Alkali-Metal-Alkoxide Powered Zincation of Fluoroarenes Employing Zinc Bis-Amide Zn(TMP)2

Reminiscent of Lochmann-Schlosser superbase recipes, the addition of two molar equivalents of KOtBu to Zn(TMP)₂ (TMP=2,2,6,6-tetramethylpiperidide) transforms this mild zinc bis-amide base to a powerful metalating agent able to perform facile regioselective zincation of a wide range of sensitive fluoroarenes. Structural authentication of the intermediates post Zn−H exchange demonstrates activation of both TMP groups to form a range of higher order bis-aryl potassium zincates, isolable as solids and further functionalized in electrophilic interception reactions. Studies assessing the role of KOtBu reveal that the first equivalent undergoes co-complexation with Zn(TMP)₂, enabling kinetic activation of the amide groups; whereas the second equivalent stabilizes the metalated intermediate preventing ligand redistribution. Showcasing its metalating power, this bimetallic KOtBu/Zn(TMP)₂ partnership, can effect zincation of toluene and benzene at room temperature.     

Structurally Defined Potassium‐Mediated Zincation of Pyridine and 4‐R‐Substituted Pyridines (R=Et,iPr, tBu,Ph, and Me2N) by Using Dialkyl–TMP–Zincate Bases

Two potassium–dialkyl–TMP–zincate bases [(pmdeta)K(μ‐Et)(μ‐tmp)Zn(Et)] ( 1 ) (PMDETA=N,N,N′,N′′,N′′‐pentamethyldiethylenetriamine, TMP=2,2,6,6‐tetramethylpiperidide), and [(pmdeta)K(μ‐nBu)(μ‐tmp)Zn(nBu)] ( 2 ), have been synthesized by a simple co‐complexation procedure. Treatment of 1 with a series of substituted 4‐R‐pyridines (R=Me₂N, H, Et, iPr, tBu, and Ph) gave 2‐zincated products of the general formula [{2‐Zn(Et)₂‐μ‐4‐R‐C₅H₃N}₂ ? 2{K(pmdeta)}] ( 3 – 8 , respectively) in isolated crystalline yields of 53, 16, 7, 23, 67, and 51 %, respectively; the treatment of 2 with 4‐tBu‐pyridine gave [{2‐Zn(nBu)₂‐μ‐4‐tBu‐C₅H₃N}₂ ? 2{K(pmdeta)}] ( 9 ) in an isolated crystalline yield of 58 %. Single‐crystal X‐ray crystallographic and NMR spectroscopic characterization of 3 – 9 revealed a novel structural motif consisting of a dianionic dihydroanthracene‐like tricyclic ring system with a central diazadicarbadizinca (ZnCN)₂ ring, face‐capped on either side by PMDETA‐wrapped K⁺ cations. All the new metalated pyridine complexes share this dimeric arrangement. As determined by NMR spectroscopic investigations of the reaction filtrates, those solutions producing 3 , 7 , 8 , and 9 appear to be essentially clean reactions, in contrast to those producing 4 , 5 , and 6 , which also contain laterally zincated coproducts. In all of these metalation reactions, the potassium–zincate base acts as an amido transfer agent with a subsequent ligand‐exchange mechanism (amido replacing alkyl) inhibited by the coordinative saturation, and thus, low Lewis acidity of the 4‐coordinate Zn centers in these dimeric molecules. Studies on analogous trialkyl–zincate reagents in the absence and presence of stoichiometric or substoichiometric amounts of TMP(H) established the importance of Zn? N bonds for efficient zincation.     

