Synthesis, Characterization, and Electrochemistry of a Series of Iron(II) Complexes Containing Self-Assembled 1,5-Diaza-3,7-diphosphabicyclo[3.3.1]nonane Ligands

Abstract

The reaction between PPh(CH(2)OH)(2), iron(II) sulfate, ammonium sulfate, and formaldehyde in aqueous solution gives the iron(II) complex [Fe(kappa(2)-O(2)SO(2))L(2)] (1), where L is the bidentate phosphine ligand 3,7-diphenyl-1,5-diaza-3,7-diphosphabicyclo[3.3.1]nonane. During the course of the reaction, the ligand L self-assembles on the metal center. The reaction between PPh(CH(2)OH)(2), iron(II) chloride, ammonium chloride, and formaldehyde under similar conditions gives cis-[FeCl(2)L(2)] (cis-2). The complex cis-2 is converted into trans-2 in Et(2)O, whereas in water it is converted into cis-[Fe(OH(2))(2)L(2)](2+), though both of these interconversions are reversible. The chloro ligands in cis-2 are readily displaced by reaction with thiocyanate, azide, and carbonate to give cis- and trans-[Fe(NCS)(2)L(2)] (cis- and trans-3), cis- and trans-[Fe(N(3))(2)L(2)] (cis- and trans-4), and [Fe(kappa(2)-O(2)CO)L(2)] (5), respectively. The complex cis-2 reacts with CO in water to give trans-[FeCl(CO)L(2)]Cl (trans-6), whereas trans-2 reacts with CO in diethyl ether to give cis-[FeCl(CO)L(2)]Cl (cis-6), though cis-6 isomerizes in water to form trans-6. The reaction of cis-2 with sodium borohydride gives the hydride chloride complex trans-[FeCl(H)L(2)] (7). Electrochemical studies have been undertaken on complexes 1, cis-2, and 7. These reveal reversible oxidations for cis-2 and 7, with the latter giving rise to an unusual 17-electron iron(III) hydride chloride complex. Crystal structures have been obtained for 1, trans-2, trans-3, 5, and 7.

Synthesis and Structure of Iron (II) Complexes of Functionalized 1,5-Diaza-3,7-Diphosphacyclooctanes

“…Molecule 11b appeared to be a bis-ligand monocationic complex of the composition [L 2 Fe(BF 4 )] + BF 4 − , where two fluorine atoms of one of the tetrafluoroborate unit were included in the coordination sphere of the iron ion and occupied two pseudo-equatorial positions (Figure 2b). A similar coordination mode was described for the complexes of bis-and tetrakis-phosphines with iron (II) sulfate and carbonate [30,31], but for the low-coordinating tetrafluoroborate anion, it was unexpected. The molecule 11b in this crystal was on the special position on the two-fold axis 2 (atoms Fe and B lied on the two-fold axis 2).…”

“…In ESI or MALDI mass-spectra of all these complexes, the peaks of ions containing two diazadiphosphacyclooctane moieties, iron ion, and in some cases, various co-ligands were observed. 31 P-NMR spectra of complexes 6-9 showed two complex second-order multiplets of the equal intensity in the ranges 25.6-34.7 and 34.2-41.2 ppm. This spectral pattern is typical for AA'BB' spin system of cis-iron (II) complexes with the strongly distorted octahedral configuration of the central ion-containing two P,P-chelating diphosphine ligands and two acetonitrile co-ligands, which occupy formally equatorial positions [21], so it indicated the analogous cis-structures of the complexes 6-9 (Scheme 1).…”

“…Ligand 3 readily reacted with iron (II) tetrafluoroborate hexahydrate [Fe(H2O)6](BF4)2 in acetone to give a mixture of two bis-ligand cis-complexes 11a and 11b (Scheme 1). In the 31 Both diazadiphosphacyclooctane ligands (N(1)P(3)N(5)P (7) and N(1B)P(3B)N(5B)P(7B)) had chair-boat conformations, so the substituents on nitrogen atoms in the chair and boat parts of the heterocycles were in an essentially different environment. That explained the nonequivalence of these substituents in NMR spectra.…”

Pyridyl Containing 1,5-Diaza-3,7-diphosphacyclooctanes as Bridging Ligands for Dinuclear Copper(I) Complexes

“…In gold(I) complexes with a P‐coordination of a ligand the close disposition of pyridyl groups to the central metal atoms is responsible for the luminescent properties , . Commonly 1,5‐diaza‐3,7‐diphosphacyclooctanes serve as P,P‐chelate ligands in the Ni, Pt, Pd, Co, and Fe transition metals complexes . Recent works illustrate a wide utilization of Ni II complexes of 1,5‐diaza‐3,7‐diphoshpacycloctanes as catalysts in the electrochemical hydrogen production , .…”

Reactions of coordinated hydroxymethylphosphines with NH-functional amines: the phosphorus lone pair is crucial for the phosphorus Mannich reaction

“…42 Such self-assembly has been further developed by Burrows and colleagues. 43, 44 The selfassembled molecules are presumed to be generated by a series of phosphorus Mannich reactions between hydroxymethylphosphines and ammonia. We hypothesized that if this process could be better understood and harnessed then it could lead to a variety of easily synthesized polyphosphine ligands and their complexes, including macrocyclic phosphine complexes (eqn (3)).…”