High Spin Cobalt Complexes Supported by a Trigonal Tris(Phosphinimide) Ligand

Abstract

Terminal, π-basic moieties occupy a prominent position in the stabilization of unusual or reactive inorganic species. The electron-releasing, π-basic properties of phosphinimides (PN) have been employed to stabilize electron-deficient early transition metals and lanthanides. In principle, a ligand field comprised of terminal PN groups should enable access to high-valent states of late first row transition metals. Herein, we report a new class of multidentate phosphinimide ligands to logically explore this hypothesis. Access to such ligands is made possible by a new procedure for the electrophilic amination of rigid, sterically encumbering, multidentate phosphines. Such frameworks facilitate terminal PN coordination to cobalt as demonstrated by the synthesis of a trinuclear CoII 3 complex and a homoleptic, three-coordinate CoIII complex. Interestingly, the CoIII complex exhibits an exceedingly rare S = 2 ground state. Combined XRD, magnetic susceptibility, and DFT studies highlight that terminally bound PNs engage in strong dπ–pπ interactions that present a weak ligand field appropriate to stabilize high-spin states of late transition metals.

Ligand Control of Oxidation and Crystallographic Disorder in the Isolation of Hexavalent Uranium Mono-Oxo Complexes

“…The ITI is a thermodynamic ground-state phenomenon which results in the observable shortening and strengthening of a metal–ligand bond trans to an MLMB or other strong donor relative to those of identical ligands bound cis to it. , In effect, ITI complexes are an invaluable lens with which to examine electrostatic interactions and orbital participation in covalent bonding in high-valent actinides. , Targeting Np 6+/7+ and Pu 6+/7+ complexes facilitates the spectroscopic, crystallographic, and theoretical investigation of the role of the actinide 5f, 6d, 7s, and 7p valence orbitals (and the pseudo-core 6p) in determining ground-state geometry and electronic structure. ,,, Preparation of these complexes is particularly challenging, as the An 4+/5+ , An 5+/6+ , and An 4+/6+ oxidation couples become less accessible as the series is traversed, enforcing a striking prevalence of the tetravalent oxidation state in molecular Np and Pu species. ,,,, The pursuit of Np and Pu complexes which exhibit an ITI is a technical challenge that not only demands strict handling protocols but also requires new ligand architectures, which enable rigorous spectroscopic and crystallographic characterization of these species. The homoleptic imidophosphorane ligand field has shown excellent utility for stabilizing and characterizing rare high-valent f-element species. ,− These bulky, weak field, anionic ligands of the type [NP­(NR 2 ) 3 ] 1– are 1σ, 2π donors that capitalize on the electron-donating nature of the dialkylamino groups to stabilize the zwitterionic N 2– –P + …”

Investigating Metal–Metal Bond Polarization in a Heteroleptic Tris-Ylide Diiron System

“…All known C 3 -symmetric diiron systems have N- or P-atom donors coordinated to the iron centers, making the carbon-based ligands in compounds 3 and [4-OTf] 0 unique and worth further investigation. Not only are C-based donors rare in diiron complexes, but even mononuclear iron complexes coordinated by three alkyl groups are scarce, with only a handful of known examples. − Notably, Smith and co-workers recently described several iron complexes coordinated by bis­(ylide)­diphenylborate ligands, which feature chelation of two ylides per chelate, and Neidig and co-workers have provided recent examples of homoleptic 3- and 4-coordinate iron alkyl complexes. , Both the ylide and phosphinimine ligand sets in 3 and [4-OTf] 0 are expected to serve as strong σ-donors. , Related ylides have actually been shown to be even stronger donors than both NHCs and phosphinimines. This was demonstrated by César and co-workers, who synthesized a series of rhodium carbonyl complexes bound by various neutral donors that included a phosphinimine, an NHC, and an ylide.…”

Structure and Reactivity of a High-Spin, Nonheme Iron(III)- Superoxo Complex Supported by Phosphinimide Ligands

“…Dissolution of isolated, polycrystalline (L Ad H)­FeO 2 gives rise to similar spectral features, supporting the notion that equivalent chemical species are generated upon oxygenation of (L Ad H)­Fe either in solution or as polycrystalline material. The magnitude of the extinction coefficients at 335 and 420 nm (∼9000 and 6000 M –1 cm –1 , respectively) are suggestive of LMCT bands stemming from the phosphinimides and/or the O 2 -derived ligand . While the 1 H NMR spectrum of (L Ad H)­Fe consists of multiple sharp, paramagnetically shifted peaks, in situ -generated (L Ad H)­FeO 2 is NMR-silent (Figure S25).…”

“…We have initiated a research program that aims to develop new molecular catalysts for sustainable oxidative processes. Along these lines, we have developed an electron-donating and oxidatively resilient ligand platform featuring anionic phosphinimide donors intended to expand the reaction chemistry of earth-abundant, first-row transition metals . Herein, we show that this ligand enables the synthesis and characterization, including the XRD analysis, of a nonheme iron complex that binds O 2 in a terminal fashion.…”