Synthesis and Structure of endo-Coordinated o-Xylylene Complexes of Zerovalent Ruthenium and Osmium, M{η4-o-(CH2)2C6H4}(PMe2Ph)3 (M = Ru, Os), and of a Tricarbonyliron Adduct of the Ruthenium Complex

Abstract

Treatment of ruthenium(II) and osmium(II) salts [M(η6-o-C6H4Me2)(PMe2Ph)3](PF6)2[M = Ru (3) or Os (4)] with KO-t-Bu gives o-xylylene (o-quinodimethane) complexes of zerovalent ruthenium and osmium, M{η4-endo-o-(CH2)2C6H4}(PMe2Ph)3[M = Ru (6) or Os (7)], in 83% and 41% yields, respectively. Crystals of 6 are monoclinic, space group C2/c, with a = 31.540(3) Å, b = 11.793(4) Å, c = 16.739(3) Å, β = 104.58(1)°, and Z = 8; those of 7 are monoclinic, space group C2/c, with a = 31.487(2) Å, b = 11.759(2) Å, c = 16.784(3) Å, β = 104.625(8)°, and Z = 8. The structures were solved by heavy-atom methods and refined by least-squares analysis to R = 0.035 and Rw = 0.027 for 3027 independent reflections (I > 3σ) (6) and R = 0.019 and Rw = 0.014 for 4258 independent reflections (I > 3σ) (7). Both molecules contain a metal atom coordinated in a distorted square-pyramidal arrangement by the double bonds of η4-endo-o-xylylene occupying two basal sites and three phosphorus atoms occupying the other sites. Variable temperature NMR (1H, 31P) spectra of 6 and 7 show the molecules to be fluxional as a consequence of hindered rotation of the M(PMe2Ph)3 fragment with respect to the o-xylylene, approximate ΔG‡ values being 56 kJ mol-1 at 314 K for 6 and 60 kJ mol-1 at 324 K for 7. Treatment of 6 with Fe(CO)4(NMe3) affords a heterobimetallic o-xylylene complex containing zerovalent ruthenium and zerovalent iron, i.e., endo-{Ru(PMe2Ph)3}-exo-{Fe(CO)3}{μ-η4,η4-o-(CH2)2C6H4} (8) in 42% yield, in which the ruthenium and iron atoms are coordinated to opposite sides of the o-xylylene ligand. Crystals of 8 are triclinic, space group P1̅, with a = 10.107(2) Å, b = 12.162(2) Å, c = 14.339(2) Å, α = 84.86(1)°, β = 80.69(1)°, γ= 86.00(1)°, and Z = 2. The structure was solved by direct methods and refined by least-squares methods to R = 0.034 and Rw= 0.024 for 5025 independent reflections (I > 3σ). In complex 8 both metal centers are coordinated in a distorted square-pyramidal arrangement. The coordination sphere of the ruthenium atom in 8 is identical to that of the ruthenium atom in 6; the basal sites of the square-pyramid about the iron atom are occupied by the exo pair of double bonds of o-xylylene, and the other three sites are occupied by the carbonyl ligands.