Mono-/bimetallic complexes

Returning briefly to CO2 as a ligand in addition to the various mono-C02 complexes referred to above, several bis(rj -CO2) transition-metal adducts are known, e.g. /ran -[Mo( ) -C02)2(PMe3)4] (5) and trans.mer-[Mo( 2-C02)2(PMc3)3(CNPr )].< 22 The first homo-bimetallic bridging-C02 complex has also been structurally characterized by X-ray analysis, viz. [(dppp)(CO)2Re(/x, j 0,0 j C)Re(CO)3(dppp)] (6) [dppp = l,3-bis(diphenyl-phosphino)propanc]. 0 3)... 

It should be added that MS-02 is not necessarily a mono-nuclear complex. It could be shown in a few cases that the catalytic activity of the metal ion is due to the formation of dinuclear metal-substrate complexes. Presumably in these species each oxygen atom of dioxygen coordinates to a different metal center. Such systems were extensively used to model the reactivity patterns of various enzymes containing a bimetallic active center. 

The solvates of alkoxides and the bimetallic complexes are described in Chapter 8, and oxocomplexes in Chapter 5. The products and mechanisms of hydrolysis for mono- and bimetallic alkoxides are considered in Chapters 9 and 10. 

The systematic study of bimetallic t-butoxides of tin and mono- and divalent metals carried out by Veith (see Table 12.10) established that the complexes of M Sn"(OBu )3 composition are formed by all alkaline metals, while those of M Snlv(OBu )5 are formed only by K, Rb, and Cs. It has been therefore concluded that Sn(OR)2 should be stronger Lewis acids than Sn(OR)4 [1692], In the molecules of its bimetallic complexes, the atoms of Sn11 have a /-tetra-hedral coordination, all the OR-groups being bridging. The compounds of Snlv display octahedral or distorted octahedral coordination (see also Chapter 4). 

Acyclic Schiff base derivatives represent a resourceful class of compartmental ligands which are prepared by self-condensation of appropriate formyl and amine precursors. The condensation reaction is simple and generally leads to the desired product in high yield. Literature data on Lnm mono- and bimetallic complexes, as well as on 4f-d transition metal bimetallic entities with these derivatives are abundant and have been reviewed recently (Vigato and Tamburini, 2004). Extension to multimetallic systems and to complexes with 5f elements... 

With the exception of the mono-rhodium complexes of the n-propylsapphyrins (i.e., 5.88 and 5.91), each of the above mono- and bimetallic complexes proved to be... 

It is difficult to find direct bonding interaction between the ferrocene iron and the second transition metal in the hetero-bimetallic complexes. Only the mono-triphenylphosphine palladium and platinum compounds fc[E2M(PPh3)] (E = O, M = Pd (Scheme 5-14) [79] E = S, M = Pd [268, 269], and Pt [269]) appear to... 

Ternary and quaternary a-hydroxy-phosphonates, an important class of biologically active compounds, are commonly obtained by addition of dialkylphosphites onto aldehydes or ketones [30]. Well-defined mono- or bimetallic complexes of rare-earth metals, titanium, or aluminum have emerged over the past two decades as effective catalysts for this so-called hydrophosphonylation of aldehydes [31] and, with more difficulty, that of ketones [31c,d, 32], which are far less reactive because of their lower electrophilicity. In some cases, good enantioselectivities could be achieved thanks to the use of chiral metal-based precatalysts [31, 32], Despite their several similarities with rare-earth elements, we were surprised to see that discrete complexes of the large Ae metals had never been utilized to catalyze hydrophosphonylation reactions. 

This section is dedicated to a description of the chemistries of trinithenium and triosmium clusters that do not contain hydrocarbon ligands. This section should be viewed as an addition to the chemistry described in sections 32.5 and 33 of COMC (1982) and section 12 of COMC (1995) as most of the main themes have been developed in the previous two decades. Overall, the interest in the cluster chemistry of ruthenium and osmium during the period 1994-2004 has tended to focus mainly on higher nuclearity and mixed metal clusters in order to enhance the developments in catalysis and bridge the gap between molecular clusters and nanoparricles. However, triruthenium and triosmium clusters continue to play a pivotal role in the chemistry of ruthenium and osmium. Both classes of clusters can be, and are, used extensively as precursors for the synthesis of higher nuclearity clusters as well as the formation of mono- and bimetallic complexes. No up-to-date review of the chemistry of either Ru3(CO)i2 or Os3(CO)i2 and their compounds is available, but several annual reviews of the chemistry of mthenium and osmium, which include the chemistry of the trinuclear clusters, are available. ... 

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