Synthesis and 171Yb-{1H} nuclear magnetic resonance spectra of ytterbium(II) aryloxides [Yb(OR′)2(L)n][(L)n=(OEt2)2, (thf)2, (thf)3, (pyridine)2 or Me2PCH2CH2PMe2] and [{Yb(µ-OR′)(X)}2](X = OR′ or NR2)(R′= C6H2But2-2,6-Me-4, R = SiMe3, thf = tetrahydrofuran)

Abstract

Crystalline homo- and hetero-leptic ytterbium(II) aryloxides derived from bulky 2,6-di-tert-butyl-4-methylphenol (R′OH) were prepared as follows: (a)[Yb(OR′)₂(OEt₂)₂]1 from 2 R′OH and [Yb(NR₂)₂(OEt₂)₂]I(R = SiMe₃); (b)[{Yb(OR′)(µ-OR′)}₂]2 by desolvating 1 or from [{Yb(NR₂)(µ-NR₂)}₂]II and 4 R′OH; and (c)[{Yb(NR₂)(µ-OR′)}₂]3 from II, and 2 R′OH or II and 2. Single-crystal X-ray diffraction studies established complex 1 to be monomeric with a distorted tetrahedral configuration and 2 to be dimeric with asymmetrically bridging ^–OR′ ligands. Complexes 1–3 were characterised by multinuclear (¹H, ¹³C, ²⁹Si and ¹⁷¹Yb) NMR spectroscopy and elemental (C, H, N) analysis. Variable-temperature ¹H and ¹³C NMR spectral data for 2 led to ΔG^‡ for the terminal/bridge ^–OR′ site-exchange process. The known aryloxide [Yb(OR′)₂(thf)₃]4 was obtained from 1 and an excess of tetrahydrofuran (thf); reacting 1 with the appropriate stoichiometric amount of thf, pyridine (py) or 1,2-bis(dimethylphosphino)ethane (dmpe) yielded [Yb(OR′)₂(thf)₂]5, [Yb(OR′)₂(py)₂]6 or [Yb(OR′)₂(dmpe)]7, respectively. The δ[¹⁷¹Yb-{¹H}] NMR spectral data for complexes 4–7 showed that displacement of diethyl ether from 1(δ 238 at 193 K) by another neutral coligand had a marked effect on the magnitude of the chemical shift, ranging from δ 286 at 233 K for 4 to δ 999 at 296 K for 7.