Reactivity of Hydrosilanes with the CrII/SiO2 Phillips Catalyst: Observation of Intermediates and Properties of the Modified CrII Sites

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Supplementing Material

Reactivity of hydrosilanes with the Cr

II

_/SiO

2

Phillips catalyst: observation of

intermediates and properties of the modified Cr

II

_sites

Caterina Barzan1_{, Silvia Bordiga}1_{, Elsje Alessandra Quadrelli}2*_{and Elena Groppo}1*

1_{University of Torino, Department of Chemistry, NIS Centre and INSTM, Via G. Quarello 15A, I10135, Italy.}

e-mail: elena.groppo@unito.it (*), caterina.barzan@unito.it, silvia.bordiga@unito.it

2_{Universite´ de Lyon, CNRS—CPE Lyon—Universite´ Lyon 1 (C2P2 UMR 5265), Bât 308F, 43 B. du 11} Novembre 1918, 69616, Villeurbanne, France. e-mail: alessandra.quadrelli@cpe.fr (*)

S1.

Reactivity of hydrosilanes with SiO2: in-situ FT-IR spectroscopy

Figure S1 shows the spectra of pure SiO2 activated at 973 K before (black) and after the interaction

with SiH4 (red). The spectrum of SiO2 is that typical of a highly dehydroxylated sample

characterized by: i) a narrow IR absorption band at 3745 cm-1_{due to the ν(OH) of isolated silanol}

groups; ii) three absorption bands at 1980, 1868 and 1640 cm-1_{due to the first overtones of the}

silica framework modes, and iii) a strong and out-of-scale absorption below 1300 cm-1_{assigned to}

the vibrational modes of the bulk [1]. Upon interaction with SiH4 (red) no substantial changes are

observed in the spectrum, besides the presence of SiH4 gas phase (magnification in the inset of

Figure S1). The spectrum does not change during time, testifying the absence of any reactivity of SiO2 towards SiH4 in the same experimental conditions of CrII/SiO2 modification. Thus, the reactivity

observed on the CrII_/SiO

2 catalyst (Figure 1 part a) must be ascribed to the presence of surface CrII

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Figure S1: FT-IR spectra of SiO2 before (black) and after (red) interaction with SiH4 at room temperature. The inset

reports a magnification of the ν(Si-H) region, where only the SiH4 gas phase is detected.

Figure S2 shows the spectra of pure SiO2 dehydroxilated at 973 K before (black) and after the

exposure to TES vapor (blue). As discussed for Figure S1, the spectrum of SiO2 is that typical of a

highly dehydroxilated sample. Upon interaction with TES at room temperature, the FT-IR spectrum is dominated by the manifestations of physisorbed TES. More in detail, the IR absorption bands around 2900 cm-1_{and 1400 cm}-1_{are due to the vibrations of the ethyl groups (ν}

asym(CH3) at 2960

cm-1_{, ν}

sym(CH3) at 2878 cm-1, νasym(CH2) at 2915 cm-1, νsym(CH2) at 2855 cm-1, δasym(CH3) at 1465 cm-1,

δsym(CH3) 1380 cm-1 and δ(CH2) at 1416 cm-1), while the sharp band at 2100 cm-1 is assigned to the

ν(Si-H) of the Si-H group in interaction with free Si-OH surface groups (whose absorption band shifts from 3745 cm-1_{to around 3650 cm}-1_{). The IR spectrum after removal of TES does not show}

any vibrational manifastations of ethyl groups or Si-H species, meaning that all the physisorbed TES is removed and that no reaction occurred at the surface of SiO2. Again this experiment testifies the

inactivity of SiO2 in presence of hydrosilanes and proves that TES reacts with the CrII surface

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Figure S2: FT-IR spectra of SiO2 before (black), after (blue) interaction with TES vapor and upon outgassing TES (light

blue) at room temperature.

References