Ligand cyclopentadienyl vinylidene

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).

B. J. and Wallis, R.C. (1980) Cyclopentadienyl-ruthenium and -osmium chemistry. XII. Some complexes containing cyclic carbene ligands. Australian Journal of Chemistry, 33, 2605-2613. (d) For a review, see Bruce, M.I. (1991) Organometallic chemistry of vinylidene and related unsaturated carbenes. Chemical Reviews, 91, 197-257. 

The use of a cyclopentadienyl ligand containing a pendant phosphine arm allowed the isolation of the cobalt alkyne complexes [<5o(ti5 i -C5H4CH2CH2l Bu 2)(Tl -PhCCR)] (R = H, Hi). In the case of ethyne, the alkyne complex could not be isedated and the vinylidene complex [ 50(115 I-C5H4CH2CH2PBu 2)(=C=CH2)1 was observed. 

When trans-halo-tetracarbonylcarbyne complexes of molybdenum and tungsten, X(CO)4M=CR, are treated with sodium cyclopentadienyl, not only the displacement of the halide, but an additional elimination of two carbonyl ligands is observed, affording dicarbonyl(rj -cyclopenta-dienyl)carbyne complexes [2,3]. A different synthetic approach converts vinylidene ligands into carbyne ligands to yield comparable bisdimethylphosphite substituted complexes of molybdenum [4]. 

The intramolecular nucleophilic addition of a pendant -OH group at the GQ,-atom of a hydroxy-vinylidene ligand is a well-known process which gives rise to cyclic oxa-cyclocarbene units.The starting vinylidene complexes can be either isolated or formed in situ by the reaction of the appropriate ruthenium precursor with hydroxy-1-alkynes. This process provides an efficient entrance to the synthesis of a wide variety of cyclic oxa-carbene complexes containing indenyl and cyclopentadienyl ruthenium fragments such as 150/ 152/ and 153-156 (Figure 23). Similarly, the... 

Many types of hydrocarbyi ligands are known for the triruthenium clusters containing a cyclopentadienyl ligand /it3-alkylidyne, /it-alkylidene, /tj-j/ -vinylidene, /t3-J7 ( )-alkyne, ... 

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