η3-Allyl Coordination at Pb(II) - Organometallics (ACS Publications)

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

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η3‑Allyl Coordination at Pb(II) Sebastian Weiß, Maximilian Auer, Klaus Eichele, Hartmut Schubert, and Lars Wesemann* Institut für Anorganische Chemie, Eberhard-Karls-Universität Tübingen, Auf der Morgenstelle 18, 72076 Tübingen, Germany

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S Supporting Information *

ABSTRACT: Allylmagnesium chloride and methyl-propenylmagnesium bromide were reacted with bulky substituted organolead and organotin halides (Ar*PbBr)2, (Ar′PbBr)2, (Ar*SnCl)2 (Ar* = 2,6-trip2C6H3-, trip = 2,4,6-triisopropylphenyl, Ar′ = 2,6-mes2C6H3-, mes = 2,4,6-trimethylphenyl). The allyl ligand coordinates in an η3-coordination mode at organoplumbylene fragments. In the solid state as well as in solution, η3-coordination was characterized by crystal structure analysis and Saunders’ isotopic perturbation technique. For the plumbylene Ar*Pb(C3H5), a solid state 207Pb magic angle spinning (MAS) NMR spectrum could be obtained. The isotropic chemical shift is −435 ppm, and the magnitude of the 207Pb chemical shift tensor of 7000(500) ppm is among the greatest observed experimentally. The methylallyl ligand coordinated at a plumbylene fragment exhibits two short and one long Pb−C interaction. In reaction with aniline, the allyl ligand reacts as a leaving group to give amidoplumbylenes.

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INTRODUCTION Allyl coordination chemistry is of fundamental interest in organometallic chemistry. The delocalized π-electron system of the allyl ligand offers the possibility to realize a variety of binding modes.1 Six different coordination modes have been structurally characterized so far. Furthermore, the allyl ligand exhibits dynamic interconversion processes, for example, a switch between η3-η1-η3-coordination. The η3-binding mode is associated with transition metal chemistry and was also found for alkali as well as alkaline earth metals. Allyl chemistry of the other main group elements is dominated by σ-coordination. For example, allyllead compounds are known for lead in oxidation state (IV).2 In substances like Ph3Pb-(CH2CH CH2), the allyl substituent is coordinated at the lead atom via the σ-binding mode. In the case of a tin(II)-compound Ar*Sn(η3-C3H5) (Ar* = 2,6-trip2C6H3-, trip = 2,4,6-triisopropylphenyl), we have presented recently an example for tinallyl η3-coordination.3 In this publication, we present examples for η3-allyllead coordination.

Scheme 1

Scheme 2

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RESULTS AND DISCUSSION Two terphenyllead bromides (Ar*PbBr)2 and (Ar′PbBr)2 (Ar* = 2,6-trip2C6H3-, trip = 2,4,6-triisopropylphenyl, Ar′ = 2,6mes2C6H3-, mes = 2,4,6-trimethylphenyl) were reacted with the Grignard reagent C3H5MgCl (Scheme 1). Methyl substitution derivatives 6 and 7 were synthesized by reactions of low valent tin and lead halides with 2-methylpropenylmagnesium bromide (Scheme 2). Allyl compounds 2, 4, 6, and 7 were characterized by elemental analyses, single crystal structure analyses as well as NMR spectroscopy. Results of single crystal structure determinations of 4 and 7 are illustrated in Figures 1 and 2. Selected interatomic distances and angles are listed. The data of the crystal structure measurements and structure solutions of 2, 4, 6, and 7 are placed in the Supporting Information (SI). © XXXX American Chemical Society

In the isolated plumbylene compounds 2, 4, and 7, the allyl ligand is coordinated at the main group element with Pb−C bond lengths in the range of 2.412(3)−2.624(3) Å, with the methylallyl ligand showing one very long Pb−C distance of 2.825(3) Å. In comparison, Pb−C bonds of alkyl groups are much shorter, with distances around 2.2 Å, whereas cyclopentadienyl ligands in cationic [CpPb]+ and [Cp*Pb]+ salts show comparable Pb−C distances [2.539(4)−2.598(11) Å].4−6 Olefin and alkyne coordination at triorgano lead cations or a low valent organolead cation reveal Pb−C distances in the range of 2.467(6)−2.989(4) Å.4,7−9 Lappert et al. have Received: October 23, 2018

