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Issue 42, 2010
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The first unpaired electron placed inside a C3-symmetry P-chirogenic cluster

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Abstract

The Pd3(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 CF3CO2H, CO and water (n = 2), and then by reductive electrolysis (n = 1). The stable enantiomeric [Pd3((S,S)-dppm*)3(CO)]+˙ (3), is the first C3-symmetry radical-cation M-M bonded cluster, therefore the odd electron is delocalized onto the Pd3 frame within this symmetry. The novel chiral species have been characterized by circular dichroism (CD) of both enantiomers of the Pd3(dppm*)3(CO)2+ clusters (2) and by EPR spectroscopy for the Pd3((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(31P) = 83.9 × 10−4 cm−1, 3 ×A(31P) = 69.7 × 10−4 cm−1, 3 ×A(105Pd) = 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 Pd3((S,S)-dppm*)3(CO)+˙ radicals (3) exhibits three phosphorus atoms placed well above the Pd3 plane, while the three others are located below the trimetallic frame within C3-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 C3-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 C3v species.

Graphical abstract: The first unpaired electron placed inside a C3-symmetry P-chirogenic cluster

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Publication details

The article was received on 25 May 2010, accepted on 04 Jun 2010 and first published on 04 Aug 2010


Article type: Paper
DOI: 10.1039/C0DT00542H
Citation: Dalton Trans., 2010,39, 10068-10075
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    The first unpaired electron placed inside a C3-symmetry P-chirogenic cluster

    C. Salomon, S. Dal Molin, D. Fortin, Y. Mugnier, R. T. Boeré, S. Jugé and P. D. Harvey, Dalton Trans., 2010, 39, 10068
    DOI: 10.1039/C0DT00542H

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