STEREOCHEMICAL INFLUENCE OF THE PENTAMETHYLCYCLOPENTADIENYL LIGAND ONTHE ISOCYANIDE INSERTION REACTIONS OF THE 1-SILA-3-HAFNACYCLOBUTANE COMPLEX, (C(5)ME(5))(C5H5)HF(CH(2)SIME(2)CH(2))
L. Kloppenburg et Jl. Petersen, STEREOCHEMICAL INFLUENCE OF THE PENTAMETHYLCYCLOPENTADIENYL LIGAND ONTHE ISOCYANIDE INSERTION REACTIONS OF THE 1-SILA-3-HAFNACYCLOBUTANE COMPLEX, (C(5)ME(5))(C5H5)HF(CH(2)SIME(2)CH(2)), Polyhedron, 14(1), 1995, pp. 69-80
The insertion reactions of CNMe and CN-t-Bu with CpCpHf(CH(2)SiMe(2)C
H(2)), 1, have been investigated to evaluate the stereoelectronic infl
uence of the Cp ligand on the competitive 1,2-silyl shift and reducti
on coupling pathways previously observed for Cp(2) Hf(CH(2)SiMe(2)CH(2
)). Under ambient conditions the addition CNMe to 1 proceed with the s
equential formation of CpCpHf(N(Me)C(=CH2) SiMe(2)CH(2)), 2, and Cp*C
pHf(N(Me) C(=CH2)SiMe(2)(CH2=)CN(Me)), 3. Alternatively, the addition
of excess CNMe below - 5 degrees C to 1 occurs with reductive coupling
to produce CpCpHf(N(Me)C(CH(2)SiMe(2)CH(2)) =CN(Me)), 4. In contrast
, the addition of two equivalents of CN-t-Bu to 1 does not afford the
corresponding cyclic enamide species but proceeds with the sequential
formation of CpCpHf(N(CMe(3))CCH(2)SiMe(2)CH(2)), 5, and Cp*CpHf(N(CM
e(3))C-C(=NCMe(3))CH(2)SiMe(2)CH(2)), 6. The molecular structures of 3
and 6 have been determined by X-ray crystallography. The puckered 1-s
ila-3,5-diaza-4-hafnacyclohexane ring of 3 adopts a chair conformation
with the folding along the N...N' vector being 19.3 degrees out of th
e N', Hf, N plane toward the smaller Cp ligand and the folding along t
he C(1)...C(1)' vector being 43.3 degrees in the opposite direction to
ward the Cp ligand. The molecular structure of 6 is consistent with n
ucleophilic attack of CN-t-Bu at the eta(2)-iminoacyl carbon of 5 occu
rring exclusively from the side opposite to the Cp ligand. The second
equivalent of CN-t-Bu displaces the eta(2)-iminoacyl group away from
the Hf atom, eventually placing the resultant imine group of 6 syn to
the Cp ligand.