Synthesis and Characterization of a N,C,N-Carbodiphosphorane

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

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Synthesis and Characterization of a N,C,N-Carbodiphosphorane Pincer Ligand and Its Complexes Marius Klein, Xiulan Xie, Olaf Burghaus, and Jörg Sundermeyer* Fachbereich Chemie and Wissenschaftliches Zentrum für Materialwissenschaften (WZMW), Philipps-Universität Marburg, Hans-Meerwein-Straße 4, 35043 Marburg, Germany

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S Supporting Information *

ABSTRACT: The reaction of 2-pyridiyldiphenylphosphine (2) with tetrachloromethane and subsequent dehalogenation of the intermediate chloro phosphonium salt [(CDPPy2)Cl]Cl (3) with tris(1-pyrrolidyl)phosphine results in the formation of a new type of carbodiphosphorane N,C,N pincer ligand, sym-bis(2-pyridyl)tetraphenylcarbodiphosphorane, CDPPy2 (1). It crystallizes in a triclinic crystal system with a crystallographic point group of P1̅. This neutral double-ylidic N,C,N ligand is capable of stabilizing a wide range of metal coordination polyhedra, varying from square planar [(CDPPy2)PdCl]Cl (4), octahedral mer-[(CDPPy2)TiCl3] (5) and fac-[(CDPPy2)Cr(CO)3] (6) to trigonal-bipyramidal [(CDPPy2)MnCl2] (9) and [(CDPPy2)CoCl2] (10) complexes. Unprecedented dinuclear complexes are formed with molybdenum and nickel carbonyls. 1 reacts with [Mo(CO)3(NCMe)3] to form the symmetric κ3-N,C,N-[(CDPPy2)Mo(CO)3(μ-CO)Mo(CO)3] (7) with one bridging carbonyl next to a bridging central carbon atom with its two lone pairs. In contrast, an unsymmetrical coordination mode with only one coordinated pyridine is observed in κ2-N,C-[(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8). Carbodiphosphorane-based ligands are unique due to their σ,π four-electron-donor character of the central carbon atom toward one metal and alternatively their 2σ four-electron-donor character toward two vicinal metal atoms.

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INTRODUCTION The interest in carbodiphosphoranes as such and as ligands in organometallic chemistry has experienced a renaissance. By analyzing the donation and back-donation bonding situation in the P−C−P backbone, Frenking and co-workers1−6 draw parallels to coordination compounds and suggested to envisage carbodiphosphoranes (CDPs) as phosphine-stabilized complexes of zerovalent carbon(0). In this model, the phosphine ligands serve as σ donors and the naked carbon atom in its excited singlet (1D) state acts as an acceptor. In contrast to singlet carbenes such as NHCs, these double-ylide carbon ligands (or carbones) have two occupied lone pairs, one of σ and one of π symmetry toward the coordinated metal. Therefore, they are neutral; nevertheless, they are very strong σ,π-donor ligands.7 Hexaphenylcarbodiphosphorane was first synthesized in 19618 and has widely been used in coordination chemistry.9,10 A chelating cyclometalated variant of hexaphenylcarbodiphosphorane was introduced by Kubo et al., who described C,C,C pincer carbene complexes of rhodium and platinum.11−14 Cyclometalated CDP chelate complexes are also known.15,16 A combination of two phosphines with a CDP backbone led to P,C,P pincer CDP complexes of the ligand C(dppm)2, which was never isolated in a free ligand base form.17−23 In their aim to investigate heterobimetallic complexes, Alcarazo et al. synthesized a monopyridylsubstituted carbodiphosphorane (Figure 1),24 but the coordination chemistry as chelate ligand has not been explored so far. Herein we report the isolation and the coordination chemistry © XXXX American Chemical Society

Figure 1. Parent hexaphenylcarbodiphosphorane and its evolution into a pincer ligand.

of the novel N,C,N pincer ligand sym-bis(2-pyridyl)tetraphenylcarbodiphosphorane, CDPPy2 (1). Independently, 1 has been considered as a ligand in an uranium(IV) complex very recently.25 Nevertheless, the ligand has not been isolated and characterized so far.

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RESULTS AND DISCUSSION sym-Bis(2-pyridyl)tetraphenylcarbodiphosphorane, CDPPy2 (1), was readily obtained as a fluorescent, yellow solid in 31% yield upon reaction of 2-pyridyldiphenylphosphine (2) with tetrachloromethane and subsequent dehalogenation of the resulting chloro phosphonium salt [(CDPPy2)Cl]Cl (3) with tris(1-pyrrolidyl)phosphine or tris(dimethylamino)phosphine. The reaction of 2-pyridyldiphenylphosphine (2) with tetrachloromethane was rather slow due to the reduced electron density at the phosphorus atom in comparison to Received: July 19, 2019

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DOI: 10.1021/acs.organomet.9b00489 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Table 1. Simulated Coupling Constants (Hz) of the 13C NMR Spectra of 1 and [(CDPPy2)PdCl]Cl (4) Obtained via Quantum Mechanical Calculations

triphenylphosphine, and a reaction time of 8 days was necessary to complete the conversion. Heating or using UV light sources to accelerate the reaction led to the emergence of byproducts. Neither changing the solvent from DCM to chloroform, 1,2-dichloroethane, or chlorobenzene nor the use of azobis(isobutyronitrile) as a radical initiator expedited the reaction or also led to byproducts. While the parent hexaphenylcarbodiphosphorane shows triboluminescence,26 only fluorescence was observed for 1 upon irradiation with UV light. The 31P NMR signal can be found at −5.59 ppm in C6D6, and the highly shielded central carbon is detected at 12.1 ppm (t, JC,P = 113.6 Hz) in the 13C NMR spectrum. This shift is characteristic for carbodiphosphoranes and refers to some character of the bonding model R 3 P→C 0←PR 3 . The quaternary ipso-carbon 13C NMR signals of the pyridyl (C2) and phenyl groups show complicated coupling patterns, which belong to a spin system of higher order and will be explained below. While the 31P isotope possesses 100% of its natural abundance, the 13C isotope has only 1%. As a result, the observed NMR-active fragment consists of a 13 C−31P−31P−12C spin system. The 13C and 12C nuclei isotopes lead to a small difference in the chemical shift of the two 31P nuclei. This phenomenon is known as the isotope shift. In this case the isotope shift of 31P caused by the 12C isotope is less than 0.01 ppm. Nevertheless, this makes the two 31 P nuclei chemically not equivalent, which results in an ABX spin system with A = 31P, B = 31P, and X = 13C nucleus. Quantum mechanically the system can be described using the equations JAB =

So 2

Ii Ii + Io

N = N1 − N2 = |JAX + JBX |

2

JPP 1 JC2P 3 JC2P 1 JC7P 3 JC7P

1

4

81 118 10 88 7

49 131 10 84 1

Furthermore, a crystal structure could be obtained by cooling a saturated solution of 1 in toluene to −20 °C. 1 crystallizes in a triclinic crystal system with a crystallographic point group of P1̅ (Scheme 1). The characteristic bending of Scheme 1. Synthesis and Molecular Structure of sym-Bis(2pyridyl)tetraphenylcarbodiphosphorane (1) in the Solid Statea

(1) (2) a

L = So

Io = |JAX − JBX | Ii + Io

Hydrogen atoms and solvent molecules have been removed for clarity. Thermal ellipsoids are given at 50% probability; a side view is given on the left side and a top view on the right side. Reagents and conditions: (a) 2/3 equiv of CCl4, DCM, 8 d, room temperature, 98%; (b), 1.1 equiv of tris(1-pyrrolidyl)phosphine, 3 h, 70 °C, 31%.

