Transition metal complexes containing organoimido ligands with remote functionality: Phenylenediimido, quinolinyl-imido and phenanthrolinyl-imido species

The synthesis of tantalum and vanadium phenylenediimido dimeric complexes was approached with the goal of making precursors for linear, one-dimensional polymers. Preparations of complexes of the general type Cl{dollar}sb3{dollar}(L){dollar}sb{lcub}rm n{rcub}{dollar}M{dollar}sp{lcub}rm V{rcub}{lcub}equiv{rcub}{dollar}N-C{dollar}sb6{dollar}H{dollar}sb4{dollar}-N{dollar}{lcub}equiv{rcub}{dollar}M{dollar}sp{lcub}rm V{rcub}{dollar}(L){dollar}sb{lcub}rm n{rcub}{dollar}Cl{dollar}sb3 {lcub}{dollar}M = Ta, V; L = THF, etc.; n = 2, 3{dollar}{rcub}{dollar} were attempted, and the subsequent reductions to achieve the desired Cl(L){dollar}sb4{dollar}M{dollar}sp{lcub}rm III{rcub}{lcub}equiv{rcub}{dollar}N-C{dollar}sb6{dollar}H{dollar}sb4{dollar}-N{dollar}{lcub}equiv{rcub}{dollar}M{dollar}sp{lcub}rm III{rcub}{dollar}(L){dollar}sb4{dollar}Cl species also were examined. It was determined that the tantalum(V) system would not produce the expected discrete dimers, but instead resulted in chloride-bridged oligomers. The vanadium analogs could be prepared for para and meta derivatives of the formulation Cl{dollar}sb3{dollar}(THF){dollar}rmsb{lcub}n{rcub}Vsp V{lcub}equiv{rcub}N{dollar}-C{dollar}sb6{dollar}H{dollar}sb4{dollar}-N{dollar}{lcub}equiv{rcub}{dollar}V{dollar}sp{lcub}rm V{rcub}{dollar}(THF){dollar}sb{lcub}rm n{rcub}{dollar}Cl{dollar}sb3 {lcub}{dollar}n = 0 or 3{dollar}{rcub}.{dollar} Efforts to reduce to the V(III) state proved it to be unattainable in all cases. However, the paramagnetic V(IV) dimers could be formed under mild reducing conditions and displayed characteristic eight-line splitting patterns for the {dollar}sp{lcub}51{rcub}{dollar}V (S = 7/2) nuclei. Monomeric tolylimido complexes were prepared for comparison and an X-ray crystal structure was determined for a presumed hydrolysis product, Cl{dollar}sb2{dollar}(PMe{dollar}sb2{dollar}Ph){dollar}sb2{dollar}V(NH-Tol){dollar}sb2.{dollar}; A collection of tungsten quinolinyl-imido derivatives was prepared by reaction of WCl{dollar}sb6{dollar} and aminoquinolines. The quinoline nitrogen functionality was designed to provide a remote site for coordination to another metal center. In the tungsten systems, the coordinatively unsaturated metal also presented an open site for donation and thus could self-assemble into polymeric materials. The products formulated as {dollar}rmlbrack Clsb4{lcub}equiv{rcub}N{dollar}-C{dollar}sb9{dollar}H{dollar}sb6{dollar}N) {dollar}sb{lcub}rm x{rcub}{dollar} were isolated as analytically pure green solids which were soluble in donor solvents for limited times. The polymers could be broken down to monomers by addition of phosphine or other suitable donor ligands. The monomeric phosphine complexes could serve as metalloligands in creating new coordination compounds. One example was formulated as (Cu{dollar}sp{lcub}rm I{rcub}{lcub}{dollar}NC{dollar}sb9{dollar}H{dollar}sb6{dollar}N{dollar}{lcub}equiv{rcub}{dollar}WCl{dollar}sb4{dollar}(PBu{dollar}sb3){rcub}sb4rbrack{dollar} BF{dollar}sb4.{dollar}; Lastly, phenanthrolinyl-imidohexamolybdate complexes were investigated. Conceptually, the remote chelating functionality would serve as a binding site through which new multi-metallic species could be coupled. The chelating effect was expected to offer an improvement over the weakly-donating nitrogen donors studied previously. However, an unanticipated transformation of (Mo{dollar}sb6{dollar}O{dollar}sb{lcub}19{rcub}rbracksp{lcub}2-{rcub}{dollar} to (Mo{dollar}sb8{dollar}O{dollar}sb{lcub}26{rcub}rbracksp{lcub}4-{rcub}{dollar} was discovered to be promoted by the phenanthroline group instead of the desired imido substitution. If the phenanthroline chelate was blocked by initial coordination to a target metal such as Ni(II), then this conversion to octamolybdate could be averted.