Anodic Mechanism of 1,1′‐Bis(diphenylphosphino)ferrocenedicarbonylnickel Determined by Low‐Temperature Spectroelectrochemistry

Abstract

[Ni(CO)2(dppf)] [1] {dppf = 1,1′‐bis(diphenylphosphino)ferrocene} was made by reductive carbonylation of [NiCl2(dppf)] with [Fe(CO)5], similar to our recent report in Organometallics, 2019, 38, 586–592. Complex [1] showed two oxidation waves in the cyclic voltammogram. UV/Vis‐NIR spectroelectrochemistry (SEC) and IR SEC at –30 °C as well as computational support by means of DFT was used to assign the oxidation state of both metal atoms after oxidation. The monocation [1]+ showed a strong NIR absorption band which was described as an IVCT [NiI→FeII] and inverse IVCT (iIVCT) or hole transfer [FeII→NiI] based on time dependence DFT (TD‐DFT). The IR SEC spectrum of [1]+ showed multiple bands associated with two similar configurations, one which had the spin delocalized over both metal atoms and a second configuration where the spin is primarily Ni localized. The second oxidation to [1]2+ occurred at the Ni atom and resulted in release of a CO ligand followed by the formation of dimeric complex determined by low temperature IR SEC.

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0)

“…A sample of [Ni­(dppe) 2 ] ( 12 ) was prepared and exposed to alkyl halides (dppe = 1,2-bis­(diphenylphosphino)­ethane); this complex is known to be unreactive toward a range of species found in typical cross-coupling reactions but is capable of undergoing outer-sphere electron transfer . The dppe ligand has similar electronic properties to dppf, as judged from the IR spectra of [Ni­(CO) 2 (dppf)] ( ν CO (DCM) = 2001, 1939 cm –1 ) and [Ni­(CO) 2 (dppe)] ( ν CO (CHCl 3 ) = 2006, 1945 cm –1 ) . [Ni­(dppe) 2 ] ( 12 ) does not undergo reaction with alkyl halides at all.…”

Unexpected Nickel Complex Speciation Unlocks Alternative Pathways for the Reactions of Alkyl Halides with dppf-Nickel(0)

“…A sample of [Ni(dppe)2] (12) was prepared [27] and exposed to alkyl halides (dppe = 1,2bis(diphenylphosphino)ethane); this complex is known to be unreactive towards a range of species found in typical crosscoupling reactions [19] but should be capable of undergoing outersphere electron transfer. The dppe ligand has similar electronic properties to dppf, as judged from IR spectra of [Ni(CO)2(dppf)] (νCO (DCM) = 2001, 1939 cm -1 ) [28] and [Ni(CO)2(dppe)] (νCO (CHCl3) = 2006, 1945 cm -1 ). [29] [Ni(dppe)2] 12 does not undergo reaction with alkyl halides at all, indicating that an open site is necessary for this reaction, and ruling out an outer sphere electron transfer mechanism.…”

Biomimics of [FeFe]-hydrogenases incorporating redox-active ligands: synthesis, redox properties and spectroelectrochemistry of diiron-dithiolate complexes with ferrocenyl-diphosphines as Fe4S4 surrogates

“…11 However, when coordinated to a metal centre, oxidation usually becomes chemically reversible and is shifted to more positive potentials. 28…”