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DOI: 10.1021/acs.organomet.8b00766 Organometallics XXXX, XXX, XXX−XXX

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Figure 1. ORTEP of the molecular structure of 4. Hydrogen atoms were placed in idealized positions. Ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Pb−C1 2.521(6), Pb−C2 2.514(8), Pb−C3 2.521(6), Pb−C4 2.326(7), C1−C2 1.402(6), C2− C3 1.402(6), C1−C2−C3 118.6(6), C4−Pb−C1 102.6(2), C4−Pb− C2 90.3(3). Figure 3. Experimental (bottom) and simulated (top) 207Pb MAS NMR spectrum of 4 at 62.79 MHz and a spinning rate of 11 kHz. The isotropic peak is marked by an asterisk.

NMR spectrum. It is among the greatest observed experimentally.14−20 Because relaxation by chemical shift anisotropy plays an important role for the 207Pb nucleus in solution, this sizable span may explain the unsuccessful attempts to obtain 207Pb NMR spectra in solution.13 207Pb NMR data were also investigated by quantum chemical calculations. On the basis of the DFT optimized geometry of 2, the 207Pb NMR chemical shift was calculated by using ADF (see the SI for details). As reference, the chemical shift of PbMe4 was calculated at the same level of theory. For Ar′Pb(C3H5), we found a 207Pb chemical shift of −1113 ppm and a span of the chemical shift tensor of 10 688 ppm. The difference between measured (−435 ppm) and calculated chemical shift (−1113 ppm) lies in the accepted range.14−16 According to the calculations, the direction of highest magnetic shielding is almost along the Pb−C(aryl) bond. Due to fluxional behavior of the allyl ligand in solution, all four methylene protons are equivalent on the NMR time scale and result in an A4X spin system and coupling pattern. In order to determine the ground state of the allyl coordination in solution, Ar*Pb(C3H5) was further investigated by using Saunders’ isotopic perturbation technique.1,21−26 Therefore, a partially deuterated allyl ligand was synthesized and coordinated at the lead atom (Scheme 3). In the room

Figure 2. ORTEP of the molecular structure of 7. Hydrogen atoms were placed in idealized positions. Ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Pb−C1 2.412(3), Pb−C2 2.624(3), Pb−C3 2.825(3), Pb−C4 2.327(3), C1−C2 1.431(4), C2− C3 1.360(4), C1−C2−C3 122.8(3), C4−Pb−C1 96.2(1), C4−Pb− C3 101.3(1).

characterized 1-aza-allyl coordination compounds of tin(II) and lead(II) {E[N(SiMe3)C(Ph)C(SiMe3)2]2} (E = Sn, Pb) and found dynamic coordination.10 In these molecules, the Pb−C bond lengths are 2.447(10) or 2.53(1) Å long. The methylallyl coordination at tin in compound 6 should be compared with the published allyltin example [Ar*Sn(C3H5)] [2.378(4), 2.380(4), 2.418(3) Å] and shows longer Sn−C bonds [2.314(3), 2.523(3), 2.679(3) Å] of the allyl moiety.3 1 H NMR signals of the allyl ligand of compounds 2 and 4 were found at slightly higher field in comparison to the signals published for Ar*Sn(C3H5), whereas the allyl carbon atoms show resonances in the 13C{1H} NMR spectrum at slightly lower field. For all substances, no signals were found in the solution 207Pb NMR spectra. However, in case of the allyl derivative 4, a solid state 207Pb magic angle spinning (MAS) NMR spectrum could be obtained (Figure 3). The isotropic chemical shift is −435 ppm. Plumbylenes show 207Pb NMR signals at very low field.11,12 An increase of the coordination number at lead by adduct formation results in resonances at higher field.13 In the presented example, the coordination number of four at the Pb(II) atom might be a reason for a resonance at higher field in comparison to plumbylenes. A striking feature of the 207Pb MAS NMR spectrum shown in Figure 3 is the magnitude of the span of the 207Pb chemical shift tensor, 7000(500) ppm, i.e., the total width of the 207Pb

Scheme 3

temperature 13C{1H} NMR spectrum, the methylene carbon atoms CH2 and CD2 exhibit one broad signal at 69.2 ppm. At −70 °C, one sharp signal at 65.1 ppm and one broad signal at 64.6 ppm were detected. Coupling with two deuterium atoms should result in a quintet which could not be resolved in the spectrum, and therefore, the broad signal was assigned to the CD2 group. This slight upfield shift of the CD2 group in B

