Synthesis and characterization of meso-[Ru(NO)Cl(dioxocyclam)] and the H-1NMR comparison with [M-II(dioxocyclam)] complexes (M-II = Ni-II and Pd-II)(dioxocyclam=1,4,8,11-tetraazacyclotetradecane-5,7-dione)

trans-[Ru(NO)X(dioxocyclam)], X=Cl- and OH-, dioxocyclam=(1,4,8,11-tetraaza cyclotetradecane-5,7-dione) have been prepared and characterized by NMR, IR and ESI-MS techniques. The trans-[Ru(NO)Cl(dioxocyclam)] shows the nitrosy l stretch at 1846 versus 1875 cm(-1) in the cyclam analogue, indicative of strong pi -donation from the deprotonated dioxocyclam ligand to the Ru-II c enter and, in turn, to the NO+ group. Upon coordination, the dioxocyclam li gand no longer undergoes facile H/D exchange of the NH and C-6 protons. The methylene protons exist in symmetric patterns indicative of the meso isome r with both C-12 and C-14 methylene carbons projecting below the RuN4 plane toward the side of the axial Cl- for the major product. A lesser amount of the rac isomer, wherein the C-12 and C-14 methylene carbons reside on oppo site sides of the RuN4 coordination plane, is detected. MMFF94 calculations determined that the meso form is more stable than rac by 3.33 kcal mol(-1) . The Ru-II-N(amide) bonds were calculated as having normal lengths (2.07 A ngstrom), but the calculated Ru-II-N(amine) bonds are elongated to 2.35 and 2.36 Angstrom. (It is known that molecular mechanics fan overestimate bond lengths for second and third row metal centers by 0.10-0.15 Angstrom. Even after correcting for the over-calculated bond distance factor, it is seen that the amine-ruthenium distances are longer, and hence the bonds are weak er, than for 'normal' R-II-amines. The presence of the axial Cl- is establi shed by the ESI-MS ion fragments at m/z = 394 for {d(2)-[Ru(NO)Cl(dioxocycl am)]H}(+). Ions for {[Ru(NO)(H2O)(dioxocyclam)]}(+) (m/z = 377) and {[Ru(NO )(dioxocyclam)]}(+)(m/z = 359), the latter from loss of HCl or H2O from the 394 and 377 ions, are detected. H-1 and C-13 NR data for meso-[Ru(NO)Cl(di oxocycram)] are compared to the mesa -[Pd-II(dioxocyclam)] complex, and to the Ni-II derivative that was synthesized at lower temperature than in prev ious literature reports. The mesa-[Ni-II(dioxocylam)] complex was identifie d previously. In the present work, it is shown that below 50 degreesC the p roduct for the Ni-II system is rac-[Ni-II(dioxocyclam)]. The assignments fo r the {Ru(NO)}(3+), Ni-II and Pd-II dioxocyclam complexes as having the dom inant isomeric forms as meso for {Ru(NO)}(3+) and Pd-II and rac for Ni-II a re supported by the H-H COSY spectrum for {RuNO)}(3+), H-H and C-H COSY spe ctra for Ni-II and the H-H COSY spectrum for Pd-II derivatives. (C) 2001 El sevier science B.V. All rights reserved.