The reactivity of the tetraphenylborate salts of the rare earth metallocene cations [(C5Me5)(2)Ln] [(mu-Ph)(2)BPh2] (Ln = Y, 1; Sm, 2) has been investigated with substrates that undergo reduction with f element complexes to probe metal-substrate interactions prior to reduction. Results with NaN3, 1-adamantyl azide, acetone, benzophenone, phenanthroline, pyridine, azobenzene, and phenazine are described. Not only were coordination complexes isolated, but substrate reduction by (BPh4)(-) was also observed. Complex 1 reacts with NaN3 to form the azide [(C5Me5)(2)YN3](x), 3, which crystallizes as [(C5Me5)(2)Y(mu-N-3)](3), 4, when obtained from 1 and 1-adamantyl azide. The samarium analogue [(C5Me5)(2)SmN3](x), 5, can be produced similarly from 2 and NaN3 and crystallized from MeCN as [(C5Me5)(2)Sm(NCMe)(mu-N-3)](3), 6, and {[(C5Me5)(2)Sm(mu-N-3)][(C5Me5)(2)Sm(NCMe)(mu-N-3)]}(n) 7. Complexes 1 and 2 react with stoichiometric amounts of acetone and benzophenone to form the ketone adducts [(C5Me5)(2)Ln(OCMe2)(2)][BPh4] (Ln = Y, 8; Sm, 9) and [(C3Me5)(2)Ln(OCPh2)(2)][BPh4] (Ln = Y, 10; Sm, 11), respectively. Phenanthroline (phen) coordinates to. 1 to form [(C5Me5)(2)Y(phen)][BPh4], 12. Complexes 1 and 2 react with pyridine (py) to form [(C5Me5)(2)Ln(py)(2)][BPh4], (Ln = Y 13; Sm, 14). Complexes 3, 8, 10, and 12 can also be made from the solvated cation [(C5Me5)(2)Y(THF)(2)][BPh4]. The reaction of 1 with PINNPh yields the diamagnetic adduct [(C5Me5)(2)Y(PhNNPh)][BPh4], 15, which transforms in benzene to the radical anion complex (C5Me5)(2)Y(PhNNPh), 16, via a one electron reduction by (BPh4)(-). Complex 1 similarly reacts with phenazine (phz) to produce the First rare earth phenazine radical anion complex {[(C5Me5)(2)Y](2)(phz)}{BPh4}, 17. Further reduction of phenazine by (BPh4)(-) in 17 yields [(C5Me5)(2)Y](2)(phz), 18, which contains the common (phz)(2-) dianion. The reduction of fluorenone by (BPh4)(-) is also reported.