Photolysis of CpCo

Vollhardt s investigations100 into electrocyclic transformations on a CpCo template produced the following unusual result. After photolysis of CpCo(CO)2 in the presence of the tosyl hydrazone of trans-4-pheny -3-buten-2-one, the only isolated product was the vinylketene complex 123. Note that the tricarbonyliron analogue of this complex has also been isolated.3,87 The mechanism of formation was not discussed, but it seems likely that the ketene carbonyl originated as a carbonyl ligand that replaced the hydrazone moiety, perhaps via a vinylcarbene intermediate. 

There are only two simple tricobalt clusters, namely [CpCofCO)], obtained by photolysis of CpCo(CO)2 386, 387), and [(R3P)Co(CO)2]3 obtained from [(R3P) Co (00)312 under hydroformylation conditions 322). Both are found to contain three bridging CO groups. 

Cycloaddition of cncdiynes. Photolysis of the enediyne 1 in the presence of catalytic quantities of CpCo(CO)2 in refluxing toluene results in the tricyclic diene 2. The reaction involves a diene rearrangement in the expected product (a).1... 

Rates of reaction of CO with (arene)Mo(CO)2 (alkane) and M(C0)5 (alkane), where M = Cr, Mo, W, have demonstrated that the reaction with Cr(CO)5 (alkane) involves an interchange mechanism while for Mo and W the mechanism is more associative. These resnlts are consistent with the known ability of the higher homologs to expand beyond a coordination number of 6. Flash photolysis and ultra high speed detection (0.4 ps, 4cm resolution) have allowed direct observation (Figure 6) of the vibrational cooling of CpCo(CO)(n-hexane), CpCo(CO)(n-hexene), and the group VI carbonyls. ... 

Stable, isolable metallacycles are also obtained from reaction of complexes that serve as sources of the CpCo fragment (e.g. CpCo(PPh3)2) and alkynes. Upon carbonylation diese typically give high yields of cobalt-complexed cyclopentadienones. Direct reaction of CpCo(CO)2 with alkynes is similarly useful. The cycloaddition of di(t-butoxy)acetylene upon photolysis with CpCo(CO)2 is an example (Scheme 5). In all these systems the final complexes lack coordinated CO, and therefore amine oxides are not suitable reagents for liberating the stable cyclopentadienones. Tetra(t-butoxy)cyclopentadienone is accessible on a preparative scale via controlled electrochemical oxidation. Other oxidants such as Cr have been used as well in other systems. 

The bisethylene complex CpCo(0284)2 reacts with PhMgBr in the presence of TMEDA (tetramethylethylenediamine) to generate the novel adduct(21)In a different report, the same substrate has been reacted with acetylenes to generate n -arene complexes and other acetylene condensation products. Photolysis of Cp 00(0284)2 in the presence of AS4S4 generates a number of products such as (22). ... 

Ru(CO)2(dppe), CpCo(CO)2, CpRh(CO)2, and CpIr(CO)2 have all been observed. For example, a difference IR spectrum for CpNb(CO)4 in Nujol after photolysis is presented in Figure 1. Poliakoff and Turner reviewed the photochemistry, reaction chemistry, and spectroscopy of Fe(CO)4 in both 1987 and 2001 and the photochemistry ofFe(CO)5 itself has been reviewed through 1999. ... 

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