C2-Symmetric P,N Ligands Derived from Carborane-Based

Article pubs.acs.org/IC

C2‑Symmetric P,N Ligands Derived from Carborane-Based Diphosphetanes: Synthesis and Coordination Chemistry Peter Coburger, Jan Schulz, Jennifer Klose, Benedikt Schwarze, Menyhárt B. Sárosi, and Evamarie Hey-Hawkins* Leipzig University, Faculty of Chemistry and Mineralogy, Institute of Inorganic Chemistry, Johannisallee 29, D-04103 Leipzig, Germany S Supporting Information *

ABSTRACT: Racemic carborane-based bisphosphanes were obtained by dismutation reactions between a carborane-based diphosphetane and diaryl dichalogenides. NMR spectroscopic and theoretical studies revealed a two-step mechanism explaining the high stereoselectivity of these reactions. The coordination chemistry of the multidentate P,N ligands 6c and 6d in copper(I) and silver(I) complexes was studied. While 6d acted exclusively as tetradentate ligand, 6c showed either tridentate or tetradentate coordination depending on the metal and the counterion.

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INTRODUCTION

Hemilabile (or hybrid) ligands have gained attention for their application in homogeneous metal-catalyzed reactions.1 Here, soft and hard donor atoms, with respect to the hard−soft acid− base principle,2 are combined within the same molecule. Therefore, one donor functionality can firmly bind to a metal center, whereas the other can easily be displaced by a substrate molecule.3 This feature can lead to improvement of catalytic reactions when compared to classical ligands bearing either soft or hard donor atoms only;1d often encountered are combinations of phosphorus and nitrogen or oxygen atoms.1 The ortho-carborane backbone displays some features that are interesting for materials science and ligand design, such as electron-withdrawing properties, a flexible Ccluster−Ccluster bond, the possibility for deboronation (or breaking of the Ccluster− Ccluster bond) to give negatively charged nido-carboranes, and the binding ability of the cluster hydrogen atoms to late transition metals.4 Accordingly, the coordination chemistry of N, P, and S ligand systems bearing a carborane backbone and their application in homogeneous catalysis have been widely studied.5 Also, mixed donor ligands (P,Si, P,S and P,N) have been developed and tested in homogeneous catalysis.5c However, hemilabile P,N ligands with an ortho-carborane backbone remain rare, and, to the best of our knowledge, only compounds 1−3 have been used in homogeneous catalysis to date (Figure 1).6 We now report the synthesis of four C2-symmetric bisphosphanes featuring a carborane backbone from carborane-substituted 1,2diphosphetanes, which are versatile starting materials due to the reactive P−P bond.7 Two of the bisphosphines are multidentate © XXXX American Chemical Society

Figure 1. Hemilabile carborane-substituted P,N ligands.

P,N ligands, and their coordination chemistry toward copper(I) and silver(I) is also reported.

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EXPERIMENTAL SECTION

General Methods. All reactions and manipulations were performed under a nitrogen atmosphere by using standard Schlenk techniques, unless stated otherwise. Solvents were either obtained from an MBraun Solvent Purification Systems or dried and stored according to common procedures.8 Diphenyl diselenide, all used disulfides, copper(I) iodide, and silver(I) triflate are commercially available compounds and were used as obtained. Diphenyl ditelluride,9 [Cu(MeCN)4]PF6,10 and diphosphetane 411 were synthesized according to the literature procedures. NMR spectra were recorded with a Bruker AVANCE DRX 400 MHz NMR spectrometer at room temperature. Assignments of 1H and 13 C{1H} NMR spectra were based on H−H DQF-COSY, H−C HSQC, and H−C HMBC two-dimensional experiments. The numbering scheme for bisphosphanes 6a−d is given in Scheme 1, and the numbering scheme for metal complexes 8−12 is given in Scheme 3. Received: September 8, 2016

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DOI: 10.1021/acs.inorgchem.6b02173 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry Scheme 1. Synthesis of Racemic Bisphosphanes 6a (Ph), 6b, 6c (2-Py), and 6d (2-Anil)a

a

For clarity, only the S,S isomers are shown in this and all following schemes.

Tetramethylsilane was used as internal standard for 1H and 13C NMR spectra. 85% H3PO4 was used as external standard for 31P NMR spectra, and BF3·OEt2 was used as external standard for 11B NMR spectra. Mass spectra were recorded with a Micromass LCT. Elemental analyses (C, H, and N) were performed with a Heraeus VARIO EL oven. IR spectra were recorded as KBr disks in the range of 4000−400 cm−1 with a PerkinElmer System 2000 IR spectrometer. Single-Crystal X-ray Diffraction. X-ray diffraction studies were performed with an Oxford Diffraction CCD Xcalibur-S diffractometer using Mo Kα radiation and ω-scan rotation. Data were collected using ω steps accumulating area detector frames spanning at least a hemisphere of reciprocal space for all structures (data were integrated with CrysAlis Pro). All data were corrected for Lorentz polarization and long-term intensity fluctuations. Absorption effects were corrected on the basis of multiple equivalent reflections. Structures were solved by direct methods and refined by full-matrix least-squares techniques against F2 by using the SHELX program package.12 Hydrogen atoms were assigned riding isotropic displacement parameters and constrained to idealized geometries. Crystallographic details of 6a, 6b, 6d, and 8−12 are given in the Supporting Information. Computational Methods. All calculations were performed with the ORCA program package.13 The relaxed potential-energy surface scan along one P···Se distance between diphenyl diselenide and diphosphetane 4 was performed with the M06-2X density functional14 and the augSV(P) basis set.15 Geometry optimizations were performed with the same density functional but using the ma-def2-SVP basis set.16 The optimized geometries were used for single-point energy and vibrational frequency calculations at 313 K at the same level of theory. Löwdin reduced orbital population analysis was used to interpret the character of each molecular orbital. Geometry optimizations and electronic structure calculations in the gas phase for 6c and 6d were performed with the TPSS density functional17 and the def2-TZVP basis set.15a,16a Density fitting techniques, also called resolution-of-identity approximation,18 and atom-pairwise dispersion corrections19 were used throughout. Toluene solvent effects were accounted for with the conductor like screening model, as implemented in ORCA. Images of the molecular orbitals of the optimized structures were rendered with the UCSF Chimera program package.20 rac-1,2-Bis[tert-butyl(phenylselano)phosphanyl]-1,2-dicarbacloso-dodecaborane(12) (6a). Diphenyl diselenide (95 mg, 0.30 mmol, 1.0 equiv) and 4 (102 mg, 0.33 mmol, 1.1 equiv) were dissolved in toluene (4 mL) and stirred for 15 h at 40 °C. Afterward, volatiles were removed in vacuo, and the resulting yellow solid was washed with acetonitrile (4 × 1.5 mL) to yield 6a (146 mg, 77%) as a light yellow solid. Crystals suitable for single-crystal X-ray diffraction were obtained from acetonitrile/toluene at room temperature. Elemental analysis: C22H38B10P2Se2, calculated (%): C 41.91, H 6.08; found (%): C 40.81, H 6.33. High-resolution mass spectrometry (HRMS) electrospray

