Intramolecular aminoalkene hydroamination catalyzed by magnesium complexes containing multidentate phenoxyamine ligands

Article abstract of DOI:10.1021/om100675c

The magnesium complexes L²MgⁱPr (L² = 4-tert-butyl-6-(triphenylsilyl)-2-[bis((3-(dimethylamino)propyl)amino)methyl] phenoxyl) and L³MgⁱPr (L³ = 4-tert-butyl-6-(triphenylsilyl)-2-[benzyl((3-(dimethylamino)propyl)amino)methyl] phenoxyl) supported by potentially tetradentate and tridentate triphenylsilyl-substituted phenoxyamine ligands have been prepared and fully characterized. The X-ray crystallographic analysis of L²Mg ⁱPr confirmed a monomeric structure in which only one of the amine side arms is bound to the four-coordinate magnesium atom. The free and coordinated side arms in L²MgⁱPr undergo an exchange process at 25 °C in solution, while the phenoxydiamine complex L ³MgⁱPr, on the other hand, shows no sign of fluxionality. Both complexes, as well as L¹MgⁱPr (L¹ = 4,6-di-tert-butyl-2-[bis((3-(dimethylamino)propyl)amino)methyl]phenoxyl), were shown to be competent catalysts in the cyclization of aminoalkenes. L ²MgⁱPr exhibited the best catalytic activity, and both triphenylsilyl-substituted complexes display zero-order rate dependence on substrate concentration and first-order rate dependence on catalyst concentration, whereas the sterically less hindered complex L¹Mg ⁱPr exhibits second-order rate dependence on substrate concentration. No Schlenk-type ligand redistributions were observed, and the catalytically active magnesium species was stable after prolonged heating to 120 °C, according to an NMR spectroscopic study.

Full text of DOI:10.1021/om100675c

Organometallics 2010, 29, 5871–5877 5871
DOI: 10.1021/om100675c
Intramolecular Aminoalkene Hydroamination Catalyzed by Magnesium
Complexes Containing Multidentate Phenoxyamine Ligands
Xiaoming Zhang, Thomas J. Emge, and Kai C. Hultzsch*
Department of Chemistry and Chemical Biology, Rutgers, The State University of New Jersey,
610 Taylor Road, Piscataway, New Jersey 08854-8087, United States
Received July 11, 2010
The magnesium complexes L2MgiPr (L2 = 4-tert-butyl-6-(triphenylsilyl)-2-[bis((3-(dimethylamino)-
propyl)amino)methyl]phenoxyl) and L3MgiPr (L3 = 4-tert-butyl-6-(triphenylsilyl)-2-[benzyl((3-
(dimethylamino)propyl)amino)methyl]phenoxyl) supported by potentially tetradentate and tridentate
triphenylsilyl-substitutedphenoxyamineligands havebeenpreparedand fullycharacterized. The X-ray
crystallographic analysis of L2MgiPr confirmed a monomeric structure in which only one of the amine
side arms is bound to the four-coordinate magnesium atom. The free and coordinated side arms in
L2MgiPr undergo an exchange process at 25 °C in solution, while the phenoxydiamine complex
L3MgiPr, on the other hand, shows no sign of fluxionality. Both complexes, as well as L1MgiPr (L1 =
4,6-di-tert-butyl-2-[bis((3-(dimethylamino)propyl)amino)methyl]phenoxyl), were shown to be compe-
tent catalysts in the cyclization of aminoalkenes. L2MgiPr exhibited the best catalytic activity, and both
triphenylsilyl-substituted complexes display zero-order rate dependence on substrate concentration
and first-order rate dependence on catalyst concentration, whereas the sterically less hindered complex
L1MgiPr exhibits second-order rate dependence on substrate concentration. No Schlenk-type ligand
redistributions were observed, and the catalytically active magnesium species was stable after prolonged
heating to 120 °C, according to an NMR spectroscopic study.
Introduction
nitrogen-containing compounds, such as amines, enamines,
and imines, which are valuable and industrially important
bulk chemicals, specialty chemicals, and pharmaceuticals.1
Research efforts have focused primarily on the development
of transition-metal-based catalyst systems (early transition
metals of group 3-5, including the lanthanides2,3 and
actinides,4 and late transition metals of groups 8-125) in the
last two decades, while the potential of main-group-metal-
based catalysts has attracted less attention. For example,
alkali-metal-based hydroamination catalysts have a long his-
tory going back more than 50 years,6 but more detailed studies
have only begun to emerge in recent years.7 It is not too
astounding that alkaline-earth-metal complexes are active
The catalyzed addition of amines to unsaturated carbon-
carbon bonds, the so-called hydroamination, offers a waste-
free, highly atom efficient, and green pathway to produce
(1) (a) Doye, S. In Science of Synthesis; Enders, D., Ed.; Thieme:
Stuttgart, Germany, 2009; Vol. 40a, p 241. (b) Muller, T. E.; Hultzsch,
€
K. C.; Yus, M.; Foubelo, F.; Tada, M. Chem. Rev. 2008, 108, 3795.
(c) Brunet, J. J.; Neibecker, D. In Catalytic Heterofunctionalization from
Hydroamination to Hydrozirconation; Togni, A., Gr€utzmacher, H., Eds.;
Wiley-VCH: Weinheim, Germany, 2001; p 91. (d) M€uller, T. E.; Beller, M.
Chem. Rev. 1998, 98, 675.
(2) An account of group 3 metal- and lanthanide-based catalysts is
provided in: (a) Hong, S.; Marks, T. J. Acc. Chem. Res. 2004, 37, 673.
Selected recent examples: (b) Stanlake, L. J. E.; Schafer, L. L. Organometallics
2009, 28, 3990. (c) Yuen, H. F.; Marks, T. J. Organometallics 2009, 28, 2423.
(d) Lu, E.; Gan, W.; Chen, Y. Organometallics 2009, 28, 2318. (e) Ge, S.;
Meetsma, A.; Hessen, B. Organometallics 2008, 27, 5339. (f ) Yu, X.; Marks,
T. J. Organometallics 2007, 26, 365. (g) Kim, J. Y.; Livinghouse, T. Org. Lett.
2005, 7, 4391. (h) Kim, J. Y.; Livinghouse, T. Org. Lett. 2005, 7, 1737.
(i) Hultzsch, K. C.; Hampel, F.; Wagner, T. Organometallics 2004, 23, 2601.
(4) A review on actinide-based catalysts: (a) Andrea, T.; Eisen, M. S.
Chem. Soc. Rev. 2008, 37, 550. Selected recent examples: (b) Broderick,
E. M.; Gutzwiller, N. P.; Diaconescu, P. L. Organometallics 2010, 29, 3242.
(c) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 6149.
(d) Stubbert, B. D.; Marks, T. J. J. Am. Chem. Soc. 2007, 129, 4253.
(5) Reviews on late-transition-metal-based catalysts: (a) Brunet, J. J.;
Chu, N. C.; Rodriguez-Zubiri, M. Eur. J. Inorg. Chem. 2007, 4711.
