ISODIAZENE COMPLEXES - SYNTHESIS AND MOLECULAR-STRUCTURES OF 2,2,6,6-TETRAMETHYLPIPERID-1-YLISODIAZENE COMPLEXES OF TUNGSTEN(IV) AND OF RHENIUM-(III) AND RHENIUM-(II)

The interaction of 1-amino-2,2,6,6-tetramethylpiperidine, C9H18NNH2, i n refluxing NEt3-SiClMe3 with WO2Cl2(dme) (dme = 1,2-dimethoxyethane), and with ReO3(OSiMe3) gave, respectively, W(C9H18N2)2-Cl3(OSiMe3) 1 a nd Re(C9H18N2)2Cl2(OSiMe3) 3. The interaction of 3 with HCI in Et2O ga ve Re(C9H18N2)2Cl3 4, which reacted with AgO3SCF3 in MeCN to give [Re( mu-O)(C9H18N2)2(MeCN)2]2-[O3SCF3]4 5, and with excess of C9H18N2HLi in tetrahydrofuran (thf) to give [ReO(C9H18N2)2]2 6. The X-ray crystal s tructures of five compounds, 1 and 3-6, have been determined; all are formulated as having 2,2,6,6-tetramethylpiperid-1-ylnitrene ligands th at formally can be regarded as isodiazenes. The tungsten complex 1 has C(s) symmetry and is octahedral with cis-C9H18N2 groups and fac chlor ides. The rhenium complexes 3 and 4 are both trigonal bipyramidal with equatorial N and axial Cl atoms. The cation in 5 comprises two edge-s haring distorted octahedra with cis-N and trans-NCMe and a planar symm etrical Re(mu-O)2Re bridge; the Re2O2 ring has a large rhombic distort ion with a consequent short non-bonded transannular O...O distance. Th e 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-signif icant 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 w ith the N-N double-bond character; the sum of the Re-N and N-N bond di stances remains essentially constant.