In stoichiometric homogeneous reaction with metal complexes for activation of inert bonds how could it be possible to observe zero order dependence on the metal center?
Could you provide more details please? The rate limiting step could be a transformation (e.g. isomerization) of non metal reactant.
Activation of Ar-X with M(PPh3)n; with isomerization the rate should somehow related to M and it's very unlikely preactivation of Ar-X.
Biswajit. Your suggestion does not work. The concentration of the ligand is dependent on the metal concentration.
Suman. In general you are right. If the reactive species M is formed in dissociation ML = M + L, The reaction rate low is rate ~ [ML]^0.5 (square root). Experimentally it could look like a very weak dependence on [ML] especially in the case of narrow range of [ML]
Just for more clarification we can consider the following reaction:
HM(PPh3)n + ArX ---> ArH + XM(PPh3)n-1 + PPh3
in this condition it's unlikely without metal proposing any mechanism. I would be really greatful if somebody propose any reason that why we can not see depence on M in kinetic study.
Ar-X bonds(including Cl) can be activated at room temp for at least 10 years and still some reactions require higher temp to be efficient. It means your activation is/may not be RDS. However, your description lacks clarity. How did you conclude it is 0th order? Did you tried catalytic with 1,2,5,10mol% catalyst? This is the best way. If you tried 1:1 and observed a linear decay you should read Dave Collum and Kanwal Singh papers on 0 order looking decays.
Dear Mihai,
so many thanks, I used non catalytic condition with ArX in excess.
Could you please introduce me the papers that you mentioned?
Thanks
http://collum.chem.cornell.edu/dbc6/Publications.html
check papers 110, 112, 118.
It may or may not be an answer to your question. Some good reading
Mihai
This is often a sign of catalysis of the reaction by heterogeneous metal particles.
Regarding catalysis by metal particles, based on mercury test no change was observed.
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