Polysiloxane-immobilized ligand

El Ashgar used a variation on the technique [16]. Specifically, 3-chloropropyltrimethoxysilane was used to alkylate diethylenetiiamine, i.e, reaction with the halide end to produce a precursor of a polymer (I, Eqn. 1). The reaction of I with tetraethylorthosilicate resulted in a "diethylenetiiamine polysiloxane immobilized ligand system."... 

Fig. 25.6. C CP-MAS NMR spectra of some polysiloxane-immobilized ligand systems. (A) (S)-CH2CH2CH2NHCH2C02CH3. (B) -CH2CH2CH2SCH2C02CH3- Asterisks indicate signals from unhydrolyzed ethoxy and methoxy groups. Ref. 15.

Fig. 25.23. CP-MAS spectra of polysiloxane-immobilized ligand systems. (A) diphenyl-ethylphosphine (B) diphenylethylphosphine-monoamine (C) diphenylethylphosphine-diam-ine and (D) diphenylethylphosphine-thiol sample.Ref. 18.

The CP-MAS spectrum of the polysiloxane-immobilized ligand system bearing —CH2CH2CH2SCH2C02Me groups, shown in Fig. 25.6B, has one relatively sharp carbonyl resonance at 172.8 ppm. The carbon signals at 9.7,... 

B) polysiloxane-immobilized monoamine ligand, (S)-CH2CH2CH2NH2, of the untreated... 

Fig. 25.9. " C CP-MAS NMR spectra obtained with 50-(jis dipolar dephasing. (A) Polysiloxane-immobilized thiol system (B) polysiloxane-immobilized thiol-monoamine system and (C) polysiloxane-immobilized thiol-diamine ligand system. Ref. 16.

The NMR spectrum of the untreated polysiloxane-immobilized monoamine ligand (Fig. 25.lA) shows three signals, at 10.7, 27.4 and 44.9 ppm, whereas the spectrum of the corresponding protonated system (washed with... 

The C NMR spectra of the polysiloxane-immobilized primary amine ligand system before and after silylation of accessible silanols with hexame-thyldisilazane, given in Fig. 25.5, show very similar peak maxima positions for each of the three methylene carbons (Table 25.1), although there is apparently a small peak narrowing for C(2) and C(3) in the (CH3)3 Si-capped... 

The CRAMPS spectrum of the polysiloxane-immobilized thiol-monoamine ligand system (Fig. 25.16B) shows no signal due to NH2 protons. This may be in part because the signal of the NH2 groups is broadened by the " N quadrupole effect on MAS averaging of the H- " N dipolar interaction, and in part because of effects of proton exchange of NH2 protons. Quadrupo-lar line broadening effects of N on attached protons have previously been observed in CRAMPS spectra of amino acids and other systems (72-74). 

From the intensity patterns of the two Si CP-MAS NMR spectra of the polysiloxane-immobilized thiol-diamine ligand system before (C) and after (D) treatment with 0.11 M hydrochloric acid, shown in Fig. 25.24, it is possible to say that the relative peak intensities of the single (-100 ppm) silanol and geminal (-91 ppm) silanol peaks are increased and that of the RSi(OSi )3 peak (-64 ppm) is decreased somewhat by treatment with hydrochloric acid. 

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