| Abstract
| - The mono(guanidinato) complex Cp(guan)ZrCl2 (1; guan = η2-(iPrN)2C(NMe2)) was preparedby treatment of CpZrCl3 (Cp = η5-C5H5) with the in situ generated lithium guanidinate salt2. 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 reactionwith 2 equiv of MeMgCl affords the dimethyl derivative Cp(guan)ZrMe2 (3). Insertion of 2equiv of diisopropylcarbodiimide into the Zr−N bonds of (Me2N)2ZrCl2(THF)2 produces thebis(guanidinato)zirconium dichloride complex (guan)2ZrCl2 (4). Alkylation of 4 with 2 equivof MeLi or PhCH2MgCl affords the dialkyl derivatives (guan)2ZrMe2 (5) and (guan)2Zr(CH2Ph)2 (6), respectively. Variable-temperature NMR experiments on 6 reveal a limiting C2-symmetric solution structure at 253 K. Complex 5 undergoes reaction with electrophiles(Me3SiOTf (OTf = OSO2CF3), B(C6F5)3, [Ph3C][B(C6F5)4]) to yield stable products of methideabstraction: neutral complexes (guan)2Zr(OTf)2 (7) and (guan)2Zr(Me)OTf (8), base-freecationic alkyl salts [(guan)2ZrMe][MeB(C6F5)3] (9) and [(guan)2ZrMe][B(C6F5)4] (10), and thedinuclear methyl-bridged cation [((guan)2ZrMe)2-μ-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 on the NMR time scale at room temperature, with decoalescenceobserved at 224 K. Dibenzyl complex 6 undergoes reaction with [Ph3C][B(C6F5)4] inCH2Cl2, yielding the cationic benzyl complex [(guan)2Zr(CH2Ph)][B(C6F5)4] (15). Spectroscopicdata imply that the benzyl ligand of 15 adopts an undistorted monodentate coordinationmode. Complexes 4, 5, and 10 were found to have low to moderate activities for thepolymerization of α-olefins.
- A bis(guanidinato) ancillary ligand set has been used to support neutral and cationic zirconium(IV) complexes, including the unusually thermally stable methylzirconium cation [(guan)ZrMe][B(C6F5)4] (10) and the structurally characterized dinuclear cation [((guan)2ZrMe)2-μ-Me][B(C6F5)4] (11). An X-ray crystallographic study of neutral bis(guanidinato) derivatives (guan)2ZrX2 (X = Cl, Me, CH2Ph, OTf) revealed varying degrees of lone-pair donation from the dimethylamino group of the guanidinato ligand to the metal center.
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