TY - JOUR
T1 - μ-Hydride Geometry and Dynamics in the Protic Acid Adducts of Triosmium Imidoyl Clusters
AU - Gobetto, Roberto
AU - Hardcastle, Kenneth I.
AU - Kabir, Shariff E.
AU - Milone, Luciano
AU - Nishimura, Nobuko
AU - Botta, M.
AU - Rosenberg, Edward
AU - Yin, Mingzhi
PY - 1995/6
Y1 - 1995/6
N2 - The μ3-imidoyl cluster, (μ-H)Os3(CO)9(μ3-η2-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)9(μ3-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).
AB - The μ3-imidoyl cluster, (μ-H)Os3(CO)9(μ3-η2-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)9(μ3-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).
UR - http://www.scopus.com/inward/record.url?scp=0002371730&partnerID=8YFLogxK
U2 - 10.1021/om00006a056
DO - 10.1021/om00006a056
M3 - Article
SN - 0276-7333
VL - 14
SP - 3068
EP - 3080
JO - Organometallics
JF - Organometallics
IS - 6
ER -