title: Cubane-type Fe4S4 clusters with chiral thiolate ligation: formation by ligand substitution, detection of intermediates by 1H NMR, and solid state structures including spontaneous resolution upon crystallization.
abstract: Cubane-type clusters [Fe(4)S(4)(SR*)(4)](2-) containing chiral thiolate ligands with R* = CH(Me)Ph (1), CH(2)CH(Me)Et (2), and CH(2)CH(OH)CH(2)OH (3) have been prepared by ligand substitution in the reaction systems [Fe(4)S(4)(SEt)(4)]/R*SH (1-3, acetonitrile) and [Fe(4)S(4)Cl(4)](2-)/NaSR*(3, Me(2)SO). Reactions with successive equivalents of thiol or thiolate generate the species [Fe(4)S(4)L(4-n)(SR*)(n)](2-) (L = SEt, Cl) with n = 1-4. Clusters 1 and 2 were prepared with racemic thiols leading to the possible formation of one enantiomeric pair (n = 1) and seven diastereomers and their enantiomers (n = 2-4). Reactions were monitored by isotropically shifted (1)H NMR spectra in acetonitrile or Me(2)SO. In systems affording 1 and 2 as final products, individual mixed-ligand species could not be detected. However, crystallization of (Et(4)N)(2)[1] afforded 1-[SS(RS)(RS)] in which two sites are disordered because of occupancy of R and S ligands. Similarly, (Et(4)N)(2)[2] led to 2-[SSSS], a consequence of spontaneous resolution upon crystallization. The clusters 3-[RRRR] and 3-[SSSS] were obtained from enantiomerically pure thiols. Successive reactions lead to detection of species with n = 1-4 by appearance of four pairs of diastereotopic SCH(2) signals in both acetonitrile and Me(2)SO reaction systems. Identical spectra were obtained with racemic, R-(-), and S-(+) thiols, indicating that ligand-ligand interactions are too weak to allow detection of diastereomers (e.g., [SSSS] vs [SSRR]). The stability of 3 in Me(2)SO/H(2)O media is described.
authors.affiliation: Department of Chemistry and Chemical Biology, Harvard University, Cambridge, Massachusetts 02138, USA.
authors.forename: Wayne
authors.initials: W
authors.lastname: Lo
authors.forename: Shaw
authors.initials: S
authors.lastname: Huang
authors.forename: Shao-Liang
authors.initials: SL
authors.lastname: Zheng
authors.forename: R H
authors.initials: RH
authors.lastname: Holm
mesh_terms: D000097:Acetonitriles / Q000737:chemistry; D015393:Chemistry, Bioinorganic / Q000379:methods*; D003460:Crystallization; D018360:Crystallography, X-Ray; D004121:Dimethyl Sulfoxide / Q000737:chemistry; D007501:Iron / Q000737:chemistry* / Q000378:metabolism; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D008968:Molecular Conformation; D009942:Organometallic Compounds / Q000032:analysis / Q000138:chemical synthesis*; D010084:Oxidation-Reduction; D013237:Stereoisomerism; D013438:Sulfhydryl Compounds / Q000737:chemistry*; D013455:Sulfur / Q000737:chemistry* / Q000378:metabolism; D047391:alpha-Cyclodextrins / Q000737:chemistry*
chemical_list: D000097:Acetonitriles; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D047391:alpha-Cyclodextrins; D013455:Sulfur; D007501:Iron; D004121:Dimethyl Sulfoxide; C032159:acetonitrile