DOI: 10.1021/acs.organomet.8b00766 Organometallics XXXX, XXX, XXX−XXX

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Organometallics comparison to the signal for the CH2 unit is an indicator for allyl η3-coordination in the ground state and can be distinguished from the η1-coordination mode which results in a slight downfield shift of the resonance of the CD2 group.1 The low valent allyltin Ar*Sn(C3H5) reacts with phenylacetylene under dimerization of two allyl units and formation of a tin carbon cage compound, whereas, in the reaction with benzonitrile, we found double insertion of the nitrile and formation of a 16-membered ring molecule.3 Therefore, the allyllead derivative 4 was also reacted with phenylacetylene or benzonitrile. However, in both cases, we were not able to characterize the reaction products. Reacting the allylplumbylenes 2 or 4 with aniline, a proton transfer reaction under liberation of propene and formation of monomeric or dimeric plumbylene amides 9 and 10 was found (Schemes 4 and 5).

Figure 5. ORTEP of the molecular structure of 10. Hydrogen atoms were placed in idealized positions. Ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Pb1−N1 2.380(9), Pb1− N2 2.412(8), Pb1−C1 2.319(11), Pb2−N1 2.407(8), Pb2−N2 2.384(9), Pb2−C2 2.329(12), N1−C3 1.425(14), N2−C4 1.415(14), N1−Pb1−C1 95.5(4), N1−Pb1−N2 78.1(3), C1−Pb1− N2 113.5(3), N2−Pb2−C2 96.5(4), N2−Pb2−N1 78.1(3), C2− Pb2−N1 104.2(3), Pb1−N1−N2−Pb2 155.7(3).

Scheme 4

Scheme 5 with the triisopropylphenyl substituted terphenyl ligand is a monomer in the solid state and the amide 10, carrying the smaller mesityl substituted terphenyl ligand, a dimer exhibiting a butterfly Pb2N2 geometry [torsion angle Pb1−N1−N2−Pb2 155.7(3)°]. The Pb−N bond length found in the monomer 2.187(2) Å is shorter than the Pb−N distances in the dimer [2.380(9), 2.412(8) Å]. In the literature, a variety of monomeric and dimeric lead amides were found which exhibit shorter and longer Pb−N bond lengths 2.075−2.471 Å.27−35

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CONCLUSION To conclude, the allyl ligand coordinates in an η3-coordination mode at organoplumbylene fragments. In the solid state as well as in solution, η3-coordination was characterized by crystal structure analysis and Saunders’ isotopic perturbation technique. In reaction with aniline, the allyl ligand reacts as a leaving group to give amidoplumbylene molecules.

Both lead amides were characterized by elemental analysis, NMR spectroscopy as well as single crystal structure analysis. In Figures 4 and 5, the molecular structures in the solid state are depicted. Due to the different steric bulkiness, the amide

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EXPERIMENTAL SECTION

All manipulations were carried out under an argon atmosphere using standard Schlenk techniques and gloveboxes. n-Hexane was dried using a. M.Braun − Solvent Purification System (SPS). All other solvents were destilled from sodium or sodium/benzophenone. All solvents were subsequently degassed by 3 × freeze/pump/thaw. Ar*PbBr, Ar*SnCl, and CD2CHCH2-MgBr were synthesized following literature procedures. 36−39 Further chemicals were purchased commercially and used as received, with the exception of aniline distilled before use. Elemental analyses were performed at the Institute of Inorganic Chemistry, University of Tübingen, using a Vario MICRO EL analyzer. NMR spectra were recorded on a Bruker DRX-250 NMR spectrometer (1H, 250.13 MHz; 13C, 62.90 MHz; 119 Sn, 93.28 MHz, 207Pb, 52.29 Hz) equipped with a 5 mm ATM probe head, a Bruker AvanceII+400 NMR spectrometer (1H, 400.11 MHz; 13C, 100.61 MHz) equipped with a 5 mm QNP (quad nucleus probe) head, and a Bruker AvanceII+500 NMR-spectrometer (1H, 500.13 MHz; 13C, 125.76 MHz; 119Sn, 186.50 MHz) equipped with a 5 mm ATM probe head and a setup for variable temperature. The chemical shifts are reported in δ values in ppm relative to external SiMe4 (1H, 13C), SnMe4 (119Sn), or PbMe4 (207Pb) using the chemical shift of the solvent 2H resonance frequency and Ξ = 25.145020% for

