Phosphinite Complexes Research Articles

Catalytic dehydrogenation of cyclooctane and triethylamine using aliphatic iridium pincer complexes

The majority of the known pincer iridium based catalysts for dehydrogenation of alkanes has arene-based backbones. Here, the catalytic activity of aliphatic iridium pincer complexes, viz. the cyclohexane-based phosphine complex (PCyP)IrHCl (4) (PCyP={cis-1,3-bis-[(di-tert-butylphosphino)methyl]cyclohexane}−) and the 2-methylpropane-based phosphinite complex (POCOP)IrHCl (5) (POCOP=1,3-bis-(di-tert-butylphosphinito)-2-methylpropane−), in dehydrogenation of cyclooctane and triethylamine was studied. They give TONs that are in the range of 0–200. In addition, improved procedures for synthesis and metallation of the PCyP ligand (3) are presented.

Synthesis of Li/OR phosphinidenoid complexes: on the evidence for intramolecular O–Li donation and the effect of cation encapsulation

Synthesis of phosphinite complexes 12-14a-c, 15a and 16a was achieved via reaction of transient Li/Cl phosphinidenoid complexes 6-10, prepared from dichloro(organo)phosphane complexes [(OC)5M{RPCl2}] 1-5 (1,6: R = CPh3, 2,7: R = C5Me5, 3-5, 8-10: R = CH(SiMe3)2, 1-3, 6-8: M = W, 9: M = Mo, 10: M = Cr), with different alcohols 11a-c (a: R = allyl, b: R = methyl, c: R = isopropyl). Deprotonation of complexes 12b, 13b with MeLi or (t)BuLi in the presence of two equivalents of 12-crown-4 led to the selective formation of phosphinidenoid complexes [Li(12-crown-4)2] [(OC)5W{RP(OCH3)}] (18a R = CPh3 and 18b R = C5Me5) which were stable in solution at ambient temperature, in contrast to Li/OMe phosphinidenoid complexes without 12-crown-4. To our surprise attempts to crystallise complex 18b yielded complex 21 having a Li-O-P subunit. The reaction of complex 17c with [Ph3C]BF4 yielded the P-C coupling product 26 and, hence, the first evidence for an oxidative SET reaction. All isolated products were characterised by multinuclear NMR spectroscopy, IR, MS and single-crystal X-ray crystallography in the case of complexes 12a,b, 13b, 14a-c, 15a, 16a and 21.

New chiral ruthenium(II)–phosphinite complexes containing a ferrocenyl group in enantioselective transfer hydrogenations of aromatic ketones

A new and versatile class of unsymmetrical ferrocenyl-phosphinite ligands possessing a stereogenic center has been prepared from commercially available, inexpensive aminoacids such as, d-, l-phenylglycine and d-, l-phenylalanine, through a concise synthetic procedure. These ligands are not very sensitive to air and moisture, and display good enantioselectivities in the ruthenium-catalyzed asymmetric transfer hydrogenation of acetophenone derivatives, in which up to 91% ee was obtained. A comparison of the catalytic properties of amino alcohols and other analogues based on a ferrocenyl backbone is also discussed briefly. The structures of these ligands and their corresponding complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy, and elemental analysis.

Selective hydroaminomethylation of olefins using simple and efficient Rh–phosphinite complex catalyst

Hydroaminomethylation of various olefins with primary and secondary amines was carried out using a simple and efficient rhodium–phosphinite complex catalyst. The influence of various reaction parameters including the effects of temperature, pressure, catalyst loading, time and solvents has been investigated. The present protocol is general with wider substrate applicability for the synthesis of an important class of aliphatic amines and arylethylamines. High activity and selectivity for amines was achieved with a very good substrate/catalyst molar ratio (turnover number 2500) under mild reaction conditions. Copyright © 2013 John Wiley & Sons, Ltd.

