The crystal and molecular structure of bis[dihydrobis(1-pyrazolyl)borato]nickel(II): evidence for the absence of Ni–H interaction in polypyrazolyl borates of nickel

Echols, H. M.; Dennis, D.

doi:10.1107/s0567740876006110

Cited by 31 publications

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“…According to the original criteria of Brookhart and Green, agostic interactions would be present in 1 but clearly absent in 2 , as the latter compound displays a pronounced δ( 1 H) downfield shift in the case of the Ni⋅⋅⋅HC coordinating methylene protons. This conclusion is also in accord with the structural study of 2 by Echols and Dennis in 1974, who concluded that steric restrictions dictate the conformation of the molecule, not an interaction of Ni with an apical H atom of one of the methylene groups of the pyrazolylborato ligand 1b. 12 A subsequent extended Hückel theory (EHT) study by Saillard and Hoffmann (SH)1c gave further evidence that the interaction between an axially approaching HC ligand (for example, CH 4 ), and the d 8 ‐ML 4 metal fragment might be actually even repulsive owing to the presence of a fully occupied and axially oriented M(d

_{italicz^{2}}

) orbital (Scheme ) 1c.…”

Section: Methodssupporting

confidence: 87%

Anagostic Interactions under Pressure: Attractive or Repulsive?

et al. 2015

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The term "anagostic interactions" was coined in 1990 by Lippard and coworkers to distinguish sterically enforced M•••H-C contacts (M = Pd, Pt) in square-planar transition metal d 8 complexes from attractive, agostic interactions. [1a] This classification raised the fundamental question whether axial [2] (Scheme 1b) in which the transition metal plays the role of a hydrogen-bond acceptor (Scheme 1b). The latter bonding description is related to another bonding concept which describes these M•••H-C contacts in terms of (iii) pregostic or preagostic interactions [3] (Scheme 1c) which are considered as being "on the way to becoming agostic, or agostic of the weak type". [4] Scheme 1.In contrast to the first two types of interactions which require the presence of a fully occupied and axially oriented M(dz 2 ) orbital, preagostic interactions are considered to lack any "involvement of dz 2 orbitals in M•••H-C interactions" and rely mainly onThe first observation of unusual axial M•••H-C interaction in planar d 8 -ML4 complexes was made by S. Trofimenko, who pioneered the chemistry of transition metal pyrazolylborato complexes. [5,6] Trofimenko also realized in 1968, on the basis of NMR studies, that the shift of the pseudo axial methylene protons in the agostic species [Mo{Et2B(pz)2}( 3 -allyl)(CO)2] (1) (pz = pyrazolyl; allyl = H2CCHCH2) "is comparable in magnitude but different in direction from that observed in Ni[Et2B(pz)2]2" (2) (Scheme 2). [6,7] Scheme 2.Indeed, the protons of the methylene group which form a close M•••C contact of [2.954(2) Å] [8] in 1 resonate at -2.41 ppm at RT, [9] while the corresponding signal of the methylene protons of 2 occurs at 3.64 ppm (q, CH2, 2 JH-H 8 Hz ) and does not show any coalescence upon cooling to -90 °C despite large differences in the calculated chemical shifts [10a] of both methylene protons (Scheme 2). In contrast, the 1 H NMR signal of the agostic methylene protons in 1 splits into two features (-0.83 and -4.3) below -53 °C [9] in agreement with the computed NMR properties of our static DFT model (1.4 and -5.88 ppm) for the agostic Mo•••Hago-C and non-coordinating methylene proton, respectively (Scheme 2). Trofimenko concluded that the agostic proton in 1 displays a "hydridic" character and that the agostic proton of 1 is "intruding into a suitable empty metal orbital." [6a] He, therefore, suggested that the M•••H-C interactions in 1 is a bonding one causing an activation of the C-H bonds as evident by the "presence of CH stretch bands at remarkably low frequency" of 2704 cm -1 . [6b] This concept was later developed and refined by Brookhart and Green (BG); who coined the expression "agostic" for these kind of interactions. [11] According to the original criteria of BG, agostic interactions would be present in 1 but clearly absent in 2 since the latter compound displays a pronounced ( 1 H) down-field shift in the case of the Ni•••H-C coordinating methylene protons. This conclusion is also in accord with the structural study of 2 by [ ][a] Prof.

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_{italicz^{2}}

) orbital (Scheme ) 1c.…”

Section: Methodssupporting

confidence: 87%

Anagostic Interactions under Pressure: Attractive or Repulsive?

et al. 2015

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“…Where C–H bond hydrogen atoms make close approaches to transition‐metal centres above the coordination plane in square‐planar d 8 complexes, the nature of any interaction present is of interest. The term originally used for this type of interaction is “anagostic”, in which repulsive forces were deemed to be operating , . However, as already mentioned, it has been recognised that some covalency can be involved leading to a “preagostic” situation, whereby weak attraction is apparent in the form of metal to C–Hσ* back‐donation and, similarly, C–Hσ to metal‐based orbital donation (agostic donation) .…”

Section: Resultsmentioning

confidence: 99%

Weak M···H–C Interactions in Neutral Complexes, Anions and Cations of Palladium(II) and Rhodium(I) Containing the iso‐Quinoline Ligand – Anagostic or Preagostic?