(3)

where Ii and Io stand for the integrals of the outside and inside signals (see Figure 2). With these equations the coupling constants can be calculated. Using the DAISY program within the Bruker software package of TopSpin 4.0, the coupling constants could be simulated and are given in Table 1. The experimental and the simulated 13C{1H} signals of the neutral bis-pyridyl-substituted CDP ligand 1 are shown in Figure 2.

the carbodiphosphorane along the P−C−P axis, which has been well-known since the determination of the chemical structure of hexaphenylcarbodiphosphorane,26,27 can be observed for 1; P1−C1−P2 amounts to 133.76(13)°. This P−C−P angle matches that of the monopyridylsubstituted derivate (133.25(10)°)24 and with one of the modifications of hexaphenylcarbodiphosphorane (131.7(3)°).26 In the solid state two of the phenyl rings of 1 are coplanar. Their ortho hydrogen atoms are pointing toward the electron-rich central carbon atom with its two electron lone pairs suggesting a weak intramolecular C···Hortho interaction. Due to repulsive interaction of the pyridyl and carbon lone pairs, pyridyl substituents are located in an anti conformation. DFT calculations at the PBE-D3(BJ)/def2-TZVPP level of theory suggest that the HOMO-1 can be interpreted as a lone pair MO of σ symmetry and the HOMO as one of π symmetry (Figure 3). In contrast to the to the hexaphenylcarbodiphosphorane the LUMO and LUMO-1 are not distributed all over the triphenylphosphine fragment but are localized at the pyridyl unit. This is in accord with the electron-withdrawing ability of the pyridyl substituent in comparison to phenyl (compare Figure S-11).

Figure 2. Experimental (left) and simulated (right) 13C {1H} signals of C2 (top) and C7 (bottom) of the ligand sym-bis(2-pyridyl)tetraphenylcarbodiphosphorane (1). B


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Organometallics

same applies in case of the Pd complex [(CDPPy2)PdCl]Cl (4); the experimental and simulated 13C{1H} signals of complex 4 are shown in Figure 4. The corresponding coupling constants can be found in Table 1. Figure 3. Kohn−Sham orbitals of HOMO-1 (a), HOMO (b), and the degenerate LUMO (c) and LUMO+1 (d) of carbodiphosphorane 1 calculated for the optimized S0 state geometry (isovalue 0.05). Calculations were performed at the PBE-D3(BJ)/def2-TZVPP level of theory.

The calculated first protonation affinity gives values of 287.2 and 192.0 kcal/mol for the second protonation affinity and are consistent with energies calculated for hexaphenylcarbodiphosphorane (280.0 and 185.6 kcal/mol).5 The atomic partial charge of the central carbon q(C) calculated by the NBO method at the PBE-D3(BJ)/def2-TZVPP level of theory is −1.41 e for 1, −1.35 e for [1H]+, and −1.10 e for [1H2]2+. The large negative value q(C) for 1 agrees with the theory of the bonding situation of the carbodiphosphoranes. q(C) for hexaphenylcarbodiphosphorane (−1.43 e) is in the same order of magnitude as in 1.5 Of great interest is the coordination behavior of this potentially tridentate or tetradentate neutral ligand 1 (Scheme 2). For a first inspection, a variety of transition-metal complexes were chosen as reaction partners of 1. As a result, we were able to identify a number of different coordination modes of 1. When [Pd(PPh3)2Cl2] was treated with 1 in THF at room temperature, a mononuclear complex could be obtained. Here the 31P NMR signal can be found at δ 31.58 ppm in CD2Cl2 and the ylidic carbon can be detected at 11.5 ppm (t, JC,P = 102.1 Hz). As already mentioned for the free ligand 1, the quaternary carbon signals of the pyridyl (C2) and the phenyl group (C7) reveal a coupling pattern, belonging to a spin system of higher order in the 13C NMR spectrum. The

Figure 4. Experimental (left) and simulated (right) 13C{1H} signals of C2 (top) and C7 (bottom) of the Pd(II) complex [(CDPPy2)PdCl] Cl (4).

Figure 5 illustrates the crystal structure obtained by layering a saturated solution of [(CDPPy2)PdCl]Cl (4) in DCM with pentane. The elemental cell carries two crystallographically independent molecules in which the cationic palladium atom is in a square-planar configuration. The ylidic Pd−C bond lengths in both independent molecules are the same within 3σ: Pd(1)−C(1) 2.004(4) and Pd(2)−C(75) 2.003(4) Å. They are shorter in comparison to palladium P,C,P pincer carbodiphosphorane complexes of C(dppm)2 (2.057−2.062(2) Å)17,20 and to a palladium cyclometalated complex of hexaphenylcarbodiphosphorane (2.126 Å).16 On the other hand, the Pd−C distance is longer in comparison to a P,C,P pincer complex incorporating a central N-heterocyclic carbene (NHC) with its π-backbonding ability (1.9356(17) Å).28 However, other non-

Scheme 2. Coordination Chemistry of sym-Bis(2-pyridyl)tetraphenylcarbodiphosphorane, CDPPy2 (1): Square-Planar [(CDPPy2)PdCl]Cl (4), Octahedral mer- [(CDPPy2)TiCl3] (5) and fac-[(CDPPy2)Cr(CO)3] (6), Trigonal-Bipyramidal [(CDPPy2)MnCl2] (9) and [(CDPPy2)CoCl2] (10), and Dinuclear sym-[(CDPPy2)Mo(CO)3(μ-CO)Mo(CO)3] (7) and [(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8) Complexes

C


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Figure 5. X-ray crystal structure of [(CDPPy2)PdCl]Cl (4). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability. For details see the Supporting Information.

Figure 6. X-ray crystal structure of [(CDPPy2)TiCl3] (5). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability. For details see the Supporting Information.

