The Contrasting Character of Early and Late Transition Metal Fluorides as Hydrogen Bond Acceptors

Abstract

The association constants and enthalpies for the binding of hydrogen bond donors to group 10 transition metal complexes featuring a single fluoride ligand (trans-[Ni(F)(2-C5NF4)(PR3)2], R = Et 1a, Cy 1b, trans-[Pd(F)(4-C5NF4)(PCy3)2] 2, trans-[Pt(F){2-C5NF2H(CF3)}(PCy3)2] 3 and of group 4 difluorides (Cp2MF2, M = Ti 4a, Zr 5a, Hf 6a; Cp*2MF2, M = Ti 4b, Zr 5b, Hf 6b) are reported. These measurements allow placement of these fluoride ligands on the scales of organic H-bond acceptor strength. The H-bond acceptor capability β (Hunter scale) for the group 10 metal fluorides is far greater (1a 12.1, 1b 9.7, 2 11.6, 3 11.0) than that for group 4 metal fluorides (4a 5.8, 5a 4.7, 6a 4.7, 4b 6.9, 5b 5.6, 6b 5.4), demonstrating that the group 10 fluorides are comparable to the strongest organic H-bond acceptors, such as Me3NO, whereas group 4 fluorides fall in the same range as N-bases aniline through pyridine. Additionally, the measurement of the binding enthalpy of 4-fluorophenol to 1a in carbon tetrachloride (-23.5 ± 0.3 kJ mol(-1)) interlocks our study with Laurence's scale of H-bond basicity of organic molecules. The much greater polarity of group 10 metal fluorides than that of the group 4 metal fluorides is consistent with the importance of pπ-dπ bonding in the latter. The polarity of the group 10 metal fluorides indicates their potential as building blocks for hydrogen-bonded assemblies. The synthesis of trans-[Ni(F){2-C5NF3(NH2)}(PEt3)2], which exhibits an extended chain structure assembled by hydrogen bonds between the amine and metal-fluoride groups, confirms this hypothesis.

Widely Applicable Hydrofluorination of Alkenes via Bifunctional Activation of Hydrogen Fluoride

“… 9 The high HF affinity of KHSO 4 could be rationalized using Hunter and co-workers’ recently reported H-bond scale (parameter β). 11 In this scale, the hydrogen bonding basicities of anionic species were found to be significantly higher than those of neutral organic HBAs ( Scheme 2 c). Hydrogen bond basicity (measured by β) of HSO 4 – is comparable to the best neutral HBA, such as R 3 PO, and is higher than that of DMPU.…”

The hydrogen bond between N—H or O—H and organic fluorine: favourable yes, competitive no

“…The types of atoms regarded as standard acceptors are listed in Table 1. They include: (a) most types of O and N atoms (but not planar trigonal N or O in a conjugated environment, such as furan or ester oxygen; Bö hm et al, 1996;Nobeli et al, 1997;Lommerse et al, 1997); (b) halide ions and halogens bonded to metal (Brammer et al, 2001;Smith et al, 2015) and in haloborates or PF 6 À ; (c) pyramidal phosphorus (Hansen et al, 2014); (d) S and Se atoms in electron-rich environments (Allen et al, 1997;Bibelayi et al, 2016). Some types of acceptors often form hydrogen bonds to > 1 donor.…”

Self-complementary nickel halides enable multifaceted comparisons of intermolecular halogen bonds: fluoride ligands vs. other halides

“…The feasibility of this approach is indicated by the crystallization of trans -[NiF{C 5 NF 3 (NH 2 )}(PEt 3 ) 2 ] which shows a hydrogen bond between the amino group on the fluoropyridyl ligand and the nickel fluoride on the adjacent molecule. 37 We therefore set about the synthesis of a nickel fluoride complex with an iodine substituent on a fluorophenyl ligand, which would enable formation of an intermolecular halogen-bond network ( Scheme 1b ) between the iodine as halogen-bond donor and the nickel-fluoride as halogen-bond acceptor. We report the synthesis and structures of a series of Ni–X complexes (X = F, Cl, Br, I) with the halide ligand as halogen-bond acceptors, iodine at the 2- or 4-position on the tetrafluorophenyl ligand as halogen-bond donor and different phosphine groups.…”