Reactivity of Yttrium Methyl Complexes: Hydrido Transfer Capability of Selected Alkylalanes

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.

Triisobutylaluminium-promoted formation of lanthanide hydrides

Discrete lanthanide(III) isobutylaluminates Ln[N(SiMe₃)₂](HAliBu₃)(AliBu₄) (Ln = La, Pr, Nd) are obtained from Ln[N(SiMe₃)₂]₃ and triisobutylaluminium (TIBA). Nd[N(SiMe₃)₂](HAliBu₃)(AliBu₄) reacts with crown ether to give the ion pair [Nd(18-c-6){N(SiMe₃)₂}(HAliBu₃)][AliBu₄], featuring a strong Nd-H interaction in the solid state. The equimolar reaction of La[N(SiMe₃)₂](HAliBu₃)(AliBu₄) with fluorene resulted in the concomitant formation of [(μ-fluorenyl)₃La₂(μ-H)(HAliBu₃)₂] and (fluorenyl)₂La[N(SiMe₃)₂]. [(μ-Fluorenyl)₃La₂(μ-H)(HAliBu₃)₂] features fluorenyl ligands with a μ-η⁶:η⁶ coordination around the hydrido-bridged dilanthanum core motif. The reported complexes are the first crystallographically characterized, ancillary ligand-free lanthanide(III) tetraisobutylaluminates, and display potential model systems for Ziegler-type polymerization catalysis.

Molecular Ln(III)-H-E(II) Linkages (Ln=Y, Lu; E=Ge, Sn, Pb)

Following the alkane-elimination route, the reaction between tetravalent aryl tintrihydride Ar*SnH3 and trivalent rare-earth-metallocene alkyls [Cp*2 Ln(CH{SiMe3 }2 )] gave complexes [Cp*2 Ln(μ-H)2 SnAr*] implementing a low-valent tin hydride (Ln=Y, Lu; Ar*=2,6-Trip2 C6 H3 , Trip=2,4,6-triisopropylphenyl). The homologous complexes of germanium and lead, [Cp*2 Ln(μ-H)2 EAr*] (E = Ge, Pb), were accessed via addition of low-valent [(Ar*EH)2 ] to the rare-earth-metal hydrides [(Cp*2 LnH)2 ]. The lead compounds [Cp*2 Ln(μ-H)2 PbAr*] exhibit H/D exchange in reactions with deuterated solvents or dihydrogen.

Molecular Main Group Metal Hydrides

This review serves to document advances in the synthesis, versatile bonding, and reactivity of molecular main group metal hydrides within Groups 1, 2, and 12-16. Particular attention will be given to the emerging use of said hydrides in the rapidly expanding field of Main Group element-mediated catalysis. While this review is comprehensive in nature, focus will be given to research appearing in the open literature since 2001.

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.

Donor-stabilised molecular Mg/Al-bimetallic hydrides

Low-molecular organometallic hydride complexes of the type [(do)_xMg{(μ₂-H)(AlMe₃)}₂] form in ethereal solvents and display inherent reactivity of existing magnesium hydrido bonding.

Magnesium, zinc, aluminium and gallium hydride complexes of the transition metals

The preparation and applications of heterobimetallic complexes continue to occupy researchers in the fields of organometallic, main group, and coordination chemistry. This interest stems from the promise these complexes hold as precursors to materials, reagents in synthesis and as new catalysis. Here we survey and organise the state-of-the-art understanding of the TM-H-M linkage (M = Mg, Zn, Al, Ga). We discuss the structure and bonding in these complexes, their known reactivity, and their largely unrealised potential in catalysis.