Synthesis and Reactions of the First Room Temperature Stable Li/Cl Phosphinidenoid Complex

P-Trityl substituted Li/Cl phosphinidenoid tungsten(0) complex (OC)5W{Ph3CP(Li/12-crown-4)Cl} (3) was prepared via chlorine/lithium exchange in complex (OC)5W{Ph3CPCl2} (2) using (t)BuLi in the presence of 12-crown-4 in tetrahydrofuran (THF) at low temperature; complex 3 possesses significantly increased thermal stability in contrast to previously reported analogue derivatives. Terminal phosphinidene-like reactivity of 3 was used in reactions with benzaldehyde and isopropyl alcohol as oxaphosphirane complex (OC)5W{Ph3CPC(Ph)O} (5) and phosphinite complex (OC)5W{Ph3CP(H)O(i)Pr} (6) were obtained selectively. Reaction of 3 with phosgene allowed to obtain the first kinetically stabilized chloroformylphosphane complex (OC)5W{Ph3CP(Cl)C(O)Cl} (4). Density functional theory (DFT) calculations revealed remarkable differences in the degree of P-Li bond dissociation 3a-d: using a continuum model 3 displays a covalent character of P-Li bond (COSMO (THF)) (a), which becomes elongated if 12-crown-4 is coordinated to lithium (b) and is cleaved if a dimethylether unit is additionally coordinated to lithium (c). A similar result was obtained for the case of 3(thf)4 in which also a solvent-separated ion pair structure is present (d). All products were unambiguously characterized by various spectroscopic means and, in the case of 2 and 4-6, by single-crystal X-ray diffraction analysis. In all structures very long P-C bonds were determined being in the range from 1.896 to 1.955 Å.

Aliphatic pincer-type POCOP ligands and their complexation behaviour with iridium: Crystal structure of an iridium(III) phosphinite complex

Reaction of 2 equivalents of 1,3-bis-(di- tert-butylphosphinito)-2-methyl-propane ( 1a) with [Ir(COD)Cl] 2 affords the first aliphatic diphosphinite PCP pincer complex with iridium, Ir(H){( t-Bu 2POCH 2) 2C(Me)}Cl ( 2). The poor yield of 2 is partly explained by the formation of a di-nuclear byproduct [IrCl(COD)] 2( μ 2-{( t-Bu 2POCH 2) 2CH(Me)}) ( 3). Reaction of 1,3-bis-(di- iso-propylphosphinito)-2-methyl-propane ( 1b) under the same condition does not give any cyclometallation, and reaction with IrCl 3·H 2O in DMF leads to complete decomposition of the pincer ligand under the formation of Ir(H)( i-Pr 2P(OH)) 3(CO) ( 4), underpinning the comparatively low thermal stability of aliphatic phosphinite pincer systems.

Asymmetric transfer hydrogenation of acetophenone derivatives with novel chiral phosphinite based η 6- p-cymene/ruthenium(II) catalysts

Enantioselective reduction of prochiral ketones to optically active secondary alcohols is an important subject in synthetic organic chemistry because the resulting chiral alcohols are extremely useful, biologically active compounds. The new chiral ligands (2 R)-2-[benzyl{(2-((diphenylphosphanyl)oxy)ethyl)}amino]butyldiphenylphosphinite, 1 and (2 R)-2-[benzyl{(2-((dicyclohexylphosphanyl)oxy)ethyl)}amino]butyldicyclohexylphosphinite, 2 and the corresponding ruthenium(II) complexes 3 and 4 have been prepared. The structures of these complexes have been elucidated by a combination of multinuclear NMR spectroscopy, IR spectroscopy and elemental analysis. 31P–{ 1H} NMR, DEPT, 1H– 13C HETCOR or 1H– 1H COSY correlation experiments were used to confirm the spectral assignments. These ruthenium(II)–phosphinite complexes have been used as catalysts for the asymmetric transfer hydrogenation of acetophenone derivatives. Under optimized conditions, aromatic ketones were reduced in good conversions and in moderate to good enantioselectivities (up to 85% ee).

Chemistry of the Oxophosphinidene Ligand. 1. Electronic Structure of the Anionic Complexes [MCp{P(O)R*}(CO)2]−(M = Mo, W; R* = 2,4,6-C6H2tBu3) and Their Reactions with H+and C-Based Electrophiles.

