Imino sulfinamidines: Synthesis and coordination chemistry of a novel class of chiral bidentate ligands

Article abstract of DOI:10.1021/ic052104m

The new imino sulfinamidine ligand PhS(NHt-Bu)=NC(Me)=N(C₆H ₃-2,6-iPr₂), LH (11) was synthesized from N-(2,6-diisopropylphenyl)acetamidine (9) and N-tert-butyl phenylsulfinimidoyl chloride (10). Reaction of LH (11) with ZnEt₂ or AlMe₃ gave the complexes LZnEt (12) and LAIMe₂ (13), respectively. The structures of 12 and 13 were determined by X-ray diffraction and were shown to contain L as a κ²-N¹,N⁶ bidentate ligand in a six-membered chelate. Formation of the magnesium complex (LMgN(TMS) ₂·L₂Mg) (14) from 11, MgI₂, and KN(SiMe₃)₂ highlighted a secondary coordination mode of L, binding through the sulfinamidine nitrogens in a four-membered chelate.

Full text of DOI:10.1021/ic052104m

Inorg. Chem. 2006, 45, 3352−3358
Imino Sulfinamidines: Synthesis and Coordination Chemistry of a Novel
Class of Chiral Bidentate Ligands
Anthony G. M. Barrett,*,† Andrew A. Gray,† Michael S. Hill,*,† Peter B. Hitchcock,‡
Panayiotis A. Procopiou,§ and Andrew J. P. White†
Department of Chemistry, Imperial College London, London, SW7 2AZ, England, School of
Chemistry, UniVersity of Sussex, Brighton, BN1 9QJ, England, and GlaxoSmithKline Medicines
Research Centre, Gunnels Wood Road, SteVenage, Hertfordshire, SG1 2NY, England
Received December 8, 2005
The new imino sulfinamidine ligand PhS(NHt-Bu)dNC(Me)dN(C6H3-2,6-iPr2), LH (11) was synthesized from N-(2,6-
diisopropylphenyl)acetamidine (9) and N-tert-butyl phenylsulfinimidoyl chloride (10). Reaction of LH (11) with ZnEt2
or AlMe3 gave the complexes LZnEt (12) and LAlMe2 (13), respectively. The structures of 12 and 13 were determined
by X-ray diffraction and were shown to contain L as a
of the magnesium complex (LMgN(TMS)2 L2Mg) (14) from 11, MgI2, and KN(SiMe3)2 highlighted a secondary
coordination mode of L, binding through the sulfinamidine nitrogens in a four-membered chelate.
κ
2-N1,N5 bidentate ligand in a six-membered chelate. Formation
‚
Introduction
The development of ancillary ligands in homogeneous
catalysis has resulted in a diverse range of catalytic systems.
While increasing ligand sophistication has resulted in
dramatic improvements in activity, the desire for stereocon-
trol in organometallic reactions is still of high priority, and
consequently, a plethora of chiral ligands have been devel-
oped. Notable successful moieties include the chiral diphos-
phines,1 salen derivatives,2 oxazolines,3-6 and N-heterocyclic
carbenes.7,8 The â-diketimines 1 are a class of monoanionic
ligands that have been used to stabilize low metal (transition
and main group) oxidation states and/or coordination num-
bers to effect a variety of catalytic processes by means of
their coordinative and electronic unsaturation.9 The success
of the â-diketiminates lies in the ease with which the steric
* To whom correspondence should be addressed. E-mail: agmb@ic.ac.uk.
† Imperial College London.
bulk of the substituents may be modified at both the
coordinating nitrogens and hydrocarbon ligand “backbone.”
‡ University of Sussex.
§ GlaxoSmithKline.
(1) Shimizu, H.; Nagasaki, I.; Saito, T. Tetrahedron 2005, 61, 5405.
(2) Katsuki, T. Synlett 2003, 281.
(3) Ghosh, A. K.; Mathivanan, P.; Cappiello, J. Tetrahedron: Asymmetry
1998, 9, 1.
Although there have been significant studies of the effects
of varying backbone substituents,10-24 there have been only
(4) Helmchen, G.; Pfaltz, A. Acc. Chem. Res. 2000, 33, 336.
(5) Sutcliffe, O. B.; Bryce, M. R. Tetrahedron: Asymmetry 2003, 14, 2297.
(6) McManus, H. A.; Guiry, P. J. Chem. ReV. 2004, 104, 4151.
(7) Perry, M. C.; Burgess, K. Tetrahedron: Asymmetry 2003, 14, 951.
(8) Cesar, V.; Bellemin-Laponnaz, S.; Gade, L. H. Chem. Soc. ReV. 2004,
33, 619.
(10) Budzelaar, P. H. M.; Van Oort, A. B.; Orpen, A. G. Eur. J. Inorg.
Chem. 1998, 1485.
(11) Caro, C. F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1999,
1433.
(12) Jazdzewski, B. A.; Holland, P. L.; Pink, M.; Young, V. G., Jr.; Spencer,
D. J. E.; Tolman, W. B. Inorg. Chem. 2001, 40, 6097.
(13) Smith, J. M.; Lachicotte, R. J.; Holland, P. L. Chem. Commun. 2001,
1542.
(9) Bourget-Merle, L.; Lappert, M. F.; Severn, J. R. Chem. ReV. 2002,
102, 3031.
3352 Inorganic Chemistry, Vol. 45, No. 8, 2006
10.1021/ic052104m CCC: $33.50
© 2006 American Chemical Society
Published on Web 03/16/2006

Imino Sulfinamidines: NoWel Chiral Bidentate Ligands
limited attempts to alter the backbone itself in order to further
modify the coordination sphere around the metal. These
include the synthesis of various triazapentadienyl ligands 2,
which have been used to form a variety of metal com-
plexes.25-33 Recently, phosphinimine donors have been
incorporated into the ligand backbone, resulting in phos-
phonium diketimide analogues 3, which have been success-
fully utilized in the synthesis of Group 13 complexes.34,35
Chivers et al. have achieved the synthesis of hybrid boraa-
midinate/amidinate ligands 4 isoelectronic to the diketimi-
nates and successfully applied their magnesium complexes
in lactide polymerization.36 The same group has also
synthesized chiral phosphine analogues 5. Attempts at
metalation, however, resulted in nucleophilic attack at the
phosphine to generate phosphine-phosphonium anions of
the type 6.37 Coordination studies of bis(phosphinimino)-
methanide ligands of type 7 have been performed, and the
Despite these efforts, an efficient, versatile route to a
â-diketiminate analogue in which the chirality is well
expressed in the vicinity of the ligated metal center has yet
to be realized. We envisioned that placing a chiral sulfina-
midine functionality into the backbone would lead to
significant distortion of the planar diketimine framework,
inducing a highly discriminating asymmetric environment
around the metal center by means of the pseudo-tetrahedral
sulfur. Ligand 8 would combine the easily variable steric
demand of the â-diketimines with the asymmetric potential
of sulfur(IV) to introduce chirality proximal to the metal.
