Abstract
Compounds containing planar-tetracoordinate carbon can be thermodynamically very stable. We have prepared a variety of examples of such compounds where the planar geometry of tetracoordinate carbon is stabilized by two metal substituents. A combination of two different metal centers, namely a transition metal (here: zirconium or hafnium) and a main group metal (here: aluminum or gallium) seems to be well suited to stabilize this “unnatural” coordination geometry of tetravalent carbon. Our new synthesis of such organometallic compounds is rather simple. The key step of the synthetic sequence is the addition of the main group metal reagent (e.g., AIR3, AIR2X, AIR2H, GaR3) to a reactive in situ generated (η2-alkyne)metallocene intermediate which directly leads to the formation of the respective stable anti-van't Hoff/LeBel compound. The described variants of this general reaction only differ in the ways of generating the reactive alkyne transition metal component. The obtained planar-tetracoordinate carbon compounds were characterized spectroscopically. For more than ten examples X-ray crystal structure analyses have been carried out.