Ligand-Enforced Switch of the Coordination Mode in Low-Valent

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

Ligand-Enforced Switch of the Coordination Mode in Low-Valent Group 6 Carbonyl Complexes Containing Pyrimidine-Based Bisphosphines Gerald Tomsu,† Matthias Mastalir,† Ernst Pittenauer,‡ Berthold Stöger,§ Günter Allmaier,‡ and Karl Kirchner*,† †

Institute of Applied Synthetic Chemistry, ‡Institute of Chemical Technologies and Analytics, and §X-Ray Center, Vienna University of Technology, Getreidemarkt 9, A-1060 Vienna, Austria S Supporting Information *

ABSTRACT: The reaction of M(CO)6 (M = Cr, Mo, W) with N,N′-bis(diisopropylphosphine)-N,N′-dimethylpyrimidine-4,6-diamines (PymR-iPr) bearing R = Me, Ph, tBu substituents in the 2-position was investigated. The pyrimidine-based bisphosphine ligands with R = Me, Ph reacted with M(CO)6 to yield mononuclear and homobimetallic complexes of the types [M(κ2P,N-PymMe-iPr)(CO)4] and [M(CO)4-μ2-(κ2P,N-PymPh-iPr)M(CO)4], respectively. Heterobimetallic complexes of the type [M1(CO)4-μ2-(κ2P,NPymMe-iPr)M2(CO)4] were obtained by reacting mononuclear complexes [M1(κ2P,N-PymMe-iPr)(CO)4] with 1 equiv of the respective M2(CO)6. Replacing these substituents by a bulky tBu group led to a switch in the coordination mode of the pyrimidine ligand. In the case of chromium, the complex [Cr(κ3P,CH,PPymtBu-iPr)(CO)3] containing an η2-Caryl−H agostic bond was selectively formed and no C−H bond cleavage took place. However, in the case of molybdenum, the reaction led to the formation of an inseparable mixture of the agostic complex [Mo(κ3P,CH,P-PymtBu-iPr)(CO)3] and the hydrido carbonyl complex [Mo(κ3P,C,P-PymtBu-iPr)(CO)3(H)], and with tungsten the hydrido carbonyl complex [W(κ3P,C,P-PymtBu-iPr)(CO)3(H)] was exclusively formed. In the presence of strong bases both complexes could not be deprotonated. In addition, hydride abstraction with Ph3C+PF6− failed. However, treatment of [W(κ3P,C,P-PymtBu-iPr)(CO)3(H)] with Ph3C+PF6− in a benzene/THF mixture resulted in protonation of one of the pyrimidine nitrogen atoms to form two isomeric cationic hydride species. X-ray structures of representative complexes are presented.

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INTRODUCTION Some of the most common types of PCP pincer complexes1 are those where the ligands bear phosphine donors tethered via CH2, O, or NR linkers to an aromatic benzene backbone in the two ortho positions. This architecture allows easy access to a broad variety of structural, electronic, and stereochemical modifications. It is thus not surprising that these types of complexes play an important role in transition-metal chemistry and have received enormous attention over the past decade.2 A common synthetic approach to obtain PCP pincer complexes involves intramolecularly directed C−H bond activation by electron-rich low-valent late-transition-metal complexes3 followed by oxidative addition of the agostic C−H bond of the P(CH)P ligand, which may lead to the formation of PCP (hydride) complexes. We have recently shown4 that in the case of Cr and Mo hexacarbonyl complexes C−H bond cleavage did not occur and complexes featuring an η2-Caryl−H agostic bond were formed. In the case of W a direct cyclometalation took place which led to the formation of the first W PCP complex, a hydrido carbonyl W(II) complex [W(κ3P,C,P-PCPNMe-iPr)(CO)3H] (Scheme 1). It has to be noted that group 6 PCP pincer complexes are scarce.2p DFT mechanistic studies © XXXX American Chemical Society

Scheme 1. C−H Bond Coordination versus C−H Bond Cleavage

indicate that the M−H bond strength grows in the order Cr−H < Mo−H < W−H, explaining the thermodynamic preference for the hydride complex only in the case of W, while the formation of Cr and Mo PCP hydride complexes is still endergonic.4 In an attempt to also obtain Cr and Mo PCP complexes with the tridentate ligand being bound in a κ3P,C,P fashion (Chart 1, type I), we replaced benzene by pyrimidine-based bisphosphines. This ligand system is, more electron deficient Received: April 2, 2018

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DOI: 10.1021/acs.organomet.8b00192 Organometallics XXXX, XXX, XXX−XXX

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Organometallics Chart 1. Coordination Modes of Pyrimidine-Based Bisphosphines

Scheme 3. Synthesis of Mono- and Binuclear Complexes with Pyrimidine-Based Bisphosphines

than the benzene-based pincer, which may render also the C− H bonds more active.5 In addition, the pyrimidine moiety can be easily functionalized in the 2-position and, as a multifunctional ligand, allows for additional binding modes as shown in Chart 1. We describe here the reaction of the hexacarbonyl complexes of Cr, Mo, and W with N,N′-bis(diisopropylphosphine)-N,N′-dimethylpyrimidine-4,6-diamines (PymR-iPr) bearing R = Me, Ph, tBu substituents in the 2position. X-ray structures of representative complexes are presented.

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RESULTS AND DISCUSSION The new pyrimidine-based PCP ligand precursors 2a−c were prepared by treating the respective 2,6-diaminopyrimidines 1a− c with 1 equiv of nBuLi and PiPr2Cl in THF (Scheme 2). They were obtained in 69−94% isolated yields and fully characterized by a combination of ESI MS and NMR spectroscopy.

with 2 equiv of Mo(CO)6. Heterobimetallic complexes were obtained by reacting mononuclear complexes with 1 equiv of the respective hexacarbonyl complex. For instance, upon treatment of 3b with 1 equiv of Cr(CO)6 and W(CO)6, respectively, the heterobimetallic complexes [Cr(CO)4-μ2(κ2P,N-PymMe-iPr)Mo(CO)4] (7) and [Cr(CO)4-μ2-(κ2P,NPymMe-iPr)W(CO)4] (8) were isolated in 55 and 68% yields (Scheme 3). All complexes were fully characterized by a combination of 1H, 13C{1H}, and 31P{1H} NMR spectroscopy, IR, ESI MS, and elemental analysis. A representative negative ion ESI MS of the heterobimetallic complex 8 in CH3CN showing the calculated and measured isotopic pattern of the anionic fragment [M + Cl]− is depicted in Figure 1. Additionally, complexes 3a,b and 5 were characterized by Xray crystallography. Structural views are shown in Figures 2−4 with selected bond distances and angles reported in the captions.

