The complex [OsTp(kappa(1)-OCMe)(2)(P(i)Pr(3))]BF(4) [Tp = hydridotris(pyrazolyl)borate] promotes the cleavage of both C(sp(3))-C(sp(2)) bonds of benzylidenecyclopropane and 3-phenylpropylidenecyclopropane to yield the complexes [OsTp(=C=CHR)(eta(2)-CH(2)=CH(2))(P(i)Pr(3))]BF(4) (R = Ph, CH(2)CH(2)Ph). The process is proposed to take place via metallacyclopropene intermediates stabilized by an ethylene chelation assistant. The driving force for the fragmentation is the high stability of the resulting ethylene-Os-vinylidene species.

The regio-and stereoselectivity of the palladium-catalysed cross-coupling reactions of indium organometallics with stereodefined 1-haloalkenes and 1,1-dihaloalkenes have been studied. Triorganoindium reagents (R 3 In; R = alkyl, alkenyl, aryl and alkynyl) can be stereospecifically coupled with stereodefined alkenyl iodides in good yields and short reaction times under palladium catalysis. Additionally, the palladium-catalysed cross-coupling reaction of R 3 In (90 mol-%) with 1,1-dibromo-1-alkenes gave dicoupling products in high yields. When the reaction was performed with 40 mol-% of aryl-, vinyl-and alkynylindium derivatives, trans-selective monosubstitution products were obtained in moderate to

Alkylidenecyclopropanes containing a chelation assistant at the terminal carbon atom of the olefinic moiety undergo an Os- or Ru-promoted ring expansion reaction to afford metal cyclobutylidene derivatives. The process occurs through a novel mechanism that implies a 1,2-migration of a CH(2) group of the three-membered ring from an olefinic carbon atom to the other one. It takes place, without direct participation of the metal, on a metallaheterocyclopentene intermediate which is generated from an eta(2)-methylenecyclopropane species stabilized by coordination of the chelation assistant.