Synthesis, Reactivity, and Computational Analysis of Halophosphines Supported by Dianionic Guanidinate Ligands

Abstract

The reported chemistry and reactivity of guanidinate supported group 15 elements in the +3 oxidation state, particularly phosphorus, is limited when compared to their ubiquity in supporting metallic elements across the periodic table. We have synthesized a series of chlorophosphines utilizing homo-and heteroleptic (dianionic)guanidinates and have completed a comprehensive study of their reactivity. Most notable is the reluctancy of these four-membered rings to form the corresponding Nheterocyclic phosphenium cations, the tendency to chemically and thermally eliminate carbodiimide and the scarcely observed ring expansion by insertion of a chloro(imino)phosphine into a P-N bond of the P-N-C-N framework.Computational analysis has provided corroborating evidence for the unwillingness of the halide abstraction reaction by demonstrating the exceptional electron acceptor properties of the target phosphenium cations and the underscoring strength of the P-X bond.

Lewis Base Stabilized Oxophosphonium Ions

“…[1] There have been regular contributions [2][3][4][5][6] to the area of N-heterocyclic phosphenium ions A since the first reports 30 years ago. [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.…”

A phosphenium cation supported by a seven-membered thiophene based ring system

“…26 These short P−Cl bonds explain the lack of reactivity with halide-abstracting agents observed in both compounds 4 and 6, as they are more tightly bound to phosphorus. 27 The solid-state structure of compound 7 shows a well-separated cation−anion pair with the distance between the oxygen and phosphorus being 3.8 Å, well outside the sum of the van der Waals radii for P−O (Α vdW = 3.3 Å). The P−N bond is on average 1.625(1) Å, which is slightly shorter than compounds 4 and 6, but still consistent with other related NHPs.…”

Reduction of dichloro(diaza-phospha)stibanes – isolation of a donor-stabilized distibenium dication

“…In addition, a higher-lying cyclic isomer 2c (30.3 kJ mol −1 ) bearing a SbCl 2 group was located at the PES when studying the intrinsic reaction for the different isomerization processes as depicted in Fig. L = amidinate donors) of Ragogna et al, 41,42 Jones et al, 43 Dehnicke et al, 44 and S. Schulz et al 45 which are described as base stabilized dihalopnictanes. Isomer 2c is a typical intermediate lying in a very shallow energy valley, therefore cannot be observed in the 31 P NMR spectra.…”

“…Tbt 2 Sb 2 2.642(1), Ter 2 Sb 2 2.6558(5), [Ar*N(Si i Pr 3 )] 2 Sb 2 2.7104(5), Ar* = 2,6-bis(diphenylmethyl)-4-isopropylphenyl) 52,55-60 displaying a considerable degree of π-bonding (cf. 42,61 However, unlike the planar N 4 P 2 Sb 2 bicyclic fragment in 6, the (NCN) 2 P 2 scaffold has a puckered arrangement of the two five-membered P 2 N 2 C rings, where the two planes are 100.4°to each other (Fig. 59 Hence, the eight-membered heterocycle can also be considered as two condensed five-membered rings.…”

“…59 Hence, the eight-membered heterocycle can also be considered as two condensed five-membered rings. 42,61 Additionally, the molecular geometry about the phosphorus atoms is trigonal pyramidal and the P-P distances are in the range of typical P-P single bonds. 59 Moreover, the short P-N distances of 1.613(2) Å are in the typical range of PN double bonds (∑r cov (PvN) = 1.62 Å).…”