Scheme 2. Synthesis of Ligands 2a−c

A suspension of the hexacarbonyl complexes M(CO)6 (M = Cr, Mo, W) and 1 equiv of the pyrimidines 2a−c in CH3CN was placed in a sealed glass tube and stirred for 16 h at 130 °C. In the case of 2a, after workup, the octahedral tetracarbonyl complexes [Cr(κ2P,N-PymMe-iPr)(CO)4] (3a), [Mo(κ2P,NPymMe-iPr)(CO)4] (3b), and [W(κ2P,N-PymMe-iPr)(CO)4] (3c) were isolated in 46−57% isolated yields (Scheme 3). The pyrimidine ligand is coordinated in κ2P,N fashion and features one pendant phosphine arm (Chart 1, type III). There was no evidence for a cyclometalation reaction to yield complexes with κ3P,C,P-coordinated pyrimidines. In the case of 2b, the reaction was exemplarily studied with Mo(CO)6 and turned out to be not selective. An inseparable mixture of monoand dinuclear complexes [Mo(κ2P,N-PymPh-iPr)(CO)4] (4) and [Mo(CO)4-μ2-(κ2P,N-PymPh-iPr)Mo(CO)4] (5), respectively, was obtained (Scheme 3). In 5, the κ2P,N-coordinated pyrimidine ligand acts as a bridging ligand between two Mo(CO)4 moieties (Chart 1, type IV). While 4 could not be isolated in pure form, 5 was prepared in 41% isolated yield upon treatment of 2b with 2 equiv of Mo(CO)6. Likewise, the homobimetallic complex [Mo(CO)4-μ2-(κ2P,N-PymMe-iPr)Mo(CO)4] (6) was formed in 37% isolated yield by reacting 2a

Figure 1. Negative ion ESI MS of [Cr(CO)4-μ2-(κ2P,N-PymMeiPr)W(CO)4] (8) in CH3CN showing the calculated and measured isotopic patterns of the anionic adduct ion [M + Cl]−. B

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Organometallics Scheme 4. Synthesis of Complexes 10−13

Figure 2. Structural view of [Mo(κ2P,N-PymMe-iPr)(CO)4] (3b) showing 50% thermal ellipsoids (most H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W1−N1 2.302(3), W1−P1 2.4726(8), W1−C20 2.020(4), W1−C21 1.956(3), W1−C22 1.983(3), W1−C23 2.029(4); P1−W1−N1 74.38(6).

NMR spectroscopy, IR, ESI MS, and elemental analysis. Additionally, complexes 10, 11, and 13 were characterized by X-ray crystallography. An important feature of the 1H NMR spectrum of 10 is the high-field shift of the proton attached to the ipso carbon, giving rise to a triplet at −1.60 ppm. In the 13C{1H} NMR spectra the ipso carbon atom exhibits a triplet at 52.6 (JCP = 6.2 Hz) (Figure 5). Proton-coupled 13C NMR data of 10 reveal a

Figure 3. Structural view of [W(κ2P,N-PymMe-iPr)(CO)4] (3c) showing 50% thermal ellipsoids (most H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W1−N1 2.302(3), W1−P1 2.4726(8), W1−C20 2.020(4), W1−C21 1.956(3), W1−C22 1.983(3), W1−C23 2.029(4); P1−W1−N1 74.38(6).

Figure 5. Section of the 1H−13C HSQC spectrum of 10 in CD2Cl2 exhibiting a cross peak between the agostic H1 and C1 atoms.

relatively small 1JHC coupling constant of 130.9 Hz, in comparison to about 160 Hz for the aromatic C−H bonds in the PymtBu-iPr ligand, which is characteristic for a strong interaction of C−H with the metal.4−13 The three CO ligands give rise to three low-field resonances as triplets centered at 237.0, 227.9, and 226 ppm. The IR of complex 10 exhibits the expected three strong νCO bands at 1945, 1843, and 1814 cm−1. As far as complex 13 is concerned, in the 1H NMR spectrum the hydride resonance appears as a multiplet at −5.07 ppm (−5.14 ppm in 12). The 31P{1H} NMR spectrum gives rise to two doublets centered at 139.0 and 121.7 ppm with a large geminal coupling constant of 83.8 Hz, which is indicative of phosphorus atoms being in mutually trans positions. The tungsten−phosphorus coupling was observed as a doublet satellite due to 183W, 14% abundantce with I = 1/2, superimposed over the dominant singlet. In the 13C{1H} NMR spectrum the most noticeable resonances are two lowfield resonances of the carbonyl carbon atoms trans and cis to the ipso carbon observed as a doublet and a triplet in a 1:2 ratio. The ipso carbon atom gives rise to a singlet at 109.1 ppm. The IR spectrum shows three strong to medium absorption νCO bands of one symmetric and two asymmetric vibration modes, which is typical for a mer CO arrangement. Structural views of 10, 11, and 13 are depicted in Figures 6−8 with selected bond distances given in the caption. The

Figure 4. Structural view of [μ2-(κ2P,N-PymPh-iPr){(Mo(CO)4}2] (5) showing 50% thermal ellipsoids (H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Mo1−N1 2.370(3), Mo1−P1 2.4575(9), Mo1−C25 2.027(3), Mo1−C26 1.954(4), Mo1− C27 2.020(3), Mo1−C28 2.014(3), Mo2−N2 2.376(3), Mo2−P2 2.4557(10), Mo2−C29 2.052(4), Mo2−C30 1.950 (3), Mo2−C31 2.037(5), Mo2−C32 2.015(5); P1−Mo1−N1 75.04(7), P2−Mo2−N2 75.57(7).

