Paracyclophanes as Versatile π-Donor Ligands Directing Formation of Extended Organometallic Networks

Abstract

The coordination properties of multidentate nonplanar aromatic ligands containing two and three benzene rings, namely [2.2]- and [2.2.2]paracyclophanes, have been explored. A gas-phase deposition approach has been used to examine metal−π interactions in a solvent-free environment as well as to prepare organometallic π-complexes of paracyclophane ligands in crystalline form. To force bridging modes of paracyclophanes and to achieve the formation of extended organometallic assemblies, a dinuclear metal complex having two centers of Lewis acidity, namely [Rh2(O2CCF3)4], has been used. As a result, a product with Rh2:L2 = 1:1 composition (1) has been obtained from the reaction of dirhodium(II,II) tetrakis(trifluoroacetate) with [2.2]paracyclophane (L2 = C16H16). Complex 1 consists of alternating dimetal units and [2.2]paracyclophane bridges that form 1-D organometallic chains: [Rh2(O2CCF3)4·(μ2-η2:η2-C16H16)]1∞. In the case of [2.2.2]paracyclophane (L3 = C24H24), two new rhodium-based products of the stoichiometries Rh2:L3 = 1:2 (2) and 3:2 (3) have been prepared in crystalline form. Complex 2 is a discrete bis adduct with terminally bound aromatic ligands, [Rh2(O2CCF3)4·(η1-C24H24)2], while 3 exhibits a unique 2-D layered structure built on an unprecedented tridentate μ3-η2:η2:η2 coordination of [2.2.2]paracyclophane. Since the layers in 3 overlay to form [2.2.2]paracyclophane-based open channels running along the c direction, the gas sorption properties of the crystalline material, {[Rh2(O2CCF3)4]3·(C24H24)2}, have been tested. In addition to mono- and tridentate coordination of C24H24 revealed in 2 and 3, a rare bidentate bridging mode of [2.2.2]paracyclophane is found in its ruthenium(I) complex obtained by gas-phase reaction of hydrocarbon with the diruthenium(I,I) carbonyl trifluoroacetate unit, [Ru2(O2CCF3)2(CO)4]. The resulting product of the Ru2:L3 = 1:1 composition exhibits a 1-D chain structure, namely [Ru2(O2CCF3)2(CO)4·(μ2-η2:η2-C24H24)]1∞ (4). Overall, three new coordination modes of [2.2.2]paracyclophane have been revealed to afford a discrete complex, as well as 1-D and 2-D extended organometallic networks. This versatility of [2.2.2]paracyclophane has been fully realized under gas-phase deposition conditions that allow one to utilize effectively the geometrical and electronic structures of aromatic ligands in the formation of new organometallic products.