Arene, cocondensation with vapors

Manganese, iron, cobalt, and nickel vapors do not give arene complexes with haloarenes. Interactions with hexafluorobenzene have been reported, but the explosive products are unlikely to be complexes containing planar C8F8 rings. The Ni-C8F8 cocondensate is a source of... 

Another route to bis( -arene)vanadium(0) compounds is the cocondensation of arenes with vaporized vanadium metal (see Metal Vapor Synthesis of Transition Metal Compounds) On treatment with 1,3-cyclohexadiene and butyllithium, 15-electron vanadocene (5) is converted to 16-electron ( -benzene)( -cyclopentadienyl)vanadium(l) (6) (Scheme 3). Use of potassium naphthalenide affords the corresponding naphthalene complex. 

The first authentic zerovalent arenelanthanoid complexes [l,3,5-(t-Bu)3C6H3]2Ln (Ln-Y, Gd) have been obtained by Cloke and coworkers in die cocondensation of vaporized metal with an excess of l,3,5-tri-(t-butyl)benzene at 77 K [63]. The products are isolated after the recrystallisation from pentane as deep purple crystals highly soluble in hydrocarbon solvents. They are stable at room temperature, and may be sublimed at ca. lOOT/lO " mbar with partial decomposition. Like all other arene derivatives of REM (Table IV.6 ) bis(arene) complexes are highly air and moisture sensitive. 

Bis(Tj6-jV,-/V-dimethylaniline)molybdenum has been prepared in good yield by cocondensation of molybdenum atoms with a fifty-fold excess of Af,Af-dimethyl-aniline vapor on a liquid nitrogen cooled surface. This method has been extended to the synthesis of other molybdenum arene complexes and is at present the only synthetic route to such compounds. 

The possibility of coordination of a two-electron ligand, in addition to arene, to the ruthenium or osmium atom provides a route to mixed metal or cluster compounds. Cocondensation of arene with ruthenium or osmium vapors has recently allowed access to new types of arene metal complexes and clusters. In addition, arene ruthenium and osmium appear to be useful and specific catalyst precursors, apart from classic hydrogenation, for carbon-hydrogen bond activation and activation of alkynes such compounds may become valuable reagents for organic syntheses. 

The first use of ruthenium atoms in the synthesis of arene ruthenium derivatives was achieved in 1978 for the preparation of the thermally unstable bisbenzene ruthenium(O) complex 196a by condensation of ruthenium vapor with benzene (191). The more stable bisbenzene osmium(O) complex (322) has also been prepared in 15% yield by cocondensation of osmium atoms with benzene (192,193). 

The macroscale codeposition of PF3 has yielded a series of M-PF3 complexes. Some of these M-PF3 complexes can only be prepared by the metal vapor-ligand cocondensation technique. Very electron-rich M-phosphine and M-phosphite derivatives have been prepared by M-PMe3 and M-P(OMe)3 depositions, as shown in Table 8. A series of new homoleptic compounds have been prepared. Cocondensation of Fe and Ni with some arene systems gives stable (Ar)2Fe/Ni species, if maintained at low temperatures. 

There are just few examples of authentic lanthanide complexes in the oxidation state zero. Bis(arene) complexes of the lanthanides (l,3,5- Bu3C6H3)2Ln (Ln = Sc, Y, La, Nd, Pr, Sm, Gd, Tb, Dy, Ho, Er, Lu) have been synthesized by cocondensation of metal vapors (see Metal Vapor Synthesis of Transition Metal Compounds) with 1,3,5-tri(ferf-butyl)benzene at 75 K. A sandwich structure with coplanar arene ligands has been proven by X-ray crystal structure analysis of the Gd and Ho complexes (Figure 86a). 

A compound of stoichiometry [(MeeCe)Fe(CO)2]2 has been prepared by reacting Fe(CO)5 with hexamethyldewarbenzene and is thought to have structure (XVI) 115). Monomeric complexes of the type (arene)Fe-(CO)2 have not yet been reported, but the PF3 analogs (CgHe)Fe(PF3)2 288) and (MeCeH5)Fe(PF3)2 377) have been prepared by cocondensation of iron metal vapor, PF3, and the arene at — 196°C. 

Well-defined arene complexes of Group 4 metals in various oxidation states have been isolated. The air- and moisture-sensitive complexes Ti(r -arene)2 (56) have a sandwich structure similar to that of the related chromium compounds [176-178]. They have been used for deoxygenation of propylene oxide and coupling reaction of organic carbonyl compounds [179]. The first synthesis of 56 was cocondensation of metal vapor with arene matrix [176]. Two more convenient methods are reduction of TiCl4 with K[BEt3H] in arene solvent [180] and reaction of TiCl4(THF)2 with arene anions followed by treatment with iodine [170,176]. The latter method involves the formation of an anionic titanate complex, [Ti(ri -arene)2] (57), which can also be formed from KH and 56 [181]. 

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