Low-temperature in situ Fourier transform infrared and UV-vis Measurements show that trimethyl-phosphine (PMe3) reacts with microporous layers of Fe-II(TTP)(NO) (TTP = meso-tetra-p-tolylporphyrinato dianion; NO = nitric oxide) to form the previously unknown six-coordinate complex Fe-II(TTP)(PMe3)(NO). Upon warming this compound to room temperature in the presence of excess phosphine, The NO ligand is completely replaced by phosphite, resulting in formation of the bis(trimethylphosphine) complex Fe-II(TTP)(PMe3)(2). Simultaneously, the NO released oxidizes free PMe3 to the corresponding,phosphine oxide (OPMe3) with concomitant formation of nitrous oxide (N2O).