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

A pentaphosphino iron(II)-chloride species [tSiP3(dmpm)FeCl][Cl] (1-Cl) (tSiP3 = tBuSi(CH2PMe2)3, dmpm = Me2PCH2PMe2) was prepared from [(tSiP3Fe)2(μ-Cl)3][Cl] and dmpm. This species was reduced to give the corresponding iron(0) complex, tSiP3(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)2FeCl2 and (dmpe)5Fe2 (5). [tSiP3(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)2Fe 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.