Josef Hofmann

ansa-Metallocene derivatives: XVI. Chiral titanocene and zirconocene derivatives with symmetrically substituted, tetramethylethanediyl-bridged ligand frameworks. Crystal structures of representative examples

Syntheses of disubstituted, tetramethylethanediyl-bridged titanocene derivatives (CH3)4C2(1-C5H3-3-R)2TiCl2, with R  t-butyl, trimethylsilyl, isopropyl, α,α-dimethylbenzyl and 1-phenylcyclohexyl, by reductive coupling of the appropriately substituted 6,6-dimethylpentafulvenes with Mg/CCl4 and reaction of the resulting di-Grignard compounds with TiCl3·3THF are described along with those of several zirconium analogues. The reaction sequence in each case gives, together with the desired racemate, comparable amounts of the corresponding meso-configurated complex. The NMR data for the racemic and meso diastereomers of these compounds and crystal structures of one meso and several racemic representatives are reported.

Übergangsmetalkoordinierte Heteroolefine als Synthesebausteine : Einfluss des Alkins auf die Geschwindigkeit und die Stereoselektivität der Reaktion mit Heteroaldehyd- bzw. -keton-Komplexen

Abstract Pentacarbonyl-(-thio- and -seleno-aldehyde) complexes and pentacarbonyl(diphenylselenoketone) complexes, (CO)5M[XC(Ph)R] (M  W: X  S, R  H (Ia); X  Se, R  H (Ib); X  Se, R  Ph (Ic); M  Cr: X  Se, R  Ph (Id)), react with bis(diethylamino)acetylene, Et2NcCNEt2 (II) by [2 + 2]-cycloaddition of the alkyne to the XC bond of I, and with electrocyclic ring opening to give the pentacarbonyl-(-thio- and -seleno-acrylamide) complexes, (CO)5M[XC(NEt2)C(NEt2)C(Ph)R] (III). If R  H, ring opening is stereospecific. According to the NMR spectra, only the E isomer (with respect to the CC double bond) is formed. Compounds IIIa and IIIb were studied by X-ray crystallography. The plane of the amido group, XC(N)C, is almost perpendicular to that of the olefin, C(N)CC. The reaction of Ic with II in 1,1,2-trichloroethane follows second-order kinetics: −d[Ic]/dt = k2[Ic][II]. The activation enthalpy ΔH* is small (27(2) kJ/mol), and the activation entropy ΔS* is strongly negative (−164(8) J/(mol K)). Cleavage of the CrSe Bond in IIId is achieved by applying a CO pressure (105 bar) at 70°C and the selenoacrylamide SeC(NEt2)C(NEt2)CPh2 is isolated in almost quantitative yield.

Übergangsmetall-koordinierte heteroalkene als synthesebausteine: Nachweis und charakterisierung einer zwischenstufe der reaktion von thio- und selenoaldehyd-komplexen mit bis(diethylamino)acetylen

Abstract Pentacarbonyl(thiobenzaldehyde)- and -(selenobenzaldehyde)tungsten, (CO) 5 W[XC(Ph)H] [X = S ( 1a ), Se ( 1b )] react with bis(diethylamino)acetylene, Et 2 NCCNEt 2 ( 2 ), by addition of the alkyne to the XC bond under electrocyclic ring opening to give substituted pentacarbonyl(thioacrylamide)- and -(selenoacrylamide)tungsten complexes, (CO) 5 W[XC(NEt 2 )C(NEt 2 )C(Ph)H]. The kinetically controlled reaction product is the Z -isomer (with respect to the CC double bond) ( 3 ). In a subsequent, slower reaction, 3 isomerizes to give the E -isomer 4 . 3b isomerizes more rapidly than 3a . For the isomerization of 3a to 4a the free enthalpy of activation Δ G ≠ is 102 kJ/mol (at 40°C in CD 3 COCD 3 ). The complex 3a was isolated and its structure established by an X-ray diffraction study.

N-ACYLIMINIUM SALTS FROM THE REACTION OF NITRILIUM SALTS WITH ALDEHYDES

Abstract The nitrilium hexachloroantimonates 2a,d,g,p react with aromatic aldehydes to give isolable N-acyliminium hexachloroantimonates 10a-m. The N-aroyliminium salts (10g-m) and acyliminium salts with an aliphatic N-acyl group (10a-f) are of remarkably different stability. Contrary to the N-aroyliminium salts, compounds 10a-f are unstable in solution, e. g. react immediately with acetonitrile. With excess of aldehyde 10n,o give insertion products of the probable structures 12a,b. For 10b,f X-ray structural analyses have been carried out. The N-acylcyanamidium hexachloroantimonate 2p reacts with aldehydes to give new classes of cyclic N-acyliminium salts 13a-f, and 14f, respectively.

