Synthesis, Structural Investigation, and Reactivity of Neutral and Cationic Bis(guanidinato)zirconium(IV) Complexes

Abstract

The mono(guanidinato) complex Cp(guan)ZrCl2 (1; guan = η2-(iPrN)2C(NMe2)) was prepared by treatment of CpZrCl3 (Cp = η5-C5H5) with the 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 reaction with 2 equiv of MeMgCl affords the dimethyl derivative Cp(guan)ZrMe2 (3). Insertion of 2 equiv of diisopropylcarbodiimide into the Zr−N bonds of (Me2N)2ZrCl2(THF)2 produces the bis(guanidinato)zirconium dichloride complex (guan)2ZrCl2 (4). Alkylation of 4 with 2 equiv of 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 C 2-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 methide abstraction: neutral complexes (guan)2Zr(OTf)2 (7) and (guan)2Zr(Me)OTf (8), base-free cationic alkyl salts [(guan)2ZrMe][MeB(C6F5)3] (9) and [(guan)2ZrMe][B(C6F5)4] (10), and the dinuclear 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 decoalescence observed at 224 K. Dibenzyl complex 6 undergoes reaction with [Ph3C][B(C6F5)4] in CH2Cl2, yielding the cationic benzyl complex [(guan)2Zr(CH2Ph)][B(C6F5)4] (15). Spectroscopic data imply that the benzyl ligand of 15 adopts an undistorted monodentate coordination mode. Complexes 4, 5, and 10 were found to have low to moderate activities for the polymerization of α-olefins.

Three asymmetric guanidinato metal complexes: Synthesis, crystal structures and their use as pre-catalysts in the Meerwein–Ponndorf–Verley reduction

“…When one equiv 2-propanol was used instead of two equiv 2-propanol in the catalytic system, the lower conversion yield was obtained (Table 4, entries 7, 10). What's more, the catalytic activity of 3 is compatible with the aluminum complex chelated phenoxide system reported by Lin [34b] but is better than other aluminum alkoxide systems (Table 4, entries [11][12][13].…”

“…Elemental analyses were performed on a Vario EL-III instrument. 1 H NMR (300 MHz) and 13 To a stirred solution of diethylamine (0.20 mL, 2.0 mmol) in diethylether (10 mL), n-BuLi (0.91 mL, 2.0 mmol) was added dropwise at 0°C. The resulting mixture was slowly warmed to room temperature for 2 h and then cooled to 0°C, N-(2,6-dimethyl)phenyl-N 0 -phenyl carbodiimide (0.444 g, 2.0 mmol) was added.…”

“…The guanidinato complexes have been applied in many areas, including synthesis [8], coordination chemistry [9] and material science [10,11]. In particular, many complexes containing guanidinato ligands were specifically identified as being excellent initiators or catalysts for various reactions, and especially used to initiate electrophilic polymerization reactions, e.g., guanidinato complexes of neodymium or ytterbium catalyzed the polymerization of styrene [12], zirconium guanidinato complex was used as the initiator of polymerization of a-olefins [13], homoleptic zinc guanidinate initiated the polymerization of lactide [14]. Even more recently, our group explored a series of guanidinatozinc compounds used as the catalysts in the Tishchenko reaction [15a], and Coles's group have also prepared many novel guanidinate compounds of magnesium, such as phosphaguanidinate and bicyclic guanidinate compounds of magnesium [15b,c].…”

Syntheses and structures of non-symmetric guanidinato zirconium and hafnium complexes and their catalytic behavior for ethylene polymerization

“…Beyond the fundamental investigation of guanidinate complexes related to their structural features, some guanidinato complexes have been identified as initiators or catalysts for polymerization reactions, e.g., trimethylene carbonate and its copolymerization with e-caprolactone [2], the polymerization of lactide [3], the polymerization of a-olefins [3], or the polymerization of styrene [4]. Regarding to the complexes of group IVB, the wide investigations have recognized that they could be used as the alternatives of unique cyclopentadienyl species in order to form suitable catalytic sites for the polymerization of a-olefins [5][6][7][8], furthermore, zirconium complexes with co-ligands of amidinato and Cp ring showed some special intramolecular reactivity and extreme activities for the living polymerization of (sterically encumbered) a-olefins at low temperature [9]. Guanidinate-supported titanium imido complexes were prepared and firstly used as a catalyst for alkyne hydroamination [10].…”

Non-Cp type homogeneous catalytic systems for olefin polymerization

“…12. Among amidinate complexes 59, 60 and 61 [153][154][155][156][157][158], EisenÕs systems 59 with MAO were found to produce isotactic polypropylene in the activity of several tens to hundreds kg PP/(mol h atm) [153][154][155] while 61 [157] produces polyethylenes in low activity. b-Diketiminate ligand has been utilized and the activation of its zirconium complexes 62 and 63 with MAO produced polyethylenes in the activities of several tens kg PE/ (mol h) at 75 psi ethylene pressure [159] and several hundreds kg PE/(mol h) 100 psi ethylene pressure [160], respectively.…”