Synthesis of P-stereogenic 1-phosphanorbornane-derived phosphine-phosphite ligands and application in asymmetric catalysis.

A convenient synthesis of enantiopure mixed donor phosphine-phosphite ligands has been developed incorporating P-stereogenic phosphanorbornane and axially chiral bisnaphthols into one ligand structure. The ligands were applied in Pd-catalyzed asymmetric allylic substitution of diphenylallyl acetate, Rh-catalyzed asymmetric hydroformylation of styrene and Rh-catalyzed asymmetric hydrogenation of an acetylated dehydroamino ester. Excellent branched selectivity was observed in the hydroformylation although low ee was found. Moderate ee's of up to 60% in allylic substitution and 50% in hydrogenation were obtained using bisnaphthol-derived ligands.

Cobalt-Catalyzed Enantioselective Hydrogenation of Trisubstituted Carbocyclic Olefins: An Access to Chiral Cyclic Amides.

The enantioselective hydrogenation of cyclic enamides has been achieved using an earth-abundant cobalt-bisphosphine catalyst. Using CoCl2 /(S,S)-Ph-BPE, several trisubstituted carbocyclic enamides were reduced with high activity and excellent enantioselectivity (up to 99 %) to the corresponding saturated amides. The methodology can be extended to the synthesis of chiral amines by base hydrolysis of the hydrogenation products. Preliminary mechanistic investigations reveal the presence of a high spin cobalt (II) species in the catalytic cycle. We propose that the hydrogenation of the carbon-carbon double bond proceeds via a sigma-bond-metathesis pathway.

P-Chirogenic Diphosphazanes with Axially Chiral Substituents and Their Use in Rh-Catalyzed Asymmetric Hydrogenation.

A convenient synthesis of enantiopure P-chirogenic diphosphazanes incorporating bulky bisphenol and 1,1'-bi-2-naphthol-derived substituents via the functionalization of a readily accessible enantiopure lithium phosphinoamide with chlorophosphoridites was developed. Since the product requires no subsequent deprotection, the protocol provides an easy, convenient synthesis of P-chirogenic ligands on the gram scale. The ligands were applied in the Rh-catalyzed asymmetric hydrogenation of benchmark substrates furnishing enantiomeric excess values up to 96%.

Selective Reductions of N,N-Bis{chloro(aryl)-phosphino}-amines Yielding Three-, Five-, Six-, and Eight-Membered Cyclic Azaphosphanes.

To date, a plethora of λ3 -P nitrogen-containing compounds is known. A large number of them are used as ligands in coordination chemistry and homogeneous catalysis. PN-containing compounds tend to build up cyclic moieties, which have received less attention in regard to their application as ligands in transition metal chemistry. Hence, different dehalogenation reactions of N,N-bis{chloro(aryl)-phosphino}-amines have been developed to synthesize different P-N-P containing cyclic compounds. Their coordination behavior to group VI transition metal carbonyls was explored.

2,4-Bis(diphenyl-phosphan-yl)-1,1,2,3,3,4-hexa-phenyl-1,3-diphospha-2,4-dibora-cyclo-butane tetra-hydro-furan sesqui-solvate.

In the title compound, C(60)H(50)B(2)P(4)·1.5C(4)H(8)O, the diphospha-diborane mol-ecule lies on an inversion centre, whereas the disordered tetra-hydro-furan solvent mol-ecule is in a general position with a partial occupancy of 0.75. The diphosphadiborane mol-ecule consists of an ideal planar four-membered B(2)P(2) ring with an additional phenyl and a -PPh(2) group attached to each B atom.

Tetra-carbon-yl[bis-(diphenyl-phosphan-yl)tetra-methyl-disiloxane-κP,P']chromium(0).

The title compound, [Cr(C(28)H(32)OP(2)Si(2))(CO)(4)], was obtained by the ligand-exchange reaction of Cr(CO)(6) with (Ph(2)PSiMe(2))(2)O in refluxing toluene. The CrC(4)P(2) coordination geometry is distorted octa-hedral, with a P-Cr-P bite angle of 99.22 (4)°.

(Isopropyl-amino)(meth-yl)diphenyl-phospho-nium iodide.

The title compound, C(16)H(21)NP(+)·I(-), was obtained by the reaction of Ph(2)PN((i)Pr)P(Ph)N((i)Pr)H with MeI involving cleavage of one of the P-N bonds in diethyl ether. The two phenyl rings form a dihedral angle of 82.98 (5)°. A weak donor-acceptor N-H⋯I inter-action is observed.

N,P,P-Triisopropyl-phosphinic amide.

The title compound, C(9)H(22)NOP, was obtained by slow diffusion of oxygen into a toluene solution of (i)Pr(2)PNH(i)Pr. In the crystal, an inter-molecular N-H⋯O hydrogen bond occurs.

