Sally R. Boss

Syntheses, structures and magnetic properties of Mn(II) dimers [CpMn(μ-X)]2(Cp = C5H5; X = RNH, R1R2N, CCR)

Manganocene, Cp2Mn, has been employed as a precursor in the synthesis of a range of Mn(II) dimers of the type [CpMn(μ-X)]2 [X = 8-NHC9H6N (1), N(Ph)(C5H4N) (2), N(4-EtC6H4)(C5H4N) (3) and CCPh (4)] as well as the bis-adduct [Cp2Mn{HNC(NMe2)2}2] (5). The solid-state structures of 1–5 are reported. Variable-temperature magnetic measurements have been used to assess the extent of Mn(μ-X)Mn communication within the dimers of 1–4 as a function of the bridging ligands (X).

Tuning heavy metal compounds for anti-tumor activity: is diversity the key to ruthenium's success?

This review aims to bring the reader up to date with the more recent ruthenium compounds that have been synthesized and tested for their cytotoxicity. The chemistry of these transition metal complexes will be introduced and the basic principles that govern their common behavior outlined. The recent history of established compounds within this field will be presented alongside those that now represent the cutting-edge. The inherent variety within this class of compounds will lead the reader to appreciate their diversity and pose questions as to their similarities aside from the presence of a shared metal ion. This review aims to discuss and contextualize the state-of-the-art research within the context of the speculative advancement of this developing field. There is an evident need to specify the molecular and cellular targets of these drug molecules in order to ultimately elucidate their mode or modes of action. The evidence presented herein suggests that new avenues of research require novel analytical probes and methods for tracing the fate of ruthenium complexes in cells in order to understand their very promising cytotoxic activity.

Oxygen scavenging by lithium zincates: the synthesis, structural characterisation and derivatisation of [Ph(2-C5H4N)N]2ZnRLi·nthf (R = But, Bun; n= 1, 2)

The 1 ∶ 2 reaction of ZnMe2 with N-2-pyridylaniline, Ph(2-C5H4N)NH 1, affords [Ph(2-C5H4N)N]2Zn 10, the treatment of which with BuLi and thf affords the diastereomeric lithium zincate [Ph(2-C5H4N)N]2ZnRLi·nthf (R = Bun, n = 2; 11a; R = But, n = 1, 11b). The sequential treatment of 10 (either in situ or after isolation) with organolithium substrates and molecular oxygen has afforded insights into the oxygen-scavenging capacity of mixed Group 1–Group 12 species. Hence, 10 reacts with BunLi, O2 and thf or dimethoxyethane (dme) to give {[Ph(2-C5H4N)N]2ZnOBunLi·nL}2 (n = 1, L = thf, 12a; n = 0.5, L = dme, 12b), with the structural relationship between 11a and 12a strongly suggesting that for R = Bun oxygenation proceeds by insertion into the Zn–C bond of an {[Ph(2-C5H4N)N]2ZnR}− ion. The employment of ButLi, O2 and thf together with 10 affords only the previously reported complex [Ph(2-C5H4N)N]2Zn[(μ3-O)But]2(Li·thf)24, the formation of which may be rationalised in terms of the But van der Waals radius and cone angle.

Selective Lability of Ruthenium(II) Arene Amino Acid Complexes

A series of organometallic complexes of the form [(PhH)Ru(amino acid)](+) have been synthesized using amino acids able to act as tridentate ligands. The straightforward syntheses gave enantiomerically pure complexes with two stereogenic centers due to the enantiopurity of the chelating ligands. Complexes were characterized in the solid-state and/or solution-state where the stability of the complex allowed. The propensity toward labilization of the coordinatively saturated complexes was investigated. The links between complex stability and structural features are very subtle. Nonetheless, H/D exchange rates of coordinated amino groups reveal more significant differences in reactivity linked to metallocycle ring size resulting in decreasing stability of the metallocycle as the amino acid side-chain length increases. The behavior of these systems in acid is unusual, apparently labilizing the carboxylate residue of the amino acid. This acid-catalyzed hemilability in an organometallic is relevant to the use of Ru(II) arenes in medicinal contexts due to the relatively low pH of cancerous cells.

