Azidopropyl functionalized mesoporous silica SBA-15 were prepared with variable azide loadings of 0.03 – 0.7 mmol g−1 (ca. 2 – 50% of maximal surface coverage) through a direct synthesis, co-condensation approach. These materials are functionalized selectively with ethynylated organic moieties through the copper-catalyzed azide alkyne cycloaddition (CuAAC) or “click” reaction. Specific loading within a material can be regulated by either the azide loading or limiting the alkyne reagent relative to the azide loading. The immobilization of ferrocene, pyrene, tris(pyridylmethyl)amine (TPA), and iron porphyrin (FeTPP) demonstrates the robust nature and reproducibility of this two step synthetic attachment strategy. Loading-sensitive pyrene fluorescence correlates with a theoretically random. surface distribution, rather than a uniform one; full site-isolation of tethered moieties ca. 15 Å in length. occurs at loadings less than 0.02 mmol g−1. The effect of surface loading on reactivity is observed in oxygenation of SBA-15-[CuI(TPA)]. SBA-15-[MnII(TPA)]-catalyzed epoxidation exhibits a systematic dependence on surface loading. A comparison of homogeneous, site-isolated and site-dense complexes provides insight into catalyst speciation and ligand activity.

Reaction of O2 with a high-spin mononuclear iron(II) complex supported by a five-azole donor set yields the corresponding mononuclear non-heme iron(III)-superoxo species, which was characterized by UV/Vis spectroscopy and resonance Raman spectroscopy. (1)H NMR analysis reveals diamagnetic nature of the superoxo complex arising from antiferromagnetic coupling between the spins on the low-spin iron(III) and superoxide. This superoxo species reacts with H-atom donating reagents to give a low-spin iron(III)-hydroperoxo species showing characteristic UV/Vis, resonance Raman, and EPR spectra.

Surface modification of mesoporous silica materials with organosilane groups holds considerable potential for many applications, including heterogenization of discrete metal catalysts and even enzymes. 1 Beyond recycling and separation advantages, site-isolation of oxidation catalysts in such hybrid materials provides potential activity enhancements, as deleterious bimolecular catalyst interactions can be attenuated significantly. 2 Though conceptually simple, a dearth of straightforward and robust synthetic procedures are available that provide systematic loadings of catalysts within mesoporous materials. Reported here is a procedure that yields predictable and randomly distributed loadings of an organoazide 3 by a "direct synthesis" 4 of the mesoporous silica (ca. 2-50% surface coverage). Subsequent coupling of the organoazide with an ethynlated molecule through a Cu-catalyzed Huisgen [3 + 2] cycloaddition reaction, a "click" reaction, 5 yields expected loadings of the desired entities. Significant differences in reactivity with O 2 are demonstrated qualitatively between siteisolated and site-dense Cu(I) complexes.Mesoporous SBA-15 silicas are attractive as a support for oxidation catalysts with large surface areas (700-900 m 2 g −1 ), large pores sizes (6-9 nm) and robust silica walls (3-6 nm). 6 Under forcing grafting conditions of excess (3-azidopropyl)-triethoxysilane (Si-N 3 ; >20 equiv) in refluxing toluene over several days, a near fully loaded surface (ca. 1 mmol g −1 ) of the organoazide is possible with calcined SBA-15. 7,8 Trace amounts of water are critical, as rigorously dry conditions only yield a maximum of ca. 0.1 mmol g −1 . If a random distribution of organosilanes is desired at less than full coverage, water is problematic, as the monomeric organotriethoxysilanes precondense in solution, leading to clustering on the surfaces. 9By contrast, reproducible and predictable loadings of Si-N 3 within an SBA-15 were accessible by a "direct" synthetic route, 10 in which various molar amounts of Si-N 3 are co-condensed with tetraethoxy-orthosilicate (TEOS) in the SBA-15 preparation (Scheme 1). 8 Key to this preparative method is that the templating P 123 organic polymer can be removed under mild Soxhlet extraction conditions rather than calcination, leaving the covalently attached organoazides in the templated pores.The pore size and surface area of each material, SBA-15-N 3 -x, as assessed by power X-ray diffraction and N 2 absorption isotherm measurements, are consistent fully with the ordered structure of the original SBA-15 material. 6,8 The azidopropyl groups are evident from both the CP-MAS 13 C solid-state NMR spectra and the IR spectra. 8 The ratio of the azide (2110 cm −1 ) to surface-bonded H 2 O bending mode (1640 cm −1 ) 11 features in the IR spectra provides a simple ratiometric assessment of the azide content. Incorporation of the Si-N 3 into the materials clearly scales in a linear fashion with the initial mol % used in the direct synthesis ( Figure 1a). Ethynylferrocene (R = Fc), 1-eth...

Nickel complexes with hydrotris(pyrazolyl)borate ( = Tp R ) ligands catalyze alkane oxidation with organic peroxide meta-Cl-C 6 H 4 C(vO)OOH (= mCPBA). The electronic and steric hindrance properties of Tp R affect the catalyses. The complex with an electron-withdrawing group containing a less-hindered ligand, that is, Tp Me2,Br , exhibits higher alcohol selectivity. Higher selectivity for secondary over tertiary alcohols upon oxidation of methylcyclohexane indicates that the oxygen atom transfer reaction proceeds within the coordination sphere of the nickel centers. A reaction of the catalyst precursor, dinuclear nickel(II)bis(μ-hydroxo) complexes, with mCPBA yields the corresponding nickel(II)-acylperoxo species, as have been characterized by spectroscopy. Thermal decomposition of the nickel(II)-acylperoxo species in CH 2 Cl 2 yields the corresponding nickel(II)-chlorido complexes through Cl atom abstraction. Employment of the brominated ligand increases the thermal stability of the acylperoxo species. Kinetic isotope effects observed on decay of the nickel(II)-acylperoxo species indicate concerted O-O breaking of the nickelbound acylperoxide and H-abstraction from the solvent molecule. † Electronic supplementary information (ESI) available. See

The nickel(II)-acylperoxo complex [Ni(Tp(CF3Me))(κ(2)-mCPBA)] (1(CF3Me)) [Tp(CF3Me) = hydrotris(3-trifluoromethyl-5-methylpyrazolyl)borate, mCPBA = m-chloroperbenzoate] was isolated and fully characterized. The electrophilic oxygenation ability of 1(CF3Me) toward sulfides and olefins was confirmed. The Michaelis-Menten-type behavior of thioanisole oxygenation indicates the existence of a pre-equilibrium of substrate association in the reaction. In addition, 1(CF3Me) retains H-atom abstraction ability for hydrocarbons with activated methylene C-H bonds (e.g., fluorene). The oxidations of styrenes and these readily oxidizable hydrocarbons follow second-order kinetics, first-order each with respect to 1(CF3Me) and substrate. The lack of clear acceleration in the decay of 1(CF3Me) in the presence of substrates with high C-H bond dissociation energies (e.g., cyclohexane) suggests that another reaction pathway contributes through the O-O-cleaved intermediate.