Bis(η2-ethylene)(η5-indenyl)iridium(I)

The asymmetric unit of the title compound, [Ir(C9H7)(C2H4)2], consists of two independent molecules. The bonding between iridium and the five-membered ring of the indenyl ligand shows the usual asymmetry associated with the typical ring slippage responsible for the enhanced activity of indenyl metal compounds when compared with the analogous cyclopentadienyl metal compound. There are three short Ir—C bonds of 2.210 (3), 2.190 (4) and 2.220 (3) Å and two long Ir—C bonds to the C atoms that are part of the fused six-membered ring of 2.349 (4) and 2.366 (3) Å for one of the independent molecules [2.208 (4), 2.222 (3), 2.197 (4) Å for the short distances and 2.371 (3) and 2.358 (3) Å for the long distances in the second molecule]. This results in both indenyl ligands being slightly kinked, with dihedral angles of 6.8 (4)° and 6.5 (4)°.

The asymmetric unit of the title compound, [Ir(C 9 H 7 )-(C 2 H 4 ) 2 ], consists of two independent molecules. The bonding between iridium and the five-membered ring of the indenyl ligand shows the usual asymmetry associated with the typical ring slippage responsible for the enhanced activity of indenyl metal compounds when compared with the analogous cyclopentadienyl metal compound. There are three short Ir-C bonds of 2.210 (3), 2.190 (4) and 2.220 (3) Å and two long Ir-C bonds to the C atoms that are part of the fused sixmembered ring of 2.349 (4) and 2.366 (3) Å for one of the independent molecules [2.208 (4), 2.222 (3), 2.197 (4) Å for the short distances and 2.371 (3) and 2.358 (3) Å for the long distances in the second molecule]. This results in both indenyl ligands being slightly kinked, with dihedral angles of 6.8 (4) and 6.5 (4) .
The author thanks the National Science Foundation for funds (CHE-01311288) for the purchase of the diffractometer. The author recognizes the payment of the open access fee by Virginia Tech University Libraries.
is displayed by indenyl metal complexes compared with cyclopentadienyl complexes has been dubbed the "indenyl effect". The effect was first described by Mawby's group (Hart-Davis et al., 1970) and was further quantified by Basolo's group (Rerek et al., 1983) We have previously reported on the synthesis and structure of η 3 -indenyliridium complexes formed by reaction of an η 5 -indenyliridiumbis(olefin) complex and small phosphine ligands such as PMe 3 or PhPMe 2 (Merola et al., 1986). The smallest olefin complex of indenyl iridium, (η 5 -Indenyl)bis(η 2 -ethylene)iridium(I), 1, is the subject of this report. The thermal ellipsoid plot for both independent molecules of 1 is shown in figure 1. The most interesting aspects of the bonding are highlighted in table 1 showing the three short and two long bond distances of the "slipped" indenyl rings. Figure 2 shows the "fold" of the indenyl ligand which imparts non-planarity of the 6-membered ring from the 5membered ring. The angle between the planes defined by C1, C2 and C9 and that defined by C3, C8, C7, C4, C5 and C6 is 6.5 (4)° and 6.8 (4)° for the "A" and "B" molecules.

Experimental
[Ir(C 2 H 2 ) 2 Cl] 2 was synthesized by the reaction between [Ir(C 8 H 14 ) 2 IrCl] 2 and ethylene (Herde et al., 1974). The title compound was prepared by the reaction between lithium indenide and [Ir(C 2 H 2 ) 2 Cl] 2 in anhydrous THF. Crystals of the title compound were grown by the slow evaporation of a pentane solution. The title compound has also been reported previously prepared by this same method (Szajek et al., 1991).

Refinement
Crystal data, data collection and structure refinement details are summarized in Table 1. Hydrogen atoms were found in difference maps and refined using a riding model with C-H distances of 0.93 Å (C indenyl ) and 0.97 Å (C ethylene ). U iso (H) values were set to 1.2U eq of the attached carbon atom.

Figure 2
Ball and stick drawing of title compound showing the fold angle of the indenyl rings for both independent molecules.
Ethylene ligands and hydrogen atoms omitted for clarity.

Crystal data
[Ir(C 9 H 7 )(C 2 H 4 ) 2 ] M r = 363.45 Monoclinic, P2 1 /c a = 7.73182 (11) Å b = 10.77708 (13)   Refinement. Refinement of F 2 against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F 2 , conventional R-factors R are based on F, with F set to zero for negative F 2 . The threshold expression of F 2 > σ(F 2 ) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F 2 are statistically about twice as large as those based on F, and R-factors based on ALL data will be even larger.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å 2 )
x y z U iso */U eq