Toward a 1,4-Diphosphinine-Based Molecular CPS-Ternary Compound

Abstract

Synthesis of the tricyclic 1,3-dithiole-2-thione-derived 1,4-dihydro-1,4-diphosphinine is presented using a base-induced ring formation protocol and chloro­(diethylamino)­(1,3-dithiole-2-thion-4-yl)­phosphane as the starting point. P-oxidation reactions of dihydrodiphosphinine by chalcogens led to bis­(P-oxide), bis­(P-sulfide), or bis­(P-selenide), respectively; all tricyclic compounds were obtained as cis/trans mixtures. 1,4-Dihydro-1,4-diphosphinine was converted into 1,4-dichloro-1,4-dihydro-1,4-diphosphinine. This compound is almost insoluble in organic solvents, furnished selectively the trans-bis­(amino) derivative upon a 2-fold P-substitution reaction with the weak nucleophile potassium bis­(trimethylsilyl)­amide, and reacted also with alcohols ROH (R = nBu, iPr, tBu) to give cis/trans mixtures of the corresponding bis­(alkoxy) derivatives. Furthermore, the dichloro derivative could be reduced to a 1,4-diphosphinine using PnBu3, but, unfortunately, the stubbornly insoluble product could be neither purified nor crystallized. Despite this, we achieved a thermal [4 + 2] cycloaddition reaction of this first CPS-ternary compound with diethylacetylene dicarboxylate to obtain the corresponding diphosphabarrelene, thus providing indirect evidence for the aromatic tricyclic diphosphinine. Detailed density functional theory studies on the formation of 1,4-diphosphinine provided insights into formation pathways as well as NMR, IR, and UV/vis data.

Access to and reactions of P-functional 1,4-dihydro-1,4-diphosphinines fused to two TTF units

“…In the cases of 4d–f , 31 P{ 1 H} NMR monitoring showed a clean conversion into the corresponding isomeric mixtures of desired products with resonance signals (Table 4) comparable with the previously reported chemical shifts from Avarvari 13 and for the 1,3-dithiole-2-thione derived tricyclic compound. 18 But for 4a,b , due to the accessibility of hydrogen atoms at the opposing ring in the TTF unit, reactions with LDA were not selective and the desired 1,4-dihydro-1,4-diphosphinines were obtained just as a minor product ( 4a ) or were not formed at all ( 4b ). The major products which were formed in these reactions were the related mono-bridged compounds ((TTF) 2 PR), also the formation of a precipitate that was not soluble in common solvents could be an indication for oligomeric side-products.…”

“…In the cases of 4d-f, 31 P{ 1 H} NMR monitoring showed a clean conversion into the corresponding isomeric mixtures of desired products with resonance signals (Table 4) comparable with the previously reported chemical shifts from Avarvari 13 and for the 1,3-dithiole-2-thione derived tricyclic compound. 18 But for 4a,b, due to the accessibility of hydrogen atoms at the opposing ring in the TTF unit, reactions with LDA were not selective and the desired 1,4-dihydro-1,4diphosphinines were obtained just as a minor product (4a) or…”

“…We cannot discount this entirely but emphasize the proven efficacy of Me 3 P as a reducing agent for P-chloro 1,4-diphosphinines. [17][18][19] Dalton Transactions Paper +0.43 and +0.57 V, with ΔE 2-1 m of +0.45, +0.35 and +0.64 V, respectively. Our results, measured in CH 2 Cl 2 , have E 1 m for the comparison set ranging from −0.10 to −0.06 V, +0.43 to +0.44 V for E 2 m and ΔE 2-1 m of +0.49 to +0.54 V. The data agreement between the almost identical PhP derivatives IVc and 5e is extremely good; our data in CH 2 Cl 2 are 0.11 to 0.14 V more negative, but ΔE 2-1 m values at +0.49 and +0.50 V must be reckoned to be indistinguishable.…”

“…13 During the past 10 years we have developed a protocol to access new P-functional compounds using a series of stepwise lithiation and phosphanylation of various five-membered ring systems, i.e., 1,3-imidazole-2-thione, 16 1,3-thiazole-2-thione 17 and 1,3-dithiole-2-thione. 18 Of particular interest is that such functional heterocycles can be converted into tricyclic P-amino substituted 1,4-dihydro-1,4-diphosphinines, while the mild subsequent reduction of the related 1,4-dichloro-1,4-dihydro-1,4-diphosphinines provided finally the corresponding tricyclic 1,4-diphosphinine derivatives. 19 Herein, we present first results on synthesis and conversion of P-chloro tetrathiafulvalenes into P-amino substituted 1,4dihydro-1,4-diphosphinines fused to two TTF units and their reactivity with chalcogens together with attempts to obtain the related 1,4-diphosphinines.…”

“…, 1,3-imidazole-2-thione, 16 1,3-thiazole-2-thione 17 and 1,3-dithiole-2-thione. 18 Of particular interest is that such functional heterocycles can be converted into tricyclic P -amino substituted 1,4-dihydro-1,4-diphosphinines, while the mild subsequent reduction of the related 1,4-dichloro-1,4-dihydro-1,4-diphosphinines provided finally the corresponding tricyclic 1,4-diphosphinine derivatives. 19…”