close

Вход

Забыли?

вход по аккаунту

?

Catalytic Hydrosilylation or Hydrogenation at One Coordination Site of [CpFe(CO)(X)] Fragments.

код для вставкиСкачать
[4] [3c]; A. Wiendnd, H.-U. Reissig, unpublished.
[5] We use the term stereospecificity as described by Eliel E. L. Eliel: Stereoc,hemie der Kohlensroffverbindungen, Verlag Chemie, Weinheim 1966,
p. 517.
[6] The configurations of E-6 and 2 - 6 were established by determination of
the C-H coupling constants between 2-H and 3-CH3:the values are 8.0 Hz
for 156 and 5.4 Hz for 2 - 6 . Cf. R. V. Dubs, W. von Philipsborn, Org.
M a p . Reson. 12 (1979) 326. The chemical shifts are also consistent with
this assignment. For further NMR data, see Table 2.
[7] For P-H elimination in metallacycles, see J. B. Collman, L. S. Hegedus,
J. R . Norton. R. G. Finke: Principles and Applications ofOrganorransirron
Meral Chemi.srry, University Science Books, Mill Valley, CA, USA 1987,
p. 459
[S] M. F. Semmelhack, R. Tarnura, J. Am. Chem. SOC.105 (1983) 6750. The
use of other olefins, besides acrylic esters and styrene, gave acyclic compounds with a different position of the double bond.
[9] Corresponding insertion products are found in smaller amounts ( < 10%)
in the reactions of 1 with methyl acrylate, but not with acrylonitrile or
Q2-methyl crotonate. See also M. D. Cooke, E. 0. Fischer, J. Organomel.
Chrm. 56 (1973) 279; [3a,d].
[lo] For competition between n-complex formation and CH insertion in the
reaction of olefins with coordinatively unsaturated metal complexes, see
P. 0. Stoutland, R. G. Bergman,J. Am. Chem. SOC.107(1985)4581; M. V.
Baker, L. D. Field, ibzd. 108 (1986) 7433, 7436.
period.''] The temperatures at which the reaction proceeds at
a measurable rate differ considerably, depending on the catalyst. Surprisingly, they correlate with the temperatures necessary for the epimerization at the Fe atom of the catalyst (80
and 60 "C for acetyl complexes 1 and 2,1101respectively; 70
and 50°C for methyl complexes 3 and 4,["] respectively).
Reaction for 24 hours at these temperatures always results in
quantitative formation of the silylated 1-phenylethanol6. In
no case was silylated enol 7 detected.
0
I1
WCH3
\
1
Ph,SiH,
OSiHPh,
OSiHPh,
1
I
6
7
Catalytic Hydrosilylation or Hydrogenation at One
Coordination Site of [Cp'Fe(CO)(X)] Fragments **
By Henri Brunner* and Konrad Fisch
The mechanisms proposed for the hydrosilylation of
olefins and ketones require that the catalytically active transition-metal complex have three coordination sites, two for
oxidative Si-H addition and one for binding of the unsaturated
These reactions often result in formation of byproducts, for example, silyl enol ethers from enolizable ketones.L4. 51 Here we describe the use of iron complexes
as homogeneous catalysts for the hydrosilylation of acetophenone with diphenylsilane. The reaction takes place at
one coordination site and does not lead to byproducts.
The acetyl complexes (+)- and (-)-1/2,161 the methyl
complexes (+)- and (-)-3-5:']
and [CpFe(CO),(CH,)j
were used as catalysts.18]
CP'
CP'
1,2
3-5
1,3: Cp' = cyciopentadienyl (Cp)
2,4: Cp' = indenyl (Ind)
5: Cp' = 1-tBu-indenyl
L = (S)-( )-(C6HJ2P- N(CH,) - CH(CH,)C,H,
+
When equimolar amounts of acetophenone and diphenylsilane are heated in the presence of 0.5-1.0 mol % of the
iron complex, the hydrosilylation begins after an induction
[*] Prof. Dr. H. Brunner, DipLChem. K. Fisch
Institut fur Anorganische Chemie der Universitat
Universitatsstrasse 31, D-8400 Regensburg (FRG)
[**I
Optically Active Transition-Me~alComplexes, Part 101. This work was
supported by the Deutsche Forschungsgemeinschaft, the Fonds der
Chernischen Industrie, and BASF AG, Ludwigshafen. Part 100:
H. Brunner, H . Peter, J. Organomel. Chem., in press.
Angeu,. Chem. Int. Ed. Engl. 29 (1990) No. 10
Presumably, loss of the phosphane ligand from complexes
1-4 is the rate-determining step for both the epimerization
and the formation of the catalytically active species.['31This
assumption is supported by the fact that small trialkylphosphanes inhibit the reaction. On the other hand, the
complex [CpFe(CO),(CH,)] is activated by methyl group
