Di-μ-bromido-bis­[(η⁴-cyclo­octa-1,5-diene)iridium(I)]

The title complex, [Ir₂(μ-Br)₂(C₈H₁₂)₂], displays a dinuclear structure with bridging Br atoms, generated by twofold symmetry. The coordination geometry around the Ir atom is pseudo-square-planar, involving two Br atoms and two η² C=C bonds. The Ir₂(μ-Br)₂ core shows a bent geometry with a hinge angle of 101.58 (3)°.

Key indicators

• Single-crystal X-ray study
• T = 100 K
• Mean [sigma](C-C) = 0.010 Å
• R factor = 0.034
• wR factor = 0.064
• Data-to-parameter ratio = 31.2

checkCIF/PLATON results

No syntax errors found



Alert level C
RINTA01_ALERT_3_C  The value of Rint is greater than 0.10
            Rint given   0.129
PLAT020_ALERT_3_C The value of Rint is greater than 0.10 .........       0.13
PLAT342_ALERT_3_C Low Bond Precision on C-C bonds (x 1000) Ang ...         10
PLAT764_ALERT_4_C Overcomplete CIF Bond List Detected (Rep/Expd) .       1.14 Ratio

Alert level G
REFLT03_ALERT_4_G Please check that the estimate of the number of Friedel pairs is
            correct. If it is not, please give the correct count in the
            _publ_section_exptl_refinement section of the submitted CIF.
           From the CIF: _diffrn_reflns_theta_max           31.55
           From the CIF: _reflns_number_total               2840
           Count of symmetry unique reflns         1731
           Completeness (_total/calc)            164.07%
           TEST3: Check Friedels for noncentro structure
           Estimate of Friedel pairs measured      1109
           Fraction of Friedel pairs measured     0.641
           Are heavy atom types Z>Si present        yes

   0 ALERT level A = In general: serious problem
   0 ALERT level B = Potentially serious problem
   4 ALERT level C = Check and explain
   1 ALERT level G = General alerts; check

   0 ALERT type 1 CIF construction/syntax error, inconsistent or missing data
   0 ALERT type 2 Indicator that the structure model may be wrong or deficient
   3 ALERT type 3 Indicator that the structure quality may be low
   2 ALERT type 4 Improvement, methodology, query or suggestion
   0 ALERT type 5 Informative message, check

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S1. Comment

Crystal data for many kinds of the binuclear complexes of d⁸ transition metal ions of type [L₂M(µ-X)]₂ (M= Rh or Ir, X = halide) and their theoretical analysis have been reported (Aullón, et al., 1998; Cotton, et al., 1999). The bromide analogues are fairly rare, however. Among these complexes cyclooctadiene complexes of group 8 transition elements [M(µ-Cl)(cod)]₂ (COD = cis,cis-1,5-cyclooctadiene; M = Ir^I or Rh^I) have been used as starting key complexes for various kinds of Ir^I or Rh^I complexes useful as efficient catalyst precursors. For example, we have reported the molecular structure of [Ir(µ-Cl){(R)-binap}]₂ (Yamagata et al., 1997), which was prepared from the reaction of [Ir(µ-Cl)(cod)]₂ with two equivalents of (R)-BINAP {(R)-(+)-2,2'-bis(diphenylphosphanyl)-1,1'-binaphthyl}, and its use as an efficient catalyst for asymmetric hydrogenation of prochiral imines (Tani, et al., 1995). The catalytic asymmetric olefin hydroamination with [Ir(µ-Cl)(diphosphine)]₂ and the structure of [Ir(µ-Cl){(R)-binap}]₂ have also been investigated by Togni and his co-workers (Dorta, et al., 1997). Although [Rh(µ-Cl)(cod)]₂ (De Ridder, et al., 1994) has an almost square planar structure (the hinge angle 169.1 (3)°), [Ir(µ-Cl)(cod)]₂ (Cotton, et al., 1986) and [Rh(µ-Br)(cod)]₂ (Pettinari, et al., 2002) show bent structures; the hinge angles are 109.4 (3)° and 148.7 (3)°, respectively. Thus, it may be interest to examine the structure of [Ir(µ-Br)(cod)]₂, (I), which is reported here. (I) is isostructural with [Ir(µ-Cl)(cod)]₂ and [Rh(µ-Br)(cod)]₂. The Ir₂(µ-Br)₂ core in (I) shows a bent geometry with the hinge angles of 101.58 (3)°. The M···M distances of (I), [Ir(µ-Cl)(cod)]₂, and [Rh(µ-Br)(cod)]₂ are 2.9034 (5), 2.910 (1), and 3.565 Å, respectively. The degree of the bending is Rh < Ir and Cl < Br. These tendencies can be explained by the differences in diffuseness of the metal d orbitals and by analyzing the <p_z²/d_z²> and <d_z²/d_z²> overlap integrals between the Slater orbitals (EH calculations) (Aullón, et al., 1998).

