An Isolable Diphosphene Radical Cation Stabilized by Three-Center Three-Electron π-Bonding with Chromium: End-On versus Side-On Coordination

Ligand Effects on the Electronic Structure of Heteroleptic Antimony-Centered Radicals

We report on the structures of three unprecedented heteroleptic Sb-centered radicals [L(Cl)Ga](R)Sb^. (2-R, R=B[N(Dip)CH]₂ 2-B, 2,6-Mes₂ C₆ H₃ 2-C, N(SiMe₃ )Dip 2-N) stabilized by one electropositive metal fragment [L(Cl)Ga] (L=HC[C(Me)N(Dip)]₂ , Dip=2,6-i-Pr₂ C₆ H₃ ) and one bulky B- (2-B), C- (2-C), or N-based (2-N) substituent. Compounds 2-R are predominantly metal-centered radicals. Their electronic properties are largely influenced by the electronic nature of the ligands R, and significant delocalization of unpaired-spin density onto the ligands was observed in 2-B and 2-N. Cyclic voltammetry (CV) studies showed that 2-B undergoes a quasi-reversible one-electron reduction, which was confirmed by the synthesis of [K([2.2.2]crypt)][L(Cl)GaSbB[N(Dip)CH]₂ ] ([K([2.2.2]crypt)][2-B]) containing the stibanyl anion [2-B]^- , which was shown to possess significant Sb-B multiple-bonding character.

Free Radical Reactivity of a Phosphaalkene Explored Through Studies of Radical Isotopologues

Muonium (Mu), an H atom analogue, is employed to probe the addition of free radicals to the P=C bond of a phosphaalkene. Specifically, two unprecedented muoniated free radicals, MesP^. -CMu(Me)₂ (1 a, minor product) and MesPMu-C^. Me₂ (1 b, major product), were detected by muon spin spectroscopy (μSR) when a solution of MesP=CMe₂ (1: Mes=2,4,6-trimethylphenyl) was exposed to a beam of positive muons (μ⁺ ). The μ⁺ serves as a source of Mu (that is, Mu=μ⁺ +e^- ). To confirm the identity of the major product 1 b, its spectral features were compared to its isotopologue, MesPH-C^. (Me)CH₂ Mu (2 a). Conveniently, 2 a is the sole product of the reaction of MesPH(CMe=CH₂ ) (2) with Mu. For all observed radicals, muon, proton, and phosphorus hyperfine coupling constants were determined by μSR and compared to DFT-calculated values.

Facile Cleavage of the P=P Double Bond in Vinyl-Substituted Diphosphenes

The reactions of the cyclic alkyl amino carbene (CAAC) 1 with phosphaalkynes generate the kinetically unstable CAAC-derived phosphirenes 4 and 5, which undergo rearrangement/dimerization reactions to give the vinyl-substituted diphosphenes 2, 3, and 6. The P=P double bond scission of 2 or 3 is unprecedentedly effected by S₈ , [AuCl(tht)], or MeOTf at room temperature, which affords a dithiophosphorane 7, a phosphepine Au complex 8, or phosphepinium cations 9 and 10, respectively. The cationic species feature little homoaromaticity while representing the first examples of the phosphorus-containing analogue of the tropylium ion.