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Half‐sandwich iridium complexes of the type [(η5‐C5Me5){(NHC)E}IrCl] (E=P, As) were prepared by the reactions of N‐heterocyclic carbene (NHC) adducts of trimethylsilylphosphinidene and trimethylsilylarsinidene, (IDipp)ESiMe3 and (IMes)ESiMe3, with [(η5‐C5Me5)IrCl2]2 (IDipp=bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene; IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene). The molecular structure of [(η5‐C5Me5){(IDipp)As}IrCl] was established by X‐ray diffraction analysis, affording the first structurally authenticated NHC‐arsinidenide complex with a short Ir−As bond length that reveals a significant degree of metal‐arsenic π‐interaction as also confirmed by theoretical calculations. [ABSTRACT FROM AUTHOR]

The half-sandwich 1,3-bis(trimethylsilyl)allyl and bis(trimethylsilyl)amido ruthenium complexes [(η5-C5Me5)RuX] (X = η3-C3H3(SiMe3)2, 1; X = N(SiMe3)2, 2) were prepared by reaction of tetranuclear [(η5-C5Me5)RuCl]4 with four equivalents of K[C3H3(SiMe3)2] or Na[N(SiMe3)2]. Complexes 1 and 2 are formally 16- and 14-electron complexes, respectively, and exhibit γ-agostic C–H…Ru interactions in the solid state, which were further investigated by density functional theory (DFT) calculations and quantum theory of atoms in molecules (QTAIM) analysis. The acid–base reaction of the amido complex 2 with 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (ImDippNH) afforded the imidazolin-2-iminato complex [(η5-C5Me5)Ru(NImDipp)] (4); 4 was also obtained from the reaction of [(η5-C5Me5)RuCl]4 with the lithium reagent [(ImDippN)Li]2. 4 represents the first terminal imidazolin-2-iminato complex with a late transition metal and shows a rare one-legged piano stool (“pogo stick”) geometry with a short Ru–N bond of 1.8607(15) Å. The reaction of 4 with tert-butyl isocyanate (tBuNCO) gave the ureato complex [(η5-C5Me5)Ru{ImDippN(C=O)NtBu}] (5) by [2 + 2] cycloaddition. This reactivity together with a DFT study on the bonding situation in 4 suggest a close similarity with related half-sandwich imido complexes [(arene)M(NR)] (M = Ru, Os) and [CpM(NR)] (M = Rh, Ir). [ABSTRACT FROM AUTHOR]

Keywords: iridium; N-heterocyclic carbenes; arsenic; arsinidenes; phosphinidenes EN iridium N-heterocyclic carbenes arsenic arsinidenes phosphinidenes 1 1 1 04/18/23 20230414 NES 230414 The cover picture shows the crystal structure of an iridium complex with an N-heterocyclic carbene-arsinidenide ligand. This complex represents an N-heterocyclic carbene analogue of rare transition metal-arsinidene complexes and has the shortest iridium-arsenic bond length reported to date, indicating the presence of strong metal-arsenic -interaction. Front Cover: N-Heterocyclic Carbene-Arsinidenide Iridium Complexes (Z. Anorg. [Extracted from the article]

The reaction of [(η 7 -C 7 H 7 )ZrCl(tmeda)] ( 1 , tmeda = N , N , N ', N '-tetramethylethylene-1,2-diamine) with the sodium dicarbollide Na 2 (C 2 B 9 H 11 ) afforded the cycloheptatrienyl-dicarbollyl (Cht-Dcb) complex [Na(tmeda)][(η 7 -Cht)Zr(η 5 -Dcb)], [Na(tmeda)][ 2 ]. In the solid state, the sodium cations act as bridging units between the sandwich anions by η 2 -and η 3 -interaction with the Cht and Dcb ligands, respectively. The reaction of [Na(tmeda)][ 2 ] with BaI 2 resulted in the formation of [Ba(thf) 5 (μ-η 7 :η 7 -C 7 H 7 )Zr(η 5 -C 2 B 9 H 11 )][(η 7 -C 7 H 7 )Zr(η 5 -C 2 B 9 H 11 )], [Ba(thf) 5 ( 2 )][ 2 ], in which the cation exhibits an unusual bridging μ-η 7 :η 7 -C 7 H 7 unit between the Dcb-Zr and the Ba(thf) 5 fragments. An analogous reaction could not be effected by the salt metathesis reaction between [Na(tmeda)][ 2 ] and 0.25 equivalents of [(η 5 -C 5 Me 5 )Ru(μ 3 -Cl)] 4 , since the ion pair [(η 5 -C 5 Me 5 )Ru(tmeda)][ 2 ] containing the 16-electron half-sandwich tmeda complex was formed instead. The tetramethylammonium salt [NMe 4 ][ 2 ] was prepared via an acid-base reaction between the amido complex [(η 7 -C 7 H 7 )Zr{N(SiMe 3 ) 2 }(thf)] and [NMe 4 ][C 2 B 9 H 12 ]. [NMe 4 ][ 2 ] is more stable than its sodium congener [Na(tmeda)][ 2 ] and might therefore act as a suitable transfer reagent for the construction of multidecker sandwich transition metal complexes in the future. [ABSTRACT FROM AUTHOR]

The sterically demanding NHCs 1,3-di-tert-butylimidazolin-2-ylidene (1a), 1,3-di-tert-butyl-4,5-dimethylimidazolin- 2-yildene (1b), and also the corresponding frustrated Lewis pair combinations 1a,b/B(C6F5)3 react readily with CO2 to form the NHC·CO2 (5a,b) and the NHC·CO2·B(C6F5)3 (9a,b) adducts, respectively. However, N2O activation and isolation of the NHC·N2O adduct (6) was only possible for NHC 1a. On heating, the NHC·N2O adduct 6 degrades to 1a, N2O, N2 and the urea derivative 7. Nevertheless, an NHC·N2O adduct of 1b was obtained with the FLP system 1b/B(C6F5)3. In contrast, for the FLP combination 1a/B(C6F5)3, N2O coordination appears to be slower than the self-deactivation. Hence, only the self-deactivation product 3 was observed under an N2O atmosphere. DFT calculations give insights into the CO2 and N2O activation process with 1a,b and 1a,b/B(C6F5)3. [ABSTRACT FROM AUTHOR]

Tris[3,5-bis(trifluoromethyl)phenyl]borane reacts with the sterically demanding Arduengo carbenes 1,3-di- tert-butylimidazolin-2-ylidene and 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene to form isolable normal adducts. In the case of 1,3-di- tert-butylimidazolin-2-ylidene, the adduct exhibits dynamic behaviour in solution and frustrated-Lewis-pair (FLP) reactivity. Fast cleavage of dihydrogen and THF, the CH activation of phenylacetylene, and carbon dioxide fixation were achieved by using solutions of this adduct in benzene. This adduct is stable at room temperature in the absence of suitable substrates; however, thermal rearrangement into an abnormal carbene-borane adduct can be observed. In contrast, the 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene adduct exhibits no evidence of FLP reactivity or of dissociation in solution. DFT calculations confirmed the experimental behaviour and stability of these carbene-borane adducts. [ABSTRACT FROM AUTHOR]

