P. Legzdins et al., SYNTHESIS, CHARACTERIZATION, AND REDOX PROPERTIES OF THE 17-VALENCE-ELECTRON COMPLEXES CP'CR(NO)(L)X, Organometallics, 13(2), 1994, pp. 562-568
Treatment of CH2Cl2 solutions of [Cp'Cr(NO)I]2 [CP'= Cp (eta5-C5H5) or
Cp (eta5-C5Me5)] with various P- and N-containing Lewis bases, L, af
fords good yields of Cp'Cr(NO)(L)I complexes [L = PPh3, P(OMe)3, P(OPh
)3, py, or C5H11N (pip)]. Photolysis of toluene solutions of CpCr(NO)(
CO)2 in the presence of PPh3 and a source of halogen such as CH2Cl2 re
sults in a 63% isolated yield of CpCr(NO)(PPh3)Cl. In donor solvents,
S, the ESR-active CpCr(NO)(L)X (X = Cl, I) compounds undergo either L
or X substitution to form the 17-valence-electron CpCr-(NO)(S)X and [C
pCr(NO)(L)(S)+ species, respectively. A kinetic analysis of the reacti
on of CpCr(NO)(THF)I with PPh3 shows the process to be second-order ov
erall (first-order in each reactant) and associative in nature. The re
duction potentials for the various CpCr(NO)(L)X complexes in THF vary
from -1.05 to -1.65 V. These reductions are irreversible and are follo
wed by loss of X-. Consistently, reduction of CpCr(NO)(PPh3)I in THF b
y Zn in the presence of P(OPh)3 affords the 18-valence-electron mixed
phosphine-phosphite complex, CpCr(NO)(PPh3)[P(OPh)3]. The redox chemis
try of the CpCr(NO)(L)X complexes is thus unusual in that the odd-elec
tron species are substitutionally less labile than are, their 18-elect
ron reduction products.