Mj. Scott et Sj. Lippard, ISOCYANIDE INSERTION REACTIONS WITH ORGANOMETALLIC GROUP-4 TROPOCORONAND COMPLEXES - FORMATION OF ETA(2)-IMINOACYL, ENEDIAMIDO, ETA(2)-IMINE, AND MU-IMIDO PRODUCTS, Organometallics, 16(26), 1997, pp. 5857-5868
The reactivity of the tropocoronand complexes [M(TC-3,n)R-2] (M = Zr(I
V), Hf(IV); n = 3, 5; R = CH2Ph, Ph) with aryl and alkyl isocyanides i
s described. Alkyl isocyanides induced migration of both benzyl groups
to afford the bis(iminoacyl) species [Hf(TC-3,n){eta(2)-(R)N = C(CH2P
h)}(2)] (n = 5, R = Cy (1), n-Bu (2); n = 3, R = Cy(3)). Different pro
ducts were isolated with aryl isocyanides, depending on the rate of su
bstrate addition. Treatment of [M(TC-3,n)(CH2Ph)(2)] with excess 2,6-d
imethylphenyl isocyanide (ArNC) generated the enediamido compounds [(T
C-3,3)MN(Ar)C(CH2Ph) = C(CH2Ph)N(Ar)] (M = Zr (4), Hf(5)) via coupling
of two bis(iminoacyl) groups, whereas slow step-wise addition produce
d [(TC-3,n)MN(Ar)C(CH2Ph)(2)C(= NAr)](M = Zr, n = 3 (6); M = Hf, n = 3
(7), n, = 5 (8)). The eta(2)-imine complex [(TC-3,5)HfN(Ar)C(CH2Ph)(2
)] (9), an intermediate in the formation of 7, was isolated and charac
terized, but the corresponding zirconium species was unstable in solut
ion, decomposing to form the imido-bridged compound {[Zr(TC-3,3)](2)(m
u-NAr)(2)} (10). Altering the nature of the carbon donor ligands also
influenced the reactivity. Addition of both aryl and alkyl isocyanides
to solutions of [Zr(TC-3,3)Ph-2] (11) afforded the gamma 2-imine comp
lexes [(TC-3,3)ZrN(R)C(Ph)(2)] R = Cy (12), Ar (13)), the stability of
which may be due in part to interactions between the metal center and
a phenyl ring. Electron-withdrawing R substituents enhance this effec
t. All new compounds were characterized by X-ray crystallography, and
plausible mechanisms for the migration reactions are outlined.