Formation and Reactivity of Transient Phosphanoxyl Manganese

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Formation and Reactivity of Transient Phosphanoxyl Manganese Complexes Tobias Heurich,† Nabila Rauf Naz,† Zheng-Wang Qu,*,‡ Gregor Schnakenburg,† and Rainer Streubel*,† †

Institut für Anorganische Chemie, Rheinische Friedrich-Wilhelms-Universität Bonn, Gerhard-Domagk-Str. 1, 53121 Bonn Germany Mulliken Center for Theoretical Chemistry, Rheinische Friedrich-Wilhelms-Universität Bonn, Beringstr. 4, 53115 Bonn Germany

‡

Organometallics Downloaded from pubs.acs.org by UNIV OF SUNDERLAND on 10/26/18. For personal use only.

S Supporting Information *

ABSTRACT: Formation of thermally unstable complexes [Mn(CO)2CpMe(R2PO-TEMP)] (Cp = cyclopentadienyl; Me = methyl; TEMP = 2,2,6,6-tetramethyl-piperidin-1-oxyl) is presented in this experimental and theoretical study; in case of R = Cy 31P NMR spectroscopic evidence is provided. Mechanistic details of the product formation and decomposition, due to a homolytic O−N bond cleavage, are revealed by high-level density functional theory calculations. Insights into stability and spin density distribution of transient phosphanoxyl complexes [Mn(CO)2CpMe(R2PO·)] and preliminary results on the acidity of related complexes [Mn(CO)2CpMe(R2P−OH)] and [W(CO)5(R2P−OH)] toward TEMP−H are presented.

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temperatures (50 to 60 °C) homolytic O−N bond cleavage leading to the formation of a radical pair involving a transient phosphanoxyl complex IV (Figure 1), namely, [W(CO)5(Ph2PO·)] (V), was initiated. Trapping reaction with the Ph3C radical (trityl) led to the cross-coupling product possessing a P−O−CPh3 unit.6 Furthermore, reaction of the reactive intermediate with group 14 hydrides (Ph3EH) led to phosphane complexes with the related P−O−E motif.7 Despite density functional theory (DFT) calculations revealed a spin density distribution of only ∼30% at the P− O oxygen atom of [W(CO)5(Ph2PO·)] (V), the precursor [W(CO)5(Ph2PO-TEMP)] could be used as an effective thermal radical initiator for the polymerization of styrene, relying on the O−N bond homolysis.6 More recently, the substitution pattern of P-ligands of W(CO)5 complexes II was changed to probe effects of the P-ligand on the stability. We found that a 1,3,2-diazaphospholane complex (Z = W(CO)5, R2 = −N(Me)(CH2)2(Me)N−) was prone to homolytic O−N bond cleavage, already at ambient temperature, but still stable enough that allowed for its isolation.8 It was also shown that styrene polymerization occurred already at room temperature if this precursor complex was employed.8 As the influence of the metal center (apart from group 6 metals) on the tendency of O−N bond homolysis in phosphane ligands of the type R2PO-TEMP was not yet investigated, new studies were launched to gain further knowledge.

INTRODUCTION One of our research interests is the exploration of synthesis and reactivity of phosphane derivatives I, including complexes having a P-bound 2,2,6,6-tetramethyl-piperidin-1-oxyl (TEMPO), that is, P-O-TEMP1 substituent (Figure 1).

Figure 1. P-O-TEMP phosphane derivatives I and II (R = substituent, Z = electron pair, MLn), phosphane complex III, and phosphanoxyl complexes IV.

Recently, Iwamoto reported that metal-free phosphane derivatives of I (Z = lone pair) gave a phosphinoyl2 and an aminyl radical due to a homolytic O−N bond cleavage occurring below room temperature.3 Shortly after, we showed by variable-temperature NMR study that intermediates I (Z = lone pair; R = Ph) can be formed featuring less sterically demanding substituents, and decomposition occurred above −20 °C.4 In the field of metal complexes II bearing this specific ligand motif of a P-O-TEMP moiety (Figure 1), the first example on a stable Au (I) complex5 was reported by Gates et al. More recently, access to the complex III, stable under ambient conditions, was achieved.6 Nevertheless, at elevated © XXXX American Chemical Society

Received: May 30, 2018

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DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics Herein, we report on generation and reactions of manganese(I) complexes bearing different ligands R2POTEMP, including a detailed DFT study on the decomposition mechanism; first results on the acidity of [LnM(R2P−OH)] complexes toward the base TEMP−H are presented.

Scheme 2. Synthesis of Transient Phosphane Mn(I) Complexes 2a−c and Obtained Decomposition Products

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RESULTS AND DISCUSSION A series of phosphane manganese complexes 1a−c were prepared using a protocol starting from [Mn(CO)3CpMe] and secondary phosphanes. Among these phosphane complexes, 1a9 and 1b10 were reported before, while 1c was new. By UV irradiation of [Mn(CO)3CpMe] in tetrahydrofuran (THF) at low temperature a red colored solution containing [Mn(CO)2CpMe(thf)] was formed,11 and subsequent addition of the phosphanes (Ph2PH, tBu2PH, Cy2PH) yielded the targeted manganese(I) complexes 1a−c. The crude products were subjected to column chromatography and obtained in moderate to good yields (Scheme 1). Scheme 1. Synthesis of Phosphane Mn (I) Complexes 1a−c