Synthesis and Deprotonation of Aminophosphane Complexes: First K/N(H)R Phosphinidenoid Complexes and Access to a Complex with a P2N‐Ring Ligand

Synthesis of 1,1′‐bifunctional aminophosphane complexes 3 a–e was achieved by the reaction of Li/Cl phosphinidenoid complex 2 with various primary amines (R=Me, iPr, tBu, Cy, Ph). Deprotonation of complex 3 a (R=Me) with potassium hexamethyldisilazide yielded a mixture of K/NHMe phosphinidenoid complex 4 a and potassium phosphanylamido complex 4 a′ . Treatment of complex 3 c (R=tBu) and e (R=Ph) with KHMDS afforded the first examples of K/NHR phosphinidenoid complexes 4 c and e . The reaction of complex 3 c with 2 molar equivalents of KHMDS followed by PhPCl₂ afforded complexes 5 c,c′ , which possess a P₂N‐ring ligand. All complexes were characterized by NMR, IR, MS, and microanalysis, and additionally, complexes 3 b – e and 5 c′ were scrutinized by single‐crystal X‐ray crystallography.     

Synthese der Stannatetraphospholane (tBuP)4SnR2 (R = tBu,nBu, C6H5) und (tBuP)4Sn(Cl)nBu Molekül- und Kristallstruktur von (tBuP)4Sn(tBu)2

Synthesis of the Stannatetraphospholanes (tBuP)₄SnR₂ (R = tBu, nBu, C₆H₅) and (tBuP)₄Sn(Cl)nBu Molecular and Crystal Structure of (tBuP)₄Sn(tBu)₂ The reaction of the diphosphide K₂[tBuP-(tBuP)₂-PtBu] 4 with the halogenostannanes (tBu)₂SnCl₂, (nBu)₂SnCl₂, (C₆H₅)₂SnCl₂ or nBuSnCl₃ in a molar ratio of 1 : 1 leads via a [4 + 1]-cyclocondensation reaction to the stannatetraphospholanes (tBuP)₄SnR₂ 3 b–3 d and (tBuP)₄Sn(Cl)nBu 3 e , respectively, with the binary 5-membered P₄Sn ring system. 3 b was characterized by a single crystal structure analysis; the 5-membered ring exists in a planar conformation. The compounds 3 b–3 e were identified by NMR and also by mass spectroscopy; the ³¹P{¹H}-NMR spectra of 3 b–3 d showed an AA′MM′ (AA′MM′X), 3 e on the other hand an ABCD (ABCDX) spin system.     

Aminophosphanes with bulky amino groups: Molecular structure,coupling constants 1J(31P, 15N) and 2J(31P, 29Si), and isotope‐induced chemical shifts 1Δ14/15N(31P)

The preferred conformation of aminophosphanes with bulky amino groups ( 1–20 ) was determined by NMR spectroscopy in solution, in two cases in the solid state ( 11,17 ) and in one case ( 11 ) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph₂PN(R)SiMe₃ (R = Bu ( 1 ), Ph ( 2 ), 2‐pyridyl ( 3 ), 2‐pyrimidyl ( 4 ), Me₃Si ( 5 )), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me ( 6 ), R = Bz, R′ = ^tBu ( 7 ), R = Et, R′ = Ph ( 8 )), amino(chloro)tert‐butylphosphanes ^tBu(Cl)PNRR′ (R = R′ = ⁱPr ( 9 ), R = Me, R′ = ^tBu ( 10 ), R = Bz, R′ = ^tBu ( 11 ), R = H, R′ = ^tBu ( 12 ), R = Et, R′ = Ph ( 13 ), R = ⁱPr, R′ = Ph ( 14 ), R = Bu, R′ = Ph ( 15 ), R = Bz, R′ = Ph ( 16 ), R = R′ = Ph ( 17 ), R = R′ = Me₃Si ( 18 )), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane ( 19 ), and benzyl(tert‐butyl)aminodichlorophosphane ( 20 ) were studied by ¹H, ¹³C, ¹⁵N, ²⁹Si, and ³¹P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants ¹J(³¹P, ¹⁵N), ²J(³¹P, ¹³C), and ²J(³¹P, ²⁹Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the P N bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by ¹³C, ¹⁵N, and ³¹P NMR spectroscopy. Isotope‐induced chemical shifts ¹Δ^15/14N(³¹P) were determined for all compounds at natural abundance of ¹⁵N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084     

SCHWEFELDIIMIDE MIT SILYL-, GERMYL-, STANNYL- UND PHOSPHINYL-HETEROSUBSTITUENTEN. SYNTHESE UND NMR-SPEKTROSKOPISCHE CHARAKTERISIERUNG