Figure 4. ORTEP of the molecular structure of 9. Hydrogen atoms were placed in idealized positions. Ellipsoids at 50% probability. Interatomic distances [Å] and angles [deg]: Pb−C1 2.322(2), Pb−N 2.187(2), C2−N 1.374(2), C2−N−Pb 126.5(1), N−Pb−C1 92.0(1). C

DOI: 10.1021/acs.organomet.8b00766 Organometallics XXXX, XXX, XXX−XXX

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Organometallics

mL) and benzene (0.5 mL). After 30 min at −40 °C, the resultant light brown suspension was warmed to room temperature and stirred for 3 h. Volatiles were then removed under reduced pressure, and the residue was extracted with hexane (10 mL) before being filtered. Hexane was removed under reduced pressure, and an orange solid can be obtained (41.0 mg, 81%). Crystals suitable for X-ray diffraction were grown from a concentrated hexane solution at −40 °C (21 mg, 41%, 0.037 mmol). 1H NMR (C6D6, 500.13 MHz): δ 2.14 (s, 12H, oCH3), 2.21 (s, 6H, p-CH3), 2.63 (d, 3JHH = 11.3 Hz, 4H, CH(CH2)2), 4.95 (quint, 3JHH = 11.3 Hz, 1H, CH(CH2)2), 6.90 (s, 4H, m-C6H2), 7.17−7.22 (m, 3H, C6H3). 13C NMR (C6D6, 125.76 MHz): δ 21.2 (pCH3), 21.2 (o-CH3), 65.0 (CH(CH2)2), 127.1 (p-C6H3), 129.0 (mC6H2), 130.1 (m-C6H3), 132.1 (CH(CH2)2), 136.0 (o-C6H2), 136.7 (p-C6H2), 141.9 (i-C6H2), 150.5 (o-C6H3), 207.2 (i-C6H3). Anal. Calcd for C27H30Pb: C, 57.73; H, 5.38. Found: C, 57.60; H, 5.37. 2,6-Trip2C6H3PbC3H5 (4). Allylmagnesium chloride solution (1.0 M in Me-THF, 65 μL, 0.065 mmol) at −40 °C was added dropwise to a stirred, orange solution of 2,6-Trip2C6H3PbBr (49.9 mg, 0.065 mmol) in hexane (2 mL) and benzene (0.5 mL). The resultant dark brown suspension was warmed to room temperature and stirred for 3 h. Volatiles were removed under reduced pressure, and the residue was extracted with hexane (8 mL) before being filtered. Hexane was removed under reduced pressure, and a light brown solid can be obtained (46.2 mg, 98%). Crystals suitable for X-ray diffraction were grown from a concentrated hexane solution at −40 °C (70%, 33 mg). 1 H NMR (C6D6, 400.11 MHz): δ 1.12 (d, 3JHH = 6.7 Hz, 12H, oCHMe2), 1.30 (d, 3JHH = 6.9 Hz, 12H, p-CHMe2), 1.43 (d, 3JHH = 6.9 Hz, 12H, o-CHMe2), 2.73 (d, 3JHH = 11.3 Hz, 4H, CH(CH2)2), 2.88 (sept, 3JHH = 7.0 Hz, 2H, p-CHMe2), 3.09 (sept, 3JHH = 6.9 Hz, 4H, oCHMe2), 4.77 (quint, 3JHH = 11.3 Hz, 1H, CH(CH2)2), 7.20 (t, 3JHH = 7.4 Hz, 1H, p-C6H3), 7.23 (s, 4H, m-C6H2), 7.52 (d, 3JHH = 7.4 Hz, 2H, m-C6H3). 