Unsuccessful/successful attempts to produce penta(heteroaryl)-phosphoranes/ -arsoranes R5E (E = P, As; R = 2-furyl, 2-thienyl)

Uwe V. Monkowius, Stefan Nogai, Hubert Schmidbaur

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Abstract

Tri(2-thienyl)phosphine (1) has been transformed into chlorotri(2-thienyl) phosphonium chloride (3) in the reaction with hexachloroethane, into tetra(2-thienyl)phosphonium bromide (4) in a NiBr2-catalyzed quaternization with 2-bromothiophene, and into the p-tolylsulfonyliminotri(2- thienyl)phosphorane (6) using "chloramine T". Attempts to generate the homoleptic penta(2-thienyl)phosphorane (2-C4H3S) 5P (5) by treating 3, 4, 6 or the known (PhO)3P = NSO 2C6H4-2-Me (9) with 2-thienyllithium were unsuccessful. Tri(2-furyl)phosphine (2) was converted into the related imine 7, but the reaction of 7 or of 9 with 2-furyllithium failed to give (2-C 4H3O)5P (8). It was only with the strained phosphorane Ph(C12H8)P=NSO2C6H 4-4-Me (C12H8 = 2,2′-biphenylylene) (10) that with 2-C4H3OLi the corresponding phosphorane Ph(C12H8)P(C4H3O-2)2 (11) could be obtained (31P NMR: δ-106.7 ppm). In the arsenic series, tri(2-thienyl)- and tri(2-furyl)arsine (12, 13) were converted into the tosylimino compounds (14, 15) and successfully transformed into the homoleptic arsoranes with 2-C4H3E-Li: penta(2-thienyl) - (16) and penta(2-furyl)-arsorane (17) are stable colourless crystalline solids, the NMR spectra of which indicate rapid pseudo-rotation in solution. The single crystal structure analysis of 17 shows an only slightly distorted trigonal-bipyramidal configuration. In crystals of the phosphine 2 and the arsine 13 the molecules have a propeller configuration with approximate C3v symmetry for the former, but Cs symmetry for the latter. The crystal structures of the precursors or intermediates 3, 4, 6, 9 and 10 have also been determined.

Original languageEnglish
Pages (from-to)1610-1617
Number of pages8
JournalDalton Transactions
Issue number10
DOIs
StatePublished - 21 May 2004
Externally publishedYes

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