Transient metal cluster reactivity

Most of the photoreactions of dimeric Co carbonyls involve cluster formation or cross coupling with other dimers. Compared to other metal-carbonyl radicals, Co(CO) is much less reactive COjCCO) is inert to irradiation in the presence of IC,H,. Even if the expected ICo(CO) were formed, its thermal instability would lead to problems. Irradiation in chlorocarbons produces Co3(CO),CCl in low yield. Under conditions where CO can be removed from solution, irradiation of COjCCO), in inert solvents leads to Co fCO) A likely mechanism involves CO loss from Co(CO) fragments that recombine to yield a transient, unsaturated dimer, which reacts with Co fCO), to give tetramer and CO. 

We conclude this introductory with a short outline of the sections that follow. In Section 2.3.2, we offer a brief introduction to pressrue and material gap problems that arise when model catalytic systems and conditions are used to emulate working catalytic systems. In Section 2.3.3, we describe the local aspects of the catalytically reactive sites in the section titled Ensemble effects and defect sites . This is followed by four sections on environmental influences on the reactivily entitled Cluster size and metal supports , Cooperativity , Surface moderation by coadsorption of organic molecules and Stereochemistry of homogeneous catalysts . The chapter is concluded with a section on surface kinetics, dealing with surface reconstruction and transient reaction intermediates. 

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