Germylenes Transition metal germylene

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... 

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

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

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

This method has been more widely used for the synthesis of bridged germylene complexes than for their silicon analogs. The reactions of transition-metal carbonyl monoanions with Me2GeCl2 give A-type bridged... 

A major problem in postulating silylenoid metal complexes as intermediates in the redistribution reactions is simply that good model compounds are lacking, and the decomposition mechanisms of silyl transition metal complexes have not been systematically investigated. While there is evidence for transient R2Si species produced by thermal or photochemical means (80-83), there are no known monomeric silylene metal complexes. Several monomeric stannylene and germylene complexes are... 

As mentioned above, cationic phosphenium is isoelectronic with carbene, silylene, germylene, stannylene, and plumbylene, because the central element has lone pair electrons and a vacant p orbital as well as two substituents. Therefore, their transition metal complexes have attracted considerable attention. It might be of special interest to compare cationic phosphenium complexes with silylene complexes because phosphorus and silicon are both situated in the third row of the periodic table. 

Treatment of Mo(II) , W(II) and Au(I) complexes with one equivalent of GeCl2 dioxane, in CH2CI2 at —78°C and subsequent wanning to room temperature, resulted in rapid and clean insertion of germylenes into the metal-hydrogen or metal-chlorine bond . This is a convenient route to synthesize functionalized transition-metal germanium compounds The reaction is exemphfied in equations 18 and 19. 

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