Lowering the Reduction Potential of a Boron Compound by Means of the Substituent Effect of the Boryl Group: One‐Electron Reduction of an Unsymmetrical Diborane(4)

We have clarified and observed the high electron affinity of pinB?BMes₂ ( 1 ; Mes=mesityl, pin=pinacolato). By using electrochemistry, it was shown that 1 has a higher electron affinity than those of B₂pin₂ and Mes₃B. One‐electron reduction of 1 gave the corresponding radical anion. The ESR spectroscopy and DFT calculation revealed the unsymmetrical distribution of electron density over the B?B bond. UV/Vis spectroscopy showed that the SOMO‐related absorption supports the deep purple color of the radical anion. DFT studies on the torsion angle dependency of the LUMO levels and relative energies revealed the reason why 1 has high electron affinity as a result of the substituent effect of the Bpin group.     

1,1′-Binaphthyl Consisting of Two Donor–π–Acceptor Subunits: A General Skeleton for Temperature-Dependent Dual Fluorescence

Temperature-dependent dual fluorescence with the anti-Kasha's rule is of great interest, but is a very challenging property to achieve in small organic molecules. The highly sensitive temperature-dependent dual fluorescence of 2,2′-bis(dimethylamino)-6,6′-bis(dimesitylboryl)-1,1′-binaphthyl ( BNMe₂-BNaph ), which essentially consists of two donor–π–acceptor (D-π-A) subunits, inspired the exploration of the importance of its structural features and the general utility of this molecular design. The reference compound MBNMe₂-BNaph , which lacks one electron-accepting Mes₂B, is found to show less sensitive temperature-dependent dual fluorescence, suggesting that the structure of BNMe₂-Bnaph , consisting of two symmetrical D-π-A subunits, is very important for achieving highly sensitive temperature-dependent dual fluorescence. In addition, it is found that another two 1,1′-binaphthyls, CHONMe₂-BNaph and CNNMe₂-BNaph , which also consist of two D-π-A subunits with Mes₂B groups replaced by CHO and CN, respectively, also show temperature-dependent dual fluorescence, with the fluorescence changing in a similar manner to BNMe₂-BNaph , indicating the general utility of the current molecular design for temperature-dependent dual fluorescence. Furthermore, the temperature-dependent dual fluorescence behaviors, such as the relative intensities of the two emission bands, the separation of the two emissions bands, and the sensitivity of the fluorescence intensity ratio to temperature, are greatly influence by the electron acceptors.     

Tuning the Photoisomerization of a N^C‐Chelate Organoboron Compound with a Metal?Acetylide Unit

To examine the impact of metal moieties that have different triplet energies on the photoisomerization of B(ppy)Mes₂ compounds (ppy=2‐phenyl pyridine, Mes=mesityl), three metal‐functionalized B(ppy)Mes₂ compounds, Re‐B , Au‐B , and Pt‐B , have been synthesized and fully characterized. The metal moieties in these three compounds are Re(CO)₃(tert‐Bu₂bpy)(C?C), Au(PPh₃)(C?C), and trans‐Pt(PPh₃)₂(C?C)₂, respectively, which are connected to the ppy chelate through the alkyne linker. Our investigation has established that the Re^I unit completely quenches the photoisomerization of the boron unit because of a low‐lying intraligand charge transfer/MLCT triplet state. The Au^I unit, albeit with a triplet energy that is much higher than that of B(ppy)Mes₂, upon conjugation with the ppy chelate unit, substantially increases the contribution of the π→π* transition, localized on the conjugated chelate backbone in the lowest triplet state, thereby leading to a decrease in the photoisomerization quantum efficiency (QE) of the boron chromophore when excited at 365 nm. At higher excitation energies, the photoisomerization QE of Au‐B is comparable to that of the silyl–alkyne‐functionalized B(ppy)Mes₂ ( TIPS‐B ), which was attributable to a triplet‐state‐sensitization effect by the Au^I unit. The Pt^II unit links two B(ppy)Mes₂ together in Pt‐B , thereby extending the π‐conjugation through both chelate backbones and leading to a very low QE of the photoisomerization. In addition, only one boron unit in Pt‐B undergoes photoisomerization. The isomerization of the second boron unit is quenched by an intramolecular energy transfer of the excitation energy to the low‐energy absorption band of the isomerized boron unit. TD‐DFT computations and spectroscopic studies of the three metal‐containing boron compounds confirm that the photoisomerization of the B(ppy)Mes₂ chromophore proceeds through a triplet photoactive state and that metal units with suitable triplet energies can be used to tune this system.     

