The catalytic conversion of N-2 to N-(SiMe3)(3) by homogeneous transition metal compounds is a rapidly developing field, yet few mechanistic details have been experimentally elucidated for 3d element catalysts. Herein we show that Fe(PP)(2)(N-2) (PP = R2PCH2CH2PR2; R = Me, 1(Me); R = Et, 1(Et)) are highly effective for the catalytic production of N(SiMe3)(3) from N-2 (using KC8/Me3SiCl), with the yields being the highest reported to date for Fe-based catalysts. We propose that N-2 fixation proceeds via electrophilic N-beta silylation and 1e(-) reduction to form unstable Fe-I(NN-SiMe3) intermediates, which disproportionate to 1(Me/Et) and hydrazido Fe-II[N-N(SiMe3)(2)] species (3(Me/Et)); the latter act as resting states on the catalytic cycle. Subsequent 2e(-) reduction of 3(Me/Et) leads to N-N scission and formation of [N(SiMe3)(2)](-) and putative anionic Fe imido products. These mechanistic results are supported by both experiment and DFT calculations.