Lithium, cyclohexadienyl complexes

The synthesis of the zero-valent, 1,3-cyclohexadiene benzene ruthenium complex 196a has been mentioned as a coproduct of the cyclohexadienyl complex 236a in the reduction of the benzene ruthenium dication 235 with lithium aluminum hydride. Reduction of 235 with sodium borohydride in THF, however, gives only the air-sensitive, yellow-green ruthenium(O) complex 196a (118). This reaction has been generalized to... 

Biphenylbis(tricarbonyt)chromium (l).1 Lithium anthracenide converts biphenyl complexed by two Cr(CO), groups into a fairly stable dianion of structure 2, in which two V-cyclohexadienyl anions are coordinated with Cr(CO)3. This dianion is alkylated by an alkyl halide to form 3, in which one benzene ring is... 

Tj -Cyclohexadienyl ruthenium complexes have been obtained either by addition of nucleophiles to the arene ring of arene ruthenium(II) complexes or by protonation of ruthenium(O) complexes. The first complex prepared, the benzene cyclohexadienyl ruthenium cation 236a, has been obtained together with the zero-valent arene cyclohexadiene ruthenium(O) complex 196a, by reaction of 235a with lithium aluminum hydride (118) [Eq. (27)]. 

Protonation of 322 with tetrafluoroboric acid in diethyl ether gives the cyclohexadienyl derivative 325 in 70% yield. Treatment of 325 with lithium aluminum hydride yields the biscyclohexadienyl osmium(II) complex 326. Treatment of 322 with PMe3 at 60°C gives the hydridophenyl osmium-(II) complex 181, rather than the expected arene bistrimethylphosphine osmium(O) compound, via intramolecular C—H bond activation of the benzene ligand (192,193) (Scheme 38). Compound 181 as well as the analogous ruthenium complex (92) have also been obtained directly by cocondensation of osmium or ruthenium atoms with benzene and tri-methylphosphine (62) [Eq. (44)]. 

The reaction of the rhenium complex XLII with lithium at 200°C is a special case, producing the dimeric )f -cyclohexadienyl species (XLIII) ... 

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