Insights into the Photoinduced Isomerization Mechanisms of a N,C–Chelate Organoboron Compound: A Theoretical Study

As the first discovered organoboron compound with photochromic property, B(ppy)Mes₂ (ppy=2-phenylpyridine, Mes=mesityl) displays rich photochemistry that constitutes a solid foundation for wide applications in optoelectronic fields. In this work, we investigated the B(ppy)Mes₂ to borirane isomerization mechanisms in the three lowest electronic states (S₀, S₁, and T₁) based on the complete active space self-consistent field (CASSCF) and its second-order perturbation (CASPT2) methods combined with time-dependent density functional theory (TD-DFT) calculations. Our results show that the photoisomerization in the S₁ state is dominant, which is initiated by the cleavage of the B-C_ppy bond. After overcoming a barrier of 0.5 eV, the reaction pathway leads to a conical intersection between the S₁ and S₀ states (S₁/S₀)_x, from which the decay path may go back to the reactant B(ppy)Mes₂ via a closed-shell intermediate (Int1-S₀) or to the product borirane via a biradical intermediate (Int2-S₀). Although triplet states are probably involved in the photoinduced process, the possibility of the photoisomerization in T₁ state is very small owing to the weakly allowed S₁→T₁ intersystem crossing and the high energy barrier (0.77 eV). In addition, we found the photoisomerization is thermally reversible, which is consistent with the experimental observations.     

Synthesis,reactivity and crystal structure of trimesitylgermylamine,Mes3GeNH2

Trimesitylgermylamine, Mes₃GeNH₂, prepared in high yield by the coupling of Mes₃GeCl (Mes  2,4,6-Me₃C₆H₂) with NaNH₂ or LiNH₂, has been fully characterized by ¹H and ¹³C NMR, IR and mass spectrometry. It is a rare example of a stable primary germylamine, melting at 166°C, which is only slowly cleaved by H₂O, CH₃OH, HCl or phenol, indicating that the central Ge atom is protected from attack by the mesityl groups. Unlike other germylamines, Mes₃GeNH₂ reacts with ^tBuCOCl to give the N-substituted amide, Mes₃GeNHCO^tBu, rather than Mes₃GeCl. Preliminary X-ray crystallographic analyses reveal that the Ge atom has approximate tetrahedral coordination with an average GeC bond length of 1.978(3) Å and a GeN bond length of 1.854(3) Å, and crowding around the Ge atom so that it is shielded from attack by approaching reactants.     

Synthesis, characterization and electrochemical behavior of some N-heterocyclic carbene-containing active site models of [FeFe]-hydrogenases