Finally, we investigated the reactivity of M(CO)6 toward ligand 2c bearing a tBu substituent in the 2-position. This reaction is markedly different, enforcing a switch in the coordination mode. In the case of Cr, the tricarbonyl complex [Cr(κ3P,CH,P-PymtBu-iPr)(CO)3] (10) was selectively isolated in 43% yield (Chart 1, type II), while with Mo an inseparable mixture of [Mo(κ3P,CH,P-PymtBu-iPr)(CO)3] (11) and the seven-coordinate hydrido carbonyl complex [Mo(κ3P,C,PPymtBu-iPr)(CO)3(H)] (12) was obtained (Scheme 4). Complexes 10 and 11 feature an η2-Caryl−H agostic bond, while 12 and 13 contain metal−C and metal−H σ bonds as a result of an oxidative addition. With the exception of 11 and 12 due to signal overlap, complexes 10 and 13 were fully characterized by a combination of 1H, 13C{1H}, and 31P{1H} C

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(which was located in difference Fourier maps and refined freely) interacts with the Cr and Mo centers (1.85(4) and 1.94(2) Å), which was also evident from the 1H NMR spectra of 10 and 11. It is noteworthy that this hydrogen is severely removed from the aromatic plane by ca. 27(2) and 21(1)° (cf. in related Ru, Rh, and Pd complexes this angle is in the range of 14−30°,6−14 while in Cr, Mo,4 and Co16 it is 32, 28, and 35°, respectively). The C1−H1 bond lengths of 0.90(3) and 1.00(2) Å are in the range observed in X-ray diffraction measurements for unactivated hydrocarbons (e.g., 1.08 Å in C6H6). While the agostic C−H arene bond in several Rh(I) and Co(I) was shown to be acidic and could be readily deprotonated in the presence of even weak bases such as pyridine and NEt3,6a,16 in the case of complex 10, even in the presence of strong bases such as NaH, nBuLi, and KOtBu, no deprotonation was observed to afford the anionic Cr(0) tricarbonyl complex [Cr(κ3P,C,P-PCPNMe-iPr)(CO)3]− (14) (Scheme 5). Likewise, also the hydride carbonyl complex 13

Figure 6. Structural view of [Cr(κ3P,CH,P-PymtBu-iPr)(CO)3]· 0.5CH3CN (10·0.5CH3CN) showing 50% thermal ellipsoids (most H atoms and solvent omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Cr1−P1 2.3432(10), Cr1−P2 2.3331(9), Cr1−C1 2.220(5), Cr1−H1 1.85(4), Cr1−C23 1.799(6), Cr1−C24 1.878(5), Cr1−C25 1.943(4); P1−Cr1−P2 154.89(4), C23−Cr1− C25 156.9(2).

Scheme 5. Attempted Deprotonation of Complexes 11 and 13

Figure 7. Structural view of [Mo(κ3P,CH,P-PymtBu-iPr)(CO)3]· (toluene) (11·toluene) showing 50% thermal ellipsoids (most H atoms and solvent omitted for clarity). Selected bond lengths (Å) and bond angles (deg): Mo1−P1 2.4569(5), Mo1−P2 2.4498(5), Mo1− C1 2.370(2), Mo1−C23 2.006(2), Mo1−C24 1.952(2), Mo1−C25 2.027(2), Mo1−H1 1.94(2); P1−Mo1−P2 151.50(2), C23−Mo1− C25 167.86(8).

did not react with bases. This strongly contrasts with the behavior of the cationic hydride carbonyl complex [W(κ3P,N,PPNP-iPr)(CO)3H]+, where deprotonation took place readily even with the weak base NEt3.17 The nature of the interaction between the W1−C1 and W1−H1 bonds in complex 13 was investigated by means of DFT calculations. The relevant Wiberg indices (WI) indicate a moderately strong W−C bond but a strong W−H bond with WI values of 0.48 and 0.51, respectively. The NPA charge of the hydride H1 is close to zero (0.08), indicating no acidic behavior. Finally, we attempted the abstract the hydride ligand of complex 13 utilizing the trityl cation Ph3C+ (as the PF6− salt). Treatment of 13 with 1 equiv of Ph3C+‑ in benzene did not result in any reaction. On the other hand, if 13 is reacted with 1 equiv of Ph3C+PF6− in benzene/THF (9/1), the formation of the complexes [W(κ 3 P,C,P-Pym H,tBu -iPr)(CO) 3 (H)]PF 6 (16a,b) in a 1/0.3 ratio was observed (Scheme 6). These isomeric complexes were isolated in 94% yield as an inseparable mixture. Surprisingly, instead of hydride abstraction, protonation of one of the pyrimidine N atoms took place. In the 1H NMR spectrum the hydride resonances of the two isomers appear as doublet of doublets at −4.97 and −5.13 ppm, respectively (Scheme 6). The 31P{1H} NMR spectrum shows

Figure 8. Structural view of [W(κ3P,C,P-PymtBu-iPr)(CO)3(H)] (13) showing 50% thermal ellipsoids (most H atoms omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W1−P1 2.4781(7), W1−P2 2.5007(7), W1−C1 2.214(2), W1−C23 2.030(3), W1−C24 1.97(2), W1−C25 2.010(3), W1−H1 1.77(4); P1−W1−P2 149.14(2), C1−W1−C24 158.2(5), C24−W1−H1 56.2(14).

overall geometry about the Cr and Mo centers in 10 and 11 is best described as distorted octahedral, where the three carbonyl ligands and the agostic η2-Caryl−H bond define the equatorial plane and the phosphine moieties the axial positions. The P1− M−P2 and trans-CCO−M−CCO bond angles are 154.87(4) and 156.9(2)° (10), and 151.50(1) and 167.86(8)° (11), respectively. The distance between the ipso carbon and the Cr and Mo atoms is relatively long (2.220(5) and 2.370(2) Å) relative to regular Cr− and Mo−carbon σ bonds (the Cr−C bond in [CrCp(NO)(NiPr2)(CH2SiMe3)] is 2.111(2) Å,14 and the Mo−C bond distance in [Mo(κ3P,C,P-POCOP-tBu)(N)(I)][Na(15-crown-5)] is 2.167(3) Å15). The H(1) atom

Scheme 6. Protonation of Complex 13 and Hydride Region of the 1H NMR Spectrum of Complexes 16a,b

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and KOtBu. Moreover, the reaction of [W(κ3P,C,P-PymtBuiPr)(CO)3(H)] with Ph3C+PF6− in benzene did not result in hydride abstraction, while the same reaction in a benzene/THF mixture resulted in protonation of one of the pyrimidine nitrogen atoms to form two isomeric cationic hydride species.

two sets of doublets centered at 148.8 and 116.8 ppm and at 136.5 and 128.6 ppm, respectively, with typical geminal coupling constants of 83.2 and 83.6 Hz. The positive ion ESI MS of 16 in CH3CN displays the fully intact cationic molecule [M + H]+ at m/z 693.4. In the negative ion mode, the anionic fragment [M − H]− at m/z 691.2 is observed, corresponding to the tricarbonyl W(0) species [W(κ3P,C,P-PymtBu-iPr)(CO)3]−. As yet the source of the proton remains obscure but may stem from THF, as in the absence of this solvent no clean reaction took place.18 It has to be noted that protonation with HBF4· Et2O resulted also in the formation of 16 but also formed intractable materials. The molecular structure of one of the two possible isomers of 16 is depicted in Figure 9 with selected bond distances and angles given in the caption.

