Reported here are the syntheses and molecular structures of three novel arylindium phosphinates, [(2,6- Mes2 C6 H3 In)2(OH)2(O2 PMe2)2] (1), [(2,6-Mes2 C6 H3 In)2(OH)(O2 PPh2)3] (2), and [(2,6-Mes2 C6 H3 In)(O2 PMe5 C3 H)2(H2 O)2] (3), which were obtained by condensation reaction of the m-terphenylindium dihydroxide [(2,6-Mes2 C6 H3 In(OH)2]4 with dimethylphosphinic acid, diphenylphosphinic acid, and 2,2,3,4,4-pentamethylphosphetanic acid, respectively.
The chemistry of group 13 element phosphinates dating back to the pioneering work of Coates and Mukherjee (1964) was comprehensively reviewed more than 15 years ago (Mason, 1998). Unarguably, aluminium phoshinates have received the most attention due to the fact that the Al-O-P linkage is isoelectronic to the Si-O-Si linkage and implications that hold for applications in material science. Among the very few known indium phosphinates, the most notable are the eight-membered heterocycles (R′2 InO2 PR2)2 (R′=Me, Et; R=Me, Ph), which were obtained by the reaction of the phosphinic acids R2 PO2 H with the indium trialkyls R3 In or the oxidation of (Me2 InPPh2)2 with pyridine oxide (Coates and Mukherjee, 1964; Hahn et al., 1990). The hydrolysis of (Me2 InO2 PPh2)2 in the presence of pyridine (py) gave the unique tetrameric heterocubane cluster [MeIn(OH)(O2 PPh2]4·4 py (Arif and Barron, 1988). Recently, we reported on the tetranuclear m-terphenylindium dihydroxide [2,6-Mes2 C6 H3 In(OH)2]4, which can be regarded as a heavier congener of the common arylboronic acids (Ahmad and Beckmann, 2009). We now describe the reactions of [2,6-Mes2 C6 H3 In(OH)2]4 with dimethylphosphinic acid, diphenylphosphinc acid, and 2,2,3,4,4-pentamethylphosphetanic acid, respectively, which gave rise to the formation of the arylindium phosphinates [(2,6-Mes2 C6 H3 In)2(OH)2(O2 PMe2)2] (1), [(2,6-Mes2 C6 H3 In)2(OH)(O2 PPh2)3] (2), and [(2,6-Mes2 C6 H3 In)(O2 PMe5 C3 H)2(H2 O)2] (3) as sole products regardless of the stoichiometric ratio of the reactants applied (Scheme 1).
Compounds 1–3 were obtained as colorless high-melting crystalline solids that are reasonably soluble in quite polar solvents, such as CHCl3, CH2 Cl2, and THF. The In/P ratios of 1 (1:1), 2 (2:3), and 3 (1:2) were determined by integration of 1H NMR resonances (see Experimental) and confirmed by elemental analysis. The 31P NMR spectra (CDCl3) and 31P MAS NMR spectra of 1–3 reveal signals at δ=40.5 and δiso=44.1 for 1, δ=31.8, 28.0 (integral ratio 1:2) and δiso=28.8, 23.6 (integral ratio 1:2) for 2, and δ=49.4 and δiso=49.7 for 3, which shifted significantly upfield from those of the parent phosphinic acids Me2 P(O)OH (δ=54.1), Ph2 P(O)OH (δ=38.7), and Me5 C3 HP(O)OH (δ=60.2), respectively. The molecular structures of 1–3 established by single crystal X-ray diffraction are depicted in Figures 1–3, respectively, and selected bond parameters are collected in the caption of the figures.
The degree of aggregation of the indium phosphinates 1–3 is smaller than in the tetranuclear starting material. While 1 and 2 are dinuclear, 3 is even mononuclear presumably due to the fact that 1,1,2,3,3-pentamethyltrimethylenephosphinate (Chandrasekhar et al., 2004; Chandrasekhar and Thirumoorthi, 2009) is bulkier than the dimethyl- and diphenylphosphinate.
In the crystal structure of 1, the two In atoms are bridged via two μ-OH groups and two μ-O2 PMe2 groups. In the crystal structure of 2, the two In atoms are bridged via one μ-OH group and three μ-O2 PPh2 groups. The spatial arrangement of the In atoms is trigonal bipyramidal and defined by a CO4 donor set.
