Ligand field states reactivity

Gnmwald-Winstein analysis, 505 Chromium(III) complexes doublet excited states reactions, 400 emission rules, 395 ligand field states reactivity, 397 magnetic behavior, 272 mixed-ligand reactivity, 398 nitrito... 

Irradiation of [Co(NHa)e]3+ in its LF 1Ala -> lT2g band with light ( = 337 nm) from a pulsed nitrogen laser causes photoreduction of the complex.102 A two-photon mechanism is presented in which a ligand field state LF absorbs a further photon to give the reactive CT state (steps 34—37). 

Ru(NH3)spy it should be a ligand field state. This state would be analogous to the reactive LF state responsible for photoaquation of Ru(NH3)5CH3CN (where the lowest absorption band is LF in character (9)) and of Rh(NH3)sL vide supra). Estimates of the energies of the lowest MLCT and LF states suggest that for Ru(NH3)spy the lowest state may be LF in character (10). 

Detailed electronic structure studies, including insights gained from ligand field theory (46), can be especially useful in interpreting the reaction profiles and understanding the reactivity and selectivity of these systems. The exploration of two-state reactivity and the value of detailed electronic structure analysis are illustrated by our studies of the H atom abstraction step catalyzed by TauD (23,47), which are presented here for each spin-state surface the hypothetical septet, the quintet, and the triplet. 

The rules have been accounted for in terms of ligand field theory, taking Q°l (see Figure 6) to be the reactive state.35 36 Figure 7 illustrates the energy level orderings of the one-electron -orbitals and the electronic states for [CrX(NH3)5]2+ complexes of effective C4v symmetry. The lowest quartet... 

A pulsed-laser photolysis study of [Cr(en)3]3+ illustrates quite dramatically the enhancement in reactivity that can result upon populating a ligand field excited state.26 Thus a significant fraction of the primary photoproduct, [Cr(en)2(enH)(OH2)]4+, is formed within the 20 ns duration of the laser pulse and is thought to arise from reaction of the lowest excited quartet state, Q° (see Figure 6). This observation establishes that the pseudo-first-order rate constant for this excited state... 

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