position was not observed before for tungsten complex III. First, we suspected that the compounds had decomposed on the solid phase during chromatography, and, therefore, other methods such as washing of the crude product mixture and recrystallization were examined. But both were also not successful to obtain firm proof for the proposed complexes 2a−c. Therefore, we changed the strategy and focused on complex 1c as a case in point, representing a medium challenging case in terms of kinetic destabilization of 2c. When 1c was first treated with 1 equiv of n-butyl-lithium and 2 equiv of TEMPO, the major product 3c was observed as singlet at 155.2 ppm in the 31P{1H} NMR spectrum in the reaction mixture. The product was isolated in moderate yields, and NMR and electrospray ionization−mass spectrometry (ESI-MS) results provided clear evidence for the salt piperidinium phosphinite complex 3c (see also below). However, if complex 1c was treated with n-butyllithium (1st) and [TEMPO]BF4 (2nd) at −78 °C a mixture of products was formed. 31P{1H} NMR spectroscopic monitoring revealed the short-lived [Mn(CO)2CpMe(Cy2PO-TEMP)] (2c) showing two resonances at 238.7 and 220.0 ppm (1:0.4) and the P−OH substituted complex [Mn(CO)2CpMe(Cy2P−OH)] (4c) at 202.4 ppm as major product. However, the intermediate 2c was not stable enough to be purified, even attempts to isolate via extraction and washing with n-pentane at low temperature failed; that is, full conversion into the stable complex [Mn(CO)2CpMe(Cy2P− OH)] (4c) occurred. Isolated complexes 4a−c possess significantly downfieldshifted NMR resonances compared to 3a−c (Table 1). The experimental assignment for 2c can be justified by the trend in the chemical shifts, as the Δδ values between the pairs 2c/4c and III/8 show similar differences of 18−37 and 30 ppm, respectively, thus also supporting the assignment of [Mn(CO)2CpMe(Cy2PO-TEMP)] (2c) in solution. This experimental assignment is further supported by our DFT NMR calculations (Table 1; see Supporting Information for more detail). In particular, the observed 31P{1H} NMR chemical shifts at 238.7 and 220.0 ppm are due to two low-lying conformers (2c0 and 2c within 0.9 kcal·mol−1) with a different

Although complex 1a is described in the literature, the molecular structure in the solid state is not known. We were able to get suitable crystals for X-ray analysis that confirmed the molecular constitution (Figure S1 in the Supporting Information). For 1c the molecular structure could be confirmed as well (Figure 2).

Figure 2. Molecular structure of complex 1c (50% probability level; hydrogen atoms are omitted for clarity). Selected bond lengths (Å) and angles (deg): P−Mn 2.224(2), P−C1 1.870(8), P−C7 1.863(7); Mn−P−C1 118.5(3), Mn−P−C7 119.5(3), C1−P−C7 105.4(3).

Starting from these complexes, syntheses of a series of Mn(I) complexes possessing a R2PO-TEMP ligand 2a−c were targeted via deprotonation of 1a−c with n-butyllithium and subsequent reaction with 2 equiv of TEMPO (Scheme 2). Under these conditions, the postulated complexes could not be confirmed by 31P{1H} NMR spectroscopy, unfortunately. Attempts to isolate the targeted products via low-temperature column chromatography provided only complexes 4a−c having a P−OH moiety (Table 1). This result was unprecedented (and unexpected), as such a facile decomB

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

Table 1. Comparison of the DFT-Calculated and Experimental 31P{1H} NMR Chemical Shifts δPa of the Mn(I) Complexes 2− 4 as well as Similar W(0) Complexes III, 8, 9b δP(2/III) R

calc

a: Ph b: tBu c: Cy w: Phd

196.3 (191.8) 258.9 232.2 (216.1) 144.6

δP(3/9)

δP(4/8)

expt

calc

expt

calc

expt

238.7 (220.0) 137.9

133.9 165.4 145.2 85.4

138.1 172.0 155.2 74.0

171.7 217.8 202.4c 124.1

178.7 214.2 202.4 106.6

a

In parts per million, values in parentheses represent chemical shifts for higher-lying conformer. bRepresented as w in the last row. c4c as DFT NMR reference. dW(CO)5 instead of Mn(CO)2CpMe.

orientation of the electron lone pair at the nitrogen atom of TEMP; similar low-lying conformers are also predicted for the complex 2a (within 1.5 kcal·mol−1) but not for 2b due to increased steric hindrance. As this study disclosed that complexes 2a−c were significantly less stable than the previously reported tungsten derivative III6,7 that did not decompose in an analogous manner (to give a P−OH substituted ligand), we decided to perform theoretical investigations to get more insight into the bonding. Indeed, such experimental findings are confirmed by our DFT calculations at the TPSS-D3/def2-QZVP + COSMO-RS // TPSS-D3/def2-TZVP + COSMO level12 in THF. The computed free energies of P−O and O−N bond homolysis (at 298 K and 1 mol·L−1 concentration) are decreasing in the order of III > 2a > 2c > 2b from 28.4, 22.0, 18.5 to 8.7 kcal· mol−1 and from 12.6, 3.2, −6.1 to −15.1 kcal·mol−1, respectively. DFT calculations show that entropic effect contributes consistently by ca. −16 kcal·mol−1 to such homolytic cleavage of single bonds. The reduced stability of manganese complexes 2a−c should be due to both less electronegative Mn(CO)2CpMe complex and more bulky substituents to the central P atom. The small and even negative free energies of O−N bond homolysis strongly suggest that such Mn(I) complexes 2a−c are rather unstable with respect to homolytic O−N bond cleavage. The DFT-predicted reaction mechanism for the formation of complex 4c as a case in point is shown in Scheme 3. Direct single-electron transfer from 5c− to TEMPO is 17.3 kcal·mol−1 endergonic to form radical 5c· (and stable Li[TEMPO] salt as byproduct) that can be efficiently trapped by another TEMPO molecule to form 2c. Direct H-abstraction from the P−H bond of the neutral complex 1c by TEMPO is 13.6 kcal·mol−1 endergonic over a sizable barrier of 25.5 kcal·mol−1 to form the reactive radical 5c· that can be efficiently trapped by another TEMPO molecule. Such neutral route should be possible only upon moderate heating. Instead, the anionic complex 5c− may form a metastable radical anion complex 2c·− with TEMPO via P−O bond formation over a free energy barrier of 18.1 kcal· mol−1, followed by either direct TEMP elimination to form anionic 6c− (the anionic part of salt 3c) or competing single electron transfer to another TEMPO to form the transient neutral complex 2c. Such ionic route with an overall barrier of 18.1 kcal·mol−1 is thus much more efficient at low temperatures. Direct recombination of anionic 5c− with cationic TEMPO+ may also lead to 2c in a single exergonic step, thus providing a more selective route to neutral complex 2c. [DFTpredicted electron binding free energies in kcal·mol−1 in THF solution: TEMPO+ (116.4) > V (114.7) > 6c· (94.6) > 8· (93.7) > 5c· (69.2) > TEMP· (61.5) > TEMPO· (52.0) > III (51.8) > 2c (32.7].

