Organometallic and coordination chemistry of (Tetramethylcyclobutadiene)cobalt sandwich and halfsandwich complexes

This thesis consists of two parts. Part one is devoted to the development of (tetramethylcyclobutadiene)cobalt (Cb*Co) tris(ligand) complexes [Cb*Co(L)3]+. An improved synthesis of the starting materials [Cb*Co(CO)3]BF4, Cb*CoI(CO)2 and [Cb*Co(C6H6)]PF6 was developed. Photolysis of [Cb*Co(C6H6)]PF6 in acetonitrile produced [Cb*Co(NCMe)3]PF6. Alternatively, the tris(acetonitrile) complex was obtained via thermal substitution of benzene by acetonitrile when heating [Cb*Co(C6H6)]PF6 in acetonitrile. Complex cation [Cb*Co(NCMe)3]+ is substitutionally labile and reacts with Lewis bases to form cations of the type [Cb*CoL3]+, notably L3 = Cp-. The first structural characterizations of tris(ligand) complex cations [Cb*CoL3]+ with L = CO and MeCN are presented. The second part of the thesis describes reaction chemistry of the novel sigma,eta4-butadienyl (carbenoid) complex ion [CpCo(sigma,eta4-C4HsynMe4)]+, formed by protonation of CpCoCb*, and chemistry of a number of products derived thereof. Above -10°C the carbenoid cation undergoes a thermal rearrangement to produce the half-open cobaltocenium ion [CpCo(eta5-C5H4Me3)]+. The protonation of CpCoCb* was shown to be reversible under conditions of low proton activity. Thus deprotonation of the s,h4-butadienyl complex with one equivalent of NEt3 mainly gave CpCoCb*, whereas reaction with excess NEt3 afforded a hexatriene complex CpCo[eta4-C4HsynMe3(CH2)]. The carbenoid complex underwent nucleophilic addition reactions. Addition of CNtBu produced a (tert-butylamino)cobaltocenium ion [CpCo{eta5-C5Me4(NHtBu)}]+. Addition of excess PPh3 gave a phosphonio cation [CpCo{eta4-C4HantiMe4(PPh3)}]+. With pyridine four reaction channels were revealed: i) reversible deprotonation to the hexatriene complex; ii) reversible nucleophilic addition at the carbenoid center to form [CpCo{eta4-C4HsynMe4(NC5H5)}]+; iii) stereoisomerization to form a more stable isomer, [CpCo{eta4-C4HantiMe4(NC5H5)}]+; iv) very slow formation of the CpCoCb*. The more stable isomeric pyridine addition product underwent nucleophilic substitution reactions with 4-picoline to afforded the 4-picoline addition product and with CN– to yield a hexa-2,4-dienenitrile complex [CpCo(eta4-C4HantiMe4CN)]. The latter on protonation gave an aminocobaltocenium ion [CpCo{eta5-C5Me4(NH2)}]+. With CNtBu [CpCo{eta5-C5Me4(NHtBu)}]+ was formed. Acid removes pyridine from [CpCo{eta4-C4HantiMe4(NC5H5)}]+ to produce an isomeric carbenoid ion [CpCo(sigma,eta4-C4HantiMe4)]+, which again could be reacted with excess NEt3 to afford the isomeric hexatriene complex CpCo[eta4-C4HantiMe3(CH2)]. Thermolyses of CpCo[eta4-C4HsynMe3(CH2)] and CpCo[eta4-C4HantiMe3(CH2)] show that the later is the lower-energy isomer and produce a dinuclear complex (my-C5H3Me3)(CoCp)2 (Co–Co) with a bridging penta-2,4-dienylidene ligand.

Grantor dc:publisher

Publikationsserver der RWTH Aachen University

Year dc:date

2007

Author dc:creator

• Butovskiy, Mikhail V.

Contributors dc:contributor

• Kölle, Ulrich

• info:eu-repo/classification/ddc/540
• Chemie
• Cobalt
• Cyclobutadiene
• Butadiene
• Butadienyl
• Carbene complexes
• Metallo-electrophiles

Statement dc:rights

• info:eu-repo/semantics/openAccess

Language dc:language

eng

Identifier

https://publications.rwth-aachen.de/search?p=id:%22RWTH-CONV-123336%22

OAI identifier oai:identifier

oai:publications.rwth-aachen.de:61701