Cobalt Boryl Complexes: Enabling and Exploiting Migratory Insertion in Base-Metal-Mediated Borylation.

Cobalt boryl complexes, which have only been sporadically reported, can be accessed systematically with remarkable (but controllable) variation in the nature of the M-B bond. Complexes incorporating a very strong trans σ-donor display unparalleled inertness, reflected in retention of the M-B bond even in the presence of extremely strong acid. By contrast, the use of the strong π-acceptor CO in the trans position, results in significant Co-B elongation and to labilization of the boryl ligand via unprecedented CO migratory insertion. Such chemistry provides a pathway for the generation of coordinative unsaturation, thereby enabling ligand substitution and/or substrate assimilation. Alkene functionalization by boryl transfer, a well-known reaction for noble metals such as Rh or Pt, can thus be effected by an 18-electron base-metal complex.

Circumventing redox chemistry: synthesis of transition metal boryl complexes from a boryl nucleophile by decarbonylation.

The very strong reducing capabilities of the boryllithium nucleophile (THF)2Li{B(NDippCH)2} (1, Dipp = 2,6-iPr2C6H3) render impractical its use for the direct introduction of the {B(NDippCH)2} ligand via metathesis chemistry into the immediate coordination sphere of transition metals (d(n), with n ≠ 0 or 10). Instead, 1 typically reacts with metal halide, amide and hydrocarbyl electrophiles either via electron transfer or halide abstraction. Evidence for the formation of M-B bonds is obtained only in the case of the d(5) system [{(HCDippN)2B}Mn(THF)(µ-Br)]2. Lower oxidation state metal carbonyl complexes such as Fe(CO)5 and Cr(CO)6 react with 1 via nucleophilic attack at the carbonyl carbon atom to give boryl-functionalized Fischer carbene complexes Fe(CO)4{C(OLi(THF)3)B(NDippCH)2} and Cr(CO)5{C(OLi(THF)2)B(NDippCH)2}. Although C-to-M boryl transfer does not occur for these formally anionic systems, more labile charge neutral bora-acyl derivatives of the type LnM{C(O)B(NDippCH)2} [LnM = Mn(CO)5, Re(CO)5, CpFe(CO)2] can be synthesized, which cleanly lose CO to generate M-B bonds. From a mechanistic standpoint, an archetypal organometallic mode of reactivity, carbonyl extrusion, has thus been shown to be applicable to the boryl ligand class, with (13)C isotopic labeling studies confirming a dissociation/migration pathway. These proof-of-methodology synthetic studies can be extended beyond boryl complexes of the group 7 and 8 metals (for which a number of versatile synthetic routes already exist) to provide access to complexes of cobalt, which have hitherto proven only sporadically accessible.

Crabtree's catalyst revisited; ligand effects on stability and durability.

The extent of time-dependent deactivation of monophosphine monoamine iridium hydrogenation catalysts by trimer formation is strongly dependent on ligand structure; attempts to counter this process lead to the observation of an oligomerisation resistant catalyst.

Structural and bonding patterns in gold clusters.

The study of gold cluster compounds originated from Malatesta's syntheses of tertiaryphosphine derivatives in the 1960s and was greatly extended between 1970 and 2000. Single crystal X-ray studies defined the major structural classes and led to the development of a theoretical model which accounted for their closed shell requirements in terms of their topological features and proved to be sufficiently flexible to be extended to related heteronuclear cluster compounds. Since the turn of the century the range of gold cluster compounds has been greatly extended by the study of organothiolato-gold cluster compounds. The structures of these compounds have revealed that the gold atoms combine with the organothiolato-ligands to generate a novel class of metallo-organothiolato-ligands which protect and stabilise the inner core of gold atoms. These developments originally suggested that the phosphine and organothiolato-clusters defined quite distinct classes of gold clusters, but recent structural and theoretical developments have reconciled many of these differences. This review summarises the structures of all the clusters of gold and suggests a theoretical model which effectively unites the broad structural properties of the two classes of compound. This model is based on the united atom model for diatomics developed by Mulliken and the compression co-ordinate is related to the interpenetration of icosahedral and cuboctahedral pseudo-spherical clusters. The predicted closed shell requirements agree well with the results of structural determinations.

Anion Control in the Self-Assembly of a Cage Coordination Complex.

An anion is encapsulated in the center of the new cage compound [Ni6 (atu)8 X]X3 (X=Cl-for the structure see picture-or Br; Hatu=amidinothiourea). A combination of Lewis acid-base and hydrogen-bonding interactions cause the square-planar [Ni(Hatu)2 ]2+ units, after deprotonation, to assemble to form this compound. A remarkable feature is the anion dependence of the cage formation; nitrate, acetate, and perchlorate are unsuitable as templates.

Anion-templated synthesis of metallacages as a means for the colorimetric detection of chlorides.

In the presence of chloride or bromide in the appropriate mixture of solvents, 6 equiv of nickel(II) and 8 equiv of Hatu [Hatu=H2NC(=NH)NHC(=S)NH2] assemble to yield the metallacages [Ni6(atu)8X][ClO4]3 (atu=deprotonated form of Hatu; X=Cl, 5; Br, 6) where four "units" of the square-planar complex Ni(atu)2 are coordinated to two further nickel centers, forming an octahedral cage around an encapsulated chloride or bromide anion. Synthesis of the cages is highly dependent on the nature of the anions and the solvents used. In methanol, the cage only forms if chloride is present; in a mixture of acetone/methanol, the cage forms in the presence of either chloride or bromide. An interesting feature of the templation process is that there is a dramatic color change associated with assembly of the building blocks in the presence of the appropriate anion to yield the cages. This color change has been used as the basis for the colorimetric detection of chloride anions in methanol. The reaction of 4 equiv of nickel(II), 8 equiv of Hatu, and 2 equiv of platinum(II) has also been carried out, yielding the mixed-metal cage [Pt2Ni4(atu)8Cl][ClO4]3 (7a); the X-ray crystal structure of this compound is reported herein.

The oxidative addition of a chlorophosphine to Pd0: formation and characterisation of a 42-electron triangulo palladium cluster.

The reactions that lead to the formation of the 42-electron cluster [PdCl(P(NPr(i)(2))(2))](3) from various sources of the [P(NPr(i)(2))(2)] moiety are investigated, and the structure of the triangulo cluster confirmed by X-ray crystallography.