The anionic phosphide-bridged complexes (H-DBU)[M(2)Cp(2)(μ-PHR*)(CO)(4)] (M = Mo, W; R* = 2,4,6-C(6)H(2)(t)Bu(3); Cp = η(5)-C(5)H(5), DBU = 1,8-diazabicyclo [5.4.0] undec-7-ene) react with molecular oxygen to give the corresponding oxophosphinidene complexes (H-DBU)[MCp{P(O)R*}(CO)(2)] as major products (Mo-P = 2.239(1) Å for the Mo complex). The latter anionic complexes are protonated by HBF(4)·OEt(2) to give the hydroxyphosphide derivatives [MCp{P(OH)R*}(CO)(2)]. In the presence of excess acid, the molybdenum complex yields the fluorophosphide complex [MoCp(PFR*)(CO)(2)] (Mo-P = 2.204(1) Å), while the tungsten compound reacts with excess HCl to give an unstable chlorophosphine complex [WCpCl(PHClR*)(CO)(2)] which is rapidly hydrolyzed to give [WCpCl{PH(OH)R*}(CO)(2)], having a complexed arylphosphinous acid (Mo-P = 2.460(2) Å). The molybdenum anion reacts with strong C-based electrophiles such as [Me(3)O]BF(4), Et(2)SO(4), C(2)H(3)C(O)Cl, and PhC(O)Cl to give the corresponding alkoxyphosphide derivatives [MoCp{P(OR)R*}(CO)(2)] (R = Me, Et, COC(2)H(3), COPh; Mo-P = 2.197(2) Å for the benzoyl compound), as a result of the attack of the electrophile at the O atom of the oxophosphinidene ligand. In contrast, the reactions with milder alkylating reagents such as the alkyl halides MeI, EtI, C(3)H(5)Br, and C(3)H(3)Br give selectively the corresponding κ(2)-phosphinite complexes [MoCp{κ(2)-OP(R)R*}(CO)(2)] [R = Me, Et, C(3)H(5), C(3)H(3); Mo-P = 2.3733(5) Å for the allyl compound] as a result of the attack of the electrophile at the P atom of the oxophosphinidene ligand. According to density functional theory (DFT) calculations, the oxygen atom of the phosphinidene ligand bears the highest negative charge in the molybdenum anion, while the highest occupied molecular orbital (HOMO) of this complex has substantial Mo-P π bonding character. Thus, it is concluded that the phosphinite complexes are formed under conditions of orbital control, while charge-controlled reactions tend to give alkoxyphosphide derivatives.

Novel neutral phosphinite bridged dinuclear ruthenium(II) arene complexes and their catalytic use in transfer hydrogenation of aromatic ketones: X-ray structure of a new Schiff base, N3,N3′-di-2-hydroxybenzylidene-[2,2′]bipyridinyl-3,3′-diamine

A novel Schiff base N3,N3′-di-2-hydroxybenzylidene-[2,2′]bipyridinyl-3,3′-diamine, 1 was synthesized from condensation of salicylaldehyde with 3,3′-diamino-2,2′-bipyridine. Reaction of 1 with two equivalents of PPh 2Cl in the presence of Et 3N proceeds in toluene to give N3,N3′-di-2-(diphenylphosphino)benzylidene-[2,2′]bipyridinyl-3,3′-diamine, 2 in quantitative yield. Ruthenium(II) dimers [Ru(η 6-arene)(μ-Cl)Cl] 2 readily react with phosphinite ligand [(Ph 2PO) 2-C 24H 16N 4], 2 in toluene at room temperature, to afford the neutral derivatives [C 24H 16N 4{OPPh 2–Ru(η 6-arene)Cl 2} 2] {arene: benzene 3, p-cymene, 4}. All the complexes were fully characterized by analytical and spectroscopic methods. 31P–{ 1H} NMR, 1H– 13C HETCOR or 1H– 1H COSY correlation experiments were used to confirm the spectral assignments. Molecular structure of the Schiff base, 1 was also determined by X-ray single crystal diffraction study. The catalytic activity of complexes 3 and 4 in the transfer hydrogenation of acetophenone derivatives was tested. Stable ruthenium(II)–phosphinite complexes were found to be efficient catalysts in the transfer hydrogenation of aromatic ketones in excellent conversions up to 99% (up to 530 per hour) in the presence of iso-PrOH/KOH.

