Ulrich Zenneck

1-Triorganylstannyl-1,2,4-triphosphole: A Versatile Starting Material for Phosphorus-Rich Cage Compounds and π-Complexes

A new, alternative route to polycyclic organophosphorus cages and to complexes with η5-1,2,4-triphospholyl or η4-1,2,4-triphosphole ligands is afforded by the moderate stability of the P−Sn bond in 1-triorganylstannyl-1,2,4-triphosphole derivatives (see scheme). These compounds are readily accessible from the corresponding triphospholyl sodium salts. All the reactions of the stannyl triphospholes tested so far give good to almost quantitative yields with high chemo- and diastereoselectivity.

[(Arene)(Diene)Fe] and [(Arene)(Diazadiene)Fe] Complexes: Preparation, Reactivity, and Catalytic Properties

Two different routes to novel [(diene)(η6-2,6-dimethylpyridine)Fe] complexes are reported, both of which utilize metal vapour reactions. The presence of two small substituents on the 2,6-position of pyridine is essential for the η6-coordination of the heterocycle. Investigations on the reactivity and stability of the [(diene)(η6-arene)Fe] complexes are presented, including those of the benzene, phosphinine, and pyridine derivatives. These investigations give some hints to the relevant factors for determining the interaction between an iron atom and a π-coordinated neutral arene ligand, and their modification by a nitrogen or a phosphorus atom. Selective substitution of the 1,5-cyclooctadiene (COD) ligand of [(COD)(η6-arene)Fe] complexes by some 1,4-diaza-1,3-diene (DAD) derivatives is possible in the case of the benzene or phosphinine arene ligands, and [(DAD)(η6-arene)Fe] complexes are formed, but all DAD derivatives tested so far cause the complete disintegration of [(COD)(η6-2,6-dimethylpyridine)Fe]. [(DAD)(η6-arene)Fe] complexes exhibit a catalytic potential, which was evaluated by experiments on the catalytic cyclodimerization of 1,3-butadiene in the presence of [(Et2AlOEt)2] as a co-catalyst. This reaction yields up to 92% of 1,5-cyclooctadiene, and an almost quantitative butadiene conversion is possible in the presence of less than 0.1% of the catalyst. Structural investigations on [(N,N′-bis(cyclohexyl)ethylenediimine)(η6-toluene)Fe] 5a reveal some details of the Fe-DAD interaction. An effective electron back-donation from occupied iron d-orbitals into the π*-LUMO of the DAD is indicated.

Structure of 2,4,6-Tri-tert-butyl-1,3,5-triphosphabenzene and of 2,4-Di-tert-butyl-1,3-diphosphabenzene: X-ray Analysis, Photoelectron Spectra and Molecular Orbital Calculations

The structure of 2,4,6-tri-tert-butyl-1,3,5-triphosphabenzene (1) as well as the He(I) photoelectron spectra of 1 and 2,4-di-tert-butyl-1,3-diphosphabenzene (2) have been investigated. It was found that 1 is planar with average C–P–C angles of 109.3° (±0.3°) and P–C–P angles of 130.7° (± 0.4°). All P–C bond lengths amount to 1.727 (± 0.008) A. The PE spectra were interpreted by comparison with the results of ab initio calculations (RHF/ 6-31G*). They reveal a splitting of the lone pairs on P in 2 of 0.7 eV.

Katalytische cocyclisierungen von ethin mit nitrilen an bis( η2-ethen)( η6-toluol)eisen als katalysator

Abstract The reactive arene complex bis(η 2 -ethene)(η 6 -toluene)iron co-cyclotrimerizes acetylene and nitriles RCN (R  CH 3 , C 2 H 5 , n-C 3 H 7 , i-C 3 H 7 , C 6 H 5 ) catalytically to give pyridine derivates. In the case of acrylonitrile the reaction fails.

Dangling or tethering the side chain: (η6-(R)-3-phenylbutanol)Ru(II) complexes. Chiral arene ruthenium complexes: Part 5

Abstract The preparation of optically pure ((R)-3-phenylbutanol)Ru(II) complexes is described. Depending on the reaction conditions and the co-ligands, the chiral alcohol side chain may dangle free at the periphery of the η6-co-ordinated arene ligand or be co-ordinated to the metal to result in a η6:η1-chelate ligand system. A key molecule is the dimeric complex [(η6-(R)-3-phenylbutanol)RuCl2]2 (2) with dangling side chains. It is accessible in good yield either by oxidation and COD ligand exchange of the Ru(0) species [(COD)(η6-(R)-3-phenylbutanol)Ru] (1) (COD=1,5-cyclooctadiene) or by complexation and dehydrogenation of (R)-3-cyclohexa-(1,4-dien-1-yl)-butanol (5). 5 is thus accessible in good yield in two steps from a commercially available starting material. Dimer 2 can be split into mononuclear complexes by heating alcohol solutions to afford tethered [(η6:η1-(R)-3-phenylbutanol)RuCl2] (6), or by reaction with an additional ligand L (L=PR3, P(OR)3, pyridine) to furnish [(η6-(R)-3-phenylbutanol)(L)RuCl2] (7a–f). If 7a–d are reacted with silver salts, the side chain is strapped through chloride elimination to form the diastereomeric salts [(η6:η1-(R)-3-phenylbutanol)(L)RuCl]+X− (8X) (X=BF4, PF6). The absolute molecular structures of the complexes have been determined in the solid state. Especially the side chains exhibit interesting conformational features. The CD spectra of 2, 6, and 7a are reported.

