Mono- and bis-diazenido complexes of rhenium(<scp>III</scp>) 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 ReIII 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 ReIII 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 ReIII diazenide [Re(OMe)(NNC6H4Me-4)2(PPh3)2], and overall this provides a route for the synthesis of Re diazenides directly from perrhenate.