A new family of chiral chelating diamines with transition-metal stereocenters: Synthesis, structure, and reactivity of the enantiomerically pure dirhenium-substituted 1,2-diamine. See abstract

Article abstract of DOI:10.1021/om010153a

Reaction of enantiopure (S)-(η⁵-C₅H₅)Re(NO)(PPh₃) (CH₃) ((S)-1) with Ph₃C⁺ BF₄^- (1 equiv) and then the N,N′-dimethyl 1,2-diamine HN(CH₃)CH₂CH₂(H₃C)NH (0.5 equiv) gives the diammonium salt (S_ReS_Re)-[(η⁵-C₅H₅)Re (NO)(PPh₃) (CH₂NH(CH₃)CH₂CH₂(H₃C)HNC H₂)(Ph₃P)(ON)Re (η⁵-C₅H₅)]²⁺ (BF₄^-)₂ (94%) as a mixture of Re/N configurational diastereomers. Reaction with t-BuOK yields the title compound (S_ReS_Re)-4 (66%) as an air-stable orange powder. Reaction with (PhCN)₂PdCl₂ gives a single diastereomer of a chelate complex, (S_ReR_NR_NS_Re)-[(η⁵- C₅H₅)Re(NO)(PPh₃) (CH₂N(CH₃)CH₂CH₂(H₃C) NCH₂)(Ph₃P)(ON)Re(η⁵- C₅H₅)]PdCl₂ (80%), the configuration and approximate C₂ symmetry of which has been established crystallographically. Racemic 1, Ph₃C⁺BF₄^- (1 equiv), and the N,N′-dimethyl 1,2-diamine HN(CH₂CH₃)CH₂CH₂(H₃ CCH₂)NH (1 equiv) give [(η⁵-C₅H₅)Re(NO)(PPh₃) (CH₂NH(CH₂CH₃) CH₂CH₂NH(CH₂CH₃))]⁺ BF₄^-, and the crystal structure of the S_ReS_N,R_ReR_N diastereomer is determined. The ReCH₂N conformations of the preceding compounds, and their influence upon the diastereoselectivities, are analyzed in detail.

Full text of DOI:10.1021/om010153a

Organometallics 2001, 20, 3087-3096
3087
A New F a m ily of Ch ir a l Ch ela tin g Dia m in es w ith
Tr a n sition -Meta l Ster eocen ter s: Syn th esis, Str u ctu r e,
a n d Rea ctivity of th e En a n tiom er ica lly P u r e
Dir h en iu m -Su bstitu ted 1,2-Dia m in e (η5-C5H5)Re(NO)-
(P P h 3)(CH2N(CH3)CH2CH2(H3C)NCH2)(P h 3P )(ON)Re(η5-C5H5)
Luke J . Alvey,1a Olivier Delacroix,1b Carsten Wallner,1b Oliver Meyer,1a
Frank Hampel,1b Slawomir Szafert,1a,c Tadeusz Lis,1c and J . A. Gladysz*,1a,b
Department of Chemistry, University of Utah, Salt Lake City, Utah 84112,
Institut fu¨r Organische Chemie, Friedrich-Alexander Universita¨t Erlangen-Nu¨rnberg,
Henkestrasse 42, 91054 Erlangen, Germany, and Department of Chemistry,
University of Wrocław, F. J oliot-Curie 14, 50-383 Wrocław, Poland
Received February 26, 2001
-
Reaction of enantiopure (S)-(η5-C5H5)Re(NO)(PPh3)(CH3) ((S)-1) with Ph3C+BF4
(1 equiv) and then the N,N′-dimethyl 1,2-diamine HN(CH3)CH2CH2(H3C)NH (0.5 equiv)
gives the diammonium salt (SReSRe)-[(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH3)CH2CH2-
-
(H3C)HNCH2)(Ph3P)(ON)Re(η5-C5H5)]2+(BF4
)
(94%) as a mixture of Re/N config-
urational diastereomers. Reaction with t-BuOK yields the title compound (SReSRe)-4
2
(66%) as an air-stable orange powder. Reaction with (PhCN)2PdCl2 gives
a
single diastereomer of a chelate complex, (SReRNRNSRe)-[(η5-C5H5)Re(NO)(PPh3)-
(CH2N(CH3)CH2CH2(H3C)NCH2)(Ph3P)(ON)Re(η5-C5H5)]PdCl2 (80%), the configuration and
approximate C2 symmetry of which has been established crystallographically. Racemic 1,
-
Ph3C+BF4 (1 equiv), and the N,N′-dimethyl 1,2-diamine HN(CH2CH3)CH2CH2(H3CCH2)-
-
NH (1 equiv) give [(η5-C5H5)Re(NO)(PPh3)(CH2NH(CH2CH3)CH2CH2NH(CH2CH3))]+BF4
,
and the crystal structure of the SReSN,RReRN diastereomer is determined. The ReCH2N
conformations of the preceding compounds, and their influence upon the diastereoselectivities,
are analyzed in detail.
In tr od u ction
tioselective synthesis, research teams are reaching into
nearly every corner of the natural and unnatural chiral
pools for new-generation systems.6
For example, the use of metal catalysts containing
ferrocene-based chelate ligands with planar and/or other
chirality elements has grown rapidly over the past
decade.7 These systems have proven highly effective,
practical, and robust. Thus, chiral diamines with fer-
rocenyl units are receiving increasing attention.8,9 This
Chiral 1,2-diamines see extensive use in enantio-
selective organic synthesis and catalysis.2 They serve
as building blocks for recoverable chiral auxiliaries2,3
and as ligands in metal catalysis.2,4 They are further
employed in the resolution of enantiomers2 and as
components of chiral NMR shift reagents.5 Despite their
many successful applications, the search continues for
chiral 1,2-diamines with improved performance char-
acteristics. As is typical throughout the field of enan-
(5) (a) Kido, J .; Okamoto, Y.; Brittain, H. G. J . Org. Chem. 1991,
56, 1412. (b) Devitt, P. G.; Mitchell, M. C.; Weetman, J . M.; Taylor, R.
J .; Kee, T. P. Tetrahedron: Asymmetry 1995, 6, 2039. (c) Hulst, R.;
Koen de Vries, N.; Feringa, B. L. Tetrahedron: Asymmetry 1994, 5,
699.
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C. A.; Campbell, S.; Dong, Y.; Grossbach, D.; Ridges, M.; Smith, L.;
Spinelli, E. J . Org. Chem. 2000, 65, 4753. (b) Rivas, F. M.; Riaz, U.;
Diver, S. T. Tetrahedron: Asymmetry 2000, 11, 1703. (c) Roland, S.;
Mangeney, P. Eur. J . Org. Chem. 2000, 611. (d) Alexakis, A.; To-
massini, A.; Chouillet, C.; Roland, S.; Mangeney, P.; Bernardinelli, G.
Angew. Chem., Int. Ed. 2000, 39, 4093; Angew. Chem. 2000, 112, 4259.
(e) Yamauchi, T.; Higashiyama, K.; Kubo, H.; Ohmiya, S. Tetra-
hedron: Asymmetry 2000, 11, 3003. (f) Mitchell, J . M.; Finney, N. S.
Tetrahedron Lett. 2000, 41, 8431. (g) Martelli, G.; Morri, S.; Savoia,
D. Tetrahedron 2000, 56, 8367. (h) Markidis, T.; Kokotos, G. J . Org.
Chem. 2001, 66, 1919.
(1) (a) University of Utah. (b) Universita¨t Erlangen-Nu¨rnberg
(permanent address of corresponding author). (c) University of
Wrocław.
(2) Recent reviews: (a) Fache, F.; Schulz, E.; Tommasino, M. L.;
Lemaire, M. Chem. Rev. 2000, 100, 2159. (b) Lucet, D.; Le Gall, T.;
Mioskowski, C. Angew. Chem., Int. Ed. 1998, 37, 2580; Angew. Chem.
1998, 110, 2724.
(3) Additional lead references from the year 2000: (a) Li, X.;
Schenkel, L. B.; Kozlowski, M. C. Org. Lett. 2000, 2, 875. (b) Wiberg,
K. B.; Bailey, W. F. Tetrahedron Lett. 2000, 41, 9365. (c) Barrett, S.;
O’Brien, P.; Steffens, H. C.; Towers, T. D.; Voith, M. Tetrahedron 2000,
56, 9633.