Hydroformylation of allyl acetate using rhodium polyether diphosphinite catalyst

Wilkinson-type polymeric Rh–phosphinite complexes were prepared using polyethylene glycol based diphosphinite ligands and tested for the homogeneous hydroformylation of allyl acetate. The effect of reaction variables such as temperature, pressure, substrate/Rh ratio on the activity and selectivity towards aldehyde products were investigated. The reaction showed high rate, turnover number and increased regioselectivity towards branched aldehyde products as compared to traditional Rh–phosphine and Rh–diphosphine based catalysts.

Recent Applications of Phosphinite POCOP Pincer Complexes Towards Organic Transformations

Pincer complexes have represented a group of very important species in organometallic chemistry in the last decade. Among these, phosphinite POCOP pincer complexes have recently been used profusely in metal mediated organic transformations due to the easiness on their synthesis, high thermal stability and enhanced catalytic activity. This minireview presents the evolution and recent advances in the chemistry and applications of this important group of compounds in different cross coupling reactions and other transformations relevant in organic synthesis. Keywords: Cross coupling reactions, POCOP pincer complexes, POCOP pincer ligands, Phosphinite complexes, Platinum group metal complexes, C-C Coupling Reactions, catalysis, PCP pincer compounds

Some phosphinite complexes of Rh and Ir, their intramolecular reactivity and DFT calculations about their application in biphenyl metathesis

Biphen(OPR 2) (with R: Ph, iPr, Cy) is reacted with [Rh(COE) 2Cl] 2. The corresponding μ-chloro-bridged dimers are received. An X-ray analysis of [Biphen(OPCy 2)RhCl] 2 is included. This compound shows a dynamic behaviour in solution, ascribed to a monomer/dimer equilibrium. The difference of the Biphen ligands to Milsteins PCP pincer-type ligand is shown. A catalytic cycle for biphenyl metathesis containing the coupling of oxidative addition and reductive elimination of the bridging C–C single bond in the biphenyl fragment using Rh I/III complexes and the concept of chelating assistance was calculated using DFT (B3PW91/LANL2DZ). According to the calculations the activation energy of the oxidative addition is about 30 kcal/mol and for the reductive elimination about 19 kcal/mol. The fac–Rh III complex is by far the most stable compound, but the formation of it is kinetically strongly disfavoured. Pre-catalysts (COD)M(Ph- O-PR 2) (M: Rh, Ir) were synthesized by pre-coordinating the phosphinite to the metal (X-ray structures of four such compounds included) followed by treatment with 2 equiv. of sec. BuLi (X-ray structures of two such compounds included). In case of Ir this synthesis is complicated by C–H activation (X-ray structure of (COD)Ir(H)(Cl)(2-Br-phenyl- O-(diisopropylphosphinite)) included) and fast oxidative addition of the Ph-C–Halide bond. For (COD)Ir(H)(Cl)(2-phenyl- O-(diisopropylphosphinite)) the C–H activation is reversible and thermodynamic parameters for the ring closure reaction were determined by VT-NMR measurement (Δ H = −21.1 ± 0.5 kJ/mol, Δ S = −62.8 ± 1.7 J/(mol K)). The pre-catalysts were reacted with Biphen(OPR 2) to enter the calculated catalytic cycle. With Rh as center metal this reaction works out cleanly to give new complexes with the three P-atoms coordinated to one Rh center. No hemi-labile character was found for these P-donors even at 105 °C in toluene. If (COD)Rh(2-phenyl- O-(diisopropylphosphinite)) is reacted with 2 equiv. of 2-iodo-phenyl- O-(diisopropylphosphinite) oxidative addition of one C–Iodo bond is observed and the corresponding mer–Rh III complex is received. Upon treatment with 2 equiv. of sec. BuLi the resulting product is(Biphen(OPiPr 2))Rh I(2-phenyl- O-(diisopropylphosphinite)) rather than mer–Rh III(2-phenyl- O-(diisopropylphosphinite)) 3. Reaction of [Rh(COD)Cl] 2 with 3 equiv. of 2-bromo-phenyl- O-(diphenylphosphinite) shows a fast scrambling of the chlorine into all possible ortho positions of the phenolate rings in the final Rh III reaction product.

