carbo‐Naphthalene: A Polycyclic carbo‐Benzenoid Fragment of α‐Graphyne

A ring carbo‐mer of naphthalene, C₃₂Ar₈ (Ar=p‐n‐pentylphenyl), has been obtained as a stable blue chromophore, after a 19‐step synthetic route involving methods inspired from those used in the synthesis of carbo‐benzenes, or specifically devised for the present target, like a double Sonogashira‐type coupling reaction. The last step is a SnCl₂/HCl‐mediated reduction of a decaoxy‐carbo‐decalin, which is prepared through successive [8+10] macrocyclization steps. Two carbo‐benzene references are also described, C₁₈Ar₆ and o‐C₁₈Ar₄(C≡C‐SiiPr₃)₂. The carbo‐naphthalene bicycle is locally aromatic according to structural and magnetic criteria, as revealed by strong diatropic ring current effects on the deshielding of ¹H nuclei of the Ar groups and on the negative value of the DFT‐calculated NICS at the center of the C₁₈ rings (?12.8 ppm). The stability and aromaticity of this smallest fused molecular fragment of α‐graphyne allows prediction of the same properties for the carbon allotrope itself.     

Synthesis and Chloride Affinity of Sterically Demanding Ditopic Lithium Bis(pyrazol‐1‐yl)borates

The synthesis and full characterization of the sterically demanding ditopic lithium bis(pyrazol‐1‐yl)borates Li₂[p‐C₆H₄(B(Ph)pz^R₂)₂] is reported (pz^R = 3‐phenylpyrazol‐1‐yl ( 3 ^Ph), 3‐t‐butylpyrazol‐1‐yl ( 3 ^tBu)). Compound 3 ^Ph crystallizes from THF as THF‐adduct 3 ^Ph(THF)₄ which features a straight conformation with a long Li···Li distance of 12.68(1) Å. Compound 3 ^tBu was found to function as efficient and selective scavenger of chloride ions. In the presence of LiCl it forms anionic complexes [ 3 ^tBuCl]⁻ with a central Li‐Cl‐Li core (Li···Li = 3.75(1) Å).     

Formation and Reactivity of an Aluminabenzene Ligand at Pentadienyl‐Supported Rare‐Earth Metals

The half‐open rare‐earth‐metal aluminabenzene complexes [(1‐Me‐3,5‐tBu₂‐C₅H₃Al)(μ‐Me)Ln(2,4‐dtbp)] (Ln=Y, Lu) are accessible via a salt metathesis reaction employing Ln(AlMe₄)₃ and K(2,4‐dtbp). Treatment of the yttrium complex with B(C₆F₅)₃ and tBuCCH gives access to the pentafluorophenylalane complex [{1‐(C₆F₅)‐3,5‐tBu₂‐C₅H₃Al}{μ‐C₆F₅}Y{2,4‐dtbp}] and the mixed vinyl acetylide complex [(2,4‐dtbp)Y(μ‐η¹:η³‐2,4‐tBu₂‐C₅H₄)(μ‐CCtBu)AlMe₂], respectively.     

Molecular and Silica‐Supported Mo and W d0 Imido‐Methoxybenzylidene Complexes: Structure and Metathesis Activity