ionization (ESI pos., dichloromethane (DCM)/MeCN): m/z calculated for C22H39B10P2Se2+ [M + H]+: 635.183 61; found: 635.183 24. IR (KBr): ν̃ = 3056 (w, vC−H), 3006 (w, vC−H), 2962 (m, vC−H), 2655 (m, vB−H), 2632 (m, vB−H), 2585 (s, vB−H), 2542 (s, vB−H), 1943 (w), 1866 (w), 1575 (m), 1474 (s), 1469 (s), 1438 (s), 1391 (m), 1367 (m), 1300 (w), 1262 (vs), 1097 (vs), 1064 (vs), 1020 (vs), 903 (w), 800 (vs, vB−B), 735 (s), 688 (s), 668 (m), 619 (w), 576 (w), 466 (w), 445 (m) cm−1. 1H NMR (400 MHz, CDCl3): δ = 1.11−1.15 (m, 18H, C(CH3)3), 1.60−3.45 (m, 10H, BH), 7.25−7.30 (m, 6H, o,p-H in C6H5), 7.57−7.60 (m, 4H, m-H in C6H5) ppm. 13C{1H} NMR (101 MHz, CDCl3): δ = 28.8 (s, C(CH3)3), 37.7 (t, 1JCP = 4JCP = 13.6 Hz, C(CH3)3), 90.6−91.6 (m, C2B10), 127.1 (s, p-C in C6H5), 128.3−128.6 (m, ipso-C in C6H5), 128.9 (s, m-C in C6H5), 133.5−133.8 (m, o-C in C6H5) ppm. 11B{1H} NMR (128 MHz, CDCl3): δ = −9.2 (4B), −8.1 (2B), −4.8 (2B), 0.3 (2B) ppm. 31P{1H} NMR (162 MHz, CDCl3): δ = 78.7 (77Se satellites, AA′ part of an AA′X spin system) ppm. 77Se{1H} NMR (76 MHz, CDCl3, X part of an AA′X spin system, values obtained from simulated spectra): δ = 338.6 (m, 1JSeP = −284 Hz, 4JSeP = 1.6 Hz, 3 JPP = 153 Hz) ppm. rac-1,2-Bis[tert-butyl(4-chlorophenylthio)phosphanyl]-1,2-dicarba-closo-dodecaborane(12) (6b). 4,4′-Dichlorodiphenyl disulfide (262 mg, 0.91 mmol, 1.00 equiv) and 4 (290 mg, 0.91 mmol, 1.00 equiv) were dissolved in toluene (7 mL) and stirred for 24 h at 60 °C. Afterward, volatiles were removed in vacuo, and the resulting yellow solid was washed with acetonitrile (4 × 1.5 mL) to yield 6b as a colorless solid (415 mg, 75%). Crystals suitable for single-crystal X-ray diffraction were obtained from acetonitrile at room temperature. Elemental Analysis: C22H36B10Cl2P2S2, calculated (%): C 43.63, H 5.99; found (%): C 42.21, H 6.42. HRMS (ESI pos., DCM/MeCN): m/z calculated for C22H37B10Cl2P2S2+ [M + H]+: 606.217 79; found: 606.217 76. IR (KBr): ν̃ = 2993 (w, vC−H), 2960 (m, vC−H), 2930 (w, vC−H), 2913 (w, vC−H), 2631 (s, vB−H), 2572 (s, vB−H), 1887 (w), 1652 (w), 1571 (w), 1474 (s), 1469 (m), 1425 (w), 1388 (m), 1362 (m), 1261 (s), 1174 (m), 1089 (vs), 1054 (s), 1011 (s), 884 (w), 875 (w), 809 (vs, vB− B), 735 (m), 727 (m), 648 (w), 620 (w), 590 (w), 542 (m), 517 (m), 484 (s) cm−1. 1H NMR (400 MHz, CDCl3): δ = 1.12−1.16 (m, 18H, CH3), 1.52−3.37 (m, 10H, BH), 7.26−7.33 (m, 4H, 2), 7.41 (d, 4H, 3 JHH = 8 Hz, 3) ppm. 13C{1H} NMR (101 MHz, CDCl3): δ = 27.7 (s, C(CH3)3), 37.8 (t, 1JCP = 4JCP = 12.1 Hz, C(CH3)3), 91.1−92.0 (m, C2B10), 128.8 (s, 2), 132.1−132.4 (m, 1), 133.1 (s, 4), 133.3−133.6 (m, 3) ppm. 11B{1H} NMR (128 MHz, CDCl3): δ = −9.1 (6B), −5.1 (2B), 0.5 (2B) ppm. 31P{1H} NMR (162 MHz, CDCl3): δ = 71.7 (s) ppm. rac-1,2-Bis[tert-butyl(pyridin-2-ylthio)phosphanyl]-1,2-dicarbacloso-dodecaborane(12) (6c). 2,2′-Dipyridyldisulfide (0.79 g, 3.59 mmol, 1.05 equiv) and 4 (1.09 g, 3.41 mmol, 1.00 equiv) were dissolved in toluene (14 mL) and stirred for 24 h at 60 °C. The reaction mixture was filtered to give a bright orange solution. Subsequently, the solvent was removed under reduced pressure, and the crude product was B


