Lothar Weber

Phosphorus Heterocycles: From Laboratory Curiosities to Ligands in Highly Efficient Catalysts

Phosphabenzenes and phosphaferrocenes were among the first compounds with P-C multiple bonds. For nearly 30 years the chemistry of these molecules was essentially a domain left to basic researchers. Recently, however, it was reported that transition metal complexes with phosphabenzene and phosphaferrocene ligands exhibit remarkable potential as catalysts. Catalysts based on rhodium (i) and various phosphabenzenes appear to be superior to classical systems in the hydroformylation of terminal and internal alkenes. In addition planar-chiral phosphaferrocene species display an excellent performance as directing ligands in a series of enantioselective asymmetric syntheses.

Luminescence properties of C-diazaborolyl-ortho-carboranes as donor-acceptor systems.

Seven derivatives of 1,2-dicarbadodecaborane (ortho-carborane, 1,2-C(2)B(10)H(12)) with a 1,3-diethyl- or 1,3-diphenyl-1,3,2-benzodiazaborolyl group on one cage carbon atom were synthesized and structurally characterized. Six of these compounds showed remarkable low-energy fluorescence emissions with large Stokes shifts of 15100-20260 cm(-1) and quantum yields (Φ(F)) of up to 65% in the solid state. The low-energy fluorescence emission, which was assigned to a charge-transfer (CT) transition between the cage and the heterocyclic unit, depended on the orientation (torsion angle, ψ) of the diazaborolyl group with respect to the cage C-C bond. In cyclohexane, two compounds exhibited very weak dual fluorescence emissions with Stokes shifts of 15660-18090 cm(-1) for the CT bands and 1960-5540 cm(-1) for the high-energy bands, which were assigned to local transitions within the benzodiazaborole units (local excitation, LE), whereas four compounds showed only CT bands with Φ(F) values between 8-32%. Two distinct excited singlet-state (S(1)) geometries, denoted S(1)(LE) and S(1)(CT), were observed computationally for the benzodiazaborolyl-ortho-carboranes, the population of which depended on their orientation (ψ). TD-DFT calculations on these excited state geometries were in accord with their CT and LE emissions. These C-diazaborolyl-ortho-carboranes were viewed as donor-acceptor systems with the diazaborolyl group as the donor and the ortho-carboranyl group as the acceptor.

The chemistry of 1,3,2-diazaborolines (2,3-dihydro-1H-1,3,2-diazaboroles)

1,3,2-Diazaborolines (2,3-dihydro-1H-1,3,2-diazaboroles) are at the interface between inorganic, organometallic and organic chemistry. The planar rings with 6 pi -electrons may be regarded as heteroarenes, as evidenced by NMR and photoelectron spectra and confirmed by quantum mechanical calculations. The capability of 1,3,2-diazaborolines to act as eta (5)-ligands adds chemical proof to this idea. High-yield syntheses of 1,3,2-diazaborolines with functional groups at boron have recently become available, providing a rich area of chemistry ranging from substitution processes via borylstannations to their conversion into oxazaborolidines

Homoleptic Isocyanide Metalates

Novelties and surprises in the chemistry of metal isocyanides: The synthesis and structure determination of homoleptic isocyanide metalates [M(CNXyl)m ]- (M=Co, m=4; M=Mn, m=5; Xyl=2,6-Me2 C6 H3 ) indicate that we need to revise our understanding of transition metal-isocyanide interactions. Further investigations will be required to determine whether these salts with isocyanide metalate ions display a chemistry as rich as that of the analogous carbonyl metalates.

Synthese und Reaktivität von 2-Brom-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol Molekülstruktur von Bis(1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol-2-yl)

Die Reaktion einer Suspension von Calciumhydrid in Toluol mit N,N′-Diethyl-o-phenylendiamin (1) und Bortribromid liefert 2-Brom-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol (2) als farbloses Ol. Verbindung 2 wird von Silbercyanid in Acetonitril glatt in 2-Cyano-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol (3) umgewandelt, wahrend die Behandlung von 2 mit der aquimolaren Menge an Methyllithium zu 1,3-Diethyl-2-methyl-2,3-dihydro-1 H1,3,2-benzodiazaborol (4) fuhrt. 1,3,2-Benzodiazaborol 2 wird von einer Kalium–Natrium-Legierung glatt zum Bis(1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol-2-yl) (7) reduziert, das aus n-Pentan in Form farbloser Nadeln kristallisiert. Verbindung 7 wird ebenfalls bei dem Versuch, aus 2 und LiSnMe3 das entsprechende 2-Trimethylstannyl-1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol herzustellen, gebildet. N,N′-Bis(1,3-diethyl-2,3-dihydro-1 H-1,3,2-benzodiazaborol-2-yl)-1,2-diaminoethan (6) ist das einzige borhaltige Produkt der Umsetzung von 2 mit Li(en)C≡CH. Die Verbindung 2–4, 6, 7 wurden auf elementaranalytischen und spektroskopischen Weg (IR, 1H, 11B{1H}, 13C{1H}NMR, MS) charakterisiert. Von 7 wurde eine Rontgenstrukturanalyse angefertigt.

