Silanediyl complexes

The chromium complexes are proved to be silanediyl complexes, as shown by the silicon-transition metal bond lengths (Table 5) and by the extreme low field shift of the 29Si NMR signals (124.9 and 121.2) at 22 °C for R = H and CH2NMe2, respectively (Table 6). The 29Si NMR shifts of these complexes are temperature-dependent due to the hindered rotation of the phenyl ring and dynamic coordination of the nitrogens to the Si atom. 

Structural type D molecules can be synthesized in a two step reaction sequence K2[Cr(CO)5] (2) reacts with the h)q)ervalent trichlorosilane (2-Me2NCH2C5H4)SiCl3 (4) in THF at —25 °C to afford the chloro-functionalized silanediyl complex 5 in 55 % yield. 

The Mo-Si bond lengths in compounds 6-8 are between 2.516(2)A and 2.5683(12)A, which correlates very well with M-Si (M = Mo, W) bond lengths already observed by Berry and coworkers [8] in similar metallocene complexes. On the other hand, compounds 1 and 2 possess significantly shorter Mo-Si bonds. In fact, to the best of our knowledge the SiBrs derivative 1 has the shortest ever observed Mo-Si bond. Its value of 2.459(3)A is in the range of the distance calculated for the silylene (silanediyl) complex (CO)sMo=SiH2 (DMo=si = 2.46A) [9]. 

Fig. la. Structure of the complex bis( -butoxysilane-diyl)tetracarbonyliron(O) x HMPA 4. b. Molecular structure of the chromium complex bis( -butoxy-silanediyl)pentacarbonylchromium(O) x HMPA 9. c. Van der Waals surface of 9... 

Major advances in organometallic chemistry during the last years have been achieved in the area of silicon-metal multiple bonding and silicon with low coordination numbers. For late transition metals, new complexes have been synthesized such as silanediyl (A), silene (B), silaimine (C), disilene (D), silatrimethylenemethane (E), silacarbynes (F), cyclic silylenes (G), silacyclopentadiene (H) and metalla-sila-allenes (I) (Figure 3). 

Transition metal derivatives are known to stabilize unusual molecules in their coordination sphere. First studies on silanediyl- and silyl complexes of iron carbonyls have been carried out [7-9],... 

In the last years transition metal-silyl complexes have received special attention for several reasons [1, 2], On the one hand, they are assumed to be important intermediates in catalytic processes [2] (transition metal-catalyzed hydrosilylation reaction, dehydrogenative coupling of silanes to polysilanes, etc.), on the other metal-substituted silanes show special properties, which can be tuned systematically by judicious choice of the metal and its ligands [3] Furthermore, silylenes (silanediyls) are stabilized by unsaturated transition metal fragments leading to metal-silicon double-bonds [4]. In the light of a possible application in MOCVD processes some of these complexes are of interest as potential single-source precursors for the manufacture of thin silicide films [5]. 

Silicon compounds with coordination number larger than four are the object of many studies first with respect to their application as catalysts in organic and inorganic syntheses and second as starting materials for the preparation of a broad variety of organosilicon compounds [1]. Additionally, hypervalent silicon hydride compounds can successfully be used as model compounds to study, for instance, the mechanism of nucleophilic substitution reactions, which is of great interest since the silicon atom is able to easily extend its coordination number [1]. Moreover, hypervalent silanes are suitable as starting materials for the synthesis and stabilization of low-valent silanediyl transition metal complexes [2-5]. 

Industrial use of an a-metallocenes for the production of isotactic polypropylene had to overcome not only technical hurdles, but has also been restricted by a complicated and scattered patent landscape. Basic patent rights like the activation of metallocene complexes by MAO, supported metallocenes [59, 62], silanediyl-bridges [49] and 2-methyl substitution [50], all of which were required for the use of awia-metallocenes in industrial polypropylene production, were owned by different companies such that no player had the freedom to move. Only in 1995,5 years after rac-dimethylsilylenbis(2-methylindenyl)zirconium dichloride had been described for the first time in a patent [50], did ExxonMobil and the former Hoechst AG announce independently their first commercial production of metallocene-catalyzed, isotactic polypropylene. Most likely, these 5 years were needed not only to solve technical problems, but also to gain access to all the necessary patent rights. 

Stirring MejSiaH with Fe2(CO)9 produces the first stable mononuclear dimethylsilanediyl iron complex (56) as an air sensitive distillable oil, while the diferriosilane CpFe(CO)2 2SiMeH loses CO photochemically to give a silanediyl bridged mixture of isomers [equation (66)]. Palladium complexes catalyse the... 

Kyushin S, Kawai H, Matsumoto H (2004) (tranj -l,2,2,3,4,4-Hexa-rcrt-butyl-l,3-cyclotetra-silanediyl)dipotassium supramolecular structure of the silylpotassium-benzene complex. Organometallics 23 311... 

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