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. 2017 Feb 8:8:14296.
doi: 10.1038/ncomms14296.

Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

Hitoshi Ube  1 , Yoshihiro Yasuda  1 , Hiroyasu Sato  2 , Mitsuhiko Shionoya  1
Affiliations

Metal-centred azaphosphatriptycene gear with a photo- and thermally driven mechanical switching function based on coordination isomerism

Hitoshi Ube et al. Nat Commun. .

Abstract

Metal ions can serve as a centre of molecular motions due to their coordination geometry, reversible bonding nature and external stimuli responsiveness. Such essential features of metal ions have been utilized for metal-mediated molecular machines with the ability to motion switch via metallation/demetallation or coordination number variation at the metal centre; however, motion switching based on the change in coordination geometry remain largely unexplored. Herein, we report a PtII-centred molecular gear that demonstrates control of rotor engagement and disengagement based on photo- and thermally driven cis-trans isomerization at the PtII centre. This molecular rotary motion transmitter has been constructed from two coordinating azaphosphatriptycene rotators and one PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form is reversibly driven by ultraviolet irradiation and heating. Such a photo- and thermally triggered motional interconversion between engaged/disengaged states on a metal ion would provide a selector switch for more complex interlocking systems.

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Conflict of interest statement

The authors declare no competing financial interests.

Figures

Figure 1
Figure 1. Schematic representation of a PtII-centred molecular gear PtCl212.
This molecular gear has two azaphosphatriptycene rotators coordinating to the central PtII ion as a stator. Isomerization between an engaged cis-form and a disengaged trans-form are reversibly driven by ultraviolet irradiation at 360 nm and heating.
Figure 2
Figure 2. 1H NMR spectra of rotator 1 and cis- and trans-PtCl212.
The signals of a methoxy group of rotator 1 (∼3.8 p.p.m.) are omitted for clarity. For the whole NMR spectra, see the Supplementary Figures 7, 11 and 16. (a) 1H NMR spectrum of (i) 1, (ii) cis-PtCl212 and (iii) trans-PtCl212 (500 MHz, CDCl3, 300 K). The 1H NMR spectra of cis-PtCl212 include meso and dl isomers in a ∼1:2 ratio. (b) Isomerism based on rotational conformation. (c) Observed and simulated spectra of 3-positions' proton at varied temperatures (500 MHz, TCE-d2/toluene-d8=1:1). Left: observed spectra in the range from 380 to 300 K. Right: simulated spectra based on the two-state exchange model. Green and orange circles denote meso and dl isomers, respectively.
Figure 3
Figure 3. X-ray crystal structures of cis- and trans-PtCl212.
(a) cis-PtCl212·(ether). (b) trans-PtCl212·(C6H6)2. In both cases, the structures are indicated as ORTEP (Oak Ridge Thermal Ellipsoid Plot) diagram with 50% thermal ellipsoid (upper) and space-filling model (bottom). Solvents are omitted for clarity, and colours are coded according to CPK (Corey, Pauling, Koltun) colouring.
Figure 4
Figure 4. Photo and thermal switching of molecular gear PtCl212.
(a) Photo- and thermally induced isomerization between cis- and trans-PtCl212. (b) 1H NMR spectra for photo- and thermally induced isomerization from cis- to trans-PtCl212 (500 MHz, 300 K). (i) A solution of single crystals of cis-PtCl212 in toluene-d8 (cis/trans=99:1); (ii) a solution of (i) after photoirradiation at 360 nm (after 30 min, cis/trans=15:85); (iii) a solution of single crystals of trans-PtCl212 in TCE-d2 (after 5 min, cis/trans=12:88); (iv) a solution of (iii) after 10 h at room temperature (cis/trans=2:98). (c) Reversible switching of the molecular gearing system, PtCl212, in TCE-d2/toluene-d8=1:1 (v v−1).
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