Silicon-zirconium bond

Halogenated hydrocarbons often bring about substitution at silicon (see Section III,C), but in the case shown in entry 4, Si-Ti (but not Si-Si) bonds are cleaved, and rearrangement to a cyclic Si5 derivative occurs. A radical process is postulated, similar to that observed in Ti-Ge (422) and H-Mn-CO (72) systems. Silicon-zirconium bonds are cleaved in an analogous way (entry 5). 

To examine the reactivity of the silyl-zirconium bond, Mori et al. used Me2PhSiLi instead of Ph2tBuSiLi. A THF solution of Me2PhSiLi 8b (1 equiv.) was added to a THF solution of Cp2ZrCl2 (1 equiv.) and diphenylacetylene 14a (1 equiv.) at -78 °C, and the solution was stirred at room temperature for 3 h. After hydrolysis of the reaction mixture, vinylsilane 15a was obtained in 36% yield along with the starting material 14a in 40% yield. When the reaction mixture was treated with D20, compound 15a-D2 having two deuteriums was obtained. One deuterium was introduced at the vinylic position and the other was incorporated into the methyl proton on the silicon (39% yield, each D content quant.). If insertion of alkyne 14a into the zirconium-carbon bond of lb occurs, vinylsilane 15a should be formed, but in this case only one deu-... 

The reasons why alkynes 14 and 19 having aryl or vinyl groups, respectively, insert into the zirconium-silicon bond of 3, whereas the alkyne 17 having alkyl groups inserts into the carbon-zirconium bond of 3, are still not clear. Presumably, electronic factors are important for the insertion reaction. 

The possible reaction mechanism for the formation of 31 is shown in Scheme 15. Insertion of alkyne 14 into silazirconacyclopropane 3 gives silazirconacyclopentene 22. Then, insertion of carbon monoxide into the carbon-zirconium bond in silazirconacyclopentene 22 gives silazirconacyclohexenone 34, whose carbonyl oxygen would coordinate to zirconium metal. Then the zirconium carbon bond migrates onto silicon to afford oxazirconacyclohexene 36 via 35 [26]. Deuterolysis of 36 would afford 31-D2, which has two deuteriums. 

The main sources of infrared radiation used in spectrophotometers are (1) a nichrome wire wound on a ceramic support, (2) the Nernst glower, which is a filament containing zirconium, thorium and cerium oxides held together by a binder, (3) the Globar, a bonded silicon carbide rod. These are heated electrically to temperatures within the range 1200- 2000 °C when they will glow and produce the infrared radiation approximating to that of a black body. 

H MAS NMR clearly shows five signals at 0.8, 1.9, 4.4, 10.1 and 12.1 ppm. The signals at 0.8, 1.9 and 4.4 are assigned to alkyl fragments bonded to silicon atoms, residual silanol groups on the silica surface and to silicon hydride species, respectively. The two downfield signals at 10.1 and 12.1 ppm are an indication of the presence of two types of zirconium hydride surface species [111]. DQ rotor-synchronized 2D H MAS NMR was used to discriminate these zirconium hydride... 

In particular, they found enhanced bonding between metal surfaces and resins such as acrylics (solvent- and water-based), epoxy chlorinated rubbers, silicones, and polysulphides. It was noted that titanium complexes caused colouration with phenolics, whilst zirconium complexes did not. 

To examine the reactivity of a zirconium-silicon bond, Mori et al. synthesized a zirconium-silicon complex from Cp2ZrCl2 and Ph/BuSiLi (1 equiv.) and investigated the reactivity of this complex [ 14]. Furthermore, they found that the reaction of Cp2ZrCl2 with 2 equivalents of Me2PhSiLi gave disilylzirconocene, which was easily converted into a zirconium-silene complex via /J-hydrogen elimination (Scheme 1) [15]. This is the first example of the formation of an early transition metal-silene complex. In this chapter, the reactivity of the zirconium-silene complex is described. 

These are only few reports on the synthesis and reactivity of complexes having a zirconium-silicon bond. Lappert reported the synthesis of complex lb from Cp2ZrCl2 and Ph3SiLi [16]. Later, Tilley [17] reported the synthesis of complex lc from Cp2ZrCl2 and Al(SiMe3)3 OEt2 [17a].Takahashi [18] and Buchwald [19] independently reported the formation of zirconium-silicon complexes Id and le by treatment of zirconocene coordinated by olefin with silane. Berry [20] and Xue [21] reported the syntheses of complexes If and lg (Scheme 2). 

Little is known about the reactivities of complexes having zirconium-silicon bonds. Reaction of lb with hydrogen chloride afforded triphenylsilane (Scheme 3) [16a]. The insertion of carbon monoxide or isocyanide into a zirconium-silicon bond of lc gave silaacylzirconium complex 4 or iminosilyl-zirconium complex 6 [17b,c]. As for carbon-carbon multiple bonds, ethylene can be inserted into a zirconium-silicon bond of lh [17g],but other multiple... 

A possible reaction course was considered (Scheme 10). The reaction of Cp2ZrCl2 with Me2PhSiLi should give chlorosilyl zirconocene lb. Insertion of alkyne 14a into the zirconium-silicon bond of lb should give 21. Hydrolysis of 21 gives vinylsilane 15a. However, in this case, one deuterium should be incorporated into 15a to give 15a-D, not 15a-D2. 

Since zirconium-silene complex 3 could be easily synthesized in situ, the insertion of various compounds into the zirconium-silicon or zirconium-carbon bonds of silazirconacyclopropane 3 will be investigated in a future study, and it is expected that a novel carbon-carbon or carbon-silicon bond-forming reaction will be developed. 

---