Treatment of parent compounds [(μ-SCH₂)₂X]Fe₂(CO)₆ (A, X = O; B, X = NBu-t; C, X = NC₆H₄OMe-p) with N-heterocyclic carbene I_Mes (I_Mes = 1,3-bis(mesityl)imidazol-2-ylidene) generated in situ through reaction of imidazolium salt I_Mes ·HCl with n-BuLi or t-BuOK afforded the monocarbene-substituted complexes [(μ-SCH₂)₂X]Fe₂(CO)₅(I_Mes) (1, X = O; 2, X = NBu-t; 3, X = NC₆H₄OMe-p). Similarly, the monocarbene and dicarbene-substituted complexes [(μ-SCH₂)₂NBu-t]Fe₂(CO)₅[I^∗_Mes(CH₂)₃I^∗_Mes]·HBr (4) and [(μ-SCH₂)₂CH₂Fe₂(CO)₅]₂[μ-I^∗_Mes(CH₂)₃I^∗_Mes] (5, I^∗_Mes = 1-(mesityl)imidazol-2-ylidene) could be prepared by reactions of parent compound B with the mono-NHC ligand-containing imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · HBr and parent compound [(μ-SCH₂)₂CH₂]Fe₂(CO)₆ (D) with di-NHC ligand I^∗_Mes(CH₂)₃I^∗_Mes (both NHC ligands were generated in situ from reaction of n-BuLi with imidazolium salt [I^∗_MesI^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr), respectively. The imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr was prepared by reaction of 1-(mesityl)imidazole with Br(CH₂)₃Br. All the new model compounds 1-5 and imidazolium salt [I^∗_Mes(CH₂)₃I^∗_Mes] · 2HBr were fully characterized by elemental analysis, spectroscopy, and X-ray crystallography. On the basis of electrochemical studies of 1 and 2, compound 2 was found to be a catalyst for proton reduction to hydrogen. In addition, an EECC mechanism for this electrocatalytic reaction is preliminarily suggested.     

Photoisomerization of PtII Complexes Containing Two Different Photochromic Chromophores: Boron Chromophore versus Dithienylethene Chromophore

In order to examine competitive photoisomerization, a series of novel photochromic Pt^II molecules that contain both dithienylethene (DTE) and B(ppy)Mes₂ units (ppy=2-phenylpyridine, Mes=mesityl) were successfully synthesized and fully structurally characterized. Their photochromic properties were examined by UV/Vis, emission and NMR spectroscopy. It was found that the DTE unit in all three compounds is the preferred photoisomerization site, exhibiting reversible photochromism with irradiation. The B(ppy)Mes₂ unit does not undergo photoisomerization in these molecules, but likely enhances the photoisomerization quantum efficiency of the DTE moiety through the antenna effect. Extended irradiation with UV light leads to the rearrangement of the ring-closed isomers of DTE. TD-DFT computational studies indicate that the DTE photocyclization proceeds via a triplet pathway through an efficient energy transfer process.     

Iodidomesityltellurium(II) iodidotrimesitylditellurium(II)(Te—Te)

In the title compound, C₉H₁₁ITe·C₂₇H₃₃ITe₂ or (Mes)TeI·(Mes₂Te)TeI(Mes) (Mes is mesityl or 2,4,6‐trimethylphenyl), a strong Te...I interaction of 3.3157 (9) Å links the Te atom of an iodidomesityltellurium(II) moiety, (Mes)TeI, and an I atom of the iodidotrimesitylditellurium(II) unit, (Mes₂Te)TeI(Mes). Further weak Te...I contacts of 4.0818 (9) Å give rise to one‐dimensional chains along the b axis in the crystal structure. An intramolecular C—H...π(arene) interaction is present in the (TeMes₂)TeI(Mes) moiety, with a C...Cg distance of 3.497 (9) Å and a C—H...Cg angle of 142° (where Cg is the centroid of a mesityl ring of the Mes₂Te moiety).     

Chirality Relay in 2,2′‐Substituted 1,1′‐Binaphthyl: Access to Propeller Chirality of the Tricoordinate Boron Center

It is a challenging issue to achieve propeller chirality for triarylboranes owing to the low transition barrier between the P and M forms of the boron center. Herein, we report a new strategy to achieve propeller chirality of triarylboranes. It was found that the chirality relay from axially chiral 1,1′‐binaphthyl to propeller chirality of the trivalent boron center can be realized when a Me₂N and a Mes₂B group (Mes=mesityl) are introduced at the 2,2′‐positions of the 1,1′‐binaphthyl skeleton ( BN‐BNaph ) owing to the strong π–π interaction between the Me₂N‐bonded naphthyl ring and the phenyl ring of one adjacent Mes group, which not only exerts great steric hindrance on the rotation of the two Mes groups but also gives unequal stability to the two configurations of the boron center for a given configuration of the binaphthyl moiety. The stereostructures of the boron center were fully characterized through ¹H NMR spectroscopy, X‐ray crystal analyses, and theoretical calculations. Detailed comparisons with the analog BN‐Ph‐BNaph , in which the Mes₂B group is separated from 1,1′‐binaphthyl by a para‐phenylene spacer, confirmed the essential role of π–π interaction for the successful chirality relay in BN‐BNaph .     

