Controlling catenation in Ge(I) chemistry through hemi-lability.

We present a novel approach for constructing chains of group 14 metal atoms linked by unsupported metal-metal bonds that exploits hemi-labile ligands to generate unsaturated metal sites. The formation/nature of catenated species (oligo-dimetallynes) can be controlled by the use of (acidic/basic) 'protecting groups' and through variation of the ligand scaffold. Reduction of ArNiPr2GeCl (ArNiPr2 = 2,6-(iPr2NCH--2)2C6H-3) - featuring hemi-labile NiPr2 donors - yields (ArNiPr2Ge)4 (2), which contains a tetrameric Ge4 chain. 2 is the first example of a linear homo-catenated Ge(I) compound featuring unsupported E-E bonds. Trapping experiments reveal that a key structural component is the central two-way Ge=Ge donor-acceptor bond: reactions with IMe4 and W(CO)5(NMe3) give the base- or acid-stabilized digermynes (ArNiPr2Ge(IMe4))2  (4) and (ArNiPr2Ge{W(CO)5})2 (5), respectively. The use of smaller N-donors leads to stronger Ge-N interactions and quenching of catenation behaviour: reduction of ArNEt2GeCl gives the digermyne (ArNEt2Ge)2, while the unsymmetrical system ArNEt2GeGeArNiPr2 dimerizes to give tetranuclear (ArNEt2GeGeArNiPr2)2through aggregation at the NiPr2-ligated Ge(I) centres.