[2,6-Bis(isopropylthiomethyl)phenyl-[kappa]³S,C¹,S']bromopalladium(II)

The title compound, [PdBr(C₁₄H₂₁S₂)] or [PdBr{C₆H₃(CH₂SⁱPr)₂-2,6}], exhibits square-planar geometry at the Pd centre, with three atoms of the square plane provided by the rigid thio­pincer ligand, i.e. 1,3-bis­(thio­methyl)­benzene.

S1. Comment

Thiopincer ligand complexes are formed by the cyclometallation of 1,3-bis(disubstitutedthiomethyl)benzene. The compounds [PdCl{C₆H₃(CH₂S^tBu)₂-2,6}] (Errington et al., 1980), and [PdCl{C₆H₃(CH₂SCH₂CH₃)₂-2,6}] and [PdCl{C₆H₃(CH₂SC₆H₅)₂-2,6}] (Lucena et al., 1996) have been prepared by this method. These complexes have been used as catalysts for various reactions, such as the catalytic dehydrogenation of alkanes (Gupta et al., 1996, 1997; Liu et al., 1999), ethers and alkylarenes (Dijkstra et al., 2001; Gorla et al., 1994; Langmire et al., 1998; Stark et al., 2000), and as Lewis acid catalysts (Dijkstra et al., 2001). They are also used as catalysts for aldol reactions between benzaldehydes and methyl isocyanoacetate (Espinet et al., 1994), as hydrogen transfer catalysts (Dani et al., 2000) and as SO₂ reversible binding sites in gas sensor materials (Albrecht & van Koten, 1999; Albrecht et al., 2000).

Recently, we have used pincer ligand complexes as starting materials for potential metallomesogens by reacting [PdBr{C₆H₃(CH₂SⁱPr)₂-2,6}] with long-chain alkoxy aryl thiols in the presence of Et₃N. This is a methodology employed in preparing a number of metal thiolato complexes (Darkwa & Milius, 1996; Darkwa et al., 1998; Nevondo et al., 2000; Moutloali et al., 2001). However, in the attempt to react [PdBr{C₆H₃(CH₂SⁱPr)₂-2,6}], (I), with thiols, (I) crystallized from the reaction mixture instead of forming a palladium thiolato complex. This indicates that Et₃N might be too weak a base to effect the desired reaction. The structure of the title palladium complex, (I), is reported here. \sch

The molecular structure of (I) is shown in Fig. 1 and selected bond distances and angles are given in Table 1. The coordination number of the Pd in (I) is four and the donor atoms are arranged in a square plane, with the S atoms trans to each other. The two Pd—S distances differ only slightly. This is in contrast with similar compounds in which the S atoms are cis to each other. In these compounds, the Pd—S distances differ significantly. For example, the two Pd—S distances [2.274 (2) and 2.256 (2) Å] in [Pd(C₆H₁₂S₃)Br₂] (Wieghart et al., 1986) are noticeably different.

In compound (I), the 1,3-bis(thiomethyl)benzene unit behaves as a tridentate ligand. Its two S atoms are separated by a distance of 4.587 (8) Å and are therefore suitably disposed to form two Pd—S bonds orientated trans to each other. The two isopropyl substituents are in axial positions on the same sides of the molecular plane, whereas the tert-butyl groups are on opposite sides in [PdCl(C₆H₄)(CH₂SⁱPr)₂] (reference? Please provide a reference for this compound). The axial conformation is preferred, as the isopropyl repulsions are minimized. Potential repulsion between the two isopropyl substituents is also minimized when they are on opposite sides. However, in contrast with the tert-butyl analogue, the two isopropyl groups in (I) are cis to each other. In this conformation, the shortest distance between H atoms is 2.315 (7) Å.