(4) Additional lead references from the years 1999-2001: (a)
Mimoun, H.; de Saint Laumer, J . Y.; Giannini, L.; Scopelliti, R.;
Floriani, C. J . Am. Chem. Soc. 1999, 121, 6158. (b) Noyori, R.; Ohkuma,
T. Angew. Chem., Int. Ed. 2001, 40, 40; Angew. Chem. 2001, 113, 41.
(c) Burk, M. J .; Hems, W.; Herzberg, D.; Malan, C.; Zanotti-Gerosa, A.
Org. Lett. 2000, 2, 4173. (d) Malkov, A. V.; Spoor, P.; Vinader, V.;
Kocovsky´, P. Tetrahedron Lett. 2001, 42, 509. (e) Catalysis not
requiring a metal: Leclerc, E.; Mangeney, P.; Henryon, V. Tetra-
hedron: Asymmetry 2000, 11, 3471.
(7) (a) Togni, A. Angew. Chem., Int. Ed. Engl. 1996, 35, 1475; Angew.
Chem. 1996, 108, 1581. (b) Richards, C. J .; Locke, A. J . Tetrahedron:
Asymmetry 1998, 9, 2377. (c) Togni, A.; Bieler, N.; Burckhardt, U.;
Ko¨llner, C.; Pioda, G.; Schneider, R.; Schnyder, A. Pure Appl. Chem.
1999, 71, 1531.
10.1021/om010153a CCC: $20.00 © 2001 American Chemical Society
Publication on Web 06/05/2001

3088 Organometallics, Vol. 20, No. 14, 2001
Alvey et al.
led us to speculate that chelate ligands that contain a
metal-based center of chiralityse.g., a nonplanar spec-
tator moiety of general formula M(A)(B)(C)(D)10smight
also provide efficient and perhaps superior stereo-
genesis. We recently detailed a long-term study of
diphosphines that contain such a chiral rhenium species
as part of the chelate backbone, as shown in A.11 These
rhenium substituent on each terminus and therefore
capable of C2 symmetry. A square-planar palladium
derivative is isolated and the crystal structure deter-
mined. Geometric features are carefully analyzed, par-
ticularly with respect to the high nitrogen diastereo-
selectivity that accompanies chelation. Supporting reac-
tions and model compounds are described, including a
crystallographically characterized 1:1 rhenium-diamine
adduct that establishes a higher Brønsted basicity for
methylenerhenium- vs proton-substituted amines.16
Resu lts
Dia m in e Syn th esis. Both enantiomers of the methyl
complex (η5-C5H5)Re(NO)(PPh3)(CH3) (1) can be ob-
tained in >99% ee from commercial Re2(CO)10 in a
routine series of steps.12 Reactions with trityl salts
Ph3C+X- give the methylidene complex [(η5-C5H5)Re-
(NO)(PPh3)(dCH2)]+X- (2+X-).17 The methylidene ligand
is electrophilic and is attacked by a variety of carbon,17-19
nitrogen,18 phosphorus,11b and sulfur15 nucleophiles. In
all cases investigated, this occurs with overall retention
at rhenium.11b,17a,19 Hence, the route to the title com-
pound in Scheme 1 was envisioned.
afforded excellent rhodium enantioselective hydrogena-
tion catalysts, and we sought to extend this concept to
other donor atoms and architectural motifs.
We wondered whether one could easily prepare 1,2-
diamines that contain chiral-at-metal fragments as part
of the nonchelating, N-alkyl substituentssfor example,
a LnMCH2NRCH2CH2NR′R′′ species or a symmetrically
substituted analogue such as B. The latter features the
18-valence-electron rhenium fragment (η5-C5H5)Re(NO)-
(PPh3), for which many derivatives are readily available
in enantiomerically pure form.12,13 Only alkoxide and
amide adducts are configurationally labile (the mecha-
nistic basis for which is known in detail).14 Therefore,
a methylene or similar spacer group between the
rhenium and diamine nitrogen is desirable. It has
furthermore been shown that the â-thio-substituted
complex (η5-C5H5)Re(NO)(PPh3)(CH2SCH3) is a much
stronger Lewis base than its organic counterpart
CH3SCH3.15 Hence, we expected that similar â-amino
rhenium species would give thermodynamically stronger
metal-nitrogen bonds.
Accordingly, (S)-120,21 and Ph3C+BF4- were combined
in CH2Cl2 at -80 °C to generate (S)-2+BF4-. Then 0.5
equiv of the inexpensive disecondary N,N′-dimethyl 1,2-
diamine HN(CH3)CH2CH2(H3C)NH was added. Workup
gave the ditertiary diammonium salt (SReSRe)-[(η5-
C5H5)Re(NO)(PPh3)(CH2NH(CH3)CH2CH2(H3C)HNCH2)-
(Ph3P)(ON)Re(η5-C5H5)]2+(BF4-)2 ((SReSRe)-32+(BF4-)2)
in 94% yield after crystallization as an air-stable bright
yellow powder. The complex (SReSRe)-32+(BF4-)2, and all
new compounds below, were characterized by microanal-
ysis and IR and NMR (1H, 13C, 31P) spectroscopy. Data
are summarized in the Experimental Section.
-
The diprotonated diamine (SReSRe)-32+(BF4
) con-
2
tains two rhenium and two nitrogen stereocenters. The
former are set by the precursor (S)-1. The trivalent
nitrogen atoms of the precursor diamine are of course
rapidly inverting, thereby interconverting meso and rac
In this paper, we report the efficient synthesis of such
a chelating diamine, featuring a methyl and a methylene-
diastereomers. In the absence of a kinetic or thermo-
-
dynamic resolution, three diastereomers of 32+(BF4
)
2
(8) (a) Spescha, M.; Duffy, N. W.; Robinson, B. H.; Simpson, J .
Organometallics 1994, 13, 4895. (b) Crameri, Y.; Foricher, J .; Scalone,
M.; Schmid, R. Tetrahedron: Asymmetry 1997, 8, 3617. (c) Woltersdorf,
M.; Kranich, R.; Schmalz, H.-G. Tetrahedron 1997, 53, 7219. (d)
Schwink, L.; Knochel, P. Chem. Eur. J . 1998, 4, 950. (e) Schwink, L.;
Ireland, T.; Pu¨ntener, K.; Knochel, P. Tetrahedron: Asymmetry 1998,
9, 1143. (f) Song, J .-H.; Cho, D.-J .; J eon, S.-J .; Kim, Y.-H.; Kim, T.-J .;
J eong, J .-H. Inorg. Chem. 1999, 38, 893. (g) Delacroix, O.; Picart-
Goetgheluck, S.; Maciejewski, L.; Brocard, J .; Nowogrocki, G. Synlett
2001, 29.
would be expected: SReSNSNSRe, SReSNRNSRe (which is
(16) (a) Some of this work is taken from: Alvey, L. J . Ph.D. Thesis,
University of Utah, 1999. (b) See also: Wallner, C. Diplom Thesis,
University of Erlangen-Nu¨rnberg, 1999.
(17) (a) Merrifield, J . H.; Strouse, C. E.; Gladysz, J . A. Organo-
metallics 1982, 1, 1204. (b) Merrifield, J . H.; Lin, G.-Y.; Kiel, W. A.;
Gladysz, J . A. J . Am. Chem. Soc. 1983, 105, 5811.
(9) (a) Lo, M. M.-C.; Fu, G. C. J . Am. Chem. Soc. 1998, 120, 10270.
(b) Rios, R.; Liang, J .; Lo, M. M.-C.; Fu, G. C. J . Chem. Soc., Chem.
Commun. 2000, 377. (c) Related studies with monoamines: Fu, G. C.
Acc. Chem. Res. 2000, 33, 412.
(10) Brunner, H. Angew. Chem., Int. Ed. 1999, 38, 1194; Angew.
Chem. 1999, 111, 1248.
(11) (a) Zwick, B. D.; Arif, A. M.; Patton, A. T.; Gladysz, J . A. Angew.
Chem., Int. Ed. Engl. 1987, 26, 910; Angew. Chem. 1987, 99, 921. (b)
Kromm, K.; Zwick, B. D.; Meyer, O.; Hampel, F.; Gladysz, J . A. Chem.
Eur. J . 2001, 7, 2015.
(12) Agbossou, F.; O’Connor, E. J .; Garner, C. M.; Quiro´s Me´ndez,
N.; Ferna´ndez, J . M.; Patton, A. T.; Ramsden, J . A.; Gladysz, J . A.
Inorg. Synth. 1992, 29, 211.