[FeI2(thf)2] was sequentially treatedwithLi(C5Me5) and the potassium salt of the phenylmethallyl(“open indenyl”) ligand oIndMe, leading toselective formation of the half-open ferrocene [(η5-C5Me5)Fe(η5-oIndMe)] (1). A variable-temperature NMR study revealed abarrier of ca. 12 kcal mol–1for the rotation ofthe phenyl group. The apparent lability and susceptibility of theoIndMeligand in 1to undergo η5–η3interconversion allowed the preparationof the complexes [(η5-C5Me5)Fe(η3-oIndMe)(L)] (2, L= CO; 3, L = IMe; 4, L = PMe3) by addition of carbon monoxide, 1,3,4,5-tetramethylimidazolin-2-ylidene(IMe), and trimethylphosphine, respectively. The η3-bound phenylmethallyl ligand in these complexes initially adoptsan antiorientation with regard to the relative positionsof the phenyl and methyl substituents, followed by anti-to-synisomerization. For L = CO, both isomerscould be isolated, and the conversion of anti-2into syn-2was monitored byNMR spectroscopy at 35, 50, 65, and 80 °C, affording an enthalpyof activation of ΔH⧧= 24(1)kcal mol–1for this equilibrium reaction. On thebasis of DFT calculations, a mechanism is proposed that proceeds viaconsecutive η3–η1–η3interconversions and involves η3-benzylintermediates. In contrast, rapid equilibration was observed for L= IMe and PMe3. Addition of 1,2-bis(dimethylphosphino)ethane(dmpe) to 1gave [(η5-C5Me5)Fe(η1-oIndMe)(dmpe)] (5), containing the oIndMeligand bound in an η1-allyl fashion. η5-to-η3hapticity interconversion was also observed upon reaction of 1with methyl iodide and CH2Cl2, whichformed the Fe(III) complexes [(η5-C5Me5)Fe(η3-oIndMe)(X)] (6, X = I; 7, X = Cl); solid-state magnetic susceptibilitymeasurements on 6revealed an S= 1/2ground state. The mixed indenyl–open indenyl complex [(η5-Ind″)Fe(η3-oIndMe)(CO)](9, Ind″ = 1,3-di(tert-butyl)indenyl)was isolated from the stepwise reaction of [FeI2(thf)2] with Na(Ind″), K(oIndMe), and CO. Themolecular structures of 1, anti-2, syn-2, syn-3, 5, syn-6, syn-7, and syn-9were established by single-crystal X-ray diffraction. [ABSTRACT FROM AUTHOR]

The reaction of the cycloheptatrienylzirconium half-sandwich complex [(η7-C7H7)ZrCl(tmeda)] (1) (tmeda = N,N,N',N'-tetramethylethylenediamine) with Li(ImDippN), generated from bis(2,6-diisopropylphenyl)imidazolin-2-imine (ImDippNH) with methyllithium, yields the imidazolin-2-iminato complex [(η7-C7H7)Zr(ImDippN)(tmeda)] (2). The corresponding tmeda-free complex [(η7-C7H7)Zr(ImDippN)] (5) can be synthesized via the 1,3-bis(trimethylsilyl)allyl complex [(η7-C7H7)Zr{η3-C3H3(TMS)2}(THF)] (3; TMS = SiMe3), which undergoes an acid-base reaction with ImDippNH to form 5 and 1,3-bis(trimethylsilyl)propene. 5 exhibits an unusual one-legged piano stool ("pogo stick") geometry with a particularly short Zr-N bond of 1.997(2) Å. Addition of 2,6-dimethylphenyl or tert-butyl isocyanide affords the complexes [(η7-C7H7)Zr(ImDippN)(CNR)] (R = o-Xy, 6; R = t-Bu, 7), while the reaction with 2,6-dimethylphenyl isocyanate results in a [2 + 2] cycloaddition to form the ureato(1−) complex [(η7-C7H7)Zr{ImDippN(C═O)N-o-Xy}] (8). 5 can also act as an initiator for the ring-opening polymerization of ε-caprolactone. These reactivity patterns together with density functional theory calculations reveal a marked similarity of the bonding in imidazolin-2-iminato and conventional imido transition-metal complexes. [ABSTRACT FROM AUTHOR]

Abstract: The reactions of [(η7-C7H7)Hf(η5-C5H5)] (1b) with the two-electron donor ligands tert-butyl isocyanide (tBuNC), 2,6-dimethylphenyl isocyanide (XyNC), 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe) and trimethylphosphine (PMe3) are reported. The 1:1 complexes [(η7-C7H7)Hf(η5-C5H5)L] (2b, L= tBuNC; 3b, L=XyNC; 4b, L=IMe, 5b, L=PMe3) have been isolated in crystalline form, and their molecular structures have been determined by X-ray diffraction analyses. The stabilities of these hafnium complexes were probed via spectroscopic and theoretical methods, and the results were compared to those previously reported for the corresponding zirconium complexes derived from [(η7-C7H7)Zr(η5-C5H5)] (1a). The X-ray crystal structure of the PMe3 adduct [(η7-C7H7)Zr(η5-C5H5)(PMe3)] (5a) was also established. [Copyright &y& Elsevier]

Abstract: The reaction of [(η7-C7H7)Zr(η5-C5H5)] with two Lewis bases, tetramethylimidazolin-2-ylidene and PMe3, is reported and their stability probed via spectroscopic and theoretical methods. The strongly σ-basic N-heterocyclic carbene forms a stable adduct which has been structurally characterised, whilst the PMe3 ligand coordinates weakly to the metal centre. Variable temperature 31P NMR spectroscopy has been used to determine the activation energy for this process (ΔG ‡ =40.5±1.9kJmol−1). DFT calculations have been performed on both complexes and the structures discussed. In addition, the enthalpies for the formation of these compounds have been calculated [ΔH 0(Zr–IMe)=−56.3kJmol−1; ΔH 0(Zr–PMe3)=−2.3kJmol−1] and show that the N-heterocyclic carbene forms a thermodynamically much more stable adduct than that with PMe3. [Copyright &y& Elsevier]

Abstract: The first directly annulated cyclopentadienyl–imidazolium salt has been synthesized and fully characterized. In the solid-state, this zwitterion arranges itself in a hydrogen-bridged head to tail trimer which optimizes ionic interactions. Substantial π–π interactions are absent. The UV spectrum of the imidazolium innersalt reflects the intimate electronic interaction arising from direct fusion of cationic and anionic fragments of the molecule. [Copyright &y& Elsevier]

Investigates the molybdenum complex link to cycloheptatrienyl-phenolate ligands. Characterization by X-ray crystal structure; Protonation of the coordinated oxygen atom by employment of HBF[sub 4]*Et[sub 2]O; Experimentation of the paramagnetic monocationic complex by ESP spectroscopy and X-ray diffraction.