Mesityltrifluorogallate. Die Kristallstrukturen von Cs[MesGaF3] und K[MesInBr3]

Mesityltrifluoro Gallates. The Crystal Structures of Cs[MesGaF₃] and K[MesInBr₃] Mes₃Ga reacts with GaBr₃ in the ratio 1:2 in a commutation reaction to MesGaBr₂ ( 1 ). 1 can be reacted with KF and CsF in MeCN to K[MesGaF₃] ( 2 ) and Cs[MesGaF₃] ( 3 ), respectively. K[MesInBr₃] ( 4 ) was isolated when MesInBr₂ was treated with KF in MeCN. The use of 15-crown-5 was leading to [K(15-crown-5)₂][Mes₂InBr₂] ( 5 ) in a substituent exchange reaction. 1-5 were characterized by NMR-, IR- and MS-techniques. The solid state structures of 3 and 4 could be established by X-ray structure determinations. According to these determinations, a layer-type arrangement of the molecules is both structures in common. In the center of the layers, ionic interactions were formed, while the separation of the layers is caused by the bulky mesityl substituents.     

Tris(2,4,6-trimethylphenyl)antimony dihydroxide; synthesis and reaction with sulfonic acids RSO3H (R = C6H5, CF3). Crystal structure of [2,4,6-(CH3)3C6H2]3SbO · HO3SC6H5

Tris(2,4,6-trimethylphenyl)antimony dihydroxide, Mes₃Sb(OH)₂, which was prepared by oxidation of Mes₃Sb with H₂O₂, has been shown to react with RSO₃H (R = C₆H₅, CF₃) to give the adducts Mes₃SbO · HO₃SR, the first examples of solid hydrogen-bonded adducts of a triorganoantimony oxide and an acid. The crystal structure of Mes₃SbO·HO₃SC₆H₅ has been determined. The three C(mesityl) atoms and the O atom form a distorted tetrahedron around Sb, the distortion by the bulky mesithyl groups being reflected in the CSbC angles (mean: 114.7(3)°) and the CSbO angles: (mean: 103.5(2)°). C₆H₅SO₃H is linked via a short hydrogen bond to O on Sb, with O(1) z^.;O(2) = 256(1) pm. The bond length SbO(1) 189.4(5) pm represents the shortest SbO distance ever reported.     

Molecular and Crystal Structure of an Organoplatinum(II) Complex with Dipyrido[3,2-a : 2′,3′-c]phenazine (dppz)

The dimesitylplatinum(II) complex PtMes₂(dppz) (Mes = mesityl = 2,4,6-trimethylphenyl) crystallizes with one equivalent of toluene (C₄₃H₄₀N₄Pt, monoclinic, P2₁/c, Z = 4, a = 14.3551(14) Å, b = 15.8319(14) Å, c = 15.369(2) Å, β = 96.784(6)°). The (dppz)Pt(C1_Mes)₂ part of the molecule was found to be planar, the mesityl substituents adopting dihedral angles of 70.3° and 85.5° with that plane. The photoemissive and reversibly reducible and oxidizable complex molecules form pairs in the crystal with the planar phenazine π “tails” overlapping in graphite-like fashion at 3.427 Å distance. The results are discussed in comparision with a recently reported structure of PtCl₂(dppz).     

