The η1-H–C⋯Hg agostic interactions in the mercury complexes of N-confused porphyrin

Abstract

Six four-coordinated complexes of the chemical formulae [Hg(2-N CH₂COOCH₂CH₃-21-H-NCTPP)X] with X = Cl (5), Br (6), I (7), [Hg(2-NCH₃-21-H-NCTPP)Cl] (4) and [Hg(2-NCH₂COOCH₂C₆H₅-21-H-NCTPP)X] with X = Cl (8), I (9) are synthesized and structurally determined. The bond path for the weak η¹-H(17)–C(17)⋯Hg agostic interactions between the Hg center and H(17) in complexes 4–9 was a through-space interaction from Hg to agostic carbon [C(17)] followed by a through-bond interaction from C(17) to an agostic proton [H(17)]. The magnitude of J[Hg–H(17)] [or the agostic upfield shift Δδ_ago of the C(17)] for these complexes increases as the halide ligand varies from iodide to chloride, ranging from 33.2 Hz (or 14.3 ppm) for I⁻ to 36 Hz (or 15.8 ppm) for Br⁻ and 36.9 Hz (or 16.0 ppm) for Cl⁻. The plot of J[Hg–H(17)] for the agostic proton H(17) versus |Δδ_ago| for the agostic carbon atom C(17) in compounds 3–9 was linearly expressed as J[Hg–H(17)] = 2.29 |Δδ_ago| + 0.13.