Scheme 3. DFT Computed Mechanism for the Formation of 2c from Reaction of Negative 5c− Complexes with TEMPO and TEMPO+, Including the Formation of 4c

Compared with the W(CO)5 coordinated radicals, the Mn(CO)2CpMe coordinated radicals show higher spin densities on the metal complex moiety (0.80 e and 0.34 e for 6c· and 5c· vs 0.48 e and 0.14 e for V and 8·) but lower spin densities on the remaining O-centers (0.20 e for 5c· vs 0.31 e for V) or Pcenters (0.63 e for 5c· vs 0.69 e for 8·), which is consistent with lower electron affinities for electron-rich manganese complexes. The homolytic O−N b ond cleavage of [Mn(CO)2CpMe(Cy2PO-TEMP)] (2c) is −6.1 kcal·mol−1 exergonic thus may occur spontaneously at room temperature, leading to the metal-centered radical 6c· along with the reactive radical TEMP. Only radical TEMP is able to directly abstract a H atom from THF molecule, which is −2.0 kcal· mol−1 exergonic over a barrier of 19.3 kcal·mol−1 to form the base TEMP−H; the resultant THF radical can easily transfer a H atom to 6c· to form the final product complex 4c. [DFTpredicted free energies of X−H bond homolysis in kcal·mol−1 in THF: X−H = THF−H· (35.1) < Ph3Sn−H (70.7) < 1c (75.1) < 4c (76.6) < PhS−H (77.8) < 7 (81.3) < THF (85.3) < TEMP−H (87.3)]. To confirm the assigned nature of the salt-like structure of 3c, we treated isolated [Mn(CO)2CpMe(Cy2P−OH)] (4c) with TEMP−H in Et2O and observed a clean conversion into C

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

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Organometallics 3c (Scheme 4); this was isolated and unambiguously characterized by NMR spectroscopy and ESI-MS (see also

Scheme 6. Reaction of Complex III with Thiophenol at Elevated Temperature

Scheme 4. Reaction of 4c with Amine Base (TEMP−H) Giving Complex 3c and Reversible Reaction to 4c in CD2Cl2

reaction mixture showed a signal at 76.6 ppm (content ∼77%) with a 183W,31P coupling constant magnitude of 260.1 Hz. After isolation and characterization, the product was identified as the piperidinium salt 9, presumably resulting from the acid− base reaction between the transient P−OH functional complex 8 and TEMP−H (Scheme 6). Single crystals of 9 were obtained from a saturated diethyl ether solution and an X-ray diffraction analysis performed that confirmed the salt constitution (Figure 3). The P−W bond

the corresponding DFT calculations). However, if 3c was dissolved in CD2Cl2, it started to convert to 4c and TEMP−H. According to our DFT calculations, the contact ion pair of 3c is 2.2 kcal·mol−1 higher in free energy than 4c and TEMP−H in THF solution; thus, it may be stable only in aggregate or solid. In contrast, the corresponding tungsten complex [W(CO)5(Ph2P−OH)] (8, Scheme 6) is ∼14 kcal·mol−1 more acidic than [Mn(CO)2CpMe(Cy2P−OH)] (4c) and thus does react with TEMP−H to form more stable ionic product in solution, as also confirmed by experiment described in a later paragraph. As proton transfer to TEMP−H occurred readily in weakly polar solvents to form the salt-like complex 3c, the acidity of the P−OH group was probed further by heating 4c with triphenylstannane in toluene (Scheme 5). This led to the Scheme 5. Reaction of Complex 4c with Triphenylstannane at Elevated Temperature to Give Complex 7

Figure 3. Molecular structure of complex 9 (50% probability level; hydrogen atoms are omitted for clarity). Selected bond lengths (Å) and angles (deg): P−W 2.5678(13), P−O1 1.532(3), P−C1 1.849(5), P−C7 1.841(4), N−C18 1.516(6), N−C22 1.516(6); W−P−O1 115.22(14), W−P−C1 113.73(15), W−P−C7 115.46(14), O1−P−C1 105.9(2), O1−P−C7105.1(2), C1−P1−C7 99.75(19).

formation of complex 7 and dihydrogen at 65 °C. In the 31 1 P{ H} NMR spectrum 7 showed a signal at 204.0 ppm (2JSn,P = 212 Hz (117Sn) and 2JSn,P = 222 Hz (119Sn)). Our DFT calculations on this reaction showed that it proceeds via a direct recombination between the P−OH proton of complex 4c and the Sn−H hydride, which is −12.0 kcal·mol−1 exergonic over a free energy barrier of 30.5 kcal·mol−1 to form complex 7 along with H2 gas. Such mechanism is consistent with the moderate heating required in the experiment; the sizable barrier is mainly due to the relatively weak acidity of the manganese complex 4c. This also led to the conclusion that a faster reaction of complex 8 and triphenylstannane can be expected. To study the proton transfer of a more acidic P−OH group to the base TEMP−H, we chose complex 8. Therefore, the idea to synthesize the P−OH derivative starting from [W(CO)5(Ph2PO-TEMP)] (III) using a hydrogen atom transfer (HAT) donor such as thiophenol13 was examined first. Here, a hydrogen atom transfer to the transiently formed radicals (after homolytic O−N bond cleavage) should occur thus forming the amine TEMP−H and [W(CO)5(Ph2P− OH)] (8). When III was heated in toluene with 2 equiv of thiophenol to 80 °C (Scheme 6), a 31P{1H} NMR spectrum of the brown

