title: N-Substituted Derivatives of the Azadithiolate Cofactor from the [FeFe] Hydrogenases: Stability and Complexation.
abstract: Experiments are described that probe the stability of N-substituted derivatives of the azadithiolate cofactor recently confirmed in the [FeFe] hydrogenases (Berggren, G., et al. Nature 2013, 499, 66). Acid-catalyzed hydrolysis of bis(thioester) BnN(CH2SAc)2 gives [BnNCH2SCH2]2 rather than azadithiol BnN(CH2SH)2. Treatment of BnN(CH2SAc)2 with NaO(t)Bu generates BnN(CH2SNa)2, which was trapped with NiCl2(diphos) (diphos = 1,2-C2H4(PR2)2; R = Ph (dppe) and Cy (dcpe)) to give fully characterized complexes Ni[(SCH2)2NBn](diphos). The related N-aryl derivative Ni[(SCH2)2NC6H4Cl](diphos) was prepared analogously from 4-ClC6H4N(CH2SAc)2, NaO(t)Bu, and NiCl2(dppe). Crystallographic analysis confirmed that these rare nonbridging [adt(R)](2-) complexes feature distorted square planar Ni centers. The analogue Pd[(SCH2)2NBn](dppe) was also prepared. (31)P NMR analysis indicates that Ni[(SCH2)2NBn](dppe) has basicity comparable to typical amines. As shown by cyclic voltammetry, the couple [M[(SCH2)2NBn](dppe)](+/0) is reversible near -2.0 V versus Fc(+/0). The wave shifts to -1.78 V upon N-protonation. In the presence of CF3CO2H, Ni[(SCH2)2NBn](dppe) catalyzes hydrogen evolution at rate of 22 s(-1) in the acid-independent regime, at room temperature in CH2Cl2 solution. In contrast to the instability of RN(CH2SH)2 (R = alkyl, aryl), the dithiol of tosylamide TsN(CH2SH)2 proved sufficiently stable to allow full characterization. This dithiol reacts with Fe3(CO)12 and, in the presence of base, NiCl2(dppe) to give Fe2[(SCH2)2NTs](CO)6 and Ni[(SCH2)2NTs](dppe), respectively.
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Raja
authors.initials: R
authors.lastname: Angamuthu
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Chi-Shian
authors.initials: CS
authors.lastname: Chen
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Tyler R
authors.initials: TR
authors.lastname: Cochrane
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Danielle L
authors.initials: DL
authors.lastname: Gray
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: David
authors.initials: D
authors.lastname: Schilter
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Olbelina A
authors.initials: OA
authors.lastname: Ulloa
authors.affiliation: School of Chemical Sciences, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, United States.
authors.forename: Thomas B
authors.initials: TB
authors.lastname: Rauchfuss
mesh_terms: D002384:Catalysis; D060326:Chemistry Techniques, Synthetic; D003067:Coenzymes / Q000138:chemical synthesis / Q000737:chemistry*; D018360:Crystallography, X-Ray; D006864:Hydrogenase / Q000737:chemistry*; D006868:Hydrolysis; D007506:Iron-Sulfur Proteins / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy; D015394:Molecular Structure; D009532:Nickel / Q000737:chemistry; D009942:Organometallic Compounds / Q000737:chemistry*; D013438:Sulfhydryl Compounds / Q000737:chemistry
chemical_list: D003067:Coenzymes; D007506:Iron-Sulfur Proteins; D009942:Organometallic Compounds; D013438:Sulfhydryl Compounds; D009532:Nickel; C118830:iron hydrogenase; D006864:Hydrogenase