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. Early Research Trimethylsiloxyaluminum dihalides are stable! (cf. Me 3 SiOBF 2 ) Me 3 SiOAlCl 2 ∆ Me 3 SiCl + AlOCl  well-defined crystals  can be distilled under vacuum at 145 ˚C  decompose upon heating at 1 atm Electron donor activity of hexamethyldisiloxane? (Me 3 Si) 2 O + 1/2 Al 2 Cl 6 Me 3 SiCl + Me 3 SiOAlCl 2 (Me 3 Si) 2 O: AlCl 3 X. Cowley, A. H.; Fairbrother, F.; Scott, N. J. Chem. Soc., 1959, 717.

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

7. Early Research Cowley, A. H.; Sisler, H. H.; Ryschkewitsch, G.E. J. Am. Chem. Soc., 1960, 501. First preparation of compound containing B–Si bond Ph 3 SiSiPh 3 + NaKPh 3 SiK + R 1 = Cl R 2 = Ph (or Me) 80–90% yield  waxy solid (mp = 55–58 ˚C)  soluble in Et 2 O, C 6 H 6, CCl 4  moisture sensitive

8. Over the years… 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

9. Over the years… 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

10. Low Oxidation/Low Coordination Number Main Group Complexes In search of stable analogs of alkenes and diimines Group 13 Group 14 Group 15 R 2 B – R 2 C RN R 2 Al – R 2 Si RP R 2 Ga – R 2 Ge RAs R 2 In – R 2 Sn RSb R 2 Tl – R 2 Pb RBi carbenoid analogs 2 R 2 C: C2R4C2R4 Early reports of monomeric (RP=PR), (RAs=AsR) and (R 2 Si=SiR 2 ) were oligomers Use bulky substituents (R) to inhibit oligomerization!

11. Realization of Alkenes Analogs Via Use of Bulky Ligands 1976, Lappert {Sn[CH(SiMe 3 ) 2 ] 2 } 2 1981, West (mesityl) 4 Si 2 ditin derivativedisilene derivative Cowley, A. H. J. Organomet. Chem., 2004, 3866.

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

13. Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR RAs=AsR red. mp 119–121 ˚C LiAlH 4 + (Me 3 Si) 2 CHAsCl 2 + 1,5-diazabicyclo[5.4.0]undec-5-ene 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 Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. J. Am. Chem. Soc., 1983, 5506. 72% yield  orange crystals  mp 110–113 ˚C  trans geometry of ligands  As–As bond length: 2.224(2)Å First compound with As– As double bond!

15. Cowley Contributions: RAs=AsR, RP=AsR and RP=SbR Cowley, A. H.; Lasch, J. G.; Norman, N. C.; Pakulski, M. Whittlesey, B. J. Chem. Soc., Chem. Commun., 1983, 881. + (Me 3 Si) 2 CHPCl 2 +

16. Four Valence Electron Species: RB, RAl, RGa, RIn  typically tetramers or hexamers  useful sources of monomers  bulky ligands can stablize monomer Al 4 (C 5 Me 5 ) 4 [{HC(CMeNAr) 2 }Al]; Ar = 2,4,6-i-Pr 2 C 6 H 2 See refs. 21, 27 in Cowley, A. H. J. Organomet. Chem., 2004, 3866.

17. Terminal Borylene Complex (C 5 Me 5 )BCl 2 + K 2 [Fe(CO) 4 ] 30% yield  Completes C 5 Me 5 M series (M = B– In)  11 B NMR chemical shift:  –35.3 ppm (cf.  >100 ppm in bridged borylenes)  FeCO 4 is C 3v ( CO = 2018, 1938, 1908, 1884 cm –1 )  NMR equivalence of C 5 Me 5 to –78 ˚C (C 5 Me 5 )BFe(CO) 4 Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

18. Terminal Borylene Complex (C 5 Me 5 )BCl 2 + K 2 [Fe(CO) 4 ] mp: 155 ˚C (dec)  no intermolecular contacts  axial (C 5 Me 5 )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 (C 5 Me 5 )] + ) Cowley, A. H.; Lomeli, V.; Voigt, A. J. Am. Chem. Soc., 1998, 6401.

