Octahedral bipyridine and bipyrimidine dioxomolybdenum(VI) complexes: characterization, application in catalytic epoxidation, and density functional mechanistic study.
Complexes of the general formula [MoO(2)X(2)L(2)] (X=Cl, Br, Me; L(2)=bipy, bpym) have been prepared and fully characterized, including X-ray crystallographic investigations of all six compounds. Additionally, the highly soluble complex [MoO(2)Cl(2)(4,4'-bis(hexyl)-2,2'-bipyridine)] has been synthesized. The reaction of the complexes with tert-butyl hydroperoxide (TBHP) is an equilibrium reaction, and leads to MoV(I) eta(1)-alkylperoxo complexes that selectively catalyze the epoxidation of olefins. Neither the Mo-X bonds nor the Mo-N bonds are cleaved during this reaction. These experimental results are supported by theoretical calculations, which show that the attack of TBHP at the Mo center through the X-O-N face is energetically favored and the TBHP hydrogen atom is transferred to a terminal oxygen of the Mo=O moiety. After the attack of the olefin on the Mo-bound peroxo oxygen atom, epoxide and tert-butyl alcohol are formed. The latter compound acts as a competitive inhibitor for the TBHP attack, and leads to a significant reduction in the catalytic activity with increasing reaction time.
Kühn
Fritz E
FE
Anorganisch-chemisches Institut der Technischen, Universität München, Lichtenbergstr. 4, 85747 Garching b. München, Germany. fritz.kuehn@ch.tum.de
Groarke
Michelle
M
Bencze
Eva
E
Herdtweck
Eberhardt
E
Prazeres
Angela
A
Santos
Ana M
AM
Calhorda
Maria J
MJ
Romão
Carlos C
CC
Gonçalves
Isabel S
IS
Lopes
André D
AD
Pillinger
Martyn
M