solid was observed. Once at room temperature, the solid was
filtered off, dried in vacuo and identified analytically (C, H,
N, Cl) and spectroscopically (1H-NMR) as [NH3Et]Cl (2.1 g,
25.8 mmol of Cl). The pentane was removed in vacuo from the
filtrate thus yielding a colourless liquid, which was identified as
Si(NHEt)4 (1.10 g, 76% yield). Found: C, 47.2; H, 11.4; N, 27.0.
C8H24N4Si requires: C, 47.0; H, 11.8; N, 27.4%. δH (C6D6,
(1)
The H- and 13C-NMR spectra show the characteristic sig-
nals of the amido groups (Table 1); moreover, similar to the
other compounds above reported, (a) the 1H–1H vicinal
coupling between the methyne and NH proton is observed in
1
3
293 K): 2.84 (qn, 2H, CH2, JHH = 7.1 Hz), 1.05 (t, 3H, CH3,
3JHH = 7.1 Hz), 0.39 (br, 1H, NH). δC (C6D6, 293 K): 36.2 (tq,
CH2, 1JCH = 133.2, 2JCH = 4.4 Hz), 20.7 (qt, CH3, 1JCH = 124.7,
2JCH = 2.9 Hz).
Si(NHiPr)n(NMe2)4Ϫn (n = 1, 2, 3), and (b) the JCH, JCH and
3JCH have been measured for Si(NHiPr)(NMe2)3 (Table 2), thus
indicating the occurrence of long range CH couplings.
1
2
SiCl(NMe2)3 (colourless liquid, 89% yield). Found: C, 36.9;
H, 8.9; Cl, 18.0; N, 22.0. C6H18ClN3Si requires: C, 36.8; H, 9.3;
Cl, 18.1; N, 21.5%. δH (C6D6, 293 K): 2.43 (s, CH3). δC (C6D6,
293 K): 37.1 (qq, CH3, 1JCH = 134.1, 3JCH = 5.0 Hz).
Conclusions
i
t
NHR2 = NH2 Pr, NH2cPr, NHEt2, NH2 Bu, NHiPr2. Only the
i
procedure for NH2 Pr is reported in detail, the others being
The aminolysis of the Si–Cl bond in SiCln(NR2)4Ϫn (n = 4; n = 3,
NR2 = NMe2; n = 2, NR2 = NEt2) yielding the [Si(amide)] func-
tionality is dramatically affected by the nature of the silicon
reagent, i.e. the number of the Si–Cl involved in the reaction
(Schemes 1–4) and the aminolysis’ rate depend on the steric
hindrance at the silicon centre. In addition, a dissociative path-
way is postulable for the reaction, based on: (a) the positive
values of ∆H# and ∆S# measured in the aminolysis of
similar.
i
A pentane solution (15 ml) of NH2 Pr (2.70 mg, 45.7 mmol)
was added dropwise to a pentane solution (15 ml) of SiCl4
(900 mg, 5.30 mmol). A colourless solid precipitated out. After
18 h stirring, the suspension was filtered: the solid was dried
in vacuo and identified analytically (C, H, N, Cl) and spectro-
i
scopically (1H-NMR) as [NH3 Pr]Cl (1.90 g, 19.9 mmol of Cl).
i
The filtrate was evaporated yielding a colourless solid, identi-
fied as Si(NHiPr)4 (1.20 g, 87% yield). Found: C, 55.0; H, 12.8;
N, 20.9. C12H32N4Si requires: C, 55.3; H, 12.4; N, 21.5%.
SiCl2(NEt2)2 with NH2 Pr; (b) the observed first-order rate law
with respect to the derivatives bearing the Si–Cl bond (Schemes
2–4).
3
δH (C6D6, 293 K): 3.22 (ds, 1H, CH, JHH = 6.4, 9.8 Hz), 1.11
The ligand exchange reaction between SiCl4 and SiCln-
(NR2)4Ϫn is a general and valuable tool yielding chloro–amido
derivatives with the desired Cl/NR2 ratio (Scheme 8), the
composition of the chloro–amido product being strictly related
to the molar ratio of the reactants. Moreover, the kinetic
investigation of this reaction indicates that (a) the reaction is
reversible; (b) the rate determining step involves only the
amido-donor species [observed first-order rate law with respect
to these species (Schemes 6, 7)]; and (c) the pathway is dissoci-
ative [positive ∆H# and ∆S# for both the forward and reverse
reaction of SiCl2(NEt2)2 with SiCl4].
3
3
(d, 6H, CH3, JHH = 6.4 Hz), 0.35 (d, 1H, NH, JHH = 9.8 Hz).
1
2
δC (C6D6, 293 K): 42.6 (dsd, CH, JCH = 133.5, JCH = 1.8, 4.8
Hz), 28.3 (q, CH3, 1JCH = 124.4 Hz).
Si(NHcPr)4 (colourless liquid, 91% yield). Found: C, 56.9; H,
10.0; N, 22.1. C12H24N4Si requires: C, 57.1; H, 9.6; N, 22.2%.
δH (C6D6, 293 K): 2.23 (m, 1H, CH), 1.04 (br, 1H, NH), 0.39 (br,
1H), 0.38 (br, 1H), 0.36 (br, 2H). δC (C6D6, 293 K): 23.8 (d, CH,
1JCH = 172.2 Hz), 8.8 (t, CH2, 1JCH = 160.5).
