Synthesis and characterization of difunctionalized derivatives of the cyclobutadiene linked dimeric cobalt sandwich compound [(η5-Cp)Co(η4-C4Ph3)]2

The dicarboxylic diester of the cyclobutadiene linked dimeric cobalt sandwich compound, {[η5-C5H4(C(O)OMe)]Co(η4-C4Ph3)}2 on controlled reduction with LiAlH4 gave the bis(hydroxymethyl) compound {[η5-C5H4(CH2OH)]Co(η4-C4Ph3)}21 in 98% yield. The diester was also reduced to the dimethyl derivative {[η5-C5H4(Me)]Co(η4-C4Ph3)}22 using LiAlH4 and AlCl3. Compound 1 was reacted with NaN3 in acetic acid at 50 °C to get the diazido methyl derivative {[η5-C5H4(CH2N3)]Co(η4-C4Ph3)}23 whereas the bis (2-acetoxy methyl) derivative {[η5-C5H4(CH2OC(O)Me]Co(η4-C4Ph3)}24 was obtained in almost quantitative yield by heating compound 1 with acetic acid at 80–85 °C. Click reaction of compound 3 with phenylacetylene resulted in the bis triazole derivative {[η5-C5H4(CH2N3C2HPh)]Co(η4-C4Ph3)}25 whereas reduction of 3 with LiAlH4 gave the bis (aminomethyl) compound {[η5-C5H4(CH2NH2)]Co(η4-C4Ph3)}26. The diacetyl derivative [{η5-C5H4[C(O)Me]}Co(η4-C4Ph3)}]27 was prepared by the reaction of in-situ generated {η5-C5H4[C(O)Me]}Co(PPh3)2, diphenyl acetylene and diphenyl diacetylene in 2:1:3 molar ratio in 42% yield. A novel dimeric derivative having two different functional groups on the cyclopentadienyl rings [{η5-C5H4[C(O)OMe]}Co(η4-C4Ph3)][{η5-C5H4[C(O)Me]}Co(η4-C4Ph3)] 8 was synthesized in 52% yield by reacting the ethynyl ester {η5-C5H4[C(O)OMe]}Co[η4-C4Ph3(CCPh)] with {η5-C5H4[C(O)Me]}Co(PPh3)2 and diphenyl acetylene in 1:2:3 molar ratio. Structural studies on compounds 1–4, 7 and 8 indicated that the two cobalt sandwich units were oriented almost anti to each other whereas compound 3 had the two cyclobutadiene rings oriented at an angle of 55.7(1)° to each other. The identity of compounds 5 and 6 was confirmed by 1H NMR, 13C NMR, IR and mass spectrometry.

Synthesis and characterization of new derivatives of the cyclobutadiene linked dimeric cobalt sandwich compound [(η5-Cp)Co(η4-C4Ph3)]2 have been carried out. A novel unsymmetrical derivative having acetyl and methoxyester substituents on the Cp rings, which has the potential for generating two different types of chiral centres has been prepared and characterized.Figure optionsDownload as PowerPoint slideHighlights
► Synthesis of new cyclopentadienyl functionalized cyclobutadiene linked dimeric cobalt sandwich compounds.
► First unsymmetrical dimeric cobalt sandwich compound having ester and acetyl groups on the Cp ring.
► Novel π–π stacking interaction between the phenyl rings of cobalt sandwich compounds.