1,3-Dioxa-[3]ferrocenophane

Multistimuli-Responsive [3]Dioxaphosphaferrocenophanes with Orthogonal Switches

Novel multistimuli‐responsive phosphine ligands comprising a redox‐active [3]dioxaphosphaferrocenophane backbone and a P‐bound imidazolin‐2‐ylidenamino entity that allows switching by protonation are reported. Investigation of the corresponding metal complexes and their redox behaviour are reported and show the sensitivity of the system towards protonation and metal coordination. The experimental findings are supported by DFT calculations. Protonation and oxidation events are applied in Rh‐catalysed hydrosilylations and demonstrate a remarkable influence on reactivity and/or selectivity.

Redox-responsive phosphonite gold complexes in hydroamination catalysis

Very high activities were observed in the redox-induced hydroamination of alkynes by employing a redox-active gold(i) complex featuring an electron-deficient, terphenyl-substituted phosphonite-based ligand. The hydroamination proceeds roughly two-fold faster with the in situ oxidized catalysts than with their reduced form.

Ferrocene-dithiolene hybrids: control of strong donor-acceptor electronic communication to reverse the charge transfer direction

We prepared a novel class of ferrocene-dithiolene hybrid molecules, FcS4dt(Me)2 and FcS4dt[Pt((t)Bu2bpy)] (where FcS4dt indicates 2-(1,3-dithia[3]ferrocenophane-2-ylidene)-1,3-dithiole-4,5-dithiolate and (t)Bu2bpy indicates 4,4'-di-tert-butyl-2,2'-bipyridine), in which the ferrocene moiety was bound to the planar conjugated dithiolene skeleton via two sulfur atoms such that the cyclopentadienyl rings were perpendicular to the dithiolene backbone. The physical properties and electronic structures of the complexes and their oxidized species [FcS4dt(Me)2](•+) and [FcS4dt[Pt((t)Bu2bpy)]](•+) were investigated by means of single-crystal X-ray diffraction (XRD) analysis, cyclic voltammetry, electron paramagnetic resonance (EPR), and UV-vis near infrared (UV-vis-NIR) spectroscopy. The electron density distributions of the highest occupied molecular orbitals (HOMOs) of FcS4dt(Me)2 and FcS4dt[Pt((t)Bu2bpy)] differed remarkably in that the HOMO of the former was ferrocene-based whereas that of the latter was dithiolene-based. The differences in the HOMO distributions originated from the energy level of the dithiolene-based π-orbital in each of the complexes, which was controlled by changing R in FcS4dt(R)2 (R = Me for FcS4dt(Me)2; 2R = Pt((t)Bu2bpy) for FcS4dt[Pt((t)Bu2bpy)]). We succeeded in analyzing the crystal structure of [FcS4dt[Pt((t)Bu2bpy)]](F4TCNQ)·C6H14·CH2Cl2 (where F4TCNQ indicates 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane), which provided a rare example of the crystal structure of a [Pt(diimine)(dithiolate)](•+) ion-based complex. A comparison of the bond lengths in FcS4dt[Pt((t)Bu2bpy)] and [FcS4dt[Pt((t)Bu2bpy)]](•+) suggested that the latter complex displayed a conjugated dithiolene-based π-radical character. These considerations agreed well with the electronic structures calculated using density functional theory (DFT) and time-dependent(TD)-DFT methods. Significant electronic communication between the ferrocene and dithiolene moieties was detected for both [FcS4dt(Me)2](•+) and [FcS4dt[Pt((t)Bu2bpy)]](•+) in the appearance of an intramolecular charge transfer band, which was hardly observed for previously reported ferrocene-dithiolene hybrid molecules. The charge transfer direction was reversed between the two cations. The electron coupling parameter HAB and the potential energy curves of the oxidized complexes were estimated based on the classical two-state Marcus-Hush theory. These results suggest that FcS4dt-based metalladithiolenes can exhibit controllable electronic structures expressed as double-minimum potential energy curves.

Coordination chemistry with phosphine and phosphine oxide-substituted hydroxyferrocenes

New unsymmetrical hydroxyferrocenes were synthesised from dibromoferrocene. The oxygen heteroatom was introduced via lithiation and quenching with bis-trimethylsilylperoxide followed by hydrolysis to unmask the hydroxyl functionality. The coordination chemistry of 1'-(diphenylphosphino)-1-hydroxyferrocene 2 was explored with palladium and rhodium precursors. A dinuclear palladium methyl complex with bridging ferrocenyloxo groups was obtained from the reaction between 2 and (cyclooctadiene)methylchloropalladium(II). With tetracarbonyldichlorodirhodium(I), two complexes were isolated. The major product was a bis ligand cis phosphine ligated complex with one ligand bound in a chelating mode and one with a pendant hydroxyl group. A minor product was crystallographically characterised as a dinuclear ferrocenyloxo-bridged rhodium carbonyl complex. The coordination chemistry of 2 and the corresponding phosphine oxide 3 was examined with group 4 metals and the resulting complexes examined as ethylene polymerisation catalysts. The ligands were found to bind in either a chelating fashion or with pendant phosphine donors. In all cases, low to moderately active ethylene polymerisation catalysts were found. The catalysts were very unstable and catalyst residues were observed in the isolated polymer indicating a short catalyst lifetime.