Isodiazene complexes: synthesis and molecular structures of 2,2,6,6-tetramethylpiperid-1-ylisodiazene complexes of tungsten(IV) and of rhenium-(III) and -(II)

Abstract

The interaction of 1-amino-2,2,6,6-tetramethylpiperidine, C₉H₁₈NNH₂, in refluxing NEt₃–SiClMe₃ with WO₂Cl₂(dme)(dme = 1,2-dimethoxyethane), and with ReO₃(OSiMe₃) gave, respectively, W(C₉H₁₈N₂)₂Cl₃(OSiMe₃)1 and Re(C₉H₁₈N₂)₂Cl₂(OSiMe₃)3. The interaction of 3 with HCl in Et₂O gave Re(C₉H₁₈N₂)₂Cl₃4, which reacted with AgO₃SCF₃ in MeCN to give [Re(µ-O)(C₉H₁₈N₂)₂(MeCN)₂]₂[O₃SCF₃]₄5, and with excess of C₉H₁₈N₂HLi in tetrahydrofuran (thf) to give [ReO(C₉H₁₈N₂)₂]₂6. The X-ray crystal structures of five compounds, 1 and 3–6, have been determined; all are formulated as having 2,2,6,6-tetramethylpiperid-1-ylnitrene ligands that formally can be regarded as isodiazenes. The tungsten complex 1 has C_s symmetry and is octahedral with cis-C₉H₁₈N₂ groups and fac chlorides. The rhenium complexes 3 and 4 are both trigonal bipyramidal with equatorial N and axial Cl atoms. The cation in 5 comprises two edge-sharing distorted octahedra with cis-N and trans-NCMe and a planar symmetrical Re(µ-O)₂Re bridge; the Re₂O₂ ring has a large rhombic distortion with a consequent short non-bonded transannular O ⋯ O distance. The dimeric complex 6 is C₂ symmetric with two distorted tetrahedral Re centres linked by a Re–Re single bond in a near-eclipsed conformation. In all the structures the metal–nitrogen and N–N bonds display significant multiple-bond character and the M–N–N angles are all essentially linear. In the rhenium complexes 3–6 there are varying small degrees of pyramidalisation at the exo N atoms which approximately correlate with the N–N double-bond character; the sum of the Re–N and N–N bond distances remains essentially constant.