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Light-Induced Rearrangement of Thioether-Substituted Phosphanide Ligands: Scope and Limitations of a Remarkable Isomerization

Lookup NU author(s): Dr Keith Izod, Dr Ewan Clark, Professor William Clegg, Dr Ross Harrington

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Abstract

Treatment of the thioether-substituted secondary phosphanes R²PH(C₆H₄-2-SR¹) [R² = (Me₃Si)₂CH, R¹ = Me (1_PH), iPr (2_PH), Ph (3_PH); R² = tBu, R¹ = Me (4_PH); R² = Ph, R¹ = Me (5_PH)] with nBuLi yields the corresponding lithium phosphanides, which were isolated as their THF (1-5_Pa) and tmeda (1-5_Pb) adducts. Solid state structures were obtained for the adducts [R²P(C₆H₄-2-SR¹)]Li(L)_n [R² = (Me₃Si)₂CH, R¹ = nPr, (L)_n = tmeda (2_Pb); R² = (Me₃Si)₂CH, R¹ = Ph, (L)_n = tmeda (3_Pb); R² = Ph, R¹ = Me, (L)_n = (THF)_1.33 (5_Pa); R² = Ph, R¹ = Me, (L)_n = (12-crown-4)₂ (5_Pc)]. Treatment of 1_PH with either PhCH₂Na or PhCH₂K yields the heavier alkali metal complexes [{(Me₃Si)₂CH}P(C₆H₄-2-SMe)]M(THF)_n [M = Na (1_Pd), K (1_Pe)]. With the exception of 2_Pa and 2_Pb, photolysis of these complexes with white light proceeds rapidly to give the thiolate species [R²P(R¹)(C₆H₄-2-S)]M(L)_n [M = Li, L = THF (1_Sa, 3_Sa–5_Sa); M = Li, L = tmeda (1_Sb, 3_Sb–5_Sb); M = Na, L = THF (1_Sd); M = K, L = THF (1_Se)] as the sole products. The compounds 3_Sa and 4_Sa may be de-solvated to give the cyclic oligomers [[{(Me₃Si)₂CH}P(Ph)(C₆H₄-2-S)]Li]₆ ((3_S)₆) and [[tBuP(Me)(C₆H₄-2-S)]Li]₈ ((4_S)₈), respectively. A mechanistic study reveals that the phosphanide-thiolate rearrangement proceeds via intramolecular nucleophilic attack of the phosphanide center at the carbon atom of the substituent at sulfur. For 2_Pa/2_Pb competing intramolecular b-deprotonation of the n-propyl substituent results in the elimination of propene and the formation of the phosphanide-thiolate dianion [{(Me₃Si)₂CH}P(C₆H₄-2-S)]²⁻.

Publication metadata

Author(s): Izod K, Clark ER, Foster P, Percival RJ, Riddlestone IM, Clegg W, Harrington RW

Publication type: Article

Publication status: Published

Journal: Chemistry: A European Journal

Year: 2013

Volume: 19

Issue: 19

Pages: 6094-6107

Print publication date: 07/03/2013

ISSN (print): 0947-6539

ISSN (electronic): 1521-3765

Publisher: Wiley - V C H Verlag GmbH & Co. KGaA

URL: http://dx.doi.org/10.1002/chem.201203918

DOI: 10.1002/chem.201203918

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