Methane matrices

Photolysis of Cp M(CO)2, M = Rh or Ir, and CpIr(CO)2 in methane matrices afforded the first direct observation of C-H activation from a photointermediate.Similarly, photolysis of Cp fr(CO)(H)2 in methane matrices yielded Cp Ir(CO)(H)(CH3). The rate of oxidative addition of alkanes to a CpRh(CO) photointermediate in the gas phase has been measured. 

The mechanism of the photochemical reaction has been the subject of some elegant experiments involving polarized light both for photolysis and for spectroscopic measurements. Unpolarized UV photolysis of Cr(CO)6 in pure methane matrices yields randomly oriented Cr(CO)s- CH4 molecules. Polarized visible photolysis leads to specifically oriented Cr(CO)s- CH4 molecules, as evidenced by the development of linear dichroism in the visible absorption band. The direction of the spectral dichroism depends upon the direction of polarization of the irradiating beam (equation 22). 

Used to calculate other frequencies (in methane matrices at 20 K). 

T -C5Me5) Ir (CO) (n -NCCgH4Cl) in hydrocarbon solvents results in activation of the solvent C-H bonds,and a study of the photoactivation of methane matrices by complexes of the type (M(n -C5Rs)(CO)2l (M Ir or Rh, R H or Me) has been reported.Photoinduced charge separation and recombination kinetics have been measured for the dimeric Ir(I) complexes [ Ir ( i-pz ) (CO) (PPh2 o(CH2)2R) ) I2 IP 3,5-dime thy Ipyrazolyl R pyridine (py), 4-phenylpyridine]. The results suggest that these complexes are well adapted to detailed studies of Intramolecular electron-transfer reactions. 

Rest and Graham reported in 1984 that the metal carbonyl complexes CpRh(CO)2, CpIr(CO)2, and Cp Ir(CO)2 can be deposited in methane matrices at 12 K and irradiated to give the corresponding methane oxidative addition products [28]. In addition, the dihydride CpIr(CO)H2 could be irradiated in a methane/argon matrix to generate CpIr(CO)(CH3)H by an alternative route [29]. While the dicarbonyl compounds were not efficient producers of the coordinatively unsaturated intermediate, Perutz found that CpRh(CO)(C2H4) lost... 

Graham has reported that irradiation of (r 6-C6Me6)Os(CO)2 in alkane solution leads to the formation of alkane oxidative addition complexes in competition with C6Me6 loss [97]. Perutz and Werner have also reported the photochemical reaction of (r 6-mesitylene)Os(CO)H2 in methane matrices leading to the formation of the methane activation product (ri6-mesitylene)Os(CO)(CH3)H [98]. 

The detection of CuH and CuMe in methane matrices at 12K following the 320 nm photolysis of copper atoms has led to the proposal that optically excited copper atoms insert into the C—H bond of methane. The HCuMe species thus produced undergoes secondary photolysis to give CuH and methyl radicals and also CuMe and hydrogen atoms. The photoproperties of silver atoms in matrices have been studied in detail. 

It has previously been shown that recombination of the fragments formed on photolysis of Cr(CO)e in methane matrices may be induced by irradiation in the... 

The effect of these two corrections is best shown (in Table 3) by the close examination of the t u mode of various isotopomers of Cr(CO)e in methane matrices at 20 K. 

Photolysis of the benzene complex rj -C6H6Cr(CO)3 in a Nujol mull at 77 K shows that for this complex the loss of CO occurs as a reversible process. This result, along with similar observations made in methane matrices at 12 K, provides further good support that loss of CO is a primary photoprocess in these complexes. " " ... 

There is still debate concerning the bonding mode of the acyl in the coordinatively unsaturated intermediate usually assumed to occur during CO insertions. An IR study of [Mn(CO)4(COMe)] and [CpFe(CO)(COMe)] in methane matrices at 12 K suggests that, at least under these conditions, the bonding is -acetyl and not rj -acetyl. ... 

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