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. 2022 Jun 8;144(22):9764-9774.
doi: 10.1021/jacs.2c02152. Epub 2022 May 24.

Carbene Complexes of Neptunium

Conrad A P Goodwin  1   2 , Ashley J Wooles  1 , Jesse Murillo  2 , Erli Lu  1 , Josef T Boronski  1 , Brian L Scott  3 , Andrew J Gaunt  2 , Stephen T Liddle  1
Affiliations

Carbene Complexes of Neptunium

Conrad A P Goodwin et al. J Am Chem Soc. .

Abstract

Since the advent of organotransuranium chemistry six decades ago, structurally verified complexes remain restricted to π-bonded carbocycle and σ-bonded hydrocarbyl derivatives. Thus, transuranium-carbon multiple or dative bonds are yet to be reported. Here, utilizing diphosphoniomethanide precursors we report the synthesis and characterization of transuranium-carbene derivatives, namely, diphosphonio-alkylidene- and N-heterocyclic carbene-neptunium(III) complexes that exhibit polarized-covalent σ2π2 multiple and dative σ2 single transuranium-carbon bond interactions, respectively. The reaction of [NpIIII3(THF)4] with [Rb(BIPMTMSH)] (BIPMTMSH = {HC(PPh2NSiMe3)2}1-) affords [(BIPMTMSH)NpIII(I)2(THF)] (3Np) in situ, and subsequent treatment with the N-heterocyclic carbene {C(NMeCMe)2} (IMe4) allows isolation of [(BIPMTMSH)NpIII(I)2(IMe4)] (4Np). Separate treatment of in situ prepared 3Np with benzyl potassium in 1,2-dimethoxyethane (DME) affords [(BIPMTMS)NpIII(I)(DME)] (5Np, BIPMTMS = {C(PPh2NSiMe3)2}2-). Analogously, addition of benzyl potassium and IMe4 to 4Np gives [(BIPMTMS)NpIII(I)(IMe4)2] (6Np). The synthesis of 3Np-6Np was facilitated by adopting a scaled-down prechoreographed approach using cerium synthetic surrogates. The thorium(III) and uranium(III) analogues of these neptunium(III) complexes are currently unavailable, meaning that the synthesis of 4Np-6Np provides an example of experimental grounding of 5f- vs 5f- and 5f- vs 4f-element bonding and reactivity comparisons being led by nonaqueous transuranium chemistry rather than thorium and uranium congeners. Computational analysis suggests that these NpIII═C bonds are more covalent than UIII═C, CeIII═C, and PmIII═C congeners but comparable to analogous UIV═C bonds in terms of bond orders and total metal contributions to the M═C bonds. A preliminary assessment of NpIII═C reactivity has introduced multiple bond metathesis to transuranium chemistry, extending the range of known metallo-Wittig reactions to encompass actinide oxidation states III-VI.

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Conflict of interest statement

The authors declare no competing financial interest.