The lithium salts of anionic N‐heterocyclic thiones and selones [{(WCA‐IDipp)E}Li(toluene)] (1: E=S; 2: E=Se; WCA=B(C6F5)3, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene), which contain a weakly coordinating anionic (WCA) borate moiety in the imidazole backbone were reacted with Me3SiCl, to furnish the silylated adducts (WCA‐IDipp)ESiMe3 (3: E=S; 4: E=Se). The reaction of the latter with [(η5‐C5Me5)MCl2]2 (M=Rh, Ir) afforded the rhodium(III) and iridium(III) half‐sandwich complexes [{(WCA‐IDipp)E}MCl(η5‐C5Me5)] (5–8). The direct reaction of the lithium salts 1 and 2 with a half or a full equivalent of [M(COD)Cl]2 (M=Rh, Ir) afforded the monometallic complexes [{(WCA‐IDipp)E}M(COD)] (9–12) or the bimetallic complexes [μ2‐{(WCA‐IDipp)E}M2(COD)2(μ2‐Cl)] (13–16), respectively. The bonding situation in these complexes has been investigated by means of density functional theory (DFT) calculations, revealing thiolate or selenolate ligand character with negligible metal‐chalcogen π‐interaction. [ABSTRACT FROM AUTHOR]

The lithium complexes [(WCA‐NHC)Li(toluene)] of anionic N‐heterocyclic carbenes with a weakly coordinating anionic borate moiety (WCA‐NHC) reacted with iodine, bromine, or CCl4 to afford the zwitterionic 2‐halogenoimidazolium borates (WCA‐NHC)X (X=I, Br, Cl; WCA=B(C6F5)3, B{3,5‐C6H3(CF3)2}3; NHC=IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene, or NHC=IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene). The iodine derivative (WCA‐IDipp)I (WCA=B(C6F5)3) formed several complexes of the type (WCA‐IDipp)I⋅L (L=C6H5Cl, C6H5Me, CH3CN, THF, ONMe3), revealing its ability to act as an efficient halogen bond donor, which was also exploited for the preparation of hypervalent bis(carbene)iodine(I) complexes of the type [(WCA‐IDipp)I(NHC)] and [PPh4][(WCA‐IDipp)I(WCA‐NHC)] (NHC=IDipp, IMes). The corresponding bromine complex [PPh4][(WCA‐IDipp)2Br] was isolated as a rare example of a hypervalent (10‐Br‐2) system. DFT calculations reveal that London dispersion contributes significantly to the stability of the bis(carbene)halogen(I) complexes, and the bonding was further analyzed by quantum theory of atoms in molecules (QTAIM) analysis. [ABSTRACT FROM AUTHOR]

Chloride abstraction from the complexes [(η6‐p‐cymene){(IDipp)P}MCl] (2 a, M=Ru; 2 b, M=Os) and [(η5‐C5Me5){(IDipp)P}IrCl] (3 b, IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBArF) in the presence of trimethylphosphine (PMe3), 1,3,4,5‐tetramethylimidazolin‐2‐ylidene (MeIMe) or carbon monoxide (CO) afforded the complexes [(η6‐p‐cymene){(IDipp)P}M(PMe3)]BArF] (4 a, M=Ru; 4 b, M=Os), [(η6‐p‐cymene){(IDipp)P}Os(MeIMe)]BArF] (5) and [(η5‐C5Me5){(IDipp)P}IrL][BArF] (6, L=PMe3; 7, L=MeIMe; 8, L=CO). These cationic N‐heterocyclic carbene‐phosphinidene complexes feature very similar structural and spectroscopic properties as prototypic nucleophilic arylphosphinidene complexes such as low‐field 31P NMR resonances and short metal‐phosphorus double bonds. Density functional theory (DFT) calculations reveal that the metal‐phosphorus bond can be described in terms of an interaction between a triplet [(IDipp)P]+ cation and a triplet metal complex fragment ligand with highly covalent σ‐ and π‐contributions. Crystals of the C−H activated complex 9 were isolated from solutions containing the PMe3 complex, and its formation can be rationalized by PMe3 dissociation and formation of a putative 16‐electron intermediate [(η5‐C5Me5)Ir{P(IDipp)}I][BArF], which undergoes C−H activation at one of the Dipp isopropyl groups and addition along the iridium‐phosphorus bond to afford an unusual η3‐benzyl coordination mode. [ABSTRACT FROM AUTHOR]

Several group 16 adducts of the type [(WCA-IDipp)E]Li(solv.) that bear an anionic N-heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA-IDipp, WCA = B(C6F5)3, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene, E = O, S, Se, Te) were prepared. This was achieved by deprotonation of the corresponding ketone (IDipp)O or thione (IDipp)S with n-BuLi and subsequent reaction with B(C6F5)3 or by direct reaction of [WCA-IDipp]Li(toluene) with elemental Se or Te. The oxygen, sulfur and selenium adducts can be protonated to give derivatives (WCA-IDipp)EH (E = O, S, Se), whereas the oxidation of the sulfur and selenium adducts yielded neutral disulfide and diselenide species (WCA-IDipp)2E2 (E = S, Se). [ABSTRACT FROM AUTHOR]

The dimer of dipiperidinoacetylene, 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne, reacts with [IrCl(COD)]2 (COD=1,5‐cyclooctadiene) to give the corresponding 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene‐iridium complex [(CBA)IrCl(COD)] with a four‐membered cyclic bent allene (CBA) ligand. Reaction with carbon monoxide affords the dicarbonyl complex cis‐[(CBA)IrCl(CO)2], which exhibits low CO stretching frequencies and an associated Tolman electronic parameter (TEP) value of 2030 cm−1, which is lower than any other TEP value reported for cyclic carbene and carbenoid ligand systems. Treatment of [(CBA)IrCl(COD)] with sodium tetrakis[3,5‐bis(trifluoromethyl)phenyl]borate (NaBARF) followed by addition of phosphines or pyridine (py) yields the cationic complexes [(CBA)IrL(COD)][BARF] (L=PPh3, PPh2Me, PPhMe2, PCy3, py) as potential hydrogen isotope exchange (HIE) catalysts. DFT calculations provide evidence for a suitable pathway for the cyclization of 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne at transition metal complex fragments, here AuCl, IrCl(COD), and IrCl(CO)2, as a general route to four‐membered CBA metal complexes. [ABSTRACT FROM AUTHOR]

The marine natural product norzooanemonin (1,3-dimethylimidazolium-4-carboxylate) has been used to prepare a series of carboxyl- or carboxylate-functionalized N-heterocyclic carbene (NHC) gold(I) complexes from [(Me2S)AuCl] in the presence of potassium carbonate. The potential of the resulting mono- and dicarbene complexes to act as cytotoxic or antibacterial drugs was investigated. [ABSTRACT FROM AUTHOR]

