Diversity in Weakly Coordinating Anions. Mono- and Polynuclear Halo(perfluoroaryl)metalates as Cocatalysts for Stereospecific Olefin Polymerization:  Synthesis, Structure, and Reactivity

Abstract

A series of mononuclear and polynuclear trityl (perfluoroaryl)borate, -aluminate, and -gallate reagents, potential cocatalysts/activators for metallocene-mediated olefin polymerization, have been synthesized via fluoride abstraction from trityl fluoride (Ph3CF) by the organo Lewis acid reagents B(C6F5)3 (1), B(o-C6F5C6F4)3 (2), and Al(C6F5)3 (3), by derivatization of Ph3C+FAl(o-C6F5C6F4)3 - (4), and by reaction of trityl fluoride with in situ generated Ga(C6F5)3 (5). Reaction of trityl fluoride with the tris(perfluoroaryl)boranes 1 and 2 yields the trityl tris(perfluoroaryl)fluoroborates Ph3C+FB(C6F5)3 - (6) and Ph3C+FB(o-C6F5C6F4)3 - (7), respectively. The three trityl tris(perfluorophenyl)fluoroaluminates (Ph3C+) x F x [Al(C6F5)3] y x - (x = 1, y = 1, 8; x = 1, y = 2, 9; x = 2, y = 3, 10) can be isolated from the reaction of trityl fluoride with the tris(perfluoroaryl)alane 3 in the appropriate molar ratios. Reaction of the trityl tris(perfluoroaryl)fluoroaluminate 4 with 3 affords the asymmetric fluoro-bridged trityl bis[tris(perfluoroaryl)]aluminate Ph3C+(C6F5)3AlFAl(o-C6F5C6F4)3 - (11), while reaction of the trityl halides Ph3CCl and Ph3CBr with 3 gives the corresponding trityl tris(perfluorophenyl)haloaluminates Ph3C+XAl(C6F5)3 - (X = Cl, 12; X = Br, 13). The isolable, symmetric fluoro-bridged trityl bis[tris(perfluoroaryl)]gallate Ph3C+F[Ga(C6F5)3]2 - (14) is derived from a “one-pot” reaction of trityl fluoride with Ga(C6F5)3, generated in situ from 4 + Ga(CH3)3. Of these new species, compounds 7 and 10−14 were characterized by single-crystal X-ray diffraction. Trityl salts 6−13 react with the C s-symmetric metallocene precatalyst Me2C(Cp)(Flu)ZrMe2 (15: Cp = C5H4; Flu = C13H8, fluorenyl) to form isolable ion-pair complexes or characterizable mixtures. Species 6 reacts with 15 to generate the known ion pair Me2C(Cp)(Flu)ZrMe+MeB(C6F5)3 - (16), and reaction of 7 with 15 gives the fluoro-bridged dimeric diastereomers [Me2C(Cp)(Flu)ZrMe]2(μ-F)+FB(o-C6F5C6F4)3 - (17). The trityl tris(perfluorophenyl)fluoroaluminates 8−10 all react with 15 to afford mixtures of Me2C(Cp)(Flu)ZrMe+FAl(C6F5)3 - (18) and diastereomeric [Me2C(Cp)(Flu)ZrMe]2(μ-Me)+(C6F5)3AlFAl(C6F5)3 - (19). Asymmetric species 11 cleanly affords the diastereomeric [Me2C(Cp)(Flu)ZrMe]2(μ-Me)+(C6F5)3AlFAl(o-C6F5C6F4)3 - (20) in reaction with the metallocene 15. Adducts of 12 and 13 with the metallocene 15 afford the decomposition products Me2C(Cp)(Flu)ZrCl(C6F5) (21) and [Me2C(Cp)(Flu)Zr(μ2-Br)]2 2+[Al(C6F5)4 -]2 (22), respectively. Complexes 17−22 were characterized by single-crystal X-ray diffraction.