(b) Widenhoefer, R. A.; Han, X. Eur. J. Org. Chem. 2006, 4555. (c) Hartwig,
J. F. Pure Appl. Chem. 2004, 76, 507. (d) Beller, M.; Breindl, C.; Eichberger,
M.; Hartung, C. G.; Seayad, J.; Thiel, O. R.; Tillack, A.; Trauthwein, H. Synlett
2002, 1579. Selected recent examples: (e) Shen, X.; Buchwald, S. L. Angew.
Chem., Int. Ed. 2010, 49, 564. (f ) Zhang, Z.; Lee, S. D.; Widenhoefer, R. A.
J. Am. Chem. Soc. 2009, 131, 5372. (g) Bender, C. F.; Hudson, W. B.;
Widenhoefer, R. A. Organometallics 2008, 27, 2356. (h) Zhou, J.; Hartwig, J. F.
J. Am. Chem. Soc. 2008, 130, 12220. (i) Liu, Z.; Hartwig, J. F. J. Am. Chem.
Soc. 2008, 130, 1570. ( j) Bender, C. F.; Widenhoefer, R. A. J. Am. Chem. Soc.
2005, 127, 1070. (k) Pissarek, J.-W.; Schlesiger, D.; Roesky, P. W.; Blechert, S.
ꢀ
( j) Gagne, M. R.; Stern, C. L.; Marks, T. J. J. Am. Chem. Soc. 1992, 114, 275.
(k) Roesky, P. W.; Stern, C. L.; Marks, T. J. Organometallics 1997, 16, 4705.
(3) Reviews on group 4 metal-based catalysts: (a) Severin, R.; Doye,
S. Chem. Soc. Rev. 2007, 36, 1407. (b) Lee, A. V.; Schafer, L. L. Eur. J.
Inorg. Chem. 2007, 2245. (c) Odom, A. L. Dalton Trans. 2005, 225.
(d) Doye, S. Synlett 2004, 1653. (e) Bytschkov, I.; Doye, S. Eur. J. Org.
Chem. 2003, 935. (f ) Pohlki, F.; Doye, S. Chem. Soc. Rev. 2003, 32, 104.
Selected recent examples: (g) Reznichenko, A. L.; Hultzsch, K. C. Organo-
metallics 2010, 29, 24. (h) Bexrud, J. A.; Schafer, L. L. Dalton Trans. 2010,
361. (i) Manna, K.; Ellern, A.; Sadow, A. D. Chem. Commun. 2010, 46, 339.
( j) Wood, M. C.; Leitch, D. C.; Yeung, C. S.; Kozak, J. A.; Schafer, L. L.
Angew. Chem., Int. Ed. 2007, 46, 354. (k) Gott, A. L.; Clarke, A. J.;
Clarkson, G. J.; Scott, P. Organometallics 2007, 26, 1729. (l) Watson, D. A.;
Chiu, M.; Bergman, R. G. Organometallics 2006, 25, 4731. (m) Bexrud,
J. A.; Beard, J. D.; Leitch, D. C.; Schafer, L. L. Org. Lett. 2005, 7, 1959.
€
Adv. Synth. Catal. 2009, 351, 2081. (l) Dochnahl, M.; Lohnwitz, K.; Pissarek,
€
J.-W.; Biyikal, M.; Schulz, S. R.; Schon, S.; Meyer, N.; Roesky, P. W.; Blechert,
S. Chem. Eur. J. 2007, 13, 6654.
r
2010 American Chemical Society
Published on Web 10/13/2010
pubs.acs.org/Organometallics

5872 Organometallics, Vol. 29, No. 22, 2010
Zhang et al.
catalysts for hydroamination reactions,8-11 due to the simi-
larity between the chemistry of alkaline-earth metals and that
of the rare-earth metals.12 However, alkaline-earth complexes
are prone to facile ligand redistribution reactions and such
Schlenk equilibria may limit their applications in asymmetric
hydroamination. Hill and co-workers reported recently that
β-diketiminate8a-c and bis(imidazolin-2-ylidene-1-yl)borate8e
alkaline-earth-metal amide complexes exhibit catalytic activ-
ity comparable to that of rare-earth-metal-based catalysts in
hydroamination. However, a facile Schlenk-type ligand redis-
tribution reaction was observed under the catalytic condi-
tions, resulting in catalyst deactivation and formation of the
homoleptic bis(β-diketiminato) and diamido species.8a,b,13
Similar Schlenk equilibria have hampered attempts to per-
form asymmetric hydroamination reactions14 using a chiral
bisoxazolinato calcium10a and a diamidobinaphthyl magne-
sium complex11 as catalyst. Thus, the lack of alkaline-earth-
metal complexes that can resist ligand redistribution reactions
under the conditions of hydroamination catalysis seems to be
a significant obstacle for the development of efficient chiral
alkaline-earth-metal-based hydroamination catalysts.
Chart 1
Our group has previously studied biphenolate and bi-
naphtholate rare-earth-metal complexes that were found to
be competent and configurational stable catalysts for asym-
metric hydroamination reactions.15 In an analogous approach,
we came to the conclusion that monoanionic multidentate
phenolate ligands may furnish alkaline-earth-metal complexes
with a well-defined coordination environment. Several phen-
oxyamine alkaline-earth-metal complexes have been studied
recently as initiators for the polymerization of cyclic esters and
lactide.16 In particular, the four-coordinate monomeric
phenoxytriamine17,18 complex L1MgiPr (1) (Chart 1) reported
by Gibson and co-workers19 appealed to us as a prospective
candidate for our catalytic study.
Herein we describe the synthesis and structural character-
ization of monomeric phenoxyamine magnesium complexes
related to complex 1 and discuss their effectiveness in cata-
lytic hydroamination/cyclization reactions of aminoalkenes
as well as their resistance toward ligand redistribution reac-
tions.
(6) (a) Seayad, J.; Tillack, A.; Hartung, C. G.; Beller, M. Adv. Synth.
Catal. 2002, 344, 795. (b) Closson, R. D.; Napolitano, J. P.; Ecke, G. G.;
Kolka, A. J. Org. Chem. 1957, 22, 646. (c) Howk, B. W.; Little, E. L.; Scott,
S. L.; Whitman, G. M. J. Am. Chem. Soc. 1954, 76, 1899. (d) Wegler, R.;
Pieper, G. Chem. Ber. 1950, 83, 1.
(7) (a) Quinet, C.; Jourdain, P.; Hermans, C.; Ates, A.; Lucas, I.;
Marko, I. E. Tetrahedron 2008, 64, 1077. (b) Ogata, T.; Ujihara, A.;
Tsuchida, S.; Shimizu, T.; Kaneshige, A.; Tomioka, K. Tetrahedron Lett.
2007, 48, 6648. (c) Horrillo-Martínez, P.; Hultzsch, K. C.; Gil, A.; Branchadell,
V. Eur. J. Org. Chem. 2007, 3311. (d) Horrillo Martínez, P.; Hultzsch, K. C.;
Hampel, F. Chem. Commun. 2006, 2221. (e) Khedkar, V.;Tillack, A.; Benisch,
C.; Melder, J.-P.; Beller, M. J. Mol. Catal. A: Chem. 2005, 241, 175. (f ) Ates,
A.; Quinet, C. Eur. J. Org. Chem. 2003, 1623. (g) Tzalis, D.; Koradin, C.;
Knochel, P. Tetrahedron Lett. 1999, 40, 6193. (h) Beller, M.; Breindl, C.;
Riermeier, T. H.; Eichberger, M.; Trauthwein, H. Angew. Chem., Int. Ed.
