Transition-Metal-Mediated Functionalization of White Phosphorus

Recently there has been great interest in the reactivity of transition-metal (TM) centers towards white phosphorus (P4 ). This has ultimately been motivated by a desire to find TM-mediated alternatives to the current industrial routes used to transform P4 into myriad useful P-containing products, which are typically indirect, wasteful, and highly hazardous. Such a TM-mediated process can be divided into two steps: activation of P4 to generate a polyphosphorus complex TM-Pn , and subsequent functionalization of this complex to release the desired phosphorus-containing product. The former step has by now become well established, allowing the isolation of many different TM-Pn products. In contrast, productive functionalization of these complexes has proven extremely challenging and has been achieved only in a relative handful of cases. In this review we provide a comprehensive summary of successful TM-Pn functionalization reactions, where TM-Pn must be accessible by reaction of a TM precursor with P4 . We hope that this will provide a useful resource for continuing efforts that are working towards this highly challenging goal of modern synthetic chemistry.

Modern applications of low-valent early transition metals in synthesis and catalysis

Low-valent early transition metals are often intrinsically highly reactive as a result of their strong propensity toward oxidation to more stable high-valent states. Harnessing these highly reducing complexes for productive reactivity is potentially powerful for C-C bond construction, organic reductions, small-molecule activation and many other reactions that offer orthogonal chemoselectivity and/or regioselectivity patterns to processes promoted by late transition metals. Recent years have seen many exciting new applications of low-valent metals through building new catalytic and/or multicomponent reaction manifolds out of classical reactivity patterns. In this Review, we survey new methods that employ early transition metals and invoke low-valent precursors or intermediates in order to identify common themes and strategies in synthesis and catalysis.

Synthesis and Reactivity of the Phosphorus Analogues of Cyclopentadienone, Tricyclopentanone, and Housene

The phosphorus analogues of cyclopentadienone, tricyclopentanone, and housene were accessed from bis(cyclopropenyl)diphosphetanedione 3, which was prepared by mixing 1,2,3-tris-tert-butylcyclopropenium tetrafluoroborate (1) and sodium phosphaethynolate [Na(OCP)(dioxane)_n ]. While photolysis of 3 results in decarbonylation, yielding bis(cyclopropenyl)diphosphene 4 and after rearrangement diphosphahousene 5, thermolysis of 3 leads to phosphatricyclo[2.1.0.0]pentanone 7. Metal-mediated valence isomerization of 7 and subsequent demetalation provides access to phosphacyclopentadienone 12.

Transfer Reagent for Bonding Isomers of Iron Complexes

The cothermolysis of As₄ and [Cp″₂Zr(CO)₂] (Cp″ = η⁵-C₅H₃tBu₂) results in the formation of [Cp″₂Zr(η^1:1-As₄)] (1) in high yields and the arsenic-rich complex [(Cp″₂Zr)(Cp″Zr)(μ,η^2:2:1-As₅)] (2) as a minor product. In contrast to yellow arsenic, 1 is a light-stable, weighable and storable arsenic source for subsequent reactions. The transfer reaction of 1 with [Cp‴Fe(μ-Br)]₂ (Cp‴ = η⁵-C₅H₂tBu₃) yields the unprecedented bond isomeric complexes [(Cp‴Fe)₂(μ,η^4:4-As₄)] (3a) and [(Cp‴Fe)₂(μ,η^4:4-cyclo-As₄)] (3b). In contrast, the analogous reaction with the Cp^Bn derivative [Cp^BnFe(μ-Br)]₂ (Cp^Bn = η⁵-C₅(CH₂(C₆H₅)₅) leads exclusively to the triple decker complex [(Cp^BnFe)₂(μ,η^4:4-As₄)] (4) possessing the tetraarsabutadiene-type ligand analogous to 3a. To elucidate the stability of the bonding isomers 3a and 3b, DFT calculations were performed. The oxidation of 4 with AgBF₄ affords [(Cp^BnFe)₂(μ,η^5:5-As₅)][BF₄] (5), which is a product expanded by one arsenic atom, instead of the expected complex [(Cp^BnFe)₂(μ,η^4:4-cyclo-As₄)]⁺.

Crystal structure of a P4-bridged (η 5-pentamethyl-cyclopentadienyl)(η 5-adamantylcyclopentadienyl) titanium(III)complex, C50H66P4Ti2

C50H66P4Ti2, orthorhombic, P21212 (no. 18), a = 14.3799(5) Å, b = 15.4444(6) Å, c = 9.5555(5) Å, V = 2122.17(16) Å3, Z = 2, Rgt(F) = 0.0338, wRref(F2) = 0.0643, T = 153(2) K.