Synthesis and Characterization of a Magnesium Boryl and a Beryllium‐Substituted Diazaborole

Reaction of a lithium boryl, [(THF)₂Li{B(DAB)}] (DAB=[(DipNCH)₂]^2?, Dip=2,6‐diisopropylphenyl), with a dinuclear magnesium(I) compound [{(^MesNacnac)Mg}₂] (^MesNacnac=[HC(MeCNMes)₂]^?, Mes=mesityl) unexpectedly afforded a rare example of a terminal magnesium boryl species, [(^MesNacnac)(THF)Mg{B(DAB)}]. Attempts to prepare the magnesium boryl via a salt metathesis reaction between the lithium boryl and a β‐diketiminato magnesium iodide compound, instead led to an intractable mixture of products. Similarly, reaction of the lithium boryl with a β‐diketiminato beryllium bromide precursor, [(^DepNacnac)BeBr] (Dep=2,6‐diethylphenyl) did not give a beryllium boryl, but instead afforded an unprecedented example of a beryllium substituted diazaborole heterocycle, [{(^DepNacnac)Be(4‐DAB^?H)}BBr]. For sake of comparison, the same group 2 halide precursor compounds were treated with a potassium gallyl analogue of the lithium boryl, viz. [(tmeda)K{:Ga(DAB)}] (tmeda=N,N,N’,N’‐tetramethylethylenediamine), but no reactions were observed.     

Structural Dynamics and Stereoselectivity of Chiral Benzylideneamine N,C-Chelate Borane Photo–Thermal Isomerization

New chiral N,C-chelate organoboron compounds based on benzylideneamines (bza) with the general formula of B(bza-R)Mes₂ (R=H or Me; Mes=mesityl) are reported. A chiral substituent group R- or S-CH(CH₃)Ph (Ph=phenyl) was introduced to the imine center, which imposed a previously unobserved pseudo- or axial-chirality on the BMes₂, creating distinct diastereomers. NMR spectroscopic studies established that the diastereomers undergo slow exchange in solution at ambient temperature. The chiral N,C-chelate B(bza-R)Mes₂ molecules undergo photoisomerization in the same manner as their non-chiral analogues, generating chiral BN-cyclooctatriene (BN-COT) derivatives. Most significantly, by tracking the photoisomerization with circular dichroism (CD) and ¹H NMR spectra along with time-dependent density functional theory (TD-DFT) computational studies, the photoisomerization was established to proceed in a highly stereoselective manner, that is, one diastereomer converts exclusively to the corresponding diastereomer product in the photoreaction.     

Controlling the fluoridophilicity of sulfonium boranes via chelation,Coulombic and hydrophobic effects

We describe the synthesis and properties of a series of sulfonium boranes featuring a dimesitylboryl unit and a dimethylsulfonium or methylphenyl sulfonium moiety connected by an ortho- or para-phenylene linker. Acid-base and fluoride anion tritration experiments carried out in aqueous media indicate that [o-(Mes₂B)C₆H₄(SMePh)]⁺ is the most Lewis acidic derivative. Structural and computational analysis indicate that the favorable properties of this cationic borane derive from the proximity of the sulfonium and boryl units which enhances the Coulombic stabilization of the ensuing zwitterions o-(Mes₂XB)C₆H₄(SMePh) with X?=?OH or F. Another important factor is the overall hydrophobicity of the sulfonium borane which, we propose, promotes anion desolvation, a factor also favoring B-X bond formation. Finally, the crystal structure of o-(Mes₂FB)C₆H₄(SMePh) shows that the zwitterion is further stabilized by formation of a BF→S chelate motif.     