(13) (a) Dewey, M. A.; Stark, G. A.; Gladysz, J . A. Organometallics
1996, 15, 4798 and references therein. (b) Saura-Llamas, I.; Gladysz,
J . A. J . Am. Chem. Soc. 1992, 114, 2136.
(14) Dewey, M. A.; Zhou, Y.; Liu, Y.; Gladysz, J . A. Organometallics
1993, 12, 3924.
(15) McCormick, F. B.; Gleason, W. B.; Zhao, X.; Heah, P. C.;
Gladysz, J . A. Organometallics 1986, 5, 1778.
(18) Tam, W.; Lin, G.-Y.; Wong, W.-K.; Kiel, W. A.; Wong, V. K.;
Gladysz, J . A. J . Am. Chem. Soc. 1982, 104, 141.
(19) O’Connor, E. J .; Kobayashi, M.; Floss, H. G.; Gladysz, J . A. J .
Am. Chem. Soc. 1987, 109, 4837.
(20) The absolute configurations at rhenium are assigned according
to a modified Cahn-Ingold-Prelog priority rule. The cyclopentadienyl
ligand is considered a pseudoatom of atomic number 30. This gives
the following sequence: η5-C5H5 > PPh3 > NO > CH2N > CH3. See:
Sloan, T. E. Top. Stereochem. 1981, 12, 1.
(21) The nonracemic complexes in this study were first synthesized
with a rhenium configuration opposite to that used in most previous
studies. Although both enantiomers were eventually prepared, all
characterization data are from the former series. To facilitate com-
parisons and analyses, the abstract, Results, and Discussion sections
are narrated from the standpoint of the latter (customary) series
(including schemes and figures). The compound configurations in the
Experimental Section correspond to the work as it was actually
conducted. One consequence deserves emphasis: the structures in
Figures 1 and 2 are the enantiomers of those crystallographically
determined.

Diamines with Transition-Metal Stereocenters
Organometallics, Vol. 20, No. 14, 2001 3089
signals (δ 4.18, br d, 2J HH ) 11.7 Hz; δ 3.74, dd, 2J HH
)
Sch em e 1. Syn th esis of a Dir h en iu m -Su bstitu ted
1,2-Dia m in e
3
11.7, J HP ) 7.2 Hz). The chemical shift/coupling
constant pattern (downfield proton with near-zero 3J HP
3
value, upfield proton with larger J HP value) differed
from that of most neutral and cationic complexes with
Re-CH2X linkages.23 However, exceptions are known,
especially when X is a nitrogen or oxygen atom (e.g.,
pyridine or methoxide adducts).18
P a lla d iu m Ch ela te. We next sought to prepare a
chelate derivative of (SReSRe)-4, preferably of a metal
fragment used extensively in catalysis. A dichloro-
palladium adduct of TMEDA has been reported,24 as
well as many related compounds.25 Note that chelation
gives tetravalent nitrogen stereocenters that, in the
absence of dissociation, will have high inversion barri-
ers. As shown in Scheme 2, three rhenium/nitrogen
diastereomers are possible. On the basis of both pre-
parative26,27 and computational28 precedent, we expected
to find the bulky rhenium moieties on opposite sides of
the square-planar palladium. Not so obvious to every
casual reader is that two diastereomers fit this criterion
(SReRNRNSRe and SReSNSNSRe).
The diamine (SReSRe)-4 and (PhCN)2PdCl2 were com-
bined in THF (Scheme 2). A precipitative workup gave
the target chelate 5 in 80% yield as an air-stable orange
powder.21 Only one 31P NMR signal (δ 24.8) and one
cyclopentadienyl 1H NMR signal (δ 5.06) were observed,
even in spectra recorded at -90 °C, suggesting very high
diastereomeric purity. The ReCH2 protons gave 1H NMR
signals with the more usual chemical shift/coupling
constant pattern (see above; δ 4.92, dd, 2J HH ) 12.3, 3J HP
2
) 11.4 Hz; δ 4.78, d, J HH ) 12.3 Hz). The IR spectrum
showed a strong νNO band (1636 cm-1), and in accord
with precedent for palladium and other metal chelates,
the :NCH3-based νCH band present for (SReSRe)-4 had
disappeared.24
Orange prisms of a CHCl3 trisolvate were grown, and
X-ray data were obtained as outlined in Table 1.
Refinement, described in the Experimental Section,
showed that the SReRNRNSRe diastereomer had formed.21
An ORTEP drawing is given in Figure 1, and selected
bond lengths, bond angles, and torsion angles are listed
in Table 2. The unit cell was gigantic, especially in
identical with SReRNSNSRe), and SReRNRNSRe. Accord-
ingly, 31P NMR spectra showed three signals (CD3CN,
δ 22.6, 22.1, 21.9; ca. 31:32:37), and 1H NMR spectra
showed four cyclopentadienyl signals (CD3CN, δ 5.31,
5.30, 5.28, 5.23; ca. 32:10:30:28). No attempt was made
to deconvolute or assign these resonances.
-
(22) (a) Braunholtz, J . T.; Ebsworth, E. A. V.; Mann, F. G.; Sheppard,
N. J . Chem. Soc. 1958, 2780. (b) Baldwin, D. A.; Leigh, G. J . J . Chem.
Soc. A 1968, 1431.
(23) (a) Georgiou, S.; Gladysz, J . A. Tetrahedron 1986, 42, 1109. (b)
Davies, S. G.; Dordor-Hedgecock, I. M.; Sutton, K. H.; Whittaker, M.
J . Am. Chem. Soc. 1987, 109, 5711.
As depicted in Scheme 1, (SReSRe)-32+(BF4
) and
2
t-BuOK (2 equiv) were combined in THF. Workup gave
the target diamine (SReSRe)-(η5-C5H5)Re(NO)(PPh3)-
(CH 2N(CH 3)CH 2CH 2(H 3C)NCH 2)(P h 3P )(ON)Re(η5-
C5H5) ((SReSRe)-4) in 66% yield as an air-stable orange
powder.21 This compound can be regarded as a di-
rhenium derivative of tetramethylethylenediamine (a
dirhena-TMEDA). Since the nitrogen stereocenters are
again trivalent, rapid inversion would be expected.
Accordingly, only one 31P NMR signal (δ 26.8) and one
cyclopentadienyl 1H NMR signal (δ 4.98) were observed,
even in spectra recorded at -80 °C. In solution, (SReSRe)-4
gradually decomposed over a period of several weeks.
The IR spectrum of (SReSRe)-4 showed a strong νNO band
(24) Mann, F. G.; Watson, H. R. J . Chem. Soc. 1958, 2772.
(25) (a) Abu-Surrah, A. S.; Fawzi, R.; Steimann, M.; Rieger, B. J .
Organomet. Chem. 1996, 512, 243. (b) Robinson, D. J .; Kennard, C. H.
L. J . Chem. Soc. A 1970, 1008. (c) Haszeldine, R. N.; Young, J . C. Proc.
Chem. Soc., London 1959, 394. (d) Iball, J .; MacDougall, M.; Scrim-
geour, S. Acta Crystallogr. 1975, B31, 1672. (e) Ito, T.; Marumo, F.;
Saito, Y. Acta Crystallogr. 1971, B27, 1695. (f) de Graaf, W.; Boersma,
J .; Smeets, W. J . J .; Spek, A. L.; van Koten, G. Organometallics 1989,
8, 2907.
(26) Lead references to a research team with many relevant papers
on group 10-11 1,2-diamine complexes: (a) De Renzi, A.; Di Blasio,
B.; Saporito, A.; Scalone, M.; Vitagliano, A. Inorg. Chem. 1980, 19,
960. (b) Albano, V. G.; Demartin, F.; De Renzi, A.; Morelli, G. Inorg.
Chim. Acta 1988, 149, 253. (c) Cucciolito, M. E.; J ama, M. A.; Giordano,
F.; Vitagliano, A.; De Felice, V. Organometallics 1995, 14, 1152. (d)
Cavallo, L.; Cucciolito, M. E.; De Martino, A.; Giordano, F.; Orabona,
I.; Vitagliano, A. Chem. Eur. J . 2000, 6, 1127.
at slightly lower frequency than that of (SReSRe)-
(27) (a) Becker, J . J .; White, P. S.; Gagne´, M. R. Inorg. Chem. 1999,
38, 798. (b) Zhang, X.; Zhu, Q.; Guzei, I. A.; J ordan, R. F. J . Am. Chem.
Soc. 2000, 122, 8093.
(28) Bernard, M.; Delbecq, F.; Sautet, P.; Fache, F.; Lemaire, M.
