Activation of N-2 by (silox)(3)Ta (1, silox = (Bu3SiO)-Bu-t) to afford (silox)(3)Ta=N-N=Ta(silox)(3) (1(2)-N-2) does not occur despite Delta G degrees(cald) = -55.6 kcal/mol because of constraints of orbital symmetry, prompting efforts at an independent synthesis that included a study of REH2 activation (E = N, P, As). Oxidative addition of REH2 to 1 afforded (silox)(3)HTaEHR (2-NHR, R = H, Me, Bu-n, C6H4-p-X (X = H, Me, NMe2); 2-PHR, R = H, Ph; 2-AsHR, R = H, Ph), which underwent 1,2-H-2-elimination to form (silox)(3)Ta=NR (1=NR; R = H, Me, Bu-n, C6H4-p-X (X = H (X-ray), Me, NMe2, CF3)), (silox)(3)Ta=PR (1=PR; R = H, Ph), and (silox)(3)Ta=AsR (1=AsR; R = H, Ph). Kinetics revealed NH bond-breaking as critical, and As > N > P rates for (silox)(3)HTaEHPh (2-EHPh) were attributed to (1) Delta G degrees(calc)(N) < Delta G degrees(calc)(P)similar to Delta G degrees(calc)(As); (2) similar fractional reaction coordinates (RCs), but with RC shorter for N < P similar to As; and (3) stronger TaE bonds for N> P similar to As. Calculations of the pnictidenes aided interpretation of UV-vis spectra. Addition of H2NNH2 or H2N-N((NC2H3Me)-N-c) to 1 afforded 1=NH, obviating these routes to 1(2)-N-2, and formation of (silox)(3)MeTaNHNH2 (4-NHNH2) and (silox)(3)MeTaNH(-(NCHMeCH2)-N-c) (4-NH(azir)) occurred upon exposure to (silox)(3)Ta=CH2 (1=CH2). Thermolyses of 4-NHNH2 and 4-NH(azir) yielded [(silox)(2)TaMe](mu-N alpha HN beta)(mu-N gamma HN delta H)(Ta(silox)(2)] (5) and [(silox)(3)MeTa](mu-eta(2)-N,N:eta(1)-C-NHNHCH2CH2CH2)[Ta(kappa-O,C-(OSi Bu2CMe2CH2)-Bu-1)(silox)(2)] (7, X-ray), respectively. (silox)(3)Ta=CPPh3 (1=CPPh3, X-ray) was a byproduct from Ph3PCH2 treatment of 1 to give 1=CH2. Addition of Na(silox) to [(THF)(2)Cl3Ta](2)(mu-N-2) led to [(silox)(2)ClTa](mu-N-2) (8-Cl), and via subsequent methylation, [(silox)(2)MeTa](2)(mu-N-2) (8-Me); both dimers were thermally stable. Orbital symmetry requirements for N-2 capture by 1 and pertinent calculations are given.