Novel Reactions of Phosphaalkynes in the Coordination Sphere of tert-Butylimido- vanadium(V) Complexes: A Simple Synthesis of 3-Aza-1,2,4,6-tetraphosphaquadricyclanes and 1,3,5-Triphosphabenzenes

Abstract

Dedicated to Professor Dieter Seebach on the occasion of his 60th birthday Cyclooligomerization reactions of phosphaalkynes in the coordination sphere of transition metals in which the metal complex fragment is incorporated in the product have played an important role in the development of phosphaalkyne chemistry.[1] Significant examples are the cyclodimerization of tert-butylphosphaacetylene (5a) to give the tricyclic zirconium complex 1, [2] cyclotrimerizations to give the vanadium and hafnium complexes 2[3] and 3, [4] and the formation of the zirconium and hafnium complexes 4[5] by cyclotetramerization. Treatment of 1, 3, and 4 with hexachloroethane leads to detachment of the metal complex fragments and formation of tBu-substituted 1,3,5,7-tetraphosphacubane (cyclodimerization of the residual molecule), [6] 1,3,5-triphosphabenzene (14a), [4] and 1,3,5,7-tetraphosphabarrelene. [5] Reactions of 2 with the same reagent have not yet been investigated. We now report on the chemoselective cyclooligomerization [7] of phosphaalkynes 5 a ± e with the vanadium(v) compounds tBuNVCl 3´D ME (6) [8] (DME 1,2-dimethoxyethane) and tBuNVCl 3 (13) [9] to produce the title compounds in good yields.Reaction of 5 a ± e with 6 in a molar ratio of 4:1 in toluene followed by column chromatography on alumina affords the previously unknown azatetraphosphaquadricyclanes 7 a ± e as yellow solids in yields of 47 ± 76 % (not optimized; Table 1).The elemental analyses and mass spectra (Table 2) indicate that the heteropolycyclic compounds are formed from four molecules of the phosphaalkyne 5 with loss of one molecule of an alkyne RCCR (see Scheme 1) and incorporation of the imide ligand from the vanadium compound 6.As an example the NMR data of 7 a are discussed here (for further spectroscopic data of the compounds 7, see Table 2).[ Table 2. Selected spectroscopic data for the azatetraphosphaquadricyclanes 7.[a]

Substituent effect on low coordination phosphorus chemistry

“…Apparently, kinetic effects play here an important role as can be shown by a detailed analysis of the reaction mechanism which will be published elsewhere [18]. 1,3,5-Triphosphinine 3 (R: tBu) has been synthesized by a metal catalyzed cycloaddition of 1 [7,8]. The stabilities of the possible isomers of 3 (R: H) have been investigated computationally in the Schleyer group [19].…”

“…The most widely used compound in the cycloaddition reactions is tBuC"P (1) [5], which is undefinitely stable at ambient conditions. Many of the most remarkable and often highly symmetric structures such as the 1,3-isodiphosphinine (2) [6], 1,3,5-triphosphinine (3) [7,8] and tetraphosphacubane (4) [9] -all of them bearing the R: tBu substituents -were obtained by using (1) as starting material. In the understanding of the electronic structure of these compounds the substituent alkyl group (R: tBu) is usually considered to play a minor role.…”

[1 + 4]-Cycloaddition of a stable silylene to 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene

“…11 In our studies on the reactions of the stable silylene Si[(NCH 2 Bu t ) 2 C 6 H 4 -1,2] 1 we became interested in the reaction of 1 with 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene 2. The latter has only recently been synthesised by metal-induced cyclotrimerisation of the phosphaalkyne Bu t CP 12,13 and although its structure and PE spectrum have been reported, 14 its chemistry has not been studied in depth. Binger and coworkers 15 have described the synthesis of tetraphosphabarrelene and semibulvalene derivatives by addition of different phosphaalkynes to 2.…”

Azadiphosphaindane‐1,3‐diyls: A Class of Resonance‐Stabilized Biradicals

“…[12,19] During the reaction, the colorless solutions turned orange, indicating the formation of the desired product (Scheme 4). This could be confirmed by 31 P NMR spectroscopy; all heteroindanediyls 1 (R = Dmp, Ter, tBu Bhp) could be identified by a characteristic singlet resonance (d = 280-285 ppm), which compares well with related 1,2,5-azadiphospholes (tBuC) 2 (m-P) 2 NtBu (d = 286 ppm) [35,36] or biradicals A (276 ppm) [19] and B (221, 258 ppm). [19] However, depending on the steric demand of R, different follow-up reactions were observed (Scheme 4).…”