Reactivity of a Neutral Yttrium(III) Trimethyl Complex toward Brønsted and Lewis Acids.

The present study corroborates that the neutral tridentate N-ligand 1,4,7-trimethyl-triazacyclononane (Me3TACN) qualifies as a versatile platform to study selective ligand exchange with rare-earth-metal alkyl complexes, herein [(Me3TACN)YMe3]. Treatment with Brønsted-acidic bis(dimethylsilyl)amine, HN(SiHMe2)2, gave selectively the mono-exchanged heteroleptic complex [(Me3TACN)YMe2{N(SiHMe2)2}]. Depending on the molecular ratio employed, the reaction of [(Me3TACN)YMe3] with AlMe3 resulted in the isolation/crystallization of [(Me3TACN)YMe2(AlMe4)] [1 : 1] or ion-separated [(Me3TACN)YMe(AlMe4)][AlMe4] [1 : 2] and [(Me3TACN)YMe(AlMe4)][Al2Me7] [1 : 3]. Analogous reactions with the heavier group 13 methyls GaMe3 and InMe3 generated mixed methyl/tetramethylgallato complex [(Me3TACN)YMe2(GaMe4)] and ion-separated [{(Me3TACN)YMe2}2{µ-Me}][InMe4]. Finally, dimethylalane, HAlMe2, converted [(Me3TACN)YMe3] into heteroaluminate [(Me3TACN)Y(HAlMe3)3], representing an AlMe3-supported, molecular yttrium trihydride complex. All compounds were investigated by single crystal X-ray diffraction (SC-XRD), homo- and heteronuclear (13C, 27Al, 89Y, 115In) NMR as well as IR spectroscopies and elemental analyses.

Distinct Reactivity of Trimethylytterbium toward AlMe3 and GaMe3 : Synthesis of Donor-Stabilized Dimethylytterbium.

Me3 TACN (1,4,7-trimethyl-1,4,7-triazacyclononane)-stabilized trimethylytterbium was obtained via a salt-metathesis protocol employing [(Me3 TACN)YbCl3 ] and methyllithium. Complex [(Me3 TACN)YbMe3 ] seems not to engage in redox chemistry with potassium graphite and is thermally quite stable in the solid state. Treatment of trivalent [(Me3 TACN)YbMe3 ] with 3 equiv. of AlMe3 afforded divalent tetramethylaluminate complex [(Me3 TACN)Yb(AlMe4 )2 ]. The reaction of [(Me3 TACN)YbMe3 ] with GaMe3 in THF gave trivalent ion pair [(Me3 TACN)YbMe2 (thf)][GaMe4 ], which is susceptible to reduction with KC8 . The thermally very labile divalent [(Me3 TACN)YbMe(µ-Me)]2 is the first discrete donor adduct of a divalent dimethyl rare-earth-metal complex.

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.

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.

Yttrium tris(trimethylsilylmethyl) complexes grafted onto MCM-48 mesoporous silica nanoparticles.

A series of tris(trimethylsilylmethyl) yttrium donor adduct complexes was synthesized and fully characterized by X-ray diffraction, 1H/13C/29Si/31P/89Y heteronuclear NMR and FTIR spectroscopies as well as elemental analyses. Treatment of Y(CH2SiMe3)3(thf)x with various donors Do led to complete (Do = TMEDA, DMAP) and partial displacement of THF (Do = NHCiPr, DMPE). Exceptionally large 89Y NMR shifts to low field were observed for the new complexes. Complexes Y(CH2SiMe3)3(tmeda) and Y(CH2SiMe3)3(dmpe)(thf) were chosen to perform surface organometallic chemistry, due to a comparatively higher thermal stability and the availability of the 31P nucleus as a spectroscopic probe, respectively. Mesoporous nanoparticles of the MCM-48-type were synthesized and used as a 3rd generation silica support. The parent and hybrid materials were characterized using X-ray powder diffraction, solid-state-NMR spectroscopy, DRIFTS, elemental analyses, N2-physisorption, and scanning electron microscopy (SEM). The presence of surface-bound yttrium alkyl moieties was further proven by the reaction with carbon dioxide. Quantification of the surface silanol population by means of HN(SiHMe2)2-promoted surface silylation is shown to be superior to titration with lithium alkyl LiCH2SiMe3.

Polymeric dimethylytterbium and the terminal methyl complex (TptBu,Me)Yb(CH3)(thf).

Divalent ytterbium bis(trimethylsilyl)amides [Yb{N(SiMe3)2}2]2 and Yb[N(SiMe3)2]2(thf)2 react with purified methyllithium to amorphous dimethylytterbium [YbMe2]n. The characterisation was performed by 171Yb and 13C CP/MAS NMR spectroscopy as well as by conducting protonolysis reactions with HC5Me5 and HTptBu,Me, affording known (C5Me5)2Yb(OEt2) and new (TptBu,Me)Yb(CH3)(thf).

Scandium bis(trimethylsilyl)methyl complexes revisited: extending the 45Sc NMR chemical shift range and a new structural motif of Li[CH(SiMe3)2].

Depending on the molar ratio employed, the reaction of ScCl3(thf)3 with Li[CH(SiMe3)2] afforded the bis and tris(alkyl) ate complexes [Sc{CH(SiMe3)2}2(µ-Cl)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(µ-Cl)Li(thf)3, respectively, in moderate yields. Treatment of these mixed alkyl/chlorido complexes with MeLi gave the mixed alkyl complexes [Sc{CH(SiMe3)2}2(µ-Me)2Li(thf)2]2 and Sc[CH(SiMe3)2]3(µ-Me)Li(thf)3. Aiming at homoleptic {Sc[CH(SiMe3)2]3} both of the mixed [CH(SiMe3)2]/Me complexes were treated with AlMe3. Although LiAlMe4 separation occurred, aluminium complex Al[CH(SiMe3)2]Me2(thf) was the only isolable crystalline complex. Ate complexes [Sc{CH(SiMe3)2}2(µ-Me)2Li(thf)2]2 and [Sc(CH2SiMe3)4][Li(thf)4] revealed the maximum downfield 45Sc NMR chemical shifts of 888.0 and 933.4 ppm, respectively, reported to date. The synthesis of putative {Sc[CH(SiMe3)2]3} was also attempted via the aryloxide route applying complexes Sc(OC6H2tBu2-2,6-Me-4)3 and [Sc(OC6H3iPr2-2,6)3]2 along with Li[CH(SiMe3)2] but the outcome was inconclusive. Instead, a cyclic octamer was found for Li[CH(SiMe3)2] in the solid state.