Transition metal germylene

The early development of transition-metal germylene chemistry is summarized in earlier reviews4b-d. Therefore we summarize the transition-metal germylene chemistry developed after 1990. Such complexes can be divided into seven different types (I-VII) depending upon the nature of bonding between the metal and germanium atom ... 

Stable mononuclear transition-metal germylene complexes with a formal triple bond between the Ge and metal atoms (Cr, Mo, W, 56-62) have been synthesized by a combination of salt-elimination and decarbonylation reaction (equation 44)150,151. The decarbonylation process for the Cr and W intermediates 61 and 62 can involve either a thermal or a photochemical reaction the molybdenum germylyne complexes 56 and 57 were obtained directly, even at low temperatures. 

TABLE 9. X-ray structural data of transition metal germylene complexes... 

The early development of transition-metal germylene chemistry is summarized in earlier... 

Over the past decade, several more transition metal germylene complexes with ix coordination have been synthesized and characterized by X-ray crystallography for... 

Germylenes, stabilized by coordination to a transition metal centre, have also been produced by irradiation of M(CO)6 in the presence of the appropriate free carbene homologue100, as shown in reaction 54. 

Germylenes can be released thermally in the presence of a transition metal complex leading to the formation of a germanium-metal bond (Equation (193)).239 The reaction occurs at room temperature when a germylsilane is used as the synthon (Equation (194)).240... 

Like silylenes and carbenes germylenes are isolobal with phosphines and may function as ligands to transition metal complexes. (Adapted from Bazlnet et ah, 2001)... 

Novel, monomeric heteroleptic derivatives of divalent Ge 40 and divalent Sn 41 have been prepared and characterized by single crystal X-ray diffraction <19990M389>. Heteroatoms in these germylene and stannylene species are not formally part of a four-membered ring however, crystal structures point to the azametallacyclobutane structures formed due to the N —> M coordination. The heteroleptic nature of 40 and 41 gives rise to an interesting reactivity in their coupling with transition metal clusters. 

In a third class of 7t-cyclopentadienyl complexes, compounds of type LVIII are bound to a transition metal via the lone pair at the germanium atom. The first compounds in this series, the pentacarbonyl-[chloro(pentamethylcyclopentadienyl)germylene]chromium(0) (LIXa) and -tungsten(O) (LIXb) were synthesized by alkylation of the ylide complexes (CO)5M—GeCl2 THF according to Eq. (22) (201). Nucleophilic substitution reactions of LIXb lead to the alkyl- and amino-substituted complexes LIXc-e [Eq. (23)] (202). 

C. Synthesis of Transition Metal Germanium Double Bond Germylene... 

TABLE 4. Transition metal complexes with bridging germylene ligands... 

R = Ph, tt-Bu, tt-Pen, tt-Hex SCHEME 27. Transition metal-catalysed addition-polymerization of germylenes to acetylenes... 

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