(C5Me5)2Y(μ-Ph)2BPh2, 1, reacted with ethyllithium at -15 °C to make (C5Me5)2Y(CH2CH3), 2, which is thermally unstable at room temperature and formed the C-H bond activation product, (C5Me5)2Y(μ-H)(μ-η(1):η(5)-CH2C5Me4)Y(C5Me5), 3, containing a metalated (C5Me5)(1-) ligand. Spectroscopic evidence for 2 was obtained at low temperature, and trapping experiments with (i)PrNCN(i)Pr and CO2 gave the Y-CH2CH3 insertion products, (C5Me5)2Y[(i)PrNC(Et)N(i)Pr-κ(2)N,N'], 4, and [(C5Me5)2Y(μ-O2CEt)]2, 5. Although 2 is highly reactive, low temperature isolation methods allowed the isolation of single crystals which revealed an 82.6(2)° Y-CH2-CH3 bond angle consistent with an agostic structure in the solid state. Complex 2 reacted with benzene and toluene to make (C5Me5)2YPh, 7, and (C5Me5)2YCH2Ph, 8, respectively. The reaction of 2 with [(C5Me5)2YCl]2 formed (C5Me5)2Y(μ-Cl)(μ-η(1):η(5)-CH2C5Me4)Y(C5Me5) in which a (C5Me5)(1-) ligand was metalated. C-H bond activation also occurred with methane which reacted with 2 to make [(C5Me5)2YMe]2, 9.