallics 2014, 33, 6905−6914. (e) Bruneau-Voisine, A.; Wang, D.; Roisnel, T.; Darcel, C.; Sortais, J.-B. Hydrogenation of Ketones with a Manganese PN3P Pincer Pre-Catalyst. Catal. Commun. 2017, 92, 1−4. (5) (a) Alig, L.; Fritz, M.; Schneider, S. First-Row Transition Metal (De)Hydrogenation Catalysis Based On Functional Pincer Ligands. Chem. Rev. 2019, 119 (4), 2681−2751. (b) Gorgas, N.; Kirchner, K. Isoelectronic Manganese and Iron Hydrogenation/Dehydrogenation Catalysts: Similarities and Divergences. Acc. Chem. Res. 2018, 51, 1558−1569. (c) Liu, W.; Sahoo, B.; Junge, K.; Beller, M. Cobalt Complexes as an Emerging Class of Catalysts for Homogeneous Hydrogenations. Acc. Chem. Res. 2018, 51, 1858. (6) Conley, B. L.; Pennington-Boggio, M. K.; Boz, E.; Williams, T. J. Discovery, Applications, and Catalytic Mechanisms of Shvo’s Catalyst. Chem. Rev. 2010, 110 (4), 2294−2312. (7) Kimura, T.; Koiso, N.; Ishiwata, K.; Kuwata, S.; Ikariya, T. H−H and N−H Bond Cleavage of Dihydrogen and Ammonia with a Bifunctional Parent Imido (NH)-Bridged Diiridium Complex. J. Am. Chem. Soc. 2011, 133 (23), 8880−8883. (8) Musa, S.; Shaposhnikov, I.; Cohen, S.; Gelman, D. Ligand-Metal Cooperation in PCP Pincer Complexes: Rational Design and Catalytic Activity in Acceptorless Dehydrogenation of Alcohols. Angew. Chem., Int. Ed. 2011, 50 (15), 3533−3537. (9) Omann, L.; Königs, C. D. F.; Klare, H. F. T.; Oestreich, M. Cooperative Catalysis at Metal−Sulfur Bonds. Acc. Chem. Res. 2017, 50 (5), 1258−1269. (10) (a) Owen, G. R. Hydrogen Atom Storage upon Z-Class Borane Ligand Functions: An Alternative Approach to Ligand Cooperation. Chem. Soc. Rev. 2012, 41 (9), 3535−3546. (b) Devillard, M.; Bouhadir, G.; Bourissou, D. Cooperation between Transition Metals and Lewis Acids: A Way To Activate H2 and H−E Bonds. Angew. Chem., Int. Ed. 2015, 54 (3), 730−732. (11) Feichtner, K.-S.; Gessner, V. H. Cooperative Bond Activation Reactions with Carbene Complexes. Chem. Commun. 2018, 54, 6540−6553. (12) (a) Coles, M. P.; Gibson, V. C.; Clegg, W.; Elsegood, M. R. J.; Porelli, P. A. Synthesis and reactivity of the first stable chromium(VI) alkylidene complexes. Chem. Commun. 1996, 1963. (b) Tsang, J. Y. K.; Buschhaus, M. S. A.; Legzdins, P.; Patrick, B. O. Ortho-Selective C−H Activation of Substituted Benzenes Effected by a Tungsten Alkylidene Complex without Substituent Coordination. Organometallics 2006, 25, 4215. (c) Wada, K.; Pamplin, C. B.; Legzdins, P.; Patrick, B. O.; Tsyba, I.; Bau, R. Intermolecular Activation of Hydrocarbon C−H Bonds under Ambient Conditions by 16-Electron Neopentylidene and Benzyne Complexes of Molybdenum. J. Am. Chem. Soc. 2003, 125, 7035. (d) Cheon, J.; Rogers, D. M.; Girolami, G. S. Mechanistic Studies of the Thermolysis of Tetraneopentyltitanium(IV). 1. Solution Evidence That Titanium Alkylidenes Activate Saturated Hydrocarbons. J. Am. Chem. Soc. 1997,