Related literature

For related literature, see: Aullón et al. (1998); Cotton et al. (1986, 1999); Dorta et al. (1997); Pettinari et al. (2002); De Ridder & Imhoef (1994); Tani et al. (1995); Yamagata et al. (1997).

S2. Experimental

To a Schlenk flask were added 2.11 g of Na₂IrBr₆ (2.94 mmol), H₂O (20 ml), isopropyl alcohol (9.0 ml) and 1,5-cyclooctadiene (2.9 ml, 24 mmol). The mixture was heated under reflux for 12 hr and then cooled to ambient temperature. The whole volume was reduced to a small volume (ca 3 ml) under reduced pressure. To the residue were added 20 ml of H₂O and 30 ml of toluene. The reddish organic layer was separated and the aqueous layer was extracted three times with toluene (20 ml each). The combined organic layer and the extracts were condensed to dryness. The resulting deep red solid was washed with ethanol, H₂O, and ethanol successively and dried in vacuo to yield [Ir(µ-Br)(cod)]₂ as a deep red solid (1.28 g, 57%). Recrystallization from THF afforded (I) as an analytically pure product. mp.: 469 K (melt, decomp. in capillary). ¹H NMR (300 MHz, CDCl₃, 308 K, δ, p.p.m.): 4.35 (m, 8H, =CH), 2.20 - 2.24 (m, 8H, –CHH–), 1.40 - 1.50 (m, 8H, –CHH–). IR (Nujol, cm^-1): 410(w), 330(w). Analysis calculated for C₁₆H₂₄Br₂Ir₂: C 25.27, H 3.18%; found: C 25.22; H 2.83%.

S3. Refinement

All H-atoms were geometrically placed (C—H = 0.95–0.99 Å) and refined as riding with U_iso(H) = 1.2U_eq(C) [or 1.5U_eq(C) for methyl groups].

Computing details

Data collection: RAPID-AUTO (Rigaku, 1998); cell refinement: RAPID-AUTO; data reduction: PROCESS in TEXSAN PROCESS (Rigaku/MSC, 2004); program(s) used to solve structure: SIR97 (Altomare et al., 1999); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 (Farrugia, 1997); software used to prepare material for publication: SHELXL97 and local routines.

Figures

Fig. 1. The molecule structure of (I), showing the atom-labelling scheme. Displacement ellipsoids are drawn at the 50% probability level. The H-atoms have been omitted. Symmetry code: (i) 1 - y, 1 - x, 3/2 - z.

Di-µ-bromido-bis[(η⁴-cycloocta-1,5-diene)iridium(I)]

Crystal data

[Ir2Br2(C8H12)2]	Dx = 2.976 Mg m^−3
Mr = 760.57	Melting point: 469 K
Tetragonal, P41212	Mo Kα radiation, λ = 0.71075 Å
Hall symbol: P 4abw 2nw	Cell parameters from 69455 reflections
a = 8.3839 (5) Å	θ = 3.4–31.3°
c = 24.1471 (19) Å	µ = 20.36 mm^−1
V = 1697.3 (2) Å^3	T = 100 K
Z = 4	Block, red
F(000) = 1376	0.19 × 0.15 × 0.11 mm

Data collection

Rigaku R-AXIS RAPID diffractometer	2840 independent reflections
Radiation source: normal-focus sealed tube	2591 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.129
Detector resolution: 10.00 pixels mm^-1	θmax = 31.6°, θmin = 3.4°
ω scans	h = −12→12
Absorption correction: numerical (ABSCOR; Higashi, 1999)	k = −12→12
Tmin = 0.114, Tmax = 0.431	l = −35→35
48361 measured reflections

