Tetra­bromidobis(dicyclo­hexyl­phosphane-κP)digallium(Ga—Ga)

Dennis H Mayo; Yang Peng; Peter Zavalij; Kit H Bowen; Bryan W Eichhorn

doi:10.1107/S1600536812035982

. 2012 Sep 5;68(Pt 10):m1245. doi: 10.1107/S1600536812035982

Tetrabromidobis(dicyclohexylphosphane-κP)digallium(Ga—Ga)

Dennis H Mayo ^a, Yang Peng ^a, Peter Zavalij ^a, Kit H Bowen ^b, Bryan W Eichhorn ^a,^*

PMCID: PMC3470134 PMID: 23125578

Abstract

The title compound, a Ga^II dimer, [Ga₂Br₄(C₁₂H₂₃P)₂], was synthesized by reaction of GaBr(THF)_n (THF is tetrahydrofuran) with dicyclohexylphosphine in toluene. At 150 K the crystallographically centrosymmetric molecule exhibits disorder in which one of the two independent cyclohexyl groups is modelled over two sites in a 62 (1):38 (1) ratio. In d ₆-benzene solution, the compound exhibits virtual C _2h symmetry as determined by ¹H NMR. The coordination environment of the Ga^II atom is distorted tetrahedral.

Related literature

For references related to the synthesis of the ‘GaBr’ precursor and to cluster formation, see: Schnoeckel (2010 ▶); Steiner et al. (2004 ▶). For other Ga—Ga containing compounds, see: Baker et al. (2003 ▶) (the analogous digallium tetraiodide compound); Uhl et al. (1989 ▶) [the first-reported Ga(II) dimer compound].

Experimental

Crystal data

[Ga₂Br₄(C₁₂H₂₃P)₂]
M _r = 855.63
Monoclinic,
a = 9.6095 (11) Å
b = 13.7083 (16) Å
c = 13.3305 (16) Å
β = 109.177 (2)°
V = 1658.6 (3) Å³
Z = 2
Mo Kα radiation
μ = 6.55 mm⁻¹
T = 150 K
0.36 × 0.27 × 0.19 mm

Data collection

Bruker SMART APEX2 CCD area-detector diffractometer
Absorption correction: multi-scan SADABS (Sheldrick, 1996 ▶) T _min = 0.185, T _max = 0.288
24854 measured reflections
4842 independent reflections
4253 reflections with I > 2σ(I)
R _int = 0.021

Refinement

R[F ² > 2σ(F ²)] = 0.034
wR(F ²) = 0.068
S = 1.00
4842 reflections
168 parameters
60 restraints
H atoms treated by a mixture of independent and constrained refinement
Δρ_max = 1.88 e Å⁻³
Δρ_min = −0.94 e Å⁻³

Data collection: APEX2 (Bruker, 2010 ▶); cell refinement: SAINT (Bruker, 2010 ▶); data reduction: SAINT; program(s) used to solve structure: SHELXS97 (Sheldrick, 2008 ▶); program(s) used to refine structure: SHELXL97 (Sheldrick, 2008 ▶); molecular graphics: XSHELL (Bruker, 2010 ▶); software used to prepare material for publication: APEX2.

Supplementary Material

Crystal structure: contains datablock(s) I, global. DOI: 10.1107/S1600536812035982/nk2174sup1.cif

e-68-m1245-sup1.cif^{(23.4KB, cif)}

Structure factors: contains datablock(s) I. DOI: 10.1107/S1600536812035982/nk2174Isup2.hkl

e-68-m1245-Isup2.hkl^{(237.2KB, hkl)}

Additional supplementary materials: crystallographic information; 3D view; checkCIF report

Table 1. Selected geometric parameters (Å, °).

Ga1—Br2	2.3612 (5)
Ga1—Br1	2.3807 (5)
Ga1—P1	2.4164 (7)
Ga1—Ga1ⁱ	2.4353 (6)

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Br2—Ga1—Br1	107.306 (18)
Br2—Ga1—P1	101.11 (2)
Br1—Ga1—P1	98.25 (2)
Br2—Ga1—Ga1ⁱ	114.05 (2)
Br1—Ga1—Ga1ⁱ	115.13 (2)
P1—Ga1—Ga1ⁱ	118.93 (2)

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Symmetry code: (i) Inline graphic .