Asymmetric allylation of aldehydes with chiral platinum phosphinite complexes

Platinum phosphinite complexes made from chiral diols catalyze the enantioselective allylation of cinnamaldehyde. This reaction proceeds with better yields at shorter reaction times in the presence of acetic acid. Enantiomeric excesses were greater when reactions were carried out with phosphinite ligands having hydrogen bond donors or acceptors.

Chemistry of palladium phosphinite (PPh2(OR)) and phosphonite (P(OPh)2(OH)) complexes: catalytic activity in methoxycarbonylation and Heck coupling reactions

The new phosphinite and phosphonite complexes (1-8) are very efficient catalysts for the methoxycarbonylation of iodobenzene and Heck cross-coupling of bromobenzene with butyl acrylate. High catalytic activity of these complexes can be explained by their in situ transformations during the reaction, stimulated by the presence of water, acid (HCl) or base (NEt(3)). Hydrolysis of phosphinite palladium complexes of the form trans-PdCl(2)[PPh(2)(OR)](2) (R = C(6)F(5), 2, (t)Bu 3, or O-menthyl 4) results in the formation of the dimeric complex [mu-ClPd(PPh(2)OH)(PPh(2)O)](2) 5, which is deprotonated by NEt(3), producing a polymeric complex of formula [Pd(P(O)PPh(2))(2)](n) 8. The reverse reaction, protonolysis of 8 with HCl, leads back to 5 and the monomeric complex 5a. The phosphinite complex PdCl(2)[PPh(2)(OBu)](2)1 with a more lipophilic ligand, PPh(2)(OBu), does not undergo hydrolysis under the same conditions. In the reaction of PdCl(2)(cod) with P(OPh)(2)(OH), the new dimer [mu-ClPd(P(OPh)(2)OH)(P(OPh)(2)O)](2) 6 was obtained, whereas reaction of Pd(OAc)(2) with P(OPh)(2)(OH) leads to the polymeric complex [Pd[P(O)(OPh)(2)](2)](n) 7. Protonolysis of 7 with HCl results in the formation of 6.

Preagostic Rh−H Interactions and C−H Bond Functionalization: A Combined Experimental and Theoretical Investigation of Rhodium(I) Phosphinite Complexes

Three Rh−phosphinite complexes with the general structural formula [RhCl(i-Pr2POXy)(L)]2 (Xy = 2,3-xylyl; L = PPh3, PMe3, t-BuNC) were synthesized. Characterization of these complexes using crystallographic and spectroscopic techniques revealed rare examples of preagostic C−H···M interactions. 1H NMR chemical shielding calculations on a geometry-optimized model complex were used to provide a connection between the solution and solid-state data, which additionally supported assignment of the preagostic interaction. One of these Rh−phosphinite complexes (L = PPh3) was used to catalyze the ortho alkylation of phosphinites and phenols with an unactivated alkene. Finally, DFT calculations were used to provide evidence for the involvement of the observed preagostic interaction in the cyclometalation step of the catalytic cycle.