5‐Coordinated methoxybenzylidene complexes M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3)₂ (Ar=2,6‐ⁱPr₂C₆H₃; ^tBu_F3=CMe₂(CF₃)) of Mo ( 1m_Mo ) and W ( 1m_W ) were synthesized by cross‐metathesis from the corresponding neophylidene/neopentylidene precursors and o‐methoxystyrene. 1m_Mo and 1m_W were grafted onto the surface of silica partially dehydroxylated at 700 °C to give well‐defined silica‐supported alkylidenes (≡SiO)M(=NAr)(=CH?C₆H₄?o‐OMe)(O^tBu_F3) (M=Mo ( 1_Mo ), W ( 1_W )). Supported methoxybenzylidene complexes were tested in metathesis of cis‐4‐nonene, 1‐nonene, and ethyl oleate, and compared to their molecular precursors and supported classical analogs (≡SiO)M(=NAr)(=CHCMe₂R)(O^tBu_F3) (M=Mo, R=Ph ( 2_Mo ), M=W, R=Me ( 2_W )). Both grafted complexes 1_Mo and 1_W show significantly better performance as compared to their molecular precursors 1m_Mo and 1m_W but are less efficient than the classical 4‐coordinated alkylidenes 2_Mo and 2_W . Noteworthy, both 1_Mo and 1_W can reach equilibrium conversion in metathesis of cis‐4‐nonene at catalyst loadings as low as 50 ppm.     

Rare‐Earth‐Metal–Hydrocarbyl Complexes Bearing Linked Cyclopentadienyl or Fluorenyl Ligands: Synthesis,Catalyzed Styrene Polymerization,and Structure–Reactivity Relationship

A series of rare‐earth‐metal–hydrocarbyl complexes bearing N‐type functionalized cyclopentadienyl (Cp) and fluorenyl (Flu) ligands were facilely synthesized. Treatment of [Y(CH₂SiMe₃)₃(thf)₂] with equimolar amount of the electron‐donating aminophenyl‐Cp ligand C₅Me₄H‐C₆H₄‐o‐NMe₂ afforded the corresponding binuclear monoalkyl complex [({C₅Me₄‐C₆H₄‐o‐NMe(μ‐CH₂)}Y{CH₂SiMe₃})₂] ( 1 a ) via alkyl abstraction and C? H activation of the NMe₂ group. The lutetium bis(allyl) complex [(C₅Me₄‐C₆H₄‐o‐NMe₂)Lu(η³‐C₃H₅)₂] ( 2 b ), which contained an electron‐donating aminophenyl‐Cp ligand, was isolated from the sequential metathesis reactions of LuCl₃ with (C₅Me₄‐C₆H₄‐o‐NMe₂)Li (1 equiv) and C₃H₅MgCl (2 equiv). Following a similar procedure, the yttrium‐ and scandium–bis(allyl) complexes, [(C₅Me₄‐C₅H₄N)Ln(η³‐C₃H₅)₂] (Ln=Y ( 3 a ), Sc ( 3 b )), which also contained electron‐withdrawing pyridyl‐Cp ligands, were also obtained selectively. Deprotonation of the bulky pyridyl‐Flu ligand (C₁₃H₉‐C₅H₄N) by [Ln(CH₂SiMe₃)₃(thf)₂] generated the rare‐earth‐metal–dialkyl complexes, [(η³‐C₁₃H₈‐C₅H₄N)Ln(CH₂SiMe₃)₂(thf)] (Ln=Y ( 4 a ), Sc ( 4 b ), Lu ( 4 c )), in which an unusual asymmetric η³‐allyl bonding mode of Flu moiety was observed. Switching to the bidentate yttrium–trisalkyl complex [Y(CH₂C₆H₄‐o‐NMe₂)₃], the same reaction conditions afforded the corresponding yttrium bis(aminobenzyl) complex [(η³‐C₁₃H₈‐C₅H₄N)Y(CH₂C₆H₄‐o‐NMe₂)₂] ( 5 ). Complexes 1 – 5 were fully characterized by ¹H and ¹³C NMR and X‐ray spectroscopy, and by elemental analysis. In the presence of both [Ph₃C][B(C₆F₅)₄] and AliBu₃, the electron‐donating aminophenyl‐Cp‐based complexes 1 and 2 did not show any activity towards styrene polymerization. In striking contrast, upon activation with [Ph₃C][B(C₆F₅)₄] only, the electron‐withdrawing pyridyl‐Cp‐based complexes 3 , in particular scandium complex 3 b , exhibited outstanding activitiy to give perfectly syndiotactic (rrrr >99 %) polystyrene, whereas their bulky pyridyl‐Flu analogues ( 4 and 5 ) in combination with [Ph₃C][B(C₆F₅)₄] and AliBu₃ displayed much‐lower activity to afford syndiotactic‐enriched polystyrene.     

