C–H-Bond Activation and Isoprene Polymerization Studies Applying Pentamethylcyclopentadienyl-Supported Rare-Earth-Metal Bis(Tetramethylaluminate) and Dimethyl Complexes

As previously shown for lutetium and yttrium, 1,2,3,4,5-pentamethylcyclopentadienyl (C5Me5 = Cp*)-bearing rare-earth metal dimethyl half-sandwich complexes [Cp*LnMe2]3 are now also accessible for holmium, dysprosium, and terbium via tetramethylaluminato cleavage of [Cp*Ln(AlMe4)2] with diethyl ether (Ho, Dy) and tert-butyl methyl ether (TBME) (Tb). C–H-bond activation and ligand redistribution reactions are observed in case of terbium and are dominant for the next larger-sized gadolinium, as evidenced by the formation of mixed methyl/methylidene clusters [(Cp*Ln)5(CH2)(Me)8] and metallocene dimers [Cp*2Ln(AlMe4)]2 (Ln = Tb, Gd). Applying TBME as a “cleaving” reagent can result in both TBME deprotonation and ether cleavage, as shown for the formation of the 24-membered macrocycle [(Cp*Gd)2(Me)(CH2OtBu)2(AlMe4)]4 or monolanthanum complex [Cp*La(AlMe4){Me3Al(CH2)OtBu}] and monoyttrium complex [Cp*Y(AlMe4)(Me3AlOtBu)], respectively. Complexes [Cp*Ln(AlMe4)2] (Ln = Ho, Dy, Tb, Gd) and [Cp*LnMe2]3 (Ln = Ho, Dy) are applied in isoprene and 1,3-butadiene polymerization, upon activation with borates [Ph3C][B(C6F5)4] and [PhNHMe2][B(C6F5)4], as well as borane B(C6F5)3. The trans-directing effect of AlMe3 in the binary systems [Cp*Ln(AlMe4)2]/borate is revealed and further corroborated by the fabrication of high-cis-1,4 polybutadiene (97%) with “aluminum-free” [Cp*DyMe2]3/[Ph3C][B(C6F5)4]. The formation of multimetallic active species is supported by the polymerization activity of pre-isolated cluster [(Cp*Ho)3Me4(CH2)(thf)2].

Thermodynamic versus kinetic control in substituent redistribution reactions of silylium ions steered by the counteranion

Substituent exchange reactions of silylium ions can be steered in opposite directions. The judicious choice of the hydrosilane and the counteranion enables the selective formation of either triaryl- or trialkylsilylium ions.

Crystal Structure and NQR Studies of Compounds (RH)[ZnBr3(R)], (RH)2[ZnBr4] and [ZnBr2(R)2] (R = Py, n-MePy: n = 2, 3, 4); on the Dominant Stability of the Monoanionic Complexes over the Dianionic and Neutral Species

The monoanionic complexes (C5H5NH)[ZnBr3(C5H5N)] (1) and (n-CH3C5H4NH)[ZnBr3(n- CH3C5H4N)] (n = 2 (2), 3 (3), 4 (4)) were prepared by crystallization from ethanol solutions through redistribution reactions between the corresponding dianionic complexes (C5H5NH)2[ZnBr4] (5) and (n-CH3C5H4NH)2[ZnBr4] (n = 2, 3 (6), 4 (7)) and the neutral complexes [ZnBr2(C5H5N)2] (10) and [ZnBr2(n-CH3C5H4N)2] (n = 2 (8), 3, 4 (9)). The crystal structures of 1, 4, 9, and 10 were determined; 1: triclinic, P1, a = 7.6957(5), b = 7.7975(4), c = 12.4768(8) Å , α = 90.857(5), β = 95.917(5), γ = 107.899(6)°, Z = 2, 150 K; 4: monoclinic, P21/c, a = 14.8369(6), b = 13.9504(5), c = 8.0041(3) Å , β = 96.318(4)°, Z = 4, 299 K; 9: monoclinic, P21/c, a = 14.2883(5), b = 8.0269(3), c = 13.6031(5) Å , β = 100.581(4)°, Z = 4, 150 K; 10: monoclinic, P21/c, a = 8.7388(5), b = 17.9730(10), c = 8.5452(5) Å , β = 100.024(6)°, Z = 4, 300 K. The cation and anion are paired up via bifurcated hydrogen bonds in the structure of 1 and via a normal N-H· · ·Br hydrogen bond in the structure of 4. 81Br NQR resonance lines coinciding in number with the Br atoms in the chemical formulae were observed for the compounds 1 - 5 and 7 - 9 throughout the temperature range from 77 to ca. 320 K. The comparison between the net charges on the Br atoms obtained by the Townes-Daily analysis or by the Mulliken population analysis seems to indicate that the formation of the intermolecular N-H· · ·Br hydrogen bonds and the π-π and the CH3-π interactions in the crystal structures of the monoanionic complexes are the driving forces to the redistribution reactions