1998, 37, 3389.
(16) (a) Ejfler, J.; Krauzy-Dziedzic, K.; Szafert, S.; Jerzykiewicz,
L. B.; Sobota, L. B. Eur. J. Inorg. Chem. 2010, 3602. (b) Sarazin, Y.;
Poirier, V.; Roisnel, T.; Carpentier, J.-F. Eur. J. Inorg. Chem. 2010, 3423.
(c) Poirier, V.; Roisnel, T.; Carpentier, J.-F.; Sarazin, Y. Dalton Trans. 2009,
9820. (d) Hung, W.-C.; Lin, C.-C. Inorg. Chem. 2009, 48, 728. (e) Zheng, Z.;
Zhao, G.; Fablet, R.; Bouyahyi, M.; Thomas, C. M.; Roisnel, T.; Casagrande,
O., Jr.; Carpentier, J.-F. New J. Chem. 2008, 32, 2279. (f ) Darensbourg, D. J.;
Choi, W.; Richers, C. P. Macromolecules 2007, 40, 3521. (g) Davidson,
(8) (a) Crimmin, M. R.; Arrowsmith, M.; Barrett, A. G. M.; Casely,
I. J.; Hill, M. S.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 9670.
(b) Crimmin, M. R.; Casely, I. J.; Hill, M. S. J. Am. Chem. Soc. 2005, 127,
2042. (c) Barrett, A. G. M.; Brinkmann, C.; Crimmin, M. R.; Hill, M. S.; Hunt,
P.; Procopiou, P. A. J. Am. Chem. Soc. 2009, 131, 12906. (d) Barrett, A. G. M.;
€
M. G.; O'Hara, C. T.; Jones, M. D.; Keir, C. G.; Mahon, M. F.; Kociok-Kohn,
G. Inorg. Chem. 2007, 46, 7686. (h) Sarazin, Y.; Howard, R. H.; Hughes,
D. L.; Humphrey, S. M.; Bochmann, M. Dalton Trans. 2006, 340.
(i) Davidson, M. G.; Jones, M. D.; Meng, D.; O'Hara, C. T. Main Group
Chem. 2006, 5, 3. ( j) Ejfler, J.; Kobyzka, M.; Jerzykiewicz, L. B.; Sobota, P.
Dalton Trans. 2005, 2047.
€
Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.; Kociok-Kohn, G.; Procopiou,
P. A. Inorg. Chem. 2008, 47, 7366. (e) Arrowsmith, M.; Hill, M. S.; Kociok-
€
Kohn, G. Organometallics 2009, 28, 1730. (f ) Arrowsmith, M.; Heath, A.; Hill,
€
M. S.; Hitchcock, P. B.; Kociok-Kohn, G. Organometallics 2009, 28, 3550.
(9) (a) Datta, S.; Gamer, M. T.; Roesky, P. W. Organometallics 2007,
26, 4392. (b) Datta, S.; Gamer, M. T.; Roesky, P. W. Organometallics 2008,
27, 1207.
(10) (a) Buch, F.; Harder, S. Z. Naturforsch. 2008, 63b, 169.
(b) Gauvin, R. M.; Buch, F.; Delevoye, L.; Harder, S. Chem. Eur. J. 2009,
15, 4382.
(11) Horrillo-Martınez, P.; Hultzsch, K. C. Tetrahedron Lett. 2009,
50, 2054.
(12) (a) Harder, S. Angew. Chem., Int. Ed. 2004, 43, 2714. (b) Buch, F.;
Brettar, J.; Harder, S. Angew. Chem., Int. Ed. 2006, 45, 2741.
(13) Avent, A. G.; Crimmin, M. R.; Hill, M. S.; Hitchcock, P. B.
Dalton Trans. 2005, 278.
(14) For reviews on asymmetric hydroamination see: (a) Reznichenko,
A. L.; Hultzsch, K. C. In Chiral Amine Synthesis: Methods, Developments
and Applications; Nugent, T., Ed.; Wiley-VCH: Weinheim, Germany, 2010; p
341. (b) Zi, G. Dalton Trans. 2009, 9101. (c) Chemler, S. R. Org. Biomol.
Chem. 2009, 7, 3009. (d) Aillaud, I.; Collin, J.; Hannedouche, J.; Schulz, E.
Dalton Trans. 2007, 5105. (e) Hultzsch, K. C. Adv. Synth. Catal. 2005, 347,
367. (f ) Hultzsch, K. C. Org. Biomol. Chem. 2005, 3, 1819. (g) Hultzsch, K. C.;
Gribkov, D. V.; Hampel, F. J. Organomet. Chem. 2005, 690, 4441. (h) Roesky,
P. W.; M€uller, T. E. Angew. Chem., Int. Ed. 2003, 42, 2708.
(15) (a) Reznichenko, A. L.; Hampel, F.; Hultzsch, K. C. Chem. Eur.
J. 2009, 15, 12819. (b) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F. J. Am.
Chem. Soc. 2006, 128, 3748. (c) Gribkov, D. V.; Hultzsch, K. C. Chem.
Commun. 2004, 730. (d) Gribkov, D. V.; Hampel, F.; Hultzsch, K. C. Eur. J.
Inorg. Chem. 2004, 4091. (e) Gribkov, D. V.; Hultzsch, K. C.; Hampel, F.
Chem. Eur. J. 2003, 9, 4796. (f ) Reznichenko, A. L.; Nguyen, H. N.;
Hultzsch, K. C. Angew. Chem., Int. Ed. 2010, 49, DOI: 10.1002/
anie.201004570.
(17) For an overview on the chemistry of complexes consisting of
phenoxytriamine and related monoanionic tetradentate ligands see:
Chomitz, W. A.; Arnold, J. Chem. Eur. J. 2009, 15, 2020.
(18) For various complexes using tetradentate phenoxyamine ligands
see for example: (a) Acosta-Ramırez, A.; Douglas, A. F.; Yu, I.; Patrick,
B. O.; Diaconescu, P. L.; Mehrkhodavandi, P. Inorg. Chem. 2010, 49,
5444. (b) Labourdette, G.; Lee, D. J.; Patrick, B. O.; Ezhova, M. B.;
Mehrkhodavandi, P. Organometallics 2009, 28, 1309. (c) Douglas, A. F.;
Patrick, B. O.; Mehrkhodavandi, P. Angew. Chem., Int. Ed. 2008, 47, 2290.
ꢀ
(d) Ang, J. C.; Mulyana, Y.; Ritchie, C.; Clerac, R.; Boskovic, C. Aust. J.