Abstract

Reactions of the salts K₂SN₂ and K[(NSN)R] (R = ′Bu, SiMe₃ and P′Bu₂) with organoelement chlorides R′R′ěl have been used to prepare four series of model sulfur diimides: R′R″E(NSN)ER″R′, ′Bu(NSN)ER″R′, Me₃Si(NSN)E″R′ and ^tBu₂P(NSN)ER″R′, respectively (E = C, Si, Ge, Sn; R′ and R″ = alkyl or aryl group). All compounds have been characterized by ′H and ¹³C NMR and—if possible—by ³¹P, ²⁹Si and ¹¹⁹Sn NMR spectroscopy. The configuration (Z or E) of the substituents R and E″R′ has been assigned in several cases using ^tBu(NSN)^tBu (1) as a reference. The E,Z assignment of ¹H, ¹³C and ¹⁵N nuclei in 1 is based on selectively ¹H-decoupled refocused INEPT ¹⁵N NMR and two-dimensional (2D) ¹³C/¹H heteronuclear shift correlations. The sulfur diimides under study are in general fluxional in solution.     

Synthesis,characterization and thermal behaviour of four homoleptic titanium silanolates

Four titanium silanolates Ti(OSiR₂R′)₄ (1, R = Ph, R′ = ^tBu; 2, R = R′ = Ph; 3, R = R′ = ⁱPr; 4, R = Me, R′ = ^tBu) were synthesised starting from Ti(OⁱPr)₄ and the corresponding silanol, and their thermally induced decomposition was studied. Colourless single crystals of Ti(OSiPh Bu) CHCl C₇H₈ ( CHCl C₇H₈) were obtained from a mixture of chloroform and toluene (1:1) at ?20 °C. The compound crystallizes in the space group R3 c with Z = 18. The metal atom shows an almost ideal tetrahedral coordination, as is demonstrated by the O? Ti? O angles of 108.4(1)–111.1(1)°. Copyright © 2005 John Wiley & Sons, Ltd.     

Investigations of the Nature of ZnII−SiII Bonds

A series of zinc(II) silylenes was prepared by using the silylene {PhC(NtBu)₂}(C₅Me₅)Si. Whereas reaction of the silylene with ZnX₂ (X=Cl, I) gave the halide‐bridged dimers [{PhC(NtBu)₂}(C₅Me₅)SiZnX(μ‐X)]₂, with ZnR₂ (R=Ph, Et, C₆F₅) as reagent the monomers [{PhC(NtBu)₂}(C₅Me₅)SiZnR₂] were obtained. The stability of the complexes and the Zn?Si bond lengths clearly depend on the substitution pattern of the zinc atom. Electron‐withdrawing groups stabilize these adducts, whereas electron‐donating groups destabilize them. This could be rationalized by quantum chemical calculations. Two different bonding modes in these molecules were identified, which are responsible for the differences in reactivity: 1) strong polar Zn?Si single bonds with short Zn?Si distances, Zn?Si force constants close to that of a classical single bond, and strong binding energy (ca. 2.39 Å, 1.33 mdyn Å^?1, and 200 kJ mol^?1), which suggest an ion pair consisting of a silyl cation with a Zn?Si single bond; 2) relatively weak donor–acceptor Zn?Si bonds with long Zn?Si distances, low Zn?Si force constants, and weak binding energy (ca. 2.49 Å, 0.89 mdyn Å^?1, and 115 kJ mol^?1), which can be interpreted as a silylene–zinc adduct.     

