Heptahexaenylidene Complexes:  Synthesis and Characterization of the First Complexes with an MCCCCCCCR₂ Moiety (M = Cr, W)

Abstract

Silica-induced elimination of dimethylamide from [(CO)5M(C⋮C)3C(NMe2)3]- [M = Cr (4a), W (4b)] affords the first isolated and characterized heptahexaenylidene complexes [(CO)5MCCCCCCC(NMe2)2] (5a,b). Complexes 4a,b were generated by sequential reaction of Me3Si(C⋮C)3SiMe3 with LiMe·LiBr, [(Me2N)3C]+Cl-, LiBu, and [(CO)5M(thf)]. Complex 5b is inert in methanol, but adds dimethylamine across the C5C6 bond to give [(CO)5WCCCCC{CHC(NMe2)2}NMe2]. The reaction of 5a,b with LiMe·LiBr and SiO2 generates the heptahexaenylidene complexes [(CO)5MCCCCCCC(Me)NMe2] (8a,b). Trapping of 8b with HNMe2 yields pentatetraenylidene complex [(CO)5WCCCCC{CHC(Me)NMe2}NMe2].

Helical orbitals and circular currents in linear carbon wires

“…Though cumulenes are not as stable as polyynes, the even [n]cumulenes have been synthesized up to the [6] cumulene, [19][20][21][22][23][24][25] the odd [n]cumulenes up to [9]cumulene, 26 and metallacumulenes of similar lengths have been reported. 27,28 Functionalized chiral allenes have been characterized, [29][30][31] and in recent work Ozcelik et al 32 presented conductance measurements on a monolayer of enantiopure allenes. Still, it is clear that strategies for further stabilization of linear carbon wires must be conceived for them to be utilized in singlemolecule devices; rotaxane-protected cumulene and polyyne wires were recently reported by Tykwinski and co-workers and hold promise in this regard.…”

Rapid Markovnikov addition of HCl to a pendant alkyne: evidence for a quinoidal cumulene

“…Furthermore, for reasons of synthetic convenience, it appears that extended cumulene ligands with odd numbers of carbon atoms are more readily accessible than those with an even number.3 a,b For example, whilst a heptahexaenylidene (n = 5) 4 has been isolated (albeit stabilised with two dimethylamino-substituents), the existence of a hexapentaenylidene (n = 4) 5 complex has only been inferred from isolation of addition products.…”

[W(CO)(dppe)2] Cumulenylidene and Acetylide Complexes Accessed via Stannylated Acetylenes and Butadiynes

“…The 13 C NMR spectra of 3 exhibited butatrienylidene resonances slightly shifted to low field with respect to the bistrimethyltin-substituted derivative at 254.1 (C R ), 142.4 (C β ), 142.5 (C γ ), and 49.1 ppm (C δ ). In general, the 13 C NMR data of the tungsten C 4 cumulenes 2-4 turned out to be quite comparable to those of the MnC 4 series except for the C δ signals, which are located at lower field. 11,12 The 119 Sn NMR spectrum of 3 showed a signal similar to 2 at -26.1 ppm.…”

“…The longest terminal cumulenic chain was found in the C 7 compound [M(CO) 5 {CdCdCdCdCdCdC(NMe 2 ) 2 )}] (M=Cr, W). 13 Other types of group 6 metal centers were also shown to stabilize long-chain cumulenylidenes. 14 Thus, recently C 4 tungsten complexes [cis-W(CO)(dppe) 2 {CdCdCdC(R)( p-C 6 H 4 -tBu)}] (R=SnMe 3 or H) were reported.…”