Chem. 2009, 62, 1124. (e) Marinescu, S. C.; Agapie, T.; Day, M. W.; Bercaw,
J. E. Organometallics 2007, 26, 1178. (f ) Chomitz, W. A.; Minasian, S. G.;
Sutton, A. D.; Arnold, J. Inorg. Chem. 2007, 46, 7199. (g) Binda, P. I.;
Delbridge, E. E. Dalton Trans. 2007, 4685. (h) Groysman, S.; Sergeeva, E.;
Goldberg, I.; Kol, M. Eur. J. Inorg. Chem. 2006, 2739. (i) Westmoreland, I.;
Arnold, J. Dalton Trans. 2006, 4155. ( j) Groysman, S.; Sergeeva, E.;
Goldberg, I.; Kol, M. Inorg. Chem. 2005, 44, 8188. (k) Zhang, D.; Hillmyer,
M. A.; Tolman, W. B. Macromolecules 2004, 37, 8198. (l) Inoue, Y.;
Matyjaszewski, K. Macromolecules 2004, 37, 4014. (m) Williams, C. K.;
Breyfogle, L. E.; Choi, S. K.; Nam, W.; Young, V. G.; Hillmyer, M. A.;
Tolman, W. B. J. Am. Chem. Soc. 2003, 125, 11350. (n) Inoue, Y.;
Matyjaszewski, K. Macromolecules 2003, 36, 7432. (o) Skinner, M. E. G.;
Tyrrell, B. R.; Ward, B. D.; Mountford, P. J. Organomet. Chem. 2002, 647,
145. (p) Bylikin, S. Y.; Robson, D. A.; Male, N. A. H.; Rees, L. H.;
€
Mountford, P.; Schroder, M. Dalton Trans. 2001, 170. (q) Robson, D. A.;
Bylikin, S. Y.; Cantuel, M.; Male, N. A. H.; Rees, L. H.; Mountford, P.;
€
Schroder, M. Dalton Trans. 2001, 157.
(19) Cox, A. R. F.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.;
Yeldon, D. Dalton Trans. 2006, 5014.

Article
Organometallics, Vol. 29, No. 22, 2010 5873
Scheme 1. Synthesis of Triphenylsilyl-Substituted Aminopheno-
late Magnesium Complexes
Results and Discussion
Figure 1. ORTEP diagram of the molecular structure of
L2MgiPr(2). Thermalellipsoids areshownatthe 50%probability
level, and hydrogen atoms as well as one position of the dis-
ordered tert-butyl group are omitted for clarity. Selected bond
Synthesis and Characterization of Monomeric Magnesium
Complexes. On the basis of our previous experience with
diolate rare-earth-metal complexes,15 we envisioned to in-
crease the steric bulk of the substituent ortho to the phenol
oxygen in order to reduce the risk of ligand redistribution via
bridging phenolate species and thereby improve catalytic
activity. As the noncoordinated second amino group may
also impact catalytic performance, we planned to substitute
one of the 3-(dimethylamino)propyl side arms by a noncoor-
dinating benzyl group. The triphenylsilyl-substituted ligands
L2H and L3H were obtained through reductive amination of a
triphenylsilyl-substituted salicylaldehyde and the correspond-
ing amines in good yields using NaHB(AcO)3 as the reducing
agent in dichloroethane (Scheme 1).
˚
lengths (A) andangles(deg):Mg1-O1 = 1.9187(15), Mg1-N2 =
2.1465(19), Mg1-C41 = 2.159(2), Mg1-N1 = 2.1691(18);
O1-Mg1-N2 = 101.61(7), O1-Mg1-C41 = 121.48(8), N2-
Mg1-C41 = 110.27(8), O1-Mg1-N1 = 89.34(6), N2-Mg1-
N1 = 96.61(7), C41-Mg1-N1 = 131.72(8), Mg1-O1-C2 =
131.24(13).
oxygen, one carbon, and two nitrogen atoms in a distorted-
tetrahedral geometry with one noncoordinating amino side
˚
˚
arm. The Mg-O (1.9187(15) A), Mg-C (2.159(2) A), and
˚
Mg-N (2.1465(19) and 2.1691(18) A) bond lengths are quite
comparable to those of complex 119 and other known magne-
sium complexes.16a-d,21 However, the angles around magne-
sium in 2 are slightly distorted when compared to 1. The bite
angle of the phenoxyamine N,O chelate ring O1-Mg1-N1
(89.34(6)°), as well as O1-Mg1-N2 (101.61(7)°) and O1-
Mg1-C41 (121.48(8)°), are more acute in 2 than in complex 1
(94.23(5), 105.19(5), and 129.58(6)°, respectively),19 while the
C41-Mg1-N1 angle is significantly widened (131.72(8)° for 2
compared to 114.91(6)° for 1). Also, the Mg1-O1-C2 angle is
significantly widened (131.24(13)° for 2 compared to 125.94°
for 1). The six-membered N,O chelate ring adopts a half-chair
geometry due to steric repulsion of the triphenylsilyl group,
while an energetically more favorable twisted-boat geometry is
found in complex 1. In 2, Mg1, C2, C3, C25, and O1 are ideally
The magnesium complexes 2 and 3 were obtained as white
crystalline solids in 73% and 81% yields via salt metathesis
i
of the lithiated phenol ligands with PrMgCl in toluene at
room temperature (Scheme 1) following a procedure analo-
gous to the preparation of 1.19 The complexes are stable for
several hours at 60 °C in solution. Similar to complex 1, the 1H
NMR spectrum of complex 2 exhibits quite broad proton
resonance signals in the aliphatic region in the temperature
range of 25-80 °C due to an apparent exchange process
between the coordinated and free side arm. At lower tempera-
ture, decoalescence of the signals was observed at ca. 0 °C and
separate signal sets for the two amine side arms were observed
at -40 °C in toluene-d8.20 Complex 3, on the other hand, lacks
an exchangeable side arm and its 1H NMR spectrum is sharp
at room temperature in C6D6. All protons of the propylene
side chain as well as the two N-methyl groups are diastereo-
topic, indicating that the side arm in 3 remains bound to mag-
nesium on the NMR time scale under these conditions. The
characteristic magnesium-methine proton septet resonates
at 0.17 ppm for 2 at -40 °C (in toluene-d8) and 0.27 ppm for 3
at 25 °C (in C6D6) in their 1H NMR spectra, while the cor-
responding magnesium-carbon resonance was observed at
9.9 ppm for 2 (in THF-d8)20b and 8.0 ppm for 3 (in toluene-d8)
in their respective 13C NMR spectra.
˚
coplanar and N1 resides 0.933 A out of this plane. The dihedral
angle between the planes consisting of Mg1, C2, C3, C25, O1
and Mg1, C25, N1 is 57.7°. Similar to the case for complex 1,
the six-membered N,N0-chelate ring adopts a chair conforma-
˚
tion with N1, N2, C30, C32 being coplanar within 0.03 A and
˚
Mg1 and C31 lying ca. þ0.86 and -0.71 A, respectively, out of
the plane.
Intramolecular Aminoalkene Hydroamination Catalyzed by
Magnesium Complexes. With magnesium complexes 1-3 in
hand, we began to study their catalytic behavior in the
The X-ray crystallographic analysis of L2MgiPr (2) revealed
further details of its molecular structure in the solid state
(Figure 1). The central magnesium ion is coordinated by one
(21) (a) Schofield, A. D.; Barros, M. L.; Cushion, M. G.; Schwarz,
A. D.; Mountford, P. Dalton Trans. 2009, 85. (b) Spielmann, J.; Bolteb,
M.; Harder, S. Chem. Commun. 2009, 6934. (c) Pajerski, A. D.; Squiller,
E. P.; Parvez, M.; Whittle, R. R.; Richey, H. G., Jr. Organometallics 2005, 24,
809. (d) Dove, A. P.; Gibson, V. C.; Hormnirun, P.; Marshall, E. L.; Segal,
J. A.; White, A. J. P.; Williams, D. J. Dalton Trans. 2003, 3088.
(e) Henderson, K. W.; Honeyman, G. W.; Kennedy, A. R.; Mulvey, R. E.;
Parkinson, J. A.; Sherrington, D. C. Dalton Trans. 2003, 1365.
