(Chlorido/bromido)[(1,2,5,6-η)-cyclo­octa-1,5-diene](4-isopropyl-1-methyl-1,2,4-triazol-5-yl­idene)rhodium(I)

Rushlow, J.; Astashkin, A.V.; Albert, D.R.; Rajaseelan, E.

doi:10.1107/S2414314621008117

metal-organic compounds

IUCrDATA

ISSN: 2414-3146

Volume 6| Part 8| August 2021| x210811

https://doi.org/10.1107/S2414314621008117

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(Chlorido/bromido)[(1,2,5,6-η)-cycloocta-1,5-diene](4-isopropyl-1-methyl-1,2,4-triazol-5-ylidene)rhodium(I)

Joshua Rushlow,^a Andrei V. Astashkin,^b Daniel R. Albert ^a and Edward Rajaseelan ^a ^*

^aDepartment of Chemistry, Millersville University, Millersville, PA 17551, USA, and ^bDepartment of Chemistry and Biochemistry, The University of Arizona, Tuscon, AZ, 85716, USA
^*Correspondence e-mail: Edward.Rajaseelan@millersville.edu

Edited by M. Weil, Vienna University of Technology, Austria (Received 22 July 2021; accepted 6 August 2021; online 13 August 2021)

A new triazole-based neutral Rh^I complex, [Rh(Cl_0.846Br_0.154)(C₆H₁₁N₃)(C₈H₁₂)], has been synthesized and structurally characterized. The Rh^I atom has a distorted square-planar coordination environment, formed by a bidentate cycloocta-1,5-diene (COD) ligand, an N-heterocyclic carbene and a halide ligand that shows substitutional disorder (Cl:Br = 0.846:0.154). No significant intermolecular interactions other than van der Waals forces are found in the crystal structure. Diffraction data indicated a two-component inversion twin with a ratio of 0.95 (5):0.05 (5).

Keywords: crystal structure; rhodium; N-heterocyclic carbenes; Cl/Br substitutional disorder.

CCDC reference: 2101889

Structure description

Transition-metal complexes containing N-heterocyclic carbene (NHC) ligands have been studied extensively in homogeneous catalysis (Díez-Gonzáles et al., 2009 ), especially in transfer hydrogenation of unsaturated bonds (Ruff et al., 2016 ; Zuo et al., 2014 ). The NHC ligands can be tuned sterically and electronically by having different substituents on the nitrogen atoms (Gusev, 2009 ). Many imidazole- and triazole-based NHC rhodium and iridium complexes have been synthesized and structurally characterized (Herrmann et al., 2006 ; Wang & Lin, 1998 ; Chianese et al., 2004 ; Nichol et al., 2009 , 2010 , 2011 , 2012 ; Idrees et al., 2017a ,b ; Rood et al., 2021 ). Their catalytic activities in the transfer hydrogenation of ketones and imines have also been studied and reported (Hillier et al., 2001 ; Albrecht et al., 2002 ; Gnanamgari et al., 2007 ).

The molecular structure of the title complex, [Rh(Cl_0.846Br_0.154)(C₆H₁₁N₃)(C₈H₁₂)] (3), is illustrated in Fig. 1. The coordination environment around the Rh^I ion, formed by the bidentate cycloocta-1,5-diene (COD), NHC, and halide (Cl,Br) ligands is distorted square-planar. The Rh—C(NHC) bond length is found to be 2.016 (5) Å. The C(NHC)—Rh—(Cl,Br) bond angle is 87.93 (14)°. The N—(carbene)—N bond angle in the triazole-based carbene is 103.1 (4)°. Fig. 2 shows the crystal packing diagram of the complex. No non-covalent interactions exist between atoms that are closer than the sum of the van der Waals radii.

Figure 1
The molecular structure of the title compound (3) with displacement ellipsoids drawn at the 50% probability level.

Figure 2
Crystal packing diagram of the title compound (3) along the a axis.

The rhodium–halide bond length in the reported structure is 2.4308 (11) Å, which is longer than previously reported Rh—Cl bond lengths, viz. 2.36–2.42 Å (Skelton et al., 2019 , 2020 ; Kalidasan et al., 2015 ), and shorter than previously reported Rh—Br bond lengths, viz 2.49–2.55 Å (Benaissa et al., 2017 ; Aznarez et al., 2018 ), consistent with a Cl/Br substitutional disorder. The substitutional bromide likely comes from the triazolium salt (2) in the synthesis (Fig. 3).