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EXPERIMENTAL SECTION

General Information. All manipulations were performed under an inert atmosphere of argon by using Schlenk techniques or in a MBraun inert-gas glovebox. The solvents were purified according to standard procedures.19 Deuterated solvents were purchased from Aldrich and dried over 3 Å molecular sieves. All starting materials are known compounds and were used as obtained from commercial resources. The synthesis of 1a−c and 2a−c is provided in the Supporting Information. 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on Bruker AVANCE-250, AVANCE-400, and AVANCE-600 spectrometers. 1H and 13C{1H} NMR spectra were referenced internally to residual protio solvent and solvent resonances, respectively, and are reported relative to tetramethylsilane (δ 0 ppm). 31P{1H} NMR spectra were referenced externally to H3PO4 (85%) (δ 0 ppm). As reaction vessels 8 mL microwave vials from Biotage or VWR with an aluminum Teflon septum cap were used. All mass spectrometric measurements were performed on an Esquire 3000plus 3D-quadrupole ion trap mass spectrometer (Bruker Daltonics, Bremen, Germany) in positive and negative ion mode by means of electrospray ionization (ESI). Mass calibration was done with a commercial mixture of perfluorinated trialkyltriazines (ES Tuning Mix, Agilent Technologies, Santa Clara, CA, USA). All analytes were dissolved in CH3CN (for positive ion detection) or MeOH/NaCl (for negative ion detection) to form a concentration of roughly 1 mg/mL in order to avoid dehydrogenations of several analytes. Direct infusion experiments were carried out using a Cole Parmer Model 74900 syringe pump (Cole Parmer Instruments, Vernon Hills, IL, USA) at a flow rate of 2 μL/min. Full scan and MS/ MS scans were measured in the range m/z 100−1000 with the target mass set to m/z 800. Further experimental conditions include the following: drying gas temperature, 150 °C; capillary voltage, −4 kV; skimmer voltage, 40 V; octapole and lens voltages, according to the target mass set. Helium was used as buffer gas for full scans and as collision gas for MS/MS scans in the low-energy CID (collision induced dissociation) mode. The activation and fragmentation widths for tandem mass spectrometric (MS/MS) experiments were set to 10−12 Da to cover the entire isotope cluster for fragmentation. The corresponding fragmentation amplitude ranged from 0.3 to 0.8 V in order to keep a low-abundance precursor ion intensity in the resulting MS/MS spectrum. All mass calculations are based on the most abundant isotope for chromium (52Cr), the first abundant isotope of molybdenum (92Mo), and the first abundant isotope for tungsten (182W). Mass spectra were averaged during a data acquisition time of 1−2 min, and one analytical scan consisted of five successive micro scans resulting in 50−100 analytical scans, respectively, for the final mass spectrum. Synthesis. [Cr(κ2P,N-PymMe-iPr)(CO)4] (1). A suspension of 2a (0.15 g, 0.39 mmol) and Cr(CO)6 (0.077 g, 0.35 mmol) in acetonitrile (2 mL) was placed in a sealed microwave glass vial (20 mL) and stirred for 16 h at 130 °C, whereupon a clear solution developed. The reaction mixture was then cooled to room temperature, and the product was obtained as a yellow crystalline material. The solvent was removed under reduced pressure, and the remaining solid was washed twice with n-pentane (10 mL) and dried under vacuum. Yield: 116 mg (54%). Anal. Calcd for C23H38N4O4P2Cr (548.52): C, 50.36; H, 6.98; N, 10.21. Found: C, 50.56; H, 7.06; N, 10.01. 1H NMR (δ, CDCl3, 20 °C): 6.40 (bs, 1H, Pym5), 3.02 (d, J = 1.4 Hz, 3H, CH3), 2.94 (d, J = 2.9 Hz, 3H, CH3), 2.85 (s, 3H, CH3), 2.55 (m, 2H, CHCH3), 2.15 (bs, 2H, CHCH3), 1.40 (dd, J = 17.2, 6.9 Hz, 6H, CHCH3), 1.12−1.06 (m, 12H, CHCH3), 1.02−0.98 (m, 6H, CHCH3). 13C{1H} NMR (δ, CDCl3, 20 °C): 229.3 (d, J = 14.7 Hz, CO), 226.1 (d, J = 2.9 Hz, CO), 220.8 (d, J = 14.0 Hz, CO), 170.4 (Pym2), 167.5 (d, J = 16.3 Hz, Pym4,6), 167.0 (d, J = 22.4 Hz, Pym4,6), 85.1 (d, J = 31.2 Hz, Pym5),

Figure 9. Structural view of [W(κ3P,C,P-PymH,tBu-iPr)(CO)3(H)]PF6 (16) showing 50% thermal ellipsoids (most H atoms and PF6− anion omitted for clarity). Selected bond lengths (Å) and bond angles (deg): W1−C23 2.008(2), W1−C24 2.030(2), W1−C25 2.011(3), W1−C1 2.218(1), W1−P2 2.4914(4), W1−P1 2.4917(5), W1−H1 1.62(2); P1−W1−P2 148.28(1), C25−W1−C1 156.67(9).

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CONCLUSION In the present study, the reaction of the hexacarbonyl complexes of Cr, Mo, and W with N,N′-bis(diisopropylphosphine)-N,N‘-dimethylpyrimidine-4,6-diamines (PymR-iPr) bearing R = Me, Ph, tBu substituents in the 2position was investigated. The objective was to obtain hydrido carbonyl M(II) complexes of the type [M(κ3P,C,P-PymRiPr)(CO)3H]. Instead, the pyrimidine-based bisphosphine ligands bearing Me and Ph substitutents reacted with M(CO)6 to yield mononuclear and homobimetallic complexes of the types [M(κ2P,N-PymMe-iPr)(CO)4] and [M(CO)4-μ2-(κ2P,NPymPh-iPr)M(CO)4], respectively. Even heterobimetallic complexes of the type [M1(CO)4-μ2-(κ2P,N-PymMe-iPr)M2(CO)4] were obtained by reacting mononuclear complexes [M1(κ2P,NPymMe-iPr)(CO)4] with 1 equiv of the respective hexacarbonyl M2(CO)6. Replacing the Me and Ph substituents by the bulky tBu substituent changed the course of the reaction dramatically. In the case of chromium the agostic complex [Cr(κ3P,CH,PPymtBu-iPr)(CO)3] was formed and no C−H bond cleavage took place. In the case of molybdenum, the reaction led to the formation of an inseparable mixture of [Mo(κ3P,CH,P-PymtBuiPr)(CO)3] and the hydrido carbonyl complex [Mo(κ3P,C,PPymtBu-iPr)(CO)3(H)], while with tungsten the hydrido carbonyl complex [W(κ3P,C,P-PymtBu-iPr)(CO)3(H)] was exclusively formed.16 Both complexes could not be deprotonated even in the presence of strong bases such as NaH, nBuLi, E