To this end, we describe the synthesis of a novel ligand
containing the imino sulfinamidine moiety and some ex-
ploratory coordination complexes of this ligand, which
displays at least two coordination modes.
monoanions have been shown to complex as bidentate N,N′
38-42
ligands when R1 ) SiMe3
or 2,4,6-Me3C6H2.43,44
(14) Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh, S. Inorg. Chem.
2001, 40, 5316.
(15) Allen, S. D.; Moore, D. R.; Lobkovsky, E. B.; Coates, G. W. J. Am.
Chem. Soc. 2002, 124, 14284.
Experimental Section
General Procedures. All manipulations were carried out using
a standard Schlenk line or within a glovebox (operating at < 2
ppm O2) containing an inert dinitrogen atmosphere. Hexane and
PhMe were redistilled from Na and THF over Na and Ph2CO. C6D6
and toluene-d8 were dried with molten K and vacuum-transferred
to a Youngs’ storage ampule prior to use. tert-Butyldichloroamine
was synthesized from tert-butyl alcohol as described by Kovacic
et al.45 All other reagents were used as commercially supplied.
N-(2,6-Diisopropylphenyl)acetamidine (9). MeCN (4.20 mL,
80.00 mmol) and 2,6-diisopropylaniline (15.76 g, 80.00 mmol) were
added to freshly ground AlCl3 (10.64 g, 80.00 mmol), and the
mixture was heated at 180 °C for 2 h.46 After this time, the mixture
was cooled and hydrochloric acid (1.2 M, 160 mL) carefully added,
followed by decolorizing charcoal (2 g), and the mixture heated to
reflux for 10 min. The mixture was allowed to cool to room
temperature before filtering, giving a dark green solution, which
was extracted with CH2Cl2 (3 × 100 mL) to remove a dark purple
impurity. The aqueous layer was basified with 15% NaOH (200
mL) to give an off-white precipitate, which was extracted with CH2-
Cl2 (3 × 100 mL). The organic extracts were combined, dried
(MgSO4), filtered, and evaporated to yield amidine 9 (12.20 g, 70%)
as a gray solid: mp 118-120 °C (MeOH); Rf 0.14 (CH2Cl2:MeOH:
(16) Moore, D. R.; Cheng, M.; Lobkovsky, E. B.; Coates, G. W. Angew.
Chem., Int. Ed. 2002, 41, 2599.
(17) Spencer, D. J. E.; Aboelella, N. W.; Reynolds, A. M.; Holland, P. L.;
Tolman, W. B. J. Am. Chem. Soc. 2002, 124, 2108.
(18) Spencer, D. J. E.; Reynolds, A. M.; Holland, P. L.; Jazdzewski, B.
A.; Duboc-Toia, C.; Le Pape, L.; Yokota, S.; Tachi, Y.; Itoh, S.;
Tolman, W. B. Inorg. Chem. 2002, 41, 6307.
(19) Avent, A. G.; Hitchcock, P. B.; Khvostov, A. V.; Lappert, M. F.;
Protchenko, A. V. Dalton Trans. 2003, 1070.
(20) Laitar, D. S.; Mathison, C. J. N.; Davis, W. M.; Sadighi, J. P. Inorg.
Chem. 2003, 42, 7354.
(21) Ragogna, P. J.; Burford, N.; D’eon, M.; McDonald, R. Chem. Commun.
2003, 1052.
(22) Shimokawa, C.; Yokota, S.; Tachi, Y.; Nishiwaki, N.; Ariga, M.; Itoh,
S. Inorg. Chem. 2003, 42, 8395.
(23) Avent, A. G.; Caro, C. F.; Hitchcock, P. B.; Lappert, M. F.; Li, Z.;
Wei, X.-H. Dalton Trans. 2004, 1567.
(24) Burford, N.; D’eon, M.; Ragogna, P. J.; McDonald, R.; Ferguson, M.
J. Inorg. Chem. 2004, 43, 734.
(25) Robinson, V.; Taylor, G. E.; Woodward, P.; Bruce, M. I.; Wallis, R.
C. J. Chem. Soc., Dalton Trans. 1981, 1169.
(26) Barker, J.; Kilner, M.; Mahmoud, M. M.; Wallwork, S. C. J. Chem.
Soc., Dalton Trans. 1989, 837.
(27) Hursthouse, M. B.; Mazid, M. A.; Robinson, S. D.; Sahajpal, A. J.
Chem. Soc., Dalton Trans. 1994, 3615.
(28) Aris, D. R.; Barker, J.; Phillips, P. R.; Alcock, N. W.; Wallbridge, M.
G. H. J. Chem. Soc., Dalton Trans. 1997, 909.
(29) Siedle, A. R.; Webb, R. J.; Behr, F. E.; Newmark, R. A.; Weil, D. A.;
Erickson, K.; Naujok, R.; Brostrom, M.; Mueller, M.; Chou, S.-H.;
Young, V. G., Jr. Inorg. Chem. 2003, 42, 932.
(30) Dias, H. V. R.; Singh, S. Inorg. Chem. 2004, 43, 7396.
(31) Dias, H. V. R.; Singh, S. Inorg. Chem. 2004, 43, 5786.
(32) Guo, J.; Wong, W.-K.; Wong, W.-Y. Eur. J. Inorg. Chem. 2004, 267.
(33) Dias, H. V. R.; Singh, S.; Cundari, T. R. Angew. Chem. 2005, 44,
4907.
