<i>o</i>-(Trifluoromethyl)aryl Interactions and Stabilization in Hypervalent Germanium Compounds

Abstract

A series of o-(trifluoromethyl)phenyl-substituted germanes have been synthesized to study the potential for weak Ge−F bonding interactions. 1H−19F coupling constants in these compounds range between 2 and 5 Hz. These coupling magnitudes are consistent with previously reported literature examples in 19F and multinuclear NMR spectra for derivatives of the [2,4,6-(CF3)3C6H2]− ligand. Solid-state structural characterization of these germanes consistently reveals Ge−F contacts at 2.8−2.9 Å, midway between the longest single bond and the longest expected van der Waals contact. For the simple unsymmetrical catenate, [3,5-(CF3)2C6H3]2Ge(H)Ge(H)[2,4,6-(CF3)3C6H2]2 (4), there are close contacts to both germanium atoms from the ortho-CF3 groups. 4 is not otherwise sterically constrained to force distal, intramolecular contacts, and thus a weak Ge−F bonding interaction is invoked for the entire series of o-(trifluoromethyl)aryl-substituted tetravalent Ge compounds. The synthetic approaches to these germanes make extensive use of Ge(II) precursors, employing both catalytic hydrogenation and insertion reactions of germylenes.