Platinum Group Metal Complexes of Macrocyclic Oxathiaethers. The Crystal Structures of 18S₄O₂, [Pt(9S₂O)₂](PF₆)₂·2CH₃NO₂, [Pt(18S₄O₂)](PF₆)₂, and [Pd(9S₂O)₂](PF₆)₂·2CH₃CN

Abstract

Improved syntheses of the mixed oxathia crown ligands 1-oxa-4,7-dithiacyclononane (9S2O) and 1,10-dioxa-4,7,13,16-tetrathiacyclooctadecane (18S4O2) are presented. The single-crystal X-ray structure of 18S4O2 has also been obtained. Crystal data for 18S4O2: C12H24O2S4; triclinic, space group P1̄; a = 7.188(3) Å, b = 5.240(1) Å, c = 10.743(3) Å; α = 99.30(2)°, β = 98.09(3)°, γ = 92.19(3)°; V = 394.57 Å3; Z = 1, R = 0.067, R w = 0.103 for 2419 reflections. The ligand structure shows the two oxygen atoms point into the macrocycle cavity while the four sulfur atoms are oriented in an exodentate fashion. Therefore, this ligand is poorly preorganized for hexadentate complexation and will have to undergo substantial reorganization to be able to complex in a multidentate fashion using its sulfur atoms. The syntheses of homoleptic complexes for both of these macrocycles with the platinum group metal ions, Pd(II) and Pt(II), are also described. The single-crystal X-ray structures for three of the complexes have been obtained, and all show that only the sulfur atoms are bound to the metal center. Crystal data for [Pt(9S2O)2](PF6)2·2CH3NO2: C14H30N2O6F12P2S4Pt; triclinic, space group P1̄; a = 9.996(5) Å, b = 11.019(3) Å, c = 8.253(2) Å; α = 92.79(2)°, β = 110.18(2)°, γ = 64.04(2)°; V = 761.5(5) Å3 ; Z = 1; R = 0.0365, R w = 0.0543 for 2680 reflections. Crystal data for [Pt(18S4O2)](PF6)2: C14H24O2F12P2S4Pt; monoclinic, space group P21/n; a = 11.110(3) Å, b = 9.244(1) Å, c = 12.642(2) Å; β = 111.48(1)°; V = 1208.2(3) Å3; Z = 2; R = 0.0343, R w = 0.0428 for 1696 reflections. Crystal data for [Pd(9S2O)2](PF6)2·2CH3CN: C14H30N2O6F12P2S4Pd; monoclinic, space group C2/c; a = 12.535(2) Å, b = 19.463(2) Å, c = 12.127(2) Å; β = 95.68(1)°, V = 2944.0(7) Å3; Z = 4; R = 0.0493, R w = 0.0651 for 1959 reflections. The oxygen atoms in all of the structures are oriented exodentate to the metal center and lie at too great of a distance (3.443(5), 3.730(5), or 3.379(5) Å, respectively) to exhibit the long-distance metal interactions exhibited in related crown thioether complexes. The effects of the lack of axial metal−oxygen interactions are seen in the absence of visible d−d electronic transitions, and the lack of any oxidation electrochemistry in the complexes. Additionally for the Pt(II) complexes, 195Pt NMR chemical shifts are observed near −4650 ppm which are consistent with a square planar S4 coordination environment around the platinum. The complexation behavior of these ligands toward Pt(II) and Pd(II) contrasts that of analogous crown thioethers ligands and mixed azathia macrocycles which show significant metal−axial donor atom interactions. The general ligand complexation characteristics of oxathia crowns are dominated by metal−ligand electronic interactions as opposed to ligand conformational factors.

Aqueous Synthesis of 14‐15‐Membered Crown Ethers with Mixed O, N and S Heteroatoms: Experimental and Theoretical Binding Studies with Platinum‐Group Metals

“…CE 2 g-2 i form a square planar S 4 geometry with Pd 2 + involving two S along with two chloride anions as described in previous studies on dithiacrown-Pd 2 + complexation. [12,28,29] Hence, it is likely that dithia-CE 2 g-2 i would require a sandwich type 2 : 1 CE-Pt 2 + complex to satisfy their coordination requirement similar to other dithiacrown ethers reported in literature. [28] On the other hand, tetrathia-CE forms hexadentate complexes with Pt 2 + with four S atoms involved in square planar S 4 coordination along with axial S 2 coordination of two chloride anions, resulting in a distorted octahedron geometry.…”

“…[12,28,29] Hence, it is likely that dithia-CE 2 g-2 i would require a sandwich type 2 : 1 CE-Pt 2 + complex to satisfy their coordination requirement similar to other dithiacrown ethers reported in literature. [28] On the other hand, tetrathia-CE forms hexadentate complexes with Pt 2 + with four S atoms involved in square planar S 4 coordination along with axial S 2 coordination of two chloride anions, resulting in a distorted octahedron geometry. [9,28,36] Among the dioxa-dithia-CEs, 2 h showed the most remarkable structural change upon complexation with Pd 2 + or Pt 2 + followed by 2 g whereas 2 i showed the least.…”

“…[2][3][4] However, thiacrown ethers form homoleptic complexes with Pd 2 + and Pt 2 + . [28][29] Hence, it is likely that the LLE results reflect the sequestration of Pd 2 + and Pt 2 + , despite the latter being in minor portion vs Pt 4 + . Results of LLE for binary Pd/Pt solutions (Table 3) reveal the preference of all CEs towards Pd 2 + than Pt 2 + except for 2 b and 2 c. CE 2 c showed the highest selectivity towards Pt 2 + (β Pt/Pd = 35) while 2 i showed the highest preference towards Pd 2 + (β Pd/Pt = 93).…”

“…The selectivity of the synthe- 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 sized CEs can be attributed to their structures and cavity size relationships. [15,[28][29][30][31]…”

“…[8] Meanwhile, oxaazathia CEs (O,N,S-bearing) showed almost similar cavity sizes for both 14 -and 15 -membered rings (2 d-2 f) although 2 f was slightly larger than 2 d and 2 e. On the contrary, opposite cavity size trend was observed for oxathia CEs (O, S-bearing), wherein it increases in the following order: 2 i > 2 h > 2 g. Despite being a 14-membered ring, 2 i still showed the largest cavity size (1.58 Å) in comparison to other oxathia CEs, especially 2 g. The cavity size enlargement of oxathia CEs may be attributed to the SÀ S repulsion and the longer SÀ C bonds. [15,28] Among all the CEs, 2 i is the only CE that can accommodate Pd 2 + (1.56 Å) while the rest have incompatibly smaller sizes ( Figure 6).…”