ic5017005_si_003.cif (1.05 MB)

Role of Axial Base Coordination in Isonitrile Binding and Chalcogen Atom Transfer to Vanadium(III) Complexes

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posted on 20.10.2014 by Subhojit Majumdar, Julia M. Stauber, Taryn D. Palluccio, Xiaochen Cai, Alexandra Velian, Elena V. Rybak-Akimova, Manuel Temprado, Burjor Captain, Christopher C. Cummins, Carl D. Hoff
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.