Steric effects in the chemistry of platinum cluster complexes

Article abstract of DOI:10.1021/om00006a026

A study of steric effects of the ligands R₂PCH₂PR₂, R = aryl, on the formation and chemistry of the clusters [Pt₃(μ₃-CO)(μ-R₂PCH₂PR ₂)₃(O₂CCF₃)]⁺, 4, and [Pt₃(μ₃-CO)(μ-R₂PCH₂PR ₂)₃]²⁺, 8, is reported. When R = 2-MeC₆H₄, reduction of [Pt(O₂CCF₃)₂(R₂PCH ₂PR₂)] by CO/H₂O gave only the binuclear complex [Pt₂H(CO)(μ-R₂PCH₂PR₂) ₂]⁺, but with smaller groups R, further reduction to 4 (R = 4-MeC₆H₄, 3-MeC₆H₄, 3,5-Me₂C₆H₃, 3,5-F₂C₆H₃, 3,5-Cl₂C₆H₃) or to [Pt4(μ-CO)₂(μ-H)(μ-R₂PCH₂PR ₂)₃(R₂PCH₂PR₂)] ⁺ (R = 4-MeC₆H₄, 3,5-F₂C₆H₃) occurred. The complexes were characterized spectroscopically and for 4(CF₃CO₂), R = 3,5-Cl₂C₆H₃, crystallographically [C₈₀H₄₂Cl₂₄F₆O₅P ₆Pt₃·0.5CH₂Cl ₂·L5H₂O, monoclinic, P2₁/n, a = 23.365(4) A, b = 24.599(4) A?, c = 19.141(7) A?, β = 102.44(2)°, Z = 4, R = 0.0727]. The complexes 8 can all form adducts with I^-, SCN^-, and CF₃CO₂^- though evidence is presented that coordination of CF₃CO₂^- is reversible in solution when R = 3,5-Cl₂C₆H₃. Reactions of 8 with the ligands L = PPh₃, PMePh₂, P(OPh)₃, and P(OMe)₃ to form the adducts [Pt₃(μ₃-CO)(μ-R₂PCH₂PR ₂)₃L]²⁺ are reversible, and the position of equilibrium depends on the steric effects of R, indicating the steric sequence R = 4-MeC₆H₄, 3-MeC₆H₄ < 3,5-Me₂C₆H₃ < 3,5-F₂C₆H₃ < 3,5-Cl₂C₆H₃.