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Title: Homoleptic Trivalent Tris(alkyl) Rare Earth Compounds

Journal Article · · Journal of the American Chemical Society
DOI:https://doi.org/10.1021/jacs.7b09521· OSTI ID:1411958
ORCiD logo [1];  [1];  [1];  [1];  [2]; ORCiD logo [1];  [3]; ORCiD logo [1]
  1. Ames Lab. and Iowa State Univ., Ames, IA (United States)
  2. Iowa State Univ., Ames, IA (United States)
  3. Kumbo Petrochemical R&D Center, Daejeon (Republic of Korea)
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Homoleptic tris(alkyl) rare earth complexes Ln{C(SiHMe2)3}3 (Ln = La, 1a; Ce, 1b; Pr, 1c; Nd, 1d) are synthesized in high yield from LnI3THFn and 3 equiv of KC(SiHMe2)3. X-ray diffraction studies reveal 1a–d are isostructural, pseudo-C3-symmetric molecules that contain two secondary Ln←HSi interactions per alkyl ligand (six total). Spectroscopic assignments are supported by comparison with Ln{C(SiDMe2)3}3 and DFT calculations. Here, the Ln←HSi and terminal SiH exchange rapidly on the NMR time scale at room temperature, but the two motifs are resolved at low temperature. Variable-temperature NMR studies provide activation parameters for the exchange process in 1a (ΔH‡ = 8.2(4) kcal·mol–1; ΔS‡ = –1(2) cal·mol–1K–1) and 1a-d9 (ΔH‡ = 7.7(3) kcal·mol–1; ΔS‡ = –4(2) cal·mol–1K–1). Comparisons of lineshapes, rate constants (kH/kD), and slopes of ln(k/T) vs 1/T plots for 1a and 1a-d9 reveal that an inverse isotope effect dominates at low temperature. DFT calculations identify four low-energy intermediates containing five β-Si–H→Ln and one γ-C–H→Ln. The calculations also suggest the pathway for Ln←HSi/SiH exchange involves rotation of a single C(SiHMe2)3 ligand that is coordinated to the Ln center through the Ln–C bond and one secondary interaction. These robust organometallic compounds persist in solution and in the solid state up to 80 °C, providing potential for their use in a range of synthetic applications. For example, reactions of Ln{C(SiHMe2)3}3 and ancillary proligands, such as bis-1,1-(4,4-dimethyl-2-oxazolinyl)ethane (HMeC(OxMe2)2) give {MeC(OxMe2)2}Ln{C(SiHMe2)3}2, and reactions with disilazanes provide solvent-free lanthanoid tris(disilazides).

Research Organization:
Ames Lab., Ames, IA (United States)
Sponsoring Organization:
USDOE Office of Energy Efficiency and Renewable Energy (EERE)
Grant/Contract Number:
AC02-07CH11358
OSTI ID:
1411958
Report Number(s):
IS-J-9441; TRN: US1800290
Journal Information:
Journal of the American Chemical Society, Vol. 139, Issue 46; ISSN 0002-7863
Publisher:
American Chemical Society (ACS)Copyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 13 works
Citation information provided by
Web of Science

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Rare earth arylsilazido compounds with inequivalent secondary interactions journal January 2018
Interconverting Lanthanum Hydride and Borohydride Catalysts for C=O Reduction and C−O Bond Cleavage journal January 2019
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Linked Research (4)

Figures / Tables (7)

Chart 1.(p. 1)figure Chart 1.
Figure 1.(p. 3)figure Figure 1.
Figure 2.(p. 4)figure Figure 2.
Figure 3.(p. 5)figure Figure 3.
Table 1.(p. 6)table Table 1.
Figure 4.(p. 7)figure Figure 4.
Scheme 1.(p. 9)figure Scheme 1.

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