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. Author manuscript; available in PMC: 2010 Jan 12.
Published in final edited form as: Org Biomol Chem. 2009 Oct 5;7(23):4881–4885. doi: 10.1039/b916020e

Synthesis and X-ray structural analysis of platinum and ethynyl-platinum corannulenes: supramolecular tectons†

Roman Maag a, Brian H Northrop b, Anna Butterfield a, Anthony Linden a, Oliver Zerbe a, Young Min Lee c, Ki-Whan Chi c, Peter J Stang b,✉, Jay S Siegel a,✉
PMCID: PMC2805086  NIHMSID: NIHMS163936  PMID: 19907778

Abstract

The synthesis and characterization of two direct platinum (1 and 6a/b) and three ethynyl-platinum corannulene derivatives (2, 8 and 9), bearing 2, 4, or 5 square planar platinum centers, are presented. The structure of the bowl bearing substituents remains comparable to corannulene and the dynamic behavior of the bowl inversion as assessed by VT NMR supports a persistent bowl structure in solution. These platinum-corannulenes are well-structured tectons for the future assembly of coordination Platonic polyhedra.

Introduction

Platonic solids have served as targets for total chemical synthesis in covalent1 as well as supramolecular variants.2,3 Their designs come from replacement of Platonic graph vertices by an appropriate molecular fragment, for example by CH in the case of cubane4 and dodecahedrane,5 or a 4-spoke Holliday junction in cubic DNA nano-constructs.6 Supramolecular targets often include symmetry and geometry-tailored organic tectons and metal–ligand junctions.2,3 Among Platonic symmetries, examples of 5-fold symmetric derivatives capable of participating in such assemblies do not yet appear. Such 5-fold symmetric tectons could provide direct access to icosahedrally symmetric supramolecular structures.7

Direct metallation 1 and metalloalkynyl 2 targets (Scheme 1), based on corannulene,8 readily spring to mind when 5-fold symmetry is the goal. Given the success with metal mediated 5-fold coupling chemistry9,10 starting from pentachlorocorannulene 3,11 accessing metallated derivatives seemed promising.

Scheme 1.

Scheme 1

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Retrosynthetic strategy for the formation of pentakis platinum (1) and ethynyl-platinum (2) corannulene derivatives from 1,3,5,7,9-pentachloro corannulene 2.

Previous work on the tetrabromide 4,8e–g provided additional precedence for dimetallation of corannulene when the halogen is bromine (Scheme 2). Even if somewhat hampered by isomeric product formation and limited to disubstitution, this initial platinum insertion work proved the principal.12 Direct metallation of 1,6-dibromo-2,7-dimethylcorannulene 510 with Pt(PEt3)4 addresses the isomer issue and provides a clean dimetallated tecton 6a with essentially diametrically opposed binding sites on corannulene.

Scheme 2.

Scheme 2

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Synthetic protocols for the direct metallation of various halo corannulenes.

Pentakis-Pt(PEt3)2Cl corannulene 1 was obtained from a reaction mixture of Pt(PEt3)4 and 3 in toluene heated to 95 °C over 5 days. The product was recrystallized twice from hot MeOH (48% overall yield). An analogous procedure yielded compound 6a in 79% yield after trituration of the crude product with n-pentane. For better crystallization and leaving group properties for the future construction of supramolecular assemblies, the bromine atoms in compound 6a were exchanged with MeCN using a silver(I) salt with the weakly coordinating hexabromocarborane anion.13 Thus, the corresponding metathesis product 6b was synthesized.