Figure 3
Reaction scheme summarizing the synthesis of the N-heterocyclic carbene ligand (2) and metal complex (3).

Synthesis and crystallization

1-Methyl triazole (1) was purchased from Matrix Scientific and the subsequent syntheses, as shown in Fig. 3, were performed using reagent-grade solvents without further purification. NMR spectra were recorded at room temperature in CDCl₃ on a 400 MHz Varian spectrometer and referenced to the residual solvent peak (δ in ppm and J in Hz). The triazolium salt (2) was prepared by reacting (1) with isopropyl (i-Pr) bromide in toluene at reflux for 24 h followed by isolation with diethyl ether. The title metal complex (3) was synthesized by in situ transmetallation from the silver carbene complex of (2) (Chianese et al., 2003 ). The pale-yellow complex (3) was obtained in quantitative yield.¹H NMR: δ 7.89 (s, 1 H, N—C₃H—N), 5.67 (m, 1 H, CH of i-Pr), 5.12 (m, 4 H, CH of COD), 4.34 (s, 3 H, CH₃-N), 2.42–2.01 (m, 4 H, CH₂ of COD), 1.57 (m, 6 H, CH₃ of i-Pr). ¹³C NMR: 184.99 (d, Rh—C, J_C-Rh = 50.9), 139.07 (N—C₃H—N), 99.80, 99.73, 99.29, 99.22 (CH of COD), 51.44 (CH₃—N), 39.79 (CH of i-Pr), 33.08, 32.67, 29.01, 28.63 (CH₂ of COD), 24.27, 23.34 (CH₃ of i-Pr). Pale-yellow X-ray quality crystals of (3) were grown from 1:1, CH₂Cl₂/pentane by slow diffusion.

Refinement

Crystal data, data collection and structure refinement details are summarized in Table 1. Using only the Cl ligand in the refinement did not account for all electron density at the ligand location, and therefore, a Cl/Br substitutional disorder was introduced for this site. The refinement was stabilized by forcing Cl and Br to have the same atomic coordinates and ADPs, using EXYZ and EADP instructions, respectively, in SHELXL (Sheldrick, 2015b ). The resulting occupancies for Cl and Br were about 85% and 15%, respectively. The crystal was refined as a two-component inversion twin with a ratio of 0.95 (5) to 0.05 (5).

Table 1
Experimental details

Crystal data
Chemical formula	[Rh(Br_0.154Cl_0.846)(C₆H₁₁N₃)(C₈H₁₂)]
M_r	378.60
Crystal system, space group	Orthorhombic, P2₁2₁2₁
Temperature (K)	100
a, b, c (Å)	9.4146 (13), 11.9706 (17), 13.702 (2)
V (Å³)	1544.2 (4)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	1.64
Crystal size (mm)	0.15 × 0.12 × 0.03

Data collection
Diffractometer	Bruker APEXII CCD
Absorption correction	Multi-scan (SADABS; Krause et al., 2015 )
T_min, T_max	0.664, 0.745
No. of measured, independent and observed [I > 2σ(I)] reflections	16824, 3254, 3015
R_int	0.057
(sin θ/λ)_max (Å⁻¹)	0.632

Refinement
R[F² > 2σ(F²)], wR(F²), S	0.027, 0.057, 1.03
No. of reflections	3254
No. of parameters	177
H-atom treatment	H-atom parameters constrained
Δρ_max, Δρ_min (e Å⁻³)	0.65, −0.42
Absolute structure	Refined as an inversion twin.
Absolute structure parameter	0.05 (5)
Computer programs: SAINT (Bruker, 2007 ), APEX2 (Bruker, 2007), SHELXT (Sheldrick, 2015a ), SHELXL (Sheldrick, 2015b), and OLEX2 (Dolomanov et al., 2009 ).

