Chapter 11 Different Reactivities of Divalent Silicon Compounds Towards Metallocene Derivatives of Molybdenum and Tungsten Stefan H. A. Petri, Stefan H. A. Petri Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this authorDirk Eikenberg, Dirk Eikenberg Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this authorPeter Jutzi, Peter Jutzi peter.jutzi@uni-bielefeld.de Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this author Stefan H. A. Petri, Stefan H. A. Petri Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this authorDirk Eikenberg, Dirk Eikenberg Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this authorPeter Jutzi, Peter Jutzi peter.jutzi@uni-bielefeld.de Fakultät für Chemie, Universität Bielefeld Universitätsstr. 25, D-33615 Bielefeld, Germany Tel.: Int. code + (521)106 6181—Fax.: Int, code + (521)106 6026Search for more papers by this author Book Editor(s):Prof. Norbert Auner, Prof. Norbert Auner Inst. für Anorganische Chemie, der Universität Frankfurt, Marie-Curie-Strasse 11, D-60439 Frankfurt am Main, Germany, Phone: 0 69/7 98-29180, -29591, Fax: 069/798-29188Search for more papers by this authorProf. Johann Weis, Prof. Johann Weis Wacker-Chemie GmbH, Geschäftsbereich S, Werk Burghausen, Johannes-Hess-Strasse 24, D-84489 Burghausen, GermanySearch for more papers by this author First published: 17 January 2000 https://doi.org/10.1002/9783527619917.ch11Citations: 1 AboutPDFPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShareShare a linkShare onFacebookTwitterLinked InRedditWechat Summary The thermal and photochemical reactivity of divalent silicon species, decamethylsilicocene (Cp*2Si) and 1, 3-di-teri-butyl-1, 3, 2-diazasilol-2-ylidene (SiLN2), towards Cp2MH2 (M = Mo, W) and Cp2Mo(PEt3) is investigated. In the case of Cp*2Si no conversion of the silicon(II)-species is observed. This is attributed to the high steric demand of the bulky Cp* ligands. In SiLN2 the silicon atom is less shielded. So the reactivity of SiLN2 in analogous reactions is much higher. The reactions with Cp2MH2 lead via silylene insertion to the corresponding metallosilanes. The photolysis of an equimolar amount of SiLN2 and Cp2Mo(PEt3) results in the formation of the first molybdenum silylene complex with a tricoordinated silicon atom. Citing Literature Organosilicon Chemistry IV: From Molecules to Materials RelatedInformation

The divalent organosilicon compounds (C5Me5)(2)Si (Cp-2*Si) and (SiNBuCHCHNBu)-Bu-t-Bu-t (SiL2N) have been compared concerning their reactivity toward metallocene derivatives of molybdenum and tungsten. While Cp-2*Si does not react with Cp2MH2 (M = Mo, W), either thermally or photochemically, the reaction of SiL2N with Cp2MH2 leads via silanediyl insertion to Cp2M(H)((SiL2H)-H-N) (M = Mo (1a), W (1b)). Irradiation of a mixture of Cp2Mo(PEt3) and Cp-2*Si yields only decomposition products, whereas photolysis of equimolar amounts of Cp2Mo(PEt3) and SiL2N results in the formation of the silanediyl complex Cp2Mo(SiL2N) (2). 2 is extremely moisture sensitive and easily adds one molecule of water to yield the metallosilanol Cp2Mo(H)((SiL2OH)-O-N) (3). 1a and 2 have been characterized by X-ray crystallography. 2 is the first molybdenum silanediyl complex with a tricoordinated silicon atom. The silicon-molybdenum interaction in 2 has to be described as a dative bond from the silicon to the metal atom.

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Reaction of decamethylsilioocene, (Me(5)C(5))(2)Si (1), with MeSCN, 2,4-Me(2)C(6)H(3)OCN, Me(2)-NCN, BrCN, and Me(3)SiCN is described. In all reactions, the formal oxidation state of the silicon atom changes from -2 in 1 to +4 In the products, and the hapticity of the pentamethylcyclopentadienyl ligands changes from eta(5) to eta(1). Under mild conditions (-78 degrees C or room temperature) 1 reacts with 2 equiv of MeSCN, 2,4-Me(2)C(6)H(3)OCN, and Me(2)NCN under C-C bond formation to the respective diazasilole derivatives 3-5. Reaction of 1 with BrCN at -78 degrees C affords the silyl cyanide 7; at room temperature, a mixture of the silyl cyanide 7 and of the silyl isocyanide 8 is formed. Reaction of 1 with Me(3)SiCN leads to the silyl cyanide 10. In the reactions described, the product formation presumably proceeds via [2 + 1] cycloaddition compounds of the azasilirene type as reactive intermediates. All products are characterized by NMR (H-1, C-13, Si-29) spectroscopy, IR spectroscopy, mass spectrometry, and microanalytical data. The structures of 3, 4, and 10 were determined by X-ray crystallography.