1
(20) (a) Assignments of signals are based on H-1H COSY spectra
(see the Supporting Information). (b) The 13C NMR spectra of 2 were
broad in the range of -60 to þ60 °C in toluene-d8, and an interpretable
spectrum could only be obtained in THF-d8.

5874 Organometallics, Vol. 29, No. 22, 2010
Zhang et al.
Table 1. Magnesium-Catalyzed Hydroamination of Primary
Aminoalkenesa
gem-diphenyl-activated aminoalkene 4f proceeded rapidly at
room temperature (Table 1, entries 17-19), despite the in-
creased steric hindrance of the 1,2-disubstituted double bond
thatgenerally requires harsher reaction conditions.1 The cycli-
zation of 4g requires heating to 100 °C and longer reaction
times due to the decreased activating effect of the gem-
dimethyl substitutents (Table 1, entries 20-22). Substitution
of the vinylic phenyl group in 4f by a methyl group requires
even harsher reaction conditions (150 °C, 48 h) for aminoalk-
ene 4h (Table 1, entries 23 and 24), and the reaction remains
incomplete. Cyclization of the aminodialkene 4d produced
the two diastereomeric products with low diastereoselectivity
(Table 1, entries 13 and 14, dr = 1.3:1), apparently due to the
remote β position of the prochiral center in the substrate. The
cyclization of aminohexenes to form piperidines (Table 1,
entries 25-28) was achieved at elevated reaction tempera-
tures, but no cyclization of aminoheptene 6 was observed even
at 120 °C (Table 1, entries 29 and 30). Reaction of the more
hindered, secondary N-benzylated aminoalkene 7 required
higher reaction temperatures (140 °C) to show appreciable
turnover (eq 1), and no conversion was observed at lower
temperatures.
entry substrate cat. (amt (mol %)) T (°C) t (h) conversn (%)b
1
2
3
4
5
6
7
8
4a
4a
4a
4a
4a
4b
4b
4b
4b
4c
4c
4c
4d
4d
4e
4e
4f
1 (10)
1 (5)
2 (3)
3 (10)
3 (5)
1 (10)
2 (10)
2 (5)
25
25
25
25
25
25
25
25
1.5
4
3
1.5
5
12
6
13
22
40
18
40
18
50
50
100
2
1.5
2
7
12
24
48
48
13
99
99
99
99
98
98
97
96
81
98
98
48
95d
79d
30
87
99
99
99
99
99
98
47
69
99
99
99
93
nr
nr
9
3 (5)
25
10
11
12
13
14
15
16
17c
18c
19c
20
21
22
23
24
25c
26c
27c
28
29c
30c
1 (10)
2 (10)
3 (10)
2 (10)
3 (10)
2 (10)
2 (20)
1 (10)
2 (10)
3 (10)
1 (10)
2 (10)
3 (10)
1 (20)
2 (20)
1 (10)
2 (10)
3 (10)
2 (10)
1 (20)
2 (15)
100
100
100
60
100
120
120
25
Despite the relatively harsh conditions for some of the cata-
lytic transformations, the spectroscopic analysis of the catalytic
reaction mixtures did not reveal any signs of a potential Schlenk-
type ligand redistribution process and a further indicator for the
integrity of the catalytic species is the well-behaved reaction
kinetics. The reaction of 3 with a stoichiometric amount of 4a
(3 equiv) revealed no observable catalyst decomposition even
after 10 h of heating to 120 °C, and an additional portion of sub-
strate was consumed rapidly (see NMR spectra in Figures S6-S9
in the Supporting Information). Thus, the catalytically active
magnesium amide species seems to be highly thermally robust.
The cyclization of 2,2-diphenylpent-4-enyl amine (4a) pro-
ceeded in the presence of 3 mol % of the triphenylsilyl-sub-
stituted catalysts 2 or 3 with a zero-order rate dependence on
substrate concentration (Figure 2). As noted in our substrate
screening, catalyst 2 exhibited the highest catalytic activity
withanNt value of 14.5 h-1 at25°Ccomparedto5.1 h-1 for 3.
While generally it is anticipated that a larger number of donor
arms should render the catalyst less electrophilic and less
active, it has been reported that an ansa-yttrocene containing
an ether functionality tethered to its silicon bridge exhibited
up to 5-fold higher catalytic activity in the cyclization of
aminoalkenes relativetothe corresponding nonfunctionalized
ansa-yttrocene.2k It was suggested that this effect results from
a stabilization of the polar olefin-insertion transition state
through an intramolecular chelation of the tethered donor
group, and it is apparent that such a chelating stabilization
(Figure 3) would be more efficient in the presence of two
donor arms present in complex 2, opposed to the presence of
only one donor arm in complex 3.
4f
4f
25
25
4g
4g
4g
4h
4h
5a
5a
5a
5b
6
100
100
100
150
150
60
60
60
120
120
120
2.5
8
40
20
20
6
a Reaction conditions: 0.2 mmol of substrate, 0.6 mL of C6D6, Ar
atmosphere. b Determined by 1H NMR spectroscopy, using ferrocene as
internal standard. nr denotes no reaction observed. c 0.1 mmol of
substrate. d dr = 1.3:1.
hydroamination/cyclization of aminoalkenes (Table 1). All
three complexes are efficient in the cyclization of 2,2-diphe-
nylpent-4-enylamine (4a) at room temperature in C6D6 at
catalyst loadings of 3-10 mol % (Table 1, entries 1-5). To
our surprise, the qualitative analysis of the catalytic results
indicates that catalyst 2 exhibits the highest catalytic activity,
followed by catalysts 3 and 1.
As anticipated,22 decreasing the steric bulk of the gem-
dialkylsubstituent inthe aminopentene substrates ledtolower
rates of cyclization (Table 1, entries 6-12) and required in-
creased reaction temperatures for the dimethyl-substituted
aminopentene 4c. The unsubstituted aminopentene 4e re-
quired 20 mol % of 2 to reach 87% conversion in 100 h at
120 °C (Table 1, entry 16). Interestingly, cyclization of the
The sterically less hindered complex 1 showed an apparent
second-order rate dependence on catalyst concentration (see
also Figure S1 in the Supporting Information). While the
reaction with 1 proceeds initially faster than with complex 2,
(22) Jung, M. E.; Piizzi, G. Chem. Rev. 2005, 105, 1735.

Article
Organometallics, Vol. 29, No. 22, 2010 5875
Figure 2. Time dependence of normalized substrate concentra-
tion in the hydroamination/cyclization of 2,2-diphenylpent-4-
enylamine (4a) ([C]0 = 0.167 mol L-1) with 1 (b), 2 (ꢀ) and 3 ([)
([cat.] = 0.005 mol L-1) in C6D6 at 25 °C.
Figure 5. Dependence of catalyst concentration on observed
rate for the hydroamination/cyclization of 4a ([subst]0 = 0.167
mol L-1) with catalyst 3 in C6D6 at 25 °C.
