Reductive elimination photochemically induced

Photochemical generation of the bent metallocene (39) has turned out to be very useful for the preparation of 3. Thus, (s-tra j-i7 -butadiene)ZrCp2 (3a) is obtained in good yield from the photochemically induced reductive elimination of biphenyl from diphenylzirconocene (10) at low temperatures in the presence of 1,3-butadiene. This is probably the most versatile and most widely applicable method to prepare (s-fr nj-i7 -diene)zirconocenes. A wide variety of examples of this class of complex [and of (s-cis-diene)zirconocenes 5, as well] has been prepared by this route using various substituted conjugated dienes (22, 23) (Scheme 2). 

The Effect of Light Photochemically Induced Reductive Elimination... 

Photochemically induced reductive elimination can also result from initial photochemical extrusion of a dative ligand. For example, irradiation of [lrH,Cl(CO)(PPhj)J leads to... 

Margulieux GW, Semproni SP, Chirik PJ. Photochemically induced reductive elimination as a route to a zirconocene complex with a strongly activated N2 ligand. Angew Chem Int Ed. 2014 53 9189-9192. 

The photochemically induced reductive eliminations of hydrogen from [IrClH2-(PPh3)a] and [IrHs(PPh3)3] appear to be concerted processes since in the presence of deuteriated analogues no HD is produced. The photoactive excited state is believed to involve population of an iridium-Ha antibonding orbital which explains the easy hydrogen loss. 

Oxidative addition, such as that exemplified by addition of H-S1R3 to photo-generated Fe(C0)4, reaction (17), is a very important, large thermal reaction class. Generally, it can be said that oxidative addition to low valent, coordinatively unsaturated metal complexes is common. Recently, Geoffroy, Hammond, and Gray188 have established that reductive elimination can be photochemically induced. A typical example is shown in reaction (67). Other small molecules can be reductively elimi-... 

Reductive elimination of dihydrogen from [Pt2H2(//-HX/i-dppm)2]+ may also be induced photochemically in acetonitrile or pyridine solution. 

Most reductive elimination reactions are induced thermally, but some important reductive elimination reactions are induced photochemically. Most examples of such reductive eliminations form dihydrogen from metal-dihydride complexes. Two examples of the photochemical reductive elimination of dihydrogen to generate intermediates that add alkanes are shown in Equations 8.6 and 8.7. In these examples, the photochemical irradiation provides the energy to induce the reductive elimination process. 

Photochemical reductive elimination offers further examples of ultrafast light-induced reactions. Irradiation of cfr-[Ru(dmpe)2H2] with 300 nm light in cyclohexane causes elimination of H2, and rearrangement of the [Ru(dmpe)2] skeleton (dmpe— Me2P-CH2-CH2-PMe2) to the trans isomer. Interestingly, aU of those processes were reported to be completed within the instrument response time of 16 ps [100]. 

Photochemical reductive eliminations induced by LMCT excitation were observed for a variety of different electron configurations at the metal. The versatility of this reaction is illustrated by a few examples. 

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