Synthesis and oxidative degradation of poly(ethene‐ran‐1,3‐butadiene)

Copolymerization of ethene and 1,3‐butadiene was conducted over SiO₂‐supported CpTiCl₃ catalyst using Ph₃CB(C₆F₅)₄ or B(C₆F₅)₃ combined with triisobutylaluminium (ⁱBu₃Al) or trioctylaluminium (Oct₃Al). When the copolymerization was carried out at 0°C, the Ph₃CB(C₆F₅)₄/ⁱBu₃Al and B(C₆F₅)₃/Oct₃Al systems selectively produced copolymers which contained about 0.5–2.5 mol‐% of trans‐1,4‐inserted butadiene units. The number‐average molecular weight (M_n) of the copolymers was around 80 000 with polydispersities in the range from 6 to 8. Oxidative degradation of the vinylene units with potassium permanganate decreased the M_n values to several thousands with polydispersities of ca. 2. This indicates that the butadiene units are randomly distributed in the copolymers. NMR analysis clarified that the decomposed product is a polyethene with carboxyl groups at both chain ends.     

(Di‐tert‐butylmethylphosphane)(η2‐di‐tert‐butylphosphanylphosphinidene)(triphenylphosphane)platinum(0)

The crystal structure of the title compound, [Pt(C₈H₁₈P₂)(C₉H₂₁P)(C₁₈H₁₅P)] or [(Ph₃P)(^tBu₂PMe)Pt(η²‐^tBu₂PP)], contains four molecules in the asymmetric unit with slightly different conformations. The P—P distances in the ^tBu₂PP ligands are similar for all four molecules [2.0661 (13)–2.0678 (13) Å] and indicate a multiple character of the P—P bond in the ^tBu₂PP ligand. Molecules of the asymmetric unit can be assembled into a tetrahedron that fulfils the requirements for a rhombic disphenoid. The coordination of the Pt atom in all four molecules is square planar, with r.m.s. deviations from the PtP₄ planes in the range 0.03–0.05 Å. All planes of the PtP₄ groups are approximately parallel to the ab plane of the unit cell. The structure represents an unusual unsymmetrical platinum phosphinidene derivative.     

Ligand Substitution Reactions on Aquapentachloro‐ and Hexachloroplatinic Acid — Synthesis and Characterization of Tetrachloroplatinum(IV) Complexes with Heterocyclic N,N Donors

Reactions of aquapentachloroplatinic acid, (H₃O)[PtCl₅(H₂O)]·2(18C6)·6H₂O ( 1 ) (18C6 = 18‐crown‐6), and H₂[PtCl₆]·6H₂O ( 2 ) with heterocyclic N, N donors (2, 2′‐bipyridine, bpy; 4, 4′‐di‐tert‐butyl‐2, 2′‐bipyridine, tBu₂bpy; 1, 10‐phenanthroline, phen; 4, 7‐diphenyl‐1, 10‐phenanthroline, Ph₂phen; 2, 2′‐bipyrimidine, bpym) afforded with ligand substitution platinum(IV) complexes [PtCl₄(N∩N)] (N∩N = bpy, 3a ; tBu₂bpy, 3b ; Ph₂phen, 5 ; bpym, 7 ) and/or with protonation of N, N donor yielding (R₂phenH)₂[PtCl₆] (R = H, 4a ; Ph, 4b ) and (bpymH)⁺ ( 8 ). With UV irradiation Ph₂phen and bpym reacted with reduction yielding platinum(II) complexes [PtCl₂(N∩N)] (N∩N = Ph₂phen, 6 ; bpym, 9 ). Identities of all complexes were established by microanalysis as well as by NMR (¹H, ¹³C, ¹⁹⁵Pt) and IR spectroscopic investigations. Molecular structures of [PtCl₄(bpym)]·MeOH ( 7 ) and [PtCl₂(Ph₂phen)] ( 6 ) were determined by X‐ray diffraction analyses. Differences in reactivity of bpy/bpym and phen ligands are discussed in terms of calculated structures of complexes [PtCl₅(N∩N)]^— with monodentately bound N, N ligands (N∩N = bpy, 10a ; phen, 10b ; bpym, 10c ).     

