Metallo-silanols

A novel potentially useful route for the synthesis of metallo-silanols is based on the reaction of metallohydridosilanes with 1,1-dimethyldioxirane [7,8] resulting in the insertion of oxygen into the Si-H bond. This procedure is supplementary to the hydrolysis route, since, in addition to the transformation of the "normal" ferrio-hydridosilanes 9a,b to the silanols 10a,b, it guarantees the formation of chiral 10c, not available by hydrolysis, from "electron rich" phosphine iron fragment substituted 9c (Eq. (2)). 

To get further insight into the reactivity of the metallo-silanols, condensation with diverse chlorosilanes has been studied. It offers easy and general access to the ferrio-disiloxanes 15a-d via interaction of 2a or its lithiation product 13 with alkyl-, aryl- or metallo-chlorosilanes in the presence of NEt3 (Eq.(3)). 

All compounds described in this report have been well characterized by means of IR and NMR spectroscopy. Most valuable is the coupling constant J(WSi) which, as has been demonstrated for J(WP) [17], can be correlated with the s-electron density of the main group element transition metal bond (e. g. J(WSi) = 44.7 Hz (21i), 71.1 Hz (22b)). Related studies concerning metallo-silanols and siloxanes with other metals of groups 6 and 8 are in progress. 

Novel Metallo-Silanols, -Silanediols, and -Silanetriols of the Iron and Chromium Group ... 

The described metallo-silanols exhibit high stability concerning condensation, however, the OH groups display reasonable reactivity in context with chlorosilanes. These properties can be used to transform the ferrio-silanols 4a, 4b via reaction with trimethylchlorosilane to the ferrio-di- and -trisiloxanes 13a, 13b characterized by a hydrogen substituted a-silicon. In the case of 4b the first siloxane unit is established after one day, the second takes five days (13b). The same reaction pattern can be applied for the generation of the ruthenio-disiloxanes 13c, 13d, resulting fi-om the treatment of the ruthenio-silanols 8c, 8e with Me2Si(R )Cl. 

Metallo-Silanols and Metallo-Siloxanes, Part 5. - Part 4 W. Malisch, K. Grun, N. Gunzelmaim, S. Moller, R. Lankat, J. Reising, M. Neumayer, O. Fey, in Selective Reactions of Metal Activated Molecules (Eds. H. Werner, J. Sundermeyer), Vieweg Verlag, Braunschweig, in press in addition Part 30 of the series Synthesis and Reactivity of Silicon Transition Metal Complexes. 

Keywords oxoflmctionalization, half-sandwich complexes, metallo-silanols... 

Metallo-silanols represent a special class of silanols which is characterized by a remarkably high stability with respect to self-condensation. This property, which is even valid for silanetriol derivatives [2], and the generally stable metal-silicon bond makes these compounds useful precursors for controlled condensation with chlorosilanes to build up unusual arrangements of fimctionalized siloxanes at metal centers. The metal fragment is responsible for highly hydridic Si-H units, creating the conditions for electrophilic oxygenation with DMD [3]. 

Part 3S of the series Metallo-Silanols and Metalto-Siloxane. In addition, Part 64 of the series Synthesis and Reactivity of Silicon Transition Metal Complexes. Part 63/34, see Ref. [1]. 

Part 16 in the series "Metallo-Silanols and Metallo-Siloxanes". In addition. Part 42 of the series "Synthesis and Reactivity of Silicon Transition Metal Complexes". Part 15/41, see W. Malisch, M. Neumayer, K. Perneker, N. Gunzelmann, K. Roschmann, in Organosilicon Chemistry III From Molecules to Materials (Eds. N. Auner, J. Weis), VCH, Weinheim, 1997, p. 407. 

Optically active organometallic compounds, especially pseudotetrahedral half-sandwich complexes of the type Cp(OC)(Ph3P)Fe-R with iron as the center of chirality have been extensively investigated in the past. However, synthetic utilization of stereocontrol by the chiral iron has been limited to systems with a-bonded carbon ligands [2]. In contrast, silicon-iron complexes have not yet found analogous application. In context with our studies concerning metallo-silanols we have established simple routes to isolate diastereomerically pure derivatives with a chiral iron fragment. 

The condensation of metallo-silanols with organochlorosilanes [4] is a common method of preparing metallo-siloxanes. It has now been applied to gain diastereomerically pure ferrio-siloxanes RS,SR)-3a-c by interaction of the ferrio-silanol (RS,SR)-1 with the organochlorosilanes 2a-c in ether or benzene at room temperature (Eq. 1),... 

Part 13 of the series "Metallo-Silanols and Metallo-Siloxanes". In addition. Part 39 of the series "Synthesis and Reactivity of Silicon Transition Metal Complexes". Part 12/38 see Ref [2a]. 

Recently, it has been demonstrated that transition metal fragment substituted silanols are both stable with respect to self-condensation and reactive towards various chlorosilanes. Due to these properties metallo-silanols provide interesting starting materials for the synthesis of special siloxane arrangements at metal centers [2]. 

Condensation of organosilanols with transition metal halides is well established [3], but comparable reactions of metallo-silanols, which should provide a convenient entrance into the field of siloxy-bridged multinuclear complexes, has not been realized. In this context we have carried out the reaction of ferrio- and tungsten-silanols L,M-SiMe20H (L M = Cp(OC)2Fe (1) CsR5(OC)2(Me3P)W, R = H (5a), Me(5b)) with the electron deficient metal halides CpnMCh (w = 2, M = Ti, Zr n = 1, M = Ti). 

Two routes proved to be most efficient for the generation of metallo-silanols the hydrolysis of metallo-chlorosilanes in the presence of an auxiliary base and... 

However, the facile isolation of metallo-silanols allows controlled condensation reactions with organochlorosilanes in the presence of an auxiliary base leading to transition metal substituted oligosiloxanes which can be considered as model compounds for silica-immobilized catalytic systems (Eq. 2a). 

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