Journal of the American Chemical Society
Article
procedures, and these modifications are detailed in the Supporting
[Sm(SitBu3)2(THF)3] (1-Sm). This complex was prepared according
to the general procedure with [SmI2(THF)2] (1.097 g, 2 mmol) and
NaSitBu3 (0.890 g, 4 mmol); 1-Sm was obtained as dark purple
crystals (0.493 g, 0.64 mmol, 32%). Anal. Calcd for C36H78O3Si2Sm:
C, 56.48; H, 10.27; Sm, 19.64. Found: C, 52.83; H, 10.36; Sm, 20.22.
μeff = 3.40 μB (Evans method). 1H NMR (400.07 MHz, C6D6/
C4D8O, 298 K): δ −1.55 (s, br, ν1/2 ≈ 10 Hz, 54H, C(CH3)3), 1.48
(m, br, ν1/2 ≈ 10 Hz, 12H, CH2), 3.91 (m, br, ν1/2 ≈ 10 Hz, 12H,
OCH2). The 13C{1H} NMR spectrum could not be assigned, and no
resonances were detected in the 29Si{1H} NMR spectrum due to the
Computational Methods. The Gaussian 16 software package,
revision C.01,42 was used for all DFT calculations, excluding those
used to calculate NMR spectroscopy parameters (see below and
approximation PBE029,43 was employed. Dispersion was considered
with Grimme’s D3 dispersion corrections and the Becke−Johnson
damping parameters (D3-BJ)44−48 in all systems, except for No,
where these corrections are not available. Dunning’s correlation
consistent basis sets of polarized triple-ζ quality were used for H, C,
N, O, and Si atoms,49−52 and Pople’s 6-311G* basis set for Ca and
K.53 Stuttgart−Bonn small-core relativistic pseudopotentials and
associate segmented basis sets were used for the Sm, Eu, Yb, and
No atoms.54−58 Initial geometries were taken from the single-crystal
XRD structures, where available, and optimized with no symmetry
constraints. The quadratically convergent SCF procedure (SCF =
XQC) was used in the case of the Sm compounds to assist with the
electronic convergence. Otherwise, default settings used for the
optimization and analysis of the harmonic vibrational frequencies
confirmed that energetic minima were located. In the systems where
pseudopotentials were employed, single-point energy calculations
were subsequently performed with the all-electron SARC basis sets for
the metals,54,59,60 including the second-order Douglas−Kroll−Hess
(DKH2) Hamiltonian to account for scalar relativistic effects.61−63
Bonding analyses were performed on the all-electron electronic
structures.
paramagnetism of 1-Sm. ATR-IR: ν 2964 (w), 2828 (m), 1471 (m),
̃
1377 (w), 1023 (m), 867 (m), 806 (m), 569 (m) cm−1.
[Eu(SitBu3)2(THF)3] (1-Eu). This complex was prepared according to
the general procedure with [EuI2(THF)2] (1.100 g, 2 mmol) and
NaSitBu3 (0.890 g, 4 mmol); 1-Eu was obtained as yellow crystals
(0.489 g, 0.64 mmol, 32%). Anal. Calcd for C36H78EuO3Si2: C, 56.36;
H, 10.25. Found: C, 51.02; H, 9.70. μeff = 8.17 μB (Evans method). 1H
NMR (400.07 MHz, C6D6/C4D8O, 298 K): −3.87 (s, br, ν1/2 ≈ 2,350
Hz, C(CH3)3), 1.39 (m, br, ν1/2 ≈ 270 Hz, CH2), 3.58 (m, br, ν1/2
≈
360 Hz, OCH2). No resonances were observed in the 13C{1H} and
29
1
Si{ H} NMR spectra due to the paramagnetism of 1-Eu. FTIR: ν
̃
2918 (w), 2834 (m), 1467 (m), 1026 (m), 869 (m), 808 (m), 752
(m), 647 (m) cm−1.
