Matthias Freytag

Reactivity of a Frustrated Lewis Pair and Small-Molecule Activation by an Isolable Arduengo CarbeneB{3,5-(CF3)2C6H3}3 Complex

Tris[3,5-bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3-di-tert-butylimidazolin-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene to form isolable normal adducts. In the case of 1,3-di-tert-butylimidazolin-2-ylidene, the adduct exhibits dynamic behaviour in solution and frustrated-Lewis-pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the C-H activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene-borane adduct can be observed. In contrast, the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene-borane adducts.

Hydrogen bonding and halogen–halogen interactions in 4-halopyridinium halides

The solid state structures of the 4-halopyridinium halides 4-XC5H4NH+X- (X=Cl, Br, I) all display chains of the form [···X–C5H4N–H+···X-···X–C5H4N–H+···X-···] involving N–H···X- hydrogen bonds and X···X- contacts; the former become longer and the latter shorter (relative to the sum of the van der Waals radii) with increasing size of X.

Calix[4]arene‐based Bis‐phosphonites, Bis‐phosphites, and Bis‐O‐acyl‐phosphites as Ligands in the Rhodium(I)‐catalyzed Hydroformylation of 1‐Octene

New calix[4]arene-based bis-phosphonites, bis-phosphites and bis-O-acylphosphites were synthesized and characterized. Treatment of these P-ligands with selected rhodium and platinum precursors led to mononuclear complexes that were satisfactorily characterized. The solid state structure of the dirhodium(I) complex 14 has been determined by X-ray diffraction. The two rhodium centres are bridged by two chloro ligands; one rhodium atom is further coordinated by calix[4]arene phosphorus atoms and the other by cyclooctadiene. The new calix[4]arene P-ligands were tested in the Rh(I) catalyzed hydroformylation of 1-octene. All Rh(I) complexes catalyzed the reaction leading to high chemoselectivity with regard to the formation of aldehydes. Yields and n/iso-selectivities depended on the reaction conditions. Average yields of 80 % and n/iso-ratios of about 1.3 to 1.5 were observed. High yields of aldehydes can be achieved using the methoxy substituted P-ligands at low Rh:ligand ratios. Auf Calix[4]arenen basierende Bis-phosphonite, Bis-phosphite und Bis-O-acyl-phosphite als Liganden in der rhodium(I)-katalysierten Hydroformylierung von 1-Octen Neue auf Calix[4]arenen basierende Bis-phosphonite, Bis-phosphite und Bis-O-acyl-phosphite wurden synthetisiert und charakterisiert. Die Umsetzung dieser Phosphorliganden mit ausgewahlten Rhodium- und Platinvorstufen fuhrte zu mononuklearen Komplexen, die vollstandig charakterisiert wurden. Durch eine Rontgenstrukturanalyse konnte die Struktur des Dirhodium( I)-Komplexes 14 im festen Zustand bestimmt werden. Die beiden Rhodiumzentren sind durch zwei Chlorliganden verbruckt, wobei das eine Rhodiumatom an die Phosphoratome des Calix[4]-arens und das andere Rhodiumatom durch das Cyclooctadien koordiniert ist. Die neuartigen phosphorhaltigen Calix[4]aren-Liganden wurden in der Rhodium(I)-katalysierten Hydroformylierung von 1-Octen getestet. Alle Rh(I)-Komplexe katalysierten die Reaktion bei hoher Chemoselektivitat, bezogen auf die Bildung von Aldehyden. Ausbeuten und n/iso-Selektivitaten waren dabei von den Reaktionsbedingungen abhangig. Durchschnittliche Ausbeuten von 80 % und n/iso-Verhaltnisse von 1.3 bis 1.5 wurden beobachtet. Hohe Ausbeuten an Aldehyden bei geringen Rhodium:Ligand-Verhaltnissen konnten durch den Einsatz von methoxysubstituierten Phosphorliganden erzielt werden.

Efficient metathesis of terminal alkynes.

Now even terminal: The 2,4,6-trimethylbenzylidyne complexes [MesC≡M{OC(CF(3))(2)Me}(3)] (M=Mo, W) were synthesized from [Mo(CO)(6)] and [W(CO)(6)], respectively. The molybdenum complex is an efficient catalyst for the metathesis of internal and terminal alkynes and also for the ring-closing metathesis of internal and terminal α,ω-diynes at room temperature and low catalyst concentrations.

Asymmetric synthesis of chiral N-(1-methylbenzyl)aminophosphines

The reactions of chlorophosphines 1 with (S)- or (R)-1-methylbenzylamines 2 proceed stereoselectively to give N-(1-methylbenzyl)aminophosphines 3, which were isolated as crystalline borane complexes with 100% diastereomeric purity. The absolute configuration of the new chiral compounds was established by X-ray analysis and chemical extrapolation.

