An Electronic Perspective on the Reduction of an N=N Double Bond at a Conserved Dimolybdenum Core

摘要

Density functional theory has been used to assess the role of the bimetallic core in supporting reductive cleavage of the N=N double bond in [Cp_2MO_2(mu-SMe)_3(mu-eta~1:eta~1-HN=NPh)]~+.The HOMO of the complex,the Mo-Mo 8 orbital,plays a key role as a source of high-energy electrons,available for transfer into the vacant orbitals of the N=N unit.As a result,the metal centres cycle between the Mo~(III)and Mo~(IV)oxidation states.The symmetry of the Mo-Mo 6 "buffer" orbital has a profound influence on the reaction pathway,because significant overlap with the redox-active orbital on the N=N unit(PI* or delta*)is required for efficient electron transfer.The orthogonality of the Mo-Mo 5 and N-N delta~* or-bitals in the eta~1:eta~1 coordination mode ensures that electron transfer into the N-N a bond is effectively blocked,and a rate-limiting eta~1:eta~1->eta~1 rearrangement is a necessary precursor to cleavage of the bond.