Manganese carbonyl complexes catalyze the hydrosilation of ketones
with PhMe2SiH and
Ph2SiH2 in C6D6
solutions. Efficacy of the manganese carbonyl precatalysts (2.4
mol %)
toward acetone hydrosilation with 1.1 equiv of
PhMe2SiH to give
(CH3)2CH(OSiMe2Ph)
(3)
varied:
(PPh3)(CO)4MnC(O)CH3
(1) (<5 min) ≫ (CO)5MnC(O)Ph
> (CO)5MnC(O)CH3 >
(CO)5MnCH3 > (CO)5MnBr (6.0 h) ≫
Mn2(CO)10 ≈
(PPh3)(CO)4MnBr ≈
(CO)5MnSiMe2Ph (2).
A
turnover frequency of 27 min-1 was measured for catalysis
using 1% 1; rapid catalysis was
possible with 0.1% 1 in the absence of solvent. As a
precatalyst, 1 is much more reactive
than Rh(PPh3)3Cl for the
PhMe2SiH hydrosilation of acetone, acetophenone, and
cyclohexanone; both catalysts exhibit similar reactivity with
Ph2SiH2. With 1 as the
precatalyst,
isolated yields of the alkoxydimethylphenylsilanes exceeded 90%, with
no evidence of
competing dehydrogenative silation to yield vinyl silyl ethers.
Photochemical activation of
(CO)5MnSiMe2Ph (2) affords
moderate hydrosilation catalytic activity in transforming
acetone
to 3. In contrast,
(CO)4CoSiMe2Ph (10) or
Co2(CO)8 in the presence of the excess
HSiMe2Ph, with or without photochemical activation, were ineffective acetone
hydrosilation catalysts.
A reaction pathway is presented for the manganese
carbonyl-catalyzed hydrosilation of
ketones that involves coordinatively unsaturated manganese silyl
intermediates, (L)(CO)MnSiR‘‘3, as the active catalysts.
Manganese carbonyl complexes catalyze the hydrosilation of ketones
with PhMe2SiH and
Ph2SiH2 in C6D6
solutions. Efficacy of the manganese carbonyl precatalysts (2.4
mol %)
toward acetone hydrosilation with 1.1 equiv of
PhMe2SiH to give
(CH3)2CH(OSiMe2Ph)
(3)
varied:
(PPh3)(CO)4MnC(O)CH3
(1) (<5 min) ≫ (CO)5MnC(O)Ph
> (CO)5MnC(O)CH3 >
(CO)5MnCH3 > (CO)5MnBr (6.0 h) ≫
Mn2(CO)10 ≈
(PPh3)(CO)4MnBr ≈
(CO)5MnSiMe2Ph (2).
A
turnover frequency of 27 min-1 was measured for catalysis
using 1% 1; rapid catalysis was
possible with 0.1% 1 in the absence of solvent. As a
precatalyst, 1 is much more reactive
than Rh(PPh3)3Cl for the
PhMe2SiH hydrosilation of acetone, acetophenone, and
cyclohexanone; both catalysts exhibit similar reactivity with
Ph2SiH2. With 1 as the
precatalyst,
isolated yields of the alkoxydimethylphenylsilanes exceeded 90%, with
no evidence of
competing dehydrogenative silation to yield vinyl silyl ethers.
Photochemical activation of
(CO)5MnSiMe2Ph (2) affords
moderate hydrosilation catalytic activity in transforming
acetone
to 3. In contrast,
(CO)4CoSiMe2Ph (10) or
Co2(CO)8 in the presence of the excess
HSiMe2Ph, with or without photochemical activation, were ineffective acetone
hydrosilation catalysts.
A reaction pathway is presented for the manganese
carbonyl-catalyzed hydrosilation of
ketones that involves coordinatively unsaturated manganese silyl
intermediates, (L)(CO)MnSiR‘‘3, as the active catalysts.
“…Diethyl ketone was used as solvent throughout these reactions. Although a cationic rhodium complex can catalyze hydrosilylation of ketones, diethyl ketone was not hydrosilylated under the reaction conditions. …”
Cationic rhodium complex-catalyzed dehydrogenative silylation of
styrene with hydrosilanes was studied. Dehydrogenative silylation was competitive with
hydrosilylation. The
selectivity was strongly dependent on the reaction temperature and the
molar ratio of styrene
to hydrosilane. The selectivity of dehydrogenative silylation was
92% when using 3 equiv
of styrene to 1 equiv of triethylsilane (1a) in refluxing
diethyl ketone. The nature of the
hydrosilane also affected the reaction. As the steric bulk of
hydrosilane increased, the
selectivity of dehydrogenative silylation increased.
Dehydrogenative silylation product (2d)
was obtained exclusively in 81% yield when using triisopropylsilane
(1d). The amount of
ligand had a large influence on the selectivity of the reaction.
As the amount of PPh3 used
increased, the selectivity of dehydrogenative silylation increased.
These results were
reasonably explained according to the mechanism involving the insertion
of styrene into
the rhodium−silicon bond which was formed by the oxidative addition
of hydrosilane to
rhodium complex.
“…All the reactions in Tables 2 and 3 were performed using the recovered catalyst from the previous reaction. 1 H and 13 C NMR data for known products were the same as the literature values 6e, j, p, 7c, 19. Spectral data for new products are given below (Table 2, entries 2, 3, 8, 13, 14 and Table 3, entries 5, 9, 13, 15).…”
Cross-linked poly(4-vinylpyridine/styrene) copolymer-supported bismuth(III) triflate ( 30 P/S-Bi) effectively activates hexamethyldisilazane (HMDS) for the silylation of alcohols and phenols. By the use of this heterogeneous catalytic system, a wide range of alcohols as well as phenols are converted into their corresponding trimethylsilyl ethers in high yield under mild reaction conditions. The catalyst was reused more than 10 times without significant loss of its catalytic activity.
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