The Haloboration of Tri‐tert‐butylazadiboriridine NB2R3: Ring Opening versus NB3 Cluster Formation

The azadiboriridine [–BR–NR–BR–] ( 1 ; R = tBu) is bromoborated at the B–B bond by alkyldibromoboranes R′BBr₂ to give the products Br–BR–NR=BR–BR′–Br ( 8 a – g : R′ = Me, Bu, iBu, Bzl, CH₂CHEt₂, CH₂Cy, CH₂(4‐C₆H₄tBu)). Two isomers of each of the products 8 a – g are formed and attributed to a cis/trans isomerism at the BN double bond; the isomerization is followed thermodynamically and kinetically by NMR methods with 8 a – d . The analogous chloroboration of 1 with BCl₃ yields Cl–BR–NR=BR–BCl₂ ( 8 h ), which at ambient temperature undergoes a degenerate exchange of the ligands Cl and BCl₂ along the B–N–B skeleton. At room temperature, the isomer Cl–BR–NR=BCl–BR–Cl ( 8 h ′) is slowly formed by an irreversible exchange of R and Cl along the B–B bond of 8 h . Different from BCl₃, the chloroborane BH₂Cl is simply added to the B–B bond of 1 under formation of the aza‐nido‐tetraborane NB₃R₃H₂Cl ( 2 b ). The chloroborane BHCl₂ gives a mixture of 8 h ′ and 2 b upon addition to 1 , apparently according to a preceding dismutation into BCl₃ and BH₂Cl. The configuration at the B3 atom of the nido‐clusters NB₃R₃H₂X (X = H, Cl) is discussed on the basis of the corresponding model molecules NB₃Me₃H₂X, whose structure and NMR signals are computed by the B3LYP method. The boranes 8 b – g can be debrominated with Li in the presence of tmen on applying ultrasound. The products are found to be the B‐borylated azadiboriridines [–BR–NR–B(BRR′)–] ( 9 b – g ). The 2‐borylazadiboriridines NB₃H₄ ( 9 h ) and NB₃Me₄ ( 9 i ) were found as local minima on the energy hyperface by the B3LYP method, but minima for structural isomers with lower energy were also found; the tetrahedral clusters NB₃R₄ give high‐energy minima with triplet ground states. Computations of the ¹¹B NMR shifts of 9 h and 9 i support the proposed structures of 9 b – g .     

Multicomponent One‐pot Reactions Towards the Synthesis of Stereoisomers of Dipicolylamine Complexes

Reported are multi‐component one‐pot syntheses of chiral complexes [M(L^ROR′)Cl₂] or [M(L^RSR′)Cl₂] from the mixture of an N‐substituted ethylenediamine, pyridine‐2‐carboxaldehyde, a primary alcohol or thiol and MCl₂ utilizing in‐situ formed cyclized Schiff bases where a C?O bond, two stereocenters, and three C?N bonds are formed (M=Zn, Cu, Ni, Cd; R=Et, Ph; R′=Me, Et, nPr, nBu). Tridentate ligands L^ROR′ and L^RSR′ comprise two chiral centers and a hemiaminal ether or hemiaminal thioether moiety on the dipicolylamine skeleton. Syn‐[Zn(L^PhOMe)Cl₂] precipitates out readily from the reaction mixture as a major product whereas anti‐[Zn(L^PhOMe)Cl₂] stays in solution as minor product. Both syn‐[Zn(L^PhOMe)Cl₂] and anti‐[Zn(L^PhOMe)Cl₂] were characterized using NMR spectroscopy and mass spectrometry. Solid‐state structures revealed that syn‐[Zn(L^PhOMe)Cl₂] adopted a square pyramidal geometry while anti‐[Zn(L^PhOMe)Cl₂] possesses a trigonal bipyramidal geometry around the Zn centers. The scope of this method was shown to be wide by varying the components of the dynamic coordination assembly, and the structures of the complexes isolated were confirmed by NMR spectroscopy, mass spectrometry, and X‐ray crystallography. Syn complexes were isolated as major products with Zn^II and Cu^II, and anti complexes were found to be major products with Ni^II and Cd^II. Hemiaminals and hemiaminal ethers are known to be unstable and are seldom observed as part of cyclic organic compounds or as coordinated ligands assembled around metals. It is now shown, with the support of experimental results, that linear hemiaminal ethers or thioethers can be assembled without the assistance of Lewis acidic metals in the multi‐component assembly, and a possible pathway of the formation of hemiaminal ethers has been proposed.     

