The reaction of the known alkenyldecaborane 5-(CH3)(2)S-6[((CH3)(3)Si)(2)C=CH]B H-10(11) with [eta(5)-C5H5)Ni(CO)](2) results in the formation of two nickelacarboranes, 1-(eta(5)-C5H5)-2-[((CH3)3Si)(2)CH]-1, 2-NiCB10H11 (I) and 1-(eta(5)C(5)H(5))-7-[((CH3)(3)Si)(2)CH]-1, 7-NiCB10H10(II). A preliminary X-ray study helped to establish the structure of compound II, although the diffraction of the crystal was poor for an accurate determination of interatomic bond distances and bond angles. Experimental details of this reaction and characterization of these compounds are presented.