Photochromism of an Organorhodium Dithionite Complex in the Crystalline-State: Molecular Motion of Pentamethylcyclopentadienyl Ligands Coupled to Atom Rearrangement in a Dithionite Ligand

Abstract

In the crystalline state, the rhodium dinuclear complex [(RhCp*)(2)(mu-CH(2))(2)(mu-O(2)SSO(2))] (1) with a photoresponsive dithionite group (mu-O(2)SSO(2)) and two pentamethylcyclopentadienyl ligands (Cp* = eta(5)-C(5)Me(5)) undergoes a 100% reversible unimolecular type T inverse photochromism upon interconversion to [(RhCp*)(2)(mu-CH(2))(2)(mu-O(2)SOSO)] (2). The photochromism can be followed directly by using stepwise crystal structure analysis (Angew. Chem., Int. Ed. 2006, 45, 6473). In this study, we found that the photoreaction of 1 was triggered by absorption of the 510 nm light (charge transfer band from sigma(S-S) to sigma*(S-S) and sigma*(Rh-Rh) orbitals assigned by DFT calculation) and included two important processes: kinetically controlled oxygen-atom transfer to produce four stereoisomers of 2 and thermodynamically controlled isomerization between the four stereoisomers of 2 to afford the most stable isomer. Although the formation rate of the four stereoisomer products was kinetically controlled and the population of the four stereoisomers produced in the system was thermodynamically controlled, both processes were regulated by the steric hindrance between the mu-O(2)SSO(2) or mu-O(2)SOSO ligand and the reaction cavity formed by the Cp* ligands. The cooperation of both processes achieved an intriguing stereospecific oxygen-atom rearrangement to produce only one stereoisomer of 2 at the final stage of the photoreaction at room temperature. We also determined the effect of the oxygen-atom rearrangement on the rotational motion of the two crystallographically independent Cp* ligands (parallel and perpendicular arrangement). Using variable-temperature (13)C CP/MAS NMR and quadrupolar echo solid-state (2)H NMR spectroscopies, before photoirradiation, the activation energies for the rotation of the parallel and perpendicular Cp* ligands in 1 were determined to be 33 +/- 3 and 7.8 +/- 1 kJ/mol, respectively, and after photoirradiation, in 2, they were much lower than those in 1 (21 +/- 2 and 4.7 +/- 0.5 kJ/mol, respectively). The large decrease in the activation energy for the parallel Cp* in 2 is attributed to the relaxation of molecular stress via a stereospecific oxygen-atom rearrangement, which suggests that the rotational motion of the Cp* ligands is coupled to the photochromism.

Proton Order–Disorder Phenomena in a Hydrogen‐Bonded Rhodium–η5‐Semiquinone Complex: A Possible Dielectric Response Mechanism

“…The Cp* ring exhibits slightly larger thermal ellipsoids than the p-HSQ-Me 4 ligand even at 101 K. These ellipsoids are increased continuously from the LT phase instead of the transition point (the Supporting Information, Figures S7 and S9), indicating the potential for libration or rotationo ft he Cp* ring around the RhÀCp* ring centroid vector.T he Cp* ligand is knownt ou ndergo rotational motion, called 2p/5 jumping motion. [23] Also, temperature-independent 13 Cr esonances corresponding to this rotational motion have been observed in [(Cp*Rh) 2 (m-CH 2 ) 2 (m-O 2 SSO 2 )],w hich presents thermal ellipsoids of almost the same size as those observed in [1]PF 6 at 101 K. [24] These observations suggest that the Cp* ring of [1]PF 6 starts rotating at low temperature, and this rotationi s accelerated with increasing temperature. Investigation of this dynamic behavior by using 13 CC P/MAS NMR spectroscopy will be discussed below.T he thermal ellipsoids of the PF 6 À anion are also increased continuously with increasing temperature from the LT phaseinstead of the phasetransition(the Supporting Information, Figures S5 and S10).…”

“…The Cp* ligand is known to undergo rotational motion, called 2 π /5 jumping motion 23. Also, temperature‐independent 13 C resonances corresponding to this rotational motion have been observed in [(Cp*Rh) 2 (μ‐CH 2 ) 2 (μ‐O 2 SSO 2 )], which presents thermal ellipsoids of almost the same size as those observed in [ 1 ]PF 6 at 101 K 24. These observations suggest that the Cp* ring of [ 1 ]PF 6 starts rotating at low temperature, and this rotation is accelerated with increasing temperature.…”

Synthesis and Spectroscopic Studies of the Photochromism of Bifunctional Derivatives of Cymantrene in Solution and without Solvent

“…Ligand exchange at the metal atom is a fundamental property of transition‐metal half‐sandwich complexes and is applied widely as the basis for the synthesis of various compounds . In particular, the photoinduced ligand exchange of some functional derivatives of cymantrene [(cyclopentadienyl)tricarbonylmanganese], (benzene)tricarbonylchromium, and related π‐complexes is often accompanied by a substantial color change of the solution and the formation of photochromic systems . Traditionally, photoinduced ligand exchange for cymantrene derivatives is performed by irradiation of solutions in alkanes, benzene, tetrahydrofuran (THF), or acetonitrile.…”

Dithionite and sulfinate complexes from the reaction of SO2with decamethylsamarocene

“…1 Besides the synthesis of sulfur-containing chemicals such as sulfuric acid, sulfur dioxide is a wellestablished ligand in coordination chemistry. With the exception of sodium dithionite 9,10 [ZnS 2 O 4 (pyridine)] n , 11 and [Sn 2 (S 2 O 4 ) 2 ], 12 only two families of structurally characterized dithionite transition metal complexes have been reported, namely [{Rh(C 5 H 4 R)} 2 (m-CH 2 ) 2 (m-O 2 SSO 2 )] (R = Me, Ph, Et, nPr, CH 2 Ph), [13][14][15][16][17][18] and [{(Z 5 -C 5 Me 5 )Mo(CO) 3 } 2 (S 2 O 4 )]. [2][3][4][5] Besides the oxidation of sulfur dioxide to sulfur trioxide for the production of sulfuric acid, 6 the reduction of sulfur dioxide to elemental sulfur (Claus process) 7 or to sodium dithionite 8 are also well-established industrial processes.…”