Hydrogen Migration and HCl Elimination Promoted by Metal-Centered Nucleophilic Attack on Osmium Hydrido−Carbynes

Abstract

The carbynes [OsHCl 2 (CCH 2 R)L 2 ] (R ) Ph, CH 3 ; L ) P i Pr 3 ) react with CO to give, after 1,2-hydride migration from osmium to C R of the carbyne ligand, the osmium carbene complexes [OsCl 2 (CO)(dCHCH 2 R)L 2 ]. For R ) Ph, reactions with excess CO lead to HCl elimination to form [OsCl(CO) 2 ((E)-CHdCHPh)L 2 ], which reacts with liberated HCl at C R to yield [OsCl 2 (CO) 2 L 2 ] and CH 2 dCHPh. Abstraction of chloride from either the carbynes or carbenes with NaBAr′ 4 (Ar′ ) 3,5-C 6 H 3 (CF 3 ) 2 ) yields the corresponding coordinatively unsaturated carbyne and carbene complexes [OsHCl(CCH 2 R)L 2 ][BAr′ 4 ] and [OsCl(CO)(d CHCH 2 R)L 2 ][BAr′ 4 ], respectively. The carbynes [OsHCl(CCH 2 Ph)L 2 ] + react with reagent L′ (L′ ) CO, HCCR′) to initially give the carbenes [OsCl(L′)(dCHCH 2 Ph)L 2 ] + after 1,2-hydride migration to C R of the carbyne ligand. These carbenes react further, eliminating HCl and undergoing selective protonation to yield either [OsCl(CO) 3 L 2 ] + and CH 2 dCHPh (with L′ ) CO) or the σ-vinyl carbyne complexes [OsCl(CCH 2 R′)((E)-CHdCHPh)L 2 ] + (with L′ ) HCCR′).

Osmium–carbon multiple bonds: Reduction and C–C coupling reactions

“…The rapidity of the process is consistent with the initial substitution of one of the acetonitrile ligands of 43 by a carbon monoxide molecule, which produces a decrease of the activation barrier for the migration as it has been previously mentioned [36]. The recoordination of the substituted acetonitrile to the resulting five-coordinated intermediate affords the allenyl complex 48.…”

Synthesis of Hydrido−Vinylidene and Hydrido−Carbyne Osmium Complexes Containing Pyrazole: New Examples of N−H···Y (Y = N, F, Cl) Hydrogen Bonds

“…Synthesis and Characterization of OsH(pz)(  C  CHPh)(Hpz)(P i Pr 3 ) 2 . Caulton and co-workers have recently reported that the carbyne complexes OsHCl 2 (⋮CCH 2 R)(P i Pr 3 ) 2 (R = Ph, CH 3 ) react with carbon monoxide to give, after a 1,2-hydride migration from osmium to the C α carbon atom of the carbyne ligand, the osmium carbene complexes OsCl 2 (CO)(CHCH 2 R)(P i Pr 3 ) 2 , which can be also prepared by reaction of the dihydrogen complex OsCl 2 (η 2 -H 2 )(CO)(P i Pr 3 ) 2 with the corresponding alkyne 3d. In addition, it should be mentioned that the approach toward generating metal−carbene complexes involves electrophilic addition to nucleophilic carbyne ligands.…”

Formation of Osmium Alkylidene, Alkylidyne, and Dinitrogen Complexes from Reactions of OsCl2(PPh3)3 with Diazoalkanes

“…It is worth noting that metal alkylidene complexes with an electron-withdrawing substituent (a carbonyl moiety) on the α carbon are often too reactive or unstable and have rarely been isolated . Previous works have shown that π-acceptor ancillary ligands such as CO and MeCN could stabilize the osmium alkylidene form relative to its hydrido-alkylidyne form. , The result from this work shows that an electron-withdrawing group at the α-carbon could also stabilize the alkylidene form.…”

“…30 Previous works have shown that π-acceptor ancillary ligands such as CO and MeCN could stabilize the osmium alkylidene form relative to its hydrido-alkylidyne form. 4,8 The result from this work shows that an electron-withdrawing group at the α-carbon could also stabilize the alkylidene form.…”

“…The reactions for processes involving α-hydrogen migration (X = H) are well-documented and have been observed for a variety of group 6–8 metal complexes . Studies by groups of Esteruelas, − Caulton − and Stephan have demonstrated that the direction of the transformation can be affected by both metal (M) and ancillary ligands (L). One might expect that the R group may also affect the equilibrium shown in eq , although such an effect has not yet been described in the literature.…”