1,4‐Addition von Grignard‐Reagentien an 2,4,6‐Tri‐<i>tert</i>‐butyl‐1,3,5‐triphosphabenzol

Renner, Jens; Bergsträßer, Uwe; Binger, Paul; Regitz, Manfred

doi:10.1002/ange.200250182

“…In addition, an extra set of three doublet of doublets was observed for 3 as a result of variable halogen (X = Cl or Br) occupancy of the different P1ÀX sites.In the 31 P{ 1 H} (C 6 D 6 ) spectra [12] of the reaction mixture from which 2 and 3 were isolated there were matching doublet and triplet signals attributed to a minor unidentified product, possibly an intermediate. Although there have been a number of studies relating to the reactivity of the 1 with a variety of substrates [6,7,13] the formation of 2 and 3 is without precedent. Scheme 1.…”

mentioning

confidence: 99%

“…In the 31 P{ 1 H} (C 6 D 6 ) spectra [12] of the reaction mixture from which 2 and 3 were isolated there were matching doublet and triplet signals attributed to a minor unidentified product, possibly an intermediate. Although there have been a number of studies relating to the reactivity of the 1 with a variety of substrates [6,7,13] the formation of 2 and 3 is without precedent. Remarkably, these structures show a trivalent arsenic atom lying above the rearranged P 3 C 3 (tBu) 3 fragments from the 1,3,5-triphosphabenzene ring, the halogen atoms having migrated from the arsenic to the ring phosphorus atoms, possibly because oxidative addition of AsX 2 + to 1 would lead to As V which is known to be is a relatively unstable oxidation state.…”

mentioning

confidence: 99%

Phosphacycles as Building Blocks for Main Group Cages

Townsend

¹

,

Shadbolt

²

,

Green

³

et al. 2013

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As part of an ongoing interest in phosphorus/carbon compounds [1] we have focused on the reactivity and synthetic utility of possible sources of electrophilic PX 2 + and AsX 2 + fragments with a view to accessing novel main group architectures. It has been suggested [2] that there is an analogy between these reactive pnictenium species and carbenes. For example, Krossing and co-workers reported [3] that PX 3 (X = Br, I) reacts in CH 2 Cl 2 at À78 8C with Ag[Al(OR F ) 4 ] (R F = C(CF 3 ) 3 ) and P 4 to give the novel phosphorus rich molecules [P 5 X 2 ][Al(OR F ) 4 ] through a process thought to involve the insertion of the electrophilic carbenoid species [PX 2 ][Al-(OR F ) 4 ] into a PÀP bond of P 4 . Allied to this interesting observation is the report by Weigand and co-workers [4] that P 4 reacts, possibly by a similar reaction pathway, in a melt of Ph 2 PCl and GaCl 3 (1:1 at 60 8C) to form a structurally related molecule [P 5 Ph 2 ][GaCl 4 ]. Similarly, Burford and co-workers have used related methodology to prepare an extensive series of catena-phosphorus cations. [5]In our initial studies we focused on the reaction of 2,4,6tri-tert-butyl-1,3,5-triphosphabenzene (1) with latent sources of PX 2 + and AsX 2 + cations. It is interesting to note that 1 reacts with the Arduengo-type carbene 1,3,4,5-tetramethylimidazol-2-ylidene to give a ring-contracted 1,2,4-triphosphole, [6] whereas the silicon analogues, stable bis-(amine)silylenes, afford (4+1) cycloaddition products. [7] It has also been found experimentally that in the case of the reaction of 1 with sources of H + , CH 3 [9] h 1 -P-bonded cationic adducts are formed.As a first step we used density functional theory (see Supporting Information) to compare the relative thermodynamic stabilities of possible products which might result from the reaction of 1 with EX 3 (E = P, As ; X = Cl, Br) and the Lewis acid GaCl 3 . These calculations indicated that under thermodynamic control, a PX 2 + electrophile could react with 1 to give a h 1 -P-bonded adduct. For the phosphenium reagents, alternative products arising from electrophilic attack at carbon, ring contraction (analogous to the product from the reaction with an Arduengo carbene [6] ) or 1,2-addition are less favorable. In contrast, for the arsenium systems, although h 1 -As coordination is preferred, the energy difference between the alternative products is small. We can in fact envisage a possible reaction pathway to such a h 1 -P/Asbonded cation where the reaction of ECl 3 (E = P or As) with GaCl 3 leads to the direct formation of the ion-separated electrophilic species [ECl 2 ] + [GaCl 4 ] À , which can then be captured by 1 (Scheme 1 a). However, there is an alternative and perhaps more plausible pathway not involving a free ECl 2 + cation and that is through a synchronous S N 2 (P/As) push-pull (GaCl 3 ) process as illustrated in Scheme 1 b. [10] This alternative route can be related to the proposal by Wild, Radom, and co-workers that phosphenium cations can be readily transferred between unsaturate...

