Photoswitchable Molecular Lock. One-Way Catenation of a Pt(II)-Linked Coordination Ring via the Photolabilization of a Pt(II)−Pyridine Bond

Abstract

An inert coordination bond that becomes labile under external stimuli can be termed "molecular lock" because a closed (locked) structure incorporating an inert bond is equilibrated with an open (unlocked) structure via the labilization of the inert bond. A Pt(II)-py bond (py ) pyridyl group) has been previously described as a thermally switchable molecular lock because its inert nature becomes labile at high temperature in the presence of a salt. 1 However, the salt-assisted thermal switching (locking/unlocking) is not a clean and facile process because of salt contamination and tedious procedures in salt removal. Here we report a precise, clean molecular lock that operates by light. We have found that the inert Pt(II)-py bond, whose photochemistry has attracted little attention, is considerably labilized upon UV irradiation (Scheme 1a). We demonstrate the photoswitchable molecular lock by the one-way catenation of coordination rings. 2,3 Namely, Pt(II)-linked ring 1 is rapidly catenated by irradiating 1 in an aqueous solution (Scheme 1b,c).Only a few reports have described the photodissociation of Pt(II)-py coordination bonds, where the dissociation is monitored by subsequent ligand substitution or isomerization. 4,5 We anticipate that, in the absence of any other ligands, the photodissociation is immediately followed by a re-coordination process, which has been often considered as an unfavorable side reaction in previous studies. 6As a result, a pyridyl ligand can be reversibly coordinated to platinum upon irradiation. On the basis of this idea, Pt(II)-ring 1 was irradiated in an aqueous medium in expectation of rapid catenation via the Pt(II)-py bond dissociation. Thus, Pt(II)-clipped coordination ring 1a was prepared from (en)Pt(NO 3 ) 2 and the corresponding ligand according to the procedure described previously. 2 A DMSO-d 6 /D 2 O (1:2) solution of 1a (2 mM) was irradiated at room temperature with an ultra-high-pressure Hg lamp filtered by a band-path glass filter (330 ( 70 nm). 7 Upon irradiation, the signals for 1a disappeared gradually along with the appearance of new signals for catenane 2a. The conversion was very rapid and, only after 15 min, 2a was quantitatively formed (Figure 1b,c). The spectra of both 1a and 2a are qualitatively identical to those of Pd(II) analogues reported previously. 2,8 Cold-spray ionization mass spectrometry (CSI-MS) measurement 9 confirmed the formation of 2a as evident from prominent signals that fully agreed with 2a: for example, m/z 618.3 [2a-(NO 3 -) 4 +(dmso) 7 ] Without irradiation, the once formed catenane 2a is "locked" and not allowed to dissociate into separate rings even in a nonaqueous solvent. In fact, when dissolved in MeCN/MeOH (1:1), catenane 2a remained unchanged and the dissociation was not observed despite the absence of effective hydrophobic interaction between the two rings. Of course, smooth dissociation into the component rings takes place if 2a is "unlocked" in a nonaqueous solvent. Upon irradiation in MeCN/MeOH (1:1), 2a disappeared Figure 1. 1 H N...

Photocrystallography

“…Studies have involved proton transfer (Ohhara et al, 2000), formation of a heterocyclic ring (Takayama et al, 2003), asymmetry generation and chiral inversion (Sekine et al, 1997), formation of a radical pair (Kawano et al, 2002), ligand substitution in organometallic compounds (Sato et al, 2007), excited-state formation . Separately, Kawano and coworkers have also described photochemical reactions that result in the formation of heterocyclic rings (Furusawa et al, 2007), organometallic catenation (Yamashita et al, 2007) and olefin dimerization (Takaoka et al, 2006). Techert and coworkers have also reported the structure of photodimerization reactions (Davaasumbuu et al, 2006).…”

Self‐Assembly of Water‐Soluble Platinum(II)‐Based Metallacalixarenes and Tuning Their Conformational Interconversion via Synergistic Effects between Solvents and Anions

“…According to the results shown (Figure S19). When the temperature was ranged from 298 K to 348 K, clearly signals and continuous down shift of the aromatic protons of 1 a in 1 H NMR spectroscopy reconfirmed the mechanism that the rotary motion occurred in 1 a between benzimidazole moieties around N‐Pt and N‐CH 2 bonds rather than dissociation and re‐coordination of the Pt−N bonds at room temperature …”

Movements Related to Opening, Closing, and Translocation Function

“…have been reported [75,76,146]. Photoinduced catenation was also obtained for a macrocycle containing a Ru(II) complex [147]. This function has been obtained by exploiting the properties of the Pt(II)-pyridine bond that is inert but can be labilized under UV irradiation.…”

“…17 A photoswitchable molecular lock[147]. On light irradiation, macrocycle 26 opens and undergoes quantitative catenation.…”