DOI: 10.1021/acs.organomet.8b00192 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

CD2Cl2, 20 °C): 5.48 (s, 1H, Pym5), 3.30 (s, 3H, CH3), 3.03 (d, J = 2.7 Hz, 6H, NCH3), 2.53−2.46 (m, 4H, CHCH3), 1.34 (dd, J = 18.4, 6.9 Hz, 12H, CHCH3), 1.12 (dd, J = 14.8, 7.0 Hz, 12H, CHCH3). 13 C{1H} NMR (δ, CD2Cl2, 20 °C): 222.2 (d, J = 8.6 Hz, CO), 214.7 (CO), 214.5 (CO) 209.4 (d, J = 9.0 Hz, CO), 173.5 (d, J = 3.8 Hz, Pym2), 167.9 (d, J = 13.9 Hz, Pym4,6), 83.4 (vt, J = 4.9 Hz, Pym5), 41.8 (CH3) 34.9 (d, J = 4.9 Hz, NCH3), 32.1 (CHCH3), 31.8 (CHCH3), 19.6 (d, J = 13.5 Hz CHCH3), 18.97 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 137.1. IR (ATR, cm−1): 2012 (νCO), 1875 (νCO), 1836 (ν CO ). ESI-MS: [M + Cl] − , found 827.2, calcd for C27H38Mo2N4O8P2Cl 827.0. [Cr(CO)4-μ2-(κ2P,N-PymMe-iPr)Mo(CO)4] (7). This complex was prepared analogously to 5 with 3b (0.08 g, 0.14 mmol) and Cr(CO)6 (0.031 g, 0.14 mmol) as starting materials. Yield: 61 mg (55%). Anal. Calcd for C27H38N4O8P2CrMo (756.52): C, 42.87; H, 5.06; N, 7.41. Found: C, 42.94; H, 5.12; N, 7.33. 1H NMR (δ, CD2Cl2, 20 °C):5.48 (s, 1H, Pym5), 3.30 (s, 3H, CH3), 3.03 (d, J = 2.6 Hz, 6H, NCH3), 2.53−2.46 (m, 4H, CHCH3), 1.37−1.31 (m, 12H, CHCH3), 1.12− 1.07 (m, 12H, CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 227.5 (d, J = 13.3 Hz, CO), 223.0 (d, J = 3.5 Hz, CO), 220.2 (d, J = 8.3 Hz, CO), 218.3 (d, J = 14.2 Hz, CO), 212.7 (CO), 212.5 (CO), 208.1 (d, J = 9.6 Hz, CO), 207.4 (d, J = 9.5 Hz, CO), 171.5 (d, J = 2.1 Hz, Pym2), 165.8 (d, J = 39.6 Hz, Pym4,6), 81.45 (vt, J = 4.8 Hz, Pym5), 39.83 (CH3), 32.92 (d, J = 4.9 Hz, NCH3), 30.01 (d, J = 16.9 Hz, CHCH3), 17.7−17.0 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 152.6, 136.9. IR (ATR, cm−1): 2011 (νCO), 1875 (νCO), 1835 (νCO). [Cr(CO)4-μ2-(κ2P,N-PymMe-iPr)W(CO)4] (8). This compound was prepared analogously to 5 with 3c (0.05 g, 0.08 mmol) and Cr(CO)6 (0.017 g, 0.08 mmol) as starting materials. Yield: 42 mg (68%). Anal. Calcd for C27H38N4O8P2CrW (844.40): C, 38.41; H, 4.54; N, 6.64. Found: C, 38.49; H, 4.58; N, 6.56. 1H NMR (δ, CD2Cl2, 20 °C): 5.45 (s, 1H, Pym5), 3.38 (s, 3H, CH3), 3.06−3.01 (m, 6H, NCH3), 2.64− 2.57 (CHCH3), 2.54−2.47 (CHCH3), 1.42−1.07 (CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 229.5 (vt, J = 13.6 Hz, CO), 225.1 (d, J = 3.7 Hz, CO), 224.9 (d, J = 3.6 Hz, CO), 220.3 (t, J = 14.9 Hz, CO), 211.1 (d, J = 4.7 Hz, CO), 210.9 (d, J = 4.7 Hz, CO), 208.7 (CO), 208.5 (CO), 203.7 (vt, J = 16.4, CO), 175.1−174.6 (Pym2), 168.7− 168.5 (Pym4,6), 167.7−167.5 (Pym4,6), 83.09 (t, J = 4.8 Hz, Pym5), 42.17 (CH3), 35.3−34.5 (NCH3), 32.9−32.6 (CHCH3), 19.9−19.0 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 152.8 (d, J = 171.0), 129.1 (d, J = 170.9, JW−P = 127.9). IR (ATR, cm−1): 2011 (νCO), 1875 (νCO), 1835 (νCO). ESI-MS: [M + Cl]−, found 877.1, calcd for C27H38N4O8P2CrWCl 877.1. [Mo(CO)4-μ2-(κ2P,N-PymMe-iPr)W(CO)4] (9). This compound was prepared analogously to 6 with 3c (0.067 g, 0.099 mmol) and Mo(CO)6 (0.026 g, 0.099 mmol) as starting materials. Yield: 57.7 g (66%) as a yellow powder. Anal. Calcd for C27H38N4O8P2CrW (888.37): C, 36.50; H, 4.31; N, 6.31. Found: C, 36.61; H, 4.39; N, 6.21 1 H NMR (δ, CD2Cl2, 20 °C): 5.50 (s, 1H, Pym5), 3.38 (s, 3H, CH3), 3.04 (d, J = 2.8 Hz, 6H, NCH3), 2.55−2.47 (m, 4H, CHCH3), 1.38− 1.33 (m, 12H, CHCH3) 1.14−1.08 (m, 12H, CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 222.2 (d, J = 8.3 Hz, CO), 214.6 (CO), 214.4 (CO), 211.0 (d, J = 4.6 Hz, CO), 209.3 (d, J = 9.5 Hz, CO), 208.6 (CO), 208.4 (CO), 203.7 (d, J = 7.2 Hz, CO), 174.0 (d, J = 3.2 Hz, Pym2), 168.8 (d, J = 13.8 Hz, Pym4,6), 167.6 (d, J = 14.2 Hz, Pym4,6). 83.5 (t, J = 4.7 Hz, Pym5), 43.0 (CH3), 35.2 (d, J = 4.7 Hz, NCH3), 35.0 (d, J = 5.1 Hz, NCH3), 32.9 (d, J = 21.6 Hz, CHCH3), 32.1 (d, J = 17.0 Hz, CHCH3), 20.9−19.0 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 137.5, 134.0 (JW−P = 128.8 Hz). IR (ATR, cm−1): 2011 (νCO), 1876 (νCO), 1836 (νCO). [Cr(κ3P,CH,P-PymtBu-iPr)(CO)3] (10). This compound was prepared analogously to 3a with 2c (0.15 g, 0.35 mmol) and Cr(CO)6 (0.077 g, 0.35 mmol) as starting materials but in toluene. (2 mL) as solvent. Yield: 84 mg (43%). Anal. Calcd for C25H44N4O3P2Cr (862.56): C, 53.37; H, 7.88; N, 9.96. Found: C, 53.49; H, 7.99; N, 9.87 1H NMR (δ, C6D6, 20 °C): 2.80 (d, J = 3.1 Hz, 6H, NCH3), 2.06−2.00 (m, 2H, CHCH3), 1.98−1.91 (m, 2H, CHCH3), 1.55 (s, 9H, CCH3), 1.24− 0.91 (m, 24H, CHCH3), −1.60 (t, J = 6.2 Hz, 1H, Cipso−H). 13C{1H} NMR (δ, C6D6, 20 °C): 237.0 (t, J = 7.5 Hz, CO), 227.9 (t, J = 12.5 Hz, CO), 226.6 (t, J = 16.1 Hz, CO), 178.3 (t, J = 3.02 Hz, Pym4,6),

