Expected and Unexpected Reactivities of Homoleptic LiNacNac and Heteroleptic NacNacMg(TMP) β-Diketiminates toward Various Small Unsaturated Organic Molecules

Homoleptic LiNacNac forms simple donor–acceptor complexes with N,N′-dicyclohexylcarbodiimide (CyN=C=NCy), triphenylphosphine oxide (Ph3P=O), and benzophenone (Ph2CO). These crystallographically characterized compounds could be regarded as model intermediates en route to reducing the N=C, P=O, and C=O bonds of unsaturated substrates. Heteroleptic NacNacMg(TMP) intriguingly functions as a TMP nucleophile both with t-BuNCO and t-BuNCS, producing a urea or thiourea derivative respectively attached to Mg, though the NacNac ligand in the former reaction also engages noninnocently with a second t-BuNCO molecule via insertion at the reactive NacNac backbone γ-carbon site.


General Experimental
All reactions were performed under a protective argon or nitrogen atmosphere using either standard Schlenk or glove box techniques. Hexane and THF were dried by heating to reflux over sodium benzophenone ketyl and then distilled under nitrogen prior to use. C6D6 and d8-THF were degassed by freeze-pump-thaw methods and stored over activated 4 Å molecular sieves. n BuLi (1.6 M in hexane) was purchased commercially from Sigma-Aldrich and used as received. TMEDA (N,N,N',N'tetramethylethylenediamine) was purchased from Sigma-Aldrich, distilled under nitrogen and stored over activated 4 Å molecular sieves prior to use. The parent NacNac(H) ligand and magnesium derivative NacNacMgTMP were made via literature procedures. 1,2 Isocyanates t-BuNCO and i-PrNCO were purchased from Sigma-Aldrich, stored in the refrigerator and used as received. N, N'dicyclohexylcarbodiimide (DCC) and triphenylphosphine oxide (Ph3PO) were purchased from Fluorochem, while benzophenone (Ph2CO) was purchased from Alfa Aesar, all were used as received.
All other reagents were purchased from commercial sources and were also used as received.
NMR spectra were recorded on a Bruker AV3 or AV400 MHz spectrometer operating 400.13 MHz for 1 H, 155.47 MHz for 7 Li, 162.0 MHz for 31 P and 100.62 MHz for 13 C. All 13 C NMR spectra were proton decoupled. 1 H, 13 C{ 1 H}, 7 Li and 31 P chemical shifts are expressed in parts per million (δ, ppm) and where appropriate referenced to residual solvent peaks or external references.
Melting points were determined in sealed argon filled capillaries and were not corrected.
All Infra-Red analysis was carried out on a PerkinElmer Spectrum 100 Optica FT-IR Spectrometer with solid state samples being prepared in the glovebox using Nujol Mull.

X-ray crystallography
Data for complexes 1-5 were collected on an Oxford Diffraction Gemini S instrument with graphitemonochromated Cu Kα (λ 1.54184 Å) radiation. Data collection and processing used CrysalisPro software. 3 All structures were solved and refined to convergence on F 2 against all independent reflections by the full-matrix least squares method using SHELXL 4 as implemented within OLEX2. 5 For 1 disordered and partially present solvent, believed to be hexane, could not be modelled properly.
This was dealt with using the SQUEEZE routine as implemented in PLATON. 6 A total of 62 electron equivalents were removed from 312 Å 3 of each unit cell's volume. Samples of 4 were found to be twinned. The model adopted was refined against an hklf 5 formatted dataset produced by CrysalisPro.
The scale factor refined to 0.7453(10):0.2547(10). Disordered groups were each modelled over two sites with appropriate restraints and constraints applied to bond lengths and displacement ellipsoids to ensure approximation to expected behaviour. The groups modelled in this way were, one NCy group of 1, and single i Pr groups inboth 2 and 5. Selected bond lengths and angles are presented in Figures S1-S5, selected crystallographic data are shown in Table 1  There are two crystallographically independent molecules featured in the structure, though only one is presented. Hydrogen atoms omitted for clarity. Organic part of DippNacNac ligand shown as wireframe for clarity.   Hydrogen atoms omitted for clarity. Aryl part of DippNacNac ligand shown as wireframe for clarity.

Synthesis of [{(MeCN-2,6-i Pr 2 C 6 H 3 ) 2 CH}Li.OC(Ph) 2 ] (3)
NacNac(Li) (0.1 mmol, 0.044 g) was added to a glass vial inside the glovebox and dissolved in hexane (1 ml) to which Ph2CO (0.125 mmol, 0.023 g) was added. Reaction was stirred for 20 minutes prior to addition of an excess of PMDETA to give a red solution. Next the solution was cooled to -20 °C, this produced formed small red crystals within 24 hours (yield 0.036 g, 0.59 mmol, 59 %).  Hydrogen atoms omitted for clarity. Aryl part of DippNacNac ligand shown as wireframe for clarity.

Selected bond lengths (Å) and bond angles (°)
Li1     There are two crystallographically independent molecules featured in the structure, though only one is presented. Hydrogen atoms omitted for clarity. Aryl part of DippNacNac ligand shown as wireframe for clarity.