Hydrosilation of the manganese acetyl (CO)5MnC(O)CH3 with monohydrosilanes

Article abstract of DOI:10.1021/ja9528801

Treatment of the manganese acetyl (CO)₅MnC(O)CH₃ (1) with 1-2 equiv of a monohydrosilane furnished mixtures of α-siloxyethyl (CO)₅MnCH(OSiR₃)CH₃ (2) and α-siloxyvinyl (CO)₅MnC(OSiR₃

Full text of DOI:10.1021/ja9528801

J. Am. Chem. Soc. 1996, 118, 10069-10084
10069
Hydrosilation of the Manganese Acetyl (CO)5MnC(O)CH3 with
Monohydrosilanes
Brian T. Gregg and Alan R. Cutler*
Contribution from the Department of Chemistry, Rensselaer Polytechnic Institute,
Troy, New York 12180
ReceiVed August 21, 1995X
Abstract: Treatment of the manganese acetyl (CO)5MnC(O)CH3 (1) with 1-2 equiv of a monohydrosilane furnished
mixtures of R-siloxyethyl (CO)5MnCH(OSiR3)CH3 (2) and R-siloxyvinyl (CO)5MnC(OSiR3)dCH2 (3) complexes.
Relative yields of 2 and 3 varied from 80% and 6% for HSiMe2Ph to 28% and 59% for HSiEt3. One of the latter
compounds, (CO)5MnC(OSiEt3)dCH2 (3j), was fully characterized, and seven examples of 2 were isolated in moderate
yields. Four R-siloxyethyl complexes 2 were further characterized as stable derivatives (CO)5MnC(O)CH(OSiR3)CH3
after carbonylation. Mechanistic studies on the HSiMe2Ph and HSiEt3 hydrosilation of 1 are noteworthy for (1) the
absence of (R3SiO)CHdCH2 and CH3CH2OSiR3 byproducts, (2) the presence of 3 but not (CO)5MnSiR3, (3) inhibition
by CO, phosphine, or acetonitrile, but neither air nor light, (4) competitive hydrosilation of other substrates (e.g.,
acetone or Cp(CO)2FeC(O)R) for which 1 is a precatalyst, (5) degradation of 2 by excess HSiR3, giving Mn2(CO)10
and (R3Si)2O as the final products, (6) the fact that this degradation results in autocatalysis by generating the transient
active catalyst (CO)4MnSiR3 (15), and (7) the fact that the hydrosilation induction period can be removed by
independently generating the putative 15. These observations are consistent with an autocatalytic hydrosilation
mechanism in which silane degradation of product 2 (or of other manganese complexes) generates the active catalyst
15, which binds 1 and rearranges to the unsaturated bimetallic µ-siloxyethylidene (CO)5MnC(CH3)(OSiMe2Ph)Mn-
(CO)4 as the key catalysis intermediate: silane addition affords 2 whereas â-deinsertion produces 3.
Introduction
Hydrosilation reactions involving these manganese acyl
complexes are of interest for three reasons. First, hydrosilation
of labile or coordinatively unsaturated acyl complexes (as
substrates) resembles the catalytically relevant reduction of acyl
ligands with molecular hydrogen4 or metal hydride complexes.5
Second, acyl ligand hydrosilation chemistry engenders other
novel ligand reactions. Examples include transforming acetyl
ligands LxMC(dO)CH3 plus hydrosilane to R-siloxyvinyl Lx-
MC(OSiR3)dCH2,6 vinyl LxMCHdCH2,7 and fully reduced
alkyl LxMCH2CH3 groups.7,8 Third, these manganese acyl/
hydrosilane systems afford extremely active catalysts for, thus
The manganese acyl complexes (CO)5MnC(O)R′ (R′ ) CH3,
Ph) represent intriguing substrates for reactions with hydrosi-
lanes.1 These thermally labile acyl complexes2 undergo hy-
drosilation at room temperature: the manganese acetyl com-
pound 1 (R′ ) CH3), for example, when treated with mono-
hydrosilanes affords isolable R-siloxyethyl complexes (CO)5-
MnCH(OSiR3)CH3 (2). Several related hydrosilation products
(CO)5MnCH(OSiR3)R′ (R′ ) CH3, Ph) prepared using mono-,
di-, and trihydrosilanes (eq 1) have been isolated or unambigu-
(3) (a) Gregg, B. T.; Cutler, A. R. Organometallics 1993, 12, 2006. (b)
Manganese alkyl and halide complexes XMn(CO)4(L) [X ) CH3, Ph, CH3-
CH(OSiR3), Br; L ) CO, PPh3, PEt3] also serve as effective precatalysts
for the hydrosilation of a variety of organic and organometallic acyl
compounds. Significantly, neither R3SiMn(CO)5 (R3Si ) Me2Ph, SiHPh2)
nor Mn2(CO)10 is an effective precatalysts. Gregg, B. T.; Cutler, A. R.
Manuscript in preparation.1d
(4) (a) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G.
Principles and Applications of Organotransition Metal Chemistry; Univer-
sity Science Books: Mill Valley, CA, 1987; Chapter 10.10. (b) Ungva´ry,
F.; Marko´, L. Organometallics 1983, 2, 1608. (c) Kova´cs, I.; Ungva´ry, F.;
Marko´, L. Organometallics 1986, 5, 209. (d) Martin, J. T.; Baird, M. C.
Organometallic 1983, 2, 1073.
(1)
ously characterized by H, 13C, and 29Si NMR spectroscopy.
On the other hand, these labile manganese acyl complexes also
function as extremely reactive catalyst precursors3 for the
hydrosilation of nonlabile iron acyls Cp(CO)(L)FeC(O)R′.1b,d
1
X Abstract published in AdVance ACS Abstracts, October 1, 1996.
(1) (a) Gregg, B. T.; Hanna, P. K.; Crawford, E. J.; Cutler, A. R. J. Am.
Chem. Soc. 1991, 113, 384. (b) Hanna, P. K.; Gregg, B. T.; Cutler, A. R.
Organometallics 1991, 10, 31. (c) Hanna, P. K.; Gregg, B. T.; Tarazano,
D. L.; Pinkes, J. R.; Cutler, A. R. In Homogeneous Transition Metal
Catalyzed Reactions; Advances in Chemistry Series No. 230; Moser, W.
R., Slocum, D. W., Eds.; American Chemical Society: Washington, DC,
1992; p 491. (d) Gregg, B. T.; Cutler, A. R. Manuscript in preparation.
(2) Reversible carbonyl ligand dissociation for 1: (a) Noack, K.;
Calderazzo, F. J. Organomet. Chem. 1967, 10, 101. (b) Kraihanzel, C. S.;
Maples, P. K. Inorg. Chem. 1968, 7, 1806. (c) Flood, T. C.; Jensen, J. E.;
Statler, J. A. J. Am. Chem. Soc. 1981, 103, 4411. (d) McHugh, T. M.; Rest,
A. J. J. Chem. Soc., Dalton Trans. 1980, 2323. (e) Ziegler, T.; Verslius,
L.; Tschinke, V. J. Am. Chem. Soc. 1986, 108, 612. (f) Axe, F. U.; Marynick,
D. S. Organometallics 1987, 6, 572. (g) Photochemical studies, Boese, W.
T.; Ford, P. C. Organometallics 1994, 13, 3525. Boese, W. T.; Lee, B.;
Ryba, D. W.; Belt, S. T.; Ford, P. C. Organometallics 1993, 12, 4739 and
references cited therein.
(5) (a) Gladysz, J. A.; Tam, W.; Williams, G. M.; Johnson, D. L.; Parker,
D. W. Inorg. Chem. 1979, 18, 1163. Tam, W.; Wong, W.-K.; Gladysz, J.
A. J. Am. Chem. Soc. 1979, 101, 1589. (b) Halpern, J. Acc. Chem. Res.
1982, 15, 332. Nappa, M. J.; Santi, R.; Halpern, J. Organometallics 1985,
4, 34. Webb, S. L.; Giandomenico, C. M.; Halpern, J. J. Am. Chem. Soc.
1986, 108, 345. (c) Warner, K. E.; Norton, J. R. Organometallics 1985, 4,
2150. Martin, B. D.; Warner, K. E.; Norton, J. R. J. Am. Chem. Soc. 1986,
108, 33. (d) Kova´cs, I.; Hoff, C. D.; Ungvary, F.; Marko, L. Organometallics
1985, 4, 1347. (e) Ruszczyk, R. J.; Huang, B. - L.; Atwood, J. D. J.
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(6) Gregg, B. T.; Cutler, A. R. Manuscript in preparation.
(7) (a) Crawford, E. J.; Hanna, P. K.; Cutler, A. R. J. Am. Chem. Soc.
1989, 111, 6891. (b) Pinkes, J. R.; Mao, Z.; Cutler, A. R. Manuscript
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Y. Organometallics 1991, 10, 1394.
S0002-7863(95)02880-0 CCC: $12.00 © 1996 American Chemical Society

10070 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
far, SiH/SiD isotope exchange,3a hydrosilane alcoholysis,9a
hydrosilation of organic aldehydes and ketones,9b,10 hydrosila-
tion-reduction of esters,9c and silation of carboxylic acids.9d
Previously, Gladysz and co-workers11 reported that treating
aldehydes with (CO)5MnSiMe3 produced R-(trimethylsiloxy)-
alkyl compounds (CO)5MnCH(OSiMe3)R. Although reported
to be unstable, these compounds were carbonylated and deriva-
tized as their acyl complexes. Akita, Moro-oka, and co-workers8
generated examples of (CO)5MnCH(OSiHPh2)R in C6D6 or THF
by hydrosilation of (CO)5MnC(O)R (eq 1) with excess H2SiPh2
and 1% (PPh3)3RhCl. The rhodium catalyst, however, is
unnecessary.1a,c In an earlier study on the reaction of triethyl-
silane and 1 in THF, Wegman12a reported that a 10-fold excess
of this silane and 1 atm of CO (at 25°C) exclusively gave
acetaldehyde and (CO)5MnSiEt3.
We now report the hydrosilation chemistry involving 1 and
13 monohydrosilanes. Ten R-siloxyethyl complexes
(CO)5MnCH(OSiR3)CH3 (2) were generated, seven of which
were isolated in 46-70% yields after column chromatography
and five of which were carbonylated to give their R-siloxypro-
pionyl derivatives (CO)5MnC(O)CH(OSiR3)CH3 (4). In six of
the hydrosilation reactions, R-siloxyvinyl byproducts (CO)5MnC-
(OSiR3)dCH2 (3) were detected, with triethylsilane producing
(CO)5MnC(OSiEt3)dCH2 (3j) as the major product. We
account for the formation of both products 2 and 3 by an
autocatalytic pathway in which silane-induced degradation of
the initially formed 2 provides the active catalyst. Observations
on forming and subsequently degrading (CO)5MnCH(OSiMe2-
Ph)CH3 (2a), (CO)5MnCH(OSiEt3)CH3 (2j), and other manga-
nese complexes with excess monohydrosilanes accordingly are
discussed.
over activated 4 Å molecular sieves. Triethylsilane was dried over
freshly activated 4 Å molecular sieves and fractionally distilled. Only
the fraction that was collected over the boiling point range 107-108
1
°C was used; its NMR spectral data, H δ 3.87 (sept, J ) 3.1 Hz,
SiH), 0.97 (t, J ) 6.8, SiCH2CH3), 0.54 (m, SiCH2CH3); 13C{1H} δ
8.3 (SiCH2CH3), 2.9 (SiCH2CH3); 29Si{1H} δ 0.42, are consistent with
the absence of the disiloxane (Et3Si)2O [13C{1H} δ 7.0 (SiCH2CH3),
6.8 (SiCH2CH3); 29Si{1H} δ 9.29] or detectable concentrations of other
triethylsilyl derivatives.
14
Manganese complexes (CO)5MnC(O)CH3 (1) and (CO)5MnCH3
were prepared by treating Mn(CO)5-K+ 15 in THF with acetyl chloride
or methyl iodide. The acetyl 1 was isolated as a pale yellow solid
(86% yield) after column chromatography on flash-grade silica gel/
hexane, before it was sublimed to a cooled probe (-78 °C) at 10-1
Torr. The p-toluoyl complex (CO)5MnC(O)-p-C6H4CH316 was prepared
by a similar procedure and was purified by column chromatography
on flash-grade silica gel/hexane. Samples of (CO)5MnCH2CH3,17 (CO)5-
MnSi(CH3)2Ph (5a),1a (PPh3)(CO)4MnC(O)CH3,18 CH3CH2OSiMe2Ph
(7a), and CH3CH2OSiEt3 (7j)9a,19 were prepared by literature procedures
1
and judged pure by IR and H NMR spectroscopy.
Hydrosilation of (CO)5MnC(O)CH3 (1) with Monohydrosilanes.
Dimethylphenylsilane. A pale yellow solution of 1 (300 mg, 1.26
mmol) in 600 mg of C6D6 was treated with HSiMe2Ph (172 mg, 1.26
mmol) before it was transferred to a NMR tube and securely stoppered
with a rubber septum. The solution turned dark orange within 25 min
as 1 was depleted (1H NMR spectral monitoring). This solution was
chromatographed on a 1 × 4 cm column of deactivated silica gel (60-
200 mesh) with hexane; an orange band was eluted (30 mL), leaving
the column pale orange. The first five drops of the eluate, which
retained contaminating (PhMe2Si)2O (1H NMR, δ 0.31, SiMe), were
discarded. Evaporation of solvent from the remaining eluate left an
orange oil (258 mg) that was identified as (CO)5MnCH(OSiMe2Ph)-
CH3 (2a) (55% yield). Anal. Calcd for C15H15O6SiMn: C, 48.13; H,
4.04. Found: C, 48.06; H, 4.04.
Monohydrosilanes. Analogous experimental conditions were used
for the other monohydrosilanes; R-siloxyethyl complexes 2b-2h were
isolated as spectroscopically pure orange oils (Table 1). For (CO)5MnCH-
(OSiMe2OSiMe3)CH3 (2d), Anal. Calcd for C12H19O7Si2Mn: C, 37.30;
H, 4.96. Found: C, 36.99; H, 4.61. Spectral data are in Table 2.
Hydrosilation of (CO)5MnC(O)CH3 (1) with Triethylsilane.
Reaction Profile. Manganese acetyl 1 (112 mg, 0.47 mmol), HSiEt3
(100 mg, 0.87 mmol), and anisole (33 mg, 0.31 mmol) were dissolved
in 600 mg of C6D6 and then transferred to a 5-mm NMR tube that was
fitted with a rubber septum. 1H NMR spectra were recorded within
10 min using spectrometer parameters that had been optimized with a
38° pulse angle for quantitative analyses of known concentrations of 1
and anisole. As a result, integration traces are believed to be accurate
to within (5%. The spectrometer pulse delay time of 10 s coincided
with measurements of spin-lattice (T1) relaxation times by a standard
inversion-recovery experiment: 1 (δ 2.22, T1 ) 0.11 s), (CO)5MnC-
(OSiEt3)dCH2 (3j) (T1 ) 1.21 and 1.27 s), and PhOCH3 (δ 3.31, T1 )
2.58 s).
Experimental Section
Synthetic manipulations were performed in a nitrogen atmosphere
using a combination of standard Schlenk line, glovebox, and vacuum
line procedures.13 Infrared spectra were recorded on a Perkin-Elmer
Model 1600 FT spectrophotometer. NMR spectral data were obtained
in C6D6 and were reported as δ values relative to residual C6D5H (1H,
7.15 ppm), C6D6 (13C, 128.00 ppm), and external SiMe4 (29Si, 0 ppm)
using Varian Model XL-200, Unity 500, and IBM-WP100 spectrom-
eters. 29Si{1H} NMR spectra of concentrated C6D6 solutions containing
Cr(acac)3 (0.5 mol %) were recorded using inverse gated decoupling
for ∼500 transients (<1 h) using a 90° pulse angle and a 1 s delay
time. Combustion microanalyses were done by Quantitative Technolo-
gies, Bound Brook, NJ.
Organic and inorganic reagents were obtained commercially and used
as received; silanes and C6D6 were stored in a glovebox under nitrogen.
Diethyl ether, hexane, and benzene were distilled from sodium
benzophenone ketyl; acetonitrile was purged with nitrogen and stored
NMR spectral scans, recorded every 10 min, were integrated vs the
anisole internal standard signal, δ 3.31 (s, PhOCH3). The following
(9) (a) Gregg, B. T.; Cutler, A. R. Organometallics 1994, 13, 1039. (b)
DiBiase-Cavanaugh, M.; Gregg, B. T.; Cutler, A. R. Manuscript submitted.
(c) Mao, Z.; Gregg, B. T.; Cutler, A. R. J. Am. Chem. Soc. 1995, 117,
10139. (d) Mao, Z.; Gregg, B. T.; Cutler, A. R. Manuscript in preparation.
(10) Reviews: (a) Ojima, I. In The Chemistry of Organic Silicon
Compounds; Patai, S., Rappoport, Z., Eds.; Wiley: New York, 1989;
Chapter 25. (b) Chaloner, P. A. Handbook of Coordination Catalysis in
Organic Chemistry; Butterworths: Boston, 1986; Chapter 7.2. (c) Marciniec,
B.; Gulin˜ski, J. J. Organomet. Chem. 1993, 446, 15.
(14) (a) Closson, R. D.; Kozikowski, J.; Coffield, T. H. J. Org. Chem.
1957, 22, 598. (b) King, R. B. Organometallic Syntheses; Academic Press:
New York, 1965; Part I, Vol. 1, p 147. (c) Mckinney, R. J.; Crawford, S.
S. Inorg. Synth. 1989, 26, 155. (c) Anderson,J. M.; Moss, J. R. Organo-
metallics 1994, 13, 5013.
(15) Gladysz, J. A.; Williams, G. M.; Tam, W.; Johnson, D. L.; Parker,
D. W.; Selover, J. C. Inorg. Chem. 1979, 18, 553.
(11) (a) Gladysz, J. A. Acc. Chem. Res. 1984, 17, 326. (b) Johnson, D.
L.; Gladysz, J. A. Inorg. Chem. 1981, 20, 2508. (c) Brinkman, K. C.;
Gladysz, J. A. Organometallics 1984, 3, 147. (d) Selover, J. C.; Vaughn,
G. D.; Strouse, C. E.; Gladysz, J. A. J. Am. Chem. Soc. 1986, 108, 1455.
(e) Vaughn, G. D.; Strouse, C. E.; Gladysz, J. A. J. Am. Chem. Soc. 1986,
108, 1462. Vaughn, G. D.; Gladysz, J. A. J. Am. Chem.. Soc. 1986, 108,
1473. Vaughn, G. D.; Krein, K. A.; Gladysz, J. A. Organometallics 1986,
5, 936. (f) Brinkman, K. C.; Vaughn, G. D.; Gladysz, J. A. Organometallics
1982, 1, 1056.
(12) (a) Wegman, R. W. Organometallics 1986, 5, 707. (b) Kovacs, I.;
Sisak, A.; Ungvary, F.; Marko, L. Organometallics 1988, 7, 1025.
(13) Shriver, D. F.; Drezdon, M. A. The Manipulation of Air-SensitiVe
Compounds, 2nd ed.; Wiley-Interscience: New York, 1986.
(16) (a) Lukehart, C. M.; Torrence, G. P.; Zeile, J. V. Inorg. Synth. 1978,
18, 56. (b) Motz, P. L.; Sheeran, D. J.; Orchin, M. J. Organomet. Chem.
1990, 383, 201.
(17) (a) Hieber, W.; Wagner, G. Justus Liebigs Ann. Chem. 1958, 618,
24. (b) Hieber, W.; Braun, G.; Beck, W. Chem. Ber. 1960, 93, 901. (c)
Green, M. L. H.; Nagy, P. L. I. J. Organomet. Chem. 1963, 1, 58.
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1806. (c) Noack, K.; Ruch, M.; Calderazzo, F. Inorg. Chem. 1968, 7, 345.
(19) Caseri, W.; Pregosin, P. S. Organometallics 1988, 7, 1373.
(20) Messerle, L. In Experimental Organometallic Chemistry; ACS
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American Chemical Society: Washington, DC, 1987; Chapter 7, p 198.