Activation and deactivation by temperature: behavior of Ph2PN(iPr)P(Ph)N(iPr)H in the presence of alkylaluminum compounds relevant to catalytic selective ethene trimerization.

Coordination, deprotonation, rearrangement, and cleavage of Ph(2)PN(iPr)P(Ph)N(iPr)H (1) by trialkylaluminum compounds R(3)Al (R=Me, Et) are reported that are relevant to the selective ethene trimerization system consisting of the ligand 1, CrCl(3)(THF)(3) and Et(3)Al that produces 1-hexene in more than 90% yield and highest purity. With increasing temperature and residence time first the formation of an adduct [Ph(2)PN(iPr)P(Ph)N(iPr)H][AlR(3)] (2), second the aluminum amide [Ph(2)PN(iPr)P(Ph)(AlR(3))N(iPr)][AlR(2)] (3) and third its rearrangement to the cyclic compound [N(iPr)P(Ph)P(Ph(2))N(iPr)][AlR(2)] (4) were observed. The cleavage of 3 by an excess of R(3)Al into an amidophosphane and an iminophosphane could be the reason for its rearrangement to complex 4, as well as to the cyclic dimer [R(2)AlN(iPr)P(Ph)(2)](2) (5). The chemistry of ligand 1 in the presence of alkylaluminum compounds gives hints on possible activation and deactivation mechanisms of 1 in trimerization catalysis.

Coordination chemistry of new selective ethylene trimerisation ligand Ph2PN(iPr)P(Ph)NH(R) (R = iPr, Et) and tests in catalysis.

The synthesis of [Ph(2)PN((i)Pr)P(Ph)NH(R)] (R = (i)Pr, Et) (1, 2) is described and the structure of 2 has been determined by single-crystal X-ray analysis. Compound 1 readily reacts with chromium(0), nickel(0), nickel(II), palladium(II), platinum(II) and iron(II) complexes to give four-membered rings (3-10) via P,P' coordination. The molecular structures of [Cr(CO)(4){Ph(2)PN((i)Pr)P(Ph)NH(R)-P,P'}] (R = (i)Pr, Et) (3, 4), [Cr(CO)(3)(NCCH(3)){Ph(2)PN((i)Pr)P(Ph)NH((i)Pr)-P,P'}] (5), [Ni{Ph(2)PN((i)Pr)P(Ph)NH((i)Pr)-P,P'}(2)] (6), cis-[MX(2){Ph(2)PN((i)Pr)P(Ph)NH((i)Pr)-P,P'}] (M = Ni, Pd, Pt; X = Cl or Br) (7, 8, 9) and trans-[Fe(NCCH(3))(2){Ph(2)PN((i)Pr)P(Ph)NH((i)Pr)-P,P'}(2)](BF(4))(2) (10) have been determined by X-ray diffraction. In the solid state, these complexes show tight phosphine bite angles in the range 67.89(2) degrees to 74.97(4) degrees and the central nitrogen atom adopts an almost planar (sp(2)) geometry. Complexes 3, 5, 6, 7 and 10 are tested for their catalytic activity in ethylene oligomerisation. Additionally, complex 10 is tested in hydrogenation of olefins.

Influence of process parameters on the reaction kinetics of the chromium-catalyzed trimerization of ethylene.

In this paper we report the results of an extensive experimental kinetic study carried out on the novel ethylene trimerization catalyst system, comprising the chromium source [CrCl(3)(thf)(3)] (thf=tetrahydrofuran), a Ph(2)P-N(iPr)-P(Ph)-N(iPr)H (PNPNH) ligand (Ph=phenyl, iPr=isopropyl), and triethylaluminum (AlEt(3)) as activator. It could be shown that the initial activity shows a first-order dependency on the ethylene concentration. Also, a first-order dependency was found for the catalyst concentration. The initial activity follows a typical Arrhenius behavior with an experimentally determined activation energy of 52.6 kJ mol(-1). At elevated temperatures (ca. 80 degrees C), a significant deactivation was observed, which can be tentatively traced back to a ligand rearrangement in the presence of AlEt(3). After a fast initial phase, a pronounced 'kink' in the ethylene-uptake curve is observed, followed by a slow, almost linear, further increase of the total ethylene consumption. The catalyst composition, in particular the ligand/chromium and the cocatalyst/chromium molar ratio, has a strong impact on the catalytic performance of the trimerization of ethylene.

An alternative mechanistic concept for homogeneous selective ethylene oligomerization of chromium-based catalysts: binuclear metallacycles as a reason for 1-octene selectivity?

An alternative concept for the selective catalytic formation of 1-octene from ethylene via dimeric catalytic centers is proposed. The selectivity of the tetramerization systems depends on the capability of ligands to form binuclear complexes that subsequently build up and couple two separate metallacyclopentanes to form 1-octene selectively. Comparison of existing catalytic processes, the ability of the bis(diarylphosphino)amine (PNP) ligand to bridge two metal centers, and the experimental background support the proposed binuclear mechanism for ethylene tetramerization.

