title: Role of axial base coordination in isonitrile binding and chalcogen atom transfer to vanadium(III) complexes.
abstract: The enthalpy of oxygen atom transfer (OAT) to V[(Me3SiNCH2CH2)3N], 1, forming OV[(Me3SiNCH2CH2)3N], 1-O, and the enthalpies of sulfur atom transfer (SAT) to 1 and V(N[t-Bu]Ar)3, 2 (Ar = 3,5-C6H3Me2), forming the corresponding sulfides SV[(Me3SiNCH2CH2)3N], 1-S, and SV(N[t-Bu]Ar)3, 2-S, have been measured by solution calorimetry in toluene solution using dbabhNO (dbabhNO = 7-nitroso-2,3:5,6-dibenzo-7-azabicyclo[2.2.1]hepta-2,5-diene) and Ph3SbS as chalcogen atom transfer reagents. The V-O BDE in 1-O is 6.3 ± 3.2 kcal·mol(-1) lower than the previously reported value for 2-O and the V-S BDE in 1-S is 3.3 ± 3.1 kcal·mol(-1) lower than that in 2-S. These differences are attributed primarily to a weakening of the V-Naxial bond present in complexes of 1 upon oxidation. The rate of reaction of 1 with dbabhNO has been studied by low temperature stopped-flow kinetics. Rate constants for OAT are over 20 times greater than those reported for 2. Adamantyl isonitrile (AdNC) binds rapidly and quantitatively to both 1 and 2 forming high spin adducts of V(III). The enthalpies of ligand addition to 1 and 2 in toluene solution are -19.9 ± 0.6 and -17.1 ± 0.7 kcal·mol(-1), respectively. The more exothermic ligand addition to 1 as compared to 2 is opposite to what was observed for OAT and SAT. This is attributed to less weakening of the V-Naxial bond in ligand binding as opposed to chalcogen atom transfer and is in keeping with structural data and computations. The structures of 1, 1-O, 1-S, 1-CNAd, and 2-CNAd have been determined by X-ray crystallography and are reported.
authors.affiliation: Department of Chemistry, University of Miami , 1301 Memorial Drive, Coral Gables Florida 33021, United States.
authors.forename: Subhojit
authors.initials: S
authors.lastname: Majumdar
authors.forename: Julia M
authors.initials: JM
authors.lastname: Stauber
authors.forename: Taryn D
authors.initials: TD
authors.lastname: Palluccio
authors.forename: Xiaochen
authors.initials: X
authors.lastname: Cai
authors.forename: Alexandra
authors.initials: A
authors.lastname: Velian
authors.forename: Elena V
authors.initials: EV
authors.lastname: Rybak-Akimova
authors.forename: Manuel
authors.initials: M
authors.lastname: Temprado
authors.forename: Burjor
authors.initials: B
authors.lastname: Captain
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Cummins
authors.forename: Carl D
authors.initials: CD
authors.lastname: Hoff
mesh_terms: D001665:Binding Sites; D018011:Chalcogens / Q000737:chemistry*; D056831:Coordination Complexes / Q000138:chemical synthesis / Q000737:chemistry*; D007700:Kinetics; D008958:Models, Molecular; D015394:Molecular Structure; D009570:Nitriles / Q000737:chemistry*; D011789:Quantum Theory; D013816:Thermodynamics; D014639:Vanadium / Q000737:chemistry*
chemical_list: D018011:Chalcogens; D056831:Coordination Complexes; D009570:Nitriles; D014639:Vanadium