Catalytic Macrocyclization of 3-Methylthietane by Re2(CO)9(SCH2CHMeCH2) and W(CO)5(SCH2CHMeCH2)

The new compounds Re2(CO)9(SCH2CHMeCH2) (2) and W(CO)5(SCH2CHMeCH2), 8, have been prepared by the reactions of Re2(CO)9(NCMe) (1) and W(CO)5(NCMe) (7) with 3-methylthietane, (SCH2CHMeCH2, 3-MT). Compounds 1, 2, 7, and 8 have been found to react with SCH2CHMeCH2 at reflux to yield substantial amounts of the polythioether macrocycle 3,7,11-trimethyl-1,5,9-trithiacyclododecane (Me312S3) by a macrocyclization process consisting of a metal-induced ring-opening cyclooligomerization of three molecules of 3-MT. Me312S3 is formed as two isomers, cis,trans,trans-3,7,11-trimethyl-1,5,9-trithiacyclododecane (c,t,t-Me312S3, 3) and cis,cis,cis-3,7,11-trimethyl-1,5,9-trithiacyclododecane (c,c,c-Me312S3, 4), due to different orientations of the methyl substituents in the ring. Small amounts of higher macrocycles with the general formula (SCH2CHMeCH2) n (n > 3) are also formed, but these could not be isolated in pure forms. A comparison of the two catalysts shows that the rhenium catalyst exhibits a higher activity and higher selectivity for the formation of Me312S3 than the tungsten complex. The reactions of 1 with 3 and 4 have yielded the new compounds Re2(CO)9(c,t,t-SCH2CHMe(CH2SCH2CHMe)2CH2) (5) and Re2(CO)9(c,c,cSCH2CHMe(CH2SCH2CHMe)2CH2) (6), respectively. The molecular structures of the free molecule 3 and the complexes 5 and 6 were established by single-crystal X-ray diffraction analyses.