(34) Masuda, J. D.; Walsh, D. M.; Wei, P.; Stephan, D. W. Organometallics
2004, 23, 1819.
(35) Welch, G. C.; Piers, W. E.; Parvez, M.; McDonald, R. Organometallics
2004, 23, 1811.
NH3, 92:7:1); IR (thin film) 3454, 3305, 3168, 1643, 1460 cm-1
;
1H NMR (300 MHz, CDCl3) δ 1.12-1.20 (m, 12H), 2.15 (s, 3H),
3.01 (sept, J ) 6.9 Hz, 2H), 4.27 (br s, 2H), 7.00-7.16 (m, 3H);
13C NMR (75 MHz, CDCl3) δ 21.8, 23.7, 28.0, 123.3, 123.5, 139.8,
143.3, 154.0; MS (CI) m/z 219 (M + H)+; HRMS (CI) m/z calcd
for C14H23N2 (M + H)+, 219.1861; found: 219.1868. Anal. Calcd
for C14H22N2: C, 77.01; H, 10.16; N, 12.83. Found: C, 76.95; H,
10.19; N, 12.74.
(36) Chivers, T.; Fedorchuk, C.; Parvez, M. Organometallics 2005, 24,
580.
(37) Chivers, T.; Copsey, M. C.; Fedorchuk, C.; Parvez, M.; Stubbs, M.
Organometallics 2005, 24, 1919.
(38) Kasani, A.; McDonald, R.; Cavell, R. G. Organometallics 1999, 18,
3775.
(39) Ong, C. M.; McKarns, P.; Stephan, D. W. Organometallics 1999, 18,
4197.
(41) Gamer, M. T.; Dehnen, S.; Roesky, P. W. Organometallics 2001, 20,
4230.
(42) Gamer, M. T.; Roesky, P. W. Z. Anorg. Allg. Chem. 2001, 627, 877.
(43) Evans, D. J.; Hill, M. S.; Hitchcock, P. B. Dalton Trans. 2003, 570.
(44) Hill, M. S.; Hitchcock, P. B. Chem. Commun. 2003, 1758.
(45) Roberts, J. T.; Rittberg, B. R.; Kovacic, P. J. Org. Chem. 1981, 46,
4111.
(40) Kamalesh Babu, R. P.; Aparna, K.; McDonald, R.; Cavell, R. G. Inorg.
Chem. 2000, 39, 4981.
(46) Robev, S. K.; Tsanova, T. M.; Dicheva, M. A. Dokl. Akad. Nauk 1989,
42, 51.
Inorganic Chemistry, Vol. 45, No. 8, 2006 3353

Barrett et al.
N-tert-Butyl Phenylsulfinimidoyl Chloride (10). Using a
slightly modified procedure of Mukaiyama,47 tert-butyldichloro-
amine (6.24 g, 43.98 mmol) was added to PhSAc (6.36 g, 41.78
mmol, 0.95 equiv) in PhH (18 mL), and the solution was heated at
80 °C for 20 min, after which time the color changed from yellow
to orange. Evaporation under reduced pressure yielded sulfinimidoyl
chloride 10 (8.50 g, 97%) as a yellow moisture-sensitive solid: IR
(thin film) 1630, 1303, 1140 cm-1; 1H NMR (300 MHz, CDCl3) δ
1.57 (s, 9H), 7.57-7.59 (m, 3H), 8.10-8.13 (m, 2H); 13C NMR
(75 MHz, CDCl3) δ 29.8, 64.4, 125.8, 129.l, 133.8, 142.9.
(d, J ) 6.0 Hz, 1H), 1.08 (d, J ) 6.4 Hz, 3H), 1.15 (s, 3H), 1.23
(d, J ) 6.4 Hz, 3H), 1.32 (d, J ) 6.0 Hz, 2H), 1.37 (d, J ) 6.0 Hz,
2H), 1.51 (s, 9H), 2.15-2.31 (m, 0.5H), 2.8 (s, 3H), 3.29-3.36
(m, 1.5H), 7.03-7.21 (m, 6H), 7.84-7.88 (m, 2H); 13C NMR (100
MHz, C6D6) δ -4.4, 16.4, 23.1, 23.3, 23.7, 25.3, 25.5, 25.7, 27.4,
27.7, 27.8, 28.7, 31.3, 52.5, 57.6, 123.0, 123.3, 124.9, 126.8, 127.4,
128.4, 129.2, 130.4, 131.9, 139.3, 144.5. Anal. Calcd for C26H40-
AlN3S: C, 68.84; H, 8.89; N, 9.26. Found: C, 68.78; H, 8.99; N,
9.23.
LMgN(TMS)2‚L2Mg (14). Precooled THF (15 mL) was added
at -78 °C to a rapidly stirred mixture of 11 (500 mg, 1.26 mmol),
KN(SiMe3)2 (502 mg, 2.52 mmol), and MgI2 (350 mg, 1.26 mmol).
The mixture was allowed to warm to room temperature and was
stirred overnight to produce a tan slurry. After evaporation under
reduced pressure, the tan solid residue was extracted with hexane
(20 mL). Filtration and slow cooling of a warm saturated solution
afforded colorless crystals of 14 (150 mg, 34%) suitable for an
X-ray structure determination: 1H NMR (400 MHz, CD3C6D5) δ
0.07 (s, 7H), 0.36-0.64 (m, 9H), 0.75-1.04 (m, 16H), 1.05-1.36
(m, 44H), 1.44-1.59 (m, 8H), 1.71-2.09 (m, 7H), 2.31-2.59 (m,
2H), 3.12-3.63 (m, 3H), 6.85-7.14 (m, 20H), 7.92-8.30 (m, 4H);
13C NMR (100 MHz, CD3C6D5) δ 2.2, 14.0, 21.2, 22.7, 22.8, 23.0,
23.1, 23.3, 23.4, 23.8, 24.0, 24.7, 27.2, 27.3, 27.8, 28.7, 30.1, 31.7,
32.9, 53.2, 122.7, 122.8, 125.8, 126.9, 128.6, 129.1, 130.5, 136.8,
138.3, 138.9, 139.2, 144.0, 143.9, 146.7, 147.0, 148.0, 167.5. Anal.
Calcd for C78H120Mg2N10S3Si2: C, 66.97; H, 8.65; N, 10.01.
