[26500-16-3]  · C8H9MnO5Si  · Pentacarbonyl(trimethylsilyl)manganese  · (MW 268.20)

(carbon-carbon bond formation with strained cyclic ethers by ring opening followed by CO insertion;1,3 synthesis of enol ethers from acetals;2 can add to aldehydes and ketones2).

Physical Data: white crystals; mp 26.5 °C;3 25.6-26.2 °C.4

Solubility: sol most organic solvents.

Form Supplied in: not commercially available.

Analysis of Reagent Purity: IR (cyclohexane, cm-1) 2094 (w), 2000 (s), 1993 (vs); NMR (cyclohexane, d) 0.49 ppm.4

Preparative Methods: 3-5 (a) a suspension of KMn(CO)5 in pentane is stirred with Bromotrimethylsilane for two days at rt to afford (CO)5MnSiMe3 in 60-80% yield after purification (eq 1);3 a similar reaction with Chlorotrimethylsilane gives a lower yield.4 (b) The desired product is obtained in 70% yield by heating Me3SiH and Decacarbonyldimanganese without solvent for 48 h at 132 °C.4 (c) Heating Me3SiH and HMn(CO)5 in similar fashion to method (b) provides (CO)5MnSiMe3 in 23% yield.4

The related compound (CO)5MnSi(t-Bu)Me2 is obtained by treating ethereal solutions of NaMn(CO)5 with t-Butyldimethylsilyl Trifluoromethanesulfonate and is used in situ.6

Purification: by sublimation or vacuum line transfer at ambient temperature.

Handling, Storage, and Precautions: the solid may be handled in air; upon prolonged exposure, it oxidizes to a brown material and should therefore be stored under inert atmosphere. Solutions of (CO)5MnSiMe3 react readily with water, giving HMn(CO)5 and Me3SiOSiMe3. While no information concerning the toxicity of this compound is available, one should assume that metal carbonyls are highly toxic; since this is a volatile solid, extra care should be taken to avoid exposure. Use in a fume hood.

Ring Opening of Cyclic Ethers.

Much of the chemistry of (CO)5Mn-silyl compounds derives from the apparent heterolysis of the Mn-Si bond, making available a combination of Lewis acidic (SiR3+) and nucleophilic (Mn(CO)5-) moieties. Thus exposure to Trimethylamine immediately gives the salt [Me3N-SiMe3]+[Mn(CO)5]-.4 More useful examples are provided by the ring opening of strained cyclic ethers to give manganese alkyls in good to excellent yields by treatment with (CO)5Mn-silyl complexes under moderate pressures of CO (eq 2).1,3,4,7 The insertion is regioselective, with the manganese fragment ending up on the less-hindered carbon (one isomer for epoxides; 10:1 ratio for 2-methyltetrahydrofuran).6 The reaction mechanism is thought to involve interaction of the ether oxygen with Me3Si+, followed by attack of Mn(CO)5- on a C-O bond.4

When performed in the presence of alkynes or activated alkenes, products derived from the sequential insertion of CO and the unsaturated substrate into the Mn-C single bond are obtained in good to excellent yields (eq 2; see Pentacarbonylmethylmanganese).8 This methodology has been employed in the efficient synthesis of spiroacetal systems.6,8 Alternatively, carbonylation may be followed by desilylation to produce lactones.2

Conversion of Acetals to Vinyl Ethers.

Treatment of acetals with (CO)5MnSiMe3 under mild conditions affords vinyl ethers (eq 3).2,9,10 Mixtures of (E)- and (Z)-isomers are produced under thermodynamic control, consistent with the mechanism shown in eq 3. Related reagents are cis-(CO)4Fe(SiMe3)2 and (CO)4CoSiMe3.2

Reductive Silylation of a-Halocarbonyl Compounds.

Silyl enol ethers and silyl ketene acetals are available from (CO)5MnSiMe3 and aromatic a-halo ketones or a-halo esters bearing simple aromatic and aliphatic substituents (eqs 4 and 5).2,11 The tolerance of the reaction to more sensitive functionality has not been explored.

Addition to Aldehydes and Ketones.

The facile addition of (CO)5Mn-SiMe3 across the carbonyl of aldehydes and ketones has been observed. The a-siloxymanganese alkyl intermediates may undergo CO insertion under CO pressure to give a-silyloxyacyl complexes, reductive coupling upon heating to give 1,2-diol TMS ethers, or b-hydride elimination to give silyl enol ethers (eq 6).1,2,7,12 Yields for the first pathway range from 26-72% for a selection of alkyl, aryl, and vinyl aldehydes,12 and are improved if the reaction is performed in the presence of (CO)5MnH.1 b-Hydride elimination is rapid for ketones.

1. Brinkman, K. C.; Gladysz, J. A. OM 1984, 3, 147.
2. Gladysz, J. A. ACR 1984, 17, 326.
3. Gladysz, J. A.; Williams, G. M.; Tam, W.; Johnson, D. L.; Parker, D. W.; Selover, J. C. IC 1979, 18, 553.
4. Berry, A. D.; MacDiarmid, A. G. Inorg. Nucl. Chem. Lett. 1969, 5, 601.
5. Malisch, W.; Kuhn, M. CB 1974, 107, 979.
6. DeShong, P.; Rybczynski, P. J. JOC 1991, 56, 3207.
7. Brinkman, K. C.; Gladysz, J. A. CC 1980, 1260.
8. DeShong, P.; Sidler, D. R. JOC 1988, 53, 4892.
9. Marsi, M.; Gladysz, J. A. TL 1982, 23, 631.
10. Marsi, M.; Gladysz, J. A. OM 1982, 1, 1467.
11. Marsi, M.; Brinkman, K. C.; Lisensky, C. A.; Vaughn, G. D.; Gladysz, J. A. JOC 1985, 50, 3396.
12. Johnson, D. L.; Gladysz, J. A. IC 1981, 20, 2508.

M. G. Finn

University of Virginia, Charlottesville, VA, USA

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