meta‐Terphenyl Phosphaalkenes Bearing Electron‐Donating and ‐Accepting Groups

Abstract

A set of para‐substituted meta‐terphenyl phosphaalkenes of the form 4‐X‐2,6‐Mes2C6H2P=C(H)C6H4‐4‐X′ (X = H, MeO or NMe2; X′ = H, CN, or NO2) have been synthesized to allow systematic studies of the impact of remote X and X′ substituents on the phosphaalkene unit. The new compounds were characterized by 1H and 31P NMR spectroscopy, UV/Vis absorption spectroscopy, single X‐ray crystal structures (for four compounds) and by electrochemical studies. The introduction of remote groups (X′) on the less hindered phenyl ring generated more significant effects on the physical properties of the materials than did substituents (X) on the hindered meta‐terphenyl rings. These effects were also explored by computational methods in order to assess the influence of substituents on structures and properties. The polarization of these molecules is less than that produced for analogous alkenes, as the phosphaalkenes bear sterically demanding groups that constrain the systems to adopt conformations that are less than ideal for maximum π‐conjugation of the central π network

Preparation and Characterization of P2BCh Ring Systems (Ch=S, Se) and Their Reactivity with N‐Heterocyclic Carbenes

“…The NHC‐adduct 4S Me has a strikingly similar structure to the known methylenethioxophosphoranes ( 10 , Scheme ), however 4S Me contains a longer P−S bond (2.0186(15) Å versus 1.928 Å) and a significantly longer P−C bond (P−C NHC in 4S Me 1.852(3) Å versus 1.656 Å) . The P−C NHC bond length is longer than expected for P=C, thus describing 4S Me as containing a multiply bound phosphorus atom is not appropriate.…”

“…Them etrical parameters of 4S Me revealed two essentially identicalP ÀCb ond lengths (PÀC NHC = 1.852(3) andP ÀC Ar = 1.867(3) )a nd as hort PÀSb ond of 2.0186(15) ,t hat is, bond parameters that are similar to those in 4S iPr .T he NHC-adduct 4S Me has as trikingly similar structure to the known methylenethioxophosphoranes (10, Scheme4), [48] however 4S Me contains al onger PÀSb ond (2.0186(15) versus 1.928 ) [49] and as ignificantly longerP ÀC bond (PÀC NHC in 4S Me 1.852(3) versus 1.656 ). [49] The PÀC NHC bond length is longer than expected for P=C, [50][51][52] thus describing 4S Me as containing am ultiply bound phosphorus atom is not appropriate.…”

Synthesis of the first metal-free phosphanylphosphonate and its use in the “phospha–Wittig–Horner” reaction

“…The two compounds are not only isolobal, but also show analogous reactivity when exposed to aldehydes, with the Mes*P=PMe 3 reacting under the formation of phosphaalkenes. [33][34][35][36] An interesting aspect of the described reagents is the fact that they are stable (days to week in solution)…”

Synthesis of 2,6-Dimesitylphenyl-C,C-Dibromophosphaalkene

“…15 We were interested if a direct bromination of 1 would be possible to facilitate the synthesis of 4-bromo substituted m-terphenyl derivatives using a procedure described by Yoshifuji and co-workers for the 1,4-dibromo-2,6-di-tertbutylphenyl analog. 16 Under similar conditions, 1 is brominated exclusively at all four meta-protons of the mesityl rings, at a large excess of Br 2 .…”