Photochemical reactions of CpM

The solution and nujol-matrix photochemical reactions of CpM(CO)2H (M = Ru or Os), (ri -C5H4CH3)2Ru2(CO)4 and Cp20s2(CO)4 were followed by IR spectroscopy (vCO). Photochemical reactions of trans-(X)-Ru(dcbpy)(CO)2X2, where X = Br or I, dcbpy = 4,4 -dicarboxylic acid-2,2 -bipyridine, were monitored similarly. IR data were reported for two polymorphs of the cluster Ru4Pt2(CO)i8, i.e. the known monoclinic and a new orthorhombic form. ... 

Systems of the type [CpM(CO)3R] (M=Group VI metal) have attracted a considerable amount of attention studies have been concerned with both their thermal and photochemical reactions. Scheme 19 shows the principal products obtained from photolysis of the species where R represents methyl or benzyl the primary process is evidently CO dissociation. The photochemical reactions of [CpM(CO)sMe] with ethylene (M = W), acetylene (M = Mo or W), and trimethylphosphine (M = Cr, Mo, or W) have been investigated the results are summarized in Scheme 20. The unusual structure (12), is proposed for the... 

Oxidative addition across Sn—C bonds has also been observed94, as demonstrated in reaction 45. This reaction also occurs thermally, but is accelerated by photolysis. A related series of reactions has been observed by Pannell and Kapoor95, looking at the photochemical decomposition of CpM(CO) PbR3 (n = 2, M = Fe n = 3, M = Cr, Mo, W R = Me, Et, Ph). In the case of the phenyl analogues the products are metallic lead, PbPh4, and CpM(CO) Ph (reaction 46). 

Reaction of CpM(CO)3R (R = Me, CH2Ph) with 2-butyne produces an alkenyl ketone metallacycle, thermally for Mo, photochemically for W (202). Addition of CNBu or PPh3 drives CO insertion into the metal position of the metallacycle, and lactone products form [Eq. (59)]. With trifluoromethyl as the original metal alkyl group multiple alkyne and CO insertions lead to an eight-membered oxymetallacycle ring [Eq. (60)]. 

The reactions listed in Table 1 occur thermally, but some can also be accomplished photochemically. Thus the reaction of [CpM(CO)3]2 with SnCl2 may be brought about by UV irradiation, and the reactions of [LCo(CO)3]2 and [CpFe(CO)2]2 are accelerated in diffuse light. 

However, these photosubstitution reactions do not appear to be very synthetically useful since the yields of the substituted products 58 and 59 are usually low with a maximum of —60%, and other products are also formed. This suggested that competing thermal and/or photochemical processes occur. For example, Alt and Schwarzle (576) showed that irradiation of CpM(CO)3CH3 (M = Cr, Mo, or W) in the presence of PMe3 gave not only the mono- and disubstituted derivatives 58 and 59 but also the binuclear, asymmetrically substituted complexes Cp(CO)(L)2M—M(CO)3Cp (60 and 61). Note that the CH3 ligand has... 

In a related photochemical reaction the first oxidative addition of CH2CI2 to a nonporphyrin cobalt(I) species has been observed for Cp Co(CO)2 When either the Co or Rh bisethylene complexes CpM(C2H4)2 of Cp are reacted with tBuC=P, diphosphacyclobutadiene ligands are generated(24). 

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