Cumulenylidene

Transition metal complexes containing allenylidene, cumulenylidene, and related ligands with heterocyclic fragments 98CRV2797. 

The ferrocenyldiphynylpropargyl cation, 77, has an intrinsic delocalization nature exhibiting a valence tautomerization band at 856 nm, and its nucleophilic trapping reactions give rise to the formation of ferrocenyldiphyenylallenes (173). The bis(acetylide) mixed-valence complexes of ferrocene and the Ru complex moiety, 78, also behave as a fulvene-cumulene structure, 79, showing a u(M=C = C—C) band at 1985 cm-1 (174). Related alleylidene and cumulenylidene complexes of transition metals have been reviewed by Bruce (175). 

Based on the insight that a dissociative mechanism plays the major role along the metathesis pathway [11], these catalysts have been designed such that only one bulky phosphine, one chloride and one cumulenylidene ligand are attached to a Ru(II) center. Because arene ligands are known to be labile on such a metal fragment, they will easily liberate free coordination sites ( ) for the interaction with the alkene substrate. Although the precise mode of action of such allenyli-... 

C. Ruthenium Cumulenylidene Complexes Bearing Bis(pyrazol-1-yl)acetato Ligands... 

Another example for the Tp versus bdmpza analogy is the synthesis of various bdmpza ruthenium cumulenylidene complexes. The... 

Class C. Neutral si -Carbon Ligands Amino- and Nonamino-Cumulenylidenes... 

Both categories of sp-hybridized neutral carbon ligands, namely the all-carbon-substituted and heteroatom-conjugated allenylidene and cumulenylidene ligands, are presented in great detail by V. Cadiemo and S. E. Garcia-Garrido in the sixth and seventh chapters of this volume, respectively. 

Carbodiphosphoranes C(PR3)2 and related ligands CL2 which are also termed double ylides differ from the other carbon ligands which are discussed in this volume in the number of lone electron pairs at the carbon donor atom. Ylides, carbenes, allenylidenes, and cumulenylidenes have one lone electron pair but carbodiphosphoranes have two lone electron pairs with a and n symmetry. The bonding situation in a carbodiphosphorane (a special class of CL2 compounds, abbreviated as CDP) is best described in terms of donor-acceptor bonding between the phosphane ligands which serve as a donor and a naked carbon atom in an... 

All-Carbon-Substituted Allenylidene and Related Cumulenylidene Ligands... 

Abstract Allenylidene complexes have gained considerable significance in the context of transition-metal carbene chemistry due to their potential applications in organic synthesis. The aim of this chapter is to draw together a general presentation of the most efficient synthetic routes, the main structural features and reactivity patterns, as well as current applications in homogeneous catalysis, of aU-carbon-substituted allenylidenes and related cumulenylidene complexes containing an odd number of carbon atoms. 

Keywords Allenylidene ligands Carbene complexes Cumulenylidene ligands Pentatetraenylidene ligands Propargylic alcohols... 

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