Structure, Spectroscopy and Photochemistry of the [M(η5-C5H5)(CO)2]2 Complexes (M=Fe, Ru)

Abstract

The structures of all possible isomeric forms of the [M(h 5 -C 5 H 5 )(CO) 2 ] 2 complexes (M=Fe, Ru) are calculated with the use of the DFT method. The results indicate that both dimers can occur in three stable forms: bridged trans and cis and non-bridged trans. Contrary to the previous reports, the cis non-bridged form turns out to be an unstable transition state. Instead, an additional stable structure, a gauche non-bridged one, is found but only in the case of the Ru compound. Without any outer-sphere interaction the trans-bridged form is of the lowest energy for both dimers. The results are compared with the experimental data. Strong impact of the medium on the stability of the individual structures in solution is emphasized. The electronic spectra of all stable forms, calculated using TDDFT method, reproduce well spectral properties of both complexes. Moreover, they are useful in interpreting the medium effect and photochemical behaviour. The photoreactivity is briefly reviewed pointing at analogies and differences between the Fe and Ru complexes.

Ultrafast vibrational and structural dynamics of dimeric cyclopentadienyliron dicarbonyl examined by infrared spectroscopy

“…[1][2][3][4] The CpFe(CO) 2 dimer ([CpFe(CO) 2 ] 2 or Cp 2 Fe 2 (CO) 4 ), as a typical transition metal carbonyl complex, has been investigated for many years. 5,6 It is known that the CpFe(CO) 2 dimer can adopt multiple isomeric forms in solution. [7][8][9] The structures of two dominant isomers are shown in Scheme 1.…”

Unraveling Confined Dynamics of Guests Trapped in Self-Assembled Pd6L4 Nanocages by Ultrafast Mid-IR Polarization-Dependent Spectroscopy

“…[8][9][10][11] Recently, Fujita and co-workers have demonstrated that the Pd 6 L 4 nanocages can trap group VIII di-ruthenium carbonyl complexes. 9,11 The group VIII di-metal carbonyl complexes are well known for their interesting photochemistry [12][13][14] and catalytic properties 15 in addition to their fluxional behavior where they exist as multiple isomers in dynamic equilibrium. [15][16][17][18][19] When encapsulated by the Pd 6 L 4 nanocage, the di-ruthenium carbonyl complexes were stabilized in their cis-bridging isomeric form 9 and were shown to undergo carbonyl photosubstitution without cleavage of the metal-metal bond 11 .…”

“…Metal-directed self-assembled coordination cages can form nanosized cavities that can act to trap and stabilize guest molecules through noncovalent interactions. − The physical and chemical properties of these host–guest complexes are dictated by the interplay of many factors including steric restrictions, electrostatics, and weak interactions such as π-stacking. − , One such example of the self-assembled coordination cages is the octahedral Pd 6 L 4 nanocage first synthesized by Fujita and coworkers . This nanocage has been successfully employed over the last two decades to carry out selective ground and excited reactions and trap and stabilize reactive species. − Recently, Fujita and coworkers have demonstrated that the Pd 6 L 4 nanocages can trap group-VIII diruthenium carbonyl complexes. , The group-VIII dimetal carbonyl complexes are well known for their interesting photochemistry − and catalytic properties in addition to their fluxional behavior, where they exist as multiple isomers in dynamic equilibrium. − When encapsulated by the Pd 6 L 4 nanocage, the diruthenium carbonyl complexes were stabilized in their cis-bridging isomeric form and were shown to undergo carbonyl photosubstitution without cleavage of the metal–metal bond . From analysis of the X-ray crystal structures, the stabilization was attributed to π-stacking interactions between the triazine walls of the cage and the cyclopentadienyl ligands of the metal carbonyl complexes, and the photochemical products were suggested to arise from the restricted dynamics of the guests within the cage .…”

“…Previous studies performed on 1 and 2 have assigned the transitions beyond 400 nm to metal-to-ligand charge transfer (MLCT) bands of the different isomeric forms. , Upon the insertion of 1 and 2 into cages A and B , a change in this spectral region is observed, with a loss of the structured MLCT features and the appearance of a broad spectral feature that extends beyond the local absorption of 1 and 2 . Because the steady-state UV–vis spectra of cages A and B do not extend beyond 400 nm (see Figures S8 and S9), the change in the UV–vis spectrum is assigned to an electronic state associated with the host–guest complex and is attributed to the formation of a host–guest charge-transfer state observed in previous studies. , The UV–vis spectra confirm that the changes in the chelating ligands of the cages and the smaller size of the diiron metal carbonyl complex still result in the formation of the host–guest charge-transfer state.…”

“…Along with changes to the electronic excited state, previous studies have shown that the Pd 6 L 4 nanocage alters the dynamic equilibrium of the diruthenium complex ( 1 ) . When free in solution, metal carbonyl complexes 1 and 2 exist as different isomers in dynamic equilibrium, with 1 existing in four forms, cis-bridging, trans-bridging, gauche-nonbridging, and trans-nonbridging, and 2 existing in two forms, cis-bridging and trans-bridging. ,,, Each isomer has a distinct vibrational spectrum in the carbonyl stretching region that can be used as a spectroscopic reporter for a given isomer. ,,, Fujita and coworkers have demonstrated that this dynamic equilibrium is altered when the diruthenium metal carbonyl complex ( 1 ) is encapsulated by a Pd 6 L 4 nanocage, with the Pd 6 L 4 nanocage acting to stabilize the cis-bridging form . Here we expand on these studies through comparing FTIR spectra of 1 and 2 with their encapsulated forms, 1 ⊂ A , 1 ⊂ B , 2 ⊂ A , and 2 ⊂ B , to determine if altering the size of the nanocage cavity and the metal carbonyl guest will result in the stabilization of the cis-bridging isomer.…”