Figure 3. Proposed stabilization of the olefin-insertion transi-
tion state through an intramolecular chelation.
Figure 6. Time dependence of substrate concentration in the
hydroamination/cyclization of 2,2-diphenylpent-4-enylamine (4a)
([subst]0 =0.123 mol L-1) using 3 ([cat.]= 0.0081 mol L-1) at
30 °C (a) first run; (b) second run with a second batch of substrate
4a added; (c) third run with a third batch of substrate 4a added.
298 K provided a good fit over the 5-20 mM catalyst
concentration range.
In contrast to previous studies on binaphtholate rare-
earth-metal complexes15b and β-diketiminate calcium amide
complexes,8b the phenoxyamine magnesium catalysts 2 and 3
did not show signs of substrate or product inhibition. No rate
depression was observed for catalyst 3 when the substrate
was added in three batches (Figure 6), and all three runs dis-
Figure 4. Time dependence of normalized substrate concentra-
tion in the hydroamination/cyclization of 4a ([subst]0 =0.167
mol L-1) in C6D6 at 25 °C using varying concentrations of 3.
the overall reaction time to reach high conversion is sub-
stantially longer due to the significant rate dependence on
substrate concentration. Second-order rate dependencies
have been observed previously, for example in a sterically
undemanding biphenolate yttrium catalyst,15e but the exact
cause for this kinetic behavior remains unclear. Further
kinetic analysis using complex 3 showed that the reaction is
first-order in catalyst (Figures 4 and 5). The data acquired at
played comparable reaction rates (9.1, 9.8, and 9.0 h-1
,
respectively). Similar observations were made for catalyst 2
(Figure S2, see the Supporting Information) when the sub-
strate was added in two batches.
The kinetic data for catalysts 2 and 3 is in agreement with a
mechanism analogous to rare-earth-metal-catalyzed hydro-
amination/cyclization reactions.1,2a,2j The zero-order rate

5876 Organometallics, Vol. 29, No. 22, 2010
Zhang et al.
dependence on substrate concentrations indicates that the
insertion of the alkene in the magnesium amide bond is rate
determining, followed by rapid protonolysis of the resulting
magnesium-alkyl intermediate.
N1-Benzyl-N3,N3-dimethylpropane-1,3-diamine.25 Benzalde-
hyde (2.12 g, 20.0 mmol) and N,N-dimethyl-1,3-propanedia-
mine (2.14 g, 21.0 mmol) were mixed in MeOH (40 mL) at room
temperature under a nitrogen atmosphere. The mixture was
stirred at room temperature overnight. The solution of the
aldimine in MeOH was carefully treated with solid NaBH4
(1.20 g, 32.0 mmol). The reaction mixture was stirred for 30
min and quenched with 1.0 M NaOH (100 mL). The product
was extracted with diethyl ether (3 ꢀ 50 mL). The ether extract
was washed with water (2 ꢀ 100 mL) and dried over MgSO4. The
solvent was evaporated to give the product as a colorless oil.
Conclusions
In summary, phenoxyamine magnesium complexes are
competent catalysts for the hydroamination/cyclization of
aminoalkenes. The sterically demanding triphenylsilyl sub-
stituent effectively shields the metal center from undesired
excessive amine binding and catalyst aggregation. Also, the
absence of Schlenk-type ligand redistribution processes is an
important requirement for the development of chiral cata-
lysts for enantioselective hydroamination reactions.14
1
Yield: 3.66 g (95%). H NMR (400 MHz, CDCl3): δ 7.29 (m,
4H, C6H5), 7.21 (m, 1H, C6H5), 3.77 (s, 2H, NCH2C6H5), 2.66 (t,
3JH,H = 7.6 Hz, 2H, NCH2CH2CH2NMe2), 2.30 (t, 3JH,H = 7.6
Hz, 2H, NCH2CH2CH2NMe2), 2.20 (s, 6H, N(CH3)2), 1.67 (m,
2H, NCH2CH2CH2NMe2). 13C{1H} NMR (125 MHz, CDCl3):
δ 140.8, 128.6, 128.3, 127.0 (aryl), 58.3 (NCH2C6H5), 54.3
(NCH2CH2CH2NMe2), 48.1, (CH2NMe2), 45.8, (N(CH3)2),
28.3 (NCH2CH2CH2NMe2).
Experimental Section
L3H. A solution of 5-(tert-butyl)-2-hydroxy-3-(triphenylsilyl)-
benzaldehyde (2.40 g, 5.5 mmol) and N1-benzyl-N3,N3-dimethyl-
propane-1,3-diamine (0.96 g, 5.0 mmol) in 1,2-dichloroethane
(30 mL) was treated with sodium triacetoxyborohydride (1.70 g,
8.0 mmol) and AcOH (0.48 g, 8.0 mmol). The mixture was stirred
at room temperature under a nitrogen atmosphere for 2 days. The
reaction mixture was quenched by addition of saturated aqueous
NaHCO3 (100 mL), and the product was extracted with diethyl
ether (3 ꢀ 50 mL). The combined extracts were washed with water
(2 ꢀ 100 mL) and dried over MgSO4. The solvent was evaporated
to give the product as a slightly yellow viscous oil which can be
used without further purification. Yield: 2.23 g (73%). Further
purification of the ligand may be achieved by dissolving the oil in
diethyl ether (100 mL) and treatment with ethereal HCl to
precipitate the hydrochloride salt. The isolated salt was dissolved
in water, neutralized with saturated aqueous NaHCO3 (100 mL),
and extracted with diethyl ether (2 ꢀ 50 mL) to give the pure
product. 1H NMR (500 MHz, CDCl3): δ 7.66 (m, 6H, Si(C6H5)3),
7.40 (m, 3H, Si(C6H5)3), 7.34 (m, 6H, Si(C6H5)3), 7.22 (m, 3H,
CH2C6H5), 7.14 (m, 2H, CH2C6H5), 7.08 (m, 2H, aryl-H), 3.83
(s, 2H, ArCH2N), 3.59 (s, 2H, C6H5CH2N), 2.48 (t, 3JH,H = 7.5
Hz, 2H, NCH2CH2CH2NMe2), 2.14 (s, 6H, N(CH3)2), 2.13 (m,
2H, NCH2CH2CH2NMe2), 1.68 (m, 2H, NCH2CH2CH2NMe2),
1.12 (s, 9H, C(CH3)3). 13C{1H} NMR (125 MHz, CDCl3): δ
160.8, 141.3, 137.2, 136.7, 135.7, 134.8, 129.9, 129.2, 128.6, 128.5,
127.7, 127.5, 120.6, 119.5 (aryl), 58.8 (ArCH2N), 58.1 (CH2C6H5),
57.8 (NCH2CH2CH2NMe2), 51.6 (NCH2CH2CH2NMe2), 45.6
(NCH2CH2CH2N(CH3)2), 34.1 (C(CH3)3), 31.7 (C(CH3)3), 24.4
(NCH2CH2CH2NMe2).
General Considerations. All operations were performed under
an inert atmosphere of nitrogen or argon using standard
Schlenk-line or glovebox techniques. Hexanes and toluene were
purified by distillation from sodium/benzophenone ketyl.
