Coordination chemistry of isomeric mixtures of linked Di(phosphaguanidine) compounds: A spectroscopic and crystallographic study

Article abstract of DOI:10.1021/om060014z

Multinuclear NMR spectroscopy and X-ray diffraction techniques have been used to identify diastereomeric mixtures of rac- and meso-di(phosphaguanidine) compounds. A brief survey of their coordination chemistry has demonstrated the formation of N,N′-bound bimetallic aluminum species and monometallic platinum complexes in which the ligand chelates to the metal through the two phosphorus donor atoms.

Full text of DOI:10.1021/om060014z

2470
Organometallics 2006, 25, 2470-2474
Coordination Chemistry of Isomeric Mixtures of Linked
Di(phosphaguanidine) Compounds: A Spectroscopic and
Crystallographic Study
Natalie E. Mansfield, Martyn P. Coles,* Anthony G. Avent, and Peter B. Hitchcock
Department of Chemistry, UniVersity of Sussex, Falmer, Brighton, BN1 9QJ, U.K.
ReceiVed January 5, 2006
Multinuclear NMR spectroscopy and X-ray diffraction techniques have been used to identify
diastereomeric mixtures of rac- and meso-di(phosphaguanidine) compounds. A brief survey of their
coordination chemistry has demonstrated the formation of N,N′-bound bimetallic aluminum species and
monometallic platinum complexes in which the ligand chelates to the metal through the two phosphorus
donor atoms.
Phosphines remain a fundamentally important ligand in
coordination chemistry and are routinely used as ancillary groups
in many transition-metal-mediated catalytic processes.1 During
the course of their development, the steric and electronic
properties have been extensively modified, facilitated by the
ease with which substituents possessing different physical and
chemical properties can be incorporated at the phosphorus atom.
We have recently developed a novel class of phosphine
compound with general formula Ph2PC{NR}{NHR} (R ) iPr,
Cy) (we refer to this class of compound as phospha(III)-
guanidines, by reference to its relationship to conventional
tetrasubstituted guanidines of general formula R′2NC{NR}-
{NHR}), featuring a C-bound amidine unit,2 and reported
different coordination behavior including anionic [N,N′]- and
[N,P]- and neutral P- and N,P-coordination and a bridging mode
between different metal centers.3
During analysis of the phosphaguanidines, different arrange-
ments of the N-substituents were noted, depending on the
orientation of the imine bond and the relative position of the
NH hydrogen atom (Figure 1).4 For example, data for the
noncomplexed species were consistent with an Esyn pattern in
the solid and solution states, while the Zanti conformation is
enforced upon chelation to a “M(CO)4” fragment.2 More recently
we have identified an equilibrium between the Esyn and Zsyn
forms for the phospha(V)guanidines, Ph2P(E)C{NR}{NHR}
(E ) S, Se),5 postulated as arising from attractive E‚‚‚H-N
nonbonded interactions. Given that chelating diphosphines
frequently offer advantages over their monodentate counterparts
(e.g., enhanced thermal stability, enforced cis-geometry about
square planar metal centers), we were keen to explore the
possibility of incorporating more than one phosphaguanidine
moiety in the same molecule.
Figure 1. The four possible conformations of N-substituents about
an amidine unit.
