Modulating the frontier orbitals of L(X)Ga-substituted diphosphenes [L(X)GaP] 2 (X = Cl, Br) and their facile oxidation to radical cations.
Mahendra Kumar SharmaSonia ChabbraChristoph WölperHanns Micha WeinertEdward J ReijerseAlexander SchneggStephan SchulzPublished in: Chemical science (2022)
Modulating the electronic structures of main group element compounds is crucial to control their chemical reactivity. Herein we report on the synthesis, frontier orbital modulation, and one-electron oxidation of two L(X)Ga-substituted diphosphenes [L(X)GaP] 2 (X = Cl 2a, Br 2b; L = HC[C(Me)N(Ar)] 2 , Ar = 2,6- i- Pr 2 C 6 H 3 ). Photolysis of L(Cl)GaPCO 1 gave [L(Cl)GaP] 2 2a, which reacted with Me 3 SiBr with halide exchange to [L(Br)GaP] 2 2b. Reactions with Me NHC ( Me NHC = 1,3,4,5-tetramethylimidazol-2-ylidene) gave the corresponding carbene-coordinated complexes L(X)GaPP( Me NHC)Ga(X)L (X = Cl 3a, Br 3b). DFT calculations revealed that the carbene coordination modulates the frontier orbitals ( i.e. HOMO/LUMO) of diphosphenes 2a and 2b, thereby affecting the reactivity of 3a and 3b. In marked contrast to diphosphenes 2a and 2b, the cyclic voltammograms (CVs) of the carbene-coordinated complexes each show one reversible redox event at E 1/2 = -0.65 V (3a) and -0.36 V (3b), indicating their one-electron oxidation to the corresponding radical cations as was confirmed by reactions of 3a and 3b with the [FeCp 2 ][B(C 6 F 5 ) 4 ], yielding the radical cations [L(X)GaPP( Me NHC)Ga(X)L]B(C 6 F 5 ) 4 (X = Cl 4a, Br 4b). The unpaired spin in 4a (79%) and 4b (80%) is mainly located at the carbene-uncoordinated phosphorus atoms as was revealed by DFT calculations and furthermore experimentally proven in reactions with n Bu 3 SnH, yielding the diphosphane cations [L(X)GaPHP( Me NHC)Ga(X)L]B(C 6 F 5 ) 4 (X = Cl 5a, Br 5b). Compounds 2-5 were fully characterized by NMR and IR spectroscopy as well as by single crystal X-ray diffraction (sc-XRD), and compounds 4a and 4b were further studied by EPR spectroscopy, while their bonding nature was investigated by DFT calculations.