The reaction of 1,2‐dipiperidinoacetylene (1) with 0.5 equivalents of SnCl2 or GeCl2⋅dioxane afforded the 1,2,3,4‐tetrapiperidino‐1,3‐cyclobutadiene tin and germanium dichloride complexes 2 a and 2 b, respectively. A competing redox reaction was observed with excess amounts of SnCl2, which produced a tetrapiperidinocyclobutadiene dication with two trichlorostannate(II) counterions. Heating neat 1 to 110 °C for 16 h cleanly produced the dimer 1,3,4,4‐tetrapiperidino‐3‐buten‐1‐yne (3); its reaction with stoichiometric amounts of SnCl2 or GeCl2⋅dioxane furnished the 1,3,4,4‐tetrapiperidino‐1,2‐cyclobutadiene tin and germanium dichloride complexes 4 a and 4 b, respectively. Transition‐metal complexes containing this novel four‐membered cyclic bent allene (CBA) ligand were prepared by reaction of 3 with [(tht)AuCl], [RhCl(CO)2]2, and [(Me3N)W(CO)5] to form [(CBA)AuCl] (5), [(CBA)RhCl(CO)2] (6), and [(CBA)W(CO)5] (7). The molecular structures of all compounds 2–7 were determined by X‐ray diffraction analyses, and density functional theory (DFT) calculations were carried out to rationalise the formation of 3 and 4 a. [ABSTRACT FROM AUTHOR]

Diphosphine chelate ligands are essential in many catalytic processes with both the electronic structure and bite angle having a dramatic influence on the coordination behavior and catalytic performance. The synthesis of a new class of diferrocenylmercury-supported diphosphine chelate ligands was accomplished by the reaction of (ortho-diphenylphosphino)ferrocenyl sulfinate (2) with t-BuLi, followed by treatment with mercury(II) chloride. Two diastereomers, 4a (pSpR-, meso-isomer) and 4b (pSpS-isomer), differ in the orientation of the ferrocene moiety relative to the central Ph2PC5H3-Hg-C5H3PPh2 bridging entity. They were isolated independently and fully characterized in solution and in the solid state by single crystal X-ray diffraction analysis. Key characteristics of these ligands are their exceptionally wide and flexible bite angles and the unique stereochemical environment that is achieved upon coordination to transition metals. Complexation to Pd(II)Cl2 gives rise to unusual square-planar trans-chelate complexes 5a (meso) and 5b (pSpS). In competition reactions, 4a and 4b show similar reactivity toward Pd(II)Cl2. The molecular structures of 5a and 5b exhibit short Pd⋯Hg contacts, possibly indicating secondary metallophilic interactions as further evidenced by bond-critical points between Pd and Hg that were identified by AIM analyses. [ABSTRACT FROM AUTHOR]

The reaction of the phosphorus and arsenic dihalides (WCA-IDipp)ECl2 (E = P, As) that bear an anionic N-heterocyclic carbene ligand with a weakly coordinating borate moiety (WCA = B(C6F5)3, IDipp = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with (IDipp)PSiMe3 afforded the monochlorides (WCA-IDipp)E(Cl)P(IDipp), which can be transformed into the cationic dipnictenes [(WCA-IDipp)EP(IDipp)][GaCl4] or neutral radicals [(WCA-IDipp)EP(IDipp)] by treatment with GaCl3 or reduction with 1,4-bis(trimethylsilyl)-1,4-dihydropyrazine. [ABSTRACT FROM AUTHOR]

Abstract: A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox‐active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2‐fc(PPh2)(SnMe3) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n‐Bu4N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg−Cl→Hgfc2 (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2)2⋅HgCl2 where the bridging mercury atom acts as a σ‐acceptor. Furthermore, a bis‐[Rh(COD)Cl] complex is introduced, which displays relatively short Rh⋅⋅⋅Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh⋅⋅⋅Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10−2 and 1.4×10−2 e/a03 at the bond critical points. [ABSTRACT FROM AUTHOR]

A diphosphine chelate ligand with a wide and flexible bite angle, a unique stereochemical environment, and redox-active and ambiphilic character is reported. Initially generated as its HgCl2 complex by reaction of 1,2-fc(PPh2)(SnMe3) (fc=ferrocenediyl) with HgCl2 in acetone, treatment with [n-Bu4N]CN readily liberates the free chiral bidentate ligand. An intermolecular ClHg-Cl→Hgfc2 (2.9929(13) Å) interaction that is unprecedented in ambiphilic ligand chemistry is seen in the solid structure of Hg(fcPPh2)2 HgCl2 where the bridging mercury atom acts as a s-acceptor. Furthermore, a bis-[Rh(COD)Cl] complex is introduced, which displays relatively short Rh...Hg contacts of 3.4765(5) and 3.4013(1) Å. Wiberg indices of 0.12 are determined for these Rh...Hg interactions and an AIM analysis reveals bond paths with an electron density ρ(r) of 1.2×10-2 and 1.4×10-2 e/a03 at the bond critical points. [ABSTRACT FROM AUTHOR]

The bis(imidazolin-2-imine) ligand N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,1′-ferrocenediamine, fc(NIm)2 (1) was prepared. Its reaction with [NiCl2(dme)] (dme = 1,2-dimethoxyethane) or [PdCl2(MeCN)2] afforded the tetrahedral, paramagnetic complex [(1-κ²N,N′)NiCl2] (6a) or the diamagnetic, square-planar complex [(1-κ²N,N′)PdCl2] (6b), respectively. For the latter, slow rearrangement to the ionic complex [(1-κFe,κ²N,N′)PdCl]Cl, [7]Cl, was observed, which was followed by ¹H NMR and UV/vis spectroscopy. Treatment of [7]Cl with NaBF4 afforded [7]BF4; the palladium atoms in both cations adopt square-planar environments with short Fe-Pd bonds (ca. 2.65 Å). In addition, a series of dicationic complexes of the type [(1-κFe,κ²N,N′)ML](BF4)2 (8a: M = Ni, L = MeCN; 8b: M = Pd, L = MeCN; 9a: M = Ni, L = PMe3; 9b: M = Pd, L = PMe3) was prepared from 6a (M = Ni) or [7]BF4 by chloride abstraction with NaBF4 or AgBF4 in the presence of acetonitrile or trimethylphosphine, respectively. In the presence of triphenylphosphine, the palladium(II) complex [(1-κFe,κ²N,N′)Pd(PPh3)](BF4)2 (10) was isolated. Iron-nickel and iron-palladium bonding in these complexes was studied experimentally by NMR, UV/vis, and Mössbauer spectroscopy and by cyclic voltammetry. Detailed DFT calculations were carried out for the cations [(1-κFe,κ²N,N′)M(MeCN)]2+ in the 8a/8b couple, with Bader's atoms in molecules theory revealing the presence of noncovalent, closed-shell metal-metal interactions. Potential energy surface scans with successive elongation of the Fe-M bonds allow an estimation of the iron-metal bond dissociation energies (BDE) as BDE(Fe-Ni) = 11.3 kcal mol-1 and BDE(Fe-Pd) = 24.3 kcal mol-1. [ABSTRACT FROM AUTHOR]

