Tristram Chivers

Pentafluorophenylboranes: from obscurity to applications

Pentafluorophenyl substituted boranes and borates are important as co-catalysts in metallocene-based industrial processes for the homogeneous polymerization of olefins. Although first prepared in the early 1960s, the remarkable properties of tris(pentafluorophenyl)borane have only recently been exploited for applications in catalysis. Spurred by these developments, the related compounds bis(pentafluorophenyl)borane and salts of the tetrakis(pentafluorophenyl)borate anion have also found application in olefin polymerization and other fields. In this article, we trace the rise of pentafluorophenyl boron compounds from curiosities to important commodities.

Chemistry of pnictogen(III)–nitrogen ring systems

This critical review covers significant recent advances in the chemistry of pnictogen(III)-nitrogen ring systems, also known as cyclopnict(III)azanes. The synthetic methodologies and reactions of the heavier pnictogen systems are compared with the well-developed chemistry of cyclophosph(III)azanes. Particular attention is focused on ring-oligomerization processes and the use of four-membered E(2)N(2) rings as building blocks for the synthesis of macrocyclic molecules. Main-group element and transition-metal complexes are also discussed (95 references).

Coordination complexes of bis(amido)cyclodiphosph(III/V and V/V)azane imides and chalcogenides

Abstract Metaphosphates with imido and chalcogenido substituents attached to a central phosphorus(V) center form ambidentate dimeric dianions that are potential components of metal-containing coordination polymers. This review summarizes the syntheses and structures of s-, p- and d-block metal complexes of these versatile ligands and their bis(amido)cyclodiphosph(V/V)azane precursors. The synthesis and structures of metal complexes of the corresponding cyclodiphosph(III/V)azane ligands are also discussed.

Imido Analogues of Common Oxo Anions: A New Episode in the Chemistry of Cluster Compounds

Oxo anions of p- and d-block elements, for example, SiO(4)(4-), PO(4)(3-), SO(4)(2-), and CrO(4)(2-), are commonly encountered species. The full or partial replacement of the oxo ligands by isoelectronic imido (NR) groups generates homoleptic polyimido anions of the type [E(NR)(x)](z-) or heteroleptic imidooxo anions with the general formula [O(y)E(NR)(x-y)](z-) (where E=main group element or transition metal). The alkali metal derivatives of this new class of anions form ternary or quaternary cluster systems, respectively. The structures of these clusters can be rationalized in terms of the self-assembly of fundamental building blocks. An understanding of the factors that control this process may allow the design of functional materials with specific properties. In addition, these anions are attracting attention as multidentate ligands with unique electronic and stereochemical properties that may engender novel metal-centered chemistry.

New insights into the chemistry of imidodiphosphinates from investigations of tellurium-centered systems.

Dichalcogenido-imidodiphosphinates, [N(PR(2)E)(2)](-) (R = alkyl, aryl), are chelating ligands that readily form cyclic complexes with main group metals, transition metals, lanthanides, and actinides. Since their discovery in the early 1960s, researchers have studied the structural chemistry of the resulting metal complexes (where E = O, S, Se) extensively and identified a variety of potential applications, including as NMR shift reagents, luminescent complexes in photonic devices, or single-source precursors for metal sulfides or selenides. In 2002, a suitable synthesis of the tellurium analogs [N(PR(2)Te)(2)](-) was developed. In this Account, we describe comprehensive investigations of the chemistry of these tellurium-centered anions, and related mixed chalcogen systems, which have revealed unanticipated features of their fundamental structure and reactivity. An exhaustive examination of previously unrecognized redox behavior has uncovered a variety of novel dimeric arrangements of these ligands, as well as an extensive series of cyclic cations. In combination with calculations using density functional theory, these new structural frameworks have provided new insights into the nature of chalcogen-chalcogen bonding. Studies of metal complexes of the ditellurido ligands [N(PR(2)Te)(2)](-) have revealed unprecedented structural and reaction chemistry. The large tellurium donor sites confer greater flexibility, which can lead to unique structures in which the tellurium-centered ligand bridges two metal centers. The relatively weak P-Te bonds facilitate metal-insertion reactions (intramolecular oxidative-addition) to give new metal-tellurium ring systems for some group 11 and 13 metals. Metal tellurides have potential applications as low band gap semiconductor materials in solar cells, thermoelectric devices, and in telecommunications. Practically, some of these telluride ligands could be applied in these industries. For example, certain metal complexes of the isopropyl-substituted anion [N(P(i)Pr(2)Te)(2)](-) serve as suitable single-source precursors for pure metal telluride thin films or novel nanomaterials, for example, CdTe, PbTe, In(2)Te(3), and Sb(2)Te(3).

