Germylenes insertion reactions

From the reaction of dihalodigermanes with alkyl halides catalyzed by Pd(PPIi3 A an unexpected germylene insertion takes place269 ... 

A germanium-nitrogen complex containing two Ge atoms disposed in an acyclic array was obtained via the formation of the intermediate germylene [(Me3Si)2N]GeCl, which was converted into a germanium(iv) adduct via an insertion reaction (Scheme 19).157... 

The insertion reaction chemistry of the well-known germylene Ge [CH(Si M03)3)2 50 is very diverse.154 323-328 This species inserts readily into the C-H bonds of mono- and dinitrile substrates (Scheme 47),154 the C-H bonds of ethers and alkanes in the presence of Phi (Scheme 48),323 the C-H bonds of ketones in the presence of MgCE (Scheme 49) and the O-H bonds of the tautomer enols in the absence of MgCl2 (Scheme 50),324 and the C-H bonds of diketones resulting in cyclic products (Scheme 51). 

The insertion reactions of 16 into the C-Hal bond of alkyl halides were found to be the most convenient model for CIDNP studies. Since in accordance with Scheme 10 the photolysis of 17 leads to the formation of triplet germylene 16, we start with the first evidence of the reactions of triplet excited 1676. 

The pre-reaction complex in the reaction of geimylene with Hg is only about half as strong (—0.9 to —1.3 kcalmoP ) as that found for silylene (—2.1 to —3.3 kcalmoP ) (Table 22). Both calculations and experiment show that the insertion of GeHg into the H—H bond require overcoming a high activation barrier (calculation ca 12.1 kcalmol experiment ca 15-20 kcalmoP ) in contrast to the reaction of SiHg with Hg, which in fact has no barrier. The calculations revealed no mechanistic differences in silylene and germylene insertions. 

Germylenes have long been known to react with multiple bonds such as C=C, C C, and C=0. In addition, insertion reactions into carbon halogen, O H, and N H bonds, are well precedented. In the last 10 years, substantial progress has been made in the reaction with C H bonds. 

There are examples of electron-deficient divalent metal derivatives called heavy analogs of carbene with the general formula R2M , including silylenes, "" germylenes, "" " stannylenes, "" "" and plumbylenes. When compared to carbenes, however, these compounds exhibit a significantly decreased reactivity in C-H insertion reactions. Theoretical studies have indicated that the heavier the metal, the larger the activation barrier and the less exothermic the reaction. Electropositive substituents, however, may increase reactivities. " ... 

The germylene 107 undergoes an oxidative insertion into an Si-Cl bond of SiCU (Equation (255)), and the reaction pathway of this process has been proposed (Equation (256)).320... 

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