Imidovanadium(V) Complexes as Reaction Partners for Kinetically Stabilized Phosphaalkynes: Synthesis of 1,2,4-Azaphosphavanada(V)-cyclobutenes, 1,3,5-Triphosphabenzenes, and 1H-1,2,4-Azadiphospholes

Abstract

Cycloaddition reactions of the kinetically stabilized phosphaalkynes 1 with the imidovanadium(v) trihalides 9 furnish the 1,2,4-azaphosphavanada(v)cyclobutenes 10. The stability of these novel metallacyclic compounds depends solely on the substitutents of the imido unit. Thus, the imidovanadium(v) species 9 with tertiary alkyl groups on the N atom form stable addition products with 1 while in the cases of compounds 9 with a lower degree of substitution at N (primary and secondary alkyl groups) the primarily formed adducts 10 undergo irreversible decomposition to afford the 1H-1,2,4-azadiphospholes 13. Reactions of an excess of the phosphaaalkyne 1 with the vanadium complexes 9 furnish the corresponding triphosphabenzenes 8 in good yields (36-68%). A catalytic reaction course has been demonstrated for the all-tert-butyl system 1a/9a in which the metallacyclic species 10a serves as the catalytically active species. Poisoning of the catalyst leads to a second reaction pathway, which results in formation of the azatetraphosphaquadricyclanes 16. By means of the stepwise use of different phosphaalkynes 1a,b this methodology provides the first access to the differently substituted triphosphabenzenes through cyclotrimerization.

Phosphaorganische Chemie: Panorama und Perspektiven

“…Das im ersten Schritt gebildete Addukt isomerisiert langsam bei Raumtemperatur. Aufbauend auf Arbeiten von Regitz et al zur effizienten Synthese von 1,3,5‐Triphosphininen durch Trimerisierung von Phosphaalkinen in Gegenwart von Vanadium( V )‐Imido‐Katalysatoren wurde über [2+2]‐Cycloadditionen mit V V ‐,105 Ti IV ‐ und Zr IV ‐Imidokomplexen106 berichtet [Gl. (39) ].…”

Synthesis and Structure of a 1,3‐Diphosphacyclobutadienediide: An Aniomesolytic Fragmentation of a 1,3‐Diphosphetane‐2,4‐diyl in Solution

“…The characteristic deshielding of the atoms in the central P 2 C 2 unit indicates a PC π‐bonding system ( δ 31 P=200.3, δ 13 C Ring =126.0 ppm (t, 2 J C,P =59.2 Hz)). These resonance signals lie in the range typical for cyclic π‐delocalized phospha‐aromatics, such as P 2 ( t BuC) 3 ⋅[K(thf)] ( δ 31 P=187.6 ppm)13 and( t BuC) 3 P 3 ( δ 31 P=232.6, δ 13 C=218 ppm, 1 J P,C =77 Hz) 14. The shielding of the silicon atoms of the SiMe 3 group ( δ 29 Si=−17.3 ppm (t, 2 J Si,P =18.3 Hz)) supports the interpretation of a “negative hyperconjugation” in accord with the X‐ray analysis.…”

Synthese und Struktur eines 1,3‐Diphosphacyclobutadiendiids – aniomesolytische Fragmentierung eines 1,3‐Diphosphetan‐2,4‐diyls in Lösung

“…Die charakteristische Entschirmung der Atome der zentralen P 2 C 2 ‐Einheit spricht für ein PC‐π‐Bindungssystem ( δ 31 P=200.3, δ 13 C Ring =126.0 ppm (t, 2 J C,P =59.2 Hz)). Die Signallagen sind im erwarteten Bereich für cyclisch π‐delokalisierte Phosphorarene wie P 2 ( t BuC) 3 ⋅[K(thf)] ( δ 31 P=187.6 ppm)13 und ( t BuC) 3 P 3 ( δ 31 P=232.6, δ 13 C=218.0 ppm ( 1 J C,P =77 Hz)) 14. Die Abschirmung der Siliciumatome der SiMe 3 ‐Gruppen ( δ 29 Si=−17.3 ppm (t, 2 J Si,P =18.3 Hz)) stützt die Interpretation als “negative Hyperkonjugation” in Übereinstimmung mit den Ergebnissen der Röntgenstrukturanalyse.…”