6
Reaction of [PhP(Li{THF}2)CH2-]2 with RNdCdNR at
low temperature and quenching the intermediate lithium species7
with [HNEt3][Cl] afforded the ethylene-linked di(phosphaguani-
i
dine) compounds [PhP(C{NR}{NHR})CH2-]2 [1a, R ) Pr;
1b, R ) Cy]. 31P{1H} NMR spectroscopic analysis of analyti-
cally pure crystals of 1a revealed two singlets (δ -29.3 and
-29.5) and two widely spaced AB quartets at δ -14.7/-27.2
(J ) 42 Hz) and δ -15.0/-26.0 (J ) 33 Hz), consistent with
two symmetric (i and ii) and two asymmetric (iii and iv) species
in solution (Figure 2). The corresponding 1H NMR spectrum is
complex, reflecting the presence of these four species (i-iv) in
addition to localized C-N single and CdN double bonds within
each amidine unit, which render the nitrogen substituents
inequivalent. Using a combination of selective decoupling, 2D-
NMR experiments, and investigation of the NOE between key
resonances, it has been determined that the major symmetric
resonances (i and ii) have an Esyn arrangement of substituents
about both amidine units, whereas the nonsymmetrical minor
isomers (iii and iv) contain a combination of Zanti and Esyn
amidines, resulting in inequivalent phosphorus atoms. Given
that the phosphorus atoms in 1 are chiral, the presence of rac-
and meso-diastereoisomers accounts for the observed 1:1 ratio
of {Esyn:Esyn} (i and ii) and {Zanti:Esyn} (iii and iv) species. As
may be expected, i and ii are in equillibrium with iii and iv,
being related by isomerization of the CdN double bond and
rotation of the C-N single bond. Monitoring the ratio of [(i) +
(ii)]:[(iii) + (iv)] by 31P NMR spectroscopy over the temperature
range 303-348 K showed only a slight variation in the relative
* To whom correspondence should be addressed. Fax: +44 (0)1273
677196. Tel: +44 (0)1273 877339. E-mail: m.p.coles@sussex.ac.uk.
(1) Applied Homogeneous Catalysis with Organometallic Compounds:
A ComprehensiVe Handbook in Two Volumes; Cornils, B., Herrmann, W.
A., Eds.; VCH: Weinheim, 1996.
(2) Grundy, J.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2003, 2573.
(3) Coles, M. P.; Hitchcock, P. B. Chem. Commun. 2002, 2794.
Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2005, 2833.
Mansfield, N. E.; Coles, M. P.; Hitchcock, P. B. Dalton Trans. 2006, DOI:
10.1039/B601235C.
(4) Ha¨felinger, G.; Kuske, F. K. H. In The Chemistry of Amidines and
Imidates; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1991; Vol. 2.
(5) Grundy, J.; Coles, M. P.; Avent, A. G.; Hitchcock, P. B. Chem.
Commun. 2004, 2410.
(6) Brooks, P.; Craig, D. C.; Gallagher, M. J.; Rae, A. D.; Sarroff, A.
J. Organomet. Chem. 1987, 323, C1. Anderson, D. M.; Hitchcock, P. B.;
Lappert, M. F.; Leung, W.-P.; Zora, J. A. J. Organomet. Chem. 1987, 333,
C13.
(7) Evidence for carbodiimide insertion has been obtained by trapping
the lithium salt as the TMEDA adduct; the crystal structure of the resultant
salt, [PhP(C{NiPr}2Li{TMEDA})CH2-]2, will be reported in a subsequent
publication.
10.1021/om060014z CCC: $33.50 © 2006 American Chemical Society
Publication on Web 04/11/2006

Coordination Chemistry of Di(phosphaguanidine) Compounds
Organometallics, Vol. 25, No. 10, 2006 2471
about the pyramidal phosphorus. In accordance with solution
NMR data, localized bonding is present in the amidine unit with
∆
values of 0.100 Å (av) and 0.103 Å for 1a and 1b,
CN
respectively [∆CN ) d(C-N) - d(CdN)].4
Upon N,N′-chelation of an anionic amidinate unit to a metal
center and formation of the four-membered metallacycle, the
configuration of nitrogen substituents is restricted to the {Eanti
:
E
anti} arrangement, reducing the possible number of species to
two symmetrical isomers. Accordingly, the product of the
reaction between 1a and 1b with 2 equiv of AlMe3 displayed
NMR spectra that were consistent with the bimetallic rac- and
i
meso-compounds [PhP(C{NR}2AlMe2)CH2-]2 [2a, R ) Pr;
2b, R ) Cy]. The 31P{1H} NMR spectra of the crude material
display two singlet resonances of equal intensity [2a, δ -27.6/
-29.1; 2b, δ -28.1 and δ -30.5], indicative of a 1:1 mixture
1
Figure 2. 31P{1H} NMR spectrum of 1a, showing the presence of
rac-/meso-{Esyn:Esyn} (i and ii) and rac-/meso-{Esyn:Zanti} (iii and
iv) diasteroisomers.
of the rac- and meso-diastereoisomers. The corresponding H
NMR data are simplified further as both N-substituents also
become equivalent, signifying symmetric delocalization of the
π-electron density within the NCN moiety. In contrast to the
observed cocrystallization of rac- and meso-1, successive
recrystallizations of 2 has allowed separation of the two
diastereoisomers, with the meso-compound proving less soluble.