Bis(η5-2,4-dimethylpentadienyl)ruthenium(ii), [(η5-C7H11)2Ru] (1, “open ruthenocene”), which has become accessible in high yield and large quantities via an isoprene-derived diallyl ruthenium(iv) complex, can be converted into the protonated open ruthenocene 2 by treatment with HBF4 and subsequently into the protonated half-open ruthenocene 3 by reaction with cyclopentadiene. The electronic structure of 3 was studied by DFT methods, revealing that the CH-agostic complex [(η5-C5H5)Ru{(1-4η)-C7H12-η2-C5,H5}]BF4 (A) represents the global minimum, which is 3.7 kcal mol−1 lower in energy than the hydride complex [(η5-C5H5)RuH(η5-C7H11)]BF4 (B). 2 and 3 were treated with the ligands N,N′-bis(1,3,4,5-tetramethylimidazolin-2-ylidene)-1,2-ethanediamine (BLMe) and N,N′-bis(1,3-diisopropyl-4,5-dimethylimidazolin-2-ylidene)-1,2-ethanediamine (BLiPr) to afford the cationic 16-electron pentadienyl and cyclopentadienyl complexes [(η5-C7H11)Ru(BLR)]BF4 (4a, R = Me; 4b, R = iPr) and [(η5-C5H5)Ru(BLR)]BF4 (5a, R = Me; 5b, R = iPr). All complexes catalyse the transfer hydrogenation of acetophenone in isopropanol, and the most active complex 4a in this reaction was employed for the hydrogenation of a broader range of aliphatic and aromatic ketones. [ABSTRACT FROM AUTHOR]

The reaction of the N-heterocyclic carbene 1,3-di-tert-butyl-4,5-dimethylimidazolin-2-ylidene (1b) with trimethylsilyl iodide, triflate and triflimidate [Me3SiX, X = I, CF3SO3 (OTf), (CF3SO2)2N (NTf2)] by mixing the neat, liquid starting materials afforded the corresponding 2-(trimethylsilyl)imidazolium salts [(1b)SiMe3]X as highly reactive, white crystalline solids. Only the triflimidate (X = NTf2) proved to be stable in solution and could be characterized by means of NMR spectroscopy (in C6D5Br) and X-ray diffraction analysis, whereas dissociation into free 1b and Me3SiOTf was observed for the triflate system, in agreement with the trend derived by DFT calculations; the iodide was too insoluble for characterization. The compounds [(1b)SiMe3]X showed the reactivity expected for frustrated carbene–silylium pairs, and treatment with carbon dioxide, tert-butyl isocyanate and diphenylbutadiyne gave the 1,2-addition products [(1b)CO2SiMe3]X (X = I, OTf, NTf2), [(1b)C(NtBu)OSiMe3]OTf and [(1b)C(Ph)C(SiMe3)CCPh]OTf, respectively. Upon reaction with [AuCl(PPh3)], metal–chloride bond activation was observed, with formation of the cationic gold(i) complexes [(1b)Au(PPh3)]X (X = OTf, NTf2). [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene-phosphinidene adduct IPr=PSiMe3 is introduced as a synthon for the preparation of terminal carbene-phosphinidyne transition metal complexes of the type [(IPr=P)MLn] (MLn=(η6-p-cymene)RuCl) and (η5- C5Me5)RhCl). Their spectroscopic and structural characteristics, namely low-field 31P NMR chemical shifts and short metal-phosphorus bonds, show their similarity with arylphosphinidene complexes. The formally mononegative IPr=P ligand is also capable of bridging two or three metal atoms as demonstrated by the preparation of bi- and trimetallic RuAu, RhAu, Rh2, and Rh2Au complexes. [ABSTRACT FROM AUTHOR]

The N-heterocyclic carbene-phosphinidene adduct IPrPSiMe3 is introduced as a synthon for the preparation of terminal carbene-phosphinidyne transition metal complexes of the type [(IPrP)MLn] (MLn=(η6-p-cymene)RuCl) and (η5-C5Me5)RhCl). Their spectroscopic and structural characteristics, namely low-field 31P NMR chemical shifts and short metal-phosphorus bonds, show their similarity with arylphosphinidene complexes. The formally mononegative IPrP ligand is also capable of bridging two or three metal atoms as demonstrated by the preparation of bi- and trimetallic RuAu, RhAu, Rh2, and Rh2Au complexes. [ABSTRACT FROM AUTHOR]

Abstract: Replacement of THF in [(η7-C7H7)Zr{C3H3(TMS)2}(thf)] (1) by trimethylphosphine (PMe3), 4-(dimethylamino)pyridine (DMAP), 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe) or 1,3,4,5-tetramethyl-2-methyleneimidazoline (H2C–IMe) resulted in the new 16-electron cycloheptatrienyl zirconium allyl complexes [(η7-C7H7)Zr{C3H3(TMS)2}(L)] (2: L = PMe3, 3: L = DMAP, 4: L = IMe, 5: L = H2C–IMe), which were all structurally characterized by X-ray diffraction analysis. The two-electron donor ligands are coordinated at the open edge of the 1,3-bis(trimethylsilyl)allyl ligand, which requires the TMS-substituents to point away from the metal (syn–syn orientation). In 5, the ylidic character of the exocyclic sp2 carbon atom of the ligand led to end-on coordination accompanied by a pronounced elongation of the C–C bond distance. According to DFT calculations on 1, 2 and 4 and a variable temperature NMR study on 2, the Zr–L bonds feature significantly higher stabilities than in the corresponding 18-electron adducts of [(η7-C7H7)Zr(η5-C5H5)]. [Copyright &y& Elsevier]

The indenyl effect has been introduced to pentadienyl (“open cyclopentadienyl”) chemistry by preparation of the phenylmethallyl (“open indenyl”) ligand oIndMe. The reaction of its potassium salt K(oIndMe) with [(η5-C5Me5)RuCl]4afforded the sandwich complex [(η5-C5Me5)Ru(η5-oIndMe)] (1), which, upon treatment with PMe3, CO, and 2,6-dimethylphenyl isocyanide (CN-o-Xy), easily underwent η5–η3hapticity interconversion and formed the complexes [(η5-C5Me5)Ru(η3-oIndMe)(L)] (2, L = PMe3; 3, L = CO; 4, L = CN-o-Xy). In these complexes, the η3-bound phenylmethallyl ligand adopts an anti-conformation with regard to the relative positions of the phenyl and methyl substituents. For the PMe3complex anti-2, slow conversion to the syn-isomer was observed, and this equilibrium reaction was monitored by NMR spectroscopy at 50 °C to determine a first order rate constant of k323 K= 6.57 × 10−6(± 0.02 × 10−6) s−1and an activation barrier of ΔG° = 26.8 kcal mol−1. DFT calculations afforded a stabilization of syn-2and syn-3by ΔG298= −1.54 and −1.74 kcal mol−1over the respective anti-isomer. [ABSTRACT FROM AUTHOR]