Acknowledgments

The authors thank the Air Force Office of Scientific Research (grant No. FA9550-11-1-0171), the NSF (grant No. 013367-001) and the DTRA for financial support. DHM acknowledges the ASEE Science, Mathematics, and Research for Transformation (SMART) Fellowship program for support. KHB thanks the AFOSR for support.

supplementary crystallographic information

Comment

GaBr(THF)_n was generated in a modified metal halide co-condensation reactor (Schnoeckel, 2010) at 900 K and co-condensed with a mixture of toluene:THF (3:1) at 77 K. Upon warming in the presence of dicyclohexylphosphine, the dimeric Ga₂Br₄(PHCy₂)₂ forms via a disproportionation reaction (Equation 1). This reaction is similar to the disproportionation of `GaI' in the presence of dicyclohexylphosphine (Baker et al., 2003).

4 GaBr(THF) + 4 Cy₂PH → Ga₂Br₄(PHCy₂)₂ + 2 Ga (Eq. 1)

Ga₂Br₄(PHCy₂)₂ exhibits 1 symmetry in the solid state, with a Ga—Ga distance of 2.435 (1) Å, but virtual C_2h symmetry in solution. The Ga—Br1 and Ga—Br2 distances are 2.3612 (5) and 2.3807 (5) Å, respectively; the Ga—P bond is 2.415 (3) Å. The Br—Ga—Br angle measures 107.30 (2)°.

The overall structure of Ga₂Br₄(PHCy₂)₂ is in close agreement with that of the Ga₂I₄(PHCy₂)₂ analogue reported by Baker et al. (2003). In Ga₂I₄(PHCy₂)₂ the Ga—Ga bond is 2.437 (1) Å; the Ga—P bonds average 2.424 (2) Å. The I—Ga—I angle in the iodo analogue is 110.07 (3)°.

The Ga—Ga distance in Ga₂Br₄(PHCy₂)₂ (2.435 (1) Å) is shorter than the 2.54 (1) Å Ga—Ga distance in the trigonal planar Ga(II) compound Ga₂(CH(TMS)₂)₄ (Uhl et al. 1989). The Ga—Br distances in Ga₂Br₄(PHCy₂)₂ (2.370 (10) Å) are slightly shorter than the Ga—Br distances (2.4246 (22) and 2.4296 (27) Å) in the anionic [Ga₅₁(P^tBu₂)₁₄Br₆]^3- cluster (Steiner et al. 2004).

Experimental

Ga₂Br₄(PHCy₂)₂: Dicyclohexylphosphine (2.5 mmol, 5 g of a 10% w/w solution in hexanes) was dissolved in toluene (5 ml). The solution was cooled to -78 °C and a cold (-78 °C) solution of GaBr(THF)_n (6.05 ml of a 380 mM solution in toluene:THF 3:1) was added. The resultant orange solution was stirred at -78 °C for 2 h, after which it was heated to 80 °C for 19 h. The resulting dark-brown solution was cooled to room temperature, the solvent removed in vacuo and the black residue dissolved in toluene (50 ml). The dark-brown solution was separated from the grey powdery residue via cannula filtration, concentrated, and cooled to -20 °C. After 7 d, colorless crystals of Ga₂Br₄(PHCy₂)₂ formed (40 mg, 0.047 mmol, 4% yield). ¹H NMR (500 MHz, C₆D₆) δ (p.p.m.): 1.03–2.05 (44 H, Cy—H), 4.10 (dt, 2 H, 1 J(P—H) = 352 Hz, 3 J(H—H) = 5 Hz, P—H). ¹³C NMR (125 MHz) δ (p.p.m.): 25.5, 27.2, 30.3, 30.8, 31.1, 31.8. ³¹P NMR (201.6 MHz) δ (p.p.m.): -36.7 (d, J = 352 Hz).