Phosphino Groups Research Articles

Synthesis, characterisation and complexation of phosphino disilenes

The treatment of disilenide Tip2SiSi(Tip)Li (1, Tip = 2,4,6-iPr3C6H2) with P-chloro phosphines affords the phosphino disilenes (2a-d; a: R = Ph, b: R = iPr, c: R = Cy, d: R = tBu), which were characterised by multinuclear NMR spectroscopy for 2a-d and a single crystal X-ray diffraction study in case of 2c. As an alternate synthetic method, the diphenyl derivative 2a could also be prepared by reaction of LiPPh2 with the thermally unstable iododisilene, Tip2SiSi(Tip)I (3), which in turn was obtained by oxidation of 1 with stoichiometric amounts of iodine. Providing the first example for a SiSi bond with an iodo functionality, disilene 3 was fully characterised by multinuclear NMR and X-ray diffraction. The thermal rearrangement of phosphine disilene 2avia a C–H insertion reaction yields the diastereomeric mixture of a 1-phospha-2,3-disilaindane 4. The structure of the cis-diastereomer of 4 was determined by X-ray diffraction. Finally, the synthesis of first transition metal complex of 2a and 2b by their coordination to the [Pd(PCy3)] fragment is reported. The solid state structure of complex 5a reveals η2-coordination of the SiSi bond of the phosphino disilene 2a with an intermediate bonding mode between π-complex and metallacyclopropane rather than coordination of the phosphino group.

Directed ortho Metallation Chemistry and Phosphine Synthesis: New Ligands for the Suzuki-Miyaura Reaction

We describe the use of the phosphinic amide moiety as an effective directed ortho metallation group for the incorporation of various phosphino groups onto a benzene ring to generate phosphine ligands. These ligands were used to generate active palladium catalysts for the Suzuki―Miyaura reaction in which deactivated aryl bromides and some aryl chlorides were used as substrates. Surprisingly and interestingly, the (2-alkylphenyl)phosphine derivatives were found to be especially active. The stereoelectronic and electronic features of the ligands were probed by use of selenium oxidation products and Vaska's rhodium complexes, respectively. Some unusual features were observed, specifically relating to the inductive effects of the alkyl side chains in relation to the electron-withdrawing phosphinic amide functions. The two probes were also compared, and the results were related to the catalytic data obtained from the Suzuki reactions. Quite unexpectedly, the ligands generate catalysts with good activity despite their being relatively electron-poor. This low electron density, resulting from the phosphinic amide functionality, renders them stable to oxidation and hydrolysis for over six months while exposed to air. Additionally, the use of the phosphinic amide directing group is unusual and rare, and has not, to our knowledge, been noted before in the preparation of phosphine ligands.

A hydroxyaminophosphane derived from 2-imidazolidone and its unusual structure in solution

Abstract A novel hydroxyamino phosphane was synthesised through the reaction of 2-imidazolidinone with ClPPh2 and subsequently reaction of the resulting bisphosphino derivative with the Grignard reagent BrMgC5H11. The interaction of the pentyl substituent with one of the two phosphino groups and the structure in solution is shown by multinuclear NMR-spectroscopy..

Rigid Bis(tetrathiafulvalenes) Doubly Bridged by Phosphino Groups and Derivatives: Synthesis and Intramolecular Mixed Valence State

The synthesis and structural characterization of the λ5-bis(phosphine sulfide) and the bimetallic complexes bis[phosphino-M(CO)5] (M = Mo, W) of the 3,4-dimethyltetrathiafulvalene (ortho-DMTTF)-based rigid dimer (PPh)2(o-DMTTF)2, containing a central 1,4-dihydro-1,4-diphosphinine ring, are described. Single-crystal X-ray analyses have been performed for the trans isomers (PhPX)2(o-DMTTF)2 (X = S, Mo(CO)5, and W(CO)5) and for the cis isomer [PhPW(CO)5]2(o-DMTTF)2. Planar or slightly folded boat-type conformations are observed for the central six-membered ring, together with different packings characterized by short intermolecular S···S contacts. The optical signature of the oxidized species in the case of the free ligand (PPh)2(o-DMTTF)2 has been evidenced by UV−vis spectroelectrochemistry measurements. Solution EPR measurements on the radical cation species of (PPh)2(o-DMTTF)2 definitely assess the full delocalization of the unpaired electron over both electroactive TTF units, with an associated coupling of 0.48 G with 12 equivalent protons. The EPR signal of the dication proves the radical nature of this species, in favor of a triplet ground state. The radical cation of the cis-[PhPW(CO)5]2(o-DMTTF)2 isomer was also investigated by EPR, for which the observed hyperfine structure demonstrates the extended delocalization of the electron, together with a larger coupling constant with the phosphorus nuclei. DFT calculations for the radical cation of (PPh)2(o-DMTTF)2 afford a boat-type conformation for the central ring and a SOMO consistent with a full delocalization of the electron over both TTF units. Moreover, the calculations indicate that in the case of the dication of (PPh)2(o-DMTTF)2 the triplet state is more stable by 11.7 kcal mol−1 than the singlet state.