Abstract: The reaction of one equivalent of Cp*2UCl2 with 2-(trimethylsilylimino)-1,3-di-tert-butylimidazoline in boiling toluene afforded a one electron oxidation of the uranium metal and the opening of the N-heterocyclic ring, resulting in the formation of an organometallic uranium(V) imine complex. This complex crystallized with one molecule of toluene in the unit cell, and its solid-state structure was determined by X-ray diffraction analysis. When the same reaction was performed in perdeuterated toluene, a myriad of organometallic complexes were obtained, however, when equimolar amounts of water were used in toluene, the same complex was obtained, and its solid state characterization shows two independent molecules in the unit cell with an additional water molecule. For comparison of the geometric parameters, the corresponding isolobal anionic uranium(IV) complex [Cp*2UCl3]− was synthesized by the reaction of Cp*2UCl2 with 1,3-di-tert-butylimidazolium chloride, and the resulting U(IV)-ate complex was characterized by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

The reactions of 1 ,3-bis(2,6-diisopropylphenyl)imidazolin-2-imine (lm[supDipp]NH, 1-H) with trimethylsilylmethyl lithium (LiCH[sub2]SiMe[sub3]) and anhydrous rare earth metal trichiorides MCI[sub3] afforded the imidazolin-2-iminato complexes [(1)MCI[sub2](THF)[sub3]] (2a, M = Sc; 2b, M = Y; 2c, M = Lu) and [(1)GdCI[sub2](THF)[sub2]]∙[LiCI(THF)[sub2]] (2d). Treatment of complexes 2 with dipotassium cyclooctatetradienide, K[sub2](C[sub8]H[sub8]) resulted in the formation of two- or three-legged piano- stool complexes of the type [(η[sup8]-C[sub8]H[sub8])M(1 )(THF)[subn]] (3a, M = Sc, n = 1; 3b, M = Y, n = 2; 3c, M = Lu, n = 2; 3d, M = Gd, n = 2). X-ray diffraction analyses of all eight complexes 2 and 3 revealed the presence of very short metal-nitrogen bonds, which are among the shortest ever observed for these elements. [(η[sup8]-C[sub8]H[sub8])Sc(1)(THF)] (3a) reacted with 2,6-dimethyiphenyl isothiocyanate (Xy-NCS) to form the [2 + 2]-cycloaddition product 4, which contains a thioureato-N, N' moiety. The related COT-titanium complex [(η[sup8]-C[sub8]H[sub8])TiCI(1)] (6) could be obtained from [(1)TiCI[sub3]] (5) by reaction with K[sub2](C[sub8]H[sub8]) and was structurally characterized. As a theoretical analysis of the nature of the metal-nitrogen bond, density functional theory (DFT) calculations have been carried out for complexes 3a and 6 and also for the model complexes [(η[sup8]-C[sub8]H[sub8])Sc(NlmMe)] (7), [(η[sup8]-C[sub8]H[sub8])Ti(NlmMe)][sup+] (8), and [(η[sup]8-C[sub8]H[sub8])Ti(NXy)] (9), revealing a marked similarity of the bonding in imidazolin-2-iminato and conventional imido metal complexes. [ABSTRACT FROM AUTHOR]

Abstract: The Lewis acid–base reaction of 2,6-bis[1,3-di-tert-butylimidazolin-2-imino)methyl]pyridine (TL tBu) and LnCl3 in THF leads to the corresponding neutral lanthanide complexes of type [(TL tBu)LnCl3], Ln=Y (1a), Er (1b), Lu (1c). The yttrium and lutetium complexes have been characterized by X-ray diffraction analysis. The solid state structures reveal that the bulky TL tBu ligand causes steric crowding around the lanthanide atoms by coordinating to the metal center in a tridentate fashion. In addition, remote C–H⋯Ln interactions (H⋯Ln ca. 2.7Å) involving one of the t Bu methyl groups are observed in both cases. A DFT (density functional theory) calculation on 1a was able to reproduce this interaction, which was additionally characterized by means of an H⋯Y compliance constant and by employing the AIM (atoms in molecules) theory. [Copyright &y& Elsevier]

Iridium, N-heterocyclic carbine, rhodium, selenium, sulfur Cover Feature: Rhodium and Iridium Complexes of Anionic Thione and Selone Ligands Derived from Anionic N-Heterocyclic Carbenes (Chem. Eur. J. 4/2022) Keywords: Iridium; N-heterocyclic carbine; rhodium; selenium; sulfur EN Iridium N-heterocyclic carbine rhodium selenium sulfur 1 1 1 01/21/22 20220119 NES 220119 B Anionic N-heterocyclic carbenes b that bear a weakly coordinating fluoroborate moiety have been used to prepare a new class of anionic imidazolin-2-thione and -selone ligands; their coordination chemistry towards rhodium and iridium was explored to reveal their ability to develop secondary arene-metal interactions with the "wings" of the carbene ligands. [Extracted from the article]

Keywords: halogen bonding; hypervalency; iodine; London dispersion; N-heterocyclic carbenes EN halogen bonding hypervalency iodine London dispersion N-heterocyclic carbenes 4214 4214 1 03/03/21 20210301 NES 210301 B Iodine complexes of anionic N-heterocyclic carbenes b (NHC) act as electrophiles towards a variety of nucleophiles, with the interactions ranging from noncovalent charge-transfer or halogen bonding to covalent 3-center, 4-electron bonding. Cover Feature: Halogen Complexes of Anionic N-Heterocyclic Carbenes (Chem. Eur. J. 13/2021) Halogen bonding, hypervalency, iodine, London dispersion, N-heterocyclic carbenes. [Extracted from the article]

Cover Feature: N-Heterocyclic Carbene Analogues of Nucleophilic Phosphinidene Transition Metal Complexes (Chem. Eur. J. 65/2020) Keywords: iridium; N-heterocyclic carbenes; osmium; phosphinidenes; phosphorus ligands EN iridium N-heterocyclic carbenes osmium phosphinidenes phosphorus ligands 14773 14773 1 11/28/20 20201120 NES 201120 B N-Heterocyclic carbene-phosphinidene complexes b can be conceived as new and true members of the class of nucleophilic phosphinidene complexes according to their spectroscopic, structural, and electronic properties, since substitution of the aryl moiety in authentic neutral arylphosphinidene complexes of the type [ArP=ML SB I n i sb ] by an N-heterocyclic carbene affords the corresponding cationic complexes [(NHC)P=ML SB I n i sb ] SP + sp with equally short and covalent metal-phosphorus double bonds. Iridium, N-heterocyclic carbenes, osmium, phosphinidenes, phosphorus ligands. [Extracted from the article]