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10071
signals were used in establishing the materials balance: 1, δ 2.22; 3j,
δ 4.29 (d, MnC(OSiEt3)dCHH); 2j, δ 1.83 (d, Mn-CH(OSiEt3)CH3);
and HSiEt3, δ 3.87 (heptet, SiH). Concentrations of these compounds
are reported as a reaction profile-time plot, Figure 2, over 110 min.
Within 70 min, 1 had transformed completely into a mixture containing
59% 3j and 28% 2j.
tube that was fitted with a rubber septum, and the first 1H NMR
spectrum of the initially pale yellow solution was recorded within 10
min.
Within 25 min, 1 was consumed in the dark orange solution; both
2a and (CO)5MnC(OMe2Ph)dCH2 (3a) were quantified (76% and 3%)
using their δ 1.73 and 4.33 doublet absorptions, respectively. Con-
spicuous absorptions at δ 0.31 ((PhMe2Si)2O), 0.55, and 0.45 also
appeared as the yield of 2a dropped to 69% (45 min) and then to 52%
(100 min). The HSiMe2Ph concentration decreased to 70% and 40%
of its initial value after 45 and 100 min (integration of its δ 4.61 heptet).
Similar quantification of the disiloxane 1H NMR absorption at δ 0.31
is not reliable, since it overlaps other aborptions in the δ 0.3 chemical
shift region that is common to organic dimethylphenylsilyl derivatives.
Relevant multinuclear NMR spectral data: 7a [13C, δ 58.65, 18.73,
-1.52], 5a [1H, δ 0.68; 13C, δ 4.01], and (PhMe2Si)2O [1H, δ 0.30;
13C, δ 0.95; 29Si, δ -0.80].
Two practical aspects of these triethylsilane reactions should be
noted. First, results were independent of whether the HSiEt3 was used
“as received” or distilled. Second, reaction times and product distribu-
tions also were independent of whether the NMR tubes were securely
sealed (e.g., with a torch after several freeze-pump-thaw cycles) or
vented through a pinhole in the septum. Unlike the reactions of other
hydrosilanes and 1, those involving HSiEt3 generated considerable
pressure (presumably H2), which for larger-scale reactions could
dislodge a new rubber septum on a thin-wall 5-mm NMR tube.
The reaction solution was chromatographed on a 1 × 10 cm column
of 40 µm (flash-grade) silica gel/hexane, from which an orange hexane
eluate (25 mL) was collected and evaporated. The resulting mixture
of an orange oil and solid was washed with hexane (2 × 2.5 mL), and
the hexane extracts were combined in a centrifuge tube, cooled to -78
°C (10 min), and centrifuged. The combined solid residues, a yellow-
orange powder (39 mg) after drying in a stream of nitrogen, was
identified by IR spectroscopy (and the absence of 1H NMR signals) as
Mn2(CO)10 (42% yield). Although all three dimer IR ν(CO) bands at
2045 (s), 2009 (vs, br), and 1980 (s, sh) cm-1 overlap absorptions for
2j and 3j, the first and third absorptions for Mn2(CO)10 are unusually
intense and qualitatively indicate its presence. Evaporating the hexane
supernatant solution afforded an orange oil (91 mg) that was identified
as (CO)5MnC(OSiEt3)dCH2 (3j), 55% yield. Anal. Calcd for
C13H17O6SiMn: C, 44.47; H, 5.17. Found: C, 44.32; H, 4.86.
Combined 1H and 13C NMR spectral monitoring of this reaction
mixture further revealed that neither (CO)5MnSiMe2Ph (5a) nor CH3-
CH2OSiMe2Ph (7a) was present. Also not detected was the ethyl
complex (CO)5MnCH2CH3, [ δ 1.28 (t, J ) 7.1 Hz), 1.13 (q) (1H)/
7.96 (MnCH2), 5.50 (13C)]. Compounds present included HSiMe2Ph
[1H NMR δ 4.61 (hept), 0.22 (d); 13C NMR δ -3.71], (PhMe2Si)2O,
and 2a. Unassigned absorptions: 1H NMR δ 3.87 (m), 3.52 (m), 3.40
(m), 1.08 (d), 0.55 (s), 0.43, 0.32, 0.29; 13C NMR δ 69.90, 68.93, 20.57,
3.63, -0.74, -0.85, -1.64. A 29Si NMR spectrum of this reaction
mixture after 3 h was consistent with (PhMe2Si)2O (δ -0.83) as the
major Si-containing species, although peaks at δ 7.38 and 5.38 and at
least six other weaker absorptions were evident. 29Si NMR resonances
for HSiMe2Ph (δ -16.83), 2a (δ 3.74), 5a, and 7a were absent.
Preparation of CH3CH(OSiMe2Ph)CH(OSiMe2Ph)CH3 (8a). The
following was adapted from the procedure for the dehydrogenative
coupling of 2,2-dimethyl-1,3-propanediol and 2 equiv of HSiMe2Ph to
give the fully characterized bis(silyl ether).9a A solution consisting of
2,3-butanediol (50 mg, 0.56 mmol), HSiMe2Ph (159 mg, 1.17 mmol),
and (CO)5MnBr (2 mg, 0.0056 mmol) was prepared in 600 mg of C6D6.
After 1.5 h, the light orange solution had darkened, and the slow, steady
gas bubbling had ceased. NMR spectral examination of the reaction
mixture established that the diol had converted to CH3CH(OSiMe2-
Ph)CH(OSiMe2Ph)CH3 (8a) (>90%), presumably as a mixture of meso
and RR,SS diastereomers: 1H NMR δ 7.63-7.61 (m, 2H, Ph), 7.25-
7.48 (m, 3H, Ph), 3.71 (m, 2H, CH), 1.13 (d, J ) 5.5 Hz), 0.39 (SiMe);
13C{1H} δ 138.77 (ipso C, Ph), 133.86, 129.65, 127.99 (Ph), 73.64
(CH), 19.58 (CH3), -0.67, -0.94 (SiMe); 29Si{1H} δ 5.05. Small
concentrations (<5%) of HSiMe2Ph and Me2PhSiOSiMe2Ph were also
observed.
Reaction of (CO)5MnC(O)CH3 (1) in THF-d8 with HSiEt3. 1H
NMR Spectral Monitoring. A 5-mm septum-stoppered NMR tube
was charged with 91 mg (0.38 mmol) of 1, 493 mg of THF-d8, 43 mg
(0.40 mmol) of anisole as the internal standard, and then 68 mg (0.58
mmol, 1.5 equiv) of freshly distilled HSiEt3. 1H NMR spectral
monitoring of the light yellow solution showed that no 1 was consumed
after 1 h. Within 2 h, the solution turned orange commensurate with
slow gas evolution; 12% of 1 was converted to (CO)5MnC(OSiEt3)dCH2
(3j), δ 4.97 (d, J ) 1.2 Hz, dCHH), 4.19 (d, J ) 1.2, dCHH). After
4 h, all of the 1 was gone; also absent were absorptions that could be
attributed to (CO)5MnCH(OSiEt3)CH3 (2j), CH3CH2OSiEt3 (7j),9a,19 or
acetaldehyde. The 3j was quantified in 69% yield by integration of
1
its vinyl H NMR resonance (δ 4.19) vs anisole, with 0.09 mmol of
the HSiEt3 (δ 3.66) remaining.
Reaction of (CO)5MnC(O)CH3 (1) with Triethylsilane. Precata-
lyst Study. Pretreatment of manganese toluoyl (CO)5MnC(O)-p-C6H4-
CH3 (14 mg, 0.005 mmol) in 600 mg of C6D6 with HSiEt3 (100 mg,
0.86 mmol) gave a somewhat darker yellow solution after 45 min. The
precatalyst solution then was pipetted into a 5-mm NMR tube, and the
substrate 1 (112 mg, 0.47 mmol) was added. Results of 1H NMR
spectral monitoring were consistent with all of the 1 converting within
15 min to a 58:42 mixture of 2j and 3j.
Reaction Profiles for (CO)5MnC(O)CH3 (1) and Dimethylphe-
nylsilane. Excess Monohydrosilane. Complex 1 (50 mg, 0.21 mmol),
HSiMe2Ph (50 mg, 0.37 mmol), and anisole (22 mg, 0.20 mmol) were
dissolved in 600 mg of C6D6. The solution was transferred to a 5-mm
NMR tube that was fitted with a rubber septum, and the first 1H NMR
spectrum was recorded within 10 min. NMR spectra were recorded
over 120 min and were integrated vs the anisole internal standard signal,
δ 3.31 (s, PhOCH3). The following signals were used in establishing
the materials balance: 1, δ 2.23 (s, MnCOCH3); 2a, δ 1.74 (d,
MnCH(OSiMe2Ph)CH3); and HSiMe2Ph, δ 4.61 (heptet, SiH). Con-
centrations of these compounds are reported as a reaction profile plot,
Figure 1.
Autocatalysis Studies. To a pale yellow solution of 1 (100 mg,
0.42 mmol) in 600 mg of C6D6 were added HSiMe2Ph (65 mg, 0.48
mmol) and anisole (60 mg, 0.55 mmol) before it was transferred to a
stoppered NMR tube. Product (CO)5MnCH(OSiMe2Ph)CH3 (2a) was
quantified by integrating the 1H NMR spectra that were recorded as a
function of time. Four additional experimental runs were carried out
under the same conditions, but in which small quantities (1-2%) of
manganese complexes were included as potential catalysts.
Reaction of (CO)5MnCH(OSiMe2Ph)CH3 (2a) with Triethylsi-
lane. To a 5-mL vial in the glovebox were added 2a (100 mg, 0.42
mmol), C6D6 (600 mg), and HSiEt3 (692 mg, 5.95 mmol). The orange-
brown solution then was transferred to a 5-mm NMR tube that was
fitted with a rubber septum, and 1H NMR spectra were recorded within
10 min. After 1 h, neither 2j nor 3j was evident, as judged by the
absence of diagnostic absorptions at δ 1.83 and 4.29, respectively. Most
of the starting 2a remained, although peak broadening precluded further
analysis. 29Si NMR spectra were recorded, and major signals were
assigned at δ 9.34 (Et3Si)2O, 3.74 (2a), and -0.83 (PhMe2Si)2O.
Although the HSiEt3 (δ 9.33) was consumed within 3 h, 2a was still
present and neither 2j (δ 16.14) nor 3j (δ 17.19) was detected. Also
absent were (CO)5MnSiMe2Ph (5a) (δ 13.03), EtOSiMe2Ph (7a) (δ
-3.58), and EtOSiEt3 (7j) (δ 17.32). Unassigned absorptions were
observed at δ 20.40, 19.91, 18.62, 11.41, 5.36, and -2.68.
Two of the experimental runs also contained (CO)5MnSiMe2Ph (5a)
(2 mg, 0.0063 mmol) or 2a (3 mg, 0.008 mmol). Two other
experiments involved pretreating pale yellow solutions of 1 (3 mg, 0.008
mmol) or (CO)5MnC(O)-p-C6H4CH3 (1 mg, 0.003 mmol) in 600 mg
of C6D6 with the silane (HSiMe2Ph, 65 mg) for 45 min. The
(CO)5MnC(O)-p-C6H4CH3 precatalyst solution turned dark yellow-
orange, whereas the 1 precatalyst solution turned dark yellow. To each
Reaction of (CO)5MnCH(OSiMe2Ph)CH3 (2a) with Dimethylphe-
nylsilane. Manganese acetyl 1 (100 mg, 0.42 mmol), HSiMe2Ph (143
mg, 1.05 mmol), and anisole (45 mg, 0.42 mmol) were dissolved in
600 mg of C6D6. The orange solution was transferred to a 5-mm NMR