Bis[µ-N,N'-bis(2,6-diisopropylphenyl)ethene-1,2-diamido]-1,4(η);1:2κN:N;3:4κN:N-bis(diethyl ether)-1κO,4κO-di-µ-hydrido-2:3κH:H-2,3-dichromium(II)-1,4-dilithium(I) pentane hemisolvate.

The title compound, [Cr(2)Li(2)(C(26)H(36)N(2))(2)(µ-H)(2)(C(4)H(10)O)(2)]·0.5C(5)H(12), is a binuclear chromium complex bridged by two hydrogen atoms. Each chromium atom is coordinated in a distorted square-planar geometry by one chelating bis-(2,6-diisopropyl-phen-yl)ethene-1,2-diamido ligand via its two N atoms. Additionally, two diametrically opposed lithium ether adducts coordinate in an η(4) mode on the backbone of the ligands. There is a crystallographic inversion center in the middle of the Cr(2)H(2) ring. One of the isopropyl groups is disordered over two positions in a 0.567 (7):0.433 (7) ratio. Disorder is also observed in the pentane hemisolvate molecule.

[Bis(diphenyl-phosphan-yl)dimethyl-silane-κP,P']tetra-carbonyl-chromium(0).

The title compound, [Cr(C(26)H(26)P(2)Si)(CO)(4)], was obtained by the reaction of Ph(2)PSiMe(2)PPh(2) with Cr(CO)(6) in refluxing toluene by ligand exchange. The CrC(4)P(2) coordination geometry at the Cr atom is distorted octa-hedral, with a P-Cr-P bite angle of 80.27 (1)°.

[2,2-Bis(diphenyl-phosphan-yl)propane-κP,P']tetra-carbonyl-chromium(0) dichloro-methane monosolvate.

The title compound, [Cr(C(27)H(26)P(2))(CO)(4)]·CH(2)Cl(2), was obtained by the reaction of Ph(2)PCMe(2)PPh(2) with Cr(CO)(6) in refluxing toluene by substitution of two carbonyl ligands. The CrC(4)P(2) coordination geometry at the Cr atom is distorted octa-hedral, with a P-Cr-P bite angle of 70.27 (2)°.

Diacetonitrile[N,N'-bis(2,6-diisopropyl-phenyl)ethane-1,2-diimine]dichloridochromium(II) acetonitrile solvate.

The title compound, [CrCl(2)(CH(3)CN)(2)(C(26)H(36)N(2))]·CH(3)CN, was synthesized by the reaction of CrCl(2)(THF)(2) with N,N'-bis-(2,6-diisopropyl-phen-yl)ethane-1,2-diimine in dichloro-methane/acetonitrile. The chromium center is coordinated by two N atoms of the chelating diimine ligand, two chloride ions in a trans configuration with respect to each other, and by two N atoms of two acetonitrile mol-ecules in a distorted octa-hedral geometry.

Bis[N,N'-bis-(2,6-diisopropyl-phen-yl)ethane-1,2-diimine]-1κN,N';2κN,N'-tri-µ-trichlorido-1:2κCl:Cl-chlorido-1κCl-tetra-hydro-furan-2κO-dichromium(II) dichloro-methane 4.5-solvate.

In the mol-ecular structure of the title compound, [Cr(2)Cl(4)(C(26)H(36)N(2))(2)(C(4)H(8)O)]·4.5CH(2)Cl(2), the two Cr(II) centers are bridged by three Cl atoms, forming a dinuclear complex. Each Cr(II) center is coordinated by one chelating bis-(2,6-diisopropyl-phen-yl)ethane-1,2-diimine ligand via both N atoms. An additional chloride ion binds to one chromium center, whereas an additional tetra-hydro-furan mol-ecule coordinates to the second Cr(II) center. The coordination geometry at each Cr(II) center can be best described as distorted octa-hedral.

1,1,2,2-Tetra-phenyl-1λ-diphosphane 1-sulfide.

In the title mol-ecule, C(24)H(20)P(2)S, the P-P bond length is 2.2263 (5) Å. The two phenyl rings attached to the three- and five-coordinated P atoms, respectively, form dihedral angles of 56.22 (5) and 71.74 (5)°.

[N,N-Bis(diphenyl-phosphino)isopropyl-amine]dibromidonickel(II).

The title compound, [NiBr(2)(C(27)H(27)NP(2))], was synthesized by the reaction of NiBr(2)(dme) (dme is 1,2-dimethoxy-ethane) with N,N-bis-(diphenyl-phosphino)isopropyl-amine in methanol/tetra-hydro-furan. The nickel(II) center is coordinated by two P atoms of the chelating PNP ligand, Ph(2)PN(iPr)PPh(2), and two bromide ions in a distorted square-planar geometry.