Christian Schulten

Amidinato– and Guanidinato–Cobalt(I) Complexes: Characterization of Exceptionally Short Co–Co Interactions

Low-coordinate, carbonyl-free first row transition metal(I) complexes are relatively rare but are finding increasing use in the activation of small molecules, as enzyme mimics, and so forth. These complexes are generally very reactive species that are stabilized by a variety of sterically bulky, mono-, di-, tri-, and higher dentate ligands. Perhaps the most versatile of these are the b-diketiminates (e.g., [{ArNC(Me)}2CH] (nacnac ; Ar= 2,6-diisopropylphenyl)), which have been utilized in the preparation of a range of Group 5–12 first row transition metal(I) complexes that have shown fascinating chemistry. In recent years, we have employed the bulky amidinate and guanidinate ligands ([(ArN)2CR] (R= tBu; piso ), N(C6H11)2 (giso ), or NiPr2 (priso )) for the stabilization of a variety of Group 2, 13, 14, and 15 metal(I) complexes, and planar four-coordinate lanthanide(II) complexes. These studies have highlighted close analogies (but also differences) between the stabilizing and ligating properties of the bulky amidinates and guanidinates, and the properties of b-diketiminates. With these characteristics in mind, we extended the coordination chemistry of the bulky ligand piso to the preparation of the first amidinato–iron(I) complex, [(k-N,N’-piso)Fe(h-toluene)] (cf. [(k-N,N’-nacnac)Fe(h-benzene)]), which was shown to weakly activate dinitrogen to give [{(k-N-,h-Ar-piso)Fe(m-N)}2] (cf. [{(k N,N’-nacnac)Fe(m-N)}2] ), with an accompanying change in the coordination mode of the piso ligand. Subsequent reports from another research group detailed unprecedented amidinato–chromium(I) complexes, which included the diamagnetic, amidinate bridged species, [{Cr[m-N(Ar’)C(R)N(Ar’)]}2] (R=H or Me, Ar’=Ar or 2,6-Et2C6H3), that contain very short Cr–Cr quintuple bonds (ca. 1.74 ). These results motivated us to extend the coordination chemistry of bulky amidinate and guanidinate ligands toward other first row transition metal(I) centers. We were particularly interested in preparing analogues of the bdiketiminate-stabilized cobalt(I) system [(k-N,N’-nacnac)Co(h-toluene)] (1), which, like other cobalt(I) complexes, has been shown to activate an assortment of small molecules. In addition, we believed that the previously demonstrated coordinative flexibility of our ligands relative to that of b-diketiminates could yield varying complex types, depending on the reaction conditions employed. Herein, we report the first amidinato– and guanidinato– cobalt(I) complexes, two dimeric examples of which exhibit the shortest Co–Co interactions reported to date. Preliminary further reactivity studies of these complexes are also reported. The paramagnetic cobalt(II) precursor complexes 2a–c (Scheme 1), were readily prepared in good yields by saltmethathesis reactions between CoX2 (X=Br or I) and the potassium salt of the appropriate ligand. The structural characterization of one complex, [{(priso)CoI}2], is the first to be reported for an amidinato– or guanidinato–cobalt(II) halide complex, and shows the complex to be dimeric with distorted tetrahedral cobalt centers. Upon reduction of 2a–c with potassium (or magnesium) in toluene, the amidinato– and guanidinato–cobalt(I) complexes 3a–c were obtained as crystalline solids in high yields. It is noteworthy that no nitrogen-coordinated complexes were obtained when the reductions were carried out under a dinitrogen atmosphere, as was the case with the reduction in toluene that gave 1. Reduction of 2a or 2b with potassium in cyclohexane under a dinitrogen atmosphere afforded the dimeric cobalt(I) complexes 4a and 4b as extremely air-sensitive solids in good yields. We have seen no evidence so far for the conversion of [*] Prof. C. Jones, Dr. C. Schulten, Dr. R. P. Rose, Dr. A. Stasch, W. D. Woodul, Prof. K. S. Murray, Dr. B. Moubaraki School of Chemistry, Monash University PO Box 23, VIC, 3800 (Australia) Fax: (+61)3-9905-4597 E-mail: cameron.jones@sci.monash.edu.au

Low‐Coordinate Iron(I) and Manganese(I) Dimers: Kinetic Stabilization of an Exceptionally Short FeFe Multiple Bond

The fundamental and applied chemistry of metal–metal bonded complexes has rapidly expanded since Cotton s landmark report of metal–metal quadruple bonding in the dianion, [Re2Cl8] 2 , nearly 50 years ago. Many of the recent advances in the field have centered on the stabilization of reactive low oxidation state/low coordination number M– M bonded complexes using sterically imposing ligand systems. Representative examples include the singly bonded zinc(I) and magnesium(I) dimers, [Cp*ZnZnCp*] (Cp* = C5Me5) [3]