Titanium and Zirconium Complexes with Non‐Salicylaldimine‐Type Imine–Phenoxy Chelate Ligands: Syntheses,Structures, and Ethylene‐Polymerization Behavior

New Ti and Zr complexes that bear imine–phenoxy chelate ligands, [{2,4‐di‐tBu‐6‐(RCH=N)‐C₆H₄O}₂MCl₂] ( 1 : M=Ti, R=Ph; 2 : M=Ti, R=C₆F₅; 3 : M=Zr, R=Ph; 4 : M=Zr, R=C₆F₅), were synthesized and investigated as precatalysts for ethylene polymerization. ¹H NMR spectroscopy suggests that these complexes exist as mixtures of structural isomers. X‐ray crystallographic analysis of the adduct 1 ?HCl reveals that it exists as a zwitterionic complex in which H and Cl are situated in close proximity to one of the imine nitrogen atoms and the central metal, respectively. The X‐ray molecular structure also indicates that one imine phenoxy group with the syn C?N configuration functions as a bidentate ligand, whereas the other, of the anti C?N form, acts as a monodentate phenoxy ligand. Although Zr complexes 3 and 4 with methylaluminoxane (MAO) or [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ displayed moderate activity, the Ti congeners 1 and 2 , in association with an appropriate activator, catalyzed ethylene polymerization with high efficiency. Upon activation with MAO at 25 °C, 2 displayed a very high activity of 19900 (kg PE) (mol Ti)^?1 h^?1, which is comparable to that for [Cp₂TiCl₂] and [Cp₂ZrCl₂], although increasing the polymerization temperature did result in a marked decrease in activity. Complex 2 contains a C₆F₅ group on the imine nitrogen atom and mediated nonliving‐type polymerization, unlike the corresponding salicylaldimine‐type complex. Conversely, with [Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ activation, 1 exhibited enhanced activity as the temperature was increased (25–75 °C) and maintained very high activity for 60 min at 75 °C (18740 (kg PE) (mol Ti)^?1 h^?1). ¹H NMR spectroscopic studies of the reaction suggest that this thermally robust catalyst system generates an amine–phenoxy complex as the catalytically active species. The combinations 1 /[Ph₃C]⁺[B(C₆F₅)₄]^?/AliBu₃ and 2 /MAO also worked as high‐activity catalysts for the copolymerization of ethylene and propylene.     

Nitric Oxide Insertion Reactivity with the Bismuth–Carbon Bond: Formation of the Oximate Anion, [ON(C6H2tBu2O)]−, from the Oxyaryl Dianion, (C6H2tBu2O)2−

The first example of NO insertion into a Bi?C bond has been found in the direct reaction of NO with a Bi³⁺ complex of the unusual (C₆H₂tBu₂‐3,5‐O‐4)^2? oxyaryl dianionic ligand, namely, Ar′Bi(C₆H₂tBu₂‐3,5‐O‐4) [Ar′=2,6‐(Me₂NCH₂)₂C₆H₃] ( 1 ). The oximate complexes [Ar′Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O)]₂(μ‐O) ( 3 ) and Ar′Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O)₂ ( 4 ) were formed as a mixture, but can be isolated in pure form by reaction of NO with a Bi³⁺ complex of the [O₂C(C₆H₂tBu₂‐3‐5‐O‐4]^2? oxyarylcarboxy dianion, namely, Ar′Bi[O₂C(C₆H₂tBu₂‐3‐5‐O‐4)‐κ²O,O’]. Reaction of 1 with Ph₃CSNO gave an oximate product with (Ph₃CS)^1? as an ancillary ligand, (Ph₃CS)(Ar′)Bi(ONC₆H₂‐3,5‐tBu₂‐4‐O) ( 5 ).     

