Rhenium complexes acetylene

The dinuclear rhenium disulfido complex with n,rj -S2 ligands (ReCp )2(/U-S2)2 (Cp =7j -C5Me4Et) (type IIa2 complex in Fig. 2) undergoes an insertion reaction of acetylene and ethylene into the S-S bond according to Scheme 57. 

The rhenium carbyne complex Re(=CCMe3)(=NAr)(OR)2 is active for metathesis of internal acetylenes when OR is OCMe(CF3)2, but not when OR is OCMe2CF3, OCMe3 or OC6H3-i-Pr2-2,65 6. The complex W(=CMe)(Cl)(PMe3)4 undergoes stoichiometric metathesis with PhC=CPh but the product PhC=CMe remains coordinated to the metal centre759. 

These -propargyl rhenium complexes undergo kinetic addition of nucleophiles at the central C atom to produce rhenacyclobutenes. The nucleophiles range from PR3 to malonate, acetylides, pyridines, and water. The derivatives of the addition of pyridines, however, are unstable and undergo further rearrangements to allene or acetylene complexes. Protonation of the metaUacyclobutenes produces u -allyl complexes. 

The reaction of the rhenium alkylidyne complex 277 with diisopropyl-acetylene and with diethylacetylene [Eq. (196)] demonstrates the sensitivity of metathesis reactions toward steric factors (57). With diisopropylace-tylene an alkylidyne complex is obtained whereas the reaction with diethylacetylene gives a metallacyclobutadiene. In the metathesis reactions the alkyne with the bulkiest groups cleaves most easily from intermediate metallacyclobutadiene complexes. The rhenacyclobutadienes with the smallest substituents thus become sinks and slow down the effective rate of metathesis. The alkylidyne alkylidene rhenium complex 278 is an active olefin metathesis catalyst (52). Reaction with hexene transforms the neo-pentylidene group into a propylidene group as shown in Eq. (197). 

The rhenium carbyne complex Re(=CCMe3)(=NAr)[OCMe(CF3)2]2 is active for metathesis of internal acetylenes, but analogous complexes, where OR is OCMe2(Cp3), OCMe3, or OC6H3-/-Pr2-2,6, are not active the rhenium centre is insufficiently electrophilic to enable the acetylenic substrate to overcome the barrier to reaction (Schrock 1988d Weinstock 1991). 

T. R. Cundari, S. C, Critchlow, R. R. Conry, E. Spaltenstein, K. A. Hall, S. Tahmassebi, and J. M. Mayer, Organometallics, 13, 322 (1994). Rhenium-Oxo-Bis(acetylene) Anions Structure, Properties, and Electronic Structure. Comparison of Re—O Bonding with That in Other Rhenium-Oxo Complexes. 

Some of the vinylidene complexes include cobalt, rhodium and rhenium in halfsandwich complexes, which are synthesized from acetylene complexes". This reaction involves an intermediate alkinyl(hydrido) complex, which can sometimes be isolated. The bonding between the metal and the a-carbon atom in vinylidene rhodium complexes is shorter than in carbene rhodium complexes, which indicates a high electron density on the center atom. 

I. Recent review topics include carbon-rich acetylenic materials as molecular scaffolding, studies of luminescent di- and poly-ynyl-rhenium complexes containing Re(CO)3(bpy) groups and Group 4 diynyl tweezer complexes in the context of other tweezer and related molecules. ... 

One important example of this class of rearrangement was reported for a rhenium complex in 199367 and, in retrospect, took advantage of the lower barrier of hydrogen migrations as compared to alkyl migrations. Mayer and co-workers prepared the tris-acetylene hydroxide complex 11, as well as the oxo hydride 12. Upon standing at room temperature for 5 days in benzene solution, the hydroxide spontaneously forms the oxo hydride with loss of one equivalent of acetylene, as shown in Eq. (8). 

One of several complexes formed by photochemically reacting CpRe(CO>3 and PhC CH in THF, was the binuclear complex Cp-(CO)2Re M-T T)--(=C=C(Ph)C(Ph)==CH2) ReCp(CO)2 (65) (129). The formation of 65 involves a photoinduced coupling of two acetylene units. The structure of 65 reveals that the vinyl substituent of a vinylidene complex is Tj -bonded to a second rhenium center. 

C ]H,o, Fluorene, iridium complex 29 232 C]3H jNO, Formanide,lV-ll-(l-naphthal-enyl)ethyl]-, rhenium complex 29 217 CijHijP, Phosphine, methyldiphenyl-, iron complex 26 61, 28 171 molybdenum complex, 27 9 nickel complex, 28 101 tungsten complexes. 27 10, 28 328,28 331 CijHio, Acetylene, diphenyl-, molybdenum complex, 26 102-105, 28 11, 13 C14H12, Benzene, 1,2-ethenediylbis-, platinum complex, 26 140 C14H14, Benzene. l,l -(l,2-ethanediyl)-bis-, 26 192... 

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