Synthesis and Characterization of Amidinate–Iron(I) Complexes: Analogies with β‐Diketiminate Chemistry

ally synthesized by the reduction of b-diketiminate metal halide precursors with s-block metals. The high reactivity of such metallacycles is lending them to an increasing array of synthetic applications, which include uses as reagents for small-molecule activation, reductive coupling, metal–imide formation, and so forth. Of most relevance to this study is the work of Holland et al. , who have shown that b-diketiminate–iron(I) fragments can activate dinitrogen to give complexes (2) with partially reduced N N bonds that are significantly elongated with respect to that in gaseous N2. [1d,2] Accordingly, complexes such as 2 have been suggested as models for the likely FeNNFe intermediates in the binding of N2 to iron sites (e.g., the iron–molybdenum cofactor) of nitrogenase enzymes. Such enzymes are of immense biological importance as they catalyze the reduction of dinitrogen to ammonium salts, which are used as building blocks in numerous biosynthetic processes. Recently we have utilized bulky amidinate and guanidinate ligands ([(ArN)2CR] R= tBu (Piso ), N ACHTUNGTRENNUNG(C6H11)2 (Giso ) or NiPr2 (Priso )) for the stabilization of a variety of Group 2, 13, 14, and 15 metal(I) complexes, and planar four-coordinate lanthanide(II) complexes. Throughout these investigations, the stabilizing and ligating properties of the bulky amidinates and guanidinates have been shown to be strikingly similar to those of b-diketiminates. As a result, we saw the potential to extend their coordination chemistry to the formation of first-row transitionmetal(I) complexes. This is of interest for a number of reasons. Firstly, such compounds should show enhanced and/or differing patterns of reactivity relative to their b-diketiminate counterparts, as the greater angular extent of the cavity between their N-aryl substituents should provide less steric protection to the coordinated transition-metal center. Also, despite the plethora of less bulky amidinate and guanidinate first-row d-block complexes in the literature, there are no known examples of carbonyl-free metal(I) species incorporating N,N’-chelating ligands. Indeed, the only metal(I) complexes are dior polynuclear species with the amidinate or guanidinate acting as a bridging ligand between copper or, in one case, nickel centers. Here, we report the first amidinate–iron(I) complex and discuss its reactivity towards dinitrogen and carbon monoxide. The amidinato–iron(II) bromide precursor complex 3 was readily prepared in good yield by treating FeBr2 with one equivalent of K ACHTUNGTRENNUNG[Piso] in THF. An X-ray crystallographic analysis (see Supporting Information) of the complex revealed it to be a bromide-bridged dimer with iron centers coordinated by delocalized Piso ligands. The metal centers have differing geometries that both lie between square planar and tetrahedral. It is of note that the complex is ther[a] Dr. R. P. Rose, Prof. C. Jones, Dipl.-Eng. C. Schulten, Dr. A. Stasch School of Chemistry, Monash University Melbourne, PO Box 23, Victoria, 3800 (Australia) Fax: (+61)3-9905-4597 E-mail : cameron.jones@sci.monash.edu.au [b] Dr. R. P. Rose, Dipl.-Eng. C. Schulten School of Chemistry, Main Building Cardiff University, Cardiff, CF10 3AT (UK) [c] Dr. S. Aldridge Inorganic Chemistry, University of Oxford South Parks Road, Oxford, OX1 3QR (UK) Supporting information for this article is available on the WWW under http://dx.doi.org/10.1002/chem.200801071.

Cycloaddition reactions of transition metal hydrazides with alkynes and heteroalkynes: coupling of TiNNPh2 with PhCCMe, PhCCH, MeCN and tBuCP

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.

Differing reactivities of PCMe and PCBut towards a triphosphabenzene and a tetraphosphabarrelene: synthesis of new phosphaalkyne pentamers (P5C5MenBut5−n, n = 0, 1 or 2)

The reaction of excess PCMe with the triphosphabenzene, 1,3,5-P3C3But3, yields a phosphaalkyne pentamer, P5C5Me2But3, which displays a pentaphosphaisolumibullvalene core structure. Its treatment with [W(CO)5(THF)] gives a complex of this cage, [{W(CO)5}2(µ-η1:η1-P5C5Me2But3)], which has been structurally characterised. In contrast, the previously reported reaction of PCBut with 1,3,5-P3C3But3, affords, in addition to the known tetraphosphabarrelene, 1,3,5,7-P4C4But4, a new phosphaalkyne pentamer (P5C5But5), which has a partially unsaturated “open cage” core. Although PCBut does not react with 1,3,5,7-P4C4But4, the reaction of PCMe with the tetraphosphabarrelene is shown to give a mixture of products. Treatment of these with [W(CO)5(THF)] leads to the isolation of the tungsten carbonyl complex, [{W(CO)5}{W(CO)4}(µ-η1:η4-P5C5MeBut4)], which has been structurally characterised. This study suggests that PCMe has a significantly greater reactivity towards cycloadditions than its bulkier counterpart, PCBut.

[Gal2Ph(SbPh3)]: A Rare Tertiary Stibane-Gallium Complex Formed via a Reductive Sb-C Bond Cleavage Reaction

Fig. 1: Molecular structure of [GaI2Ph(SbPh3)] (hydrogens omitted for clarity, 30% ellipsoids). Key geometric parameters (Ä, Ga(l)-I(l) 2.5583(6), Ga(l)-Ga(2) 2.5471(6), Ga(l)-C(l) 1.967(4), Sb(l)-C(7) 2.127(4), Sb(l)-C(13) 2.119(4), Sb(l)-C(19) 2.121(4), C(13)-Sb(l)-C(19) 103.06(14), C(13)-Sb(l)-C(7) 102.53(14), C(7)-Sb(l)-C(19) 101.53(13), C(l)-Ga(l)-I(l) 113.23(11), C(l)Ga(l)-I(2) 115.35(12), I(l)-Ga(l)-I(2) 112.73(2).