The dihydride-dihydrogen complex [OsH2(η5-C5H5)(η2-H2)(PiPr3)]BF4 (2) has been prepared by addition of HBF4·OEt2 to OsH3(η5-C5H5)(PiPr3) (1), and its reactions with benzylideneacetone, methyl vinyl ketone, acetophenone, and benzylideneacetophenone have been studied. The reaction with benzylideneacetone leads initially to [OsH2(η5-C5H5){κ1-OC(CH3)CHCHPh}-(PiPr3)]BF4 (3), which in dichloromethane is converted to the hydroxyallyl derivative [OsH(η5-C5H5){η3-CH2C(OH)CHCH2Ph}(PiPr3)]BF4 (4). Complex 4 releases 4-phenylbutan-2-one, and the resulting metallic fragment activates a Cβ(sp2)−H bond of a new molecule of benzylideneacetone to give (5), which affords (6) by deprotonation with NaOCH3. The reaction of 2 with methyl vinyl ketone gives ethyl methyl ketone and (9). The latter can also be obtained from Os(η5-C5H5)Cl{η2-CH2CHC(O)CH3}(PiPr3) (7) via the intermediate [Os(η5-C5H5){CH2CHC(O)CH3}(PiPr3)]BF4 (8). Treatment of 9 with NaOCH3 leads to an equilibrium mixture of (10) and the hydride-vinylidene OsH(η5-C5H5){CCHC(O)CH3}(PiPr3) (11). The reaction of 2 with acetophenone gives 1-phenylethanol and the orthometalated derivative (13), which is deprotonated with NaOCH3 to give (14), while the reaction of 2 with benzylideneacetophenone leads to (15), which yields (16) by deprotonation. Complexes 3, 10, and 13 have been characterized by X-ray diffraction analysis.

We have synthesized a new type of metallaaromatic complexes, namely the hydride-β-iridanaphthalenes Tp Me2 Ir(H)[C(CH 2 R′)-C 6 H 4 -o-C(R)C(R)] (benzo-3-H,CH 2 R′), by reaction of the benzo-iridacyclopentadiene Tp Me2 Ir[C 6 H 4 -o-C(R)C(R)](OH 2 ) (benzo-1-OH 2 ) (Tp Me2 = hydrotris(3,5-dimethylpyrazolyl)borate, R = CO 2 Me) with olefins of the type CH 2 CHR′ (R′ = H, Me, C 6 H 4 -p-Me, OPh). These reactions are proposed to take place with the initial coordination of the olefin and isomerization to a carbene form and subsequent insertion into the Ir−C(phenylic) bond and a final α-H elimination. The reaction with ethoxyethylene does not afford the corresponding derivative but rather gives a mixture of three, isolable, compounds, which are proposed to derive from three different types of insertion of the olefin, one of them a typical 1,2-insertion and the other two as (different) carbenes. The related reactions of the iridacyclopentadiene Tp Me2 Ir[C(R) C(R)-C(R)C(R)](OH 2 ) (1-OH 2 ) are also discussed. For different combinations of precursor and olefin, we have observed differences in the regio-and stereochemistry of the insertions. ■ INTRODUCTIONMetalloaromatic species continue to attract the attention of both experimental 1 and theoretical chemists. 2 Since the first report in 1982 by Roper et al. of an osmabenzene, 3 several types of metallabenzenes have been reported. Many of them were obtained by serendipitous procedures, but several routes have been designed for the rational synthesis of derivatives of different metals, as for instance the reaction described by Haley et al., 4 which uses the C 5 precursor (Z)-3-(2-iodovinyl)-1,2-diphenylcyclopropene and has been applied to the synthesis of Ir and Pt metallabenzenes. Almost all of the metallabenzenes reported contain one or more substituents in the ring, in many cases as a consequence of the method of preparation or as a tool to provide stability to the metallaaromatic ring. 2c The simplest species, a parent metallabenzene without substituents on the C atoms of the aromatic ring, has been reported recently and was generated by the coupling in an iridium compound of two molecules of acetylene and a CH 2 fragment of a molecule of CH 2 Cl 2 , the solvent of the reaction. 5 Higher metallaaromatics such as metallanaphthalenes and metallaanthracenes are much less common. 6 For the case of metallanaphthalenes, to the best of our knowledge, only the three transition-metal complexes shown in Figure 1 have been described to date 7 and, as can be observed, in all of these cases the metal occupies the α-position of the aromatic ring. 8 The first derivative reported, the Tp Me2 -α-iridanaphthalene, 7a was generated by the mild oxidation of a bicyclic derivative (Scheme 1), for which also exists an analogue without the fused benzo ring, and it also transforms upon oxidation into a metalFigure 1. (a) The three known metallanaphthalenes. 7 (b) The structures of α-metallanaphthalenes (A) and β-metallanaphthalenes (B).Article pubs.acs.org/Organometallics