[Yb(SitBu3)2(THF)2] (1-Yb). This complex was prepared according
to the general procedure with [YbI2(THF)2] (1.142 g, 2 mmol) and
NaSitBu3 (0.890 g, 4 mmol); 1-Yb was obtained as orange crystals
(0.608 g, 0.85 mmol, 42%). Anal. Calcd for C32H70O2Si2Yb: C, 53.67;
The natural bond orbital (NBO 7.0) software package,64,65
integrated with Gaussian 16, was used to compute natural localized
molecular orbitals (NLMOs) and natural population analysis of the
Ln−silicon bonding orbitals. WFX files generated from Gaussian 16
were used for the QCT analysis, including QTAIM and IQA analysis,
which was performed with the AIMAll software package.66 The IQA
analysis was implemented using encomp = 4, and the WFX file was
edited to include the appropriate ⟨Model⟩ tag.
NMR chemical shifts were computed with the Amsterdam density
functional theory (ADF) program.67,68 Spin−orbit coupled, single-
point calculations, using the optimized geometries described above,
employed the PBE0 hybrid and SAOP functionals. All-electron Slater-
type orbital triple-ζ-quality basis sets (TZ2P) were employed for the
Mg, Ca, Yb, No, and Si atoms, and double-ζ-quality basis sets (DZP)
were employed for all other atoms, in conjunction with the two-
component zero-order regular approximation (ZORA) Hamilto-
nian.69−71 The 29Si NMR chemical shifts are reported relative to
tetramethylsilane (TMS).
1
H, 9.85; Yb, 24.17. Found: C, 50.43; H, 9.53; Yb, 24.53. H NMR
(500.19 MHz, C6D6/C4D8O, 298 K): δ 1.37 (s, 54H, C(CH3)3), 1.45
(m, 8H, CH2), 3.56 (m, 8H, OCH2). 13C{1H} NMR (125.77 MHz,
C6D6/C4D8O, 298 K): δ 26.06 (CH2), 26.12 (C(CH3)3), 34.71
(C(CH3)3), 68.21 (OCH2). 29Si{1H} NMR (79.48 MHz, C6D6/
C4D8O, 298 K): 54.19 (1JYb−Si = 976 Hz). 171Yb{1H} NMR (87.52
MHz, C6D6/C4D8O, 298 K): 1044.64 (1JYb−Si = 976 Hz). ATR-IR: ν
2961 (w), 2828 (m), 1467 (m), 1378 (w), 1023 (m), 869 (m), 806
(m), 567 (m) cm−1.
̃
[Mg(SitBu2Me)2(THF)2] (2-Mg). A Schlenk flask charged with
MgBr2 (0.921 g, 5 mmol) and NaSitBu2Me (1.803 g, 10 mmol)
was cooled to −78 °C, and THF (40 mL) was added. The resulting
beige reaction mixture was warmed to room temperature and stirred
for 18 h. Volatiles were removed in vacuo, and the product was
extracted into heptane (50 mL). Removal of heptane under reduced
pressure gave crude 2-Mg as a colorless solid (1.200 g, 2.48 mmol,
49%). Colorless needles suitable for single-crystal XRD were obtained
from a concentrated heptane solution stored at −25 °C. Anal. Calcd
for C26H56O2Si2Mg: C, 64.90; H, 11.73. Found: C, 61.96; H, 12.23.
General Procedure for the Synthesis of 1-Ln and 2-Ln. A
mixture of [LnI2(THF)2] and 2 equiv of NaSiR3 in a Schlenk flask was
cooled to −78 °C, and THF (10 mL/mmol) was added. The reaction
mixture was warmed to room temperature and stirred for 18 h.
Volatiles were removed in vacuo, and the product was extracted into
hexane (25 mL/mmol) and filtered. Concentration of the resultant
solution and storage at 5 °C overnight resulted in the formation of
crystals of the product, with further crops obtained at −25 °C.