33.7 (s, J = 6.8 Hz, NCH3), 32.8 (s, CH3) 32.5 (CHCH3, NCH3), 32.4 (CHCH3, NCH3) 26.4 (d, J = 15.0, CHCH3), 19.8 (d, J = 10.5 Hz, CHCH3), 19.6 (CHCH3), 19.5 (CHCH3), 19.2 (d, J = 10.3 Hz, CHCH3). 31P{1H} NMR (δ, CDCl3, 20 °C): 150.5, 69. 7. IR (ATR, cm−1): 2010 (νCO), 1871 (νCO), 1833 (νCO). [Mo(κ2P,N-PymMe-iPr)(CO)4] (3b). This compound was prepared analogously to 3a with 2a (0.15 g, 0.39 mmol) and Mo(CO)6 (0.093 g, 0.35 mmol) as starting materials. Yield: 131 mg (57%). Anal. Calcd for C23H38N4O4P2Mo (592.49): C, 46.63; H, 6.46; N, 9.46. Found: C, 46.76; H, 6.59; N, 9.38. 1H NMR (δ, CD2Cl2, 20 °C): 6.48 (bs, 1H, Pym5), 3.04 (d, J = 1.3 Hz, 3H, CH3), 2.95 (d, J = 3.0 Hz, 3H, CH3), 2.78 (s, 3H, CH3), 2.47 (m, 2H, CHCH3), 2.18 (bs, 2H, CHCH3), 1.33 (dd, J = 18.2, 6.9 Hz, 6H, CHCH3), 1.17−1.06 (m, 12H, CHCH3), 0.99 (dd, J = 12.4, 7.0 Hz, 6H, CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 222.5 (d, J = 7.8 Hz, CO), 216.4 (CO), 216.2 (CO), 210.1 (d, J = 8.9 Hz, CO), 169.7 (Pym2), 168.1 (d, J = 14.3 Hz, Pym4,6), 167.6 (d, J = 22.6 Hz, Pym4,6), 85.8 (d, J = 31.1 Hz, PymH5), 34.4 (d, J = 5.9 Hz, NCH3), 33.7 (CH3), 32.0 (CHCH3, NCH3), 31.9 (CHCH3, NCH3), 26.9, (d, J = 15.7 Hz, CHCH3)., 19.95 (d, J = 10.0 Hz, CHCH3), 19.87 (CHCH3), 19.85 (CHCH3), 19.7 (d, J = 16.7 Hz, CHCH3).18.9 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 134.0, 70.5. IR (ATR, cm−1): 2010 (νCO), 1875 (νCO), 1835 (νCO). ESI-MS: [M + Cl]− found 622.9, calcd for C23H38MoN4O4P2Cl 623.1. [W(κ2P,N-PymMe-iPr)(CO)4] (3c). This compound was prepared analogously to 3a with 2a (0.15 g, 0.39 mmol) and W(CO)6 (0.124 g, 0.35 mmol) as starting materials. Anal. Calcd for C23H38N4O4P2W (680.37): C, 40.60; H, 5.63; N, 8.23. Found: C, 40.81; H, 5.71; N, 8.12. Yield: 121 mg (46%) as a yellow powder. 1H NMR (δ, CD2Cl2, 20 °C): 6.52 (bs, 1H Pym5), 3.05 (s, CH3), 2.97 (d, J = 3.2 Hz, 3H, CH3), 2.85 (s, 3H, CH3), 2.51−2.45 (m, 2H, CHCH3), 2.19 (bs, 2H, CHCH3), 1.37−0.98 (m, 24H, CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 211.7 (d, J = 4.8 Hz, CO), 210.0 (CO), 209.8 (CO), 204.3 (d, J = 7.3 Hz, CO), 170.2 (Pym2), 169.1 (d, J = 13.8 Hz, Pym4,6), 167.5 (d, J = 23.3 Hz, Pym4,6), 85.8 (PymH5), 34.8 (CH3), 34.7 (d, J = 4.8 Hz, NCH3), 32.8 (CHCH3, NCH3), 32.7 (CHCH3, NCH3), 26.8 (d, J = 15.4 Hz, CHCH3), 20.2−19.7 (CHCH3), 19.02 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 126.0 (JW−P = 123.1 Hz), 71.1. IR (ATR, cm−1): 2004 (νCO), 1865 (νCO), 1829 (νCO). Formation of [Mo(κ2P,N-PymPh-iPr)(CO)4] (4) and [Mo(CO)4-μ2(κ2P,N-PymPh-iPr)Mo(CO)4] (5). Following the synthetic protocol for 3a, the reaction of 2b (0.15 g, 0.34 mmol) and Mo(CO)6 (0.089 g, 0.34 mmol) resulted in the formation of an inseparable 2/1 mixture of 4 and 5. Due to signal overlap only selected NMR data are provided. 31 1 P{ H} NMR (δ, CD2Cl2, 20 °C): 132.2 (4), 71.2 (4), 135.5 (5). [Mo(CO)4-μ2-(κ2P,N-PymPh-iPr)Mo(CO)4] (5). A suspension of 2b (0.15 g, 0.34 mmol) and Mo(CO)6 (0.177 g, 0.68 mmol) in acetonitrile. (2 mL) was placed in a sealed microwave glass vial (20 mL) and stirred for 16 h at 130 °C. The reaction mixture was then cooled to room temperature, and the product was obtained as a crystalline material. The solvent was removed under reduced pressure, and the remaining solid was washed twice with n-pentane (10 mL) and dried under vacuum. Yield: 124 mg (41%) as a yellow powder. Anal. Calcd for C32H40N4O8P2Mo2 (862.56): C, 44.56; H, 4.67; N, 6.50. Found: C, 44.68; H, 4.77; N, 6.39. 1H NMR (δ, CD2Cl2, 20 °C): 7.63−7.62 (m, 3H, Ph3−5), 7.45−7.43 (m, 2H, Ph2,6), 5.62 (s, 1H, Pym5), 3.09 (d, J = 2.6 Hz, 6H, NCH3), 2.53−2.47 (m, 4H, CHCH3), 1.32 (dd, J = 18.2, 6.9 Hz, 12H, CHCH3), 1.18 (dd, J = 14.7, 7.0 Hz, 12H, CHCH3). 13C{1H} NMR (δ, CD2Cl2, 20 °C): 222.4 (d, J = 8.4 Hz, CO), 209.2 (d, J = 9.3 Hz, CO), 209.1 (CO), 208.8 (CO), 172.4 (d, J = 4.4 Hz, Py2), 168.0 (d, J = 13.8 Hz, Pym4,6), 145.8 (P11), 131.1 (Ph2,6), 128.8 (Ph3,4), 128.7 (Ph3,4), 127.8 (Ph5), 84.2 (t, J = 4.7 Hz, Pym5), 34.4 (d, J = 5.7 Hz, NCH3), 31.0 (d, J = 16.7 Hz, CHCH3), 18.7−18.2 (CHCH3). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 135.4. IR (ATR, cm−1): 2014 (νCO), 1906 (νCO), 1869 (νCO), 1833 (νCO). ESIMS: [M + Cl]−, found 889.0, calcd for C32H40Mo2N4O8P2Cl 889.0. [Mo(CO)4-μ2-(κ2P,N-PymMe-iPr)Mo(CO)4] (6). This compound was prepared analogously to 5 with 2a (0.15 g, 0.39 mmol) and Mo(CO)6 (0.206 g, 0.78 mmol) as starting materials. Yield: 117.2 mg (37%) as a yellow powder. Anal. Calcd for C27H38N4O8P2Mo2 (800.49): C, 40.51; H, 4.79; N, 7.00. Found: C, 40.62; H, 4.91; N, 6.91 1H NMR (δ, F