Studies on the 1,2-Migrations in Pd-Catalyzed Negishi Couplings with JosiPhos Ligands

We report an initial investigation with the goal of determining the factors that control the 1,2-migration in the Negishi cross-coupling, which is promoted by palladium catalyst systems generated with JosiPhos ligands. Several of the factors that were demonstrated to be important for the 1,2-migration include (1) the nucleophilicity of the organometallic reagent, which possibly influences the transmetalation step in direct competition with the intermediate beta-hydride elimination of the alkenyl Pd(II) species; (2) the structural features of the vinyl tosylates and phosphates, in which substrates possessing a bulky C1 substituent displayed highest propensity for undergoing the 1,2-migration under the coupling reaction conditions; and (3) the structure of the JosiPhos ligand, where both the sterical bulk and choice of substituents on the ferrocenyl phosphino group greatly influence the catalytic activity of the palladium complex and its capacity to facilitate the 1,2-migration.

Unprecedented rearrangement during the formation of P–P homoatomic N-phosphino formamidine complexes

A variety of homoatomic P–P donor–acceptor homoleptic (R = R′) and heteroleptic (R ≠ R′) N-phosphino formamidine complexes [ iPr 2N–C(H) N–PR 2–PR′ 2]Cl were synthesized from the addition of N-phosphino formamidine (phosfam) donor reagent iPr 2N–C(H) N–PR 2 on halogenophosphane compounds R′ 2PCl which are synthetic sources for the corresponding phosphenium derivatives R 2P +. We have demonstrated that the dynamic equilibrium observed between the different species is shifted either completely to the side of the free species or to the side of the donor–acceptor adduct [ iPr 2N–C(H) N–PPh 2–PPh 2]Cl by changing the solvent or by varying the temperature. Activation parameters of Δ S ≠ = (−130 ± 7.2) J mol −1 K −1, Δ H ≠ = (8.4 ± 0.6) kJ mol −1 and Δ G ≠ (298.15 K) = (53.6 ± 2.3) kJ mol −1 were determined by an Eyring analysis over the temperature range of 193–293 K. The negative entropy of activation is consistent with an associative pathway and the low value of Δ H ≠ suggests that the energy barrier for this reaction is entropically controlled. Phosphine–phosphenium adducts is the most appropriate term to describe the dynamic process observed at variable temperature for complexes [ iPr 2N–C(H) N–PR 2 → PR′ 2] +, but the 31P NMR chemical shift and the calculated electronic charges are more in favor of a phosphinophosphonium Lewis drawing [ iPr 2N–C(H) N–PR 2–PR′ 2] +. Formation of the homoatomic P–P heteroleptic formamidine complexes [ iPr 2N–C(H) NPR′ 2PR 2]Cl (R = Ph, R′ = Et, iPr) results in the formal insertion of the phosphino group of the corresponding alkyl chlorophosphanes R′ 2PCl into the N–P bond of the starting phosfam ligand iPr 2N–C(H) N–PR 2. Computed data are in agreement with the transient formation of a heteroatomic N–P intermediate [ iPr 2N–C(H) N(PR 2)PR′ 2]Cl, which then rearranges to the more thermodynamically favored homoatomic P–P compound [ iPr 2N–C(H) N–PR 2–PR′ 2]Cl.

