Alleviating Strain in Organic Molecules by Incorporation of Phosphorus: Synthesis of Triphosphatetrahedrane

Abstract

Phosphatetrahedranes ( t BuCP) 2 and ( t BuC) 3 P were recently reported and represent the first tetrahedranes containing a mixed carbon/phosphorus core. Herein, we report that tetrahydrofuran (THF) solutions of the parent triphosphatetrahedrane HCP 3 may be generated in 31% yield (NMR internal standard yield) by combining [Na(THF) 3 ][P 3 Nb(ODipp) 3 ] (Dipp = 2,6diisopropylphenyl), INb(ODipp) 3 (THF), and bromodichloromethane in thawing THF. While HCP 3 was found to be stable in dilute THF solutions for extended periods of time, the concentration of the solution at −40 °C led to the formation of a black precipitate, which has been tentatively assigned as a polymerized form of HCP 3 . HCP 3 reacts readily with (dppe)Fe(Cp*)Cl (dppe = 1,2-bis(diphenylphosphino)ethane, Cp*= η 5 -C 5 Me 5 ) in the presence of Na[BPh 4 ] to form a purple cationic iron complex of triphosphatetrahedrane (50% yield), which was structurally characterized in a single-crystal X-ray diffraction experiment. Additionally, we present a series of homodesmotic equations analyzed via quantum chemical calculations that suggest triphosphatetrahedrane is the least strained of the mixed C/P phosphatetrahedranes.

Formation of the elusive tetrahedral P 3 N molecule

“…The incorporation of only one nitrogen atom into the P 4 ( 2 ) tetrahedron increases the strain energy in P 3 N ( 10 ) to 195.1 kJ mol −1 . This is in a same region as the previously reported strain energy in P 3 CH ( 9 ) (156.2 kJ mol −1 ) ( 26 ), which is higher than that of cyclopropane (119.6 kJ mol −1 ) ( 34 ). These results are in agreement with our calculated dissociation reaction enthalpies for various P/N tetrahedrons (table S9).…”

“…To sum up, the identification of the tetrahedral molecule 1,2,3triphospha-4-azatricyclo [1.1.0.0 2,4 ] butane (P 3 N, 10) progresses our fundamental understanding of the chemical bonding of highly strained binary pnictogen molecules carrying nitrogen and phosphorus and affords a formidable strategy to prepare traditionally "nonexisting" interpnictides such as PN 3 and P 2 N 2 via nonequilibrium chemistry, which have escaped any preparation and spectroscopic detection thus far. A "radical" approach to a "P 3 transfer chemistry" (26) or the controlled combination of diphosphorus (P 2 ) (37,38), diphosphatriazolate anion (P 2 N 3 − ) (39,40), and phosphorus mononitride (PN) (41,42) in solution might enable a preparative synthesis and isolation of molecular P 3 N (10) in the future.…”

“…Cummins et al developed a formidable preparative synthetic approach to binary pnictogen tetrahedral molecules exploiting transition metal complexes acting as effective anionic cyclic triphosphorus (P 3 3− ) transfer agents; when combined with an electrophile (E 3+ ; E = P, As, Sb), P 4 (2), AsP 3 (5), and SbP 3 (8) were prepared (20)(21)(22)(23)(24)(25). This strategy was expanded to synthesize the tetrahedron 1,2,3-triphospha tricyclo [1.1.0.0 2,4 ] butane (P 3 CH, 9) (26).…”

Capture the missing: formation of (PbBi3)− and {[AuPb5Bi3]2}4− via atom exchange or reorganization of the pseudo‐tetrahedral Zintl anion (Pb2Bi2)2−

“…1 Stepwise "carbon copying" of the C atoms on the tetrahedral vertexes by P atoms resulted in a series of tetrahedral derivatives, such as neutral ( t BuC) 3 P, ( t BuC) 2 P 2 , and (HC)P 3 . [2][3][4][5] Isoelectronic replacement of one vertex of P 4 by another pnictogen atom or by chalcogenide cations Ch + (Ch = S, Se, Te) has led to the isolation of AsP 3 or the corresponding (ChP 3 ) + cations, respectively. [6][7][8] (Pseudo-)tetrahedral Zintl-type anions derived from partial or full isoelectronic replacement of vertexes of P 4 by group 13-15 element (semi-)metal atoms paved way to a series of main group (pseudo-)tetrahedral anions with overall charges of −8, −5, −4, −3, or −2, which were used as starting materials for the formation of a multitude of binary or ternary (semi-)metal complexes and clusters.…”

Recent Breakthroughs in P4 Chemistry: Towards Practical, Direct Transformations into P1 Compounds

“…Unlike many other industrially relevant inorganic small molecules (e.g. H 2 , N 2 ), the challenge in P 4 functionalization typically arises not because the molecule lacks kinetic reactivity, [8] but rather from the difficulty in channeling its reactivity through a specific mechanistic pathway to cleanly provide a single product of interest. This reflects the fact that any transformation of the P 4 tetrahedron into P 1 products must necessarily achieve six separate P−P bond‐cleavage steps alongside many distinct P−E bond‐formation steps, all in a controlled manner.…”