13C{1H} NMR (C6D6, 100.61 MHz): δ 23.4 (oCHMe2), 24.4 (p-CHMe2), 26.2 (o-CHMe2), 30.8 (o-CHMe2), 34.9 (p-CHMe2), 69.4 (CH(CH2)2), 121.3 (m-C6H2), 125.4 (p-C6H3), 131.8 (CH(CH2)2), 132.8 (m-C6H3), 139.1 (i-C6H2), 147.3 (oC6H2), 148.5 (o-C6H3), 149.0 (p-C6H2), 214.4 (i-C6H3, identified by the deutero species). Anal. Calcd for C39H54Pb: C, 64.16; H, 7.46. Found: C, 63.99; H, 7.34. 2,6-Trip2C6H3SnC4H7 (6). 2-Methyl-propenylmagnesium bromide solution (0.5 M in THF, 158 μL, 0.079 mmol) at −40 °C was added dropwise to a stirred, yellow solution of 2,6-Trip2C6H3SnCl (50.0 mg, 0.079 mmol) in hexane (2 mL) and benzene (0.5 mL). After 30 min at −40 °C, the dark brown suspension was warmed to room temperature and stirred for a further 3 h. All volatiles were removed under reduced pressure; the residue was extracted with hexane (8 mL) before being filtered. The solvent was removed under reduced pressure, and a dark brown solid can be obtained (50.8 mg, 98%). Crystals suitable for X-ray diffraction were grown from a concentrated hexane solution at −40 °C (52%, 26.9 mg). 1H NMR (C6D6, 400.11 MHz): δ 1.13 (d, 3JHH = 6.7 Hz, 12H, o-CHMe2), 1.25 (d, 3JHH = 7.0 Hz, 12H, p-CHMe2), 1.47 (d, 3JHH = 7.0 Hz, 12H, o-CHMe2), 1.47 (s, 3H, CH3C(CH2)2), 2.84 (sept, 3JHH = 6.9 Hz, 2H, p-CHMe2), 2.88 (s, 4H, CH3C(CH2)2), 3.16 (sept, 3JHH = 6.9 Hz, 4H, o-CHMe2), 7.17−7.29 (m, 3H, o,p-C6H3), 7.23 (s, 4H, m-C6H2). 13C{1H} NMR (C6D6, 100.61 MHz): δ 23.2 (o-CHMe2), 24.1 (CH3C(CH2)2), 24.4 (p-CHMe2), 26.7 (o-CHMe2), 31.2 (o-CHMe2), 34.8 (p-CHMe2), 69.1 (CH3C(CH2)2), 121.5 (m-C6H2), 126.6 (p-C6H3), 130.0 (mC6H3), 137.3 (i-C6H2), 146.5 (o-C6H3), 147.3 (o-C6H2), 149.2 (pC6H2), 149.6 (CH3C(CH2)2), 173.3 (i-C6H3). Anal. Calcd for C40H56Sn: C, 73.28; H, 8.61. Found: C, 73.04; H, 8.66. 2,6-Trip2C6H3PbC4H7 (7). 2-Methyl-propenylmagnesium bromide solution (0.5 M in THF, 130 μL, 0.065 mmol) at −40 °C was added dropwise to a stirred, orange solution of 2,6-Trip2C6H3PbBr (50.0 mg, 0.065 mmol) in hexane (2 mL) and benzene (0.5 mL). After 30 min at −40 °C, the dark brown suspension was warmed to room temperature and stirred for a further 3 h. All volatiles were removed under reduced pressure; the residue was extracted with hexane (8 mL) before being filtered. The solvent was removed under reduced pressure, and a dark brown solid can be obtained (46.4 mg, 96%). Crystals suitable for X-ray diffraction were grown from a concentrated