Arsenic monophosphide (AsP) species supported by two different N‐heterocyclic carbenes were prepared by reaction of (IDipp)PSiMe3 (1) (IDipp=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) with (IMes)AsCl3 (2) (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene) to afford the dichloride [(IMes)As(Cl)P(IDipp)]Cl (3), which upon reduction with KC8 furnished heteroleptic [(IMes)AsP(IDipp)] (4). The corresponding mono‐ and dications [(IMes)AsP(IDipp)][PF6], [5]PF6, and [(IMes)AsP(IDipp)][GaCl4]2, [6][GaCl4]2, respectively, were prepared by one‐electron oxidation of 4 with ferrocenium hexafluorophosphate, [Fc]PF6, or by chloride abstraction from 3 with two equivalents of GaCl3, respectively. Compounds 4–6 represent rare examples of heterodiatiomic interpnictogen compounds, and X‐ray crystal structure determinations together with density functional theory (DFT) calculations reveal a consecutive shortening of the As−P bond lengths and increasing bond order, in agreement with the presence of an arsenic–phosphorus single bond in 4 and a double bond in 62+. The EPR signal of the cationic radical [5]+. indicates a symmetric spin distribution on the AsP moiety through strong hyperfine coupling with the 75As and 31P nuclei. [ABSTRACT FROM AUTHOR]

Heteroleptic N-heterocyclic dicarbene–diphosphorus species were prepared by reaction of the carbene–phosphinidene adduct (IPr)PSiMe3 (1, IPr = 1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) with the carbene–phosphorus trichloride adduct (IMes)PCl3 (2, IMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene), which furnished the dichloride [(IPr)PPCl(IMes)]Cl (3). Reduction of 3 with potassium graphite (KC8) afforded [(IPr)PP(IMes)] (4). The corresponding radical cation [(IPr)PP(IMes)]Ṗ+ (5Ṗ+) is isolated as [5]PF6 by reaction of 4 with ferrocenium hexafluorophosphate, whereas complexes containing the corresponding dication [(IPr)PP(IMes)]2+ (62+) can be isolated as the gallate and borate salts [6](GaCl4)2 and [6](BArF)2 by chloride abstraction from 3 with GaCl3 or sodium tetrakis[bis(3,5-trifluoromethyl)phenyl]borate (NaBArF), respectively. The asymmetric set of N-heterocyclic carbene ligands allows to establish 1JPP coupling constants of 249 Hz for 4 and 543 Hz for [6](GaCl4)2. Based on X-ray diffraction analyses, the molecular structures of 4, 5Ṗ+ and 62+ reveal a consecutive shortening of the P–P bond lengths, in agreement with the presence of a phosphorus–phosphorus single bond in 4 and a double bond in 62+, which is best described as a dicationic diphosphene according to density functional theory (DFT) calculations. [ABSTRACT FROM AUTHOR]

Die Reaktion von 2 ‐ (Trimethylsilyl)imidazoliumtriflat 9 mit Diarylborhalogeniden (4 ‐ R ‐ C6H4)2BX (R=H, X=Br; R=CH3, X=Cl; R=CF3, X=Cl) führte zu den NHC ‐ stabilisierten Boreniumkationen 10 a – c. Cyclovoltammetrische Untersuchungen offenbarten eine lineare Korrelation zwischen den Hammett ‐ Parametern σp der para ‐ Substituenten und den Halbstufenpotentialen. Die chemische Reduktion mittels Decamethylcobaltocen, [(C5Me5)2Co], lieferte die entsprechenden Radikale 11 a – c; ihre Charakterisierung durch EPR ‐ Spektroskopie bestätigte den paramagnetischen Charakter von 11 a – c und ergab große Hyperfeinkopplungskonstanten zu den Bor ‐ Isotopen 11B und 10B, während die Delokalisierung des ungepaarten Elektrons in das NHC vernachlässigbar ist. DFT ‐ Berechnungen der Anteile der Spindichteverteilung zwischen dem Carben (NHC) und dem Borylfragment (BR2) offenbarte für 11 a – c ein Spindichteverhältnis (BR2 /NHC) von ca. 9:1, wodurch ihr eindeutiger Borylcharakter unterstrichen wird. Die Molekülstruktur der stabilsten Spezies 11 c wurde durch Röntgenstrukturanalyse bestimmt. Lange haltbar: Die Reaktion eines frustrierten N ‐ heterocyclisches Carben ‐ Silylium ‐ Lewis ‐ Paares mit Diarylhalogenboranen ergab eine Serie von NHC ‐ gestützten Boreniumkationen. Deren Ein ‐ Elektronen ‐ Reduktion lieferte persistente Borylradikale, die mittels EPR ‐ Spektroskopie, Einkristall ‐ Röntgendiffraktometrie und DFT ‐ Methoden untersucht wurden. Die Radikale offenbaren eine nahezu ausschließliche Lokalisierung des ungepaarten Elektrons auf den Diarylboryl ‐ Fragmenten. [ABSTRACT FROM AUTHOR]

The reaction of the 2-(trimethylsilyl)imidazolium triflate 9 with diarylboron halides (4-R-C6H4)2BX (R=H, X=Br; R=CH3, X=Cl; R=CF3, X=Cl) afforded the NHC-stabilized borenium cations 10 a- c. Cyclic voltammetry revealed a linear correlation between the Hammett parameter σp of the para substituent and the half-wave potential. Chemical reduction with decamethylcobaltocene, [(C5Me5)2Co], furnished the corresponding radicals 11 a- c; their characterization by EPR spectroscopy confirmed the paramagnetic character of 11 a- c, with large hyperfine coupling constants to the boron isotopes 11B and 10B, while delocalization of the unpaired electron into the NHC is negligible. DFT calculations of the percentage of spin density distribution between the carbene (NHC) and the boryl fragments (BR2) revealed for 11 a- c a spin density ratio (BR2/NHC) of ca. 9:1, which underlines their distinct boryl radical character. The molecular structure of the most stable species 11 c was established by X-ray diffraction analysis. [ABSTRACT FROM AUTHOR]

