Synthesis, structural investigation, and reactivity of neutral and cationic bis(guanidinato)zirconium(IV) complexes

Citation
Ap. Duncan et al., Synthesis, structural investigation, and reactivity of neutral and cationic bis(guanidinato)zirconium(IV) complexes, ORGANOMETAL, 20(9), 2001, pp. 1808-1819
Citations number
88
Language
INGLESE
art.tipo
Article
Categorie Soggetti
Organic Chemistry/Polymer Science
Journal title
ORGANOMETALLICS
ISSN journal
0276-7333 → ACNP
Volume
20
Issue
9
Year of publication
2001
Pages
1808 - 1819
Database
ISI
SICI code
0276-7333(20010430)20:9<1808:SSIARO>2.0.ZU;2-C
Abstract
The mono(guanidinato) complex Cp(guan)ZrCl2 (1; guan = eta (2)-((PrN)-Pr-i) (2)C(NMe2)) was prepared by treatment of CpZrCl3 (Cp = eta (5)-C5H5) with t he in situ generated lithium guanidinate salt 2. The dimethylamino group of 1 resists quaternization by alkylating and silylating reagents. Complex 1 undergoes ligand redistribution when treated with 2 equiv of MeLi, but reac tion with 2 equiv of MeMgCl affords the dimethyl derivative Cp(guan)ZrMe2 ( 3). Insertion of 3 equiv of diisopropylcarbodiimide into the Zr-N bonds of (Me2N)(2)ZrCl2(THF)(2) produces the bis(guanidinato)zirconium dichloride co mplex (guan)(2)ZrCl2 (ii). Alkylation of 4 with 2 equiv of MeLi or PhCH2MgC l affords the dialkyl derivatives (guan)(2)ZrMe2 (5) and (guan)(2)Zr(CH2-Ph )(2) (6), respectively. Variable-temperature NMR experiments on 6 reveal a limiting C-2-symmetric solution structure at 253 K. Complex 5 undergoes rea ction with electrophiles (Me3SiOTf (OTf = OSO2CF3), B(C6F5)(3), [Ph3C][B(C6 F5)(4)]) to yield stable products of methide abstraction: neutral complexes (guan)(2)Zr(OTf)(2) (7) and (guan)(2)Zr(Me)OTf (8), base-free cationic alk yl salts [(guan)(2)ZrMe][MeB(C6F5)(3)] (9) and [(guan)(2)ZrMe][B(C6F5)(4)] (10), and the dinuclear methyl-bridged cation [((guan)(2)ZrMe)(2)-mu -Me][B (C6F5)(4)] (11). Complexes 1, 4-7, and 11 have been characterized by X-ray diffraction. Dinuclear cation 11 exhibits bridge-terminal methyl exchange o n the NMR time scale at room temperature, with decoalescence observed at 22 4 Ii. Dibenzyl complex 6 undergoes reaction with [Ph3C][B(C6F5)(4)] in CH2C l2, yielding the cationic benzyl complex [(guan)(2)Zr(CH2Ph)][B(C6F5)(4)] ( 15). Spectroscopic data imply that the benzyl ligand of 15 adopts an undist orted monodentate coordination mode. Complexes 4, 5, and 10 were found to h ave low to moderate activities for the polymerization of alpha -olefins.