Mono- and bis-diazenido complexes of rhenium(III) containing bidentate ditertiary phosphine ligands. The crystal and molecular structures of [Re(NNC6H4Me-4)2(Ph2PCH2CH2PPh2)2][PF6]·2dmf, [Re(NNC6H4Cl-4)2(Me2PCH2CH2PMe2)2][PF6] and [ReCl(NNC6H4Me-4)(Me2PCH2CH2PMe2)2][PF6]

Abstract

Reaction of the Re^III bis-diazenido starting materials [ReCl(NNC₆H₄X-4)₂(PPh₃)₂](X = Cl 1 or Me 2) with excess dppe (Ph₂PCH₂CH₂PPh₂) in methanol–toluene under reflux gave the novel orange-brown, formally 20-electron Re^III bis-diazenido cations [Re(NNC₆H₄X-4)₂(dppe)₂]⁺(X = Cl or Me) in good yield by addition of a suitable anion to the cooled reaction mixture. Reaction of 1 and 2 with the more reducing dmpe (Me₂PCH₂CH₂PMe₂) ligand gave the formally 20-electron bis-diazenido cation [Re(NNC₆H₄X-4)₂(dmpe)₂]⁺ for X = Cl but the 18-electron mono-diazenido cation [ReCl(NNC₆H₄X-4)(dmpe)₂]⁺ for X = Me. The structures of complexes [Re(NNC₆H₄Me-4)₂(dppe)₂][PF₆]·2dmf (dmf = dimethylformamide)5, [Re(NNC₆H₄Cl-4)₂(dmpe)₂][PF₆]6 and [ReCl(NNC₆H₄Me-4)(dmpe)₂][PF₆]7 have been determined: 5, triclinic, space group P, a= 13.046(3), b= 13.250(3), c= 12.233(4)Å, α= 110.74(2), β= 95.86(2), γ= 115.83(2)°, Z= 1, R= 0.040; 6 monoclinic, space group P2₁/c, a= 8.992(2), b= 21.947(2), c= 18.982(2)Å, β= 91.45(1)°, Z= 4, R= 0.056; 7 orthorhombic, space group Pnma, a= 19.298(2), b= 11.327(2), c= 13.960(2)Å, α=β=γ= 90°, Z= 4, R= 0.042. All three complexes have pseudo-octahedral co-ordination with four P donors in a planar equatorial array. The M–N–N angle of the diazenide ligands is found to be dependent on the steric requirements of the diphosphine ligands, the smaller dmpe ligand permitting the M–N–N angles in 6 to decrease to 147.3(5) and 149.0(4)° compared to values of around 162.7(2)° for the dppe complex 5. Reaction of [NH₄][ReO₄] with the arylhydrazine hydrochloride 4-MeC₆H₄NHNH₂·HCl in CH₂Cl₂ in the presence of SiMe₃Cl and pyridine (py) gave the new hydrazide [ReCl₃{NN(SiMe₃)C₆H₄Me-4}₂(py)]. Subsequent reaction with PPh₃ in MeOH gave the Re^III diazenide [Re(OMe)(NNC₆H₄Me-4)₂(PPh₃)₂], and overall this provides a route for the synthesis of Re diazenides directly from perrhenate.