Reduction of Bis(phosphonio)isophosphindolides to Phosphane-Functionalized Benzo[c]phospholides

Abstract

Keywords: Phosphorus heterocycles / Phospholides / Nickel complexes / Reductions / NMR spectroscopy Bis(phosphonio)benzo[c]phospholides (isophosphindolides) alkali metals followed a more complicated course and gave a mixture of 2, 3, and the substitution product 8, which was 1a,b have been found to react with magnesium or alkali metal naphthalenides MC 10 H 8 (M = Li, Na, K) with reduction further reduced to the phosphanido-substituted benzo-[c]phospholide 9. The latter could be formed selectively by of one or both of the phosphonio groups. The main products are the mono-or bis(phosphanyl)-substituted heterocycles 2, first converting 1a into 8 by treatment with PhNa and then treating this with lithium. NMR data of the phosphane-3, 6, 7, which have been characterized by in situ NMR studies and in some cases isolated. Subsequent reaction of 2 with substituted benzo[c]phospholides and the structural features of 4 are discussed. excess [Ni(CO) 4 ] gave the complex 4, which has been characterized by X-ray diffractometry. Reactions of 1a with proceed with selective cleavage of one PϪC bond in each

Structural and Electronic Properties of Neutral Phosphoniobenzo[c]phospholides

“…3-Diphenylphosphanyl-1-triphenylphosphoniobenzo[c]-phospholide (3) was prepared as described previously, [8] by reduction of bis(triphenylphosphonio)benzo[c]phospholide chloride (1[Cl]) with active magnesium, which was generated by the decomposition of [Mg(THF) 3 (anthracene)] [10] in boiling toluene (Scheme 1). Further investigation of this reaction revealed that direct use of Mg/anthracene as a reducing agent gave slightly lower yields of the product, but required less effort for the preparation of the reagent and shorter induction times.…”

“…The chemical shifts of the exocyclic phosphorus nuclei fall in the expected ranges associated with the different types of functionalities. The resonance of the endocyclic phosphorus atom in 2 appears more upfield than that in 3, whereas the corresponding resonances in 6, 7 are more downfield and exhibit similar chemical shifts as the bis(methyldiphenylphosphonio)benzo[c]phospholide cation (δ 31 P ϭ 229.0 [8] ). Besides the resonances of the C 6 H 5 groups, the 1 H NMR spectra of all the compounds display the expected ABCD patterns for the protons of the benzophospholide moiety.…”

“…The molecular structures are shown in Figure 1, and selected bond lengths are given in Table 3. The corresponding data of the cation 1 [16] and the anionic complex 5 [8] were included for comparison.…”

“…[17] Endocyclic and exocyclic PϪC distances in the zwitterions 2, 3, 6 and 7 are similar to those in the ions 1 and 5, [8,16] and are intermediate between pure single and double bond lengths. Comparison of the C1ϪP2 and P2ϪC3 bond lengths in the same molecule Table 3.…”

“…[7] In the course of the investigation of the chemical properties of bis(phosphonio)benzophospholides, we established that reduction of 1 gives easy access to both neutral, zwitterionic phosphoniobenzophospholides 2, 3, and phosphanylbenzophospholide anions 4 (see Scheme 1). [8] Although a structural study of the carbonylnickel complex 5 revealed that the endocyclic bond lengths and angles are very similar to those of cation 1, [8] one can expect that an the inductive electron-withdrawing power of the substituents in the 3-position of the fused ring system. Computational studies of monophosphoniobenzophospholides, as well as the corresponding anions with no phosphonio substituents, and cations with two phosphonio substituents, allowed for the interpretation of the special properties of the neutral species in terms of a partial π-bond localisation.…”