Benchmarking of Halogen Bond Strength in Solution with Nickel Fluorides: Bromine versus Iodine and Perfluoroaryl versus Perfluoroalkyl Donors.

ABSTRACT: The energetics of halogen bond formation in solution have been investigated for a series of nickel fluoride halogen bond acceptors; trans-[NiF(2-C₅ NF₄ )(PEt₃ )₂ ] (A1), trans-[NiF{2-C₅ NF₃ (4-H)}(PEt₃ )₂ ] (A2), trans-[NiF{2-C₅ NF₃ (4-NMe₂ )}(PEt₃ )₂ ] (A3) and trans-[NiF{2-C₅ NF₂ H(4-CF₃ )}(PCy₃ )₂ ] (A4) with neutral organic halogen bond donors, iodopentafluorobenzene (D1), 1-iodononafluorobutane (D2) and bromopentafluorobenzene (D3), in order to establish the significance of changes from perfluoroaryl to perfluoroalkyl donors and from iodine to bromine donors. ¹⁹ F NMR titration experiments have been employed to obtain the association constants, enthalpy, and entropy for the halogen bond formed between these donor-acceptor partners in protiotoluene. For A2-A4, association constants of the halogen bonds formed with iodoperfluoroalkane (D2) are consistently larger than those obtained for analogous complexes with the iodoperfluoroarene (D1). For complexes formed with A2-A4, the strength of the halogen bond is significantly lowered upon modification of the halogen donor atom from I (in D1) to Br (in D3) (for D1: 5≤K₂₈₅ ≤12 m^-1 , for D3: 1.0≤K₁₉₃ ≤1.6 m^-1 ). The presence of the electron donating NMe₂ substituent on the pyridyl ring of acceptor A3 led to an increase in -ΔH, and the association constants of the halogen bond complexes formed with D1-D3, compared to those formed by A1, A2 and A4 with the same donors.

SUBMITTER: Pike SJ 

PROVIDER: S-EPMC6771525 | biostudies-literature | 2019 Jul

REPOSITORIES: biostudies-literature