[(CDPPy2)PdCl]Cl (4) or in the free ligand 1. This results in a larger N−N distance in comparison to the Pd complex 4, implying a larger bite angle N−M−N for the Ti complex 5. This is consistent with expectations, since the crystal radius (cr) (0.81 Å) and the effective ionic radius (ir) (0.67 Å) are larger for Ti3+ with a coordination number of 6 in comparison to Pd2+ (cr = 0.78 Å and ir = 0.64 Å) in a square-planar coordination unit.39 The octahedral complex fac-[(CDPPy2)Cr(CO)3] (6) could be obtained in high yields upon treating the carbodiphosphorane 1 with [Cr(CO)3(NCMe)3] in THF. Layering a DCM solution with pentane results in the formation of red needles of 6·2THF, which crystallizes in a monoclinic crystal system with a space group of P21/n (Figure 7). The chromium atom is

constrained-geometry NHC-Pd complexes show Pd−C bond lengths similar to those observed in 4.29−31 Shorter Pd−C bonds were observed in a NHC-Pd pincer complex carrying two pyridyl fragments (1.918(5) Å)32 and in a corresponding palladium carbodicarbene complex with tridentate N,C,N coordination (1.973(3) Å).33 The short Pd−C bond can be explained by the pincer effect involving a very strong σ-dative bond stabilizing the cationic 16-valence-electron fragment. A π bond can be excluded in this case, as the carbon-centered p type orbital and the empty dx2−y2 orbital at the metal do not match in their symmetry. This should lead to an interesting dipolar zwitterionic +Pd−C− σ-bond situation, which will be the focus of planned reactivity studies. The Pd−Cl bond length illustrates the contribution of the carbon donor to the thermodynamic trans effect on the opposing Pd−Cl bond: 2.393(1) and 2.401(1) Å. Pd−Cl distances for the reported [(NHC)Pd(allyl)Cl] complexes have an average value of 2.35 Å.34,35 Non-carbene/-carbon but carbanionic tridentate N,C,N pincer ligand Pd complexes show slightly shorter Pd−C bond lengths and thus a distinctively longer trans-Pd−Cl bond length.36,37 The P−C−P angle is 132.4° (average), and the sum of the C−Pd−N and N−Pd−Cl angles is 360°, where the C−Pd−N angles are 85.6° (average) and the N−Pd−Cl angles are 93.7 and 95.1° (average). When 1 is reacted with TiCl3, the meridional octahedral complex [(CDPPy2)TiCl3] (5) is generated. Crystals of 5 containing three DCM solvent molecules in the unit cell were obtained from DCM/pentane. 5 crystallizes in a hexagonal crystal system with a point group of P63 (Figure 6). Half of the molecule is generated by a symmetry operation. To the best of our knowledge, complex 5 is the first reported titanium(III) carbodiphosphorane complex. Despite of the larger ionic radius of Ti(III), the Ti−C1 bond length is 2.144(6) Å, shorter than the Ti−C distance in a mer-N,C,N pincer ligand Ti(IV) complex (2.275(5) Å).38 As a result the Ti−Cl bond lengths are slightly longer for [(CDPPy2)TiCl3] (5) at 2.498(2) Å (Ti1−Cl1) and 2.380(1) Å (Ti1−Cl2) in comparison to 2.370(2) and 2.3517(10) Å for the cited complex of Sarsfield et al. The sum of the angles Cl1−Ti1−N1, Cl1−Ti1−N1#, C1−T1−N1 and C1−T1−N1# and the sum of the angles Cl1−Ti1−Cl2, Cl1−Ti1−Cl2#, C1−T1−Cl2 and C1−T1−Cl2# are 360°. Cl1−Ti1−N1 is 96.50(11)°, Cl1− Ti1−C1 is 83.50(11)°, Cl1−Ti1−Cl2 is 88.43(4)°, and C1− T1−Cl2 is 91.57(4)°. The angle P1−C1−P1# has a value of 129.9(4)° and is distinctly smaller than P−C1−P in

Figure 7. X-ray crystal structure of [(CDPPy2)Cr(CO)3] (6). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability.

coordinated in a slightly distorted fac configuration. The strong thermodynamic trans effect of the π-acidic carbonyl ligands is directing the pincer ligand into a fac array where the pyridyl units are puckered with respect to each other. The Cr1−C1 distance is 2.212(2) Å and is distinctly longer than the C−M distances in the Pd or the Ti complexes [(CDPPy2)PdCl]Cl (4) and [(CDPPy2)TiCl3] (5). The Cr1−C38 bond 1.808(3) Å of the carbonyl ligand trans to the ylidic carbon σ,π donor is shorter in comparison to those trans to pyridine, indicating a stronger d to π* back-bonding. Consequently, the C38−O3 distance 1.189(3) Å is slightly more elongated. The reference distances of Cr1−C36 and Cr−C37 are 1.820(3) and 1.835(3) Å. The P1−C1−P1 angle is 133.6(2)° and thus is larger than the P−C1−P angle in the Pd and Ti complexes [(CDPPy2)D


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S,S-C6H4)].42 It is plausible that, independently from the ratio of 1 to [Mo(CO)3(NCMe)3], a dinuclear complex with two N,C-chelating ligand units toward [Mo(CO)4] and/or [Mo(CO)3(MeCN)] fragments are formed. The presence of a labile MeCN ligand induces one of the terminal CO ligands of the neighboring metal center to kick out this labile ligand. In a strict application of the 18-valence-electron rule, this process should be accompanied by the formation of a Mo−Mo bond. In fact, the Mo−Mo distance of 3.0456(5) Å in 7 is only slightly smaller than the sum of the covalent radii of two Mo atoms (2 × 1.54(5) Å).43 Due to this weak Mo−Mo bonding interaction, the P−C−P angle of the dinuclear molybdenum complex is extremely small (120.4(2)°) in comparison to those of the previously discussed complexes. In the ATR-IR spectrum of the solid sample, only a broad band at 1886 cm−1, a sharper band at 1776 cm−1, and a broad band at 1741 cm−1, which is partially mixing with the sharper band, can be observed. DFT calculations suggest seven bands. The vibration modes can be found in Figure S-17 of the Supporting Information. Two of them at 1966 and 1941 cm−1 correspond to the broader signal at 1886 cm−1 in the experimental spectrum. The calculated bands at 1886 and 1884 cm−1, which are close together, are related to the sharper band at 1776 cm−1 (experimental), and the remaining bands in the DFT calculation (1867, 1865, and 1827 cm−1) are combined to the experimentally observed broad signal at 1741 cm−1. So far, we have not been able to obtain a mononuclear nickel carbonyl complex of 1, as was observed with the parent hexaphenylcarbodiphosphorane.44 Independently from the stochiometry, there is a high preference for the formation of the dinuclear complex [(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8) of low symmetry. As expected, the best yield is obtained when 1 and [Ni(CO)4] are reacted in a 1:2 ratio. Similarly to molybdenum complex 7, a bridging CO and a bridging doubleylidic carbon are connecting two interacting Ni−Ni atoms in 8. Ligand template 1 is acting as a bridging neutral eight-electron donor. One Ni atom is further coordinated to one terminal CO and one pyridine unit while the other Ni is coordinated to two terminal CO ligands; the pyridine remains in a dangling nonbonding situation. By thermal, photochemical, or chemical activation, we were not able to induce an intramolecular substitution of a geminal carbonyl ligand by pyridine. Therefore, DFT calculations at the PBE-D3(BJ)/def2TZVPP level were pursued. They suggest that the observed compound 8 is about 1.15 eV (111 kJ/mol) more stable than a symmetric complex hypothetically formed via an intramolecular decarbonylation step (Figure S-21 in the Supporting Information). The proposed molecular structure is proven by X-ray analysis. Single crystals were obtained by layering a DCM solution of 8 with n-pentane. 8 crystallizes in a monoclinic crystal system with a space group of P21/n (Figure 9). The ylidic C−Ni bond distances C1−Ni1A 2.0909(16) Å and C1−Ni2 2.0629(15) Å are between the C−M distances of the palladium and the titanium complexes 4 and 5. Again the Ni−Ni distance is 2.4881(3) Å, which is almost twice the covalent radius of Ni (1.24(4) Å).43 It is obvious that the smaller atomic radius of nickel and the shorter Ni−Ni bond in comparison to Mo−Mo45 would lead to too much strain if a coordination mode of higher symmetry similar to that of 7 would be formed. Again the bridging two-electron CO ligand is unsymmerically bridging the two Ni atoms: Ni1A−C37 1.803(2) Å is distinctly shorter than Ni2−C37 2.236(2) Å.