Organometallics 2000, 19, 5715.
-
3
2+(BF4
)
2
(1630 vs 1647 cm-1) and a broad, weak
:NCH3-derived νCH band (2774 cm-1).22 As expected, the
diastereotopic ReCH2 protons gave separate 1H NMR

3090 Organometallics, Vol. 20, No. 14, 2001
Sch em e 2. F or m a tion of a P a lla d iu m Ch ela te of (SReSRe)-4: P ossible Dia ster eom er s
Alvey et al.
comparison to those of the >100 existing crystal struc-
tures of chiral rhenium complexes: eight molecules of
(SReRNRNSRe)-5 and 24 of CHCl3. This complicated the
refinement, and consequently, the esd values associated
with the metrical parameters are greater than normal.
Nonetheless, the data unequivocally establish structure,
relative and absolute configurations, and conformation.
The most striking feature of Figure 1 is the ap-
proximate C2 symmetry axis passing through palladium.
Neglecting minor differences in bond lengths and angles,
this exchanges the two chlorine atoms, the amine
nitrogen atoms, the chelate carbon atoms, and rhenium
moieties. Both nitrogen stereocenters adopt R configu-
rations in response to rhenium stereocenters of S
configuration. As with other 1,2-diamine chelates, the
five-membered ring is puckered (a λ or left-hand helical
conformation in Figure 1),29 with the C3-C30 bond at
a -63.1° angle to the N1-Pd-N2 plane. The PdCl2 bond
lengths and angles (2.299(7)/2.334(8) Å, 90.2(3)°) are
very close to those of three other crystallographically
characterized 1,2-diamine adducts (2.283(1)-2.30(1) Å,
91.47(4)-90.7(3)°).25a-c The Pd-N bond lengths and
angles (2.06(2)/2.07(2) Å; 85.9(9)°) are also very close
(2.082(3)-2.09(2) Å, 85.70(12)-85.1(9)°).
PPh3 ligand, as quantified by a P-Re-C-N torsion
angle of 142(2)° (at Re2, 147(5)°). Analogous solid-state
conformations are found for all other complexes of the
formula [(η5-C5H5)Re(NO)(PPh3)(CH2X)]n+(X′-)n.11b,15,30
This directs the X group into the least congested
interstice, between the smaller nitrosyl and cyclo-
pentadienyl ligands.23 The deviation from an idealized
anti P-Re-C-X conformation renders one dia-
stereotopic ReCH2 proton roughly orthogonal to phos-
phorus (occupying the interstice between the cyclopen-
tadienyl and PPh3 ligands) and the other syn. Experi-
ments have established a Karplus-type 3J HP relationship,
1
such that the H NMR signal with the smaller coupling
can be assigned to the “orthogonal” proton.23
A number of complexes are known in which the atom
â to rhenium bears three sterically differentiated sub-
stituents (L/M/S). The conformations about the ReCH2-
X(L)(M)(S)30b-c or ReD-C(L)(M)(S)13,31 linkages have
also been analyzed (D ) non-carbon ligating atom).
Typically, the largest group (L) exhibits a torsion angle
near 180°, such that the Re-C and X-L or Re-D and
C-L bonds are roughly anti to each other. This feature
is evident in (SReRNRNSRe)-5, which has a large â-pal-
ladium moiety and Re-C-N-Pd torsion angles of
165.8(11)/158.9(13)°. As illustrated by the stylized rep-
resentation C in Figure 2, these torsion angle relation-
Figure 2 shows a Newman-type projection of (SReRN
-
RNSRe)-5 down the C1-Re1 bond.21 The rhenium is
formally octahedral, as analyzed in many previous
papers. The chelate nitrogen is roughly anti to the bulky
(30) (a) Merrifield, J . H.; Strouse, C. E.; Gladysz, J . A. Organo-
metallics 1982, 1, 1204. (b) Meyer, O.; Arif, A. M.; Gladysz, J . A.
Organometallics 1995, 14, 1844. (c) Peng, T.-S.; Arif, A. M.; Gladysz,
J . A. J . Chem. Soc., Dalton Trans. 1995, 1857.
(31) Otto, M.; Boone, B. J .; Arif, A. M.; Gladysz, J . A. J . Chem. Soc.,
Dalton Trans. 2001, 1218.
(29) House, D. A. In Comprehensive Coordination Chemistry; Wilkin-
son, G.; Gillard, R. D.; McCleverty, J . A., Eds.; Pergamon Press:
Oxford, U.K., 1987; Vol. 2, p 23.

Diamines with Transition-Metal Stereocenters
Organometallics, Vol. 20, No. 14, 2001 3091
F igu r e 1. Molecular structure of (RReSNSNRRe)-5.21
Ta ble 1. Su m m a r y of Cr ysta llogr a p h ic Da ta
(SReRNRNSRe)-
5‚3CHCl3
(RReRN,SReSN)-
6+BF4-‚CH2Cl2
21
F igu r e 2. Partial views of the structure of (RReSNSNRRe)-
5.21
formula
C55H57Cl11
N4O2P2PdRe2
1736.74
-
C61H78 B2Cl2F8-
N6O2P2Re2
1606.15
173(2)
Nonius KappaCCD
triclinic
P1h
a
fw
Ta ble 2. Selected Bon d Len gth s (Å), Bon d An gles
(d eg), a n d Tor sion An gles (d eg) in
collecn temp (K)
diffractometer
cryst syst
space group
cell dimens
a, Å
b, Å
c, Å
V, Å3
85(2)
KUMA KM4
tetragonal
P41212
21
(SReRNRNSRe)-5‚3CHCl3
Pd-N1
Pd-Cl1
N1-C3
C3-C30
2.05(2)
2.303(7)
1.57(3)
1.44(3)
Pd-N2
Pd-Cl2
N2-C30
2.07(2)
2.337(7)
1.46(3)
20.096(4)
20.096(4)
33.398(17)
13 488(8)
8
9.45120(10)
13.8930(2)
26.6314(4)
3281.34(8)
2
Cl1-Pd-Cl2
N1-Pd-Cl1
N1-Pd-Cl2
C3-N1-Pd
C30-C3-N1
90.1(3)
91.8(7)
175.7(7)
105.0(15)
107(2)
N1-Pd-N2
N2-Pd-Cl2
N2-Pd-Cl1
C30-N2-Pd
C3-C30-N2
86.2(9)
92.1(6)
176.1(7)
104.4(16)
114(2)
Z
d
d
calcd, g/cm3
obsd, g/cm3 (CCl4/CH2I2,
22 °C)
1.711(1)
1.72
1.626
-
cryst dimens, mm
no. of rflns measd
range/indices (h, k, l)
0.35 × 0.20 × 0.20 0.20 × 0.10 × 0.10
Re1-C1
Re1-P1
Re1-N3
N3-O3
2.19(2)
2.325(7)
1.86(2)
1.07(2)
Re2-C10
Re2-P2
Re2-N4
N4-O4
2.17(3)
2.327(8)
1.70(2)
1.26(3)
9926
26 057
-12 to +12;
-18 to +18;
-30 to +34
1.54-27.49
15 034
9148
3.885
51.05
69.74
780
-15 to +15;
0-22;
0-34
2.27-23.05
7509
θ limit, deg
total no. of unique data
C1-Re1-P1
P1-Re1-N3
N3-Re1-C1
N1-C1-Re1
88.4(6)
90.9(7)
101.0(9)
123.8(17)
C10-Re2-P2
P2-Re2-N4
N4-Re2-C10
N2-C10-Re2
89.4(8)
92.2(8)
98.3(11)
119.0(19)
no. of obsd data, I > 2σ(I) 3954
abs coeff, mm-1
min transmissn, %
max transmissn, %
no. of variables
4.368
30.2
43.6
406
N1-C1
N1-C2
1.45(3)
1.52(3)
N2-C10
N2-C20
1.51(4)
1.49(3)
no. of restraints
0
21
C1-N1-Pd
C2-N1-Pd
C1-N1-C2
C1-N1-C3
C2-N1-C3
113.1(17)
106.5(15)
112.2(19)
109(2)
C10-N2-Pd
C20-N2-Pd
C10-N2-C20
C10-N2-C30
C20-N2-C30
109.5(17)
108.6(16)
115(2)
113(2)
106(2)
goodness of fit
1.030
0.1254
0.957
0.0644
2
Rint ) ∑|Fo
-
Fo2(mean)|/∑[Fo
]
2
R1 ) ∑||Fo| - |Fc||/∑|Fo|
0.1500; 0.0644a
0.1744; 0.1509a
0.1132; 0.0487a
0.1301; 0.1052a
wR2 ) (∑[w(Fo - Fc2)2]/
2
111(2)
∑[w(Fo2)2])1/2
N1-C3-C30-N2
-54.8(30)
∆F (max), e/Å3
1.381
1.787
N3-Re1-C1-N1
N4-Re2-C10-N2
P1-Re1-C1-N1
P2-Re2-C10-N2
Pd-N1-C1-Re1
Pd-N2-C10-Re2
C2-N1-C1-Re1
C20-N2-C10-Re2
C3-N1-C1-Re1
C30-N2-C10-Re2
51.8(21)
54.7(23)
a
All; observed.
