Poly(methylhydrosiloxane): Overview and Conversion Method of its Waste to Useful Commodities

Poly(methylhydrosiloxane) (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.

Preparation

Poly(methylhydrosiloxane) is prepared by the hydrolysis of monomethyldichlorosilane:

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. Dimethyldichlorosilane is then used instead of monomethyldichlorosilane.

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

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

Uses

Poly(methylhydrosiloxane) (PMHS) is an easily han dled, inexpensive, non-toxic, and mild reducing agent. Although relatively inert towards organic functionality, PMHS can transfer its hydride to a variety of metalcatalysts (including Sn, Ti, Zn, Cu, and Pd) which can then participate in a wide range of reductions. Alternatively, when made hypercoordinate by the action of fluo ride or other nucleophiles, PMHS can act directly as a reducing agent. PMHS is attractive as a substitute for more expensive or hazardous silanes or siloxanes and as the stoichiometric reductant in catalytic organotin-mediated processes.¹