We report a two-step postsynthetic functionalization reaction of zeolite HZSM-5 that proceeds with high selectivity at room temperature. In the first step the framework acid sites of the zeolite are reacted with phenylsilane to replace the acidic proton with a hydrosilyl (-SiH3) group covalently linked to the framework. This group readily couples to acetone in a second step to form a framework- bound hydrosilyl isopropyl ether that is thermally stable at 473 K, but decomposes in the presence of moisture. We characterized these reactions using Si-29, H-1, and C-13 MAS NMR, as appropriate. Theoretical modeling using density functional theory and cluster models of the zeolite acid site confirmed that both steps were exothermic and provided theoretical chemical shift values in excellent agreement with experiment.