Cp2TiCH2 complexes in synthetic applications

Abstract

The reactive 16e-species Cp2Ti=CH2 can be generated in situ from either its aluminum alkyl adducts or olefin adducts (metallacyclobutanes). This complex reacts with a wide variety of unsaturated functionalities including :;;c=O, :::c=C~, -c=c-and -C=N. In most instances the ;:c:O groups are methylenated. Key to the utility of these complexes is their lack of basic properties in contrast with phosphorous ylides; all of the normal "Wittig" side reactions are eliminated using these reagents. Acid chlorides and anhydrides are converted into enolate complexes, which can be used in aldol type chemistry. The combination of the reactivity toward C=O and C=C results in an efficient method for the conversion of unhindered carbonyl centers into quarternary carbon centers. BACKGROUNDAlkylidene complexes of high oxidation state transition metals have been recognized for the past several years. They were first proposed as intermediates in numerous reactions (1), and have been isolated recently as tantalum (2), tungsten (3), and titanium (4) complexes. The low valent analogs prepared earlier show different types of reactions and trends in stability (5). The high oxidation state complexes /CH 3

An investigation of catalyst/cocatalyst/support interactions in silica-supported olefin polymerization catalysts based on Cp*TiMe3*

“…Furthermore, the methylene may not be highly enriched in 13 C since it is largely derived from methyl ligands initially associated with the unlabeled AlMe 3 reagent. Evidence for the methylene was therefore sought in reactivity characteristic of Tebbe complexes, namely the olefination of ketones [38]. Thus exposure to cyclopentanone vapor led to the evolution of methylenecyclopentane, while reaction with acetone gave isobutene.…”

Synthesis and Reactivity of the Cationic Methylene Complex [Cp2ReCH2]+

“…Additional information about the structure of the carbene complex can be gained from an unsymmetrical carbene ligand. The observation of two inequivalent Cp resonances in the 1 H and 13 C NMR spectra of [Cp 2 ReCH(CH 3 )]B(Ar′) 4 (3) indicates that the methyl group is aligned with one Cp while the hydrogen of the carbene ligand is aligned with the other Cp (structure A; Scheme 3).…”

Synthesis and characterization of some bis(cyclopentadienyl)titanium(IV) complexes with internally functionalized oximes(LH): sol–gel transformations of Cp2TiCl2, Cp2TiClL and Cp2TiL2 to nano‐sized anatase titania

“…It would be interesting to mention here that the formation and structure of [CpMO(Cl)] 4 [6a,c,d,7] as well as the presence of Cp 2 TiO as an intermediate in the methylation reactions of carbonyl compounds using [Cp 2 TiCH 2 AlClMe 2 ] has already been reported. [12] …”