Hypothetical compound 7 seems too sterically crowded to form; however, extending the site of metallation with alkyne spacers could alleviate steric problems associated with metallation of vicinal sites. Methods to convert the halide family 3–5 into their respective TMS-alkyne derivatives are established.10,11b A one-pot method for converting TMS-alkyne to Pt-alkyne derivatives was found using CsF, CuI and Pt(PEt3)2I2 in a solvent mixture of DMF/CH2Cl2/H2O (Scheme 3). DMF seems to be an important solvent in this reaction, it is believed to be crucial for the stabilization of the intermediate copper acetylenes. Without DMF, the reaction mixture does not exhibit the red color, which is indicative for the formation of the cuprates. Pentakis-ethynyl, tetrakis-ethynyl, and bis-ethynyl platinum derivatives 2, 8 and 9, were prepared in 35%, 89%, and 85% yield, respectively, from halides 3–5. The in situ platination of the corresponding TMSA-corannulenes proceeds in high yields and is especially attractive for derivatives with adjacent TMSA substituents because the isolation of the free alkynes, which may undergo Bergman cyclizations,14 can be avoided. Furthermore, subsequent alkynylation reactions on the platinum center do not occur.

Scheme 3.

Scheme 3

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The two-step conversion of halo corannulenes 3–5 to ethynyl–platinum corannulenes 2, 8–9. a, See ref. 12, 13. b, (i) CsF/H2O, (ii) CuI/DMF (iii) Pt(PEt3)2I2/CH2Cl2.

X-Ray quality single crystals were obtained for compounds 1, 6b, and 9 (Fig. 1).‡ The bowl depth from hub centroid to rim plane is 0.764(12) Å in 1, slightly shallower than the 0.87 Å15 of the parent corannulene. The flattening could occur through a relief of steric crowding either around the rim or transannularly. Notable is the stereochemistry at the five platina in 1, four of which bear phosphines in a trans stereochemistry and one cis. This novel relationship could support the idea that transannular strain causes the bowl to flatten, but in any case raises the question of whether this stereochemistry persists in solution.

Fig. 1.

Fig. 1

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Asymmetric unit of the X-ray structure of 1 (top) – hydrogens omitted, 6b (middle) and 9 (bottom).

High-resolution 700 MHz 1H spectra of 1 display five distinct rim proton resonances. Four appear as singlets consistent with only cis aryl-Pt-Cl relationships; one is a doublet (8.2 Hz), consistent with coupling to a trans phosphine. The 31P NMR reveals a cluster of eight PEt3 groups oriented trans about Pt between 13–16 ppm and two PEt3 groups oriented cis about Pt at 11 and 5 ppm. A 31P EXSY experiment displays fast exchange among all eight P signals from the trans oriented Pt complexes, which accounts for the loss in the 2J 31P,31P coupling for these signals. In contrast, the EXSY shows no exchange between the 31P signals of the cis-Pt complex, and 31P COSY confirms the 14.7 Hz 2J 31P,31P coupling. Satellite signals due to the 1J 31P,195Pt coupling are also evident in the spectrum. Interestingly, increased CSA-mediated relaxation of 195Pt leads to considerable broadening of these signals on the 400 MHz spectrometer. The satellites have the appropriate integral according to the 33% abundance of 195Pt and the direct 31P,195Pt coupling constant of 2834 Hz corresponds well to P-Pt bond length of 2.296 Å found in the X-ray diffraction analysis as well as a cis P-Pt-Cl geometry.16 Satellite signals are additionally observed for the signals corresponding to the cis aryl-Pt-Cl geometry displaying coupling constants of 4200 and 2800 Hz, reflecting one trans and one cis P-Pt-Cl relation. All together this makes a compelling case for equivalence of the solution and solid structure of 1. The single cis stereochemistry likely results from steric crowding on the endo side of the bowl.

The structure of 6b was crystallized as the acetonitrile adduct with two non bound carborane anions. It is not anticipated that this will cause any great structural distortions, but such complexes may have a benefit in complexation chemistry as the nitriles should be very labile ligands.17

The bowl depth of 6b is 0.893(13) Å, slightly shallower than its reaction precursor 5 (0.92 Å),10 but slightly deeper than the parent corannulene (0.87 Å).15 The proximity of the ethyl groups on the endo phosphine, reminds one of the attractive van der Waals interactions seen in sym-pentamanisylcorannulene. Variable temperature 31P NMR experiments on 6a revealed an inversion barrier of 10.7 ± 0.2 kcal/mol,9c on a par with the ca. 11 kcal/mol expected for corannulene.

