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atoms in the step 3 + 5."". b, 91 (3) It is obvious from Table 1 that for the Coe and NiO complexes of 4-octyne both steps, i.e., C-H bond activation andligand detachment, are subject to a kinetic isotope effect. For the ligand detachment 3 -5 the data for 1 b and 1 d permit the estimation of an isotope effect kH/kD = 1.10 (per deuterium) for either CoO or Nie. The C-H bond activation step 2 + 3 (or, less likely, I-Me -+ 4) is associated with slightly differing kH/kD values of 1.25 and 1.36 for Coo and Nie, respectively.f'O] Obviously, the various transition-metal ions cause a switching in regard to the bottleneck of the multistep event which is shown in Scheme 1 in a simplified manner.As indicated in Figure 3 , a quite remarkable inverse relationship exists between the magnitude of the kinetic isotope [R hC I LzI CPhzNz ": CzH,Ph-H 6a

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