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The Research of Alan H. Cowley (Abridged)

The Research of Alan H. Cowley (Abridged). by Keith T. Quisenberry February 20, 2006 Chisholm Group Presentation. Alan H. Cowley: a Major Player in Main Group Chemistry. Alan Herbert Cowley. University of Manchester B.Sc. (1955), M.S. (1956), Ph.D. (1958) University of Florida

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The Research of Alan H. Cowley (Abridged)

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  1. The Research of Alan H. Cowley (Abridged) by Keith T. Quisenberry February 20, 2006 Chisholm Group Presentation

  2. Alan H. Cowley: a Major Player in Main Group Chemistry

  3. Alan Herbert Cowley University of Manchester B.Sc. (1955), M.S. (1956), Ph.D. (1958) University of Florida Postdoctoral Fellow/Instructor (1958–60) Exploratory Group of Imperial Chemical Industries Technical Officer(Billingham Div.) (1961) University of Texas at Austin Assistant Prof. (1962–67), Associate Prof. (1967–70), Prof. (1970–84), George W. Watt Cent. Prof. (1984–88) Imperial College, London, England Sir Edward Frankland Prof. (1988–89) University of Texas at Austin Robert A. Welch Chair of Chemistry (1989–current)

  4. Alan Herbert Cowley Royal Society of Chemistry for Main Group Element Chemistry (1980) Centenary Medal and Lectureship, Royal Society of Chemistry (1986) American Chemical Society Southwest Regional Award (1986) Fellow of the Royal Society (1988) Chemical Pioneer Award of the American Institute of Chemists (1994) von Humboldt Prize (1996) Mexican Academy of Sciences (2004)

  5. Electron donor activity of hexamethyldisiloxane? . . X (Me3Si)2O: AlCl3 (Me3Si)2O + 1/2 Al2Cl6 Me3SiCl + Me3SiOAlCl2 Trimethylsiloxyaluminum dihalides are stable! (cf. Me3SiOBF2) • well-defined crystals • can be distilled under vacuum at 145 ˚C • decompose upon heating at 1 atm ∆ Me3SiCl + AlOCl Me3SiOAlCl2 Cowley, A. H.; Fairbrother, F.; Scott, N. J. Chem. Soc., 1959, 717. Early Research

  6. - - + + + + - - - - + + Early Research First preparation of compound containing B–Si bond borazine Cowley, A. H.; Sisler, H. H.; Ryschkewitsch, G.E. J. Am. Chem. Soc., 1960, 501.

  7. + R1 = Cl R2 = Ph (or Me) 80–90% yield Early Research First preparation of compound containing B–Si bond Ph3SiSiPh3 + NaK Ph3SiK • waxy solid (mp = 55–58 ˚C) • soluble in Et2O, C6H6, CCl4 • moisture sensitive Cowley, A. H.; Sisler, H. H.; Ryschkewitsch, G.E. J. Am. Chem. Soc., 1960, 501.

  8. Studies of unusual main group compounds Groups 13 and 15 complexes of low oxidation and coordination numbers • synthetic chemistry • structural assays • bonding descriptions • reactivity studies Thin Films • deposition studies (e.g.; MOCVD, molecular beam epitaxy) • single source precursors (e.g., nitrides, carbides, nobel metals) New Catalysts Over the years…

  9. Studies of unusual main group compounds Groups 13 and 15 complexes of low oxidation and coordination numbers • synthetic chemistry • structural assays • bonding descriptions • reactivity studies Use of appropriate ligands that confer thermodynamic or kinetic stabilization • bulky substituents • moieties that impart electronic influence Over the years…

  10. C2R4 2 R2C: carbenoid analogs Group 13Group 14Group 15 R2B–R2C RN R2Al– R2Si RP R2Ga– R2Ge RAs R2In– R2Sn RSb R2Tl– R2Pb RBi Early reports of monomeric (RP=PR), (RAs=AsR) and (R2Si=SiR2) were oligomers Use bulky substituents (R) to inhibit oligomerization! Low Oxidation/Low Coordination Number Main Group Complexes In search of stable analogs of alkenes and diimines

  11. Realization of Alkenes Analogs Via Use of Bulky Ligands 1976, Lappert 1981, West ditin derivative disilene derivative {Sn[CH(SiMe3)2]2}2 (mesityl)4Si2 Cowley, A. H. J. Organomet. Chem., 2004, 3866.

  12. Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR red. RAs=AsR Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506.

  13. LiAlH4 + (Me3Si)2CHAsCl2 + 1,5-diazabicyclo[5.4.0]undec-5-ene Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR red. RAs=AsR mp 119–121 ˚C Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506.

  14. Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR First compound with As–As double bond! • orange crystals • mp 110–113 ˚C • trans geometry of ligands • As–As bond length: 2.224(2)Å 72% yield Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506.

  15. Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR + (Me3Si)2CHPCl2 + Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. Whittlesey, B. J. Chem. Soc., Chem. Commun., 1983, 881.