It has therefore been possible to obtain X-ray diffraction data
for both rac- and meso-2a (Figure 4).8
The molecular structure of the aluminum complexes is in
agreement with the spectroscopic data, revealing a chelating
[N,N′]-coordination of the amidinate at each metal. In the case
of rac-2a, four molecules are present in the unit cell, corre-
sponding to a 1:1 mixture of the R,R and S,S diastereoisomers.
In all cases, the resultant geometry at aluminum is distorted
tetrahedral within which the bite angle of the phosphaguanidi-
nate ligand represents the smallest angle [meso-2a, 68.83(11)°;
rac-2a 68.8(2)° av; 2b, 69.07(9)°]. Symmetrical bonding to the
Figure 3. Molecular structure of meso-1a (′ -x, -y+1, -z+1; ′′
-x, -y+1, -z) and meso-1b (-x+1, -y+1, -z+1); ellipsoids
drawn at the 30% probability level; hydrogens omitted except NH
and bridging carbon positions. meso-1a: C(1)-N(1) 1.283(3),
C(1)-N(2) 1.375(3), P(1)-C(1) 1.870(2), P(1)-C(8) 1.850(2),
P(1)-C(9) 1.836(2); N(1)-C(1)-N(2) 119.8(2), N(1)-C(1)-P(1)
124.09(19), N(2)-C(1)-P(1) 115.77(18), C(1)-P(1)-C(8)
103.97(11), C(1)-P(1)-C(9) 101.49(11), C(8)-P(1)-C(9)
99.94(11). meso-1b: C(1)-N(1) 1.273(4), C(1)-N(2) 1.376(4),
P-C(1) 1.880(3), P-C(20) 1.849(3), P-C(14) 1.828(3). N(1)-
C(1)-N(2) 120.0(3), N(1)-C(1)-P 124.5(2), N(2)-C(2)-P
115.6(2), C(1)-P-C(20) 96.55(14), C(1)-P-C(14) 101.67(15),
C(14)-P-C(20) 102.64(15).
(8) Crystallographic data for 1a: C28H44N4P2, M ) 498.61, T ) 173(2)
K, triclinic, space group P1h (No. 2), a ) 11.5200(7) Å, b ) 11.9380(7) Å,
c ) 12.5195(10) Å, R ) 83.491(3)°, â ) 90.327(3)°, γ ) 63.088(3)°, U )
1522.2(2) Å3, Z ) 2, Dc ) 1.09 Mg m-3, µ(Mo KR) ) 0.16 mm-1
,
independent reflections ) 5248 (Rint ) 0.061), R1 [for 3962 reflections
with I > 2σ(I)] ) 0.054, wR2 (all data) ) 0.126. Crystallographic data for
1b: C40H60N4P2, M ) 658.86, T ) 173(2) K, triclinic, space group P1h
(No. 2), a ) 9.2204(7) Å, b ) 10.0638(8) Å, c ) 11.1221(9) Å, R )
110.804(5)°, â ) 97.381(5)°, γ ) 94.342(4)°, U ) 948.53(13) Å3, Z ) 1,
Dc ) 1.15 Mg m-3, µ(Mo KR) ) 0.15 mm-1, independent reflections )
2502 (Rint ) 0.072), R1 [for 1910 reflections with I > 2σ(I)] ) 0.058,
wR2 (all data) ) 0.135. Crystallographic data for meso-2a [Note: atoms
C(13) and C(14) are disordered and were left isotropic]: C32H54Al2N4P2,
M ) 610.69, T ) 173(2) K, triclinic, space group P1h (No. 2), a )
8.0203(3) Å, b ) 9.6862(5) Å, c ) 13.3190(6) Å, R ) 107.397(2)°, â )
93.777(3)°, γ ) 102.148(3)°, U ) 956.02(7) Å3, Z ) 1, Dc ) 1.06 Mg
amounts of {Esyn:Esyn} and {Zanti:Esyn} (303 K, 2.6:1; 348 K,
2.2:1), with the thermodynamically more stable symmetric form
predominating in solution.
