Analogous .alpha.,.alpha.'-bis-carbenoid, triply bonded species: synthesis of a stable .lambda.3-phosphino carbene-.lambda.5-phosphaacetylene

Stable heteroaromatic carbenes of the benzimidazole and 1,2,4-triazole series

“…In the case of the reaction of carbene 19 with sulfur, a deeply-colored (red and brown) compound 34 was also isolated. Compound 34 has the composition (C 27 H 34 N 2 ) 2 S 7 ⋅4С 6 H 6 and includes benzene of solvation [probably the structure of the compound is of type Crb + -S -(S + =S -) 3 =Crb, where Crb is a fragment of carbene 19 in an azolium state (Crb + -) or in a neutral form (Crb=)]. Compound 34 is very unstable to oxygen and moisture, and upon dissolution in chloroform it forms thione 33a in a 16% yield and salt 4c with the anion HS 3 O 4 -in 60% yield.…”

“…In numerous works Wanzlick and co-workers, along with many other authors, advanced the chemistry of stable nucleophilic carbenes of the thiazole, benzothiazole, imidazoline and imidazole series based on in situ experiments 2 . This area received a considerable impetus when Bertrand et al 3,4 and Arduengo et al 5,6 isolated the first representatives of phosphanylsilylcarbenes and imidazol-2-ylidenes, respectively, thus demonstrating stability of singlet nucleophilic carbenes under normal experimental conditions. Subsequently, other new classes of stable carbenes have been reported, including acyclic diaminocarbenes 7 , 1,2,4-triazol-5-ylidenes 8 , and thiazol-2-ylidenes 9 .…”

Electronic Structure and Reactivity of Metal Carbenes

“…The most prominent examples are probably the olefin metathesis reaction by the Herrmann/Grubbs catalyst or the methane functionalization, which are described later in more detail. 4 T. Strassner Fischer-type carbene complexes (Scheme 4) are electrophilic heteroatomstabilized carbenes coordinated to metals in low oxidation states. They can be prepared from M(CO) 6 (M=Cr, Mo, W) by reaction of an organolithium compound with one of the carbonyl ligands to form an anionic lithium acyl "ate" complex.…”

“…Wittig-type alkenation of the carbonyl group is possible with Ti carbene compounds, easily prepared in situ by the reaction of CH 2 Br 2 with a low-valent titanium species generated by treatment of TiCl 4 with Zn, where the presence of a small amount of Pb in Zn was found to be crucial [39,40]. It is synthetically equivalent to Cl 2 Ti=CH 2 .…”

N-Heterocyclic Carbenes

“…Seppelt [9] and Bertrand [10] employed the elements of sulfur and phosphorus to construct molecules in which the conceptual 'resonance' relationship between a-dicarbenes and acetylenes could be perturbed by the introduction of the heavier main group elements. These pioneering studies provided thiaacetylenes [9] and phosphaacetylenes [10] that exhibited 'carbene-like' Anthony J. Arduengo However, an easily produced and easily handled carbene remained elusive until August 27, 1990, [11] when researchers in DuPont's Central Research and Development Department managed to place a stable crystalline carbene in a bottle (Scheme 4).…”