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[Rh2(MEPY)4] is a versatile catalyst for asymmetric synthesis but its preparation requires purification by chromatography on surface‐modified silica. A higher yielding procedure based on a more convenient work‐up is presented herein. Moreover, a much improved method for the preparation of [BiRh(OTfa)4] is described, which makes this heterobimetallic complex readily available. Subsequent exchange of the trifluoroacetate ligands opens access to a so far underappreciated family of (chiral) paddlewheel complexes. While [BiRh] complexes comprising four carboxylate ligands are highly adequate for intermolecular asymmetric cyclopropanation reactions, [BiRh(MEPY)4] as the heterobimetallic cousin of [Rh2(MEPY)4] was found to be surprisingly unreactive; DFT calculations uncover the reasons for this inertia. [ABSTRACT FROM AUTHOR]

Cyclopropanation reactions of styrene derivatives with donor–acceptor carbenes formed in situ are significantly more enantioselective when catalyzed by the heterobimetallic bismuth–rhodium complex 5 a endowed with N‐phthalimido tert‐leucine paddlewheel ligands rather than by its homobimetallic dirhodium analogue 1 a. This virtue is likely the result of two synergizing factors: the conical shape of 5 a translates into a narrower calyx‐like chiral binding site about the catalytically active Rh center; the Bi atom, although fully solvent exposed, does not decompose aryl diazoacetates and is hence incapable of promoting a racemic background reaction. Moreover, ligand variation proved that successful catalyst design mandates that the anisotropy of the conical heterobimetallic core be matched by proper directionality of the ligand sphere. [ABSTRACT FROM AUTHOR]

The photophysical properties of four, two-coordinate, linear diamidocarbene copper(i) complexes, [(DAC)2Cu][BF4] (1), (DAC)CuOSiPh3 (2), (DAC)CuC6F5 (3) and (DAC)Cu(2,4,6-Me3C6H2) (4) (DAC = 1,3-bis(2,4,6-trimethylphenyl)-5,5-dimethyl-4,6-diketopyrimidinyl-2-ylidene) have been investigated. Complex 1 shows a high photoluminescence quantum efficiency (ΦPL) in both the solid state (ΦPL = 0.85) and in CH2Cl2 solution (ΦPL = 0.65). The emission band of 1, both as a crystalline solid and in solution, is narrow (fwhm = 2300 cm−1) relative to the emission bands of 2 (fwhm = 2900 cm−1) and 3 (fwhm = 3700 cm−1). Complexes 2 and 3 are each brightly luminescent in the solid state (ΦPL = 0.62 and 0.18, respectively), but markedly less so in CH2Cl2 solution (ΦPL = 0.03 and ＜0.01, respectively). Complex 4 is not emissive in either the solid state or in solution. Phosphorescence of 1 in CH2Cl2 solution shows negligible quenching by oxygen in CH2Cl2 solution. This insensitivity to quenching is attributed to the excited state redox potential being insufficient for electron transfer to oxygen. [ABSTRACT FROM AUTHOR]

The synthesis of the Cu-borate complexes [(6Mes)Cu(HBR3)] featuring the unusual [HBEt3]− ( 5) and [HB(C6F5)3]− ( 6) ligands is described. Experimental and computational studies show both compounds feature a direct Cu-H interaction, but that while 5 is two-coordinate, 6 displays an additional, stabilizing Cu-Cipso(C6F5) interaction. [ABSTRACT FROM AUTHOR]

The synthesis of the Cu-borate complexes [(6Mes)Cu(HBR3)] featuring the unusual [HBEt3]− ( 5) and [HB(C6F5)3]− ( 6) ligands is described. Experimental and computational studies show both compounds feature a direct Cu-H interaction, but that while 5 is two-coordinate, 6 displays an additional, stabilizing Cu-Cipso(C6F5) interaction. [ABSTRACT FROM AUTHOR]

The reaction of the ring-expanded N-heterocyclic carbenes (RE-NHCs) with [ZnMe 2 ] affords the structurally characterised complexes [(6-Mes)ZnMe 2 ] ( 1 ) and [(7-Mes)ZnMe 2 ] ( 2 ). The activity of the two complexes, along with that of the free carbenes, for the ring-opening polymerisation of rac -lactide has been probed. Even for such strongly σ-donating carbenes, dissociation from the metal centre cannot be ruled out. [ABSTRACT FROM AUTHOR]

