Thiolate Bridges in the Design of Nickel, Iron, and Palladium Complexes for Catalysis, Magnetic Interactions, and Polymer-Supported Dimanganese Complexes

Abstract

Natural processes have inspired the synthesis of inorganic and organometallic small molecules. A Cys-X-Cys biomimetic N2S2 ligand scaffold has been developed as a metal binding site to afford metallodithiolates. Metallodithiolates have been demonstrated to serve as bidentate ligands to form myriad hetero-polymetallic complexes. A new series of trimetallic M-Pd-M complexes and a Ni4Pd2 paddlewheel were synthesized using metallodithiolates. These complexes were characterized through single-crystal X-ray diffraction and tested for their ability to catalyze Suzuki-Miyaura and Sonogashira carbon-carbon cross-coupling reactions. Two complexes were successful with maximum isolated yields of 65%, for the Suzuki catalysis, and 75% for the Sonogashira catalysis on a 0.3 mmol scale with 0.015 mmol of pre-catalyst (5 mol%). An Fe-Pd-Fe trimetallic complex based on (N2S2) Fe(NO) was studied for potential spin-coupling of its two {Fe(NO)}7 units. An S = 1 triplet signal was observed through parallel mode EPR spectroscopy, and an antiferromagnetic coupling constant of J = -20 ±5 cm^-1 was calculated from this spectrum. Also, SQUID magnetometry showed that the two {Fe(NO)}7 units were weakly coupled at room temperature (µeff = 2.4 B.M.), with a singlet ground state at lower temperatures with J = -21 cm^-1, in good agreement with the EPR results. In a different molecular realm of cluster chemistry, the substitution of ^12CO with ^13CO on a sawhorse diosmium carbonyl complex was explored mechanistically with kinetic experiments and theoretical computations. The kinetic experiments supported a dissociative mechanism with a positive enthalpy of activation and an unexpectedly negative entropy of activation. This was resolved through computations, which suggested a dissociative interchange mechanism involving a bimolecular transition state with both the outgoing and incoming CO to account for the negative entropy of activation. Finally, four new thioester acetamide ligands for sulfur-bridged dimanganese compounds were synthesized to observe how their differing functional groups affected the isomerization of their respective dimanganese complexes. One of the ligands was modified and attached to poly(dimethylsiloxane) (PDMS) and metallated with zinc to afford a metallopolymer cross-linked through metal-ligand interactions. A synthetic route for attaching these types of thioester acetamide ligands to a polycarbonate terpolymer was also developed.