476196-72-2Relevant academic research and scientific papers
Synthesis and structural characterization of lithium and trimethyltin complexes of 2,6-bis(oxazolinyl)phenyl
Stol, Marianne,Snelders, Dennis J. M.,De Pater, Jeroen J. M.,Van Klink, Gerard P. M.,Kooijman, Huub,Spek, Anthony L.,Van Koten, Gerard
, p. 743 - 749 (2005)
The treatment of 2,6-bis(oxazolinyl)phenyl bromide (Phebox-Br) with n-BuLi affords a Phebox-Li complex. Subsequent transmetalation with [SnClMe 3] affords a Phebox-Sn complex. The Phebox ligand can coordinate to a transition metal in various terdentate fashions; both the oxazoline oxygen and the imine nitrogen are perfectly positioned for chelation; NCN , OCO , or mixed terdentate coordination modes are theoretically possible using this ligand. The structural properties and NMR spectra of [Sn(Me,Me-Phebox)Me3] (2) and [Li(R,R′-Phebox)] complexes 3a (R = R′ = Me), 3b (R = iPr, R′ = H), and 3c (R = tBu, R′ = H) were investigated. It was found that 2 exhibits no chelation of the Phebox ligand to the Sn center in this case. The [Li(R,R′-Phebox)] complex 3a has been crystallographically characterized and is in the form of a molecular dimer (i.e. [Li(Phebox)]2), containing two formally three-center - two-electron bonds in a four-membered Li2C2 ring. The formal Phebox anion is bonded to the lithium cation via the two ortho imine N centers and the intraannular aromatic C atom. The 13C{1H} NMR signal of Cipso, being a seven-line pattern with coupling constant 1J(13C-7Li) = 18 Hz, confirms that the dimeric structure is maintained in solution at room temperature. Variable-temperature (VT) NMR studies of 3a indicate that a fluxional process is occurring at room temperature, which can be frozen out below -16°C (ΔG? = 56 kJ/mol). This fluxional process is not observed in VT-NMR studies on 3b,c. This is likely due to the presence of bulky (iPr or tBu) substituants that effectively shut down the pathways to rapid inversion of the puckering of the five-membered chelate ring.
