μ-Hydride Geometry and Dynamics in the Protic Acid Adducts of Triosmium Imidoyl Clusters

Roberto Gobetto, Kenneth I. Hardcastle, Shariff E. Kabir, Luciano Milone, Nobuko Nishimura, M. Botta, Edward Rosenberg, Mingzhi Yin

Risultato della ricerca: Contributo su rivistaArticolo in rivistapeer review

Abstract

The μ3-imidoyl cluster, (μ-H)Os3(CO)932-C=NCH2CH2CH2) (1) forms the neutral acid adducts (μ-H)2Os3(CO)9(μ-η2-C=NCH2CH2CH2)X (X = Cl (2), Br (3), CF3CO2 (4), CF3SO3 (6)), upon addition of the corresponding acids HX to chloroform solutions of the μ3-imidoyl cluster at room temperature. Solid state structures of 3 and 4 reveal that X is in an axial position on the third Os atom and on the same face of the cluster as the μ-imidoyl ligand which bridges two Os atoms. Thermolysis, at 40—80 °C under CO, of 3 isomerizes it to 8 where the bromide has migrated 180° to occupy an axial position in the opposite face of the cluster. In addition, loss of HBr to form 1 and competitive formation of (μ-H)(μ-Br)Os3(CO)10 (7) occurs. For X = CF3CO2 and CF3SO3 partial dissociation of the neutral adduct into (μ-H)2Os3(CO)93-imidoyl)+ (5) and X- is observed in solution, while for X = Cl and Br this cation is only observed when the acid adduct is treated with AgSbF6. The same cation can be generated by treatment of 1 with the noncoordinating acid HBF4. The location of the metalbound hydrogens in the solid state structures of 3 and 8 reveals that the halogen atom is loosely associated with one of the metal-bound hydrogens while this is not the case for the trifluoroacetate derivative 4. An investigation of the variable-temperature 1H- and 13CNMR using one and two-dimensional methods reveals the presence of three isomers in solution for 2, 3, and 8 but only two for 4 and 6. For 2 and 3, exchange between two of the three isomers precedes direct exchange of the two hydride ligands, while for 8 direct exchange of the inequivalent hydrides is the lowest energy process. Mechanisms for these diverse exchange processes are presented in the light of their solid state structures and the two-dimensional NMR results. Compound 3 crystallizes in the orthorhombic space group Pna21 with unit cell parameters a = 29.608(6) Å, b = 7.687(2) Å, c = 17.121(6) Å, V = 3.897(3) Å3, and Z = 4. Least squares refinement of 4051 observed reflections gave a final agreement factor of R = 0.044 (Rw= 0.045). Compound 4 crystallizes in the trigonal space group P31 with unit cell parameters a = 8.976(3) Å, c = 23.27(1) Å, V = 1624(2) Å3, and Z = 3. Least squares refinement of 2973 observed reflections gave a final agreement factor of R = 0.030 (Rw= 0.036). Compound 8 crystallizes in the monoclinic space group P21/c with a = 18.253(8) Å, b = 14.129(5) Å, c = 17.728(6) Å, β= 116.32(3)°, V = 4098(6) Å3, and Z = 8. Least squares refinement of 2948 observed reflections gave a final agreement factor of R = 0.056 (Rw= 0.050).

Lingua originaleInglese
pagine (da-a)3068-3080
Numero di pagine13
RivistaOrganometallics
Volume14
Numero di pubblicazione6
DOI
Stato di pubblicazionePubblicato - giu 1995
Pubblicato esternamente

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