C, Ξ = 37.290632% for 119Sn, and Ξ = 20.920599% for 207Pb.40 The multiplicity of the signals is abbreviated as s = singlet, d = doublet, t = triplet, quint = quintet, sept = septet, and m = multiplet or unresolved. The proton and carbon signals were assigned by detailed analysis of 1 H, 13C{1H}, 1H−1H COSY, 1H−13C HSQC, 1H−13C HMBC, and 13 C{1H} DEPT 135 spectra. Solid-state 207Pb NMR spectra were obtained at 62.79 MHz on a Bruker Avance IIIHD NMR spectrometer equipped with a 300 MHz wide-bore magnet. A powder sample of the allyllead compound 4 was packed into a 4 mm o.d. zirconia rotor under the inert atmosphere of a glovebox. Crosspolarization from 1H to 207Pb was attempted, but no signals were observed. Direct 207Pb excitation produced spectra with a severe baseline roll, ascribed to acoustic ringing (Supporting Information). A pulse sequence designed to suppress acoustic ringing removed the baseline roll indeed, but also most of the desired signal.41 Hence, the spectrum shown here is the result of the direct excitation (1.33 μs 30° pulse, 0.2 s recycle delay, 800 000 scans), followed by a cubic spline baseline correction. The position of the isotropic peak was verified by changing the MAS spinning rate from 10 to 11 kHz. Referencing against external PbMe4 was achieved by the substitution method: an external sample of CHCl3 in acetone was spun at 2 kHz, and the external magnetic field was adjusted such that the 1H chemical shift of CHCl3 matched a predetermined chemical shift wrt. external 1% TMS in CHCl3. Cubic spline baseline correction was performed using Bruker TopSpin 3.5. Spectral simulations were carried out using WSolids1.42 X-ray data were collected with a Bruker Smart APEX II diffractometer with graphite-monochromated Mo Kα radiation or a Bruker APEX II Duo diffractometer with a Mo IμS microfocus tube and TRIUMPH monochromator. The programs used were Bruker’s APEX2 v2011.8-0, including SADABS for absorption correction, SAINT for data reduction, and SHELXS for structure solution, as well as the WinGX suite of programs version 1.70.01 or the GUI ShelXle, including SHELXL for structure refinement.43−47 DFT calculations were carried out with Gaussian 09.48 The molecular structure of compound 2 was optimized using the BP86 functional, along with the implemented def2-TZVP basis set for C and H atoms, except Pb.49−54 For lead atoms, Stuttgart Dresden effective core potentials were employed, in combination with optimized valence basis sets as implemented in Gaussian 09.49−54 Dispersion corrections were included by adding the D3 version of Grimme’s dispersion with Becke-Johnson damping.55 The geometry optimization was performed without imposing any symmetry constraints, and the structure obtained was confirmed as a true minimum by calculating analytical frequencies, which gave two spurious imaginary frequencies. Natural bond orbitals were obtained using the NBO 6.0 software.56−58 Plots were generated with the software Chemcraft.59 On the basis of the optimized geometry, NMR calculations were performed using ADF60−62 with the GGA revPBE-D3(BJ) functional and ZORA TZ2P basis set for Pb and TZP for C and H.63−71 Elemental analyses were obtained from the crystalline substances in all cases. (2,6-Mes2C6H3PbBr)2 (1). A solution of (2,6-Mes2C6H3Li)2 (100.0 mg, 0.156 mmol) in THF (4 mL) at −40 °C was added to a suspension of lead(II) bromide (114.6 mg, 0.312 mmol) in THF (4 mL). The suspension turns immediately purple; after stirring 16 h at room temperature, the suspension turns yellow. All volatiles were removed under reduced pressure; the residue was extracted with toluene (12 mL) before being filtered. The solution was concentrated under reduced pressure to a volume of ca. 6 mL and overlaid with hexane (6 mL). After 3 days at −40 °C, yellow crystals were obtained (103 mg, 55%). 1H NMR (C6D6, 400.11 MHz): δ 2.18 (s, 12H, oCH3), 2.19 (s, 6H, p-CH3), 6.83 (s, 4H, m-C6H2), 7.32 (t, 3JHH = 7.5 Hz, 1H, p-C6H3), 7.67 (d, 3JHH = 7.5 Hz, 2H, m-C6H3). 13C NMR (C6D6, 100.61 MHz): δ 21.2 (p-CH3), 21.7 (o-CH3), 127.4 (p-C6H3), 128.9 (m-C6H2), 135.6 (m-C6H3), 137.1 (p-C6H2), 137.5 (o-C6H2), 138.7 (i-C6H2), 150.0 (o-C6H3), 285.8 (i-C6H3). Anal. Calcd for C48H50Pb2Br2: C, 48.00; H, 4.20. Found: C, 48.27; H, 4.24. 2,6-Mes2C6H3PbC3H5 (2). Allylmagnesium chloride solution (1.0 M in Me-THF, 91 μL, 0.091 mmol) at −40 °C was added dropwise to a stirred, yellow solution of 1 (54.5 mg, 0.045 mmol) in hexane (2 13

