Designed Enclosure Enables Guest Binding Within the 4200 A Cavity of a Self-Assembled Cube

Metal–organic self-assembly has proven to be of great use in constructing structures of increasing size and intricacy, but the largest assemblies lack the functions associated with the ability to bind guests. Here we demonstrate the self-assembly of two simple organic molecules with CdII and PtII into a giant heterometallic supramolecular cube which is capable of binding a variety of mono- and dianionic guests within an enclosed cavity greater than 4200 Å3. Its structure was established by X-ray crystallography and cryogenic transmission electron microscopy. This cube is the largest discrete abiological assembly that has been observed to bind guests in solution; cavity enclosure and coulombic effects appear to be crucial drivers of host–guest chemistry at this scale. The degree of cavity occupancy, however, appears less important: the largest guest studied, bound the most weakly, occupying only 11¿% of the host cavity

Unsaturated Rh(I) and Rh(III) Naphthyl-based PCP complexes. Major steric effect on reactivity

The addition of an equimolar amount of hydrochloric acid (4.0 M in dioxane) to THF solutions of the binuclear Rh(I) complex [(C10H5(CH2PiPr2)2)Rh(η1-N2)]2 (1a) at room temperature led to an inseparable mixture of 1a, [(C10H5(CH2PiPr2)2)Rh(Cl)(H)] (2a), and [(C10H5(CH2PiPr2)2)Rh(Cl)2 (dioxane)]2 (3a). Exclusive formation of 2a was achieved by slow addition of an equimolar amount of hydrochloric acid (0.4 M in dioxane) to a THF solution of 1a at −35 °C, whereas exclusive formation of 3a was obtained when a second equivalent or an excess (10 equiv) of hydrochloric acid (4.0 M in dioxane) was added to THF solutions of 2a (or to reaction mixtures, which consist of 1a, 2a, and 3a). 3a was structurally characterized. In striking difference to the reactivity pattern of 1a, treatment of THF solutions of the bulky tBu derivative 1b with an equimolar amount or even a large excess (25 equiv) of hydrochloric acid (4.0 M in dioxane) exclusively yielded the hydrido chloro complex [(C10H5(CH2PtBu2)2)Rh(Cl)(H)] (2b). Chloride abstraction from 2a and 2b with AgBF4 exclusively yielded the hydrido rhodium(III) complexes [(C10H5(CH2PR2)2)Rh(H)(F−BF3)] (9a and 9b) with coordination of the counteranion. On the other hand, when an equimolar amount of AgBArF4 was added to methylene chloride (or diethyl ether) solutions of 2a and 2b the cationic, the solvent-stabilized rhodium hydride complexes of type [(C10H5(CH2PR2)2)Rh(solv)(H)][BArF4] (10a and 10b) were formed. If the electron density of the metal centers of 9 (and 10) is reduced further by substitution of the coordinated anion of 9 (or the solvent molecule of 10) with a carbonyl ligand, instant migration of the hydride ligand to the aromatic unit to yield the stable carbonyl complexes of type [(C10H5(CH2PR2)2(H)Rh(CO)][X] (X = BArF4 11a,11b; X = BF4 11a′,11b′) with η2 Caryl−H agostic interactions was observed. Treatment of 2b with CO gas yielded both isomeric forms of [(C10H5(CH2PtBu2)2)Rh(H)(Cl)(CO)] 14b (CO trans to the hydride ligand) and 14b′ (CO trans to the aromatic pincer core). In contrast, when an excess of CO gas was added to THF (or methylene chloride), solutions of 2a, 14a′ was exclusively formed within 20 min at room temperature