Taming the Cationic Beast: Novel Developments in the Synthesis and Application of Weakly Coordinating Anions

“…[144][145][146] Ac lear difference between bridged WCAsf eaturing Lewis acids based on aluminum and boron is that aluminum forms the most stable bridged anion with the hard fluoride ligand bridging,w hereas the softer cyanide ligand has been used for the formation of an umber of bridged WCAsb ased upon the B(C 6 F 5 ) 3 Lewis acid. [155,156] [147,148] In an elegant extension, as eries of very large WCAs based upon the general motif [E{CNB(C 6 F 5 ) 3 } n ] À (where E = N, C, or Ba nd n = 2, 3, or 4) have been reported as anumber of synthetically useful salts and their formation also investigated by computational methods.…”

“…[144,155] Ty pical examples include [( F RO) 3 Al-X-Al-(OR F ) 3 ) 2 ] À X = F, [142] Cl, [145] X = OH; [146] [155] and [Ph 3 [155] Fort he Synthesis of Reactive Cations:W ei nclude some recent and exemplary examples highlighting this approach for the formation of reactive cations.S imple halide abstraction from the ruthenium fluoride complexes [Ru(L) 2 (CO) 2 F 2 ] (where L = PPh 3 or NHC) by the Lewis acids BF 3 ,P F 5 ,a nd B(C 6 F 5 ) 3 gives the corresponding fluoride-containing WCAs. Moreover,t his approach is ideally suited to the formation of bridged WCAso ft he type [LA-X-LA] À ,a nd even higher aggregates of bridging species of the type [LA-X-LA-X-LA] À can be formed.…”

“…Since 2004, notable examples of this approach have been reported using the following Lewis acids B(C 6 F 5 ) 3 , [198,210] Al(C 6 F 5 ) 3 , [199,210] Al(OC(CF 3 ) 3 ) 3 , [144,145] Al(OC-(C 5 F 10 )C 6 F 5 ) 3 , [144] Ga(C 6 F 5 ) 3 , [155] and TMS-F-Al(OR F ) 3 (TMS = trimethylsilyl) [211] as well as the triarylboranes FcB-(o-tol) 2 ,F cB(o-Xyl) 2 ,F cBMes 2 , [212,213] PhBMes 2 , [214] or B(o-C 6 F 5 C 6 F 4 ) 3 [155] (where Fc = ferrocene; o-tol = 2-(CH 3 )C 6 H 5 ; oxyl = 2,6-(CH 3 ) 2 C 6 H 4 ;M es = 1,3,5-(CH 3 )C 6 H 4 ).…”

Synthesis and Characterization of Dichlorotitanium Alkoxide Complex and Its Activity in the Polymerization of α-Olefins

“…Extensive studies has focused on improving these coactivators; good results have been reported for methylalumoxane (MAO), 32 perfluoroarylboranes, 33,34 perfluoroarylborates and aluminates, 35,36 or mixtures of alkylaluminum and perfluoroarylborane and borates. [37][38][39] Alkoxides have been considered as alternatives for Cp ligands. The titanium complexes based on these ligands, and among them, those with the general formula Ti(OR) 2 Cl 2 or Ti(OR) 4 have been known for a while and are used as Lewis acid catalysts or at stoichiometric amounts for a wide scope of organic reactions such as hetero-Diels-Alder reactions, Michael additions, and others.…”

Synthesis, characterization and catalytic activity of the complex titanium bis(dimethylmalonate)–bis(diethylamido) in the polymerization of propylene

“…For early transition complexes, the metals generally belong to groups 3 or 4. High activities in the polymerization process can be achieved with the use of co-catalysts such as methylalumoxane (MAO) [5], perfluoroarylboranes [6][7][8], perfluoroarylborates and aluminates [9,10], or mixtures of alkyl aluminum and perfluoroaryl borane and borate [11][12][13]. The polymers obtained by these systems are generally highly stereoregular and display narrow polydispersities.…”