Phosphite Bearing [(μ-ADT)^RFe₂(CO)₆] (ADT = Azadithiolate) Moieties: A Tool for the Building of Multimetallic [FeFe]-Hydrogenase Mimics

Abstract

A new phosphite ligand having three [(μ-ADT) R Fe 2 (CO) 6 ] (R= p-HOC 6 H 4 ) moieties (2) has been prepared in good yield by the reaction of complex [(μ-ADT) R Fe 2 (CO) 6 ] (R= p-HOC 6 H 4 ) 1a with PCl 3 . Coordination of this phosphite to [PdCl 2 (MeCN) 2 ] or [PtCl 2 (DMSO) 2 ] forms heterometallic square planar complexes 5 (C 84 H 48 Cl 2 Fe 12 N 6 O 42 P 2 MS 12) (M = Pt, Pd) in e x c e l l e n t y i e l d s . T h r e e -l e g g e d p i a n o s t o o l c o m p l e x e s 6 (C 52 H 39 Cl 2 Fe 6 N 3 O 21 PMS 6 ) (M = Rh, Ir) were obtained by the reaction of phosphite 2 with [MCl 2 Cp*] 2 (M = Rh, Ir) in good yields. The formation of complexes 5 and 6 demonstrates the versatility of this new ligand for forming different heteropolymetallic complexes under mild reaction conditions.Moreover, the open-chain derivatives [(μ-ADT) R Fe 2 (CO) 6 ] (R= HOCH 2 CH 2 , o-HOC 6 H 4 ) (1b and 1c, respectively) form cyclic complexes 4 by spontaneous intramolecular CO substitution by the P atom in one of the three [FeFe] fragments. The electrocatalytic behavior of complexes 2 and 4 upon the addition of AcOH is similar to that of related [(μ-ADT)Fe 2 (CO) 6 ] derivatives. The successive additions of AcOH cause an increase in the current intensity in the wave at about −1.80 V for heteropolymetallic complexes 5 and 6. However, the appearance of a new wave around −1.40 V in complexes 5 points to an acid-promoted side reaction in the electrochemical process.

A cross-metathesis approach for polymetallic [FeFe]-hydrogenase mimics

“…16 In parallel, the use of easily available phosphites having three [FeFe]-moieties allowed the coordination of these polymetallic ligands to different square-planar and piano-stool complexes. 17 Moreover, the synthesis of heterometallic [FeFe]-mimics was carried out using tetranuclear complexes, in which the two [FeFe]-moieties were tethered by a bipyridine moiety suitable to complex different metals. 18 The electronic and electrocatalytic properties of these compounds were highly influenced by the presence of additional transition metal complexes either enhancing the electronic communication between the [FeFe] centers or inhibiting it, depending on the metal.…”