The 1,4-disubstituted butatrienes, (Z)-R-CH=C=C=CH-R (1, R = SiMe3, t-Bu), reacted with RhCl(PAr3)(3) (Ar = Ph, p-tolyl) to give rhodium-(Z)-butatriene complexes 3. The butatrienes coordinated to Rh with the central double bond in an eta(2)- fashion. (Z)-Butatrienes on 3 isomerized to (E)-form at 70 degreesC to afford (E)-butatriene complexes 4 with excellent E/Z ratios (E/Z = 97/3-99/1). The molecular structure of 4b (R = SiMe3, Ar = p-tolyl) was determined by X-ray diffraction analysis. Hydrosilation of I was catalyzed by rhodium complexes to give allenes as major products accompanied by 1,3-dienes as minor ones, which are results of 2,1-addition and 2,3-anti-addition of the silane.