Lead clusters complexes

The broken bonds (boldface = dissociated fragment) BDEs (boldface = recommended data reference in parentheses) Methods (reference in parentheses)  

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Table 24.5 (continued) BDEs in Lead Clusters/Complexes... 

Many carbonyl and carbonyl metallate complexes of the second and third row, in low oxidation states, are basic in nature and, for this reason, adequate intermediates for the formation of metal— metal bonds of a donor-acceptor nature. Furthermore, the structural similarity and isolobal relationship between the proton and group 11 cations has lead to the synthesis of a high number of cluster complexes with silver—metal bonds.1534"1535 Thus, silver(I) binds to ruthenium,15 1556 osmium,1557-1560 rhodium,1561,1562 iron,1563-1572 cobalt,1573 chromium, molybdenum, or tungsten,1574-1576 rhe-nium, niobium or tantalum, or nickel. Some examples are shown in Figure 17. 

It is apparent that the chemistry of such systems is rich, but the preparation by either thermal or photochemical substitution normally leads to complex mixtures of compounds. Recently, substituted products, which can be prepared in high yield, have been utilized as precursors. Two classes of reactions (Table IX) may be employed for the preparation of cluster derivatives those involving displacement in systems typified by complexes (a), (b), (c), and (d), or addition reactions to the nominally "unsaturated species H2Os3(CO)10 (see also Section 11,1,2). 

A few clusters of interest containing germanium and transition metals have been reported.136-138 Dimethylgermane was found to replace only the bridging carbonyls between cobalt in a mixed germanium/cobalt/iron cluster complex (Equation (107)), and replacement of the carbonyl bridging the iron metal centers was not observed.137 A similar reaction leads to replacement of a bridging carbonyl in a mixed cobalt/silicon cluster (Equation (108)).136... 

Heating 26 with an excess of PPhj under pressure in chlorobenzene leads to the loss of one coordination site. One more Os-Os bond is broken upon formation of the complex Os3(CO)6(CNR)(p3-CNCH2QH4)-(PPh3)(p-PPh2)(p-T r -C6o) [74], The T r binding mode observed in this complex is very unusual for Cg0. One further example, where can act as a four-electron ligand is the fullerene carbido pentaosmium cluster complex 28 shown in Scheme 7.13 [75,76], The ri T -complex 28 is formed in a mixture with the normal T r r carbido pentaosmium complex 27. The two complexes can be converted into one another at elevated temperatures. 

Observations Leading to the Discovery of H/D Exchange in Hydrido-Metal Cluster Complexes... 

Replacement of two carbon atoms in nickelocene by boron leads to complex 26 having the ir6/d8 arrangement to which cluster formalism can be applied. The diamagnetic sandwich 26 is isoelectronic with ferrocene... 

There are a limited number of structures reported for Fe—Pb complexes and these are recorded in Tables 16-18. For a series of iron carbonyl lead clusters, the Fe—Pb bond lengths vary from 2.624 A for an electron-deficient three-coordinate planar Pb cluster [FefCO jjPbl to 2.828 A for a tetrahedral bridging anionic Pb cluster... 

Thermolysis of BuP Cr(CO)5 2 at 100°C leads to P-P coupling and formation of a trinuclear cluster complex Cr3(CO)10(p-3-P Bu)(P2Bu2).175 This contrasts with thermolysis of similar complexes with other R groups, which leads instead to trimetallated diphosphene compounds ( Bu Cr(CO)5 P=P Cr(CO)5 Bu) ju.-Cr(CO)5. n5... 

C NMR is generally applicable to organometallic and organo cluster compounds, but has the advantage of giving a direct probe on the acetylenic carbon atoms in alkyne-substituted clusters. With the development of more powerful NMR instruments, this technique has been used extensively to characterize organo-substituted cluster complexes in solution. For smaller clusters, the combination of 13C NMR with 31P NMR and resonance studies from metallic nuclei, where appropriate, frequently leads to complete structure elucidation. 

A competing reaction is trimerization to Fc3(CO)i2. This process can be reversible and the dimers or clusters are suitable staging grounds for breakup of the clusters. These often lead to complex equilibria, which have been investigated by Bor and coworkers for a number of systems. ... 

Geometrically, the main group element tends to retain a tetrahedral nearest neighbor environment, whereas the transition metal element tends to retain an octahedral environment. As a consequence, transition metal clusters with more than six metal atoms have a tendency toward ligand loss, leading to the formation of condensed clusters (multiple interstitial metal atoms). This leads eventually to close-packed structures that mimic bulk metal structures (see Polynuclear Organometallic Cluster Complexes). On the... 

The anion [Re(CO)5] (13) is formed by reduction of (1) with Na/Hg. This extremely reactive species yields a variety of Re carbonyl clusters (see Polynuclear Organometallic Cluster Complexes). Further reduction to [Re(CO)4] is possible with Na in HMPA. The electrochemistry of M2(CO)io shows that these species oxidize at the same potential and, in MeCN, give [M(CO)s(MeCN)]+. However, (1) is more difficult to reduce than Mn2(CO)io and electrochemical reduction leads to the typical clusters obtained from (13) under chemical conditions. 

Primary charged species formed by galactic cosmic ray ionization are N 2, 0 2, O, N, and free electrons. The latter are rapidly attached to gas molecules, giving rise to simple negative ions, mostly 0"2. Subsequent ion molecule reactions of primary positive and negative ions lead to complex positive and negative cluster ions. Ultimately these are removed by ion-ion recombination involving either a binary or a ternary mechanism [33]. 

Since most of the clusters used for hydrogenation also catalyze the double bond shift (cf. Section VI.A), the situation is complicated by isomerization for acetylenes with an internal C=C unit an E/Z problem also arises. The examples reported demonstrate that carbon-carbon triple bonds are more readily reduced than carbon-carbon double bonds. However, in most cases further hydrogenation and isomerization lead to complex product mixtures. 

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