142.2(20)
147.5(21)
165.8(11)
158.9(13)
45.0(28)
ships lead to a “W”-shaped conformational preference
for the P-Re-C-X-L or P-Re-D-C-L units. This will
play a key role in analyzing the diastereoselectivity of
chelate formation (see Discussion).
36.7(31)
Ot h er R ea ct ion s. The synthesis of (SReSRe)-
-77.6(23)
-86.2(24)
3
2+(BF4-)2 in Scheme 1 gives a mixture of diastereo-
mers. We wondered if other approaches might give more
enriched samples. Thus, (SReSRe)-32+(BF4
)
2
and tri-
NMR tube.21 The added base was expected to be weaker
-
ethylamine (0.3 equiv) were combined in CD3CN in an
than the diconjugate base (SReSRe)-4 but sufficiently

3092 Organometallics, Vol. 20, No. 14, 2001
Ta ble 3. Selected Bon d Len gth s (Å), Bon d An gles (d eg), a n d Tor sion An gles (d eg) in
Alvey et al.
a
(RReRN,SReSN)-6+BF 4-‚CH2Cl2
Re1-C50
Re1-P1
Re1-N1
N1-O1
2.160(6)/2.158(7)
2.3555(18)/2.354(2)
1.763(6)/1.743(6)
1.212(7)/1.214(7)
1.501(10)/1.509(11)
N2-C53
N2-C50
N2-C51
N3-C54
N3-C55
1.514(8)/1.473(9)
1.545(8)/1.538(9)
1.505(9)/1.504(10)
1.454(9)/1.472(10)
1.419(11)/1.429(9)
C53-C54
C50-Re1-P1
N1-Re1-P1
N1-Re1-C50
N2-C50-Re1
C50-N2-C51
88.99(18)/90.2(2)
91.27(19)/89.2(2)
98.4(3)/96.3(3)
115.6(4)/114.2(5)
111.1(5)/115.0(6)
C50-N2-C53
C54-C53-N2
C51-N2-C53
C53-C54-N3
C55-N3-C54
113.3(5)/112.9(6)
114.9(6)/110.4(6)
112.9(5)/112.8(6)
108.5(6)/107.8(7)
116.0(7)/113.6(7)
N1-Re1-C50-N2
P1-Re1-C50-N2
C51-N2-C50-Re1
C53-N2-C50-Re1
H2A-N2-C50-Re1
56.9(5)/66.9(5)
148.0(4)/156.1(5)
-88.3(6)/-71.7(7)
143.3(4)/157.0(5)
-26.1/-42.4
N2-C53-C54-N3
C50-N2-C53-C54
C51-N2-C53-C54
C50-N2-C51-C52
-171.8(6)/-48.8(9)
66.9(8)/-84.7(8)
-60.6(8)/142.9(8)
174.6(6)/-63.8(9)
a
The slash (/) separates data for the two independent cations.
Sch em e 3. Syn th esis of a 1:1 Rh en iu m
1,2-Dia m in e Ad d u ct
strong for proton exchange and diastereomer equilibra-
tion. Accordingly, the 31P NMR spectrum collapsed to
one broad signal, and the H NMR spectrum gave one
1
broad cyclopentadienyl signal (δ 5.26). The volatiles
were removed, and the residue was reprecipitated to
return (SReSRe)-32+(BF4-)2 as a mixture of diastereomers
(31P NMR δ 22.6, 22.1, 21.9; ca. 33:35:32) in nearly the
same ratio as the starting sample (31:32:37).
Another strategy would be to attempt a synthesis
under kinetic control. Thus, (SReSRe)-4 and the strong
acid HBF4‚OEt2 (2 equiv) were combined in THF at -80
°C in a NMR tube.21 The 31P NMR spectrum showed
several signals, and the resulting (SReSRe)-32+(BF4
)
-
2
was isolated and analyzed by NMR (CD3CN). The 31P
spectrum showed four peaks (δ 22.6, 22.5, 22.1, 21.9;
1
ca. 21:21:21:37) and the H spectrum four cyclopenta-
dienyl peaks (δ 5.31, 5.30, 5.28, 5.23; ca. 21:21:37:21).
Hence, all attempts to obtain diastereomerically en-
riched (SReSRe)-32+(BF4-)2 were unsuccessful.
In the course of the preceding efforts, reactions of
methylidene complex 1 and other types of amines were
attempted, normally in search of model compounds or
data. One experiment used racemic
1 and the
N,N′-diethyl analogue of the original diamine,
HN(CH2CH3)CH2CH2(H3CH2C)NH. Although the initial
conditions were directed at the synthesis of a homologue
of (SReSRe)-32+(BF4-)2, a crystalline byproduct was
obtained, the 1:1 adduct [(η5-C5H5)Re(NO)(PPh3)-
(CH2NH(CH2CH3)CH2CH2NH(CH2CH3))]+BF4- (6+BF4-).
Hence, the reaction was conducted with the proper
stoichiometry as shown in Scheme 3, and the crude
tertiary ammonium salt 6+BF4 was isolated in 92%
-
yield. The microanalysis fit the molecular formula.
The 1H NMR spectrum showed three cyclopentadienyl
signals in a 63:22:15 ratio (δ 5.28, 5.32, 5.55), and traces
of additional components (e2% each) were seen by 31P
NMR. Two signals might be due to rhenium-nitrogen
diastereomers. Another possibility would be a tautomer,
the secondary ammonium salt 7+BF4- (Scheme 3). The
major species (δ 5.28, 5.32) are much closer to those of
dicationic (SReSRe)-32+(BF4
) than those of neutral
2
-
equilibrium 6+BF4-/7+BF4 is of particular interest,
(SReSRe)-4 (δ 5.31-5.23 vs 4.98). The 31P NMR signals
and IR νCO values show similar trends.
-
since it reflects the relative Brønsted basicities of two
nitrogen atoms that differ in a single substituent
(ReCH2 vs H). The 1H NMR couplings were not well
enough resolved to establish the location of the am-
monium proton. However, other data strongly suggest
Crystallization gave a dichloromethane solvate (75%),
and X-ray data were collected (Table 1). Refinement
showed two independent cations in the unit cell. Key
metrical parameters are given in Table 3. As shown in
Figure 3 (top, bottom), both cations were SReSN,RReRN
diastereomers of 6+BF4-, differing in the conformations
-
that 6+BF4 dominates in solution. For example, the
1
cyclopentadienyl H NMR chemical signals of the two

Diamines with Transition-Metal Stereocenters
Organometallics, Vol. 20, No. 14, 2001 3093
N3′ ) 2.727 Å). The conformation of the CH2CH2-
NHCH2CH3 group in the first cation precludes a similar
interaction. Such 2.1-2.2 Å distances are typical of
weak ammonium hydrogen bonds,33 something that
each cation finds a separate means of achieving. Since
both cations exhibit similar Re-CH2 conformations,
only the Newman projection of the first is given (middle,
Figure 3). This shows that (SReSN,RReRN)-6+BF4 has
-
a Re-CH2 conformation similar to that of (SReRNRN
-
SRe)-5 (Figure 2, top), with P-Re-C-N torsion angles
of 148.0(4)/156.1(4)° as compared to 142(2)/147(5)°. With
respect to the ReCH2-N conformation, the largest group
on nitrogen (CH2CH2NHCH2CH3) is roughly anti to the
Re-CH2 bond, as indicated by torsion angles of 143.3(4)/
157.0(5)°. This is again similar to (SReRNRNSRe)-5
(Figure 2, bottom), in which the analogous Re-CH2-
N-Pd torsion angles are 165.8(11)/158.9(13)°.