New Strategies to Phosphino–Phosphonium Cations and Zwitterions

By employing strategies based on frustrated Lewis pair chemistry, new routes to phosphino‐phosphonium cations and zwitterions have been developed. B(C₆F₅)₃ is shown to react with H₂ and P₂tBu₄ to effect heterolytic hydrogen activation yielding the phosphino‐phosphonium borate salt [(tBu₂P)PHtBu₂] [HB(C₆F₅)₃] ( 1 ). Alternatively, alkenylphosphino‐phosphonium borate zwitterions are accessible by reaction of B(C₆F₅)₃ and PhC?CH with P₂Ph₄, P₄Cy₄, or P₅Ph₅ affording the species [(Ph₂P)P(Ph)₂C(Ph)?C(H)B(C₆F₅)₃] ( 2 ), [(P₃Cy₃)P(Cy)C(Ph)?C(H)B(C₆F₅)₃] ( 3 ), and [(P₄Ph₄)P(Ph)C(Ph)?C(H)B(C₆F₅)₃] ( 4 ). A related phosphino‐phosphonium borate species—[(Ph₄P₄)P(Ph)C₆F₄B(F)(C₆F₅)₂] ( 5 ) is also isolated from the thermolysis of B(C₆F₅)₃ and P₅Ph₅.     

New Homoleptic Rare Earth 3,5‐Diphenylpyrazolates and 3,5‐Di‐tert‐butylpyrazolates and a Noteworthy Structural Discontinuity

Direct thermally induced reactions between rare earth metals (Ln = Y,Ce, Dy, Ho, and Er) activated by Hg metal and 3,5‐diphenylpyrazole (Ph₂pzH) or 3,5‐di‐tert‐butylpyrazole (tBu₂pzH) yielded either homoleptic complexes [Ln_n(R₂pz)_3n] or a heteroleptic complex [Ln(Ph₂pz)₃(Ph₂pzH)₂] From Ph₂pzH, [Ce₃(Ph₂pz)₉], [Dy₂(Ph₂pz)₆], [Ho₂(Ph₂pz)₆], and [Y(Ph₂pz)₃(Ph₂pzH)₂] were isolated. The first has a bowed trinuclear Ce₃ backbone with two η² pyrazolate ligands on the terminal metal atoms and one on the middle, and bridging by both μ‐η²:η² and μ‐η²:η⁵ ligands between the terminal and the central Ce atoms. Although both the Dy and Ho complexes are dinuclear, the former has the rare μ‐η²:η¹ bridging whilst the latter has μ‐η²:η² bridging. Thus the dysprosium complex is seven‐coordinate and the holmium is eight‐coordinate, in contrast to any correlation with Ln³⁺ ionic radii, and the series has a remarkable structural discontinuity. The heteroleptic Y complex is eight coordinate with three chelating Ph₂pz and two transoid unidentate Ph₂pzH ligands. From tBu₂pzH, dimeric [Ln₂(tBu₂pz)₄] (Ln = Ce, Er) were isolated and are isomorphous with eight coordinate Ln atoms ligated by two chelating terminal tBu₂pz and two μ‐η²:η² tBu₂pz donor groups. They are also isomorphous with previously reported La, Nd, Yb, and Lu complexes.     

