Order in disorder:solution and solid-state studies of [(M2M5II)-M-III] wheels (M-III = Cr, Al; M-II = Ni, Zn)

A family of heterometallic Anderson-type ‘wheels’ of general formula [MIII2MII5(hmp)12](ClO4)4 (where MIII = Cr or Al and MII = Ni or Zn giving [Cr2Ni5] (1), [Cr2Zn5] (2), [Al2Ni5] (3) and [Al2Zn5] (4); hmpH = 2-pyridinemethanol) have been synthesised solvothermally. The metallic skeleton common to all structures describes a centred hexagon with the MIII sites disordered around the outer wheel. The structural disorder has been characterised via single crystal X-ray crystallography, 1–3D 1H and 13C solution-state NMR spectroscopy of the diamagnetic analogue (4), and solid-state 27Al MAS NMR spectroscopy of compounds (3) and (4). Alongside ESI mass spectrometry, these techniques show that structure is retained in solution, and that the disorder is present in both the solution and solid-state. Solid-state dc susceptibility and magnetisation measurements on (2) and (3) reveal the Cr–Cr and Ni–Ni exchange interactions to be JCr–Cr = −1 cm−1 and JNi–Ni,r = −5 cm−1, JNi–Ni,c = 10 cm−1. Fixing these values allows us to extract JCr–Ni,r = −1.2 cm−1, JCr–Ni,c = 2.6 cm−1 for (1), the exchange between adjacent Ni and Cr ions on the ring is antiferromagnetic and between Cr ions on the ring and the central Ni ion is ferromagnetic.EKB thanks the EPSRC for funding (EP/N01331X/1, EP/P025986/1). UGN acknowledges funding from the Villum Young Investigator (VKR022364) and the Danish Council for Independent Research – Natural Sciences (DFF – 7014-00198). ME thanks MINECO for funding (MAT2015-68204-R)Peer reviewe

Methyl Complexes of the Transition Metals

Organometallic chemistry can be considered as a wide area of knowledge that combines concepts of classic organic chemistry, that is, based essentially on carbon, with molecular inorganic chemistry, especially with coordination compounds. Transition-metal methyl complexes probably represent the simplest and most fundamental way to view how these two major areas of chemistry combine and merge into novel species with intriguing features in terms of reactivity, structure, and bonding. Citing more than 500 bibliographic references, this review aims to offer a concise view of recent advances in the field of transition-metal complexes containing M-CH fragments. Taking into account the impressive amount of data that are continuously provided by organometallic chemists in this area, this review is mainly focused on results of the last five years. After a panoramic overview on M-CH compounds of Groups 3 to 11, which includes the most recent landmark findings in this area, two further sections are dedicated to methyl-bridged complexes and reactivity.Ministerio de Ciencia e Innovación Projects CTQ2010–15833, CTQ2013-45011 - P and Consolider - Ingenio 2010 CSD2007 - 00006Junta de Andalucía FQM - 119, Projects P09 - FQM - 5117 and FQM - 2126EU 7th Framework Program, Marie Skłodowska - Curie actions C OFUND – Agreement nº 26722

Complexes of Iron(II) and Iron(III) Containing Aryl-Substituted N-Heterocyclic Carbene Ligands

Iron­(II) and iron­(III) complexes containing the 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) ligands have been prepared and characterized. Four-coordinate iron­(II) carbene species are sensitive to the steric bulk of the carbene ligand and can adopt both monomeric and halide-bridged dimeric structures with 2:1 and 1:1 carbene to iron stoichiometries, respectively. Iron­(III) carbene complexes bind a single carbene ligand, which is easily exchanged in solution. The structural and solution phase characterization of all compounds is reported, and their relevance to iron-catalyzed C–C coupling reactions is discussed

NHC Complexes of Cobalt(II) Relevant to Catalytic C–C Coupling Reactions

Alkyl compounds of cobalt­(II) containing aryl-substituted N-heterocyclic carbene ligands have been prepared by reaction of the precursor chloro complexes [CoCl₂(IMes)₂] and [Co₂Cl₂(μ-Cl)₂(IPr)₂] (IMes = 1,3-dimesityl-imidazol-2-ylidene; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) with Grignard reagents. Examples of alkyl complexes possessing both four-coordinate and three-coordinate geometries are reported. The chloro complex [CoCl₂(IMes)₂] adopts a pseudotetrahedral geometry displaying an <i>S</i> = ³/₂ ground state, whereas the alkyl complex [Co­(CH₃)₂(IMes)₂] adopts a square-planar geometry consistent with an <i>S</i> = ¹/₂ ground state. In contrast to [Co­(CH₃)₂(IMes)₂], [Co­(CH₂SiMe₃)₂(IPr)] exhibits a three-coordinate trigonal-planar geometry displaying an <i>S</i> = ³/₂ ground state. The catalytic efficacy of [CoCl₂(IMes)₂] in Kumada couplings is examined, as is the chemistry of the alkyl complexes toward CO. The structure and reactivity of these compounds is discussed in the context of C–C coupling reactions catalyzed by cobalt NHCs

