Synthesis of New Cationic Donor-Stabilized Phosphenium Adducts and Their Unexpected P-Substituent Exchange Reactions

Abstract

The reaction between two 1,3-dialkylimidazolium-2-carboxylates 1a and 1b and two different dichlorophosphines (RPCl(2), with R = Ph and NEt(2)) led to new donor-stabilized phosphenium adducts. When the reaction was performed with the 1,3-dimethylimidazolium-2-carboxylate 1a and PhPCl(2) in a 2:1 ratio, the phosphine 4a, bearing two imidazolium moieties, was obtained and led to 5a, after an anion exchange reaction with KPF(6), the latter being fully characterized by an X-ray structure analysis. In similar conditions, the bis-imidazolium phosphine or phosphene-di-ium, 4b, which is analogous to 4a, has been obtained by the addition of PhPCl(2) to the 1-dodecyl-3-methylimidazolium-2-carboxylate 1b. However, by the use of dichloro(diethylamino)phosphine, (Et(2)N)PCl(2), instead of PhPCl(2), the reaction with 1a did not afford the biscationic phosphorus product 6a, an analogue to 4a, but, instead, the water-soluble mixed mono-imidazolium chlorophosphine 7a. Subsequently, additional kinetic experiments have been investigated to rationalize the different reactivities observed with imidazolium-2-carboxylates and the phosphorus halide derivatives. We, thus, found that the bis-imidazolium phosphine 4b was very rapidly formed in the above-mentioned reaction and was slowly converted, thereafter, back to the mixed mono-imidazolium chlorophosphine 8b in the presence of the residual starting dichlorophosphine. Additionally, the addition of PhPCl(2) to the phosphene-di-ium 4b represents, to our knowledge, the first example of a P-substituent exchange reaction involving a P-C bond formation in imidazolium phosphines. On the other hand, the air stability and the solubility of these new cationic functional phosphines in different media render such ligands very appealing in coordination chemistry for catalysis in mono- or biphasic media.

Donor‐Stabilized Phosphenium Adducts as New Efficient and Immobilizing Ligands in Palladium‐Catalyzed Alkynylation and Platinum‐Catalyzed Hydrogenation in Ionic Liquids

“…The formation of the phosphorus-carbon bond between the N-heterocycle and the phosphorus atom was confirmed by the presence of a doublet at 141.39 ppm in the 13 C NMR spectrum, with a typical coupling constant 1 J P,C of 47 Hz. [10,11] This observation, combined with a 2:1 ratio for furyl versus imidazolium groups in its proton NMR spectrum, unambiguously proved the formation of the expected ligand 3d.…”

“…[10] Besides, this synthesis provides access to new dicationic or mixed halide donor-stabilized phosphenium adducts by extension of the reactivity of 1 towards others chlorophosphines. [11] Moreover, the measurement of the A 1 symmetric stretching frequency of the related Ni(CO) 3 A C H T U N G T R E N N U N G (3a-c) complexes has shown that the ligands 2 and 3 behave as phosphite-like strong p-acceptors. This unexpected result is the consequence of the C!P bond in imidazolium-2-phosphines which displaces the formal positive charge from the imidazolium ring to the phosphorus center.…”

On the Theme of Amidiniophosphines: Synthesis and Reactivity of Benzo-, Diimidazolo-Tris-Annelated P-Aminodiazaphosphepines

“…15,16 In the P-Ph series, the P-coordinating limit towards a Rh(I) center was shown to be reached for the imidazolo-imidazoliophosphine (mono-N-methylated analogue of A Ph ), competitive Ncoordination being also observed, the dicationic diimidazoliophosphine B Ph being non coordinating at all. 17,12 Considering a promoted oxygen atom as a Lewis acid, 18 the corresponding P-oxides C R , D R can be considered as non-metallic P-coordination complexes. 12b In this case, the P-substituent R was demonstrated to have a critical influence on the oxidation potential of dications B R :…”

First donor stabilized-phosphenium rhodium complexes

“…As a result of this observation and of the recent calculations on donor P-acceptor systems [5], ligands 2 and 3 will be drawn as donor stabilized-phosphenium structure instead of classical imidazolium-2-phosphines. Moreover, this electronic property combined with their hydrophilic character, which strongly depends on the imidazol-2-ylidène number and nature or counter-anion nature [7], renders such ligands very promising for the development of A mixture of imidazolium-2-phosphine hexafluorophosphate (0.246 g, 0.58 mmol) (prepared according to the literature [6]) and [RhCl(1,5-COD)] 2 (0.142 g, 0.29 mmol) (commercial compound from Strem) in CH 2 Cl 2 (7 mL) were stirred at room temperature for 3 h. The solvent was then removed under vacuum to afford a yellow solid (0.383 g, 99%). 1 Scheme 2.…”

“…Besides, among these cationic ligands, the imidazolium-2-phosphines are furthermore very interesting in basic research, because they represent rare examples of base-donor P-acceptor adducts involving an electron rich P III -center as Lewis acceptor [5]. We have thus focused our interest on such ligands, with special emphasis on the development of short and/or easy synthetic methods and recently found a straightforward synthesis of imidazolium-2-phosphines 2a-c and 3 based on the direct addition of chlorophosphines [6,7] to the 1,3-dimethylimidazolium-2-carboxylate 1, see Scheme 1.On the other hand, our preliminary IR studies performed by the measurement of mCO carbonyl absorption band in the related Ni (CO) 3 (2a-c) complexes have shown an unexpected weak basicity of ligands 2 comparable to phosphites. This result could be the consequence of the nature of the C ?…”