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DOI: 10.1021/acs.organomet.8b00766 Organometallics XXXX, XXX, XXX−XXX

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52.39 MHz): δ 3277. Anal. Calcd for C60H62N2Pb2: C, 58.80; H, 5.10; N, 2.29. Found: C, 58.91; H, 5.07; N, 2.10.

hexane solution at −40 °C (51%, 25 mg). 1H NMR (C6D6, 400.11 MHz): δ 1.13 (d, 3JHH = 6.8 Hz, 12H, o-CHMe2), 1.21 (s, 3H, CH3C(CH2)2), 1.26 (d, 3JHH = 7.0 Hz, 12H, p-CHMe2), 1.43 (d, 3JHH = 6.8 Hz, 12H, o-CHMe2), 2.33 (s, 4H, CH3C(CH2)2), 2.84 (sept, 3 JHH = 6.9 Hz, 2H, p-CHMe2), 3.21 (sept, 3JHH = 6.9 Hz, 4H, oCHMe2), 7.21 (s, 4H, m-C6H2), 7.30 (t, 3JHH = 7.3 Hz, 1H, p-C6H3), 7.72 (d, 3JHH = 7.3 Hz, 2H, m-C6H3). 13C{1H} NMR (C6D6, 100.61 MHz): δ 23.5 (o-CHMe2), 24.2 (CH3C(CH2)2), 24.4 (p-CHMe2), 26.4 (o-CHMe2), 30.9 (o-CHMe2), 34.9 (p-CHMe2), 87.2 (CH3C(CH2)2), 121.4 (m-C6H2), 125.2 (p-C6H3), 135.5 (m-C6H3), 137.2 (iC6H2), 147.4 (o-C6H3), 147.5 (o-C6H2), 149.0 (p-C6H2), 150.9 (CH3C(CH2)2), i-C6H3 could not be observed. Anal. Calcd for C40H56Pb: C, 64.57; H, 7.59. Found: C, 64.57; H, 7.50. 2,6-Trip2C6H3PbC3H3D2 (8). Freshly prepared allyl-d2-magnesium chloride solution (0.085 M in THF, 1.53 mL, 0.130 mmol) at −40 °C was added dropwise to a stirred, orange solution of 2,6-Trip2C6H3PbBr (100 mg, 0.130 mmol) in hexane (4 mL) and benzene (1 mL). After 30 min at −40 °C, the orange solution was warmed to room temperature and stirred for a further 3 h. Volatiles were removed under reduced pressure, and the residue was extracted with hexane (10 mL) before being filtered. Crystals suitable for X-ray diffraction were grown from a concentrated hexane solution at −40 °C (55 mg, 58%). 1H NMR (C6D6, 500.13 MHz): δ 1.13 (d, 3JHH = 6.8 Hz, 12H, o-CHMe2), 1.30 (d, 3JHH = 6.9 Hz, 12H, p-CHMe2), 1.44 (d, 3JHH = 7.0 Hz, 12H, o-CHMe2), 2.74 (d, 3JHH = 11.5 Hz, 2H, CH2CHCD2), 2.89 (sept, 3JHH = 6.9 Hz, 2H, p-CHMe2), 3.08 (sept, 3JHH = 6.9 Hz, 4H, o-CHMe2), 4.76 (br t, 3JHH = 11.5 Hz, 1H, CH2CHCD2), 7.18 (m, 1H, p-C6H3), 7.25 (s, 4H, m-C6H2), 7.44 (d, 3JHH = 7.4 Hz, 2H, m-C6H3). 2H NMR (C6D6, 76.77 MHz): δ 2.71 (br s, 2D, CH2CHCD2). 13C{1H} NMR (C6D6, 100.61 MHz): δ 23.3 (oCHMe2), 24.4 (p-CHMe2), 26.1 (o-CHMe2), 30.8 (o-CHMe2), 34.9 (p-CHMe2), 69.2 (overlapping s and quint, CH2CHCD2), 121.1 (mC6H2), 125.3 (p-C6H3), 131.5 (CH2CHCD2), 131.8 (m-C6H3), 139.6 (i-C6H2), 147.2 (o-C6H2), 148.5 (o-C6H3), 148.8 (p-C6H2), 214.1 (iC6H3). Anal. Calcd for C39H52D2Pb: C, 63.99; H, 7.71. Found: C, 64.16; H, 7.32. 2,6-Trip2C6H3PbNH-Ph (9). To a solution of 4 (48.0 mg, 0.066 mmol) in C6D6 (0.6 mL) was added aniline (6 μL, 0.066 mmol). The resulting dark red solution was stirred for 24 h. The solvent was removed under reduced pressure, and the residue was solved in hexane (0.2 mL). After 3 days at −40 °C, red crystals suitable for Xray diffraction were obtained (45.6 mg, 89%). 