4,6-Di-tert-butyl-2-[bis((3-(dimethylamino)propyl)amino)-
methyl]phenol (L1H),19 L1MgiPr (1),19 and 5-(tert-butyl)-2-hy-
droxy-3-(triphenylsilyl)benzaldehyde23 were synthesized accord-
ing to literature protocols. The aminoalkene substrates 4a,7d,15b
4b,5j,7d 4c,24a 4d,15e 4e,2j 4f,2h,15b,24b 4g,24b 5a,24b 5b,15b 6,3m and 75j
were prepared as reported previously and dried by distillation
twice from CaH2. The hydroamination products are known com-
pounds and were identified by comparison to the literature NMR
spectroscopic data.2h-j,3g,5j,7d,15b 1H and 13C NMR spectra were
recorded on Varian (300, 400, 500 MHz) spectrometers at 25 °C
unless stated otherwise. Chemical shifts are reported in ppm
downfield from tetramethylsilane with the undeuterated portion
of the solvent as internal standard. Elemental analyses were
performed by Robertson Microlit Laboratories, Inc., Madison,
NJ. Despite repeated attempts the elemental analyses of com-
plexes 2 and 3 gave low carbon content, potentially as a result of
carbide formation. Three exemplary analyses for each complex
are provided.
L2H. 5-tert-Butyl-2-hydroxy-3-(triphenylsilyl)benzaldehyde
(2.18 g, 5.0 mmol) and bis[3-(dimethylamino)propyl]amine
(1.4 g, 7.5 mmol) were mixed in 1,2-dichloroethane (30 mL)
and then treated with sodium triacetoxyborohydride (1.7 g,
8.0 mmol) and AcOH (0.48 g, 8.0 mmol). The mixture was
stirred at 30 °C under a nitrogen atmosphere for 2 days. The
reaction mixture was quenched by addition of aqueous satu-
rated NaHCO3 (100 mL), and the product was extracted
with diethyl ether (3 ꢀ 50 mL). The combined organic layers
were washed with water (3 ꢀ 100 mL) and dried over MgSO4.
The solvent was evaporated under vacuum to give the product
as a light yellow viscous oil which was used without further
purification. Yield: 2.48 g (82%). 1H NMR (500 MHz, CDCl3):
L2MgiPr (2). At -78 °C, a 2.5 M hexanes solution of n-BuLi
(0.42 mL, 1.05 mmol) was added to a solution of L2H (607 mg,
1.00 mmol) in toluene (10 mL). The mixture was warmed to room
i
temperature, and after 1 h, a 2.0 M PrMgCl solution in THF
(0.53 mL, 1.05 mmol) was added. After it was stirred for a further
2 h, the solution was filtered; the filtrate was evaporated under
reduced pressure. A small amount of hexanes was added to wash
the solid at -78 °C and then removed in vacuo, affording 2 as
δ7.65(m, 6H, Si(C6H5)3), 7.36 (m, 9H, Si(C6H5)3), 7.07(d, 4JH,H
3.0 Hz, 2H, aryl-H), 3.80 (s, 2H, ArCH2N), 2.56 (t, JH,H
=
=
3
1
a light yellow crystalline solid. Yield: 491 mg (73%). H NMR
7.5 Hz, 4H, N(CH2CH2CH2NMe2)2), 2.22 (t, 3JH,H = 7.5 Hz,
4H, N(CH2CH2CH2NMe2)2), 2.16 (s, 12H, N(CH3)2), 1.66 (m,
4H, N(CH2CH2CH2NMe2)2), 1.13 (s, 9H, C(CH3)3). 13C{1H}
NMR (125 MHz, CDCl3): δ 161.1, 141.1, 136.6, 135.8, 134.7,
129.2, 128.3, 127.7, 120.6, 119.2 (aryl), 59.1 (ArCH2N), 57.8
(N(CH2CH2CH2NMe2)2), 51.7 (N(CH2CH2CH2NMe2)2), 45.6
(N(CH2CH2CH2N(CH3)2)2), 34.2 (C(CH3)3), 31.7 (C(CH3)3),
24.5 (N(CH2CH2CH2NMe2)2).
(400 MHz, toluene-d8, -40 °C): δ 7.93 (m, 6H, Si(C6H5)3), 7.54
4
(d, JH,H = 2.8 Hz, 1H, aryl-H), 7.23 (m, 9H, Si(C6H5)3), 7.16
(d, 4JH,H = 2.8 Hz, 1H, aryl-H), 4.06 (d, 2JH,H = 14.0 Hz, 1H,
ArCH2N), 2.80 (t, 3JH,H = 12.0 Hz, 1H, NCH2CH2CH2NMe2),
2.71 (d, 2JH,H = 14.0 Hz, 1H, ArCH2N), 2.58 (t, 3JH,H = 12.0 Hz,
1H, NCH2CH2CH2NMe2), 2.05 (s, 3H, N(CH3)2), 2.00 (t, 3JH,H
=
12.0 Hz, 1H, NCH2CH2CH2NMe2), 1.87 (d, JH,H = 8.0 Hz,
3
(23) Thadani, A. N.; Huang, Y.; Rawal, V. H. Org. Lett. 2007, 9,
3873.
(24) (a) Tamaru, Y.; Hojo, M.; Higashimura, H.; Yoshida, Z.-I.
J. Am. Chem. Soc. 1988, 110, 3994. (b) Kondo, T.; Okada, T.; Mitsudo,
T. J. Am. Chem. Soc. 2002, 124, 186.
(25) Khan, N. H.; Ahmad, G.; Serajuddin, A. S. M. Pakistan J. Biol.
Sci. 1968, 11; 49 [CA70:96290].
(26) (a) SMART, SAINTplus, TWINABS, XPREP programs; Bruker
Analytical X-Ray, Madison, WI, 2008. (b) Sheldrick, G. M. SHELXTL-
Bruker. Acta Crystallogr. 2008, A64, 112.

Article
Organometallics, Vol. 29, No. 22, 2010 5877
3
3H, MgCH(CH3)2), 1.84 (t, JH,H = 12.0 Hz, 1H, NCH2CH2-
CH2NMe2), 1.79 (d, 3JH,H = 8.0 Hz, 3H, MgCH(CH3)2), 1.71,
1.56 (m, 1H, NCH2CH2CH2NMe2), 1.47 (s, 3H, N(CH3)2), 1.40
(9H, s, C(CH3)3), 1.32 (m, 1H, NCH2CH2CH2NMe2), 1.24
(s, 3H, N(CH3)2), 1.19 (m, 1H, NCH2CH2CH2NMe2), 1.06 (s,
3H, N(CH3)2), 1.01, 0.98, 0.83, 0.38 (m, 1H, NCH2CH2CH2NMe2),
0.17 (m, 1H, MgCH(CH3)2). 1H NMR (500 MHz, THF-d8,
25 °C): δ 7.61 (m, 6H, Si(C6H5)3), 7.26 (m, 9H, Si(C6H5)3), 7.04
(d, 4JH,H = 3.0 Hz, 1H, aryl-H), 7.00 (d, 4JH,H = 3.0 Hz, 1H,
aryl-H), 3.74 (br s, 2H, ArCH2N), 2.68 (s, 4H, N(CH2CH2CH2-
NMe2)2), 2.16 (br s, 4H, N(CH2CH2CH2NMe2)2), 2.00 (br s, 12H,
N(CH2CH2CH2N(CH3)2)2), 1.76 (br s, 4H, N(CH2CH2CH2N-
Me2)2), 1.26 (d, 3JH,H = 7.5 Hz, 6H, MgCH(CH3)2), 1.09 (s, 9H,
C(CH3)3), -0.29 (m, 1H, MgCH(CH3)2). 13C{1H} NMR (500
MHz, THF-d8, 25 °C): δ 171.4, 139.8, 138.6, 137.7, 136.2, 132.0,
130.2, 129.0, 122.7, 122.4 (aryl), 62.4 (ArCH2N), 60.9 (N(CH2CH2-
CH2NMe2)2), 54.2 (N(CH2CH2CH2NMe2)2), 46.3 (N(CH2CH2-
CH2N(CH3)2)2), 35.3, (C(CH3)3), 33.2 (C(CH3)3), 27.3 (MgCH-
(CH3)2), 23.1 (N(CH2CH2CH2NMe2)2), 9.9 (MgCH(CH3)2).