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Inorganic Chemistry

(2B), −0.1 (2B) ppm. 31P{1H} NMR (162 MHz, C4D8O): δ = 57.5 (bs) ppm. rac-[Ag(6d-κ4P,P,N,N)]OTf (9). Silver(I) triflate (100 mg, 0.38 mmol, 1.11 equiv) was added to a solution of 6d (192 mg, 0.34 mmol, 1.00 equiv) in THF (3 mL) under exclusion of light. The mixture was stirred for 10 min at room temperature. After filtration and washing of the residue with THF (3 × 3 mL), 9 was obtained as an orange solid (120 mg, 41%). Crystals suitable for single-crystal X-ray diffraction were obtained from acetonitrile/toluene at 40 °C. Elemental analysis: C22H40B10AgF3N2P2S2, calculated (%): C 33.54, H 4.90, N 3.40; found (%): C 34.56, H 5.27, N 2.53. HRMS (ESI pos., DCM/MeCN): m/z calculated for C23H40B10AgN2O3P2S3+ [M-OTf]+: 674.215 97; found: 674.215 09. IR (KBr): ν̃ = 3357 (w, vN−H), 3274 (m, vN−H), 2964 (s, vC−H), 2574 (m, vB−H), 1733 (w), 1592 (m), 1481 (m), 1446 (m), 1370 (m), 1292 (s), 1262 (vs), 1221 (m), 1156 (s), 1097 (vs), 1026 (vs), 801 (vs, vB−B), 753 (m), 730 (w), 631 (m), 516 (m), 454 (m) cm−1. 1H NMR (400 MHz, CD3CN): δ = 1.19−1.24 (m, 18H, CH3), 1.69−3.42 (m, 10H, BH), 4.88 (bs, 4H, NH2), 6.72 (td, 3JHH = 7.6 Hz, 4JHH = 1.3 Hz, 2H, 4), 6.83 (dd, 3JHH = 8.2 Hz, 4JHH = 1.4 Hz, 2H, 2), 7.15 (ddd, 3JHH = 8.3 Hz, 3JHH = 7.1 Hz, 4JHH = 1.3 Hz, 2H, 3), 7.38 (d, 3 JHH = 7.8 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, CD3CN): δ = 27.3 (t, J = 7.1 Hz, C(CH3)3), 41.7 (s, C(CH3)3), 97.3−97.9 (m, C2B10), 114.3 (t, J = 4.6 Hz, 1), 117.5 (s, 2), 120.7 (s, 4), 131.4 (s, 3), 136.7 (s, 5), 148.4 (s, 6) ppm. 11B{1H} NMR (128 MHz, CD3CN): δ = −12.3 (2B), −8.4 (4B), −1.9 (2B), −1.3 (2B) ppm. 31P{1H} NMR (162 MHz, CD3CN): δ = 71.8 (d (satellites), 1JP107Ag = 320 Hz), 71.8 (d (satellites), 1 109 JP Ag = 367 Hz) ppm. rac-[Cu(6c-κ4P,P,N)]PF6 (10). [Cu(MeCN)4]PF6 (166 mg, 0.46 mmol, 1.00 equiv) and 6c (297 mg, 0.55 mmol, 1.20 equiv) were mixed in THF (5 mL) and stirred for 15 h. Afterward, volatile substances were removed from the reaction mixture in vacuo. Washing with THF (3 × 3 mL) gave 10·THF (207 mg, 55%) as a yellow solid. Crystals suitable for single-crystal X-ray diffraction were obtained by evaporation of solvent from a THF solution. Elemental analysis: C24H44B10CuF6N2OP2S2, calculated (%): C 35.18, H 5.14, N 3.42; found (%): C 35.40, H 5.49, N 3.22. HRMS (ESI pos., MeCN): m/z calculated for C20H36B10CuN2P3S2+ [M-PF6+]: 602.207 88; found: 602.208 09. 1H NMR (400 MHz, CD3CN): δ = 1.24−1.29 (m, 18H, CH3), 1.65−3.70 (m, 10H, BH), 7.41 (ddd, 3JHH = 7.5 Hz, 3JHH = 5.3 Hz, 4JHH = 1.2 Hz, 2H, 4), 7.69 (dt, 3JHH = 8.2 Hz, 4JHH = 5JHH = 1.0 Hz, 2H, 2), 7.88 (ddd, 3 JHH = 7.5 Hz, 3JHH = 7.5 Hz, 4JHH = 1.7 Hz, 2H, 3) 8.61 (ddd, 3JHH = 5.3 Hz, 4JHH = 1.8 Hz, 5JHH = 0.9 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, CD3CN): δ = 26.7 (bs, C(CH3)3), 41.1 (s, C(CH3)3), 91.5−91.9 (m, C2B10), 123.7 (s, 4), 125.5 (s, 2), 139.7 (s, 3), 151.3 (t, J = 3.0 Hz, 5), 155.6−155.7 (m, 1) ppm. 11B{1H} NMR (128 MHz, CD3CN): δ = −11.1 to −9.0 (4B), −8.3 (2B), −3.5 (2B), 0.6 (2B) ppm. 31P{1H} NMR (162 MHz, CD3CN): δ = −144.7 (hept, 1JPF = 706 Hz, PF6), 51.2 (bs) ppm. rac-[CuI(6c-κ3P,P,N)] (11). CuI (94 mg, 0.49 mmol, 1.05 equiv) and 6c (250 mg, 0.46 mmol, 1.00 equiv) were suspended in THF (15 mL), and the resulting dark orange mixture was stirred for 12 h at room temperature. Subsequently, the mixture was filtered, and the solvent was removed under reduced pressure. The remaining solid was washed with toluene (2 × 2 mL) to afford 11 (285 mg, 84%) as an orange solid. Crystals suitable for single-crystal X-ray diffraction were obtained from THF at 4 °C. Elemental analysis: C20H36B10CuIN2P2S2, calculated (%): C 32.95, H 4.98, N 3.84; found (%): C 32.61, H 5.90, N 2.48. HRMS (ESI pos., MeCN): m/z calculated for C20H36B10CuN2P2S2+ [M-I]+: 602.207 88; found: 602.207 07. IR (KBr): ν̃ = 2963 (s, vC−H), 2634 (w, vB−H), 2580 (m, vB−H), 1572 (m), 1452 (s), 1416 (s), 1370 (w), 1262 (vs), 1098 (vs), 1021 (vs), 865 (w), 801 (vs, vB−B), 761 (s), 719 (w), 634 (w), 533 (w), 517 (w), 482 (w), 465 (w) cm−1. 1H NMR (400 MHz, C4D8O): δ = 1.49−1.58 (m, 18H, CH3), 1.81−3.39 (m, 10H, BH), 7.27 (ddd, 3JHH = 6.8 Hz, 3JHH = 5.1 Hz, 4JHH = 1.5 Hz, 2H, 4), 7.58−7.79 (m, 4H, 2, 3), 8.74 (ddd, 3JHH = 5.2 Hz, 4JHH = 1.8 Hz, 5JHH = 0.9 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, C4D8O): δ = 28.3 (bs, C(CH3)3), 41.8 (s, C(CH3)3), 95.2−95.7 (m, C2B10), 123.8 (s, 4), 127.6 (s, 2), 138.8 (s, 3), 152.5 (s, 5), 153.5−153.6 (m, 1) ppm. 11B{1H} NMR (128 MHz, C4D8O): δ = −15.8 to −5.4 (6B), −3.2 (2B), −0.1 (2B) ppm. 31P{1H} NMR (162 MHz, C4D8O): δ = 49.1 (bs) ppm.