When crystalline (SReSN,RReRN)-6+BF4-‚CH2Cl2 was
dissolved, two cyclopentadienyl 1H NMR signals (δ 5.28,
5.32; 69:31) and one 31P NMR signal were observed. The
tautomer 7+BF4- has a configurationally labile nitrogen
stereocenter and can only give one set of signals. The
1H NMR signals therefore represent either two dia-
-
-
stereomers of 6+BF4 or 7+BF4 and one diastereomer
of 6+BF4-. We have prepared other pairs of Re-
CH2N+HRR′/ReCH2NRR′ compounds and always find
widely separated 31P and cyclopentadienyl 1H NMR
signals.34 We therefore conclude, as further supported
by chemical shift arguments above, that the signals
represent diastereomers of 6+BF4-. This in turn indi-
cates that (1) 6+BF4 is more stable than 7+BF4 and
-
-
-
(2) the diastereomers of 6+BF4 rapidly equilibrate in
solution, quite possibly via 7+BF4
.
-
Discu ssion
The very high diastereoselectivity with which the
chelate complex (SReRNRNSRe)-5 forms represents one
of the most interesting aspects of the preceding data.
Since different nitrogen-based diastereomers of such
metal 1,2-diamine catalysts would logically give differ-
ent enantioselectivities, this point is analyzed first.
Here, the configurationally labile alkoxide and amido
complexes mentioned in the Introduction, (η5-C5H5)Re-
(NO)(PPh3)(OCHRR′) and (η5-C5H5)Re(NO)(PPh3)(N(R′′)-
CHRR′), are relevant. They undergo epimerization at
both rhenium and carbon, and thermodynamic dia-
stereomer ratios are easily obtained. The direction of
equilibrium can be rationalized by the model shown in
Scheme 4, in which both diastereomers (D and E) are
viewed in W-type conformations with respect to phos-
phorus, rhenium, oxygen/nitrogen, carbon, and the
largest group on carbon. As noted in the torsion angle
analyses above, this directs the largest groups anti
about the Re-O/N and O/N-C bonds.
F igu r e 3. Structures of the cations of (RReRN,SReSN)-
6+BF4-: (top) first independent cation; (middle) Newman
projection (partial) down the C-Re bond; (bottom) second
independent cation.
of the ReCH2N-alkyl groups. The ammonium proton
electron density was located in each, confirming the
absence of the tautomer 7+BF4-. As a check, the
N-CH2CH3 bond lengths were compared. Those at the
nitrogen â to rhenium (1.505(9)/1.504(10) Å) were
significantly longer than at the nitrogen ꢀ to rhenium
(1.419(11)/1.429(9) Å). The former values are typical for
tertiary ammonium salts, whereas tertiary and second-
ary amines exhibit shorter nitrogen-carbon bonds
(average values in the Cambridge Structural Data-
base: 1.502 and 1.469 Å).32
The cations in Figure 3 are depicted with calculated
ammonium proton positions. In the first, the closest
ReCH2NH-BF4- contact (2.095 Å) is much shorter than
in the second (3.870 Å). On the other hand, the second
has a short ReCH2NH-N contact (2.158 Å, with N2′/
In the less stable diastereomer (E), a slight destabi-
lizing interaction between the medium-sized carbon
substituent and the cyclopentadienyl ligand can be
identified. In the more stable diastereomer (D), the
medium-sized carbon substituent is aligned with the
(33) (a) Dewey, M. A.; Knight, D. A.; Klein, D. P.; Arif, A. M.;
Gladysz, J . A. Inorg. Chem. 1991, 30, 4995. (b) Amoroso, A. J .; Arif, A.
M.; Gladysz, J . A. Organometallics 1997, 16, 6032.
(34) Prommesberger, M. Unpublished research reports, University
of Erlangen-Nu¨rnberg.
(32) Allen, F. H.; Kennard, O.; Watson, D. G.; Brammer, L.; Orpen,
A. G.; Taylor, R. J . Chem. Soc., Perkin Trans. 2 1987, S1 (compare
the last five entries on page S9 with entries 2-5 on page S10).

3094 Organometallics, Vol. 20, No. 14, 2001
Alvey et al.
Sch em e 4. Mod els for Rela tive Sta bilities of
Dia ster eom er s
be represented as C and F in Scheme 4. The palladium
is clearly the largest group on nitrogen and methyl the
smallest. In F , a destabilizing interaction between the
chelate backbone and the cyclopentadienyl ligand is
present. Thus, (SReRNRNSRe)-5 can be viewed as a
“doubly matched” diastereomer, whereas (SReSNSNSRe)-5
is doubly mismatched. Since we have no evidence that
chelate formation is under thermodynamic control, the
diastereoselectivity might be a function of similar
interactions in transition states. Regardless, this model
constitutes a very plausible mechanism for 1,3-chirality
transfer from rhenium to nitrogen. One corollary is that
the corresponding N,N′-diethyl chelate (i.e., the same
diamine used for 6+BF4-) would have a greater tendency
to give other diastereomers, since the ethyl group will
be closer in effective size to the chelate backbone.
Purely organic chiral 1,2-diamines that contain car-
bon stereocenters in the nonchelating N-alkyl substit-
uents are known. One example is G-a (Scheme 5),26a,b
which, like (SReSRe)-4, has tertiary nitrogen stereo-
centers. Enantiomerically pure G-a has a carefully
characterized coordination chemistry. To our knowledge
chelate diastereomers have never been observeds
despite possibilities analogous to those of (SReSRe)-4 in
Scheme 2. As would be expected, structurally character-
ized complexes always have the larger CH(CH3)Ph
groups on opposite sides of the chelate plane. Interest-
ingly, the related disecondary diamine G-b gives all
three possible PtCl2 chelate isomers.35 Scheme 5 also
shows a 1,2-diamine with only nitrogen stereocenters
(H).25a When this ligand chelates PdCl2, rac and meso
diastereomers can be detected. The major rac dia-
stereomer has been crystallized and structurally char-
acterized. More importantly, NMR spectra show no
trace of the meso diastereomer. Hence, we believe that
the diastereomers of chelate 5 (Scheme 2) are also slow
to equilibrate in solution.
small nitrosyl ligand. Although such compounds cer-
tainly adopt an ensemble of conformations in solution,
this simple explanation has rationalized all data to date.
Our new results with 6+BF4- also indirectly support this
model. First, the diastereomers rapidly equilibrate in
solution. Second, the two independent cations in Figure
3 (SReSN,RReRN) both correspond to diastereomer D (D
) CH2 and nitrogen in place of Câ). Although this cannot
be taken as a proof of the dominant diastereomer in
solution, it is always the more probable case, and even
more so here, since nature would have to perpetrate the
same deception twice.
From the standpoint of concept and design in new
chiral diamines for enantioselective synthesis, the rep-
resentative ferrocene-containing examples in Figure 4
In the same sense, the observed chelate diastereomer
(SReRNRNSRe)-5 and the alternative (SReSNSNSRe)-5 can
Sch em e 5. Oth er Ch ela tin g 1,2-Dia m in es a n d P a lla d iu m Com p lexes

Diamines with Transition-Metal Stereocenters
Organometallics, Vol. 20, No. 14, 2001 3095
selective organic catalysis and other extensions of this
work will be reported in due course.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were conducted
under dry inert atmospheres. Analytical data were recorded
on standard instruments, most of which were listed in a
previous paper.37 Rather than enumerate the many small
differences between the two locations in which synthetic work
was conducted, readers are referred to two dissertations.16
Chemicals were treated as follows: CHCl3, distilled from P2O5;
CH2Cl2 and ethyl acetate, distilled from CaH2; toluene, hexane,
benzene, ether, and THF, distilled from Na/benzophenone;
C6D6, CD2Cl2, and CD3CN (Cambridge) and t-BuOK (Aldrich),
used as received; HN(R)CH2CH2(R)NH (Aldrich), dried and
distilled from KOH (R ) CH3) or dried over 4 Å molecular
sieves (R ) CH2CH3); Ph3C+BF4- (Fluka), recrystallized from
CH2Cl2/ethyl acetate.38
(RReRRe)-[(η5-C5H5)Re(NO)(P P h 3)(CH2NH(CH3)CH2CH2-
F igu r e 4. Representative ferrocenes containing chiral
diamines.
