Cumulene-transition-metal complex,

Transition-Metal Complexes of Arynes, Strained Cyclic Aikynes, and Strained Cyclic Cumulenes... 

To date, no mononuclear transition metal complexes of three- or four-membered cycloalkynes have been reported. A number of polynuclear complexes of cyclobutyne have been prepared.90 However, since this article is limited to complexes in which the aryne, alkyne, or cumulene is coordinated to a single metal atom, a review of this topic is not included. 

Tetraethynylmethane (39), a potential monomer for a three-dimensional superdiamonoid carbon network [1], was elusive for many years [51, 52], until its synthesis was accomplished in 1993 by Feldman and co-workers [53]. The key step in the synthesis was the acid-mediated Johnson orthoester variant of the Claisen rearrangement, which provided the central quaternary methane C-atom with suitable functional groups for the ultimate transformation into 39 [Scheme 13-9(b)]. Solid 39, like tetraethynylethene (20), decomposes rapidly at room temperature in either the presence or absence of oxygen. The earlier efforts to prepare tetraethynylmethane had yielded the peralkynylated derivatives 40-42 [Scheme 13-9(c, d)] [51, 52]. Tetraethy-nylallene represents another potential precursor for a three-dimensional carbon network [1], but remains elusive of the perethynylated [K]cumulenes, so far only the silyl-protected [3]cumulenes 43a and 43b [Scheme 13-9 (e)] have been prepared [54]. With 44 [Scheme 13-9 (f)], the first transition metal complex of a perethynylated ligand is now available [55]. 

Bennett MA, Schwemlein HP (1989) Angew Chem Int Ed Engl 28 1296 Buchwald SL, Broene RD (1995) In Abel EW, Stone EGA, Wilkinson G (eds) Hegedus LH (vol ed) Comprehensive organometallic chemistry 11, vol 12. Pergamon, Oxford, p 771 Jones WM,Klosin J (1998) Transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes. In Stone EGA, West R (eds) Adv Organomet Chem, vol 42. Academic, San Diego, p 147... 

Gomprehensive reviews of the chemistry of heavy allenes and cumulenes, heteroaldehyde, heteroketone, phosphaalkene " " and 77 -ketenyl (77 -G(PPh3)=GO) " complexes, which include platinum complexes, have been published. A review of transition metal complexes of arynes, strained cyclic alkynes, and strained cyclic cumulenes also includes information relative to this section. " ... 

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). 

---