Cumulenylidene complexes

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). 

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... 

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. 

In this chapter an updated state of the art of the chemistry of allenylidene and higher cumulenylidene complexes has been presented. The spectacular growth of this chemistry seen in recent years stems mainly from the versatile reactivity of... 

Heteroatom-substituted allenylidene and higher odd-chain cumulenylidene complexes [M]=C(=C) =CR R ( = 1, 3, 5 R /R = NR2, OR, SR, SeR) are directly related to the classical Fischer-type carbene complexes, being regarded as their functional carbo-mers [5-7]. However, although two of the first allenylidene complexes synthesized were the amino-allenylidene derivatives [M =C=C=CPh (NMe2) 1(00)5] (M = Or, W) [8], the chemistry of these compounds has been much less developed [9, 10]. In fact, as aheady discussed in Chapter 6 the chemistry of metallacumulenes is largely dominated by the all-carbon substituted representatives... 

Cumulenylidene complexes constitute a class of organometallic compounds in which a chain of sp-hybridized carbon atoms is terminated by a sp -hybridized carbon atom (CR2 group) at one end and by a metal-ligand fragment (Lr,M) at the other end. 

The metal-ligand fragment L M, the number of carbon atoms x, and the substituents at the terminal sp -carbon may vary considerably and, correspondingly, the properties and reactivities. The early members of the series of cumulenylidene complexes (x=l, 2, 3 carbene, vinylidene and allenylidene complexes) have established themselves as invaluable building blocks in stoichiometric synthesis and as highly potent catalyst precursors. The higher members might potentially be very useful candidates for application as one-dimensional wires and in opto-electronic devices. 

The number of pentatetraenylidene complexes (x= 5) reported in the literature is even less. All in all, 11 complexes have been described. Complexes with an even larger number of carbon atoms in the chain are unknown. Therefore, cumulenylidene complexes with more than three carbon atoms in the chain are still rather elusive classes of metallacumulenes [1] and their involvement in a catalytic process has not yet been observed. 

Based on these experimental data, DFT calculations have been carried out on several series of cumulenylidene complexes. The infiuence on bonding and the electronic structure of various factors such as... 

From these theoretical analyses of the electronic structure of cumulenylidene complexes it follows that different strategies are required for the stabilization of cumulenylidene complexes with an even and with an odd number of carbon atoms. 

Iridium-carbon multiple bonds allenylidene complexes, 7, 355 carbene complexes, 7, 344 carbyne complexes, 7, 361 higher cumulenylidene complexes, 7, 358 vinylidene complexes, 7, 352 Iridium-carbon single-bonded complexes alkenyl complexes, 7, 319 alkyl and aryl complexes, 7, 303 in C-C bond-forming catalysis, 7, 335 characteristics, 7, 303... 

Mononuclear osmium half-sandwiches, with rf-cyclopentadienyls and 7]5-indenyls alkenyls and allenyls with t/-M-C bonds, 6, 558 alkenyl vinylidenes, 6, 593 alkyl, aryl, acyl complexes, 6, 552 with alkylidyne complexes, 6, 599 alkynyl and enynyl complexes, 6, 567 allenylidene and cumulenylidene complexes,... 

V. Cadierno, M. P. Gamasa, and J. Gimeno, Recent Developments in the Reactivity of Allenylidene and Cumulenylidene Complexes, Eur. J. Inorg. Chem. 2001, 571-591. 

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