Transition-metal complexes of cyclopentadienylphosphines XIV. Reduction reactions of various derivatives of the chelate fragment [{η5:η1-C5H4(CH2)2PPh2}MIII]2+, M = Rh, Ir

Article abstract of DOI:10.1016/S0022-328X(96)06803-9

Iodide abstraction by silver salts from the complexes [{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}MI₂], (1, M = Rh; 2, M = Ir), yields products whose structures are dependent on the coordinating ability of the anion originally associated with silver. Silver trifluoroacetate gave fully characterized disubstituted derivatives of the type [{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}M(CF₃COO)₂], (3, M = Rh; 4, M = Ir), in which the trifluoroacetate anions are bound in a monodentate fashion. Silver hexafluorophosphate gave a dinuclear dicationic compound [{{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}Rh(μ-I)}₂][PF₆]₂, 5, in which the metal atoms are bridged by iodide. Complex 3 crystallizes in the triclinic space group P1 with two molecules in the unit cell, with a = 8.3060(7) A, b = 18.289(2) A, c = 7.9724(8) A, α = 94.178(8)°, β= 106.477(8)°, γ = 93.964(7)° and V = 1153.2(2) A³. Least squares refinement leads to conventional R values R(F₀) = 0.041 and Rw = 0.042 for 3361 reflections having I > 3σ(I). Complex 5 crystallizes in the monoclinic space group P2₁/c with two molecules of 5 and two molecules of acetone in the unit cell, the dimensions of which are a = 13.838(1) A, b = 13.403(1) A, c = 14.362(1) A, β = 104.73(1)° and V = 2576.2(5) A³. Least squares refinement leads to conventional R values R(F₀) = 0.034 and Rw = 0.040 for 2246 reflections having I > 2σ(I). Surprisingly, the treatment of the bis-trifluoroacetato complexes 3 and 4 with lithium triethylhydroborate yields quantitatively the ethylene metal(I) derivatives [{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}M(C₂H₄)], (9, M = Rh; 10, M = Ir), whereas unstable polyhydride derivatives result from the reaction of the diiodo complex 1 with lithium triethylhydroborate, and from the reaction of the bis-trifluoroacetato complex 3 with sodium tetrahydroborate. The chemical or electrochemical reduction of complex 5 leads to the solvated rhodium(III) species, [{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}RhI(THF)][PF₆], 6, together with a dinuclear rhodium(II) species, [{{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}RhI}₂], 7. The protonation of 7 with tetrafluoroboric acid affords the monocationic dinuclear complex [{{η⁵:η¹-C₅H₄(CH₂)₂PPh₂}RhI}₂}H][BF₄], 8, in which the added proton bridges the rhodium atoms.