Journal article
Synthesis of bulky hydride ligands: m -terphenylborohydride complexes with trivalent uranium and neodymium
Dalton transactions : an international journal of inorganic chemistry, Vol.54(23), pp.9135-9139
05/28/2025
DOI: 10.1039/d5dt01076d
PMID: 40433924
Appears in UI Libraries Support Open Access
Abstract
Here we describe the first coordination complexes containing a bulky m-terphenyltrihydroborate ligand. Treating [UI3(thf)4] and NdCl3 with three equiv. of Li(H3BArtBu4)(Et2O) (where ArtBu4 = 2,6-(3,5-tBu2C6H3)2C6H3) yielded [M(H3BArtBu4)3(thf)2] (M = U and Nd). [U(H3BArtBu4)3(dme)2] is also described, and structural comparisons reveal the influence of the Lewis base on H3BArtBu4 positioning.
Actinide borohydride complexes have been known since the discovery of [U(BH4)4] during the Manhattan Project.1 The simplest borohydride, BH41−, for example, forms molecular complexes with the general formula [M(BH4)4] with M = Th–Pu,1a,2 and similar homoleptic complexes are known with methyltrihydroborate (MeBH31−).3
Despite the well-known examples of borohydride complexes with actinides in the +4 oxidation state,4 conventional borohydride ligands like BH41− and MeBH31− are too small to form neutral, mononuclear, and homoleptic complexes with trivalent actinides because of their larger ionic radius and reduced charge. The only homoleptic examples with borohydrides are those with chelating ligands like aminodiboranates and phosphinodiboranates.5 Even though these latter ligands saturate a larger percentage of the metal coordination sphere, their complexes with trivalent actinides are only known to exist as dimers or oligomers in the solid state. In this context, a mononuclear and homoleptic borohydride complex has yet to be isolated with a trivalent f-element.
We therefore set out to develop sterically bulky borohydride ligands for the isolation of homoleptic and mononuclear complexes with trivalent actinides. A structural scaffold that has proven effective at isolating low-coordinate transition metal, lanthanide, and actinide complexes is m-terphenyl. The demanding steric presence of m-terphenyl groups generally serve to shield open coordination sites and stabilize metals and main group elements with low coordination numbers.6 Notable and recent examples with uranium are provided in Fig. 1a. Arnold and coworkers demonstrated how the bulky terphenyl ligand (2,6-(4-tBu-C6H4)2C6H3)1– could be used to isolate the first structurally authenticated homoleptic tris(aryl)U(iii) complex.7 Boncella and Odom used the m-terphenylamido ligand (NHAriPr6)1− where AriPr6 = 2,6-(2,4,6-iPr3C6H2)2C6H3 to isolate a rare example of a formally U(ii) complex.8 Though not a homoleptic example, Goodwin and coworkers recently described how the m-terphenylthiolate ligand (SAriPr6)1− can be used to isolate low coordinate U(iii) complexes like [UIII(SAriPr6)2(BH4)].9 These and other examples of coordinatively unsaturated m-terphenyl complexes led us to explore the development of m-terphenylborohydride ligands for low-valent actinide chemistry
Details
- Title: Subtitle
- Synthesis of bulky hydride ligands: m -terphenylborohydride complexes with trivalent uranium and neodymium
- Creators
- Peter A Zacher III - University of IowaDaniel K Unruh - University of IowaScott R Daly - University of Iowa
- Resource Type
- Journal article
- Publication Details
- Dalton transactions : an international journal of inorganic chemistry, Vol.54(23), pp.9135-9139
- DOI
- 10.1039/d5dt01076d
- PMID
- 40433924
- NLM abbreviation
- Dalton Trans
- ISSN
- 1477-9234
- eISSN
- 1477-9234
- Publisher
- Royal Society of Chemistry; CAMBRIDGE
- Grant note
- National Nuclear Security Administration: DE-NA0004151 National Nuclear Security Administration: CHE-2017828 NSF
We thank the National Nuclear Security Administration (DE-NA0004151) for support of this research. We also thank Vincent Groner and Jim Boncella at Washington State University for assistance with the synthesis of the I-ArtBu4 precursor. XRD data were collected using the instrument supported by NSF CHE-1828117. Some of the NMR data were collected using the instrument supported by NSF CHE-2017828.
- Language
- English
- Date published
- 05/28/2025
- Academic Unit
- Core Research Facilities; Chemistry
- Record Identifier
- 9984825533402771
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