The structure of 9 revealed a bowl depth of 0.872(9) Å, essentially that of corannulene. Both Pt centers have a trans orientation of the PEt3 ligands and all bond lengths are within normal parameters. The angle between the vectors emanating from roughly diametrically opposing positions on the rim is 140–150° with substantial flexibility due to the low-energy mode of bowl inversion.

In conclusion, the efficient synthesis and structure determination of platinum corannulene derivatives bodes well for the assembly of these supramolecular tectons into higher-order coordination Platonic polyhedra.2,3,6,19

Experimental

Materials and Methods: compounds 3–5 were prepared according to literature procedures8e–g,10,11b Reactions were conducted under nitrogen atmospheres unless noted. Dry toluene was used from an MBraun solvent purification system. CH2Cl2 and n-hex. were used after simple distillation. K2PtCl4 and PEt3 (10% in hexanes) (Pressure Chemical Co., Strem Chemicals) were used as purchased, 18 Pt(PEt3)4 and Pt(PEt3)2I2 were prepared by known procedures. Deuterated solvents were purchased from Cambridge Isotope Laboratory (Andover, MA). NMR spectra were recorded on a Varian Unity 300 and on Bruker 300, 400, 500, 600 and 700 MHz spectrometers. The 1H NMR chemical shifts are reported relative to residual solvent signals, and 31P NMR resonances are referenced to an external sample of 85% H3PO4 (δ 0.0). Infrared spectra were recorded on a JASCO FT/IR–4100 spectrophotometer.

1,3,5,7,9-Pentakis[chlorobis(triethylphosphine)platinum]-corannulene (1)

In a 100 mL Schlenk flask was placed 1.1 g (19.3 mmol) of KOH under inert atmosphere, followed by 10 mL of degassed EtOH and 1 mL degassed H2O. The flask was stirred at room temperature until homogeneous. Upon homogeneity, 2.5 g (21.2 mmol) of PEt3 was added via syringe. In a separate 50 mL Schlenk flask was placed 1.6 g (3.85 mmol) of K2[PtCl4] under inert atmosphere, followed by 5 mL of degassed H2O. The aqueous K2[PtCl4] was then transferred to the KOH/PEt3 flask via cannula. The reaction mixture was allowed to stir at room temperature for 1 h and then at 60 °C for 3 h. The reaction was then allowed to cool and the solvent was evaporated under high vacuum. The crude Pt(PEt3)4 product was taken up in freshly distilled toluene (10 mL) and transferred via cannula through a syringe containing glass wool (to filter particulates) into a Schlenk flask containing 110 mg (0.25 mmol) of 3 under inert atmosphere. The reaction mixture was then closed and allowed to stir at 90–95 °C for 5 days. After 5 days the solvent was evaporated under reduced pressure and the product was recrystallized twice from MeOH. Yield: 318 mg (48%). 1H{31P} NMR (700 MHz, CD2Cl2): 7.91 (s, 1H); 7.82 (s, 1H); 7.79 (s, 1H); 7.71 (s, 1H); 7.68 (s, 1H); 2.1–1.3 (m, 60H, CH2); 1.25–0.85 (m, 72H, trans-CH3); 0.71 (t, 9H, cis-CH3); 0.45 (t, 9H, cis-CH3). 13C{1H} NMR (150.9 MHz, CDCl3): 138–128 (Ar-C) 16.5 - 12.7 (CH2); 7.7-6.6 (CH3). 31P{1H} NMR (175 MHz): 15.51, 15.23, 15.10, 14.98, 14.92, 14.72, 14.15, 13.62 (8 trans P); 10.89 (d, 2JP-P = 14.7 Hz, cis P); 5.11 (d, 2JP-P = 14.7 Hz, cis P). For 1JPt-P see spectrum in the supplementary information. HR-ESI (TOF, m/z): Calcd. for C80H155Cl5P10Pt5: 2578.61448; found: 2578.61485 (M+). Calcd. for C80H155Cl4P10Pt5: 2543.64686; found: 2543.64588 ([M–Cl]+, main intensity).

