Arenes coordinated, reactions

The authors synthesized three amino acid substituted calix[4]arenes and investigated their coordination reactions towards Pd11 using electrospray mass spectrometry.384... 

Reactions of cobalt and nickel atoms with toluene and other arenes yield condensates in which the metal is in a very reactive state (105). However, none of the products of reaction of these condensates with other ligands has contained the arene coordinated to the metal. It seems possible that the condensates contain ditoluenecobalt and ditoluene-nickel, but in these complexes (unlike the chromium or iron complexes) the two arene rings are probably not symmetrically bonded to the metals. 

A series of cobalt carbonyl complexes of polyphosphazenes have been prepared via arene coordination sites. Examples are shown as 3.65 and 3.66.112 These are synthesized via the reactions of (NPC12) with the sodium salt of the appropriate metal-arene terminated alcohol. Mixed-substituent polymers with trifluoroethoxy or phenoxy cosubstituents have also been prepared. 

Arenes are inert to nucleophilic attack and normally undergo electrophilic substitution. However, arenes coordinate to Cr(CO)6 to form the i/fi-arenechromium tricarbonyl complex 79, and facile nucleophilic attack on the arene generates the anionic jy5-cyclohexadienyl complex 80, from which substituted arene 81, or cyclohexadiene is obtained by oxidative decomplexation. In this reaction, strongly... 

Whilst metallocenes have an enormously rich chemistry, in the case of arene coordination it is the half-sandwich ( piano-stool ) class of complex which finds the widest utility in organic synthesis, in particular within the chemistry of Cr(CO)3(ti6-arene) complexes. These are generally prepared directly from the thermal reaction of Cr(CO)6 and arene in a high-boiling solvent (e.g. Bu20, 2-picoline). For less robust arenes, the labile complexes Cr(L)3(CO)3 (L = NH3, THF, MeCN, py) may be employed under milder conditions (Figure 7.38). 

Hexafluoro-2-butyne undergoes 1,4 addition by reaction with Rh(dik)(diolefin) (dik = acac, dpm, dbm diolefin = cod, norbornadiene), with formation of a C—C bond between the alkyne and the methyne carbon atom of the /3-diketonate. Additional trimer-ization of hexafluoro-2-butyne to hexakis(trifluoromethyl)benzene and /j -arene coordination of the latter to rhodium affords 103 (equation 73). 

The second strategy involves stabilization of the mono-Cp r/°-non-benzyl dialkyl metal cation with 7t-arene coordination. The arene coordination becomes the primary stabilization factor enabling the detection or isolation of the mono-Cp dimethyl cations. Thus, the reaction of Cp MMe3 (M = Zr, Hf) with 1 equiv. of B(C6Fs)3 in toluene/hexanes (1 10) solutions at ambient temperature affords the cationic arene complexes [(Gp M(Me)2(7]6-PhMe)][MeB(C6Fs)3] 304 as the solvent-separated ion pairs stabilized by the coordination of the aromatic solvent (Equation (22)).244 The crystal stmeture of the hafnium complex [(Cp Hf(Me)2(7]6-PhMe)][MeB(C6Fs)3] confirms the formation of the separated, discrete ion pairs in which the bent-sandwich cation is coordinated to an 7]6-toluene ligand.245... 

The process involves initial formation of Ph M by halide replacement, followed by hydrogen transfer to allow arene -coordination . The reaction conditions complement those of the metal halide-aluminum halide-aluminum metal method and may be useful with specifically substituted arenes. 

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