Cyclopentadienyl complexes mononuclear

Deprotonation with aluminum alkys, 9, 272 mononuclear carbonyl iridium complexes, 7, 302 for palladium cyclopentadienyl complexes, 8, 390 in Ru and Os half-sandwich preparations, 6, 569 in silver carbene synthesis, 2, 206 Desulfurization... 

Chemistry involving transformations of the cyclopentadienyl (Cp) ligand itself will be discussed in Chapter 7 however, much of the chemistry of cyclopentadienyl complexes involves the ligand acting purely as a spectator. Thus there arises a broad area of chemistry involving complexes with both carbonyl and cyclopentadienyl ligands. The most common classes of such compounds (Table 3.4) are the mononuclear complexes... 

Cyclopentadienyl complexes are often prepared as dimeric species, but less frequently as higher clusters. Several techniques are used to prepare cyclopentadienyl dimers. A generally useful reaction is of a mononuclear carbonyl with dicyclopentadiene. The proper conditions for preparation of Cp2Fe2(CO)4 have been studied . ... 

Thermolysis of the mononuclear (1,4-diphenyl-l-azabutadiene)iron complex 45 gives a diastereomeric mixture of the trinuclear complexes 46a and 46b, which are regarded as analogs of ferrocene with the ry -azaferracyclopenta-dienyl ligand 46. " Co-thermolysis of 45 with other metal carbonyl species produces heterodinuclear 77 -azaferra-cyclopentadienyl complexes 47 (Scheme 4). 

Dinuclear ruthenium(ii) complexes 199, which have been used as catalysts in a large number of hydrogen-transfer reactions, are known to dissociate in solution into the mononuclear hydride complexes 200 and the coordinatively unsaturated dienone derivatives 201 (Scheme 15). Remarkably, hydrides 200 are selectively formed when THF solutions of 199 are heated under hydrogen atmosphere. This process involves the conversion of 201 into 200 via heterolytic addition of The related amino-cyclopentadienyl complexes 202 and 203 are also known, being... 

Molecular examples of trivalent molybdenum are known in mononuclear, dinuclear, and tetranuclear complexes, as illustrated in Figure 5. The hexachloride ion, MoCk (Fig- 5a) is generated by the electrolysis of Mo(VI) in concentrated HCl. Hydrolysis of MoCP in acid gives the hexaaquamolybdenum(III) ion, Mo(H20) g, which is obtainable in solution of poorly coordinating acids, such as triflic acid (17). Several molybdenum(III) organometaUic compounds are known. These contain a single cyclopentadienyl ligand (Cp) attached to Mo (Fig. 5d) (27). 

In an attempt to change the electronics of the chromium atom, we are replacing the carbon based cyclopentadienyl ring with ligands containing harder donor atoms. For example, we have employed the tris(pyrazolyl)borate moiety, an isoclectronic replacement for Cp featuring tridentate N-coordination.[9] Figure 2 shows the molecular structure of Tp SU Cr-Ph, a representative Cr° alkyl. It will be noted, that this complex is mononuclear, due to the steric protection of the extremely bulky tris(pyrazolyl)borate. 

Treatment of the complex (XXVII X = Cl) with acetylacetone (acacH) in alkali gives the mononuclear a-acetylacetonyl compound [Rh(acac)(C8Hi2)]. The stable, diamagnetic complex cyclo-octa-l,5-dicne-cyclopentadienylrhodium(I), [Rh(C6H6) (CgH )], is formed from the dimer (XXVII X = Cl) and cyclopentadienyl sodium (44, 45). The analogous complex, with cyclopentadiene as the chelating diene, has been prepared in 1-2% yield (91) by the reaction ... 

A. Synthesis of Mononuclear Cyclopentadienyl and Indenyl Rhodium Complexes of OFCOT... 

Tables I and II summarize the structural studies of mononuclear and binuclear vinylidene complexes, and Table III those of propadienylidene complexes which had been reported to mid-1982. As can be seen, the C=C bond lengths range from 1.29 to 1.38 A, and the M-C bond (1.7-2.0 A) is considerably shorter than those found in alkyl or simple carbene complexes. Both observations are consistent with the theoretical picture outlined above, and in particular, the short M-C bonds confirm the efficient transfer of electron density to the n orbitals. In mononuclear complexes, the M—C=C system ranges from strictly linear to appreciably bent, e.g., 167° in MoCl[C=C(CN)2][P(OMe3)2]2(fj-C5H5) these variations have been attributed to electronic rather than steric factors. In the molybdenum complex cited, the vinylidene ligand bends towards the cyclopentadienyl ring (111).

In the following section we will concentrate on the most important classes of compounds which have been studied with the dimethylsilyl-bis(cyclopentadienyl) ligand system (30). In Scheme 14, five different types of complexes are portrayed, showing two principally different coordination modes of type 30 connection of two metal centres in binuclear units (type 38, 39 and 40) and chelation of one metal centre in mononuclear complexes (type 41 and 42). 

Mononitrosyl complexes, with chromium, 5, 301 Mononuclear bis(cyclopentadienyl) zirconium(III) complexes, characteristics, 4, 746... 

Mononuclear dicarbonyl(cyclopentadienyl)hydridoiron complexes, characteristics, 6, 173 Mononuclear a-donor ligands, in molybdenum carbonyls,... 

Mononuclear osmium half-sandwiches, with rf-cyclopentadienyls and 7]5-indenyls alkenyls and allenyls with t/-M-C bonds, 6, 558 alkenyl vinylidenes, 6, 593 alkyl, aryl, acyl complexes, 6, 552 with alkylidyne complexes, 6, 599 alkynyl and enynyl complexes, 6, 567 allenylidene and cumulenylidene complexes,... 

In both the examples given above, there is concomitant loss of one or more neutral ligands. Elimination of CO is the rule in reactions of mononuclear metal carbonyls (e.g., entry 12) and cyclopentadienyl metal carbonyls (e.g., entry 4), but not those of polynuclear carbonyls (e.g., entry 16) or carbonyl halides (e.g., entry 33). Elimination of tertiary phosphines often occurs, especially when more than two molecules are present in the initial complex however, this is not always the case (see entry 24). Clearly, steric requirements and the dictates of the 18-electron rule determine the composition of the product, and normally act in concert when they conflict, as in the case of R3SiRuH3(PR3) (n = 2 or 3 entry 22), variable stoichiometry may result. Chelating diphosphines, with somewhat reduced steric requirements, are usually retained (e.g., entry 19), while complexed olefins are invariably lost the bulky ligand P(cyclohexyl)3 is associated with unusual products (entries 47 and 48). Particular mention may be made of the 17-electron species Cl3SiVH(Cp)2 and (Cl3Si)2V(Cp)2 shown... 

Some years ago we observed that Group IV metallocenes, i.e., the elusive monomeric units bis(i7-cyclopentadienyl)zirconium and -hafnium, readily form 1 1 complexes with conjugated dienes in their 5-trans conformation (22). To our knowledge, these complexes (3) are the first and, at the time, only known examples of mononuclear (i-/ranj-i7 -diene)metal complexes, i.e., compounds in which both double bonds of the i-irans conformer of a conjugated diene are coordinated to the same transition metal center 21). Some examples of this class of transition metal complexes are stable, isolable compounds even at room temperature 23). 

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