Diphosphorus Release and Heterocumulene Oligomerisation by Nickel Complexes

The generation of diphosphorus molecules P2 under mild conditions in solution is a useful strategy to generate diphosphines via [4+2] cycloadditions. We recently described the release of P2 units from the nickel butterfly complex [{(IMes)Ni(CO)}2(μ2,η2:η2-P2)] (IMes=1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) upon addition of CO gas. Herein, we developed an alternative protocol for the same process using heterocumulenes. In addition to formation of P4 (the dimerisation product of P2), the reactions afford nickel complexes of novel pincer-type ligands. Aryl isothiocyanates undergo a trimerisation within the coordination sphere of nickel and afford square planar nickel complexes with S-C-S pincer-ligand frameworks. Carbon disulfide coordinates to the [(IMes)Ni]-fragment in an η2-fashion, affording a dinuclear complex. Similar products are formed when the N-heterocyclic carbene nickel(0) complex [(IMes)Ni(vtms)2] is used as a precursor (vtms=vinyltrimethylsilane).

A Planar Ti2 P2 Core Assembled by Reductive Decarbonylation of - O-C≡P and P-P Radical Coupling

The complex [(nacnac)Ti(OAr)]₂ (μ₂ :η² ,η² -P₂ ) (1) is formed via reductive decarbonylation of the phosphaethynolate ion ^- [OCP], which serves as a P atom source. Complex 1 is the first structurally characterized Group 4 transition metal P₂ complex and its structure reveals the rhombic Ti₂ P₂ core is essentially planar with short bond lengths suggesting some degree of multiple bonding character between the Ti-P and P-P sites. Computational studies of 1 provide an understanding of the Ti₂ P₂ core as well as the origin of the highly downfield ³¹ P NMR spectroscopic signal.

Direct Synthesis of Phospholyl Lithium from White Phosphorus

The selective construction of P-C bonds directly from P4 and nucleophiles is an ideal and step-economical approach to utilizing elemental P4 for the straightforward synthesis of organophosphorus compounds. In this work, a highly efficient one-pot reaction between P4 and 1,4-dilithio-1,3-butadienes was realized, which quantitatively affords phospholyl lithium derivatives. DFT calculations indicate that the mechanism is significantly different from that of the well-known stepwise cleavage of P-P bond in P4 activation. Instead, a cooperative nucleophilic attack of two Csp2 Li bonds on P4 , leading to simultaneous cleavage of two P-P bonds, is favorable. This mechanistic information offers a new view on the mechanism of P4 activation, as well as a reasonable explanation for the excellent yields and selectivity. This method could prove to be a useful route to P4 activation and the subsequent production of organophosphorus compounds.

Reductive cleavage of P4 by iron(i) centres: synthesis and structural characterisation of Fe2(P2)2 complexes with two bridging P22− ligands

The one-electron reduction of a new Fe₂(P₂)₂ complex affords the first delocalised mixed-valent Fe(ii,iii) complex with an Fe₂P₄ core.

Activation of white phosphorus by low-valent group 5 complexes: formation and reactivity of cyclo-P4 inverted sandwich compounds

We report the synthesis and comprehensive study of the electronic structure of a unique series of dinuclear group 5 cyclo-tetraphosphide inverted sandwich complexes. White phosphorus (P4) reacts with niobium(III) and tantalum(III) β-diketiminate (BDI) tert-butylimido complexes to produce the bridging cyclo-P4 phosphide species {[(BDI)(N(t)Bu)M]2(μ-η(3):η(3)P4)} (1, M = Nb; 2, M = Ta) in fair yields. 1 is alternatively synthesized upon hydrogenolysis of (BDI)Nb(N(t)Bu)Me2 in the presence of P4. The trinuclear side product {[(BDI)NbN(t)Bu]3(μ-P12)} (3) is also identified. Protonation of 1 with [HOEt2][B(C6F5)4] does not occur at the phosphide ring but rather involves the BDI ligand to yield {[(BDI(#))Nb(N(t)Bu)]2(μ-η(3):η(3)P4)}[B(C6F5)4]2 (4). The monocation and dication analogues {[(BDI)(N(t)Bu)Nb]2(μ-η(3):η(3)P4)}{B(Ar(F))4}n (5, n = 1; 6, n = 2) are both synthesized by oxidation of 1 with AgBAr(F). DFT calculations were used in combination with EPR and UV-visible spectroscopies to probe the nature of the metal-phosphorus bonding.