We are unable to definitively assign either of the pairs of
isomers as rac or meso using spectroscopy alone, and recrys-
tallization of the crude mixture afforded an intimately mixed
1:1 combination of these two forms that could not be separated.
Prolonged heating of a [2H]8-toluene solution of 1a (80 °C, 5
days) showed no change in the ratio of rac:meso, consistent
with the expected high barrier to inversion at phosphorus.
However, varying the reaction conditions (temperature, rate of
addition, concentrations) has allowed meso-enriched mixtures
to be isolated (as verified by X-ray diffraction data, vide infra),
m-3, µ(Mo KR) ) 0.18 mm-1, independent reflections ) 3707 (Rint
)
0.070), R1 [for 2723 reflections with I > 2σ(I)] ) 0.058, wR2 (all data) )
0.194. Crystallographic data for rac-2a [Note: four independent molecules
present]: C32H54Al2N4P2, M ) 610.69, T ) 173(2) K, triclinic, space group
P1h (No. 2), a ) 13.0307(4) Å, b ) 13.0404(4) Å, c ) 45.5588(15) Å, R
) 83.446(1)°, â ) 82.619(2)°, γ ) 85.102(2)°, U ) 7607.6(4) Å3, Z ) 8,
Dc ) 1.07 Mg m-3, µ(Mo KR) ) 0.19 mm-1, independent reflections )
21 836 (Rint ) 0.085), R1 [for 15 142 reflections with I > 2σ(I)] ) 0.096,
wR2 (all data) ) 0.238. Crystallographic data for 2b [Note: the cyclohexyl
group on N(2) is disordered with resolved orientations included with
isotropic C atoms and SADI restraints]: C44H70Al2N4P2, M ) 770.94, T )
173(2) K, triclinic, space group P1h (No. 2), a ) 9.2687(3) Å, b )
11.2746(3) Å, c ) 12.3529(4) Å, R ) 107.300(2)°, â ) 92.690(2)°, γ )
103.330(2)°, U ) 1189.98(6) Å3, Z ) 1, Dc ) 1.08 Mg m-3, µ(Mo KR) )
0.16 mm-1, independent reflections ) 4672 (Rint ) 0.050), R1 [for 3803
reflections with I > 2σ(I)] ) 0.061, wR2 (all data) ) 0.172. Crystallographic
data for 3b′ [Note: the toluene solvate molecules were included with
isotropic C atoms; for the solvate disordered across an inversion center,
SADI restraints were applied and H atoms omitted]: C40H60I2N4P2Pt‚1.5-
(C7H8), M ) 1245.95, T ) 173(2) K, monoclinic, space group P21/c (No.
14), a ) 16.8514(8) Å, b ) 12.2242(4) Å, c ) 25.0259(11) Å, â )
98.138(2)°, U ) 5103.3(4) Å3, Z ) 4, Dc ) 1.62 Mg m-3, µ(Mo KR) )
4.06 mm-1, independent reflections ) 7044 (Rint ) 0.094), R1 [for 4934
reflections with I > 2σ(I)] ) 0.052, wR2 (all data) ) 0.104.
1
enabling full H NMR spectroscopic assignments to be made
for all four isomers of 1a.
X-ray data8 collected on representative crystals of 1a and 1b
are consistent with the meso-form in each case (Figure 3), in
which the two ends of the molecule are related by crystal-
lographic symmetry. Both derivatives exhibit similar gross
structural features, although two molecules are noted in the unit
cell of 1a, which differ slightly in their molecular geometry.
