Redox Communication between Two Diarylamido/Bis(phosphine) (PNP)M Moieties Bridged by Ynediyl Linkers (M = Ni, Pd, Pt)

Abstract

A series of binuclear homo- and heterobimetallic complexes of the general type (PNP)­M–[linker]–M­(PNP) have been prepared (M = Ni, Pd, Pt; PNP = a diarylamido/bis­(phosphine) pincer ligand; −[linker]– = −CC–, −CCCC–, −CCC6H4CC−). Each (PNP)­M site can be oxidized by one electron, and this work reports the investigation of the mixed-valence behavior in terms of the communication between the two redox sites and the degree of the delocalization in the monooxidized cation. The compounds were evaluated using cyclic voltammetry, UV–vis–NIR and EPR spectroscopy, X-ray crystallography, and DFT calculations. The complex with the longest examined linker, (PNP)­Ni–CCC6H4CC–Ni­(PNP) (9Ni), exhibited no discernible communication between the redox sites. The homobimetallic complexes (PNP)­M–CCCC–M­(PNP) (6M) displayed a lower degree of communication in comparison to the −CC– linker analogues (PNP)­M–CC–M­(PNP) (3M). Within each of these two subsets, the relative degree of communication and delocalization was determined to be Pd < Ni ≤ Pt. On the Robin–Day scale, compounds 6M can be assigned class I for M = Pd and class II for M = Ni, Pt. Complex 3Pd also falls into class II, while 3Ni and 3Pt may be viewed as borderline class II/III cases. It is likely that the communication in the Ni systems has the advantage of the smaller size of Ni, resulting in a greater physical proximity of the redox sites, while the 5d metal Pt possesses the greatest ability for orbital interaction with the −CC– linker.

Enabling Valence Delocalization in Iron(III) Macrocyclic Complexes through Ring Unsaturation

“…These fall within the range associated with recent species assigned as either valence-trapped with very strong coupling (Robin-Day class II−III) 65,67,68 or completely valence-delocalized (Robin-Day class III). 67−69 The moderate solvatochromism of 3b 2+ , 39,67,70 and the two separate ν(C�C) bands in the IR spectrum of 3c 2+ preclude a completely valence-delocalized description. 25,53 Therefore, 3b/c 2+ are conservatively assigned as valence-trapped complexes exhibiting moderate (3c 2+ ) to strong (3b 2+ ) coupling (Robin-Day class II, perhaps approaching class II−III).…”

Synthesis of fluorinated aminium cations coupled with carborane anions for use as strong one-electron oxidants

“…We have used this method recently to synthesize WCA salts of ferrocenium. 29 One can view the 0.5Ph(IOAc) 2 /Me 3 SiX/Na[WCA] (X = Cl or OTf) combination as an equivalent of a “deelectronator”, as coined by Krossing et al , 8 analogously to the 0.5Cl 2 /Ag[WCA] or the 0.5Br 2 /Ag[WCA] pair.…”

Synthesis and Structure of a Ferrocenylsilane-Bridged Bisphosphine

“…Organic bisphosphines, i.e., organic molecules that bear two phosphine moieties as coordinating sites, represent an important class of ancillary ligands in transition-metal coordination chemistry and catalysis [1][2][3][4]. Especially transition-metal-based catalysts in synthetic organic chemistry often require specific custom-tailored bisphosphine ligands in order to realize their full catalytic performance [1][2][3][4][5]. Furthermore, bisphosphine ligands can be applied as bridging blocks in metal-organic-frameworks (MOFs) [6][7][8][9].…”