Refinement

Refinement on F^2	Secondary atom site location: difference Fourier map
Least-squares matrix: full	Hydrogen site location: inferred from neighbouring sites
R[F^2 > 2σ(F^2)] = 0.034	H-atom parameters constrained
wR(F^2) = 0.064	w = 1/[σ^2(Fo^2) + (0.0225P)^2 + 4.3085P] where P = (Fo^2 + 2Fc^2)/3
S = 1.09	(Δ/σ)max = 0.002
2840 reflections	Δρmax = 1.33 e Å^−3
91 parameters	Δρmin = −2.56 e Å^−3
0 restraints	Absolute structure: Flack (1983), 1112 Friedel pairs
Primary atom site location: structure-invariant direct methods	Absolute structure parameter: 0.02 (2)

Special details

Experimental. Indexing was performed from 3 oscillations which were exposed for 1.3 minutes. The camera radiuswas 127.40 mm. Readout performed in the 0.100 mm pixel mode. A total of 300 images, corresponding to 600.0 °. osillation angles, were collected with 4 different goniometer setting. Exposure time was 100 s per degree. The camera radiuswas 127.40 mm. Readout performed in the 0.100 mm pixel mode.

Geometry. All e.s.d.'s (except the e.s.d. in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell e.s.d.'s are taken into account individually in the estimation of e.s.d.'s in distances, angles and torsion angles; correlations between e.s.d.'s in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell e.s.d.'s is used for estimating e.s.d.'s involving l.s. planes. Least-squares planes (x,y,z in crystal coordinates) and deviations from them (* indicates atom used to define plane)

- 1.1015 (0.0026) x + 8.0857 (0.0009) y + 5.5390 (0.0060) z = 7.6598 (0.0050)

* 0.0000 (0.0000) Ir * 0.0000 (0.0000) Br * 0.0000 (0.0000) Br_$1

Rms deviation of fitted atoms = 0.0000

8.0857 (0.0009) x - 1.1015 (0.0026) y + 5.5390 (0.0060) z = 7.6329 (0.0044)

Angle to previous plane (with approximate e.s.d.) = 78.42 (0.03)

* 0.0000 (0.0000) Ir_$1 * 0.0000 (0.0000) Br * 0.0000 (0.0000) Br_$1

Rms deviation of fitted atoms = 0.0000

Refinement. Refinement of F² against ALL reflections. The weighted R-factor wR and goodness of fit S are based on F², conventional R-factors R are based on F, with F set to zero for negative F². The threshold expression of F² > σ(F²) is used only for calculating R-factors(gt) etc. and is not relevant to the choice of reflections for refinement. R-factors based on F² 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 (Ų)

	x	y	z	Uiso*/Ueq
Ir	0.71261 (3)	0.51576 (3)	0.771695 (9)	0.01892 (6)
Br	0.55064 (8)	0.55356 (8)	0.68431 (2)	0.02227 (14)
C1	0.8208 (8)	0.5503 (8)	0.8497 (2)	0.0225 (14)
H1	0.7181	0.5761	0.8637	0.027*
C2	0.8474 (9)	0.3900 (9)	0.8320 (2)	0.0233 (14)
H2	0.7609	0.3170	0.8337	0.028*
C3	1.0064 (9)	0.3299 (9)	0.8105 (3)	0.0267 (15)
H3A	1.0216	0.2178	0.8222	0.032*
H3B	1.0935	0.3942	0.8269	0.032*
C4	1.0161 (9)	0.3402 (9)	0.7468 (3)	0.0262 (15)
H4A	1.1289	0.3534	0.7356	0.031*
H4B	0.9768	0.2390	0.7306	0.031*
C5	0.9189 (8)	0.4778 (9)	0.7238 (2)	0.0232 (13)
H5	0.8512	0.4563	0.6931	0.028*
C6	0.9213 (9)	0.6350 (8)	0.7443 (3)	0.0241 (15)
H6	0.8515	0.7107	0.7279	0.029*
C7	1.0287 (9)	0.6909 (10)	0.7912 (3)	0.0289 (15)
H7A	1.0621	0.8023	0.7841	0.035*
H7B	1.1259	0.6238	0.7921	0.035*
C8	0.9438 (10)	0.6819 (9)	0.8479 (3)	0.0303 (17)
H8A	1.0241	0.6633	0.8772	0.036*
H8B	0.8910	0.7852	0.8556	0.036*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Ir	0.02031 (13)	0.02195 (14)	0.01450 (9)	0.00101 (10)	−0.00110 (9)	−0.00051 (9)
Br	0.0270 (4)	0.0221 (3)	0.0177 (3)	0.0016 (3)	−0.0040 (2)	0.0020 (2)
C1	0.022 (4)	0.026 (4)	0.019 (3)	−0.004 (3)	−0.002 (2)	0.004 (2)
C2	0.021 (4)	0.033 (4)	0.016 (3)	−0.002 (3)	−0.002 (2)	0.003 (2)
C3	0.025 (4)	0.033 (4)	0.023 (3)	0.003 (3)	0.000 (3)	0.009 (3)
C4	0.030 (4)	0.027 (4)	0.022 (3)	0.006 (3)	0.008 (3)	−0.001 (3)
C5	0.020 (3)	0.033 (4)	0.017 (3)	0.004 (3)	0.000 (2)	0.005 (3)
C6	0.028 (4)	0.021 (3)	0.023 (3)	−0.002 (3)	0.002 (3)	0.005 (2)
C7	0.025 (4)	0.034 (4)	0.028 (3)	−0.008 (3)	0.000 (3)	0.000 (3)
C8	0.036 (4)	0.032 (4)	0.023 (3)	−0.008 (3)	−0.008 (3)	−0.005 (3)

