Decaborane(14) reacts with 1-(CH3)(3)SiC=CC4H9 in the presence of dimethyl sulfide to give the new alkenyl-decaborane 5-(S(CH3)(2))-6-[(CH3)(3)Si(C4H9)C=CH]B10H11 (I). Crystal data for 5-(S(CH3)(2))-6-[(CH3)(3)Si(C4H9)C=CH]B10H11 : space group P2(1)/n, monoclinic, a = 9.471(1) Angstrom, b = 13.947(3) Angstrom, c = 17.678(3) Angstrom, beta = 100.32(1)degrees. A total of 3366 unique reflections were collected over the range 2.0 degrees less than or equal to 2 theta less than or equal to 56.0 degrees, of which 1763 reflections had F-o(2) greater than or equal to 3 sigma(F-o(2)) and were used in the final refinement. R(F) = 0.083; R(WF) = 0.094. The single-crystal X-ray structure of 5-(S(CH3)(2))-6-[((CH3)(3)Si)(2)C=CH]B10H11 (A) is also reported. Crystal data for 5-(S(CH3)(2))-6-[((CH3)(3)Si)(2)C=CH]B10H11 : space group, P2(1)2(1)2(1), orthorhombic, a = 9.059 (3) Angstrom, b = 12.193(4) Angstrom, c = 21.431(3) Angstrom. A total of 4836 unique reflections were collected over the range 6 degrees less than or equal to 2 theta less than or equal to 140 degrees, of which 3705 reflections had F-o(2) greater than or equal to 3 sigma(F-o(2)) and were used in the final refinement. R(F) = 0.052; R(WF) = 0.059. The reactions of 5-(S(CH3)(2))6-[(CH3)(3)Si(C4H9)C=CH]B10H11 and 5-(S(CH3)(2))6-[((CH3)(3)Si)(2)C=CH]B10H11 with a variety of alkyl isocyanides were investigated. All of the alkenyl monocarbon carboranes reported are the result of incorporation of the carbon atom from the isocyanide into the alkenyldecaborane framework and reduction of N=C bond to a N-C single bond. The characterization of these compounds is based on H-1 and B-11 NMR data, IR spectroscopy, and mass spectrometry.