2,5-Dimethyl-1,6-bis[trans-bromobis(triethylphosphine)platinum]-corannulene (6a)

Schlenk conditions: To a degassed solution of 1,6-dibromo-2,5-dimethylcorannulene (50 mg, 0.115 mmol) in toluene (20 ml) was added via syringe a solution of Pt(PEt)4 (176 mg, 0.264 mmol) in toluene (20 ml). The reaction mixture turned red and stirring was continued at room temperature for 24 hrs. The now yellow solution was heated to reflux another 24 hrs. After cooling to room temperature, the solution was filtered through a pad of celite (open to air) and the filtrate was evaporated to give a reddish, oily residue. The residue was covered with n-pentane and cooled to −78°C. After supersonication, the supernatant was removed and the procedure is repeated until a yellow powder was obtained. (117 mg, 79%). FT/IR: 2964 (m), 2932 (m), 2906 (m), 2876 (m), 2360 (w), 2334 (w), 1610 (w), 1455 (m), 1411 (m), 1375 (w), 1331 (w), 1287 (w), 1256 (w), 1144 (w), 1034 (s), 1009 (w), 986 (w), 926 (w), 828 (w), 793 (w), 764 (s), 729 (m), 688 (m). 1H NMR (400 MHz, C6D6): 8.45 (d, 3JH-H = 8.7 Hz, 2H); 7.90 (s, 2H); 7.72 (d, 3JH-H = 8.7 Hz, 2H); 3.17 (s, CH3, 3H); 1.70-1.40 (m, CH2, 24H); 0.72 (dt, 3JH-H = 7.7 Hz, 3JH-P = 15.9 Hz, CH3, 36H). 13C{1H} NMR (150.9 MHz, CDCl3): 139.59 (t, 1JC-Pt = 490 Hz, 2JC-P = 9 Hz), 138.08, 135.37, 133.79, 133.54, 133.08, 131.45, 130.93, 128.63, 124.68, 123.90, 24.25 (Ar-CH3), 15.31 (virtual quint. 1JC-P = 16.8 Hz), 8.13 (virtual t, 2JC-P = 2.7 Hz). 31P NMR (162 MHz, C6D6): 10.92 (s, 1JPt-P = 2725 Hz). HR-ESI (TOF, m/z): Calcd. for C46H72Br2P4Pt2: 1299.22970; found: 1299.22965 (M+). Calcd. for C46H72BrP4Pt2: 1219.30250; found: 1219.30579 ([M − Br]+).

2,5-Dimethyl-1,6-bis[trans-acetonitrilobis(triethylphosphine)-platinum]corannulene hexabromocarboranate (6b)

Glovebox: 2,5-dimethyl-1,6-bis[Pt(PEt3)2Br]corannulene (6, 7.1 mg, 5.47 mmol) and silver(I) hexabromocarboranate (8 mg, 11 mmol) were placed in a 2 ml-vial and suspended in D3CCN (1 ml). The yellow suspension became clearer, prior to the precipitation of AgBr. The vial was covered in aluminium foil and the reaction mixture was stirred for 20 hrs. at room temperature. The clear supernatant solution was analyzed by NMR spectroscopy; single crystals were grown by slow diffusion of n-hexane into a solution of 6b in acetone.

1,6-Bis{[trans-iodobis(triethylphosphine)platinum]ethynyl}-2,5-dimethylcorannulene (9)

