HETERONUCLEAR MONOAZADIENYL COMPLEXES, ISOLOBALLY RELATED TO CYCLOPENTADIENYL COMPOUNDS

The complex Ru(CO)3Cl{RC=C(H)C(H)=N-i-Pr} (2a, R = Ph; 2b, R = Me), which is isolobally related to C5H5Cl (Cp-CI), has been used as a building block for the preparation of heteronuclear monoazadienyl (MAD-yl) complexes via reactions with CO(CO)4, Fe(CO)2CP-, and Mn(CO)5-. These reactions have afforded the new complexes RuCo(CO)6{RC=C(H)C(H)=N-i-Pr} (5), CpFeRu(CO)4{PhC=C(H)C(H)=N-i-Pr} (6), and RuMn(CO)8{RC=C(H)C(H)=N-i-Pr} (8), all containing the ruthena-azadienyl cycle. The complexes have been characterized by IR and IH and C-13 NMR spectroscopy, and the structures of RuCo(CO)6{MeC=C(H)C(H)=N-i-Pr} (5b) and CpFeRu(CO)4{PhC=C(H)C(H)=N-i-Pr} (6a) have been determined by X-ray structure analyses. Crystals of 5b are monoclinic, space group P2(1)/c, with a = 7.127 (i) angstrom, b = 13.931 (1) angstrom, c = 16.536 (1) angstrom, beta = 93.92 (1)-degrees, and Z = 4. The structure was refined to R = 0.030 for 2978 observed reflections. Crystals of 6a are monoclinic, space group P2(1)/c, with a = 9.223 (1) angstrom, b = 11.243 (1) angstrom, c = 19.179 (4) angstrom, beta = 103.18 (1)-degrees, and Z = 4. The structure was refined to R = 0.048 for 2921 observed reflections. Upon thermolysis of complexes 5 and 6a, featuring sigma(N),sigma(C),pi(C=C)-coordinated MAD-yl ligands, a CO ligand is substituted by the pi(C=N) bond of MAD-yl, but the resulting complex is only stable in the FeRu case (complex 7). Upon thermolysis or photolysis of the RuMn complex 8, featuring a sigma(N),sigma(C)-coordinated MAD-yl ligand, one or two CO ligands are substituted by the pi bonds of the MAD-yl ligand, yielding the RuMn(CO)7- and RuMn(CO)6(MAD-yl) complexes 9 and 10, respectively. The reaction of 5a and 8b with I2 as well as electrochemical measurements involving 7 show that the intermetallic bond in the new heteronuclear complexes is not stable toward oxidation. Complex 10a is a hydrogenation catalyst for styrene, where the reversible hapticity change of the Mn-coordinated ruthena aza dienyl cycle from eta5 to eta3 and successively to eta1 has been proposed to be crucial for the uptake of the alkene and hydrogen by the catalyst.