Found: C, 66.94; H, 8.57; N, 9.98.
N-tert-Butyl Phenylsulfinimidoyl N-(2,6-Diisopropylphenyl)-
acetamidine (11). Amidine 9 (5.00 g, 22.93 mmol) was added
portionwise to a suspension of KH (3.15 g, 27.56 mmol) in THF
(120 mL) at 0 °C. The mixture was stirred for 1 h, cooled to -78
°C, and sulfinimidoyl chloride 10 (5.95 g, 27.61 mmol) in THF
(25 mL) added dropwise. The reaction mixture was stirred for 1 h,
allowed to warm to room temperature, stirred for a further 1 h,
and quenched with saturated aqueous NH4Cl (50 mL). The mixture
was extracted with CH2Cl2 (3 × 75 mL), and the combined organic
extracts were dried (MgSO4), filtered, and evaporated. The residue
was chromatographed on neutral alumina (hexane; hexane/CH2-
Cl2, 3:17; EtOAc/CH2Cl2/NEt3 10:90:1) to yield 11 (7.21 g, 79%)
as a yellow oil, which solidified upon standing: mp 130-132 °C
(DMSO); Rf 0.20 (CH2Cl2:MeOH:NH3, 240:10:1); IR (thin film)
1
3192, 1568, 1460, 1363, 1280, 1239 cm-1; H NMR (400 MHz,
DMSO-d6) δ 0.62-1.10 (4d, J ) 6.9 Hz, 12H), 1.36 (s, 9H), 1.58
(s, 3H), 2.12-2.28, 2.88 (2m, overlapping sept, J ) 6.9 Hz, 2H),
6.77 (br s, 1H, NH), 6.81 (t, J ) 7.6 Hz, 1H), 6.87 (dd, J ) 7.6,
1.2 Hz, 1H), 6.95 (dd, J ) 7.6, 1.2 Hz, 1H), 7.49-7.57 (m, 3H),
7.76 (d, J ) 7.3 Hz, 2H); 13C NMR (75 MHz, C6D6) δ 21.4, 23.3,
24.1, 24.9, 27.3, 28.0, 30.2, 53.4, 123.1, 122.9, 127.0, 128.9, 129.4,
138.5, 139.4, 143.9, 146.8, 167.5; MS (CI) m/z 398 (M + H)+;
HRMS (CI) m/z calcd for C24H36N3S (M + H)+, 398.2630; found:
398.2619. Anal. Calcd for C24H35N3S: C, 72.50; H, 8.87; N, 10.57.
Found: C, 72.60; H, 8.93; N, 10.49.
Crystallographic Structural Determination. Table 1 provides
a summary of the crystallographic data for compounds 11-14. Data
for 11 (2θmax ) 46°) and 13 (2θmax ) 52°) were collected on an
Enraf Nonius KappaCCD diffractometer, while those for 12 (2θmax
) 66°) and 14 (2θmax ) 66°) were collected on an Oxford
Diffraction Xcalibur3 diffractometer. CCDC 289163 to 289166,
respectively.
LZnEt (12). ZnEt2 (1M, 5.0 mL, 5.00 mmol) in hexane was
added to 11 (1.00 g, 2.52 mmol) in PhMe (15 mL) at 0 °C. The
solution was allowed to warm to room temperature, stirred
overnight, evaporated under reduced pressure, and the residue
dissolved in hexane (25 mL) and filtered. The filtrate was
evaporated to yield 12 (1.09 g, 88%) as a yellow solid. Crystals
suitable for an X-ray structure determination were obtained from a
concentrated solution of 12 in hexane: IR (solid) 1738, 1479, 1364,
1217 cm-1; 1H NMR (400 MHz, CD3C6D5) δ -0.07-0.05 (m, 2H,
ZnCH2), 0.52 (d, J ) 6.9 Hz, 3H), 0.79 (d, J ) 6.9 Hz, 3H), 0.96
(t, J ) 8.1 Hz, 3H, ZnCH2CH3), 1.12 (d, J ) 6.9 Hz, 3H), 1.15 (d,
J ) 6.9 Hz, 3H), 1.33 (s, 9H), 1.70 (s, 3H), 1.85 (sept, 1H, J ) 6.9
Hz), 3.11 (sept, 1H, J ) 7.3 Hz), 6.82-6.86 (m, 1H), 6.91-7.07
(m, 5H), 7.77-7.80 (m, 2H); 13C NMR (100 MHz, CD3C6D5) δ
0.6, 12.2, 23.1, 23.5, 24.0, 24.7, 27.6, 28.3, 33.0, 55.4, 123.6, 125.7,
127.2, 129.9, 141.6, 141.8, 144.6, 146.2, 170.9.
LAlMe2 (13). AlMe3 (2M, 0.6 mL, 1.20 mmol) in hexane was
added to 11 (432 mg, 1.09 mmol) in PhMe (8 mL) at -78 °C. The
solution was allowed to warm to room temperature, stirred
overnight, evaporated under reduced pressure, and the residue
dissolved in hexane (20 mL) and filtered. The filtrate was
evaporated to yield 13 (400 mg, 81%) as a crystalline yellow solid.
Crystals suitable for an X-ray structure determination were obtained
from a concentrated solution of 13 in hexane: IR (solid) 1738,
1571, 1366, 1217 cm-1; 1H NMR (300 MHz, C6D6) δ -0.77 (s,
3H, AlCH3), -0.26 (s, 3H, AlCH3), 0.77 (d, J ) 6.0 Hz, 1H), 0.94
Results and Discussions
The synthesis of racemic imino sulfinamidine 11 was
achieved in two steps from amidine 9. Deprotonation with
KH followed by treatment with N-tert-butyl phenylsulfin-
imidoyl chloride at -78 °C afforded ligand 11 in 79% yield
(Scheme 1). The X-ray structural analysis of crystals of 11
revealed the presence of two independent molecules (A and
B) in the asymmetric unit (molecule A is shown in Figure
1, and molecule B is shown in Figure S1 in the Supporting
Information). The two molecules have similar conformations,
the rms fit of the {N-S-N-C(Me)-N} ligand backbone
(including the attached carbons of the tert-butyl, phenyl, and
2,6-diisopropylphenyl substituents) being ca. 0.14 Å. The
largest difference between the two independent molecules
is the orientation of the S-phenyl ring, this ring being almost
orthogonal (ca. 86°) to the S(1)-N(2) bond in molecule A
compared to ca. 57° in molecule B.