The monomeric compounds contain the expected ethylene bridge
between the two phosphine units, with a C-bound amidine unit
and phenyl substituent completing the coordination environment

2472 Organometallics, Vol. 25, No. 10, 2006
Mansfield et al.
Figure 4. Molecular structure of meso-2a (′ -x+1, -y+1, -z+1)
and rac-(S,S)-2a; ellipsoids drawn at the 30% probability level;
hydrogens omitted except at bridging carbon positions. meso-2a:
Al-N(1) 1.932(3), Al-N(2) 1.923(3), P-C(8) 1.872(3), C(8)-
N(1) 1.333(4), C(8)-N(2) 1.325(4); N(1)-Al-N(2) 68.83(11),
C(1)-P-C(2) 102.99(14), C(1)-P-C(8) 99.43(13), C(2)-P-C(8)
101.36(13). rac-2a [av value of all 4 molecules]: Al(1)-N(1)
1.929(6), Al(1)-N(2) 1.937(6), Al(2)-N(3) 1.923(6), Al(2)-N(4)
1.932(6), P(1)-C(9) 1.870(7), P(2)-C(24) 1.867(7), C(9)-N(1)
1.339(8), C(9)-N(2) 1.333(8), C(24)-N(3) 1.334(8), C(24)-N(4)
1.340(8); N(1)-Al(1)-N(2) 68.8(2), N(3)-Al(2)-N(4) 68.7(2),
C(1)-P(1)-C(3) 105.5(3), C(1)-P(1)-C(9) 101.3(3), C(9)-P(1)-
C(3) 101.3(3), C(2)-P(2)-C(18) 105.6(3), C(2)-P(2)-C(24)
100.6(3), C(18)-P(2)-C(24) 99.4(3).
Figure 5. Different isomeric forms of 3a identified in solution.
aluminum atom is observed with full delocalization throughout
the N-C-N moiety [∆CN ≈ 0]. All other parameters are
unremarkable when compared with the growing library of
related amidinate and phosphaguanidinate complexes incorpo-
rating the dialkyl and diaryl aluminum fragments.3,9
To demonstrate the ability of the di(phosphaguanidine) to also
function as a chelating diphosphine ligand, compound 1a was
reacted with PtCl2(COD), to afford the dichloride, PtCl2([PhP(C-
{NiPr}{NHiPr})CH2-]2), 3a. In this instance, the amidine unit
is predicted to remain intact, and hence a mixture of isomeric
products is expected. Indeed, the 31P{1H} NMR spectrum of
the product shows four different phosphorus environments at δ
44.9, 43.2, 42.4, and 32.0, each of which displays platinum
satellites indicating coordination to the metal center. In com-
bination with results from 1H and 195Pt NMR experiments, it is
deduced that these resonances originate from three species, the
two low-frequency signals of which correspond to a symmetrical
compound and the remaining peaks from an asymmetrical
variant of 3a. The predominant conformation for the amidine
unit in 3a is Zanti, indicating a change in the energy profile of
the different substituent positions compared with the proligand.
However, the presence of a broad doublet centered at δ 5.32 in
3a is characteristic of an NH resonance from an Esyn amidine,2
Figure 6. Molecular structure of rac-(R,R)-3b′; ellipsoids drawn
at the 30% probability level; hydrogens omitted except at NH and
bridging carbon positions. Pt-P(1) 2.234(2), Pt-P(2) 2.244(3),
P(1)-C(9) 1.856(10), P(2)-C(28) 1.867(10), C(9)-N(1)
1.376(12), C(9)-N(2) 1.275(12), C(28)-N(3) 1.288(11), C(28)-
N(4) 1.357(12); P(1)-Pt-P(2) 86.29(9), P(1)-Pt-I(1) 91.26(7),
P(2)-Pt-I(2) 91.19(7), I(1)-Pt-I(2) 91.73(3), C(1)-P(1)-Pt
107.6(3), C(3)-P(1)-Pt 116.1(3), C(9)-P(1)-Pt 116.9(3), C(1)-
P(1)-C(3) 105.1(5), C(1)-P(1)-C(9) 103.0(5), C(3)-P(1)-C(9)
106.9(4), C(2)-P(2)-Pt 108.2(3), C(22)-P(2)-Pt 115.1(3), C(28)-
P(2)-Pt 114.6(3), C(2)-P(2)-C(22) 107.3(5), C(2)-P(2)-C(28)
102.4(5), C(22)-P(2)-C(28) 108.2(5).
