Checking the Route to Cluster Helicates

Two Synthetic Approaches to Coinage Metal(I) Mesocates: Electrochemical versus Chemical Synthesis

We report two different approaches to isolate neutral and cationic mesocate-type metallosupramolecular architectures derived from coinage monovalent ions. For this purpose, we use a thiocarbohydrazone ligand, H₂L (1), conveniently tuned with bulky phosphine groups to stabilize the M^I ions and prevent ligand crossing to achieve the selective formation of mesocates. The neutral complexes [Cu₂(HL)₂] (2), [Ag₂(HL)₂] (3), and [Au₂(HL)₂] (4) were prepared by an electrochemical method, while the cationic complexes [Cu₂(H₂L)₂](PF₆)₂ (5), [Cu₂(H₂L)₂](BF₄)₂ (6), [Ag₂(H₂L)₂](PF₆)₂ (7), [Ag₄(HL)₂](NO₃)₂ (8), and [Au₂(H₂L)₂]Cl₂ (9) were obtained by using a metal salt as the precursor. All of the complexes are neutral or cationic dinuclear mesocates, except the silver nitrate derivative, which exhibits a tetranuclear cluster mesocate architecture. The crystal structures of the neutral and cationic copper(I), silver(I), and gold(I) complexes allow us to analyze the influence of synthetic methodology or the counterion role on both the micro- and macrostructures of the mesocates.

Conversion of a double-tetranuclear cluster silver helicate into a dihelicate via a rare desulfurization process

We show the first example of a bisthiosemicarbazone silver double-tetranuclear cluster helicate [Ag4L2]2 obtained by electrochemical synthesis which undergoes a rare desulfurization process giving rise to a cationic silver dihelicate [Ag2(H2L)2]SO4.

Silver complexes stabilized by large silanethiolate ligands - crystal structures and luminescence properties

Bulky silanethiolate and disiladithiolate ligands were applied to synthesize one mononuclear and three trinuclear silver complexes including two cyclic "microclusters" and a linear tri-nuclear silanethiolate complex. All obtained compounds are characterized by X-ray diffraction and FT-IR. NMR and emission spectroscopies were used where possible. The first trinuclear anionic silver thiolate is structurally characterized. The influence of the different charge of cyclic silver complexes as well as the overall ligand environment on the structural properties is demonstrated. The impact of the different synthetic routes on the final structures of the obtained clusters - cyclic or linear - is discussed.

Triple-Stranded Cluster Helicates for the Selective Catalytic Oxidation of C-H Bonds

Triple-stranded cluster helicates with heptametallic dicubane cores are synthesized by entrapping metals in the cavities of linear triple helicates based on a C₂-symmetrical hexadentate Schiff-base ligand of ortho-substitued biphenol. The helicates are stable in both the solution and solid states, and the copper species could selectively catalyze the oxidation of C-H bonds of alkanes to ketones.

Endogenous arene hydroxylation promoted by copper(I) cluster helicates

A novel neutral triple-stranded hexanuclear copper(I) cluster helicate [Cu(I)(6)L(3)]·2CH(3)CN derived from a thiosemicarbazone ligand could be synthesized and crystallographically characterized. The MALDI mass spectrum of this complex suggests that the tetranuclear copper(I) cluster helicate [Cu(I)(4)L(2)] is also present in solution. These copper(I) cluster helicates are capable, in the presence of O(2), of hydroxylating the arene linker of their supporting ligand strands. The resulting dinuclear complex [Cu(II)(2)L'(OH)] is formed by two copper(II) centers, a new ligand arising from the hydroxylation reaction, and one hydroxide group. The magnetic investigation of this compound shows a strong antiferromagnetic coupling between the two Cu(II) centers. The kinetic studies for the hydroxylation process show values of ΔH(≠)=-70 kJ mol(-1), similar to those mediated by the tyrosinase enzymes.