Despite the N-H proton being located on N(1) [meaning
that S(1)-N(2) is formally a double bond], the N(1)-S(1)
and S(1)-N(2) bond distances are the same [1.644(3) and
1.640(3) Å, respectively, in molecule A, 1.645(3) and 1.631-
(3) Å, respectively, in molecule B]. The N(2)-C(11) and
C(11)-N(3) bond lengths are unexceptional (Table 2).
Presumably, the intermolecular N-H‚‚‚N hydrogen bonds
are the cause of the comparable bond lengths of N(1)-S(1)
(47) Mukaiyama, T.; Matsuo, J.-I.; Yanagisawa, M. Chem. Lett. 2000, 1072.
3354 Inorganic Chemistry, Vol. 45, No. 8, 2006

Imino Sulfinamidines: NoWel Chiral Bidentate Ligands
Table 1. Crystallographic Data for Compounds 11-14
data
11
12
13
14
chemical formula
solvent
fw
T (°C)
space group
a (Å)
C24H35N3S
-
C26H39N3SZn
-
C26H40AlN3S
0.5C6H14
496.74
C78H120Mg2N10S3Si2
C6H14
1484.99
-100
P21/n (no. 14)
21.9499(7)
18.8731(6)
23.4952(7)
-
107.934(3)
-
9260.3(5)
4
1.065
0.71073
0.164
397.61
491.03
-100
-100
-100
P1h (no. 2)
10.4125(4)
11.9105(7)
20.7215(11)
102.952(3)
94.096(3)
107.637(3)
2359.7(2)
4a
P21/n (no. 14)
13.5781(4)
11.6793(4)
16.7892(5)
-
93.342(3)
-
2657.95(14)
4
1.227
0.71073
1.019
0.037
0.101
P21/c (no. 14)
8.4281(2)
15.3512(4)
23.3402(3)
-
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
99.795(1)
-
2975.77(11)
4
1.109
0.71073
0.159
F
calcd (g cm-3
)
1.119
0.71073
0.151
0.059
0.150
λ (Å)
µ (mm-1
R1b
)
0.044
0.115
0.103
0.150
wR2c
2 2
a There are two crystallographically independent molecules in the asymmetric unit. b R1 ) ∑||Fo| - |Fc||/Σ|Fo|. c wR2 ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo ) ]}1/2
;
w-1 ) σ2(Fo ) + (aP)2 + bP.
2
of the LiI species (LH‚LiI‚thf)2 (see the Supporting
Information).
In both independent molecules, the 2,6-diisopropylphenyl
ring is oriented almost orthogonally to the plane at the parent
nitrogen, the N(3)-Ar torsion angle being ca. 83° and 74°
in A and B, respectively. Each of the two independent
molecules is linked across a center of symmetry to a
neighboring molecule of the same type (i.e., A to A′ and B
to B′) by a pair of N-H‚‚‚N hydrogen bonds from the
N(1)-H proton in one molecule to the N(2) nitrogen in the
Ci-related counterpart, forming discrete dimer pairs in each
case. For molecule A, the N-H‚‚‚N hydrogen bonds have
N‚‚‚N 2.989(4) Å, H‚‚‚N 2.09 Å, and N-H‚‚‚N 175°, while
for molecule B, the parameters are N‚‚‚N 2.963(4) Å, H‚‚‚
N 2.06 Å, and N-H‚‚‚N 180°.
With ligand precursor 11 in hand, studies into its coordi-
nation behavior were commenced by reaction of 11 with an
excess of ZnEt2 in toluene. Upon removal of volatile
components, the 1H NMR spectrum of the crude residue was
consistent with the formation of a single product. Extraction
with hexane followed by crystallization gave material suitable
for an X-ray solid-state structure determination, and this
showed a 1:1 complex between ligand L, an ethylzinc moiety
with a distorted trigonal planar coordination geometry at the
metal center [{Zn,N(1),N(5),C(30)} is coplanar to better than
0.01 Å], and a six-membered N,N′ chelate ring (Figure 2).
The angles at the metal are 98.36(4)°, 125.15(6)°, and
136.49(6)°, the smallest being associated with the bite of
the chelating ligand (Table 3). It is not immediately clear
why the ethyl ligand is situated away from the exterior
bisector of the N(1)-Zn-N(5) angle toward N(5), there
being no noticeable steric hindrance.
Figure 1. Molecular structure of one (A) of the two independent molecules
present in the crystals of 11. The N-H‚‚‚N hydrogen bond (a) has N‚‚‚N
2.989(4) Å, H‚‚‚N 2.09 Å, and N-H‚‚‚N 175°.
Scheme 1. Synthesis of Imino Sulfinamidine 11
Table 2. Selected Bond Lengths (Å) and Angles (deg) for the Two
Independent Molecules (A and B) Present in the Crystals of 11
A
B
N(1)-S(1)
1.644(3)
1.383(4)
1.640(3)
1.645(3)
1.380(4)
1.631(3)
N(2)-C(11)
S(1)-N(2)
C(11)-N(3)
1.291(4)
1.289(4)
N(2)-S(1)-N(1)
N(2)-S(1)-C(5)
N(1)-S(1)-C(5)
C(11)-N(2)-S(1)
N(3)-C(11)-N(2)
104.18(14)
106.39(15)
101.50(15)
110.9(2)
107.16(14)
105.39(15)
100.32(16)
112.7(2)
While the Zn-N(5) bond length of 2.0209(10) Å is
comparable to other three-coordinate-zinc-to-imino-nitrogen
distances in other complexes,48-51 there are no close ana-
121.4(3)
122.1(3)
and S(1)-N(2). While the S(1)-N(2)-C(11)-N(3) portion
of the backbone adopts a syn conformation (see Table 6 for
the torsion angles along the ligand backbone), N(1) is
oriented distal from the N(3) nitrogen, rather than forming
an intramolecular hydrogen bond as was seen in the structure
(48) Chinn, M. S.; Chen, J. Inorg. Chem. 1995, 34, 6080.
