Synthesis and reactions of new 1,2- and 1,3-cyclopentadienyl disubstituted cobalt sandwich compounds (η5-C5H3R2)Co(η4-C4Ph4) (RCH2OH, CHO, CCH, CH2N3, CH2NH2, CH2OAc, CHNPh)

Synthesis and characterization of a series of 1,3- and 1,2-cyclopentadienyl disubstituted derivatives of η5-CpCo(η4-C4Ph4) has been described. The 1,3- and 1,2-cyclopentadienyl diester derived cobalt sandwich compounds {η5-C5H3[C(O)OMe]2}Co(η4-C4Ph4) were prepared by literature procedure and were separated by column chromatography. The reduction of these diester derivatives using LiAlH4 gave the bis(hydroxymethyl) derivatives, [1,3-η5-C5H3(CH2OH)2] Co(η4-C4Ph4) 1 and [1,2-η5-C5H3(CH2OH)2]Co(η4-C4Ph4) 2 which were oxidized to the dialdehydes [1,3-η5-C5H3(CHO)2]Co(η4-C4Ph4) 3 and [1,2-η5-C5H3(CHO)2]Co(η4-C4Ph4) 4 by using tetrapropylammonium perruthenate along with N-methyl morpholine oxide. Reaction of the dialdehydes with (chloromethyl)triphenylphosphonium chloride/n-BuLi followed by elimination of HCl using n-BuLi resulted in the 1,2- and 1,3-cyclopentadienyl disubstituted dialkynes [1,3-η5-C5H3(CCH)2]Co(η4-C4Ph4) 5 and [1,2-η5-C5H3(CCH)2]Co(η4-C4Ph4) 6. The reactions of 1 and 2 with NaN3 in acetic acid resulted in the bis(azidomethyl) derivatives [1,3-η5-C5H3(CH2N3)2]Co(η4-C4Ph4) 7 and [1,2-η5-C5H3(CH2N3)2]Co(η4-C4Ph4) 8. Heating of bis(hydroxymethyl) compounds 1 and 2 in acetic acid at 85–90 °C resulted in the formation of bis(2-acetoxymethyl) derivatives [1,3-η5-C5H3(CH2OAc)2]Co(η4-C4Ph4) 9 and [1,2-η5-C5H3(CH2OAc)2]Co(η4-C4Ph4) 10. The reactions of 1 and 2 with thiophenol in the presence of trifluoroacetic acid in dichloromethane gave bis(phenylmethyl thioether) derivatives 11 [1,3-η5-C5H3(CH2SPh)2]Co(η4-C4Ph4) and [1,2-η5-C5H3(CH2SPh)2]Co(η4-C4Ph4) 12. The click reaction of the 1,2-dialkyne 6 with benzyl azide resulted in the 1,2-bis(triazole) derivative 13. The 1,3-diazide 8 was reduced to bis(aminomethyl) derivative [1,3-η5-C5H3(CH2NH2)2]Co(η4-C4Ph4) 14. Condensation of the 1,3-dialdehyde 3 with aniline resulted in the 1,3-bis(phenylimino) derivative 15. All the new compounds synthesized in this study were characterized by 1H and 13C NMR, FT-IR, HRMS, CHN analysis. The compounds 2–6, 8 and 10 have also been structurally characterized by single crystal X-ray diffraction analysis.

Graphical abstract1,2- and 1,3-bis(hydroxymethyl) cyclopentadienyl derivatives of (η5-Cp)Co(η4-C4Ph4) have been used as precursors for the synthesis of cyclopentadienyl 1,2- and 1,3-disubstituted cobalt sandwich compounds (η5-R2C5H3)Co(η4-C4Ph4) [RCHO, CCH, CH2N3, CH2SPh, CH2OAc, CH2NH2, CHNPh].Figure optionsDownload full-size imageDownload as PowerPoint slideHighlights► Cp ring substitution products derived from 1,2- and 1,3-diesters of (η5-Cp)Co(η4-C4Ph4). ► First synthesis of dialkyne and bis(azidomethyl) derivatives from the same. ► Crystal structures of 7 new disubstituted cobalt sandwich compounds.