Chiral 1,8-bis(tert-butylphenylphosphino)naphthalene oxides and sulfides: resolution and structures

Abstract Chiral racemic 1,8-bis( tert -butylphenylphosphino)naphthalene oxide ( 2a ) was resolved into enantiomers by fractional crystallization of its diastereomeric adducts 3a with (+)-(2 S ,3 S )-di- O -benzoyl tartaric acid (DBTA), followed by neutralization. Racemic 1,8-bis( tert -butylphenylphosphino)naphthalene ( 1a ) was oxidized with sulfur to two isomers of 1,8-bis( tert -butylphenyl-phosphino)naphthalene monosulfide, rac - 4a and rac - 4a ′, or 1,8-bis( tert -butylphenylphosphino)naphthalene disulfide, rac - 5a . The compounds were characterized by NMR spectroscopy ( 1 H, 31 P, 13 C). Crystal structures were determined by the X-ray method for (−)- 3a, rac - 4a , rac - 4a ′ and rac - 5a ; this allowed the determination of the absolute configuration ( S , S ) for the more soluble adduct (−)- 3a . It was found that rac - 1a undergoes partial epimerization in boiling xylene to give the meso form.

Preparation and structures of 1-dimethylamino-2-bis(dimethylamino)- and 1-chloro-2-bis(diethylamino)-1-phospha-2-phosphonium acenaphthene: the first examples of the 1,2-dihydro-1,2-diphospha-acenaphthene ring system

Abstract This paper describes the preparation of 1,8-bis[bis(dimethylamino)phosphino]naphthalene ( 2a ) and the attempted preparation of its isopropyl analogue 2c , which led to the formation of 1-naphthyl-bis(diisopropylamino)phosphine ( 4 ), and to other unidentified products. The X-ray structures of 2a and 4 are discussed in comparison to those of 1,8-bis[bis(diethylamino)phosphino]naphthalene ( 2b ) and 1-naphthyl-di- tert -butylphosphine ( 5 ), respectively. In the structures of 2a , 2b and 4 the (R 2 N) 2 P groups (R=alkyl) are eclipsed with respect to the naphthalene plane, whereas the R 2 P groups (R=alkyl or aryl) in 5 , as in 1,8-bis(diorganophosphino)naphthalenes in general, adopt a conformation between bisecting and eclipsed. Furthermore, the reactions of 2a and 2b with BX 3 ether adducts (X=F, Cl) are described, which furnished the heterocyclic [σ 3 P–σ 4 P + ]-diphosphorus compounds, 1-dimethylamino-2-bis(dimethylamino)-, 1-diethylamino-2-bis(diethylamino)- and 1-chloro-2-bis(diethylamino)-1-phospha-2-phosphonium-acenaphthene ( 6a , 6b and 7b ); the first examples of the 1,2-dihydro-1,2-diphospha-acenaphthene ring system. The X-ray structures of 6a and 7b display a relief of strain compared to the parent bis-aminophosphines 2a and 2b , quantified by negative splay angles [−7.89° ( 6a ) and −9.40° ( 7b ); cf. +12.16° ( 2a ) and +12.0° ( 2b )] and the bonded [225.38 ( 6a ) and 223.16 ( 7b ) pm] compared to the non-bonded phosphorus–phosphorus distances [311.9 ( 2a ) and 311.7 ( 2b ) pm]. A mechanism is discussed for the formation of 6b and 7b from 2b and gaseous hydrogen chloride.

Platinum(II) Complexes of P-Chiral 1, 8-Bis(diorganophosphino)naphthalenes; Crystal Structures of dmfppn,rac-[PtCl2(dmfppn)], andrac-[PtCl2(dtbppn)] (dmfppn = 1, 8-di(methyl-pentafluorophenylphosphino)naphthalene and dtbppn = 1, 8-di(tert-butylphenylphosphino)naphthalene)

