Cationic imidazolium‐2‐phosphanes were obtained by the addition of a chlorophosphane (R2PCl, R = Ph, iPr or Cy) to 1,3‐dimethylimidazolium‐2‐carboxylate without the need for a purification step. An additional anion exchange reaction with KPF6 led to the corresponding halide‐free ligands in excellent yields. The molecular structure of one of them was examined both in the solid state and in solution. The lone pair of electrons on the phosphorus atom is not delocalised to the imidazolium fragment and thus remains available for further metal coordination. As such compounds can be described as phosphenium cations stabilised by a N‐heterocarbene donor base, the electronic properties of the Lewis acceptor phosphorus centre was evaluated upon nickel tricarbonyl coordination, and the properties are surprisingly similar to those found for phosphites. The stronger π‐acceptor character of these imidazolium‐2‐phosphanes relative to that of neutral tertiary phosphanes can thus explain the higher catalytic activities observed with the corresponding rhodium complexes in styrene hydroformylation reactions. Additionally, a preliminary study of platinum coordination chemistry indicated that the steric demand of 1,3‐dimethylimidazolium‐2‐phosphanes is comparable to mixed arylalkylphosphanes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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.

The catalytic properties of rhodium complexes containing the α‐, β‐, or γ‐amino‐phosphane ligands Ph2PCH2NEt2 (α‐P,N‐1), Ph2PCH(Ar)NHPh [α‐P,N‐2; Ar = η6(o‐C6H4Cl)Cr(CO)3], Ph2PCH2NPh2 (α‐P,N‐3), Ph2PCH2CH(Ph)NHPh (β‐P,N), Ph2PCH2(o‐C6H4–NMe2) (γ‐P,N‐1), Ph2PCH(o‐C6H4–CH2NHPh) (γ‐P,N‐2), and the α,β‐diamino‐phosphane ligand Et2NCH2P(Ph)CH2CH(Ph)NHPh (α,β‐N,P,N), in styrene hydroformylation have been examined. The results show that the activity increases when the number of backbone carbon atoms linking P and N decreases from 3 to 1. IR and 31P HPNMR studies in solution show that all P,N ligands adopt exclusively a κ1‐P coordination mode in rhodium chloride carbonyl complexes under high CO pressure. In the solid state a κ1‐P‐α‐amino‐phosphane coordination has been ascertained by X‐ray methods in trans‐[RhCl(CO)(γ‐P,N‐1)2]. In contrast, an equilibrium between the κ2‐P,N and κ1‐P‐coordination modes has been observed as a function of the CO pressure for the complex containing the β‐P,N ligand. The basicity of the dangling amino group also plays an important role on the catalytic activity and a mechanism involving the nitrogen function in the catalytic cycle is proposed.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

No abstract

The functional phosphine Ph2PCH2C(O)NPh2 (L 1 ) was obtained by P−C selective coupling of Ph2PCl with Li[CH2 C( O)NPh2] and we have studied the influence of the −NPh2 substituent on the reactivity of the corresponding enolate Li[Ph2PCH C( O)NPh2] toward Ph2P−Cl and M−Cl bonds (M = Pd, Pt). A selective P−C coupling reaction with Ph2PCl allowed the synthesis of the new diphosphine ligand (Ph2P)2CHC(O)NPh2 [bis(diphenylphosphino)-N,N-diphenylacetamide] (L 2 ). The dicationic dinuclear complex [Cu2{(Ph2P)2CHC(O)NPh2-P,P,O}2](BF4)2 (3) has been obtained from the reaction of [Cu(NCMe)4](BF4) with L 2 . A preliminary X-ray diffraction study revealed a μ2-η3 tripod-like bonding for L 2 in this centrosymmetric dimeric complex:  each copper atom is P,O-chelated by one ligand and P-bonded to the other ligand. An eight-membered Cu2P4C2 ring is thus formed with the functional diphosphine ligand. The dynamic behavior has been studied in CHCl3 solution of mono- and binuclear copper(I) complexes of L 1 and L 2 . Reversible oxygen-metal dissociation occurs in the presence of donor solvents such as NCMe or SMe2. The reaction of Li[Ph2PCH C( O)NPh2] with [(C N)Pd(μ-Cl)2] afforded the complexes [(C N)Pd{Ph2PCH C( O)NPh2}] [(9) (C N) = dimethylbenzylamine (dmba); (10) (C N) = 8-methylquinoline (8-mq)]. The molecular structure of [(8-mq)Pd{Ph2PCH C( O)NPh2}] has been determined by single-crystal X-ray diffraction:  it crystallizes in the monoclinic space group P21/c with Z = 4 in a unit cell of dimensions a = 8.801(2) Å, b = 31.483(6) Å, c = 10.939(2) Å, β = 101.37(2)°. The structure has been solved from diffractometer data by Patterson and Fourier methods and refined by full-matrix least-squares methods on the basis of 2863 observed reflections to R and R w values of 0.0268 and 0.0338, respectively. A temperature dependence of the reaction of Li[Ph2PCH C( O)NPh2] with [PtCl2(NCPh)2] has been observed which leads to cis-Pt[Ph2PCH C( O)NPh2]2 (11) at −60 °C and to trans-Pt[Ph2PC{C(NH)Ph}{C(O)NPh2}]2 (12) at 0 °C. The high reactivity of cis-Pt[Ph2PCH C( O)NPh2]2 toward p-MeC6H4NCO leads to two diastereoisomeric products cis-Pt[Ph2PCH{C(O)N(p-MeC6H4)}{C(O)NPh2}]2 (16a,b in a 1:1 ratio), which contain new chiral heterodifunctional phosphines.