Carbo‐biphenyls and Carbo‐terphenyls: Oligo(phenylene ethynylene) Ring Carbo‐mers

Ring carbo‐mers of oligo(phenylene ethynylene)s (OPEn, n=0–2), made of C₂‐catenated C₁₈ carbo‐benzene rings, have been synthesized and characterized by NMR and UV‐vis spectroscopy, crystallography and voltammetry. Analyses of crystal and DFT‐optimized structures show that the C₁₈ rings preserve their individual aromatic character according to structural and magnetic criteria (NICS indices). Carbo‐terphenyls (n=2) are reversibly reduced at ca. ?0.42 V/SCE, i.e. 0.41 V more readily than the corresponding carbo‐benzene (?0.83 V/SCE), thus revealing efficient inter‐ring π‐conjugation. An accurate linear fit of E_1/2^red1 vs. the DFT LUMO energy suggests a notably higher value (?0.30 V/SCE) for a carbo‐quaterphenyl congener (n=3). Increase with n of the effective π‐conjugation is also evidenced by a red shift of two of the three main visible light absorption bands, all being assigned to TDDFT‐calculated excited states, one of them restricting to a HOMO→LUMO main one‐electron transition.     

Promoting Difficult Carbon–Carbon Couplings: Which Ligand Does Best?

A Pd complex, cis‐[Pd(C₆F₅)₂(THF)₂] ( 1 ), is proposed as a useful touchstone for direct and simple experimental measurement of the relative ability of ancillary ligands to induce C?C coupling. Interestingly, 1 is also a good alternative to other precatalysts used to produce Pd⁰L. Complex 1 ranks the coupling ability of some popular ligands in the order P^tBu₃>o‐TolPEWO‐F≈tBuXPhos>P(C₆F₅)₃≈PhPEWO‐F>P(o‐Tol)₃≈THF≈tBuBrettPhos?Xantphos≈PhPEWO‐H?PPh₃ according to their initial coupling rates, whereas their efficiency, depending on competitive hydrolysis, is ranked tBuXPhos≈P^tBu₃≈o‐TolPEWO‐F>PhPEWO‐F>P(C₆F₅)₃?tBuBrettPhos>THF≈P(o‐Tol)₃>Xantphos>PhPEWO‐H?PPh₃. This “meter” also detects some other possible virtues or complications of ligands such as tBuXPhos or tBuBrettPhos.     

A non‐PFT (polymerization filling technique) approach to poly(ethylene‐co‐norbornene)/MWNTs nanocomposites by in situ copolymerization with scandium half‐sandwich catalyst

The in situ synthesis of ethylene‐co‐norbornene copolymers/multi‐walled carbon nanotubes (MWNTs) nanocomposites was achieved by rare‐earth half‐sandwich scandium precursor [Sc(η⁵‐C₅Me₄SiMe₃)(η¹‐CH₂SiMe₃)₂(THF)] (1) activated by [Ph₃C][B(C₆F₅)₄], through a non‐PFT (Polymerization Filling Technique) approach. MWNTs nanocomposites with low aluminum residue were obtained with excellent yields even though small amounts of triisobutylaluminium were needed as scavenger to prevent catalyst poisoning by MWNT impurities. MWNT bundles were disaggregated and highly coated with Poly(ethylene‐co‐norbornene) [P(E‐co‐N)] as revealed by transmission electron microscopy. Interestingly, P(E‐co‐N) copolymers showed T_g over 130 °C as well as norbornene content over 50 mol %; both values were higher than those obtained by the cationic active species in 1 /[Ph₃C][B(C₆F₅)₄]. A series of copolymerization reactions by 1 /[Ph₃C][B(C₆F₅)₄]/AlⁱBu₃ without MWNTs produced copolymers with the same unexpected features. The NMR analysis revealed the presence of rac‐ENNE and rac‐ENNNE sequences. Thus, AlⁱBu₃ changed the stereoirregular alternating copolymer microstructure produced by 1 /[Ph₃C][B(C₆F₅)₄]. We conclude that AlⁱBu₃ is not only a scavenger for CNT impurities, but it reacts with the THF ligand to give coordinatively unsaturated active species. Finally, P(E‐co‐N)/MWNT masterbatches were mixed with commercial TOPAS to produce cyclic olefin copolymer nanocomposites with excellent dispersion of filler. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 47: 5709–5719, 2009     

