Electrophilic Routes to Tertiary Adamantyl and Diamantyl Phosphonium Salts

Abstract

In highly nonpolar media both 1-adamantyl and 1-diamantyl triflates are sufficiently stable to react with nucleophiles in a controlled manner. Several tertiary phosphonium triflate salts with a single adamantyl or diamantyl residue were prepared directly in this way, starting with the secondary phosphine. Three compounds with the 1-phosphodiamantane structure were characterised by X-ray.

Key words

ligands - phosphorus - electrophilic addition - adamantly - diamantyl

References and Notes

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1

Present address: Dept. of Chemistry, University of Jaffna, Jaffna, Sri Lanka.

6

Despite the presumed non-existence of authentic (1-Ad)₃P, it is cited in Chemical Abstracts in four distinct patents.

16

An early experiment under more forcing conditions [(1), Cy₂PH, AcOH, 120 ˚C)] failed to produce the desired phosphine.

24

CCDC files 824773-824775 contain the supplementary crystallographic data. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

25

The related t-Bu₃PH cation appears frequently in the CCDC crystallographic database. The average C-P bond length (13 structures) is 1.863 Å; c.f. 1.883 Å in 14.

28

Experimental data:
Caution: The tertiary triflates 2 and 10 are powerful electrophiles and should be treated with care; avoid contact.
Sample Preparation 11 and 12 via 10: Anhydrous AgOTf (105 mg, 0.4 mmol) was added to a solution of 1-bromodiamantane (100 mg, 0.37 mmol) in anhyd 2,2-dimethylbutane (10 mL) at 0 ˚C and stirred with exclusion of light for 1.5 h. The solution was filtered under argon by cannula and the solvent was removed under vacuum at 0 ˚C to afford 1-diamantyl triflate(10) as colourless crystals. ^¹H NMR (500 MHz, CDCl₃, 25 ˚C): d = 1.54-2.40 (m). ^¹³C NMR (125 MHz, CDCl₃, 25 ˚C): d = 118.7 (q, J _CF = 316.7 Hz, CF₃), 109.9 (C1), 43.6 (C10), 42.9 (C2), 42.4 (C7), 37.9 (C5), 36.8 (C8), 36.4 (C6), 32.8 (C3), 32.1 (C9), 24.8 (C4). After repeating on a 1.2-millimolar scale and cannula filtration HPPh₂ (210 mg, 196 µL, 1.12 mmol)was added and the solution was warmed to r.t. After 2 h stirring at r.t., a white solid precipitated. Solvent was removed and the solid was washed with EtOAc and dried in vacuo to give 1-diamantyldiphenylphosphonium triflate(11) as a white solid (506 mg, 92% yield); mp 272-274 ˚C. ^¹H NMR (400 MHz, CDCl₃, 25 ˚C): d = 9.24 (d, 1 H, HP, J _HP = 506 Hz), 8.07 (m, 4 H, H12), 7.74 (m, 2 H, H14), 7.64 (m, 4 H, H13), 2.57 (d, J _HH = 14.2 Hz, 2 H, H3), 2.17 (br m, 1 H, H4), 2.04 (br m, 3 H, H7, H9), 1.92 (br m, 2 H, H2), 1.85 (br m, 2 H, H8), 1.81 (br m, 1 H, H6), 1.77 (br m, 5 H, H10, H3, H8), 1.64 (br m, 3 H, H8, H5). ^³¹P NMR (162 MHz, CDCl₃, 25 ˚C): d = 3.6. ^¹³C NMR (100 MHz, CDCl₃, 25 ˚C): d = 134.8 (d, J _CP = 2.7 Hz, C14), 134.5 (d, J _CP = 9.4 Hz, C12), 130.4 (d, J _CP = 12.3 Hz, C13), 114.2 (d, J _CP = 78.3 Hz, C11), 42.9 (d, J _CP = 37.9 Hz, C1), 37.9 (C10), 37.7 (C2), 37.6 (C6), 36.5 (C8), 36.4 (C7), 36.1 (C5), 32.7 (d, J _CP = 3.8 Hz, C3), 25.2 (d, J _CP = 9.7 Hz, C9), 24.6 (C4). A portion was oxidised: triflate 11 (160 mg, 0.42mmol), t-BuOK (246.8 mg, 2.2 mmol) in CH₂Cl₂ (20 mL), together with 30% H₂O₂ (1.0 mL) were stirred for 14 h. After workup and flash chromatography (EtOAc) 1-diamantyldiphenylphosphine oxide(12) was obtained (124 mg, 76% yield); mp 261-262 ˚C. ^¹H NMR (400 MHz, CDCl₃, 25 ˚C): d = 7.99 (m, 4 H, H12), 7.49 (m, 6 H, H13, H14), 3.11 (d, J _HH = 12.7 Hz, 2 H, H3), 2.03 (br m, 2 H, H2), 1.91 (br m, 1 H, H4), 1.31 (br m, 1 H, H9), 1.76 (br m, 2 H, H7), 1.70 (br m, 5 H, H5, H6, H8), 1.59 (br m, 4 H, H8, H10), 1.43 (d, J _HH = 12.9 Hz, 2 H, H3). ^³¹P NMR (162 MHz, CDCl₃, 25 ˚C): d = 39.6. ^¹³C NMR (100 MHz, CDCl₃, 25 ˚C): d = 132.4 (d, J _CP = 7.5 Hz, C12), 132.2 (d, J _CP = 88.3 Hz, C11), 131.1 (d, J _CP = 2.5 Hz, C14), 128.1 (d, J _CP = 10.7 Hz, C13), 42.7 (d, J _CP = 66.9 Hz, C1), 39.3 (C5), 38.9 (C8), 38.8 (d, J _CP = 4.0 Hz, C7), 37.6 (C6), 37.5 (d, J _CP = 1.4 Hz, C2), 37.3 (C10), 34.1 (C3), 25.9 (d, J _CP = 11.2 Hz, C9), 25.2 (C4). HRMS (ES⁺): m/z calcd for C₂₆H₂₉PO: 389.2034; found: 389.2041.