Synthesis, Structures, and Multinuclear NMR Spectra of Tin(II) and Lead(II) Complexes of Tellurium-Containing Imidodiphosphinate Ligands: Preparation of Two Morphologies of Phase-Pure PbTe from a Single-Source Precursor

Group 14 metal complexes of heavy chalcogen-centered anions, M[(TeP(i)Pr(2))(2)N](2) (5, M = Sn; 6, M = Pb) and M(TeP(i)Pr(2)NP(i)Pr(2)Se)(2) (7, M = Sn; 8, M = Pb), were synthesized in 64-89% yields by metathesis of alkali-metal salts of the ligands with group 14 metal dihalides. Crystallographic characterization of the complexes revealed that 5, 6, and 8 engage in metal...chalcogen secondary bonds to generate dimers, whereas 7 is monomeric in the solid state. Multinuclear ((1)H, (31)P, (77)Se, and (125)Te) solution NMR data for these homoleptic complexes evinced dynamic behavior leading to the equivalence of the two ligand environments. The Pb(II) complex 6 was utilized as a single-source precursor to micrometer-scale lead telluride particles via two divergent techniques: aerosol-assisted chemical vapor deposition of the complex in THF/CH(2)Cl(2) solution onto glass substrates yielded rectangular prisms, while solution injection of 6 in tri-n-octylphosphine onto Si/SiO(2)(100) substrates heated to 200-220 degrees C resulted in the formation of wires. PXRD and EDX analysis of the products confirmed the phase purity of the PbTe materials.

Chemical vapour deposition of II–VI semiconductor thin films using M[(TePiPr2)2N]2 (M = Cd, Hg) as single-source precursors

The aerosol-assisted chemical vapour deposition (AACVD) of CdTe has been carried out using Cd[(TePiPr2)2N]2 at substrate temperatures between 375 and 475 °C. XRD shows the formation of cubic CdTe between 425 and 475 °C. At low deposition temperature (375 °C), a mixture of hexagonal tellurium and cubic cadmium telluride is observed. SEM images reveal that the growth temperatures do not have a profound effect on the morphologies of films. Surface analysis by XPS of films deposited at 475 °C showed the growth of Te-rich films. The AACVD of Hg[(TePiPr2)2N]2 resulted in deposition of hexagonal tellurium.

THE FUTURE OF MAIN GROUP CHEMISTRY

After a brief reflection on the important discoveries in main group chemistry during the past century, this article provides some suggestions concerning areas in which studies of s- and p-block element compounds are likely to have a major impact on the discipline of chemistry and upon society in general in the context of significant advances that have been made in the last decade. These areas range from fundamental to applied aspects of the subject. In the former category, novel aspects of chemical bonding and new reagents for synthetic applications are considered. From a more practical perspective alternative energy sources (especially hydrogen storage), new materials (notably nanomaterials and chemical sensors), catalysis (in the context of green chemistry), and medicinal chemistry (both diagnostic and therapeutic applications) are discussed.

Ni[(EPiPr2)2N]2 Complexes : Stereoisomers (E = Se) and Square-Planar Coordination (E = Te)

The reaction of ((i)Pr 2PE) 2NM.TMEDA (M = Li, E = Se; M = Na, E = Te) with NiBr 2.DME in THF affords Ni[(SeP (i)Pr 2) 2N] 2 as either square-planar (green) or tetrahedral (red) stereoisomers, depending on the recrystallization solvent; the Te analogue is obtained as the square-planar complex Ni[(TeP (i)Pr 2) 2N] 2.

Applications of the Laddering Principle — A Two‐Stage Approach to Describe Lithium Heterocarboxylates

Since the development of the laddering principle in the mid-1980s, it has become a useful concept for describing structural features in a wide variety of organoalkali metal (particularly organolithium) and other main-group element oligomers. Here a brief account of the laddering principle is given, and a two-stage approach to understanding structural diversity is described for several lithium heterocarboxylates. “Primary laddering” describes the initial aggregation of monomeric units, whereas “secondary laddering” deals with the assembly of these primary laddered units into larger structures. Both homo- and heteromolecular clusters can be formed by these processes. In this context, several examples are discussed, with particular emphasis on the effects of solvation and heteroatoms.