Bis‐Ylide Ligands from Acyclic Proximal Diphosphonium Precursors

Abstract

Keywords: Ylides / Ylide ligands / Phosphorus / Rhodium / Electrostatic interactions 1,2-or 1,3-Phenylene-diphosphonium bis-ylides have been prepared and their stabilities compared by analysis of the effects of the substitution pattern of the phenylene bridge and the steric hindrance of the P-alkyl substituents in the diphosphonium precursors RPh 2 P + (C 6 H 4 ) + PPh 2 RЈ (R,RЈ = Me, Et). In the o-phenylene series, the vicinity of the phosphorus centers allows the distal P + /Ccharge separation of the mono-ylide intermediate to be canceled by the formation of a cyclic ylidophosphorane. The ring strain in the latter was released through phenylene-P(σ 5 ) bond cleavage to afford relaxed diphosphonium bis-ylides, which were isolated as [a] 4058 Scheme 3. Preparation of the acyclic diphosphoniums 10 and 11 from o-dppb via the mono-ethyl phosphonium 9. .org phonium ylides. In contrast, in the m-phenylene series, in which the two phosphonium centers are in remote positions, the bis-ylide could be fully characterized. By reaction with a cationic rhodium(I) precursor, the latter bis-ylide was shown to act as a strongly donating carbon ligand, generalizing recent observations in the ortho series. [6] The role of steric and electrostatic interactions in the control of structural and reactivity features of acyclic proximal diphosphoniums has been highlighted herein. Experimental SectionGeneral: Diethyl ether, toluene, and thf were dried and distilled from sodium/benzophenone, pentane, dichloromethane, 1,1,2,2-tetrachloroethane (tce), and acetonitrile over P 2 O 5 . All other reagents were used as commercially available. All reactions were carried out under argon using Schlenk and vacuum-line techniques. 1 H, 13 C, and 31 P NMR spectra were recorded with Bruker DPX 300 and Avance 500 spectrometers. Chemical shifts (δ) are given in ppm with positive values to high frequency measured relative to tetramethylsilane for 1 H and 13 C NMR, and to H 3 PO 4 for 31 P NMR. Coupling constants (J) are given in Hz. 103 Rh chemical shifts are given to high frequency from δ( 103 Rh) = 3.16 MHz.Phosphonium 9: Ethyl trifluoromethanesulfonate (574 μL, 4.48 mmol) was added to a solution of 1 (2.0 g, 4.48 mmol) in tce (12.0 mL) and the solution was then stirred for 12 h at 110°C. After evaporation of the solvent, the solid residue was washed with Et 2 O (30.0 mL), affording 9 as a white powder (2.41 g, 86 %); m.p. 68-69°C. 1 H NMR (CD 3 CN, 25°C): δ = 7.85-7.50 (m, 14 H, H ar ), 7.42-7.22 (m, 6 H, H ar ), 6.99-6.90 (pseudo-t, J HH = J HP+ = 6.9 Hz, 4 H, H ar ), 3.57 (dq, J HH = 7.5, J HP+ = 12.9 Hz, 2 H, CH 2 ), 1.37 (dt, J HH = 7.5, J HP+ = 20.4 Hz, 3 H, CH 3 ) ppm. 13 C NMR (CD 3 CN, 25°C): δ = 142.8 (dd, J CP+ = 14.9, J CP = 14.9 Hz, C), 139.2 (d, J CP+ = 11.3 Hz, CH ar ), 136.5 (pseudo-t, J CP+ = J CP = 11.8 Hz, C), 135.1 (d, J CP+ = 2.8 Hz, CH ar ), 134.5 (d, J CP+ = 2.9 Hz, CH ar ), 133.3 (dd, J CP+ = 9.6, J CP = 1.9 Hz, CH ar ), 133.0 (d, J CP = 19.1 Hz, CH ar ), 131.6 (d, J CP = 9.9 Hz, CH ar ), 131.3 (d, J CP+ = 12.4 Hz, CH ar ), 13...

Classification of the Electronic Properties of Chelating Ligands in cis-[LL′Rh(CO)2] Complexes

“…2144.0 cm –1 ) are indeed very similar at the B3PW91 level of calculation. The meta -phenylene-bis-phosphonium ylide RhCO 2 complex 3b was recently prepared and the experimental v IR av (CO) = 2018.0 cm –1 is very close to that of the ortho -isomer 3a ( v IR av (CO)) = 2017.5 cm –1 ) . These findings also favor an insulating o -phenylene bridge (Scheme ).…”

A Palladium(II) Complex of a C4 Chelating Bis(NHC) Diphosphonium Bis(ylide) Ligand

“…These two related systems lie respectively in phosphino- and NHC-phosphonium ylide ligands of catalytically active metal complexes. Bis­(ylides) featuring two lone pairs of electrons centered on the same carbon atom or distributed over two positions present unique reactivity that make them attractive, very electron rich carbon bases. Due to the availability of phosphonium precursors, complexes of diphosphonium bis­(ylides) have been more exemplified over the years .…”

1,2-Bis(di-tert-butylphosphino)imidazole (dtbpi): A Versatile Imidazole-Based, Rigid, Bulky Bisphosphine Ligand for Transition Metals

“…The presence of the very bulky NP( t Bu) 2 donor next to the ylidic methylene group should undoubtedly favor the Z isomer from a steric point of view, as pointed out earlier. Furthermore, as Canac and Chauvin have shown recently, the σ-donating abilities of phosphonium ylides are exceptionally high, exceeding even those of “abnormal” N-heterocyclic carbene ligands, which are considered among the strongest neutral donor ligands known. , Therefore, electronic considerations are also in favor of the Z isomer, since the strong ylidic donor would preferentially coordinate trans to the chloride ligand. However, with regard to the rearrangement observed for E -6 , we cannot exclude that the formation of only the Z isomer is the consequence of an analogous rearrangement reaction.…”