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A set of nine new robust, tunable cerium complexes supported by an ansa-bis(cyclopentadienyl) ligand, [Me₂Si(η⁵-Cp^R)₂]CeX (^anCp^R)CeX, are excellent homogeneous visible-light photocatalysts for the monodefluoroalkylation of trifluorotoluene with Mg(CH₂C₆H₅)₂THF₂ (R = Me₄, SiMe₃, X = N(SiMe₃)₂ (N″), X = CH(SiMe₃)₂ (R''), Cl, OC₆H₂^tBu₂-2,6,Me-4 (OAr)). The trends in photocatalytic activity within the series are explained by photophysical spectroscopic analyses. The aryloxide complex [Me₂Si(Cp^SiMe3)₂]CeOAr, which has the highest activity (95% substrate conversion in 27 h), shows the most negative (most reducing) excited-state reduction potential (-2.71 V vs Fc). The precatalyst excited-state lifetimes are also exceptionally long. Detailed photoluminescence, NMR spectroscopic, and kinetic studiesmore » on chloride [Me₂Si(Cp^Me4)₂]CeCl suggest that the "ate" complex [{Me₂Si(Cp^Me4)₂}₂Ce^IIIClBn][MgBn] is the active catalyst in the alkylation reaction to form PhCF₂CH₂Ph with high selectivity over PhCF₂H. Finally, the reaction rates are up to 30 times higher than previously reported for organometallic rare-earth photocatalysts for these Ce complexes and comparable to established Ir-based photoredox systems.« less

Isostructural, diamagnetic diluents are commonly used in magnetic investigations to eliminate interactions between neighboring electron spins. For divalent lanthanides, these diluents are currently limited to closed-shell ytterbium(II) complexes; ytterbium(II), however, is a poor size-match for the large early- and mid-lanthanides, precluding access to certain ligand frameworks. To aid in the study of lanthanide(II) complexes with unconventional electronic structures and magnetic properties, three strontium tris-cyclopentadienyl complexes, [K(2.2.2-cryptand)][SrCpR3], with common substituted cyclopentadienyl ligands, CpR = C5Me4H (Cptet), C5H4(SiMe3) (Cp'), and C5H3(SiMe3)2 (Cp″) were synthesized, characterized, and examined as diamagnetic diluents. En route to their synthesis, two new Sr metallocenes, [SrCpR2] CpR =more » Cptet, Cp', were also prepared. [K(2.2.2-cryptand)][SrCptet3] was used to dilute the new complex [K(2.2.2-cryptand)][EuIICptet3], and the EPR spectra of the diluted material shows narrower linewidths than those of pure [K(2.2.2-cryptand)][EuIICptet3], suggesting an increase in the spin-spin relaxation time that enables determination of the europium hyperfine coupling constant.« less

Rare earth tris(alkyl) complexes such as M(CH₂SiMe₃)₃(sol)_n are widely used as precursors for many compounds and as homogeneous catalysts for alkene polymerization and alkane functionalization. However, the thermal instability of those most conveniently made from the commercially available lithium salt of the neosilyl anion, LiCH₂SiMe₃, Li(r), restricts their utility. We present a new range of synthetically useful, more kinetically stable rare earth neosilyl solvates, derived from a full kinetic study of the various possible decomposition mechanisms of 7 known and 12 new solvated rare earth neosilyl complexes M(CH₂SiMe₃)₃(sol)_n M = Sc(III), Y(III), Lu(III), Sm(III), and sol = THF; TMEDA; DMPE;more » diglyme ((CH₃)₂(OCH₂CH₂)₂O, G₂), triglyme ((CH₃)₂(OCH₂CH₂)₃O, G₃). Surprisingly, simply using higher-denticity donors to sterically disfavor neosilyl γ-H elimination is not effective. While Sc(r)₃((CH₃)₂(OCH₂CH₂)₂O) has a half-life, t_1/2, of 258.1 h, six times longer than for Sc(r)₃(C₄H₈O)₂ (t_1/2 = 43 h), Lu(r)₃((CH₃)₂(OCH₂CH₂)₂O) and Y(r)₃((CH₃)₂(OCH₂CH₂)₂O) do not show the expected, analogous increased t_1/2. This is because new decomposition pathways appear for poorly fitting donors. Finally, kinetic studies demonstrate the impact of small, and increasing amounts of LiCl on the kinetics of the reactivity of the smaller alkyls Y(r)₃(THF)₂ and Lu(r)₃(THF)₂; molecules used in hydrocarbon chemistry and catalysis for fifty years. A new route to pure Y(r)₃(THF)₂, which avoids the traditional use of Li(r), is presented.« less