1,1,3,3-Tetramethylguanidine solvated lanthanide aryloxides: pre-catalysts for intramolecular hydroalkoxylation

The synthesis and structural characterization of six 1,1,3,3-tetramethylguanidine (H-TMG) solvated lanthanide aryloxide complexes are reported. Ln[N{Si(CH₃)₃}₂]₃ (Ln = Nd, La) was reacted with two equivalents of both H-TMG and HOAr {HOAr = HOC₆H₂(CMe₃)₂-2,6 (H-DBP) or HOC₆H₂(CMe₃)₂-2,6-CH₃-4 (H-4MeDBP)} and one equivelent of ethanol (HOEt) to yield the corresponding [Nd(H-TMG)₂(4MeDBP)₂(OEt)] (1) and [La(H-TMG)₂(DBP)₂(OEt)] (2). Compounds 1 and 2 were further reacted with 4-pentyn-1-ol {HO(CH₂)₃CCH} to isolate [Nd(H-TMG)₂(4MeDBP)₂{O(CH₂)₃CCH}] (3) and [La(H-TMG)₂(DBP)₂{O(CH₂)₃CCH}] (4), respectively. Three equivalents of HOAr and one equivalent of H-TMG were additionally reacted with Ln[N{Si(CH₃)₃}₂]₃ to generate [Nd(4MeDBP)₃(H-TMG)] (5) and [La(DBP)₃(H-TMG)] (6). In order to examine the formation of 1–6, the interaction of H-TMG and HOAr was further examined in solution and the hydrogen bonded complexes (H-TMG:HOAr), 7 and 8, were isolated. Upon successful isolation of 1–6, the utility of 1, 2, 4 and 5 as pre-catalysts for the intramolecular hydroalkoxylation of 4-pentyn-1-ol was investigated. The bulk powders for all complexes were found to be in agreement with the crystal structures based on elemental analyses, FT-IR spectroscopy, and ¹H and ¹³C NMR investigations.