10072 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
1
precatalyst solution was added the reactant 1 (100 mg), and the H
NMR spectra were monitored. Results for all five experimental runs
appear in Figure 4.
Acetonitrile Inhibition. 1 (100 mg, 0.42 mmol) and HSiMe2Ph
(65 mg, 0.48 mmol) were dissolved in 600 mg of C6D6, and the solution
was monitored by H NMR spectroscopy. After 15 min, 1 was 56%
1
consumed; 40 mg of CD3CN (0.90 mmol) then was injected into the
reaction mixture. Continued monitoring was consistent with 61%
conversion of 1 to 2a after 18, 25, and 60 min.
Effect of HSi(SiMe3)3. To a solution of 1 (50 mg, 0.21 mmol) and
HSiMe2Ph (29 mg, 0.21 mmol) in 600 mg of C6D6 was added HSi-
(SiMe3)3 (10 mg, 0.040 mmol). The acetyl complex 1 was consumed
within 40 min and was replaced by 2a (71%), as arrived at by 1H NMR
quantitative integration vs unreacted HSi(SiMe3)3.
Presence of Air. A pale yellow solution of 1 (100 mg, 0.42 mmol)
in 600 mg of C6D6 was aerated by sucking it into a glass pipet and
then expelling it back into the reaction vial. This operation was repeated
six times before HSiMe2Ph (136 mg, 1.0 mmol) and anisole internal
standard were added. Then the pale yellow solution was transferred
to a NMR tube, again in the air. Within 30 min the starting 1 was
depleted in the resulting dark orange solution, and a 76% yield of 2a
was realized.
CO Inhibition of the Reactions between Monohydrosilanes and
1. With Dimethylphenylsilane. A 5-mm NMR tube with its attached
J. Young valve was charged with 50 mg (0.21 mmol) of (CO)5MnC-
(O)CH3 (1), 26 mg (0.24 mmol) of anisole, and 600 mg of C6D6. The
C6D6 had been dried over activated 4A molecular sieves for 20 h and
purged with a gentle stream of carbon monoxide (in the NMR tube)
for 5 min. The HSiMe2Ph (35 mg, 0.26 mmol) then was injected into
the NMR tube by a microliter syringe, and the rubber septum was
replaced by the top of the J. Young valve. The NMR tube and its pale
yellow solution was rotated end-over-end at 10 revolutions/min, and
1
the tube periodically was removed for H NMR spectral monitoring.
After 1.5 h, only a trace of 2a was evident; its concentration increased
to a maximum of 8-10% after 2.5 h with 39% and 38% of 1 and
HSiMe2Ph consumed, respectively. Nearly all of the silane had
transformed to (PhMe2Si)2O, although several minor SiMe2 resonances
were noted near δ 0.3. Between 4 and 8 h, the ratio of disiloxane to
silane increased from 2:3 to 3:2 with only trace concentrations of 2a.
The silane was consumed after 10.5 h, leaving 38% of the starting 1
and <5% 5a. An IR spectrum of this solution confirmed the presence
of 1 along with Mn2(CO)10 as a minor component. 13C and 29Si NMR
spectra of the dark orange solution were consistent with the presence
of (PhMe2Si)2O as the only detectable silicon species.
Carbonylation of r-Siloxyethyl Complexes (CO)5MnCH(OSiR3)-
CH3 (2). (CO)5MnCH(OSiMe2Ph)CH3 (2a). An orange acetonitrile
solution (30 mL) containing 258 mg of 2a (0.69 mmol) was transferred
to the 100-mL glass bottle of a Fisher-Porter pressure apparatus,19 which
also had a magnetic stirring bar. The reactor was pressurized with
carbon monoxide to 82 psig and then vented; this cycle was repeated
six times before a final 82 psig CO pressure was maintained. After 1
h of vigorous stirring, the solution had turned light yellow. The pressure
then was vented, and an IR spectrum of the solution showed that the
ν(CO) absorptions of 2a at 2106, 2044, 2005, and 1982 cm-1 had been
replaced by terminal ν(CO) bands at 2113, 2047, and 2011 cm-1 and
Without rotation of the NMR tube, 85% of the 1 was consumed
within 4.5 h, although only 5-8% yields of 2a were realized. During
this reaction, the top 1 cm of the solution in the static NMR tube
remained pale yellow as the remaining solution turned dark orange.
With Triethylsilane. A 5-mm NMR tube with its attached J. Young
valve was charged with 100 mg (0.42 mmol) of 1 and 600 mg of C6D6.
A gentle stream of CO was gently bubbled through the solution for 5
min; then 68 mg (0.58 mmol) of HSiEt3 was injected with a microliter
syringe, and the NMR tube valve was closed. 1H NMR spectral
monitoring of the pale yellow solution indicated that 30% of 1 had
been consumed within 5 h. This was accounted for by a 9:1:0.5 mixture
of (CO)5MnC(OSiEt3)dCH2 (3j), (CO)5MnCH(OSiEt3)CH3 (2j), and
CH3CH2OSiEt3 (7j).
a medium intensity acyl ν(CO) band at 1635 cm-1
.
The solution was evaporated, and the resulting light yellow oil was
chromatographed on flash-grade silica gel with hexane in a 2.5 × 5
cm quartz column. (The silica gel contained 1% zinc silicate phosphor.)
Eluting with hexane removed any Mn2(CO)10 (typically <2%) as a faint
yellow band; subsequent elution with 70:30 methylene chloride-hexane
(40 mL) removed the product as a pale yellow, almost colorless, band
(a UV lamp was used for detection). This fraction afforded 247 mg of
(CO)5MnC(O)CH(OSiMe2Ph)CH3 (4a) as a light yellow oil (89% yield).
Anal. Calcd for C16H15O7SiMn: C, 47.77; H, 3.76. Found: C, 47.93;
H, 3.65. Spectral data are recorded in Table 2.
The same procedure was followed for carbonylating other R-siloxy-
ethyl complexes 2, and in all cases the acyl derivatives (CO)5MnC-
(O)CH(OSiR3)CH3 (4) were isolated as stable, pale yellow oils after
column chromatography. (CO)5MnC(O)CH(OSiMePh2)CH3 (4b): iso-
lated yield 82%. Anal. Calcd for C21H17O7SiMn: C, 54.32; H, 3.69.
Found: C, 54.65; H, 3.60. (CO)5MnC(O)CH(OSiMe2OEt)CH3 (4c):
isolated yield 87%. Anal. Calcd for C12H15O8SiMn: C, 38.93; H, 4.08.
Found: C, 38.95; H, 4.04. (CO)5MnC(O)CH(OSiMe2OSiMe3)CH3
(4d): isolated yield 91%. Anal. Calcd for C13H19O8Si2Mn: C, 37.68;
H, 4.62. Found: C, 37.70; H, 4.61.
(CO)5MnCH(OSiMe2Et)CH3 (2e). Dimethylethylsilane (111 mg,
1.26 mmol) was added to a solution of (CO)5MnC(O)CH3 (1) (300
mg, 1.26 mmol) in 600 mg of C6D6. After 1 h, the resulting dark orange
solution was transferred to a Fisher-Porter bottle that had been charged
with a magnetic stirring bar and acetonitrile (10 mL), and the reaction
was stirred vigorously under 82 psig of CO for 1 h. This left a yellow
solution, which was evaporated at room temperature to give an orange
oil. It was chromatographed on indicator-grade silica gel, from which
the following fractions were isolated: fraction 1, with 25 mL of hexane
gave Mn2(CO)10 (22 mg); fraction 2 with 25 mL of 1:1 CH2Cl2-hexane
eluted as a yellow-orange band that left a yellow-orange oil (286 mg);
fraction 3 with 15 mL of 1:1 CH2Cl2 came down as a pale yellow
band that contained 1 (33 mg, 11% recovery). Fraction 2, which
contained substantial Mn2(CO)9(CH3CN)11c in addition to the (CO)5MnC-
(O)CH(OSiMe2Et)CH3 (4e), was rechromatographed using 8:1 CH2-
Cl2-hexane. This cleanly removed a pale yellow band, which afforded
4e as a spectroscopically pure oil, 122 mg (29% yield).
NMR spectral data for 7j were available from a previous study:9a,19
1H NMR δ 3.55 (q, J ) 6.9, OCH2CH3), 1.11 (t, J ) 7.0, OCH2CH3),
0.96 (m, SiCH2CH3), 0.56 (m, SiCH2CH3); 13C{1H} NMR δ 58.4
29
(OCH2CH3), 18.5 (OCH2CH3), 6.9 (SiCH2CH3), 4.9 (SiCH2CH3);
-
Si{1H} δ 17.32.
The reaction of 1 with HSiEt3 in the presence of 1 atm of CO was
repeated twice using 10 mg (0.042 mmol) of 1, 50 mg (0.42 mmol) of
HSiEt3, and either 600 mg of C6D6 or 493 mg of THF-d8. 1H NMR
analyses of the very pale yellow solutions after 5 h showed that <5%
of 1 had been consumed and only a trace (<5%) of 3j was evident. A
control reaction in C6D6 was carried out under the same conditions
except that 1 atm of nitrogen was substituted for the CO. Within 80
min, 1 was converted to the same 2:1 ratio of products 3j and 2j that
had been documented in the reaction profile studies, irrespective of
the obvious pressure buildup.
Inhibition of the (CO)5MnC(O)CH3 (1) Reaction with Dimeth-
ylphenylsilane. Acetone Competition. A C6D6 solution (600 mg)
of 1 (50 mg, 0.21 mmol) was treated with HSiMe2Ph (57 mg, 0.42
mmol) and acetone (24 mg, 0.42 mmol). Within 40 min, all of the
silane was converted to a mixture of (CH3)2CH(OSiMe2Ph)19 and
1
(CO)5MnCH(OSiMe2Ph)CH3 (2a), as judged from their H and 13C
NMR spectra. No other products were evident; 89% of the acetone
was transformed to (CH3)2CH(OSiMe2Ph) and 24% of the 1 to 2a, with
the residual acetone and 1 also being quantitated by 1H NMR
spectroscopy.
Phosphine Inhibition. A clear solution containing C6D6 (600 mg),
1 (48 mg, 0.20 mmol), HSiMe2Ph (27 mg, 0.20 mmol), and PPh3 (53
mg, 0.20 mmol) was prepared and transferred to a NMR tube. This
solution remained pale yellow, and 1H NMR spectral monitoring
confirmed that 82% of the HSiMe2Ph remained intact, with the
remainder as (PhMe2Si)2O. No hydrosilation of 1 was detected (3 h).
The starting 1 was accounted for as a mixture of trans- and cis-
Results
18
1. Reactions of (CO)5MnC(O)CH3 (1) with Monohydrosi-
(PPh3)(CO)4MnC(O)CH3 (7% and 13%, respectively), 1 (69%), and
(CO)5MnCH3 (10%).
lanes that Afford Stable r-Siloxyethyl Complexes

