Theoretical designs for germaacetylene (RC≡GeR'): a new target for synthesis

The effect of substitution on the potential energy surfaces of RC≡GeR (R = F, H, OH, CH(3), SiH(3), Tbt, Ar*, SiMe(SitBu(3))(2) and SiiPrDis(2)) was explored using density functional theories (B3LYP/LANL2DZdp and B3PW91/6-31G(d)). Our theoretical studies indicate that all the triply bonded RC≡GeR species prefer to adopt trans-bent geometry, which is in agreement with the theoretical model (mode (B)). Additionally, we show that the stabilities of the RC≡GeR species bearing smaller substituents (R = F, H, OH, CH(3) and SiH(3)) decrease in the order R(2)C=Ge: > RC≡GeR > :C=GeR(2). On the other hand, the triply bonded RC≡GeR molecules with bulkier substituents (R = Tbt, Ar*, SiMe(SitBu(3))(2), SiiPrDis(2)) were found to possess the global minimum on the singlet potential energy surface and are both kinetically and thermodynamically stable. That is to say, both electronic and steric effects of bulky substituents play a crucial role in making triply bonded germaacetylenes (RC≡GeR) an interesting synthetic target.