Triruthenium and triosmium carbonyl clusters containing chiral bidentate NHC-thiolate ligands derived from levamisole

Abstract

The trinuclear complexes [M3(mu-Cl)(mu-S approximately CH)(CO)9] (M=Ru, Os; S approximately CH=1-ethylenethiolate-3-H-4-(S)-phenylimidazolin-2-ylidene) and [M3(mu-H)(mu-S approximately CMe)(CO)9] (M=Ru, Os; S approximately CMe=1-ethylenethiolate-3-methyl-4-(S)-phenylimidazolin-2-ylidene) have been prepared by treating [Ru3(CO)12] and [Os3(CO)10(MeCN)2] with levamisolium chloride or [M3(mu-H)(CO)11]- with methyl levamisolium triflate, respectively. The chiral N-heterocyclic carbene-thiolate ligands S approximately CH and S approximately CMe arise from the oxidative addition of the C-S bond of levamisolium or methyl levamisolium cations to anionic trinuclear clusters.

Sulfur-functionalized N-heterocyclic carbenes and their transition metal complexes

“…C-S activation was only observed in Pd, Ru, and Os complexes involving the cationic ligand 10·HCl or the N-methylated derivative (11) [48][49][50]. Trinuclear carbonyl metal clusters with Ru [50] and Os [48,50] have been reported with 10·HCl and 11 in which the metal, Ru (14a, b) or Os (14c, d) added oxidatively across the C-S bond (Fig. 4); the N-methylated (−)-levamisole (11) forms the chloride bridging complexes, and the protonated (−)-levamisole (10·HCl) forms the hydride bridging complexes as a mixture of two diastereScheme 3.…”

“…Isolation of the free S-NHC compound (9a) was unsuccessful and resulted in the formation of the S-NHC dimer 9b which oxidizes in air and elevated temperature to the bis-disulfide macrocycle (10) containing two urethane functionalities (Scheme 2) [46]. Cat- A very elegant synthesis forming S-NHC complexes with thiolate donors was developed by Cabeza et al [48][49][50] using the inexpensive, commercially available and enantiopure natural product (−)-levamisole (10). N-Methylated levamisole (11), a masked NHC-thiolate ligand generated by reaction of methyl triflate and (−)-levamisole (10) [51,52], can be complexed to palladium forming a dimeric (12) or monomeric complex (13) as outlined in Scheme 3.…”

“…4); the N-methylated (−)-levamisole (11) forms the chloride bridging complexes, and the protonated (−)-levamisole (10·HCl) forms the hydride bridging complexes as a mixture of two diastereScheme 3. Palladium NHC-thiolate complexes (12, 13) derived from (−)-levamisole (10) [48,49]. omers in an approximately 1 to 1 ratio.…”

“…Chiral compounds (−)-levamisole derived NHC-thiolate complexes 12-14 [48][49][50] and the planar chirality containing ferrocenyl thioether complexes 57 and 58 [34] were described above. Hoveyda's [40] asymmetric aryl sulfonate ligand and silver complex (84 and 85) is described under sulfonate functionalized NHCs (Section 2.5).…”

“…Typically, neutral (−)-levamisole (10) does not undergo C-S bond activation, and binds through the sp 2 nitrogen as a two electron donor to metals such as Co, Ni, Cu, Zn, Pd and Pt [53][54][55][56]. C-S activation was only observed in Pd, Ru, and Os complexes involving the cationic ligand 10·HCl or the N-methylated derivative (11) [48][49][50]. Trinuclear carbonyl metal clusters with Ru [50] and Os [48,50] have been reported with 10·HCl and 11 in which the metal, Ru (14a, b) or Os (14c, d) added oxidatively across the C-S bond (Fig.…”