(49) Chisholm, M. H.; Gallucci, J. C.; Zhen, H.; Huffman, J. C. Inorg.
Chem. 2001, 40, 5051.
(50) Boss, S. R.; Haigh, R.; Linton, D. J.; Schooler, P.; Shields, G. P.;
Wheatley, A. E. H. Dalton Trans. 2003, 1001.
Inorganic Chemistry, Vol. 45, No. 8, 2006 3355

Barrett et al.
Figure 3. 1H NMR spectrum of 12 at 298 K in CD3C6D5.
Figure 2. Molecular structure of 12.
Table 3. Selected Bond Lengths (Å) and Angles (deg) for 12
Zn-N(1)
1.9655(11)
1.9570(14)
1.6390(11)
1.3161(16)
98.36(4)
Zn-N(5)
2.0209(10)
1.6198(12)
1.3419(17)
Zn-C(30)
N(1)-S(2)
N(3)-C(4)
S(2)-N(3)
C(4)-N(5)
N(1)-Zn-N(5)
N(5)-Zn-C(30)
N(1)-Zn-C(30)
136.49(6)
125.15(6)
logues for the Zn-N(1) linkage. One of the closest is for a
four-coordinate zinc to a tert-butyl-substituted imine nitrogen
in bis(1,4-di-tert-butyl-1,4-diazabutadiene-N,N′) zinc52 where
the Zn-N separations are 1.999 and 2.014 Å, though this is
formally zinc(0) cf. zinc(II) here in 12. The Zn-C distance
of 1.9570(14) Å is very similar to those seen in related three-
coordinate mono-zinc structures with six-membered N,N′
chelate rings [1.947(4), 1.951(5), 1.955(5), and 1.963(5)
Å].53-55 The most noticeable changes in the bonding pattern
within the ligand backbone on going from the free ligand
11 to the zinc complex 12 (Table 6) are a marked contraction
of the N(1)-S(2) [1.6198(12) Å cf. 1.644(3) and 1.645(3)
Å for the two independent molecules A and B in the structure
of 11] and N(3)-C(4) linkages [1.3419(17) cf. 1.383(4) and
1.380(4) Å in 11] and a lengthening of the C(4)-N(5) bond
[1.3161(16) Å cf. 1.291(4) and 1.289(4) Å in 11]. The S(2)-
N(3) distance is unchanged [1.6390(11) cf. 1.640(3) and
1.631(3) Å in 11].
Figure 4. Molecular structure of 13.
spectra. The highly asymmetric nature of complex 12 is
highlighted by the presence of two distinct chemical environ-
ments for the isopropyl groups of the aniline. The large
difference in shift for the two methine signals can be
rationalized by examination of the X-ray structure: the
isopropyl group vicinal to the phenyl group is at a distance
of 3.00 Å to the sulfinamidine phenyl ring, which is likely
to be close enough to encounter the shielding effect of the
phenyl ring current.
To further evaluate the ability of ligand 11 to act as a
bidentate ligand, it was allowed to react with 1 equiv of
AlMe3 followed by crystallization of the product from hexane
to give the complex 13. The single-crystal structure of the
dimethyl-aluminum complex 13 (Figure 4) is similar to that
of its ethyl-zinc counterpart 12. The ligand coordinates with
a six-membered N,N′ chelate ring that adopts a twisted
geometry, {N(1),C(1),N(2),N(3)} being coplanar to better
than 0.01 Å with Al and S(2) ca. -0.22 and +0.54 Å out of
this plane, respectively, (the positive direction being toward
the C(26) side of the plane). The geometry at the metal center
is distorted tetrahedral with X-Al-Y angles in the range
99.18(6)-113.07(8)°, the smallest being associated with the
bite of the chelating ligand (Table 4). The Al-N distances
are asymmetric with that to N(3) [1.9076(16) Å] being ca.
0.06 Å shorter than that to N(1) [1.9716(14) Å]. The latter
bond length is similar to those seen for some other Me2Al-
N(imide) linkages with another nitrogen in the fourth
coordination site.56-58 There are no good analogues for the
The chelate ring adopts a folded conformation, {Zn,N-
(1),C(4),N(5)} being coplanar to within ca. 0.01 Å with S(2)
and N(3) ca. 0.73 and 0.22 Å out of this plane, respectively,
in the direction of the S-phenyl group (Table 6). As was
seen for both independent molecules in the structure of the
free ligand 11, the 2,6-diisopropylphenyl unit is oriented
almost orthogonally to the chelate ring, the N(5)-Ar torsion
angle being ca. 88°.
A selected portion of the 1H NMR spectrum of 12 is shown
in Figure 3 with assignments obtained from 2D-COSY
(51) Coles, M. P.; Hitchcock, P. B. Eur. J. Inorg. Chem. 2004, 2662.
(52) Gardiner, M. G.; Hanson, G. R.; Henderson, M. J.; Lee, F. C.; Raston,
C. L. Inorg. Chem. 1994, 33, 2456.
(53) Cheng, M.; Moore, D. R.; Reczek, J. J.; Chamberlain, B. M.;
Lobkovsky, E. B.; Coates, G. W. J. Am. Chem. Soc. 2001, 123, 8738.
(54) Cole, S. C.; Coles, M. P.; Hitchcock, P. B. Organometallics 2004,
23, 5159.
(55) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; White, A. J. P.; Williams,
D. J. Dalton Trans. 2004, 570.
3356 Inorganic Chemistry, Vol. 45, No. 8, 2006

Imino Sulfinamidines: NoWel Chiral Bidentate Ligands
Table 4. Selected Bond Lengths (Å) and Angles (deg) for 13
Al-N(1)
1.9716(14) Al-N(3)
1.969(2) Al-C(26)
1.6242(15) S-N(2)
1.9076(16)
1.961(2)
1.6297(14)
1.329(2)
109.21(7)
111.56(8)
Al-C(25)
N(3)-S
N(2)-C(1)
N(1)-Al-N(3)
N(1)-Al-C(26) 111.49(7)
N(3)-Al-C(26) 113.07(8)
1.337(2)
99.18(6)
N(1)-C(1)
N(1)-Al-C(25)
N(3)-Al-C(25)
C(25)-Al-C(26) 111.66(9)
Scheme 2. Numbered Schematic of the Ligand Backbone in 11-14
Al-N(3) linkage (with the adjacent sulfur), one of the closer
being (N,N′,N"-tri-tert-butyl-methanesulfonodi-imidamide-
N,N′)-dimethylaluminum where the Al-N distances in the
two independent molecules range between 1.903 and 1.916
Å.59
Figure 5. Molecular structure of 14.