Structural data

CCDC reference: 2101889

Crystal structure: contains datablock I. DOI: https://doi.org/10.1107/S2414314621008117/wm4151sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2414314621008117/wm4151Isup2.hkl

checkCIF report

Computing details top

Data collection: SAINT (Bruker, 2007); cell refinement: APEX2 (Bruker, 2007); data reduction: SAINT (Bruker, 2007); program(s) used to solve structure: SHELXT (Sheldrick, 2015a); program(s) used to refine structure: SHELXL (Sheldrick, 2015b); molecular graphics: OLEX2 (Dolomanov et al., 2009); software used to prepare material for publication: OLEX2 (Dolomanov et al., 2009).

(Chlorido/bromido)[(1,2,5,6-η)-cycloocta-1,5-diene](4-isopropyl-1-methyl-\ 1,2,4-triazol-5-ylidene)rhodium(I) top

Crystal data top

[Rh(Br_0.154Cl_0.846)(C₆H₁₁N₃)(C₈H₁₂)]	D_x = 1.628 Mg m⁻³
M_r = 378.60	Mo Kα radiation, λ = 0.71073 Å
Orthorhombic, P2₁2₁2₁	Cell parameters from 3850 reflections
a = 9.4146 (13) Å	θ = 2.6–25.5°
b = 11.9706 (17) Å	µ = 1.64 mm⁻¹
c = 13.702 (2) Å	T = 100 K
V = 1544.2 (4) Å³	Plate, clear light colourless
Z = 4	0.15 × 0.12 × 0.03 mm
F(000) = 771

Data collection top

Bruker APEXII CCD diffractometer	3015 reflections with I > 2σ(I)
φ and ω scans	R_int = 0.057
Absorption correction: multi-scan (SADABS; Krause et al., 2015)	θ_max = 26.7°, θ_min = 2.3°
T_min = 0.664, T_max = 0.745	h = −11→11
16824 measured reflections	k = −15→15
3254 independent reflections	l = −17→17

Refinement top

Refinement on F²	Hydrogen site location: inferred from neighbouring sites
Least-squares matrix: full	H-atom parameters constrained
R[F² > 2σ(F²)] = 0.027	w = 1/[σ²(F_o²) + (0.0271P)² + 0.176P] where P = (F_o² + 2F_c²)/3
wR(F²) = 0.057	(Δ/σ)_max < 0.001
S = 1.03	Δρ_max = 0.65 e Å⁻³
3254 reflections	Δρ_min = −0.42 e Å⁻³
177 parameters	Absolute structure: Refined as an inversion twin.
0 restraints	Absolute structure parameter: 0.05 (5)
Primary atom site location: dual

Special details top

Geometry. All esds (except the esd in the dihedral angle between two l.s. planes) are estimated using the full covariance matrix. The cell esds are taken into account individually in the estimation of esds in distances, angles and torsion angles; correlations between esds in cell parameters are only used when they are defined by crystal symmetry. An approximate (isotropic) treatment of cell esds is used for estimating esds involving l.s. planes.