UV–visible spectroscopy for zirconocene activation by MAO in olefin polymerization: activity versus wavenumber

Activation of ansa‐zirconocenes of the type Rac [Zr{1‐Me₂Si(3‐R‐(η⁵‐C₉H₅))(3‐R′‐(η⁵‐C₉H₅))}Cl₂] [R = Et, R′ = H ( 1 ); R = Pr, R′ = H ( 2 ); and R = Et, R′ = Pr ( 3 ), R, R′ = Me ( 4 ) and R, R′ = Bu ( 5 )] by MAO has been studied by UV–visible spectroscopy. Compounds 1–3 have been tested in the polymerization of ethylene at different Al:Zr ratios. UV–vis spectroscopy was used to determine a correlation between the electronic structures of ( 1–5 ) and their polymerization activity. Copyright © 2009 John Wiley & Sons, Ltd.     

Structural Analysis of Zincocenes with Substituted Cyclopentadienyl Rings

New zincocenes [ZnCp′₂] ( 2 – 5 ) with substituted cyclopentadienyl ligands C₅Me₄H, C₅Me₄tBu, C₅Me₄SiMe₂tBu and C₅Me₄SiMe₃, respectively, have been prepared by the reaction of ZnCl₂ with the appropriate Cp′‐transfer reagent. For a comparative structural study, the known [Zn(C₅H₄SiMe₃)₂] ( 1 ), has also been investigated, along with the mixed‐ring zincocenes [Zn(C₅Me₅)(C₅Me₄SiMe₃)] ( 6 ) and [Zn(C₅Me₅)(C₅H₄SiMe₃)] ( 7 ), the last two obtained by conproportionation of [Zn(C₅Me₅)₂] with 5 or 1 , as appropriate. All new compounds were characterised by NMR spectroscopy, and by X‐ray methods, with the exception of 7 , which yields a side‐product ( C ) upon attempted crystallisation. Compounds 5 and 6 were also investigated by ¹³C CPMAS NMR spectroscopy. Zincocenes 1 and 2 have infinite chain structures with bridging Cp′ ligands, while 3 and 4 exhibit slipped‐sandwich geometries. Compounds 5 and 6 have rigid, η⁵/η¹(σ) structures, in which the monohapto C₅Me₄SiMe₃ ligand is bound to zinc through the silyl‐bearing carbon atom, forming a Zn? C bond of comparable strength to the Zn? Me bond in ZnMe₂. Zincocene 5 has dynamic behaviour in solution, but a rigid η⁵/η¹(σ) structure in the solid state, as revealed by ¹³C CPMAS NMR studies, whereas for 6 the different nature of the Cp′ ligands and of the ring substituents of the η¹‐Cp′ group (Me and SiMe₃) have permitted observation for the first time of the rigid η⁵/η¹ solution structure. Iminoacyl compounds of composition [Zn(η⁵‐C₅Me₄R)(η¹‐C(NXyl)C₅Me₄R)] resulting from the reactions of some of the above zincocenes and CNXyl (Xyl=2,6‐dimethylphenylisocyanide) have also been obtained and characterised.     

From Dibismuthenes to Three‐ and Two‐Coordinated Bismuthinidenes by Fine Ligand Tuning: Evidence for Aromatic BiC3N Rings through a Combined Experimental and Theoretical Study