Inenylcarben-Komplexe aus Alkinylcarben-Komplexen und elektronenreichen Alkinen

The alkoxy(phenylethynyl)carbene]pentacarbonyl complexes, (CO)5M[C(OR)CCPh] (1) [M = W, R = Me (a), Et (b); M = Cr, R = Me (c)], react with bis(diethylamino)ethyne, diethylaminopropyne, and methylthiopropyne, respectively, to give inenyl-carbene complexes, (CO)5M{C(R1)[C(R2) = C(OR)CCPh]} (R1 = NEt2, R2 = NEt2, Me; R1 = MeS, R2 = Me), by insertion of the CC bond of the alkyne into the metal-carbene bond. The reaction is stereoselective. The structure of (CO)5W{C(NEt2)[C(NEt2)CCPh]} was established by an X-ray diffraction study.

Ungewöhnliche 1,4-Insertion eines 1,4-Diazabutadiens in die C-H-Bindung von Benzyliden(pentacarbonyl)wolfram

Abstract Benzylidene(pentacarbonyl)tungsten, (CO)5W[C(Ph)H] (1), reacts with diacetyldianil, PhNC(Me)(Me)CNPh (2), by insertion of the NCCN fragment into the benzylidenehydrogen bond to give the aminocarbene complex (CO)5W{C(Ph)[N(Ph)CMeCMeN(H)Ph]} (3). The structure of 3 is established by an X-ray diffraction study. In 3, the two phenyl and methyl groups are mutually cis with respect to the partial C(benzylidene)N and the CC double bond, respectively. In the presence of acids, 3 rapidly rearranges to give (CO)5W{C(Ph)[N(Ph)C(H)MeCMeNph]} (4).

2-Azoniaallenyliden-Komplexe des Mangans : Synthese, Struktur und Reaktivität

Abstract Cp(CO) 3 Mn ( 1 ) reacts with [NC(R 1 )R 2 ] − and [Et 3 O]BF 4 to give alkylideneamino(ethoxy)carbene complexes, Cp(CO) 2 MnC(OEt)NC(R 1 )R 2 ( 3 ) [C(R 1 )R 2  CPh 2 ( a ), C(C 6 H 4 ) 2 O ( b ), C(CMe 3 ) 2 ( c ), C(CMe 3 )Tol ( d ), Tol = C 6 H 4 Me- p ]. From 1 , [NCPh 2 ] − and MeOSO 2 F the complex Cp(CO) 2 MnC(OMe)NCPh 2 ( 4a ) is obtained. The reaction of 1 with [NC( i Pr)Ph] − and Me 3 SiCl, however, yields an isocyanide complex, Cp(CO) 2 MnC  NC(Ph)CMe 2 ( 7 ). Photolysis of 3a in THF in the presence of PTol 3 affords Cp(CO)(PTol 3 )MnC(OEt)NCPh 2 ( 6a ). According to the X-ray structure analysis of 4a the CNC fragment is strongly bent (CNC angle: 130.0(2)°) and both CN distances are significantly different. Alkoxide abstraction from 3a - c 4a and 6a by BF 3 gives 2-azoniaallenylidene complexes 13a - c and 14a , [Cp(CO)(R)Mn CNC(R 1 )R 2 ]BF 4 [R  CO( 13 ), PTol 3 ( 14a )], respectively. The structure of 14a -BF 4 has also been determined by an X-ray diffraction analysis. The MnCNC fragment is almost linear and allows the formation of two orthogonal π-systems. Both CN distances differ significantly. The complexes are best described as hybrids of three resonance structures with that of the carbocationic structure beeing the main contributor. Accordingly, 13a -BF 4 adds a number of nucleophiles (OEt 2 , PMe 3 , H − , Me − , t BuSH, PHPh 2 , PH 2 Mes) at the terminal carbon of the MnCNC fragment to give, depending on the nucleophile, cationic or, after H + abstraction, neutral isocyanide complexes.

Regio- and stereo-selective formation of methylenecyclopropane complexes from allenes and benzylidenepentacarbonyl tungsten

Benzylidenepentacarbonyl tungsten reacts with dimethylallene and phenylallene, respectively, by regiospecific and stereoselective transfer of the benzylidene group to the allene and co-ordination of the product methylenecyclopropane which can be cleaved almost quantitatively from the metal by Br–; the structure of the 2-phenyl-3,3-dimethylmethylenecyclopropane complex is established by an X-ray structure analysis.

Phosphine complexes of main group elements. [(Me3Si)C(PMe2)2]2Ge2I2, and intramolecular germylene (germanediyl) donor–germylene acceptor complex with a germylene–phosphane chelating ligand

The addition of I2 to the bis-germylene complex [(Me3Si)C(PMe2)2]2Ge2(GeI–GeI)(1) surprisingly results in the oxidation of only one Ge atom and rearrangement of one of the phosphinomethanide ligands; the Gel2 formed is complexed by a chelating germylene–phosphine ligand in the form of a homonuclear donor–acceptor complex.

Dichalcogenolanes by ring-expansion of transition metal-coordinated thietanes and selenetanes

Pentacarbonyltungsten-coordinated selenetanes react with seleno- and telluro-cyanate by insertion of the chalcogen atom into the Se–C bond of the selenetanes to give 1,2-diselenolanes and -selenatellurolane, respectively; the analogous reaction of (CO)5W[[graphic omitted](OEt)H] with tellurocyanate affords a 1,2-thiatellurolane complex.