Organometallic compounds photochemistry with

In comparison with the photochemistry of organosilicon compounds, the photochemistry of organometallic compounds of the heavier Group 14 elements has received little attention. In recent years, however, a number of synthetically useful photoreactions of such species have been developed, and it would seem opportune to review this area of research. In particular, organogermanium and organotin reagents are becoming... 

The importance of tertiary amines in the photochemically induced electron transfer reactions has also been addressed5. Direct irradiation of aromatic or aliphatic amines often leads to the scission of C—N, N—H or C—H bonds that lead to the subsequent chemical reactions by radical pathways6. In this section, photochemical reactions of amines reported since 1978 will be considered with emphasis on photoinduced electron transfer. Photochemical reactions of inorganic and organometallic compounds will not be included unless photochemistry of amine moieties is the primary interest. 

We have organized this review of the photochemistry of organometallic compounds of the heavier group 14 elements by compound class, with the exception of photoinduced electron transfer processes which we treat under a separate heading. This review describes the recent literature which has appeared since the publication in 1995 of an earlier review of this topic1. 

The photochemistry of inorganic and organometallic compounds emphasizes both basic understanding of the photophysics involved and the primary photochemical reactions that occur, as well as the synthetic utility of photochemical reactions. Indeed, in many instances photochemical routes are the methods of choice for certain syntheses, e.g., of h -CjH5Mn(CO)3. This complex loses CO thermally and yields substituted complexes only when heated to high temperatures (T), yet photolysis readily induces CO loss with high quantum yield. Irradiation in the presence of appropriate ligands leads to the desired substituted products. 

We have also initiated MUssbauer spectroscopic studies of photochemical reactions of inorganic and organometallic compounds (iron chelate complexes, iron carbonyl and organotin compounds) isolated in low temperature matrices. Such systems provide a complimentary approach to solid-phase photochemistry since the reaction mechanisms may be simplified by isolating the reactant molecules in inert matrices (light transmission through the reactant is also facilitated by diluting tlie colored reactant with a transparent medium). Furthermore, we have a hope for the possible outcome of such studies — their application to syntheses of novel species which may be unstable at ordinary temperatures, unless trapped in inert matrices. 

Included in the published account of the plenary lectures presented at the International Conference on Chemical Thermodynamics held during 1986 is an interesting article on metal-ligand bond energies in organometallic compounds, which includes data on metal carbonyls. Relevant n.m.r. data are to be found in two different sources,and ion-pairing effects on the structures and reactivities of metal carbonyl anions have been described. A timely review of the photochemistry of M-M bonds deals almost exclusively with metal carbonyl derivatives these also feature in articles on transition metal-hydrogen bonds. ... 

Some references of reviews besides the ones already cited are given [1,3, 5-9, 19, 23-25, 28, 31, 33]. Organometallic photochemistry [36] was excellently treated in [37] and may be compared with inorganic photochemistry to gain further inspiration [38-40]. A recent multiauthored book strongly overlaps with the subject matter of the present section, and should certainly be consulted [41]. Electron transfer reactions play a determinant role in many photocatalytic processes several recent reviews and books may be cited on this topic [42-44]. The photochemistry of the M-CO bond [45] and the theme of photocatalysis by transition metal complexes [46] have recently been reviewed. Covalently linked donor-acceptor systems for mimicry of photosynthetic energy transfer have been discussed in [47]. Several special issues of Coordination Chemistry Reviews have been devoted to the photochemistry and photophysics of coordination compounds [48-50], and a special issue to photochemistry [51]. Further developments in photochemistry were the subject of a special issue of Chemical Reviews [52]. Practical considerations useful for designing photochemical experiments may be found in [53]. 

We have seen that compounds can be thermally dissociated to produce new complexes. Another way of imparting energy to a molecule to induce reaction is to shine on it light of an appropriate wavelength. There are many important applications of photochemistry in organometallic chemistry but it has been used less frequently with metal ammine and other classical complexes. 

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