β-Phosphinoethylboranes as Ambiphilic Ligands in Nickel−Methyl Complexes

The ambiphilic β-phosphinoethylboranes Ph2PCH2CH2BR2 (BR2 = BCy2 (1a), BBN (1b)), which feature the ethano spacer CH2CH2 between the Lewis acidic boryl and Lewis basic phosphino groups, were synthesized in nearly quantitative yields via the hydroboration of vinyldiphenylphosphine. Compounds 1a,b were fully characterized by elemental analysis and by NMR and IR spectroscopy. X-ray crystallographic studies of compound 1b revealed infinite helical chains of the molecules connected through P···B donor–acceptor interactions. The ability of these ambiphilic ligands to concurrently act as donors and acceptors was highlighted by their reactions with (dmpe)NiMe2. The zwitterionic complexes (dmpe)NiMe(Ph2PCH2CH2BCy2Me) (2a) and (dmpe)NiMe(Ph2PCH2CH2[BBN]Me) (2b) were generated via the abstraction of one of the methyl groups, forming a borate, and intramolecular coordination of the phosphine moiety to the resulting cationic metal center. Compound 2b was characterized by X-ray crystallography. Furthermore, B(C6F5)3 abstracts the methyl group of a coordinated borate ligand to generate a free, three-coordinate borane center in [(dmpe)NiMe(1a)]+[MeB(C6F5)3]– (3).

First Catenane‐Containing Phosphino Groups: A Step toward a Catenane Ligand

A novel [2] catenane containing a diphenylphosphino group on each ring was prepared. Synthesis of the new catenane involved the use of tetraamide rings to form an efficient pseudorotaxane intermediate. The catenane was found to be applicable as a ligand for metal-catalyzed reactions such as Suzuki-Miyaura coupling.

Internal‐rotation and inversion potential energy surfaces for methylamine and methylphosphine

AbstractUsing the HF, MP2, and DFT methods with a 6‐311G** basis set, we examine the internal‐rotation and inversion of the amino and phosphino groups in methylamine and methylphosphine. The resulting energy surfaces are reported as a function of rotation and inversion descriptors. Both surfaces are characterized by several special points: three minimum energy states, three first‐order internal‐rotation transition states, six first‐order inversion transition states, and six second‐order inversion transition states. The MP2 method gave better agreement with experiment. For methylamine, the MP2 energy barrier for internal‐rotation is 8.73 kJ/mol; for first‐order inversion it is 22.80 kJ/mol and for second‐order inversion it is 22.41 kJ/mol. For methylphosphine, the MP2 energy barriers are 7.53, 149.88, and 149.65 kJ/mol, respectively. The energy barriers include ZPE correction contributions. © 2007 Wiley Periodicals, Inc. Int J Quantum Chem, 2008

Synthesis of Highly Functionalized Alkenylphosphines by Lewis Acid‐Mediated Silylphosphination of Substituted Propiolates.

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Amphiphilic Polymer-Supported Phosphine-Rh Complexes

Amphiphilic polymer-supported triarylphosphine ligands A and B were designed and prepared in order to use them in a water-based biphasic catalytic system. Thus, polymeric rhodium complexes of A and B prepared in situ by mixing the polymeric ligands and [Rh(acac)(CO)2](P/[Rh] = 5:1) were applied to hydroformylation of octene under aqueous conditions [water-substrate(product) biphasic system] with TOFs of up to 3700 (with A) and 1630 (with B), respectively. The hydroformylation reactions with polymers C and D, which were not functionalized with phosphino groups, in the presence of [Rh] and TPPTS exhibited much lower catalytic performance.

Synthesis of Highly Functionalized Alkenylphosphines by Lewis Acid-mediated Silylphosphination of Substituted Propiolates

Abstract A synthesis of highly substituted alkenylphosphines by Lewis acid-mediated silylphosphination of substituted propiolates is described. The addition proceeded smoothly to give the corresponding acrylates, where the phosphino group attached at the β and the silyl group located at the α position of the resulting acrylate, in exclusively syn-stereochemistry.

Synthesis of Phosphorus Ligands from Zirconium Reagents. A Useful Approach

The use of several zirconium reagents as the Schwartz reagent [Cp2ZrHCl]n, the dimethylzirconocene Cp2ZrMe2, the zirconocene [Cp2Zr], and the diphenylzirconocene Cp2ZrPh2 allows the synthesis of a variety of new linear and cyclic P-C and P-N ligands. 1,1 diphosphines can be prepared from unsaturated monophosphines. A useful methodology involving ring opening reactions permits the preparation of phosphinite-phosphine and bis-phosphinite ligands. N-functionalized imines and β-diimines substituted with phosphino groups are obtained from cyanophosphines or dinitriles. Carbozirconation of chlorophospha-imine leads to the unprecedented P-metalated iminophosphorane which presents a versatile reactivity towards electrophiles and small unsaturated molecules. Constraint three and four phosphorus cycles can be easily isolated using [Cp2M] (M = Zr or Ti). Interactions between benzynezirconocene and unsaturated phosphines afford numerous methods to prepare linear and cyclic phosphorus reagents. Enantiomerically pure iminophosphines can be synthetized from phosphinozirconocene complexes. Keywords: substituted phospholane, phosphorus-zirconium salts, Schwartz reagent, metallocene transition complexes, 1,1-diphosphines

Highly efficient P–N nickel(ii) complexes for the dimerisation of ethylene

New P-N ligands featuring a phosphino group and an iminophosphorane moiety were successfully employed in the nickel-catalysed dimerisation of ethylene.

