Holmium(iii) Supermesityl-imide Complexes Bearing Methylaluminato/gallato Ligands

Heterobimetallic µ2-imide complexes [Ho(µ2-Nmes*){Al(CH3)4}]2 (1, supermesityl = mes* = C6H2tBu3-2,4,6) and [Ho(µ2-Nmes*){Ga(CH3)4}]2 (2) have been synthesized from homoleptic complexes Ho[M(CH3)4]3 (M = Al, Ga) via deprotonation of H2Nmes* or with K[NH(mes*)] according to a salt metathesis-protonolysis tandem reaction. Single-crystal X-ray diffraction of isostructural complexes [Ho(µ2-Nmes*){M(CH3)4}]2 (M = Al, Ga) revealed asymmetric Ho2N2 metallacycles with very short Ho–N bond lengths and secondary Ho⋯arene interactions.

While a series of dimeric LA-stabilized rare-earth metal imides (type II) has been reported previously [7], we now report on additional aniline-derived rare-earth metal imide complexes employing methylaluminate and methylgallate complexes.The intention was to investigate fundamental differences of organogallium versus organoaluminum moieties since GaMe3 should behave as a weaker LA towards nitrogen than AlMe3.

Procedure A
A solution of Ho[M(CH3)4]3 in toluene (3 mL) was added to a vigorously stirred suspension of potassium (2,4,6-tri-tert-butylphenyl)amide in toluene (2 mL).The reaction mixture was stirred for 2 h at ambient temperature and the toluene solution then separated by centrifugation, decanted, and filtrated.The solid residue (product and K[M(CH3)4] was extracted with additional toluene (5 × 2 mL).The extract was dried under vacuum and triturated with n-hexane (2 × 2 mL).After that the solid was washed with n-hexane (2 × 2 mL), followed by drying under reduced pressure.Compounds 1 and 2 were obtained as powder or by crystallization from the mother liquor at ambient temperature.

Procedure B
A solution of 2,4,6-tri-tert-butylaniline in n-hexane (3 mL) was added to a solution of Ho[M(CH3)4]3 in n-hexane (2 mL).The reaction mixture was stirred for 8 h at 80 °C.The solution turned orange and a precipitate was formed.The mixture was chilled to ambient temperature, the solid product was separated by centrifugation and washed with n-hexane (2 × 2 mL).The procedure was repeated twice with the combined extracts.Compounds 1 and 2 were dried in vacuo and obtained as orange powder.

X-Ray Crystallography
Crystal data for compounds 1 and 2 are given in Table 3.Bond lengths and angles are listed in Table 2. Crystals of 1 and 2 were grown using standard techniques from saturated toluene solutions.Suitable single crystals for X-ray structure analyses were selected in a glovebox and coated with Parabar 10312 and fixed on a nylon loop/glass fiber.
Data for compound 2 were collected on a Stoe IPDS 2T instrument equipped with a fine focus sealed tube and graphite monochromator using MoKα radiation (λ = 0.71073 Å) performing ω scans.Raw data were collected and integrated using Stoe's X-Area software package [32].A numerical absorption correction based on crystal shape optimization was applied using Stoe's X-Red [33] and X-Shape [34].X-ray data for compound 1 were collected on a Bruker AXS, TXS rotating anode instrument using a Pt 135 CCD detector, and graphite monochromated using MoKα radiation (λ = 0.71073 Å), employing ω-scans.Raw data were processed using APEX [35] and SAINT [36], corrections for absorption effects were applied using SADABS [37].The structure was solved by direct methods and refined against all data by full-matrix least-squares methods on F 2 using SHELXTL [38] and ShelXle [39].All graphics were produced employing ORTEP-3 [40] and POV-Ray [41].Further details of the refinement and crystallographic data are listed in the CIF files.CCDC 1426090 (1) and 1426091 (2) contain all the supplementary crystallographic data for this paper.These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.