Small Cyclopolyphosphinophosphonium Cations: Systematic Development of Fundamental catena‐Phosphorus Frameworks

Abstract

Recognizing that catenation of carbon is principally responsible for the diversity and extent of organic chemistry, the "diagonal relationship" between carbon and phosphorus in the Periodic Table is often quoted [1,2] in the discussion of the numerous catenated polyphosphines [2][3][4][5][6] and polyphosphorus anions. [2][3][4][7][8][9][10][11][12] catena-Phosphorus cation systems are less well developed despite the classical chemistry of phosphonium salts, but the pioneering contributions of Schmidpeter and coworkers [13][14][15] and Schmutzler et al. [16] have highlighted new aspects of structure and bonding that prompt the establishment of a comprehensive polyphosphinophosphonium series. Our high-yielding and facile methods for the synthesis of the prototypical phosphinophosphonium 1, [17] diphosphinophosphonium 2, [18] and cyclotetraphosphinophosphonium 5 [18] cations have now been applied to the preparation of the first examples of cyclodiphosphinophosphonium 3 and cyclotriphosphinophosphonium 4 cations (Scheme 1). Isolation of these new frameworks is surprising in light of the exclusive formation of 5 over possible tetra-and hexaphosphorus derivatives with phenyl substituents at the phosphorus centers.[18] Derivatives of 3 and 4 provide representative frameworks that complete a series of the smallest cyclopolyphosphinophosphonium cations 3-5, and their characterization is pivotal in the systematic development of fundamental phosphorus chemistry.31 P NMR spectra of reaction mixtures containing (PtBu) 3 (6 a) with excess MeOTf show quantitative formation of [(PtBu) 3 Me][OTf] (3 a-OTf; Figure 1 a and Scheme 2 a). The spectrum can be approximated as an AMX [19] spin system and is consistent with the solid-state structure of 3 a-OTf (Figure 2 a), thus demonstrating stereoselective methylation of 6 a at either of the syn-configured centers to give a racemic Scheme 1. Prototypical catena-polyphosphinophosphonium cation frameworks. 31 P NMR spectra at 101.3 MHz: a) mixture of MeOTf (2 equiv) and (PtBu) 3 , which shows the approximate AMX pattern of 3 a-OTf; b) mixture of MeOTf (2 equiv) and (PCy) 4 , which shows the approximate A 2 MX pattern of 4 a-OTf; c) experimental (top) and simulated (inverted) AB 2 X pattern of pure 4 b-OTf.

Dimers and Trimers of Diphosphenes: A Wealth of Cyclo‐Phosphanes

“…[22] The inner angles of the P 3 ring vary from 58.55(3) to 60.97(3)8; thus, all angles are close to the ideal value of 608, which is typical for cyclo-triphosphanes. [39][40][41][42][43][44] The PÀC and PÀCl distances are all within the range of typical single bonds. The two Ter substituents are at an angle of 65.48 to one another (angle between the least-squares planes of the Pbound aryl groups), and thus the central P 4 Cl 2 scaffold is effectively shielded by the ortho-mesityl groups.…”

catena‐Phosphorus Cations

“…Triphosphinophosphonium ( D ) and tetraphosphinophosphonium ( E ) cations were first proposed on the basis of elemental analysis data for compounds isolated from the alkylation of cyclotetra‐ and cyclopentaphosphines with CCl 4 or MeI,40–42 but examples have only recently been definitively characterized 39. 43–46 Triflate salts of cations with frameworks C‐1 ,44 D ‐1 ,44 and E‐1 45 can be prepared in high yields by methylation or protonation ( D ‐1 only) of cyclopolyphosphines (Scheme ). Frameworks D ‐2 and E‐2 are also formed by insertion of a phosphenium ion into cyclotri‐ and tetraphosphines to give ring‐expanded cations (Scheme ).…”

Lewis Base Stabilized Oxophosphonium Ions

“…[7,8] The area has seen a recent resurgence [6,[9][10][11][12][13][14][15][16][17][18][19][20][21][22][23] which may be due to the popularity of the isovalent singlet carbenes and, as such, the use of phosphenium ions as ligands in transition metal chemistry has been exploited. [24][25][26][27][28][29][30] In the context of main group chemistry, [31] phosphenium ions have been involved in the preparation of phosphinophosphonium systems, [32][33][34][35][36][37][38][39][40] as well in reactions with P 4 , [39,[41][42][43][44] and other reagents. [15] Approximately 20 years ago, the synthesis of terminal thioxo-and selenoxophosphonium ions were targeted by Burford et al, [45][46][47] however these attempts resulted in the formation of dimeric structures B.…”