Triple Bonding to Germanium:  Characterization of the Transition Metal Germylynes (η5-C5H5)(CO)2M⋮Ge-C6H3-2,6-Mes2 (M = Mo, W; Mes = −C6H2-2,4,6-Me3) and (η5-C5H5)(CO)2M⋮Ge-C6H3-2,6-Trip2 (M = Cr, Mo, W; Trip = −C6H2-2,4,6-i-Pr3) and the Related Single Bonded Metallogermylenes (η5-C5H5)(CO)3M-G̈e-C6H3-2,6-Trip2 (M = Cr, W)

The synthesis and characterization of several m-terphenyl stabilized germylyne transition metal complexes and related metallogermylenes are reported. The reaction of Na[M(η5-C5H5)(CO)3] (M = Cr, or W) with Ge(Cl)C6H3-2,6-Trip2 (Trip = −C6H2-2,4,6-i-Pr3) below room temperature affords the metallogermylenes (η5-C5H5)(CO)3M-G̈e-C6H3-2,6-Trip2 (M = Cr, 1; W, 5). However, for the analogous reaction with Na[Mo(η5-C5H5)(CO)3], the metallogermylene was not isolated. Instead, the germylyne complex (η5-C5H5)(CO)2Mo⋮Ge−C6H3-2,6-Trip2 (3) was obtained directly with elimination of carbon monoxide. The corresponding chromium and tungsten compounds (η5-C5H5)(CO)2M⋮Ge−C6H3-2,6-Trip2 (M = Cr, 2; W, 6) could be obtained by refluxing 1 or 5 in toluene or by photolysis. The related germylyne (η5-C5H5)(CO)2W⋮Ge−C6H3-2,6-Mes2 (7), as well as the recently reported molybdenum analogue (η5-C5H5)(CO)2Mo⋮Ge−C6H3-2,6-Mes2 (4), which was the first example of a triply bonded germanium species, are also described. All compounds were characterized by 1H and 13C NMR, UV−vis, and IR spectroscopy, and by C, H analysis. The X-ray crystal structures of 13, 5, and 7 have also been determined. The M⋮Ge (M = Cr, Mo, W) triple bonds in the germylynes are typically ca. 0.4 Å shorter than the M−Ge single bonds in the metallogermylenes. In addition, angles at germanium in the germylynes are nearly linear (range 170.9(3)−175.99(6)°) whereas in the metallogermylenes the corresponding angles are 114.7(6) and 117.8(2)°, consistent with the presence of a lone pair at germanium. The synthesis of the series of compounds 17 has enabled, for the first time, a comparison of single and triple bond lengths between closely related species involving the same coordination number and substituents at the heavier group 14 element.