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Published November 12, 2012 | Published + Supplemental Material
Journal Article Open

Synthesis of a Bis(thiophenolate)pyridine Ligand and Its Titanium, Zirconium, and Tantalum Complexes

Abstract

A precursor to a new tridentate LX_2 type ligand, bis(thiophenol)pyridine ((SNS)H_2 = (2-C_6H_4SH)_2-2,6-C_5H_3N), was prepared. Bis(thiophenolate)pyridine complexes of Ti, Zr, and Ta having dialkylamido coligands were synthesized and structurally characterized. The zirconium complex (SNS)Zr(NMe_2)_2 (4) displays C_2 symmetry in the solid state, unlike a related bis(phenolate)pyridine compound, C_s-symmetric (ONO)Ti(NMe_2)_2. This change is likely the result of strain about the sulfur atom in the six-membered chelate with longer metal–sulfur and carbon–sulfur bonds. Solid-state structures of tantalum complexes (SNS)Ta(NMe_2)_3 (5) and (SNS)TaCl(NEt_2)_2 (6) also display pronounced C_2 twisting of the SNS ligand. 1D and 2D NMR experiments show that 5 is fluxional, with rotation about the Ta–N(amide) bonds occurring on the NMR time scale that interchange the equatorial amide methyl groups (ΔG^‡_(393) = 25.0(3) kcal/mol). The fluxional behavior of 6 in solution was also studied by variable-temperature ^1H NMR. Observation of separate signals for the diastereotopic protons of the methylene unit of the diethylamide indicates that the complex remains locked on the NMR time scale in one diastereomeric conformation at temperatures below −50 °C, fast rotation about the equatorial amide Ta–N bonds occurs at higher temperature (ΔG^‡_(393) = 13.4(3) kcal/mol), and exchange of diastereomeric methylene protons occurs via inversion at Ta that interconverts antipodes (ΔG^‡_(393) ≈ 14(1) kcal/mol).

Additional Information

© 2012 American Chemical Society. Received: August 15, 2012. Published: October 18, 2012. This work was supported by a KAUST Center-In-Development Grant to King Fahd University of Petroleum and Minerals (Dhahran, Saudi Arabia) and the USDOE Office of Basic Energy Sciences (Grant No. DE-FG03-85ER13431). We thank Ian A. Tonks and Matthew S. Winston for helpful discussions related to the research present in this paper. We also thank Lawrence M. Henling and Michael W. Day of Caltech for solving crystal structures. The Bruker KAPPA APEXII X-ray diffractometer was purchased via an NSF CRIF:MU award to the California Institute of Technology (CHE-0639094).

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Supplemental Material - om300789h_si_001.pdf

Supplemental Material - om300789h_si_002.cif

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August 19, 2023
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