Formation of [Ph₂P₅]⁺, [Ph₄P₆]²⁺, and [Ph₆P₇]³⁺ Cationic Clusters by Consecutive Insertions of [Ph₂P]⁺ into PP Bonds of the P₄ Tetrahedron

Abstract

Many transition-metal complexes containing a broad variety of degraded or aggregated P n units, resulting from P 4 activation, have been discovered and described. [1][2][3] In comparison, the functionalization of P 4 with main-group fragments represents a new and rapidly developing field. Recently, Bertrand and co-workers have found that carbenes react with white phosphorus, with or without inducing its fragmentation or aggregation [4] . Similarly, heavier carbenelike main-group-element derivatives containing Al, [5] Ga, [6] Tl, [7] and Si, [8] insert into the PÀP bonds of the P 4 tetrahedron. [9] Krossing and co-workers have reported the insertion of in situ-prepared, highly electrophilic, carbene-analogous [PX 2 ] + cations (X = Br, I) into one of the P À P bonds of P 4 , yielding phosphorus-rich binary cage cations [P 5 X 2 ] + (1, see below). Although highly reactive, these cations could be successfully isolated using non-oxidizing, weakly coordinating counteranions of type [Al(OR) 4 ] À (OR = polyfluorinated aliphatic alkoxide). [10] In contrast to the well-developed chemistry of oligophosphorus anions, [11] 1 represents the only structurally characterized cationic homoatomic phosphorus cluster reported.www.angewandte.de acid/chloropnictogen systems with P 4 and the behavior of the reaction products in organic solvents.

Synthesis of Cationic R2P5+ Cages and Subsequent Chalcogenation Reactions

“…The solvent-free reaction of alkyl-substituted phosphanes R 2 PCl with GaCl 3 and P 4 in a 1:1:1 stoichiometry proceeds according to a previously reported melt approach [7] and yields R 2 P 5 + cations 1 a + -1 d + as [GaCl 4 ] À salts (Scheme 2).…”

“…[5]. This is a characteristic feature of bridgehead P atoms in butterfly-shaped [19] or related EP 4 cages (E = Ga, [20] Si, [21] PX 2 (X = Br, I, [3] Ph [7] )). The molecular structures of the cations are depicted in Figure 3.…”

“…However, isolation was hampered by the presence of the additional equivalent of GaCl 3 , leading to the separation of a yellow oil upon addition of n-hexane. [7] The 31 P{ 1 H} NMR spectrum of the reaction mixture containing 1 eA C H T U N G T R E N N U N G [GaCl 4 ] displayed several complex multiplet resonances of low intensity. [22] The singlet is superimposed by the doublet of the isotopomer Cy 2 PA C H T U N G T R E N N U N G ( 77 Se)Cl·GaCl 3 ( 1 JA C H T U N G T R E N N U N G (PSe) = 854 Hz; for example, iPr 2 PA C H T U N G T R E N N U N G ( 77 Se)Cl: 1 JA C H T U N G T R E N N U N G (PSe) = 840 Hz).…”

“…[4] Chloro-and organo-substituted P 5 + -cage compounds, for example, were obtained from mixtures of dichlorophosphanes RPCl 2 , ECl 3 (E = Al, Ga) and P 4 in fluorobenzene. [7] The facile insertion of up to two additional Ph 2 P + moieties into the PÀP bonds of 1 e + led us to speculate as to whether this reactivity might be exploited for the preparation of other cationic phosphorus-element cages. [6] Furthermore, additional Ph 2 P + insertion steps led to the formation of the larger cages Ph 4 P 6 2+ (2 2+ ) and Ph 6 P 7 3 + (3 3 + ; Figure 1).…”

Phosphacycles as Building Blocks for Main Group Cages

“…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.…”