Allenylidene complexes, syntheses

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... 

Allenylidene complexes, synthesis /z-allenylidene complexes, 225-227 binuclear compounds, 225, 225... 

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. 

Scheme 1 Synthesis of the allenylidene complex 1 from l,l-diphenyl-2-propyn-l-ol...

Scheme 8 Synthesis of the polystyrene-supported allenylidene complex 19...

Scheme 9 Synthesis of allenylidene complexes 20 bearing a tethered arene/NHC ligand...

P-P = dppe X- = BlCfiFslv Scheme 10 Synthesis of the bis(allenylidene) complex 26... 

Scheme 1 Synthesis of the first amino-allenylidene complexes 2...

Scheme 8 Synthesis of the amino-allenylidene complex 32 through a [3,3] Aza-Cope rearrangement...

Scheme 15 Synthesis of dimethylamino(organyl)allenylidene complexes 53...

Scheme 19 Synthesis of the trienyl(amino)allenylidene complex 64...

This chapter is intended to highlight the most important developments on the synthesis and reactivity of allenylidene complexes excluding catalytic processes. 

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. 

Metal allenylidene complexes (M=C=C=CR2) are organometallic species having a double bond betv een a metal and a carbon, such as metal carbenes (M=CR2), metal vinylidenes (M=C=CR2), and other metal cumulenylidenes like M=C=C= C=CR2 [1]. These metal-carbon double bonds are reactive enough to be employed for many organic transformations, both catalytically and stoichiometrically [1, 2]. Especially, the metathesis of alkenes via metal carbenes may be one ofthe most useful reactions in the field of recent organic synthesis [3], vhile metal vinylidenes are also revealed to be the important species in many organic syntheses such as alkyne polymerization and cycloaromatization [4, 5]. 

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