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.

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.

Ambident PCN heterocycles: N- and P-phosphanylation of lithium 1,3-benzazaphospholides.

Synthetic and structural aspects of the phosphanylation of 1,3-benzazaphospholides 1(Li), ambident benzofused azaphosphacyclopentadienides, are presented. The unusual properties of phospholyl-1,3,2-diazaphospholes inspired us to study the coupling of 1(Li) with chlorodiazaphospholene 2, which led to the N-substituted product 3. Reaction of 1(Li) with chlorodiphenyl- and chlorodicyclohexylphosphane likewise gave N-phosphanylbenzazaphospholes 4 and 5, whereas with the more bulky di-tert-butyl- and di-1-adamantylchlorophosphanes, the diphosphanes 6 and 7 are obtained; in the case of 7 they are isolated as a dimeric LiCl(THF) adduct. Structural information was provided by single-crystal X-ray diffraction and solution NMR spectroscopy experiments. 2D exchange spectroscopy confirmed the existence of two rotamers of the aminophosphane 5 at room temperature; variable-temperature NMR spectroscopy studies of 6 revealed two dynamic processes, low-temperature inversion at ring phosphorus (DeltaH( not equal)=22 kJ mol(-1), DeltaS( not equal)=2 J K(-1) mol(-1)) and very low-temperature rotation of the tBu(2)P group. Quantum chemical studies give evidence that 2-unsubstituted benzazaphospholides prefer N-phosphanylation, even with bulky chlorophosphanes, and that substituents at the 2-position of the heterocycle are crucial for the occurrence of P-N rotamers and for switching to alternative P-substitution, beyond a threshold steric bulk, by both P- and 2-position substituents.

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)°.

P-[N-(Diphenyl-phospho-rothio-yl)iso-propyl-amino]-N-isopropyl-P-phenyl-thio-phosphinic amide.

The title compound, C(24)H(30)N(2)P(2)S(2), was obtained by the reaction of Ph(2)PN(iPr)P(Ph)N(iPr)H with elemental sulfur in tetra-hydro-furan. In the solid state, intra-molecular N-H⋯S hydrogen bonding influences the mol-ecular conformation; a P-N-P-N torsion angle of 2.28 (9)° is observed. The two phenyl rings attached to one P atom form a dihedral angle of 74.02 (4)°.

Sterically and polarity-controlled reactions of tBuLi with P=CH-NR heterocycles: novel heterocyclic P- and P,O-ligands and preliminary tests in transition-metal catalysis.

(1R)-1,3-Benzazaphospholes 1 a-c, P=CH-NR heterocycles of the indole type, react with tBuLi in two ways, depending on the steric demand of the N-substituent and the polarity of the medium. The presence of small N-alkyl groups induces CH-deprotonation in the 2-position to give hetaryllithium reagents 2 a and 2 b, whereas bulky N-substituents and nonpolar solvents change the reactivity towards addition at the P=C bond. The preferred regioselectivity is tert-butylation at phosphorus, occurring with excellent diastereoselectivity for trans-adducts 3 b and 3 c, but the inverse tert-butylation at C2 to 5 b was also observed. N-Neopentyl groups, with intermediate steric demand, give rise to formation of mixtures in ethers but allow switching either to selective CH lithiation in THF/KOtBu or to addition in pentane. Bulkier N-adamantyl groups always cause preferred addition. Protonation, silylation, and carboxylation were used to convert the P=CLi-NR, (E)-tBuP-CHLi-NR, and LiP-CH(tBu)-NR species into the corresponding sigma(2)-P or sigma(3)-P compounds 4 b and 6 a,b, 7 b,c, or 8 b-10 b with additional N and/or O donor sites. Slow diffusion-controlled air oxidation of 10 b led to the meso-diphosphine 11 b. Preferred eta(1)-P coordination was shown for an [Rh(cod)Cl] complex 12 b, and the potential of the new ligands 4 b and 7 b in catalysis was demonstrated by examples of Pd-catalyzed C-N coupling and Ni-catalyzed ethylene oligomerization (TON>6300). Crystal structures of 6 b, 11 b, and 12 b are presented.