Phenylpyrazole‐Based Hypervalent Phosphorus Compounds: From Positional Isomerism to Stacking Interactions

Abstract

The lithium salt of 3,5‐dimethyl‐1‐phenyl‐1H‐pyrazole (PyrC6H4Li) reacts with (Et2N)2PCl to give the precursor [PyrC6H4P(NEt2)2] (2), which, after reaction with PCl3, affords PyrC6H4PCl2 (3) in 79 % yield. The phosphorus atom in 3 has four‐coordinate disphenoidal geometry with an axial arrangement of Cl atoms. The length of the hypervalent N–P bond in this compound [1.775(1) Å] is comparable to that of common single bonds. The structure of 3 is better described by canonical formulae containing charges on the N, P, and Cl atoms. The 1H NMR spectrum of 3 in CDCl3 shows five pairs of nonequivalent Me groups, which correspond to the positional isomers that exist in the equilibrium mixture. Compound 3 easily exchanges chlorine with methyl iodide to form the diiodo derivative 4 (PyrC6H4PI2) with nonequivalent P–I bonds. The reduction of 3 with aluminium foil or [GeCl2(diox)] gave cationic diphosphines [(PyrC6H4P)2(μ‐Cl)][AlCl4] (8) and [(PyrC6H4P)2(μ‐Cl)][GeCl3] (9), respectively, with a chloride bridge between the phosphorus atoms. Compounds 4, 8 and 9 show a disphenoidal arrangement around the hypervalent phosphorus atoms. The dichloro and diiodo derivatives 3 and 4 are destroyed on heating in pyridine to give diphosphines [(PyrC6H4PCl)2] (10) and [(PyrC6H4P)2(μ‐I)]+[I] (12), respectively, containing hypervalent (trivalent four‐coordinate) phosphorus. The crystal structure of 10 shows multiple C···C, C···Cl, H···H, and C···H short contacts between the adjacent molecules. Compound 3 exchanges chlorine for oxygen atoms on heating in dimethylformamide to give the dioxide PyrC6H4PO2 (13) with an N–PV distance [1.808(1) Å] even longer than that in 3.

Organophosphorus Compounds in Organic Electronics

“…The reaction of the dichloro precursor 52 (Figure ) in the presence of GeCl 2 gives a face‐to‐face dimer, which is formally an 18 π‐electron dication 53 (Figure ) with “π‐stacked aromaticity” . A similar P−P bridged dimer formation was reported by the same authors for a related P,N,N‐heterocyclic compound, though not being aromatic . Another extraordinary example of a novel aromatic phosphorus system was reported by Cummins et al.…”

“…[88] As imilar PÀP bridged dimer formation was reported by the same authors for ar elatedP ,N,N-heterocyclic compound, though not being aromatic. [89] Another extraordinary example of an ovel aromatic phosphorus system was reported by Cummins et al The highly aromatica nion [P 2 N 3 ] À (54;F igure 10), which is isolobal to the cyclic P 5 anion and the widely explored cyclopentadienyl anion, was obtained through an inorganic "click" reaction of NaN 3 and "P 2 ". The latter is released as an intermediate from P 2 A 2 (A = Anthracene).…”

Structural Variability of R 2 C Adducts of 3a,6a-Diaza-1,4-diphosphapentalene: Tuning the N→P Bonding

“…Considering the structure of 4 it is worth discussing the N→P bonding interaction in greater details. Our previous work concerning pyrazol‐based hypervalent phosphorus compounds has documented the ability of the P atom to form two related but different types of P–N interactions. The first is direct attractive noncovalent interaction with the nitrogen atom, based in large measure on a charge transfer from the N lone pair into the antibonding orbital σ*(P–Cl) that is turned away from the N atom ( 8a , Scheme ).…”

“…The second is covalent interaction caused by big positive charge at the hypervalent phosphorus atom due to P–Cl bonds elongation ( 8b ). The isomers 8a and 8b exist in solution as an equilibrium mixture …”

2,2′‐Azobispyridine in Phosphorus Coordination Chemistry: A New Approach to 1,2,4,3‐Triazaphosphole Derivatives

“…Following our interest in the chemistry of hypervalent phosphorus(III) compounds, we have studied the reaction of 2,2′‐azobispyridine and its reduced form (2,2′‐hydrazobispyridine, hbpy ) with PCl 3 . An open question also concerns the stability of hypervalent phosphorus compounds A and A′ depicted in Scheme , which are analogs of phenylpyrazol‐based hypervalent phosphorus compounds ( B , B′ ) reported previously:…”