New carbosilane monomers R1R2R3SiXSiH3 (X=CH2CH2 and CH(CH3); R1=H, R2=Me, R3=Ph (1a); R1=H, R2, R3=Ph (2a); R1, R2, R3=Et (3a) bearing primary and/or tertiary SiH groups undergo Cp2TiCl2/n-BuLi catalyzed dehydropolymerization selectively at the primary SiH site to afford the corresponding oligosilanes 1–3, [R1R2R3SiXSiH]n (n=12–15). Treatment of the oligosilanes 1 and 2 with methanol in the presence of a catalytic amount of biguanide base results in the chemoselective transformation of the pendant carbosilyl SiH to SiOMe groups, yielding the methoxy- substituted oligosilanes 4 and 5 (R1=OMe), respectively. The reaction of 3 with methanol under a similar base catalyzed conditions reveals only 5% conversion of the skeletal SiH to SiOMe groups. The oligosilanes 1–5 are characterized by IR, UV, 1H, 13C, 29Si, (1H–29Si) HSQC-NMR spectroscopy, GPC and TGA.