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10073
Table 1. Reaction Products from (CO)5MnCOCH3 (1) and HSiR3
entry
amt of (CO)5MnCOCH3 (mmol)a
silane reactant (equiv)
NMR yield (% 2)a
NMR yield (% 3)b
isolated yieldc (% 2)
1
2
3
4
5
6
7
8
9
10
11
12
13
14.
15
1.26
0.42
0.21
1.26
1.26
1.26
0.84
0.84
0.84
0.84
0.42
0.47
0.44
0.17
0.17
HSiMe2Ph (1.0)
HSiMe2Ph (1.0)
HSiMe2Ph (1.8)
HSiMePh2 (1.0)
HSiMe2(OEt) (1.1)
HSiMe2OSiMe3 (1.0)
HSiMe2Et (1.1)
HSiMeEt2 (1.1)
HSiMe(OSiMe3)2 (1.2)
HSiMe(OMe)2 (1.2)
HSiMe2Cl (2.0)
HSiEt3 (1.9)
80, 2a
76, 2a
76, 2a
81, 2b
63, 2c
69, 2d
63, 2e
47, 2f
63, 2g
50, 2h
64, 2i
28, 2j
23, 2j
6, 2j
6, 3a
4, 3a
6, 3a
<2
55
54
59
70
60
46
57
d
d
d
d
5, 3c
6, 3d
12, 3e
22, 3f
<2
<2
<2
59, 3je
46, 3j
38, 3j
42, 3j
HSiEt3f (1.1)
f
HSiEt3 (1.2)
HSiEt3f (6.0)
17, 2j
d
1
a Reactions in 600 mg of C6D6 containing anisole or ferrocene internal standard; NMR yields determined by integration of H NMR spectra.
1
Starting 1 was consumed within 0.5-0.75 h under the conditions noted. b R-Siloxyvinyl complexes 3 characterized by H and 13C NMR spectra.
1
c Orange oils after column chromatography on silica gel. R-Siloxyethyl complexes 2 were characterized by their H and 13C NMR spectra and by
their R-siloxypropionyl derivatives (CO)5MnC(O)CH(OSiR3)CH3. Acceptable microanalyses were obtained for (CO)5MnCH(OSiMe2Ph)CH3 (2a)
and (CO)5MnCH(OSiMe2OSiMe3)CH3 (2d). d Product was unstable and decomposed upon attempted purification. e Isolated yield, 55%. f Reaction
required 70 min to 2 h to consume 1.
(CO)5MnCH(OSiR3)CH3 (2). The manganese acetyl complex
1 at room temperature underwent rapid reactions with the
monohydrosilanes in Table 1. Upon treatment with 1.0-1.2
equiv of these silanes, pale yellow C6D6 solutions of 1 turned
dark orange-brown within 25-45 min. 1H NMR spectral
monitoring of these solutions indicated that for most of the
monohydrosilanes studied 1 transformed to the R-siloxyethyl
complexes (CO)5MnCH(OSiR3)CH3 (2a-2i) as the major
products (eq 2).
68-70 and 35 for the methine and methyl carbons, respectively,
also agree with those reported for (CO)5MnCH(OSiPh2H)CH3
(which was generated only in solution)1a,c,8 and CpFe(CO)2-R-
siloxyethyl complexes (fully characterized).1b,c,7,8 IR spectra
of the complexes 2 in benzene show four terminal carbonyl ν-
(CO) bands between 2120 and 1980 cm-1 that characterize the
Mn(CO)5R system with C4V local symmetry.21 These and other
spectral assignments appear in Table 2. In addition, five
examples of 2 were carbonylated and fully characterized as their
more stable acyl derivatives, vide infra.
Triethylsilane differs from the other monohydrosilanes studied
in that its reaction with 1 yielded the manganese R-(triethylsi-
loxy)ethyl 2j only as a minor product. Instead, the major
product proved to be (CO)5MnC(OSiEt3)dCH2 (3j), eq 2. In
reactions involving 50-200 mg of 1 with 1.2-2.0 equiv of
HSiEt3 in C6D6 solutions, 1 was consumed within 0.75-1.5 h,
and 79-87% of it was accounted for as 1.9-2.1:1.0 mixtures
of 3j and 2j. Results of 1H, 13C, and 29Si NMR spectral studies
also were in accord with an optimal reaction stoichiometry of
1.5-1.8 equiv of HSiEt3 for generating the R-(triethylsiloxy)-
vinyl complex 3j.
Isolated yields of 3j ranged from 55% to 64% after column
chromatography, with the higher yields corresponding to
preparations involving up to 4 g of 1. The Experimental Section
has further details on separating 3j from the major contaminant
Mn2(CO)10. The resulting stable 3j, a yellow oil, was fully
The R-siloxyethyl complexes 2a-2i were isolated by rapid
chromatography on short columns of deactivated silica gel in
order to preclude their decomposition during prolonged chro-
matography. Some of each product nevertheless was sacrificed
when its chromatography forerun, which also contained disi-
loxane contaminant, was discarded in order to render 2
spectroscopically pure. This was particularly noticeable for
(CO)5MnCH(OSiMe2Ph)CH3 (2a), and in part accounts for its
25% drop in isolated yield from that quantified by NMR
spectroscopy (Table 1).
1
characterized. Its H NMR spectrum shows two diagnostic
vinylic doublets at δ 5.08 and 4.29 with a small geminal
coupling (2J ) 1.4 Hz). IR spectra in benzene exhibit a three-
band pattern for terminal carbonyl ν(CO) bands.21
The minor product was identified as the R-(triethylsiloxy)-
1
ethyl complex 2j by its H and 13C NMR spectral data (Table
2). It proved to be more difficult to work with as it readily
decomposed to Mn2(CO)10 and unidentified organic materials,
We isolated seven R-siloxyethyl complexes 2 in 46-70%
yields as thermally sensitive orange oils. Of these, 2a and
(CO)5MnC(O)CH(OSiMe2OSiMe3)CH3 (2d) (the most stable
examples) were obtained analytically pure. Once isolated, 2a-
2d were stable in benzene solution for at least 6 h, which also
holds if they are generated carefully using 1 equiv of mono-
hydrosilane.
Structural assignment of the R-siloxyethyl complexes 2
follows from their NMR and IR spectra. Their 1H NMR spectra,
for example, exhibit diagnostic methine quartets at δ 5.0-5.2
(J ) 6.5 Hz) and methyl doublets at δ 1.7-1.8 for the
MnCHCH3 spin systems. Their 13C NMR spectral signals at δ
(21) These fundamental carbonyl ν(CO) stretching frequencies are
assigned (in decreasing frequency) as having A1, B1, and E + A1 symmetry.
Many (CO)5MnR complexes reported herein have four terminal carbonyl
ν(CO) bands due to the appearance of separate E (very intense, broad) and
A1 (medium intensity, 20-40 cm-1 lower in energy) fundamentals. This
band splitting is associated with the presence of “less symmetrical” alkyl
or acyl ligands R on (CO)5MnR. Other complexes exhibit a three-band
pattern for terminal carbonyl ν(CO) bands with relative intensities weak-
medium-very strong/broad. (a) Cotton, F. A.; Musco, A.; Yagupsky, G.
Inorg. Chem. 1967, 6, 1357. (b) Kaesz, H. D.; Bau, R.; Hendrickson, D.;
Smith, J. M. J. Am. Chem. Soc. 1967, 89, 2844. (c) Braterman, P. S. Metal
Carbonyl Spectra; Academic Press: New York, 1975; pp 72, 223.

10074 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
Table 2. Spectroscopic Characterization of Manganese Acetyl Hydrosilation Products
complex
IR (C6H6) ν(CO) (cm-1
)
1H NMR (C6D6) δ (ppm)
13C{1H} NMR (C6D6) δ (ppm)
(CO)5MnCH(CH3)OSiMe2Ph (2a)
2107 (w)
2044 (m)
2005 (vs)
1982 (m,sh)
7.56 (m, 2H, Ph)
7.21 (m, 2H, Ph)
5.07 (q, J ) 6.5 Hz, CH)
1.74 (d, J ) 6.5 Hz, CH3)
0.33 (s, SiMe)
133.8 (ipso-C, Ph)
69.6 (MnCH)
35.0 (MnCHCH3)
-1.1 (SiCH3)
-1.6 (SiCH3)
210.3 (CtO)
135.6 (ipso-C, Ph)
70.1 (MnCH)
(CO)5MnCH(CH3)OSiPh2Me (2b)
(CO)5MnCH(CH3)OSiMe2OEt (2c)
2107 (w)
7.71 (m, 4H, Ph)
7.53 (m, 6H, Ph)
2044 (m)
2006 (vs)
1983 (m, sh)
5.20 (q, J ) 6.5 Hz, MnCH)
1.77 (d, J ) 6.5 Hz, MnCHCH3)
0.61 (s, SiCH3)
5.17 (q, J ) 6.4 Hz, MnCH)
3.48 (q, J ) 6.9 Hz, SiOCH2)
1.85 (d, J ) 6.4 Hz, MnCHCH3)
1.11 (t, J ) 6.9 Hz, SiOCH2CH3)
0.10 (s, SiCH3)
35.3 (MnCHCH3)
-2.3 (SiCH3)
213.1 (CtO)
2107 (w)
2045 (m)
2007 (vs)
1982 (m, sh)
68.7 (MnCH)
58.2 (SiOCH2CH3)
34.9 (MnCHCH3)
18.5 (SiOCH2CH3)
-2.6 (SiCH3)
-2.9 (SiCH3)
213.4 (CtO)
68.4 (MnCH)
34.9 (MnCHCH3)
-0.1 (SiCH3)
-0.6 (SiCH3)
214.2 (CtO)
69.3 (MnCH)
35.1 (MnCHCH3)
8.9 (SiCH2CH3)
6.9 (SiCH2CH3)
-2.0 (SiCH3)
-2.4 (SiCH3)
212.9 (CtO)
0.08 (s, SiCH3)
(CO)5MnCH(CH3)OSiMe2OSiMe3 (2d)
(CO)5MnCH(CH3)OSiMe2Et (2e)
2107 (w)
5.21 (q, J ) 6.3 Hz, CH)
1.87 (d, J ) 6.5 Hz, CH3)
0.14 (br s, SiCH3)
2045 (m)
2007 (vs)
1983 (m, sh)
2106 (w)
4.98 (q, J ) 6.5 Hz, CH)
1.77 (d, J ) 6.6 Hz, CH3)
0.96 (t, J ) 7.9 Hz, SiCH2CH3)
0.57 (m, SiCH2CH3)
2044 (m)
2005 (vs)
1985 (m, sh)
0.07 (s, SiCH3)
(CO)5MnCH(CH3)OSiEt2Me (2f)
2106 (w)
5.09 (q, J ) 6.4, CH)
2044 (m)
2007 (vs)
1982 (m, sh)
1.80 (d, J ) 6.4 Hz, CH3)
0.99 (t, J ) 7.3, SiCH2CH3)
0.49 (m, J ) 7.3, SiCH2CH3)
0.06 (s, SiCH3)
69.6 (MnCH)
35.3 (MnCHCH3)
8.6 (SiCH2CH3)
7.2 (SiCH2CH3)
-2.3 (SiCH3)
212.7 (CtO)
68.2 (MnCH)
35.0 (MnCHCH3)
1.9 (SiOSiCH3)
1.8 (SiOSiCH3)
-1.9 (CHOSiCH3)
-2.9 (CHOSiCH3)
212.6 (CtO)
(CO)5MnCH(CH3)OSi(OSiMe3)2Me (2g)
2107 (w)
5.28 (q, J ) 6.6 Hz, CH)
1.90 (d, J ) 6.6 Hz, CH3)
0.17 (s, CHOSiCH3)
0.15 (s, SiOSiCH3)
2044 (m)
2007 (vs)
1983 (m, sh)
0.14 (s, SiOSiCH3)
(CO)5MnCH(CH3)OSi(OMe)2Me (2h)
2108 (w)
5.26 (q, J ) 6.0 Hz, CH)
3.38 (s, SiOCH3)
1.87 (d, J ) 6.0 Hz, CH3)
0.11 (s, SiCH3)
2045 (m)
2008 (vs)
1982 (m, sh)
68.2 (MnCH)
49.9 (SiOCH3)
34.8 (MnCHCH3)
-7.7 (SiCH3)
-8.5 (SiCH3)
(CO)5MnCH(CH3)OSiMe2Cl (2ia)
(CO)5MnCH(CH3)OSiEt3 (2ja)
5.19 (q, J ) 6.4 Hz, CH)
1.79 (d, J)6.4, CH3)
0.29 (s, SiCH3)
5.11 (q, J ) 6.5 Hz, CH)
1.83 (d, J ) 6.5 Hz, CH3)
1.00 (m, SiCH2CH3)
0.75 (m, SiCH2CH3))
68.2 (MnCH)
210.0 (CtO)
69.1 (MnCH)
34.8 (MnCHCH3)
6.8 (SiCH2CH3)
5.3 (SiCH2CH3)
(CO)5MnC(OSiMe2Ph)dCH2 (3ab)
(CO)5MnCH(OSiMe2OEt)dCH2 (3cb)
(CO)5MnCH(OSiMe2OSiMe3)dCH2 (3db)
5.10 (d, J ) 1.5 Hz, (E)-CHH)
4.33 (d, J ) 1.5 Hz, (Z)-CHH)
0.43 (s, SiMe)
5.38 (d, J ) 1.5 Hz, dCHH)
4.43 (d, J ) 1.5, dCHH)
0.22 (s, SiMe)
5.31 (d, J ) 1.5 Hz, dCHH)
4.42 (d, J ) 1.5 Hz, dCHH)
0.24 (s, OSiMe2O)
0.14 (s, OSiMe3)
(CO)5MnCH(OSiMe2Et)dCH2 (3eb)
5.07 (d, J ) 1.5 Hz, dCHH)
4.30 (d, J ) 1.5 Hz, dCHH)
0.96 (m, SiCH2CH3)
212.9 (CtO)
173.7 (COSi)
109.6 (dCH2)
9.1 (SiCH2CH3)
6.8 (SiCH2CH3)
-1.9 (SiCH3)
0.57 (m, SiCH2CH3)
0.18 (s, SiCH3)

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10075
Table 2 (Continued)
complex
IR (C6H6) ν(CO) (cm-1
)
1H NMR (C6D6) δ (ppm)
13C{1H} NMR (C6D6) δ (ppm)
(CO)5MnCH(OSiEt2Me)dCH2 (3fb)
5.09 (d, J ) 1.4 Hz, dCHH)
4.34 (d, J ) 1.4 Hz, dCHH)
0.96 (m, SiCH2CH3)
212.1 (CtO)
174.2 (COSi)
109.1 (dCH2)
0.54(m, SiCH2CH3)
0.17 (s, SiCH3)
7.1 (SiCH2CH3)
6.9 (SiCH2CH3)
-4.5 (SiCH3)
(CO)5MnCH(OSiEt3)dCH2 (3j)
2086 (w)
2045 (vs)
2017 (s sh)
5.08 (d, J ) 1.4 Hz, (E)-CHH)
4.29 (d, J ) 1.4, (Z)-CHH)
1.02 (m, SiCH2CH3)
210.9 (CtO)
174.1 (COSi)
108.6 (dCH2)
0.71 (q, J ) 7.9, SiCH2CH3)
6.9 (SiCH2CH3)
5.6 (SiCH2CH3)
264.0 (MnCdO)
210.1 (CtO)
(CO)5MnC(O)CH(CH3)OSiMe2Ph (4a)
2114 (m)
2048 (w)
7.61 (m, 2H, Ph)
7.32 (m, 3H, Ph)
2011 (vs)
1635 (m) (CdO)
3.73 (q, J ) 6.6 Hz, CH)
0.90 (d, J ) 6.6, CH3)
0.36 (s, SiCH3)
137.1 (ipso-C, Ph)
84.4 (MnCOCH)
19.2 (COCHCH3)
-1.2 (SiCH3)
0.33 (s, SiCH3)
-2.1 (SiCH3)
(CO)5MnC(O)CH(CH3)OSiPh2Me (4b)
(CO)5MnC(O)CH(CH3)OSiMe2OEt (4c)
2114 (m)
2048 (w)
2013 (vs)
1634 (m)
7.65 (m, 4H, Ph)
7.22 (m, 6H, Ph)
3.95 (q, J ) 6.8 Hz, COCH)
0.94 (d, J ) 6.8 Hz, CHCH3)
0.61 (s, SiCH3)
263.8 (MnCdO)
210.2 (CtO)
135.7 (ipso-C, Ph)
135.3 (ipso-C, Ph)
85.3 (MnCOCH)
19.3 (COCHCH3)
-2.3 (SiCH3)
21134 (w)
2048 (w)
2014 (vs)
1635 (w) (CdO)
3.82 (q, J ) 6.8 Hz, COCH)
3.53 (q, J ) 6.9 Hz, SiOCH2)
1.08 (d, J ) 6.8 Hz, COCHCH3)
1.04 (t, J ) 6.9 Hz, SiOCH2CH3)
0.12 (s, SiCH3)
264.3 (MnCdO)
210.3 (CtO)
83.9 (MnCOCH)
58.3 (SiOCH2CH3)
19.4 (COCHCH3)
18.5 (SiOCH2CH3)
-2.3 (SiCH3)
-3.2 (SiCH3)
264.3 (MnCdO)
210.4 (CtO)
83.8 (MnCOCH)
19.5 (COCHCH3)
1.7 (Si(CH3)3)
0.2 (Si(CH3)2)
-0.9 (Si(CH3)2)
244.3 (MnCdO)
210.4 (CtO)
84.1(MnCOCH)
19.5 COCHCH3
8.6 SiCH2CH3)
6.8 (SiCH2CH3)
-2.3 (SiCH3)
0.06 (s, SiCH3)
(CO)5MnC(O)CH(CH3)OSiMe2OSiMe3 (4d)
(CO)5MnC(O)CH(CH3)OSiMe2Et (4e)
2114 (m)
2048 (w)
2016 (vs)
1634 (m) (CdO)
3.84 (q, J ) 6.6 Hz, COCH)
1.09 (d, J ) 6.6 Hz, CHCH3)
0.12 (s, 3H, Si(CH3)2)
0.09 (s, 3H, Si(CH3)2)
0.06 (s, 9H, Si(CH3)3)
2114 (m)
2047 (w)
2012 (vs)
1636 (m)
3.63 (q, J ) 6.6 Hz, COCH)
0.97 (d, J ) 6.6 Hz, CHCH3)
0.88 (t, J ) 7.8, SiCH2CH3)
0.51 (m, SiCH2CH3)
0.03 (s, SiCH3)
0.01 (s, SiCH3)
a Product unstable and mixed with Mn2(CO)10. b Minor component and not isolated.
especially in the presence of free HSiEt3. Even under optimal
reaction conditions, 2j degraded slowly as it formed or upon
attempts to chromatograph or concentrate the reaction mixtures.
starting acetyl complex 1, which slowly eluted from the column
and did not interfere with purifying the R-siloxyethyl products
2.
Overall, the reactivity of monohydrosilanes toward 1 cor-
relates with four groups of silane substituents. Monohydrosi-
lanes bearing two methyl groups and one phenyl, alkoxy, or
siloxy group (HSiMe2Ph, HSiMe2OEt, or HSiMe2OSiMe3) are
extremely reactive and afforded the more stable R-siloxyethyl
complexes 2a, 2c, and 2d, but only low concentrations of their
R-siloxyvinyl compounds 3. Diphenylmethylsilane also fits into
this category and gave 2b but no 3b. Trialkylsilanes, the second
group of silanes, furnished significant concentrations of
(CO)5MnC(OSiR3)dCH2 (3) in addition to diminished yields
of less stable 2. Interestingly, yields of 3 varied with the number
of ethyl groups present: HSiMe2Et (12% yield of 3e), HSiMeEt2
(22% 3f), HSiEt3 (60% 3j).
Other R-siloxyvinyl compounds analogous to 3j evidently
accumulate as byproducts during the hydrosilation of 1 with
other monohydrosilanes. In five of these hydrosilation reactions
(Table 2), 1H NMR spectral monitoring also revealed vinyl CH
doublets near δ 5.1-5.4 and 4.3-4.4 (J ) 1.5 Hz) that were
assigned to the R-siloxyvinyl compounds (CO)5MnC-
(OSiR3)dCH2 (3).
Three of these R-siloxyvinyl compoundss(CO)5MnC(OSi-
Me2Ph)dCH2 (3a), (CO)5MnC(OSiMe2OEt)dCH2 (3c), and
(CO)5MnC(OSiMe2OSiMe3)dCH2 (3d)sformed in 5-6%
yields and were not further characterized. Two other examp-
less(CO)5MnC(OSiMe2Et)dCH2 (3e) and (CO)5MnC(O-
SiMeEt2)dCH2 (3f)sdeveloped in moderate yields (12-22%);
their 13C NMR spectral assignments (δ 174 and 109 for the
vinyl carbons) resemble those of 3j. We did not attempt to
isolate these siloxyvinyl compounds. Under our chromatogra-
phy conditions, these siloxyvinyl compounds hydrolyzed to the
The remaining two monohydrosilane groups either produced
unstable R-siloxyethyl complexes 2 or did not react. Thus,
silanes that retain one chlorine (HSiMe2Cl) or two alkoxy or
siloxy substituents [HSiMe(OMe)2 or HSiMe(OSiMe3)2], slowly
generated unstable R-siloxyethyl products. Finally, the mono-