The In-O bond, lengths vary between 2.104(8) and 2.247(4) Å and compare well with those of the starting compound [(2,6-Mes2 C6 H3 In(OH)2]4 (Ahmad and Beckmann, 2009), the previously reported indium phosphinates (Arif and Barron, 1988; Hahn et al., 1990), and the recently published indium phosphonates (Chandrasekhar et al., 2013). The structures of 1 and 2 contain μ-OH groups, whereas that of 3 possesses two H2 O molecules that coordinate to the In atom and engage in hydrogen bonding with the P=O groups of the phosphinate moieties [O···O 2.647(6) and 2.659(7) Å]. Consistently, the IR spectra (KBr) show absorptions at =3624 cm-1 for 1, =3587 cm-1 for 2, and =3626 cm-1 for 3 that are indicative of O-H stretching vibrations.
The m-terphenylindium dihydroxide [(2,6-Mes2 C6 H3 In(OH)2]4 (Ahmad and Beckmann, 2009) and the 2,2,3,4,4-pentamethylphosphetanic acid Me5 C3 HP(O)OH (Emsley et al., 1984) were prepared according to literature procedures. The other two phosphinic acids Me2 P(O)OH and Ph2 P(O)OH were obtained commercially and used as received. The 1H, 13C, and 31P NMR spectra were recorded in CDCl3 using Jeol GX 270 and Varian 300 Unity Plus spectrometers and are referenced to SiMe4 (1H, 13C) and aqueous H3 PO4 (31P). The 31P MAS NMR spectra were obtained using a JEOL Eclipse Plus 400 MHz NMR spectrometer equipped with a 6-mm rotor operating at spinning frequencies between 8 and 10 kHz. Infrared (IR) spectra were recorded using a Nexus FTIR spectrometer with a Smart DuraSamplIR. Microanalyses were obtained from a Vario EL elemental analyzer.
Synthesis of [(2,6-Mes2 C6 H3 In)2(OH)2 (O2 PMe2)2] (1)
A mixture of [2,6-Mes2 C6 H3 In(OH)2]4 (200 mg, 0.11 mmol) and Me2 P(O)OH (40 mg, 0.40 mmol) in THF (25 mL) was stirred overnight at r.t. The solvent was completely removed in vacuum and the solid residue recrystallized from THF to give 1 (153 mg, 0.14 mmol, 64%; Mp. 290–292°C).
1H-NMR: δ=7.36–7.32 (m, 2H), 7.02, 6.97 (d, 4H), 6.89, 6.87 (s, 8H), 2.54, 2.39 (s, 12H), 2.00, 1.98 (s, 24H), 0.90 (d, 12H). 13C NMR: δ=148.5, 148.3, 142.8, 142.1, 137.9, 136.9, 136.2, 136.0, 135.5, 135.3, 128.4, 128.2, 128.0, 127.8, 127.3, 126.4, 21.8, 21.7, 21.4, 21.3, 21.2, 20.9, 18.3, 17.3. 31P NMR: δ=40.5. 31P MAS NMR: δiso=44.1. IR (KBr): (OH)=3624 cm-1. Anal. calcd for C52 H80 In2 O6 P2 (1092.74): C, 57.14; H, 7.32. Found: C, 57.15; H, 7.23.
Synthesis of [(2,6-Mes2 C6 H3 In)2(OH)(O2 PPh2)3] (2)
A mixture of [2,6-Mes2 C6 H3 In(OH)2]4 (190 mg, 0.10 mmol) and Ph2 P(O)OH (140 mg, 0.64 mmol) in THF (25 mL) was stirred overnight at r.t. The solvent was completely removed in vacuum and the solid residue recrystallized from CH2 Cl2/hexane (1:3) to give 2 (0.27 mg, 0.17 mmol, 87 %; Mp. 330°C [dec.]).
1H-NMR: δ=7.41–7.35 (m, 5H), 7.30 (t, 1H), 7.25–7.18 (m, 5H), 7.13–7.05 (m, 4H), 6.93 (d, 2H), 6.74 (s, 4H) 2.18 (s, 6H), 2.09 (s, 12H). 13C-NMR: δ=149.2, 147.7, 142.3, 142.2, 137.3, 136.8, 136.5, 135.9, 135.7, 131.7, 131.6, 130.9, 130.2, 130.1, 129.4, 128.5, 128.3, 128.1, 127.7, 127.6, 127.2, 127.1, 127.0, 125.7, 21.5, 21.4. 31P NMR: δ=31.8 (s, 1P), 28.0 (s, 2P). 31P MAS NMR: δiso=28.8 (s, 1P), 23.6 (s, 2P). IR (KBr): (OH)=3587 cm-1. Anal. calcd for C84 H80 In2 O7 P3 (1524.03): C, 66.14; H, 5.24. Found: C, 66.15; H, 5.19.
