Nitrogen-ligated iron complexes:: Photolytic approach to the FeN+ moiety

The synthesis of (PNP)FeCl, (PNP)Fe[NH(xylyl)], and (PNP)FeN3 are reported(PNP = (tBu(2)PCH(2)SiMe(2))(2)N-). While the azide is thermally stable, it is photosensitive to lose N-2 and form [(PNP=N)Fe](2), in which the nitride ligand has formed a double bond to one phosphorus, and this N bridges to a second iron to form a 2-fold symmetric dimer. The reaction energy to form the (undetected) monomeric [eta(3)-(Bu2PCH2SiMe2NSiMe2CH2PtBU2)-Bu-t=N]Fe is - 15.9 kcal/mol, so this P-III -> P-V oxidation is favorable. The eta(2) version of this same species is less stable by 23.7 kcal/mol, which shows that the loss of one P -> Fe bond is caused by dimerization, and therefore, it does not precede and cause dimerization. A comparison is made to Ru analogs.