Stable germa- and stannaethenes

Abstract

Stable germa- and stannaethenes have been synthe- sized by addition of germylenes and stannylenes to a krypto-diborylcarbene. Extreme nmr-deshielding of tin is decisive proof for tricoordinated tin atoms in the stannaethenes. Considerable ylid character of germa- and stannaethenes is deduced from nmr-shielding of boron atoms adjacent to the tricoordinated carbon atom. X-ray analysis of a germa- and a stannaethene revealed strong distortion from planarity at the C=Ge and C=Sn bond: twisting of 36° and 61° and pyramidalization at carbon of 5° and 16° as measured by the fold angle. The distances from germanium and tin to the tricoordinated carbon (182.7(4) and 202.5(4) pm) are distinctly shorter (8.4 and 6.4%) than to tetracoordinated carbon atoms. © 1987 IUPAC