Cobalt complexes, photochemistry

It will become evident from this discussion of cobalt(III) and chromium(III) photochemistry that a fortunate combination of many factors makes these systems especially amenable to mechanistic investigation this is not the case for most other inorganic systems. For this reason, the progress made toward understanding the photochemical reactions of cobalt(III) and chromium(III) complexes may not be easily duplicated in other areas and it is useful to inquire whether conclusions reached here can be generalized. It is my belief that they can, and this and the next section are intended to place the subsequent discussion in the perspective of inorganic photochemistry. 

Much less is known about photoinitiated ligand exchange reactions of coordination complexes of cobalt(III) and other de ions than is the case for chromium(III). With the exception of the cobalt(III) ammines, however, available data suggest that photochemical ligand exchange reactions of cobalt(III) and d6 systems involve the thermally equilibrated 17 g and/or 37, states of the complex as intermediates. The reasoning is completely analogous to that described earlier with respect to chromium(III) photochemistry. 

Robert Plane I would like to comment on the photochemistry of these complexes, particularly the chromium which I think are well chosen for at least two of Dr. Gray s reasons. First, in the case of chromium, unlike cobalt, the charge transfer band is well separated, so that one can study the d-d transitions, at least in certain systems where one has six ligands all alike, and there is no Jahn-Teller splitting, and one has a fairly good idea as to the assignment of bands. 

Heterostannenes, preparation and characteristics, 3, 870 Heterosubstituted arenes, metallation, 9, 17 Hexaaryldiplumbanes, preparation, 3, 887 Hexabutyldistannane, preparation, 3, 856 Hexacarbenes, in cobalt(III) complexes, 7, 19 Hexacarbonyl complexes, with molybdenum kinetics and reactivity, 5, 395 photochemistry, 5, 393 solid-support studies, 5, 394 spectroscopic and theoretical studies, 5, 392 Hexadentate iV-substituted triazacyclononane, synthetic applications, 1, 70... 

The photochemistry of the water-insoluble [Co(sep)](B(C6H5)4)3 complex was studied in aprotic solvents (THF, AN, and DMF) [309]. When THF solution was irradiated with visible light, the cobalt(III) complex has been reduced by the tetraphenylborate anion to give a white [Co(sep)](B(C6H5)4)2 precipitate. From the residual solution biphenyl and phenol were isolated as the main products. This photoreaction proceeded much slower in DMF solution. 

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