Ring expansion versus exo−endo isomerization in (2-pyridyl)methylenecyclobutane coordinated to hydrido(trispyrazolyl)borate- and cyclopentadienyl-osmium complexes

5 páginas, 1 figura, 1 esquema, 1 tabla.The reactions of (2-pyridyl)methylenecyclobutane with the metal fragments [OsTp(PiPr3)]þ and [OsCp(PiPr3)]þ (Tp = hydridotris(pyrazolyl)borate, Cp = cyclopentadienyl) are shown. Complex [OsTp(κ1-OCMe2)2(PiPr3)]BF4 (1) reacts with the organic substrate to give [OsTp{η2-C(CH2CH2CH2)dCH-C5H4N}(PiPr3)]BF4 (2), which evolves into the cyclopentylidene derivative [OsTp(dCCH2CH2CH2CH-C5H4N)(PiPr3)]BF4 (3) as a result of the ring expansion of the methylenecyclobutane unit of the coordinated substrate. The reaction of (2-pyridyl)methylenecyclobutane with [OsCp(NCCH3)2(PiPr3)]PF6 (4) leads to [OsCp{η2-C(CH2CH2CH2)dCH-C5H4N}-(PiPr3)]PF6 (5). In contrast to 2, complex 5 evolves by means of exo-endo isomerization of the C-C doublebondof the coordinated substrate toafford [OsCp{η2-C(dCHCH2CH2)-CH2-C5H4N}(PiPr3)]PF6 (6).Financial support from the Spanish MICINN (Projects CTQ2008-00810 and Consolider Ingenio 2010 (CSD2007-00006)) and the Diputación General de Aragón (E35) is acknowledged.Peer reviewe