A variety of donor adducts of tris(pentafluorophenyl)borane were experimentally generated by reaction of a Lewis base with an excess of B(C6F5)3 in pentane. In this way, nitrile complexes (C6F5)3B·NCR (R = CH3 1a, p-CH3−C6H4 1b, p-NO2−C6H4 1c), isonitrile complexes (C6F5)3B·CNR (R = C(CH3)3 3a, C(CH3)2CH2C(CH3)3 3b, 2,6-(CH3)2−C6H3 3c), and the phosphine adduct (C6F5)3B·P(C6H5)3 (6) could be prepared. The compounds were characterized by IR and NMR spectroscopy and by X-ray structure analyses (1a, 1c, 3a, 3b, and 6). Coordination of the nitriles as well as the isonitriles to the neutral Lewis acid leads to a substantial increase in the C⋮N bond strength. This is evident from a marked shift of the ν̃C ⋮ N IR band to higher wavenumbers, and this interpretation is supported by the small but experimentally significant decrease of the C⋮N bond length observed by X-ray diffraction. The experimental work is complemented by a density functional study on the model complexes (C6F5)3B·L, L = CNCH3, NCCH3, PH3, CO. A detailed analysis revealed that the bonding in (C6F5)3B·L complexes is mainly dominated by electrostatic interaction, which in turn is responsible for the observed structural and spectroscopic changes. In the context of this work, the bonding of the neutral B(C6F5)3 Lewis acid is compared to the positively charged organometallic d0-Cp3M+ system (M = Zr, Hf). It was found that electrostatic effects are more pronounced for B(C6F5)3 than for the transition metal fragments. The question as to the existence of a nonclassical main group carbonyl complex, (C6F5)3B·CO, is addressed.

Treatment of the phosphorus ylide Ph 3 PdCH 2 (2a) with B(C 6 F 5 ) 3 (1) yields the adduct Ph 3 P + -CH 2 -B(C 6 F 5 ) 3 -(3a), which was characterized by X-ray crystal structure analysis. The ylide Ph 3 PdCHPh (2b) reacts analogously with B(C 6 F 5 ) 3 at 0 °C to form Ph 3 P + -CHPh-B(C 6 F 5 ) 3 -(3b), but this adduct formation is reversible. Increasing the temperature leads to the formation of Ph 3 P + -CH 2 -(p-C 6 H 4 )-B(C 6 F 5 ) 3 -(4), which is formed by an electrophilic aromatic substitution reaction of the electron-deficient borane reagent at the ylidic phenyl group. Compound 4 is also cleaved upon prolonged thermolysis to eventually yield Ph 3 P + -CHPh-(p-C 6 F 4 )-BF(C 6 F 5 ) 2 -(5), which is the product of thermodynamic control in this series. Compound 5 arises from a nucleophilic aromatic substitution reaction of the nonstabilized phosphorus ylide at a -C 6 F 5 ring of the B(C 6 F 5 ) 3 reagent. Compound 5 was also characterized by an X-ray crystal structure analysis.

No abstract

Addition of methyllithium or p-tolyllithium to the C-6 carbon atom of the lithium (N-phenylformimidoyl)cyclopentadienide reagent 5 resulted in the formation of the dianionic sp3-C1-alkylidene-bridged Cp/amido ligand systems [C5H4−CHR−NPh]2- (6a, R = CH3; 6b, R = p-tolyl; each with Li+ cations). Transmetalation of 6a from lithium to zirconium was achieved by treatment with ZrCl4(THF)2 (7a) to yield the metallacyclic sp3-C1-linked spiro constrained geometry complex (η5-C5H4−CHMe−NPh-κN)2Zr (2a). Treatment of 6a with Cl2Ti(NMe2)2 (7c) gave the alkylidene-bridged Cp/amido titanium complex (η5-C5H4−CHMe−NPh-κN)Zr(NMe2)2 (2b). Analogous treatment of Cl2Zr(NEt2)2(THF)2 (7b) with 6a or 6b furnished the related (CpCN)Zr complexes (C5H4−CHR−NPh)Zr(NEt2)2 (2c, R = CH3; 2d, R = p-tolyl) each in ≥70% yield. The complexes 2a and 2b were both characterized by X-ray crystal structure analyses. The observation that both exhibit Cp(centroid)−M−N angles that are by ca. 10° smaller than those of their respective dimethylsilanediyl-bridged analogues renders the CpCN group metal complexes as more constrained than their conventional (Cp*SiN)M analogues. Lithium 4-methylanilide adds to the C-6 carbon atom of the non-CH-acidic pentafulvene (C5H4)CHCMe3 (13a) to yield Li[C5H4−CH(CMe3)(NH-p-tolyl)] (14a), which was subsequently NH-deprotonated by treatment with LDA to yield the dianionic reagent [C5H4−CH(CMe3)(N-p-tolyl)]2- (6c, as the dilithium compound). Analogous addition of lithium tert-butylamide to 13a, followed by NH-deprotonation by treatment with tert-butyllithium, yielded Li2[C5H4−CH(NCMe3)CMe3] (6d). Lithium tert-butylamide added to 1,2,3,4-tetramethylpentafulvene (13b) to yield Li[C5Me4−CH2−NH(CMe3)] (14c), which was subsequently NH-deprotonated by treatment with tert-butyllithium to yield Li2[C5Me4−CH2N(CMe3)] (6e). Transmetalation of 6c by treatment with Cl2Ti(NMe2)2 (7c) or Cl2Zr(NEt2)2(THF)2 (7b) cleanly gave the respective CpCN group 4 metal complexes [C5H4−CH(CMe3)(N−p-tolyl)]M(NR2)2 (2e, M = Ti; 2f, M = Zr). Similarly, the sp3-C1-bridged “constrained geometry” system [C5H4−CH(CMe3)(NCMe3)]Zr(NEt2)2 (2g) was obtained in good yield (70%) from the reaction of 6d with 7b, and treatment of 6e with 7b furnished the (Cp*CN)Zr complex [C5Me4−CH2−N(CMe3)]Zr(NEt2)2 (2h, 65% isolated). Activation of the (CpCN)M(NR2)2 systems by treatment with a large excess of methylalumoxane in toluene solution gave homogeneous Ziegler−Natta catalysts for the polymerization of ethylene (carried out at 60 °C) and the copolymerization of ethene with 1-octene (at 90 °C).

Pyrrogallolarenes 2 were prepared by acid-catalyzed condensation of pyrrogallol with aldehydes. Compound 2a crystallizes from a methanol solution of quinuclidine hydrochloride to give a dimeric molecular capsule surrounding one disordered quinuclidinium cation. The molecules of 2a are connected by direct hydrogen bonds and by bridging methanol and water molecules. The chloride anion is positioned outside the capsule and is hydrogen bonded to the hydroxy groups of 2a. The shortest distance between the cation and anion was found to be 6.7 A. Crystallization of 2b from aqueous acetonitrile resulted in a dimeric capsule linked by a polar belt of 16 hydrogen bonding water molecules. Four acetonitrile molecules occupy the cavity of this dimeric capsule and assume two binding sites that differ in hydrogen bonding and electronic environment. Compounds 2 also form hydrogen-bonded dimeric molecular capsules in alcohols and aqueous acetonitrile solutions. These assemblies readily encapsulate tetramethylammonium, tetramethylphosphonium, quinuclidinium, and tropylium cations to give complexes stable on the NMR time scale at 233 K.