Metal Vapors with Ligands

Condensation of metal vapors with various 6e ligands (cf. preparation of diene complexes, Chapter 8) allows the synthesis of many complexes which would be difficult or impossible to obtain by other methods owing to the reactivity of substituents. The following bisarene complexes were obtained in this manner [Cr(arene)2], where arene = PhX (X = F, Cl, CF3, COOMe, Me, /-Pr) or (X = F, Cl, CF3, 

The condensation of metallic titanium with benzene gave the first sandwich arene compound of titanium(O), [Ti(PhH)2]. This is a diamagnetic red-orange complex. 

Several compounds of vanadium of the type [V(PhX)2] were synthesized (X = H, F, Cl, CF3). The compound [V(1,4-C6H4F2)2] was also prepared. 

The condensation of metal vapors with hexafluorobenzene and benzene gives unstable arene complexes of V, Cr, Mn, Fe, Co, Ni, and Pd, for instance, [Cr(C6H6)(C5F6)]. The condensation of vapors of chromium or iron with the mixture of vapors of benzene and PF3 or hexafluorobenzene and PF3 leads to the formation, with low yields, of the derivatives [Cr(C6F6)(PF3)3], [Cr(PhH)(PF3)3], and [Fe(PhH)(PF3)2]. Heteroleptic compounds of chromium, for example, [ (CgF ) (Pp3)3], are stable in contrast to [Cr(C6F6)2] which is unstable and explosive. The condensation method was also utilized for the preparation of hexahapto pyridine complexes of chromium. 

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The ligand source is simply a nozzle or other vapor dispersion device to introduce volatile co-reactants or gases into the vacuum system and thence to the co-condensation site co-condensation of metal vapors with solutions of involatile substrates requires special techniques, which will be discussed in Section 1.08.6. 

Although some Ln complexes such as [Ln(CO)J (n = 0-6) or [Ln(butadiene)3] have been isolated by cocondensation of metal vapor with the ligand, the lanthanides show only very little ability to form Jt complexes. Indeed, the complexes in the usual oxidation state III cannot provide backbonding in the absence of d electrons. For this same reason, complexes with double metal-ligand bonds such as M=0, M=NR or M=CR2 are unknown whereas such complexes are well known with the transition metals (see Chap. 9.3). 

Thermochemical properties of the lanthanide elements and ions have recently been reviewed by Johnson (1977) and Morss (1976). It is well known that with any particular ligand, the thermodynamic stability of the dipositive oxidation state of the lanthanide varies according to the sequence Eu > Yb > Sm. The ease of preparation of divalent compounds is in the same order. For example, co-condensation of Yb metal vapor with 1-hexyne yields a compound in which Yb is present as 85-92% Yb " in the case of samarium, trivalent products are obtained (W.J. Evans et al., 1981). Eu and Yb cyclooctatetraenyl have been prepared (Hayes et al., 1969), but the samarium compound is as yet unknown. 

The metal-vapor technique was applied to cobalt atoms and r-BuC = P (01JOM(635)212). The mixture of products that resulted includes the mixed-ligand sandwiches 170 and 171. Further interaction of complex 170 with [W(C0)5(THF)] leads to the coordination of the W(CO)5-group via the phosphorus heteroatom of the four-membered ring to yield 172. 

Complexation with polyaromatic systems has also been observed. For instance, Mlnaphthalenelj, M = Cr (88,183), Mo (183), V (183), or Ti (183) may be synthesized in a solution reactor with the appropriate, metal vapors at liquid-nitrogen temperature. The Cr/naphthalene complex is less stable (dec. 160°C) than CrtCsH ) (m.p. 283-284° C). In fact, the naphthalene ligand is sufficiently labile to allow reaction under mild conditions, to afford CrL (L = CO or Bu NC), or Cr(naphth)Ls [L = PFj, P(OMe)3, or PMea]. The Mo, V, and Ti species are equally reactive. Analogous 1-methylnaphthalene complexes were also isolated (183). In addition, the complexes shown in Fig. 38 were synthesized by reaction, at the temperature of liquid nitrogen, of Cr atoms with 1,4-diphenylbutane (35, 201, 202). Analogous complexes were formed with 1,5-diphenylbutane (202). 

Co-condensation of Hf and Zr atoms from an electron-gun evaporation device, with P(Me)3 and arenes at 77K gave good yields of the species [M(arene)2P(Me3)]. Metal vapor synthesis led to Fe(i7 -arene)L2 and Fe(i7 -arene)-(i7 -diene), where L is a phosphorus ligand. In addition, complexes of stoichiometry Fe(T) -diene)L3 (where L is again a... 

S.2.2.2. Dimers and Clusters with Nonbridging Ligands 8.2.2.2.I. Syntheses from Metal Vapors. 

The co-condensation at low temperature of a metal vapor (commonly produced by resistance or electron-beam heating of metals) with a vapor of weakly stabilizing organic ligands (such as -pentane, toluene, tetrahydrofu-ran, acetone, or acetonitrile), using commercially available reactors, affords solid matrices, where reactions between the ligand molecules and metal atoms can take place (Scheme 1(A) Figure 1) [5]. 

The simplest case of M-M bonds was observed in Mj+ dimers without surrounding coordinate ligands. These compounds (with n = 0) were synthesized for a number of metals by fast condensation of metal vapors in inert-gas matrices at low temperatures [130-135]. 

Introduction. In a typical experiment, the metal vapor is co-condensed at a liquid nitrogen-cooled surface with the ligand substrate vapor. Upon... 

Infrared spectroscopic studies have been particularly useful in demonstrating the generality of this reaction. The spectra of the films of the complexes, obtained by depositing each of the metal vapors and excess 1,5-COD on a cold window and pumping off the excess ligand at -70°C, are all extremely similar, i.e., the spectra of the new compounds of Fe, Co, and Pd are almost identical to the spectrum of Ni(COD)2 with its known tetrahedral structure (25). 

The only route to dibenzenetitanium so far described is the reaction of titanium atoms with benzene the reductive routes that give access to arene complexes of Group V and VI metals fail for titanium. Although yields of about 30% are reported for the preparation of dibenzene-, ditoluene-, and dimesitylenetitanium, the reactions are more sensitive than most to the effect of excess metal. Unless the ligand-to-titanium ratio is high and the rate of deposition of titanium vapor kept low, the products seem to be catalytically decomposed by finely divided Ti metal 4a, 7). 

The reactions of cycloheptatriene with metal vapors may be altered by the addition of other ligands (133, 140) ... 

Fig. 15.41 An inexpensive apparatus constructed from a modified rotating evaporator and used to vaporize metals for condensation with ligands. [Adapted from Murkle. R. J. Pctiiiohn. T. M. Logowski, 1.1. Oreanomviottics 1985,4. L529-(J3I. Used with pemus-don.)...

Bis(amido) phosphine-donor complexes, with Zr(IV), 4, 816 Bis(amido) pyridines, with Zr(IV) and Hf(IV), 4, 790 Bis(aminoalkylidyne) complexes, diiron carbonyl complexes with cyclopentadienyl ligands, 6, 248-251 Bisaminosilylenes, in molybdenum carbonyls, 5, 406 Bis(tj-arc nc) complexes, as metal vapor synthesis milestone, 1, 236... 

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