Cyclization Reactions of Coordinated Alkynes in Tungsten(II) Complexes

Abstract

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) n C⋮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).

Towards Structural‐Functional Mimics of Acetylene Hydratase: Reversible Activation of Acetylene using a Biomimetic Tungsten Complex

“…In the early 1980’s, [W(C 2 H 2 )(CO)(dtc) 2 ] and [WO(C 2 H 2 )(dtc) 2 ] (dtc=S 2 CNMe 2, S 2 CNEt 2 ) were used to study alkynes as four‐electron donors 4. 5 About 20 years later, the scorpionate complexes [Tp′WOI(C 2 H 2 )] and [Tp′WOI(C 2 H 2 )] (Tp′=hydridotris(3,5‐dimethylpyrazolyl)borate)] were used to examine vinyl– and vinylidene–tungsten bonding 6–8. The only structural‐functional model of AH was reported by Sarkar et al 9.…”

“…[4,5] About 20 years later, the scorpionate complexes [Tp'WOI(C 2 H 2 )] and [Tp'WOI-(C 2 H 2 )] (Tp' = hydridotris(3,5-dimethylpyrazolyl)borate)] were used to examine vinyl-and vinylidene-tungsten bonding. [6][7][8] Theo nly structural-functional model of AH was reported by Sarkar et al [9,10] Originally [Et 4 N] 2 [WO(mnt) 2 ] (mnt = malonitrile) was designed to model W-dependent aldehyde ferredoxin oxidoreductase. [9] Thec omplex was also found to perform approximately nine turnovers of acetylene hydration.…”

Conversion of Tungsten(IV) Oxo−Alkyne Complexes to Oxo−Vinylidene Complexes

“…9 Intramolecular elaborations have led to the formation of cycloalkynes of the type Tp′W-[PhCtC(cyclopentyl)](CO)(I), Tp′W(cyclooctyne)(CO)(I), and Tp′W(cyclodecyne)(CO)(I). 10 The cyclooctyne and cyclodecyne complexes were formed by cyclization of the Additionally, the deprotonated η 2 -acetylide complexes that are proposed as intermediates during elaboration are unusual complexes. To date, no examples of monomeric η 2 -acetylide complexes have been isolated or observed by NMR.…”

Synthesis and Reactivity of Molybdenum and Tungsten Alkyne Complexes Containing 6‐Methylpyridine‐2‐thiolate Ligands

“…This reactivity was previously demonstrated with WÀ C 2 H 2 complexes employing the scorpionate ligand hydridotris-(3,5-dimethlypyrazolyl) borate. [36,37] Hence, a THF solution of 4a and 4b, respectively, was cooled below À 78 °C before BuLi and methyl iodide were successively added (Scheme 4). After stirring at r.t. for 2 h and subsequent evaporation of the solvent, 1 H-NMR spectroscopy in CDCl 3 revealed the formation of the desired propyne complex [W-(CO)(HC 2 Me)(6-MePyS) 2 ] (5a) with resonances of the coordinated HC 2 Me at 13.57 and 12.13 ppm along with residual starting material 4a, the butyne complex 1a, and 2-methyl-6-(methylthio)pyridine.…”