119, 6804. (e) Lockwood, M. A.; Clark, J. R.; Parkin, B. C.; Rothwell, I. P. Intramolecular activation of aromatic C−H bonds by tantalum alkylidene groups: evaluating ‘cyclometallation resistant’ aryloxide ligation. Chem. Commun. 1996, 1973. (13) Gutsulyak, D. V.; Piers, W. E.; Borau-Garcia, J.; Parvez, M. Activation of Water, Ammonia, and Other Small Molecules by PCCarbeneP Nickel Pincer Complexes. J. Am. Chem. Soc. 2013, 135 (32), 11776−11779. (14) Comanescu, C. C.; Iluc, V. M. Synthesis and Reactivity of a Nucleophilic Palladium(II) Carbene. Organometallics 2014, 33 (21), 6059−6064. (15) (a) Comanescu, C. C.; Iluc, V. M. C−H Activation Reactions of a Nucleophilic Palladium Carbene. Organometallics 2015, 34 (19), 4684−4692. (b) Comanescu, C. C.; Iluc, V. M. E−H (E = B, Si, Ge) Bond Activation of Pinacolborane, Silanes, and Germanes by Nucleophilic Palladium Carbene Complexes. Chem. Commun. 2016, 52 (58), 9048−9051. (c) Comanescu, C. C.; Iluc, V. M. E−H (E = N, O) Bond Activation by a Nucleophilic Palladium Carbene. Polyhedron 2018, 143, 176−183. (d) LaPierre, E. A.; Piers, W. E.; Gendy, C. Divergent Reactivity of CO2, CO, and Related Substrates at the Nickel Carbon Double Bond of (PCCarbeneP)Ni(II) Pincer Complexes. Organometallics 2018, 37 (20), 3394−3398. (e) LaPierre, E. A.; Piers, W. E.; Gendy, C. Redox-State Dependent Activation of Silanes and Ammonia with Reverse Polarity (PCCarbeneP)Ni Complexes: Electrophilic vs. Nucleophilic Carbenes. Dalt. Trans. 2018, 47 (46), 16789− 16797. (f) LaPierre, E. A.; Piers, W. E.; Spasyuk, D. M.; Bi, D. W. Activation of Si−H Bonds across the Nickel Carbene Bond in Electron Rich Nickel PCCarbeneP Pincer Complexes. Chem. Commun. 2016, 52 (7), 1361−1364. (16) Gessner, V. H.; Becker, J.; Feichtner, K.-S. Carbene Complexes Based on Dilithium Methandiides. Eur. J. Inorg. Chem. 2015, 2015, 1841−1859. (17) (a) Becker, J.; Modl, T.; Gessner, V. H. Methandiide as a NonInnocent Ligand in Carbene Complexes: From the Electronic Structure to Bond Activation Reactions and Cooperative. Chem. Eur. J. 2014, 20 (36), 11295−11299. (b) Weismann, J.; Waterman, R.; Gessner, V. H. Metal-Ligand Cooperativity in a Methandiide Derived Iridium Carbene Complex. Chem. - Eur. J. 2016, 22, 3846− 3855. (18) Feichtner, K.-S.; Scherpf, T.; Gessner, V. H. Cooperative Bond Activation Reactions with Ruthenium Carbene Complex PhSO2(Ph2PNSiMe3)CRu(p-Cymene): RuC and N−Si Bond Reactivity. Organometallics 2018, 37 (5), 645−654. (19) Weismann, J.; Gessner, V. H. Si−H Activation by Means of Metal Ligand Cooperation in a Methandiide Derived Carbene Complex. Chem. Commun. 2015, 51 (80), 14909−14912. (20) Scharf, L. T.; Weismann, J.; Feichtner, K.-S.; Lindl, F.; Gessner, V. H. Versatile Modes of Cooperative B−H Bond Activation Reactions in Ruthenium-Carbene Complexes: Addition, Ring-Opening and Insertion. Chem. - Eur. J. 2018, 24 (14), 3439−3443. (21) Weismann, J.; Scharf, L. T.; Gessner, V. H. Cooperative P−H Bond Activation with Ruthenium and Iridium Carbene Complexes. Organometallics 2016, 35 (15), 2507−2515. (22) Pyykkö, P.; Atsumi, M. Molecular Single-Bond Covalent Radii for Elements 1−118. Chem. - Eur. J. 2009, 15, 186−197. (23) For examples, see: (a) Tourneux, J.-C.; Berthet, J.-C.; Cantat, T.; Thuery, P.; Mezailles, N.; Ephritikhine, M. Exploring the Uranyl Organometallic Chemistry: From Single to Double Uranium−Carbon Bonds. J. Am. Chem. Soc. 2011, 133, 6162−6165. (b) Cooper, O. J.; Mills, D. P.; McMaster, J.; Moro, F.; Davies, E. S.; Lewis, W.; Blake, A. J.; Liddle, S. T. Uranium−Carbon Multiple Bonding: Facile Access to the Pentavalent Uranium Carbene [U{C(PPh2NSiMe3)2}(Cl)2(I)] and Comparison of UVC and UIVC Bonds. Angew. Chem., Int. Ed. 2011, 50, 2383−2386. (c) Cavell, R. G.; Kamalesh Babu, R. P.; Kasani, A.; McDonald, R. Novel Metal-Carbon Multiply Bonded Twelve-Electron Complexes of Ti and Zr Supported by a Bis(Phosphoranimine) Chelate. J. Am. Chem. Soc. 1999, 121, 5805− 5806. (i) Cantat, T.; Demange, M.; Mézailles, N.; Ricard, L.; Jean, Y.; Le Floch, P. A Bis(thiophosphinoyl)methylene Ruthenium Carbene K