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“…Although there have been a number of studies relating to the reactivity of the 1 with a variety of substrates [6,7,13] the formation of 2 and 3 is without precedent. Scheme 1.…”

mentioning

confidence: 99%

“…Although there have been a number of studies relating to the reactivity of the 1 with a variety of substrates [6,7,13] the formation of 2 and 3 is without precedent. Remarkably, these structures show a trivalent arsenic atom lying above the rearranged P 3 C 3 (tBu) 3 fragments from the 1,3,5-triphosphabenzene ring, the halogen atoms having migrated from the arsenic to the ring phosphorus atoms, possibly because oxidative addition of AsX 2 + to 1 would lead to As V which is known to be is a relatively unstable oxidation state.…”

mentioning

confidence: 99%

Phosphacycles as Building Blocks for Main Group Cages

Townsend¹,

Shadbolt²,

Green³

et al. 2013

View full text Add to dashboard Cite

As part of an ongoing interest in phosphorus/carbon compounds [1] we have focused on the reactivity and synthetic utility of possible sources of electrophilic PX 2 + and AsX 2 + fragments with a view to accessing novel main group architectures. It has been suggested [2] that there is an analogy between these reactive pnictenium species and carbenes. For example, Krossing and co-workers reported [3] that PX 3 (X = Br, I) reacts in CH 2 Cl 2 at À78 8C with Ag[Al(OR F ) 4 ] (R F = C(CF 3 ) 3 ) and P 4 to give the novel phosphorus rich molecules [P 5 X 2 ][Al(OR F ) 4 ] through a process thought to involve the insertion of the electrophilic carbenoid species [PX 2 ][Al-(OR F ) 4 ] into a PÀP bond of P 4 . Allied to this interesting observation is the report by Weigand and co-workers [4] that P 4 reacts, possibly by a similar reaction pathway, in a melt of Ph 2 PCl and GaCl 3 (1:1 at 60 8C) to form a structurally related molecule [P 5 Ph 2 ][GaCl 4 ]. Similarly, Burford and co-workers have used related methodology to prepare an extensive series of catena-phosphorus cations. [5]In our initial studies we focused on the reaction of 2,4,6tri-tert-butyl-1,3,5-triphosphabenzene (1) with latent sources of PX 2 + and AsX 2 + cations. It is interesting to note that 1 reacts with the Arduengo-type carbene 1,3,4,5-tetramethylimidazol-2-ylidene to give a ring-contracted 1,2,4-triphosphole, [6] whereas the silicon analogues, stable bis-(amine)silylenes, afford (4+1) cycloaddition products. [7] It has also been found experimentally that in the case of the reaction of 1 with sources of H + , CH 3 [9] h 1 -P-bonded cationic adducts are formed.As a first step we used density functional theory (see Supporting Information) to compare the relative thermodynamic stabilities of possible products which might result from the reaction of 1 with EX 3 (E = P, As ; X = Cl, Br) and the Lewis acid GaCl 3 . These calculations indicated that under thermodynamic control, a PX 2 + electrophile could react with 1 to give a h 1 -P-bonded adduct. For the phosphenium reagents, alternative products arising from electrophilic attack at carbon, ring contraction (analogous to the product from the reaction with an Arduengo carbene [6] ) or 1,2-addition are less favorable. In contrast, for the arsenium systems, although h 1 -As coordination is preferred, the energy difference between the alternative products is small. We can in fact envisage a possible reaction pathway to such a h 1 -P/Asbonded cation where the reaction of ECl 3 (E = P or As) with GaCl 3 leads to the direct formation of the ion-separated electrophilic species [ECl 2 ] + [GaCl 4 ] À , which can then be captured by 1 (Scheme 1 a). However, there is an alternative and perhaps more plausible pathway not involving a free ECl 2 + cation and that is through a synchronous S N 2 (P/As) push-pull (GaCl 3 ) process as illustrated in Scheme 1 b. [10] This alternative route can be related to the proposal by Wild, Radom, and co-workers that phosphenium cations can be readily transferred between unsaturate...

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An Iron‐Catalyzed Route to Dewar 1,3,5‐Triphosphabenzene and Subsequent Reactivity

Barrett

¹

,

Diefenbach

²

,

Mahon

³

et al. 2022

Angewandte Chemie

2

0

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The application of an alkyne cyclotrimerization regime with an [Fe(salen)] 2 -μ-oxo (1) catalyst to triphenylmethylphosphaalkyne (2) yields gram-scale quantities of 2,4,6-tris(triphenylmethyl)-Dewar-1,3,5-triphosphabenzene (3). Bulky lithium salt LiHMDS facilitates a rearrangement of 3 to the 1,3,5-triphosphabenzene valence isomer (3'), which subsequently undergoes an intriguing phosphorus migration reaction to form the ring-contracted species (3''). Density functional theory calculations provide a plausible mechanism for this rearrangement. Given the stability of 3, a diverse array of unprecedented transformations was investigated. We report novel crystallographically characterized products of successful nucleophilic/electrophilic addition and protonation/oxidation reactions.

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1,4‐Addition von Grignard‐Reagentien an 2,4,6‐Tri‐tert‐butyl‐1,3,5‐triphosphabenzol

Cited by 5 publications

References 22 publications

Phosphacycles as Building Blocks for Main Group Cages

Phosphacycles as Building Blocks for Main Group Cages

Phosphacycles as Building Blocks for Main Group Cages

An Iron‐Catalyzed Route to Dewar 1,3,5‐Triphosphabenzene and Subsequent Reactivity

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