Warren P. Giering

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.

Regiospecific carboncarbon bond formation by oxidative coupling of η1-allyl or η1-propargyl ligands of organoiron complexes

Abstract Novel and regiospecific coupling reactions of η 5 -C 5 H 5 (CO) 2 Fe(η 1 -allyl) and (η 5 -C 5 H 5 (CO) 2 Fe(η 1 -propargyl) complexes due to oxidation by silver hexafluorophosphate are reported. The mono- and bi-nuclear products contain (substituted) hexadiene and hexatetraene ligands while variable amounts of protonation products are also formed.

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 synthesis of a cationic binuclear iron complex containing the η2-butatriene ligand and its reactions with oxygen nucleophiles

Abstract The synthesis of the first complex containing the unsubstituted η 2 -butatriene ligand [Fp 2 (CH 2 CCCH 2 )] 2+ (PF − 6 ) 2 (IV) is accomplished in 50% yield by oxidation of FpCH 2 CCCH 2 Fp with trityl hexafluorophosphate. IV reacts with aqueous sodium hydroxide to afford CH 2 CFpCOCH 3 (IX) and with aqueous sodium bicarbonate to yield a mixture of IX and CH 2 CFpCOCH 2 Fp (VIII). The binuclear allene complexes Fp + (CH 2 CCXCH 2 Fp) X =OAc, OPh, OPh- p -NO 2 are formed by the addition of the respective anions to IV. Ethylation of VIII with triethyloxonium hexafluorophosphate gives CH 2 CFpC + (OEt)CH 2 Fp. The major product resulting from the reaction between IV and methanol is η 3 -(CH 3 OCH 2 CFpC(CO 2 Me)CH 2 )-η 5 -C 5 H 5 (CO)Fe, (XIVa). Methoxide yields η 3 -(CH 2 CC(CO 2 Me)CH 2 )(CO)-η 5 -C 5 H 5 Fe as the major product in addition to smaller yields of XIVa and the isolable cis and trans isomers (XVI and XVII) of [η 5 -C 5 H 5 (CO)-η 2 -1,2-(CH 2 CHOMe)Fe][Fe(CO) 2 -η 5 -(C 5 H 5 )]. These isomers equilibrate above 100°C. Ethoxide and isopropoxide give similar results. In contrast, the only characterizable product obtained from the reaction between t-butoxide and IV was Fp 2 .

A study of the metalation of 1,4-disubstituted 2-butynes by sodium η5-cyclopentadienyldicarbonylferrate and hydrido-η5-cyclopentadienyldicarbonyliron

Abstract The metathesis between Na[η5-C5H5(CO)2Fe] (NaFp) and 1,4-dichloro-2-butyne or 2-butyne-l,4-diol bis(benzene)sulfonate afforded primarily FpCH2C CCH2Fp (I) and small amounts of FpC(CH2)CHCH2 (VIII) and FpCH2CCCH3 (IX). 1,4-Dibromo-2-butyne gave only small amounts of VIII and IX and none of the binuclear complex I. The yields of VIII and IX increased dramatically when t-butanol was present in the reaction mixture. In the presence of methanol, ethanol, or i-propanol,η3-E-[CH2CHCMe(CO2R)]-η5-C5H5(CO)Fe (R = Me, Et, i-Pr) was isolated in addition to VIII and IX. Complex VIII also was prepared by the reductive demetalation of Fp[CH2CHC(Fp)CH2]+PF6− which was obtained by protonation of I.

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.

The chemistry of the transition metalcarbon σ-bond. Insertion reactions between stannous chloride and h1-allyl and h1-propargyl complexes of h5-cyclopentadienyldicarbonyliron

Abstract The reactions between h5-CpFe(CO)2R (R = CH2CHCH2; CH2CMe=CH2; CH2CHCHMe; CH2CHCMe2) and stannous chloride in tetrahydrofuran afford the insertion products h5-CpFe(CO)2SnCl2R. When treated with stannous chloride in methanol or with excess stannous chloride in tetrahydrofuran, h5-CpFe(CO)2CH2CMeCH2 affords primarily h5-CpFe(CO)2SnCl3. The allenyl, 2-butynyl or cationic isobutylene complexes (R = CHCCH2; CH2 CCMe; CH2CMe+2) yield only h5-CpFe(CO)2SnCl3. Stannous iodide reacts with h5-CpFe(CO)2CH2CHCH2 in benzene to form h5-CpFe(CO)2I. Plumbous chloride in methanol fails to react with the above complexes.

Alkenyliron complexes. Cycloaddition reactions of organoiron metalloalkadienes

Abstract The metalloalkadienes, 2-Fp-1,3-butadiene ( 5 ), 1-Fp-1,3-butadiene ( 6 ), and 1-Fp-3-methyl-1,3-butadiene ( 7 ) (Fp = η-C 5 H 5 (CO) 2 Fe) form Diels-Alder adducts with a variety of electrophilic dienophiles. Kinetic experiments have demonstrated that 5 is at least 100 times more reactive toward dimethyl acetylene dicarboxylate than 2-trimethylsiloxy-1,3-butadiene. 5 and toluene sulfonyl isocyanate from an imino lactone that is thought to arise via a stepwise process involving ionic species. The synthetic utility of 5 is limited by its low decomposition point (110°C) and the formation of nearly equimolar quantities of the 1,3- and 1,4-positional isomers of cycloadducts derived from several asymmetric dienophiles.

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 ) + .