In an effort to analyze the ligand bond parameters when
coordinated to platinum, different combinations of ligand and
platinum starting materials have been investigated. Recently we
have successfully characterized the di-iodide PtI2([PhP(C{NCy}-
{NHCy})CH2-]2) (3b′) by X-ray crystallography, confirming
the chelation of the diphosphine ligand in the solid state (Figure
6). In this instance the structurally characterized isomer corre-
sponds to the rac-(R,R)-{Esyn:Zsyn} form, indicating that other
combinations of substituents are energetically accessible and
may be present as low-concentration species in solution. The
geometry about the cis-square planar metal is unremarkable
compared with PtI2(dppe),10 with a notable twist of 7.5° present
between the mean “P2Pt” and “PtI2” planes.
suggesting that the asymmetric species corresponds to the {Zanti
:
E
syn} isomer. This diastereoisomer is in exchange with one of
the symmetrical species (but not the other), which we therefore
assign as the corresponding {Zanti:Zanti}. Taking into account
the 1:1 ratio of rac- and meso-1a used in the reaction and the
high barrier to inversion at phosphorus, the mixture is therefore
assigned as rac-{Zanti:Zanti} [δ 44.9], meso-{Zanti:Zanti} [δ 43.2],
and meso-{Zanti:Esyn} [δ 42.4 {Zanti} and 32.0 {Esyn}], illustrated
in Figure 5.
(9) Lechler, R.; Hausen, H.-D.; Weidlein, U. J. Organomet. Chem. 1989,
359, 1. Coles, M. P.; Swenson, D. C.; Jordan, R. F.; Young, V. G., Jr.
Organometallics 1997, 16, 5183. Coles, M. P.; Swenson, D. C.; Jordan, R.
F.; Young, V. G., Jr. Organometallics 1998, 17, 4042. Kincaid, K.; Gerlach,
C. P.; Giesbrecht, G. R.; Hagadorn, J. R.; Whitener, G. D.; Shafir, A.;
Arnold, J. Organometallics 1999, 18, 5360. Dagorne, S.; Guzei, I. A.; Coles,
M. P.; Jordan, R. F. J. Am. Chem. Soc. 2000, 122, 274. Schmidt, J. A. R.;
Arnold, J. Organometallics 2002, 21, 2306. Grundy, J.; Coles, M. P.;
Hitchcock, P. B. J. Organomet. Chem. 2002, 662, 178. Clare, B.; Sarker,
N.; Shoemaker, R.; Hagadorn, J. R. Inorg. Chem. 2004, 43, 1159. Boere´,
R. T.; Cole, M. L.; Junk, P. C. New J. Chem. 2005, 29, 128.
To conclude, we have synthesized the first examples of linked
phosphaguanidine compounds, as a 1:1 ratio of rac- and meso-
diastereoisomers. Different conformations of the amidine unit
afford a mixture of symmetric and asymmetric species, and
(10) Parkin, I. P.; Slawin, A. M. Z.; Williams, D. J.; Woolins, J. D.
Phosphorus, Sulfur Silicon 1991, 57, 273.