10076 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
hydrosilanes HSiPh2Cl, HSi(OMe)3, HSiPh3, and HSi(SiMe3)3
are inert toward 1 under our reaction conditions.
2. Carbonylation of R-Siloxyethyl Complexes (CO)5MnCH-
(OSiR3)CH3 (2). In order to further characterize the unstable
(R-siloxyethyl)manganese complexes 2, we prepared their acyl
derivatives (CO)5MnC(O)CH(OSiR3)CH3 (4). Carbonylation
of 2 proved to be straightforward, in terms of both implementing
the reactions and isolating the stable R-siloxypropionyl products
4. These reactions (eq 3) were complete within 1 h at 82 psig
Figure 1. Reaction profile for the reaction between (CO)5MnC(O)-
CH3 (1) and dimethylphenylsilane. Conditions: (CO)5MnC(O)CH3 (1)
(50 mg, 0.21 mmol), Me2PhSiH (50 mg, 0.37 mmol, 1.75 equiv), and
anisole (22 mg, 0.20 mmol) in 600 mg of C6D6 (25 °C). All
concentrations were determined by quantative H NMR spectroscopy
(vs anisole).
of CO (22 °C) using either acetonitrile (0.02 M) or acetonitrile-
benzene (1:1 to 3:1). Chromatography of the reaction mixtures
then provided pale yellow oils; these exhibited a medium
intensity IR ν(CO) band at 1635 cm-1 and a 13C NMR spectral
resonance near δ 264 that signal the presence of an acyl group.
Further spectroscopic characterization of these analytically pure
R-siloxypropionyl products 4 appears in Table 2.
Optimal yields of (CO)5MnC(O)CH(OSiMe2Ph)CH3 (4a),
(CO)5MnC(O)CH(OSiMePh2)CH3 (4b), (CO)5MnC(O)CH-
(OSiMe2OEt)CH3 (4c), and (CO)5MnC(O)CH(OSiMe2OSiMe3)-
CH3 (4d) (82-91%) required carbonylating the isolated R-si-
loxyethyl complexes 2a-2d in acetonitrile. Attempted
carbonylation of 2a as the isolated material in THF or as the
unpurified reaction mixture after diluting with acetonitrile
dramatically reduced the yields of 4a. Carbonylation of the
hydrosilation reaction mixture containing (CO)5MnCH(OSiMe2-
Et)CH3 (2e) (63%) after adding acetonitrile thus yielded only
29% (CO)5MnC(O)CH(OSiMe2Et)CH3 (4e).
Our conditions for carbonylating purified (R-siloxyethyl)-
manganese complexes 2 were milder than those reported by
Gladysz and coworkers for synthesizing (CO)5MnC(O)CH-
(OSiMe3)CH3 (4k).11a,c They prepared 4k by treating an
acetonitrile solution of (CO)5MnSiMe3 (5k) with acetaldehyde
and 250 psi of CO for 12 h. The extended reaction time in
part also reflects the sluggish initial reaction between 5k and
acetaldehyde.11b,c Carbonylation of purified (CO)5MnCH2-
(OSiMe3) in acetonitrile nevertheless was reported to also require
200 psig CO (6 h).11f Spectral data for Gladysz’s 4k agrees
with that presently reported for the R-siloxypropionyl com-
pounds 4a-4e in Table 2.
3. Reaction Profiles for (CO)5MnC(O)CH3 (1) with
Monohydrosilanes. Reactivity of (CO)5MnCH(OSiR3)CH3
(2) toward Excess Silane. Optimal conditions for the hydrosi-
lation of 1 required 1.0-1.2 equiv of monohydrosilane, since
the resulting (CO)5MnCH(OSiR3)CH3 (2) degraded in the
presence of excess hydrosilane. In order to study this silane-
induced degradation of 2 by multinuclear NMR spectroscopy,
we monitored reactions involving (a) 1 with excess HSiMe2Ph
or HSiEt3, (b) preformed (CO)5MnCH(OSiMe2Ph)CH3 (2a) with
HSiEt3, and (c) (CO)5MnCH(OSiEt3)CH3 (2j) with HSiMe2Ph.
The reaction between 2a and HSiMe2Ph was conducted by
treating 1 with 1.76 equiv of HSiMe2Ph (run 3, Table 1), and
their concentrations were quantified by 1H NMR spectroscopy.
A reaction profile recording the time dependence of [1],
[HSiMe2Ph], and [2a] appears in Figure 1. The 5-10 min
induction period preceeds the buildup to the [2a]max (a 76%
yield) within 40 min, although [2a] and [HSiMe2Ph] subse-
quently decreased with time. After 120 min, [2a] and [HSiMe2-
Ph] had dropped to 50% of the maximum and 6% of the initial
values, respectively. Interestingly, (CO)5MnCH(OSiMe2-
1
Ph)dCH2 (3a) maintained a constant concentration (4-6%
yield) after 30 min.
Increasing the [HSiMe2Ph]i to 2.5 equiv afforded the maxi-
mum yield of 2a (76%) after 25-30 min, in addition to 3a (3%)
and low concentrations of PhMe2Si-containing degradation
materials, primarily (PhMe2Si)2O, Scheme 1. The yield of 2a
then dropped to 50% within 1.5 h as the silane decreased to
40% of its initial concentration. Again, the disiloxane accounted
for ca. 80% of the silane residue, although NMR spectral data
(experimental) also indicated low concentrations of several
unidentified silicon-containing products. This silane degradation
consumed all of the HSiMe2Ph and left Mn2(CO)10 as the final
organomanganese product. In related studies, Akita, Moro-oka,
and co-workers8 established that treatment of 1 with excess H2-
SiPh2 produced mixtures of alkenes as the primary organic
products.
Silane-induced degradation of 2a also is noteworthy for
several potential products that were absent (Scheme 1). For
HSiMe2Ph, manganese complexes not evident included
(CO)5MnCH2CH317 and (CO)5MnSiMe2Ph (5a). Other potential
organic byproducts that also were not detected by 1H, 13C, and
29Si NMR spectroscopy included CH2dCHOSiMe2Ph (6a), CH3-
CH2OSiMe2Ph (7a),9a,19 Me2PhSiSiMe2Ph, and CH3CH(OSiMe2-
Ph)CH(OSiMe2Ph)CH3 (8a). We previously had prepared the
manganese silyl 5a,1a and we now report generating 8a, a
mixture of diastereomers, by (CO)5MnBr-catalyzed silation of
its butane-2,3-diol.9a It was characterized by 1H, 13C, and 29Si
NMR spectroscopy.
Similar profiles for the reaction of 1 and HSiEt3 probed the
interdependency of (CO)5MnCH(OSiEt3)CH3 (2j) and the more
abundant (CO)5MnC(OSiEt3)dCH2 (3j) (eq 2). A reaction
profile for 1 and 1.9 equiv of HSiEt3 appears in Figure 2,
whereas Figure 3 illustrates a 1H NMR spectrum of this reaction
(after 60 min) from which [2j], [3j], [HSiEt3], and [1] were
measured. In this reaction, 1 transformed within 70 min to a
mixture with [3j]/[2j] ) 2.0 and a 59% NMR spectral yield of
3j. After 2 h, the reaction was worked up as described in the
Experimental Section to give 3j (55%) and Mn2(CO)10 (42%),
thus accounting for 97% of the manganese.

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10077
Scheme 1. HSiR3-Induced Degradation of (CO)5MnCH(OSiR3)CH3 (2).
C6D6). The presence of Mn2(CO)10 was established by IR
spectroscopy, and for some experimental runs was quantified
(21-33%) after chromatography of the reaction mixture.
Reliable materials balances for this degradation were precluded
1
by the overlap of H NMR spectral absorptions for (Et3Si)2O
and for smaller amounts of unidentified organosilanes.
Silane-induced degradation of 2j was minimized by restricting
the initial amount of HSiEt3 to 1 equiv of the starting
concentration of 1, although at the expense of lower product
yields and longer reaction times. Figure 2 has a reaction profile
for 1.12 equiv of HSiEt3 vs 1 (Table 1, entry 3): both [3j] and
[2j] maximized (46% and 23% yields, respectively) just as 1
was consumed after 135 min. The curve tracking the drop in
[HSiEt3] superimposes that for [1], and both [2j] and [3j]
remained constant for at least an additional hour.
The HSiEt3 reactions proved to be the slowest in terms of
consuming 1, 60-70 min vs 45 min with HSiMeEt2 and 30
min with HSiMe2Et or HSiMe2Ph under comparable conditions,
in addition to producing the highest yields of an R-siloxyvinyl
complex 3j as a 2:1 mixture with 2j. We looked at the effect
of increasing HSiEt3 concentrations on the distribution of the
products 2j and 3j, entries 14 and 15 in Table 1. In these
parallel experiments, treatment of relatively dilute C6D6 solutions
of 1 with either 1.2 or 6.0 equiv of HSiEt3 afforded nearly the
same amounts of 3j. Yields of 2j, however, increased from
6% to 17% upon increasing the HSiEt3 from 1.2 to 6.0 equiv,
in spite of its sensitivity toward excess HSiEt3.
NMR spectral monitoring of the HSiEt3 reaction with 1 also
ruled out several potential byproducts (Scheme 1). As with the
reaction of HSiMe2Ph and 1, relevant organic compounds that
were not detected include CH2dCHOSiEt3 (6j), CH3CH-
(OSiEt3)CH(OSiEt3)CH3 (8j), and acetaldehyde. Although CH3-
CH2OSiEt3 (7j) was seen in small concentrations (<5%) during
a few hydrosilation runs, the potential manganese carbonyl
byproducts (CO)5MnH, (CO)5MnCH2CH3, and (CO)5MnC-
HdCH2 were not observed.
Figure 2. Reaction profile for the reaction between (CO)5MnC(O)-
CH3 (1) and triethylsilane. Conditions: (CO)5MnC(O)CH3 (1) (112 mg,
0.468 mmol), HSiEt3 (100 mg, 1.84 equiv), and anisole (33 mg, 0.306
mmol) in 600 mg of C6D6 (25 °C). Total Mn refers to the sum of the
concentrations of 1, (CO)5MnCH(OSiEt3)CH3 (2j), and (CO)5MnC-
(OSiEt3)dCH2 (3j). All concentrations were determined by quantitative
1H NMR spectroscopy (vs anisole) at 10 min intervals.
This reaction profile illustrates that (CO)5MnC(OSiEt3)dCH2
(3j) forms independently of (CO)5MnCH(OSiEt3)CH3 (2j). Both
attained maximum concentrations at 70 min (when 1 was
depleted); thereafter [2j] decreased by 19% as [3j] dropped 5%.
Within a total of 270 min, 2j was depleted although [3j] only
decreased a total of 16%. We also plotted a “total manganese”
concentration equal to [1] + [2j] + [3j], which diminished 13%
(after 70 min) with respect to the [1]i, 24% (110 min, [3j]/[2j]
) 2.4), and 43% (270 min, not illustrated). From inspection
of Figure 2, it is apparent that the decreasing [2j] dominates
the linear drop in our total Mn concentration concomitant with
the buildup of Mn2(CO)10. Other experimental runs afforded
similar results, although typically [3j] decreased only ca. 5%.
Degradation of 2j requires a second equivalent of triethyl-
silane (Scheme 2). The first transformed 1 to 2j or 3j: after
70 min of reaction, the ratio of [HSiEt3] consumed to starting
[1] was 1.03. The second equivalent of HSiEt3 consumed
(primarily) 2j: even after 110 min of reaction, the ratio of the
total [HSiEt3] used to [1]i plus [2j] consumed was 1.09. (The
[2j] consumed was ascribed to the difference of the [1]i and
the observed total Mn concentration.) Involvement of HSiEt3
in degrading 2j also is apparent from the parallel relationship
(Figure 2) for attenuation of the [HSiEt3] and total Mn
concentration (or [2j]) after 80 min.
Ruling out (CO)5MnSiEt3 (5j) as a potential byproduct was
more difficult. 29Si and 13C NMR spectra that were recorded
during the reactions of 1 with HSiEt3 were inconsistent with
the presence of 5j. On the other hand, we could not indepen-
dently synthesize 5j22 using procedures that we had used for
15
(CO)5MnSiMe3 and (CO)5MnSiMe2Ph (5a).1a Treatment of
Et3SiCl with Mn(CO)5-K+ or Na+ provided a pale orange oil
that could have contained 5j, based on its IR spectrum, ν(CO)
(hexane) 2050 (w), 2015 (m) 1980 (vs, br) cm-1
. Upon
Excess HSiEt3 decomposed 2j to (Et3Si)2O and Mn2(CO)10
(and presumably alkene mixtures).8 29Si NMR spectral moni-
toring during these reactions of HSiEt3 with 1 established that
concentrations of (Et3Si)2O (δ 9.36) increased at the expense
of 2j (δ 16.17) with excess HSiEt3 (δ 0.42), whereas the
concentration of 3j (δ 17.23) remained constant (in agreement
with 1H NMR spectral monitoring). Reaction times for
completely degrading 2j varied from 2 h (100 mg of 1 and 2.0
equiv of HSiEt3/600 mg of C6D6) to 4.5 h (200 mg/600 mg of
attempted purification, this material decomposed to a complex
mixture that was dominated by Mn2(CO)10 and (Et3Si)2O. We
have no reason to believe, however, that 5j formed during
hydrosilation of 1 by HSiEt3, particularly since the analogous
(22) Reviews on metal silyl complexes: (a) Tilley, T. D. In The
Chemistry of Organic Silicon Compounds; Patai, S., Rappoport, Z., Eds.;
Wiley-Interscience: New York, 1989; Part 2, Chapter 24. (b) Tilley, T. D.
In The Silicon-Heteroatom Bond; Patai, S., Rappoport, Z., Eds.; Wiley:
New York, 1992; Chapter 10.