(H3C)HNCH2)(P h 3P )(ON)Re(η5-C5H5)]2+(BF 4-)2 ((RReRRe)-
3
2+(BF 4-)2).21 A Schlenk flask was charged with (R)-1 (0.7131
g, 1.276 mmol)12 and CH2Cl2 (20 mL) and cooled to -80 °C
are offered for comparison. These place the ferrocene
units endocyclic to the chelate backbone (I),8d,e exocyclic
to the chelate backbone (J ),8a within the N-alkyl sub-
stituents (K),8c or in other motifs (L).9a,b Both J and L
contain planar chirality elements. To our knowledge, no
other transition-metal fragments, chiral or otherwise,
have been similarly applied as architectural units in
chiral diamines. In view of the tremendous breath of
transition-metal fragments available, and the intrinsic
diversity elements within, we find this oversight sur-
prising. The conversion of commercial Re2(CO)10 to the
nonracemic methyl complex (S)-1 and then (SReSRe)-4
requires nine steps and proceeds in 37% overall yield.
This is not as efficient as the synthesis of I (four steps
from ferrocene, 76%) but compares favorably with that
of L (six steps from a tetrasubstituted pyridine, 10%).
(acetone/CO2 @ 1300 m). A second Schlenk flask was charged
with Ph3C+BF4 (0.4226 g, 1.280 mmol) and CH2Cl2 (20 mL)
-
and cooled to -80 °C. The solution in the second Schlenk flask
was added to the first, dropwise via cannula over 30 min, to
generate (R)-2+BF4- 17,18 After 10 min, HN(CH3)CH2CH2(H3C)-
.
NH (0.068 mL, 0.64 mmol) was added. After 8 h, the cold bath
was removed and the mixture warmed to room temperature.
The sample was filtered (glass frit) and reduced to 10 mL
under vacuum (10 mmHg). Benzene (40 mL) was added and
the sample kept at -10 °C for 12 h. The yellow microcrystals
were collected by filtration, washed with hexane (5 mL), and
dried by oil pump vacuum to give (RReRRe)-32+(BF4-)2 (0.8243
g, 0.5986 mmol, 94%). Anal. Calcd for C52H56B2F8N4O2P2Re2:
C, 45.36; H, 4.10. Found: C, 45.36; H, 4.17. IR (cm-1, KBr):
νNH 3548 s br, νNO 1647 s. NMR (δ, CD3CN): 1H 7.60-7.12
(m, 6Ph), 6.05-5.80 (br s, 2NH), 5.31, 5.30, 5.28, 5.23 (4s,
2C5H5; ca. 32:10:30:28), 4.54-4.32 (m, 2H of ReCH2), 4.10-
3.88 (m, 2H of ReCH2), 3.60-3.48 (m, 2H of 2NCH2), 3.40-
3.06 (m, 2H of 2NCH2), 2.81, 2.75, 2.70 (3d, J HH ) 5.1, 2NCH3;
ca. 34:37:29); 31P{1H} 22.6, 22.1, 21.9 (3s; ca. 31:32:37).
(RR eRR e)-(η5-C5H 5)R e(NO)(P P h 3)(CH 2N(CH 3)CH 2CH 2-
(H3C)NCH2)(P h 3P )(ON)Re(η5-C5H5) ((RReRRe)-4).21 A Schlenk
flask was charged with (RReRRe)-32+(BF4-)2 (0.9270 g, 0.6730
mmol) and THF (20 mL). Then t-BuOK (1.35 mL, 1.0 M in
THF, 1.35 mmol) was added. After 30 min, solvent was
removed by oil pump vacuum. Toluene (10 mL) was added,
and the mixture was filtered through a medium-porosity glass
frit. Heptane (30 mL) was added to the filtrate and the sample
kept at -10 °C for 12 h. The orange precipitate was collected
by filtration and dried by oil pump vacuum to give (RReRRe)-4
(0.5236 g, 0.04462 mmol, 66%): mp 97.8 °C (DSC), 101 °C dec
(capillary). Anal. Calcd for C52H54N4O2P2Re2: C, 51.99; H, 4.53.
Found: C, 51.88; H, 4.69. IR (cm-1, C6H6): νCH (:NCH3)22 2774
w br, νNO 1630 s (KBr, 1624). MS (positive FAB, 3-NBA/C6H6,
m/z): 1199 (45.8), 1200 (27.2), 1201 (M+, 100), 1202 (55.6), 1203
(76.7), 1204 (38.7), 1205 (12.2), 1206 (3.5). NMR (δ, C6D6): 1H
7.59-7.51 (m, 12H of 6Ph), 7.07-6.95 (m, 18H of 6Ph), 4.98
(s, 2C5H5), 4.18 (br d, J HH ) 11.7, w1/2 ) 5.3 Hz, 2ReCHH′),
Chiral diamines that are unsymmetrically substituted
or have chirality elements only on one terminus are also
highly effective in certain enantioselective reactions.2,36
Thus, possible applications of 6+BF4- (Scheme 3) or its
conjugate base should not be overlooked. However,
within the context of this study, this half-protonated
diamine is more important for the physical insight
provided. As noted above, the lower stability of the
tautomer 7+BF4- shows that the Brønsted basicity of a
ReCH2-substituted amine is much greater than that of
an analogous hydrogen-substituted amine. In other
words, a (η5-C5H5)Re(NO)(PPh3)CH2- substituent is a
much stronger electron donor than hydrogen toward
nitrogen.
In summary, this study has described a very efficient
synthesis of a new and architecturally novel chiral 1,2-
diamine capable of C2 symmetry. It is the first 1,2-
diamine in which the chirality is derived from a metal
as opposed to a carbon stereocenter. It readily forms
chelates with very high diastereoselectivity, and the
rhenium fragment confers a unique combination elec-
tronic and steric properties. Applications in enantio-
1
3
3.74 (dd, J HH ) 11.7, w1/2 ) 2.8 Hz, J HP ) 7.2, 2ReCHH′),
3.20 (m, 2NCHH′), 2.65 (s, 2NCH3), 2.50 (m, 2NHH′); 13C{1H}
137.7 (d, J CP ) 50.1, i-Ph), 134.3 (d, J CP ) 10.9, o-Ph), 130.3
(s, p-Ph), 128.8 (s, m-Ph), 91.5 (s, C5H5), 60.2 (s, NCH2), 47.1
(s, NCH3), 31.2 (d, ReCH2); 31P{1H} 26.8 (s).
(35) Fanizzi, F. P.; Maresca, L.; Natile, G.; Lanfranchi, M.; Manotti-
Lanfredi, A. M.; Tiripicchio, A. Inorg. Chem. 1988, 27, 2422.
(36) (a) So¨dergren, M. J .; Andeersson, P. G. J . Am. Chem. Soc. 1998,
120, 10760 and reviews cited therein. (b) Fehr, C. Angew. Chem., Int.
Ed. Engl. 1996, 35, 2567; Angew. Chem. 1996, 108, 2726.
(37) Alvey, L. J .; Meier, R.; Soo´s, T.; Bernatis, P.; Gladysz, J . A.
Eur. J . Inorg. Chem. 2000, 1975.
(38) Buhro, W. E.; Georgiou, S.; Ferna´ndez, J . M.; Patton, A. T.;
Strouse, C. E.; Gladysz, J . A. Organometallics 1986, 5, 956.

3096 Organometallics, Vol. 20, No. 14, 2001
Alvey et al.
129.2 (d, J CP ) 11.0, m-Ph), 91.0 (s, C5H5), 55.9 (s, +NCH2-
CH2N:),40 48.9 (s, +NCH2CH3),40 44.1 (s, +NCH2CH2N:),40 43.6
(s, :NCH2CH3),40 26.5 (s, ReCH2), 15.3 (s, :NCH2CH3),40 7.6 (s,
+NCH2CH3);40 31P{1H} 21.2.
Cr ysta llogr a p h y. Crystals were obtained as described
above and data collected as outlined in Table 1. Standard
reflections showed no crystal decay.
Cell parameters of (RReSNSNRRe)-5‚3CHCl3 were determined
from 80 reflections with 15° < 2θ < 23°. The space group was
determined from systematic absences and subsequent least-
squares refinement. Lorentz, polarization, and absorption
(numerical via SHELX7641) corrections were applied. The
structure was solved by standard heavy-atom techniques with
SHELXS and refined with SHELX-93.42 Rhenium, palladium,
and chlorine atoms were refined with anisotropic thermal
parameters. Other atoms were refined isotropically, with the
cyclopentadienyl, phenyl, and NO moieties as rigid groups.