length is 2.5678(13) Å, which is longer than that in the related triethylammonium salt with 2.554(1) Å.14 The P−O bond length is elongated in 8 (1.532(3) vs 1.521(3) Å), too. As the transient complex [W(CO)5(Ph2P−OH)] (8) was not spectroscopically detected, we decided to synthesize 8 via an independent route. To get access to the P−OH complex, two possible routes were tested. The molybdenum derivative of 8 was described by Kraihanzel et al. as unstable under reduced pressure.15 This compound was obtained by hydrolysis of the P-Cl derivative with potassium hydroxide. For the related derivatives of chromium and tungsten, Lorenz et al. stated that these compounds cannot be obtained in pure form.16 The reaction of the chlorophosphane complex 1017 ([W(CO)5(Ph2PCl)]) with lithium hydroxide in THF yielded a bluish oil from which, after recrystallization, a colorless solid was obtained, melting after 1 day at room temperature probably due to traces of remaining THF. To avoid this inconvenience a route, previously described by Kraihanzel et D

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

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Organometallics al.,15 was adopted; that is, a base-assisted hydrolysis with subsequent acidification of the intermediate salt [HNEt3][W(CO)5(Ph2PO)] was followed, and product 8 was obtained as colorless solid that was surprisingly well-soluble in n-pentane. It revealed a comparatively low melting point of 60 °C. The 31 1 P{ H} NMR spectrum of 8 in benzene-d6 showed a singlet with satellites at 106.6 ppm (1JW,P = 278.4 Hz). As the chemical shift of the resonance signal of OH protons is dependent on the concentration and the solvent, the effect of both was investigated. It was shown that the solvent has, as expected, the largest influence as to be seen in Table 2. Table 2. Comparison of the 1H and 31P{1H} NMR Data of Complex 8 in Different Solventsa solvent

δP, ppm

δH (OH), ppm

THF-d8 CD2Cl2 CDCl3 C6D6

97.4 106.0 107.7 105.5

8.70 4.47 4.15 2.69

Figure 4. Molecular structure of complex 8 (50% probability level; hydrogen atoms are omitted for clarity). Selected bond lengths (Å) and angles (deg): P−W 2.4803(8), P−O 1.625(3), P−C1 1.830(3), P−C7 1.824(3), W−P−O1110.70(10), W−P1−C1 119.55(11), W− P1−C7 117.01(10), O1−P−C1 102.65(14), O1−P−C7 103.53(15), C1−P−C7 101.33(15).

c ≈ 0.1 mol·L−1; T = 25 °C.

a

Scheme 7. Formation of Complex 9 by Reaction of Complex 8 with TEMP−H

1

The H NMR chemical shift of the OH proton is evidently shifting toward lower field with increasing polarity of the solvent and the increasing opportunity to form hydrogen bonding. The latter is evidenced by THF-d8, as the signal appears at the most downfield-shifted value (8.70 ppm). The concentration dependence was analyzed for the case of benzene-d6 (Table 3), to avoid any influence of a coordinating solvent on the chemical shift. Table 3. Comparison of the 1H NMR Data at 25 °C of the P−OH Group of Complex 8 in Benzene-d6 with Different Concentrations c, mol·L−1

δH (OH), ppm

0.01 0.05 0.10 0.35

2.54 2.62 2.69 2.88

energies compared to the previously investigated tungsten derivative [W(CO)5(Ph2PO-TEMP)]. The resulting shortlived phosphanoxyl Mn(I) complexes possess higher spin density on the metal fragment and less on the oxygen atom. Stimulated by the theoretical results, the reaction of [W(CO)5(Ph2PO-TEMP)] with PhSH as HAT reagent was studied that led to a piperidinium salt likely derived via proton transfer from the transient P−OH W(0) complex to the piperidine base (TEMP−H); this was verified via reaction of the isolated P−OH W(0) complex with piperidine.

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It became apparent that the chemical shift value of the OH group only slightly shifts to lower field with an increasing concentration. The molecular structure of 8 was confirmed for the solid state (Figure 4), which shows a shorter P−W (2.4803(8) Å) but a considerably longer P−O (1.625(3) Å) bond than those in complex 9. Finally, the salt 9 was indeed obtained in a clean reaction (Scheme 7) between the complex 8 with the amine base TEMP−H in n-pentane, thus providing strong evidence for the transient existence of 8 in the reaction shown in Scheme 6.

EXPERIMENTAL SECTION

All manipulations involving air- and moisture-sensitive compounds were performed under an atmosphere of purified argon by using standard Schlenk-line techniques or a glovebox. Solvents were dried with appropriate drying agents and degassed before use. The 1H, 13 C{1H}, and 31P{1H} NMR spectroscopic data (δ in ppm) were recorded unless otherwise noted at 25 °C on a Bruker AV III 500 MHz Prodigy NMR spectrometer. The standard for 1H and 13C NMR is tetramethylsilane (Me4Si); for 31P NMR it is 85% phosphorus acid (H3PO4). Mass spectra were recorded on a MAT 95 XL Thermo Finnigan spectrometer (selected data given). Infrared spectra were recorded on a Bruker Alpha Diamond ATR FTIR spectrometer (selected data given). Melting points were determined using a Büchi Type S apparatus with samples sealed in capillaries under argon, and they are uncorrected. Elemental analyses were performed using an ElementarVarioEL instrument. For irradiation a mercury UV lamp from Heraeus (UV-TQ 150, 384 mm, 200 to 280 nm, 150 W) was used. Phosphane manganese complexes 1a−c: 2.17 g (10.0 mmol) of [Mn(CO)3CpMe] in THF (250 mL) was irradiated using a mercury UV lamp at 10 °C for 3.5 h. During the photolysis, argon was passed through the vigorously stirred reaction mixture, and the color of the reaction mixture changed from yellow to bordeaux. Afterward, all