Refinement. Refined as a 2-component inversion twin.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	U_iso*/U_eq	Occ. (<1)
Rh1	0.36461 (3)	0.48473 (3)	0.25898 (2)	0.01379 (10)
Cl1	0.55744 (11)	0.42693 (9)	0.15236 (8)	0.0233 (4)	0.846 (4)
N3	0.5884 (4)	0.5139 (3)	0.4182 (3)	0.0158 (8)
N1	0.5001 (4)	0.3511 (3)	0.4233 (3)	0.0166 (9)
N2	0.6009 (4)	0.3527 (3)	0.4974 (3)	0.0183 (9)
C1	0.4910 (5)	0.4478 (4)	0.3733 (3)	0.0158 (10)
C7	0.2352 (5)	0.5923 (5)	0.3445 (3)	0.0173 (11)
H7	0.2842	0.6223	0.4036	0.021*
C14	0.1882 (5)	0.4807 (5)	0.3551 (3)	0.0152 (10)
H14	0.2100	0.4475	0.4204	0.018*
C11	0.1905 (5)	0.4756 (6)	0.1477 (3)	0.0215 (12)
H11	0.2079	0.4212	0.0936	0.026*
C6	0.6157 (6)	0.7057 (4)	0.4812 (4)	0.0242 (11)
H6A	0.5236	0.6976	0.5138	0.036*
H6B	0.6295	0.7839	0.4621	0.036*
H6C	0.6917	0.6831	0.5259	0.036*
C13	0.0626 (6)	0.4277 (5)	0.3048 (4)	0.0213 (11)
H13A	−0.0251	0.4480	0.3405	0.026*
H13B	0.0727	0.3454	0.3077	0.026*
C12	0.0468 (5)	0.4631 (4)	0.1982 (4)	0.0220 (12)
H12A	−0.0105	0.4066	0.1630	0.026*
H12B	−0.0047	0.5351	0.1952	0.026*
C2	0.6523 (5)	0.4534 (4)	0.4915 (3)	0.0178 (10)
H2	0.7250	0.4817	0.5327	0.021*
C5	0.7597 (5)	0.6392 (4)	0.3365 (4)	0.0264 (12)
H5A	0.8372	0.6178	0.3805	0.040*
H5B	0.7747	0.7159	0.3138	0.040*
H5C	0.7579	0.5884	0.2804	0.040*
C8	0.1612 (5)	0.6824 (4)	0.2836 (3)	0.0178 (10)
H8A	0.1784	0.7560	0.3144	0.021*
H8B	0.0575	0.6685	0.2850	0.021*
C4	0.6193 (5)	0.6320 (4)	0.3907 (3)	0.0172 (10)
H4	0.5426	0.6579	0.3455	0.021*
C10	0.2598 (5)	0.5757 (5)	0.1375 (3)	0.0174 (11)
H10	0.3189	0.5812	0.0770	0.021*
C9	0.2102 (5)	0.6876 (4)	0.1767 (4)	0.0203 (11)
H9A	0.1306	0.7149	0.1359	0.024*
H9B	0.2888	0.7421	0.1711	0.024*
C3	0.4187 (6)	0.2494 (4)	0.4057 (4)	0.0235 (11)
H3A	0.4571	0.2107	0.3485	0.035*
H3B	0.3190	0.2687	0.3939	0.035*
H3C	0.4253	0.2005	0.4629	0.035*
Br1	0.55744 (11)	0.42693 (9)	0.15236 (8)	0.0233 (4)	0.154 (4)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Rh1	0.01309 (16)	0.01269 (16)	0.01558 (16)	0.00094 (13)	0.00034 (14)	−0.00176 (14)
Cl1	0.0209 (6)	0.0254 (6)	0.0236 (6)	0.0018 (4)	0.0048 (4)	−0.0043 (4)
N3	0.0149 (17)	0.013 (2)	0.0191 (18)	−0.0001 (16)	−0.0009 (13)	−0.0020 (17)
N1	0.015 (2)	0.014 (2)	0.021 (2)	0.0024 (16)	−0.0019 (16)	−0.0009 (17)
N2	0.014 (2)	0.020 (2)	0.021 (2)	0.0021 (15)	−0.0009 (15)	0.0000 (17)
C1	0.013 (2)	0.013 (2)	0.021 (2)	0.0036 (18)	0.0033 (19)	−0.003 (2)
C7	0.015 (2)	0.022 (3)	0.014 (2)	0.003 (2)	0.0024 (19)	−0.003 (2)
C14	0.014 (2)	0.014 (3)	0.018 (2)	0.004 (2)	0.0045 (16)	0.002 (2)
C11	0.021 (2)	0.028 (3)	0.015 (2)	0.003 (3)	−0.0064 (17)	−0.004 (3)
C6	0.034 (3)	0.016 (3)	0.023 (2)	0.000 (2)	0.000 (2)	−0.0004 (19)
C13	0.016 (3)	0.016 (3)	0.032 (3)	0.000 (2)	0.006 (2)	0.003 (2)
C12	0.019 (3)	0.018 (3)	0.030 (3)	−0.001 (2)	−0.0046 (19)	−0.001 (2)
C2	0.018 (2)	0.019 (3)	0.017 (2)	0.0019 (19)	−0.0027 (19)	−0.0001 (17)
C5	0.026 (3)	0.020 (3)	0.033 (3)	−0.002 (2)	0.007 (2)	0.002 (2)
C8	0.016 (3)	0.016 (2)	0.021 (2)	0.0029 (19)	0.0001 (18)	−0.0018 (18)
C4	0.021 (3)	0.012 (2)	0.018 (2)	−0.002 (2)	−0.001 (2)	0.0037 (17)
C10	0.020 (3)	0.021 (3)	0.011 (2)	0.005 (2)	−0.0014 (19)	−0.001 (2)
C9	0.020 (3)	0.021 (3)	0.020 (3)	0.003 (2)	0.001 (2)	0.001 (2)
C3	0.024 (3)	0.013 (3)	0.033 (3)	−0.004 (2)	0.003 (2)	−0.001 (2)
Br1	0.0209 (6)	0.0254 (6)	0.0236 (6)	0.0018 (4)	0.0048 (4)	−0.0043 (4)