DOI: 10.1021/acs.organomet.8b00192 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

Calculations were performed using the Gaussian 09 software package25 and the B3LYP functional, without symmetry constraints. That functional includes a mixture of Hartree−Fock26 exchange with DFT27 exchange correlation, given by Becke’s three-parameter functional28 with the Lee, Yang, and Parr correlation functional, which includes both local and nonlocal terms.29,30 The basis set used for the geometry optimizations consisted of the Stuttgart/Dresden ECP (SDD) basis set31 to describe the electrons of Mn and a standard 6-31G(d,p) basis set32 for all other atoms. A natural population analysis (NPA)33 and the resulting Wiberg indices34 were used to study the electronic structure and bonding of the optimized species. The NPA analysis was performed with the NBO 5.0 program,35 and the three-dimensional representations of the orbitals were obtained with Molekel.36

178.2 (d, J = 4.53 Hz, Pym2), 52.6 (Cipso, Pym5), 39.5 (CCH3), 32.0 (d, J = 17.4 Hz, CHCH3), 31.3 (d, J = 18.5 Hz, CHCH3), 30.7 (d, J = 5.7 Hz, NCH3), 29.46 (CCH3), 18.6 (CHCH3), 18.1 (d, J = 12.2 Hz, CHCH3), 17.7 (CHCH3), 17.2, (d, J = 8.5 Hz, CHCH3). 31P{1H} NMR (δ, C6D6, 20 °C): 166.1. IR (ATR, cm−1): 1945 (νCO), 1843 (νCO), 1814 (νCO). Formation of [Mo(κ3P,CH,P-PymtBu-iPr)(CO)3] (11) and [Mo(κ3P,C,P-PymtBu-iPr)(CO)3(H)] (12). Following the synthetic protocol for 10, the reaction of 2c (0.15 g, 0.35 mmol) and Mo(CO)6 (0.093 g, 35 mmol) in toluene (2 mL) as solvent resulted in the formation of an inseparable 2/1 mixture of 11 and 12. Small amounts of 11 could be obtained in pure form after crystallization from hot toluene. Due to signal overlap only selected NMR data are provided. 1H NMR (δ, CD2Cl2, 20 °C): −5.14 (m, 1H, MoH) (12). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 149.4 (11), 151.6 (d, J = 83.0 Hz) (12), 131.9 (d, J = 82.9 Hz) (12). [W(κ3P,C,P-PymtBu-iPr)(CO)3(H)] (13). This compound was prepared analogously to 10 with 2c (0.15 g, 0.35 mmol) and W(CO)6 (0.124 g, 0.35 mmol) as starting materials. Anal. Calcd for C25H44N4O3P2W (694.44): C, 43.24; H, 6.93; N, 8.07. Found: C, 43.32; H, 7.02; N, 8.98. Yield: 131 mg (54%) as a yellow powder. 1H NMR (δ, C6D6, 20 °C): 2.94 (bs, 6H, NCH3), 2.06 (bs, 4H, CHCH3), 1.65 (s, 9H, CCH3), 1.33−0.64 (m, 24H, CHCH3), −5.07 (m, 1H, WH). 13C{1H} NMR (δ, C6D6, 20 °C): 208.4 (d, J = 16.4 Hz, CO), 200.1 (t, J = 7.4 Hz, CO), 173.7 (Pym2), 173.0 (Pym4,6), 109.1 (Cipso, Pym5), 39.21 (CCH3), 33.0 (d, J = 25.7 Hz, CHCH3) 32.2 (d, J = 30.4 Hz, CHCH3), 31.7 (t, J = 6.0 Hz, NCH3), 30.4 (CCH3), 20.4 (d, J = 6.1 Hz, CHCH3), 19.7 (d, J = 8.3 Hz, CHCH3), 18.7, (CHCH3). 31 1 P{ H} NMR (δ, C6D6, 20 °C): 139.0 (d, J = 83.8 Hz, JW−P = 214.5 Hz), 121.7 (d, J = 83.8 Hz, JW−P = 227.2 Hz). IR (ATR, cm−1): 1914 (νCO), 1865 (νCO), 1842 (νCO). [W(κ3P,C,P-PymH,tBu-iPr)(CO)3(H)] (16a,b). Complex 13 (0.020 g, 0.029 mmol) was treated with Ph3C+PF6− (0.011g, 0.029 mmol) in benzene/THF (9/1, 1 mL) for 1 h. The reaction mixture was then filtered through a syringe filter, and the solvent was removed under vacuum. The remaining solid was dissolved in CH2Cl2 (0.5 mL) and precipitated upon addition of n-pentane (15 mL) and dried under vacuum. Yield of 16a,b: 22.7 mg (94%). 1H NMR (δ, C6D6, 20 °C): 9.38 (s, 1H, NH), 3.33−3.19 (m, 6H, NCH3), 2.84−2.75 (m, 4H, CHCH3), 1.49 (s, 9H, CCH3), 1.40−1.36 (m, 12h, CHCH3), 1.18− 1.12 (m, 12H, CHCH3), −4.96 (dd, J = 60.7 Hz, 22.3 Hz, W−H), −5.12 (dd, J = 62.9 Hz, 22.1 Hz, WH). 