S2. Experimental

Palladium acetate (0.5 g, 2.23 mmol) was dissolved in glacial acetic acid (40 ml) and then charged with compound (I) (0.71 ml, 2.23 mmol), and the mixture was refluxed for 0.5 h. To this was added LiBr (0.5 g, 12.2 mmol) and the reaction was stirred at room temperature for 1 h. The solvent was removed and the residue extracted with CH₂Cl₂ and passed through silica gel (7 cm), which was washed with a copious amount of CH₂Cl₂. The solvent was removed in vacuo from the combined CH₂Cl₂ washings to leave an orange residue, which was recrystallized from CH₂Cl₂-hexane (?:? v/v) at 123 K to give an orange-yellow solid, (I) (0.83 g, 94%). Analysis calculated for [PdBr{C₆H₃(CH₂SⁱPr)₂-2,6}]: C 38.23, H 4.81%; found: C 38.5, H 4.6%. ¹H NMR (CDCl₃, d, p.p.m.): 6.97 (s, 3H, C₆H₃), 4.20 (s, 4H, CH₂), 3.64 (q, 2H, J_HH = 6.8 Hz, ⁱPr), 1.58 (d, 12H, J_HH = 6.8 Hz, ⁱPr).

S3. Refinement

Although all H atoms could be located in the difference Fourier map, they were placed in idealized positions and refined as riding atoms, with C—H = 0.95–1.00 Å and U_iso(H) = 1.2 or 1.5 times U_eq(C). Are these the correct constraints? Torsion angles involving methyl H atoms were refined. Please provide these in CIF-format for addition to the archived CIF.

Computing details

Data collection: COLLECT (Nonius, 2001); cell refinement: SCALEPACK (Otwinowski & Minor, 1997); data reduction: SCALEPACK; program(s) used to solve structure: SHELXS97 (Sheldrick, 1997); program(s) used to refine structure: SHELXL97 (Sheldrick, 1997); molecular graphics: ORTEP-3 for Windows (Farrugia, 1997); software used to prepare material for publication: PLATON (Spek, 1997).

Figures

Fig. 1. A view of the molecule of (I) with the atomic numbering scheme. Displacement ellipsoids are drawn at the 50% probability level and H atoms are shown as small spheres of arbitrary radii.

[2,6-Bis(isopropylthiomethyl)phenyl-κ³S,C¹,S]bromopalladium(II)

Crystal data

[PdBr(C14H21S2)]	F(000) = 872
Mr = 439.77	Dx = 1.855 Mg m^−3
Monoclinic, P21/c	Mo Kα radiation, λ = 0.71073 Å
Hall symbol: -P 2ybc	Cell parameters from 3396 reflections
a = 8.5591 (2) Å	θ = 2.2–27.5°
b = 10.6777 (2) Å	µ = 3.96 mm^−1
c = 17.6816 (4) Å	T = 173 K
β = 103.042 (1)°	Rectangular block, light yellow
V = 1574.3 (1) Å^3	0.30 × 0.26 × 0.18 mm
Z = 4

Data collection

Nonius KappaCCD area-detector diffractometer	3557 independent reflections
Radiation source: fine-focus sealed tube	3143 reflections with I > 2σ(I)
Graphite monochromator	Rint = 0.023
ϕ and ω scans with θ offsets	θmax = 27.5°, θmin = 2.2°
Absorption correction: empirical (using intensity measurements) (SCALEPACK; Otwinowski & Minor, 1997)	h = −11→11
Tmin = 0.350, Tmax = 0.490	k = −13→13
14692 measured reflections	l = −22→22

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)] = 0.024	H atoms treated by a mixture of independent and constrained refinement
wR(F^2) = 0.052	w = 1/[σ^2(Fo^2) + (0.0158P)^2 + 1.0617P] where P = (Fo^2 + 2Fc^2)/3
S = 1.08	(Δ/σ)max = 0.001
3557 reflections	Δρmax = 1.07 e Å^−3
168 parameters	Δρmin = −0.60 e Å^−3
0 restraints	Extinction correction: SHELXL97 (Sheldrick, 1997), Fc^*=kFc[1+0.001xFc^2λ^3/sin(2θ)]^-1/4
Primary atom site location: structure-invariant direct methods	Extinction coefficient: 0.00217 (17)

Special details

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.