There were four CHCl3 positions per palladium, but two were
half-occupied, giving a tris(solvate). Hydrogen atom positions
were calculated and added to the structure factor calculations
but were not refined. The absolute configuration was confirmed
by Flack’s parameter (0.023(18)).43
(R R e S N S N R R e )-[(η5-C 5H 5)R e (N O )(P P h 3)(C H 2N (C H 3)-
CH2CH2(H3C)NCH2)(P h 3P )(ON)Re(η5-C5H5)]P dCl2 ((RReSN
-
SNRRe)-5).21 A Schlenk flask was charged with (RReRRe)-4
(0.1339 g, 0.1114 mmol) and THF (10 mL). A second Schlenk
flask was charged with (PhCN)2PdCl2 (0.0427 g, 0.1113
mmol)39 and THF (10 mL). The second solution was added to
the first via cannula. After 30 min, the solvent was removed
by oil pump vacuum. Benzene (20 mL) was added. The sample
was filtered (medium-porosity glass frit) and added to hexane
(50 mL). The pale orange precipitate was collected by filtration
and dried by oil pump vacuum to give (RReSNSNRRe)-5 (0.1223
g, 0.0887 mmol, 80%): mp 156 °C dec (capillary). Anal. Calcd
for C52H54N4O2P2Re2: C, 45.30; H, 3.95. Found: C, 45.09; H,
4.01. IR (cm-1
CD2Cl2): 1H 7.55-7.30 (m, 6Ph), 5.06 (s, 2C5H5), 4.92 (dd, 2J HH
, C6H6/KBr): νNO 1636/1634 s. NMR (δ,
3
2
) 12.3, J HP ) 11.4, w1/2 ) 2.7 Hz, 2ReCHH′), 4.78 (br d, J HH
) 12.3, w1/2 ) 2.4 Hz, 2ReCHH′), 2.33 (s, 2NCH3), 1.49 (d, J HH
) 9.9, 2NCHH′), 1.14 (d, J HH ) 9.6, 2NHH′); 13C{1H} 136.3
(d, J CP ) 53.0, i-Ph), 134.2 (d, J CP ) 10.4, o-Ph), 131.2 (s, p-Ph),
129.2 (d, J CP ) 10.3, m-Ph), 91.6 (s, C5H5), 61.8 (s, NCH2), 54.9
(s, NCH3), 31.0 (d, ReCH2); 31P{1H} 24.8 (s).
Cell parameters of (RReRN,SReSN)-6+BF4-‚CH2Cl2 were de-
termined and refined from 71 466 reflections. Lorentz, polar-
ization, and absorption44 corrections were applied. The struc-
ture was solved by direct methods and showed two independent
molecules in the unit cell. The parameters were refined with
all data by full-matrix least-squares on F2 using SHELXL-
93.42 Non-hydrogen atoms were refined with anisotropic
thermal parameters. The electron density for the ammonium
hydrogens was located (N2, N2′), but for refinements all
Vapor diffusion of hexane into a CHCl3 solution of (RReSN
-
SNRRe)-5 (3 days) gave orange prisms of (RReSNSNRRe)-5‚
3CHCl3 that were used for X-ray crystallography (below).
[(η5-C5H 5)R e(NO)(P P h 3)(CH 2NH(CH 2CH 3)CH 2CH 2NH-
(CH2CH3))]+BF 4 (6+BF 4-). Racemic 2+BF4 was generated
from racemic 1 (0.303 g, 0.542 mmol)12 in CH2Cl2 (15 mL) and
Ph3C+BF4- (0.197 g, 0.597 mmol) in CH2Cl2 (5 mL) analogously
-
-
to the procedure for (R)-2+BF4 above. After 10 min, HN-
-
-
(CH2CH3)CH2CH2(H3CH2C)NH (0.039 mL, 0.27 mmol) was
added. The solution turned bright yellow. After 1.5 h, the cold
bath was removed and the mixture warmed to room temper-
ature. Hexane (40 mL) was added. The yellow precipitate was
isolated by filtration and dissolved in CH2Cl2 (10 mL). An ether
layer (40 mL) was added. After 2 h, the yellow powder was
collected by filtration and dried by oil pump vacuum to give
crude 6+BF4- (0.379 g, 0.498 mmol, 92%; see text for analysis
of isomers). Anal. Calcd for C30H38BF4N3OPRe: C, 47.37; H,
5.03. Found: C, 46.99; H, 5.10. IR (cm-1, KBr): νNH 3552 w
br, νNO 1640 (C6H6 1644) vs. NMR (δ, CD2Cl2): 1H 7.49-7.47
(m, 6H of 3Ph), 7.36-7.34 (m, 9H of 3Ph), 5.55, 5.32, 5.28 (3s,
C5H5; ca. 15:22:63), 4.31 (d, J HH ) 13.2, ReCHH′), 3.9-3.7 (br
m, 3H), 3.41 (m, 1H), 3.3-3.2 (br m, 2H), 3.05 (s, 1H), 2.95-
2.80 (br m, 3H), 2.71-2.61 (br m, 2H), 1.23, 1.13 (2 pseudo-t,
J HH ) 7.1, 6H, 2CH3; ca. 78:22); 13C{1H} (partial) 134.7 (d, J CP
) 53.3, i-Ph), 133.6 (d, J CP ) 9.2, o-Ph), 131.2 (s, p-Ph), 129.2
(d, J CP ) 11.0, m-Ph), 94.8, 91.4, 91.0 (3s, C5H5); 31P{1H} 21.9,
21.8, 21.2 (major), 20.5, 20.3 (5s).
The yellow powder was dissolved in CH2Cl2 (10 mL) and
layered with benzene (40 mL). After 4 days, yellow cubic
crystals were collected by filtration, washed with hexane, and
dried by oil pump vacuum to give (RReRN,SReSN)-6+BF4-‚CH2Cl2
(0.316 g, 0.406 mmol, 75%). Anal. Calcd for C30H38BF4N3OPRe‚
CH2Cl2: C, 44.03; H, 4.77. Found: C, 44.22; H, 4.81. NMR (δ,
CD2Cl2): 1H 7.49-7.47 (m, 6H of 3Ph), 7.36-7.34 (m, 9H of
3Ph), 5.32, 5.28 (2s, C5H5; 31:69), 4.31 (d, J HH ) 13.2, 1H of
ReCHH′), 3.9-3.7 (br m, 3H), 3.41 (m, 1H), 3.3-3.2 (br m, 2H),
3.05 (s, 1H), 2.95-2.80 (br m, 3H), 2.71-2.61 (br m, 2H), 1.23,
1.13 (2 pseudo-t, J HH ) 7.1, 6H, CH3 12:88); 13C{1H} 134.7 (d,
J CP ) 53.3, i-Ph), 133.6 (d, J CP ) 9.2, o-Ph), 131.2 (s, p-Ph),
hydrogen atoms were fixed in idealized positions. Both BF4
anions showed partial disorder of one fluorine atom (F3,F3a
and F3′,F3b), which could be resolved with a occupation ratio
of 55:45. Scattering factors for both structures, and ∆f′ and
∆f′′ values, were taken from the literature.45
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft (DFG; GL 300-1/4 and postdoctoral
fellowship, O.M.) and the US NIH for support and
J ohnson Matthey PMC for a loan of palladium.
Su p p or tin g In for m a tion Ava ila ble: Tables of bond
lengths and angles, atomic coordinates, and anisotropic
displacement parameters for (RReSNSNRRe)-5‚3CHCl3 and
(RReRN,SReSN)-6+BF4-‚CH2Cl2. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM010153A
(40) These assignments were made based upon chemical shifts
predicted by ChemNMR-Pro (Cambridge Software).
(41) Sheldrick, G. M. SHELX-76; University of Cambridge, Cam-
bridge, U.K., 1976.
(42) (a) Sheldrick, G. M. SHELX-93, Program for Refinement of
Crystal Structures; University of Go¨ttingen, Go¨ttingen, Germany,
1993. (b) Sheldrick, G. M. SHELXL-93. In Crystallographic Computing
3; Sheldrick, G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University
Press: Oxford, U.K., 1993; pp 175-189.
(43) Flack, H. D. Acta Crystallogr, 1981, A37, 734. Limiting values
are 0 for the correct structure and +1 for the inverted structure.
(44) (a) “Collect” Data Collection Software; Nonius BV, 1998. (b)
Otwinowski, Z.; Minor, W. “Scalepack” Data Processing Software. In
Methods Enzymol. 1997, 276 (Macromolecular Crystallography, Part
A), 307.
(45) Cromer, D. T.; Waber, J . T. In International Tables for X-ray
Crystallography; Ibers, J . A., Hamilton, W. C., Eds.; Kynoch: Bir-
mingham, England, 1974.
(39) Anderson, G. K.; Lin, M. Inorg. Synth. 1990, 28, 60.