CoCo loco! Ligand‐bridged dimers (see picture) with the shortest known Co–Co interactions are the first amidinato and guanidinato cobalt(I) complexes. The nature of the interactions has been probed by magnetic and theoretical investigations, and has been shown to be multiconfigurational. Preliminary reactivity studies of the complexes have also been carried out.

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Reactions of lithium complexes of the bulky guanidinates [{(Dip)N}(2)CNR(2)](-) (Dip=C(6)H(3)iPr(2)-2,6; R=C(6)H(11) (Giso(-)) or iPr (Priso(-)), with NiBr(2) have afforded the nickel(II) complexes [{Ni(L)(μ-Br)}(2)] (L=Giso(-) or Priso(-)), the latter of which was crystallographically characterized. Reduction of [{Ni(Priso)(μ-Br)}(2)] with elemental potassium in benzene or toluene afforded the diamagnetic species [{Ni(Priso)}(2)(μ-C(6)H(5)R)] (R=H or Me), which were shown, by X-ray crystallographic studies, to possess nonplanar bridging arene ligands that are partially reduced. A similar reduction of [{Ni(Priso)(μ-Br)}(2)] in cyclohexane yielded a mixture of the isomeric complexes [{Ni(μ-κ(1)-N-,η(2)-Dip-Priso)}(2)] and [{Ni(μ-κ(2)-N,N'-Priso)}(2)], both of which were structurally characterized. These complexes were also formed through arene elimination processes if [{Ni(Priso)}(2)(μ-C(6)H(5)R)] (R=H or Me) were dissolved in hexane. In that solvent, diamagnetic [{Ni(μ-κ(1)-N-,η(2)-Dip-Priso)}(2)] was found to slowly convert to paramagnetic [{Ni(μ-κ(2)-N,N'-Priso)}(2)], suggesting that the latter is the thermodynamic isomer. Computational analysis of a model of [{Ni(μ-κ(2)-N,N'-Priso)}(2)] showed it to have a Ni-Ni bond that has a multiconfigurational electronic structure. An analogous copper(I) complex [{Cu(μ-κ(2)-N,N'-Giso)}(2)] was prepared, structurally authenticated, and found, by a theoretical study, to have a negligible Cu···Cu bonding interaction. The reactivity of [{Ni(Priso)}(2)(μ-C(6)H(5)Me)] and [{Ni(μ-κ(2)-N,N'-Priso)}(2)] towards a range of small molecules was examined and this gave rise to diamagnetic complexes [{Ni(Priso)(μ-CO)}(2)] and [{Ni(Priso)(μ-N(3))}(2)]. Taken as a whole, this study highlights similarities between bulky guanidinate ligands and the β-diketiminate ligand class, but shows the former to have greater coordinative flexibility.

Iron maiden! The first amidinate–iron(I) complexes, including a dinitrogen‐bridged example (see picture), have been synthesized and shown to be structurally more diverse than their β‐diketiminate counterparts.

The first structurally authenticated [2+2] cycloaddition products of any transition metal hydrazide complexes are reported; cycloaddition products of transition metal hydrazides with alkynes and heteroalkynes have been obtained for the first time; these are the first structurally authenticated cycloaddition products for any transition metal M=NNR(2) functional group.

Reactions of a dimetallated N,N'-dimethyl substituted porphyrinogen Sm(II) complex with a series of t-butyl substituted heteroalkynes affords a diverse range of reactivity. The phosphaalkyne t-BuC[triple bond]P gives a dinuclear Sm(III) P-P reductively coupled complex of (t-BuC=PP=C-t-Bu)(2-) featuring a new mu-eta(2)(1,2-C,P) binding mode. In contrast, the nitrile aza analogue t-BuC[triple bond]N forms Sm(II) adducts that undergo reductive C-C bond cleavage at elevated temperatures to afford a trimeric Sm(III) cyanide (mu-C[triple bond]N(-)) complex. The isomeric isonitrile t-BuN[triple bond]C undergoes the related reductive C-N bond cleavage reactivity at milder temperatures, allowing the trapping of the tert-butyl fragment as a Sm(III) eta(2)-iminoacyl (t-BuC=N-t-Bu)(-) complex.

Deoxygenation of carbon dioxide was achieved using transient terminal phosphinidene chromium and tungsten complexes 2a,b. The overall reaction is exothermic according to DFT calculations on the model terminal P-methyl phosphinidene complex Me-2b; this was also supported by the calculated thermodynamic oxygen-transfer potential. The oxaphosphiran-3-one complex intermediates 3a,b possess an unprecedented bonding situation as some characteristics of a side-on bound carbon dioxide to the (formally) low-coordinated phosphorus centre come to the fore. This is expressed by equidistant P-C and P-O bonds and unusual bond strength relationship, i.e. P-C > P-O, as revealed by the relaxed force constants and other related parameters. The decomposition of 3a,b via CO extrusion yields terminal phosphinidene oxide complexes 4a,b which dimerise to the final products, the 1,3-dioxa-2,4diphosphetane complexes 5a,b-8a,b. Additional experimental evidence for the transient formation of phosphinidene oxide complexes 4a,b was obtained by a cross dimerisation experiment using transient chromium and tungsten complexes 2a,b. First comparative investigations on the reaction of Li-Cl phosphinidenoid complex 10 and CO 2 at low temperature revealed the formation of the carbamoylphosphane complex 11. Scheme 1 Known deoxygenation processes of CO 2 via transient a-lactones I (oxiranones, E ¼ C) or via side-on carbon dioxide transition metal complexes II.

The first complexes and cyclodimerisations of methylphosphaalkyne, P[triple bond]CMe, are reported to arise from its reactions with a range of platinum(0) complexes and [W(CO)5(THF)]. A number of differences between the chemistry of this phosphaalkyne and that of its bulkier analogues have been highlighted and explained on steric grounds.