washed with acetonitrile (3 × 2 mL) to yield 6c (1.50 g, 82%) as a pale yellow solid. Elemental analysis: C20H36B10N2P2S2, calculated (%): C 44.59, H 6.74, N 5.20; found (%): C 43.22, H 6.37, N 4.71. HRMS (ESI pos., tetrahydrofuran (THF)): m/z calculated for C20H37B10N2P2S2+ [M + H]+: 539.288 15; found: 539.288 66. IR (KBr): ν̃ = 3044 (w, vC−H), 2987 (m, vC−H), 2953 (m, vC−H), 2922 (m, vC−H), 2895 (m, vC− H), 2863 (m, vC−H), 2632 (s, vB−H), 2546 (vs, vB−H), 2569 (vs, vB− H), 1635 (w), 1573 (vs), 1561 (s), 1471 (m), 1448 (vs), 1417 (vs), 1393 (m), 1367 (s), 1277 (w), 1262 (m), 1173 (m), 1149 (m), 1115 (s), 1085 (m), 1067 (s), 1046 (m), 986 (m), 878 (w), 802 (m), 759 (vs, vB−B), 732 (m), 720 (s), 618 (m), 582 (w), 518 (m), 477 (m), 431 (w) cm−1. 1 H NMR (400 MHz, CDCl3): δ = 1.17−1.19 (m, 18H, CH3), 1.70−3.40 (m, 10H, BH), 7.14 (ddd, 3JHH = 7.4 Hz, 3JHH = 4.9 Hz, 4JHH = 1.0 Hz, 2H, 4), 7.64 (td, 3JHH = 7.7 Hz, 4JHH = 2.0 Hz, 2H, 3), 7.81 (dt, 3JHH = 8.1 Hz, 4JHH = 5JHH = 1.0 Hz, 2H, 2), 8.49 (ddd, 3JHH = 4.8 Hz, 4JHH = 2.0 Hz, 5 JHH = 0.9 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, CDCl3): δ = 27.7 (bs, C(CH3)3), 37.5−38.1 (m, C(CH3)3), 89.1−92.8 (m, C2B10), 120.9 (s, 4), 125.4−125.7 (m, 2), 136.4 (s, 3), 149.5 (s, 5), 157.2−157.4 (m, 1) ppm. 11B{1H} NMR (128 MHz, CDCl3): δ = −10.5 to −8.5 (6B), −5.3 (2B), 0.5 (2B) ppm. 31P{1H} NMR (162 MHz, CDCl3): δ = 63.3 (s) ppm. rac-1,2-Bis[tert-butyl(anilin-2-ylthio)phosphanyl]-1,2-dicarbacloso-dodecaborane(12) (6d). 2,2′-Diaminodiphenyl disulfide (0.80 g, 3.22 mmol, 1.01 equiv) and 4 (1.01 g, 3.18 mmol, 1.00 equiv) were dissolved in toluene (20 mL) and stirred for 15 h at 60 °C. Afterward, volatile substances were removed in vacuo, and the resulting yellow solid was washed with acetonitrile (4 × 3 mL) to yield 6d as a pale yellow solid (1.51 g, 81%). Crystals suitable for single-crystal X-ray diffraction were obtained from acetonitrile/toluene at room temperature. Elemental analysis: C22H40B10N2P2S2, calculated (%): C 46.62, H 7.11, N 4.94; found (%): C 45.40, H 6.87, N 4.42. HRMS (ESI pos., DCM/MeCN): m/z calculated for C22H41B10N2P2S2+ [M + H]+: 567.319 55; found: 567.318 50. IR (KBr): ν̃ = 3473 (m, vN−H), 3381 (m, vN−H), 3008 (w, vC−H), 2944 (m, vC−H), 2894 (m, vC−H), 2864 (m, vC−H), 2625 (m, vB−H), 2570 (s, vB−H), 1608 (vs), 1481 (vs), 1447 (s), 1394 (m), 1367 (m), 1304 (m), 1261 (s), 1157 (m), 1064 (s), 1020 (s), 927 (w), 802 (vs, vB−B), 742 (vs, vB−B), 675 (w), 619 (w), 537 (w), 511 (m), 450 (m), 410 (w) cm−1. 1H NMR (400 MHz, CDCl3): δ = 1.10−1.14 (m, 18H, CH3), 1.75−3.30 (m, 10H, BH), 4.17 (bs, 4H, NH2), 6.67 (dd, 3 JHH = 8.1 Hz, 4JHH = 1.3 Hz, 2H, 5), 6.77 (td, 3JHH = 7.6 Hz, 4JHH = 1.2 Hz, 2H, 3), 7.07 (td, 3JHH = 7.6 Hz, 4JHH = 1.4 Hz, 2H, 4), 7.45 (dd, 3JHH = 7.8 Hz, 4JHH = 1.2 Hz, 2H, 2) ppm. 13C{1H} NMR (101 MHz, CDCl3): δ = 27.7 (bs, C(CH3)3), 37.6−37.8 (m, C(CH3)3), 91.5−92.5 (m, C2B10), 115.5 (s, 5), 115.8 (m, 1), 118.9 (s, 3), 128.4 (s, 4), 134.7− 134.8 (m, 2), 146.2 (s, 6) ppm. 11B{1H} NMR (128 MHz, CDCl3): δ = −11.1 to −9.1 (6B), −5.1 (2B), 0.4 (2B) ppm. 31P{1H} NMR (162 MHz, CDCl3): δ = 72.1 (s) ppm. rac-[Cu(6d-κ4P,P,N,N)]I (8). THF (5 mL) was added to a mixture of CuI (44 mg, 0.23 mmol, 1.10 equiv) and 6d (118 mg, 0.21 mmol, 1.00 equiv). The reaction mixture was stirred for 18 h at room temperature. Afterward, the mixture was filtered, and the residue was washed with THF (3 × 1 mL). The solvent was removed from the collected THF phases in vacuo to afford 8 (159 mg, quantitative yield) as an orange solid. Crystals suitable for single-crystal X-ray diffraction were obtained from acetonitrile/toluene at room temperature. Elemental analysis: C22H40B10CuIN2P2S2, calculated (%): C 34.90, H 5.32, N 3.70; found (%): C 35.08, H 5.61, N 2.69. HRMS (ESI pos., MeCN): m/z calculated for C22H40B10CuN2P2S2 [M-I]+: 630.238 81; found: 630.239 29. IR (KBr): ṽ = 3451 (m, vN-H), 3351 (m, vN-H), 3281 (m), 3222 (m), 2962 (s, vC-H), 2926 (m, vC-H), 2866 (m, vC-H), 2638 (m, vB-H), 2572 (s, vB-H), 1655 (w), 1605 (m), 1590 (m), 1558 (m), 1395 (w), 1261 (s), 1159 (m), 1096 (s), 1065 (s), 1021 (vs), 861 (w), 801 (vs, νBB), 750 (m), 728 (m), 694 (w), 625 (w), 542 (w), 454 (m) cm−1. 1H NMR (400 MHz, C4D8O): δ = 1.17−1.21 (m, 18H, CH3), 1.69−3.42 (m, 10H, BH), 5.18 (bs, 4H, NH2), 6.61 (t, 3JHH = 7.6 Hz, 2H, 4), 6.78 (d, 3JHH = 7.9 Hz, 2H, 2), 6.99 (t, 3JHH = 7.4 Hz, 2H, 3), 7.90 (d, 3JHH = 7.9 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, C4D8O): δ = 27.5 (bs, C(CH3)3), 41.3 (m, C(CH3)3), 95.2−95.9 (m, C2B10), 114.7 (s, 1), 118.6 (s, 2), 120.3 (s, 4), 129.6 (s, 3), 137.8 (s, 5), 147.6 (s, 6) ppm. 11 1 B{ H} NMR (128 MHz, C4D8O): δ = −11.8 (2B), −9.1 (4B), −3.1 C


