Ring expansion of spirocydie ligands in pentacarbonylchromium complexes to tetrahydroindene derivatives

Article abstract of DOI:10.1002/cber.19961290605

Pentacarbony 1 (pentamethylenevinylidene) chromium, [(CO)₅Cr=C=C(CH₂)₅] (1), reacts with 1-methylthio-l-propyne (2a) and N-(1-propynyl)phenothiazine (2b) by regiospecific addition of the C=C bond of the alkyne to the C=C bond of the vinylidene ligand of 1. Initially, complexes with a spirocyclic cyclobutenylidene ligand are formed, [(CO)₅Cr=CC(Me)=C(SMe)t(CH₂)₅] (3) and [(CO)₅-Cr=C-C(Me)=C{N(C₆H₄) ₂S}C(CH₂)₅] (10). Subsequent thermally initiated ring expansion affords the 2-methyl4,5,6,7-tetrahydroindenyl(methyl)thioether complex [(CO)₅Cr-S(Me)(Me-C₉H₁₀)] (4) and the N-(2-methyl-4,5,6,7-tetrahydroindenyl)phenothiazine complex f(CO)₅Cr-S(C₆H₄)₂ N-(Me-C₉H₁₀)] (11), respectively. In both complexes, 4 and 11, the ligand is coordinated to the metal via the sulfur atom. The constitutions were established by (H,H)-, (H,C)- and NOE-correlated NMR spectroscopy. In the reaction of 1 with 2a, in addition to 3 and 4, the metfayl(propynyl)thioetner complex f{CO)₅Cr-S(Me)C=CMe] (5) was formed. An isolable 3-methylthio-substituted cyclobutenylidene complex, [(CO)₅Cr=C-C(Me)=C(SMe}CPh₂] (9) was obtained from [(CO)₅Cr=C=CPh₂] (8) and 2a. The 4,5,6,7-tetrahydroindenylthioether ligand of 11 was cleaved from the metal by exposure of 11 adsorbed on silica gel to air or by treatment of 11 with [NEt₄]Br in dichloromethane. VCH Verlagsgesellschaft mbH, D-69451 1996.