  16. Four Valence Electron Species: RB, RAl, RGa, RIn • typically tetramers or hexamers • useful sources of monomers • bulky ligands can stablize monomer Al4(C5Me5)4 See refs. 21, 27 in Cowley, A. H. J. Organomet. Chem., 2004, 3866. [{HC(CMeNAr)2}Al]; Ar = 2,4,6-i-Pr2C6H2

  17. Terminal Borylene Complex (C5Me5)BCl2 + K2[Fe(CO)4] (C5Me5)BFe(CO)4 30% yield • Completes C5Me5M series (M = B–In) • 11B NMR chemical shift:  –35.3 ppm (cf.  >100 ppm in bridged borylenes) • FeCO4 is C3v ( CO = 2018, 1938, 1908, 1884 cm–1) • NMR equivalence of C5Me5 to –78 ˚C Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

  18. Terminal Borylene Complex (C5Me5)BCl2 + K2[Fe(CO)4] • no intermolecular contacts • axial (C5Me5)B unit • B–Fe bond length: 2.010(3) Å (cf. 1.95–2.03 Å) • B–C(Cp) bond length: 1.814(4) Å (cf. 1.683 Å in [BBr (C5Me5)]+) mp: 155 ˚C (dec) Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

  19. Nature of the Four Electron Monomer (RM) RM M´Ln RM M´Ln RM M´Ln RM M´Ln DFT studies on singlet and lowest-lying triplet state… • ground state is a singlet • singlet-triplet gap increases with atomic number • pronounced lone pair character • No backbonding seen in RM (R = C5H5) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc., 1999, 12113.

  20. [Al(C5Me5)]4 + B(C6F5)3 (C5Me5)Al B(C6F5)3 Group 13–Group 13 Donor–Acceptor Bonds Lewis acid adduct of allanediyl 40% yield, mp 126–129 ˚C (dec) • mass spectral data confirms proposed formula • 11B NMR chemical shift indicative of tetracoordinate center • 19F NMR values were similar to other Lewis base complexes of B(C6H5)3 • NMR equivalence of C5Me5 indicates 5-attachment Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

  21. (C5Me5)Al B(C6F5)3 Group 13–Group 13 Donor–Acceptor Bonds • No intermolecular contacts • (B–Al–Cpcent) = 172.9(1)˚ • Al–B bond length: 2.169(3) Å • Short Al–C bond legth: 2.171(3) Å av (cf. 2.344 Å for [(C5Me5)Al ]4) • Sum of B–C bond angles: 339.8(2)˚ (cf. (C6H5)3P B(C6F5)3) 40% yield Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

  22. [Al(C5Me5)]4 + In(C6F5)3 (C5Me5)Al In(C6F5)3 • (3-coordination seen in [(3-C5Me5)(Me)AlCl]2 mp 158 ˚C • C6F5 transfer from (C5Me5)Al In(C6F5)3 ? (3-C5Me5)Al(C6F5)2 Group 13–Group 13 Donor–Acceptor Bonds Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950.

  23. [(C5Me5)Al]4 + Al(C6F5)3 ·PhCH3 27Al NMR data:  –115.7 ppm (s), 106.9 ppm (s) (cf.  –150 ppm ((C5Me5)Al) and 52 ppm (Al(C6F5)3 ·PhCH3)) Valence Isomer of Dialane (R2AlAlR2) DFT studies show… HAl AlH3 less stable than H2AlAlH2 by 9.17 kcal/mol (C5H5)Al AlH3 more stable than H2AlAlH2 by 10.79 kcal/mol Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Cowley, A. H. Chem. Commun., 2001, 75.

  24. 2001, Cowley Ga B 2000, Jutzi B B (C5Me5)M M’(C6F5)3 (C5Me5)M M’(C6F5)3 2001, Jutzi Ga Ga 2002, Power In B [nacnac’]Ga B(C6F5)3 [Tp’]In InI3 [Tp’]Ga GaI3 [Ar(dipp)2]In B(C6F5)3 Group 13–Group 13 Donor–Acceptor Bonds 2005, Cowley Al Ga 2005, Cowley Ga Al 1996, Piggott In In See refs in Cowley, A. H. Chem. Commun., 2004, 2369.

  25. N-heterocyclic Carbenes 1962, Wanzlick 1991, Arduengo R = adamantyl; R’ = H Electronic behavior like that of electron-rich phosphines

  26. E R’ N-heterocyclic Carbenes PMe3 + (PCF3)4 Me3P: PCF3 + (ER’3)n R = Mes; E = P; R’ = Ph; n = 5 R = Mes; E = As; R’ = C6F5; n = 4 R = Mes; E = P; R’ = CF3; n = 4 R = Mes; E = As; R’ = Ph; n = 6 Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.

  27. .. . . E: E R’ R’ Nature of the Carbene Bond Fischer-like Schrock-like • P–Ccarbene and As–Ccarbene bonds are ca. 4% shorter than typical single bonds • 31P NMR shifts ( –23.0 and –23.6 ppm) outside of phosphaalkene range • Reaction with Lewis Acid? Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.

  28. .. . . E: E BH3 R’ R’ BH3 E R’ Nature of the Carbene Bond BH3 Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.

  29. References Cowley, A. H. J. Organomet. Chem., 2000, 168. Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105. Cowley, A. H. J. Organomet. Chem., 2004, 3866. Cowley, A. H. Chem. Commun., 2004, 2369. Cowley, A. H.; Fairbrother, F.; Scott, N. J. Chem. Soc., 1959, 717. Cowley, A. H.; Sisler, H. H.; Ryschkewitsch, G.E. J. Am. Chem. Soc., 1960, 501. Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506. Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. Whittlesey, B. J. Chem. Soc., Chem. Commun., 1983, 881. Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401. Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc., 1999, 12113. Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Silverman, J. S.; Cowley, A. H. J. Am. Chem. Soc., 2000, 950. Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Cowley, A. H. Chem. Commun., 2001, 75.

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