Alkynyl-Phosphine Substituted Fe2S2 Clusters: Synthesis, Structure and Spectroelectrochemical Characterization of a Cluster with a Class III Mixed-Valence [FeFe]3+ Core

Abstract

Phosphinoalkynes P(C≡CC 6 H 4 Me-4)Ph 2 (1) and P(C≡CC 6 H 4 C≡CC 6 H 4 Me-4)Ph 2 (2) have been prepared from CuI catalysed reactions of the corresponding 1-alkyne and PClPh 2. The trimethylamine-N-oxide promoted reaction of PPh 3 , 1 or 2 with [Fe 2 (µ-pdt)(CO) 6 ] (pdt = propanedithiolate) affords derivatives [Fe 2 (µ-pdt)(CO) 5 {PRPh 2 }] [R = Ph (3), C≡CC 6 H 4 Me (5), C≡CC 6 H 4 C≡CC 6 H 4 Me (6)] or, at elevated temperatures, [Fe 2 (µpdt)(CO) 4 (PPh 3 ) 2 ] (4). The cyclic voltammograms of compounds 3 and 4 feature almost fully reversible one-electron oxidation processes and an irreversible reduction, whilst the electrochemical response of the alkynyl phosphine substituted complexes 5 and 6 is irreversible for both oxidation and reduction. IR spectroelectrochemical studies of 4 are consistent with an oxidation processes leading to a delocalized or (Class III) mixed valence [FeFe] 3+ core in which the iron centers have an average oxidation state of 1.5.The molecular structures of the alkynyl phosphine substituted clusters 5 and 6 are also reported.