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Inorganic Chemistry Table 1. Summary of the Reaction of Diphosphetane 4 with Different Dichalcogenides

a b

entry

dichalcogenide

conditionsa

conversionb

isolated yield

product

1 2 3 4 5 6 7

S2(2-Anil)2 S2(2-Py)2 S2(C6H4-4-Cl)2 Se2Ph2 S2(C6H4-3-COOH)2 Te2Ph2 S2Cl2

A B B C A/D E F

100% 100% 100% 100% 0% 0% 100% (decomposition)

81% 82% 75% 77% 0% 0% 0%

6d 6c 6b 6a

A: toluene, 60 °C, 15 h; B: toluene, 60 °C, 24 h; C: toluene, 40 °C, 15 h, D: THF, 60 °C, 15 h; E: toluene, 100 °C, 3 d; F: toluene, RT, 15 h. Conversions were determined by 31P{1H} NMR spectroscopy.

Scheme 2. Two Potential Mechanisms for Stereoselective Dismutation Reactions, Shown Exemplarily for the Reaction with Diphenyl Diselenide

rac-[Ag(OTf)(6c-κ4P,P,N,N)] (12). AgOTf (87 mg, 0.34 mmol, 1.00 equiv) and 6c (200 mg, 0.37 mmol, 1.10 equiv) were dissolved in THF (6 mL) under the exclusion of light. The solution was stirred for 6 h at room temperature to give a dark red solution. Afterward, the solvent was removed under reduced pressure, and the crude product was washed with toluene (2 × 1 mL) to afford 12 (214 mg, 76%) as a yellow solid. Crystals suitable for single-crystal X-ray diffraction were obtained by evaporation of solvent from a THF solution. Elemental Analysis: C21H36AgB10F3O3P2N2S3, calculated (%): C 31.70, H 4.56, N 3.52; found (%): C 32.71, H 4.90, N 3.12. HRMS (ESI pos., THF): m/z calculated for C20H36AgB10N2P2S2+ [M-OTf]+: 646.18458; found: 646.18411. IR (KBr): ṽ = 3075 (w, vC-H), 2997 (w, vC-H), 2963 (m, vC-H), 2868 (w, vC-H), 2630 (m, vB-H), 2581 (s, vB-H), 1581 (s), 1560 (m), 1457 (s), 1416 (vs), 1398 (m), 1385 (w), 1368 (m), 1299 (vs), 1262 (s), 1242 (vs), 1215 (vs), 1169 (vs), 1112 (vs), 1087 (s), 1068 (s), 1046 (s), 1022 (vs), 994 (m), 802 (m, νB-B), 763 (s), 731 (w), 715 (m), 636 (vs), 573 (w), 525 (m), 477 (w), 460 (w) cm−1. 1H NMR (400 MHz, CD3CN): δ = 1.27−1.32 (m, 18H, CH3), 1.68−3.30 (m, 10H, BH), 7.34 (ddd, 3JHH = 7.5 Hz, 3JHH = 5.0 Hz, 4JHH = 1.1 Hz, 2H, 4), 7.49 (dt, 3JHH = 8.1 Hz, 4JHH = 5JHH = 1.1 Hz, 2H, 2), 7.77 (td, 3JHH = 7.8 Hz, 4JHH = 1.8 Hz, 2H, 3), 8.56 (ddd, 3JHH = 5.0 Hz, 4JHH = 1.9 Hz, 5JHH = 1.0 Hz, 2H, 5) ppm. 13C{1H} NMR (101 MHz, CD3CN): δ = 27.2 (bs, C(CH3)3), 40.4 (s, C(CH3)3), 95.4−95.8 (m, C2B10), 123.3 (s, 4), 125.8 (s, 2), 139.0 (s, 3), 150.6 (s, 5), 152.8 (s, 1) ppm. 11B{1H} NMR (128 MHz, CD3CN): δ = −12.4 (2B), −8.7 to −7.7 (4B), −2.3 (2B), 0.8 (2B) ppm. 31P{1H} NMR (162 MHz, CD3CN): δ = 48.4 (d (satellites), 1 107 JP Ag = 292 Hz), 48.4 (d (satellites), 1JP109Ag = 337 Hz) ppm.

To test the scope of this reaction, different dichalcogenides were treated with 4 (Table 1). For entries 1−4, Table 1, complete conversion of the starting material was observed, and the products could be isolated in good yields. In case of the dicarboxylic acid S2(C6H4-3-COOH)2 (entry 5), steric repulsion between the tert-butyl substituents on the phosphorus atoms and the bulky carboxyl groups may raise the activation barrier and thus hinder conversion under the given conditions. Dismutation reactions can be equilibrium reactions.21b,c This might be the case for the reaction between 4 and diphenyl ditelluride (entry 6). Since P−Te bonds are comparatively weak, the equilibrium might be shifted strongly toward the starting materials, so that no conversion is observable. The racemic isomers of bisphosphanes 6a−d were formed as the main product, and only small amounts of the meso isomers could be detected (4−5%, as judged by 1H NMR spectroscopy). Two mechanisms are suitable to explain the stereoselectivity of the dismutation reactions (Scheme 2). The first one involves nucleophilic attack of the lone pair of electrons at phosphorus on the diaryl dichalcogenide to give phosphinophosphonium salt 7 and a benzeneselenolate anion, which subsequently attacks 7 (Scheme 2). In the second mechanism, a four-membered transition state between 4 and the diaryl dichalcogenide is formed, yielding the bisphosphane in a concerted reaction (Scheme 2). The latter mechanism was proposed for the isomerization of 1,1,3,3-tetramethyl-2-(trifluoromethyl)diarsaphosphane.22 NMR spectroscopic and computational studies were performed to support one of these mechanisms. A solution of 1 equiv of diphosphetane 4 and two different dichalcogenides, S2(2-Py)2, S2(2-Anil)2, Se2Ph2, or S2(C6H4-4-Cl)2, (1 equiv each) in toluene was stirred at 60 °C for 1 d. Three products were

