Transition-Metal-Mediated Functionalization of White Phosphorus

Abstract

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-P_n , 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-P_n 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-P_n functionalization reactions, where TM-P_n 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.

Keywords: P ligands; coordination compounds; radicals; transition metals; white phosphorus.

Scheme 1

Production of white phosphorus (P₄) from the calcium phosphate part of apatite minerals (a) and the synthesis of organophosphorus compounds via PCl₃ (b) or PH₃ (c) (R=organic residue; X=Cl, Br, I; THPC=tetrakishydroxymethylphosphonium chloride).

Scheme 2

A selection of possible reaction pathways for the activation of white phosphorus (P₄). Only the P_n backbones of the fragments are shown; charges and substituents are omitted for clarity.

Figure 1

Structural motifs of selected transition‐metal complexes bearing P_n ligands; [M]=transition‐metal complex fragment.

Scheme 3

Early transition metallocene‐mediated activation of P₄ with concomitant functionalization.

Scheme 4

Functionalization of P₄ mediated by rhodium and iridium triphos complexes. Reaction conditions: (a) for 9 a: THF, 70 °C; for 9 b THF, 120 °C. (b) for 9 a: open system, THF, 70 °C, ‐H₂ or closed system, THF, 40 °C, ‐H₂; for 9 c: open system, THF, reflux, ‐C₂H₆. (c) for 11 a, 11 b: THF, 70 °C; for 11 c, 11 d, 11 e: THF, 60 °C, 20 atm H₂. (d) for 11 a, 11 e: +MeOTf; for 11 c: +HBF₄⋅OMe₂.

Scheme 5

Arylation of P₄ by a low‐coordinate cobalt‐tin cluster (a) and ruthenium‐mediated halogenation (b) and subsequent alkylation of P₄ (c).

Scheme 6

Oxidation of P₄‐derived P₁ and P₂ ligands in the coordination sphere of transition metals.

Scheme 7

P₁ functionalization mediated by the molybdenum phosphido complex 26.

Scheme 8

Phosphorus functionalization mediated by the niobium phosphide anion 29. (i) Recovery of starting material 29 from 35 proceeds by: 1.+Tf₂O in Et₂O at −35 °C; 2.+[Mg(thf)₃(C₁₄H₁₀)]/‐Mg(OTf)₂, ‐C₁₄H₁₀ in THF at −100 °C; 3.+0.25 equiv P₄ in THF at r.t.; 4.+Na‐amalgam/‐Hg in THF at r.t.

Scheme 9

Transformations of the phosphorus monoxide ligand P=O promoted by combinations of two metal complexes (Ar=3,5‐Me₂C₆H₃; R=C(CD₃)₂Me; Np=CH₂ tBu).

Scheme 10

Functionalization of P₂ units mediated by dinuclear group 6 complexes.

Scheme 11

Reactivity of neutral cyclo‐P₃ complexes with electrophiles (top) and nucleophiles (bottom); [Ni]=[Ni(C₆H₂ tBu₃)] (triphos=1,1,1‐tris(diphenylphosphanylmethyl)ethane).

Scheme 12

Functionalization of cyclo‐P₃ units with electrophiles mediated by oligonuclear complex anions (Ar=3,5‐Me₂C₆H₃; Np=CH₂ tBu; Mes*=2,4,6‐tBu₃C₆H₂).

Scheme 13

Phosphorus transfer reactions promoted by the anionic niobium cyclo‐P₃ complex 62; [Nb]=[Nb(ODipp)₃] (1,3‐CHD=1,3‐cyclohexadiene).

Scheme 14

Hydrolysis and halogenations of P₄ in the coordination sphere of mononuclear (a) and dinuclear (b) ruthenium complexes; [Ru]=[CpRu(PPh₃)₂]; [Ru′]=[CpRu(dppe)] (dppe=1,2‐bis(diphenylphosphanyl)ethane); [Ru′′]=[CpRu(TPPMS)₂] (TPPMS=Ph₂P(m‐C₆H₄SO₃Na)); [Ru′′′]=[Cp*Ru(dppe)].

Scheme 15

Halogenation of P₄ by silver complexes (a,b) and arylation of P₄ with organolithium compounds in the coordination sphere of N‐heterocyclic carbene (NHC) gold cations.

Scheme 16

Addition reactions of unsaturated organic molecules to P₄ butterfly complexes; [Ni]=[CpNi(IMes)] (IMes=1,3‐bis(2,4,6‐trimethylphenyl)imidazolin‐2‐ylidene); [Fe]=[Cp′′′Fe].