10078 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
1
Figure 3. 1H NMR spectrum of the reaction between (CO)5MnC(O)CH3 (1) and HSiEt3. Conditions: See Figure 2. H NMR spectrum after 60
min; S ) (CO)5MnCH(OSiEt3)CH3 (2j) and V ) (CO)5MnC(OSiEt3)dCH2 (3j).
Scheme 2. HSiEt3-Induced Degradation of
(CO)5MnCh(OSiEt3)CH3 (2j)
the conversion of 1 plus hydrosilane to either R-siloxyethyl 2
or R-siloxyvinyl 3 complexes with carbon monoxide, PPh3, air,
acetone, acetonitrile, tris(trimethylsilyl)silane (a hydrogen atom
donor),24 and tetrahydrofuran (THF). Of these potential inhibi-
tors, the influence of carbon monoxide proved to be the most
intriguing. Maintaining 1 atm of CO over a properly agitated
solution of 1 and HSiMe2Ph limited the hydrosilation product
2a to a maximum 8-10% yield at 2.5 h. Nevertheless, 1 lost
39% (2.5 h) and then 68% (10 h) of its concentration
commensurate with consuming 98% of the HSiMe2Ph. Disi-
loxane (PhMe2Si)2O remained the major product, along with
lesser quantities of (CO)5MnSiMe2Ph (5a) (<5%) and Mn2-
(CO)10, but no 3a.
The presence of carbon monoxide likewise inhibited the
formation of both products from 1 and HSiEt3 in C6D6. After
1.5 h and under conditions that parallel reactions in the absence
of CO had gone to completion, less that 5% of 1 was consumed.
Although the amount of 1 decreased 30% after 5 h, 85% of its
products corresponded to 3j, with only small amounts of 2j
(10%) and CH3CH2OSiEt3 (7j) (5%).
Somewhat different results were communicated by Akita,
Moro-oka, and co-workers8 for treating 1 with excess H2SiPh2.
In these reactions, the presence of CO (1 atm) favored higher
alkenes. Although these products presumably derived from the
initially formed (CO)xMnCH(OSiHPh2)CH3 (x ) 4, 5), the fates
of the manganese and silicon moieties were not reported.
Inhibition results for the HSiMe2Ph reaction with 1 proved
to be more straightforward with other reagents. Neither the
presence of air nor tris(trimethylsilyl)silane (0.19 equiv) had
any noticeable effect on either the rate or outcome of this
reaction. Similar results were obtained after treating 1 with
HSiMe2Ph in the dark. In contrast, addition of PPh3 (1.0 equiv)
or CD3CN (2.1 equiv) blocked the HSiMe2Ph reaction with 1.
With PPh3, the starting 1 after 3 h was accounted for as trans-
reactions with HSiMe2Ph cleanly provided 2a without traces
of 5a or CH3CH2OSiMe2Ph (7a).1a
We also briefly studied the HSiEt3-induced degradation of
2a. During this reaction, HSiEt3 (1.2 equiv) slowly degraded
2a in C6D6 solutions to the expected disiloxanes without yielding
either 2j or 3j. This result precludes 2a regenerating 1 and
HSiMe2Ph. Since in independent studies we observed that
mixtures of HSiMe2Ph and HSiEt3 or HSiEtMe2 containing a
limited amount of 1 afforded 2a and 2j or 2e with equal
facility,23 the reaction between 1 and HSiMe2Ph and presumably
other monohydrosilanes must be irreversible. Similar results
have been observed for the inverse reaction: treating 2j,
admixed with 3j, with HSiMe2Ph did not produce 2a.
4. Inhibition of the HSiMe2Ph and HSiEt3 Reactions with
(CO)5MnC(O)CH3 (1). We attempted to (selectively) inhibit
(23) (a) Gregg, B. T.; Cutler, A. R. Unpublished results. (b) Attempts to
discern between intramolecular and intermolecular pathways via crossover
experiments, thus far, have given ambiguous results. Interpretation of results
from reactions involving 1 and DSiMe2Ph/HSiMe2Et mixtures is compli-
cated by independent 1-catalyzed SiH/SiD exchange.3a
(24) Chatgilialoglu, C. Acc. Chem. Res. 1992, 25, 188.

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10079
and cis-(PPh3)(CO)4MnC(O)CH318 (7% and 13%, respectively),
1 (69%), and (CO)5MnCH3 (10%). These products represent
the previously documented2 (and independently confirmed)
reaction of 1 with PPh3 and its room temperature decarbony-
lation, respectively, in the absence of HSiMe2Ph.
Acetone also blocked the hydrosilation of 1 by competing
for the HSiMe2Ph. A 2:2:1 mixture of HSiMe2Ph/acetone/1
accordingly yielded only 8% of the manganese acetyl-derived
2a (along with 92% unreacted 1), but 89% (CH3)2CHOSiMe2-
Ph.19 This acetone hydrosilation (eq 4) was consistent with our
Figure 4. Reaction profiles: dimethyphenylsilane autocatalyzed hy-
drosilation of (CO)5MnC(O)CH3 (1). Conditions: (a) (CO)5MnC(O)-
CH3 (1) (100 mg, 0.42 mmol), Me2PhSiH (65 mg, 0.48 mmol, 1.1
equiv), and anisole (60 mg, 0.55 mmol) in 600 mg of C6D6 (25 °C).
previously established use of 1 as a precatalyst for the
hydrosilation of ketones and aldehydes9b and of Cp(CO)2FeC-
(O)CH3.1b,d Similar results for the hydrosilation of Cp(CO)2-
FeC(O)CH3 were recorded when 2a or (CO)5MnCH3 was used
as a precatalyst.1d
1
All concentrations were determined by quantative H NMR spectros-
copy (vs anisole). (b) (CO)5MnSiMe2Ph (5a) (2 mg, 0.0063 mmol,
1.5%) added. (c) Catalyst premix: (CO)5MnC(O)CH3 (1) (3 mg, 0.008
mmol, 1.9%) and Me2PhSiH (65 mg, 0.48 mmol) in 600 mg of C6D6
reacted 45 min prior to addition of 1 (100 mg, 0.42 mmol). (d) (CO)5-
MnCH(OSiMe2Ph)CH3 (2a) (3 mg, 0.008 mmol, 1.9%) added. (e)
Catalyst premix: (CO)5MnC(O)-p-C6H4CH3 (1 mg, 0.003 mmol, 0.9%)
and HSiMe2Ph (65 mg, 0.48 mmol) in 600 mg of C6D6 reacted 45 min
prior to addition of 1 (100 mg, 0.42 mmol).
Changing the solvent to THF-d8 (at concentrations compa-
rable to those of the C6D6 experiments) more than doubled the
1
reaction time of 1 with HSiEt3. During H NMR monitoring
of these THF-d8 runs, moreover, we detected only (CO)5MnC-
(OSiEt3)dCH2 (3j) (69%). Although (CO)5MnCH(OSiEt3)CH3
(2j) was not detected, its intermediacy and subsequent degrada-
tion cannot be ruled out. Thus, 31% of the starting 1 (0.12
mmol) that was unaccounted for matches the 0.23 mmol of
unaccounted HSiEt3, assuming that 1 uses 2 equiv of HSiEt3 in
the formation and subsequent degradation of 2j.
An important issue that we must deal with is the discrepancy
between our data and Wegman’s observations12a on the HSiEt3
reaction with 1. He described the results of a kinetics study
for 1 (0.05 M in THF) and a 10-fold excess of HSiEt3 at 25 °C
and under 1 atm of carbon monoxide. Under these conditions,
acetaldehyde (identified by gas chromatography) and (CO)5-
MnSiEt3 (5j) (by IR spectroscopy) were reported as the primary
products.
and 1 atm of COsconditions comparable to those reported by
Wegmanswe observed <5% consumption of 1 over 5 h. The
net effect of the carbon monoxide and to a lesser degree using
THF in place of benzene was to dramatically reduce the reaction
rate, while selectively producing 3j (albeit in very low yields).
5. Mechanistic Observations Concerning the Active
Catalyst. If 1 plus hydrosilane affords low concentrations of
an active catalyst for the hydrosilation of a variety of organic
and organometallic acyl groups, then perhaps this same active
catalyst promotes the hydrosilation of 1. Under these conditions,
the hydrosilation of 1 would be autocatalytic; either the initial
hydrosilation product 2a (e.g., with HSiMe2Ph) or its silane-
induced degradation product(s) would serve as the active
catalyst(s) (eq 5).
We never detected acetaldehyde during our studies on the
reaction between HSiEt3 and 1 in C6D6. A 2% yield of
1
acetaldehyde easily would have been detected by H NMR
spectroscopy, as it was during a reaction between 1 and
HMo(CO)3Cp.25 Acetaldehyde, moreover, represents an un-
likely product, since we independently demonstrated that 1
efficiently catalyzes aldehyde and ketone hydrosilation.9b In-
deed, the reaction between HSiEt3 and 1 did produce small
amounts of CH3CH2OSiEt3 (7j) (<5%, typically in the presence
of CO).
Most of our studies were carried out under conditions different
from those used by Wegman.12a Our concentrations of 1 were
much higher, 0.67 M in C6D6 and 0.84 in THF-d8, and we used
only 1.1-2.0 equiv of HSiEt3. When our HSiEt3 reactions were
separately carried out under more dilute conditions in 1 (0.067
M in C6D6 and 0.084 M in THF-d8) with 10 equiv of HSiEt3
Autocatalytic hydrosilation of 1 is consistent with the
S-shaped reaction profile and the presence of an induction
period27 that could be eliminated by adding preformed active
catalyst(s). Reaction profiles for 1 and HSiMe2Ph (1:1.1), plots
of [2a] vs time, appear in Figure 4. The shorter 2 min induction
period vs that recorded in Figure 1 is attributed to doubling the
(25) Treatment of equimolar quantities of HMo(CO)3Cp and (CO)5MnC-
(O)CH3 (1a) (0.084 mmol in 600 mg of C6D6) afforded 4% acetaldehyde
after 2 h and 23% after 8 h (1H NMR spectral monitoring). Gregg, B. T.;
Cutler, A. R. Unpublished observations. This bimolecular reductive elimina-
tion26 occurs very slowly for (CO)5MnH and manganese acyl complexes,
(CO)5MnC(O)R.5a,d-f
(27) (a) Moore, J. W.; Pearson, R. G. Kinetics and Mechanism, 3rd ed.;
Wiley: New York, 1981; p 26. (b) Steinfeld, J. I; Francisco, J. S.; Hase,
W. L. Chemical Kinetics and Dynamics; Prentice Hall: Engelwood Cliffs,
NJ, 1989; p 182. (c) Schmid, R.; Sapunov, V. N. Non-Formal Kinetics;
Verlag Chemie: Deerfield Beach, FL, 1982; p 54.
(26) Jones, W. D.; Huggins, J. M.; Bergman, R. G. J. Am. Chem. Soc.
1981, 103, 4415. See also ref 5.

10080 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Scheme 3. (CO)5MnSiMe3-Aldehyde Chemistry11
Gregg and Cutler
initial concentration of 1. Including the coordinatively saturated
(CO)5MnSiMe2Ph (5a) (1.5%) in this hydrosilation had no effect
on its reaction profile; reactions still required 25 min to go to
completion.
(OSiMe2Ph)CH3 (2a) (76%), small amounts of (CO)5MnCH-
(OSiMe2Ph)dCH2 (3a) (6%), disiloxane (PhMe2Si)2O, and
residual silane. Other monohydrosilanes in Table 1 showed
similar reactivity toward 1, although the relative proportion of
the R-siloxyvinyl complexes 3 varied. The use of HSiEt3
maximized the amounts of the R-siloxyvinyl complex: (CO)5-
MnCH(OSiEt3)dCH2 (3j) formed in over 50% yield and in
approximately a 2:1 ratio with (CO)5MnCH(OSiEt3)CH3 (2j).
A limited number of examples of (CO)5MnCH(OSiMe3)R
(9) that have been prepared include (CO)5MnCH2OSiMe3,
(CO)5MnCH(OSiMe3)Ph, and several chelated R-(trimethylsi-
loxy)alkyl compounds with another ligating heteroatom. These
were synthesized by Gladysz and co-workers11 using ligand
reactions (Scheme 3) that are quite independent of those reported
herein. They prepared (CO)5MnCH(OSiMe3)Ph, for example,
by treating benzaldehyde with (CO)5MnSiMe3 (5k).11b Interest-
ingly, (CO)5MnCH(OSiMe3)Ph is unstable as it decomposes by
homolytic cleavage and radical coupling to PhCH(OSiMe3)-
CH(OSiMe3)Ph plus Mn2(CO)10. The stable rhenium analog
(CO)5ReCH(OSiMe3)Ph, however, was prepared and fully
characterized.11d
Of particular relevance to the present study is Gladysz’s
observation that treating enolizable aldehydes and ketones with
(CO)5MnSiMe3 (5k) cleanly produces organic vinyl silyl ethers
rather than manganese R-(trimethylsiloxy)alkyl complexes 9.
Although only a few examples of 9 had been detected,
carbonylation of the reaction mixtures yielded their stable
R-(trimethylsiloxy)acyl derivatives 10 (Scheme 3).11c For
example, the reaction between acetaldehyde and 5k gave
CH2dCHOSiMe3 (6k) or in the presence of CO 4k. The
formation of 6k was ascribed to intermediacy of coordinatively
unsaturated (CO)4MnCH(OSiMe3)CH3 (11k) (Scheme 3), which
undergoes â-elimination.11,28,29 Taken togeather, these observa-
tions suggest that the presence of a coordinatively unsaturated
intermediate (e.g., 11) in the hydrosilation pathway of an acyl
ligand (and in the absence of exogenous CO) should furnish
organic vinyl silyl ethers.
We eliminated the induction period and accelerated the
reaction between 1 and HSiMe2Ph by including the product 2a
or other plausible precursors to the active catalyst in the initial
reaction mixture. Under these conditions, 1 typically was
consumed within 5-8 min (Figure 4). The proposed active
catalyst(s) were generated by treating 1 (1.9%), 2a (1.9%), or
the manganese toluoyl (CO)5MnC(O)-p-C6H4CH3 (0.9%) in
C6D6 with the full amount of silane (1.1 equiv with respect to
substrate 1) for 45 min prior to adding the substrate. This time
for generating the active catalyst, signaled by the solution turning
from pale yellow to dark orange, corresponded to consuming
the starting manganese acetyl, methyl, or p-toluoyl precatalyst.
The latter catalytic system, in particular, was that used in our
previous kinetics study on the H/D isotope exchange between
HSiMe2Et and DSiMe2Ph.3a
We also used (CO)5MnC(O)-p-C6H4CH3 in the same catalyst
premix procedure to accelerate the HSiEt3 transformation of 1
(eq 6). Pretreating this manganese p-toluoyl precatalyst (2%)
The R-siloxyethyl complexes 2 that we isolated from the
hydrosilation of 1 were surprisingly stable at room temperature
as long as excess hydrosilane was avoided. Starting with either
purified or in situ generated 2a (using 1.0 equiv of silane), for
example, we noted the absence of organic products correspond-
with the full amount of HSiEt3 for 45 min prior to adding the
substrate 1 transformed it into a 58:42 mixture of 3j and 2j
within 10 min. The control reaction using 1.9 equiv of HSiEt3
but without the manganese precatalyst required 70 min.
Discussion
(28) Similar intermediates have been proposed for the Co2(CO)8/PPh3-
catalyzed transformation of aldehyde (RCHO), HSiR3, and CO to R-si-
loxyaldehydes RCH(OSiR3)CHO and for the hydrosilation of the cobalt
acyl complex (CO)4CoC(O)CHMe2.12b (a) Chatani, N.; Murai, S.; Sonoda,
N. J. Am. Chem. Soc. 1983, 105, 1370. (b) Chatani, N.; Fugii, S.; Yamasaki,
Y.; Murai, S.; Sonoda, N. J. Am. Chem. Soc. 1986, 108, 7361. (c) Murai,
S.; Seki, Y. J. Mol. Catal. 1987, 41, 197. (d) Murai, T.; Yasui, E.; Kato,
S.; Hatayama, Y.; Suzuki, S.; Yamasaki, Y.; Sonoda, N.; Kurosawa, H.;
Kawasaki, Y.; Murai, S. J. Am. Chem. Soc. 1989, 111, 7938.
1. Hydrosilation of (CO)5MnC(O)CH3 (1). General
Observations. Of the 10 monohydrosilanes that reacted with
(CO)5MnC(O)CH3 (1) in benzene at room temperature (eq 2),
the HSiMe2Ph- and HSiEt3-derived reaction products exemplify
the hydrosilation chemistry of 1. Treatment of 1 with 1 equiv
of HSiMe2Ph, for example, cleanly yielded (CO)5MnCH-