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Ų)

	x	y	z	Uiso*/Ueq
Pd	0.411298 (19)	0.251864 (15)	0.129904 (10)	0.01833 (7)
Br	0.20572 (3)	0.33613 (2)	0.201056 (15)	0.02724 (8)
S2	0.62898 (7)	0.27911 (5)	0.23289 (3)	0.02001 (13)
S1	0.22741 (7)	0.21627 (6)	0.01587 (4)	0.02271 (13)
C6	0.7309 (3)	0.1691 (2)	0.11323 (14)	0.0194 (5)
C8	0.7733 (3)	0.1792 (2)	0.20030 (13)	0.0221 (5)
H8A	0.8823	0.2148	0.2176	0.026*
H8B	0.7730	0.0948	0.2235	0.026*
C12	0.7099 (3)	0.4330 (2)	0.21583 (14)	0.0231 (5)
H12	0.7456	0.4302	0.1658	0.028*
C1	0.5709 (3)	0.1892 (2)	0.07326 (14)	0.0204 (5)
C10	0.0347 (3)	0.3577 (3)	−0.09938 (16)	0.0350 (6)
H10A	−0.0171	0.4384	−0.1152	0.052*
H10B	−0.0475	0.2935	−0.1003	0.052*
H10C	0.1017	0.3342	−0.1353	0.052*
C7	0.3575 (3)	0.1835 (3)	−0.05069 (15)	0.0295 (6)
H7B	0.3215	0.1058	−0.0800	0.035*
H7A	0.3501	0.2530	−0.0884	0.035*
C2	0.5282 (3)	0.1687 (2)	−0.00683 (14)	0.0210 (5)
C14	0.8539 (3)	0.4641 (2)	0.28091 (15)	0.0300 (6)
H14A	0.8991	0.5448	0.2702	0.045*
H14B	0.9353	0.3986	0.2843	0.045*
H14C	0.8200	0.4691	0.3302	0.045*
C13	0.5790 (3)	0.5306 (2)	0.20912 (16)	0.0333 (6)
H13A	0.5371	0.5298	0.2563	0.050*
H13B	0.4922	0.5116	0.1641	0.050*
H13C	0.6231	0.6136	0.2026	0.050*
C9	0.1392 (3)	0.3688 (2)	−0.01728 (15)	0.0283 (5)
H9	0.0659	0.3912	0.0174	0.034*
C11	0.2621 (4)	0.4731 (3)	−0.00953 (17)	0.0409 (7)
H11A	0.3421	0.4516	−0.0393	0.061*
H11B	0.3153	0.4838	0.0453	0.061*
H11C	0.2084	0.5513	−0.0296	0.061*
C5	0.8458 (3)	0.1358 (2)	0.07241 (14)	0.0261 (5)
H5	0.9545	0.1261	0.0992	0.031*
C4	0.8026 (3)	0.1167 (2)	−0.00704 (15)	0.0290 (6)
H4	0.8816	0.0938	−0.0346	0.035*
C3	0.6440 (3)	0.1310 (2)	−0.04649 (14)	0.0262 (5)
H3	0.6141	0.1151	−0.1007	0.031*

Atomic displacement parameters (Ų)