Table 5. Selected Bond Lengths (Å) and Angles (deg) for 14
Mg(1)-N(1)
Mg(1)-N(31)
Mg(2)-N(3)
Mg(2)-N(63)
N(1)-S(2)
2.035(2) Mg(1)-N(5)
2.055(2) Mg(1)-N(33)
2.162(2) Mg(2)-N(61)
2.114(2) Mg(2)-N(90)
1.605(2) S(2)-N(3)
2.117(2)
2.064(2)
2.103(2)
2.020(2)
1.662(2)
1.307(3)
1.668(2)
1.282(3)
1.675(2)
1.285(3)
1.708(2)
123.75(10)
131.06(10)
71.90(9)
100.68(9)
The pattern of bonding in the ligand backbone shows a
couple of interesting features (Table 6). Using the numbering
system illustrated in Scheme 2, compared to the free ligand
11, the N1-S2 linkage in 13 has contracted slightly [1.6242-
(15) cf. 1.645(3) Å in 11], but unlike the zinc complex 12,
both N-S linkages are still the same (in the zinc complex,
N1-S2 was markedly shorter than S2-N3). The N3-C4
bond is also shorter than in 11 [1.337(2) Å cf. 1.380(4) and
1.383(4) Å in 11], a contraction that was also noticed in the
zinc species [1.3419(17) Å]. The imino linkage C4-N5 is
lengthened compared to the free ligand [1.329(2) Å cf. 1.289-
(4) and 1.291(4) Å in 11], a feature that was also seen, though
to a lesser extent, for the zinc complex [1.3161(16) Å]. The
2,6-diisopropylphenyl unit is oriented approximately or-
thogonally to the chelate ring, the N(1)-Ar torsion angle
being ca. 84°.
In an effort to prepare a magnesium amide complex, 11
was allowed to react with 2 equiv of KN(SiMe3)2 and 1 equiv
of MgI2. Evaporation of volatile components and extraction
into hexane followed by slow cooling of a saturated solution
yielded complex 14 as a crystalline solid. The X-ray analysis
revealed a 2:3 metal/ligand complex with three different
coordination modes (Figure 5). The S(2) ligand coordinates
to the Mg(1) center in an analogous manner to that seen in
both the zinc (12) and aluminum (13) complexes. The six-
membered chelate ring adopts a folded geometry, {Mg(1),N-
(3),C(4),N(5)} being coplanar to within ca. 0.05 Å with N(1)
and S(2) lying ca. 0.30 and 0.76 Å out of this plane in the
direction of the S-phenyl ring. Additionally, the S(2) ligand
bridges to the Mg(2) center via N(3) [the longest of all the
Mg-N contacts at 2.162(2) Å] and is thus overall tridentate.
By contrast, the S(32) and S(62) ligands, though bidentate,
N(3)-C(4)
1.370(3) C(4)-N(5)
N(31)-S(32)
N(33)-C(34)
N(61)-S(62)
N(63)-C(64)
N(90)-Si(91)
N(1)-Mg(1)-N(5)
1.619(2) S(32)-N(33)
1.379(3) C(34)-N(35)
1.623(2) S(62)-N(63)
1.377(3) C(64)-N(65)
1.713(2) N(90)-Si(95)
95.64(9) N(1)-Mg(1)-N(31)
N(1)-Mg(1)-N(33) 119.52(10) N(5)-Mg(1)-N(31)
N(5)-Mg(1)-N(33) 115.54(9) N(31)-Mg(1)-N(33)
N(3)-Mg(2)-N(61) 113.99(9) N(3)-Mg(2)-N(63)
N(3)-Mg(2)-N(90) 115.62(9) N(61)-Mg(2)- N(63) 70.68(9)
N(61)-Mg(2)-N(90) 122.42(9) N(63)-Mg(2)-N(90) 124.42(10)
coordinate using the N1 and N3 nitrogens to form four-
membered N2SMg chelate rings. The four-membered chelate
ring formed by the S(32) ligand is coplanar to within ca.
0.01 Å, while that formed by the S(62) ligand is folded with
Mg(2) lying ca. 0.24 Å out of the {N(61),S(62),N(63)} plane.
For each of the three ligands, the 2,6-diisopropylphenyl unit
is oriented approximately orthogonally to the chelate ring,
the N(5)-Ar, N(35)-Ar, and N(65)-Ar torsion angles being
ca. 86°, 77°, and 75°, respectively. The geometry at the Mg-
(1) center is severely distorted from ideal tetrahedral (Table
5), the angles subtended at the metal center ranging between
71.90(9)° and 131.06(10)° [the most acute angle is, unsur-
prisingly, associated with the bite of the four-membered
chelate ring]. The coordination geometry at Mg(2) is also
distorted from ideal tetrahedral, but to a slightly lesser extent,
the X-Mg(2)-Y angles being in the range 70.68(9)-
124.42(10)° [again the most acute angle is associated with
the bite of the four-membered chelate ring].
The Mg-N distances within the two four-membered
chelate rings are 2.055(2) and 2.064(2) Å for the S(32) ligand
to Mg(1) and 2.103(3) and 2.114(2) Å for the S(62) ligand
to Mg(2). In each case, these are symmetric, with those to
Mg(2) noticeably longer than their counterparts to Mg(1);
the reason for this lengthening at Mg(2) is not immediately
apparent, though it may be associated with the steric bulk
of the adjacent trimethylsilyl moieties. The distances at Mg-
(1) are similar to those seen in related four-membered bis-
(N,N′) magnesium complexes.60-64 By contrast, the Mg-N
(56) Kanters, J. A.; Van Mier, G. P. M.; Nijs, R. L. L. M.; Van der Steen,
F.; Van Koten, G. Acta Crystallogr. C: Cryst. Struct. Commun. 1988,
C44, 1391.
(57) Liang, L.-C.; Yang, C.-W.; Chiang, M. Y.; Hung, C.-H.; Lee, P.-Y.
