Highly selective dimerization and trimerization of isobutene to linearly linked products by using nickel catalysts.

The unique linear linkage of isobutene to generate highly valuable C8 precursors for plasticizers is feasible by using special nickel catalysts. (4-Cyclooctene-1-yl)(1,1,1,5,5,5-hexafluoro-2,4-acetylacetonato)nickel and aluminum-alkyl-activated nickel acetylacetonates produce isobutene dimers with high selectivities of up to 95%. Moreover, selectivity for the head-to-head products (2,5-dimethylhexenes) is remarkably high at up to 99%. Additionally, novel C12 isobutene trimers are also formed with a very high selectivity of up to 99% for the linear linkage. The trimer structure (2,5,8-trimethylnonenes) reflects the stepwise characteristic of the reaction mechanism. Pathways of insertion and activation and the deactivation processes of the catalyst are discussed in detail.

(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.

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)°.

Combination of spectroscopic methods: in situ NMR and UV/Vis measurements to understand the formation of group 4 metallacyclopentanes from the corresponding metallacyclopropenes.

By reaction of the dichloride rac-(ebthi)HfCl(2) [ebthi = 1,2-ethylene-1,1'-bis(eta(5)-tetrahydroindenyl)] with lithium in the presence of bis(trimethylsilyl)acetylene, the hafnacyclopropene rac-(ebthi)Hf(eta(2)-Me(3)SiC(2)SiMe(3)) (1-Hf) was obtained. The reaction of the blue-green complex 1-Hf with an excess of ethylene at room temperature leads by insertion of the olefin to the yellow-green hafnacyclopentene 2-Hf which is only stable in solution and eliminates the alkyne at 100 degrees C under ethylene to form the corresponding yellow hafnacyclopentane 3-Hf, which was characterized by X-ray crystal structure analysis. The reaction of 1-Hf to give stepwise via 2-Hf the complex 3-Hf was investigated in detail and compared to the formation and stability of the corresponding zirconacyclopropene 1-Zr, zirconacyclopentene 2-Zr, and zirconacyclopentane 3-Zr. Moreover, the reaction of the titanocene alkyne complex 1-Ti with ethylene was studied. For investigating the reaction behavior of the alkyne complexes 1-M, NMR spectroscopy was used and the results were compared with UV/vis spectroscopy, suggesting the existence of a bis-pi-complex prior to the formation of the hafnacyclopentene 2-Hf.

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.

trans-Di-µ-acetato-[µ-N,N-bis-(diphenyl-phosphino)aniline]bis-[chlorido-molybdenum(II)](Mo-Mo)-dichloro-methane-tetra-hydro-furan (1/0.3/1.7).

The mol-ecular structure of the title compound, [Mo(2)(CH(3)COO)(2)Cl(2)(C(30)H(25)NP(2))]·0.3CH(2)Cl(2)·1.7C(4)H(8)O, features an Mo-Mo dumbbell bridged by two acetate groups which are trans to each other. Perpendicular to the plane spanned by the acetate groups, the Ph(2)PN(Ph)PPh(2) ligand bridges both Mo atoms, having a P-N-P angle of 114.09 (19)°. In a trans position to the PNP ligand are two Cl atoms, one on each molybdenum centre. The Mo-Mo bond distance is 2.1161 (9) Å, within the range known for Mo-Mo quadruple bonds. The Mo complex is located on a crystallographic twofold rotation axis which runs through the N-C bond of the ligand. The site occupation factors of the disordered solvent molecules were fixed to 0.15 for dichloromethane and 0.85 for tetrahydrofuran.