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10081
ing to (a) homolytic cleavage and generation of the bis(silyl)
ether CH3CH(OSiMe2Ph)CH(OSiMe2Ph)CH3 (8a), (b) further
reaction with hydrosilane and elimination of CH3CH2OSiMe2-
Ph (7a), or (c) â-deinsertion to form the silyl vinyl ether
CH2dCH(OSiMe2Ph) (6a).
Although transformation of acyl complexes plus hydrosilane
R-siloxyvinyl derivatives similar to 3 is unprecendented, a
number of other mono- and bimetallic 1-oxyvinyl complexes
had been characterized. Interest in these 1-oxyvinyl systems
centers on (1) using nucleophilic R-(metaloxy)vinyl or R-alkox-
yvinyl compounds LxMC(OR)dCHR to form carbon-carbon
bonds30 and (2) transforming acyl ligands to bimetallic µ(η1-
C:η1-O) ketene (or enolate) complexes.31 R-Alkoxyvinyl
compounds, for example, derive from deprotonating alkoxy-
carbene compounds (eq 7),32 as exemplified by the (Z)-rhenium
and iron alkoxy-1-propenyl compounds reported by the Glad-
ysz33 and Davies34 groups, respectively.
extensive literature of Mn(CO)5 chemistry38 also includes several
examples of 1-oxyvinyl complexes. Thus, 5-(CO)5Mn-2(3H)-
furanone and 6-(CO)5Mn-3,4-dihydro-(2H)-pyran-2-one com-
plexes 1239 and the recently reported Mn2(CO)9{µ-OdC-
[C(H)dC(OEt)]2} (13)40 contain 1-oxyvinyl functionalities. A
particularly intriguing example is the trimethylsilyl enol ether
derivative 14 of the bimetallic µ-malonyl compound Cp*(NO)-
(PPh3)Re[µ-(COCH2CO)-C1,O3:C3]Mn(CO)4,41 which O’Connor
used in establishing keto-enol tautomerization of a metal acyl
system.
2. Hydrosilation of CH3C(O)Mn(CO)5 (1). Mechanistic
Constraints. Any mechanism advanced for the reactions of
HSiMe2Ph, HSiEt3, or other monohydrosilanes with (CO)5MnC-
(O)CH3 (1) must account for the following observations: (1)
the absence of the organic byproducts CH2dCHOSiR3 (6) and
CH3CH2OSiR3 (7); (2) the presence of (CO)5MnCH(OSiR3)dCH2
(3) but not (CO)5MnSiMe2Ph (5); (3) the formation of 3, which
needs just 1 equiv of hydrosilane, independent of (CO)5MnCH-
(OSiR3)CH3 (2); (4) the inhibition by CO, phosphine, or
acetonitrile, but neither air nor light; (5) the competitive
hydrosilation of other substrates (e.g., acetone or Cp(CO)2FeC-
(O)R) for which 1 is a precatalyst; (6) the autocatalysis during
which product degradation affords the active catalyst; and,
perhaps most informative, (7) the presence of an induction
period that can be removed by independently generating the
putative active catalyst.
Our working hypothesis for the mechanism of the reaction
of HSiR3with 1 accordingly engenders an intermolecular
pathway in which a coordinatively unsaturated manganese silyl,
(CO)4MnSiR3 (15), serves as the active catalyst (Scheme 4).
According to this intermolecular, autocatalytic pathway, the
active catalyst 15 ligates 1 as the bimetallic µ-acetyl 16 and
rearranges to (CO)5MnC(CH3)(OSiR3)Mn(CO)4 (17). This
unsaturated µ-siloxyethylidene serves as the key catalysis
intermediate. It can coordinate silane to give 18, which then
reductively eliminates the R-siloxyethyl product 2. Alterna-
tively, 17 can competitively â-deinsert to give 19, which then
dissociates the R-siloxyvinyl product 3.
Organometallic 1-oxyvinyl enolates35,36 LxMC(O-)dCHR are
precursors to other 1-oxyvinyl compounds. Floriani accordingly
-
trapped Cp(PPh3)(CO)FeC(O)dCH2 as its titanoxy and zir-
conoxy derivatives Cp(PPh3)(CO)FeC(OMClCp2)dCH2.37 At-
tempts to generate the corresponding R-siloxyvinyl complex
Cp(PPh3)(CO)FeC(OSiMe3)dCH2 by silylating the same enolate
instead gave Cp(PPh3)(CO)FeC(O)CH2SiMe3.35b,c Gladysz
converted the analogous rhenium R-silylacetyl to its R-silox-
yvinyl tautomer Cp(PPh3)(NO)ReC(OSiMe3)CdCH2.35g The
(29) The mechanism proposed for transforming 5k and acetaldehyde to
6k invokes 2k as the initial product. Although 2k was detected in unspecified
concentrations by NMR spectroscopy, 6k proved to be the isolable product.
A more plausible pathway for this reaction would have the coordinatively
unsaturated 11 as the common precursor to 6k or 4k. We do not know
why 2k should be less stable than (CO)5MnCH(OSiMe2Et)CH3 (2e), for
example, but we also cannot account for the limited stability of (CO)5MnCH-
(OSiEt3)CH3 (2j). The salient difference between the reactivity of 5k toward
acetaldehyde and the hydrosilation of 1 is that the former process provides
vinyl silyl ethers as a major product whereas the hydrosilation process yields
isolable manganese R-siloxyalkyl complexes 2.
(30) Blackburn, B. K.; Davies, S. G.; Whittaker, M. In Stereochemistry
of Organometallic an Inorganic Compounds, Bernal; I., Ed.; Elsevier:
Amsterdam, 1989; Vol. 3, Chapter 2.
(31) (a) Geoffroy, G. L.; Bassner, S. L. AdV. Organomet. Chem. 1988,
28, 1. (b) Ozawa, F.; Park, J. W.; Mackenzie, P. B.; Schaefer, W. P.;
Henling, L. M.; Grubbs, R. H. J. Am. Chem. Soc. 1989, 111, 1319. (c)
Waymouth, R. M.; Santarsiero, B. D.; Coots, R. J.; Bronikowski, M. J.;
Grubbs, R. H. J. Am. Chem. Soc. 1986, 108, 1427.
(32) (a) Cutler, A. R.; Hanna, P. K.; Vites, J. C. Chem. ReV. 1988, 88,
1363. (b) Bruce, M. I. Chem. ReV. 1991, 91, 197.
(33) Bodner, G. S.; Smith, D. E.; Hatton, W. G.; Heah, P. C.; Georgiou,
S.; Rheingold, A. L.; Geib, S. J.; Hutchinson, J. P.; Gladysz, J. A. J. Am.
Chem. Soc. 1987, 109, 7688.
Coordinatively unsaturated (CO)4MnSiR3 (15) previously had
been implicated as the active catalyst for the SiH/Si′D isotope
exchange between HSiMe2Et and DSiMe2Ph at room temper-
ature (Scheme 5).3a In these reactions, (CO)5MnC(O)-p-C6H4-
CH3 was added as the precatalyst, and results of a kinetics study
are consistent with it transforming into 15 during a reproducible
induction period. The coordinatively unsaturated silyls 15a and
15e evidently function as the active catalysts in a ping-pong Bi
(34) (a) Baird, G. J.; Davies, S. G.; Jones, R. H.; Prout, K.; Warner, P.
J. Chem. Soc., Chem. Commun. 1984, 745. Curtis, P. J.; Davies, S. G. J.
Chem. Soc., Chem. Commun. 1984, 747. (b) Baird, G. J.; Davies, S. G.;
Maberly, T. R. Organometallics 1984, 3, 1764.
(35) (a) Theopold, K. H.; Becker, P. N.; Bergman, R. G. J. Am. Chem.
Soc. 1982, 104, 5250. (b) Aktogu, N.; Felkin, H.; Davies, S. G. J. Chem.
Soc., Chem. Commun. 1982, 1303. (c) Aktogu, N.; Felkin, H.; Baird, G. J.;
Davies, S. G.; Watts, O. J. Organomet. Chem. 1984, 262, 49. (d) Davies,
S. G.; Dordor-Hedgecock, I. M.; Warner, P.; Jones, R. H.; Prout, K. J.
Organomet. Chem. 1985, 285, 213. (e) Liebeskind, L. S.; Welker, M. E.
Organometallics 1983, 2, 194. (f) Liebeskind, L. S.; Welker, M. E.; Fengl,
R. W. J. Am. Chem. Soc. 1986, 108, 6328. (g) Heah, P. C.; Patton, A. T.;
Gladysz, J. A. J. Am. Chem. Soc. 1986, 108, 1185. (h) Ojima, I.; Kwon, H.
B. J. Am. Chem. Soc. 1988, 110, 5617.
(38) Treichel, P. M. In ComprehensiVe Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Eds.; Pergamon Press: Oxford, U.K., 1982;
Vol. 4, Chapter 29.
(39) Kraihanzel, C.; Herman, L. J. Organomet. Chem. 1986, 15, 397.
(40) Adams, R. D.; Chen, G.; Chen, L.; Wu, W.; Yin, J. J. Am. Chem.
Soc. 1991, 113, 9406.
(41) O’Connor, J. M.; Uhrhammer, R.; Rheingold, A. L.; Roddick, D.
M. J. Am. Chem. Soc. 1991, 113, 4530. O’Connor, J. M.; Uhrhammer, R.;
Rheingold, A. L.; Staley, D. L.; Chadha, R. K. J. Am. Chem. Soc. 1990,
112, 7585.
(36) (a) Brinkman, K.; Helquist, P. Tetrahedron Lett. 1985, 26, 2845.
(b) Akita, M.; Kondoh, A. J. Organomet. Chem. 1986, 299, 369.
(37) (a) Berno, I.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Organo-
metallics 1990, 9, 1995. (b) Weinstock, P.; Floriani, C.; Chiesi-Villa, A.;
Guastini, C. J. Am. Chem. Soc. 1986, 108, 8298.

10082 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
Scheme 4. Intermolecular Pathways for HSiR3 and (CO)5MnC(O)CH3 (1)
Scheme 5. (CO)5MnC(O)-p-C6H4CH3-Catalyzed SiH/Si′D Isotope Exchange
Bi mechanism that operates under rapid equilibrium conditions
(Scheme 5). Silane SiH/Si′D isotope exchange thus intercon-
verts 15a and 15e by sequentially adding one substrate silane
and then releasing a product silane. The implicit silane
oxidative-addition and reductive-elimination steps in this pro-
posed mechanism, although precedented,42 could be replaced
by η2-(H-Si) complexation43 and σ-metathesis44 steps.
A particularly salient observation is that the induction period
common to both the manganese toluoyl-catalyzed SiH/Si′D
isotope exchange and the reaction of HSiR3 with 1 can be
removed by a pretreatment procedure. This procedure involves
treating the precatalyst, e.g., 1, with excess hydrosilane prior
to initiating the actual catalysis. Thus, the induction period for
the SiH/Si′D isotope exchange can be eliminated by mixing the
manganese toluoyl complex with excess of one hydrosilane.
After 0.75 h, all of the precatalyst has been consumed, and
catalysis immediately commences upon adding the other silane.
The timing is critical since the active catalyst is short lived:
productive catalysis of silane exchange stopped within 1.25 h.45
A similar pretreatment procedure also was used to demon-
strate autocatalytic reactions of HSiMe2Ph and HSiEt3 with 1,
Figure 4 and eq 6. Significantly, these reaction rates dramati-
cally increased after pretreating catalytic quantities of (CO)5MnC-
(O)-p-C6H4CH3 (or even 1) with excess HSiMe2Ph or HSiEt3
(for 45 min) prior to adding the substrate 1.
The unsaturated siloxyethylidene 17 intermediate in our
proposed mechanism for the reaction of HSiR3 with 1 (Scheme
4) serves as a common precursor to yielding either R-siloxyethyl
2 or R-siloxyvinyl 3 as products of competing pathways.
Analogous dicobalt siloxyethylidene compounds Co2(CO)6(µ-
CO){µ-R(COSiR′3)} have been fully characterized.46 For the
(42) Isolobal examples (hydrido)(silyl)(alkyl)Co(III),42a (hydrido)-
(silyl)2Co(III),42b (hydrido)(silyl)2Fe(CO)Cp,42c [(CO)5Mn](CO)4MnH-
(SnBu3), and (CO)4MnH(SnBu3)242d have been characterized as the products
of similar oxidative-addition/reductive-elimination sequences. Other ex-
amples of (hydrido)(silyl)(alkyl)metal complexes also have been reported/
implicated as intermediates in hydrosilation catalysis.42e (a) Wrighton, M.
S.; Seitz, M. S. Angew. Chem., Int. Ed. Engl. 1988, 27, 289. Hardin, S.;
Turney, T. W. J. Mol. Catal. 1987, 39, 237. Archer, N. J.; Haszeldine, R.
N.; Parish, R. V. J. Chem. Soc., Dalton Trans. 1979, 695. (b) Reichel, C.
L.; Wrighton, M. S. Inorg. Chem. 1980, 19, 3858. Anderson, F. R.;
Wrighton, M. S. J. Am. Chem. Soc. 1984, 106, 995. (c) Randolph, C. L.;
Wrighton, M. S. J. Am. Chem. Soc. 1986, 108, 3366. (d) Akita, M.; Oku,
T.; Moro-oka, Y. J. Chem. Soc., Chem. Commun. 1989, 1790. Akita, M.;
Oku, T.; Tanaka, M.; Moro-oka, Y. Organometallics 1991, 10, 3080. (e)
Brunner, H.; Fisch, K. Angew. Chem., Int. Ed. Engl. 1990, 29, 1131; J.
Organomet. Chem. 1991, 412, C11. (f) Sullivan, R. J.; Brown, T. L. J. Am.
Chem. Soc. 1991, 113, 9155. (g) Campion, B. K.; Heyn, R. H.; Tilley, T.
D.; Rheingold, A. L. J. Am. Chem. Soc. 1993, 115, 5527 and references
therein.
(45) An alternative procedure of eliminating the induction period for the
SiH/Si′D isotope exchange involved (CO)5MnSiMe2Ph (5a) as the precata-
lyst under photochemical conditions.3a Under similar photochemical condi-
tions 5a also catalyzed the hydrosilation of ketones and esters.9b,c
Photocatalysis of the hydrosilation of 1 using 5a, however, was not pursued
because of the photochemical lability of the substrate 1. Under nonphoto-
chemical conditions, 5a does not promote these catalytic processes.
(46) Sisak, A.; Sironi, A.; Moret, M.; Zucchi, C.; Ghelfi, F.; Palyi, G. J.
Chem. Soc., Chem. Commun. 1991, 176.
(43) (a) Luo, X. -L.; Crabtree, R. H. J. Am. Chem. Soc. 1989, 111, 2527.
(b) Lead reference for (η2-H-SiR3)(CO)(L)MnCp complexes: Schubert,
U. AdV. Organomet. Chem. 1990, 30, 151.
(44) Woo, H. -G.; Tilley, T. D. Acc. Chem. Res. 1993, 26, 22.

