Synthesis, characterization and reactivity of carbazole-bis(oxazoline) lanthanide complexes




Zou, Jin

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Carbazole-bis(oxazoline) (Czx) lanthanide dialkyl, CzxLn(CH2SiMe3)2, and dichloride CzxLnCl2(THF)n, complexes were synthesized by protonolysis and salt metathesis protocols. The X-ray crystal structures of CzxLn(CH2SiMe3)2 (Ln = Er and Yb) and CzxLnCl2(THF) (Ln = Y, Er and Yb) were determined. The carbazole-bis(oxazoline) ancillary ligand provides high stability but relatively low activity in some reactions for the corresponding lanthanide complexes, possibly due to steric crowding caused by the dimethyl groups on the oxazoline ring. The synthesis of a series of divalent ytterbium monohalide complexes, CzxYbX(THF)2 (X = I, Cl) or CzxYbI(DME) was achieved by salt metathesis or sodium amalgam reduction methods. The salt metathesis reaction of CzxYbI(THF)2 with Li(CHSiMe3)2 or NaN(SiMe3)2 gave the corresponding divalent ytterbium alkyl and amide complexes, CzxYb[CH(SiMe3)2](THF) or CzxYb[N(SiMe3)2](THF), respectively. The solution behaviour of CzxYbI(THF)2 was investigated via variable temperature NMR spectroscopy and supported a dynamic process involving dissociation of THF at, or above, 280K. Similar dynamic solution behaviour was found in other divalent ytterbium complexes as well. Reaction of 2,2’-bipyridine with CzxYbI(THF)2, afforded a trivalent ytterbium complex with a coordinated bipyridyl radical anion illustrating that the divalent complex is a strong, one electron reducing agent. Despite this, treatment of CzxYbI(THF)2 with LiCH2SiMe3 gave a trivalent ytterbium dialkyl complex, CzxYb(CH2SiMe3)2, also prepared by salt metathesis starting from CzxYbCl2(THF) and LiCH2SiMe3. Reaction of the trivalent ytterbium dialkyl complex, CzxYb(CH2SiMe3)2, with a primary aryl phosphine, ArPH2, (Ar = Mes, Is), unexpectedly formed the divalent ytterbium secondary phosphides, CzxYb(PHAr)(THF)2. The same ytterbium phosphide complexes were also prepared by salt metathesis starting from either the divalent CzxYbI(THF)2 or the trivalent CzxYbCl2(THF) complexes. Non-reducible lanthanide dichloride complexes, CzxLnCl2(THF) (Ln = Sc, Y, Er) reacted with sodium aryl phosphides (NaPHAr) to generate the lanthanide mono(secondary phosphide) complexes, CzxLnCl(PHAr)(THF).