Cp*Co complexes

Brunner s group investigated the influence of thermal or photoinduced activation of Fe(Cp) (CO) complexes in the hydrosilylation of acetophenone (4b) with diphenylsilane, forming quantitatively the silylated l-phenylethanol59 (Scheme 4.26) [56,57]. Brunner... 

The dinnclear halides (51) are starting materials for a great variety of synthetic transformations, some of which are depicted in Scheme 35, giving either Cp Co derivatives by redaction or valence disproportionation upon reaction with acceptor ligands, or Cp Co complexes by valence... 

The dihydrodiboraanthracene 3 easily forms the dianion 32-, which reacts with the corresponding organometal halides to give the bis(allyl-nickel) triple-decker 21 and the trinuclear Cp Co complex 22 (where Cp ... 

The nucleophilicity of an organocobalt(III) species was utilized by Hummel and Ellman to achieve condensation of an azobenzene and an aldehyde to afford an A/ -aryl-2//-indazole derivative (Scheme 10.13) [35]. A combination of a cationic Cp Co complex bearing a noncoordinating B(CgF5)4 anion and acetic acid promotes direct addition of the azobenzene to the aldehyde through azo-directed ortho-metalation and subsequent insertion of the C=0 bond into the aryl-Co bond. While these catalytic steps are likely reversible, intramolecular dehydrative condensation of the azo and the alcohol moieties in the aldehyde adduct serves as a driving force for the formation of the indazole product. The reaction shows a substrate scope comparable to that of the same reaction catalyzed by a Cp Rh catalyst [36] and is applicable to both symmetrical and unsymmetrical azobenzene derivatives and to aromatic, heteroaromatic, and aliphatic aldehydes. 

Tetrakis-Cp uranium complexes are readily prepared via metathesis of UCl and KCp in refluxing benzene. These complexes are a relatively rare example of a pseudotetrahedral complex with four Tj -Cp rings, (rj-ring) (25). The Cp derivative has been shown to react with CO and CO2 to give acyl and carboxylato complexes. This complex also reacts with alkyl haUdes to afford the U(IV) complex, Cp UX (X = halide). 

Cp(CO)2Re(THF) forms the complex 105 upon reaction with thiophene (89JA8753, 910M2436). Similar species are known for 2- and 3-methyl-, 2,5-dimethyl, and tetramethylthiophene (91IC1417). Thiophene in 105 is S-coordi-nated, and the sulfur atom is pyramidal. Treatment of 105 with Fc2(CO)9 produces 106, where the thiophene ligand is bridge-coordinated via the sulfur atom to rhenium and four carbon atoms of the dienic system with iron (the coordination mode). The pyramidal nature of the sulfur atom is preserved. The -coordination of thiophene separates the dienic and sulfur counterparts of the ligand and decreases the TT-electron delocalization, which leads to the enhanced basicity of the sulfur atom. 

Ti -Cyclopentadienyl(triphenylphosphine)cobalt reacts with phosphites and forms complexes of 1-alkoxyphosphole oxides 251 (R = Me, Et, Ph) through a step involving (ri -cyclopentadienyl)(phosphite)cobalt (80JA4363). (ri -Cp)Co(PF3)2 reacts with hexafluorobut-2-yne and 252 is formed, which hydrolyzes into 253 (X = OH) [73JCS(CC)583 75JCS(D)197]. The five-member ring has the envelope conformation, in which the carbon atoms are coplanar, and the phosphorus atom deviates from this plane in the direction opposite to the cobalt atom. The heterocycle is a four-electron donor relative to the metal center. 

Similar triple-decker complexes are known, e.g., [(17-p-MeC6H4CHMe2) Ru(i7 -Et2C2B3H3)Ru(i7 VMeC6H4CHMe2)] and [(i7 -Cp)Co(i7 -Et2C2 B3H3)... 

Whether these results will also have an impact on the theory of metallaallenes is difficult to predict at least for the compounds Cp (CO)2Mn = M = Mn(CO)2Cp, (M = Ge, Sn, Pb) a linear structure is established and also linear p-carbido complexes are known [198], Recently, a germanium compound has been synthesized which is directly comparable with 22. In this case, the starting material for the synthesis is not a monomeric base adduct, but a dimeric germylene complex which is cleaved by Na2Fe(CO)4 in pyridine to form 72 [199],... 

Transition metal alkyls are often relatively unstable earlier views had attributed this either to an inherently weak M—C bond and/or to the ready homolysis of this bond to produce free radicals. Furthermore, the presence of stabilizing ir-acceptor ligands such as Cp , CO, or RjP was regarded as almost obligatory. However, (1) the M—C bond is not particularly weak compared say to the M—N bond, and (2) the presence of the new type of ligand on the metal could make the complex kinetically stable thus, even isoleptic complexes, i.e., compounds of the form MR , might be accessible 78, 239). These predictions have largely been borne out (see Table VII). 

C02-Bridged bimetallic zirconocene complexes have been formed from 1 and metallocarboxylic acids [229]. Reachon of 1 with metal enolates Cp(CO)3WCHR COX (X = OEt, Me, Ph) gives Cp(CO)3WCH(R )CH(R)OZrCp2(Cl). The structure for R = H and R = Me was solved by an X-ray analysis and the chemical reactivity of these organometallic products have been studied [230]. 

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