Binuclear cyclopentadienyls

Binuclear cyclopentadienyl carbonyls react with (R3Ge)2Hg ... 

The binuclear iron complexes (317) have been found to undergo a thermal rearrangement to afford the complexes (318), which were evidently formed via a metathesis between Si—Si and Fe—Fe bonds in (317). A similar rearrangement has been observed in a disilyl-bridged bis(cyclopentadienyl)tetracarbonyldiruthenium complex. Unprecedented and stable in — rf J7 -pentafulvadiene)dimthenium complexes (320) have been prepared" from a two-electron oxidation of frani -l,2-bis(mthenocenyl)ethylenes (319), and dimethyl analogues have been similarly obtained from trans- and cM-l,2-dimethyl-l,2-bis(ruthenocenyl)ethylenes. 

Alike metallocomplex anion-radicals, cation-radicals of odd-electron structure exhibit enforced reactivity. Thus, the 17-electron cyclopentadienyl dicarbonyl cobalt cation-radical [CoCp(CO)2] undergoes an unusual organometallic chemical reaction with the neutral parent complex. The reaction leads to [Co2Cp2(CO)4]. This dimeric cation-radical contains a metal-metal bond unsupported by bridging ligands. The Co—Co bond happens to be robust and persists in all further transformations of the binuclear cation-radical (Nafady et al. 2006). 

Recently, in a study of a large number of organo-iron compounds 120), it has been found possible to treat the isomer shift as being due to a sum of partial isomer shifts 8,. from individual ligands which for 7r-cyclopentadienyl derivatives could be correlated with proton NMR chemical shifts in the same compounds. The Mossbauer spectra of two cases of theoretical interest are worthy of mention. First, the spectra of both the mono- and binuclear iron tricarbonyl derivatives of cyclooctatetraene 115) show similar 8 and A values. The small 8 values are consistent with zero oxidation state for the iron atom and essentially complete covalent bonding between the iron and the tt electrons of the ring, so that, at least for the mononuclear... 

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). 

Binding energy, pentacarbonyliron, 6, 3 Binuclear complexes bis-Cp titanium halides, 4, 522 with Ni-M and Ni-C cr-bonds heterometallic clusters, 8, 115 homometallic clusters, 8, 111 Binuclear dicarbonyl(cyclopentadienyl)hydridoiron complexes, with rand C5 ligands, 6, 178 Binuclear iridium hydrides, characteristics, 7, 410 Binuclear monoindenyl complexes, with Ti(IV), 4, 397 Binuclear nickel(I) carbonyl complexes, characteristics, 8, 13 Binuclear osmium compounds, with hydrocarbon bridges without M-M bonds, 6, 619... 

The ligand-exchange reactions are widely used in the syntheses of binuclear metal-carbonyl, r 5-cyclopentadienyl, and r 6-arene complexes [11, vol. 6], Examples of these type of transformations are reactions (3.133)-(3.135) [11, vol. 6] ... 

A rare example of isospecific 3,4-polymerization of isoprene mediated by a constrained-geometry rare-earth metal initiator was reported by Z. Hou [270]. Binuclear silyl-linked cyclopentadienyl phosphido lanthanide dialkyl complexes were synthesized in good yields and activated with an equimolar amount of [Ph3C] [B(C6Fs)4] (Scheme 68). Cationic alkyl species were proposed as intermediates and an activation scenario was presented based on DFT calculations [270]. 

Similarly, with spiro[4.4]nona-1,3-diene and spiro[2.4]hepta-4,6-diene, Fe(CO)5 produces the 7r-cyclopentadienyl-type binuclear complexes (248, reference 3), while Fe2(CO)fl affords the tt complexes (90) and (91), respectively. With the latter olefin, the complex of structure... 

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