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The previously known anion [(C6F5)3B(mu-OH)B(C6F5)3]- (2) has been prepared by a two-step procedure, involving deprotonation of (C6F5)3BOH2 to give [B(C6F5)3OH]- (1), followed by addition of B(C6F5)3. The solution structure and the dynamics of 2 have been investigated by 1H and 19F NMR spectroscopy. The reaction of [NHEt3]2 with NEt3 resulted in the formation of [NHEt3]+ [(C6F5)3BOH]-, [NHEt3]+ [(C6F5)3BH]-, and (C6F5)3B- (CH2CH=N+ Et2). This indicates that in the presence of a nucleophile anion 2 can dissociate to B(C6F5)3 and 1. The reaction of [HDMAN]2 with 1,8-bis(dimethylamino)naphthalene (DMAN) confirmed this trend. In the presence of water, 2 transformed into the adduct [(C6F5)3BO(H)H...O(H)B(C6F5)3]- (3), containing the borate 1 hydrogen-bonded to a water molecule coordinated to B(C6F5)3. The same compound is formed by treating (C6F5)3BOH2 with 0.5 equiv of a base. A competition study established that for 1 the Lewis acid-base interaction with B(C6F5)3 is about 5 times preferred over H-bonding to (C6F5)3BOH2. The X-ray single-crystal analysis of [2-methyl-3H-indolium]3 provided the first experimental observation of an asymmetric H-bond in the [H3O2]- moiety, the measured O-H and H...O bond distances being significantly different [1.14(2) vs 1.26(2) A]. The reaction of NEt3 with an equimolar mixture of B(C6F5)3 and bis(pentafluorophenyl)borinic acid, (C6F5)2BOH, afforded the novel borinatoborate salt [NHEt3]+ [(C6F5)3BOB(C6F5)2]- ([NHEt3]4). X-ray diffraction showed that the B-O bond distances are significantly shorter than in [(C6F5)3B(mu-OH)B(C6F5)3]-. Variable-temperature 19F NMR revealed high mobility of the five aryl rings, at variance with the more crowded anion 2. 2D NMR correlation experiments showed that in CD2Cl2 the two anions [(C6F5)3BOH]- and [(C6F5)3BH]- form tight ion pairs with [NHEt3]+, in which the NH proton establishes a conventional (BO...HN) or an unconventional (BH...HN), respectively, hydrogen bond with the anion. The diborate anions 2-4, on the contrary, gave loose ion pairs with the ammonium cation, due both to the delocalized anionic charge and to the more sterically encumbered position of the oxygen atoms that should act as H-bond acceptors.

Summary: Sixteen C1‐symmetric zirconocene and one hafnocene complexes bearing the 2,5‐R2‐7H‐cyclopenta[1,2‐b:4,3‐b′]dithiophene ligand (R = H, Me, Et, Ph) linked to a substituted indenyl ligand have been synthesized and tested in propylene polymerization. Most of the C1‐symmetric zirconocenes of this type are highly active in propylene polymerization at low MAO/Zr ratios and produce poly(propylene)s (PP) in a broad range of isotacticity and melting points. The molecular weight and crystallinity of the PPs are strongly dependent upon the type of substituents on the indenyl moiety: PPs with Tm between 75 and 156 °C and viscosity average molecular weights between 100 000 and 400 000 have been obtained at 50–70 °C in liquid propylene.General formula of the indenyl‐based zirconocenes.magnified imageGeneral formula of the indenyl‐based zirconocenes.

The reaction of pyrroles and indoles with B(C(6)F(5))(3) and BCl(3) produces 1:1 B-N complexes containing highly acidic sp(3) carbons, for example, N-[tris(pentafluorophenyl)borane]-5H-pyrrole (1) and N-[tris(pentafluorophenyl)borane]-3H-indole (2), that are formed by a new formal N-to-C hydrogen shift, the mechanism of which is discussed. With some derivatives, restricted rotation around the B-N bond and/or the B-C bonds was observed by NMR techniques, and some rotational barriers were calculated from experimental data. The acidity of the sp(3) carbons in these complexes is shown by their ability to protonate NEt(3), with formation of pyrrolyl- and indolyl-borate ammonium salts. The driving force for this reaction is given by the restoration of the aromaticity of the heterocycle.

The stoichiometric reactions of N-methylpyrrole and N-methylindole with B(C6F5)3 produce the zwitterionic species 2-[tris(pentafluorophenyl)borane]-5H-1-methylpyrrole (3) and 2-[tris(pentafluorophenyl)borane]-3H-1-methylindole (4), in which a C(α)−B bond and an acidic sp3 methylene carbon are formed in the heterocyclic part of the molecule. Both derivatives present a restricted rotation around the C(α)−B and/or B−C6F5 bonds, and their rotational barriers (13.8 and 14.8 kcal mol-1 for 3 and 4, respectively) were calculated from 1H NMR experimental data. A kinetic study of the reaction, carried out by following the conversion by NMR, gave rate constant values (at 298 K in dichloromethane) of 3 × 10-5 and 6 × 10-5 M-1 s-1 for 3 and 4, respectively. Complexes 3 and 4 react quantitatively with triethylamine to give the corresponding triethylammonium salts 5 and 6. Both the zwitterionic complexes and their ammonium salts are efficient activators of Ind2ZrMe2 for the polymerization of ethylene.

Reaction between 7-azaindole and B(C6F5)3 quantitatively yields 7-(C6F5)3B-7-azaindole (4), in which B(C6F5)3 coordinates to the pyridine nitrogen of 7-azaindole, leaving the pyrrole ring unreacted even in the presence of a second equivalent of B(C6F5)3. Reaction of 7-azaindole with H2O-B(C6F5)3 initially produces [7-azaindolium]+[HOB(C6F5)3]- (5) which slowly converts to 4 releasing a H2O molecule. Pyridine removes the borane from the known complexes (C6F5)3B-pyrrole (1) and (C6F5)3B-indole (2), with formation of free pyrrole or indole, giving the more stable adduct (C6F5)3B-pyridine (3). The competition between pyridine and 7-azaindole for the coordination with B(C6F5)3 again yields 3. The molecular structures of compounds 4 and 5 have been determined both in the solid state and in solution and compared to the structures of other (C6F5)3B-N-heterocycle complexes. Two dynamic processes have been found in compound 4. Their activation parameters (DeltaH = 66 (3) kJ/mol, DeltaS = -18 (10) J/mol K and DeltaH = 76 (5) kJ/mol, DeltaS = -5 (18) J/mol K) are comparable with those of other (C6F5)3B-based adducts. The nature of the intramolecular interactions that result in such energetic barriers is discussed.

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The stereomutations in a class of tris(pentafluorophenyl)borane-benzotriazole adducts are investigated by means of variable-temperature 19 F NMR and X-ray crystallography. At low temperature the presence of a pair of conformational enantiomers is confirmed by NMR spectra obtained in a chiral medium. Two different energy barriers, corresponding to an enantiomerization process and a B-N rotation, were observed and their values measured (∆G q ) 10.7 and 12.8 kcal mol -1 in the case of 1). In the case of the bisadduct 3, two conformational diastereoisomers with different populations were detected at low temperature, while only one diastereoisomer is present in the crystalline state.