Geometric parameters (Å, º)

Ir—C5	2.105 (6)	C3—H3A	0.9900
Ir—C1	2.111 (6)	C3—H3B	0.9900
Ir—C6	2.121 (7)	C4—C5	1.518 (9)
Ir—C2	2.123 (6)	C4—H4A	0.9900
Ir—Br	2.5293 (7)	C4—H4B	0.9900
Ir—Br^i	2.5335 (7)	C5—C6	1.408 (10)
Ir—Ir^i	2.9034 (5)	C5—H5	0.9500
Br—Ir^i	2.5335 (7)	C6—C7	1.519 (10)
C1—C2	1.429 (10)	C6—H6	0.9500
C1—C8	1.511 (10)	C7—C8	1.546 (10)
C1—H1	0.9500	C7—H7A	0.9900
C2—C3	1.517 (10)	C7—H7B	0.9900
C2—H2	0.9500	C8—H8A	0.9900
C3—C4	1.542 (9)	C8—H8B	0.9900
C5—Ir—C1	99.1 (3)	C2—C3—H3A	109.3
C5—Ir—C6	38.9 (3)	C4—C3—H3A	109.3
C1—Ir—C6	81.9 (3)	C2—C3—H3B	109.3
C5—Ir—C2	82.2 (3)	C4—C3—H3B	109.3
C1—Ir—C2	39.4 (3)	H3A—C3—H3B	108.0
C6—Ir—C2	90.5 (3)	C5—C4—C3	112.3 (6)
C5—Ir—Br	90.09 (17)	C5—C4—H4A	109.1
C1—Ir—Br	163.4 (2)	C3—C4—H4A	109.1
C6—Ir—Br	97.13 (19)	C5—C4—H4B	109.1
C2—Ir—Br	156.9 (2)	C3—C4—H4B	109.1
C5—Ir—Br^i	157.1 (2)	H4A—C4—H4B	107.9
C1—Ir—Br^i	91.95 (18)	C6—C5—C4	125.1 (6)
C6—Ir—Br^i	163.9 (2)	C6—C5—Ir	71.1 (4)
C2—Ir—Br^i	94.1 (2)	C4—C5—Ir	110.8 (4)
Br—Ir—Br^i	84.52 (3)	C6—C5—H5	117.5
C5—Ir—Ir^i	104.1 (2)	C4—C5—H5	117.5
C1—Ir—Ir^i	134.09 (18)	Ir—C5—H5	88.1
C6—Ir—Ir^i	137.95 (19)	C5—C6—C7	124.0 (7)
C2—Ir—Ir^i	105.7 (2)	C5—C6—Ir	69.9 (4)
Br—Ir—Ir^i	55.074 (17)	C7—C6—Ir	113.7 (4)
Br^i—Ir—Ir^i	54.939 (16)	C5—C6—H6	118.0
Ir—Br—Ir^i	69.987 (19)	C7—C6—H6	118.0
C2—C1—C8	124.8 (7)	Ir—C6—H6	86.4
C2—C1—Ir	70.7 (3)	C6—C7—C8	111.8 (6)
C8—C1—Ir	111.5 (4)	C6—C7—H7A	109.3
C2—C1—H1	117.6	C8—C7—H7A	109.3
C8—C1—H1	117.6	C6—C7—H7B	109.3
Ir—C1—H1	87.7	C8—C7—H7B	109.3
C1—C2—C3	123.5 (7)	H7A—C7—H7B	107.9
C1—C2—Ir	69.8 (4)	C1—C8—C7	112.1 (6)
C3—C2—Ir	113.5 (4)	C1—C8—H8A	109.2
C1—C2—H2	118.2	C7—C8—H8A	109.2