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CONCLUSION Investigations on thermally labile, metal-coordinated P-OTEMP-substituted phosphane Mn(I) complexes revealed large differences to formerly reported group 6 metal(0) complexes. The P-O-TEMP substituted manganese derivatives were thermally unstable and yielded P−OH-substituted Mn(I) complex derivatives, thus precluding their isolation. State-ofthe-art DFT calculations disclosed that Mn(CO) 2Cp Me complexes showed much lower O−N bond dissociation E

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics

warmed to 0 °C, and a solution of TEMPO (415.6 mg, 2.66 mmol, 2 equiv) in 2 mL of THF was added, resulting in a color change from dark red to brown yellow. The whole reaction mixture was stirred for 4 h at 0 °C. 31P{1H} NMR (121.51 MHz, reaction mixture): δ = 137.9 (s, 92%, 3a). All volatiles were evaporated at reduced pressure (2 × 10−2 mbar). Purification of the remaining oil was done by lowtemperature column chromatography (Al2O3, T = −20 °C, h = 8 cm, ø = 3 cm; eluent: petrolether/THF = 1:2), yielding a brownish oily compound, which was washed with n-pentane to get complex 4a as colorless powder (3a could not be obtained). Yield: 200 mg (0.37 mmol, 29%). 1H NMR (300.13 MHz, CDCl3): δ = 1.90−2.01 (br s, 3H, CH3 of CpMe), 4.55−4.75 (m, 4H, CH of CpMe), 7.40−7.81 (m, 10 H, o-, m-, and p-HPh).13C{1H} NMR (75.48 MHz, CDCl3): δ = 13.7 (s, CH3 of CpMe), 81.9 (s, o-CH of CpMe), 82.9 (s, m-CH of CpMe), 99.5 (s, ipso-C of CpMe), 127.6 (s, o-CPh), 128.1 (br s, p-CPh), 130.4 (br s, m-CPh), 143.5 (d, 1JP,C = 47.0 Hz, ipso-CPh), 232.0 (dSat, 2 JP,C = 21.9 Hz, CO). 31P{1H} NMR (121.51 MHz, CDCl3): δ = 178.7 (s). IR (v(CO), neat): ṽ, cm−1 = 2046 (m), 1921 (vs). MS calcd for C20H17O3PMn: m/z = 392.27; found: (EI, 70 eV): m/z (%): 392.04 [M]·+ (12) Anal. Calcd (%) for C20H17O3PMn: C 61.24; H 4.64. Found: C 59.80; H 4.69. The microanalysis shows slight deviation from calculated values. But this is due to some grease present (coming from column chromatography) in the sample as can be seen as well in the 1H NMR spectrum (see Supporting Information). Complexes 3b and 4b. To a solution of phosphane complex 1b (300.0 mg, 0.89 mmol) in THF (5 mL), n-butyllithium (0.6 mL, 0.89 mmol, 1.6 molar solution in n-hexane) was added dropwise at room temperature resulting in an instant color change from yellow to dark red. After it was stirred for 30 min, a solution of TEMPO (278.8 mg, 1.78 mmol, 2 equiv) in 2 mL of THF was added, which resulted in a change in color from dark red to brown-yellow. The whole reaction mixture was stirred for the next 18 h at room temperature. 31P{1H} NMR (121.51 MHz, reaction mixture): δ = 172.0 (s, 87%, 3b). The volatiles were evaporated at reduced pressure (2 × 10−2 mbar). Purification of the resulting compound was done by low-temperature column chromatography (Al2O3, T = −20 °C, h = 8 cm, ø = 3 cm; eluent: petrolether/Et2O/THF = 1:0.5:1), yielding a brownish oily compound as third fraction, which was washed 3 to 4 times with a diethyl ether and n-pentane mixture at −50 °C to get 4b as a brown powder instead of 3b. Yield: 115 mg (0.33 mmol, 36%). 1H NMR (300.13 MHz, THF-d8): δ = 1.13−1.31 (br s, 18H, CH3 of tBu), 1.78 (s, 3 H, CH3 of CpMe), 4.3 (br s, 4H; CH of CpMe). 13C{1H} NMR (75.48 MHz, THF-d8): δ = 13.5 (s, CH3 of CpMe), 28.7 (s, 6 H, CH3oftBu), 42.4 (d, 1JP,C = 15.46 Hz, Cquart of tBu), 80.0 (s, o-CH of CpMe), 83.2 (s, m-CH of CpMe), 97.9 (s, ipso-C of CpMe), 233.8 (dSat, 2 JP,C = 23.5 Hz, CO). 31P{1H} NMR (121.51 MHz, THF-d8): δ = 214.2 (s). IR (neat): ṽ, cm−1 = 3550 (br, ν(O−H)), 1914 (m, v(C O)), 1843 (vs, v(CO)). MS calcd for C16H26O3PMn: m/z = 352.29; found: (EI, 70 eV): m/z (%): 352.1 [M−H]·+ (1) Anal. Calcd (%) for C16H26O3PMn: C 54.44; H 7.92. Found: C 54.55; H 7.44. Complex 3c. To a solution of complex 4c (200 mg, 0.5 mmol) in diethyl ether (8 mL), 2,2,6,6-tetramethylpiperidine (0.1 mL, 0.5 mmol) was added at room temperature. After it was stirred for 2 h, colorless solid started to precipitate in the reaction mixture. The solvent was evaporated (2 × 10−2 mbar), and the colorless precipitate was washed with n-pentane. Yield: 96 mg (0.17 mmol, 35%). 1H NMR (300.13 MHz, THF-d8): δ = 1.01−1.83 (br, 40H, Cy and TEMP), 2.01 (s, 3H, CH3 of CpMe), 4.39 (s, 4H, CH of CpMe), 6.49 (br s, 2 H, NH2). 13C{1H} NMR (75.48 MHz, THF-d8): δ = 13.5 (s, CH3 of CpMe), 17.2 (s, CH2−CH2−CH2), 27.1−28.1 (m, CH2 of Cy), 39.6 (s, CH2−CMe2), 58.8 (s, CMe2), 47.1 (br s, ipso-CCy), 79.83 (s, o-CH of CpMe), 80.7 (s, m-CH of CpMe), 98.6 (s, ipso-C of CpMe), 235.9 (br s, CO). 31P{1H} NMR (121.51 MHz, THF-d8): δ = 155.2 (s). IR (neat): ṽ, cm−1 = 3210 (w, v(N−H)), 3184 (w, v(N− H)), 2361 (m, v(O−N−H)), 1924 (s, v(CO)), 1858 (s, v(C O)), 1104 (s, v(P−O)). MS pos-ESI, calcd for [C9H20N]+: m/z = 142.1590; found: m/z 142.1595 [TEMP−H2]+, MS neg-ESI, calcd for