Coinage metal complexes of the N-heterocyclic carbene-phosphinidene adduct IPr ⋅PPh (IPr=1,3-bis(2,6-diisopropylphenyl)imidazolin-2-ylidene) were prepared by its reaction with CuCl, AgCl, and [(Me2S)AuCl], which afforded the monometallic complexes [(IPr ⋅PPh)MCl] (M=Cu, Ag, Au). The reaction with two equivalents of the metal halides gave bimetallic [(IPr ⋅PPh)(MCl)2] (M=Cu, Au); the corresponding disilver complex could not be isolated. [(IPr ⋅PPh)(CuOTf)2] was prepared by reaction with copper(I) trifluoromethanesulfonate. Treatment of [(IPr ⋅PPh)(MCl)2] (M=Cu, Au) with Na(BArF) or AgSbF6 afforded the tetranuclear complexes [(IPr ⋅PPh)2M4Cl2]X2 (X=BArF or SbF6), which contain unusual eight-membered M4Cl2P2 rings with short cuprophilic or aurophilic contacts along the chlorine-bridged M⋅⋅⋅M axes. Complete chloride abstraction from [(IPr ⋅PPh)(AuCl)2] was achieved with two equivalents of AgSbF6 in the presence of tetrahydrothiophene (THT) to form [(IPr ⋅PPh){Au(THT)}2][SbF6]2. The cationic tetra- and dinuclear complexes were used as catalysts for enyne cyclization and carbene transfer reactions. [ABSTRACT FROM AUTHOR]

The coordination chemistry of the tridentate pincer ligand TL tBu, which contains two electron-rich imidazolin-2-imine moieties, has been explored. The reaction of TL tBu with metal dihalides gave complexes of the general formula [(TL tBu)MX2] (M = Mn, Fe, Co, Ni; X = Cl, Br). These complexes were characterized by X-ray diffraction analysis, which showed them to have different geometries in the solid state. Although [(TL tBu)MnCl2] ( 1) is best described as distorted square-pyramidal, the complexes [(TL tBu)FeCl2] ( 2) and [(TL tBu)CoCl2] ( 3) show distorted tetrahedral geometries with the TL tBu ligand bound in a κ2 fashion and one of its imidazolin-2-imine fragments not coordinated to the metal atom. [(TL tBu)NiBr]Br ( 4) crystallizes with a slightly distorted square-planar cation. The reaction of the triflate (OTf) salts [M(OTf)2 · nMeCN] (M = Mn, n = 1; M = Fe, Co, n = 2; OTf = CF3SO3) with TL tBu resulted in [(TL tBu)M(OTf)][OTf] (M = Mn, 5; M = Fe, 6) and [(TL tBu)Co(NCMe)][OTf]2 ( 7). Complexes 6 and 7 were characterized by X-ray diffraction analysis, and both showed distorted square-planar geometries. Magnetic measurements of 5, 6 and 7 showed them to possess a S = 5/2, 2 and 1/2 ground states, respectively. The bromide ions in complex 4 were exchanged by reaction with AgBF4 to afford [(TL tBu)Ni(NCMe)][BF4]2 ( 8), which showed a distorted square-planar geometry in the solid state. The reactions of 1 and 6 with AgOTf resulted in the oxidation of the complexes and the formation of [(TL tBu)MnCl(OTf)][OTf] ( 9) and [(TL tBu)Fe(OTf)2][OTf] ( 10), respectively. Complexes 9 and 10 both display distorted square-pyramidal geometries in the solid state. The ground state of 10 was found to be S = 5/2 by superconducting quantum interference device (SQUID) magnetometry measurements. The oxidation of 5, 6 and 7 with the iodosobenzene derivative ( tBuSO2)C6H4IO was investigated. Although the reactions of 6 and 7 gave no evidence for the formation of transient oxo species, crystals were obtained from the reaction of 5. These crystals showed the formation of [TL tBu*Mn(OH)](OTf)2 ( 11), in which one of the tBu groups of the TL tBu ligand has undergone a C-H activation by a putative MnIV=O bond. The complex shows a distorted square-pyramidal geometry in the solid state, and the carbon atom of the CH-activated tBu group occupies the apical position. [ABSTRACT FROM AUTHOR]

A variety of Lewis acid—base pairs consisting of tris(pentafluorophenyl)borane, B(C6F5)3, in combination with sterically demanding five- and six-membered N-heterocyclic carbenes (NHCs) of the imidazolin-2-ylidene, imidazolidin-2-ylidene, and tetrahydropyrimidin-2-ylidene types were investigated with respect to their potential to act as frustrated Lewis pairs (FLP) by reaction with dihydrogen (H2) and tetrahydrofuran (THF). A sufficient degree of "frustration" was usually established by introduction of a 1,3-di-tert-butyl or 1,3-diadamantyl carbene substitution pattern, which allows an unquenched acid—base reactivity and thus leads to heterolytic dihydrogen activation and ring-opening of THF. In contrast, 1,3-bis(2,6-diisopropylphenyl)-substituted carbenes showed ambiguous behavior, and the corresponding five-membered imidazolin-2-ylidene formed a stable carbene-B(C6F5)3 adduct, whereas fast C—F activation and formation of a zwitterionic pyrimidinium-fluoroborate was observed for the six-membered tetrahydropyrimidin-2-ylidene. A stable adduct was also isolated for the combination of the acyclic carbene bis(diisopropylamino)methylene with B(C6F5)3, and consequently no reactivity toward H2 and THF was observed. To rationalize the reactivity of the carbene-borane Lewis pairs, the thermodynamics of adduct formation with B(C6F5)3 were calculated for 10 different carbenes; the stability (or instability) of these adducts can be used as a good measure of the degree of "frustration". [ABSTRACT FROM AUTHOR]

Abstract: The reactions of the half-open trozircene [(η7-C7H7)Zr(η5-2,4-C7H11)] (1) with the two-electron donor ligands tert-butyl isocyanide (CN-tBu), 1,2-bis(dimethylphosphino)ethane (dmpe), trimethylphosphine (PMe3) and 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe, :C[N(Me)C(Me)]2) have led to the 1:1 adducts 3, 4, 5 and 6, respectively. The latter three were structurally characterized by X-ray diffraction analysis. Additionally, the stability of the adducts was probed by DFT calculations employing the B3LYP and M05-2X functionals showing that the strongly σ-basic N-heterocyclic carbene forms a thermodynamically much more stable adduct than the other three. [ABSTRACT FROM AUTHOR]

Abstract: Two imidazolin-2-imine zinc complexes [Zn(8MeBL)Cl2] (1) and [Zn(8MeBL)(OAc)2] (2) were synthesised, completely characterised and investigated for their activity in the solvent-free ring-opening polymerisation of d,l-lactide. It could be shown that these compounds are able to act as efficient initiators for lactide polymerisation, and polylactides with molecular weights (M w) of around 23,000–55,000g/mol could be obtained with relatively narrow polydispersities. 1 and 2 exhibit an advantageous combination of robustness towards humidity and high activity in the polymer melt. A comparative DFT study on 1 and 2 and their guanidine counterparts revealed that the two complex series possess a strikingly similar electronic structure. Although the imidazolin-2-imine is more basic, its zinc complexes have only a slightly greater positive charge on the zinc atom in comparison to the corresponding guanidine complexes. Accordingly, their activity in the initiation of the ring-opening polymerisation is increased which is directly related to the Lewis acidity of the zinc atom. These findings allow more insights into the mechanism of the lactide polymerisation with neutral N-donor stabilised zinc complexes. [Copyright &y& Elsevier]