Yttrium Complexes with Group 13 Heterobenzene-Type Ligands.

The yttrium gallabenzene complex [(1-Me-3,5-tBu2 -C5 H3 Ga)(µ-Me)Y(2,4-dtbp)] is accessible from Y(GaMe4 )3 and K(2,4-dtbp) via a tandem salt metathesis/methane elimination (2,4-dtbp=2,4-di-tert-butyl-pentadienyl). The pentadienyl ligand in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] (E=Al, Ga) is easily displaced by salt metathesis with KC5 Me5 and KTpMe,Me (TpMe,Me =tris(pyrazolyl-Me2 -3,5)borato) affording [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(TpMe,Me )] and [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(C5 Me5 )]. The yttrium center in [(1-Me-3,5-tBu2 -C5 H3 E)(µ-Me)Y(2,4-dtbp)] readily forms adducts with neutral Lewis bases like 4-DMAP (4-dimethylaminopyridine), PMe3 , DMPE (1,2-bis(dimethylphosphino)ethane), and DME (1,2-dimethoxyethane). In stark contrast, addition of TMEDA (N,N,N',N'-tetramethylethylenediamine) results in methyl/pentadienyl exchange between aluminum and yttrium resulting in [(1-(2,4-dtbp)-1-Me-3,5-tBu2 -C5 H3 Al)Y(Me)(tmeda)]. The bonding features of the newly synthesized complexes are analyzed by single-crystal X-ray diffraction (SCXRD) and heteronuclear (89 Y, 31 P) NMR spectroscopy.

Schlenk's Legacy-Methyllithium Put under Close Scrutiny.

Commercially available stock solutions of organolithium reagents are well-implemented tools in organic and organometallic chemistry. However, such solutions are inherently contaminated with lithium halide salts, which can complicate certain synthesis protocols and purification processes. Here, we report the isolation of chloride-free methyllithium employing K[N(SiMe3 )2 ] as a halide-trapping reagent. The influence of distinct LiCl contaminations on the 7 Li-NMR chemical shift is examined and their quantification demonstrated. The structural parameters of new chloride-free monomeric methyllithium complex [(Me3 TACN)LiCH3 ], ligated by an azacrown ether, are assessed by comparison with a halide-contaminated variant and monomeric lithium chloride [(Me3 TACN)LiCl], further emphasizing the effect of halide impurities.

CeCl3 /n-BuLi: Unraveling Imamoto's Organocerium Reagent.

CeCl3 (thf) reacts at low temperatures with MeLi, t-BuLi, and n-BuLi to isolable organocerium complexes. Solvent-dependent extensive n-BuLi dissociation is revealed by 7 Li NMR spectroscopy, suggesting "Ce(n-Bu)3 (thf)x " or solvent-separated ion pairs like "[Li(thf)4 ][Ce(n-Bu)4 (thf)y ]" as the dominant species of the Imamoto reagent. The stability of complexes Li3 Ln(n-Bu)6 (thf)4 increases markedly with decreasing LnIII size. Closer inspection of the solution behavior of crystalline Li3 Lu(n-Bu)6 (thf)4 and mixtures of LuCl3 (thf)2 /n-BuLi in THF indicates occurring n-BuLi dissociation only at molar ratios of <1:3. n-BuLi-depleted complex LiLu(n-Bu)3 Cl(tmeda)2 was obtained by treatment of Li2 Lu(n-Bu)5 (tmeda)2 with ClSiMe3 , at the expense of LiCl incorporation. Imamoto's ketone/tertiary alcohol transformation was examined with 1,3-diphenylpropan-2-one, affording 99 % of alcohol.

Deuterated Molecular Ruby with Record Luminescence Quantum Yield.

The recently reported luminescent chromium(III) complex 13+ ([Cr(ddpd)2 ]3+ ; ddpd=N,N'-dimethyl-N,N'-dipyridine-2-yl-pyridine-2,6-diamine) shows exceptionally strong near-IR emission at 775 nm in water under ambient conditions (Φ=11 %) with a microsecond lifetime as the ligand design in 13+ effectively eliminates non-radiative decay pathways, such as photosubstitution, back-intersystem crossing, and trigonal twists. In the absence of energy acceptors, such as dioxygen, the remaining decay pathways are energy transfer to high energy solvent and ligand oscillators, namely OH and CH stretching vibrations. Selective deuteration of the solvents and the ddpd ligands probes the efficiency of these oscillators in the excited state deactivation. Addressing these energy-transfer pathways in the first and second coordination sphere furnishes a record 30 % quantum yield and a 2.3 millisecond lifetime for a metal complex with an earth-abundant metal ion in solution at room temperature.

Rare-earth-metal trimethylsilylmethyl ate complexes.

En route to putative rare-earth-metal alkylidene complex Li[Lu(CH2SiMe3)2(CHSiMe3)], according to Schumann's original protocol, the reaction of YCl3 with LiCH2SiMe3 in a mixture of diethyl ether and n-pentane afforded a neosilyl ate complex of composition Li3Y(CH2SiMe3)6. Tetrametallic complex Li3Y(CH2SiMe3)6 shows an unprecedented structural motif in the solid state and was further characterized by heteronuclear 1H/13C/7Li/29Si/89Y, as well as VT NMR and DRIFT spectroscopies. Analysis of the thermolysis product via heteronuclear NMR spectroscopy and its reactivity towards benzophenone gave strong evidence for an alkylidene formation upon decomposition. Application of a similar protocol for the smallest rare-earth-metal scandium led to the isolation of ate complex [Li(thf)4][LiSc2(CH2SiMe3)8] as the preferred crystallized product. Here, the reaction of adduct ScCl3(thf)3 and LiCH2SiMe3 was performed in Et2O/n-hexane, in the absence of additional THF. The reaction of LaCl3(thf) with 3 equiv. of LiCH2SiMe3 in THF/Et2O at -40 °C yielded the ate complex [Li(thf)4][La(CH2SiMe3)4(thf)], which is the first of its kind.

Pentadienyl migration and abstraction in yttrium aluminabenzene complexes including a single-component catalyst for isoprene polymerization.

Aluminabenzene complex [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(2,4-dtbp)] (2,4-dtbp = 2,4-di-tert-butylpentadienyl) reacts with LiN(SiHMe2)2 according to a methyl/silylamido exchange and formation of [(1-Me-3,5-tBu2-C5H3Al){µ-N(SiHMe2)2}Ln(2,4-dtbp)] which engages in a donor(THF)-dependent reversible Ln-to-Al-pentadienyl migration. The reaction of [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(2,4-dtbp)] with [CPh3][B(C6F5)4] results in pentadienyl group abstraction affording cationic complex [(1-Me-3,5-tBu2-C5H3Al)(µ-Me)Y(benzene)][B(C6F5)4] which acts as a single-component catalyst in isoprene polymerization.