volatiles were removed from the reaction mixture under reduced pressure (2 × 10−2 mbar). Then the secondary phosphanes (Ph2PH, t Bu2PH, Cy2PH) were added dropwise in equal amounts (1.73, 1.78, and 1.98 mL, respectively, each 10.0 mmol) using a syringe into the bordeaux colored solution of [Mn(CO)2CpMe(thf)], and the reaction mixture was stirred for 24 h after warming to room temperature. The solvent was removed from the yellow colored solution under reduced pressure (2 × 10−2 mbar) resulting in the formation of a yellowish oily product, which was subjected to column chromatography (SiO2, h = 8 cm, ø = 2.5 cm; eluent: petrol ether/Et2O = 1:1) to isolate the compounds. All compounds were eluted as second fraction, which gave after solvent removal in vacuo (2 × 10−2 mbar) oily compounds, but complex 1b was obtained as a yellow crystalline solid. All compounds 1a−c were isolated in moderate to good yields. Complex 1a. mp 91 °C. Yield: 3.0 g (7.9 mmol, 79%). 1H NMR (300.13 MHz, CDCl3): δ = 1.95 (s, 3H, CH3 of CpMe), 4.05 (br s, 4H, CH of CpMe), 4.72 (d, 1JP,H = 336.0 Hz; 1 H, PH), 7.26−7.51 (m, 10H, HPh). 13C{1H} NMR (75.48 MHz, CDCl3): δ = 13.4 (s, CH3 of CpMe), 81.0 (s, o-CH of CpMe), 81.8 (s, m-CH of CpMe), 99.1 (s, ipsoCofCpMe), 127.2 (s, o-CPh), 127.5 (br s, p-CPh), 129.4 (br s, m-CPh), 142.5 (d, 1JP,C = 46.02 Hz, ipso-CPh), 225.0 (br s, cis-CO), 231.5 (dSat, 2 JP,C = 22.8 Hz, trans-CO).31P{1H} NMR (121.51 MHz, CDCl3): δ = 71.6 (s).31P NMR (121.51 MHz, CDCl3): δ = 71.6 (d,1JP,H = 336.0 Hz). IR (v(CO), neat): ṽ, cm−1 = 2018 (m), 1913 (vs). MS calcd for C20H18MnO2P: m/z = 376.04; found: (EI, 70 eV, Mn): m/z (%): 376.04 [M]·+ (12). Anal. Calcd (%) for C20H18MnO2P: C 63.84; H 4.82. Found: C 63.84; H 4.67. Complex 1b. mp 81 °C. Yield: 2.7 g (8.0 mmol, 80%). 1H NMR (300.13 MHz, CDCl3): δ = 1.30 (d, 2JP,H = 13.5 Hz, 18 H; CH3 of t Bu), 1.72 (s, 3 H, CH3 of CpMe), 3.95 (m, 4 H, CH of CpMe), 4.10 (d, 1JP,H = 312.2 Hz; 1 H, PH). 13C{1H} NMR (75.48 MHz, CDCl3): δ = 13.1 (s, CH3 of CpMe), 26.9 (s, CH3 of tBu), 35.0 (d, 1JP,C = 16.6 Hz, Cquart of tBu), 79.5 (s, o-CH of CpMe), 82.7 (s, m-CH of CpMe), 96.4 (s, ipso-C of CpMe), 224.4 (br s, cis-CO), 232.6 (dSat, 2JP,C = 22.9 Hz, trans-CO). 31P{1H} NMR (121.51 MHz, CDCl3): δ = 114.5 (s). 31 P NMR (121.51 MHz, CDCl3): δ = 114.5 (d, 1JP,H = 312.2 Hz). IR (v(CO), neat): ṽ, cm−1 = 1930 (s), 1865 (vs). MS calcd for C16H26MnO2P: m/z = 336.11; found: (EI, 70 eV): m/z (%): 336.10 [M]·+ (16). Complex 1c. mp 72 °C. Yield: 3.1 g (7.9 mmol, 79%). 1H NMR (300.13 MHz, C6D6): δ = 1.01−1.79 (br m, 22H, CH2 of Cy), 1.83 (s, 3H, CH3 of CpMe), 3.82−4.10 (m, 4H, CH of CpMe), 4.76 (br s, 1H, PH). 13C{1H} NMR (75.48 MHz, C6D6): δ = 12.7 (s, CH3 of CpMe), 26.1 (d,2JP,C = 7.7 Hz; o-CCy), 27.0 (d, 3JP,C = 8.9 Hz; m-CCy), 27.1 (d, 4JP,C = 6.51 Hz; p-CCy), 27.0 (s, ipso-CCy), 30.1 (br s, m-CCy), 80.5 (d,4JP,C = 3.8 Hz; o-CH of CpMe), 81.2, 81.7 (d, 3JP,C = 11.8 Hz; m-CH of CpMe), 97.7 (s, ipso-C of CpMe), 232.4 (br s, CO). 31P{1H} NMR (121.51 MHz, C6D6): δ = 76.3 (s).31P NMR (121.51 MHz, C6D6): δ = 76.3 (d, 1JP,H = 316.1 Hz). IR (v(CO), neat): ṽ, cm−1 = 1942 (s), 1878 (vs). MS calcd for C16H26MnO2P: m/z = 388.14; found: (EI, 70 eV): m/z (%): 388.10 [M]·+ (5). Anal. Calcd (%) for C20H18MnO2P: C 61.85; H 7.79. Found: C 60.86; H 7.60. The microanalysis shows slight deviation from calculated values. But this is due to some grease present (coming from column chromatography) in the sample as can be seen as well in the 1H NMR spectrum (see Supporting Information). Complex 2c. To a solution of phosphane complex 1c (200 mg, 0.5 mmol) in THF (8 mL), n-butyllithium (0.35 mL, 0.5 mmol) was added at −78 °C. After it was stirred for 30 min, [TEMPO]BF4 (0.12 g, 0.5 mmol) was added as solid under argon. Reaction mixture was left stirring for the next 3 h while warming to −10 °C. An aliquot was taken from the reaction mixture under ambient conditions, and a 31 1 P{ H} NMR spectrum measured (121.51 MHz,): δ = 220.0 and 238.7 ppm (ratio: 0.4:1). Complexes 3a and 4a. A solution of phosphane complex 1a (500.0 mg, 1.33 mmol) in THF (7 mL) was cooled to −80 °C with subsequent dropwise addition of n-butyllithium (0.9 mL, 1.46 mmol, 1.1 equiv, 1.6 molar solution in n-hexane). The reaction mixture immediately turned dark red. After it was stirred for 30 min, it was F