The reaction of 1, 8-dilithionaphthalene 2, with 2 equivalents of rac-Me(C6F5)PCl, gave a 6 : 1 mixture of rac- and meso-1, 8-di(methyl-pentafluorophenylphosphino)naphthalene (dmfppn, rac-3h and meso-3h), but no reaction was observed when the sterically crowded rac-tBu(C6F5)PCl was used. In 31P NMR experiments, rac-3h and mmeso-3h exhibited characteristic signals (virtual quintets), which indicate that there is significant coupling through space (3JPF + 7JPF ≈ 15 Hz). Compound rac-3h was isolated by fractional crystallisation and treated with aqueous H2O2 to yield the corresponding bis-phosphine dioxide, rac-7h. In contrast to rac-3h, there was no sign of through-space coupling in rac-7h, which again illustrates that the latter operates via the lone pairs at phosphorus. Platinum(II) complexes were prepared from the new, P-chiral chelate rac-3h, and the related ligand 1, 8-di(tert-butylphenylphosphino) naphthalene (rac-dtbppn, rac-3e). All isolated new compounds were characterised by multinuclear NMR and IR spectroscopy, mass spectrometry, and elemental analysis. Single-crystal X-ray structure determinations were performed for rac-dmfppn (rac-3h), rac-[PtCl2(dtbppn)] (rac-17e), and rac-[PtCl2(dmfppn)] (rac-17h). rac-3h displays crystallographic twofold symmetry. In rac-17h, the electron-withdrawing effect of the C6F5 groups causes a shortening of the Pt—P bond to ca. 220 pm (cf. 223 pm in rac-17e). Platin(II)-Komplexe von P-chiralen 1, 8-Bis(diorganophosphino)naphthalinen; Rontgenstrukturanalysen von dmfppn, rac-[PtCl2(dmfppn)] und rac-[PtCl2(dtbppn)] (dmfppn = 1, 8-Di(methyl-pentafluorphenylphosphino)naphthalin und dtbppn = 1, 8-Di(tert-butylphenylphosphino)naphthalin) Die Reaktion von 1, 8-Dilithionaphthalin (2) mit 2 Aquivalenten rac-Me(C6F5)PCl ergab ein 6 : 1 Gemisch von rac-und meso-1, 8-Di(methyl-pentafluorphenylphosphino)naphthalin (dmfppn, rac-3h und meso-3h). Wurde jedoch das sterisch anspruchsvollere rac-tBu(C6F5)PCl verwendet, konnte keine Reaktion beobachtet werden. In den 31P NMR Spektren zeigten rac-3h und meso-3h) charakteristische Signale (virtuelle Quintetts), die auf eine signifikante Kopplung durch den Raum deuten (3JPF + 7JPF ≈ 15 Hz). Die Verbindung rac-3h wurde durch fraktionierende Kristallisation isoliert und ein Teil davon mit wassr. H2O2-Losung versetzt, wodurch das entsprechende Bis-phosphinoxid (rac-7h) erhalten wurde. Anders als rac-3h, zeigte rac-7h keine Anzeichen fur Kopplungen durch den Raum (through-space coupling), was erneut illustriert, das diese Kopplungen durch die nicht-bindenden Elektronenpaare am Phosphor vermittelt werden. Von dem neuen, P-chiralen Chelat-Liganden rac-3h und dem strukturell verwandten Liganden 1, 8-Di(tert-butylphenylphosphino)-naphthalin (rac-dtbppn, rac-3e) wurden Platin(II)-Komplexe hergestellt. Alle neuen Produkte wurden durch NMR und IR Spektroskopie, Massenspektrometrie und Elementaranalysen charakterisiert. Von den Verbindungen rac-dmfppn (rac-3h), rac-[ PtCl2(dtbppn)] (rac-17e) und rac-[PtCl2(dmfppn)] (rac-17h) wurden Einkristall-Rontgenstrukturanalysen angefertigt. rac-3h zeigt kristallographische, zweizahlige Symmetrie. In rac-17h fuhrt der elektronenziehende Effekt der C6F5-Gruppen zu einer Verkurzung der Pt—P Bindung auf ca. 220 pm (vgl. 223 pm in rac-17e).

N-Heterocyclic Carbene Stabilized Boryl Radicals

The reaction of the 2-(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4-R-C6 H4 )2 BX (R=H, X=Br; R=CH3 , X=Cl; R=CF3 , X=Cl) afforded the NHC-stabilized borenium cations 10 a-c. Cyclic voltammetry revealed a linear correlation between the Hammett parameter σp of the para substituent and the half-wave potential. Chemical reduction with decamethylcobaltocene, [(C5 Me5 )2 Co], furnished the corresponding radicals 11 a-c; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a-c, with large hyperfine coupling constants to the boron isotopes 11 B and 10 B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR2 ) revealed for 11 a-c a spin density ratio (BR2 /NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X-ray diffraction analysis.

Hydrogen bonds C–H⋯Cl as astructure-determining factor in the gold(I) complexbis(3-bromopyridine)gold(I)dichloroaurate(I)

The crystal structure of the title compound involves three types of secondary interaction; hydrogen bonds of the form C–H⋯Cl account for the mutually perpendicular arrangement of the cations and anions.