31P{1H} NMR (δ, CD2Cl2, 20 °C): 148.8 (d, J = 83.2 Hz, JW−P = 197.8 Hz), 136.5 (d, J = 84.0 Hz, JW−P = 197.8 Hz), 128.6 (d, J = 83.6 Hz, JW−P = 197.8 Hz), 116.8 (d, J = 83.6 Hz, JW−P = 197.8 Hz), −144.41 (hept, J = 711.4 Hz). IR (ATR, cm−1): 2009.2 (νCO), 1927 (νCO), 1866 (νCO). ESI-MS: [M + H]+ found 693.4, calcd for C25H45N4O3P2W 693.2; [M − H]− found 691.4, calcd for C25H43N4O3P2W 693.2. X-ray Structure Determination. X-ray diffraction data of 3b,c, 5, 10·0.5CH3CN, 11·toluene, 13, and 16 were collected at T = 100 K in a dry stream of nitrogen on a Bruker Kappa APEX II diffractometer system using graphite-monochromated Mo Kα radiation (λ = 0.71073 Å) and fine sliced φ and ω scans. Data were reduced to intensity values with SAINT, and an absorption correction was applied with the multiscan approach implemented in SADABS.20 The structures were solved by the dual-space approach implemented in SHELXT21 and refined with SHELXL20 (16) and JANA200622 (3b,c, 5, 10· 0.5CH3CN, 11·toluene, and 13). Non-hydrogen atoms were refined anisotropically. The H atoms connected to C atoms were placed in calculated positions and thereafter refined as riding on the parent atoms. The agostic hydrogen atoms in 10·0.5CH3CN and 11·toluene, the hydride H in 13 and 16, and the amine H in 16 were located from difference Fourier maps. They were refined freely in 11·toluene and 13. In 10·0.5CH3CN the C−H distance was restrained to 0.9 Å, and in 16 the W−H distance was restrained to 1.6 Å. Contributions of disordered solvents to the intensity data were removed for 5 and 13 using the SQUEEZE routine of the PLATON software suite.23 Molecular graphics were generated with the program MERCURY.24 Computational Details. The computational results presented have been achieved in part using the Vienna Scientific Cluster (VSC).

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ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00192. Synthesis of ligand precursors and ligands 1a−c and 2a− c, complete crystallographic data, 1H, 13C{1H}, and 31 1 P{ H} NMR spectra of all new complexes, and computational details (PDF) Optimized Cartesian coordinates for the DFT-calculated structure of 13 (XYZ)

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AUTHOR INFORMATION

Corresponding Author

*K.K.: e-mail, [email protected]; tel, (+43) 1 58801 163611; fax, (+43) 1 58801 16399. ORCID

Karl Kirchner: 0000-0003-0872-6159 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS Financial support by the Austrian Science Fund (FWF) is gratefully acknowledged (Project No. P29584−N28). REFERENCES

(1) Coining of the name “pincer”: van Koten, G. Pure Appl. Chem. 1989, 61, 1681−1694. (2) For reviews on pincer complexes, see: (a) Gossage, R. A.; van de Kuil, L. A.; van Koten, G. Acc. Chem. Res. 1998, 31, 423−431. (b) Albrecht, M.; van Koten, G. Angew. Chem., Int. Ed. 2001, 40, 3750−3781. (c) van der Boom, M. E.; Milstein, D. Chem. Rev. 2003, 103, 1759−1792. (d) Singleton, J. T. Tetrahedron 2003, 59, 1837− 1857. (e) Liang, L. C. Coord. Chem. Rev. 2006, 250, 1152−1177. (f) The Chemistry of Pincer Compounds; Morales-Morales, D., Jensen, C. M.; Eds.; Elsevier: Amsterdam, 2007. (g) Nishiyama, H. Chem. Soc. Rev. 2007, 36, 1133−1141. (h) Benito-Garagorri, D.; Kirchner, K. Acc. Chem. Res. 2008, 41, 201−213. (i) Choi, J.; MacArthur, A. H. R.; Brookhart, M.; Goldman, A. S. Chem. Rev. 2011, 111, 1761−1779. (j) Selander, N.; Szabo, K. J. Chem. Rev. 2011, 111, 2048−2076. (k) Bhattacharya, P.; Guan, H. Comments Inorg. Chem. 2011, 32, 88− 112. (l) Schneider, S.; Meiners, J.; Askevold, B. Eur. J. Inorg. Chem. 2012, 2012, 412−429. (m) Organometallic Pincer Chemistry; van Koten, G., Milstein, D., Eds.; Springer: Berlin, 2013; Top. Organomet. Chem. Vol. 40. (n) Szabo, K. J.; Wendt, O. F. Pincer and Pincer-Type Complexes: Applications in Organic Synthesis and Catalysis; Wiley-VCH: Weinheim, Germany, 2014. (o) Asay, M.; Morales-Morales, D. Dalton Trans. 2015, 44, 17432−17447. (p) Murugesan, S.; Kirchner, K. Dalton Trans. 2016, 45, 416−439.

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DOI: 10.1021/acs.organomet.8b00192 Organometallics XXXX, XXX, XXX−XXX

Article

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DOI: 10.1021/acs.organomet.8b00192 Organometallics XXXX, XXX, XXX−XXX