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

Article

Organometallics [C20H29O3PMn]−: m/z = 403.1240; found: m/z = 403.1235 [C20H29O3PMn]−. Complex 4c. To a solution of phosphane complex 1c (500.0 mg, 1.28 mmol) in THF (7 mL), n-butyllithium (0.9 mL, 1.28 mmol, 1.6 molar solution in n-hexane) was added dropwise at room temperature that resulted instantly in a dark red solution. After it was stirred for 30 min, a solution of TEMPO (400.0 mg, 2.56 mmol, 2 equiv) in 2 mL of THF was added, resulting in a change in color from dark red to brown-yellow. The reaction mixture was stirred for the next 18 h at room temperature. 31P{1H} NMR (121.51 MHz, reaction mixture): δ = 155.7 ppm (s, 96%, 3c). Purification of the compound 3c was previously done by low-temperature column chromatography (Al2O3, T = −20 °C, h = 8 cm, ø = 3 cm; eluent: petrolether/THF = 1:2), yielding a brownish oily compound, which was washed with n-pentane to get 4c as a very light brown powder in lieu of 3c. mp 110 °C. Yield: 220 mg (0.55 mmol, 42%). 1H NMR (300.13 MHz, CDCl3): δ = 1.09−1.92 (m, 22H, CH2 of Cy),2.01 (s, 3H, CH3 of CpMe), 4.39 (s, 4H, CH of CpMe). 13C{1H} NMR (75.48 MHz, CDCl3): δ = 13.9 (s, CH3 of CpMe), 27.0−27.7 (m, CH2 of Cy), 44.5 (d, 1JP,C = 24.25 Hz, ipso-CCy), 80.4 (s, o-CH of CpMe), 81.4 (s, m-CH of CpMe), 98.3 (s, ipso-C of CpMe), 232.8 (dSat, 2JP,C = 25.0 Hz, CO). 31P{1H} NMR (121.51 MHz, CDCl3): δ = 202.4 (s). IR (neat): ṽ, cm−1 = 3556 (br, v(O−H)), 1920 (m, v(C = O)), 1831 (vs, v(C = O)). MS calcd for C20H30O3PMn: m/z = 404.1; found: (EI, 70 eV): m/z (%): 404.13 [M]·+ (5) Anal. Calcd (%) for C20H17O3PMn: C 59.41; H 7.48. Found: C 59.50; H 7.57. Complex 7. Complex 4c (725 mg, 1.8 mmol) was dissolved in toluene (5 mL), and 0.45 mL of triphenylstannane (629.4 mg, 1.8 mmol) was added. The solution was then heated to 65 °C for 48 h, and afterward volatiles were removed under reduced pressure (2 × 10−2 mbar) from the dark brown solution. Purification was done by washing with n-pentane at lower temperature. Yield: 556 mg (0.74 mmol, 42%). 1H NMR (500.13 MHz, C6D6): δ = 1.09−1.90 (m, 22 H, CH2 of Cy), 2.04 (s, 3 H, CH3 of CpMe), 4.21 (br s, 4 H, CH of CpMe), 7.21−7.84 (m, 15 H, m-, p-, and o-HPh of SnPh). 31P{1H} NMR (202.48 MHz, C6D6): δ = 204.0(s, 2JSn,P = 201.0 Hz, 2JSn,P = 210.8 Hz). 119Sn{1H} NMR (186.50 MHz, C6D6): δ = −98.5 (dSat, 2 JSn,P = 210.8 Hz, 1JSn,C = 639.2 Hz). IR (v(C = O), neat): ṽ, cm−1 = 1901 (m), 1892(s), 798(m). MS calcd for C38H44O3P120SnMn: m/z = 754.14; found: (EI, 70 eV, 120Sn): m/z (%): 754.1 [M]·+ (2). Reaction of Complex III with Thiophenol. Complex III (67 mg, 0.1 mmol) was dissolved in 0.5 mL of toluene, and subsequently 0.02 mL (0.2 mmol, 2 equiv) of thiophenol was added. The solution was heated to 80 °C for 2 h resulting in a brown color. The reaction mixture was not purified further and just measured by 31P{1H} NMR. 31 1 P{ H} NMR (121.51 MHz): δ = 76.6 (sSat, 1JW,P = 260.1 Hz, 77%). Complex 8. Complex 10 (544.4 mg, 1.0 mmol) was dissolved in 10 mL of diethyl ether. While it was stirred, 18 μL (1.0 mmol) of water and 0.28 mL (2.0 mmol, 2 equiv) of triethylamine were added, resulting in a colorless precipitate. The solution was acidified with 0.13 mL (1.0 mmol) of a 7.7 molar aqueous hydrogen chloride solution. After solvent removal under reduced pressure (2 × 10−2 mbar) complex 8 was extracted with n-pentane, recrystallized from npentane at −50 °C, and obtained as colorless solid. mp 60 °C. Yield: 254 mg (0.48 mmol, 48%). 1H NMR (500.13 MHz, C6D6): δ = 2.88 (s, 1 H, OH), 6.93−6.99 (m, 2 H, p-HPh), 6.99−7.06 (m, 4 H, mHPh), 7.36−7.46 (m, 2 H, o-HPh). 13C{1H} NMR (125.77 MHz, C6D6): δ = 128.7 (d, 3JP,C = 10.1 Hz, m-CPh), 130.1 (d, 2JP,C = 13.9 Hz, o-CPh), 130.9 (d, 4JP,C = 2.1 Hz, p-CPh), 141.0 (d, 1JP,C = 43.3 Hz, ipso-CPh), 196.9 (dSat, 2JP,C = 7.9 Hz, 1JW,C = 125.5 Hz, cis-CO), 199.5 (dSat, 2JP,C = 24.5 Hz, 1JW,C = 139.5 Hz, trans-CO). 31P{1H} NMR (202.48 MHz, C6D6): δ = 106.6 (sSat, 1JW,P = 278.4 Hz, 1JP,C = 43.3 Hz). IR (neat, ATR diamond): ṽ, cm−1 = 3537 (m, υ(O−H)), 2070 (s, v(CO)), 1991 (m, v(CO)), 1882 (vs, v(CO)), 820 (s, v(P−O)). MS calcd for C17H11O6P184W: m/z = 525.98; found (EI, 70 eV, 184W): m/z (%) 526.0 [M]·+(26). Anal. Calcd (%) for C17H11O6PW: C 38.81; H 2.11. Found: C 38.88; H 2.23. Ionic Complex 9. Complex 10 (544.4 mg, 1.0 mmol) was dissolved in 5 mL of THF. Then 42 mg (1.0 mmol) of lithium hydroxide dihydrate was added and stirred for 16 h. Afterwards 0.1

