Terpyridine–Porphyrin Hetero‐Pacman Compounds

Abstract

The two different coordination spheres afforded by Pacman architectures offer cooperativity derived from two different metal centers. A modular strategy is developed to produce a hetero-Pacman scaffold featuring a porphyrin and terpyridine for metal-ion binding. A double Suzuki reaction was employed to first attach a terpyridine moiety to a xanthene backbone and then attach a porphyrin. The new hetero-Pacman scaffold has been characterized and all building blocks have been isolated and structurally characterized. The principle objective to incorporate different metal centers was confirmed by isolating a trinuclear complex comprising two porphyrinic units and a bis(terpyridine)-iron unit. The compounds described herein expand the Pacman scaffold concept by allowing for the incorporation of a terpyridine-metal complex proximate to a porphyrin-cofactor active site for small-molecule activation.

Sensitised LnIII Emission and Excited‐State Dynamics of Cofacial ‘Pacman’ Porphyrin Terpyridine Complexes

“…Additional low‐temperature 1 H NMR measurements (data not shown) were also undertaken at T =−30 °C to establish if rapid ligand exchange was potentially obscuring the 1:2 ML 2 complex equilibria, but there was no evidence for the formation of higher‐order complexes. This behaviour differs to that previously observed with Fe II ; in this case, a 1:2 ML 2 complex was crystallised then structurally characterised by X‐ray diffraction . In the present case, however, it is likely the larger ionic radius of the Ln III cations (about 1.03 Å for Lu III , coordination number (CN)=9 versus about 0.61 Å for Fe II , CN=6, low spin) together with our deliberate use of the strongly coordinating inner‐sphere nitrate anions prevents the formation of higher‐order species due to steric restraints.…”

“…We have previously demonstrated that the appended terpyridine chelate in [Zn(PXT)] can interact with 3d and 4d transition‐metal cations, such as Fe II or Ru II , and rationalised that this unit may also be suitable for binding larger 4f lanthanide metal cations …”

High‐Yielding Synthesis of a Hetero‐Pacman Compound and the Characterization of Intermediates and Side‐Products

“…Sect. [54] A similar positive effect on the yield of a palladium-catalyzed cross-coupling reaction with 1 to yield a Pacman-type compound has been reported just recently. One interesting feature to note is that the mass spectroscopic analysis of 3a is hampered by a fast reaction with the solvent methanol in the ESI-MS.…”

“…Compounds 2,7-di-tert-butyl-9,9-dimethylxanthene-4,5-diboronic acid (1), [52] (10-bromo-5,15-dimesitylporphyrinato)zinc (2), [69] 4Ј-bromo-2,2Ј:6Ј,2ЈЈ-terpyridine (4), [54,70] and [Ru(CH 3 CN) 2 (bpy)Cl 2 ] [71] were prepared according to literature procedures. thf, dioxane, toluene, dcm, dmf, hexane, ethyl acetate, and methanol and most starting materials were obtained from Sigma-Aldrich and used without further purification.…”

“…A very similar compound to 3a (with an additional third meso-mesityl substituent) has already been synthesized by a different route in a yield of around 25 % [by using [Pd 2 (dba) 3 ], tricyclohexylphosphine, a bromide-substituted version of 3a, bis(neopentylglycolato)diboron, and KOAc in dioxane and acidic workup]. [54][55][56][57] The xanthene backbone seems to have no structural influence. Interestingly, when 3a was recrystallized from chloroform/methanol, one of the boronic acid functionalities became methylated to form 3b, which could be isolated in crystalline form (3b·2.5CH 3 OH, Figure 1).…”