Dominic S. Wright, Rob Less, Sophia Solomon, Hayley Simmonds
The dehydrocoupling of element-H bonds (equ. 1) has been dominated by transition metal reagents and catalysts. However, it is becoming clear that high reactivity and catalytic activity can also be obtained in this type of reaction using main group metal-based systems (even in the absence accessible d-orbitals in the valence shell). Redox-active main group bases like M(NMe2)n (M = can be highly effective in the stoichiometric dehydrocoupling of P-P and even N-N bonds, with some unusual reactivity being observed.1,2 Surprisingly, even simple Sn(IV) organometallics like Cp*2SnCl2 can function as catalysts in the formation of P-P bonds and are directly analogous in their behaviour to transition metal systems based on Zr(IV).3 This behaviour can also be extended to other dehydrocoupling reactions. Al(III) amides have been shown to be as active as a number of precious metal catalysts in the dehydrocoupling of B-N bonds, and exhibit closely related reaction characteristics.4,5 Where more redox-active group 13 metals are employed unique chemistry can be observed (which is not seen for transition metals). A case in point is the reaction of Ga{N(SiMe3)2}3 with NH3BH3 which gives the unusual product 1 (below), in which a combination of B-N coupling and N(SiMe3)2 ligand rearrangement has occurred.5,6
Thomas C. Wilson, Robert J. Less, Dominic S. Wright
The pentacyanocyclopentadienide anion, 1 (Fig. 1), has been little studied and has been claimed to be ‘almost totally non-coordinating’.1 However, recent studies2 have shown this not to be the case, and altering the synthesis to give a thermodynamic driving force for the reaction has proved successful (Eqn. 1).
The readily accessible sodium salt Na[1] can then be reacted with metal halide salts (Eqn. 2) to yield novel complexes. Due to the presence of five electron-withdrawing groups, 1 acts as a s-donor through the cyano groups, rather than as a p ligand via the C5 ring. Both CoCl2 and CuCl2 were reacted with Na[1], and the resulting complexes are reported here. In addition to this, a family of Group 11 phosphine complexes involving 1 are also reported.3 The latter are the first complete series of cyclopentadienyl compounds to be structurally characterised for any group in the Periodic Table. The ion paired gold complex, Au(PPh3)2[1], is shown below (Fig. 2).
Figure 1 (left): The pentacyanocyclopentadienide anion, 1 ; Figure 2 (right): Au(PPh3)2[1]
Timothy C. King,* Dominic S. Wright, Ali Alavi
Department of Chemistry, University of Cambridge
Boron-doped graphite provides a range of technological differences compared to undoped graphite, including reduced oxidation and erosion rates (specifically with respect to plasma facing materials used in fusion reactors) and improved electrode performance in Li ion batteries. However, numerous previous invesigations have succeeded only with limited boron doping and normally samples are only several monolayers thick. Interest has recently been piqued in this area due to several computational studies on the hydrogen storage ability of boron-doped graphite, specifically BC3. These studies have stressed the importance of developing a reliable synthetic method of obtaining bulk samples of boron-rich material since chemisorption of H2 relies on cooperativity between the layers within the bulk and, for example, boron-doped monolayers and graphite itself are inactive in H-H bond cleavage.
We describe here a single-source method of obtaining bulk amounts of ‘BC3’. This involves a facile carbonisation/graphitisation step that produces a material capable of storing 5 wt% hydrogen (only slight below the US-DoE minimum target).
Figure 1. The synthesis of boron doped graphites from a single-source precursor.
Sarah B. J. Dane, Vesal Naseri, Dominic S. Wright
Phosphorus ylides (Fig 1A) have become a classical tool for organic synthesis ever since the discovery that they could be used for olefination reactions by Wittig. Schildbauer1 has extensively studies these as ligands but one elusive member of this family are dianions of the type [RP(CH2)3]2- (Fig 1A), recently it has become possible to prepare and characterise them.
Figure 1: (A) the structure of a classical phosohprus ylide. (B) the stutrure of [RP(CH2)3]2- type dianions, (C) Isoelectronic
p-block element imido and oxo-anions, isoelectronic with [RP(CHR')3]2- dianions.
Our interest in the phosphoylide dianions [RP(CHR')3]2-, arises from their being valence-isoelectronic with a broad family of tripodal p-block element imido ligands of the type [RmE(NR)3]n- (Figure 1C), whose coordination chemistry has been investigated extensively in the past few decades. They are also isoelectronic with important classes of phosphorus oxo-anions, such as phosphonate anions [RPO3]2-, which have broad applications in the synthesis of framework materials.
DFT calculations show that [RP(CHR`)3]2- are both σ-donors and π-acceptors: the σ-donor character is via the lone pairs on the CH2 groups and the π-acceptor character is via the vacant σ* orbital of the P-C(R) bond. Reacting the phosphonium salt [PhP(CH3)3][I] with 3 eqv of tBuLi in thf gives [Li2{PhP(CH2)3}.2THF]2 (1) (Fig 2A). Transmetallations with Fe2I produces the hydride compls [{PhP(CH2)3Fe}4(µ4-H)]-.Li(thf)4+ (2) (Fig 2B), a rare example of a [metal]4[µ4-H] compound.2
Figure 2: (a) Structure of (1) [Li2{PhP(CH2)3}.2THF]2, (b) The tetranuclear hydride comples [{PhP(CH2)3Fe}4(µ4-H)]-.Li(thf)4+ (2)