Azavinylidenephosphoranes: A Class of Cyclic Push–Pull Carbenes

Abstract

The synthesis of a novel family of cyclic push-pull carbenes, namely, azavinylidene phosphoranes, is described. The methodology is based on a formal [3+2] cycloaddition between terminal alkynes and phosphine-imines followed by an oxidation/deprotonation step. Carbenes 6, obtained by simple deprotonation, exhibit typical transient carbene reactivity like the intramolecular CH insertion reaction and a pronounced ambiphilic character exemplified by [2+1] cycloaddition with electron-poor methyl acrylate. Owing to the cyclic structure, carbenes 6 also exhibit an excellent coordination ability toward transition metals. Rh(I) complex 10 was obtained in excellent yield and was fully characterized by multinuclear NMR spectroscopy and X-ray crystallography. The corresponding Rh(I) -carbonyl complex was also prepared; this indicates that carbenes 6 belong to the strongest σ-donating ligands to date. DFT calculations confirmed the high σ-donation ability of 6 and their classification as push-pull carbenes with a relatively small singlet-triplet energy gap of 23.2-24.3 kcal mol(-1) .

Synthesis of Norbornene-Based Phosphine-Stabilized Silylium Ions Behaving as Masked Frustrated Lewis Pairs

“…One of our main objectives is the stabilization of electron-deficient species, and recently, a framework based on norbornene was designed to stabilize silylenes using phosphines as Lewis bases . Of special interest, we have shown that, due to the weak coordination of the phosphine ligand, phosphine-stabilized silylenes remain highly reactive.…”

Phosphine/Sulfoxide‐Supported Carbon(0) Complex

“…The IR spectrum of 6 shows the characteristic CO‐stretching frequencies with an average value of 2016 cm −1 , which is in the range of those observed for cyclic or acyclic bent allenes (2018 and 2014 cm −1 respectively) . Therefore, phosphine/sulfoxide carbone 2 appears to be stronger electron‐donating ligand than classical NHCs (2060–2036 cm −1 ) but weaker compared to cyclic carbodiphosphoranes (2001 cm −1 ) (Figure ) …”

Rhodium (II)-Catalyzed Synthesis of Tetracyclic 3,4-Fused Indoles and Dihydroindoles

“…Rhodium-stabilized donor/acceptor carbenes as reactive intermediates have been widely applied in modern organic synthesis [14][15][16][17][18][19][20][21][22][23][24][25][26]. Among them, N-sulfonyl-1,2,3-triazole as an alternative source of carbene precursor has been used to achieve the transannulation reaction for the direct synthesis of heterocycles [27][28][29][30][31][32][33][34][35][36][37][38][39][40][41].…”