Methylenecyclopropenes complexes

Oxidative activation of cyclopropenes is much less frequently encountered. The reactions of various platinum(O) complexes with the electron-deficient methylenecyclopropene 170 affords platinacyclobutene complexes, as reported nearly 30 years ago <1978ICA19>. More recent investigation has established that in the presence of two or more equivalents of the metal, bicyclic diplatinum complexes can be generated (Scheme 40) <1996JBS75>. 

Metal complexes of the methylenecyclopropenes in which the ring skeleton is retained include 382 and 383 the negative end of the dipolar form of these molecules is bonded to the metal atom. 

The reactions of bis(alkynyl)metallocenes Cp2M(C=CR)2 (M = Zr, Hf R = Me, Pr11, Bu11, Gy) with B(C6F5)3 afford the corresponding metallocene borate betaines of structure type 760.586 An assumed intramolecular alkyne insertion reaction leads to their less stable methylenecyclopropene-derived isomers, which are effectively trapped by the added / /7-butylisocyanide to yield complexes 764 which contain a methylenecyclopropene derived [Pg.906]

The spirit is to show some of the results, but also to guide users of the approach by pointing to the problems and limitations of the method. The review covers some of the newer applications in the spectroscopy of organic molecules acetone, methylenecyclopropene, biphenyl, bithiophene, the protein chromophores indole and imidazole, and a series of radical cations of conjugated polyenes and polyaromatic hydrocarbons. The applications in transition metal chemistry include carbonyl, nitrosyl, and cyanide complexes, some dihalogens, and the chromium dimer. 

We have shown [13,79, 80] that the electronic spectra of c -l,3-buta-diene [81], cyclopentadiene, aromatic five-membered heterocycles [48,79], and norbornadiene [80] can be understood on the basis of a model with two interacting double bonds. Cyclopentadiene (CP) is the prime example of a ring-shaped molecule with a conjugated rr-electron system, and its structure can be related to that of short polyenes such as cM-1,3-butadiene (CB) and the simplest heterocycles, such as pyrrole (PY), furan (FU), and thiophene (TP). In the series, ci5-l,3-butadiene, cyclopentadiene, norbornadiene (NB), the latter is the most complex system, with the two ethylenic units coupled through indirect conjugation and 77, a interaction. One more system will be added here to the set of molecules with two interacting double bonds methylenecyclopropene (MCP) [(1) in Fig 3] the simplest cross-conjugated 77-electron system. 

Ahlers W, Erker G, Frohlich R et al (1999) Coupling of o-acetylide ligands at Group 4 metallocene complexes to yield methylenecyclopropene-type frameworks. J Organomet Chem 578 115-124... 

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