mL (1.0 mmol) of a 2 molar aqueous hydrogen chloride solution was added. After the solvent was removed under reduced pressure (2 × 10−2 mbar), the blue residue was extracted with n-pentane. From the solution a beige residue was obtained after solvent removal under reduced pressure (2 × 10−2 mbar). It was dissolved in 10 mL of npentane, and 0.17 mL (1.0 mmol) of 2,2,6,6-tetramethylpiperidine was added, whereupon a colorless solid precipitated. Complex 9 was obtained after filtration and washing with small amounts of diethyl ether and n-pentane. mp 162 °C. Yield: 380 mg (0.57 mmol, 57%). 1 H NMR (500.13 MHz, CD2Cl2): δ = 1.40 (sSat, 1JC,H = 127.5 Hz, 12 H, CH3), 1.53−1.59 (m, 4 H, CH2−CH2−CH2), 1.69−1.77 (m, 2 H, CH2−CMe2), 7.26−7.33 (m, 2 H, p-HPh), 7.34−7.42 (m, 4 H, mHPh), 7.62−7.72 (m, 2 H, o-HPh), 8.79 (br s, 2 H, NH2). 13C{1H} NMR (125.77 MHz, CD2Cl2): δ = 16.9 (s, CH2−CH2−CH2), 36.9 (s, CH2−CMe2), 56.2 (s, CMe2), 128.1 (d, 3JP,C = 8.9 Hz, m-CPh), 129.0 (d, 4JP,C = 1.9 Hz, p-CPh), 130.2 (d, 2JP,C = 12.7 Hz, o-CPh), 149.8 (d, 1 JP,C = 34.1 Hz, ipso-CPh), 200.6 (dSat, 2JP,C = 9.0 Hz, 1JW,C = 126.1 Hz, cis-CO), 203.5 (dSat, 2JP,C = 16.1 Hz, 1JW,C = 142.2 Hz, trans-CO). 31 1 P{ H} NMR (202.48 MHz, CD2Cl2): δ = 74.0 (sSat, 1JW,P = 259.6 Hz, 1JP,C = 34.1 Hz). IR (neat): ṽ, cm−1 = 3254 (w, v(N−H)), 3240 (m, v(N−H)), 2284 (m, v(O−N−H)), 2058 (s, v(CO)), 1974 (s, v(CO)), 1858 (vs, v(CO)), 1094 (s, v(P−O)), 1013 (s, δ(N− H)). MS pos-ESI, calcd for [C9H20N]+: m/z = 142.16; found: m/z 142.16 [TEMP−H2]+), MS neg-ESI, calcd for [C17H10OP184W]−: m/ z = 524.97; found: m/z = 525.0 [W(CO)5(Ph2PO)]−. Anal. Calcd (%) for C26H30NO6PW: C 46.80; H 2.10; N 4.53. Found: C 46.86; H 2.10; N 4.51.

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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.8b00367. (PDF) (ZIP) Accession Codes

CCDC 1843387−1843390 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 Authors

*E-mail: [email protected]. (R.S.) *E-mail: [email protected]. (Z.-W.Q.) ORCID

Zheng-Wang Qu: 0000-0001-6631-3681 Rainer Streubel: 0000-0001-5661-8502 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We are grateful to the Deutsche Forschungsgemeinschaft (SFB 813 “Chemistry at Spin Centers” and STR 411/45-1) for financial support; we also appreciate the X-ray determination support of Prof. Dr. A. C. Filippou and Prof. Dr. D. Menche.

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DEDICATION The work is dedicated to Prof. Dr. A. C. Filippou on the occasion of his 60th birthday. G

DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

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DOI: 10.1021/acs.organomet.8b00367 Organometallics XXXX, XXX, XXX−XXX