Polynuclear aryl derivatives of group 11 metals: Synthesis, solid state-solution structural relationship, and reactivity with phosphines

Article abstract of DOI:10.1021/om00106a031

The synthesis of homoleptic aryl derivatives of group 11 metals has been performed by reacting the monochlorides [CuCl], [AgCl], and [AuCOCl] with MesMgBr (Mes ≡ 2,4,6-Me₃C₆H₂). The resulting products [Cu₅Mes₅] (1), [Ag₄Mes₄] (2), and [Au₅Mes₅]·2THF (3) have been isolated as crystalline thermally stable compounds. They have, in the solid state, cyclic structures whose molecular geometries are discussed within. MW determination by cryoscopy in benzene and ¹H NMR spectra in both C₆D₆ and C₆D₁₂ showed that the three oligomeric structures were in equilibrium with the respective dimeric form of the molecule. In each case the dimeric form was the prevailing species in solution. The solution equilibrium was very rapidly established for the silver and gold complexes and was relatively slower for the copper complex. In the case of the copper complex the rate of equilibrium was solvent dependent, being much faster in toluene (t_1/2 for Cu₅Mes₅ being ca. 0.66 h) than in cyclohexane (t_1/2 being ca. 56 h). The addition of electron-rich arenes to cyclohexane solutions of 1 greatly enhanced the rate of conversion of the pentamer to dimer. Addition of ligands to the solution containing the dimers allowed us to isolate complexes of different molecular complexity. The addition of THT (tetrahydrothiophene) to a THF solution of 1 resulted in the formation of the complex [Cu₄Mes₄THT₂] (5). The results of the reactions of 1-3 with phosphines are reported and appear to be strongly dependent on the nature of the metal. PPh₃ and dppe (Ph₂PCH₂CH₂PPh₂) stabilize the copper(I) dimer in solution, and subsequently they promote a ligand rearrangement with the formation of the corresponding cuprate. dppm (Ph₂PCH₂PPh₂) reacts with 1 and 2 with the protolysis and elimination of the mesityl group to form [Cu₃(Ph₂PCHPPh₂)₃]·2C ₇H₈ (8) and [Ag₃(Ph₂PCHPPh₂)₃]·2C ₇H₈ (9), respectively. Complex 2 reacts with dppe in the same way as 1 or 3 depending on the nature of the solvent. Full characterization of the complexes was prevented by their thermal and photochemical instability. The reaction of phosphines PPh₃, dppm, and dppe did not affect the [AuMes] functionality; in all three cases formation of the [P-Au-Mes] dicovalent gold(I) complexes [AuMesPPh₃] (10), [Au₂Mes₂(μ-dppm)] (11), and [Au₂Mes₂(μ-dppe)] (12) was observed. The structures of six compounds have been determined. Crystallographic details for complexes 1, 2, 3, 5, 9, and 12 are as follows: Complex 1: space group P2₁/n (monoclinic), a = 16.094 (4) A?, b = 16.022 (4) A?, c = 19.259 (5) A?, β = 97.49 (3)°, V = 4924 (2) A?³, Z = 4, D_calcd = 1.232 g cm^-3. The final R factor was 0.10 for 1629 observed reflections. Complex 2: space group R3 (rhombohedral), a = b = c = 18.395 (3) A?, α = β = γ = 116.28 (2)°, V = 3038 (4) A?³, Z = 3, D_calcd = 1.489 g cm^-3. The final R factor was 0.062 (R_w = 0.064) for 1966 observed reflections. Complex 3: space group Pnma (orthorhombic), a = 21.864 (10) A?, b = 27.188 (11) A?, c = 8.951 (5) A?, V = 5321 (4) A?³, Z = 4, D_calcd = 2.153 g cm^-3. The final R factor was 0.052 (R_w = 0.050) for 2023 observed reflections. Complex 5: space group P1 (triclinic), a = 12.907 (3) A?, b = 20.624 (6) A?, c = 8.708 (2) A?, α = 102.14 (3)°, β = 107.38 (3)°, γ = 89.64 (3)°, V = 2159 (1) A?³, Z = 2, D_calcd = 1.396 g cm^-3. The final R factor was 0.057 (R_w = 0.062) for 3117 observed reflections. Complex 9: space group P2₁/n (monoclinic), a = 14.004 (2) A?, b = 23.632 (4) A?, c = 24.572 (4) A?, β = 101.66 (1)°, V = 7964 (2) A?³, Z = 4, D_calcd = 1.384 g cm^-3. The final R factor was 0.061 for 5695 observed reflections. Complex 12: space group P1 (triclinic), a = 11.700 (2) A?, b = 12.475 (2) A?, c = 7.647 (1) A?, α = 101.52 (1)°, β = 95.81 (1)°, γ = 109.55 (1)°, V = 1013.4 (3) A?³, Z = 1, D_calcd = 1.650 g cm^-3. The final R factor was 0.036 for 3659 observed reflections.