Synthesis and reactivity of zirconium and hafnium complexes incorporating chelating diamido-N-heterocyclic-carbene ligands

Early transition metal complexes employing a diamido N-heterocyclic carbene (NHC) ligand set (denoted [NCN]) render the centrally disposed NHC moiety stable to dissociation. Aminolysis reactions with the mesityl-substituted ligand precursor (^Mes[NCN]H₂) and M(NMe₂)₄ (M = Zr, Hf) provide bis(amido)-NHC-metal complexes that can be further converted to chloro and alkyl derivatives. Activation of ^Mes[NCN]M(CH₃)₂ with [Ph₃C][B(C₆F₅)₄] yields {^Mes[NCN]MCH₃}{B(C₆F₅)₄}, which is surprisingly inactive for the polymerization of 1-hexene. The zirconium cation did, however, show moderate ability to catalytically polymerize ethylene. The hafnium dialkyls are thermally stable with the exception of the diethyl complex, ^Mes[NCN]Hf(CH₂CH₃)₂, which undergoes β-hydrogen transfer and subsequent C–H bond activation with an ortho-methyl substituent on the mesityl group. The hafnium dialkyl complexes also insert carbon monoxide and substituted isocyanides to yield η²-acyls and η²-iminoacyls, respectively. In some circumstances, further C–C bond coupling occurs to yield enediolates and eneamidolate metallocycles. The molecular structures of ^Mes[NCN]Hf(CH₂CHMe₂)₂, ^Mes[NCN]Hf(η²-(2,6-Me₂C₆H₃NCCH₃)(CH₃), ^Mes[NCN]Hf(η²-(2,6-Me₂C₆H₃NCCH₃)₂, ^Mes[NCN]Hf(OC(CH₃)C(CH₃)NXy), and [^Mes[NCN]Hf(OC(ⁱBu)C(ⁱBu)O)]₂ are included.     

New Insights into the Formation and Reactivity of Molecular Organostannonic Acids

The controlled base hydrolysis of 2,6‐Mes₂C₆H₃SnCl₃ ( 1 ; Mes=mesityl) provided 2,6‐Mes₂C₆H₃Sn(OH)Cl₂?H₂O ( 2 ) and the trinuclear organostannonic acid trans‐[2,6‐Mes₂C₆H₃Sn(O)OH]₃ ( 3 ), respectively. In moist C₆D₆, 3 reversibly reacts with water to give the monomeric organostannonic acid 2,6‐Mes₂C₆H₃Sn(OH)₃ ( 3a ). The reaction of 3 with (tBu₂SnO)₃, Ph₂PO₂H, and NaH, gives rise to the multinuclear hypercoordinated organostannoxane clusters [tBu₂Sn(OH)OSnR(OH)₂OC(OSntBu₂OH)₂(O)SnR(OH)(H₂O)]₂ ( 5 ), [RSn(OH)₂(O₂PPh₂)]₂ ( 6 ), and Na₃(RSn)₄O₆(OH)₃ ( 7 ), respectively (R=2,6‐Mes₂C₆H₃). The characterization of the new compounds is achieved by multinuclear NMR spectroscopy and electrospray mass spectrometry in solution and ¹¹⁹Sn MAS NMR spectroscopy, IR spectroscopy, and X‐ray crystallography in the solid‐state.     

Structural Diversity of Calcium Organocuprates(I): Synthesis of Mesityl Cuprates via Addition and Transmetalation Reactions of Mesityl Copper(I)

The addition of [(L)₄Ca(I)Mes] (Lewis base L=thf, Et₂O) to mesityl copper(I) and the transmetalation reaction of mesityl copper(I) with activated calcium are suitable pathways for the synthesis of dimesityl cuprates(I) of calcium. However, the structures of the calcium cuprates(I) depend on the preparative procedure. The transmetalation reaction leads to the formation of [Mes‐Cu‐Mes]^? anions whereas the addition yields dinuclear [(Mes‐Cu)₂(μ‐Mes)]^? anions. The solvent‐separated counterions are [Ca(thf)₆]²⁺ and [(thf)₅CaI]⁺, respectively. In contrast to these findings, the addition of [(L)₄Ca(I)Mes] to mesityl copper(I) in an Et₂O/toluene mixture led to formation of tetrameric solvent‐free iodocalcium dimesityl cuprate(I) [ICa(μ‐η¹,η⁶‐Mes₂Cu)]₄, representing a rare example of a heavy Normant‐type organocuprate.     

