Synthesis, Structures, and Reactivity of Weakly Coordinating Anions with Delocalized Borate Structure:  The Assessment of Anion Effects in Metallocene Polymerization Catalysts

Abstract

The formation of adducts of tris(pentafluorophenyl)borane with strongly coordinating anions such as CN(-) and [M(CN)(4)](2)(-) (M = Ni, Pd) is a synthetically facile route to the bulky, very weakly coordinating anions [CN[B(C(6)F(5))(3)](2)](-) and [M[CNB(C(6)F(5))(3)](4)](2-) which are isolated as stable NHMe(2)Ph(+) and CPh(3)(+) salts. The crystal structures of [CPh(3)][CN[B(C(6)F(5))(3)](2)] (1), [CPh(3)][ClB(C(6)F(5))(3)] (2), [NHMe(2)Ph](2)[Ni[CNB(C(6)F(5))(3)](4)].2Me(2)CO (4b.2Me(2)CO), [CPh(3)](2)[Ni[CNB(C(6)F(5))(3)](4)].2CH(2)Cl(2) (4c.2CH(2)Cl(2)), and [CPh(3)](2)[Pd[CNB(C(6)F(5))(3)](4)].2CH(2)Cl(2) (5c.2CH(2)Cl(2)) are reported. The CN stretching frequencies in 4 and 5 are shifted by approximately 110 cm(-1) to higher wavenumbers compared to the parent tetracyano complexes in aqueous solution, although the M-C and C-N distances show no significant change on B(C(6)F(5))(3) coordination. Zirconocene dimethyl complexes L(2)ZrMe(2) [L(2) = Cp(2), SBI = rac-Me(2)Si(Ind)(2)] react with 1, 4c or 5c in benzene solution at 20 degrees C to give the salts of binuclear methyl-bridged cations, [(L(2)ZrMe)(2)(mu-Me)][CN[B(C(6)F(5))(3)](2)] and [(L(2)ZrMe)(2)(mu-Me)](2)[M[CNB(C(6)F(5))(3)](4)]. The reactivity of these species in solution was studied in comparison with the known [[(SBI)ZrMe](2)(mu-Me)][B(C(6)F(5))(4)]. While the latter reacts with excess [CPh(3)][B(C(6)F(5))(4)] in benzene to give the mononuclear ion pair [(SBI)ZrMe(+).B(C(6)F(5))(4)(-)] in a pseudo-first-order reaction, k = 3 x 10(-4) s(-1), [(L(2)ZrMe)(2)(mu-Me)][CN[B(C(6)F(5))(3)](2)] reacts to give a mixture of L(2)ZrMe(mu-Me)B(C(6)F(5))(3) and L(2)ZrMe(mu-NC)B(C(6)F(5))(3). Recrystallization of [Cp' '(2)Zr(mu-Me)(2)AlMe(2)][CN[B(C(6)F(5))(3)](2)] affords Cp' '(2)ZrMe(mu-NC)B(C(6)F(5))(3) 6, the X-ray structure of which is reported. The stability of [(L(2)ZrMe)(2)(mu-Me)](+)X(-) decreases in the order X = [B(C(6)F(5))(4)] > [M[CNB(C(6)F(5))(3)](4)] > [CN[B(C(6)F(5))(3)](2)] and increases strongly with the steric bulk of L(2) = Cp(2) << SBI. Activation of (SBI)ZrMe(2) by 1 in the presence of AlBu(i)(3) gives extremely active ethene polymerization catalysts. Polymerization studies at 1-7 bar monomer pressure suggest that these, and by implication most other highly active ethene polymerization catalysts, are strongly mass-transport limited. By contrast, monitoring propene polymerization activities with the systems (SBI)ZrMe(2)/1/AlBu(i)(3) and CGCTiMe(2)/1/AlBu(i)(3) at 20 degrees C as a function of catalyst concentration demonstrates that in these cases mass-transport limitation is absent up to [metal] approximately 2 x 10(-5) mol L(-1). Propene polymerization activities decrease in the order [CN[B(C(6)F(5))(3)](2)](-) > [B(C(6)F(5))(4)](-) > [M[CNB(C(6)F(5))(3)](4)](2-) >> [MeB(C(6)F(5))(3)](-), with differences in activation barriers relative to [CN[B(C(6)F(5))(3)](2)](-) of DeltaDeltaG = 1.1 (B(C(6)F(5))(4)(-)), 4.1 (Ni[CNB(C(6)F(5))(3)](4)(2-)) and 10.7-12.8 kJ mol(-)(1) (MeB(C(6)F(5))(3)(-)). The data suggest that even in the case of very bu...

Reactivity of Metallocene Catalysts for Olefin Polymerization: Influence of Activator Nature and Structure

“…[151 -153] Adducts formed by the coordination of anions such as CN - (64) and [Ni(CN) 4 ] 2-with B(C 6 F 5 ) 3 act as excellent activators for dialkylmetallocenes. [154,155] Very recently, an anion was reported having imidazole fragment 65 as the linking group. [156] The surprising observation that Al(C 6 F 5 ) 3 can abstract both methyl groups in dimethylmetallocene to form the dicationic bis(aluminate) complex 66 was brought to the attention by Chen et al [157] A 30-fold increase in catalytic activity was observed.…”

PGSE NMR Diffusion Overhauser Studies on [Ru(Cp*)(η6‐arene)][PF6], Plus a Variety of Transition‐Metal, Inorganic, and Organic Salts: An Overview of Ion Pairing in Dichloromethane

“…However, a number of reports in the recent literature suggest that the choice of the anion can be important, both in terms of the structure of the salt and its reactivity. [1][2][3][4][5][6][7][8][9][10][11][12][13] Relevant examples include an anion dependence in 1) Diels-Alder catalysis, [1] 2) polymerization chemistry, [2] 3) catalytic hydrogenation, [3] 4) asymmetric ring opening reactions of oxabicyclic alkenes, [4] 5) asymmetric cyclopropanation, [5] and 6) C,H-activation reactions, [6] amongst others. The anions may or may not coordinate to the metal center.…”

Metallocenes

“…11), and a weakly active titanocene catalyst at low temperature (114), respectively. Linked anionic structures such as (Ph 3 C)[(C 6 F 5 ) 3 B-CN-B(C 6 F 5 ) 3 ] are competent metallocene activators (115). Many other noncoordinating anions (116) have been discovered that enable high activity polymerization, including (C 6 F 5 ) 3 B-CN-B(C 6 F 5 ) 3 reactors, metallocene catalyst formulations nearly always comprise a solid support of well-controlled morphology and porosity (118).…”