Matrix isolation methane complexes

The photochemical activation of hydrocarbons by 430 was the first such report for any group 9 Tp complex,and has subsequently been the subject of numerous independent mechanistic studies. The earliest of these involved matrix isolation (Ar, CH4, N2, CO) infrared and electronic spectroscopic studies of 430, and its analogue Bp Rh(CO)2 (262). On this basis it was established that the initial photoreaction results in loss of CO and mono-dechelation of the, initially ic, Tp ligand to afford (K -Tp )Rh(CO), which in N2 and CO matrices was rapidly trapped. It was also noted that at 12K no evidence of C-H activation was observed in either the methane matrix, or in Nujol muUs. However, at 77 K activation of Nujol was observed, thus establishing a thermal requisite for the C-H activation step, i.e. while photolysis generates the active species , subsequent C H oxidative addition is a thermal process. 

It is a simple enough matter to extend this to complexes which, even if all the v(CO) absorptions were observed, would stUl have more force constants than observed frequencies (i.e., underdetermined force fields). As an example, consider the force field (Table 5) of HMn(CO)5 isolated in a methane matrix at 20 K which has three IR absorptions and five force constants. The close correspondence between the force constants calculated by different means is quite striking. 

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