Anal. Calcd for C42H59MgN3OSi: C, 74.81; H, 8.82; N, 6.23.
Found: C, 72.33, 72.56, 73.03; H, 8.41, 8.31, 8.45; N, 5.88, 5.88, 5.89.
Crystallography of 2. Clear, colorless brick-shaped crystals of
2 suitable for X-ray diffraction analysis were obtained by slow
evaporation of the solvent from a hexanes solution at room
temperature. Data were collected on a Bruker SMART APEX
diffractometer: C42H59MgN3OSi, Mr = 674.32, monoclinic, space
independent parts in SHELXL (occupation ratio 55%:45%),
and using vel ADP restraints (ISOR in SHELXL for all tert-butyl
C atoms) and ADPconstraints (EADPfor atoms C29A andC29B
only). Hydrogen atoms were constrained to idealized positions
using a riding model.
L3MgiPr (3). Complex 3 was prepared following the same
procedure as described for complex 2 by starting from L3H
(306 mg, 0.5 mmol) to give 3 as a white crystalline solid. Yield:
275 mg (81%). 1H NMR (500 MHz, C6D6, 25 °C): δ 7.97 (m, 6H,
Si(C6H5)3), 7.56 (d, 1H, 4JH,H = 3.0 Hz, aryl-H), 7.25 (m, 9H,
4
Si(C6H5)3), 7.10 (m, 3H, CH2C6H5), 7.03 (d, JH,H = 3.0 Hz,
1H, aryl-H), 6.91 (m, 2H, CH2C6H5), 4.01, 3.30 (d, 2JH,H = 14.0
Hz, 1H, ArCH2N), 3.82, 3.67 (d, 2JH,H = 14.0 Hz, 1H, CH2C6H5),
2.49 (t, 3JH,H = 10.0 Hz, 1H, NCH2CH2CH2NMe2), 2.11 (s, 3H,
N(CH3)2), 2.08 (t, 3JH,H = 10.0 Hz, 1H, NCH2CH2CH2NMe2),
1.87 (d, 3JH,H = 8.0 Hz, 3H, MgCH(CH3)2), 1.86 (m, 1H, NCH2-
CH2CH2NMe2), 1.83 (d, 3JH,H = 8.0 Hz, 3H, MgCH(CH3)2), 1.55
(s, 3H, N(CH3)2), 1.29(m, 1H, NCH2CH2CH2NMe2), 1.26(m, 1H,
NCH2CH2CH2NMe2), 1.22 (s, 9H, C(CH3)3), 0.62 (m, 1H, NCH2-
CH2CH2NMe2), 0.27 (m, 1H, MgCH(CH3)2). 13C{1H} NMR (125
MHz, C6D6, 25 °C): δ 170.0, 137.1, 136.8, 135.2, 132.1, 130.9, 130.8,
128.8, 128.5, 128.4, 128.1, 127.6, 122.1, 119.8 (aryl), 60.0 (ArCH2N),
59.7 (CH2C6H5), 55.9 (NCH2CH2CH2NMe2), 49.0 (NCH2CH2-
CH2NMe2), 45.4 (N(CH3)2), 43.3 ((N(CH3)2), 33.8 (C(CH3)3),
31.9 (C(CH3)3), 26.5 (MgCH(CH3)2), 26.4 (MgCH(CH3)2), 21.4
(NCH2CH2CH2NMe2), 8.0 (MgCH(CH3)2). Anal. Calcd for
C44H54MgN2OSi: C, 77.80; H, 8.01; N, 4.12. Found: C, 74.94,
74.68, 74.78; H, 8.18, 7.99, 7.81; N, 3.75, 3.68, 4.01.
˚
˚
group P21/c, a = 10.7798(7) A, b = 14.4804(9) A, c = 25.3779(15)
3
A, β= 94.550(1)°, V= 3948.9(4) A , Z=4, Fcalcd =1.134gcm-3
,
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˚
˚
General Procedure for NMR-Scale Catalytic Hydroamina-
tion/Cyclization Reactions. In the glovebox, a screw-cap NMR
tube was charged with ferrocene (6.0 mg, 32.3 μmol), complex 2
(13.5 mg 20.0 μmol), C6D6 (0.6 mL), and the substrate (0.20
mmol). The NMR tube was sealed, removed from the glovebox,
and placed inthe thermostated oilbathorthermostated 1H NMR
probe, and the conversion was monitored by NMR spectroscopy
by following the disappearance of the olefinic signals of the
substrate relative to the internal standard ferrocene.
F(000) = 1464, Mo KR radiation (λ = 0.710 73 A), μ = 0.110
mm-1, crystal dimensions 0.24 ꢀ 0.04 ꢀ 0.06 mm, T = 100(2) K,
8110 independent reflections for 1.9 e θ e 26.4°, GOF = 1.008,
R1(I > 2σ(I)) = 0.0518, wR2(all data) = 0.1236, largest difference
peak and hole 0.377 and -0.319 e A-3. X-ray data for a minor
˚
twin component (average reflection intensity ratio <20%; related
to component 1 by a 2-fold approximately along the crystal-
lographic c axis) were processed along with the major component
(SAINTplus and TWINABS programs26a) but were not used in
the structure determination (SHELXTL programs26a,b) of 2. Cell
parameters were obtained from the 4826 reflections from the
major component selected by the SAINTplus program within
the range 2.5 < θ < 26.3°. Lorentz, polarization, and empirical
absorption corrections were applied. The space group was deter-
mined from systematic absences (XPREP program26a). The
structure was solved by direct methods (SHELXS program26b).
All positional and atomic displacement parameters (ADP) were
refined with all 8110 data by full-matrix least squares on F2 using
SHELXL.26b Non-hydrogen atoms were refined anisotropically.
The tert-butyl group was disordered and was refined as two
Acknowledgment. Financial support by the ACS Pe-
troleum Research Fund (PRF No. 49109-ND1) is grate-
fully acknowledged.
Supporting Information Available: A CIF file giving X-ray
crystallographic data for 2 and figures giving additional kinetic
and thermal stability data and spectroscopic data of the new
ligands L2H and L3H and complexes 2 and 3. This material is
available free of charge via the Internet at http://pubs.acs.org.