In the reaction of the nucleophilic decamethylsilicocene, ((Me(5)C(5))(2)Si (1), with the electrophilic heterocumulenes CO2, COS, CS2, and RNCS, multistep processes are observed, which in most cases proceed via several highly reactive intermediates. In all reactions, the formal oxidation state of the silicon atom changes from +2 in 1 to +4, and the hapticity of the pentamethylcyclopentadienyl ligands changes from eta(5) to eta(1). In the reaction of 1 with CO2, COS, or RNCS, double-bond species of the type (Me(5)C(5))(2)Si = X (X = O, S) are formed, which are stabilized via different routes. Thus, reaction of 1 with CO2 in toluene as solvent finally leads to the spiro compound [(Me(5)C(5))(2)SiO2]C-2 (4), whereas in pyridine as solvent, the eight-membered heterocycle [(Me(5)C(5))(2)SiO2CO](2) (5) is formed. The dithiadisiletane [(Me(5)C(5))(2)SiS](2) (9) results from the reaction of 1 with COS. Dithiasiletane derivates of the type (Me(5)C(5))(2)SiS2C = NR (10, 11) are the final products from the reaction of 1 with RNCS (R = CH3, C6H5). Multistep rearrangement processes have to be postulated to explain the formation of the dithiadisiletane derivate 15 in the surprising reaction of 1 with CS2; ligands that initially are bonded to the silicon (Me(5)C(5)) and to the carbon atom (S) have to be completely exchanged to build up the final product. The silaheterocycles 4, 5, 10, and 15 and also some of the basic molecular framework have been unknown in the literature. The crystal strucutres of 4, 5, 10, and 15 were determined by X-ray crystallography and are presented.

Reactions of decamethylsilicocene, (Me(5)C(5))(2)Si (1), with representative organic carbonyl compounds are described. They proceed via [2 + 1] cycloaddition products of the oxasilirane type as reactive intermediates to give different types of compounds. The formal oxidation state of silicon is changed from +II in the substrate to +IV in the final products; at the same time the hapticity of the pentamethylcyclopentadienyl ligands changes from eta(5) to eta(1). In the reaction of 1 with aldehydes such as benzaldehyde and trans-cinnamaldehyde as well as with acetone, formation of the respective dioxasilolane derivatives 2, 3, and 5 takes place. Here, C-C bond formation is observed for the first time in the reaction of a divalent silicon compound; reaction with the aldehydes is stereospecific. In the reaction of 1 with acetophenone or benzophenone, the bicyclic ring systems 6 and 7, respectively, containing an oxasilacyclopentene unit are formed by rearrangement of the transient oxasiliranes, The 1,3,2-dioxasilole 9 is the product of the reaction of 1 with benzil. The new compounds are characterized by NMR (H-1, C-13, Si-29) spectroscopy and by mass spectrometry and microanalytical data. The X-ray crystal structure analysis of 2 is presented.

Carbonyl protonated aromatic ketones a—i [R—C(OH+)—C6H4CH2OCH3] containing a 4-methoxymethylphenyl group and R = H, CH3, C2H5, n-C3H7, C6H5, 4-CH3OC6H4, 4-CF3C6H4, and CF3, respectively, are generated in the ion source by 70eV electron impact induced dissociation of the benzylic alcohols 1—10. The ions a—i may dissociate to yiled acylium ions of different stability. The spontaneous fragmentations of metastable a—i have been studied by mass-analysed ion kinetic energy spectrometry and the reactions observed generally agree with the mechanisms suggested before for similar protonated aromatic ketones. In particular, these ions form intermediate ion/neutral complexes consisting of an acylium ion RCO+ and a benzyl methyl ether molecule, and fragment by an internal ion/molecule reaction generating C7H+7 and RCOOCH3 as well as by a direct dissociation releasing RCO+. By varying R it is shown that the competition between these fragmentations of metastable ions depends strongly on the stability of RCO+. In the case of carbonyl protonated benzophenones the proton migrates predominantly to the more basic (substituted) phenyl group. Labelling experiments show that a proton transfer between the two phenyl groups of the protonated benzophenones does not occur.