The reaction of B(C6F5)(3) with zirconocene dimethyl complexes L(2)ZrMe(2) in hydrocarbon solvents affords base-free cationic zirconium complexes L(2)ZrMe(+)MeB(C6F5)(3-) (L = eta(5)-C5H5, 1; eta(5)-Me(2)C(5)H(3), 2; eta(5)-Me(5)C(5), 3; eta(5)-(TMS)(2)C5H3, 4) in quantitative yields. A similar reaction using ((t)Bu(2)C(5)H(3))(2)ZrMe(2) results in the formation of the cationic metallacyclic product ((t)Bu(2)C(5)H(3))[(t)BuC(5)H(3)C(Me(2))CH2]Zr(+)MeB(C6F5)(3-) (6) through what is presumably an intramolecular C-H activation process. Complexes 3 and 6 undergo rapid hydrogenolysis to yield the corresponding cationic hydride complexes (Me(5)C(5))(2)ZrH(+)MeB(C6F5)(3-) (7), (Me(5)C(5))(2)ZrH+HB(C6F5)(3-) (8) (stepwise), and ((t)Bu(2)C(5)H(3))(2)ZrH(+)MeB(C6F5)(3-) (9), respectively. Complex 2 undergoes slow conversion to {[(Me(2)C(5)H(3))(2)ZrMe](2)(mu-F)}(+)MeB(C6F5)(3-) (12) in C6D6 under an inert atmosphere at 25 degrees C. Complexes 2, 3, 4, 6, 8, and 12 have been characterized by X-ray diffraction (crystal data : 2, monoclinic, P2(1)/n, a = 12.261(2) Angstrom, b = 20.010(6) Angstrom, c = 13.053(5) Angstrom, beta = 90.80(2)degrees, R = 0.027; 3, monoclinic, P(2)1/n, a = 9.405(1) Angstrom, b = 19.336(3) Angstrom, c = 10.382(1) Angstrom, beta = 96.54(1)degrees, R = 0.039; 4, triclinic, , a = 11.639(4) Angstrom, b = 12.877(4) Angstrom, c = 19.224(4) Angstrom, alpha = 77.89(2)degrees, beta = 74.33(2)degrees, gamma = 77.04(3)degrees, R = 0.043; 6, monoclinic, P2(1), a = 12.610(5) Angstrom, b = 20.995(4) Angstrom, c = 21.389(5) Angstrom, beta = 106.13(3)degrees, R = 0.066; 8, triclinic, , a = 11.899(4) Angstrom, b = 12.643(4) Angstrom, c = 13.681(4) Angstrom, alpha = 84.47(2)degrees, beta = 76.12(3)degrees, gamma = 65.34(3)degrees, R = 0.060; 12, triclinic, P-1, a = 12.308(1) Angstrom, b = 13.898(3) Angstrom, c = 15.182(2) Angstrom, alpha = 101.63(1)degrees, beta = 90.42(1)degrees, gamma = 115.22(1)degrees, R = 0.031). These structure determinations allow detailed analysis of the metrical aspects of L(2)ZrMe(+)MeB(C6F5)(3-) ion pairing on the solid state. As revealed by dynamic H-1 NMR, complexes 1-4 undergo rapid intramolecular Zr-Me/B-Me exchange (Delta G(double dagger) (sigma, kcal/mol, degrees C, complex) = 18.7(2, 80, 1); 19.7(2, 80, 2); 19.8(2, 80, 3); 18.0(2, 35, 4)) and for 2 and 4, symmetrizing ion-pair dissociation-recombination processes (Delta G(double dagger) (sigma, kcal/mol, degrees C, complex) = 18.3(2, 80, 2); 14.4(2, 35, 4)). Complexes 1-4, 7, and 8 are highly active homogeneous catalysts for the polymerization of ethylene with activities (3.2-6.8 X 10(6)g polyethylene/mol Zr h atm at 25 degrees C) comparable to methylalumoxane-based zirconocene catalysts. Complexes 1-3, 7 and 8 are also active for the atactic polymerization of propylene. In regard to polymerization chain transfer mechanisms, NMR endgroup analysis and labeling experiments using CH2 double bond (CHCH3)-C-13 indicate the predominant pathway for 1 and 2 is beta-H elimination, while for 3 it is beta-CH3 elimination. These experiments unambiguously rule out propylene C-H activation processes as an important chain transfer pathway. Complex 9 is highly active for the catalytic dimerization of propylene (N-t = 0.25 s(-1) at 20 degrees C) to form a mixture of 2-methyl-1-pentene and 2-methyl-2-pentene.