C-H BOND-MAKING AND BOND-BREAKING PROCESSES IN HETERONUCLEAR MONOAZADIENYL COMPLEXES - REACTIVITY OF HFERU(CO)5(RC=C(H)C(H)=N-IPR) TOWARD CO

In the photochemically induced reaction of Ru2(CO)6{RC=C(H)CH2N-iPr} (1a, R = Ph; 1b, R = Me) with Fe2(CO)9 the heteronuclear complex HFeRu(CO)5{RC=C(H)C(H)=N-iPr} (5) is formed in 35% yield. HRu2(CO)6{RC=C(H)C(H)=N-iPr} (4), which is prepared quantitatively by photolysis of H2RU4(CO)8(RC=C(H)C(H)=N-iPr}2 under a CO atmosphere, can act as an intermediate in this reaction and is proposed to be formed from 1 by a beta-H-elimination reaction. Complex 5 is most likely formed via oxidative addition of the Ru-H bond in 4 to a Fe(CO)4 fragment. Complex 5 reacts with CO at 293 K to give reductive elimination of the monoazadiene ligand and formation of Fe(CO)5/RU3(CO)12, probably via a mechanism involving opening of the hydride bridge. In the reaction of 5 with CO at 373 K the hydride is shifted to the monoazadienyl (MAD-yl) ligand, which is reduced from formally monoanionic to dianionic. In the case of R = Ph selective hydride transfer to C(beta) is observed, resulting in the formation of FeRu(CO)6-{PhC(H)C(H)C(H)N-iPr} (6a), which features an unprecedented coordination mode of the MAD-yl ligand. For R = Me, both transfer to C(beta) (affording 6b) and to Cim is observed, the latter affording FeRu(CO)6{MeC=C(H)CH2N-iPr} (7). This R-group dependence and also the difference in the reactivity of 5 and its homonuclear Ru2 analogue 2 is rationalized by the strength of the pi-C=C coordination in the intermediate HFeRu(CO)6{RC=C(H)C(H)=N-iPr} (9). Complex 9a could not be prepared by the reaction of [FeRu(CO)6{PhC=C(H)C(H)=N-iPr}][BF4] (8a) with NaBH4, which afforded one diastereomer of FeRu(CO)6{PhCC(H)C(H)N-(H)-iPr} (10a), but 9a was formed by the conversion of 8a on silica. The X-ray crystal structures of 6a and 9a have been determined. Crystals of 6a are monoclinic, space group P2(1)/c, with unit-cell dimensions a = 12.106(14) angstrom, b = 9.490(10) angstrom, c = 16.780(7) angstrom, beta = 97.61(7)-degrees, V = 1911(3) angstrom3, Z = 4, final R = 0.055, and R(w) = 0.040 for 2215 reflections with I > 3.0 sigma(I) and 245 parameters. Crystals of 9a are orthorhombic, space group P2(1)2(1)2(1), with a = 9.819(1) angstrom, b = 11.928(1) angstrom, c = 17.338(1) angstrom, V = 2030.7(3) angstrom3, Z = 4, and final R = 0.044 for 1434 reflections with I > 2.5sigma(I) and 254 parameters. The most important conclusion of this work is that isostructural FeRu- and Ru2-MAD-yl complexes show a large difference in reactivity, which can be rationalized by stronger pi-coordination of the MAD-yl ligand to Fe as compared to Ru.