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. 2023 Dec 19;29(71):e202302903.
doi: 10.1002/chem.202302903. Epub 2023 Nov 7.

Reductive Coupling of a Diazoalkane Derivative Promoted by a Potassium Aluminyl and Elimination of Dinitrogen to Generate a Reactive Aluminium Ketimide

Matthew J Evans  1 , Mathew D Anker  1 , Claire L McMullin  2 , Martyn P Coles  1
Affiliations

Reductive Coupling of a Diazoalkane Derivative Promoted by a Potassium Aluminyl and Elimination of Dinitrogen to Generate a Reactive Aluminium Ketimide

Matthew J Evans et al. Chemistry. .

Abstract

The reaction of 9-diazo-9H-fluorene (fluN2 ) with the potassium aluminyl K[Al(NON)] ([NON]2- =[O(SiMe2 NDipp)2 ]2- , Dipp=2,6-iPr2 C6 H3 ) affords K[Al(NON)(κN1 ,N3 -{(fluN2 )2 })] (1). Structural analysis shows a near planar 1,4-di(9H-fluoren-9-ylidene)tetraazadiide ligand that chelates to the aluminium. The thermally induced elimination of dinitrogen from 1 affords the neutral aluminium ketimide complex, Al(NON)(N=flu)(THF) (2) and the 1,2-di(9H-fluoren-9-yl)diazene dianion as the potassium salt, [K2 (THF)3 ][fluN=Nflu] (3). The reaction of 2 with N,N'-diisopropylcarbodiimide (iPrN=C=NiPr) affords the aluminium guanidinate complex, Al(NON){N(iPr)C(N=CMe2 )N(CHflu)} (4), showing a rare example of reactivity at a metal ketimide ligand. Density functional theory (DFT) calculations have been used to examine the bonding in the newly formed [(fluN2 )2 ]2- ligand in 1 and the ketimide bonding in 2. The mechanism leading to the formation of 4 has also been studied using this technique.

Keywords: aluminyl; diazomethane; guanidinate; ketimide; reductive coupling.

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Conflict of interest statement

The authors declare no conflict of interest.

Figures

Figure 1
Figure 1
Reactivity of main group compounds with diazomethane derivatives. (a) [Al]=[Al(bo2e‐CArNDipp)]−; (b) [Ga]=[Ga(DABDipp)]−; (c) [Al]=[Al(MeDABDipp)], R2CN2=(Me3Si)(H)CN2 and [Al]=[Al(BIANDipp)], R2CN2=Ph2CN2; (d) [Mg]=Mg(BDIMes), R2CN2=Ph2CN2 and fluN2. See text for definitions of ligands.
Scheme 1
Scheme 1
Synthesis of 1. (i) Toluene (1); (ii) Toluene/THF (1⋅THF); (iii) 18‐crown‐6, hexane/THF (1⋅crown); (iv) (2.2.2)cryptand, hexane/THF (1⋅crypt).
Figure 2
Figure 2
(a) Photograph of an NMR solution of 1⋅THF in C6D6. (b) Displacement ellipsoid plots of 1 (30 % ellipsoids; H‐atoms omitted; C‐atoms except at key positions represented as spheres). (c) View along the b‐axis of 1. (d) View in the AlN3‐plane of the anion from the crystal structure of 1⋅crypt.
Figure 3
Figure 3
Summary of bond lengths (Å) and angles (°) for the [(fluN2)2]2− ligand in 1, 1⋅THF and 1⋅crypt.
Scheme 2
Scheme 2
Resonance structures (VII–IX) for the [(fluN2)2]2− dianion with the delocalized hybrid X (flu‐groups not shown).
Figure 4
Figure 4
Highest occupied molecular orbital (HOMO) of 1’DFT from NBO7 analysis (BP86/BS2//BP86/BS1).
Scheme 3
Scheme 3
Synthesis of 2 and 3. (i) 80 °C, Toluene/THF. (ii) 80 °C, DMAP, toluene/THF.
Figure 5
Figure 5
Displacement ellipsoid plots of 2⋅THF (30 % ellipsoids; H‐atoms omitted; C‐atoms except at key positions represented as spheres).
Figure 6
Figure 6
Highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) of 2DFT from NBO7 analysis (BP86/BS2//BP86/BS1).
Figure 7
Figure 7
(a) Displacement ellipsoid plots of 3 (20 % ellipsoids; H‐atoms and disordered components omitted; C‐atoms except at key positions represented as spheres; symmetry generated atoms greyscale. ‘=‐x, 1‐y, ‐z; “=1‐x, 1‐y, ‐z). (b) View perpendicular to chain showing zig‐zag arrangement of planar [NFlu]2 2− units bridged by [K2(THF)3]2+ dications. Selected bond lengths (Å): N1‐N1’ 1.227(17), N2‐N2’ 1.240(9), N1‐C1 1.532(13), N2‐C14 1.456(7). (c) Resonance structures (XI–XIII) for the [(fluN)2]2− dianion (flu‐groups not shown).
Scheme 4
Scheme 4
General pathways observed for the reaction of M‐NR2 amide (insertion) and M=NR imide (cycloaddition) bonds with carbodiimides.
Scheme 5
Scheme 5
Synthesis of 4. (i) 80 °C, C6D6, 18 h; (ii) iPrN=C=NiPr, 15 min.
Figure 8
Figure 8
Displacement ellipsoid plot of one of the independent molecules of 4 (30 % ellipsoids; H‐atoms except NCHflu omitted; C‐atoms except at key positions represented as spheres). Selected bond lengths (Å) and angles (°) {corresponding value from molecule 2}: Al1‐N1 1.842(4) {1.863(1)}, Al1‐N2 1.867(4) {1.841(4)}, Al1‐N3 1.908(4) {1.901(4)}, Al1‐N5 1.948(4) {1.942(4)}, C42‐N3 1.352(6) {1.354(6)}, C42‐N5 1.334(6) {1.333(6)}, C42‐N4 1.389(6) {1.379(6)}, N4‐C43 1.271(6) {1.253(6)}. N3‐Al−N5 69.83(17) {70.06(16)}, N3‐C42‐N4 122.6(4) {122.5(4)}, N3‐C42‐N5 110.5(4) {110.3(4)}, N4‐C42‐N5 126.0(4) {126.0(4)}, C42‐N4‐C43 129.1(5) {131.4(5)}.
Figure 9
Figure 9
Computed free energy profile (BP86‐D3BJ(PCM=THF)/BS2//BP86/BS1 in kcal mol−1) for addition of iPrN=C=NiPr to Al(NON)(N=flu) (2DFT ) leading to formation of 4DFT . Note: formal charges omitted for clarity.
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