Mixed-metal clusters synthesis

For metal carbonyl clusters, methods (b), "-" (c), (d), and (e), - - or variations of them have been successfiilly employed. Thus an effective strategy for mixed-metal cluster synthesis is chloride ion displacement from a coordinated R2PCI ligand by a carbonyl metallate. Several new routes to I1-PR2 clusters have been developed in recent years. Vahrenkamp and Keller have successfully adapted a method first described by Benson et al. involving elimination of propene in reactions of complexes... 

Synthesis, molecular dynamics and reactivity of mixed-metal clusters. G. L. Geoffrey, Acc. Chem. Res., 1980,13,469-476 (29). 

The premise of this review is that synthetic procedures for very mixed"-metal clusters are comparatively well understood, but that reactivity and physical properties are less well studied. Metal core transformations (modifications of a preexisting cluster) fall into both the synthesis and reactivity categories. A summary is presented here, but as they have been reviewed elsewhere (see Refs. 4, 107-109), the account below is necessarily brief. Section lI.E. 1. considers core transformations where the cluster core nuclearity is pre.served, whereas Section 11.E.2. summarizes reactions involving a change in core size. 

The focus of research on very mixed"-metal clusters has been on their synthesis and structure, and the limited physical measurements of these clusters have thus far been largely restricted to fluxionality and electrochemical investigations. Studies of ligand fluxionality are summarized in Section 111.A. and reports of electrochemical investigations are reviewed in Section Ill.B. The few reports of the magnetic behavior of these clusters are discussed in Section lll.C. 1., and theoretical studies are summarized in Section I1I.C.2. 

SYNTHESIS OF GOLD-CONTAINING MIXED-METAL CLUSTER COMPLEXES... 

Synthesis of Gold-containing Mixed-metal Cluster Complexes 325... 

Several synthetic methods are now available for the preparation of mixed-metal clusters.1 However, when particular clusters are desired, two main points of concern for their synthesis often remain the availability and price of the precursors, and the yield of the reaction. Mixed-metal clusters containing ruthenium have attracted considerable interest mainly because of the variety of structural and bonding types encountered, and of their potential for homogeneous and heterogeneous catalysis.2... 

Several methods have been described that allow the directed syntheses of mixed-metal clusters.1 One of these procedures involves the addition of coordinatively unsaturated monomeric complexes to Os3(/t-H)2(CO)10, as illustrated below for the synthesis of Os3Pt(/t-H)2(PR3)(CO)10 (R = C6Hj 1 or Ph), eq. (I)2... 

It has been said that noticeably few metal clusters have been prepared by designed or rational synthetic procedures (52, 55). Indeed, most clusters have been prepared by placing together a variety of reagents, allowing them to react, and then examining the reaction mixtures to find out what compounds have been prepared. This is particularly true of mixed-metal clusters, and a real need exists for the development of synthetic procedures that can be used for the designed synthesis of particular compounds. 

Metal carbonyl dimers have proved to be useful reagents for the synthesis of mixed-metal clusters. This is particularly true for Fe and Co clusters since Fe2(CO) and Co2(CO)8 are readily available starting materials. The prediction of the reaction products is usually fruitless. However, examination of the available data indicates that the initial dimeric unit is preserved in approximately half of the reactions. Typical examples are illustrated in Eqs. (4-6) (102), (7) (28), and (8-10) (121). 

A logical extension of the synthesis of [Co6(CO)i5]2- from [Co(EtOH) J [Co(CO)4]2 has been successfully applied to the preparation of mixed-metal clusters. Thermal decomposition of [Ni(EtOII) J[Co (CO) 4]2 prepared in situ gives the red hexanuclear dianion [Ni2Co4(CO) n]2", through the following redox condensation and redistribution processes (44) ... 

For the past few years metal carbonyl clusters have been under study In this laboratory from several viewpoints. First, we have a continuing interest in developing better methods for the directed synthesis of mixed-metal clusters and considerable progress has been made in this area (1-6). We have more recently been evaluating the reactivity features of mixed-metal clusters with a variety of substrates. We have chosen to concentrate our efforts on one particular cluster, l FeRuj O), 1, and to examine its reactivity in as much detail as possible. 

Treatment of 3-borolenes or 2-boraindans with bulky lithium amides yields the dihthiated aromatic borolide dianions, which are applicable as hgand precursors for transition-metal complexes. Many borole complexes including a number of unusual multidecker sandwich complexes and mixed-metal clusters have been described. 4 3,2i2 An unexpected new entry into the synthesis of borole complexes has been recently discovered. Bochmann found that attack of B(C6Fs)3 at a zirconium bound diene leads to a pentafluorophenylborole complex throngh snccessive C-H activation steps. ... 

In addition to practical applications, metal cluster-derived catalysts, particularly intrazeolite metal cluster compounds, may aid in the identification of catalytically important bonding and structural patterns and thereby further our molecular understanding of surface science and heterogeneous catalysis. The ship-in-bottle technique for the synthesis of bulky metal-mixed metal cluster compounds inside zeolites and/or interlayered minerals has gained growing attention for the purpose of obtaining catalytic precursors surrounded by the interior constraint, imposing molecular shape selectivity. Such approaches may pave the way to offer the molecular architecture of hybrid (multifunctional) tailored catalysts to achieve the desired selectivity and stability for industrial processes. 

S. J. Sherlock, Synthesis and Characterization of Some Novel Group IB and Mercury Mixed Metal Clusters, Ph.D. thesis. State University of New York, Stony Brook, New York, Chapter 2, 1985. 

Adams et al. [78,79] have reported a series of synthesis of mixed-metal cluster compounds. One example, Pt2Ru4(CO)is, is depicted in Figure 1(b). This mixed cluster compound was investigated to study the effect of Pt-Ru nanoparticles developed after the precursor annealing on carbon [80]. In line with the spectroscopic and microscopic measurements, the authors demonstrated that mixed Pt-Ru nanoparticles, with an extremely narrow size distribution (particle size 1.4nm), reflect an interaction that depends on the nature of the carbon support. Furthermore, as revealed by EXAFS, the Pt-Pt, Pt-Ru, and Ru-Ru coordination distances in the precursor (2.66, 2.64, and 2.84 A) [79] changed to 2.73, 2.70, and 2.66 A, respectively, on the mixed-metal nanoparticles supported on carbon black, with an enhanced disorder [80]. Furthermore, some metal segregation could be... 

The reaction of metal carbonyl complexes with carbonyl anions is a widely used technique for synthesis of mixed-metal clusters. This reaction is also termed reductive condensation or redox condensation. The metal carbonyl anion may be generated in situ or may be separately isolated. The mixed-metal product is usually an anion protonation can be used to generate a neutral cluster hydride. 

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