The reduction of N,C,N‐chelated bismuth chlorides [C₆H₃‐2,6‐(CH?NR)₂]BiCl₂ [where R=tBu ( 1 ), 2′,6′‐Me₂C₆H₃ ( 2 ), or 4′‐Me₂NC₆H₄ ( 3 )] or N,C‐chelated analogues [C₆H₂‐2‐(CH?N‐2′,6′‐iPr₂C₆H₃)‐4,6‐(tBu)₂]BiCl₂ ( 4 ) and [C₆H₂‐2‐(CH₂NEt₂)‐4,6‐(tBu)₂]BiCl₂ ( 5 ) is reported. Reduction of compounds 1 – 3 gave monomeric N,C,N‐chelated bismuthinidenes [C₆H₃‐2,6‐(CH?NR)₂]Bi [where R=tBu ( 6 ), 2′,6′‐Me₂C₆H₃ ( 7 ) or 4′‐Me₂NC₆H₄ ( 8 )]. Similarly, the reduction of 4 led to the isolation of the compound [C₆H₂‐2‐(CH?N‐2′,6′‐iPr₂C₆H₃)‐4,6‐(tBu)₂]Bi ( 9 ) as an unprecedented two‐coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene {[C₆H₂‐2‐(CH₂NEt₂)‐4,6‐(tBu)₂]Bi}₂ ( 10 ) was obtained by the reduction of 5 . Compounds 6 – 10 were characterized by using ¹H and ¹³C NMR spectroscopy and their structures, except for 7 , were determined with the help of single‐crystal X‐ray diffraction analysis. It is clear that the structure of the reduced products (bismuthinidene versus dibismuthene) is ligand‐dependent and particularly influenced by the strength of the N→Bi intramolecular interaction(s). Therefore, a theoretical survey describing the bonding situation in the studied compounds and related bismuth(I) systems is included. Importantly, we found that the C₃NBi chelating ring in the two‐coordinated bismuthinidene 9 exhibits significant aromatic character by delocalization of the bismuth lone pair.     

From Anilines to Aryl Ethers: A Facile,Efficient, and Versatile Synthetic Method Employing Mild Conditions

We have developed a simple and direct method for the synthesis of aryl ethers by reacting alcohols/phenols (ROH) with aryl ammonium salts (ArNMe₃⁺), which are readily prepared from anilines (ArNR′₂, R′=H or Me). This reaction proceeds smoothly and rapidly (within a few hours) at room temperature in the presence of a commercially available base, such as KO^tBu or KHMDS, and has a broad substrate scope with respect to both ROH and ArNR′₂. It is scalable and compatible with a wide range of functional groups.     

From Anilines to Aryl Ethers: A Facile,Efficient, and Versatile Synthetic Method Employing Mild Conditions

We have developed a simple and direct method for the synthesis of aryl ethers by reacting alcohols/phenols (ROH) with aryl ammonium salts (ArNMe₃⁺), which are readily prepared from anilines (ArNR′₂, R′=H or Me). This reaction proceeds smoothly and rapidly (within a few hours) at room temperature in the presence of a commercially available base, such as KO^tBu or KHMDS, and has a broad substrate scope with respect to both ROH and ArNR′₂. It is scalable and compatible with a wide range of functional groups.     

[NiL2X2] oder [HL][NiLX3] – Reaktion sterisch anspruchsvoller Trialkylphosphine L mit NiX2 (X = Cl,Br) in Ethanol

[NiL₂X₂] or [HL][NiLX₃] – Reaction of Sterically Demanding Trialkylphosphines L with NiX₂ (X = Cl, Br) in Ethanol The reaction of some sterically demanding trialkylphosphines L = PR₂R′ (R = ⁱPr, R′ = ^tBu; R = ^tBu, R′ = ⁱPr, Me) with NiX₂ (X = Cl, Br) in ethanol affords instead of the expected non-electrolytes [NiL₂X₂] tertiary phosphonium nickelates [HL][NiLX₃] due to participation of the solvent. In case of the less bulky P^tBu₂Me both complex types were obtained. [Ni(P^tBu₂Me)₂Cl₂] is tetrahedral and therefore one of the two examples of paramagnetic bis(trialkylphosphine)dihalogenonickel(II) complexes known so far. In solution the latter compound undergoes an equilibrium of tetrahedral (paramagnetic) and planar (diamagnetic) conformer. Vis spectra as well as the results of magnetic measurements and ¹H and ³¹P NMR investigations are reported.     