Catalytic Ammonia Oxidation to Dinitrogen by Hydrogen Atom Abstraction

Catalysts for the oxidation of NH₃ are critical for the utilization of NH₃ as a large‐scale energy carrier. Molecular catalysts capable of oxidizing NH₃ to N₂ are rare. This report describes the use of [Cp*Ru(P^tBu₂N^Ph₂)(¹⁵NH₃)][BAr^F₄], (P^tBu₂N^Ph₂=1,5‐di(phenylaza)‐3,7‐di(tert‐butylphospha)cyclooctane; Ar^F=3,5‐(CF₃)₂C₆H₃), to catalytically oxidize NH₃ to dinitrogen under ambient conditions. The cleavage of six N?H bonds and the formation of an N≡N bond was achieved by coupling H⁺ and e^? transfers as net hydrogen atom abstraction (HAA) steps using the 2,4,6‐tri‐tert‐butylphenoxyl radical (^tBu₃ArO^.) as the H atom acceptor. Employing an excess of ^tBu₃ArO^. under 1 atm of NH₃ gas at 23 °C resulted in up to ten turnovers. Nitrogen isotopic (¹⁵N) labeling studies provide initial mechanistic information suggesting a monometallic pathway during the N???N bond‐forming step in the catalytic cycle.     

From Hexaoxy‐[6]Pericyclynes to Carbo‐Cyclohexadienes,Carbo‐Benzenes,and Dihydro‐Carbo‐Benzenes: Synthesis,Structure, and Chromophoric and Redox Properties

When targeting the quadrupolar p‐dianisyltetraphenyl‐carbo‐benzene by reductive treatment of a hexaoxy‐[6]pericyclyne precursor 3 with SnCl₂/HCl, a strict control of the conditions allowed for the isolation of three C₁₈‐macrocyclic products: the targeted aromatic carbo‐benzene 1 , a sub‐reduced non‐aromatic carbo‐cyclohexadiene 4 A , and an over‐reduced aromatic dihydro‐carbo‐benzene 5 A . Each of them was fully characterized by its absorption and NMR spectra, which were interpreted by comparison with calculated spectra from static structures optimized at the DFT level. According to the nucleus‐independent chemical shift (NICS) value (NICS≈?13 ppm), the macrocyclic aromaticity of 5 A is indicated to be equivalent to that of 1 . This is confirmed by the strong NMR spectroscopic deshielding of the ortho‐CH protons of the aryl substituents, but also by the strong shielding of the internal proton of the endocyclic trans‐CH?CH double bond that results from the hydrogenation of one of the C?C bonds of 3 . Both the aromatics 1 and 5 A exhibit a high crystallinity, revealed by SEM and TEM images, which allowed for a structural determination by using an X‐ray microsource. A good agreement with calculated molecular structures was found, and columnar assemblies of the C₁₈ macrocycles were evidenced in the crystal packing. The non‐aromatic carbo‐cyclohexadiene 4 A is shown to be an intermediate in the formation of 1 from 3 . It exhibits a remarkable dichromism in solution, which is related to the occurrence of two intense bands in the visible region of its UV/Vis spectrum. These properties could be attributed to the dibutatrienylacetylene (DBA) unit that occurs in the three chromophores, but which is not involved in a macrocyclic π‐delocalization in 4 A only. A versatile redox behavior of the carbo‐chromophores is evidenced by cyclic voltammetry and was analyzed by calculation of the ionization potential, electron affinity, and frontier molecular orbitals.     