J. Organomet. Chem. 2003, 679, 135.
(58) Liu, X.; Gao, W.; Mu, Y.; Li, G.; Ye, L.; Xia, H.; Ren, Y.; Feng, S.
Organometallics 2005, 24, 1614.
(59) Walfort, B.; Leedham, A. P.; Russell, C. A.; Stalke, D. Inorg. Chem.
2001, 40, 5668.
Inorganic Chemistry, Vol. 45, No. 8, 2006 3357

Barrett et al.
Table 6. Comparative Bond Lengths (Å) and Torsion Angles (deg) for the Ligand Backbone in the Structures of 11, 12, 13, and 14a
11
A
11
B
12
13
14b
Bond Lengths
N1-S2
S2-N3
N3-C4
C4-N5
1.644(3)
1.640(3)
1.383(4)
1.291(4)
1.645(3)
1.631(3)
1.380(4)
1.289(4)
1.6198(12)
1.6390(11)
1.3419(17)
1.3161(16)
1.6242(15)
1.6297(14)
1.337(2)
1.605(2)
1.662(2)
1.370(3)
1.307(3)
1.619(2)
1.668(2)
1.379(3)
1.282(3)
1.623(2)
1.675(2)
1.377(3)
1.285(3)
1.329(2)
Torsion Angles
C-N1-S2-N3
N1-S2-N3-C4
S2-N3-C4-N5
N3-C4-N5-C
94.7
100.8
-100.2
-131.1
-125.1
166.0
147.8
-167.3
-9.9
-145.5
-20.4
174.7
-158.7
-14.1
173.6
-42.7
6.5
-45.4
21.7
-50.4
22.0
-165.4
-7.6
-179.6
-178.2
-175.2
171.7
176.9
a Atom numbering from Scheme 2. b The three columns for structure 14 are for the three separate ligands in the structure, based around S(2), S(32), and
S(62), respectively.
distances between the S(2) ligand and Mg(1) [2.035(2) and
2.117(2) Å] are asymmetric, showing the difference between
the two nitrogen donors.
tion modes between complexes 12 and 14 may be attributed
to the relative hardness/softness of the Zn and Mg centers.
The harder magnesium dication appears to prefer a higher
coordination number (four) and so switches the more
sterically encumbered six-membered coordination mode of
ligand 11 to its four-membered chelate in order to reduce
the steric environment around the metal, thus allowing for
further coordination.
The pattern of bonding in the backbones of all three
ligands is roughly similar (Table 6) though two differences
are noticeable; for the S(2) ligand, the N1-S2 distance is
slightly shorter than in the other two [1.605(2) Å cf. 1.619-
(2) and 1.623(2) Å] and the C4-N5 separation is slightly
longer [1.307(3) cf. 1.282(3) and 1.285(3) Å]. The N1-S2
distances are all shorter than seen in the free ligand (11) [as
was the case for the zinc (12) and aluminum (13) species],
and presumably the relative lengthening of this bond in the
S(32) and S(62) ligands is a consequence of the increased
steric congestion of the four-membered chelate rings. In all
three ligands, the N1-S2 bond lengths are significantly
shorter than the S2-N3 distances. For the C4-N5 bond
length, that for the S(2) ligand resembles those seen in the
zinc (12) and aluminum (13) species, which have very similar
coordination modes, whereas those for the S(32) and S(62)
ligands resemble the distances seen for the two independent
molecules in the structure of the free ligand (11). This is
not surprising given that the coordination modes of the S(32)
and S(62) ligands do not make use of the N5 nitrogen. The
N3-C4 distances in all three ligands are similar to those in
the free ligand (11).
We have also observed an analogous homoleptic zinc
complex L2Zn where both six-membered and four-membered
chelates were present (see the Supporting Information). The
preference of the mixed chelation modes over the expected
double six-membered chelate is attributed to the steric bulk
around the metal center. By switching to the four-membered
coordination mode, the bulky 2,6-diisopropylaniline can
reposition further from the metal, thus releasing some steric
strain from the metal center. The difference in the coordina-
Conclusions
A novel chiral imino sulfinamidine ligand LH (11) has
been synthesized from readily available reagents. The ligand
was employed in the synthesis of mononuclear Zn(II) and
Al(III) alkyl complexes, which were structurally character-
ized by X-ray crystallography. Complexes 12 and 13
contained L binding in a bidentate fashion through a six-
membered chelate, potentially placing the metal within a
highly chiral environment. Further coordination modes of
11 were observed in the binuclear Mg(II) complex 14 in
which three molecules bound as bi- and tridentate ligands
through both six-membered and four-membered chelates in
a novel homoleptic/heteroleptic amide complex. Further
investigation into complexes of other metals and the different
coordination modes of ligand 11 is now in progress.
Acknowledgment. We thank GlaxoSmithKline for the
generous endowment (to A.G.M.B.), the Royal Society and
the Wolfson Foundation for a Royal Society Wolfson
Research Merit Award (to A.G.M.B.), the Wolfson Founda-
tion for establishing the Wolfson Centre for Organic
Chemistry in Medical Sciences at Imperial College London,
the Royal Society for a University Research Fellowship
(M.S.H.), and the Engineering and Physical Sciences Re-
search Council and GlaxoSmithKline for generous support
of our studies.
Supporting Information Available: X-ray structure determi-
nation and details of the crystallographic data as CIF files, including
additional structures of (LH‚LiI‚thf)2 and L2Zn. This material is
available free of charge via the Internet at http://pubs.acs.org.
(60) Fleischer, R.; Stalke, D. Inorg. Chem. 1997, 36, 2413.
(61) Fleischer, R.; Stalke, D. J. Organomet. Chem. 1998, 550, 173.
(62) Schmidt, J. A. R.; Arnold, J. J. Chem. Soc, Dalton Trans. 2002, 2890.
(63) Xia, A.; El-Kaderi, H. M.; Heeg, M. J.; Winter, C. H. J. Organomet.
Chem. 2003, 682, 224.
(64) Boere, R. T.; Cole, M. L.; Junk, P. C. New J. Chem. 2005, 29, 128.
IC052104M
3358 Inorganic Chemistry, Vol. 45, No. 8, 2006