PdCl]Cl (4) and [(CDPPy2)TiCl3] (5). The Cr−N1 and Cr− N2 distances are 2.166(2) and 2.157(2) Å, respectively. The X-ray structure is supported by IR spectroscopy, where the IR spectrum (see Figure S-12 in the Supporting Information) shows three characteristic vibrations bands at 1734, 1776, and 1882 cm−1. This strongly agrees with DFT calculations performed at the PBE-D3(BJ)/def2-TZVPP level of theory. The calculations suggest two asymmetric stretching modes at 1836 and 1870 cm−1 and one symmetric stretching vibration at 1917 cm−1. The vibration modes can be found in Figure S-14 in the Supporting Information. Interestingly the asymmetric CO stretching vibrations are shifted to lower wavenumbers in comparison to [Cr(CO)6] (2003 cm−1),40 although the two pyridyl fragments are reasonably good π acceptor ligands. This indicates the strong σ-donor and potential π-donor ability of the carbodiphosphorane 1 pushing electron density into the d orbitals of the metal. Surprisingly, when 1 is reacted with the corresponding [Mo(CO)3(NCMe)3] in THF, a dinuclear carbonyl complex with one bridging carbonyl and one bridging carbon of the double ylide is formed. Both ylidic carbon lone pairs and pyridyl ligands prefer to bind to two different molybdenum atoms. The crystal structure of [(CDPPy2)Mo(CO)3(μCO)Mo(CO)3] (7) is displayed in Figure 8. 7 crystallizes in

Figure 8. X-ray crystal structure of [(CDPPy2)Mo(CO)3CO)Mo(CO)3] (7). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability.

the orthorhombic crystal system in space group Pbca. Each molybdenum atom is pseudo-octahedrally coordinated. Due to the larger atom radius and coordination number 4 at the ylidic carbon, the C1−Mo1 and C1−Mo2 distances of 2.355(4) and 2.383(4) Å are significantly larger in comparison to those in the chromium complex; consequently, both CO ligands trans to the ylidic carbon acting here as a 2σ four-electron donor have longer Mo−C and smaller C−O bond distances: O5− C46 1.171(5) Å and O6−C42 1.170(5) Å. The bridging carbonyl ligand is asymmetrically bonded as a two-electron donor with distances Mo1−C40 2.131(5) Å and Mo2−C40 2.370(4) Å. The shorter distance is only marginally longer in comparison to a terminal CO in a Mo(CO)4 complex: e.g., 2.031(15) Å.41 The deviation from the highest possible molecular symmetry is due to the constraints of the ligand backbone and is further illustrated by the different torsion angles N1−C19−P1−C1 36.8° and N2−C2−P2−C1 26.1°. The reaction mechanism toward formation of a dinuclear instead of a mononuclear complex might be compared with that discussed in the formation of [Et4N]2[Mo2(CO)7(μ-1,2E


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127.5(3)°. In complex 9, the angle Cl1−Co−Cl2 of 118.83(7)° is significantly larger than in 10 with Cl1−Mn− Cl2 107.25(2)°. At the same time C1−Co distance of 2.015(6) Å in 10 is much shorter than the C1−Mn distance of 2.184(1) Å in 9. The same trend is observed for the corresponding M− Cl distances. This is explained by the effective ionic radii of high-spin d7-Co2+ and d5-Mn2+ ions (74.5 pm vs 83 pm).39 Figure 11 shows the X-band powder EPR spectra of 9 and 10 at 4 K. The X-band EPR spectrum of the powder of 9 shows a surprisingly strong half-field signal at g = 4.0, even at room temperature (not shown here). The half-field signal is also strong when the frozen solution is measured. Furthermore, the spectrum indicates the beginning evolution of six hyperfine lines at the positive and negative half of the signal. The g = 2.0 signal also shows the beginning resolution into six hyperfine lines, but with broader line width. There is no certain evidence of resolved fine structure splitting of the S = 5/2 spin system, although a tentative simulation suggests upper limits of 13 and 1.4 mT for D and E, respectively (simulation not shown here). Due to strong intermolecular interaction the spectrum of the powder of 10 is broadened. When a 3 mmol/L solution is frozen, the spatial isolated molecules show nicely resolved g values (gx = 6.06, gy = 2.91, gz = 1.68). An extra unidentified signal appears between gx and gy but does not disturb the extraction of g values. No signal could be detected at room temperature in liquid solution. The g values are typical for a Co(II) high-spin S = 3/2 system in a lower symmetry environment.46

Figure 9. X-ray crystal structure of [(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability.

At the same time the CO group is slightly bent away from the plane that is created by C1−Ni1A−Ni2. This is illustrated by the torsion angle C1−Ni1A−Ni2−C37 (160.5°). The P1− C1−P2 angle of 119.23(9)° is extremely small. Similarly to the IR spectrum of 8, the calculated spectrum and the experimental spectrum diverge. While experimentally two weaker bands at 1996 and 1933 cm−1 are observed, DFT calculations suggest four bands at 1986, 1947, 1940, and 1868 cm−1. However, when a Gaussian line shape is adjusted to the calculated bands, only two broader bands can be observed and they match the shape of the experimental spectrum. The vibration modes and the calculated spectrum are displayed in Figure S-20 in the Supporting Information. While 8 fulfills the 18-valence-electron rule, the two paramagnetic complexes 9 and 10 with a weaker ligand field were selected as target model complexes. The reaction of 1 with MnCl2 and CoCl2 in THF leads to greenish-yellow [(CDPPy2)MnCl2] (9) and yellow [(CDPPy2)CoCl2] (10), respectively. Single crystals were obtained from DCM and pentane. Both compounds turned out to be structurally related but not isostructural (Figure 10). 9 crystallizes in a monoclinic