migration,[141which results in formation of the same intermediate, [CpFe(CO)(COCH,)], as that obtained by loss
of the phosphane ligand from 1. In the presence of 1.O mol YO
of [CpFe(CO),(CH,)] at 70 "C, the catalytic hydrosilylation is also complete within 24 hours.
The acetyl complexes 1 and 2 can be recovered at the
end of the catalytic reaction by chromatography on A1,0,
with pentane/diethyl ether (4/1) as eluent. The complex
[CpFe(CO),(CH,)], however, is consumed during the catalysis.
A possible mechanism for the catalytic hydrosilylation involves initial addition of diphenylsilane to the 16-electron
fragment formed by thermal loss of the phosphane ligand or
methyl migration. The adduct then reacts with acetophenone
to form coordinated 6,release of which re-forms the 16-electron fragment. There are two possibilities for the addition of
silane to the coordinatively unsaturated complex fragment :
(1) oxidative addition with cleavage of an Si-H bond and
(2) formation of an M-Si-H three-center bond, like that already found for [CpMn(CO),(silane)] complexes." - "1
We rule out addition of the Si-H bond to the acetyl group
of the complexes, since this addition would require additional catalysts['*] and since the methyl complexes 3 and 4 also
catalyze the hydrosilylation. We explain the absence of silyl
enol ether 7 by a hydrosilylation mechanism involving an
Fe-Si-H three-center bond rather than an Fe-H species. By
contrast, the hydrosilylation of acetophenone with diphenylsilane catalyzed by hydridorhodium complexes always affords enol ether 7 (in varying amounts) in addition to silyl
ether 6.143 The different induction periods found for the
catalysts are presumably due to deactivation of the catalytically active species at the start of the reaction by traces of
impurities.
0 VCH Verlagsgesellschafi mbH. 0-6940
Weinheim, 1990
0570-0833~90~1010-1l31
$3.50+.25/0
1131
The lack of optical induction when the optically active
catalysts 1-4 are used is the result of rapid racemization of
the catalytically active species. Surprisingly, optical induction is still not observed with the optically active complex 5,
whose planar chiral structure does not isomerize even at
200 "C. We interpret this result to mean that acetophenone
attacks the coordinated diphenylsilane from the side not facing the complex. The newly formed asymmetric center is thus
too far from the planar chiral group.
The complex [CpFe(CO),(CH,)] and also the complex
[IndFe(CO),(CH,)] can be used as hydrogenation catalysts.
For example, they catalyze the hydrogenation of a-methylstyrene to isopropylbenzene at 100 "C under H, (50 bar) in
However, owing to rapid deactivation of the comof the dimeric compounds
plexes employed-formation
[Cp'Fe(CO),], , which are catalytically inactive-only a few
catalytic cycles are achieved. The phosphane complexes 3
and 4 decompose during hydrogenation of a-methylstyrene
(90 "C, bar H,, THF) so rapidly that only a few percent of
hydrogenated product is formed. We explain the catalytic
hydrogenation by formation of an qZ-H, complex from the
unsaturated intermediate [Cp'Fe(CO)(COCH,)] under the
reaction conditions; this complex, formed in competition
with T H F and olefin complexes, reacts with a-methylstyrene
similarly to the reaction of the Fe-bonded SiH group with
acetophenone. Such q2-H, complexes have also been postulated to be formed during decomposition of [CpFe(CO),(CH,)] and [IndFe(CO),(CH,)] in the presence of hydrogen.r2*1
The majority of the reactions of organometallic compounds proceed via intermediates containing a free coordination site at the metal. It should be possible to use these free
coordination sites for catalysts of known structure.r211
[17] The [CpMn(CO),(sibdne)jcomplexes do not catalyze the hydrosilylation of
acetophenone with diphenylsilane; we have obtained evidence for a stoichiometric reaction.
[18] E. J. Crawford. P. K. Hanna, A. R. Cutler, J. A m . Chem. SOC.l i f (1989)
6891.
1191 1S O mL (1 1.6 mmol) of a-methylstyrene, 0.50 g (2.6 mmol) of [CpFe(CO),(CH,)] in 5 mL ofTHF, 50 bar H,. 110 " C ;degree of hydrogenation
90% ('H NMR integration).
