Controlled Formation of Heteroleptic [Pd₂(L_a)₂(L_b)₂]⁴⁺ Cages

Abstract

Metallosupramolecular architectures are beginning to be exploited for a range of applications including drug delivery, catalysis, molecular recognition, and sensing. For the most part these achievements have been made with high-symmetry metallosupramolecular architectures composed of just one type of ligand and metal ion. Recently, considerable efforts have been made to generate metallosupramolecular architectures that are made up of multiple different ligands and/or metals ions in order to obtain more complex systems with new properties. Herein we show that the addition of an electron-rich 2-amino-substituted tripyridyl ligand, 2,6-bis(pyridin-3-ylethynyl)pyridine (2A-tripy), to a solution of the [Pd2(tripy)4](4+) cage resulted in the clean generation of a heteroleptic [Pd2(tripy)2(2A-tripy)2](4+) architecture. The formation of the mixed-ligand cage [Pd2(tripy)2(2A-tripy)2](4+) was confirmed using (1)H NMR spectroscopy, diffusion-ordered spectroscopy, and rotating-frame nuclear Overhauser effect spectroscopy and high-resolution electrospray ionization mass spectrometry. Density functional theory calculations suggested the cis isomer was more stable that the trans isomer. Additionally, the calculations indicated that the heteroleptic palladium(II) cages are kinetically metastable intermediates rather than the thermodynamic product of the reaction. Competition experiments supported that finding and showed the cages are long-lived in solution at room temperature. Finally, it was shown that the addition of 2A-tripy to a range of preformed [Pd2(Ltripy)4](4+) cages cleanly generated the mixed-ligand systems. Three other systems displaying different exo and endo functionalities within the cage assembly were generated, suggesting that this method could be applied to synthesize a range of highly functionalized heteroleptic cis-[Pd2(La)2(Lb)2](4+) cages.

Donor‐Site‐Directed Rational Assembly of Heteroleptic cis‐[Pd2L2L′2] Coordination Cages from Picolyl Ligands

“…Nevertheless, approaches to control the arrangement and assembly of template‐free [M 2 L 2 L ′ 2 ] cages are currently being developed in several groups . For example, Crowley reported a strategy to achieve kinetically trapped cis ‐[Pd 2 L 2 L ′ 2 ] cages through ligand substitution reactions of an unfunctionalized homoleptic cage precursor with 2‐amino‐functionalized pyridyl ligands . Recently, we reported that [Pd 2 L 2 L ′ 2 ] cages can be accessed by utilizing ligands of complementary shape.…”

Towards Water Soluble Mitochondria-Targeting Theranostic Osmium(II) Triazole-Based Complexes

“…Key to the development of complexes for these applications is the design of the ligands supporting these metals. We, and others, have paid particular attention to the use of copper-catalysed coupling of alkynes and azides to form 1,2,3-triazole-based ligands [7][8][9][10] and have investigated the photophysical properties of their resultant complexes. A significant number of reports have appeared detailing the photophysical and photochemical properties of triazole-based complexes of Re(I), Ru(II) and Ir(III) [11][12][13][14][15][16][17][18][19][20][21][22][23][24][25].…”

Tunable Fullerene Affinity of Cages, Bowls and Rings Assembled by PdII Coordination Sphere Engineering

“…Fujita and Yoshizawa used pyridine/lutidine pairs around cis ‐protected Pd II to construct prismatic cages, and we recently expanded this concept to work on “naked” Pd II centers, using a combination of inward and outward pointing picolines to give cis ‐[Pd 2 L 2 L′ 2 ] cages . Crowley achieved similar structures with 2‐amino‐modified pyridine ligands …”

“…[12] Crowley achieved similars tructures with 2-aminomodifiedp yridine ligands. [13] When considering other sterically more demanding donor functionalities, we recently started to substitute pyridines with quinolines, which carry an hydrogen atom on the annelated benzene ring that causes steric congestion aroundt he metal binding site. [14] We tested this methodo nb is-monodentate banana-shapedl igandsw ith ad ibenzo-2.2.2-bicyclo-octane backbonea nd showedt hat the pyridine derivative L 1 leads to the formation of atypical[Pd 2 L 1 4 ] 4 + cage while 6-quinolinyl derivative L 2 cleanly forms bowl [Pd 2 L 2 3 (MeCN) 2 ] 4 + when palladium precursor[ Pd(MeCN) 4 ](BF 4 ) 2 was mixed with L 2 in a2 :3 ratio in acetonitrile.…”