19. Nature of the Four Electron Monomer (RM)  ground state is a singlet  singlet-triplet gap increases with atomic number  pronounced lone pair character  No backbonding seen in RM (R = C 5 H 5 ) DFT studies on singlet and lowest-lying triplet state… RM M´L n Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc., 1999, 12113.

20. 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  11 B NMR chemical shift indicative of tetracoordinate center  19 F NMR values were similar to other Lewis base complexes of B(C 6 H 5 ) 3  NMR equivalence of C 5 Me 5 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. [Al(C 5 Me 5 )] 4 + B(C 6 F 5 ) 3 (C 5 Me 5 )Al B(C 6 F 5 ) 3

21. Group 13–Group 13 Donor–Acceptor Bonds 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. (C 5 Me 5 )Al B(C 6 F 5 ) 3  No intermolecular contacts  (  B–Al–Cp cent ) = 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 [(C 5 Me 5 )Al ] 4 )  Sum of B–C bond angles: 339.8(2)˚ (cf. (C 6 H 5 ) 3 P B(C 6 F 5 ) 3 )

22. 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. [Al(C 5 Me 5 )] 4 + In(C 6 F 5 ) 3 (C 5 Me 5 )Al In(C 6 F 5 ) 3 mp 158 ˚C (  3 -C 5 Me 5 )Al(C 6 F 5 ) 2  C 6 F 5 transfer from (C 5 Me 5 )Al In(C 6 F 5 ) 3 ?  (  3 -coordination seen in [(  3 -C 5 Me 5 )(Me)AlCl] 2

23. Valence Isomer of Dialane (R 2 AlAlR 2 ) Gorden, J. D.; Voigt, A; Charles, L. B.; Macdonald, C. L. B.; Cowley, A. H. Chem. Commun., 2001, 75. DFT studies show… HAl AlH 3 less stable than H 2 AlAlH 2 by 9.17 kcal/mol (C 5 H 5 )Al AlH 3 more stable than H 2 AlAlH 2 by 10.79 kcal/mol [(C 5 Me 5 )Al] 4 + Al(C 6 F 5 ) 3 ·PhCH 3 27 Al NMR data:  –115.7 ppm (s), 106.9 ppm (s) (cf.  –150 ppm ((C 5 Me 5 )Al) and 52 ppm (Al(C 6 F 5 ) 3 ·PhCH 3 ))

24. Group 13–Group 13 Donor–Acceptor Bonds (C 5 Me 5 )M M’(C 6 F 5 ) 3 2005, Cowley Al Ga 2005, Cowley Ga Al 2002, Power In B [Ar(dipp) 2 ]In B(C 6 F 5 ) 3 2001, Jutzi Ga Ga [Tp’]Ga GaI 3 [nacnac’]Ga B(C 6 F 5 ) 3 (C 5 Me 5 )M M’(C 6 F 5 ) 3 2000, Jutzi B B 2001, Cowley Ga B 1996, Piggott In In [Tp’]In InI 3 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. N-heterocyclic Carbenes PMe 3 + (PCF 3 ) 4 Me 3 P: PCF 3 + (ER’ 3 ) n E R’ R = Mes; E = P; R’ = Ph; n = 5 R = Mes; E = As; R’ = C 6 F 5 ; n = 4 R = Mes; E = P; R’ = CF 3 ; n = 4 R = Mes; E = As; R’ = Ph; n = 6 Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.

27. Nature of the Carbene Bond E: R’.. E R’.. Fischer-likeSchrock-like  P–C carbene and As–C carbene bonds are ca. 4% shorter than typical single bonds  31 P 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. Nature of the Carbene Bond E: R’.. E R’.. Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105. BH 3 E R’ BH 3

29. References 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. J. Organomet. Chem., 2004, 3866. 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. Cowley, A. H. J. Organomet. Chem., 2000, 168. Cowley, A. H. Chem. Commun., 2004, 2369. Cowley, A. H. J. Organomet. Chem., 2001, 617–617, 105.