Stereoselective [4+2] Diels−Alder cycloadditions occur
between unsaturated tertiary phosphine, phosphole,
and arsine molybedenum carbonyl complexes, e.g.,
(Ph2E-trans-CH2CHCHCH3)Mo(CO)5
[E = P, As] and 3,4-dimethyl-1-phenylphosphole (DMPP). The coordinated DMPP undergoes a
[1,5] phenyl migration at about 145 °C
prior to or concomitant with the [4+2] intramolecular cycloaddition
reaction with the alkene moiety of the dienophile
to produce a new class of conformationally rigid bidentate ligands
containing the 1-phosphanorbornene bicyclic ring
system. The characteristic 1H,
13C{1H}, and
31P{1H} NMR spectroscopic features of
these compounds are described.
Crystal structures of most of the new compounds are
reported.
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