Ta. Mobley et al., STEREOCHEMICAL INVESTIGATIONS OF THE MECHANISM OF C-H BOND ACTIVATION- DIASTEREOMERIC AND ISOTOPIC SCRAMBLING IN (HYDRIDO)ALKYLIRIDIUM COMPLEXES, Organometallics, 17(16), 1998, pp. 3574-3587
The diastereomeric complexes (RS),(SR)-((2,2-dimethylcyclopropyl)(Cp)
(PMe3)IrH) (2a) and (RR),(SS)-((2,2-dimethylcyclopropyl)(Cp) (PMe3)I
rH) (2b) and their alpha-deuterated analogues (2a-alpha(d1), 2b-alpha(
d1)) were synthesized in racemic form and separated by low-temperature
(-80 degrees C) column chromatography. Thermolysis (140 degrees C) of
diastereomerically pure 2a or 2b in C6D6 results in its interconversi
on to the other diastereomer. Thermolysis of the deuterium-labeled ana
logues 2a-alpha(d1) and 2b-alpha(d1) results additionally in scramblin
g of deuterium from the alpha-position of the dimethylcylopropyl ring
to the metal hydride position. Diastereomer interconversion and isotop
ic scrambling occur at similar rates, which are faster than the rate o
bserved for the reductive elimination of dimethylcyclopropane and subs
equent oxidative addition of C6D6. Quantitative analysis of these rate
data is reported. The similarity of these rates is discussed in terms
of a common intermediate mechanism involving a metal alkane (or ''sig
ma-alkane'') complex. This mechanism is used as a basis far comparison
of the rearrangement processes in the current iridium system and the
previously reported analogous rhodium system.