Search

The lithium salt of the anionic SPS pincer ligand composed of a central hypervalent λ4-phosphinine ring bearing two ortho-positioned diphenylphosphine sulfide side arms reacts with [Mn(CO)5Br] to give fac-[Mn(SPS)(CO)3]. This isomer can be converted photochemically to mer-[Mn(SPS)(CO)3], with a very high quantum yield (0.80 ± 0.05). The thermal backreaction is slow (taking ca. 8 h at room temperature), in contrast to rapid electrodecatalyzed mer-to-fac isomerization triggered by electrochemical reduction of mer-[Mn(SPS)(CO)3]. Both geometric isomers of [Mn(SPS)(CO)3] have been characterized by X-ray crystallography. Both isomers show luminescence from a low-lying ³IL (SPS-based) excited state. The light emission of fac-[Mn(SPS)(CO)3] is largely quenched by the efficient photoisomerization occurring probably from a low-lying Mn-CO dissociative excited state. Density functional theory (DFT) and time-dependent DFT calculations describe the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of fac- and mer-[Mn(CO)3(SPS)] as ligand-centered orbitals, largely localized on the phosphinine ring of the SPS pincer ligand. In line with the ligand nature of its frontier orbitals, fac-[Mn(SPS)(CO)3] is electrochemically reversibly oxidized and reduced to the corresponding radical cation and anion, respectively. The spectroscopic (electron paramagnetic resonance, IR, and UV-vis) characterization of the radical species provides other evidence for the localization of the redox steps on the SPS ligand. The smaller HOMO-LUMO energy difference in the case of mer-[Mn(CO)3(SPS)], reflected in the electronic absorption and emission spectra, corresponds with its lower oxidation potential compared to that of the fac isomer. The thermodynamic instability of mer-[Mn(CO)3(SPS)], confirmed by the DFT calculations, increases upon one-electron reduction and oxidation of the complex. [ABSTRACT FROM AUTHOR]

Oxidation of the square planar Rh(I) complex [Rh(SPSMe)(PPh3)] (SPSMe = l-methyl-l-P-2,6-bis(diphenylphosphinosulfide)-3,5-(bisphenyl)-phosphinine) (1) based on mixed SPS-pincer ligand with hexachloroethane yielded the Rh(III) dichloride complex [Rh(SPSMe)(PPh3)Cl2] (2), which was structurally characterized. The homoleptic Rh(III) complex [Rh(SPSMe)2][Cl] (4) was obtained via the stoichiometric reaction of SPSMe anion (3) with [Rh(tht)3Cl3] (tht = tetrahydrothiophene). Complex 4, which was characterized by X-ray diffraction, was also studied by cyclic voltammetry. Complex 4 can be reversibly reduced at E= -1.16 V (vs SCE) to give the neutral 19-electron Rh(II) complex [Rh(SPSMe)2] (5). Accordingly, complex 5 could be synthesized via chemical reduction of 4 with zinc dust. EPR spectra of complex 5 were obtained after electrochemical or chemical reduction of 4 in THF or CH2Cl2. Hyperfine interaction with two equivalent 31P nuclei was observed in liquid solution, while an additional coupling with a spin ½ nucleus, probably 103Rh, was detected in frozen solution. The 31P couplings are consistent with DFT calculations that predict a drastic increase in the axial P-S bond lengths when reducing (SPSMeM)2Rh(III). In the reduced complex, the unpaired electron is mainly localized in a rhodium dz² orbital, consistent with the g-anisotropy measured at 100 K. [ABSTRACT FROM AUTHOR]