Cobalt Catalyzed Carbon Nanotube Growth on Graphitic Paper Supports

The catalytic growth of multi-wall carbon nanotubes on carbon paper is reported. The study employed three cobalt carbonyl clusters as catalyst precursors. These were deposited on graphitic paper prior to chemical vapour deposition (CVD) of methane or ethyl- ene. The clusters show differentiated growth behaviour in accordance with precursor size, and with Co2(CO)8 displaying additional activ- ity in the growth of helical nanotube structures. We therefore report an approach for the decoration of graphitic papers with carbon nano- tubes with a view to the production of high area supports. Since their identification by Iijima in 1991 (1), carbon nano- tubes (CNTs) have been the subject of intensive research owing to their unique electronic and mechanical properties (2). While various synthetic strategies for their production have been devised, chemi- cal vapor deposition (CVD) has been established as one of the more commonly used techniques by virtue of its versatility in terms of the effect of experimental parameters (such as flow speed and composi- tion of the gaseous carbon precursors, deposition temperature and time) on the type of CNTs produced. Nevertheless, the development of procedures that are able to achieve sufficient morphological and structural product control remains an ongoing challenge. This is, on the one hand, due to there being an as yet incomplete understanding of the tube formation mechanism and, on the other hand, groups reporting a lack of control over catalyst morphology. The result of these issues is that irregular tube structures are generally obtained. In the case of morphological control, both experimental and compu- tational studies have demonstrated the importance of catalyst parti- cle size in influencing the resulting tube diameters (3). More fun- damentally, particle diameters in the nanometer regime are known to affect the metal melting point through the Gibbs-Thomson effect. In addition, the temperature at which liquefaction of nanoparticulate species occurs (and which can be assumed to influence the agglom- eration behavior), has been shown to depend on saturation of the metal species with carbon (4). These issues pose intrinsic problems in that it is not trivial to maintain narrow particle size distributions for commonly employed nanoparticulate catalysts derived from either physical vapour deposition or wet chemical methods (such as sputtering and metal salt reduction). In seeking to overcome these limitations, researchers have more recently focused on the employ- ment of molecular clusters as catalyst precursors, and on the deposi- tion of these on various supports. Most notably, use of the high pressure carbon monoxide (HiPco) process to produce single- walled carbon nanotubes (SWCNTs) using iron pentacarbonyl has offered control over nanotube yield and morphology by means of controlling the deposition parameters (5). In recent years, considerable effort has been directed towards addressing both the issue of seed size control and the development of a wider range of suitable supports with which to provide CNT- based high surface area systems. In this context, some of the present authors have previously reported CNT syntheses using both nickel formate precursors and colloidal cobalt nanoparticles on supports

Toward an understanding of the oxygen scavenging properties of lithium zincates

The reaction of ZnMe2 with 2-pyridylamine [HN(2-C5H4N)Ph 1], LitBu and thereafter with dry air has concomitantly yielded {[Ph(2-C5H4N)N]2ZnOMeLi·thf}2 (2) and [Ph(2-C5H4N)N]2Zn[(μ3-O) Bu]2(Li·thf)2 (3). The structure of 2 implies the insertion of oxygen into a [(R2N)2ZnMe]– ion. To probe this mechanism, we have prepared, characterized, and derivatized [Ph(2-C5H4N)N]2ZnRLi (R = nBu, n = 2, L = thf, 4a; R = tBu, n = 1, L = thf, 4b) (Figure 1). The sequential reaction of [Ph(2-C5H4N)N]2Zn with nBuLi, thf and O2 gives {[Ph(2C5H4N)N]2ZnOBuLi·nL}2 (n = 1, L = thf, 5), the structures of 4a and 5 strongly suggesting that oxygenation proceeds by insertion into the Zn C bond of an {[Ph(2-C5H4N)N]2ZnnBu}– ion. The treatment of [Ph(2-C5H4N)N]2Zn with tBuLi, thf, and O2 affords only the previously reported 3—this being in part rationalized in terms of the steric requirements of OtBu. Moreover, the structure of 3 is closely related to that of 5. Formally, this can be described in terms of the rearrangement of M O (M = Li, Zn) interactions in response to the presence or absence of a [Ph(2-C5H4N)N]2Zn moiety. Structural characterization of {[Ph(2-C5H4N)N]2ZnBuLi·dme}(6), {[Ph(2-C5H4N)N]2ZnOBuLi·0.5dme}2 (7), and [Ph(2-C5H4N)N]2 Zn[(μ3-O)Bu]2(Li2·dme) (8), further support this postulated oxygen insertion.

New motifs in lithium zincate chemistry: a solid-state structural study of PhC(O)N(R)ZnR′2Li·2thf (R, R′ = alkyl, aryl) and [PhC(O)N(Ph)Li·thf]·[PhC(O)N(Ph)Zn(But)2Li·thf]

The facile reaction of ZnMe2 with secondary carboxylic amides of the type PhC(O)N(R)H (R = Me 14, Pri15, Ph 16) yields PhC(O)N(R)ZnMe (R = Me 17, Pri18, Ph 19). These complexes describe a hexamer (for 17) and tetramers (for 18 and 19) in the solid state which are best viewed as stacks of cyclic trimers and dimers, respectively. In turn, 17–19 react with ButLi to afford either the lithium zincate PhC(O)N(R)Zn(But)2Li·2thf (R = Me 20, Pri21) or the co-complex [PhC(O)N(Ph)Li·thf]·[PhC(O)N(Ph)Zn(But)2Li·thf] 22. In the solid state both 20 and 21 reveal dimeric structures based on a (LiO)2 core in which each alkali metal centre is doubly thf-solvated and trivalent zinc centres reside peripheral to the cluster. The structure of 22 reveals an adduct in which a dimeric lithium (carboxylic) amide core interacts with two PhC(O)N(Ph)Zn(But)2Li molecules, affording a structure intermediate between a ladder and an “open” pseudo-cubane. This is the first full characterisation of a complex between an alkali metal zincate and another organometallic species and it affords new insights into how these two classes of molecule interact. The straightforward formation of [PhC(O)N(R)ZnMe2]− (R = Me 23, Ph 24) ions has been successfully achieved by treating the appropriate lithium carboxylic amide with ZnMe2. In the solid-state, PhC(O)N(Ph)ZnMe2Li·2thf 24 is revealed to be isostructural with 20 and 21.