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CONCLUSION

We isolated and characterized CDPPy2 (1), a highly versatile N,C,N pincer ligand based on a central carbodiphosphorane four-electron-donor functionality and two pyridyl units. The base form of this neutral and electronically flexible six- or eightelectron donor was characterized by means of its XRD structure, DFT calculations, and NMR spectroscopy, including simulation of its higher order coupling pattern. The availability of a carbon lone pair of π symmetry next to a very strong σdative bond in a mononuclear pincer configuration is a unique feature of 1, which differs from ordinary NHC-based carbon pincer ligands. This feature makes this type of ligand attractive for applications such as stabilization of higher oxidation states of the central metal atoms as well as for catalytic applications: e.g., replacing pincers with central amido bonds of similar σ,πdonor characteristics. The fundamental coordination modes of 1 were evaluated by means of XRD structural analyses in a representative set of metal complexes of different geometic and electronic metal configurations, including square-planar (d8) [(CDPPy2)PdCl]Cl (4), octahedral (d1) mer-[(CDPPy2)TiCl3] (5), and (ls-d6) fac-[(CDPPy2)Cr(CO)3] (6) as well as trigonal-bipyramidal (hs-d5) [(CDPPy2)MnCl2] (9) and (hs-d7) [(CDPPy2)CoCl2] (10) complexes. Characterization of the unprecedented dinuclear carbonyl complexes with bridging carbonyl and bridging carbone ligands κ3-N,C,N[(CDPPy2)Mo(CO)3(μ-CO)Mo(CO)3] (7) and κ2-N,C[(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8) demonstrate the potential of this ligand beyond the scope of its pincer type characteristicsas a template to bridge two metals in close proximity to each other. All of these perspectives will be further explored in the future.

Figure 10. X-ray crystal structures of [(CDPPy2)MnCl2] (9) and [(CDPPy2)CoCl2] (10). Hydrogen atoms and solvent molecules have been omitted for clarity; thermal ellipsoids are given at 50% probability.

crystal system with a space group of P21/n as yellow needles and four units in the elemental cell, whereas 10 crystallizes in a triclinic crystal system with crystallographic point group of P1̅ and two units in the elemental cell. Due to the ligand constraints, both molecular structures adopt a slightly distorted trigonal bipyramidal configuration with axial pyridine and equatorial chlorido and double-ylide ligands. In both complexes the sum of the equatorial angles is 360°. Both P− C1−P angles are essentially the same: 9, 127.7(1)°; 10, F


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Figure 11. X-band powder EPR spectra of [(CDPPy2)MnCl2] (9) (left) measured at 4 K and a microwave power of 40 dB (0.03 mW) for the powder (black) and 46 dB (7.5 mW) for the frozen solution (red) and of [(CDPPy2)CoCl2] (10) (right) measured at 4 K and a microwave power of 28 dB (0.47 mW) for the powder (black) and 40 dB (0.03 mW) for the frozen solution (red, simulation blue).

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66% yield (63.94 g, 242.9 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ −3.6 ppm. 1H NMR (CCl2D2, 300 MHz): δ 8.73 (d, JH,H = 4.3 Hz, 1H), 7.56 (tt, JH,H = 7.7, 1.9 Hz, 1H), 7.42−7.32 (m, 10H), 7.20−7.14 (m, 10H), 7.07 (dd, JH,H = 7.7, 0.7 Hz, 1H) ppm. 13C NMR (CCl2D2, 75 MHz): δ 164.2 (d, JC,P = 3.6 Hz), 150.5 (d, JC,P = 12.5 Hz), 136.4 (d, JC,P = 10.7 Hz), 135.9, 134.5 (d, JC,P = 19.8 Hz), 129.2, 128.8 (d, JC,P = 7.3 Hz), 128.1 (d, JC,P = 15.5 Hz), 122.3 ppm. APCI-HRMS: m/z 264.0936 [M + H]+. Synthesis of [(CDPPy2)Cl]Cl (3).

EXPERIMENTAL SECTION

All reactions were carried out under an inert atmosphere using standard Schlenk techniques. Air- or moisture-sensitive substances were stored in a nitrogen-flushed glovebox. Solvents were purified according to common literature procedures47 and stored under an inert atmosphere over molecular sieves (3 or 4 Å). 1H, 13C, and 31P NMR spectra were recorded on a Bruker Avance III HD 250, Avance II 300, Avance III HD 300, or Avance III HD 500 spectrometer. The chemical shift δ is denoted relative to SiMe4 (1H, 13C) or 85% H3PO4 (31P). 1H and 13C NMR spectra were referenced to the solvent signals.48 Multiplicity is abbreviated as follows: s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad). Highresolution mass spectrometry was performed on a Thermo Fisher Scientific LTQ-FT Ultra or a Jeol AccuTOF GCv. instrument and elemental analysis on an Elementar Vario Micro Cube apparatus. IR spectra were recorded in a glovebox on a Bruker Alpha ATR-FT-IR spectrometer. EPR measurements were performed with an X-Band Bruker ESP 300 spectrometer equipped with an Oxford helium cryostat. All measurements were taken below saturation to avoid any distortions. Density functional theory (DFT) using the PBE49,50 functional was performed. Therefore, the def2-TZVPP51−53 basis set was used, employing the resolution-of-identity approximation.54,55 Further D3-dispersion correction56 was considered by applying Becke−Johnson damping.57−60 To verify that the ground states and excited states are minima on the potential energy surface, analytical harmonic vibrational frequency calculations were conducted. Structural optimizations and TD-DFT calculations were performed using Orca 3.0.3.61 The structurally optimized molecules were used for TD-DFT calculations (PBE0-D3/def2-TZVPP), employing the resolution-of-identity approximation for both Coulomb integrals and HF exchange integrals.54,55 Preparation of 2-Pyridyldiphenylphosphine (2). This compound was synthesized by following a modified strategy by Huang et al.62 A 12.46 g portion (731.5 mmol, 2 equiv) of sodium was dissolved in liquid ammonia at −78 °C, and 95.94 g (365.8 mmol, 1 equiv) of triphenylphosphine was added. After the mixture was stirred for 1.5 h, 19.56 g (365.8 mmol, 1 equiv) of ammonium chloride was added. After this mixture was stirred for a further 1 h, a solution of 34.3 mL (365.8 mmol, 1 equiv) of chloropyridine and 60 mL of diethyl ether were added. The mixture was warmed to room temperature and the ammonia allowed to evaporate. The residue was treated with dichloromethane, washed with water, and purified by flash column chromatography over silica gel using dichloromethane/ pentane (1/4) to give 2-pyridiyldiphenylphosphine as a white solid in