Complexes of Iron(II) and Iron(III) Containing Aryl-Substituted N-Heterocyclic Carbene Ligands

Iron­(II) and iron­(III) complexes containing the 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) ligands have been prepared and characterized. Four-coordinate iron­(II) carbene species are sensitive to the steric bulk of the carbene ligand and can adopt both monomeric and halide-bridged dimeric structures with 2:1 and 1:1 carbene to iron stoichiometries, respectively. Iron­(III) carbene complexes bind a single carbene ligand, which is easily exchanged in solution. The structural and solution phase characterization of all compounds is reported, and their relevance to iron-catalyzed C–C coupling reactions is discussed

NHC Complexes of Cobalt(II) Relevant to Catalytic C–C Coupling Reactions

Alkyl compounds of cobalt­(II) containing aryl-substituted N-heterocyclic carbene ligands have been prepared by reaction of the precursor chloro complexes [CoCl₂(IMes)₂] and [Co₂Cl₂(μ-Cl)₂(IPr)₂] (IMes = 1,3-dimesityl-imidazol-2-ylidene; IPr = 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene) with Grignard reagents. Examples of alkyl complexes possessing both four-coordinate and three-coordinate geometries are reported. The chloro complex [CoCl₂(IMes)₂] adopts a pseudotetrahedral geometry displaying an <i>S</i> = ³/₂ ground state, whereas the alkyl complex [Co­(CH₃)₂(IMes)₂] adopts a square-planar geometry consistent with an <i>S</i> = ¹/₂ ground state. In contrast to [Co­(CH₃)₂(IMes)₂], [Co­(CH₂SiMe₃)₂(IPr)] exhibits a three-coordinate trigonal-planar geometry displaying an <i>S</i> = ³/₂ ground state. The catalytic efficacy of [CoCl₂(IMes)₂] in Kumada couplings is examined, as is the chemistry of the alkyl complexes toward CO. The structure and reactivity of these compounds is discussed in the context of C–C coupling reactions catalyzed by cobalt NHCs

Complexes of Iron(II) and Iron(III) Containing Aryl-Substituted N-Heterocyclic Carbene Ligands

Iron­(II) and iron­(III) complexes containing the 1,3-dimesitylimidazole-2-ylidene (IMes) and 1,3-bis­(2,6-diisopropylphenyl)­imidazol-2-ylidene (IPr) ligands have been prepared and characterized. Four-coordinate iron­(II) carbene species are sensitive to the steric bulk of the carbene ligand and can adopt both monomeric and halide-bridged dimeric structures with 2:1 and 1:1 carbene to iron stoichiometries, respectively. Iron­(III) carbene complexes bind a single carbene ligand, which is easily exchanged in solution. The structural and solution phase characterization of all compounds is reported, and their relevance to iron-catalyzed C–C coupling reactions is discussed

Mechanistic Studies of Catalytic Carbon–Carbon Cross-Coupling by Well-Defined Iron NHC Complexes

The mechanism of iron-catalyzed carbon–carbon cross-coupling reactions between Grignard reagents and alkyl halides has been investigated using well-defined N-heterocyclic carbene (NHC) compounds. The iron­(II) precatalyst, [Fe₂Cl₂(μ-Cl)₂(IPr)₂], was employed in several C–C cross coupling reactions exhibiting the ability to efficiently couple primary and secondary alkyl halides with several aryl and alkyl Grignard reagents. For selected substrates, a 2 mol % catalyst loading (4 mol % Fe) afforded conversions of >99% and were achieved with <8% homocoupling of the electrophile. The mechanism of the coupling reaction was studied by means of radical clock, radical trap, and single-turnover experiments, which support a radical-based cycle involving an Fe­(II/III) redox couple. The implications of this mechanism on the efficacy of iron-NHC-catalyzed cross-coupling reactions are discussed