	U^11	U^22	U^33	U^12	U^13	U^23
Pd	0.01639 (10)	0.02108 (10)	0.01757 (11)	0.00138 (6)	0.00393 (7)	−0.00024 (7)
Br	0.02441 (13)	0.02933 (14)	0.03057 (15)	0.00438 (9)	0.01167 (10)	−0.00072 (11)
S2	0.0200 (3)	0.0226 (3)	0.0172 (3)	−0.0008 (2)	0.0037 (2)	−0.0008 (2)
S1	0.0174 (3)	0.0282 (3)	0.0216 (3)	0.0011 (2)	0.0023 (2)	0.0000 (2)
C6	0.0204 (11)	0.0171 (10)	0.0206 (12)	0.0004 (8)	0.0040 (9)	0.0000 (9)
C8	0.0209 (11)	0.0234 (12)	0.0206 (12)	0.0039 (9)	0.0021 (9)	0.0005 (10)
C12	0.0269 (12)	0.0229 (12)	0.0206 (13)	−0.0043 (9)	0.0074 (10)	−0.0011 (10)
C1	0.0208 (11)	0.0190 (11)	0.0214 (12)	−0.0018 (9)	0.0048 (9)	−0.0003 (10)
C10	0.0312 (14)	0.0388 (15)	0.0305 (15)	0.0071 (11)	−0.0025 (11)	0.0049 (12)
C7	0.0220 (12)	0.0436 (15)	0.0217 (13)	0.0039 (11)	0.0022 (10)	−0.0058 (12)
C2	0.0193 (11)	0.0222 (11)	0.0212 (12)	0.0001 (9)	0.0040 (9)	−0.0002 (10)
C14	0.0268 (13)	0.0325 (14)	0.0301 (15)	−0.0073 (10)	0.0049 (11)	−0.0030 (12)
C13	0.0350 (14)	0.0228 (12)	0.0390 (16)	0.0007 (11)	0.0018 (12)	−0.0025 (12)
C9	0.0269 (12)	0.0304 (13)	0.0262 (14)	0.0063 (10)	0.0030 (10)	0.0025 (11)
C11	0.0513 (18)	0.0349 (15)	0.0303 (16)	−0.0088 (13)	−0.0037 (13)	0.0058 (13)
C5	0.0192 (11)	0.0298 (13)	0.0282 (14)	0.0030 (9)	0.0031 (10)	−0.0017 (11)
C4	0.0238 (12)	0.0363 (14)	0.0294 (14)	0.0046 (11)	0.0115 (10)	−0.0014 (12)
C3	0.0275 (12)	0.0333 (13)	0.0183 (12)	0.0003 (10)	0.0061 (10)	−0.0020 (11)

Geometric parameters (Å, º)