Novel Routes to 1,2-Diphosphete and 1,2,4-Triphospholyl π-Complexes

New specific routes to 1,2-diphosphete-, 1,2,4-triphosphol-, and 1,2,4-triphospholyl-π-complexes are reported, which are based on dichloro-1,2-diphosphetene and 1-stannyl-1,2,4-triphosphol as the heterocyclic educts. Details are given for Sn, Mn, Fe, and Co complexes. ESR-data of paramagnetic 1,2,4-triphospholyl sandwich complexes of Co and Mn proof the absence of degenerate SOMOs in these cases.

Cage Chirality of PC Cage Compounds: Highly Diastereoselective Formation of Diastereomeric P5‐Deltacyclenes, Separation of Diastereomers, and Removal of the Chiral Auxiliary

An effective cyclic addition reaction of diastereomeric (R*)diphenyltin-3,5-di(tert-butyl)-1,2,4-triphosphole derivatives 6 a-c (R* = (-)-cis-myrtanyl (a), (-)-trans-myrtanyl (b), m-(2-bornyl-2-ene)phenyl (c) with two equivalents of tert-butylphosphaalkyne 1 leads to 1:1 mixtures of diastereomeric stannylated pentaphosphadeltacyclene derivatives 7 a-c with seven stereogenic centers in the cage unit. The (-)-cis-myrtanyl derivative 7 a could be separated into its diastereomers; destannylation of diastereomer 7 a(RR) led to the P-H cage 8 as a pure enantiomer. Circular dichroism (CD) spectroscopy of the pure diastereomer 7 a(RR) and the enantiomer 8 give evidence for identical stereoisomers of the P(5)-deltacyclene cage units and prove a strong dominance of the chiral cages over the chiral auxiliary groups with respect to their chiroptical properties. Absolute X-ray structure investigations of the majority of the compounds presented in the paper reveal the details of the stereochemistry of the asymmetric P-C cage units. In this paper we demonstrated for the first time a general preparative route to stereochemically fully defined asymmetric P-C cage compounds by separation of diastereomers and replacement of the chiral auxiliary group.

A dimeric gold(I) triphospholyl complex

The reaction of 1-trimethylstannyl-3,5-di( tert -butyl)-1,2,4-triphosphol with PPh 3 AuCl affords [(1,2,4-triphospholyl)Au(PPh 3 )] ( 5 ) in high yield. NMR spectra of 5 are indicative for a highly dynamic compound in solution. The molecular structure of 5 in the solid state is that of the dimer [(1,2,4-triphospholyl)Au(PPh 3 )] 2 . Its most striking feature is a remarkable range of different metaltriphospholyl ligand bonds which create a pronounced asymmetric core of the molecule. The central AuAu distance of 3.14 A indicates a weak interaction of the metal atoms.

ε6-Phosphinine-and ε6-1,3-Diphosphinine Iron Complexes

Abstract Efficient synthetic routes are described, leading to novel η6-phosphinine- (1) and η6-1,3-diphosphinine (4, 5) iron(0) complexes. 1 is a catalyst for pyridine formation by a [2+2+2]-cyclic addition reaction of nitriles and alkynes and s4 is a useful source of unsaturated free four and six membered organophosphorus rings.

The Complexed 1,3‐Diphospha‐2‐Arsaallyl Radical and Its Cationic and Anionic Derivatives

Photolysis of [Cp*As{W(CO)(5)}(2)] (1a) in the presence of Mes*P=PMes* (Mes*=2,4,6-tri-tert-butylphenyl) leads to the novel 1,3-diphospha-2-arsaallyl radical [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)] (2a). The frontier orbitals of the radical 2a are indicative of a stable pi-allylic system that is only marginally influenced by the d orbitals of the two tungsten atoms. The SOMO and the corresponding spin density distribution of the radical 2a show that the unpaired electron is preferentially located at the two equivalent terminal phosphorus atoms, which has been confirmed by EPR spectroscopy. The protonated derivative of 2a, the complex [(CO)(5)W(mu,eta(2):eta(1)-P(2)As(H)Mes*(2))W(CO)(4)] (6a) is formed during chromatographic workup, whereas the additional products [Mes*P=PMes*{W(CO)(5)}] as the Z-isomer (3) and the E-isomer (4), and [As(2){W(CO)(5)}(3)] (5) are produced as a result of a decomposition reaction of radical 2a. Reduction of radical 2a yields the stable anion [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)](-) in 7a, whereas upon oxidation the corresponding cationic complex [(CO)(5)W(mu,eta(2):eta(1)-P(2)AsMes*(2))W(CO)(4)][SbF(6)] (8a) is formed, which is only stable at low temperatures in solution. Compounds 2a, 7a, and 8a represent the hitherto elusive complexed redox congeners of the diphospha-arsa-allyl system. The analogous oxidation of the triphosphaallyl radical [(CO)(5)W(mu,eta(2):eta(1)- P(3)Mes*(2))W(CO)(4)] (2b) also leads to an allyl cation, which decomposes under CH activation to the phosphine derivative [(CO)(5)W{mu,eta(2):eta(1)-P(3)(Mes*)(C(5)H(2)tBu(2)C(CH(3))(2)CH(2))}W(CO)(4)] (9), in which a CH bond of a methyl group of the Mes* substituent has been activated. All new products have been characterized by NMR spectrometry and IR spectroscopy, and compounds 2a, 3, 6a, 7a, and 9 by X-ray diffraction analysis.