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RESULTS AND DISCUSSION Synthesis of Bisphosphanes and Mechanistic Investigations. Starting from the racemic diphosphetane 4,11c bisphosphanes 6a−d were synthesized by reaction with the respective diaryl dichalcogenides. These so-called dismutation reactions have already been studied in detail between noncyclic diphosphanes and diorganyl dichalcogenides.21 D


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Inorganic Chemistry Scheme 3. Syntheses of Copper(I) and Silver(I) Complexes

Figure 2. 31P{1H} NMR spectrum of a mixture of 4, S2(2-Anil)2, and S2(2-Py)2 in toluene after stirring at 60 °C overnight. Thin: simulated AB spin system (162 MHz, δ = 64.3 and 71.3 ppm, 3JPP = 143 Hz).

E


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Inorganic Chemistry

Figure 3. Optimized structures and frontier molecular orbitals of the species involved in the formation of 6a. Se: cyan; P: red; C: gray; H: white. Surface isovalue: 0.03.

always observed by 31P{1H} NMR spectroscopy, exemplarily shown for the reaction of 4 and S2(2-Py)2 and S2(2-Anil)2 in Figure 2. The spectrum shows two singlets for 6c and 6d and two doublets corresponding to an AB spin system, which was attributed to an unsymmetrical bisphosphane bearing a thioanilyl moiety on one and a thiopyridyl moiety on the other phosphorus atom, on the basis of the shifts and the coupling constant.23 Since 6a−d did not show any further reaction with different dichalcogenides, these findings can only be explained by the twostep mechanism (via 7 in Scheme 2). Furthermore, the reactivity of the investigated dichalcogenides was deduced from the 31 1 P{ H} NMR spectra on the basis of the ratio of integrals of the signals of the respective bisphosphanes in the reaction mixtures

and follows the order S2(C6H4-4-Cl)2 < S2(2-Py)2 < S2(2-Anil)2 ≪ Se2Ph2 (ratio 1:10:20:380 by NMR). The high reactivity of Se2Ph2 can be explained by the lower strength of Se−Se bonds compared to S−S bonds.24 In addition, computational studies were performed. A relaxed potential-energy surface scan along one P···Se distance between diphosphetane 4 and Se2Ph2 revealed a two-step reaction mechanism for the formation of 6a (Scheme 2). The formation of intermediate 7 involves the dissociation of Se2Ph2. The calculated change in free enthalpy of the reaction (ΔG) at 313 K for the formation of 7 and SePh− is 72.31 kcal mol−1. The subsequent formation of 6a is exergonic, with ΔG = −88.77 kcal mol−1. Thus, the two reaction steps are energetically coupled, F


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Inorganic Chemistry

Figure 4. Molecular structures of 6a, 6b, and 6d in the solid state with ellipsoids drawn at 50% probability level. Only the S,S enantiomers are shown. In the case of 6d, only the non-disordered molecule in the asymmetric unit is depicted. Hydrogen atoms are omitted for clarity.

with an overall ΔG of −16.46 kcal mol−1. Furthermore, the frontier molecular orbitals of the species involved in the formation of 6a also support the two-step mechanism. The first step involves nucleophilic attack of the highest occupied molecular orbital (HOMO) of 4 (Figure 3) at the lowest unoccupied molecular orbital (LUMO; the σ*(Se−Se) orbital) of Se2Ph2. This results in the formation of 7 and SePh−. The second step involves nucleophilic attack of the HOMO of SePh− at the LUMO of 7 (the σ*(P−P) orbital; Figure 3). Formation of a Se−P bond and breaking of the P−P bond results in formation of 6a. Characterization of Bisphosphanes 6a−d. The racemic bisphosphanes 6a−d were characterized by multinuclear NMR and IR spectroscopy, HRMS, and elemental analysis. The 11 1 B{ H} NMR spectra show four broad signals in the range from −11 to 0.5 ppm (ratio 6:2:2); the 31P{1H} NMR spectra exhibit singlets at 63.3 (6c), 71.0 (6d), 71.7 (6b), and 78.8 (6a) ppm. Additionally, 6a displays 77Se satellites in the 31P{1H} NMR spectrum and a multiplet at 338.6 ppm in the 77Se{1H} NMR spectrum for the AA′X spin system. The respective coupling constants (1JSeP = −284 Hz, 4JSeP = 1.6 Hz, 3JPP = 153 Hz) were obtained by simulation with the noncommercial program

SpinWorks.25 Through-space interactions between the phosphorus atoms are indicated by a rather large 3JPP coupling constant.26 This is in accordance with the behavior of previously published carborane-substituted bisaminophosphanes.23 Single-crystal X-ray diffraction experiments were performed for 6a, 6b, and 6d (see Supporting Information). Their molecular structures in the solid state are depicted in Figure 4. Bisphosphanes 6a, 6b, and 6d crystallize in the monoclinic space group P21/c with similar bond lengths and angles to previously reported carborane-substituted bisphosphanes (Table 2).23,27 In contrast to 6a and 6b, 6d crystallizes with two molecules in the asymmetric unit, whereby one of them has a disordered aniline substituent. As observed in solution, attractive interactions between the phosphorus atoms are indicated by the rather small P1−C1−C2 bond angles and P···P distances that are smaller than the sum of their van der Waals radii.23,28 Electronic Structures of 6c and 6d. Geometry optimizations and electronic structure calculations in the gas phase were performed to gain insight into the potential coordination modes of the P,N ligands 6c and 6d. Selected frontier molecular orbitals are depicted in Figure 5. The HOMO (E = −5.15 eV) of 6d shows a large contribution of the lone pair of electrons at the G


