Activation of CO by the oxorhenium(V) complex [(DAAm)Re(O)(CH3)](1 ) [DAAm = N,N-bis-(2-arylaminoethyl)methylamine; aryl = C6F5] resulted in the isolation of the rhenium(V) acyl complex [(DAAm)ReC(O)(CH3)](2 ). Recently, activation of CO by oxorhenium(V) complexes [(DAAm)Re(O)(CH2R )] [R  = phenyl(4 ), 4-fluorophenyl(5 ), 4-methylphenyl(6 ), and 4-methoxyphenyl(7 )] resulted in the isolation of the respective rhenium(V) acetyl complexes [(DAAm)Re)(O)(C(O)CH2R)] [R = phenyl(8 ), 4-fluorophenyl(9 ), 4-methylphenyl(10 ), 4-methoxyphenyl(11 )]. The formation of transition metal acyl complexes are generally understood to proceed through an intramolecular mechanism involving the formation of a metal CO adduct. The mechanism for the formation of these rhenium(V) acetyl complexes were probed experimentally. The relative rates for CO insertion were measured for the formation of all acetyl derivatives. First order dependencies with respect to CO and rhenium were determined. The reactivity for complexes 5-7  was found to proceed through the same proposed mechanism as 1  with one distinction; the rate of reaction for 5  -7  is dramatically increased to that of 1  . Kinetic studies of CO insertion allowed for the determination of the following activation parameters: 1, 4  (?H� = 10(1), 12(1) kcal/mol; ?S� = -56(4), -38(4) eu; ?G�  = 26(3), 23(3) kcal/mol (25 �C)). The data suggest that CO insertion into the oxorhenium(V)benzyl complexes are consistent with an intramolecular and an intermolecular mechanism.

Synthesis and mechanistic elucidation of the activation of CO by oxorhenium(V) complexes

248th National Meeting (2014)

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