Abstract
The Ce(III) hydrotris(3,5-dimethylpyrazolyl)borate complex [Ce(TpMe2)2(κ2-dmpz)] (1) (TpMe2 = {HB(dmpz)3}−; dmpz = 3,5-dimethylpyrazolide) was isolated in fair yield from the reaction of [Ce(I)3(THF)4] with two equivalents of [K(TpMe2)] via the facile decomposition of TpMe2. [Ce(TpMe2)2(bipy)] (2) was synthesized in poor yield by the “one-pot” reaction of [Ce(I)3(THF)4], bipy (bipy = 2,2′-bipyridine), KC8 and two equivalents of [K(TpMe2)] in tetrahydrofuran (THF). The reaction of 2 with N-methylmorpholine-N-oxide produced the known decomposition product [Ce(TpMe2)(μ-BOpMe2)]2 (3) (BOpMe2 = {HBO(dmpz)2}2−) in poor yield, presumably by N–O and B–N bond cleavage of a reactive intermediate. The reaction of 2 with trimethylsilylazide gave [Ce(TpMe2)2(N3)] (4) in poor yield; the fate of bipy and the trimethylsilyl group is unknown. Complexes 1–4 were characterized by single crystal XRD, NMR and FTIR spectroscopy and elemental analysis. Complex 2 was additionally probed by UV/Vis/NIR and Electron Paramagnetic Resonance (EPR) spectroscopies, Cyclic Voltammetry (CV) and magnetometry, which together indicate a formal 4f1 Ce(III) center coordinated by a bipy·− radical anion in this system.
Highlights
Complexes that exhibit terminal unsupported multiple bonds between a transition metal and a p-block element are legion, and interest in these species has surged in tandem with their increasing applicability in synthetic processes [1]
Zi and Walter [14] have shown that U(IV) and Th(IV) oxo and imido complexes can be prepared by the respective addition of N-oxides or organoazides to An(II) synthons, which mimic the reactivity of An(II) complexes the metal is formally in the +4 oxidation state
We envisaged that an analogous Ce(II) synthon, [Ce(TpMe2)2(bipy)], could react with N-oxides or organoazides to give complexes that contain terminal unsupported Ce(IV)=O or Ce(IV)=NR multiple bonds, provided the Ce(III) → Ce(IV) oxidation potential in these complexes could be overcome by these reagents. [Ce(TpMe2)2(bipy)] should contain a formal Ce(III) 4f1 center and the coupling of this unpaired spin with a ligand radical could lead to unusual physicochemical properties
Summary
Complexes that exhibit terminal unsupported multiple bonds between a transition metal and a p-block element are legion, and interest in these species has surged in tandem with their increasing applicability in synthetic processes [1]. The corresponding lanthanide (Ln) chemistry is underdeveloped, as the large orbital energy mis-match between Ln valence orbitals and the 2pz orbital of C, N and O makes these bonds highly polarized, making them prone to decomposition and oligomerisation pathways [2,3]. We envisaged that an analogous Ce(II) synthon, [Ce(TpMe2)2(bipy)], could react with N-oxides or organoazides to give complexes that contain terminal unsupported Ce(IV)=O or Ce(IV)=NR multiple bonds, provided the Ce(III) → Ce(IV) oxidation potential in these complexes could be overcome by these reagents. It is noteworthy that interesting multiconfigurational behavior has previously been observed in [Yb(Cp*)2(bipy)] [19,20], where the electronic ground state contains contributions from Yb(III)/bipy·− (4f13) and Yb(II)/bipy (4f14) configurations, but the donor properties of Cp* ligands are not comparable to those of TpMe2 ligands. The synthesis and characterization of [Ce(TpMe2)2(bipy)] and its reactivity towards N-oxides and organoazides is described
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