Hydrosilation of (CO)5MnC(O)CH3 with Monohydrosilanes
J. Am. Chem. Soc., Vol. 118, No. 42, 1996 10083
Scheme 6. (PPh3)3RhCl-Catalyzed Hydrosilation of
Acetophenone
Intermediacy of coordinatively unsaturated R-siloxyethyl
complexes analogous to (CO)4MnCH(OSiR3)CH3 (11) had been
advanced in order to account for the noncatalytic hydrosilation
of organometallic acyl compounds50 such as (PPh3)(CO)3CoC-
(O)CH3 (eq 8).51 Treatment of this cobalt acetyl with 2 equiv
of monohydrosilanes, including HSiMe2Ph and HSiEt3, cleanly
gives the saturated cobalt silyl, e.g., (PPh3)(CO)3CoSiR3, plus
the ethoxysilane 7. Neither CH2dCHOSiR3 (6) nor (PPh3)(CO)3-
CoCH(OSiR3)CH3 was detected. This intramolecular hydrosi-
lation mechanism appears in Scheme 7 as it might apply to 1.52
This intramolecular mechanism also is consistent with the
generation of 2 from 11 (via addition of CO), with the absence
of air or light influence, and with the presence of CO and THF
inhibition. We, however, would expect (CO)5MnSiR3 (5), 6
(cf. Scheme 3), and CH3CH2OSiR3 (7) as byproducts. The
absence of these byproducts,53 even in the presence of excess
hydrosilanes, precludes the transience of 11 and therefore
operation of this mechanism. Competitive inhibition by acetone
or Cp(CO)2FeC(O)Rssubstrates for which 1 functions as a
hydrosilation precatalyst54 showever is consistent with the
intermolecular pathway. These acyls compete with 1 as the
substrate for the active catalyst 15.
A surprising outcome of this study is that the reactions of
HSiR3 with 1 differ from those with (PPh3)(CO)3CoC(O)CH3
(eq 8) or even (CO)5MnC(O)-p-C6H4R (R ) H, CH3),53 which
afford the products anticipated for the intramolecular mecha-
nism. With 1 as the substrate, a changeover to the intermo-
lecular pathway (Scheme 4) occurs, and the unsaturated
(CO)5MnC(CH3)(OSiR3)Mn(CO)4 (17) now functions as the
bimetallic counterpart to the unsaturated R-siloxyethyl complex
11 in the intramolecular mechanism. Provided that (CO)4MnSiR3
(15), the proposed active catalyst, efficiently traps 1 and
HSiEt3-1 reaction, its reaction profile (Figure 3) is in accord
with 3j forming independently of 2j. Only 1 equiv of HSiEt3
is required to generate 3j and to eliminate presumably 1 equiv
of H2.
We anticipated that competition between branching pathways
involving 17 should be sensitive to the hydrosilane concentra-
tion, with higher concentrations of hydrosilane favoring the
production of 2. For the HSiEt3-1 reaction, increasing the
HSiEt3 concentration from 1.2 to 6.0 equiv (Table 1) accordingly
increased the yields of 2j from 6% to 17%. The corresponding
increase in yield of 3j (from 38% to 42%), however, complicated
further analysis, since a much greater increase in 2j concentra-
tion conceivably could be masked by its sensitivity toward
excess HSiEt3.
It is the â-deinsertion step involving 17, however, that
distinguishes this mechanism. Assigning the â-elimination step
to this bimetallic intermediate nicely accounts for generating
an R-siloxyvinyl complex 3 instead of forming organic vinyl
silyl ethers CH2dCH(OSiR3) (6). Examples of 6 would be
expected to form at least as byproducts via â-elimination on a
mononuclear (CO)4MnCH(OSiR3)CH3 (11), as discussed for
Gladysz’s trimethylsiloxy derivative 11k (Scheme 3).
Organic vinyl silyl ethers also are byproducts of rhodium-
(I)-catalyzed hydrosilation of ketones.10 With acetophenone,
for example, a number of rhodium catalysts afford the
CH2dC(OSiR3)Ph as well as CH3CH(OSiR3)Ph (Scheme 6).47
The accepted mechanism48 has a rhodium R-siloxyalkyl inter-
mediate 20 that either reductively eliminates the silyl ether or
deinserts across a â-hydrogen to give the silyl vinyl ether.49
(50) Hydrosilation of cobalt acyls,12b the Co2(CO)8-catalyzed siloxym-
ethylation of aldehydes,28 and the hydrosilation / reduction of the acyl ligand
on Cp(L)(CO)FeC(O)CH2CH2Ph.42d
(51) Gregg, B. T.; Cutler, A. R. Organometallics 1992, 11, 4276.
(52) Intramolecular hydrosilation of 1 would require the coordinatively
unsaturated 11 as the pivotal intermediate. This intermediate would originate
via 1 dissociating carbon monoxide2 and oxidatively adding HSiR3 to give
(CO)4Mn(H)(SiR3)(COCH3).42 Rearrangement to 11 would occur either by
reductive elimination and subsequent insertion involving ligated aldehyde5f
or by a 1,3-silatropic shift52a and hydride migration. Association of CO at
11 would produce the observed R-siloxyalkyl product 2. Alternatively,
competing pathways for using 11 include â-elimination of CH2dCHOSiR3
and association of HSiR3 and then reductive elimination of CH3CH2OSiR3
(7). (a) Brinkman, K. C.; Blakeney, A. J.; Krone-Schmidt, W.; Gladysz, J.
A. Organometallics 1984, 3, 1325.
(53) This intramolecular pathway evidently is involved in the hydrosi-
lation of manganese benzoyl and p-toluoyl complexes (CO)5MnC(O)-p-
C6H4R (R ) H, CH3).1a,3a These reactions provide the benzyl silyl ether
(80-90%) plus the stable manganese silyl, e.g., (CO)5MnSiMe2Ph (5a) (ca.
25-40%). Yields of 5a increase with CO pressure, but decrease with
increasing hydrosilane concentration. These and other observations (to be
published) are consistent with the presence of a coordinatively unsaturated
manganese silyl (CO)4MnSiMe2Ph (15a) intermediate that degrades rela-
tively slowly in the presence of excess silane.
(47) (a) Benes, J.; Hetflejs, J. Collect. Czech. Chem. Commun. 1976,
41, 2264. (b) Sakurai, H.; Miyoshi, K.; Nakadaira, Y. Tetrahedron Lett.
1977, 2671. (c) Matsumoto, H.; Hoshino, Y.; Nagai, Y. Bull. Chem. Soc.
Jpn. 1981, 54, 1279. (d) Payne, N. C.; Stephan, D. W. Inorg. Chem. 1982,
21, 182. (e) Lappert, M. F.; Maskell, R. K. J. Organomet. Chem. 1984,
264, 217. (f) Brunner, H.; Becker, R.; Riepl, G. Organometallics 1984, 3,
1354. Brunner, H.; Kurzinger, A. J. Organomet. Chem. 1988, 346, 413.
(g) Ojima, I.; Donovan, R. J.; Clos, N. Organometallics 1991, 10, 2606.
(h) Wright, M. E.; Cochran, B. B. J. Am. Chem. Soc. 1993, 115, 2059.
(48) (a) Ojima, I.; Kogure, T; Kumagai, M.; Horiuchi, S.; Sato, T. J.
Organomet. Chem. 1976, 122, 83. Ojima, I.; Kogure, T.; Kumagai, M. J.
Org. Chem. 1977, 42, 1671. Ojima, I.; Kogure, T. Organometallics 1982,
1, 1390. (b) Hayashi, T.; Yamamoto, K.; Kumada, M. J. Organomet. Chem.
1976, 113, 127. (c) Corriu, R. J. P.; Moreau, J. J. E. NouV. J. Chim. 1977,
1, 71. (d) Peyronel, J. F.; Kagan, H. B. NouV. J. Chim. 1978, 2, 211. Kagan,
H. B.; Peyronel, J. F.; Yamagishi, T. In AdVances in Chemistry Series No.
173; King, R. B., Ed.; American Chemical Society: Washington, DC, 1979;
p 50. (e) Kolb, I.; Hetflejs Coll. Czech. Chem. Comm. 1980, 45, 2224. (f)
Zheng, G. Z.; Chan, T. H. Organometallics 1995, 14, 70 and references
therein.
(49) We note however that 1-catalyzed hydrosilation of enolizable ketones
such as acetophenone does not provide the organic vinyl silyl ethers, e.g.,
PhC(OSiR3)dCH2. Using 1 as the precatalyst for the HSiEt3 or HSiMe2Ph
hydrosilation of acetophenone thus yields only its siloxybenzyls, PhCH-
(OSiR3)CH3.9b
(54) In work to be published we demonstrate that pretreating the
manganese acetyl 1 or p-toluoyl complexes with excess HSiMe2Ph under
the same conditions that were used in the silane exchange studies affords
extremely active catalysts for the hydrosilation of FpC(O)CH3,9a organic
ketones,9b and esters.9c

10084 J. Am. Chem. Soc., Vol. 118, No. 42, 1996
Gregg and Cutler
Scheme 7. Intramolecular Pathways for HSiR3 and (CO)5MnC(O)CH3 (1)
rearranges to 17, subsequent â-deinsertion and dissociation of
the fragment (CO)4MnH provide R-siloxyvinyl complexes 3 (vs
an organic vinyl silyl ether 6 from 11), whereas addition of
hydrosilane to 17 yields 2 (vs an ethoxysilane from 10).33,34
The absence of detectable (CO)5MnSiR3 (5) during the
reactions between HSiR3 and 1 may seem surprising given that
unsaturated (CO)4MnSiR3 (15) is the proposed active catalyst
and that CO dissociation is involved in generating 15 from 1.
The absence of 5 cannot be attributed to subsequent reaction
chemistry: 5a neither reacts with hydrosilanes under these
reaction conditions nor serves as a precatalyst (Figure 4).3 We
believe that unstable 5 forms as a transient,3a promotes catalysis,
and degrades in the presence of HSiR3 to the observed
disiloxanes.
A remaining issue concerns the origin of the purported active
catalyst 15. We hypothesize three plausible sources of 15. First,
silane-induced degradation of the product 2 could continuously
replenish the low concentrations of the unstable catalyst 15 as
it decomposed. Results of the reaction profiles for the HSiMe2-
Ph-1 hydrosilation (Figure 4) demonstrate that 2a functions
as an efficient precatalyst. Second, according to the intermo-
lecular hydrosilation mechanism advanced in Scheme 4, the
active hydrosilation catalyst 15 could be regenerated. Finally,
the origin of 15 when 1 and HSiR3 are mixed without the
pretreatment procedure remains an unresolved issue. A possible
explanation is that a few turnovers of the intramolecular
mechanism or other unspecified hydrosilane-induced degradation
of 1 could generate the initial 15. Interestingly, (CO)5MnC-
(O)-p-C6H4CH3, perhaps the most effective reagent for the
pretreatment procedure (Figure 4), evidently reacts by the
intramolecular route and generates 15/5.
and (2) these reactions also provide an R-siloxyvinyl byproduct
(CO)5MnC(OSiR3)dCH2 (3). These reactions readily occur at
room temperature with 1-2 equiv of HSiR3, all without adding
a catalyst. In contrast, hydrosilation of the isolobal iron acetyl
compounds Cp(CO)(L)FeC(O)CH3 yields Cp(CO)(L)FeCH-
(OSiR3)CH3,1 but these reactions require a catalyst; hydrosilation
of the cobalt acetyl compounds (PR3)(CO)3CoC(O)CH350 cleanly
produces equimolar mixtures of (CO)3(PR3)CoSiR3 plus CH3-
CH2OSiR3 (7), although these reactions occur without benefit
of a catalyst.
The formation of 3, our second result, instead of (CO)5MnSiR3
(5) plus 7 [or CH2dCHOSiR3 (6)] forms the basis of our
working hypothesis for an intermolecular catalysis pathway. This
catalysis pathway features the coordinatively unsaturated
(CO)4MnSiR3 (15) as the active catalyst. It binds the substrate
1 and rearranges to the µ-siloxyethylidene intermediate
(CO)5MnC(CH3)(OSiR3)Mn(CO)4 (17) (Scheme 4), which
transforms to 2 or 3.
One postulated route to generate the unstable active catalyst
15 is autocatalysis that entails silane degradation of product 2
(but not 3). This autocatalysis is consistent with the dramatic
rate enhancements for the hydrosilation of 1 that attend
pretreatment of catalytic quantities of 1, (CO)5MnC(O)C6H4-
CH3, or even 2 with excess silane before adding the substrate
1. Under these pretreatment conditions,3,9 transient concentra-
tions of 15 are believed to be generated, although further studies
are required in order to elucidate the processes by which 15
derives from hydrosilane-induced degradation of manganese
alkyl complexes.
Acknowledgment. We gratefully acknowledge receiving
generous financial support from the Department of Energy,
Office of Basic Energy Science. We also are indebted to Dr.
Chongfu Xu for doing a key experiment and to Dr. Paul Hanna
and Edward Crawford (RPI) for their preliminary observations.
Conclusions
Two significant results of this study are that (1) reactions
between (CO)5MnC(O)CH3 (1) and monohydrosilanes afford
isolable R-siloxyethyl complexes (CO)5MnCH(OSiR3)CH3 (2)
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