Search

The reductive tetramerisation of CO by Lewis base activated dimagnesium(i) compounds, in the presence of Mo(CO)6, led to the competitive formation of magnesium squarate and metallo-ketene complexes (see picture).

The activation of dinitrogen (N2) by transition metals is central to the highly energy intensive, heterogenous Haber-Bosch process. Considerable progress has been made towards more sustainable homogeneous activations of N2 with d- and f-block metals, though little success has been had with main group metals. Here we report that the reduction of a bulky magnesium(II) amide [(TCHPNON)Mg] (TCHPNON = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) with 5% w/w K/KI yields the magnesium-N2 complex [{K(TCHPNON)Mg}2(-N2)]. DFT calculations and experimental data show that the dinitrogen unit in the complex has been reduced to the N22- dianion, via a transient anionic magnesium(I) radical. The compound readily reductively activates CO, H2 and C2H4, in reactions in which it acts as a masked dimagnesium(I) diradical.

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3 = NMe3 or N-methylpiperidine (NMP)), with -diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac = [HC(MeCNAr)2]-, Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al6 cores, having zero-valent Al axial sites and mono-valent AlH2- equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg‒Al bonded magnesio-aluminate complexes, [(ArNacnac)(Me3N)Mg‒Al(-H)3[{Mg(ArNacnac)}2(-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.

Reduction of a range of amido- and aryloxy-aluminum dihydride complexes, e.g. [AlH2(NR3){N(SiMe3)2}] (NR3 = NMe3 or N-methylpiperidine (NMP)), with -diketiminato dimagnesium(I) reagents, [{(ArNacnac)Mg}2] (ArNacnac = [HC(MeCNAr)2]-, Ar = mesityl (Mes) or 2,6-xylyl (Xyl)), have afforded deep red mixed valence aluminum hydride cluster compounds, [Al6H8(NR3)2{Mg(ArNacnac)}4], which have an average Al oxidation state of +0.66, the lowest for any well-defined aluminum hydride compound. In the solid-state, the clusters are shown to have distorted octahedral Al6 cores, having zero-valent Al axial sites and mono-valent AlH2- equatorial units. Several novel by-products were isolated from the reactions that gave the clusters, including the Mg‒Al bonded magnesio-aluminate complexes, [(ArNacnac)(Me3N)Mg‒Al(-H)3[{Mg(ArNacnac)}2(-H)]]. Computational analyses of one aluminum hydride cluster revealed its Al6 core to be electronically delocalized, and to possess one unoccupied, and six occupied, skeletal molecular orbitals.

Reactions of a dimagnesium(I) compound, [{(DipNacnac)Mg}2] (DipNacnac = [HC(MeCNDip)2]-, Dip = 2,6-diisopropylphenyl), pre-activated by coordination with simple Lewis bases (4-dimethylaminopyridine, DMAP; or TMC, :C(MeNCMe)2), with 1 atmosphere of CO in the presence of one equivalent of Mo(CO)6 at room temperature, led to the reductive tetramerisation of the diatomic molecule. When the reactions were carried out at room temperature, there is an apparent competition between the formation of magnesium squarate, [{(DipNacnac)Mg}(C4O4){-Mg(DipNacnac)}]2, and magnesium metallo-ketene products, [{(DipNacnac)Mg}{-(C4O4)Mo(CO)5}{Mg(D)(DipNacnac)}], which are not inter-convertible. Repeating the reactions at 80 °C led to the selective formation of the magnesium squarate, implying that this is the thermodynamic product. In an analogous reaction, in which THF is the Lewis base, only the metallo-ketene complex, [{(DipNacnac)Mg}{-(C4O4)Mo(CO)5}{Mg(THF)(DipNacnac)}] is formed at room temperature, while a complex product mixture is obtained at elevated temperature. In contrast, treatment of a 1:1 mixture of the guanidinato magnesium(I) complex, [(Priso)Mg‒Mg(Priso)] (Priso = [Pri2NC(NDip)2]-), and Mo(CO)6, with CO gas in a benzene/THF solution, gave a low yield of the squarate complex, [{(Priso)(THF)Mg}(C4O4){-Mg(THF)(Priso)}]2, at 80 °C. Computational analyses of the electronic structure of squarate and metallo-ketene product types corroborate the bonding proposed, from experimental data, for the C4O4 fragments of these systems.

The potassium salt of an extremely bulky β-diketiminate, [K(Ar*Nacnac)] (Ar*Nacnac, [(Ar*NCMe)2CH]−; Ar*, C6H2Me{C(H)Ph2}2-4,2,6) was reacted with either CaI2 or YbI2(THF)2, which afforded [(Ar*Nacnac)MI] (M = Ca or Yb). These are the first examples of structurally characterised, donor solvent-free, N-arene substituted β-diketiminato calcium and ytterbium complexes that incorporate a terminal iodide ligand. Reduction of [(Ar*Nacnac)CaI] with sodium metal gave a complex product mixture, from which a few crystals of the β-diketiminate C–H activated product, [{Ca(μ-Ar*Nacnac-H)}2], were obtained and crystallographically characterised. In an attempt to form a terminal ytterbium hydride compound, treatment of [(Ar*Nacnac)YbI] with K[HBEt3] gave a good yield of the contact ion pair compound [(Ar*Nacnac)Yb(HBEt3)].

A 1,2-disilylene reductively activates a series of unsaturated small molecule substrates (viz. ButNC:, C2H4, CO2 and N2O), yielding a range of novel compound types (see picture; Dip = 2,6-diisopropylphenyl, Ar = 4-C6H4But).

Searching for a connection between the two-electron redox behavior of Group-14 elements and their possible use as platforms for the photoreductive elimination of chlorine, we have studied the photochemistry of [(o-(Ph2 P)C6 H4 )2 GeIV Cl2 ]PtII Cl2 and [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtIII Cl3 , two newly isolated isomeric complexes. These studies show that, in the presence of a chlorine trap, both isomers convert cleanly into the platinum germyl complex [(o-(Ph2 P)C6 H4 )2 ClGeIII ]PtI Cl with quantum yields of 1.7 % and 3.2 % for the GeIV -PtII and GeIII -PtIII isomers, respectively. Conversion of the GeIV -PtII isomer into the platinum germyl complex is a rare example of a light-induced transition-metal/main-group-element bond-forming process. Finally, transient-absorption-spectroscopy studies carried out on the GeIII -PtIII isomer point to a ligand arene-Cl. charge-transfer complex as an intermediate.

UV irradiation of solutions of a guanidinate coordinated dimagnesium(I) compound, [{(Priso)Mg}

An extremely bulky xanthene bridged diamide ligand (TCHPNON = 4,5-bis(2,4,6-tricyclohexylanilido)-2,7-diethyl-9,9-dimethyl-xanthene) has been developed and used to prepare two monomeric diamido-calcium complexes [(TCHPNON)Ca(D)n] (D = THF, n = 2, 3; D = toluene, n = 1, 4). Reduction of 4 with 5% w/w K/KI under an N2 atmosphere gave the first well-defined, anionic s-block complex of activated dinitrogen, [{K(TCHPNON)Ca}2(-2:2-N2)] 5, presumably via a transient calcium(I) intermediate.