The mononuclear N-heterocyclic carbene (NHC) copper alkoxide complexes [(6-NHC)CuO tBu] (6-NHC=6-MesDAC ( 1), 6-Mes ( 2)) have been prepared by addition of the free carbenes to the tetrameric tert-butoxide precursor [Cu(O tBu)]4, or by protonolysis of [(6-NHC)CuMes] (6-NHC=6-MesDAC ( 3), 6-Mes ( 4)) with tBuOH. In contrast to the relatively stable diaminocarbene complex 2, the diamidocarbene derivative 1 proved susceptible to both thermal and hydrolytic ring-opening reactions, the latter affording [(6-MesDAC)Cu(OC(O)CMe2C(O)N(H)Mes)(CNMes)] ( 6). The intermediacy of [(6-MesDAC)Cu(OH)] in this reaction was supported by the generation of Cu2O as an additional product. Attempts to generate an isolable copper hydride complex of the type [(6-MesDAC)CuH] by reaction of 1 with Et3SiH resulted instead in migratory insertion to generate [(6-MesDAC-H)Cu(P( p-tolyl)3)] ( 9) upon trapping by P( p-tolyl)3. Migratory insertion was also observed during attempts to prepare [(6-Mes)CuH], with [(6-Mes-H)Cu(6-Mes)] ( 10) isolated, following a reaction that was significantly slower than in the 6-MesDAC case. The longer lifetime of [(6-Mes)CuH] allowed it to be trapped stoichiometrically by alkyne, and also employed in the catalytic semi-reduction of alkynes and hydrosilylation of ketones. [ABSTRACT FROM AUTHOR]

The electrophilic character of free diamidocarbenes (DACs) allows them to activate inert bonds in small molecules, such as NH3 and P4. Herein, we report that metal coordinated DACs also exhibit electrophilic reactivity, undergoing attack by Zn and Cd dialkyl precursors to afford the migratory insertion products [(6-MesDAC-R)MR] (M=Zn, Cd; R=Et, Me; Mes=mesityl). These species were formed via the spectroscopically characterised intermediates [(6-MesDAC)MR2], exhibiting barriers to migratory insertion which increase in the order MR2 = ZnEt2 < ZnMe2 < CdMe2. Compound [(6-MesDAC-Me)CdMe] showed limited stability, undergoing deposition of Cd metal, by an apparent β-H elimination pathway. These results raise doubts about the suitability of diamidocarbenes as ligands in catalytic reactions involving metal species bearing nucleophilic ligands (M-R, M-H). [ABSTRACT FROM AUTHOR]

Thetwo-coordinate ring-expanded N-heterocyclic carbene copper(I)complexes [Cu(RE-NHC)2]+(RE-NHC = 6-Mes, 7-o-Tol, 7-Mes) have been prepared and shown to be effectivecatalysts under neat conditions for the 1,3-dipolar cycloadditionof alkynes and azides. In contrast, the cationic diamidocarbene analogue[Cu(6-MesDAC)2]+and the neutral species [(6-MesDAC)CuCl]2and [(6-MesDAC)2(CuCl)3] show goodactivity when the catalysis is performed on water. [ABSTRACT FROM AUTHOR]

Treatment of CuCl with 1 equiv of the in situ prepared N-mesityl-substituted diamidocarbene 6-MesDAC produced a mixture of the dimeric and trimeric copper complexes [(6-MesDAC)CuCl]2 (1) and [(6-MesDAC)2(CuCl)3] (2). Combining CuCl with isolated, free 6-MesDAC in 1:1 and 3:2 ratios gave just 1 and 2, respectively, while increasing the ratio to >5:1 allowed the isolation of small amounts of the tetrameric copper complex [(6-MesDAC)2(CuCl)4] (3). Efforts to bring about metathesis reactions of 1 with MOtBu (M = Li, Na, K) proved successful only for M = Li to afford the spectroscopically characterized ate product [(6-MesDAC)CuCl·LiOtBu·2THF] (5). Attempts to crystallize this species instead gave a 1:1 mixture of 1 and the monomer [(6-MesDAC)CuCl] (6). The X-ray structures of 1-3 and 1 + 6, along with the cation [Cu(6-MesDAC)2]+ (4), have been determined. [ABSTRACT FROM AUTHOR]