Regio- and Stereoselective Synthesis of Alkenylphosphines: A Rhodium-Catalyzed Hydrophosphination of Alkynes Using a Silylphosphine

A novel rhodium-catalyzed hydrophosphination of alkynes using a silylphosphine as a phosphino group source is described. A variety of alkynes, both terminal and internal ones with aryl, alkyl, and carboxyl groups, gave the corresponding alkenylphosphines in a highly regioselective and syn-selective manner. Alkenes with an electron-withdrawing group also gave the corresponding adducts in good yields.

Rapid geometrical equilibrium of palladium(II) complexes with tris[2-(diphenylphosphino)ethyl]phosphine disulfide and diselenide and their catalytic activity for Suzuki coupling reaction

Palladium(II) complexes with a tetradentate pseudo-tripodal ligand having two phosphino groups and two phosphine sulfide or selenide groups, pp 3X 2 (pp 3 = tris[2-(diphenylphosphino)ethyl]phosphine, X = S ( 1) or Se ( 2)), were prepared from [PdCl(pp 3)]Cl. Both of these phosphine chalcogenide complexes 1 and 2 showed rapid equilibrium between the five-coordinate [PdCl(pp 3X 2)]Cl with two bound phosphine chalcogenide groups and four-coordinate [PdCl 2(pp 3X 2)] with two dissociated pendant ones in chloroform. The thermodynamic parameters for the reaction, [PdCl(pp 3X 2)] + + Cl −⇄[PdCl 2(pp 3X 2)], were obtained by low-temperature 31P NMR as follows: K 298 = 3.7 × 10 3 and 5.4 × 10 2 mol −1, Δ H ∘ = 11.3 ± 0.3 and 13.4 ± 0.4 kJ mol −1, and Δ S ∘ = 106 ± 2 and 97 ± 2 J mol −1 K −1 for 1 and 2, respectively. The rate for the geometrical change at 246.7 K for 1 was appreciably faster than that for 2. These thermodynamic and kinetic results indicate that the phosphine selenide Se atoms can stabilize the five-coordinate structure by effective π-back donation from Pd(II) compared with the phosphine sulfide S atoms. Difference in retention of the catalytic activity for Suzuki coupling, 2 > 1 > [PdCl(pp 3 or p 3)]Cl, was explained by difference in the π-accepting ability that stabilizes the catalytically active Pd(0) species. Considering the rapid dissociation-coordination equilibrium of the phosphine chalcogenide groups on Pd(II), it is probable that the oxidative addition and the subsequent transmetallation of the Pd(II) species are hardly blocked by the phosphine chalcogenide groups.

Nitrogen-Assisted Ortho Lithiation: One-Pot Synthesis of New Classes of Bidentate and Tetradentate Mixed P∼N Ligands

Metalation of one aryl group of Ph3PNR (R = methyl, isopropyl) affords an easy access to the corresponding lithium salt, which in turn reacts with chlorophosphines R2PCl (R = Ph, i-Pr) to yield a new class of bidentate ligand featuring one iminophosphorane and one phosphino group. Reaction of the phenyl derivative with [Pd(COD)Cl2] yielded the expected six-membered palladacycle complex, which was structurally characterized. Extension of this new synthetic methodology toward the elaboration of enantiomerically pure tetradentate ligands has also been achieved.

