Ultrafast Observation of a Solvent Dependent Spin State Equilibrium in CpCo(CO)

Abstract

We report the observation of a solvent-dependent spin state equilibrium in the 16-electron photoproduct CpCo(CO). Time-resolved infrared spectroscopy has been used to observe the concurrent formation of two distinct solvated monocarbonyl photoproducts, both of which arise from the same triplet CpCo(CO) precursor. Experiments in different solvent environments, combined with electronic structure theory calculations, allow us to assign the two solvated photoproducts to singlet and triplet CpCo(CO)(solvent) complexes. These results add to our previous picture of triplet reactivity for 16-electron organometallic photoproducts, in which triplets were not believed to interact strongly with solvent molecules. In the case of this photoproduct, it appears that spin crossover does not present a significant barrier to reactivity, and relative thermodynamic stabilities determine the spin state of the CpCo(CO) photoproduct in solution on the picosecond time scale. While the existence of transition metal complexes with two thermally accessible spin states is well-known, this is, to our knowledge, the first observation of a transient photoproduct that exhibits an equilibrium between two stable spin states, and also the first observed case in which a solvent has been able to coordinate as a token ligand to two spin states of the same photoproduct.

Spin‐forbidden reactions: computational insight into mechanisms and kinetics

“…The example of Fe(CO) 4 just discussed above is one case which is particularly well understood. The chemistry of the 16‐electron fragments CpMn(CO) 2 and CpCo(CO), derived from photolysis of the corresponding tri‐ and di‐carbonyl complexes, are two more systems that have received extensive attention …”

“…The chemistry of the 16-electron fragments CpMn(CO) 2 and CpCo(CO), derived from photolysis of the corresponding tri-and di-carbonyl complexes, are two more systems that have received extensive attention. [58][59][60]…”

Experimental and Theoretical Study of the Silicon-Hydrogen Bond Activation by Rhodium Dicarbonyl Complex in Solution

“…The role spin flip model in the photochemical reaction mechanism has also been investigated. Both Co and Rh complexes have undergone difference multiplicity in reaction mechanism [10,11]. Interestingly, the reactivity in these complexes has been dominated by triplet state in explaining the general interaction between unsaturated metal complexes and substrates.…”

A model study on the photodecarbonyl reaction of (η5-C5H5)M(CO)2 (M = Co, Rh, Ir)

“…Nevertheless, most of the E-H bond insertion reactions by CpML 2 organometallic compounds are heavily focused on their thermodynamical aspects, with a few discussions of their initially photochemical aspects. Indeed, to our knowledge, there has been little mechanistic study regarding the photolysis of the CpML 2 complex, [24][25][26][27][28][29][30][31][32][33][34][35][36] much less related theoretical research. In addition to the limitations of the spectroscopic instruments, there are many fundamental questions about the photolysis of CpML 2 in hydrosilane solution that need to be answered.…”