Complexes of Dichlorogermylene with Phosphine/Sulfoxide-Supported Carbone as Ligand.

Due to their remarkable electronic features, recent years have witnessed the emergence of carbones L2C, which consist in two donating L ligands coordinating a central carbon atom bearing two lone pairs. In this context, the phosphine/sulfoxide-supported carbone 4 exhibits a strong nucleophilic character, and here, we describe its ability to coordinate dichlorogermylene. Two original stable coordination complexes were obtained and fully characterized in solution and in the solid state by NMR spectroscopy and X-ray diffraction analysis, respectively. At 60 °C, in the presence of 4, the Ge(II)-complex 5 undergoes a slow isomerization that transforms the bis-ylide ligand into an yldiide.

Phosphine/Sulfoxide-Supported Carbon(0) Complex.

A new carbon(0) complex 2 with two different L ligands, a phosphine and a sulfoxide, was synthesized and fully characterized. This new type of carbone exhibits excellent coordination ability, in contrast to the related phosphine/sulfide-supported carbon(0) complexes. Several organometallic complexes were isolated and, of special interest, the νav (CO) value of RhI -dicarbonyl complex indicates that 2 has a donor capability superior to classical NHCs.

A Simply Synthesized, Tough Polyarylene with Transient Mechanochromic Response.

A simple and high-yielding route to tough polyarylenes of the type poly(meta,meta,para-phenylene) (PmmpP) is developed. PmmpP is tough even in its as-synthesized state which has an intermediate molar mass of Mw ≈60 kg mol-1 and exhibits outstanding mechanical properties at further optimized molecular weight of Mw =96 kg mol-1 , E=0.9 GPa, ϵ=300 %. Statistical copolymers with para,para-spiropyran (SP) are mechanochromic, and the toughness allows mechanochromism to be investigated. Strained samples instantaneously lose color upon force release. DFT calculations show this phenomenon to be caused by the PmmpP matrix that allows build-up of sufficiently large forces to be transduced to SP, and the relatively unstable corresponding merocyanine (MC) form arising from the aromatic co-monomer. MC units covalently incorporated into PmmpP show a drastically reduced half life time of 3.1 s compared to 4.5 h obtained for SP derivatives with common 6-nitro substitution.

Metal complexes with oxygen-functionalized NHC ligands: synthesis and applications.

Ligand design has met with considerable success with both categories of hybrid ligands, which are characterized by chemically different donor groups, and of N-heterocyclic carbenes (NHCs). Their spectacular development and diversity are attracting worldwide interest and offers almost unlimited diversity and potential in e.g. coordination/organometallic main group and transition metal chemistry, catalysis, medicinal chemistry and materials science. This review aims at providing a comprehensive update on a specific class of ligands that has enjoyed much attention in the past few years, at the intersection between the two categories mentioned above, that of hybrid NHC ligands in which the functionality associated with the carbene donor is of the oxygen-donor type. For each type of oxygen-donor present in such chelating (Section 1) or bridging (Section 2) hybrid ligands, we will examine the synthesis, structures and reactivity of their metal complexes and their applications, with a special focus on homogeneous catalysis (Section 3). Thus, hydrogenation, C-H bond activation, C-C, C-N, C-O bond formation, hydrolysis of silanes, oligomerization, polymerization, metathesis, hydrosilylation, C-C bond cleavage, acceptorless dehydrogenation, dehalogenation/hydrogen transfer, oxidation and reduction reactions will be successively presented in a tabular manner, to facilitate an overview and a rapid identification of the relevant publications describing which metals associated with a given oxygen functionality are most suitable. The literature coverage includes the year 2015.

Expanding the Scope of Electron-Deficient C-H Building Blocks: Direct Arylation of Pyromellitic Acid Diimide.

Direct C-H activation of pyromellitic diimide (PMDI) is reported for the first time. The method avoids cumbersome pathways involving bromination usually required for further cross-coupling. Good to excellent yields of mono- and di-substituted PMDI derivatives can be obtained under optimized reaction conditions. The reaction scope was also explored, and the materials were characterized with respect to their thermal, optical, and electronic properties.

Synthesis, Structures, and Single-Molecule Magnet Behaviour of High-Nuclearity Nickel(II) Dicubane-Type Complexes with Pyridyl-Alcohol Ligands.

The condensation reaction between two chemically different tetranuclear cubane-like clusters [Ni(µ3 -Cl)(Cl)(HL)]4 (1; HL=2-methyl-1-(pyridin-2-yl)propan-2-ol) and [Ni(µ3 -OH)(Cl)(HL)]4 (2) provides new access to higher nuclearity complexes, as shown with the synthesis of the octanuclear complex [Ni8 (µ3 -Cl)3 (µ3 -OH)5 (µ-Cl)2 Cl6 (HL)7 ] (3). In one instance, we also isolated the heptanuclear complex [Ni7 (µ3 -Cl)2 (µ3 -OH)6 Cl4 (H2 O)2 (HL)6 ]Cl2 (4). Magnetic properties measured by superconducting quantum interference device (SQUID) susceptometry evidenced S=8 and S=5 ground states for complexes 3 and 4, respectively. In particular, alternating current (ac) susceptometry evidenced slow relaxation of the magnetisation for complex 3, and suggests a similar behaviour at sub-kelvin temperatures for complex 4.

Synthesis and characterization of palladium(II) and nickel(II) alcoholate-functionalized NHC complexes and of mixed nickel(II)-lithium(I) complexes.