3 was synthesized by a strategy related to that of Appel et al.63 A 63.94 g portion (242.8 mmol, 1.5 equiv) of 2-pyridyldiphenylphosphine was dissolved in 140 mL of dichloromethane, and 15.6 mL (153.8 mmol, 1 equiv) of CCl4 was added. The solution was stirred for 8 days at room temperature. The resulting dark solution was treated with 14.1 mL (72.1 mmol, 1 equiv) of 1,2-epoxybutane, and the volume of the reaction mixture was reduced to one-third. After the addition of 80 mL of diethyl ether a white precipitate was formed, which was collected, washed with diethyl ether several times, and dried under vacuum. The phosphonium salt [(CDPPy2)Cl]Cl was collected as a colorless solid in 98% (48.2 g, 79.08 mmol) yield. 31 1 P{ H} NMR (CCl2D2, 101 MHz): δ −19.17 ppm. 1H NMR (CCl2D2, 300 MHz): δ 8.86 (d, JH,H = 3.7 Hz, 2H), 7.42−7.32 (m, 10H), 7.68 (t, JH,H = 3.7 Hz, 4H) 7.55−7.42 (m, 12H) ppm. 13C NMR (CCl2D2, 75 MHz): δ 151.4 (t, JC,P = 9.8 Hz), 148.8, 137 (t, JC,P = 5.0 Hz), 134.5 (t, JC,P = 4.9 Hz), 133.8, 130.5 (t, JC,P = 12.2 Hz), 129.3 (t, JC,P = 6.4 Hz), 126.8 122.9 (d, JC,P = 93.5 Hz) ppm. APCI-HRMS: m/z 573.1411 [M − Cl]+. Synthesis of sym-Bis(2-pyridyl)tetraphenylcarbodiphosphorane, CDPPy2 (1). 1 was synthesized by a strategy related to that of Appel et al.63 A 20.0 g portion (32.92 mmol, 1 equiv) was suspended in toluene, treated with 8.1 mL (34.84 mmol, 1.1 equiv) of tris(1-pyrrolidyl)phosphine, and heated to 70 °C for 3 h. The suspension was then heated to 105 °C and immediately filtered. The filtrate was cooled to room temperature. The precipitate that formed was recrystallized in toluene and washed with 2 × 10 mL of diethyl ether. The yellow solid was dried in vacuo at 50 °C and collected in a 31% yield (5.56, 10.32 mmol). 31P{1H} NMR (Tol-d8, 202 MHz): δ −5.28 ppm. 31P{1H} NMR (C6D6, 101 MHz): δ −5.59 G


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Organometallics ppm. 1H NMR (Tol-d8, 500 MHz): δ 8.64−8.60 (m, 2H, H6), 8.31 (ddd, JH,H = 0.95, 1.76, 4.70 Hz, 2H, H3), 7.98−7.91 (m, 8H, H8), 7.10−7.05 (m, 2H, H5), 7.01−6.97 (m, 12H, H9, H10), 6.54 (dddd, JH,H = 1.28, 2.50, 4.69, 7.31 Hz, 2H, H4) ppm. 1H NMR (C6D6, 300 MHz): δ 8.69 (m, 2H, H6), 8.35 (m, 2H, H3), 8.06 (m, 8H, H8), 7.01 (m, 14H, H5, 12H, H9, H10), 6.50 (m, 2H, H4) ppm. 13C NMR (Tol-d8, 125 MHz): δ 162.3−160.7 (m, C2), 148.9 (t, JC,P = 9.2 Hz, C3), 138.3 (dd, JC,P = 44.2, 91.3 Hz, C7), 134.9 (t, JC,P = 4.7 Hz, C5), 133.0 (t, JC,P = 5.0 Hz, C8), 129.1 (C10), 128.2 (C6), 127.6 (t, JC,P = 6.0 Hz, C9), 122.9 (C4), 12.1 (t, JC,P = 114.5 Hz, C1) ppm. 13C NMR (C6D6, 75 MHz): δ 162.3−160.6 (m, C2), 149.0 (t, JC,P = 9.3 Hz, C3), 138.6−137.1 (m, C7), 135.0 (m, C5), 133.0 (t, JC,P = 5.0 Hz, C8), 129.4 (C10), 128.8 (t, JC,P = 11.1 Hz , C6), 127.7 (t, JC,P = 7.8 Hz, C9), 123.0 (C4), 12.1 (t, JC,P = 113.6 Hz, C1) ppm. APCIHRMS: m/z 539.1820 [M-H]+. Elem. anal. (%) found C, 77.47; H, 5.269; N, 5.21; C35H28N2P2 requires C, 78.06; H, 5.24; N, 5.20. IR (cm−1): 3037 w, 1568 w, 1476 w, 1433 w, 1417 w, 1248 m, 1223 m, 1172 m, 1095 m, 1023 m, 988 m, 779 m, 741 m, 690 s, 617 w, 520 s, 493 s, 436 m. Synthesis of [(CDPPy2)PdCl]Cl (4). A 65 mg portion (0.12 mmol, 1 equiv) of 1 was dissolved in 5.0 mL of THF and treated with 84 mg (0.12 mmol, 1 equiv) of bis(triphenylphosphine)palladium(II) dichloride at room temperature for 6 h. The solvent was then evaporated, and the precipitate was washed with 5 × 10 mL of diethyl ether and 3 × 10 mL of pentane. The dark green residue was dried in vacuo and collected in a 96% yield (82 mg, 0.12 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ 31.58 (s) ppm. 1H NMR (CCl2D2, 300 MHz): δ 9.81 (dd, JH,H = 1.1, 5.7 Hz, 2H, H3), 8.16 (ddt, JH,H = 1.8, 3.9, 7.8 Hz, 2H, H3), 7.66−7.58 (m, 8H, H4, H6, H10), 7.54−7.50 (m, 8H, H8), 7.45−7.42 (m, 8H, H9) ppm. 13C NMR (C6D6, 75 MHz): δ 166.2−165.0 (m, C2), 157.4 (t, JC,P = 5.0 Hz, C3), 140.5 (t, JC,P = 5.0 Hz, C5), 134.3 (s, C10), 133.0 (t, JC,P = 5.6 Hz, C8), 130.1 (t, JC,P = 6.2 Hz, C9), 129.8 (t, JC,P = 10.6 Hz, C6), 129.1 (s, C4), 127.3−126.3 (m, C7), 11.5 (t, JC,P = 102.1 Hz, C1) ppm. LIFDIHRMS: m/z 679.04586 [M − Cl]+. Anal. Found: C, 58.34; H, 4.02; N, 3.63. Calcd for C35H28N2P2PdCl2: C, 58.72; H, 3.94; N, 3.91. Synthesis of [(CDPPy2)TiCl3] (5). A 100 mg portion (0.18 mmol, 1 equiv) of 1 was dissolved in 5.0 mL of THF and treated with 68 mg (0.18 mmol, 1 equiv) of trichlorotris(tetrahydrofuran)titanium at room temperature for 15 h. The solvent was then evaporated, and the precipitate was washed with 2 × 10 mL of diethyl ether and 2 × 10 mL of pentane. The dark green residue was dried in vacuo and collected in a 53% yield (68 mg, 0.10 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ 18.24 (s) ppm. 1H NMR (CCl2D2, 300 MHz): δ 10.68 (m, 1H), 8.56 (d, JH,H = 4.1 Hz, 1H), 7.86−7.76 (m, 1H), 7.69−7.55 (m, 6H), 7.49−7.38 (m, 10H), 7.09 (s, 6H), 6.75 (t, JH,H = 7.3 Hz, 1H) ppm. 13C NMR (CCl2D, 75 MHz): δ 152.2 (d, JC,P = 1.6 Hz), 151.2 (m), 141.4 (s), 137.9 (t, JC,P = 5.0 Hz), 133.7 (t, JC,P = 5.1 Hz), 133.6 (s), 129.6 (t, JC,P = 6.2 Hz), 127.0 (s), 126.25 (m) ppm. Anal. Found: C, 55.36; H, 4.25; N, 3.95. Calcd for C35H28N2P2TiCl3: C, 56.68; H, 4.07; N, 4.04. Synthesis of [(CDPPy2)Cr(CO)3] (6). A 100 mg portion (0.18 mmol, 1 equiv) of 1 was dissolved in 5.0 mL of THF and treated with 48 mg (0.18 mmol, 1 equiv) of [Cr(CO)3(NCMe)3] at room temperature for 15 h. The solvent was then evaporated, and the precipitate was washed with 2 × 10 mL of diethyl ether and 2 × 10 mL of pentane. The dark red residue was dried in vacuo and collected in a 78% yield (98 mg, 0.10 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ 6.97 (s) ppm. 1H NMR (CCl2D2, 300 MHz): δ 9.67 (d, JH,H = 5.3 Hz, 2H), 8.20 (s, 4H), 7.63 (t, JH,H = 7.0 Hz, 2H), 7.57 (s, 6H), 7.48 (d, JH,H = 7.3 Hz, 2H), 7.28 (t, JH,H = 6.4 Hz, 2H), 7.06 (s, 2H), 6.82 (s, 4H), 6.68 (s, 4H) ppm. 13C NMR (CCl2D, 75 MHz): δ 154.4 (m), 150.7 (m), 134.6 (m), 132.8 (m), 131.8 (m), 130.9 (m), 130.4 (m), 128.0 (m), 126.8 (t, JC,P = 9.6 Hz), 124.6 (s), 16.4 (t, JC,P = 107.3 Hz) ppm. Anal. Found: C, 67.90; H, 4.23; N, 4.01, Calcd for C38H28N2P2CrO3: C, 67.66; H, 4.18; N, 4.15. IR (cm−1): 3072 w, 2963 w, 1882 s, 1776 s, 1734 s, 1587 m, 1480 m, 1436 m, 1257 s, 1102 m, 1068 m, 1026 m, 999 m, 773m, 754 s, 740 s, 728 s, 710 m, 692 m, 665 m, 640 m, 550 s, 515 m, 490 m.