Chemistry of the Phosphinidene Oxide Ligand

Reaction of [Mo2Cp2(mu-H)(mu-PHR*)(CO)4] with DBU followed by O2 gives the first anionic phosphinidene oxide complex (H-DBU)[MoCp{P(O)R*}(CO)2] (1) (DBU = 1,8-diazabicyclo [5.4.0] undec-7-ene; R* = 2,4,6-C6H2tBu3). This anion displays three different nucleophilic sites located at the O, P, and Mo atoms, as illustrated by the reactions reported. Thus, reaction of 1 with excess HBF4.OEt2 gave the fluorophosphide complex [MoCp(PFR*)(CO)2] via the hidroxophosphide intermediate [MoCp{PR*(OH)}(CO)2]. Related alkoxyphosphide compounds [MoCp{P(OR)R*}(CO)2] (R = Me, C(O)Ph) were prepared by reaction of 1 with [Me3O]BF4 and PhC(O)Cl, respectively, whereas reaction of 1 with MeI or C3H5Br gave the P,O-bound phosphinite complexes [MoCp(kappa2-OPRR*)(CO)2] (R = Me, C3H5). Metal-based electrophiles were found to bind at either O or Mo positions. Thus, reaction of 1 with [ZrCl2Cp2] gave the phosphinidene oxide bridged [MoCp{P(OZrClCp2)R*}(CO)2], whereas reaction with SnPh3Cl gave trans-[MoCp{P(O)R*}(CO)2(SnPh3)], an heterometallic complex having an intact terminal P(O)R* ligand.

Exo- and Endocyclic Oxazolinyl−Phosphane Palladium Complexes: Catalytic Behavior in Allylic Alkylation Processes

The new bidentate chiral N,P-donor oxazolinyl−phosphane ligands 7−15 are described. Upon coordination to the palladium metal, ligands 7−12 gave endocyclic oxazolinyl−phosphane complexes having seven-membered rings, while ligands 13−15 afforded exocyclic oxazolinyl−phosphinite complexes with six-membered rings, depending on the relative CN oxazoline bond and metal ring position. Ionic palladium(II) complexes containing N,P-bidentate ligands and allyl groups (η3-C3H5 for 16−22 and η3-1,3-Ph2-C3H3 for 23−26) were prepared and fully characterized. X-ray structures were determined for complexes 18 and 19. Pd catalytic systems containing ligands 7−15 were tested in the asymmetric allylic alkylation of the racemic substrates rac-3-acetoxy-1,3-diphenyl-1-propene (I) and rac-3-acetoxy-1-cyclohexene (III). The endocyclic systems show better activites and selectivites (ee values up to 82%) than the exocyclic ones (ee values up to 72%) for substrate I. In particular, palladium endocyclic oxazoline−phosphinite systems containing the PCy2 group (20, 21) give the highest activities, but the best enantioselectivities were observed for those containing PPh2 (18, 19).

Mixed Phosphite‐Phosphine and Phosphinite‐Phosphine Palladacyclic Complexes as Highly Active Catalysts for the Amination of Aryl Chlorides.

AbstractFor Abstract see ChemInform Abstract in Full Text.

Mixed Phosphite‐Phosphine and Phosphinite‐Phosphine Palladacyclic Complexes as Highly Active Catalysts for the Amination of Aryl Chlorides

AbstractTri‐tert‐butylphosphine adducts of ortho‐palladated phosphite and phosphinite complexes formed in situ are excellent catalysts for the Buchwald–Hartwig amination of aryl chloride substrates.

The synthesis of phosphorus heterocycles from tetra-tert-butyltetraphosphacubane.

Tetra-tert-butyltetraphosphacubane, P(4)C(4)(t)Bu(4), reacts with water in the presence of 'GaI' to yield two products, namely 4,6,7,8-tetra-tert-butyl-1,2,3-triphospha-5-phosphoniatetracyclo[3.2.1.0(2,4).0(3,8)]oct-6-ene tetraiodogallate(III), (C(20)H(37)P(4))[GaI(4)], and triiodo(3,5,7,8-tetra-tert-butyl-1,2,4lambda(5),6-tetraphosphatetracyclo[4.1.1.0(2,5).0(7,8)]octan-4-one)gallium(III), [GaI(3)(C(20)H(38)OP(4))], both of which have been structurally characterized. The X-ray crystal structure determination of the former compound shows it to be an ion-separated salt, while the latter compound is a neutral phosphinite complex of GaI(3).