Cyclization Reactions of Coordinated Alkynes in Tungsten(II) Complexes

Displacement of a CO ligand from [Tp‘(CO)₂W{HC⋮CH}][OTf] with iodide leads to the neutral parent acetylene complex Tp‘(CO)(I)W{HC⋮CH} (2). Deprotonation of 2 followed by methylation is regioselective and yields a single isomer of the propyne complex Tp‘(CO)(I)W{HC⋮CCH₃} (3). Deprotonation of 3 followed by alkylation with RI (R = Me, I(CH₂)_n (n = 3−7)) is also regioselective and leads to a single isomer, Tp‘(CO)(I)W{RC⋮CCH₃} (4−9). Deprotonation of Tp‘(CO)(I)W{I(CH₂)_nC⋮CCH₃} (n = 5 (7), 7 (9)) leads to an η²-allenyl intermediate which undergoes intramolecular alkylation (i.e. endocyclic cyclization) to form Tp‘(CO)(I)W{cyclooctyne} (10) and Tp‘(CO)(I)W{cyclodecyne} (11), respectively. The exocyclic cyclization precursor Tp‘(CO)(I)W{PhC⋮C(CH₂)₅I} (12) was obtained by deprotonation of the propargyl carbon of Tp‘(CO)(I)W{PhC⋮CCH₃} followed by alkylation with I(CH₂)₄I. The cyclopentyl derivative Tp‘(CO)(I)W{PhC⋮C(cyclopentyl)} was generated by deprotonation of 12 followed by intramolecular alkylation (i.e. exocyclic cyclization). A coordinated cyclodecyne ligand is observed in the X-ray structure of Tp‘(CO)(I)W{cyclodecyne} (11).