Trimethylene methane complex

Harrington PJ (1995) Transition metal allyl complexes trimethylene methane complexes. In Abel EW, Stone FGA, Wilkinson G (eds) Comprehensive organometallic chemistry, vol 12, Chap 8.4. Pergamon, Oxford, p 923... 

In cases where the diene is unstable, a dihalo starting material may be used with the iron carbonyl acting as a reducing agent. Both the trimethylene methane complex 10.5 (Scheme 10.3) and the cyclobutadiene complex 10.7 (Scheme 10.4) have been made in this way. The cyclobutadiene-iron complex 10.7 is a convenient storable form of this highly unstable diene. It can be liberated by oxidation and, if this is done in the presence of a dienophile, the Diels-Alder product is obtained. The Diels-Alder reaction with 2,5-dibromobenzoquinone gave the expected e do-product 10.8. An intramolecular photochemical [2-1-2] cycloaddition, followed by a Favorskii reaction, gave a cubane dicarboxylic acid 10.10. ... 

Trimethylene methane complexes are also susceptible to nucleophilic attack. Powerful nucleophiles attack at a methylene carbon to give anionic T -allyl complexes 10.64, which may be protonated or alkylated (Scheme 10.18). 

Parallel chemistry is observed with the trimethylene methane complexes 10.136 (Scheme 10.34)." In this case, however, the cationic tv -complex 10.137, although observable by NMR at low temperature," cannot be isolated. It could be trapped with nucleophiles, but different nucleophiles gave different types of product. Allyltrimethylsilane gave a new trimethylene methane complex 10.138," while methanol yielded an if -diene complex 10.139. The different structural types produced, trimethylene methane versus diene complex, are likely to be due to kinetic and thermodynamic control as addition of methanol would be expected to be reversible under acidic conditions. 

Cioptically active L-amino acid esters results in optically active cazbenes Qr(CO)s =C(NRiR2)Ar. Some of these react regiospecifically and with moderate diastereoselectivi to fmm pytrcdin(mes. i Treatment of Ct(CX))s C(OEt)ni with the cyclic alletie HC=OC(CH2)s 2 in a trimethylene methane complex which reacts... 

Allylic substitutions. The TT-allylpalladium ions are electrophilic agents. Dial-lylation of (benzothiazol-2-ylthio)methyl ketones is readily achieved using allyl methyl carbonate as reaction partner. The generation of a Pd-complexed trimethylene-methane from 2-(trimethylsilylmethyl)allyl esters is well known the interception of this species by imines gives 3-methylenepyrrolidines. ... 

An important use of transition metal complexation has been in the stabilization of reactive molecules including cyclobutadiene, trimethylene-methane, o-xylylene, carbenes, carbynes, and others. In many cases, release of the ligand by chemical means has proven possible, making the complexed precursors valuable as shelf-stable sources of the reactive species for structural study or synthetic deployment. There also has been considerable interest in analogous complexes of benzyne, other strained cycloalkynes, and highly reactive acetylenes. 

As described in the previous section, a-elimination of dialkyltitanocenes is of limited use for the preparation of titanocene-alkylidenes. Since thioacetals are readily available from carbonyl compounds or through alkylation of bis(phenylthio)methane and related organosulfur compounds, a thioacetal-titanocene(II) system enables the use of different types of carbene complexes. Use of appropriate thioacetals is of crucial importance in this system for the preparation of alkylidene complexes 48, the corresponding diphenyl thioacetals are the starting materials of choice. No carbene complexes are formed from dialkylthio-acetals. To generate vinylcarbene complexes 49, trimethylene thioacetals of aji-unsaturated aldehydes or l,3-bis(phenylthio)propene derivatives are employed (Scheme 4.41). The low-valent titanium species 44 is also easily prepared by the reduction of titanocene dichloride with magnesium in the presence of triethyl phosphite at room temperature. The presence of molecular sieves 4A is essential for the reproducibility of this preparation. In relatively large-scale preparations, care should be taken to control the reaction temperature [92, 93g]. 

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