Synthesis and Solid-state Structures of 1,3- and 1,4-Bis(diethylgallyl) benzene

The compounds 1,3-bis(diethylgallyl)benzene (3) and 1,4- bis(diethylgallyl)benzene (6) were prepared by reaction of the corresponding chloromercuriobenzenes with an excess of triethylgallium by applying pressure and higher temperatures. These compounds very easily undergo redistribution reactions in solution and in the solid state. Extremely air-sensitive crystals suitable for an X-ray crystal structure analysis were obtained from triethylgallium as solvent. The structural studies revealed the presence of tetra-coordinated carbon and gallium atoms in symmetric aryl-diethylgallyl bridging units. The coordination behavior of 3 and 6 in the solid state is quite different from that of the corresponding methyl-substituted compounds

Hafnium–phosphinimide complexes

A series of phosphinimide complexes of Hf are prepared and characterized. Reaction of the phosphinimine t-Bu3PNH with Hf(NEt2)4 gave (t-Bu3PN)Hf(NEt2)3 (1) but this species was not readily converted to the corresponding HfCl3-derivative. The reaction of 2 equiv. of t-Bu3PNH with Hf(NEt2)4, however, gave (t-Bu3PN)2Hf(NEt2)2 (2), which was readily converted to (t-Bu3PN)2HfCl2 (3) and (t-Bu3PN)2HfMe2 (4). Employing t-Bu3PNLi and HfCl4 afforded (t-Bu3PN)3HfCl (5) while reaction with CpHfCl3 gave rise to ligand redistribution reactions affording (t-Bu3PN)2HfCl2 and Cp2HfCl2. However, Cp(t-Bu3PN)2HfCl (7) was prepared by treating (t-Bu3PN)2HfCl2 with CpNa. The related species of Cp2(t-Bu3PN)HfCl (8) was synthesized by the reaction of Cp2HfCl2 and t-Bu3PNLi. Ligand redistribution was avoided in the reaction of Cp*HfCl3 as Cp*(t-Bu3PN)HfCl2 (9) and Cp*(i-Pr3PN)HfCl2 (10) were readily obtained and derivatized as Cp*(t-Bu3PN)Hf(NMe2)2 (11) and Cp*(t-Bu3PN)HfMe2 (12), respectively. Similarly, ((Me3Si)2C5H3)(t-Bu3PN)HfCl2 (13) was converted to ((Me3Si)2C5H3)(t-Bu3PN)HfMe2 (14). Reactions with Lewis acid activators were used to prepare Cp*(t-Bu3PN)HfMe(THF)MeB(C6F5)3 (15), (Cp*(t-Bu3PN)HfMe)(B(C6F5)4) (16), and (t-Bu3PN)2Hf(H2B(C6F5)2)2 (17). Preliminary testing of 3, 9, and 13 in ethylene polymerization is reported. Compounds 3, 4, 7, 9, and 17 are characterized crystallographically.