Generation of Polyunsaturated Cumulene Chains by Unprecedented Insertions of the Ynamine MeCCNEt2 in Ruthenium(II) Allenylidene Complexes

Abstract

Allenylidene (propadienylidene) complexes [ML n ] ¼ C ¼ C ¼ CR 1 R 2 , which belong to the series of unsaturated carbenes [ML n ]¼C(¼C) i ¼CR 1 R 2 (i > 0) have received increasing interest during the last few years. [1] These derivatives have a great potential to promote novel carbon±carbon and carbon±heteroatom coupling reactions, because of the electrophilic (C a and C g ) and nucleophilic (C b ) character of the carbon nuclei of the allenylidene chain. While simple nucleophilic and electrophilic additions are well-studied, cycloaddition processes are scarce, in particular those involving CC dipolar substrates. [2] In 1998 Fischer and co-workers reported the synthesis of cyclobutenylidene and alkenylallenylidene Group 6 metal complexes which are formed as a mixture by the cycloaddition of ynamines to both the C a ¼C b and C b ¼C g bonds of an COMMUNICATIONS

Indenylruthenium(II) Aminoallenylidenes: New Building Blocks for the Synthesis of Highly Unsaturated Alkynyl and Allenylidene Complexes

“…Selected bond lengths (Å) and angles (deg) are collected in Figure . For further structural data see ref .

2 ORTEP view of the molecular structure of the cation of [Ru{CCC(NEt 2 )[(CMeCH)C(Me)CPh 2 ]}(η 5 -C 9 H 7 )(PPh 3 ) 2 ][PF 6 ] ( 18 ), drawn at the 10% probability level.

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“…These processes are representative examples of a new synthetic approach to building up unprecedented highly unsaturated hydrocarbon chains. Part of this work has been communicated previously 1 …”

Radical revelations: the pnictogen effect in linear acetylenes

“…Indeed, mono-substituted acetylenes, such as aminoalkynes and generally depicted as RR 1 R 2 C–C≡CX (X ≠ H, C), have been recently put into the spotlight owing to their peculiar reactivity and applicability as valuable organic synthons. 22–27 Unfortunately, the synthesis of XC≡CX moieties is often challenging, being hampered by particularly pronounced reactivity and promiscuity, making their wide-range application difficult. However, it is known that the nature of the heteroatom determines the stability and properties of these compounds, even when the former belongs to the same group of the periodic table.…”