Article

Organometallics

Chem. Phys. 2010, 132 (15), 154104. (b) Grimme, S.; Ehrlich, S.; Goerigk, L. Effect of the Damping Function in Dispersion Corrected Density Functional Theory. J. Comput. Chem. 2011, 32 (7), 1456− 1465. (c) Smith, D. G. A.; Burns, L. A.; Patkowski, K.; Sherrill, C. D. Revised Damping Parameters for the D3 Dispersion Correction to Density Functional Theory. J. Phys. Chem. Lett. 2016, 7 (12), 2197− 2203. (34) Deglmann, P.; Furche, F.; Ahlrichs, R. An Efficient Implementation of Second Analytical Derivatives for Density Functional Methods. Chem. Phys. Lett. 2002, 362 (5−6), 511−518. (35) Reed, A. E.; Curtiss, L. A.; Weinhold, F. Intermolecular Interactions from a Natural Bond Orbital, Donor-Acceptor Viewpoint. Chem. Rev. 1988, 88 (6), 899−926. (36) Glendening, E. D.; Reed, A. E.; Carpenter, J. E.; Weinhold, F. NBO, version 3.1. (37) (a) Sheldrick, G. A short history of SHELX. Acta Crystallogr., Sect. A: Found. Crystallogr. 2008, 64 (1), 112−122. (b) Sheldrick, G. Crystal structure refinement with SHELXL. Acta Crystallogr., Sect. C: Struct. Chem. 2015, 71 (1), 3−8.

