Cyclosiloxanes Containing a Gallium Atom as Ring Member from the Reaction of tert-Butoxygallane with Di- and Trisiloxanediols

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.

Synthesis and Reactivity of the First Isolated Hydrogen-Bridged Silanol-Silanolate Anions

We report on the first examples of isolated silanol–silanolate anions, obtained by utilizing weakly coordinating phosphazenium counterions. The silanolate anions were synthesized from the recently published phosphazenium hydroxide hydrate salt with siloxanes. The silanol–silanolate anions are postulated intermediates in the hydroxide‐mediated polymerization of aryl and alkyl siloxanes. The silanolate anions are strong nucleophiles because of the weakly coordinating character of the phosphazenium cation, which is perceptible in their activity in polysiloxane depolymerization.

Gallium Hydrides with a Radical-Anionic Ligand

The reaction of Cl₂GaH with a sodium salt of the dpp-Bian radical-anion (dpp-Bian^•-)Na (dpp-Bian = 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene) affords paramagnetic gallane (dpp-Bian^•-)Ga(Cl)H (1). Oxidation of (dpp-Bian^2-)Ga-Ga(dpp-Bian^2-) (2) with N₂O results in the dimeric oxide (dpp-Bian^•-)Ga(μ²-O)₂Ga(dpp-Bian^•-) (3). A treatment of the oxide 3 with phenylsilane affords paramagnetic gallium hydrides (dpp-Bian^•-)GaH₂ (4) and (dpp-Bian^•-)Ga{OSi(Ph)H₂}H (5) depending on the reagent's stoichiometry. The reaction of digallane 2 with benzaldehyde produces pinacolate (dpp-Bian^•-)Ga(O₂C₂H₂Ph₂) (6). In the presence of PhSiH₃, the reaction between digallane 2 and benzaldehyde (2: PhSiH₃: PhC(H)O = 1:4:4) affords compound 4. The newly prepared complexes 1, 3-6 consist of a spin-labeled diimine ligand-dpp-Bian radical-anion. The presence of the ligand-localized unpaired electron allows the use of the ESR spectroscopy for characterization of the gallium hydrides reported. The molecular structures of compounds 1, 3-6 have been determined by the single-crystal X-ray analysis.

Correction: Ga[OSi(OtBu)3]3·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry

Correction for 'Ga[OSi(O^tBu)₃]₃·THF, a thermolytic molecular precursor for high surface area gallium-containing silica materials of controlled dispersion and stoichiometry' by James P. Dombrowski et al., Dalton Trans., 2016, 45, 11025-11034.

In situ generated polysiloxanes stabilizing μ3-oxo bridged Sb3 triangles

The reaction of RSbO3H2 with t-butylsilanetriol has led to the isolation of organoantimony(v) based molecular triangles stabilized by siloxane frameworks. Depending on the reaction conditions employed or the substituents present on the antimony atom, either a combination of a disiloxane and a tetrasiloxane framework or a trisiloxane framework was generated in situ leading to the stabilization of the Sb3 triangle.

Synthesis of substituted β-diketiminate gallium hydrides via oxidative addition of H–O bonds

Substituted β-diketiminate gallium hydrides of the general formulaLGa(H)X have been obtained from the oxidative addition reactions of compounds with OH groups intoLGa (L= HC[CMeNAr]₂⁻, Ar = 2,6-iPr₂C₆H₃).

Silica-grafted 16-electron hydride pincer complexes of iridium(III) and their soluble analogues: synthesis and reactivity with CO

The dihydride complexes [IrH2(POCOP)] (1a) and [IrH2(PCP)] (1b) (POCOP = 1,3-bis((di-tert-butylphosphino)oxy)benzene; PCP = 1,3-bis((di-tert-butylphosphino)methyl)benzene) react with the surface silanols of mesoporous amorphous silica (SBA-15) to give H2 and the silica-grafted, 16-electron iridium(III) monohydride species [IrH(O-SBA-15)(pincer)] (2a and 2b). These materials contain a single iridium(III) species, that is a highly dispersed, coordinatively unsaturated siloxo hydride complex, as indicated by solid-state spectroscopic data. The siloxo complexes [IrH((i)Bu-POSS)(POCOP)] (3a) and [IrH((i)Bu-POSS)(PCP)] (3b) ((i)Bu-POSS = OSi8O12(i)Bu7) were prepared as soluble analogues of 2a and 2b to support their spectroscopic characterization. The coordinatively unsaturated, 16-electron species 2a and 2b react with CO to give the six-coordinate iridium(III) adducts [IrH(O-SBA-15)(CO)(POCOP)] (7a) and [IrH(O-SBA-15)(CO)(PCP)] (7b). Due to dissimilar electronic properties of the pincer ligands, 7a undergoes reductive elimination of the silanol forming the Ir(I) complex [Ir(CO)(POCOP)] (8a), whereas 7b is stable in oxidation state of III. The homogeneous siloxo carbonyl complexes [IrH((i)Bu-POSS)(CO)(POCOP)] (9a), [IrH((i)Bu-POSS)(CO)(PCP)] (9b), and [IrH(OSiMe3)(CO)(POCOP)] (11a) were prepared to substantiate the reactivity and the characterization of the silica grafted species.

