Artificial metalloproteins (ArMs) containing Co4O4 cubane active sites were constructed via biotin-streptavidin technology. Stabilized by hydrogen bonds (H-bonds), terminal and cofacial CoIII–OH2 moieties are observed crystallographically in a series of immobilized cubane sites. Solution electrochemistry provided correlations of oxidation potential and pH. For variants containing Ser and Phe adjacent to the metallocofactor, 1e−/1H+ chemistry predominates until pH 8, above which the oxidation becomes pH-independent. Installation of Tyr proximal to the Co4O4 active site provided a single H-bond to one of a set of cofacial CoIII–OH2 groups. With this variant, multi-e−/multi-H+ chemistry is observed, along with a change in mechanism at pH 9.5 that is consistent with Tyr deprotonation. With structural similarities to both the oxygen-evolving complex of photosystem II (H-bonded Tyr) and to amorphous water oxidation catalysts (Co4O4 core), these findings bridge synthetic and biological systems for water oxidation, highlighting the importance of secondary sphere interactions in mediating multi-e−/multi-H+ reactivity.

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.

Molecular aluminosilicate Al(SH)(micro-O)Si(OH)(O(t)Bu)(2) ( = [HC{C(Me)N(Ar)}(2)](-), Ar = 2,6-(i)Pr(2)C(6)H(3)) has been prepared from Al(SH)(2) and ((t)BuO)(2)Si(OH)(2) in high yield. When reacted with one equiv. of water, the unique aluminosilicate containing two terminal hydroxy groups Al(OH.THF)(mu-O)Si(OH)(O(t)Bu)(2) can be isolated. However, when is reacted with the bulkier silanol ((t)BuO)(3)SiOH, no reaction is observed. The desired Al(SH)(micro-O)Si(O(t)Bu)(3) can be prepared in a two-step synthesis between AlH(2) and ((t)BuO)(3)SiOH giving first Al(H)(micro-O)Si(O(t)Bu)(3), which reacts further with elemental sulfur to give as the only product. Direct hydrolysis of was conducted to obtain Al(OH)(micro-O)Si(O(t)Bu)(3), however, such hydrolysis always resulted in a complete decomposition of the starting material. Therefore we used boric acid, which condenses in non-polar solvents and slowly evolve water, to hydrolyze to under mild conditions. Compounds , and have been characterized by single-crystal X-ray diffraction.

Reaction between the silanediol (HO)(2)Si(OtBu)(2) and gallium amides, LGaCl(NHtBu) and LGa(NHEt)(2) (L = [HC{C(Me)N(Ar)}(2)](-), Ar = 2,6-iPr(2)C(6)H(3)), respectively, resulted in the facile isolation of molecular gallosilicates LGaCl(μ-O)Si(OH)(OtBu)(2) (1) and LGa(NHEt)(μ-O)Si(OH)(OtBu)(2) (2). Compound 2 easily reacts with 1 equiv of water to form the unique gallosilicate-hydroxide LGa(OH·THF)(μ-O)Si(OH)(OtBu)(2) (3). Compounds 1-3 contain the simple Ga-O-SiO(3) framework and are the first structurally authenticated molecular gallosilicates. These compounds may be used not only as models for gallosilicate-based materials but also as further reagents because of the presence of reactive functional groups attached to both gallium and silicon atoms. Accordingly, seven molecular heterometallic compounds were obtained from the reactions between compound 3 and group 4 amides M(NMe(2))(4) (M = Ti, Zr) or M(NEt(2))(4) (M = Ti, Zr, Hf). Hence, by tuning the reactions conditions and stoichiometries, it was possible to isolate and structurally characterize the complete 1:1 and 2:1 series (4-10). Completely inorganic cores of types M-O-Ga-O-Si-O and spiro M[O-Ga-O-Si-O](2) were obtained and characterized by common spectroscopic techniques.

The synthesis of molecular heterometallic alumosilicates in good yields has been achieved by reaction between LAl(OH·thf)(μ‐O)Si(OH)(OtBu)2 (1, L = [HC{C(Me)N(Ar)}2]–, Ar = 2,6‐iPr2C6H3) and group 4 amides. These reactions lead to inorganic cycles (type I) and spirocycles (type II) containing six‐membered rings with unprecedented inorganic cores (O–Al–O–Si–O)nM (n = 1, 2; M = Ti, Zr and Hf). Noteworthy, for the heavier metals, Zr and Hf, higher steric bulk in the alkyl substituent of the amide moiety is required to obtain type I compounds. The solid‐state structures for all compounds were determined and reveal a tetrahedral environment for all metal atoms, dihedral angles close to 90° for spirocyclic compounds, and isomorphous structures for the Zr and Hf derivatives.

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Homo- or hetero alumoxanesilicates or bridged M–OH–M hydroxidesilicates with unusual or unprecedented inorganic cores have been obtained in reactions between 1 and nBuLi, AlMe3, GaMe3 or ZnMe2. The aluminum derivatives serve as models for MAO.

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.