Syntheses And Reactivities Of Highly Strained Cyclic Osmium Vinylidenes And Cyclic Osmium Carbynes

Cyclic metallavinylidenes and cyclic metal carbynes have attracted extensive attentions due to their unique structures.However,the intrinsic large ring strain and high reactivity of these frameworks make their synthesis encounter great challenge.In this dissertation,new methods for the synthesis of cyclic metallavinylidenes and cyclic metal carbynes were developed,and thus several novel five-membered,six-membered cyclic metallavinylidenes,and five-membered cyclic metal carbynes have been constructed.The related formation mechanisms and reactivities of them were studied in detail.In addition,the reactions of cyclic osmium carbyne with azides were investigated and a novel azametallacyclopropenes complex was obtained.The reactivity of azametallacyclopropenes towards acid and alkynes were also investigated.The dissertation consists of the following six chapters.In chapter 1,synthesis and reactivity of metallacyclic allenoids,cyclic metallavinylidenes,and cyclic carbynes closely related to the main objective of this dissertation,were summarized.In addition,the research objectives and plan of this dissertation are presented.In chapter 2,synthesis of fused 4-osmacyclohexa-2,3,5-trienone was described,and related mechanisms have been thoroughly studied.Two key intermediates,?2-ethynyl ketone coordinated osmacycle and 4-osmacyclohexa-2,5-dienone,were isolated and fully characterized.It is the first time to discover the conversion from 4-osmacyclohexa-2,5-dienone to 4-osmacyclohexa-2,3,5-trienone via oxidative dehydrogenation.In addition,the reactions of ?2-ethynyl ketone coordinated osmacycle with nitrogen nucleophiles were also presented.In chapter 3,synthesis of five-membered cyclic osmium vinylidenes and cyclic osmium carbynes via the reactions of osmacycle with electrophilic hypervalent iodine were described.One intermediate,3-osmacyclopent-2-enone,was isolated by controlling the quantity of hypervalent iodine.The first single five-membered cyclic osmium carbyne have been prepared by the reaction of cyclic osmium vinylidenes with methyl trifluoromethanesulphonate.In chapter 4,the synthesis of azaomsacyclopropenes and reactions of them with acid have been demonstrated,Azametallacyclopropene is one of smallest unsaturated metallacycle.Because of the high ring strain,the synthesis of them remains a challenge.The reactions of osmapentalyne with azides were studied and the fused azaomsacyclopropenes were constructed.The reactions of azaomsacyclopropenes with acid were also studied.The first metallapentalene with amino substituent was obtained.In addition,the fisrt osmapentalyne with amino substituent was also prepared.In chapter 5,the ring expansion reactions of azaomsacyclopropene have been investigated.Firstly,the[3+1]ring expansion reactions of azaosmacyclopropene with 1-pentyn-3-ol or methyl propionate were studied and MCCCCO pentadentate chelates were generated.Some special sliver bridging compounds were isolated during the mechanistic study.Secondly,an unusual MCCCCC pentadentate chelate was synthesized via the reaction of azaosmacyclopropene with 2-methyl-1-buten-3-yne.In addition,ligand substitution reactions of the azaosmacyclopropene with isonitriles were investigated.In chapter 6,the innovation of the dissertation is concluded and the prospect of this research is presented.