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Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH₃ , LiCH₂ CH₃ and LiC₆ H₅ to Mo≣Mo Bonds.

ABSTRACT: LiCH₃ and LiCH₂ CH₃ react with the complex [Mo₂ (H)₂ (μ-Ad^Dipp2 )₂ (thf)₂ ] (1⋅thf) with coordination of two molecules of LiCH₂ R (R=H, CH₃ ) and formation of complexes [Mo₂ {μ-HLi(thf)CH₂ R}₂ (Ad^Dipp2 )₂ ], 5⋅LiCH₃ and 5⋅LiCH₂ CH₃ , respectively (Ad^Dipp2 =HC(NDipp)₂ ; Dipp=2,6-ⁱ Pr₂ C₆ H₃ ; thf=C₄ H₈ O). Due to steric hindrance, only one molecule of LiC₆ H₅ adds to 1⋅thf generating the complex [Mo₂ (H){μ-HLi(thf)C₆ H₅ }(μ-Ad^Dipp2 )₂ ], (4⋅LiC₆ H₅ ). Computational studies disclose the existence of five-center six-electron bonding within the H-Mo≣Mo-C-Li metallacycles, with a mostly covalent H-Mo≣Mo-C group and predominantly ionic Li-C and Li-H interactions. However, the latter bonds exhibit non-negligible covalency, as indicated by X-ray, computational data and the large one-bond ^6,7 Li,¹ H and ^6,7 Li,¹³ C NMR coupling constants found for the three-atom H-Li-C chains. By contrast, the phenyl group in 4⋅LiC₆ H₅ coordinates in an η² fashion to the lithium atom through the ipso and one of the ortho carbon atoms.

SUBMITTER: Perez-Jimenez M

PROVIDER: S-EPMC9303556 | biostudies-literature | 2022 Feb

REPOSITORIES: biostudies-literature

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Publications

Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH3 , LiCH2 CH3 and LiC6 H5 to Mo≣Mo Bonds.

Pérez-Jiménez Marina M Campos Jesús J Jover Jesús J Álvarez Santiago S Carmona Ernesto E

Angewandte Chemie (International ed. in English) 20220111 8

LiCH3 and LiCH2 CH3 react with the complex [Mo2 (H)2 (μ-AdDipp2 )2 (thf)2 ] (1⋅thf) with coordination of two molecules of LiCH2 R (R=H, CH3 ) and formation of complexes [Mo2 {μ-HLi(thf)CH2 R}2 (AdDipp2 )2 ], 5⋅LiCH3 and 5⋅LiCH2 CH3 , respectively (AdDipp2 =HC(NDipp)2 ; Dipp=2,6-< ...[more]

PMID: 34913550

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Project description:Quantum chemical calculations are reported for the complexes of alkaline earth metals AeOLi2 (Ae = Be-Ba) at the BP86-D3(BJ)/def2-QZVPP and CCSD(T)/def2-QZVPPQZVPP levels. The nature of the Ae-OLi2 bond has been analyzed with a variety of methods. The AeOLi2 molecules exhibit an unprecedented σ donor bond Ae→OLi2 where the (n)s2 lone-pair electrons of the Ae atom are donated to vacant O-Li2 antibonding orbitals having the largest coefficient at lithium. This is a covalent bond where the accumulation of the associated electronic charge is located at two positions above and below the Ae-OLi2 axis. The bifurcated component of orbital interactions is structurally related to the recently proposed collective bonding model, but exhibits a completely different type of bonding. The most stable isomer of AeOLi2 has a C 2v geometry and a singlet (1A1) electronic ground state. The bond dissociation energy (BDE) of the Ae-OLi2 bonds exhibits a zig-zag trend from BeOLi2 to BaOLi2, with BeOLi2 having the largest BDE (D e = 73.0 kcal mol-1) and MgOLi2 possessing the lowest BDE (D e = 42.3 kcal mol-1) at the CCSD(T) level. The calculation of the atomic partial charges by the Hirshfeld and Voronoi methods suggests that Be and Mg carry small negative charges in the lighter molecules whereas the heavier atoms Ca-Ba have small positive charges. In contrast, the NBO and QTAIM methods give positive charges for all Ae atoms that are larger for Ca-Ba than that calculated by the Hirshfeld and Voronoi approaches. The molecules AeOLi2 have large dipole moments where the negative end is at the Ae atom with the polarity Ae→OLi2. The largest dipole moments are predicted for the lighter species BeOLi2 and MgOLi2 and the smallest value is calculated for BaOLi2. The calculation of the vibrational spectra shows a significant red-shift toward lower wave numbers for the Ae-OLi2 stretching mode in comparison to diatomic AeO. Besides the Ae→OLi2 σ-donor bonds there are also three dative bonds due to Ae←OLi2 backdonation which consist of one σ bond and two π bonds. The appearance of strong Ae→OLi2 σ donation leads to quadruple bonds AeOLi2 in all systems AeOLi2, even for the lightest species with Ae = Be, Mg. The valence orbitals of Ca, Sr, and Ba, which are involved in the dative interactions, are the (n)s and (n-1)d AOs whereas Be and Mg use their (n)s and (n)p AOs. The EDA-NOCV results are supported by the AdNDP calculations which give four 2c-2e bonding orbitals. Three bonding orbitals have occupation numbers ∼2. One σ orbital has smaller occupation numbers between 1.32 and 1.73 due to the delocalization to the lithium atoms. The analysis of the electronic structure with the ELF method suggests multicenter bonds with mainly trisynaptic and tetrasynaptic basins, which also support the results of the EDA-NOCV calculations.

Dataset Information

Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH₃ , LiCH₂ CH₃ and LiC₆ H₅ to Mo≣Mo Bonds.

Publications

Supported σ-Complexes of Li-C Bonds from Coordination of Monomeric Molecules of LiCH<sub>3</sub> , LiCH<sub>2</sub> CH<sub>3</sub> and LiC<sub>6</sub> H<sub>5</sub> to Mo≣Mo Bonds.

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