A Long-Chain Phosphine Designed as a Metallomesogen Generator—Synthesis and Coordination Properties

Abstract

The long-chain phosphine Me₂PC≡C(p-C₆H₄CHNR ^C8) [L; R^C8 = p-C₆H₄OC(O)(p-C₆H₄OC₈H₁₇)] has been prepared in two steps starting from 4-ethynylbenzaldehyde (1): (a) condensation of 1 with H₂NR^C8 (2) afforded the corresponding imine 3 (yield 86%) which displays liquid-crystalline behaviour; (b) deprotonation of 3 with LiNPrⁱ₂ and subsequent reaction with Me₂PCl gave a mixture of the phosphine–alkyne L and the precursor 3 (L : 3 = 60 : 40). Reaction of this mixture with [PtCl₂(PhCN)₂] produced cis-[PtCl₂L₂] (4) and provided an efficient means of separating the phosphine from 3. The crystal structure of imine 3 has been determined by single-crystal X-ray diffraction and analysis of this structure provides a basis for understanding both the mesogenic character of 3 and its absence in the complex 4.