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phosphorus−metal bonds should be of comparable or just slightly lower strength. Coordination Chemistry of 6c and 6d toward Copper(I) and Silver(I). The reaction of 6c and 6d with CuI or AgOTf in THF yielded copper(I) complexes 8, 10, and 11 and silver(I) complexes 9 and 12, respectively. Complexes 8−12 were characterized by multinuclear NMR and IR spectroscopy, HRMS, and elemental analysis. Molecular Structures of Complexes 8−12. Single-crystal X-ray diffraction studies were performed on complexes 8−12 (see Supporting Information). The molecular structures are shown in Figures 6−11; selected bond lengths and angles are given in Table 3. All complexes are present as racemic isomers. In 8 and 9, the metal(I) cation is coordinated by both phosphorus and nitrogen atoms of the tetradentate ligand 6d in a distorted tetrahedral fashion. The resulting MP2C2 ring is planar. In 9, additionally, one oxygen atom of the triflate counterion is weakly coordinated at silver (Ag−O: 2.866(2) Å, sum of van der Waals radii: 3.24 Å),28 resulting in a 4 + 1 coordination. The metal− phosphorus bond lengths in both complexes are within the range of those of previously reported complexes.27a,29 Compared to 6d, complexes 8 and 9 show a significant widening of certain bond angles (e.g., P1−C1−C2, P1−S1−C3, and P1−S1−C3−C4). This effect is more pronounced for the silver(I) complex, in which the C1−C2 bond is additionally lengthened. This demonstrates the flexibility of this new class of P,N ligands, which can accommodate different geometries depending on the metal center. A similar coordination environment as observed in the copper(I) complex 8 is present in 10. Here, both pyridyl groups

Table 2. Selected Distances, Bond Lengths [Å], and Angles [deg] for 6a, 6b, and 6da P1···P2 P1−Se1/S1 C1−C2 P1−C1−C2 P1−S1/Se1−C3 P2−S2/Se2−C5 P1−S1/Se1−C3−C4 P2−S2/Se2−C5−C6

6a

6b

6d

3.167(1) 2.2478(7) 1.760(4) 111.9(2) 97.67(8) 95.51(8) 58.6(2) 53.6(2)

3.2048(5) 2.1080(5) 1.768(2) 112.53(9) 100.27(6) 101.58(5) −39.6(1) −50.2(2)

3.2200(9) 2.1137(9) 1.775(3) 112.0(1) 99.14(9) 100.68(8) 53.0(2) 49.2(2)

a

For 6d, only the values for the non-disordered molecule in the asymmetric unit are shown. Numbering scheme according to Figure 4.

nitrogen atoms, while the HOMO−2 displays large contributions of the lone pair of electrons at the phosphorus atoms (E = −5.58 eV). The LUMO (E = −1.79 eV) exhibits large Ccluster−P bonding character. Therefore, the phosphorus atoms exhibit σdonor and π-acceptor properties, and the nitrogen atoms exhibit strong donor properties. In contrast to 6d, in 6c the lone pair of electrons at the nitrogen atoms are considerably lower in energy (HOMO−3, −6.42 eV), while the lone pair of electrons at the phosphorus atoms is similar in energy and shape (HOMO, E = −5.69 eV). Furthermore, the LUMO is now located at the pyridyl substituent. In addition, 6c has orbitals with partial acceptor character located at the phosphorus atoms (LUMO+1 and LUMO+2). However, these orbitals show a dominant contribution of the pyridyl substituents. Thus, 6c should form significantly weaker nitrogen−metal bonds than 6d, while the

Figure 5. Optimized structures and frontier molecular orbitals of 6d (top) [left: HOMO, (E = −5.15 eV), right: LUMO (E = −1.79 eV)] and 6c (bottom) [left: HOMO (E = −5.69 eV), right: LUMO (E = −2.10 eV)]. S: yellow, N: orange; P: red; C: gray; H: white. Surface isovalue: 0.03. H


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Figure 9. Molecular structure of 11 in the solid state with ellipsoids drawn at 50% probability. Only the R,R isomer and the non-disordered molecule in the asymmetric unit is shown. Hydrogen atoms are omitted for clarity.

Figure 6. Molecular structure of 8 in the solid state with ellipsoids drawn at 50% probability. Only the S,S isomer is shown. Hydrogen atoms and counterion are omitted for clarity.

Figure 10. Molecular structure of 12 (pentacoordinate) in the solid state with ellipsoids drawn at 50% probability. Only the R,R isomer is shown. Hydrogen atoms are omitted for clarity.

Figure 7. Molecular structure of 9 in the solid state with ellipsoids drawn at 50% probability. Only the S,S isomer is shown. Hydrogen atoms are omitted for clarity.

Figure 8. Molecular structure of 10 in the solid state with ellipsoids drawn at 50% probability. Only the S,S isomer is shown. Hydrogen atoms and counterion are omitted for clarity.

Figure 11. Molecular structure of 12 (tetracoordinate) in the solid state with ellipsoids drawn at 50% probability. Only one of the tetracoordinate molecules in the asymmetric unit is depicted. Only the S,S isomer is shown. Hydrogen atoms are omitted for clarity.

and both phosphorus atoms coordinate to the metal center in a distorted tetrahedral fashion with similar Cu−N and Cu−P bond I


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Inorganic Chemistry Table 3. Selected Bond Lengths [Å] and Angles [deg] for 8−12a C1−C2 P1−Cu/Ag P2−Cu/Ag N1−Cu/Ag N2−Cu/Ag P1−C1−C2 P2−C2−C1 P1−S1−C3 P2−S2−C5 P1−S1−C3−C4 P2−S2−C5−C6

8

9

10

11b

12 (5)c

12 (4)c

1.775(2) 2.2114(5) 2.2162(5) 2.056(1) 2.061(1) 113.86(8) 113.97(9) 106.00(6) 106.13(5) 53.3(1) 54.5(1)

1.857(5) 2.4893(9) 2.482(1) 2.367(3) 2.324(3) 115.6(2) 115.5(2) 105.8(1) 106.9(1) 58.2(4) 59.3(4)

1.78(1) 2.231(2) 2.209(2) 2.007(6) 2.017(7) 114.5(5) 113.5(5) 102.4(3) 101.6(3) 7.1(7) 8.6(8)

1.793(4) 2.2567(7) 2.2553(7) 2.115(2) 3.458(2) 113.8(1) 114.9(1) 102.53(8) 102.76(8) 3.7(2) 62.9(2)

1.817(5) 2.459(1) 2.464(1) 2.471(3) 2.472(3) 117.0(2) 116.7(2) 104.0(1) 104.4(2) 10.8(4) 12.2(4)

1.857(5) [1.854(4)] 2.469(1) [2.446(1)] 2.444(1) [2.442(1)] 2.484(3) [2.543(3)] 2.757(3) [2.709(3)] 116.1(2) [116.5(2)] 117.6(2) [116.1(2)] 105.0(1) [104.0(1)] 103.7(1) [104.1(1)] 4.5(3) [5.7(4)] 27.0(4) [20.6(4)]

a

Numbering scheme according to Figures 6−11. bFor 11, only the values for the nondisordered molecule in the asymmetric unit are shown. Coordination numbers for the three independent molecules of 12 are given in parentheses; the values of the second, tetracoordinate complex are given in brackets. c