1H NMR (C6D6, 400.11 MHz): δ 1.13 (d, 3JHH = 6.7 Hz, 12H, o-CHMe2), 1.20 (d, 3 JHH = 6.9 Hz, 12H, p-CHMe2), 1.35 (d, 3JHH = 6.9 Hz, 12H, oCHMe2), 2.79 (sept, 3JHH = 6.9 Hz, 2H, p-CHMe2), 3.20 (sept, 3JHH = 6.9 Hz, 4H, o-CHMe2), 6.40 (d, 3JHH = 7.8 Hz, 2H, o-C6H5), 6.59 (m, 3 JHH = 7.2 Hz, 5JHH = 1.1 Hz, 1H, p-C6H5), 7.13 (t, 3JHH = 7.8 Hz, 2H, m-C6H5), 7.20 (s, 4H, m-C6H2), 7.35 (t‘,3JHH = 7.6 Hz, 1H, p-C6H3), 7.82 (d, 3JHH = 7.5 Hz, 2H, m-C6H3), 8.45 (br s, 1H, NH). 13C{1H} NMR (C6D6, 100.61 MHz): δ 23.4 (o-CHMe2), 24.2 (p-CHMe2), 26.3 (o-CHMe2), 31.2 (o-CHMe2), 34.8 (p-CHMe2), 117.0 (o-C6H5), 117.9 (p-C6H5), 121.5 (m-C6H2), 125.8 (p-C6H3), 129.0 (m-C6H5), 136.1 (i-C6H2), 136.4 (m-C6H3), 146.7 (o-C6H3),147.7 (o-C6H2), 149.3 (p-C6H2), 153.6 (i-C6H5), 268.3 (i-C6H3). Anal. Calcd for C42H55NPb: C, 64.58; H, 7.10; N, 1.79. Found: C, 64.46; H, 7.13; N, 1.93. (2,6-Mes2C6H3PbNH-Ph)2 (10). To a solution of 2 (20.0 mg, 0.036 mmol) in hexane (0.4 mL) was added aniline (3.3 μL, 0.036 mmol). After 1 day at room temperature, yellow crystals suitable for X-ray diffraction were obtained (10.2 mg, 46%). 1H NMR (C6D6, 500.13 MHz): δ 2.03 (s, 24H, o-CH3), 2.17 (s, 12H, p-CH3), 4.12 (s, 2H, NH), 5.95 (d, 3JHH = 7.2 Hz, 4H, o-C6H5), 6.60 (t, 3JHH = 7.2 Hz, 2H, p-C6H5), 6.64 (s, 8H, m-C6H2), 6.96 (t, 3JHH = 7.8 Hz, 4H, mC6H5), 7.21−7.27 (m, 6H, m-C6H3, p-C6H3). 13C NMR (C6D6, 125.76 MHz): δ 21.2 (p-CH3), 22.1 (o-CH3), 119.6 (p-C6H5), 121.1 (o-C6H5), 126.9 (p-C6H3), 128.1 (m-C6H5), 129.6 (m-C6H2), 133.9 (m-C6H3), 135.7 (o-C6H2), 136.2 (p-C6H2),139.8 (i-C6H2), 149.3 (oC6H3), 150.0 (i-C6H5), 242.4 (i-C6H3). 15N NMR (C6D6, 50.68 MHz): δ 86.3 (identified by 1H−15N-HSQC). 207Pb NMR (C6D6,

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ASSOCIATED CONTENT

* Supporting Information S

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.organomet.8b00766. Crystallographic details (1, 2, 4, 6, 7, 9, 10), NMR spectra (1, 2, 4, 6−10), and details of quantum chemical calculations (PDF) Cartesian coordinates of DFT optimized geometry Ar′Pb(C3H5) (2) (XYZ) Accession Codes

CCDC 1874645−1874651 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by emailing [email protected], or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Lars Wesemann: 0000-0003-4701-4410 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors acknowledge support by the state of BadenWürttemberg through bwHPC and the German Research Foundation (DFG) through grant no INST 40/467-1 FUGG. L.W. is grateful to the DFG for financial support (grant no WE 1876/12-1, 13-1).

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REFERENCES

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