Synthesis of [(CDPPy2)Mo(CO)3(μ-CO)Mo(CO)3] (7). A 60 mg portion (0.11 mmol, 1 equiv) of 1 was dissolved in 5.0 mL of THF and treated with 67 mg (0.22 mmol, 2 equiv) of [Mo(CO)3(NCMe)3] at room temperature for 15 h. The solvent was then evaporated, and the precipitate was washed with 2 × 10 mL of diethyl ether and 2 × 10 mL of pentane. The brown residue was dried in vacuo and collected in a 76% yield (78 mg, 0.09 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ 6.60 (s) ppm. 1H NMR (CCl2D2, 300 MHz): δ 9.49 (d, JH,H = 5.0 Hz, 2H), 8.16 (d, JH,H = 4.4 Hz, 4H), 7.70 (t, JH,H = 8.3 Hz, 2H), 7.56 (s, 6H), 7.52 (t, JH,H = 8.4 Hz, 2H), 7.30 (t, JH,H = 5.7 Hz, 2H), 7.10 (t, JH,H = 6.6 Hz, 2H), 6.85 (t, JH,H = 6.8 Hz, 4H), 6.76 (t, JH,H = 5.9 Hz, 4H) ppm. 13C NMR (CCl2D, 75 MHz): δ 161.8 (m), 155.0 (s), 151.1 (t, JC,P = 9.7 Hz), 133.8 (t, JC,P = 5.2 Hz), 133.5 (t, JC,P = 5.5 Hz), 132.6 (t, JC,P = 5.0 Hz), 129.6 (t, JC,P = 6.3 Hz), 128.8 (t, JC,P = 5.5 Hz), 128.0 (t, JC,P = 9.8 Hz), 16.8 (t, JC,P = 107.2 Hz) ppm. Anal. Found: C, 53.60; H, 2.94; N, 3.38. Calcd for C40H28N2P2MoO5: C, 54.44; H, 3.05; N, 3.02. IR (cm−1): 2962 m, 2905 w, 1886 m, 1776 m, 1741 m, 1571 w, 1579 w, 1479 w, 1435 w, 1257 s, 1084 s, 1011 s, 952 m, 864 m, 791 s, 739 m, 726 m, 708 s, 690 m, 618 w, 553 m, 506 m, 490 m, 441 m, 405 w. Synthesis of [(CDPPy2)Ni(CO)(μ-CO)Ni(CO)2] (8). A 60 mg portion (0.11 mmol, 1 equiv) of 1 was dissolved in 5.0 mL THF and treated with 0.03 mL (0.22 mmol, 2 equiv) of nickel tetracarbonyl at −78 °C. The reaction mixture was warmed to room temperature and stirred for 16 h. Additionally the mixture was heated at 35 °C for 2 h. The solvent was then evaporated, and the precipitate was washed with 5 × 10 mL of diethyl ether and 3 × 10 mL of pentane. The dark brown residue was dried in vacuo and collected in a 51% yield (44 mg, 0.09 mmol). 31P{1H} NMR (CCl2D2, 101 MHz): δ 34.20 (s) ppm. 1H NMR (CCl2D2, 300 MHz): δ 8.78 (d, JH,H = 4.5 Hz, 1H), 7.91 (t, JH,H = 8.6 Hz, 1H), 7.71 (ddt, JH,H = 1.8, 3.0, 7.6 Hz, 2H), 7.59−7.43 (m, 11H), 7.30 (t, JH,H = 5.7 Hz, 2H), 6.51 (d, JH,H = 6.7 Hz, 12H) ppm. 13C NMR (CCl2D, 75 MHz): δ 157.2 (m), 150.7 (d, JH,H = 19.1 Hz), 136.8 (d, JH,H = 9.1 Hz), 134.3 (d, JH,H = 14.4 Hz), 132.5(d, JH,H = 9.2 Hz), 129.6 (s), 123.9 (d, JH,H = 11.4 Hz), 128.9 (d, JH,H = 11.9 Hz), 128.4 (d, JH,H = 9.5 Hz), 125.9 (s) ppm. Anal. Found: C, 59.58; H, 3.86; N, 3.77. Calcd for C38H28N2P2NiO4: C, 60.99; H, 3.68; N, 3.65. IR (cm−1): 3051 w, 1996 w, 1933 w, 1657 w, 1630 w, 1539 m, 1482 w, 1434 m, 1353 m, 1284 w, 1160 m, 1119 m, 1097 m, 1046 m, 1016 m, 839 w, 740 m, 692 s, 640 w, 617 w, 539 s, 498 w. Synthesis of [(CDPPy2)MnCl2] (9). A 100 mg portion (0.18 mmol, 1 equiv) of 1 was dissolved in 5.0 mL o THF and treated with 21.2 mg (0.18 mmol, 1 equiv) of manganese(II) chloride at room temperature for 14 h. The solvent was then evaporated, and the precipitate was washed with 2 × 10 mL of diethyl ether and 2 × 10 mL of pentane. The yellow residue was dried in vacuo and collected in a 66% yield (82 mg, 0.12 mmol). LIFDI-HRMS: m/z 663.04739 [M]+. Anal. Found: C, 63.48; H, 4.82; N, 4.06. Calcd for C35H28N2P2MnCl2: C, 63.27; H, 4.25; N, 4.22. Synthesis of [(CDPPy2)CoCl2] (10). A 100 mg portion (0.18 mmol, 1 equiv) of 1 was dissolved in 5.0 mL of THF and treated with 21.9 mg (0.18 mmol, 1 equiv) of cobalt(II) chloride at room temperature for 14 h. The solvent was then evaporated, and the precipitate was washed with 2 × 10 mL of diethyl ether and 2 × 10 mL of pentane. The dark green residue was dried in vacuo and collected in a 95% yield (118 mg, 0.17 mmol). LIFDI-HRMS: m/z 667.04768 [M]+. Anal. Found: C, 61.34; H, 4.28; N, 4.00. Calcd for C35H28N2P2CoCl2: C, 62.89; H, 4.22; N, 4.19.

