1450820-40-2Relevant academic research and scientific papers
Redox-switchable ring-closing metathesis: Catalyst design, synthesis, and study
Arumugam, Kuppuswamy,Varnado Jr., C. Daniel,Sproules, Stephen,Lynch, Vincent M.,Bielawski, Christopher W.
, p. 10866 - 10875 (2013)
High yielding syntheses of 1-(ferrocenylmethyl)-3-mesitylimidazolium iodide (1) and 1-(ferrocenylmethyl)-3-mesitylimidazol-2-ylidene (2) were developed. Complexation of 2 to [{Ir(cod)Cl}2] (cod=cis,cis-1,5-cyclooctadiene) or [Ru(PCy3)Cl2(=CH-o-O-iPrC6H4)] (Cy=cyclohexyl) afforded 3 ([Ir(2)(cod)Cl]) and 5 ([Ru(2)Cl2(=CH-o-O- iPrC6H4)]), respectively. Complex 4 ([Ir(2)(CO) 2Cl]) was obtained by bubbling carbon monoxide through a solution of 3 in CH2Cl2. Spectroelectrochemical IR analysis of 4 revealed that the oxidation of the ferrocene moiety in 2 significantly reduced the electron-donating ability of the N-heterocyclic carbene ligand (ΔTEP=9 cm-1; TEP=Tolman electronic parameter). The oxidation of 5 with [Fe(η5-C5H4COMe)Cp][BF4] as well as the subsequent reduction of the corresponding product [5][BF4] with decamethylferrocene (Fc*) each proceeded in greater than 95 % yield. Moessbauer, UV/Vis and EPR spectroscopy analysis confirmed that [5][BF 4] contained a ferrocenium species, indicating that the iron center was selectively oxidized over the ruthenium center. Complexes 5 and [5][BF 4] were found to catalyze the ring-closing metathesis (RCM) of diethyl diallylmalonate with observed pseudo-first-order rate constants (k obs) of 3.1×10-4 and 1.2×10-5 s-1, respectively. By adding suitable oxidants or reductants over the course of a RCM reaction, complex 5 was switched between different states of catalytic activity. A second-generation N-heterocyclic carbene that featured a 1',2',3',4',5′- pentamethylferrocenyl moiety (10) was also prepared and metal complexes containing this ligand were found to undergo iron-centered oxidations at lower potentials than analogous complexes supported by 2 (0.30-0.36 V vs. 0.56-0.62 V, respectively). Redox switching experiments using [Ru(10)Cl2(=CH-o-O-iPrC6H4)] revealed that greater than 94 % of the initial catalytic activity was restored after an oxidation-reduction cycle.