Übergangsmetall-substituierte Acylphosphane und Phosphaalkene. XI: Phosphaalkenyl-, Disilylphosphido- und Diacylphosphidokomplexe des Dicarbonylpentamethylcyclopentadienylosmium. Zur Kenntnis von [(η5-C5Me5)Os(CO)2]2

Abstract The reaction of Os 3 (CO) 12 with C 5 Me 5 H in boiling decalin gives the complexes (η 5 -C 5 Me 5 )(CO) 2 OsH and [(η 5 -C 5 Me 5 )(CO) 2 Os] 2 . Both compounds were converted into (η 5 -C 5 Me 5 )(CO) 2 OsP(SiMe 3 ) 2 (III) via the intermediate form (η 5 -C 5 -Me 5 )(CO) 2 OsBr. Complex III was treated with ArC(O)Cl (Ar = Ph, 2,4,6-Me 3 C 6 H 2 ) to give mixtures of the phosphaalkenyl complexes (η 5 -C 5 Me 5 )(CO) 2 OsPC(OSiMe 3 )(Ar) (IVa, b) and the diacylphosphido complexes (η 5 -C 5 Me 5 )(CO) 2 -OsP[C(O)Ar] 2 (Va, b). Pivaloyl chloride underwent reaction with III to give complex Vc as the only product. The synthesis of the complexes IVa, b includes an E/Z isomerization process.

Synthesis and Structure of 2-Hydro-, 2-Alkyl-, 2-Alkynyl-, and 2-Stannyl-2,3-dihydro-1H-1,3,2-diazaboroles

1,3-Di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (4a) and 1,3-bis(2,6-dimethylphenyl)-2,3-dihydro-1H-1,3,2-diazaborole (4b) were formed by the reaction of the corresponding 2-bromo or 2-iodo derivatives 1a and 2b with LiAlH4. Treatment of 1a with n-butyllithium afforded 2-n-butyl-1,3-di-tert-butyl-2,3-dihydro-1H-1,3,2-diazaborole (5a), whereas 1,3-di-tert-butyl-2-cyano-2,3-dihydro-1H-1,3,2-diazaborole (3a) was converted into the 2-tert-butyl derivative 6a or the 2-ethynyl-1,3,2-diazaborole 7a by means of tert-butyllithium or by the ethylenediamine adduct of lithium acetylide. Similarly, 1,3-di-tert-butyl-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8a) and 1,3-bis(2,6-dimethylphenyl)-2-trimethylstannyl-2,3-dihydro-1H-1,3,2-diazaborole (8b) were accessible from 1a or 2b and trimethylstannyllithium. In the complex 9a the compound 3a serves as an η1 ligand towards the [Cr(CO)5] unit via the cyano group. These novel compounds were characterized by 1H-, 11B-, 13C-, and 119Sn-NMR spectroscopy, as well as by X-ray structure analyses of 4b, 8a, and 9a.

Übergangsmetall-substituierte acylphosphane und phosphaalkene: VIII. Dicarbonylcyclopentadienyleisen-substituierte phosphaalkene mit Fe-P-einfachbindung: synthese und struktur

Abstract Phosphaalkenyliron complexes with covalent metal-phosphorus bonds are synthesized from (η5-C5H5)(CO)2FeP(SiMe3)2 and acid chlorides RC(O)Cl (R = Ph, 2,4,6-Me3C6H2, t-Bu). The molecular structure of (Z)-(η5-C5H5)(CO)2FePC(OSi-Me3)(t-Bu) is established by X-ray structure analysis.

Substitutionsreaktionen an Pentacarbonyl(dimethyloxosulfoniummethylid)chrom(0)

Abstract From the reactions of with some tertiary phosphines pentacarbonylphosphoniumylidchromium complexes are obtained. Triphenylarsine reacts analogously to give the corresponding arsoniumylide complex. The chemical and spectroscopic properties of these compounds are described. Furthermore the mechanism of the reaction is discussed.

Crystal Structures of the Carborane Dianions [1,4-(PhCB10H10C)2C6H4]2− and [1,4-(PhCB10H10C)2C6F4]2− and the Stabilizing Role of the para-Phenylene Unit on 2 n+3 Skeletal Electron Clusters†

While carboranes with 2 n+2 and 2 n+4 (n=number of skeletal atoms) skeletal electrons (SE) are widely known, little has been reported on carboranes with odd SE numbers. Electrochemical measurements on two-cage assemblies, where two C-phenyl-ortho-carboranyl groups are linked by a para-phenylene or a para-tetrafluorophenylene bridge, revealed two well separated and reversible two-electron reduction waves indicating formation of stable dianions and tetraanions. The salts of the dianions were isolated by reduction with sodium metal and their unusual structures were determined by X-ray crystallography. The diamagnetic dianions contain two 2 n+3 SE clusters where each cluster has a notably long carborane C–carborane C distance of ca 2.4 Å. The π conjugation within the phenylene bridge plays an important role in the stabilization of these carboranes with odd SE counts.