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Tom Hooper, Russell Group

Tom Hooper, Russell Group. New Routes to Aromatic Phosphorus Heterocycles 5 th European Workshop on Phosphorus Chemistry, Regensburg 11 th March 2008. Phosphorus the Carbon Copy?. Targeting phosphorus analogues of organic compounds Isolobal relationship between CH and P

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Tom Hooper, Russell Group

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  1. Tom Hooper, Russell Group New Routes to Aromatic Phosphorus Heterocycles 5th European Workshop on Phosphorus Chemistry, Regensburg 11th March 2008

  2. Phosphorus the Carbon Copy? • Targeting phosphorus analogues of organic compounds • Isolobal relationship between CH and P • Phosphorus containing analogues of the cyclopentadienyl anion – fully characterised series • Routes are often synthetically challenging and low yielding Mathey, Cooord. Chem. Rev., 1994, 137, 1.

  3. Coordination Chemistry of the Phosphorus Containing Cyclopentadienyl Analogues • Very interesting as ligands due to the various η1-, η3- and η5- coordination modes plus the possibility of coordination from phosphorus lone-pairs • Hundreds of examples in the literature • F. Mathey, Coord. Chem. Rev., 1994, 137, 1. • First non-carbon containing sandwich complex Urnezius, Brennessel, Cramer, Ellis, Schleyer, Science, 2002, 295, 832

  4. Previous Routes to Polyphospholide Anions • Current routes are often complex multistep syntheses and/or use phosphaalkynes Nixon et al., Polyhedron, 1989, 8, 2407 Becker et al., Nova Acta Leopold.,1985, 59, 55 Binger, Regitz et al., Angew. Chem., Int. Ed., 1991, 30, 208 Russell et al., Angew. Chem., Int. Ed., 2003, 42, 2778 Russell et al.,Organometallics, 2005, 24, 5789

  5. Example of 1,2,3-Triphospholyl Anion Synthesis • Challenging multi-step synthetic route • One of the only practical routes to the 1,2,3-isomer • Other routes to these types of compounds are similarly non-facile Maigrot, Sierra, Charrier and Mathey, Bull. Soc. Chim. Fr., 1994, 131, 397.

  6. 1,2-Diphosphinobenzene • Commercially available starting material • Initial idea was to deprotonate using 1, 2, 3, and 4 equivalents of n-butyllithium in a coordinating solvent, THF • Reactions showed distinct colour changes and all yielded soluble products but only the dilithiation showed a clean 31P NMR spectrum • 31P{1H} NMR: Singlet at –127 ppm • 31P NMR: Doublet at –127 ppm (1JPH = 96 Hz)

  7. P C Li H O Reactions With n-Butyllithium • Reaction with 4 equivalents of n-butyllithium in THF yields a soluble orange product • However no signal in 31P NMR spectrum • Crystal structure suggests hexamer of trilithiates • Central cluster of P12Li20 • Reacts as if all protons had been removed Li20[{C6H4(P)PH}6{OEt}2].(thf)14

  8. Reaction With ECl3 (E = P, As, Sb) • Reaction proceeds quickly in THF • [C6H4P3]- gives interesting AA'B second order 31P NMR spectrum • As and Sb analogues also observed in 31P NMR at 304 and 312 ppm • Sb analogue decomposes over a few days δ = 335 and 260 ppm 1JPP = 514 and 488 Hz Russell, Hooper et al., Chem. Commun., 2008, 856

  9. P C Li O Structure of [C6H4P3][Li(12-C-4)2] • Crystallised by complexing the lithium with two 12-crown-4 1.431(6) Å 1.364(6) Å 120.3(4)° cf. P-P 2.22 Å P=P ~2.0 Å P-C 1.84 Å P=C 1.66 Å 101.1(1)° 2.092(2) Å 1.404(6) Å 98.9(2)° 1.779(5) Å 1.423(6) Å

  10. -13.7 -7.4 -6.5 -10.8 NICS values Aromaticity Calculations • [C9H7] anion compared to [C6H4P3] anion • Benzene = -9.7 • Cyclopentadienyl anion = -14.3 Schleyer et al., J. Am. Chem. Soc., 1996, 118, 6317

  11. P C Li As O Structure of [C6H4P2As][Li(12-C-4)2] • First example of 1,3-P-2-As-cyclopentadienyl analogue 1.437(5) Å 1.371(6) Å 122.1(3)° cf. As-P ~2.34 Å As=P ~2.13 Å P-C 1.84 Å P=C 1.66 Å 97.69(4)° 2.202(1) Å 1.413(6) Å 99.1(1)° 1.425(5) Å 1.773(4) Å

  12. Hittorf’s Phosphorus P C Organophosphorus Cage • However, another product crystallised from the reaction mixture • α-P8(4) cage • First isolated organo derivative of this type of cage • Also characterised by mass spectrometry • All P environments magnetically inequivalent so 31P NMR non-trivial • All P-P bond lengths within the narrow range 2.22-2.24 Å • P-P-P bond angles 87-104° • P8 cluster is one of the principle components of Hittorf’s phosphorus Baudler et al., Angew. Chem. Int. Ed. Engl., 1987, 26, 347

  13. Complexation of 1,2,3-triphosphaindenyl with d-block Metals • Reactions with MXn often unsuccessful • In reactions with metal salts, 1,2,3-triphosphaindenyl often shows reducing behaviour yielding metallic precipitate • However recent reactions have yielded promising but as yet not fully characterised results

  14. Summary and Future Work • Explored the reactions of 1,2-diphosphinobenzene • Novel and facile route to triphosphaindenyl species • First isolated organo-α-P8(4) cage • Complexation of indenyl analogues with d- and f-block metal centres • Fine tune electronic properties by exploring the chemistry of some compounds analogous to 1,2-diphosphinobenzene

  15. Acknowledgements • Dr Chris Russell • Prof. Michael Green • Prof. John McGrady and Dr Dimitrios Pantazis • Dr Jon Charmant and Dr Mairi Haddow • Dr Rich Kilby, Dr Olly Presly and Steve Mansell • Rhodia • University of Bristol and EPSRC

  16. d 122.7 ppm d 31.9 ppm d 104.2 ppm P8 Cage 31P NMR Spectrum • Three resonances – but all 8 31P centres magnetically inequivalent • Modelled spectrum shows similar shifts

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