Toward a Photochemical and Thermal Molecular Machine:  Reversible Ligand Dissociation and Binding in a Ruthenium(II)-2,2‘-bipyridine Complex with Tris(2-pyridylmethyl)amine

Abstract

A Ru(II) complex having tris(2-pyridylmethl)amine (TPA) and 2,2'-bipyridine (bpy), [Ru(TPA)(bpy)]X(2) (X = ClO(4), PF(6)), exhibited a severe distortion of the coordination of the axial pyridine moiety of TPA due to steric hindrance. The complex showed interesting dissociation-binding behavior of the axial pyridine arm to form a solvent adduct with TPA ligation in a unique meridional tridentate fashion. The complex undergoes thermal dissociation to form solvent-coordinated species via an S(N)2-like mechanism with activation energy of 117 kJ/mol. In contrast, the complex showed reversible photochemical dissociation and rebinding via an S(N)1-like mechanism by MLCT irradiation. The photochemical dissociation was accelerated approximately 200-fold faster than the thermal process. The dissociation process involves selective binding behavior toward external ligands (solvents) with pi-acceptor character, which is indispensable, and no sigma-donating molecules could bind to the Ru(II) center. The guest molecule can be released upon photoirradiation after its thermal binding.

A [4+2] mixed ligand approach to ruthenium DNA metallointercalators [Ru(tpa)(N–N)](PF6)2 using a tris(2-pyridylmethyl)amine (tpa) capping ligand

“…The former are assigned to MLCT transitions from the ruthenium to the tpa ligand, while the latter are apparently a superposition of several poorly resolved peaks and due to a MLCT from the ruthenium to the bidentate N-N ligand [26]. These assignments are supported by the TDDFT calculations reported in Section 2.5.…”

“…Ruthenium complexes 1-5 were prepared from [Ru(tpa) (dmso)Cl]PF 6 and the bidentate N-N ligand by the route described in the literature for parent compound [Ru(tpa)(bpy)](PF 6 ) 2 , as shown in Scheme 1 [24][25][26]. After purification by column chromatography on silica with a mixture of methanol/water/sodium chloride (12:6:1) as the eluent and recrystallization from acetone/diethylether, they were obtained as crystalline solids in reasonable yield in a procedure optimized for purity.…”

“…The ease of modification and functionalization of the N-donor groups in such podant tetradentate ligands will also allow one to fine-tune the electronic and photophysical properties of the metal center [22]. In addition, the known lability of one of the tpa pyridylmethyl substituents under certain conditions might also open the way to systems in which a switch of DNA binding from intercalating to covalent might be possible [26]. To explore their potential suitability for such applications, we investigated a series of tpa complexes 1-5 with increasing aromatic surface area of the bidentate ligand ( Fig.…”

Preparation, crystal structures and oxidation activity of two novel nickel(II) complexes of tripodal ligand containing coordinated solvent molecules

“…The nickel(II) ion is in a six-coordinated environment defined by three pyrazole nitrogen atoms and one amine nitrogen from TMPzA, one nitrogen atom from an acetonitrile molecule and an oxygen atom from a coordinated water molecule. The case of the acetonitrile molecule coordinated to the metal center with another tripodal ligand has been encountered [13]. The geometry of (1) is best described as a distorted octahedron with the amine nitrogen and the acetonitrile nitrogen in the axial sites, the three nitrogen atoms of the pyrazole ring of the ligand and the water oxygen defined the mean plane.…”

Effect of Deprotonation of a Benzimidazolyl Ligand on the Redox Potential and the Structures of Mononuclear Ruthenium(II) Complexes

“…The six methylene protons are all inequivalent with respect to their chemical environment, and each CH 2 group displays an AB quartet (Figure 3a). Compared with the 1 H NMR spectra of the reported complex coordinated by the ligands bearing 2-pyridylmethyl moieties, [28] the quartet centered at δ = 5.08 is attributed to the CH 2 group attached to the benzimidazolyl unit, and the other two quartets to the CH 2 groups of the pyridylmethyl units. Upon addition (Figure 3b), which suggests that no other reaction or decomposition occurs during the deprotonation process.…”