C3—C2—H2	118.2	C1—C8—H8B	109.2
Ir—C2—H2	86.8	C7—C8—H8B	109.2
C2—C3—C4	111.6 (6)	H8A—C8—H8B	107.9
C5—Ir—Br—Ir^i	107.2 (2)	C3—C4—C5—C6	47.0 (10)
C1—Ir—Br—Ir^i	−128.8 (6)	C3—C4—C5—Ir	−34.0 (8)
C6—Ir—Br—Ir^i	145.6 (2)	C1—Ir—C5—C6	−64.8 (4)
C2—Ir—Br—Ir^i	37.3 (5)	C2—Ir—C5—C6	−100.5 (4)
Br^i—Ir—Br—Ir^i	−50.44 (3)	Br—Ir—C5—C6	101.3 (4)
C5—Ir—C1—C2	−65.7 (4)	Br^i—Ir—C5—C6	177.3 (4)
C6—Ir—C1—C2	−100.8 (4)	Ir^i—Ir—C5—C6	155.1 (3)
Br—Ir—C1—C2	171.5 (5)	C1—Ir—C5—C4	56.5 (5)
Br^i—Ir—C1—C2	94.1 (4)	C6—Ir—C5—C4	121.3 (7)
Ir^i—Ir—C1—C2	54.2 (5)	C2—Ir—C5—C4	20.8 (5)
C5—Ir—C1—C8	55.1 (6)	Br—Ir—C5—C4	−137.4 (5)
C6—Ir—C1—C8	20.1 (5)	Br^i—Ir—C5—C4	−61.4 (7)
C2—Ir—C1—C8	120.8 (7)	Ir^i—Ir—C5—C4	−83.6 (5)
Br—Ir—C1—C8	−67.7 (9)	C4—C5—C6—C7	3.1 (11)
Br^i—Ir—C1—C8	−145.0 (5)	Ir—C5—C6—C7	105.7 (6)
Ir^i—Ir—C1—C8	175.1 (4)	C4—C5—C6—Ir	−102.6 (6)
C8—C1—C2—C3	2.1 (10)	C1—Ir—C6—C5	115.5 (4)
Ir—C1—C2—C3	105.4 (6)	C2—Ir—C6—C5	76.9 (4)
C8—C1—C2—Ir	−103.3 (6)	Br—Ir—C6—C5	−81.2 (4)
C5—Ir—C2—C1	114.7 (4)	Br^i—Ir—C6—C5	−176.2 (5)
C6—Ir—C2—C1	76.6 (4)	Ir^i—Ir—C6—C5	−37.5 (5)
Br—Ir—C2—C1	−173.8 (4)	C5—Ir—C6—C7	−119.3 (7)
Br^i—Ir—C2—C1	−88.0 (4)	C1—Ir—C6—C7	−3.8 (6)
Ir^i—Ir—C2—C1	−142.7 (4)	C2—Ir—C6—C7	−42.4 (6)
C5—Ir—C2—C3	−4.1 (6)	Br—Ir—C6—C7	159.4 (5)
C1—Ir—C2—C3	−118.8 (8)	Br^i—Ir—C6—C7	64.5 (10)
C6—Ir—C2—C3	−42.3 (6)	Ir^i—Ir—C6—C7	−156.9 (4)
Br—Ir—C2—C3	67.4 (8)	C5—C6—C7—C8	−93.9 (8)
Br^i—Ir—C2—C3	153.1 (5)	Ir—C6—C7—C8	−12.8 (8)
Ir^i—Ir—C2—C3	98.4 (5)	C2—C1—C8—C7	48.2 (9)
C1—C2—C3—C4	−93.8 (8)	Ir—C1—C8—C7	−32.8 (8)
Ir—C2—C3—C4	−13.2 (8)	C6—C7—C8—C1	29.7 (9)
C2—C3—C4—C5	30.8 (9)

Symmetry code: (i) −y+1, −x+1, −z+3/2.