A solution of 1,6-bis[2-(trimethlsilyl)ethynyl]-2,5-dimethyl- corannulene (50.7 mg, 0.108 mmol) in DMF (5 ml) and CH2Cl2 (7.5 ml) was prepared in a 50 ml Schlenk flask, equipped with stir bar. CsF (35 mg, 0.226 mmol) in H2O (0.5 ml) was added and the mixture gets slightly darker and turbid. After 5 min. CuI (43 mg 0.226 mmol) was added in one step and the mixture was stirred for 10 min. at room temperature, resulting in a red suspension. A solution of Pt(PEt3)2I2 (156 mg, 0.228 mmol) in CH2Cl2 (2 ml) was added, followed by another 2 ml of DMF. The mixture was stirred for 2 days and became a clear yellow solution (except insoluble copper salts). The solvents were removed under reduced pressure and the residue was taken up with CH2Cl2 and filtered through a pad of celite. EtOH was added, and the solvents were removed giving a yellow solid. Column chromatography on silica gel with n-hex/CH2Cl2 gave 9 as a yellow solid (132 mg, 85%): 1H NMR (600 MHz, CDCl3): 8.01 (d, 3JH-H = 8.7 Hz, 2H); 7.85 (s, 2H); 7.75 (d, 3JH-H = 8.8 Hz, 2H); 2.89 (s, 6H); 2.29–2.12 (m, 24H); 1.19 (dt, 3JH-H = 7.7 Hz, 3JH-P = 16.6 Hz, 36H). 13C{1H} NMR (150.9 MHz, CDCl3): 135.98, 135.79, 134.26, 133.20, 132.42, 130.72, 130.22, 127.02, 126.64, 124.98, 124.54, 100.54 (t, 2JC-P = 14.6 Hz, 1JC-Pt = 1452 Hz), 98.25 (t, 3JC-P = 2.7 Hz, 2JC-Pt = 400 Hz), 16.90 (virtual t, 1JC-P = 17.6 Hz), 16.88, 8.54 (t, 2JC-P = 10.7 Hz). 31P{1H} NMR (162 MHz, CDCl3): 6.77 (s, 1JPt-P = 2326 Hz); FT/IR: 2963 (m), 2932 (m), 2908 (w), 2875 (w), 2364 (w), 2098 (m), 1454 (m), 1411 (m), 1378 (m), 1348 (w), 1324 (w), 1254 (w), 1034 (s), 1007 (w), 822 (w), 797 (w), 766 (s), 731 (s), 702 (m). HR-ESI (TOF, m/z): Calcd. for C50H72I2P4Pt2: 1441.20352; found: 1441.20491 ([M + H]+). Calcd. for C50H72IP4Pt2(MeCN): 1354.31803; found: 1354.31780 ([M − I + MeCN]+, main intensity).

1,2,5,6-Tetrakis{[trans-iodobis(triethylphosphine)platinum]-ethynyl}corannulene (8)

A solution of 1,2,5,7-tetrakis(2-[trimethylsilyl]ethynyl)-corannulene (100 mg, 0.158 mmol) in DMF (5 ml) and CH2Cl2 (4 ml) was prepared in a 50 ml Schlenk flask, equipped with stir bar, and cooled in an ice-bath. CsF (106 mg, 0.698 mmol) in H2O (2 ml) was added and the mixture gets slightly darker and turbid. After 5 min. CuI (132 mg, 0.693 mmol) was added in one step and the mixture was stirred for 10 min. at room temperature, resulting in a red suspension. A solution of Pt(PEt3)2I2 (475 mg) in CH2Cl2 (4 ml) was added, followed by another 5 ml of DMF. The mixture was stirred for 2 days and became a clear yellow solution (except insoluble copper salts). CH2Cl2 was removed under reduced pressure and a mixture of MeOH/H2O was added, resulting in a bright yellow precipitate. The precipitate was washed with H2O and MeOH and dissolved in CH2Cl2 and filtered through a pad of celite. EtOH was added; CH2Cl2 was removed giving 2 as a bright yellow precipitate, which was filtered again and washed with EtOH and Et2O (362 mg, 89%): 1H NMR (500 MHz, CDCl3): 7.94 (d, 3JH-H = 8.8 Hz, 2H); 7.93 (s); 7.83 (d, 3JH-H = 8.8 Hz, 2H); 2.39–2.18 (m, CH2, 48H); 1.28–1.13 (m, CH3, 72H). 13C{1H} NMR (150.9 MHz, CDCl3): 135.42, 134.25, 133.73, 131.39, 130.74, 130.19, 128.07, 127.92, 127.43, 126.12, 125.61, 108.00 (t, 2JC-P = 12.5 Hz; 1JC-Pt = 1481 Hz), 106.87 (t, 2JC-P = 12.5 Hz), 97.99 (t, 3JC-P = 2.6 Hz), 97.66 (t, 3JC-P = 2.6 Hz; 2JC-Pt = 405 Hz), 16.67 (t, 1JC-P = 16.6 Hz, CH2), 16.59 (t, 1JC-P = 16.6 Hz, CH2), 8.66 (s, CH3), 8.64 (s, CH3). 31P{1H} NMR (107.2 MHz, CDCl3): 1.93 (s, 1JPt-P = 2354 Hz); 1.81 (s, 1JPt-P = 2359 Hz); FT/IR: 2962 (m), 2930 (m), 2911 (m), 2875 (m), 2362 (w), 2088 (w), 1989 (s, C≡C), 1608 (w), 1452 (m), 1413 (m), 1379 (m), 1344 (m), 1322 (w), 1254 (m), 1033 (s), 1006 (m), 763 (s), 730 (s), 712 (s). HR-ESI (TOF, m/z): Calcd. for C76H126I3P8Pt4(MeCN): 2489.37316; found: 2489.37573 ([M − I + MeCN]+). Calcd. for C76H126I2P8Pt4(MeCN)2: 1201.74851; found: 1201.74765 ([M − 2I + 2MeCN]2+, main intensity).

