Synthesis and Characterization of Pentaphosphino Zero-Valent Iron Complexes and Their Corresponding Iron(II)-Chloride and -Hydride Complexes

A pentaphosphino iron(II)-chloride species [(SiP3)-Si-t(dmpm)FeCl][Cl] (1-Cl) ((SiP3)-Si-t = (BuSi)-Bu-t(CH2PMe2)(3), dmpm = Me2PCH2PMe2) was prepared from [((SiP3Fe)-Si-t)(2)(mu-Cl)(3)][Cl] and dmpm. This species was reduced to give the corresponding iron(0) complex, (SiP3)-Si-t(dmpm)Fe (3), in near quantitative yield. Analogous complexes [SiP3(dmpe)FeCl][Cl] (2-Cl) and SiP3(dmpe)Fe (4) (SiP3 = MeSi(CH2PMe2)(3), dmpe = Me2PCH2CH2PMe2) were prepared in the same manner as 1 and 3 but with lower yields because of competitive ligand rearrangement reactions that gave byproduct of trans-(dmpe)(2)FeCl2 and (dmpe)(5)Fe-2 (5). [(SiP3)-Si-t(dmpm)FeH][A] (6) was prepared from the reaction of 3 with weak acids (HA), and the pK(a) of 6 was established to be approximately 25. Attempts to prepare pentaphosphino-iron(0) complexes of the form SiP3(PR3)(2)Fe using PPh3 and PMe3 resulted in cyclometalated products, SiP3FeH((o-C6H4)PPh2) (7) and SiP3FeH(CH2PMe2) (8). Synthesis and characterization of these complexes, including crystal structures of 1-5, are reported.