Andrea Sanders

The preparation and characterization of benzocyclobutenylidene-, naphtho[b]cyclobutenylidene-, and η2-benzocyclobutadiene-η5-cyclopentadienyldicarbonyliron hexafluorophosphate

Abstract The preparation and characterization of the first isolable cationic mononuclear complexes bearing a η 2 -cyclobutadienoid ligand or a carbene ligand lacking heteroatom stabilization are described. The reaction between 1-bromo-benzocyclobutene and Na[η 5 -C 5 H 5 (CO) 2 Fe] (NaFp) afforded η 1 -1-benzocyclobutenyl-η 5 -cyclopentadienyldicarbonyliron (III). Treatment of III with trityl hexafluorophosphate gave benzocyclobutenylidene-η 5 -cyclopentadienyldicarbonyliron hexafluorophosphate (V). Naphtho [ b ] cyclobutenylidene-η 5 -cyclopentadienyldicarbonyliron hexafluorophosphate (VI) was formed in an analogous manner. Both V and VI gave 1,1-disubstituted cyclobutenes when treated with nucleophilic reagents. η 2 -Benzocyclobutadiene-η 5 -cyclopentadienyldicarbonyliron hexafluorophosphate, (XIX), which was prepared by the oxidation of bis-1,2-(η 5 -cyclopentadienyldicarbonyliron)benzocyclobutene by trityl hexafluorophosphate, afforded trans -1,2-disubstituted benzocyclobutenes when treated with nucleophilic reagents. The η 2 -benzocyclobutadiene ligand of XIX was displaced by I− and trapped as the Diels--Alder adduct by 1,3-diphenylisobenzofuran.

The preparation and characterization of mono- and binuclear cationic iron complexes of η2-cyclobutadiene

Abstract The preparation of the first η 2 -cyclobutadiene complexes is reported. Treatment of the 3-chlorocyclobutenyl complex Fp CHCHCHC HCl (Fpη 5 -C 5 H 5 (CO) 2 Fe) with Ag + generates the highly reactive η 2 -cyclobutadiene complex Fp(C 4 H 4 ) + , which was trapped by dienes to afford Diels-Alder adducts. The oxidation of Fp CHCHCHC HFp with Ph 3 C + or Ag + gave Fp 2 (C 4 H 4 ) 2+ which possesses a bridging cyclobutadiene ligand.

Complexes of η5-cyclopentadienyldicarbonyliron derived from cis-3,4-dichlorocyclobutene

Abstract The metathesis between Na[η5-C5H5(CO)2Fe] (NaFp) and cis-3,4-dichlorocyclobutene afforded trans-Fp CHCHCHC HCl V and trans-Fp CHCHCHC HFp III. Both V and III underwent quantitative thermal isomerization to the trans,trans-butadienes, FpCHCHCHCHCl VII and FpCHCHCHCHFp VI, respectively. Complex V was hydrolyzed and isomerized on neutral alumina to the trans-butenal complex FpCH2CHCHCHO. Protonation of III gave Fp2C4H+5, which was converted by triethylamine to the cyclobutenyl complex, Fp CHCHCHC H2. Treatment of VI with I2 or HCl in methylene chloride afforded ICHCHCHCHI and Fp2[C4H6]+2·2HCl−2, respectively.

The reductive metalation of 1,2-dihalobenzocyclobutenes by NaFe(CO)2Cp and HFe(CO)2Cp

Abstract The reactions between cis - and trans -1,2-dibromo- or 1,2-diidobenzocyclobutene and NaFe(CO) 2 Cp (NaFp) were investigated. The mechanism of formation of 1,2-bis(cyclopentadienyldicarbonyliron)benzocyclobutene (I) and 1-(cyclopentadienyldicarbonyliron)benzocyclobutene (II) is thought to involve initial formation of benzocyclobutadiene, addition of a Fp radical to benzocyclobutadiene and subsequent addition of a second Fp radical to form I, or hydrogen abstraction from FpH to form II.

Benzocyclobutenylidene-h5-cyclopentadienyldicarbonyl-iron(II). A hydride abstractor more specific than the triphenylcarbenium ion

Abstract Benzocyclobutenylidene- h 5 -cyclopentadienyldicarbonyliron(II) hexafluorophosphate converts h 5 -CpFe(CO) 2 R (R = cyclo-C 3 H 5 , CH 2 -cyclo-C 3 H 5 ) to the respective allene and butadiene complexes whereas Ph 3 C + primarily yields addition products; both carbenium ions add to h 1 - allyl- and substituted h 1 -allyl-iron complexes with the exception of the 3,3-dimethylpropenyl complex which is converted in both cases to h 5 -CpFe(CO) 2 (CH 2 CHCMeCH 2 ) + .