SiCl2(NHtBu)2 (colourless liquid, 88% yield). Found: C, 39.1;
H, 8.0; Cl, 29.2; N, 11.9. C8H20Cl2N2Si requires: C, 39.5; H, 8.3;
Cl, 29.1; N, 11.5%. δH (C6D6, 293 K): 1.49 (br, 1H, NH), 1.11
(s, 9H, CH3). δC (C6D6, 293 K): 50.6 (m, C, 2JCH = 1.5; 4.1 Hz),
32.5 (qsd, CH3, 1JCH = 125.6, 3JCH = 4.4, 3.2 Hz).
Experimental
SiCl2(NEt2)2 (colourless liquid, 95% yield). Found: C, 39.8;
H, 8.1; Cl, 29.4; N, 11.2. C8H20Cl2N2Si requires: C, 39.5; H,
8.3; Cl, 29.1; N, 11.5%. δH (C6D6, 293 K): 2.88 (q, 2H, CH2,
3JHH = 7.1 Hz), 0.94 (t, 3H, CH3, 3JHH = 7.1 Hz). δC (C6D6, 293
K): 39.5 (CH2), 14.6 (CH3).
All operations were carried out in a glove-box, under an atmos-
phere of dinitrogen. Elemental analyses (C, H, N) were
performed using a Fisons Instruments analyser (Mod. EA
1108); the chlorine content of the samples was determined by
potentiometric titration using a standard solution of silver
SiCl3(NiPr2) (colourless liquid, 91% yield). Found: C, 30.9;
H, 5.8; Cl, 45.1; N, 6.2. C6H14Cl3NSi requires: C, 30.7; H,
6.0; Cl, 45.3; N, 6.0%. δH (C6D6, 293 K): 2.79 (sept, 1H, CH,
3JHH = 6.2 Hz), 1.05 (d, 6H, CH3, 3JHH = 6.2 Hz). δC (C6D6, 293
K): 40.3 (CH), 23.8 (CH3).
nitrate (Aldrich). NMR spectra were recorded with
a
BRUKER AMX 300 spectrometer (300 MHz for 1H). 1H-
and 13C-NMR spectra are referred to TMS. The multiplicity is
indicated as s (singlet), d (doublet), t (triplet), q (quartet), qn
(quintet), sept (septet), tq (triplet of quartets), qt (quartet of
triplets), qq (quartet of quartets), ds (doublet of septets), dsd
(doublet of septets of doublets), qqd (quartet of quartets of
doublets), qsd (quartet of septets of doublets), m (multiplet).
The following reagents were used as received: SiCl4 (silicon
tetrachloride, Fluka), NHMe2 (dimethylamine, Fluka), NH2Et
(ethylamine, Fluka). The following amines were refluxed over
BaO for 3 hours, distilled and stored under an atmosphere of
The ligand exchange reaction: synthesis of SiClx(NR2)4؊x (NR2 ؍
NMe2, x ؍
2, 3; NR2 ؍
NEt2, x ؍
3; NR2 ؍
NHiPr, x ؍
2, 3)
Only the procedure for NR2 = NMe2 is reported in detail, the
others being similar.
A pentane solution (15 ml) of SiCl4 (1.05 g, 6.18 mmol)
was contacted with a pentane solution (15 ml) of SiCl(NMe2)3
(2.40 g, 12.3 mmol). After 18 h stirring, the solvent was
removed in vacuo, yielding a colourless liquid, which was iden-
tified as SiCl2(NMe2)2 (3.2 g, 93% yield). Found: C, 25.5; H, 6.8;
Cl, 38.1; N, 15.2. C4H12Cl2N2Si requires: C, 25.7; H, 6.5; Cl,
37.9; N, 15.0%. δH (C6D6, 293 K): 2.34 (s, CH3). δC (C6D6, 293
K): 36.7 (CH3).
i
dinitrogen; NH2 Pr (isopropylamine, Fluka), NH2cPr (cyclo-
t
propylamine, Fluka), NHEt2 (diethylamine, Fluka), NH2 Bu
(tert-butylamine, Fluka), NHiPr2 (diisopropylamine, Fluka).
Reaction of SiCl4 with NHR2 (NHR2 ؍
NHMe2, NH2Et,
i
NH2 Pr, NH2cPr, NHEt2, NH2tBu, NHiPr2
NHR2 = NHMe2, NH2Et. Only the procedure for NH2Et is
reported in detail, the others being similar.
The gaseous amine NH2Et was bubbled into a pentane solu-
tion (25 ml) of SiCl4 (1.20 g, 7.06 mmol) for 15 min, the mixture
having been cooled to 263 K. The precipitation of a colourless
SiCl3(NMe2) (colourless liquid, 85% yield). Found: C, 13.4;
H, 3.5; Cl, 60.0; N, 8.0. C2H6Cl3NSi requires: C,13.5; H, 3.4; Cl,
59.6; N, 7.8%. δH (C6D6, 293 K): 2.17 (s, CH3).
SiCl(NHiPr)3 (colourless liquid, 92% yield). Found: C, 45.5;
H, 10.5; Cl, 14.7, N, 17.5. C9H24ClN3Si requires: C, 45.4; H,
D a l t o n T r a n s . , 2 0 0 3 , 4 1 3 – 4 1 9
418