Figure 12. Section of the 1H NMR spectra of 6d (in CDCl3), 8 (in CD3CN), and 9 (in THF-d8). Numbering according to Scheme 3.

lengths and a planar CuP2C2 ring, as observed in 8. However, when the weakly coordinating hexafluorophosphate anion is replaced by iodide (complex 11), a different coordination environment is observed, that is, tridentate coordination of the ligand 6c (P,P,N) and the iodide in a distorted tetrahedral fashion. The second nitrogen atom is not interacting with the copper atom [N2···Cu1 > sum of van der Waals radii (2.95 Å)].28 Furthermore, the Cu−N bond in 11 is considerably longer than that in in 8, which might be due to the steric demand of the iodo ligand; additionally, the CuP2C2 ring in 11 adopts an envelope conformation. Also, this complex crystallizes with one molecule of THF and two molecules of 11 (one disordered) in the asymmetric unit. The situation for 12 is more complex. The compound crystallizes with three independent molecules of 12 (and one molecule of THF) in the asymmetric unit. In one of them, the metal center is coordinated by the two phosphorus and the two nitrogen atoms of 6c and one oxygen atom of a triflate counterion, as was observed for 9. The coordination geometry is between square-pyramidal and trigonal-bipyramidal (τ = 0.47).30

In the other two molecules, the silver cation is coordinated by both phosphorus atoms but only one nitrogen atom of 6c and one oxygen atom of the triflate counterion (Ag−O: 2.307(3) Å and 2.292(3) Å). Although the second pyridyl ring is tilted away from the silver cation (Figure 11), the Ag−N distance (Table 3) is significantly shorter than the sum of the van der Waals radii (3.27 Å).28 Therefore, weak interactions cannot be excluded, and the coordination number of the silver atom could be described as 4 + 1. All Ag−N distances in 12 are significantly longer than those in 9, while the Ag−P bond lengths are similar. In conclusion, the different electronic structures of 6c and 6d are reflected in their coordination chemistry. Compound 6c has weaker Cu−N bonds than 6d, as indicated by the displacement of one pyridyl ligand by iodide in 11, while in 8 both nitrogen atoms bind firmly to the metal center. The elongated Ag−N bonds in 12 compared to 9 indicate the same trend for the silver(I) complexes. Spectroscopic Properties. The 31P{1H} NMR spectra of complexes with ligand 6d display a broad singlet at 57.5 ppm (for 8) and a singlet with two sets of satellites at 71.8 ppm (for 9) due J


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Inorganic Chemistry

Figure 13. Section of the 1H NMR spectra of 6c, 10, 11 and 12 in THF-d8. Numbering scheme according to Scheme 3.

to coupling of 31P to 109Ag and 107Ag, respectively [1JP107Ag = 320 Hz, 1JP109Ag = 367 Hz; assigned based on their different natural abundances (109Ag, N = 48.2%; 107Ag, N = 51.8%)].31 In the ligand 6d, the amino groups act as +M substituents at the phenylene rings, while in complexes 8 and 9, the amino substituents become −I substituents due to coordination to the metal center. This is clearly reflected in the aromatic region of the respective 1H NMR spectra of 6d, 8, and 9 (Figure 12). This indicates that the tetradentate coordination of 6d that is observed in the solid state is also retained in solution, and the molecules adopt a C2-symmetric conformation. The complexes of ligand 6c show a broad singlet at 49.1 ppm for 11, a broad singlet at 51.2 ppm for 10 (along with a septet at −144.7 ppm (1JPF = 706 Hz) for the hexafluorophosphate counterion), and two doublets at 48.4 ppm for 12 (1JP107Ag = 292 Hz, 1JP109Ag = 337 Hz) in the 31P{1H} NMR spectra. Furthermore, the signals in the aromatic region in the 1H NMR spectra are shifted upon coordination to the metal cation (Figure 13). In 10, the signals for the protons 2, 3, 4, and 5 are shifted downfield (+0.12, +0.41, +0.53, and +0.56 ppm, respectively). In contrast, in 11 and 12, only the resonances for protons 3, 4, and 5 are shifted downfield (+0.06, +0.19, and +0.36 ppm in 11; +0.16, +0.26 and +0.18 ppm in 12), while the resonance for proton 2 is shifted upfield (−0.03 and −0.21 ppm in 11 and 12, respectively). The shifts of 11 and 12 are similar for those observed in [{M(μ-Br)(C5H4N-2-SePtBu2)-κN,P)}2] (M = Cu, Ag).32 Since hexafluorophosphate is a weakly coordinating anion and only one set of signals is observed for the pyridyl rings in 10, the complex apparently adopts a C2-symmetric conformation also in solution. In contrast, 11 exhibits a different signal pattern for the pyridyl rings, indicating dynamic binding behavior of the pyridyl rings and the iodide. A definite conclusion about the conformation of complex 12 in solution cannot be drawn. However, since triflate is a rather weakly coordinating anion, a

C2-symmetric structure with coordination of both nitrogen and phosphorus atoms of ligand 6c seems likely. In summary, 6d acts as a tetradentate ligand with the two phosphorus and nitrogen atoms binding firmly to the metal center in solution and in the solid state. However, ligand 6c displays rather weak bonding of the nitrogen atoms to the metal center, making this compound potentially useful for applications as hemilabile ligand in homogeneous catalysis.

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CONCLUSIONS

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ASSOCIATED CONTENT

Four new bisphosphanes were obtained by highly stereoselective dismutation reactions of a carborane-based diphosphetane and dichalcogenides. A plausible mechanism was identified. Copper(I) and silver(I) complexes were obtained with the polydentate P,N ligands 6c and 6d; the different electronic structures of 6c and 6d are reflected in their coordination chemistry. We are now extending the coordination chemistry of 6c to catalytically active metal ions such as Rh+, Ru2+, and Ni2+ for application in homogeneous catalysis.4a,5b

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b02173. NMR spectra (1H, 13C{1H}, 11B{1H}, 31P{1H}) of compounds 6a−6d and 8−12 (and 77Se{1H} for 6a) (PDF) Crystallographic data of compounds 6a, 6b, 6d, and 8−12 (CIF) K


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AUTHOR INFORMATION

Corresponding Author

*E-mail: [email protected]. ORCID

Evamarie Hey-Hawkins: 0000-0003-4267-0603 Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge financial support from the Studienstiftung des deutschen Volkes (doctoral grant for P.C). We thank M. Devenish (School of Chemistry, Monash Univ., Australia) for synthetic support.

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