Figures

Figure 1
Figure 1
Key An=C and An ← C linkage types in early An-chemistry reported previously and in this work. Use of bracketed [An] (An = U or Th), [U], and [Np] is to acknowledge the various range of metal oxidation states and coligands that are omitted for clarity.
Scheme 1
Scheme 1. Synthesis of 1, 2, and 3M–6M (M = Ce, Np)a
Complex 3Np was not isolated. DME = 1,2-dimethoxyethane; Bn = benzyl; IMe4 = {C(NMeCMe)2}.
Figure 2
Figure 2
Solid-state molecular structure of complex 4Np at 100 K. Displacement ellipsoids are set at 50% probability and nonmethanide hydrogen atoms are omitted for clarity. Selected bond lengths [Å] and angles [°]: Np1-I1 3.0727(6), Np1-I2 3.1798(6), Np1-N1 2.423(6), Np1-N2 2.458(6), Np1-C1 2.753(7), Np1-C32 2.676(8), P1-N1 1.612(6), P1-C1 1.749(7), P2-N2 1.618(6), P2-C1 1.723(7), I1-Np1-I2 135.87(2), N1-Np1-I1 93.1(2), N1-Np1-I2 84.7(12), N1-Np1-N2 105.8(2), N1-Np1-C1 63.3(2), N1-Np1-C32 144.1(2), N2-Np1-I1 91.1(2), N2-Np1-I2 131.9(2), N2-Np1-C1 62.0(2), N2-Np1-C32 110.0(2), C1-Np1-I1 133.8(2), C1-Np1-I2 83.8(2), C32-Np1-I1 88.2(2), C32-Np1-I2 70.0(2), C32-Np1-C1 134.6(2), and P1-C1-P2 128.6(4).
Figure 3
Figure 3
Solid-state molecular structure of complex 5Np at 100 K. Displacement ellipsoids are set at 50% probability and hydrogen atoms and lattice solvent are omitted for clarity. Selected bond lengths [Å] and angles [°]: Np1-I1 3.1065(5), Np1-O1 2.524(5), Np1-O2 2.636(5), Np1-N1 2.431(6), Np1-N2 2.414(6), Np1-C1 2.425(7), P1-N1 1.602(6), P1-C1 1.627(7), P2-N2 1.631(6), P2-C1 1.652(7), O1-Np1-I1 153.9(2), O1-Np1-O2 61.8(2), O2-Np1-I1 95.3(2), N1-Np1-I1 103.6(2), N1-Np1-O1 81.3(2), N1-Np1-O2 122.4(2), N2-Np1-I1 95.2(2), N2-Np1-O1 101.5(2), N2-Np1-O2 102.2(2), N2-Np1-N1 128.8(2), N2-Np1-C1 65.2(2), C1-Np1-I1 109.3(2), C1-Np1-O1 95.9(2), C1-Np1-O2 152.9(2), C1-Np1-N1 63.6(2), and P1-C1-P2 170.4(5).
Figure 4
Figure 4
Solid-state molecular structure of complex 6Np at 120 K. Displacement ellipsoids are set at 50% probability and hydrogen atoms and lattice solvent are omitted for clarity. Selected bond lengths [Å] and angles [°]: Np1-I1 3.1571(4), Np1-N1 2.485(4), Np1-N2 2.492(5), Np1-C1 2.490(6), Np1-C32 2.677(5), Np1-C39 2.751(6), P1-N1 1.620(5), P1-C1 1.675(6), P2-N2 1.614(5), P2-C1 1.671(5), N1-Np1-I1 91.8(2), N1-Np1-N2 120.9(2), N1-Np1-C1 64.0(2), N1-Np1-C32 81.4(2), N1-Np1-C39 154.2(2), N2-Np1-I1 98.1(2), N2-Np1-C32 132.7(2), N2-Np1-C39 81.0(2), C1-Np1-I1 127.5(2), C1-Np1-N2 64.1(2), C1-Np1-C32 98.7(2), C1-Np1-C39 123.6(2), C32-Np1-I1 124.3(2), C32-Np1-C39 73.2(2), C39-Np1-I1 98.7(2), and P1-C1-P2 136.5(3).
Figure 5
Figure 5
Comparison of solution UV–vis–NIR spectra of 4Np (black line, 0.49 mM), 5Np (blue line, 0.51 mM), and 6Np (red line, 0.58 mM), all in toluene shown between 7000 and 35,000 cm–1 (1429–286 nm) at ambient temperature. Inset: Expanded view of ∼8000–16,000 cm–1 region.
Figure 6
Figure 6
NBO representations of the Np=CBIPM σ- and π-bond interaction in 5Np. (a) Np=CBIPM σ-bond. (b) Np=CBIPM π-bond. Hydrogen atoms are omitted for clarity.
Scheme 2
Scheme 2. Reaction of 5Np with Benzaldehyde to Produce the Alkene 7
See this image and copyright information in PMC

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