Material and Methods
All manipulations were performed under an inert gas atmosphere of dried nitrogen in standard (Schlenk) glassware. Solvents were dried according to known procedures and saturated with N2. The deuterated solvents used for the NMR spectroscopic measurements and the n-hexane for the crystallization was distilled prior to use over Na-K alloy. Commercially available chemicals were purchased from Aldrich or Fluka and used as received. Elemental analyses were performed by the Analytisches Labor des Instituts für Anorganische Chemie der Universität Göttingen. 1H (300.129, and 500.13 MHz), 13C (75.46 MHz) and 119Sn (111.97 MHz) NMR spectra were recorded on Bruker AM 300 and Bruker AM 500 spectrometers. EI mass spectra were recorded on a Finnigan MAT 8230 or a Varian MAT CH5 instrument. Melting points were measured in sealed glass tubes and were not corrected.
Synthesis of compound 3:
A solution of 1 (2.0 g, 3.98 mmol) in toluene (50 mL) was added slowly nBuLi (1.7 mL) at 0 oC after of 30 min was added dropwise to a stirred suspension of SnCl2 (0.83 g, 3.98 mmol) in toluene (10 mL) at room temperature. The solution was heated to 80 °C and stirred for 18 hrs. After cooling the solution was filtered and reduced under vacuum to yield a yellow solid of 3 ( 2.1 g, 80 %). Recrystallization from n-hexane (10 mL) at 2 oC for 1 week afforded crystals suitable for X-ray diffraction analysis. Mp: 194-196 oC. MS (EI, 70 eV) m/z (%): [M+] 656 (24), [M+]-Cl 621 (7), [M+]-SnCl 501 (10). 1H NMR (500.12 MHz, C6D6) d: 1.05 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.14 (s, 18H, (CH3)3-Ca), 1.21 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.31 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.47 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 3.12 (sept, 2H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 4.09 (sept, 2H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 6.14 (s, 1H, CHb), 6.94-7.15 (m, 6H, Haromat). 13C NMR (125.75 MHz, C6D6) d: 24.69 (CH(CH3)3), 24.79 (CH(CH3)3), 27.1 (CH(CH3)3), 28.63 (CH(CH3)3), 28.93 (CH(CH3)3), 29.53 (CH(CH3)3), 32.95 (CH3)3C-Ca), 43.63 (CH3)3C-Cb), 105.12 (Cb), 124.51 (C-p), 125.71 (C-m), 127.4 (C-m), 143.64 (C-i), 144.28 (C-o), 145.64 (C-o), 174.96 (C=N). 119Sn NMR (186.5 MHz, C6D6) d: - 243.3. Anal. Calcd for C35H53ClSnN2 (655.97 g/mol): C, 64.09; H, 8.14; N, 4.27. Found: C, 63.92; H, 8.07; N, 4.27.
Synthesis of compound 4:
A solution of 1 (2.0 g, 3.98 mmol) in toluene (50 mL) was added slowly nBuLi (1.7 mL) at 0 oC after of 30 min was added dropwise to a stirred suspension of PbCl2 (0.83 g, 3.98 mmol) in toluene (10 mL) at room temperature. The solution was heated to 80 °C and stirred for 18 hrs. After cooling, the solution was filtered and reduced under vacuum to yield a yellow solid of 4 (2.1 g, 80 %). Recrystallization from ether (10 mL) at 2 oC for 1 week affored crystals suitable for X-ray diffraction analysis. Mp: > 400 oC. 1H NMR (500.12 MHz, C6D6) d: 1.05 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.14 (s, 18H, (CH3)3-Ca), 1.21 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.31 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 1.47 (d, 6H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 3.12 (sept, 2H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 4.09 (sept, 2H, (CH3)2CH, 3J(H, H) = 6.84 Hz), 6.14 (s, 1H, CHb), 6.94-7.15 (m, 6H, Haromat). 13C NMR (125.75 MHz, C6D6) d: 24.69 (CH(CH3)3), 24.79 (CH(CH3)3), 27.1 (CH(CH3)3), 28.63 (CH(CH3)3), 28.93 (CH(CH3)3), 29.53 (CH(CH3)3), 32.95 (CH3)3C-Ca), 43.63 (CH3)3C-Cb), 105.12 (Cb), 124.51 (C-p), 125.71 (C-m), 127.4 (C-m), 143.64 (C-i), 144.28 (C-o), 145.64 (C-o), 174.96 (C=N). Anal. Calcd for C23H29ClN2Pb (576.14 g/mol): C, 47.95; H, 5.07; N, 4.86. Found: C, 47.87; H, 5.08; N, 4.77.
Single-crystal X-ray crystallography studies:
The data for 3, 4 and 5 were collected from shock-cooled crystals at 100(2) K. The data for 3 was collected on a Enraf Nonius Kappa-CCD, the data for 4 on a Bruker three-circle diffractometer equipped with a SMART 6000 CCD detector and a mirror-system-monochromated Cu Ka source and for 5 on a Bruker TXS-Mo rotating anode with APEX II detector on a D8 goniometer. The Enraf Nonius used graphite-monochromated MoKa radiation and the Bruker TXS-Mo rotating anode used INCOATEC Helios mirror optics as radiation monochromator. All three diffractometers were equipped with a low‑temperature device. The data of 3, 4 and 5 were integrated with SAINT, and an empirical absorption (SADABS) was applied [18]. The structures were solved by direct methods (SHELXS-97) [19] and refined by full-matrix least-squares methods against F2 (SHELXL-97) [20]. All non-hydrogen-atoms were refined with anisotropic displacement parameters. The hydrogen atoms were refined isotropically on calculated positions using a riding model with their Uiso values constrained to equal to 1.5 times the Ueq of their pivot atoms for terminal sp3 carbon atoms and 1.2 times for all other carbon atoms. Crystallographic data (excluding structure factors) for the structures reported in this paper have been deposited with the Cambridge Crystallographic Data Centre. The CCDC numbers are listed in Table 1. Copies of the data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
Electronic structure calculations
The molecular and electronic structures of 3 and 4 were studied using Density Functional Theory (DFT) at the B3LYP/LANL2DZdp level of theory[21] with Effective Core Potentials (ECPs) on Cl, Ge, Sn and Pb[22]. The basis sets were obtained from the EMSL basis set exchange[23]. Geometries were optimized and identified as minima by their vibrational analyses. All the calculations employed GAMESS-US 24 MAR 2007 (R6)[24]. Due to the size of the complexes, i-propyl groups were eliminated to reduce the computational requirements. Structures and orbitals were visualized using Jmol v.11[25]