1,3,5,7,9-Pentakis{[trans-iodobis(triethylphosphine)platinum]-ethynyl}corannulene (2)

A suspension of 1,3,5,7,9-pentakis(2-[trimethylsilyl]ethynyl)-corannulene (100 mg, 0.137 mmol) in DMF (15 ml) and CH2Cl2 (15 ml) and THF (10 ml) was prepared in a 50 ml Schlenk flask, equipped with stir bar. CsF (108 mg, 0.711 mmol) in H2O (2 ml) was added and the mixture gets slightly darker. After 5 min. CuI (136 mg, 0.711 mmol) was added in one step and the mixture was stirred for 20 min. at room temperature, resulting in a red suspension. A solution of Pt(PEt3)2I2 (488 mg, 0.711 mmol) in CH2Cl2 (5 ml) was added, followed by another 5 ml of DMF. The mixture was stirred for 2 days and became a clear yellow solution (except insoluble copper salts). The solvents were removed under reduced pressure and the residue was taken up in CH2Cl2 and filtered through a pad of celite. EtOH was added, CH2Cl2 was removed and the brownish yellow precipitate was filtered and washed with EtOH (crude yield: 397 mg). Column chromatography on silica gel with n-hex./EtOAc gave 3 as a yellow solid (139 mg, 35%): 1H NMR (500 MHz, CDCl3): 7.88 (s, 5H); 2.35-2.12 (m, CH2, 60H); 1.19 (dt, 3JH-H = 7.7 Hz, 3JH-P = 16.6 Hz, CH3, 90H). 13C{1H} NMR (150.9 MHz, CDCl3): 133.31, 131.45, 126.74, 126.36, 99.37 (t, 3JC-P = 2.7 Hz; 2JC-Pt = 400 Hz), 95.1 (t, 2JC-P = 14.5 Hz; 1JC-Pt = 1450 Hz), 16.76 (t, 1JC-P = 17.5 Hz), 8.35 (t, 2JC-P = 7.6 Hz). 31P{1H} NMR (202.5 MHz, CDCl3): 7.23 (s, 1JPt-P = 2329 Hz); FT/IR: 2963 (m), 2931 (m), 2911 (m), 2875 (m), 2098 (m, C≡C), 1605 (w), 1453 (m), 1421 (s), 1377 (m), 1350 (w), 1302 (w), 1253 (m), 1195 (m), 1076 (w), 1033 (s), 1005 (m), 878 (w), 764 (s), 730 (s), 702 (m), 633 (m); HR-ESI (TOF, m/z): Calcd. for C90H155I4P10Pt5(MeCN): 3070.41867; found: 3070.41640 ([M − I + MeCN]+). Calcd. for C90H155I3P10Pt5(MeCN)2: 1492.27005; found: 1492.26967 ([M − 2I + 2MeCN]2+, main intensity).

