Issue 1, 2024

13Ccarbene nuclear magnetic resonance chemical shift analysis confirms CeIV[double bond, length as m-dash]C double bonding in cerium(iv)–diphosphonioalkylidene complexes

Abstract

Diphosphonioalkylidene dianions have emerged as highly effective ligands for lanthanide and actinide ions, and the resulting formal metal–carbon double bonds have challenged and developed conventional thinking about f-element bond multiplicity and covalency. However, f-element–diphosphonioalkylidene complexes can be represented by several resonance forms that render their metal–carbon double bond status unclear. Here, we report an experimentally-validated 13C Nuclear Magnetic Resonance computational assessment of two cerium(IV)–diphosphonioalkylidene complexes, [Ce(BIPMTMS)(ODipp)2] (1, BIPMTMS = {C(PPh2NSiMe3)2}2−; Dipp = 2,6-diisopropylphenyl) and [Ce(BIPMTMS)2] (2). Decomposing the experimental alkylidene chemical shifts into their corresponding calculated shielding (σ) tensor components verifies that these complexes exhibit Ce[double bond, length as m-dash]C double bonds. Strong magnetic coupling of Ce[double bond, length as m-dash]C σ/π* and π/σ* orbitals produces strongly deshielded σ11 values, a characteristic hallmark of alkylidenes, and the largest 13C chemical shift tensor spans of any alkylidene complex to date (1, 801 ppm; 2, 810 ppm). In contrast, the phosphonium-substituent shielding contributions are much smaller than the Ce[double bond, length as m-dash]C σ- and π-bond components. This study confirms significant Ce 4f-orbital contributions to the Ce[double bond, length as m-dash]C bonding, provides further support for a previously proposed inverse-trans-influence in 2, and reveals variance in the 4f spin–orbit contributions that relate to the alkylidene hybridisation. This work thus confirms the metal–carbon double bond credentials of f-element–diphosphonioalkylidenes, providing quantified benchmarks for understanding diphosphonioalkylidene bonding generally.

Graphical abstract: 13Ccarbene nuclear magnetic resonance chemical shift analysis confirms CeIV [[double bond, length as m-dash]] C double bonding in cerium(iv)–diphosphonioalkylidene complexes

Supplementary files

Article information

Article type
Edge Article
Submitted
24 Aug 2023
Accepted
27 Nov 2023
First published
06 Dec 2023
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY license

Chem. Sci., 2024,15, 238-249

13Ccarbene nuclear magnetic resonance chemical shift analysis confirms CeIV[double bond, length as m-dash]C double bonding in cerium(IV)–diphosphonioalkylidene complexes

C. F. Baker, J. A. Seed, R. W. Adams, D. Lee and S. T. Liddle, Chem. Sci., 2024, 15, 238 DOI: 10.1039/D3SC04449A

This article is licensed under a Creative Commons Attribution 3.0 Unported Licence. You can use material from this article in other publications without requesting further permissions from the RSC, provided that the correct acknowledgement is given.

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