Synthesis of [(2,6-Mes2 C6 H3 In)(Me5 C3 HPO2)2(H2 O)2] (3)
A mixture of [2,6-Mes2 C6 H3 In(OH)2]4 (110 mg, 0.06 mmol) and Me5 C3 HP(O)OH (100 mg, 0.47 mmol) in THF (25 mL) was stirred overnight at r.t. The solvent was completely removed in vacuum and the solid residue was recrystallized from CH2 Cl2/hexane (1:3) to give 3 (167 mg, 0.20 mmol, 86 %; Mp. 263–265°C).
1H NMR: δ=7.33 (t, 1H), 6.94 (d, 2H), 6.89 (s, 4H), 2.39 (s, 6H), 1.99 (s, 12H), 1.00–0.70 (m, 32H). 13C NMR: δ=148.8, 142.0, 136.6, 135.8, 128.8, 128.5, 128.2, 126.6, 49.8, 49.0, 41.9, 24.2, 22.6, 21.2, 21.1, 19.1. 31P NMR: δ=49.4. 31P MAS NMR: δiso=49.7. IR (KBr): (OH)=3626 cm-1. Anal. calcd for C40 H62 InO6 P2 (815.66): C, 58.84; H, 7.60. Found: C, 58.67; H, 7.43.
Intensity data were collected on a STOE IPDS 2T diffractometer at 150 K with graphite-monochromated Mo-Kα (0.7107 Å) radiation. The structures were solved by direct methods and difference Fourier synthesis using SHELXS-97 and SHELXL-97 implemented in the program WinGX 2002 (Farrugia, 1999). Full-matrix least-squares refinements on F2 were performed using all data. All nonhydrogen atoms were refined using anisotropic displacement parameters. Hydrogen atoms attached to carbon atoms were included in geometrically calculated positions using a riding model and were refined isotropically.
Disorder was resolved in for C12, C13, C32, and C33 of 1 as well as C71 of 3 and refined with occupancy ratios of 50:50. The crystal lattice of 3 contained larger voids, the defuse electron density of which was accounted by Platon’s Squeeze routine (Van der Sluis and Spek, 1990; Spek, 2003). Crystal and refinement data are collected in Table 1. Figures were created using DIAMOND (Brandenburg and Putz, 2006). Crystallographic data (excluding structure factors) for the structural analyses have been deposited with the Cambridge Crystallographic Data Centre. Copies of this information may be obtained free of charge from The Director, CCDC, 12 Union Road, Cambridge CB2 1EZ, UK (fax: +44-1223-336033; e-mail: email@example.com or http://www.ccdc.cam.ac.uk).
|Formula||C52 H80 In2 O6 P2||C84 H80 In2 O7 P3||C40 H62 InO6 P2|
|Formula weight, g mol-1||1092.74||1524.03||815.66|
|Crystal size, mm||0.7×0.6×0.5||0.7×0.6×0.5||0.6×0.6×0.4|
|ρcalcd, Mg m-3||1.387||1.397||1.130|
|μ (Mo-Kα), mm-1||0.988||0.758||0.596|
|θ range, deg||1.76 to 25.25||1.81 to 29.24||2.66 to 29.26|
|No. of reflns collected||4603||49527||67449|
|Completeness to θmax||97.0%||98.5%||97.9%|
|No. indep. reflns||4603||19,461||25,594|
|No. obsd reflns with (I>2σ(I))||2530||7420||5543|
|No. refined params||279||865||0.542|
|R1 (F) (I>2σ(I))||0.0827||0.0542||0.0533|
|wR2 (F2) (all data)||0.2178||0.1127||0.1076|
|Largest diff peak/hole, e Å-3||1.153 /-1.400||0.464 /-1.079||0.364 /-0.379|
We are indebted to Prof. Dr. Vadapalli Chandrasekhar (IIT Kanpur, India) for a gift of 2,2,3,4,4-pentamethylphosphetanic acid. Dr. Malte Hesse (Universität Bremen) is thanked for the collection of the X-ray diffraction data. The Deutsche Forschungsgemeinschaft (DFG) is gratefully acknowledged for financial support.
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