What a Difference One Electron Makes! Generating Low‐Coordinate Ti–C and V–C Multiply Bonded Frameworks through One Electron Oxidatively Induced α‐Hydrogen Abstractions

Abstract

Low‐coordinate, high oxidation state titanium and vanadium complexes containing terminal metal–carbon multiply bonded functionalities have been prepared directly or indirectly through one electron oxidatively induced α‐hydrogen abstraction reactions. This synthetic approach offers a mild entry to reactive M=C and M≡C motifs, and does not depend on external stimulants such as heat, light or base to promote the α‐hydrogen‐abstraction step. In addition, this strategic protocol avoids the use of powerful electrophiles, thus generating terminal and nucleophilic M–C multiple bonds in low‐coordination environments. In some cases terminal alkylidenes containing β‐hydrogen atoms can also be introduced through this route. This microreview surveys the synthesis and chemistry surrounding isolable titanium and vanadium complexes bearing terminal alkylidene and alkylidyne ligands. Particular emphasis will be placed on the synthesis of the high oxidation state M–C multiple bond. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006)

Endohedral fullerene with μ3-carbido ligand and titanium-carbon double bond stabilized inside a carbon cage

“…2c). The length of the Ti ¼ C bond in TiLu 2 C@I h -C 80 , 1.874(6) Å, falls into the range of the Ti ¼ C bond lengths in Ti alkylidenes characterized by single-crystal X-ray diffraction (usually 1.8-1.9 Å, see Supplementary Table 1 for a list of values) 22,23 . The structure of the planar TiLu 2 C cluster with m 3 -carbido ligand bonded to three metal atoms is rather unusual and has only few analogues in organometallic chemistry, and none of them involves Ti [45][46][47][48] .…”

“…Since the invention of the Ziegler-Natta process of olefin polymerization, many Ti-based organometallic complexes have been used as catalysts of industrial importance. For instance, compounds with Ti ¼ C double bonds of the general formula L 2 Ti ¼ CR 2 (where L is a ligand and R is H or alkyl) known as Schrock carbenes or alkylidenes are widely used in olefination reactions [22][23][24][25][26] . Ti in L 2 Ti ¼ CR 2 is usually a 16-electron system with LUMO localized on the metal.…”

“…For example, the archetypical Schrock carbene (Cp) 2 33 , whereas X 2 Ti ¼ CH 2 (X ¼ H, F, Cl) species were isolated in low-temperature inert gas matrices 34,35 . At the same time, Ti alkylidenes with a higher coordination number, when Ti-based LUMO is further coordinated, can form stable molecules 22,23,[36][37][38][39] .…”

Methane as a Selectivity Booster in the Arc‐Discharge Synthesis of Endohedral Fullerenes: Selective Synthesis of the Single‐Molecule Magnet Dy2TiC@C80 and Its Congener Dy2TiC2@C80

“…[18] Note that large downfield shifts for metal-bonded carbon atoms are not unusual in Ti alkylidenes with aT i = Cbond. [19] Particularly large shifts in the range of 400-600 ppm are reported for a-C atoms in m 3 -bridging alkylidynes of titanium in titanocubane frameworks. [20] Theh igh selectivity makes Dy 2 TiC@C 80 -I as uitable synthetic target for further studies of its properties.C omparison of the Vis/NIR and IR absorption spectra prove that the Dy and Lu compounds are isostructural (Figure 2).…”

(Imido)vanadium Complexes as Efficient Catalyst Precursors for Olefin Polymerization/Oligomerization

“…], displays promising possibilities for synthesis of functional polymers as well as valuable organic compounds [58][59][60][61][62], as demonstrated especially by molybdenum [63,64] and ruthenium [65,66]. Transition metal-alkylidene complexes, especially high-oxidationstate early transition metal alkylidene complexes attract considerable attention [63,64,[67][68][69][70][71][72], because they play essential roles as catalysts in olefin metathesis and Wittigtype or group transfer reactions [58][59][60][61][62][63][64][67][68][69][70][71][72], as demonstrated especially by molybdenum [58][59][60][61][62][63][64]. However, as described below, no examples that proceed olefin metathesis reaction using vanadium(V)-alkylidene complexes were known until our recent reports [73][74][75][76].…”