Stereochemical Control of Valence and Its Application to the Reduction of Coordinated NO and N2

摘要

The electronic structures of transition metal complexes of NO are controlled by the stereochemistry about the metal atom (stereochemical control of valence). The six-coordinate complex, trans-[CoNO(NCS)-(C6H4 [As(CH3)2]2)2]⁺, consists of [Co(III)-(N=O^-)]²⁺ (angleCo-N-O = 135°), while the pentacoordinate trigonal bipyramidal complex, [CoNO(C6H4[As(CH3)2]2)2] ²⁺, is best formulated as [Co(I)-(N≡O⁺]²⁺ (angleCo-N-O = 179°). Evidence indicates that complexes of (NO)⁺ and N2 are electronically similar. Hence, the principles of stereochemical control of valence may be applied to metal complexes of N2. In a linearly coordinated Mⁿ˜m(N≡N) complex, valence electrons can be transferred from the metal to the N₂ ligand producing a bent, protonated, and/or metallated Mⁿ⁺²-(N=N^2-) complex. This reduction of N₂ can be effected by the addition of an appropriate ligand to M or by a change in the coordination geometry about M. Stereo-chemical control of valence leads to the rejection of one of the previously proposed mechanisms for reduction by nitrogenase.