Gyroscope like molecules consisting of trigonal or square planar osmium rotators within three-spoked dibridgehead diphosphine stators: syntheses, substitution reactions, structures, and dynamic properties

Abstract

Reactions of (NH₄)₂OsX₆ (X = Cl, Br) with CO and the phosphines P((CH₂)_mCHCH₂)₃ (m = 6, a; 7, b; 8, c) give cis,cis,trans-Os(CO)₂(X)₂(P((CH₂)_mCHCH₂)₃)₂ (46–73%). These are treated with Grubbs’ catalyst (7 mol%, 0.0010 M, C₆H₅Cl). Subsequent hydrogenations (PtO₂) yield the gyroscope like complexes cis,cis,trans-Os(CO)₂(X)₂(P((CH₂)_n)₃P) (n = 2m + 2; X = Cl, 6a–c; Br, 7a–c; 5–31%) and the isomers cis,cis,trans-Os(CO)₂(X)₂(P(CH₂)_n−1CH₂)((CH₂)_n)(P(CH₂)_n−1CH₂) (X = Cl, 6′a–c; Br, 7′a–c; 12–51%) derived from a combination of interligand and intraligand metatheses. Reductions of 6a,c, 6′b, and 7′b with C₈K under CO atmospheres afford trans-Os(CO)₃(P((CH₂)_n)₃P) (9a,c, 79–82%) and trans-Os(CO)₃(P(CH₂)₁₅CH₂)((CH₂)₁₆)(P(CH₂)₁₅CH₂) (9′b, 53–84%). Reaction of 9a and CF₃SO₃H yields the cationic hydride complex mer,trans-[Os(H)(CO)₃(P((CH₂)₁₄)₃P)]⁺ CF₃SO₃⁻ (9a-H⁺ CF₃SO₃⁻; quantitative by NMR). Preparative reactions of 9a,c or 9′b and [H(OEt₂)₂]⁺ BAr_f⁻ (BAr_f⁻ = B(3,5-C₆H₃(CF₃)₂)₄⁻) afford 9a,c-H⁺ BAr_f⁻ (80%) or 9′b-H⁺ BAr_f⁻ (68%). Reactions of 6a, 6′b, and 7a with MeLi or PhLi give cis,cis,trans-Os(CO)₂(Me)₂(P((CH₂)₁₄)₃P) (11a, 98%), cis,cis,trans-Os(CO)₂(Me)₂(P(CH₂)₁₅CH₂)((CH₂)₁₆)(P(CH₂)₁₅CH₂) (98%), and cis,cis,trans-Os(CO)₂(Ph)₂(P((CH₂)₁₄)₃P) (12a, 58%). NMR data for 6a–c, 7a–c, 9a,c, 9a,c-H⁺ X⁻, and 11a indicate that rotation of the OsL_y moieties is fast on the NMR time scale at room temperature. In contrast, the phenyl groups in 12a act as “brakes” and two sets of ¹³C NMR signals are observed for the methylene chains (2 : 1). The crystal structures of 6a–c, 7b,c, 7′a, 9a, 9a-H⁺ BAr_f⁻, 11a, and 12a are analyzed with respect to OsL_y rotation in solution and the solid state.