The synthesis of Pd(II) and Ni(II) alcohol-functionalized N-heterocyclic carbene (NHC) complexes was explored to examine the possible influence of the functional arm attached to the NHC backbone on their structure and reactivity and, in the case of a Ni(II) complex, on its catalytic properties in ethylene oligomerization. Starting from the alcohol-functionalized imidazolium salt [ImDiPP(C2OH)]Cl (2), the new functionalized NHC palladium(II) complex [PdCl(acac){ImDiPP(C2OH)-CNHC}] (3) was synthesized and fully characterized. Two byproducts, [PdCl{µ-ImDiPP(C2O)-CNHC,O}]2 (4) and trans-[PdCl2{ImDiPP(C2OH)-CNHC}2] (5), formed during the synthesis of 3, were also fully characterized. Acids promoted the transformation of 3 into the new CNHC-bound complex [PdCl(µ-Cl){ImDiPP(C2OH)-CNHC}]2 (6), unveiling the lability of the acac ligand and the resistance of the Pd-NHC bond to acids. Complex 6 reacted with a base to afford complex 4, in which alkoxide coordination to Pd(II) has occurred to generate a CNHC,O chelate. The stability of 3 was also assessed under basic conditions, and the new complex [Pd(acac){ImDiPP(C2O)-CNHC,O}] (7) was characterized. The new nickel(II) alcoholate-functionalized NHC complex [NiCl{µ-ImDiPP(C2O)-CNHC,O}]2 (8) was synthesized by the reaction of the imidazolium salt 2 with n-BuLi and [NiCl2(dme)]. The reaction of 8 with HCl regenerates the imidazolium and alcohol functions to give [ImDiPP(C2OH)]2[NiCl4] (9). The mixed-metal Ni(II)-Li(I) complexes [Ni2{µ-ImDiPP(C2O)-CNHC,µ-O}4Li]BF4 (10), [Ni2{µ-ImDiPP(C2O)-CNHC,µ-O}4Li]Cl (11), and [Ni{ImDiPP(C2O)-CNHC,µ-O}2LiBr] (12) were isolated and characterized. However, it was not possible to synthesize a Ni(II) alcohol-functionalized NHC complex in high yield. Small amounts of the square-planar complex [NiCl2{ImDiPP(C2OH)-CNHC}2] (13) could be isolated, and this complex was characterized by single-crystal X-ray diffraction. In 13, only the CNHC atom of the alcohol-functionalized NHC ligand is bound to the metal. The structures of the imidazolium salt 2·2H2O and of the complexes 3, 4, 4-polymorph, 5, 6·CH2Cl2, and 8-13 were established by single-crystal X-ray diffraction.

Synthesis and characterization of oxygen-functionalised-NHC silver(I) complexes and NHC transmetallation to nickel(II).

The new alcohol- and ether-functionalised-NHC silver(I) complexes bis(1-(2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImDiPP(C2OH)}2]Cl (4), bis(1-(2-hydroxyethyl)-3-mesityl-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImMes(C2OH)}2]Cl (5), bis(1-(2-hydroxyethyl)-3-methyl-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImMe(C2OH)}2]Cl (6), bis(1-(2,6-diisopropylphenyl)-3-(2-hydroxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) tetrafluoroborate, [Ag{ImDiPP(C2OH)}2]BF4 (9), and bis(1-(2,6-diisopropylphenyl)-3-(2-methoxyethyl)-1H-imidazol-2(3H)-ylidene)silver(I) chloride, [Ag{ImDiPP(C2OMe)}2]Cl (13), were synthesized and fully characterized by NMR spectroscopy and single crystal X-ray diffraction. For some complexes, an uncommon heteronuclear coupling (4)J((107/109)Ag-H) was unveiled. Their ability to transfer the NHC ligand to Ni(II) was assessed in the presence of different nickel(II) sources; the bis-NHC Ni(II) complex bis(1-(2,6-diisopropylphenyl)-3-(2-methoxyethyl)-1H-imidazol-2(3H)-ylidene)nickel(II) chloride, [NiCl2{ImDiPP(C2OMe)}2] (15), was obtained from 13 and shown by X-ray diffraction study to have a trans-arrangement of the two NHC ligands. However, in contrast to other Ag(I) NHC complexes the transmetallation reaction failed with the hydroxyl-functionalised silver complexes, possibly due to the acidity of the alcohol OH function, leading overall to reprotonation of the C(NHC) and isolation of the corresponding imidazolium salts.

Synthesis of cubane-type Ni(II) complexes from pyridyl-alcohol ligands; their single-molecule magnet behaviour.

The reactions of NiCl2·2H2O or [NiCl2(DME)] (DME = dimethoxyethane) with 2-methyl-1-(pyridin-2-yl)propan-2-ol (HL) and 2-(pyridin-2-yl)ethanol (HLEt), in a 1:1 ratio, afforded the tetranuclear, cubane-type clusters [Ni(µ3-Cl)Cl(HL)]4 (3) and [Ni(µ3-Cl)Cl(HLEt)]4 (4), respectively. These are tetramers of the hypothetical mononuclear formula-isomers [NiCl2(HL)] and [NiCl2(HLEt)], respectively, and represent rare examples of structurally characterized cubane-like transition metal dihalogenide complexes. The 2:1 reactions between HL or HLEt and [NiCl2(DME)] yielded, instead, the mononuclear [NiCl2(HL)2] (1) and the dinuclear complex [Ni(µ-Cl)(HLEt)2]2Cl2 (2), respectively. The reaction of 3 with NaOH afforded selectively the cubane-type cluster [Ni(µ3-OH)Cl(HL)]4 (5) which differs only in the nature of the capping anions (Cl vs. OH, respectively). The magnetic properties of the unusual tetranuclear cubanes 3 and 5 have been investigated and revealed in both cases single-molecule magnet (SMM) behaviour.