The synthesis and stabilization of alumo- and gallodisilicates [HC{C(Me)N(2,6-iPr2C6H3)}2]M[(μ-O)Si(OH)(OtBu)2]2 [M = Al (1), Ga (2)] containing two silicate subunits have been achieved through reactions between 2 equiv of the silanediol (tBuO)2Si(OH)2 and the aluminum hydride [HC{C(Me)N(2,6-iPr2C6H3)}2]AlH2 or the gallium amide [HC{C(Me)N(2,6-iPr2C6H3)}2]Ga(NHEt)2, respectively. Compounds 1 and 2 exhibit M(O-SiO2-OH)2 moiety and represent the first molecular metallosilicate-based analogues of neighboring silanol groups found in silicate surfaces. The substitution of both SiOH groups led to the formation of bimetallic compounds with 4R topologies, which are regularly found in zeolitic materials. Thus, reactions between group 4 metal amides M'(NEt2)4 (M' = Ti, Zr, Hf) and 1 and 2 resulted in the formation of nine heterometallic silicates (3-11) containing inorganic M(O-Si-O)2M' and [M(O-Si-O)2]2M' cores with 4R and spiro-4R topologies, respectively. The latter have M···M distances of 0.81 nm. NMR studies of the heterometallic derivatives showed a fluxional behavior at room temperature due to a high flexibility of the eight-membered ring.
The synthesis and stabilization of molecular four-coordinated lanthanide alumosilicates was achieved by the use of a highly encumbered alumosilicate ligand LAl(OH·thf)(μ-O)Si(OH)(OtBu) (1, L = HC{C(Me)N(2,6-iPrCH)}). Reactions between 1 and tris-cyclopentadienyl lanthanides (LnCp; Ln = Ce, Nd, Sm, Gd, Tb, Dy, Y, Er) derived in the isolation of eight compounds (2-9) where the ligand is observed in three different bonding modes: adducts (2, 3), spirocyclic (4) or cyclic (5-9) coordination compounds. The observed reactivity can be related to the ionic radius of the lanthanide atom and the nature of the oxygen donor-atom from the hydroxide (Al-OH) or hydroxyl (Si-OH) moieties in 1. Compounds 2-9 present general O-Al-O-Si-O-Ln connectivities with different degrees of substitution over the -OH groups in 1 and structural features with only slight variations over the alumosilicate moiety (O-Al-O-Si-O) upon the lanthanide coordination. The spirocyclic samarium derivative presents two tetra-coordinated samarium atoms with a tetrahedral and distorted square planar geometries, respectively, as a result of a highly strained polycyclic architecture.
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