Abstract
Out-of-plane deformations of metalloporphyrin skeletons have been well documented as playing important roles in relevant biological processes. In contrast, out-of-plane binding to the N-core of large metal cations as period 6 post-transition elements has remained poorly investigated. We describe herein monometallic complexes of Pb(II) and Bi(III) with 5,10 single strapped porphyrin ligands bearing a carboxylic acid group with two possible “in/out” orientations, in which the metal ions are bound to the N-core of the macrocycle either from the strap side or from the naked side. In the case of Pb(II), both the kinetics of insertion and resulting OOP stereoselectivity are influenced by the “in/out” stereoisomerism of the overhanging COOH. Remarkably, Bi(III) insertion proceeded quasi-instantaneously at RT owing to the transmetalation of its Pb(II) counterpart. The addition of a cyano group in position of the carboxylic acid group generates a ligand exhibiting an increased stereoselectivity in the metalation processes with Pb(II) and Bi(III): these cations are coordinated exclusively from the naked and strap side of the macrocycle, respectively. This difference in behavior is likely explained by steric hindrance for the divalent cation, which is counterbalanced by the establishment of the second sphere of coordination with the strap for the trivalent cation. Such a behavior is thought of interest for the further design of adaptable supramolecular coordination assemblies.
Highlights
Lead(II) and bismuth(III) porphyrin complexes are known to form generally under harsh conditions [1,2,3] and to be mononuclear, that is one metal cation for one porphyrin unit dimeric structures have been reported [4,5]. These observations are valid for unfunctionalized macrocycles and the behavior of the porphyrin can be changed if not domesticated by additional functional groups around its binding site. With this target in mind, coordination of either lead(II) or bismuth(III) cations [6, 7] have been significantly investigated in decorated porphyrin ligands, those bearing one or two straps in diametrically opposed meso positions [8,9,10]
Our group has previously studied the influence of different types of functionalities such as the overhanging carboxylic acid porphyrins that open the way to a new supramolecular coordination chemistry
Coordination studies of Pb(II) and Bi(III) cations with/without cyano group beside the carboxylic acid have shown different conformational behaviors of the strap leading to unexpected metal complexes
Summary
Lead(II) and bismuth(III) porphyrin complexes are known to form generally under harsh conditions [1,2,3] and to be mononuclear, that is one metal cation for one porphyrin unit dimeric structures have been reported [4,5] These observations are valid for unfunctionalized macrocycles and the behavior of the porphyrin can be changed if not domesticated by additional functional groups around its binding site. With this target in mind, coordination of either lead(II) or bismuth(III) cations [6, 7] have been significantly investigated in decorated porphyrin ligands, those bearing one or two straps in diametrically opposed meso positions [8,9,10]. The coordination chemistry of overhanging carboxylic acid porphyrin 3 bearing an additional coordinating function (cyano) above the center of the macrocycle may be of interest to form adaptable supramolecular coordination assemblies [12,20,21]
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