The first unpaired electron placed inside a C3-symmetry P-chirogenic cluster.
The Pd(3)(dppm*)(3)(CO)(n+) enantiomers (n = 2 (2), 1 (3)) were prepared either from (R,R)- or (S,S)-P-chirogenic bis(phenyl-m-xylylphosphino)methane (dppm*; 1) and Pd(OAc)(2) in the presence of CF(3)CO(2)H, CO and water (n = 2), and then by reductive electrolysis (n = 1). The stable enantiomeric [Pd(3)((S,S)-dppm*)(3)(CO)](+)˙ (3), is the first C(3)-symmetry radical-cation M-M bonded cluster, therefore the odd electron is delocalized onto the Pd(3) frame within this symmetry. The novel chiral species have been characterized by circular dichroism (CD) of both enantiomers of the Pd(3)(dppm*)(3)(CO)(2+) clusters (2) and by EPR spectroscopy for the Pd(3)((S,S)-dppm*)(3)(CO)(+)˙ paramagnetic compounds (3, g = 2.041). Evidence for reduced symmetry with respect to the achiral cluster was also obvious from the hyperfine splittings of the EPR signal which display three different hyperfine coupling values: 3 ×A((31)P) = 83.9 × 10(-4) cm(-1), 3 ×A((31)P) = 69.7 × 10(-4) cm(-1), 3 ×A((105)Pd) = 12.5 × 10(-4) cm(-1). In the absence of an X-ray structure for the paramagnetic clusters, DFT computations were performed to address the geometry. The optimized geometry of the Pd(3)((S,S)-dppm*)(3)(CO)(+)˙ radicals (3) exhibits three phosphorus atoms placed well above the Pd(3) plane, while the three others are located below the trimetallic frame within C(3)-symmetry due to intramolecular steric hindrance. This makes them chemically different with respect to the carbonyl group and explains the experimental EPR spectrum well. Consequently this C(3)-symmetry deformation also induces a change in the shape of the SOMO (semi-occupied molecular orbital) towards this same symmetry compared to the corresponding achiral C(3v) species.
Salomon
Christine
C
Département de Chimie, Université de Sherbrooke, Sherbrooke, J1K 2R1, Québec, Canada. Pierre.Harvey@USherbrooke.ca.
Dal Molin
Sophie
S
Fortin
Daniel
D
Mugnier
Yves
Y
Boeré
René T
RT
Jugé
Sylvain
S
Harvey
Pierre D
PD
D004563:Electrochemistry; D004578:Electron Spin Resonance Spectroscopy; D004583:Electrons; D008280:Magnetics; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000737:chemistry*; D010165:Palladium / Q000737:chemistry*; D013237:Stereoisomerism
D009942:Organometallic Compounds; D010165:Palladium