Hexa- and trinuclear organoantimony oxo clusters stabilized by organosilanols

Reactions of Ph2SbCl3 with RSi(OH)3 [where R = tert-Bu, cyclo-C6H11] and Ph2Si(OH)2 in toluene in the presence of triethylamine as a base were performed. Single-crystal X-ray structural elucidation of the products revealed the formation of hexanuclear antimony(V) and mixed-valent antimony (III/V) oxo-hydroxo clusters built up of an incomplete cubane subunit. Interestingly, in all the reactions, at least one Sb-C bond cleavage has been observed, leading to the formation of novel cluster assemblies [(Ph2Sb)4(PhSb)2(C4H9SiO3)2(O)6(OH)2] (1), [(Ph2Sb)4(PhSb)2(C6H11SiO3)2(O)6(OH)2] (2), [(Ph2Sb)(PhSb)2(Ph2SiO2)2(O)3(OH)2](-)Et3NH(+) (3), and [(Ph2Sb)4(Sb)2(Ph2SiO2)2(O)6(OH)2] (4), respectively.

Site isolated complexes of late transition metals grafted on silica: challenges and chances for synthesis and catalysis

Grafting, quo vadis? The reasons for the aggregation of late transition metal complexes on oxide supports under reducing conditions and/or in the presence of π-accepting ligands are discussed, and strategies are suggested to prevent it.

Molecular gallosilicates and their group 4 multimetallic derivatives

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.

Synthesis, Structural and Spectroscopic Characterization, Catalytic Properties, and Thermal Transformations of New Cyclic Di- and Trisiloxanediolato Tantalum Complexes

The reaction between Ta(OEt)5 and 1,1,3,3-tetramethyl-1,3-disiloxanediol, (HOSiMe2OSiMe2OH), leads to new siloxy complexes in which the dimeric nature of Ta(OEt)5 is maintained with both bridging ethoxide and disiloxanediolato bridges. With equal amounts of the reagents, two terminal OEt groups are replaced to form [Ta(OEt)2]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 1, whereas with an excess of diol, the remaining terminal OEt groups are also replaced but with a trisiloxanediolato unit to form [Ta(OSiMe2OSiMe2OSiMe2O)]2(mu-OEt)2(mu-OSiMe2OSiMe2O)2, 2. Complexes 1 and 2 catalyze the transformation of HOSiMe2OSiMe2OH to polysiloxanes. Thermal treatment of 1 results in the formation of a 1:2 mixture of Ta2O5/SiO2; no new phases are observed. The molecular structures of 1 and 2 are confirmed by X-ray crystallography.

Polyhedral Cobalt(II) and Iron(II) Siloxanes: Synthesis and X-ray Crystal Structure of [(RSi(OH)O2)Co(OPMe3)]4 and [(RSiO3)2(RSi(OH)O2)4(μ3-OH)2Fe8(THF)4] (R = (2,6-iPr2C6H3)N(SiMe3))

The cobalt(II) and iron(II) siloxane compounds were prepared by the reaction of lipophilic N-bonded silanetriol 1 with metal silylamides M[N(SiMe3)2]2 (M = Co (2), Fe (3)) in a 1:1 and 3:4 molar ratio, respectively. A plot of 1/chi versus temperature in the range of 2-300 K indicates the paramagnetic behavior of 2 and 3. The composition and molecular structures of 2 and 3 were fully determined by IR, elemental analysis, and X-ray crystal structural analyses. Compound 2 possesses a pseudo-4-fold (S4) symmetry, whereas 3 reveals an inversion center. Compound 2 represents a tetracobalt(II) drum while 3 exhibits an octairon(II) cage containing siloxane ligands.