The synthesis, structures, and reactivity of a series of 14-electron complexes including L2Cl2Ti-(Et2C2B4H4) (1-3, L-2 = 2 PMe3, Me2P(CH2)(2)PMe2, or Me2P(CH2)(3)PMe2], [Me2P(CH2)(3)PMe2](2)Me2Ti- (Et2C2B4H4) (22), and related compounds are reported together with the preparation and spectroscopic characterization of the analogous zirconium species L2Cl2Zr(Et2C2B4H4) (L-2 = 2PMe(3) or Me2P(CH2)(3)PMe2 (24 and 25). Compounds 1-3, 22, and 25 are catalyst precursors for the polymerization of ethylene at 1 atm pressure in the presence of methylaluminoxane, thus extending Ziegler-Natta chemistry for the first time to complexes of the [R2C2B4H4](2-) Small carborane ligands. Although the choice of phosphine ligand has a dramatic effect on catalyst activity, NMR data reveal aluminum-phosphine binding under conditions approximating the catalytic mixtures for the PMe3 and Me2P(CH2)(2)PMe2 (dmpe) systems, whereas the state of Me2P(CH2)(3)PMe2 (dmpp) coordination is not clear. Multiple catalyst species are probably active in these reaction mixtures, giving rise to polyethylene products of broad polydispersity; melting points and C-13 NMR data provide evidence for significant chain branching. (dmpp)Me2Ti(Et2C2B4H4) produces a highly active ethylene polymerization catalyst with much narrower molecular weight distributions than the other systems described here. The complexes (PMe3)(2)Cl2Ti(Et2C2B4H4) (1), (dmpp)Cl2Ti(Et2C2B4H4) (3), and (dmpp)Me2Ti(Et2C2B4H4) (22) have been structurally characterized by X-ray crystallography.