Synthesis Of Osmafuran, Osmanaphthalene And Osmapyridine By [4+1], [5+1] And [4+2] Cyclization Methods

The chemistry of transition-metal-containing aromatic compounds is currentlyattracting wider research interests because they can display both the reactivitiesrelated to organometallic compounds and the aromatic properties including ringplanarity,low chemical shift.Previous study has led to the isolation andcharacterization of an impressive number of transition-metal-containing aromaticcompounds including metallabenzene,metallabenzyne,metallapyridine,metallapyrylium,metallathiabenzene,metallapyrrole,metallafuran,metallathiophene,metallanaphthalene,metallanaphthalyne and metallabenzofurans.Among them,themetallanaphthalene,metallanaphthalyne,and the hetero-atom containingmetallaaromatics such as metallapyridine are very rare.In this dissertation,theresearch was carried out based on the reaction between OsCl₂(PPh₃)₃ andHC≡CCH(OH)Ph.The osmafurans were synthesized by[4+1]cyclization reaction.The[5+1]cyclization reaction was successfully used in the synthesis ofmetallanaphthalene and metallanaphthalyne.The first formal[4+2]cycloadditionreaction between hydride osmium alkenylcarbyne and acetonitrile afforded the firstlate-transition-metal-containing metallapyridine and its derivative metallapyridinium.This dissertation contains five chapters.In chapter 1,the research background of transition-metal-containing aromatics wasreviewed.On of the major issues of this field is the synthesis of novel aromaticmetallacycles.In this regard,some strategies were proposed based on the previouswork of our group,including constructing metallafuran by[4+1]cyclization,metallanaphthalene and metallanaphthalyne by[5+1]cyclization,and metallapyridineby[4+2]cycloaddition reaction,respectively.In chapter 2,the reaction between OsCl₂(PPh₃)₃ and HC≡CCH(OH)Ph wasinvestigated,giving the osmium vinyl complex 2-1 (Scheme 1) with intramolecularcoordinated hydroxyl group.The reactivity of 2-1 was investigated (Scheme 2) andthe metallafurans 2-2 and 2-3 were synthesized by heating the DCE (ClCH₂CH₂Cl) solution of 2-1 under reflux and treating 2-1 with Cs₂CO₃,respectively.Thecompound 2-1 can also react with CO and DPPB to give osmium vinyl compound 2-4and 2-5,respectively.In chapter 3,the hydride osmium alkenylcarbyne compound 3-2 was synthesizedfrom the reaction of 2-1 and HBF₄ (Scheme 3).The first metallanaphthalene dimmer3-3 and the second metallanaphthalyne 3-4 can be selectively synthesized from 3-2 via intramolecular C-H activation of phenyl (Scheme 3).Furthermore,thetransformation of 3-3 to 3-4 represented the first example of the conversion ofmetallabenzene to metallabenzyne,providing a potentially useful synthetic method forthe formation of metallabenzyne.Interestingly,3-2 can also react with H₂O in thepresence of AgBF₄,CO via the formal[4+1]cyclization to give the osmium vinylcompound 3-5 (Scheme 4) with intramolecular coordinated hydroxyl group.In Chapter 4,the formal[4+2]cycloaddition reaction between the hydride osmiumalkenylcarbyne 3-2 and acetonitrile was firstly reported,affording the firstlate-transition-metal-containing metallapyridine 4-2 (Scheme 5) and its derivativemetallapyridinium 4-1.The paramagnetism of 4-1 and 4-2 is unprecedented in thechemistry of transition-metal-containing aromatic compounds.The osmapyridinium4-1 can also undergo aromatic nucleophilic addition reaction with H₂O (Scheme 6).This reaction pattern is also very rare in the chemistry of aromatic metallacycles. In chapter 5,the innovation of this dissertation was summarized and the prospect ofthis research is presented.