For the C-H alumination of 2-methyl-thiophene, a kH/kD of 2.8 was observed based on independent reactions under catalytic conditions. In contrast to the zinc system, this indicates that a C-H bond cleavage is involved in the turnoverlimiting step for C-H alumination. Further contrasts between the Zn/Al were forthcoming from analysis of the 1 H and 2 H NMR spectra which revealed minimal deuterium incorporation into the NacNac C position during C-H alumination even after long reaction times (Fig. ). This suggested a mechanistic divergence in these C-H zincation and C-H alumination reactions.