A comparative study of biradicaloids as ligands in iron tetracarbonyl complexes

Abstract

Iron tetracarbonyl complexes of the biradicaloids [P(μ-N-Ter)]2 (Ter: 2,6-dimesitylphenyl) and [P(μ-C-IPr)]2 (IPr: 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene) have been isolated. These two biradicaloids act here as σdonating, monodentate ligands. Experimental and theoretical data suggest that they can best be described in their zwitterionic resonance structures in these complexes. Single-crystal XRD and IR spectroscopy reveal that the donor strength of both is comparable to N-heterocyclic carbenes (NHCs). [P(μ-C-IPr)]2 is a slightly stronger donor than [P(μ-N-Ter)]2. Furthermore, an improved, scalable, and facile synthesis of both biradicaloids is presented.

Phosphonium‐substituted Diphosphaindenylide (PPI): Exploration of Biradical Character and Ligand Properties

“…Such TMS-substituted ylides have recently been used by the Grützmacher group and their further utilization for the preparation of P-heterocycles will be reported soon. [21] The bis(chlorophosphane) 3 was isolated in 91 % yield as the diasteriomerically pure meso isomer (vide infra). In the 31 P{ 1 H} NMR spectrum of 3 in THF-d 8 , the endocyclic PCl moieties give rise to a doublet at 133.9 ppm, while the P(p-tol) 3 group appears as a triplet at 26.2 ppm ( 2 J PP = 120 Hz).…”

“…First, treatment of 1 with the TMS‐substituted ylide 2 in 1,2‐difluorobenzene, DFB, affords the bis(chlorophosphane) 3 . Such TMS‐substituted ylides have recently been used by the Grützmacher group and their further utilization for the preparation of P‐heterocycles will be reported soon [21] . The bis(chlorophosphane) 3 was isolated in 91 % yield as the diasteriomerically pure meso isomer ( vide infra ).…”

Heteroatom-Based Diradical(oid)s

“… This heterocycle in turn could represent a singlet diradicaloid as well. Schulz and Grützmacher also comparatively studied the behaviors of C 2 P 2 and N 2 P 2 with iron carbonyls …”

“…Schulz and Gruẗzmacher also comparatively studied the behaviors of C 2 P 2 and N 2 P 2 with iron carbonyls. 428 The heavier homologue to the carbene-stabilized dicarbondiphosphide, dicarbondiarsenide [As(μ-C{NHC})] 2 (138), 429 was prepared by Ghadwal via the method starting from the Nheterocyclic olefin. 430 Interestingly, K[sec-Bu 3 BH] was used as reducing agent, and [HAs(μ-C{NHC})] 2 is a likely transient intermediate that then eliminated H 2 to yield 138.…”