The reaction of the C=N bond in PhCH=NPh with the carbanionic species Ph2PCH2-, leading to the N-phenyl beta-aminophosphine Ph2PCH2CH(Ph)NHPh, L1, is described. This molecule reacts with different organic electrophiles to afford related compounds Ph2PCH2CH(Ph)NPhX (X = SiMe3, L2; COPh, L4), [Ph2MePCH2CH(Ph)NHPh]+(I-), L3, and [Ph2PCH2CH(Ph)N(Ph)CO]2, L5, containing two amido and two phosphino functions. The coordination properties of L1, L2, and L4 have been studied in palladium chemistry. The X-ray structure of [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] shows the bidentate coordination mode for the L1 ligand with equatorial C(Ph)-N(Ph) phenyl groups. [PdCl2(Ph2PCH2CH(Ph)NHPh-kappaP,kappaN)] crystallizes at 298 K in the space group P2(1)/n with cell parameters a = 10.689(2) A, b = 21.345(3) A, c = 12.282(2) A, beta = 90.294(12) degrees, Z = 4, D(calcd) = 1.526. The reaction between 2 equiv of L1 and [PdCl(eta3-C3H5)]2 affords the [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] complex in which an unexpected N-H.Cl intramolecular interaction has been observed by an X-ray diffraction analysis. [PdCl(eta3-C3H5)(Ph2PCH2CH(Ph)NHPh-kappaP)] crystallizes at 298 K in the monoclinic space group Cc with cell parameters a = 10.912(1) A, b = 17.194(2) A, c = 14.169(2) A, beta = 100.651(9) degrees, Z = 4, D(calcd) = 1.435. Neutral and cationic alkyl or allyl palladium chloride complexes containing L1 are also reported as well as a neutral allyl palladium chloride complex containing L4. Variable-temperature 31P[1H] NMR studies on the allyl complexes show that the eta3/eta1 allyl interconversion is enhanced by a positive charge and also by a N-H.Cl intramolecular interaction.

The chemoselective reactivity of metal-coordinated phosphino enolates has been studied by the reactions of cis-[Ni{R‘2PCH C( O)R}2] (R = Ph, p-C6H4Me, Me; R‘ = Ph, iPr, not all combinations) and [(C N)Pd{Ph2PCH C( O)Ph}] (C N = o-C6H4CH2NMe2, dmba or C10H8N, 8-mq) with different metal electrophiles. In the reaction of cis-[Ni{Ph2PCH C( O)Ph}2] (1a) with [PtCl2(COD)] (COD = 1,5-cyclooctadiene), a transmetalation of the P,O ligands was observed, yielding the known complex cis-[Pt{Ph2PCH C( O)Ph}2] (3). However, reaction of cis-[Ni{R‘2PCH C( O)R}2] with anhydrous CoI2 afforded the heterobinuclear complexes cis-[Ni{R‘2PCH C( O)R}2]CoI2 (5a, R = Ph, R‘ = Ph; 5b, R = p-C6H4Me, R‘ = Ph; 5c, R = Me, R‘ = Ph; 7, R = Ph, R‘ = iPr) which contain the phosphino enolate ligand in an unusual chelating-bridging μ-η1(O):η2(P,O) coordination mode in a nonplanar NiO2Co unit. The magnetic properties of these complexes are discussed. The SHOP-type catalyst [Ni(Ph){Ph2PCH C( O)Ph}(PPh3)] also behaved as an oxygen-donor metalloligand toward CoI2 to give a paramagnetic Co(II) complex. In contrast, reaction of [(C N)Pd{Ph2PCH C( O)Ph}] with [Au(PPh3)]+ occurred with formation of [(dmba)Pd{Ph2PCH(AuPPh3)C(O)Ph}](BF4) (4a) in which a Cenolate−Au bond has been formed while the P,O chelate has remained coordinated to palladium. This reaction generates a new stereogenic center, as also evidenced by 1H NMR spectroscopy. The solid state structures of complexes 4a·1/2C7H8 and 5b·CH2Cl2 have been determined by single-crystal X-ray diffraction:  4a·1/2C7H8 crystallizes in the triclinic space group P1̄ with Z = 2 in a unit cell of dimensions a = 16.778(4) Å, b = 14.269(5) Å, c = 10.838(6) Å, α = 79.27(4)°, β = 71.59(3)°, and γ = 72.68(2)°; 5·CH2Cl2 crystallizes in the monoclinic space group P21/n with Z = 4 in a unit cell of dimensions a = 12.940(1) Å, b = 18.329(2) Å, c = 18.495(2) Å, and β = 91.627(8)°. The structures have been solved from diffractometer data by direct and Fourier methods and refined by full-matrix least-squares methods on the basis of 7240 (4a·1/2C7H8) and 3644 (5b·CH2Cl2) observed reflections to R and R w values of 0.0363 and 0.0406 (4a·1/2C7H8) and 0.040 and 0.038 (5b·CH2Cl2), respectively.

Synthesis of imidazolium carboxylate compounds was efficiently achieved by electrochemical reduction of imidazolium precursors under very mild conditions.