Adolf Schäfer

Mehrfachbindungen zwischen hauptgruppenelementen und übergangsmetallen: IV. Chrom-schwefel- und chrom-selen-bindungen: Knüpfung, umwandlungsreaktionen und alkylidenaddition

Abstract New dinuclear chromium—sulfur complexes containing one or two sulfur atoms are formed upon reaction of the ionic complex K[(η 5 -C 5 Me 5 )Cr(CO) 3 ] (Me = CH 3 ; 1) with trithiazyl trichloride at temperatures below ambient. The μ(η 1 :η 2 )-disulfur complex 2a of composition (η 5 -C 5 Me 5 ) 2 Cr 2 (CO) 5 S 2 undergoes concomitant CO-elimination and desulfurization on heating or in the presence of triphenylphosphine; the CrSCr-complex (η 5 -C 5 Me 5 ) 2 Cr 2 (CO) 4 S ( 2c ) is formed in these cases. When diazomethane is treated with 2a , a novel μ,η 2 -thio- formaldehyde complex ( 2d ) results, again following CO- and S-extrusion. While the triple-bonded CrSCr-skeleton present in 2c does not allow alkylidene additions, such reactions, which proceed cleanly, are observed with the corresponding μ 5 -seleno derivative (η 5 -C 5 H 5 ) 2 Cr 2 (CO) 4 Se ( 4 ) synthesized from Na[(η 5 -C 5 H 5 )Cr(CO) 3 ] and sodium selenite in the presence of hydrochloric acid.

Übergangsmetall-methylen-komplexe: LX. Thermolysen von μ-alkyliden-komplexen der übergangsmetalle: Eine erste vergleichende studie☆

Abstract μ-Alkylidene transition metal complexes decompose under standardized thermolysis conditions (180°C/15 min, and 250°C/30 min, respectively) preferably by elimination of the bridging hydrocarbon ligand. Although the range of products as determined by gas chromatography is very complex in many cases, three decomposition patterns are found to be the dominating ones: (i) elimination of the carbene bridge as alkane of the same number of carbon atoms, after take-up of two hydrogen atoms from the ancillary π-bonded ligands; this process is strongly supported by successive methyl substitution of the cyclopentadienyl groups; (ii) dimerization (coupling) of the carbene bridges with concomitant formation of the corresponding olefin, particularly when bis(μ-alkylidene) complexes are being thermolyzed: (iii) elimination of the carbene with intramolecular isomerization, this latter process governs the thermolysis behaviour of bridging C 3+ -ligands; C 2 bridges may either couple to butenes and hexenes or isomerize to ethylene, thus interlinking the behaviour of C 1 and C 3+ derivatives. Carbocyclic carbene bridges thermolytically departing from the attendent metals either undergo ring opening [C 4 → butene(1)] or isomerize to give the cyclic olefines (same number of carbon atoms) following 1,2-hydrogen shift reactions. μ-Formylmethylene ligands are converted into acetaldehyde (after take-up of hydrogen) or lose carbon monoxide, followed by fragmentation processes typical of μ-methylene complexes. Metal effects are less important for the further fate of the thermolytically eliminated alkylidene bridges: nevertheless, some systematic patterns can be recognized: thus, iron strongly promotes carbene/carbene coupling reactions, as compared to ruthenium, cobalt, and rhodium; on the other hand, rhodium supports isomerization of longer-chain alkylidene bridges to internal olefins. It is worth emphasizing the great stability ot the ruthenium parent compound [(η 5 -C 5 H 5 )Ru(μ-NO)] 2 that is detectable in the solid decomposition residues of its alkylidene addition products of the type (μ-CRR′)[(η 5 -C 5 H 5 )Ru(NO)] 2 .