[20] T. C. Forschner, A. R. Cutler, Inorg. Chim. Acfa 102 (1985) 113.
[21] Reports have appeared describing the use of [(arene)Cr(CO),(q'HSiHPh,)] complexes as catalysts for the activation of the Si-H bond of
diphenylsilane in thermal reactions: 0. B. Afanasova. E. Zubarev, T.M.
Sokolova, E. A. Chernyshew, Zh. Obshch. Khim. 57 (1987) 1909. E.
Chem. Commun. 1990, 681
Matarasso-Tchiroukhine, J. Chem. SOC.
Electrostatic Control of the Molecular and Crystal
Structure of an Olefinic Double Betaine **
By Robert Weiss,* Reinhardt Roth, Ruiner H . Lowuck,
and Mutthius Brerner
Dedicated to Professor Hans Jiirgen Bestmann
on the occasion of his 65th birthday
E/Z-isomeric olefinic double betaines of the type 1/2 were
previously unknown. The quadrupole system 2, which has
an alternating charge pattern, should be significantly more
stable than system 1, because of the more favorable electrostatic interactions between the charged substituents in 2.
Model calculations have shown that, depending on the substituents, this difference in stability can be up to
40 kcal mol-'.['] Here we describe the first synthesis of a
stable compound of type 1 as well as its unusual molecular
and crystal structure.
Received: May 23, 1990 [Z 3975 IE]
German version: Angew. Chem. 102 (1990) 1189
CAS Registry numbers
( - ) - I , 67375-04-6; (+)-1, 67291-26-3; (-)-2, 74984-64-8; (+)-2, 74945-73-6;
(-)-3, 59727-90-1; (+)-3, 59568-04-6; (-)-4, 123075-70.7; (+)-4, 123163.871; ( - ) - 5 , 129286-99-3; ( + ) - 5 , 129388-44-9; 6, 51276-65-4; CpFe(CO),CH,,
12080-06-7; Ph,SiH,, 775-12-2; acetophenone, 98-86-2; a-methylstyrene, 9883-9; isopropylbenzene, 98-82-8.
[l] J. L. Speier, Adv. Organomet. Chem. 17 (1979) 407.
[2] I . Ojima, K. Hirai in J. D. Morrison (Ed.): Asymmetric Synlhesis, Vol. 5 ,
Academic Press, Orlando, FL. USA 1985, p. 103.
[3] F. Seitz, M. S. Wrighton, Angew. Chem. lOO(1988) 281; Angew. Chrm. Inr.
Ed. Engl. 27 (1989) 289.
[4] K. Yamamoto, T. Hayashi, M. Kumada, J. Organornet. Chem. 46 (1972)
C65.
151 H. Brunner, U. Obermann, Chem. Ber. 122 (1989) 499.
[6] H. Brunner. H. Vogt, J. Orgunomet. Chem. 191 (1980) 181.
[7] H. Brunner, H. Vogt, J. Orgunomet. Chem. 2i0 (1981) 223.
[8] The structural formulas show the forms of 1-5 that are levorotatory at
1 = 436 nm. The Fe center has the R configuration, the C center,
the S configuration.
[9] 1.0 mL (8.0 mmol) of acetophenone, 1.6 mL (8.0 mmol) of diphenylsilane,
0.5-1.0 mol % of catalyst. The hydrosilylation can be monitored by 'H
NMR spectroscopy. The induction period can be from several minutes to
a few hours.
[lo] A simple rate law cannot be formulated for the epimerization, which occurs over hours[l4].
Ill] The half-lives for epimerizatlon of 3 and 4 in [D,]benzene are 70 min at
70'C and 37 min at SO°C[12]
[I21 H. Brunner, K. Fisch, P. G. Jones, J. Salbeck. Angew. Chem. I01 (1989)
1558; Angew. Chem. Int. Ed. Engl. 28 (1989) 1521.
[13] Replacement of the aminophosphane L by PPh, in complexes 1 - 4 does
not affect the catalytic activity.
[14] H. Brunner, H Vogt, Chem. Eer. 114 (1981) 2186.
1151 D. L. Lichtenberger, A. Rai-Chaudhuri,Inorg. Chem. 29 (1990) 975.
[16] H. Rabaa, JLY. Saillard, U. Schubert, J. Organomet. Chem. 330 (1987) 397.
1 132
Q VCH Verlagsge.~ellschofimhH. D-6940 Weinheim, f990
1
2
The starting point of the synthesis was our observation
that, in structure-determined analogy to p-chloranil,[21
dichloromaleic anhydride (3) can be substituted in a bis-onio
fashion by 4-dimethylaminopyridine (DMAP, 6). The yellow
4
3
L = N D N M a 2
e!
I.
e
coo
la
e!
I.
5
[*I Prof. Dr. R. Weiss, Dr. R. Roth, Dip1:Chem. R. H. Lowack,
Dr. M. Bremer
Institut fur Organische Chemie der Universitat
Henkestrasse 42, D-8520 Erlangen (FRG)
[**I This work was supported by the Fonds der Chemischen Industrie. R. H . L.
Thanks the Studienstiftung des deutschen Volkes for a doctoral fellowship.
$3.50+ .25/0
0570-0833~90jlOl0-1132
Angew Chem. Int. Ed. Engl. 29 (1990) No. 10
Документ
Категория
Без категории
Просмотров
0
Размер файла
250 Кб
Теги
site, one, coordination, catalytic, hydrogenation, fragmenty, cpfe, hydrosilylation
1/--страниц
Пожаловаться на содержимое документа