Structures of 1,2-Propadienylgermane (Allenylgermane) and 1,2-Propadienylstannane (Allenylstannane) Determined by Gas-Phase Electron Diffraction and Quantum Chemical Calculations
作者:Tatyana Strenalyuk、Svein Samdal、Harald Møllendal、Jean-Claude Guillemin
DOI:10.1021/om060056n
日期:2006.4.1
Allenylgermane and allenylstannane (H2C(4)=C-(3)=C(2)HM(1)H3, M=Ge,Sn) have been synthesized, and their structures have been determined by ab initio and density functional theory calculations and gas electron diffraction. The only stable conformation of the MH3 group has one of the M-H bonds synperiplanar to the double bond. The most important structural parameters (r(a)/pm and angle/degree) are as follows (Ge/Sn): M-1-C-2 = 194.2(5)/213.2(7), C-2=C-3 = 131.2(3)/130.7(4), angle M1C2C3 = 120.7(3)/121.0(7). The C-4 atom is bent slightly toward the M atom, making the C-2=C-3=C-4 bond angles 178.3(8)degrees/ 177.4(18)degrees. The difference between the two bond lengths C-3=C-4 and C-2=C-3 is kept constant at the values obtained from the theoretical calculations. Uncertainties are estimated error essentially equal to 2.5 times one standard deviation from the least-squares refinement. The corresponding MP2 values using a cc-pVTZ basis set for all atoms, except for Sn, where the basis set is cc-pVTZ-PP, are as follows (Ge/Sn): M-1-C-2 = 193.0/211.7, C-2=C-3=130.8/130.6, Delta CC=C-3=C-4 - C-2=C-3=0.2/0.6, angle M1C2C3 = 120.7/120.1 and angle C2C3C4 = 178.1/177.8. The r(a)(C-Sn) in vinylstannane is 215.1(6) pm, a decrease of 1.9 pm compared to allenylstannane, while the MP2 calculations predict an increase of 0.4 pm. The calculated rotational barrier for the MH3 group is 2.2 and 1.1 kJ mol(-1), respectively, for allenylgermane and allenylstannane.