Sigma-bond metathesis reactions of zirconocene alkyl cations with phenylsilane

The zirconocene methyl cations [C5R5)(2)ZrMe(ClC6D5)][B(C6F5)(4)] (C5R5 = C5H5 (1a), C5H4Me (1b)) react with PhSiH3 in the dark to yield [{(C5R5)(2)Zr(mu-H)}(2)][B-3(C6F5)(4)](2) (5a,b) and a mixture of PhxMeyHzSi products. The reaction proceeds by initial Zr-C/Si-H sigma-bond metathesis via a four-center transition state in which Si is to Zr. In the presence of light, significant amounts of [{(C5R5)(2)Zr(mu-Cl)}(2)] [B(C6F5)(4)](2) (4a,b) are formed by photochemical reaction of (C5R5)(2)ZrH+ species with the chlorobenzene solvent. The azazirconacycle [rac-(EBI)Zr{eta(2) (C,N)-CH2CHMe(6-phenyl-2-pyridyl)}] [B(C6F5)(4)] (2, EBI = 1,2-ethylene-bis-indenyl) does not react with PhSiH3 at 23 degrees C. However at 85 degrees C, 2 deinserts propene to afford the eta(2)-pyridyl complex [rac-(EBI)Zr{eta(2)(C,N)-(6-phenyl-2-pyridyl)}][B(C6F5)(4)] (6), which is catalytically isomerized to [rac-(EBI)Zrfq(2)(C,N)-2-(2-pyridyl)phenyl}][B(C6F5)(4)] (7) by PhSiH3. The key step in this process is Zr-C/Si-H Gr-bond metathesis of 6 with PhSiH3 via a transition state in which Si is a to Zr. The less crowded azazirconacycle [CP2Zr{eta(2)(C,N)-CH2CHMe-(6-methyl-2-pyridyl)}] [B(C6F5)(4)] (3) reacts with PhSiH3 directly to afford [{Cp2Zr(SiPhH2)}(2)][B(C6F5)(4)](2) (8) via a transition state in which Si is a to Zr. Steric factors may play a role in determining the selectivity of these reactions.