Metastable P-Tellurium-Substituted Phosphaalkenes: Formation, ¹²⁵Te- and ³¹P-NMR Spectroscopic Characterization, and Decomposition

Abstract

The formation and decomposition of P-tellurium-substituted phosphaalkenes was followed by ³¹P- and ¹²⁵Te-NMR spectroscopy. Acyclic compounds with C˭P-Te moieties are in general thermally labile, but bulky substituents enhance the lifetime of a number of species. The P-chlorophosphaalkene (Me₃Si)₂C˭PCl (1a) reacts with the disilyltelluride (iPrMe₂Si)₂Te (2) leading to the mixed-substituted telluride (Me₃Si)₂C˭PTeSiMe₂iPr 3a which reacts with another equivalent of 1a furnishing the tellurobis(phosphaalkene) [(Me₃Si)₂C˭P]₂Te (4a). 4a is a shortlived compound decomposing thermally with precipitation of elemental tellurium, leading to a known diphosphabicyclobutane 5a. In a similar way, the bulkier P-chlorophosphaalkene (iPrMe₂Si)₂C˭PCl (1b) reacts with (iPrMe₃Si)₂Te furnishing [(iPrMe₂Si)₂C˭P]₂Te (4b), which loses tellurium much more slowly than 4a and can be kept in cold solutions for an extended time. Reactions of in situ-prepared lithium aryltellurolates LiTeAr 6 – 9 [Ar˭Ph: 6, Ar˭2,4,6-Me₃Ph (˭Mes): 7, Ar˭2,4,6-iPr₃Ph (˭TIP): 8, Ar˭2,4,6-tBu₃Ph (˭Mes*): 9] with 1a provide P-aryltellurophosphaalkenes 10 – 13, which decompose with the loss of diarylditellurides leading to 5a. After a 2 + 4 cycloaddition trapping experiment of 12 with cyclopentadiene, a metastable P-aryltelluro phosphanorbornene 14 was detected by ³¹P-NMR. Reactions of elemental tellurium with P-phosphanylphosphaalkenes (Me₃Si)₂C˭PPR′R′;′ 15 – 17 (R′, R′′˭iPr: 15; R′˭iPr, R′′˭tBu: 16; R′, R′′˭tBu: 17) lead to metastable insertion products (Me₃Si)₂C˭PTePR′R′′ 18 – 20 that decompose with formation of the tellurobisphosphanes (R′R′′P)₂Te 21 – 23, and of the bicyclic diphosphane 5a, which isomerises thermally to the diphosphabicyclooctane 24. The P-di-i-propylphosphanyl-phosphanorbornene 25 dismutates under the action of tellurium into the symmetric diphosphanes iPr₄P₂ and bis-phosphanorbornene 26. The tellurium-free products 24 and 26 were characterized by X-ray crystallography.

GRAPHICAL ABSTRACT

Keywords:

• Phosphaalkenes
• P-Tellurophosphaalkenes
• tellurophosphanes
• diphoshanes
• ¹²⁵Te-NMR
• X-ray crystallography