Arene, cocondensation with

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... 

When alkylarenes are cocondensed with Re atoms, C H activation of the ahphatic side chains occurs and a variety of novel arene derivatives of Re with /r-arylidene and hydride bridges, [Re2( -arene)2(/(r-CHAr)(/r-H)2], are formed, for example, products containing o-xylyl ligands. Similar reactions are observed with saturated hydrocarbons, for example, cocondensation with CMc4 gives (146). 

Cocondensation of Re atoms with alkylbenzenes is a synthetic route to K-alkylidene compounds [Re2(n-H)2(fi-L)(n -arene)2] with L = CHAr, CMePh or CHCH2Ph ° cocondensation of Re atoms with benzene and trimethylphosphine forms [Re2 PMe3)4 n -C5Hg)2]. ... 

As was suggested in the preceding discussion, most of the arene complexes isolated by metal-atom techniques are benzene derivatives. However, heterocyclic ligands are also known to act as 5- or 6-electron donors in transition-metal 7r-complexes (79), and it has proved possible to isolate heterocyclic complexes via the metal-atom route. Bis(2,6-di-methylpyridine)Cr(O) was prepared by cocondensation of Cr atoms with the ligand at 77 K (79). The red-brown product was isolated in only 2% yield the stoichiometry was confirmed by mass spectrometry, and the structure determined by X-ray crystal-structure analysis, which supported a sandwich formulation. 

Mixed arene-2,5-dihydro-l,2,5-thiadiborole-iron complexes have been synthesized by a novel route thermally unstable bis(arene)iron sandwich complexes, prepared by cocondensation of iron atoms with arene, react in the temperature range of -100 to -60°C with free Et2C2B2Mc2S to form reactive intermediates that decom-... 

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). 

Protonation of 322 with tetrafluoroboric acid in diethyl ether gives the cyclohexadienyl derivative 325 in 70% yield. Treatment of 325 with lithium aluminum hydride yields the biscyclohexadienyl osmium(II) complex 326. Treatment of 322 with PMe3 at 60°C gives the hydridophenyl osmium-(II) complex 181, rather than the expected arene bistrimethylphosphine osmium(O) compound, via intramolecular C—H bond activation of the benzene ligand (192,193) (Scheme 38). Compound 181 as well as the analogous ruthenium complex (92) have also been obtained directly by cocondensation of osmium or ruthenium atoms with benzene and tri-methylphosphine (62) [Eq. (44)]. 

Laboratory in Oxford, and Geoffrey Ozin at the University of Toronto in the early 1970s. With the metal atom cocondensation technique (which as described in Chaps. 6 and 7 was also used to prepare a series of zerovalent arene and olefin metal complexes), they reported simultaneously that the elusive palladium and platinum tetracarbonyls, Pd(CO)4 and Pt(CO)4, as well as the coordinatively unsaturated fragments M(CO)3, M(CO)2, and M(CO) (M = Pd, Pt) were formed by cocondensation reactions of Pd and Pt atoms with CO in inert gas matrices at 4-10 K [119-122]. The comparison of the CO bond stretching force constants for Pd(CO)ra and Pt(CO)ra (n - 1-4) revealed that, in analogy to Ni(CO) , the most stable compounds were the tetracarbonyls. In a xenon matrix, Pd(CO)4 existed up to about 80 K [120]. Ozin s group as well as others... 

Sixteen-electron bis(arene) complexes of formally zero-valent zirconium, hafnium, and titanium have been made by cocondensation of the metal atoms with bulky ligands such as 1,3,5-tri-t-butylbenzene71 ... 

The cocondensation of Nb atoms with toluene has yielded bis( -toluene)niobium, which serves as a useful intermediate for the preparation of a wide series of mono- and bis-arene derivatives. While Ti, V, Nb, Cr, Mo, and W form (Ar)2M sandwich complexes, Mn, Tc, and Re appear less promising, because Mn-arene complexes have already been shown to be unstable, Tc is radioactive, and Re remains to be investigated. As already mentioned, Ti forms fairly labile bis(arene)Ti complexes. The unstable 16-electron sandwich complexes from elements of group 4 can be stabilized with phosphine ancillary ligands, yielding bis-arene derivatives as in Table 6. 

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). 

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. 

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]. 

The key initiation step in cationic polymerization of alkenes is the formation of a carbocationic intermediate, which can then interact with excess monomer to start propagation. The mechanism of the initiation of cationic polymerization and polycondensation has been extensively studied. Trivalent carbenium ions play the key role, not only in acid-catalyzed polymerization of alkenes, but also in poly condensation of arenes (n -bonded monomers), as well as in cationic polymerization of ethers, sulfides, and nitrogen compounds (nonbonded electron-pair donor monomers). Pentacoordinated carbonium ions, on the other hand, play the key role in the electrophilic reactions of a-bonds (single bonds), including the oligocondensation of alkanes and the cocondensation of alkanes and alkenes. 

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. 

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