Polymethylhydrosiloxane

Polymethylhydrosiloxane (PMHS) is a polymer with the general structure -(CH₃(H)Si-O)-. It is used in organic chemistry as a mild and stable reducing agent easily transferring hydrides to metal centers and a number of other reducible functional groups.[1] A variety of related materials are available under the following CAS registry numbers 9004-73-3, 16066-09-4, 63148-57-2, 178873-19-3. These include the tetramer ((MeSiHO)₄), copolymers of dimethylsiloxane and methylhydrosiloxane, and trimethylsilyl terminated materials.

Polymethylhydrosiloxane

Names
Other names Methyl hydrogen siloxane; Poly(methyl siloxane); Poly(methylhydrosiloxane); Polysilicone 4
Identifiers
CAS Number	9004-73-3
Abbreviations	PMHS
ChemSpider	none
ECHA InfoCard	100.119.568
CompTox Dashboard (EPA)	DTXSID8047501
Properties
Chemical formula	(CH3(H)SiO)n
Molar mass	variable
Density	1.006 g/cm^3
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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Infobox references

This material is prepared by the hydrolysis of methyldichlorosilane:

n MeSiHCl₂ + n H₂O → (MeSiHO)_n + 2n HCl

The related polymer polydimethylsiloxane (PDMS) is made similarly, but lacking Si-H bonds, it exhibits no reducing properties.

Illustrative of its use, PMHS is used for in situ conversion of tributyltin oxide to tributyltin hydride:[2]

2"(MeSiH)" + (Bu₃Sn)₂O → "Me₂Si₂O" + 2 Bu₃SnH

References

1. J. M. Lavis, R. E. Maleczka, Jr. "Polymethylhydrosiloxane" Encyclopedia of Reagents for Organic Synthesis 2003, John Wiley & Sons. doi:10.1002/047084289X.rn00062
2. Jordi Tormo and Gregory C. Fu (2002). "Tributylstannane (Bu₃SnH)-Catalyzed Barton-McCombie deoxygenation of Alcohols: 3-Deoxy-1,2:5,6-bis-O-(1-methylethyilidine)-α-D-ribo-hexafuranose". Organic Syntheses. 78: 239.

Further reading

• Larson, G. L.; Fry, J. L., "Ionic and organometallic-catalyzed organosilane reductions", Organic Reactions 2008, 71, 1-737. doi:10.1002/0471264180.or071.01