Sajjad

Schwerdtfeger²,

Harrison

et al. 2017

Eur J Inorg Chem

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DFT-D calculations show that the above-plane M···H-C separations in square-planar complexes of Pd II and Rh I containing the iso-quinoline ligand are influenced by whether the complexes are neutral, anionic or cationic, due mainly to changes in atomic charge on the metal, H and C atoms, but the nature of the cis-ligands also plays a part because of the development of weak intramolecular interactions. The Pd···H-C separations are effected by strong σ-withdrawing or π-donating substituents placed at C 7 of the iso-quinoline ligand with the shortest anagostic Pd···H separation of 2.218 Å achieved using [a]

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“…[21] Such a situation is represented in Scheme 1 for b-hydrogen elimination or its reverse, alkene insertion into a MÀH bond. This scenario was first discussed for [EtTiCl 3 (dmpe)] (11). [146] Green et al concluded that in 11 "the ethyl group models a stage about half-way along the reaction coordinate for a b-elimination reaction".…”

Section: Introductionmentioning

confidence: 97%

“…[15] Trofimenko subsequently played a pivotal role in the investigation of these M···HC interactions in transition-metal systems throughout the early 1970s, and provided samples of [Ni{H 2 B(pz) 2 } 2 ] (7; pz = C 3 N 2 H 3 ) and [Mo{Et 2 B(pz) 2 }(h 3 -C 3 H 4 Ph)(CO) 2 ] (8, Figure 1) to Cotton and Echols, who determined their structures by single-crystal X-ray diffraction and NMR spectroscopy, and reported the presence of such interactions in 8 and their absence in 7. [10,11] By analogy to bonding concepts in borane chemistry, Cotton classified the interaction in 8 as "a three-center, twoelectron bond encompassing the C···H···Mo atoms" [10a] and drew comparisons with the concept in organolithium chemistry accounting for "three-center bonds of the form C···H···Li". [4] Around the same time, Maitlis et al discovered an interaction between the palladium center and the d-CÀH bond in trans-[Pd(CMeCMeCMeCMeH)Br(PPh 3 ) 2 ] (9; Figure 1) and concluded "This type of interaction has not been observed before, though Trofimenko noted that the methylene hydrogens of the ethyl groups in [Ni{Et 2 B(pz) 2 } 2 ] are shifted downfield".…”

Section: Introductionmentioning

confidence: 99%

Agostic Interactions in d⁰Metal Alkyl Complexes

2004

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The phenomenon of agostic interactions is reviewed and the nature of the interaction is revisited. A historical perspective is followed by an overview of experimental techniques used to diagnose agostic behavior, and previous interpretations of agostic bonding are presented. A series of simple metal alkyl complexes is considered and a new model for the phenomenon in d(0) systems is developed which sets them apart from agostic late-transition-metal complexes. Factors such as the valence electron count and coordination number of the metal center are revealed to be unimportant in facilitating the interaction in most d(0) systems. The charge density distribution in several transition-metal alkyl complexes is explored by experimental and theoretical techniques, including the powerful "Atoms in Molecules" approach. Local charge concentrations are shown to play an important role in the agostic interaction. Finally, we demonstrate for the first time a way to manipulate and control the magnitude and disposition of such local charge concentrations, and hence the strength of agostic interactions in d(0) metal alkyl complexes.

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The crystal and molecular structure of bis[dihydrobis(1-pyrazolyl)borato]nickel(II): evidence for the absence of Ni–H interaction in polypyrazolyl borates of nickel

Cited by 31 publications

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Anagostic Interactions under Pressure: Attractive or Repulsive?

Anagostic Interactions under Pressure: Attractive or Repulsive?

Weak M···H–C Interactions in Neutral Complexes, Anions and Cations of Palladium(II) and Rhodium(I) Containing the iso‐Quinoline Ligand – Anagostic or Preagostic?

Agostic Interactions in d⁰Metal Alkyl Complexes

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The crystal and molecular structure of bis[dihydrobis(1-pyrazolyl)borato]nickel(II): evidence for the absence of Ni–H interaction in polypyrazolyl borates of nickel

Cited by 31 publications

References 0 publications

Anagostic Interactions under Pressure: Attractive or Repulsive?

Anagostic Interactions under Pressure: Attractive or Repulsive?

Weak M···H–C Interactions in Neutral Complexes, Anions and Cations of Palladium(II) and Rhodium(I) Containing the iso‐Quinoline Ligand – Anagostic or Preagostic?

Agostic Interactions in d0Metal Alkyl Complexes

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Agostic Interactions in d⁰Metal Alkyl Complexes