Res. Chem. Intermed.
, Vol. 33, No. 8–9, pp. 725–737 (2007)
Also available online - www.brill.nl/rci
Radical ions from and spin adducts to
, MASSIMO BENAGLIA, MAURIZIO GUERRA
and DANTE MACCIANTELLI
ISOF-CNR, Area della Ricerca di Bologna, Via P. Gobetti 101, I-40129 Bologna, Italy
Received 10 May 2006; accepted 16 June 2006
Abstract—The radical cation and anion of the title compound were obtained either by treatment with
mercury triﬂuorocatetate in triﬂuoroacetic acid or by reduction with potassium in tetrahydrofurane.
For both species the ESR spectra indicated magnetic non-equivalence of the two phosphorus atoms,
as well as of the two methyl groups. Spectra attributed to the corresponding spin adducts were also
observed when reacting the title compound with in situ-generated alkoxyl and thiyl radicals. MO
calculations carried out for both the ionic radicals and the neutral spin adducts led to questioning the
actual nature of some of the latter species.
Keywords: ESR; DFT calculations; radical ions.
Multiple-bonded compounds containing sterically protected phosphorus atoms ﬁnd
a variety of applications both in organic synthesis and in coordination chemistry .
This is not however the case for bidentate ligands containing carbon-phosphorus
double bonds, which are scarcely used due to their poor stability. An exception
is provided by 3,4-bisphosphinidene-1-cyclobutenes bearing 2,4,6-trisubstituted
phenyl rings at the phosphorus atoms, and since the ﬁrst reports of the synthesis of a
member of this family [2, 3] several other structurally related derivatives have been
synthesized [4–11]. The thermal (E, E) → (E, Z) isomerization of some of these
compounds , their complexing ability toward such metals as Cu, Cr, Mo, W and
Pd [7, 9, 12–14] and their use in organic synthesis [15–17] have been investigated.
We report here on an ESR study of the radical ions (2, 3) obtained by oxidation or
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