DIMERIC (PENTAMETHYLCYCLOPENTADIENYL)RHODIUM AND (PENTAMETHYLCYCLOPENTADIENYL)IRIDIUM COMPLEXES .5. STRUCTURAL STUDIES ON THE HOMOGENEOUS HYDROGENATION CATALYSTS [(ETA5-C5ME5)IRBR]2(MU-BR)2 AND [(ETA5-C5ME5)IRI]2(MU-I)2 AND SYSTEMATICS IN THE SERIES [(ETA5-C5ME5)IRX]2(MU-X)2 (X = CL, BR, I)

The complexes di-μ-bromo-dibromobis(η5-pentamethylcyclopentadienyl)diiridium(III), [(η5-C5Me5)IrBr]2(μ-Br)2, and di-μ-iodo-diiodobis(η5-pentamethylcyclopentadienyl)diiridium(III), [(η5-C5Me5)IrI]2(μ-I)2, have each been investigated by means of a single-crystal X-ray structural analysis. Crystal data are as follows. [(η5-C5Me5)IrBr]2(μ-Br)2: triclinic, space group P, a=8.757 (1)Å, b=8.956 (1) Å, c=16.166 (2) Å, α=91.51 (1)°, β=104.95 (1)°, γ=93.58 (1)°, V=1221.4 (3) Å3, Z=2 (dimers). [(η5-C5Me5)IrI]2(μ-I)2: orthorhombic, space group Pccn, a=13.410 (1) Å, b=21.537 (3) Å, c=9.084 (1) Å, V=2623.6 (6) Å3, Z=4 (dimers). Diffraction data for each complex were collected with a Syntex P21 automated diffractometer (Mo Kα, 5°<2θ<45°) and the structures were solved by using the Syntex XTL structure determination system. Final discrepancy indices were RF=4.0% and RWF=3.9% for the bromo complex (3210 independent data) and RF=3.7% and RWF=2.9% for the iodo derivative (1724 reflections). The bromo complex crystallizes with two independent molecules in the unit cell, each having precise Ct symmetry. Dimensions of note are Ir⃨Ir=3.911 (1) and 3.892 (1) Å, Ir-Br(terminal)=2.515 (1) and 2.522 (1) Å, Ir-Br(bridging)=2.574 (1) and 2.576 (1) Å in molecule I and 2.564 (1) and 2.567 (1) Å in molecule II, and Ir-Br-Ir=98.80 (4) and 98.68 (4)°. The iodo complex also has precise Ci symmetry, the crystallographic asymmetric unit consisting of half of a dimeric molecule. Important dimensions are Ir⃛Ir=4.072 (1) Å, Ir-I(terminal)=2.694 (1) Å, Ir-I(bridging)=2.707 (1) and 2.712 (1) Å, and Ir-I-Ir=97.42 (2)°. The geometric details of these molecules and of the analogous chloro complex, [(η5-C5Me5)IrCl] 2(μ-Cl)2, are compared and the structural trends outlined. © 1979, American Chemical Society. All rights reserved.