Supplementary Material

SI

Acknowledgments

We thank the SNF-Swiss, NIH-USA (Grants GM-057052, GM-080820), and WCU-Korea (R33-2008-000-10003-0) for financial support. We thank Mihaiela Stuparu, Simon Duttwyler, Sasha Blumentritt and Simon Jurt for experimental assistance.

Footnotes

†

Electronic supplementary information (ESI) available: Spectral data for 1, 2 and 6a. CCDC reference numbers 743465, 747515 and 747516. For ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/b916020e

‡

X-Ray crystal data for compound 1: C80H155Cl5P10Pt5, Mr = 2579.11, monoclinic, space group P21/n, a = 38.9473(4), b = 14.4159(1), c = 39.1396(4) Å, β = 110.8408(3)°, V = 20537.5(3) Å3, Z = 8, Dx = 1.668 g cm−3, T = − 113 °C, Nonius KappaCCD area-detector diffractometer, Mo Kα radiation, λ = 0.71073 Å, μ = 7.079 mm−1, θmax = 25.0°, 238902 measured reflections, 35803 symmetry-independent reflections (Rint = 0.104), 26731 reflections with I > 2σ(I), refinement on F3, 2361 parameters, 6428 restraints, R(F) [I > 2σ(I) reflections] = 0.0658, wR(F2) [all reflections] = 0.1334, S(F2) = 1.138. X-Ray crystal data for compound 6b: C50H78N2P4Pt2·2CH6B11Br, Mr = 2453.86, orthorhombic, space group P21212, a = 31.0338(2), b = 33.4144(2), c = 8.0692(1) Å, V = 8367.57(13) Å3, Z = 4, Dx = 1.948 g cm−3, T = −113 °C, Nonius KappaCCD area-detector diffractometer, Mo Kα radiation, λ = 0.71073 Å, μ = 9.184 mm−1, θmax = 25.0°, 65724 measured reflections, 14693 symmetry-independent reflections (Rint = 0.090), 12856 reflections with I > 2σ(I), refinement on F2, 959 parameters, 396 restraints, R(F) [I > 2σ(I) reflections] = 0.0683, wR(F2) [all reflections] = 0.1864, S(F2) = 1.025. X-Ray crystal data for compound 9: C50H72I2P4Pt2·1.5(CHCl3), Mr = 1619.89, monoclinic, space group P21/n, a = 20.7278(2), b = 14.8192(1), c = 22.0662(2) Å, β = 115.2373(6)°, V = 6131.09(9) Å3, Z = 4, Dx = 1.755 g cm−3, T = −113 °C, Nonius KappaCCD area-detector diffractometer, Mo Kα radiation, λ = 0.71073 Å, μ = 5.877 mm−1, θmax = 27.5°, 141083 measured reflections, 14009 symmetry-independent reflections (Rint = 0.077), 11811 reflections with I > 2σ(I), refinement on F2, 557 parameters, 126 restraints, R(F) [I > 2σ(I) reflections] = 0.0782, wR(F2) [all reflections] = 0.2250, S(F2) = 1.059.

Note added in proof

During the typesetting of this manuscript we were able to obtain 31P,1H-HSQC data (cf. page 6 of the supplementary information), which confirms a small additional peak in the 1H NMR (δ 7.77 ppm) and 31P (δ 14.89 ppm) NMR of 1 belongs to the all trans isomer. Crude integration of the peaks indicates that the all trans component constitutes ca. 10% of the solution structure under these conditions.

Contributor Information

Peter J. Stang, Email: stang@chem.utah.edu.

Jay S. Siegel, Email: jss@oci.uzh.ch.

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