Ligand-metal codeposition

Preparation of a Typical Au-Acetone Colloid. The metal atom reactor has been described previously. (39,59, 60) As a typical example, a W-A1 0 crucible was charged with 0.5Qg Au metal (one piece). Acetone (300 mL, dried over K2C0 ) was placed in a ligand inlet tube and freeze-pump-thaw degassed with several cycles. The reactor was pumped down to 1 x 10 Torr while the crucible was warmed to red heat. A liquid N2 filled Dewar was placed around the vessel and Au (0.2g) and acetone (80g) were codeposited over a 1.0 hr period. The matrix was a dark purple color at the end of the deposition. The matrix was allowed to warm slowly under vacuum by removal of the liquid N2 from the Dewar and placing the cold Dewar around the reactor. 

The metal vapor ligand codeposition method has extended the array of such sandwich complexes. A wide range of substituents can be tolerated on the arene ring unusual arene M complexes have been prepared. Elschenbroichmade the interesting compound bis(j7 -phosphabenzene)vanadium, which is less air sensitive than the ligand itself. It turned out that the phosphorus heteroatom has a much stronger influence on the electron affinity of the free arene than of the bound arene. 

Table 3 Mixed bis(arene)chromium compounds prepared by metal vapor-ligand codeposition...

Table 4 Mixed arene/ligand complexes of Cr prepared via metal vapor-ligand codeposition method...

Pure phosphine-metal atom studies with the early transition metals have been lacking. The only complex prepared this way prior to 1978 was Cr(Pp3)6. King and Chang, with the unique aminophosphine systems Me2NPF2 and MeN(Pp2)2, have generated a variety of new homoleptic M-(L) systems (see Homoleptic Compound). The codeposition of Cr vapor with these ligands yields the complexes shown ... 

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. 

Cyclopentadiene reacts with transition metals by oxidative addition of one H—C bond at the saturated carbon. Metal-atom vapors of Mo and W codeposit with cyclopentadiene to form (h -C5Hj)2MH2. Irradiation of Mo(CO)j with cyclopentadiene in isooctane yields (h -C5H5)Mo(CO)2C5H2-h ) that involves overall H transfer between ligands. 

Benzene, benzene-d , and fluorobenzene were found (770, 777) to react with chromium, cobalt, iron, and nickel atoms on codeposition in the neat ligand at 77 K, or in argon matrices at 10-12 K. IR studies of the products indicated that the initial reaction of these transition-metal atoms with an aromatic system is 7r-complex formation. Studies of ligand concentration-effects showed that the chromium-atom reaction is approximately second-order with respect to benzene, yielding the previously known (782) complex (CeH6)2Cr, whereas, with the other metals, the reaction is first-order, yielding MfCsHs), M = Co, Fe, or Ni. The absence of CrfCeH ) is probably a reflection of (a) the fact that the... 

The difficulty in attempting to determine the mechanism of alloy deposition from the current-potential relationship observed in complex solutions, which sometimes contain more than one ligand, was alluded to in the introduction to this chapter (cf., Section 1.2.2). The comments made here are not meant to criticize the experimental work presented in these papers in the field of induced codeposition of Mo with iron-group metals. It is only given to show the limits of validity of mathematical models, particularly when the solution is complex and the number of freely adjustable parameters is large. 

The iron vapor-toluene reaction has evoked interest because of the lability of the proposed bis(arene)iron complex to ligand subsitu-tion and to loss of both toluene molecules to free the metal atom. In the latter case the toluene molecules may be usefully regarded as metal atom carriers which can be used to direct the latent reactivity of the atom in subsequent solution phase chemistry. In this way the metal atom experiment can benefit from the convenience and additional versatility afforded by bench-top chemical manipulations. These results are relevant to a reported preparation of a dehydroxy-lated silica-supported Fischer-Tropsch catalyst from a static reactor codeposition of Fe and toluene.(46) In the liquid phase, iron atoms "bottled" in this way have also been utilized in an exceedingly mild method for making minute catalytically active superparamagnetic clusters on the surface and within the cavities of a dehydrated sodium zeolite Y.(38) Using the rotary reactor, preformed solutions of solvated iron atoms (as the toluene complex) are cannulated below their decomposition temperature out of the flask to a cold slurry of the support in toluene. Diffusion of intact... 

Nitric oxide, a three-electron ligand, is too volatile to be cocondensed at —196°C for macroscale preparations. The BF3 adduct of NO, which is less volatile, has been used. Deposition of BF3-NO and appropriate metal/ligand systems yields the corresponding complexes. The codeposition of a wide series of isocyanides gives macroscale amounts of NiL4 and FeLf. 

Axial interaction of an aryl unit with the [Ru-Ru] bond tends to increase the metal-metal distances. Petrukhina et al. isolated two complexes by codeposition of 2 and 8 with [2.2]paracyclophane to yield (17) and (18), respectively (Scheme 11) [68]. A sandwich structure with the aromatic moiety entrapped between two dimetal imits is observed. The [Ru-Ru] distance increases from 2.627(9) A in 8 to 2.656(3) A in 18 on axial coordination of the arene moiety. Similarly, a change of [Ru-Ru] distance from 2.673(1) A in 2 to 2.678(3) A in 17 was also observed. The inter-centroid distances between the two rings in [2.2]paracyclophane group are shorter (2.974(4) A in 17 and 2.982(5) A in 18) compared to the free [2.2] paracyclophane ligand (3.09 A). This supports the hypothesis that coordination of aryl group to the electrophilic ruthenium centers allows the aromatic decks to move closer which also increases the [Ru-Ru] bond distances. 

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