Geometric parameters (Å, º) top

Rh1—Cl1	2.4308 (11)	C6—H6C	0.9800
Rh1—C1	2.016 (5)	C6—C4	1.521 (6)
Rh1—C7	2.125 (5)	C13—H13A	0.9900
Rh1—C14	2.121 (4)	C13—H13B	0.9900
Rh1—C11	2.242 (5)	C13—C12	1.528 (7)
Rh1—C10	2.221 (5)	C12—H12A	0.9900
Rh1—Br1	2.4308 (11)	C12—H12B	0.9900
N3—C1	1.359 (6)	C2—H2	0.9500
N3—C2	1.376 (6)	C5—H5A	0.9800
N3—C4	1.492 (6)	C5—H5B	0.9800
N1—N2	1.390 (5)	C5—H5C	0.9800
N1—C1	1.347 (6)	C5—C4	1.519 (7)
N1—C3	1.458 (6)	C8—H8A	0.9900
N2—C2	1.301 (6)	C8—H8B	0.9900
C7—H7	1.0000	C8—C9	1.538 (6)
C7—C14	1.415 (8)	C4—H4	1.0000
C7—C8	1.530 (7)	C10—H10	1.0000
C14—H14	1.0000	C10—C9	1.517 (7)
C14—C13	1.508 (7)	C9—H9A	0.9900
C11—H11	1.0000	C9—H9B	0.9900
C11—C12	1.527 (7)	C3—H3A	0.9800
C11—C10	1.371 (8)	C3—H3B	0.9800
C6—H6A	0.9800	C3—H3C	0.9800
C6—H6B	0.9800

