-Bond Metathesis [e,f]-Bond Metathesis [e,f]Bis(t-butyl isocyanide)palladium(0) (1) catalyzed ring-enlargement
oligomerization of 1,1,2,2-tetramethyl-1,2-disilacyclopentane (2)
through Si(IP(JSi -bond metathesis to give cyclic dimer (3%), trimer (32%),
tetramer (34%), pentamer (14%), hexamer (6%), heptamer (3%), and octamer
(1%) (93% in total). The cyclic structure of the tetramer was established
by a single-crystal X-ray diffraction method, which showed that the four
Si(IP(JSi bonds of the tetramer were arranged in nearly parallel.
Reactivities of the dimer, trimer, and tetramer in the presence of 1
revealed that the present Si(IP(JSi -bond metathesis proceeded by reversible
mechanism in which the (IP(JMe2Si(CH2)3SiMe2(IP(J
unit of 2 was successively inserted into the Si(IP(JSi bond of the oligomer
to give higher oligomer. Isolation of 6-membered bis(silyl)palladium intermediate,
which arose from oxidative addition of 2 onto 1, supported
the mechanism. The cyclic tetramer reacted with 2,6-diisopropylphenylisocyanide
in the presence of Pd(OAc)2 to afford 24-membered-ring tetraimine,
in which the isocyanides were inserted into all the Si(IP(JSi linkages of the
tetramer.
