Reactivity of Heptaphosphide Zintl Anions Towards Unsaturated Bonds
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Reactivity of Heptaphosphide Zintl Anions Towards Unsaturated Bonds. Robert Turbervill University of Oxford. 10 th European Workshop on Phosphorus Chemistry 2012 (Regensburg, Germany) March 18 th -20 th 2013.

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Reactivity of Heptaphosphide Zintl Anions Towards Unsaturated Bonds

Robert Turbervill

University of Oxford

10th European Workshop on Phosphorus Chemistry 2012 (Regensburg, Germany)

March 18th-20th 2013


Zintl phases Unsaturated Bonds: Ionic, salt-like intermetallics formed between group 1 (alkali) or group 2 (alkaline- earth) elements and post transition metals or metalloids from groups 13, 14, 15 or 16.


Manriquez, V.; Honle, W.; von Schnering, H. G. Unsaturated BondsZ. Anorg. Allg. Chem. 1986, 539, 95.

Zintl phases: Ionic, salt-like intermetallics formed between group 1 (alkali) or group 2 (alkaline- earth) elements and post transition metals or metalloids from groups 13, 14, 15 or 16.


Synthesis Unsaturated Bonds

Stoichiometric mixtures of elements loaded in an inert atmosphere glovebox

Nb tube

Arc welder used to seal niobium tubes

Nb tubes sealed in silica ampoules under vacuum

Tube furnace at high temperature (600°C) for 3 days

Nb tube


Structure and solution chemistry Unsaturated Bonds

pyridine

Three phosphorus environments (basal, waist, apical)

Each two-coordinate phosphorus carries a formal negative charge

Highly fluxional in solution and solid state

K3P7(s) + H2O + 18-crown-6

[K(18-crown-6)]2[HP7]

Contains 5-10% unidentified impurity phase as synthesized

85% yield, multigram scale, analytically pure

Sen, T.; Poupko, R.; Fleischer, U.; Zimmermann, H.; Luz, Z. J. Am. Chem. Soc.2000, 122, 889

However, in practice, most reactivity can be done with the Zintl phase


Chemistry so far… Unsaturated Bonds

[P7{FeCp(CO)2}3]Fenske, 1996

[P7Tl]2–Goicoechea, 2010

[Fe(HP7)2]2–Goicoechea, 2011

η1-

η2-

η4-

2 electron donor to metal centre

4 electron donor to metal centre

6 electron donor to metal centre

Many examples of metallated cages, very little “phospha-organic” chemistry…


Reactions of [HP Unsaturated Bonds7]2- with CO2 analogues

DMF, 20 °C

[HP7]2– + RN=C=E

[P7C(E)(HNR)]2–

amide functionalized cage

amidine functionalized cage

Works for RN=C=O (R = Ad, Dipp), RN=C=NR (R = Dipp, iPr, Cy)

NH observed at 5.88 ppm

NH observed at 6.29 ppm

Turbervill, R. S. P.; Goicoechea, J. M. Chem. Commun.2012, 48, 1470-1472 and unpublished work


–50 ºC Unsaturated Bonds31P NMR [P7(NHDipp)(NDipp)]2-

RT 31P NMR spectrum shows that the cluster anions are fluxional in solution


Reactions of [HP Unsaturated Bonds7]2- with carbodiimides

31P NMR spectrum shows 5 resonances:+12.5, –29.0, –64.2, –113.8, –129.5 ppm

Protonation only possible for [P7C(NDipp)(NHDipp)]2–(R = Dipp, iPr, Cy)

Turbervill, R. S. P.; Goicoechea, J. M. Organometallics, 2012, 31, 2452-2462


Reactions of [P Unsaturated Bonds7]3-with alkynes

NMR spectra consistent w/ AA’BXX’ system

1JP–P = –493 Hz; 2JP–P = 10 Hz; 2JH–P = 48 Hz; 3JH–P = 18 Hz; 3JH–H = 8 Hz

Turbervill, R. S. P.; Goicoechea, J. M. Chem. Commun., 2012, 48, 6100-6102


Preliminary coordination chemistry Unsaturated Bonds

[P3C2H2]– + [Ru(COD){CH3C(CH2)2}2]

THF, 45 °C

[Ru(P3C2H2){CH3C(CH2)2}2]– + COD


Preliminary coordination chemistry Unsaturated Bonds

Arsenic analogue structurally characterised as [K(2,2,2-crypt)]+ salt


Accessible 1,2,3-tripnictolides Unsaturated Bonds

Several anions are accessible via direct reaction of an alkyne with K3E7 (E = P, As)

All structurally authenticated as either P or As; [K(2,2,2-crypt)]+ or [K(18-crown-6)]+ salts


1,2,3-Triphospholide complex formation Unsaturated Bonds

31P NMR spectrum shows upfield shifts of approximately 200-250 ppm on complexation

Analysis of complexes by IR spectroscopy reveals that the ligands have increased π-acceptor properties relative to Cp− (c.f. 1,2,4-triphospholides; Nixon/Green)

IR νCO (cm−1):

[(P3C2H2)Mo(CO)3]−: 1916, 1834, 1814

[(C5H5)Mo(CO)3]−: 1884, 1760

Turbervill, R. S. P.; Jupp, A; McCullough, P. S. B.; Ergöçmen, D.; Goicoechea J. M., accepted


Coordination chemistry of [P Unsaturated Bonds3C2(2-py)H]–

CD2Cl2, 20 °C

[P3C2(2-py)H]– + Mo(COD)(CO)4

[κ2-(P3C2H{2-py})Mo(CO)4]–

κ2-complex loses CO in solution to form the η5-complex

Turbervill, R. S. P.; Goicoechea J. M., submitted


Bimetallic systems Unsaturated Bonds

Turbervill, R. S. P.; Goicoechea J. M., submitted


Conclusions and future work Unsaturated Bonds

  • [P7]3– cages possess a rich chemistry with organic compounds

  • Useful reagent to access elusive “phospha-organic” molecules

  • Currently exploring salt methathesis and redox chemistry of 1,2,3-tripnictolides

  • Promising results with other organic substrates


Acknowledgements Unsaturated Bonds

Other DPhil student: Caroline Knapp (presenting a poster here)

Part II students: Andrew Jupp, Phil McCullough (2011-12), Bethan Westcott (2012-13)

Summer student (ERASMUS): Doruk Ergöçmen (2012)

NMR: Dr. Nick Rees

Supervisor: Dr. Jose Goicoechea

Funding:

Andy

Ben

Jack

Caroline

Jose

Jordan

Bethan

Gaby


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