title: Synthesis and coordination chemistry of (PNEt2)2-bridged [2]ferrocenophanes.
abstract: The trivalent phosphorus-bridged [2]ferrocenophane complex 2 having NEt2groups on the respective phosphorus centers was prepared, and its reactions as a diphosphine ligand were examined for iron and chromium carbonyl complexes. Both the phosphorus centers of 2 coordinated to Fe(CO)4fragments to form (μ-2)-[Fe(CO)4]2, while the bulkier Cr(CO)5fragment formed only a monochromium complex [Cr(κ1-2)(CO)5]. Dissociation of CO from [Cr(κ1-2)(CO)5] changed the coordination mode of 2 from κ1to κ2to form [Cr(κ2-2)(CO)4] having a three-membered ring. A similar approach for the monoiron complex [Fe(κ1-2)(CO)4] did not afford a κ2complex but instead an Et2NPC(O)PNEt2-bridged [3]ferrocenophane complex in which a CO fragment was inserted into the P-P bond of 2 and both the phosphorus centers coordinated to Fe(CO)3as a chelate diphosphine. The reaction of this product with an Fe(CO)4fragment gave μ-{Fe(C5H4PNEt2)2-κP:κP}-[Fe(CO)3]2(8), in which one terminal CO and the CO group between the two phosphorus atoms were lost to give an [FeFe]hydrogenase mimic having a bis(phosphido)ferrocene chelate as a bridging unit. The two NEt2groups of the bridging unit were expected to work as protonation sites. The protonated NEt2groups contributed to an improvement in the reduction potential of the complex to a less negative area, i.e., -2.3 V for the free 8 to -1.0 V for the diprotonated 8. The catalytic reduction of the proton, however, required a more negative potential of -2.0 V, which is almost comparable to that of the phosphido-bridged [FeFe]hydrogenase model complex having no protonation site.
authors.affiliation: Department of Chemistry, Graduate School of Science, Hiroshima University, Kagamiyama 1-3-1, Higashi-hiroshima 739-8526, Japan. mizuta@sci.hiroshima-u.ac.jp.
authors.forename: Yuki
authors.initials: Y
authors.lastname: Maeno
authors.forename: Yuko
authors.initials: Y
authors.lastname: Ishizu
authors.forename: Kazuyuki
authors.initials: K
authors.lastname: Kubo
authors.forename: Shoko
authors.initials: S
authors.lastname: Kume
authors.forename: Tsutomu
authors.initials: T
authors.lastname: Mizuta