Stereoselective Preparation, Structures, and Reactivities of Phosphine-Bridged Mixed-Metal Trinuclear and Pentanuclear Complexes with Tris[2-(diphenylphosphino)ethyl]phosphine

The phosphine-bridged linear trinuclear and pentanuclear complexes with Pd(II)-Pt(II)-Pd(II), Ni(II)-Pt(II)-Ni(II), and Rh(III)-Pd(II)-Pt(II)-Pd(II)-Rh(III) metal-ion sequences were almost quantitatively formed by the stepwise phosphine-bridging reaction of the terminal phosphino groups of tris[2-(diphenylphosphino)ethyl]phosphine (pp3), which is the tetradentate bound ligand of the starting Pd(II) and Ni(II) complexes. The solid-state structures of the trinuclear complexes were determined by X-ray structural analyses, and the structures of the polynuclear complexes in solution were characterized by NMR spectroscopy. The trans and cis isomers of the trinuclear and pentanuclear complexes, which arise from the geometry around the Pt(II) center, were selectively obtained simply by changing the counteranion of the starting complexes: the tetrafluoroborate salts, [MX(pp3)](BF4) [M = Pd(II) or Ni(II), X = Cl- or 4-chlorothiophenolate (4-Cltp-)], gave only the trans isomers, and the chloride salt, [PdCl(pp3)]Cl, gave only the cis isomers. The formation of the trinuclear complex with the 4-Cltp- and chloro ligands, trans-[Pt(4-Cltp)2{PdCl(pp3)}2](BF4)2, proceeded with exchange between the thiolato ligand in the starting Pd(II) complex, [Pd(4-Cltp)(pp(3))](BF4), and the chloro ligands in the starting Pt(II) complex, trans-[PtCl2(NCC6H5)2], retaining the trans geometry around the Pt(II) center. In contrast, the formation reaction between [PdCl(pp3)]Cl and trans-[PtCl2(NCC6H5)2] was accompanied by the trans-to-cis geometrical change on the Pt(II) center to give the trinuclear complex, cis-[PtCl2{PdCl(pp3)}2]Cl2. The mechanisms of these structural conversions during the formation reactions were elucidated by the 31P NMR and absorption spectral changes. The differences in the catalytic activity for the Heck reaction were discussed in connection with the bridging structures of the polynuclear complexes in the catalytic cycle.

Phosphino-functionalised acetals of polyvinyl alcohol as the matrix for the immobilisation of Rh-based pre-catalysts for interfacial catalysis

Use of polyvinyl alcohol (PVA) to support the immobilisation of phosphines shall be presented. Phosphino functionalisation is introduced in the polymer by a one-step transacetalation reaction and high acetalation degrees are reached. By complexation of the phosphino groups to a [(COD)RhCl] complex fragment, [Rh]-modified polymers are obtained with Rh contents of higher than 15% and the transition metal in a defined molecular environment. The phosphino or [Rh]-modified PVAs are characterised unambiguously by comparing their spectroscopic data with those of model compounds, the syntheses of which are reported as well. Use of the [Rh]-modified polymers as pre-catalysts will be presented with the hydroformylation of 1-octene being taken as an example. It leads to a selectivity in the product distribution that is identical to that of the model complexes. Recycling experiments were performed and the catalyst rest state on the polymer was identified after 10 consecutive runs. Adsorption of the [Rh]-modified PVA on an inorganic support leads to the formation of stable polymer layers on its surface, which cannot be mobilised by extraction with organic solvents. The stability of these layers, together with their tuneable polarity, allow for their application in interfacial catalysis comparable to SAPC or SILC.

Conformational Composition of Cyclopentadienylphosphine Investigated by Microwave Spectroscopy and Quantum Chemical Calculations

The properties of cyclopentadienylphosphine have been investigated by means of Stark-modulation microwave spectroscopy and quantum chemical calculations at the MP2/aug-cc-pVTZ, B3LYP/6-311++G(d,p), and G3 levels of theory. Spectra attributable to two rotamers denoted conformers I and II have been assigned. Conformer I has a symmetry plane (Cs symmetry) consisting of the bisectors of the cyclopentadiene ring and of the phosphino group with the lone electron pair of phosphorus pointing toward the carbon ring. In conformer II, the phosphino group is rotated approximately 120 degrees out of this plane. Relative intensity measurements have been made, and it was found that conformer II is more stable than I by 1.3(4) kJ/mol. The preferred conformer represents a borderline case of intramolecular hydrogen bond stabilization. The experimental and MP2/ aug-cc-pVTZ rotational constants differ by several percent, which indicates that the aug-cc-pVTZ basis set is not large enough to be able to predict an accurate structure for the two conformers that are close to the equilibrium geometries. 5-Substituted 1,3-cyclopentadienyl derivatives may undergo circumambulatory rearrangements. However, there is no manifestation of this effect in the microwave spectrum of cyclopentadienylphosphine.