Metallacyclopentadienes and related heterocycles via 1,1‐organoboration of alkyn‐1‐ylmetal compounds

Metallacyclopentadienes (metalloles) containing M = Si, Ge, Sn, Pb, Ti, Pt can be prepared by 1,1-organoboration of alkyn-1-ylmetal compounds LnMCCR1(R1 = H, alkyl, aryl, silyl, etc; L depends on M, and can be hydrogen, alkyl, aryl, Cl, Br, amino groups, a chelating diphosphane, and one or more L can be again alkynyl groups). These reactions proceed via activation of the MC bond(s) by an electron-deficient triorganoborane BR3 (R = alkyl, aryl; non-cyclic, monocyclic, bicyclic, and tricyclic boranes), at first intermolecular and then intramolecular. In the course of these reactions, the MC bonds are cleaved, zwitterionic alkynylborate-like intermediates are formed, in which the metal-containing fragments are coordinated side-on to the CC bonds. In most cases, the 1,1-organoboration reactions tolerate various functional groups at the alkyne as well as at the metal. The characterization of intermediates and final products by X-ray structural analysis and by multinuclear magnetic resonance spectroscopy (NMR) is documented and described. © 2006 Wiley Periodicals, Inc. Heteroatom Chem 17:188–208, 2006; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20222