1360615-49-1Relevant articles and documents
Acetylene-expanded dendralene segments with exotopic phosphaalkene units
Geng, Xue-Li,Ott, Sascha
, p. 12153 - 12162 (2011)
Bis-TMS protected C,C-diacetylenic phosphaalkene (A2PA) 1 (Mes*P=C(C=CTMS)2; Mes=2,4,6-tBu3Ph) has been used as a building block for the construction of butadiyne-expanded dendralene fragments in which phosphaalkenes feature as exotopic double bonds. Treatment of 1 with CuCl gives rise to a CuI acetylide that is selectively formed at the acetylene trans to the Mes* group. The cis-TMS-acetylene engages in similar chemistry, albeit at higher temperatures and longer reaction times. The differentiation between the two acetylene termini of 1 allows for the controlled synthesis of the title compounds by a variety of different Cu- and Pd-catalyzed oxidative acetylene homo- and heterocoupling protocols. Crystallographic characterization of A2PA 1 and dimeric Mes*P=C(C=CR1)C4(R2C=C)C=PMes* (3 b, R1=R2=Ph; 6, R1=R2=TMS), and 10 (R1=R2=C=CPh) verifies that the stereochemistry across the P=C bond is conserved during the coupling reactions, whereas spectroscopic evidence reveals cis/trans isomerization in an iodo-substituted A2PA intermediate 4 (Mes*P=C(C=CTMS)(C=CI). UV/Vis spectroscopic and electrochemical studies reveal that efficient π conjugation operates through the entire acetylenic phosphaalkene framework, even in the cross-conjugated dimeric structures. The P centers contribute considerably to the frontier molecular orbitals of the compounds, thereby leading to smaller HOMO-LUMO gaps than in all-carbon-based congeners. Phenyl- and/or ethynylphenyl substituents at the A2PA framework influence the HOMO and LUMO to a varying degree depending on their relationship to the Mes* group, thus enabling a fine-tuning of the frontier molecular orbitals of the compounds.