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ASSOCIATED CONTENT

S Supporting Information *

CThe Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.9b00489. Crystal data tables of 1 (1940090), 4 (1940127), 5 (1940135), 6 (1940086), 7 (1940125), 8 (1940128), 9 H


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Morales-Morales, D., Jensen, C. M., Eds.; Elsevier Science: Amsterdam, 2007; Chapter 15, pp 347−355. (13) Kubo, K.; Okitsu, H.; Miwa, H.; Kume, S.; Cavell, R. G.; Mizuta, T. Carbon(0)-Bridged Pt/Ag Dinuclear and Tetranuclear Complexes Based on a Cyclometalated Pincer Carbodiphosphorane Platform. Organometallics 2017, 36, 266−274. (14) Petz, W.; Neumüller, B.; Klein, S.; Frenking, G. Syntheses and Crystal Structures of [Hg{C(PPh3)2}2][Hg2I6] and [Cu{C(PPh3)2}2] I and Comparative Theoretical Study of Carbene Complexes [M(NHC)2] with Carbone Complexes [M{C(PH3)2}2] (M = Cu+, Ag+, Au+, Zn2+, Cd2+, Hg2+). Organometallics 2011, 30, 3330−3339. (15) Petz, W.; Neumüller, B. New Platinum Complexes with Carbodiphosphorane as Pincer Ligand via Ortho Phenyl Metallation. Polyhedron 2011, 30, 1779−1784. (16) Marrot, S.; Kato, T.; Gornitzka, H.; Baceiredo, A. Cyclic Carbodiphosphoranes: Strongly Nucleophilic σ-Donor Ligands. Angew. Chem., Int. Ed. 2006, 45, 2598−2601. (17) Stallinger, S.; Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P. Novel Route to Carbodiphosphoranes Producing a New P,C,P Pincer Carbene Ligand. Chem. Commun. 2007, 510−512. (18) Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P. Synthesis and Structure of the First Heterodinuclear PCP−Pincer− CDP Complex with a Pd−Au d8−d10 Pseudo-Closed-Shell Interaction. Organometallics 2009, 28, 6617−6620. (19) Reitsamer, C.; Schuh, W.; Kopacka, H.; Wurst, K.; Ellmerer, E. P.; Peringer, P. The First Carbodiphosphorane Complex with Two Palladium Centers Attached to the CDP Carbon: Assembly of a Single-Stranded Di-Pd Helicate by the PCP Pincer Ligand C(dppm)2. Organometallics 2011, 30, 4220−4223. (20) Reitsamer, C.; Stallinger, S.; Schuh, W.; Kopacka, H.; Wurst, K.; Obendorf, D.; Peringer, P. Novel Access to Carbodiphosphoranes in the Coordination Sphere of Group 10 Metals: Template Synthesis and Protonation of PCP Pincer Carbodiphosphorane Complexes of C(dppm)2. Dalton Trans. 2012, 41, 3503−3514. (21) Reitsamer, C.; Hackl, I.; Schuh, W.; Kopacka, H.; Wurst, K.; Peringer, P. Gold(I) and Gold(III) Complexes of the [CH(dppm)2]+ and C(dppm)2 PCP Pincer Ligand Systems. J. Organomet. Chem. 2017, 830, 150−154. (22) Maser, L.; Herritsch, J.; Langer, R. Carbodiphosphorane-Based Nickel Pincer Complexes and Their (de)Protonated Analogues: Dimerisation, Ligand Tautomers and Proton Affinities. Dalton Trans. 2018, 47, 10544−10552. (23) Maser, L.; Vondung, L.; Langer, R. The ABC in Pincer Chemistry − From Amine- to Borylene- and Carbon-Based PincerLigands. Polyhedron 2018, 143, 28−42. (24) Alcarazo, M.; Radkowski, K.; Mehler, G.; Goddard, R.; Fürstner, A. Chiral Heterobimetallic Complexes of Carbodiphosphoranes and Phosphinidene-Carbene Adducts. Chem. Commun. 2013, 49, 3140−3142. (25) Su, W.; Pan, S.; Sun, X.; Wang, S.; Zhao, L.; Frenking, G.; Zhu, C. Double Dative Bond between Divalent Carbon(0) and Uranium. Nat. Commun. 2018, 9, 4997−5004. (26) Hardy, G. E.; Zink, J. I.; Kaska, W. C.; Baldwin, J. C. Structure and Triboluminescence of Polymorphs of Hexaphenylcarbodiphosphorane. J. Am. Chem. Soc. 1978, 100, 8001−8002. (27) Vincent, A. T.; Wheatley, P. J. Crystal Structure of Bis(triphenylphosphoranylidene)methane [Hexaphenylcarbodiphosphorane, Ph3P:C:PPh3]. J. Chem. Soc., Dalton Trans. 1972, 617−622. (28) Plikhta, A.; Pöthig, A.; Herdtweck, E.; Rieger, B. Toward New Organometallic Architectures: Synthesis of Carbene-Centered Rhodium and Palladium Bisphosphine Complexes. Stability and Reactivity of [PCBImPRh(L)][PF6] Pincers. Inorg. Chem. 2015, 54, 9517−9528. (29) Teci, M.; Brenner, E.; Matt, D.; Gourlaouen, C.; Toupet, L. Directional Properties of Fluorenylidene Moieties in Unsymmetrically Substituted N-Heterocyclic Carbenes. Unexpected CH Activation of a Methylfluorenyl Group with Palladium. Use in Palladium Catalysed Suzuki−Miyaura Cross Coupling of Aryl Chlorides. Dalton Trans. 2014, 43, 12251−12262.

(1940108), and 10 (1940109) and DFT calculations and IR spectra of 6−8 (PDF) Cartesian coordinates of calculated structures (XYZ) Accession Codes

CCDC 1940086, 1940090, 1940108−1940109, 1940125, 1940127−1940128, and 1940135 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 for J.S.: [email protected]. ORCID

Jörg Sundermeyer: 0000-0001-8244-8201 Notes

The authors declare no competing financial interest.

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REFERENCES

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Synthesis and Characterization of a N,C,N-Carbodiphosphorane

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