Reactivity of an Intramolecular Fluorophosphonium Fluoroborate

The reactions of the intramolecular frustrated Lewis pair‐adduct Ph₂PC(p‐Tol)?C(C₆F₅)B(C₆F₅)₂(CNtBu) with XeF₂ gave Ph₂P(F)C(p‐Tol)?C(C₆F₅)B(F)(C₆F₅)₂ ( 3 ). This species reacts with two equivalents of Al(C₆F₅)₃?C₇H₈ producing the salt, [Ph₂P(F)C(p‐Tol)?C(C₆F₅)B(C₆F₅)₂][F(Al(C₆F₅)₃)₂] ( 4 ), whereas reaction with HSiEt₃/B(C₆F₅)₃ gave Ph₂P(F)C(p‐Tol)?C(H)B(C₆F₅)₃ ( 5 ). The photolysis of 3 resulted in aromatization affording the phenanthralene derivative Ph₂P(F)C(p‐Tol(o‐C₆F₄))?CB(F)(C₆F₅)₂ ( 6 ).     

Promoting Difficult Carbon–Carbon Couplings: Which Ligand Does Best?

A Pd complex, cis‐[Pd(C₆F₅)₂(THF)₂] ( 1 ), is proposed as a useful touchstone for direct and simple experimental measurement of the relative ability of ancillary ligands to induce C−C coupling. Interestingly, 1 is also a good alternative to other precatalysts used to produce Pd⁰L. Complex 1 ranks the coupling ability of some popular ligands in the order P^tBu₃>o‐TolPEWO‐F≈tBuXPhos>P(C₆F₅)₃≈PhPEWO‐F>P(o‐Tol)₃≈THF≈tBuBrettPhos≫Xantphos≈PhPEWO‐H≫PPh₃ according to their initial coupling rates, whereas their efficiency, depending on competitive hydrolysis, is ranked tBuXPhos≈P^tBu₃≈o‐TolPEWO‐F>PhPEWO‐F>P(C₆F₅)₃≫tBuBrettPhos>THF≈P(o‐Tol)₃>Xantphos>PhPEWO‐H≫PPh₃. This “meter” also detects some other possible virtues or complications of ligands such as tBuXPhos or tBuBrettPhos.     

Tuning Coordination in s‐Block Carbazol‐9‐yl Complexes

1,3,6,8‐Tetra‐tert‐butylcarbazol‐9‐yl and 1,8‐diaryl‐3,6‐di(tert‐butyl)carbazol‐9‐yl ligands have been utilized in the synthesis of potassium and magnesium complexes. The potassium complexes (1,3,6,8‐tBu₄carb)K(THF)₄ ( 1 ; carb=C₁₂H₄N), [(1,8‐Xyl₂‐3,6‐tBu₂carb)K(THF)]₂ ( 2 ; Xyl=3,5‐Me₂C₆H₃) and (1,8‐Mes₂‐3,6‐tBu₂carb)K(THF)₂ ( 3 ; Mes=2,4,6‐Me₃C₆H₂) were reacted with MgI₂ to give the Hauser bases 1,3,6,8‐tBu₄carbMgI(THF)₂ ( 4 ) and 1,8‐Ar₂‐3,6‐tBu₂carbMgI(THF) (Ar=Xyl 5 , Ar=Mes 6 ). Structural investigations of the potassium and magnesium derivatives highlight significant differences in the coordination motifs, which depend on the nature of the 1‐ and 8‐substituents: 1,8‐di(tert‐butyl)‐substituted ligands gave π‐type compounds ( 1 and 4 ), in which the carbazolyl ligand acts as a multi‐hapto donor, with the metal cations positioned below the coordination plane in a half‐sandwich conformation, whereas the use of 1,8‐diaryl substituted ligands gave σ‐type complexes ( 2 and 6 ). Space‐filling diagrams and percent buried volume calculations indicated that aryl‐substituted carbazolyl ligands offer a steric cleft better suited to stabilization of low‐coordinate magnesium complexes.