[Ca(SitBu3)2(THF)2] (1-Ca). A Schlenk flask charged with CaBr2
(0.400 g, 2 mmol) and NaSitBu3 (0.890 g, 4 mmol) was cooled to
−78 °C, and THF (35 mL) was added. The resulting amber reaction
mixture was warmed to room temperature and stirred for 18 h.
Volatiles were removed in vacuo, and the product was extracted into
heptane (50 mL). Removal of heptane under reduced pressure gave
crude 1-Ca as a pale yellow solid (0.518 g, 0.89 mmol, 44%). Pale
yellow needles suitable for single-crystal XRD were obtained from a
concentrated heptane solution stored at −25 °C. Anal. Calcd for
Consistently low carbon values were obtained and attributed to
1
silicon carbide formation. H NMR (400.07 MHz, C6D6, 298 K): δ
0.26 (s, 6H, CH3), 1.26 (m, 8H, CH2), 1.32 (s, 36H, C(CH3)3), 3.58
(m, 8H, OCH2). 13C{1H} NMR (100.60 MHz, C6D6, 298 K): δ
−1.06 (CH3), 21.99 (C(CH3)3), 25.48 (CH2), 32.18 (C(CH3)3),
69.92 (OCH2). 29Si{1H} NMR (79.48 MHz, C6D6, 298 K): δ 4.51.
ATR-IR: ν 2914 (w), 2879 (w), 2838 (m), 1465 (m), 1032 (m), 873
̃
(m), 814 (m), 754 (m), 645 (m), 577 (m) cm−1
.
[Ca(SitBu2Me)2(THF)3] (2-Ca). A Schlenk flask charged with CaBr2
(0.400 g, 3 mmol) and NaSitBu2Me (0.721 g, 4 mmol) was cooled to
−78 °C, and THF (35 mL) was added. The resulting yellow reaction
mixture was warmed to room temperature and stirred for 18 h.
Volatiles were removed in vacuo, and the product was extracted into
heptane (50 mL). Removal of heptane under reduced pressure gave
crude 2-Ca as a colorless solid (0.468 g, 0.82 mmol, 41%). Colorless
needles suitable for single-crystal XRD were obtained from a
concentrated heptane solution stored at −25 °C. Anal. Calcd for
1
C32H70CaO2Si2: C, 65.91; H, 12.10. Found: C, 64.72; H, 12.15. H
1
NMR (400.07 MHz, C6D6, 298 K): δ 1.26 (m, 8H, CH2), 1.41 (s,
54H, C(CH3)3), 3.59 (m, 8H, OCH2). 13C{1H} NMR (100.60 MHz,
C6D6, 298 K): δ 24.85 (CH2), 25.12 (CH2), 31.24 (C(CH3)3), 31.57
(C(CH3)3), 34.66 (C(CH3)3), 69.33 (OCH2). 29Si{1H} NMR (79.48
C30H66CaO3Si2: C, 63.09; H, 11.65. Found: C, 61.99; H, 11.89. H
NMR (400.07 MHz, C6D6, 298 K): δ 0.29 (s, 6H, CH3), 1.32 (m,
12H, CH2), 1.34 (s, 36H, C(CH3)3), 3.61 (m, 12H, OCH2). 13C{1H}
NMR (100.60 MHz, C6D6, 298 K): δ −0.17 (CH3), 22.17
(C(CH3)3), 25.51 (CH2), 32.62 (C(CH3)3), 68.92 (OCH2). 29Si{1H}
MHz, C6D6, 298 K): δ 25.64. ATR-IR: ν
(m), 1471 (m), 1026 (w), 871 (w), 806 (m), 566 (w).
̃
2967 (w), 2878 (w), 2832
NMR (79.48 MHz, C6D6, 298 K): δ 3.06. ATR-IR: ν 2932 (w), 2867
̃
9820
J. Am. Chem. Soc. 2021, 143, 9813−9824