Synthesis And Reaction Of 2H-phosphinidole By A Spatial Constrained Phosphinidene And Alkenes

Electrophilic phosphinidene complexes are an important,highly reactive and low coordinated organophosphorus compounds.The tipycal reactions of these organophosphorus species are the insertion reaction and cycloaddition reaction.Most of the C-C bond insertion reaction of phosphinidene was achieved through the skeletal rearrangement of a strained three-membered ring intermediate,and has never been succeeded with inert C（sp²）-Arσ-bonds of alkenes.In recent years,the intromolecular C（sp²）-H bond insertion reaction of phosphinidene andwas achieved with the spatial constraint strategy.Similarly,a novel cyclization between phosphinidene complex and alkyne was reported by inhibiting the classic[1+2]cycloaddition reaction in a spatial constraint sphere.We studied the reaction behavior of phosphinidene and alkene under the spatial constraint sphere.The inert C（sp²）-Arσ-bond was successful activated and a new highly activate intermediate2H-phosphindole complex was formed during the reaction.The 2H-phosphindole complex is more reactive than the 2H-phosphole in the cycloaddition reactions.This led us to disclose the cycloaddition reactions of intermediate 2H-phosphindole complex with unactivated benzenes,nitriles and CS₂.It is noteworthy that2H-phosphole couldn’t been reacted with benzenes,nitrile and CS₂.The details are as follows:（1）A serials of 7-（2-vinylphenyl）-7-phosphanorborndiene complexes were synthesized from phospholes to discover the reactivity of phosphinidene complex and C=C double bonds in a spatial constraint sphere.The experimental results disclosed that the spatial constraint effect inhibited the normal[1+2]cycloaddition between phosphinidene complex and intromolecular C=C bond.Instead,the in situ formed phosphinidene complex inserted into the C（sp²）-Arσ-bond selectively.The verification experiments and computed results revealed that the reaction process contains a 2H-phosphindole complex intermediate without any strained intermediate.（2）The cycloaddition between highly reactive 2H-phosphindole complex and nonactivated benzenoid hydrocarbons.The metal-free successive dearomatization[4+2]cycloaddition between 2H-phosphinidole and aromatic benzene rings,provides structurally complex peri-fused heptacyclic skeletons with phosphorus at the bridgehead.The comparative density functional theory（DFT）caculations and the RFV values of the reactions of benzene with 2H-phosphindole W（CO）₅ complex,2H-phosphindole or 2H-indene disclosed that the low coordinated phosphorus atom plays a major role to enhance the reactivity of 2H-phosphindole towards benzene.（3）Described the cycloaddition reaction of 2H-phosphindole complex as phospha-dienes with small molecule CS₂.2H-phosphindole complex can overcome the high energy of two C=S bonds of CS₂.The successive[4+2]cycloaddition with CS₂ afforded phosphorus-and sulfur-containing spiro rings.The influence of substitions of C=C bonds on the cycloaddtion reaction was disclosed.To the best of our knowledge,this is the example of two C=S bonds of CS₂ as dienophile in the[4+2]cycloaddition.（4）We reported the[4+2]cycloaddition reactions of 2H-phosphindole complexes and nitriles to produce the 2-aza-1-phosphanorborndiene complexes.We further revealed the relationship between the hydrolysis of C=N bond in the products and the structureof nitriles.A possible reaction mechanism was proposed for the formation of complex spiro aza-rings from 2H-phosphindole complex and nitriles withα-H.