C1—Rh1—Cl1	87.93 (14)	C4—C6—H6C	109.5
C1—Rh1—C7	92.47 (19)	C14—C13—H13A	108.9
C1—Rh1—C14	88.55 (19)	C14—C13—H13B	108.9
C1—Rh1—C11	161.7 (2)	C14—C13—C12	113.4 (4)
C1—Rh1—C10	162.22 (19)	H13A—C13—H13B	107.7
C1—Rh1—Br1	87.93 (14)	C12—C13—H13A	108.9
C7—Rh1—Cl1	158.76 (15)	C12—C13—H13B	108.9
C7—Rh1—C11	89.1 (2)	C11—C12—C13	112.0 (4)
C7—Rh1—C10	82.02 (19)	C11—C12—H12A	109.2
C7—Rh1—Br1	158.76 (15)	C11—C12—H12B	109.2
C14—Rh1—Cl1	162.14 (16)	C13—C12—H12A	109.2
C14—Rh1—C7	38.9 (2)	C13—C12—H12B	109.2
C14—Rh1—C11	81.30 (16)	H12A—C12—H12B	107.9
C14—Rh1—C10	97.40 (18)	N3—C2—H2	124.1
C14—Rh1—Br1	162.14 (16)	N2—C2—N3	111.7 (4)
C11—Rh1—Cl1	97.08 (13)	N2—C2—H2	124.1
C11—Rh1—Br1	97.08 (13)	H5A—C5—H5B	109.5
C10—Rh1—Cl1	91.19 (13)	H5A—C5—H5C	109.5
C10—Rh1—C11	35.8 (2)	H5B—C5—H5C	109.5
C10—Rh1—Br1	91.19 (13)	C4—C5—H5A	109.5
C1—N3—C2	108.6 (4)	C4—C5—H5B	109.5
C1—N3—C4	124.6 (4)	C4—C5—H5C	109.5
C2—N3—C4	126.8 (4)	C7—C8—H8A	108.7
N2—N1—C3	119.4 (4)	C7—C8—H8B	108.7
C1—N1—N2	113.8 (4)	C7—C8—C9	114.3 (4)
C1—N1—C3	126.9 (4)	H8A—C8—H8B	107.6
C2—N2—N1	102.8 (4)	C9—C8—H8A	108.7
N3—C1—Rh1	128.5 (3)	C9—C8—H8B	108.7
N1—C1—Rh1	128.4 (3)	N3—C4—C6	109.8 (4)
N1—C1—N3	103.1 (4)	N3—C4—C5	110.2 (4)
Rh1—C7—H7	113.5	N3—C4—H4	108.0
C14—C7—Rh1	70.4 (3)	C6—C4—H4	108.0
C14—C7—H7	113.5	C5—C4—C6	112.6 (4)
C14—C7—C8	125.4 (4)	C5—C4—H4	108.0
C8—C7—Rh1	112.8 (3)	Rh1—C10—H10	114.0
C8—C7—H7	113.5	C11—C10—Rh1	72.9 (3)
Rh1—C14—H14	113.8	C11—C10—H10	114.0
C7—C14—Rh1	70.7 (3)	C11—C10—C9	126.1 (4)
C7—C14—H14	113.8	C9—C10—Rh1	107.7 (3)
C7—C14—C13	126.5 (5)	C9—C10—H10	114.0
C13—C14—Rh1	109.9 (3)	C8—C9—H9A	108.9
C13—C14—H14	113.8	C8—C9—H9B	108.9
Rh1—C11—H11	114.6	C10—C9—C8	113.2 (4)
C12—C11—Rh1	110.1 (3)	C10—C9—H9A	108.9
C12—C11—H11	114.6	C10—C9—H9B	108.9
C10—C11—Rh1	71.3 (3)	H9A—C9—H9B	107.7
C10—C11—H11	114.6	N1—C3—H3A	109.5
C10—C11—C12	123.6 (5)	N1—C3—H3B	109.5
H6A—C6—H6B	109.5	N1—C3—H3C	109.5
H6A—C6—H6C	109.5	H3A—C3—H3B	109.5
H6B—C6—H6C	109.5	H3A—C3—H3C	109.5
C4—C6—H6A	109.5	H3B—C3—H3C	109.5
C4—C6—H6B	109.5

Rh1—C7—C14—C13	−100.9 (4)	C11—C10—C9—C8	46.9 (6)
Rh1—C7—C8—C9	−8.0 (5)	C12—C11—C10—Rh1	102.2 (4)
Rh1—C14—C13—C12	−40.3 (5)	C12—C11—C10—C9	2.4 (7)
Rh1—C11—C12—C13	−16.0 (6)	C2—N3—C1—Rh1	−178.6 (3)
Rh1—C11—C10—C9	−99.8 (5)	C2—N3—C1—N1	0.9 (5)
Rh1—C10—C9—C8	−34.5 (5)	C2—N3—C4—C6	−50.2 (6)
N1—N2—C2—N3	0.2 (5)	C2—N3—C4—C5	74.5 (5)
N2—N1—C1—Rh1	178.7 (3)	C8—C7—C14—Rh1	104.6 (4)
N2—N1—C1—N3	−0.8 (5)	C8—C7—C14—C13	3.7 (7)
C1—N3—C2—N2	−0.8 (5)	C4—N3—C1—Rh1	1.1 (6)
C1—N3—C4—C6	130.1 (5)	C4—N3—C1—N1	−179.4 (4)
C1—N3—C4—C5	−105.2 (5)	C4—N3—C2—N2	179.5 (4)
C1—N1—N2—C2	0.4 (5)	C10—C11—C12—C13	−96.4 (6)
C7—C14—C13—C12	39.9 (7)	C3—N1—N2—C2	179.3 (4)
C7—C8—C9—C10	29.2 (6)	C3—N1—C1—Rh1	−0.1 (7)
C14—C7—C8—C9	−89.4 (6)	C3—N1—C1—N3	−179.7 (4)
C14—C13—C12—C11	37.3 (6)

Acknowledgements

JR was supported in this work by the Millersville University Murley Summer Undergraduate Research Fellowship.

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