Pd—C1	1.984 (2)	C7—C2	1.500 (3)
Pd—S1	2.2924 (6)	C7—H7B	0.9900
Pd—S2	2.3110 (6)	C7—H7A	0.9900
Pd—Br	2.5471 (3)	C2—C3	1.396 (3)
S2—C8	1.821 (2)	C14—H14A	0.9800
S2—C12	1.835 (2)	C14—H14B	0.9800
S1—C7	1.827 (2)	C14—H14C	0.9800
S1—C9	1.834 (2)	C13—H13A	0.9800
C6—C5	1.391 (3)	C13—H13B	0.9800
C6—C1	1.409 (3)	C13—H13C	0.9800
C6—C8	1.504 (3)	C9—C11	1.517 (4)
C8—H8A	0.9900	C9—H9	1.0000
C8—H8B	0.9900	C11—H11A	0.9800
C12—C13	1.515 (3)	C11—H11B	0.9800
C12—C14	1.521 (3)	C11—H11C	0.9800
C12—H12	1.0000	C5—C4	1.385 (3)
C1—C2	1.397 (3)	C5—H5	0.9500
C10—C9	1.528 (3)	C4—C3	1.387 (3)
C10—H10A	0.9800	C4—H4	0.9500
C10—H10B	0.9800	C3—H3	0.9500
C10—H10C	0.9800
C1—Pd—S1	85.08 (7)	C2—C7—H7A	109.5
C1—Pd—S2	85.17 (7)	S1—C7—H7A	109.5
S1—Pd—S2	170.19 (2)	H7B—C7—H7A	108.1
C1—Pd—Br	178.91 (7)	C3—C2—C1	120.1 (2)
S1—Pd—Br	94.549 (17)	C3—C2—C7	119.3 (2)
S2—Pd—Br	95.180 (16)	C1—C2—C7	120.6 (2)
C8—S2—C12	99.47 (11)	C12—C14—H14A	109.5
C8—S2—Pd	99.25 (8)	C12—C14—H14B	109.5
C12—S2—Pd	104.50 (8)	H14A—C14—H14B	109.5
C7—S1—C9	103.34 (12)	C12—C14—H14C	109.5
C7—S1—Pd	101.59 (8)	H14A—C14—H14C	109.5
C9—S1—Pd	106.57 (8)	H14B—C14—H14C	109.5
C5—C6—C1	120.0 (2)	C12—C13—H13A	109.5
C5—C6—C8	120.9 (2)	C12—C13—H13B	109.5
C1—C6—C8	119.0 (2)	H13A—C13—H13B	109.5
C6—C8—S2	109.99 (15)	C12—C13—H13C	109.5
C6—C8—H8A	109.7	H13A—C13—H13C	109.5
S2—C8—H8A	109.7	H13B—C13—H13C	109.5
C6—C8—H8B	109.7	C11—C9—C10	112.8 (2)
S2—C8—H8B	109.7	C11—C9—S1	113.32 (18)
H8A—C8—H8B	108.2	C10—C9—S1	110.21 (18)
C13—C12—C14	111.6 (2)	C11—C9—H9	106.7
C13—C12—S2	109.21 (16)	C10—C9—H9	106.7
C14—C12—S2	110.04 (17)	S1—C9—H9	106.7
C13—C12—H12	108.7	C9—C11—H11A	109.5
C14—C12—H12	108.7	C9—C11—H11B	109.5
S2—C12—H12	108.7	H11A—C11—H11B	109.5
C2—C1—C6	119.1 (2)	C9—C11—H11C	109.5
C2—C1—Pd	120.80 (16)	H11A—C11—H11C	109.5
C6—C1—Pd	120.02 (17)	H11B—C11—H11C	109.5
C9—C10—H10A	109.5	C4—C5—C6	120.4 (2)
C9—C10—H10B	109.5	C4—C5—H5	119.8
H10A—C10—H10B	109.5	C6—C5—H5	119.8
C9—C10—H10C	109.5	C5—C4—C3	120.1 (2)
H10A—C10—H10C	109.5	C5—C4—H4	120.0
H10B—C10—H10C	109.5	C3—C4—H4	120.0
C2—C7—S1	110.57 (17)	C4—C3—C2	120.3 (2)
C2—C7—H7B	109.5	C4—C3—H3	119.9
S1—C7—H7B	109.5	C2—C3—H3	119.9
C1—Pd—S2—C8	−17.61 (10)	S2—Pd—C1—C2	−169.34 (18)
Br—Pd—S2—C8	163.42 (8)	S1—Pd—C1—C6	−172.78 (18)
C1—Pd—S2—C12	84.76 (10)	S2—Pd—C1—C6	8.30 (17)
Br—Pd—S2—C12	−94.21 (8)	C9—S1—C7—C2	120.36 (18)
C1—Pd—S1—C7	−9.81 (11)	Pd—S1—C7—C2	10.00 (19)
Br—Pd—S1—C7	169.17 (9)	C6—C1—C2—C3	−1.1 (3)
C1—Pd—S1—C9	−117.67 (11)	Pd—C1—C2—C3	176.56 (18)
Br—Pd—S1—C9	61.31 (9)	C6—C1—C2—C7	177.2 (2)
C5—C6—C8—S2	158.03 (18)	Pd—C1—C2—C7	−5.1 (3)
C1—C6—C8—S2	−24.4 (3)	S1—C7—C2—C3	173.68 (19)
C12—S2—C8—C6	−80.86 (17)	S1—C7—C2—C1	−4.7 (3)
Pd—S2—C8—C6	25.66 (16)	C7—S1—C9—C11	−63.1 (2)
C8—S2—C12—C13	158.45 (17)	Pd—S1—C9—C11	43.5 (2)
Pd—S2—C12—C13	56.24 (17)	C7—S1—C9—C10	64.4 (2)
C8—S2—C12—C14	−78.77 (18)	Pd—S1—C9—C10	170.97 (16)
Pd—S2—C12—C14	179.03 (15)	C1—C6—C5—C4	−2.9 (4)
C5—C6—C1—C2	3.4 (3)	C8—C6—C5—C4	174.7 (2)
C8—C6—C1—C2	−174.3 (2)	C6—C5—C4—C3	0.1 (4)
C5—C6—C1—Pd	−174.32 (17)	C5—C4—C3—C2	2.1 (4)
C8—C6—C1—Pd	8.1 (3)	C1—C2—C3—C4	−1.6 (4)
S1—Pd—C1—C2	9.58 (18)	C7—C2—C3—C4	−180.0 (2)