Zur Reaktivität des Ferriophosphaalkens (Z)‐[Cp*(CO)2FeP=C(tBu)NMe2] gegenüber Propiolsäureestern HC≡C‐CO2R (R=Me,Et) und Acetylendicarbonsäureestern RO2C‐C≡C‐CO2R (R=Me,Et, tBu)

On the Reactivity of the Ferriophosphaalkene (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] towards Propiolates HC≡C‐CO₂R (R=Me, Et) and Acetylene Dicarboxylates RO ₂C‐C≡C‐CO₂R (R=Me, Et, tBu) The reaction of equimolar amounts of (Z)‐[Cp*(CO)₂Fe‐P=C(tBu)NMe₂] 3 and methyl‐ and ethyl‐propiolate ( 2a, b ) or of 3 and dialkyl acetylene dicarboxylates 1a (R=Me), 1b (Et), 1c (tBu) afforded the five‐membered metallaheterocycles [Cp*(CO) =C(tBu)NMe₂] ( 4a, b ) and [Cp*(CO) =C(tBu)NMe₂] ( 5a—c ). The molecular structures of 4b and 5a were elucidated by single crystal X‐ray analyses. Moreover, the reactivity of 4b towards ethereal HBF₄ was investigated.     

Judicious Ligand Design in Ruthenium Polypyridyl CO2 Reduction Catalysts to Enhance Reactivity by Steric and Electronic Effects

A series of Ru^II polypyridyl complexes of the structural design [Ru^II(R?tpy)(NN)(CH₃CN)]²⁺ (R?tpy=2,2′:6′,2′′‐terpyridine (R=H) or 4,4′,4′′‐tri‐tert‐butyl‐2,2′:6′,2′′‐terpyridine (R=tBu); NN=2,2′‐bipyridine with methyl substituents in various positions) have been synthesized and analyzed for their ability to function as electrocatalysts for the reduction of CO₂ to CO. Detailed electrochemical analyses establish how substitutions at different ring positions of the bipyridine and terpyridine ligands can have profound electronic and, even more importantly, steric effects that determine the complexes’ reactivities. Whereas electron‐donating groups para to the heteroatoms exhibit the expected electronic effect, with an increase in turnover frequencies at increased overpotential, the introduction of a methyl group at the ortho position of NN imposes drastic steric effects. Two complexes, [Ru^II(tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 3 ]²⁺; 6‐mbpy=6‐methyl‐2,2′‐bipyridine) and [Ru^II(tBu?tpy)(6‐mbpy)(CH₃CN)]²⁺ (trans‐[ 4 ]²⁺), in which the methyl group of the 6‐mbpy ligand is trans to the CH₃CN ligand, show electrocatalytic CO₂ reduction at a previously unreactive oxidation state of the complex. This low overpotential pathway follows an ECE mechanism (electron transfer–chemical reaction–electron transfer), and is a direct result of steric interactions that facilitate CH₃CN ligand dissociation, CO₂ coordination, and ultimately catalytic turnover at the first reduction potential of the complexes. All experimental observations are rigorously corroborated by DFT calculations.     

Adding a Structural Context to the Deprotometalation and Trans‐Metal Trapping Chemistry of Phenyl‐Substituted Benzotriazole

Organometallic bases are becoming increasingly complex, because mixing components can lead to bases superior to single‐component bases. To better understand this superiority, it is useful to study metalated intermediate structures prior to quenching. This study is on 1‐phenyl‐1H‐benzotriazole, which was previously deprotonated by an in situ ZnCl₂ ? TMEDA/LiTMP (TMEDA=N,N,N′,N′‐tetramethylethylenediamine; TMP=2,2,6,6‐tetramethylpiperidide) mixture and then iodinated. Herein, reaction with LiTMP exposes the deficiency of the single‐component base as the crystalline product obtained was [{4‐R‐1‐(2‐lithiophenyl)‐1H‐benzotriazole ? 3THF}₂], [R=2‐C₆H₄(Ph)NLi], in which ring opening of benzotriazole and N₂ extrusion had occurred. Supporting lithiation by adding iBu₂Al(TMP) induces trans‐metal trapping, in which C?Li bonds transform into C?Al bonds to stabilise the metalated intermediate. X‐ray diffraction studies revealed homodimeric [(4‐R′‐1‐phenyl‐1H‐benzotriazole)₂], [R′=(iBu)₂Al(μ‐TMP)Li], and its heterodimeric isomer [(4‐R′‐1‐phenyl‐1H‐benzotriazole){2‐R′‐1‐phenyl‐1H‐benzotriazole}], whose structure and slow conformational dynamics were probed by solution NMR spectroscopy.