Robert J. Less

Recent perspectives on main group-mediated dehydrocoupling of P–P bonds

Transition metal-mediated dehydrocoupling is a developing synthetic tool for the preparation of an extensive range of main group element-element bonded species, with broad applications to molecular and polymeric materials. Recent results have stressed the relationship between this class of transition metal reagents and their entirely main group counterparts. But what are the similarities and differences between transition metal and main group systems?

Formation of a new class of 7π radicals via sterically induced P–P bond cleavage of the dimers [(CH)2(NR)2P]2

The 2c-2e- P-P bonded dimers [(CH)2(NR)2P]2 dissociate in solution to give the persistent new 7pi radicals [(CH)2(NR)2P]*, which are isoelectronic with the well known S/N thiazolyl radicals.

Synthesis and magnetic properties of the novel dithiadiazolyl radical, p-NCC6F4C6F4CNSSN*.

The dithiadiazolyl radical p-NCC6F4C6F4CNSSN* (4) retains its monomeric nature in the solid state with molecules linked together into chains via supramolecular CN-S interactions. Variable temperature magnetic studies on 4 show that it behaves as a near-ideal Curie paramagnet (|theta| less than 0.1 K), indicating negligible intermolecular exchange. The effective magnetic moment (1.78 micro(B)) is temperature independent and in excellent agreement with the value expected for an S = 1/2 paramagnet with g = 2.01(1.74 micro(B)). The lack of exchange coupling between radicals is attributed to the absence of significant orbital overlap between radical centres.

Neptunium(IV) and uranium(VI) complexation by hydroxamic acids

Hydroxamic acids complex more readily with Ac(IV) than Ac(VI). Formohydroxamic acid (FHA) is a hydrophilic organic ligand which can readily complex with Np(IV), as indicated by near infrared spectroscopy. Distribution experiments have also shown that FHA can strip Np(IV) from 30% TBP/OK into aqueous nitric acid. In contrast U(VI) does not complex as strongly with FHA and the reaction is greatly inhibited by nitric acid, as observed by UV-Vis spectroscopy. After stripping Np(IV) it has also been proven, by 13C NMR spectroscopy, that FHA can be decomposed to gaseous products in concentrated nitric acid leaving no organic waste products in solution. This experimental evidence proves that FHA can be used to selectively strip Np(IV) from a 30% TBP/OK solution of Np(IV) and U(VI) into aqueous nitric acid and is thus a viable new reagent for inclusion in an advanced PUREX process.

A simple approach to coordination compounds of the pentacyanocyclopentadienide anion.

Deprotonation of [Et(3)NH][C(5)(CN)(5)] with metal bases provides a very simple approach to coordination compounds containing the pentacyanocyclopentadienide anion [C(5)(CN)(5)](-) (1). The three-dimensional polymer [Na(thf)(1.5)(1)](∞) and the molecular dimer [{(tmeda)(2)Na(1)}(2)] are obtained by reaction of this precursor with NaH in the presence of thf or tmeda (Me(2)NCH(2)CH(2)NMe(2)). Their single-crystal X-ray structures both reveal σ-bonded C≡N-Na arrangements and π stacking between [C(5)(CN)(5)](-) ions. DFT calculations on the [C(5)(CN)(5)](-) ion have been used to investigate the structures and bonding in [Na(thf)(1.5)(1)](∞) and [{(tmeda)(2)Na(1)}(2)]. The absence of π bonding of the metal ions in both complexes is due to dispersion of the negative charge from the C(5) ring unit to the C[triple chemical bond]N groups in the [C(5)(CN)(5)](-) ion, making the coordination chemistry of this anion distinctly different from that of cyclopentadienide C(5)H(5)(-).

A quadruply-bonded [Cr2(guanidinate)4]4−tetraanion

The reaction of chromocene, Cp(2)Cr, with dilithiated 2,3-diphenylguanidine [(PhNH)(2)C=NH = L(2)H(3)] gives the novel, quadruply-bonded tetraanion [Cr(2)(L(2)H)(4)](4-).

Multi-Functional Magnetic Materials Based on Dithiadiazolyl Free Radicals

Abstract The crystal structures of a series of dithiadiazolyl free radicals, p-XC6F4CNSSN (X˭F,Cl,Br and CN) are described in terms of dipolar interactions which induce chain-like motifs in the solid state. When X˭CN two morphologies are observed; the β-phase is polar and undergoes a phase transition to a weakly ferromagnetic state at 36K, an unprecedented temperature for an organic radical. The polar structure which gives rise to weak ferromagnetism in β-p-NCC6F4CNSSN, also provides a number of other potential solid state properties which may interact independently or cooperatively with the magnetic behaviour.

A mechanistic study of the C–P bond cleavage reaction of 1,2-(PH2)2-C6H4 with nBuLi/Sb(NMe2)3

In situ 31P NMR spectroscopic studies of the reaction of the primary diphosphine 1,2-(PH2)2-C6H4 with the mixed-metal base system nBuLi/Sb(NMe2)3, combined with X-ray structural investigations, strongly support a mechanism involving a series of deprotonation steps followed by antimony-mediated reductive C-P bond cleavage. The central intermediate in this reaction is the tetraphosphide dianion [C6H4P2]2(2-) ([]) from which the final products, the 1,2,3-triphospholide anion [C6H4P3]- () and [PhPHLi] (.Li), are evolved. An EPR spectrocopic study suggests that homolytic C-P bond cleavage is likely to be involved in this final step.

Selenium for sulfur substitution in a thiazyl ring: identification of the phenyl-selenathiadiazolylium cation, [PhCNSeSN]+

Abstract The sequential replacement of sulfur by selenium in the phenyl-1,2,3,5-dithiadiazolylium cation occurs in an exceptional one-pot reaction between [PhCNSSN]Cl and SeO 2 . The cations [PhCNSeSN] + and [PhCNSeSeN] + are identified by mass spectroscopy. One e − reduction of these ions generates their corresponding radicals, which are identified by EPR spectroscopy.

Isolation of the first diselenadiazolyl complex, Pd3[PhCNSeSeN]2[PPh3]4·2PhMe

The selenium–nitrogen radical PhCNSeSeN is shown to be partially associated in solution; it undergoes an oxidative addition reaction to Pd(PPh3)4via Se–Se bond cleavage, and the structure of the first diselenadiazolyl–metal complex, Pd3[PhCNSeSeN]2[PPh3]4 is reported.