Complex: Synthesis, X-ray Crystal Structure, and DFT Calculations of Its Thermally Promoted Reverse α-Hydride Migration Process. Organometallics 2005, 24, 4838−4841. (24) Klein, H.-F.; Schmidbaur, H. Tetrakis(Trimethylphosphane)Nickel(0). Angew. Chem., Int. Ed. Engl. 1970, 9 (11), 903−904. (25) (a) Molitor, S.; Feichtner, K.-S.; Kupper, C.; Gessner, V. H. Substitution Effects on the Formation of T-Shaped Palladium Carbene and Thioketone Complexes from Li/Cl Carbenoids. Chem. - Eur. J. 2014, 20 (34), 10752−10762. (b) Rothstein, P. E.; Comanescu, C. C.; Iluc, V. M. Formation of Palladium η2-Bound Chalcogenoketones across a Pd+−C−Bond. Chem. - Eur. J. 2017, 23 (67), 16948−16952. (26) (a) Doyle, L. E.; Piers, W. E.; Borau-Garcia, J.; Sgro, M. J.; Spasyuk, D. M. Mechanistic studies on the addition of hydrogen to iridaepoxide complexes with subsequent elimination of water. Chem. Sci. 2016, 7, 921. (b) Rothstein, P. E.; Comanescu, C. C.; Iluc, V. M. Formation of Palladium η2-bound Chalcogenoketones across a Pd+− C− Bond. Chem. - Eur. J. 2017, 23, 16948−16952. (c) Doyle, L. E.; Piers, W. E.; Bi, D. W. Cationic PCP iridaepoxide and carbene complexes for facile water elimination and activation processes. Dalton Trans. 2017, 46, 4346−4354. (27) Gessner, V. H. Formation of a Palladium Thioketone Complex from a Thiophosphinoyl Stabilized Li/Cl Carbenoid. Organometallics 2011, 30, 4228−4231. (28) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Petersson, G. A.; Nakatsuji, H.; Li, X.; Caricato, M.; Marenich, A. V.; Bloino, J.; Janesko, B. G.; Gomperts, R.; Mennucci, B.; Hratchian, H. P.; Ortiz, J. V.; Izmaylov, A. F.; Sonnenberg, J. L.; Williams-Young, D.; Ding, F.; Lipparini, F.; Egidi, F.; Goings, J.; Peng, B.; Petrone, A.; Henderson, T.; Ranasinghe, D.; Zakrzewski, V. G.; Gao, J.; Rega, N.; Zheng, G.; Liang, W.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Throssell, K.; Montgomery, J. A., Jr.; Peralta, J. E.; Ogliaro, F.; Bearpark, M. J.; Heyd, J. J.; Brothers, E. N.; Kudin, K. N.; Staroverov, V. N.; Keith, T. A.; Kobayashi, R.; Normand, J.; Raghavachari, K.; Rendell, A. P.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Millam, J. M.; Klene, M.; Adamo, C.; Cammi, R.; Ochterski, J. W.; Martin, R. L.; Morokuma, K.; Farkas, O.; Foresman, J. B.; Fox, D. J. Gaussian 09, revision E.01; Gaussian, Inc.: Wallingford, CT, 2016. (29) (a) Hohenberg, P.; Kohn, W. Inhomogeneous Electron Gas. Phys. Rev. 1964, 136 (3B), B864−B871. (b) Kohn, W.; Sham, L. J. Self-Consistent Equations Including Exchange and Correlation Effects. Phys. Rev. 1965, 140 (4A), A1133−A1138. (30) Adamo, C.; Barone, V. Toward Reliable Density Functional Methods without Adjustable Parameters: The PBE0Model. J. Chem. Phys. 1999, 110 (13), 6158−6170. (31) (a) Roy, L. E.; Hay, P. J.; Martin, R. L. Revised Basis Sets for the LANL Effective Core Potentials. J. Chem. Theory Comput. 2008, 4 (7), 1029−1031. (b) Ehlers, A. W.; Böhme, M.; Dapprich, S.; Gobbi, A.; Höllwarth, A.; Jonas, V.; Köhler, K. F.; Stegmann, R.; Veldkamp, A.; Frenking, G. A Set of F-Polarization Functions for PseudoPotential Basis Sets of the Transition Metals Sc-Cu, Y-Ag and La-Au. Chem. Phys. Lett. 1993, 208 (1−2), 111−114. (c) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for the Transition Metal Atoms Sc to Hg. J. Chem. Phys. 1985, 82 (1), 270−283. (d) Wadt, W. R.; Hay, P. J. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for Main Group Elements Na to Bi. J. Chem. Phys. 1985, 82 (1), 284− 298. (e) Hay, P. J.; Wadt, W. R. Ab Initio Effective Core Potentials for Molecular Calculations. Potentials for K to Au Including the Outermost Core Orbitals. J. Chem. Phys. 1985, 82 (1), 299−310. (32) Weigend, F.; Ahlrichs, R. Balanced Basis Sets of Split Valence, Triple Zeta Valence and Quadruple Zeta Valence Quality for H to Rn: Design and Assessment of Accuracy. Phys. Chem. Chem. Phys. 2005, 7 (18), 3297−3305. (33) (a) Grimme, S.; Antony, J.; Ehrlich, S.; Krieg, H. A Consistent and Accurate Ab Initio Parametrization of Density Functional Dispersion Correction (DFT-D) for the 94 Elements H-Pu. J. L


Cooperative Bond Activation Reactions with Nickel and Palladium

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