Scheme 17

Iron‐mediated protonation of P₄‐butterfly ligands; HX=[(Et₂O)H][BF₄], [(Et₂O)₂H][Al(OC(CF₃)₃]; [Fe]=[Cp′′′Fe(CO)₂]; [Fe′]=[Cp*Fe(CO)₂].

Scheme 18

Synthesis of phosphorus/silicon analogues of benzene (a) and phosphorus‐rich cage compounds (b) by Zr‐mediated P₄ functionalization (L=[PhC(NtBu)₂], [Zr]=[Cp′′₂Zr], Cp′′=1,3‐tBu₂C₅H₃).

Scheme 19

Tungsten‐ and iron‐promoted transformations of cyclo‐P₄ ligands; [W]=[W(CO)₅].

Scheme 20

Functionalization of the cyclo‐P₄ ligands in the cobalt sandwich complex 121; [Co]=[(1,2,4‐tBu₃C₅H₂)Co].

Scheme 21

Functionalization of a cyclo‐P₄ ligand with diorganochlorophosphanes R₂PCl (R=Cy, tBu, Ph, Mes, N(iPr)₂) mediated by a low valent α‐diimine cobalt complex, and subsequent rearrangement and fragmentation reactions (L=bis(2,6‐diisopropylphenyl)phenanthrene‐9,10‐diimine).

Scheme 22

Functionalization of the bridging P₄ chain in the ferrate 133 with electrophiles (Ar=4‐ethylphenyl; Ar^F=3,5‐(CF₃)₂C₆H₃).

Scheme 23

Functionalization of the catena‐P₄ unit in the cobaltate complex 136 with chlorophosphanes; [Co]=[CoBIAN] (BIAN=bis(mesityl)iminoacenaphthene); [Ga]=[Ga(nacnac)] (nacnac=CH[CMeN(2,6‐iPr₂C₆H₃)]₂).

Scheme 24

Functionalization of a cyclo‐P₅ ligand by nucleophiles (a,b), iodination (c) and thf ring‐opening (d); [Fe]=[Cp*Fe], [Ru]=[Cp*Ru], [Sm]=[L₂Sm], L=N,N′‐bis(2,6‐diisopropylphenyl)formamidinate).

Scheme 25

Functionalization of the cyclo‐P₅ ligand in pentamethylpentaphosphaferrocene 140 a by heavy carbene analogues. [Fe]=[Cp*Fe], L=[PhC(NtBu)₂, nacnac=CH[CMeN(2,6‐iPr₂C₆H₃)]₂), dme=dimethoxyethane, NHC=1,3,4,5‐tetramethylimidazol‐2‐ylidene.

Scheme 26

Functionalization of the cyclo‐P₆ middle deck in early transition‐metal triple‐decker complexes; [Mo]=[Cp*Mo], [V]=[Cp*V].

Scheme 27

Niobium‐mediated functionalization of a P₈ framework; [Nb]=[Nb(OR′)₃] (OR′=(adamantane‐2‐ylidene)(mesityl)methanolate); Ar=Ph, 4‐Cl‐C₆H₄, 4‐Me‐C₆H₄, 4‐OMe‐C₆H₄, 4‐NMe₂‐C₆H₄, 4‐CF₃‐C₆H₄). (i) Recovery of starting material 157 (0.5 equiv) proceeds by: 1. +O(OCCF₃)₂, +2 equiv Me₃SiI/‐Me₃SiO(OCCF₃) in Et₂O; 2. +SmI₂/‐SmI₃ in THF; 3. +P₄ in toluene.

Scheme 28

Radical functionalization of P₄ mediated by early (a) and late (b) transition metals. (i) only for Cp^BIG; (ii) MCp^R=NaCp^BIG, NaCp′′′, LiCp*, NaCp^iPr4; (iii) only for MCp^R=NaCp′′′, LiCp* (Cp^BIG=C₅(4‐nBu‐C₆H₄)₅; Cp′′′=C₅H₂ tBu₃; Cp*=C₅Me₅; Cp^iPr4=C₅HiPr₄).

Figure 2

Proposed mechanism for nickel‐electrocatalyzed arylation of white phosphorus in DMF or MeCN carried out in an undivided cell (bpy=2,2′‐bipyridine).

Scheme 29

Photocatalytic functionalization of P₄ to triarylphosphanes and tetraarylphosphonium salts.