DFT and time-resolved IR investigation of electron transfer between photogenerated 17- and 19-electron organometallic radicals

Abstract

The photochemical disproportionation mechanism of [CpW(CO)

Investigation of organometallic reaction mechanisms with one and two dimensional vibrational spectroscopy

“…With the assignment of radicals R 1 through R 4 presented in the preceding section, we can build a complete picture of the ligand substitution dynamics, as depicted in Figure 5 is surprising but comparable to earlier results reported for tungsten radicals [21][22][23][24]. The observation of similar reactivity for the two different metals is a strong indication of the generality of the reaction mechanism.…”

“…Thus, we assign R 3 (1910 cm -1 ) to the 17e radical CpFe(CO)P(OMe) 3 and R 4 (1899 cm [167]. We have reported that steric effects play a major role in determining the dynamics of 19e radicals for the analogous tungsten system (see Chapter 3) [21,23]. We thus expect that a 19e radical with two Lewis bases is less likely to form in the presence of a larger Lewis bases.…”

“…We assign R 2 to the 19-electron intermediate CpFe(CO) 2 P(OMe) 3 on the basis of DFT calculations, which are discussed in detail in Section 5.7. Note that in the presences of phosphines and phosphites, it is well-known metal-metal bonded dimers like [CpFe(CO) 2 ] 2 may undergo disproportionation reactions to form ionic products [138], and these reactions can occur on both the picosecond [23,24] and microsecond [21] time-scales (see Chapters 3 and 4). We did not observe these products in our experiments because the Fe dimer does not form ionic products as readily as other metals, such as Mo or W, and because the non-polar solvent, hexane, does not favor the formation and stabilization of disproportionation products [138,147,195].…”

“…The observed and calculated vibrational frequencies are summarized in Table 5.2, and the molecular structures for the radicals are depicted in Figure 5.11. DFT calculations have been shown reliable for predicting the energetics, vibrational frequencies, electronic structure, and molecular geometries of organometallic radicals [21][22][23][24]132,170,[207][208][209]. Figure 5.11a shows the 17e radical CpFe(CO) 2 (R 1 ) which serves as the reference point for the reported energies of all other radical species.…”

“…Pump-probe spectroscopy has been extensively used to understand these types of dynamics [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19], and this work applies the same pump-probe methodologies as well as a relatively new technique, two dimensional infrared spectroscopy, to the photophysics and reactions of several prototypical organometallic complexes [20][21][22][23][24][25][26].…”