title: Amide-Directed Formation of Five-Coordinate Osmium Alkylidenes from Alkynes.
abstract: The amide-directed synthesis of five-coordinate osmium alkylidene derivatives from alkynes is reported. These types of complexes, which have been elusive until now because of the tendency of osmium to give hydride alkylidyne species, are prepared by reaction of the dihydride OsH2Cl2(PiPr3)2(1) with terminal alkynes containing a distal amide group. Complex1reacts withN-phenylhex-5-ynamide andN-phenylhepta-6-ynamide to give OsCl2{=C(CH3)(CH2)nNH(CO)Ph}(PiPr3)2(n= 3 (2), 4 (3)). The relative position of carbonyl and NH groups in the organic substrates has no influence on the reaction. Thus, treatment of1withN-(pent-4-yn-1-yl)benzamide leads to OsCl2{=C(CH3)(CH2)3NHC(O)Ph}(PiPr3)2(4). The new compounds are intermediate species in the cleavage of the C-C triple bond of the alkynes. Under mild conditions, they undergo the rupture of the Cα-CH3bond of the alkylidene, which comes from the alkyne triple bond, to afford six-coordinate hydride-alkylidyne derivatives. In dichloromethane, complex2gives a 10:7 mixture of OsHCl2{≡C(CH2)3C(O)NHPh}(PiPr3)2(5) and OsHCl2{≡CCH(CH3)(CH2)2C(O)NHPh}(PiPr3)2(6). The first complex contains a linear separation between the alkylidyne Cαatom and the amide group, whereas the spacer is branched in the second complex. In contrast to the case for2, complex4selectively affords OsHCl2{≡C(CH2)3NHC(O)Ph}(PiPr3)2(7). In spite of their instability, these compounds give the alkylidene-allene metathesis, being a useful entry to five-coordinate vinylidene complexes, including the dicarbon-disubstituted OsCl2(=C=CMe2)(PiPr3)2(8) and the monosubstituted OsCl2(=C=CHCy)(PiPr3)2(9).
authors.affiliation: Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela , Jenaro de la Fuente, 15782 Santiago de Compostela, Spain.
authors.forename: Noelia
authors.initials: N
authors.lastname: Casanova
authors.affiliation: Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Esteruelas
authors.affiliation: Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela , Jenaro de la Fuente, 15782 Santiago de Compostela, Spain.
authors.forename: Moisés
authors.initials: M
authors.lastname: Gulías
authors.affiliation: Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Carmen
authors.initials: C
authors.lastname: Larramona
authors.affiliation: Centro Singular de Investigación en Química Biolóxica e Materiais Moleculares (CIQUS) and Departamento de Química Orgánica, Universidade de Santiago de Compostela , Jenaro de la Fuente, 15782 Santiago de Compostela, Spain.
authors.forename: José L
authors.initials: JL
authors.lastname: Mascareñas
authors.affiliation: Departamento de Química Inorgánica, Instituto de Síntesis Química y Catálisis Homogénea (ISQCH), Centro de Innovación en Química Avanzada (ORFEO-CINQA), Universidad de Zaragoza-CSIC , 50009 Zaragoza, Spain.
authors.forename: Enrique
authors.initials: E
authors.lastname: Oñate