Carbyne complexes rearrangement

It is interesting that, to promote the ring-opening metathesis polymerisation of cycloolefins, metal carbyne complexes can also be used in such a case, the carbyne complex is rearranged to form the actual metal carbene complex [scheme (9)] capable of initiating the polymerisation [95] ... 

Analogous (bromo)- and (iodo)(diethylamino)carbene complexes of CrfCO), undergo thermal rearrangement also . The bromo complex rearranges to the corresponding carbyne complex above — 20°C both in CH2CI2 and in the solid. 

The molybdenum carbyne complex 24 is the product of the unusual rearrangement, shown in Eq. (23) (66), involving formal a,) -migration of hydrogen in a vinyl ligand. Heating of the cyclopentadienyl complex 23 to 80°C in hexane results in loss of one trimethylphosphite ligand and... 

Reaction of the Mo Schrock carbyne complex in equation 10.58 with HBF4 results in protonation at Ccaibyne, followed by rearrangement to the thermodynamically more stable Mo-H complex. The BF4 ion is such a weakly coordinating ligand that substitution at the metal does not occur.98... 

Treatment of the carbyne complexes (// -cyclopentadienyl)(CO)[P(OMe)3]M = CR 1, where M = molybdenum or tungsten and R = cyclopropyl, with hydrogen chloride in diethyl ether results in a rearrangement reaction to give 7 -acyl complexes 2 in quantitative yield. 

Irradiation of [W(H)Tp (CO)3] in the presence of alkynes yields r]2-vinyl, r 2-acyl, metallafuran, and carbyne complexes likely through cls-insertion of alkynes into a photogenerated [WH(Tp )(CO)2], while cis 2,1-insertion initially leads to ri2-vinyl and r]3-allyl, and subsequent c/s-1,2-insertion produces t]2-acyl, metallafuran, and carbyne species. [W(r]2(C,0)-C(Bu )CHC(=0)-CH=CHBu")(Tp )(CO)2] has been characterized by X-ray. Support for the T]1-vinyl intermediates is derived from the r]2-acyl complex [W(t]2(C, <9)-C(=0)CH=CHC(CH3)3)Tp (C0)2]. Irradiation of [W(H)Tp (CO)3] with Me3SiC=CCH3 yields two isomers of [W(ri3-syn-CH2CHCHSiMe3)(Tp )(CO)2]. When this allyl complex was heated, rearrangement to a carbyne species occurred (Fig. 2.34).159... 

Additional developments in the synthesis of enediyne motifs, beyond the now well-established Pd-catalyzed routes, have recently been reported. Casey et al. (377, 399) demonstrated that cw-enediyne complexes can be readily obtained via dimerization of Cp(CO)2Re-aIkynylcarbene complexes at 100°C (cf. Fig. 27), as well as from the addition of a,oc)-diynes to manganese carbyne complexes that rearrange to enediynes below room temperature. In parallel, Cummins and co-workers have demonstrated that sequential reductive coupling of Mo(IV) acetylides and alkyne metathesis can also be used as a novel route to both ( )- and (Z)-enediyne constructs (523). 

Several hundred examples of vinylidene complexes have been prepared. Vinylidene complexes have been prepared by rearrangement of alkyne complexes, additions of acid or base to acetylide complexes, by deprotonation of carbyne complexes, by dehydration of acyl complexes, and by ot-hydrogen shifts from vinyl complexes. Syntheses from alkjme and from acetylide complexes are most common. A complex of a terminal alkyne and a transition metal can exist as an alkyne complex or as a vinylidene complex. Although the free vinylidene is much higher in energy than the free alkyne, the vinylidene complex is often more stable tlnan the alkyne complex. Vinylidene complexes are most often obtained with late transition metals because this tautomer possesses less repulsion between the filled (i-orbitals of the metal and the filled ir-orbitals of the ligand. 

In addition to the ring opening/carbonylation pathways illustrated in Eqs. 2-5, photooxidation of metal carbynes can result in other types of ligand rearrangement. An example is the cyclization of butenyl carbyne complex 8 depicted in Eq. 6. Deuterium... 

It has been proposed that these carbyne-acyl rearrangements start with the protonation of the car-byne carbon atom to initially give a carbene complex. For the next step two different pathways have been proposed i) An intramolecular carbene carbonyl coupling to yield a 7C-ketene complex,... 

Dixneufs group [19, 20] has reported the intramolecular rearrangement of a ruthenium-bound allenylidene ligand into an indenylidene ligand. The stoichiometric protonation of arene-ruthenium-allenylidene complexes lla-c with TfOH at -40 °C gave the alkenyl carbyne complex 12, which, upon raising the temperature to -20 °C, completely transformed into the related, isolable arene-ruthenium, indenylidene complexes 13a-c (Scheme 14.6). The protonation of the allenylidene carbon at C2 generates a very electrophilic carbyne carbon at... 

With a carbyne complex of related structure, W - u dme 1 3, the first insertion complex, a metallabenzene derivative, irreversibly rearranges to the more stable r -cyclopentadienyl complex that has been isolated see section. ... 

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