Synthesis and characterisation of ruthenium carbonyl complexes with cyclometallated ligands derived from senecialdimine

From thermal reactions of Ru-3(CO)(12) with senecialdimine, (CH3)(2)C=CHCH=NR (R = iPr (a), t-Bu (b)), in refluxing heptanes the following complexes have been isolated and characterised: Ru-2(CO)(6)[(CH3)(2)C(H)CC(H)NR] (2a,b), Ru-2(Co)(6)[C(H)C(CH3)C(H)C(H)=NR] (3a,b), [HRu6(CO)(18)][2-(C(H)=C(CH3)(2))-4-CH3-C5H3N] (4a), HRu3(CO)(9)[(CH3)(2)C(H)CH2C=NR] (5a), and Ru-2(CO)(6)[C(H)C(CH3)C(H)C=N(H)R] (6b). The complexes 3a, 4a, and 6b have been characterised by X-ray structure determinations. Crystals of 3a are monoclinic, space group P2(1)/n, with a = 11.217(4)Angstrom, b = 10.991(2)Angstrom, c = 14.214(3)Angstrom, beta = 94.38(2)degrees, Z = 4 and R = 0.0264. Crystals of 4a are monoclinic, space group P2(1)/n, with a = 10.483(2)Angstrom, b = 15.910(3)Angstrom, c = 24.995(5)Angstrom, beta = 101.56(2)degrees, Z = 4 and R = 0.0279. Crystals of 6b are monoclinic, space group P2(1)/n, with a = 11.449(2)Angstrom, b = 12.012(2)Angstrom, c = 13.561(3)Angstrom, beta = 102.69(2)degrees, Z = 4 and R = 0.0239. The other complexes were characterised spectroscopically. Complex 6b contains a novel eta(4)-coordinated metallacyclopentadiene fragment, the second of its kind reported so far. The anomalous eta(4)-coordination is attributed to the presence of an amino substituent on one of the metallated carbon atoms causing redistribution of electrons over the ligand skeleton. Possible formation pathways of the complexes are described.