Dual Metalation Site Zr-Metal–Organic Frameworks: Controlled Synthesis of Metal–Organic Framework-Bound Proximal Metal Complexes

Isolating multiple metal ion species within a confined microenvironment can facilitate cooperative interactions that underpin multielectron processes and synergistic or tandem catalysis. Herein, we report the design and synthesis of three flexible Zr-MOFs (UAM-1001-Py, UAM-1002-Py, and UAM-1003-Py) constructed from a trifunctional linker featuring two distinct coordination sites, based on bispyrazole and pyridyl donors, that can be postsynthetically metalated. Using UAM-1002-Py and UAM-1003-Py, we successfully isolated both cis and trans-PdCl₂ isomers within each framework; however, enhanced rigidity along the a-axis in UAM-1003-Py slightly altered the metalation outcome. Reactivity studies with Na[BH(Et)₃] revealed selective leaching of cis-PdCl₂ from the bispyrazole sites, while the trans-PdCl₂ pyridyl sites remained largely intact due to stronger donor coordination, the trans effect, and significant steric protection. Using UAM-1001-Py, site-selective metalation occurred to give a dimer [Ni₂(μ-Cl)₃(H₂O)Cl] with vacant pyridyl sites, while a [Rh₂(μ-CO)₃Cl₂] dimer at bispyrazole sites and a monomeric [Rh(CO)₂Cl] complex at the pyridyl site were formed simultaneously. Sequential metalation of UAM-1001-Py afforded a heterometallic system, with a [Ni₂(μ-Cl)₃(H₂O)Cl] dimer binding the bispyrazole site and a [Rh(CO)₂Cl] species at the pyridyl site. This work establishes a modular approach for advancing precise control over metal incorporation to construct homo and heteronuclear multimetallic species that underpin complex chemical transformations.