Boron‐Doped Tri(9,10‐anthrylene)s: Synthesis,Structural Characterization,and Optoelectronic Properties

The reaction of 9,10‐dibromo‐9,10‐dihydro‐9,10‐diboraanthracene (9,10‐dibromo‐DBA, 3 ) with two equivalents of 9‐lithio‐2,6‐ or 9‐lithio‐2,7‐di‐tert‐butylanthracene gave the corresponding 9,10‐dianthryl‐DBAs featuring two ( 4 ) or four ( 5 ) inward‐pointing tert‐butyl groups. Compound 4 exists as two atropisomers, 4 and 4′ , due to hindered rotation about the exocyclic B? C bonds. X‐ray crystallography of 5 suggests that the overall interactions between facing tert‐butyl groups are attractive rather than repulsive. Even in solution, 4 / 4′ and 5 are stable toward air and moisture for several hours. Treatment of 3 with 10‐lithio‐9‐R‐2,7‐di‐tert‐butylanthracenes carrying phenyl (R=Ph), dimesitylboryl (R=Mes₂B), or N,N‐di(p‐tolyl)amino (R=Tol₂N) groups gave the corresponding 9,10‐dianthryl‐DBA derivatives 9 – 11 in moderate to good yields. In these molecules, all four solubilizing tert‐butyl groups are outward pointing. The solid‐state structures of 4 , 5 , 9 , and 10 reveal twisted conformations about the exocyclic B? C bonds with dihedral angles of 70–90°. A significant electron‐withdrawing character was proven for the Mes₂B moiety, but no appreciable +M effect was evident for Tol₂N. Compounds 5 , 9 , and 11 show two reversible DBA‐centered reduction waves in the cyclic voltammogram. In the case of 10 , a third reversible redox transition can be assigned to the Mes₂B–anthryl substituents. The UV/Vis absorption spectrum of 5 is characterized by a very broad band at λ_max=510 nm, attributable to a twisted intramolecular charge‐transfer interaction from the anthryl donors to the DBA acceptor. The corresponding emission band shows pronounced positive solvatochromism (λ_em=567 nm, C₆H₁₂; 680 nm, CH₂Cl₂) in line with a highly polar excited state. The charge‐transfer bands of 10 and 11 , as well as the emission bands of 9 and 10 , are redshifted relative to those of 5 . The Tol₂N derivative 11 is essentially nonfluorescent in solution, but emits bright wine‐red light in the solid state.     

Activation of Ethylene by N-Heterocyclic Carbene Coordinated Magnesium(I) Compounds

Reactions of a series of magnesium(I) compounds with ethylene, in the presence of an N-heterocyclic carbene (NHC), have been explored. Treating [{(^MesNacnac)Mg}₂] (^MesNacnac=[HC(MeCNMes)₂]⁻, Mes=mesityl) with an excess of ethylene in the presence of two equivalents of :C{(MeNCMe)₂} (TMC) leads to the formal reductive coupling of ethylene, and formation of the 1,2-dimagnesiobutane complex, [{(^MesNacnac)(TMC)Mg}₂(μ-C₄H₈)]. In contrast, when the reaction is repeated in the presence of three equivalents of TMC, a mixture of the β-diketiminato magnesium ethyl, [(^MesNacnac)(TMC)MgEt], and the NHC coordinated magnesium diamide, [(^MesNacnac^-H)Mg(TMC)₂], results. Four related products, [(^ArNacnac)(TMC)MgEt] (Ar=2,6-dimethylphenyl (Xyl) or 2,6-diisopropylphenyl (Dip)) and [(^ArNacnac^-H)Mg(TMC)₂] (Ar=Xyl or Dip), were similarly synthesised and crystallographically characterized. Computational studies have been employed to investigate the mechanisms of the two observed reaction types, which appear dependent on the substitution pattern of the magnesium(I) compound, and the stoichiometric equivalents of TMC used in the reactions.