Coordination Chemistry of Di(phosphaguanidine) Compounds
Organometallics, Vol. 25, No. 10, 2006 2473
{Zanti}), 3.66 (d, J ) 7.2, 1H, NH {Esyn}), 3.36 (sept, J ) 6.1, 1H,
dNCH {Zanti}), 2.74 (m, 1H, CH2), 2.40 (m, 1H, CH2), 2.22 (m,
1H, CH2), 2.08 (m, 1H, CH2), 1.40 (d, J ) 6.1, 3H, dNCHMe2
{Esyn}), 1.33 (d, J ) 5.9, 3H, dNCHMe2 {Zanti}), 1.26 (d, J ) 6.1,
3H, dNCHMe2 {Esyn}), 1.23 (d, J ) 6.2, 3H, dNCHMe2 {Zanti}),
‡, 0.45 (d, J ) 6.3, 3H, NHCHMe2 {Zanti}) [* remaining aromatic
resonances for all isomers overlap in the region δ 7.13-6.99; ‡
with the exception of one of the NHCHMe2 {Zanti} resonances,
which appears at high field, the remaining doublets corresponding
to the NHiPr substituents were overlapping with those of the other
isomers and could not be deconvoluted]. 31P NMR (121 MHz):
meso-{Esyn:Esyn} δ -29.5 (s); rac-{Esyn:Esyn} δ -29.3 (s); meso-
{Esyn:Zanti} δ -14.7 (d, J ) 42.3 Hz), -27.2 (d, J ) 42.3 Hz);
rac-{Esyn:Zanti} δ -15.0 (d, J ) 33.9 Hz), -26.0 (d, J ) 33.9
Hz).
solid-state X-ray diffraction of the meso-{Esyn:Esyn} conforma-
tion has been performed. These compounds react via the amidine
unit to afford bimetallic aluminum methyl complexes and
through the phosphorus atoms in a chelating bonding mode to
platinum. Further studies of the factors that influence the
diastereomeric ratio during the synthesis of this class of
compound are ongoing and will be reported in due course.
Experimental Section
General Procedures. All manipulations were carried out under
dry nitrogen using standard Schlenk and cannula techniques or in
a conventional nitrogen-filled glovebox. Solvents were dried over
appropriate drying agent and degassed prior to use. dppe (Aldrich),
nBuLi (2.5 M solution in hexanes, Acros), iPrNdCdNiPr (Aldrich),
CyNdCdNCy (Aldrich), and AlMe3 (2.0 M solution in hexanes,
Aldrich) were purchased from commercial sources and used without
further purification. [HNEt3][Cl] (Alrdich) was recrystallized from
chloroform and stored under a dry nitrogen atmosphere. PtCl2(COD)
and PtI2(COD) were made according to literature procedures.11
Elemental analyses were performed by S. Boyer at London Metro-
politan University. NMR spectra were recorded using a Bruker
Avance DPX 300 MHz spectrometer at 300 (1H), 75 (13C{1H}),
and 121 (31P{1H}) MHz, or a Bruker AMX 500 MHz spectrometer
at 500 (1H), 125 (13C{1H}) and 202 (31P{1H}) MHz. NMR were
recorded in [2H]6-benzene at 298 K unless otherwise stated. Proton
and carbon chemical shifts were referenced internally to residual
solvent resonances; coupling constants, J, are quoted in Hz.
[PhP(C{NiPr}{NHiPr})CH2-]2 (1a). A solution of iPrNdCd
NiPr (0.290 mL, 1.83 mmol) in THF (∼10 mL) was added dropwise
to a solution of [PhP(Li{THF}2)CH2-]2 (0.500 g, 0.92 mmol) also
in THF (∼15 mL) at -78 °C. The resultant yellow suspension was
stirred for 2 h at low temperature, affording a paler yellow
suspension, to which a slurry of [HNEt3][Cl] (0.250 g, 1.83 mmol)
in THF (∼10 mL) was added. The reaction mixture was allowed
to warm slowly to ambient temperature over a period of 5 h,
affording a clear colorless solution, which was stirred for a further
16 h. Removal of volatiles under reduced pressure yielded the
product species as a crude white solid. Recrystallization from hexane
at -30 °C afforded colorless crystals of the product species.
Yield: 0.32 g, 69%. Anal. Calc for C28H44N4P2 (498.30): C 67.45,
H 8.89, N 11.24. Found: C 67.52, H 9.06, N 11.00. 1H NMR (500
MHz): meso-{Esyn:Esyn} δ 7.42 (m, 4H, o-C6H5), *, 4.59 (m, 2H,
dNCH), 4.25 (sept, J ) 6.5, 2H, NHCH), 3.52 (d, J ) 6.7, 2H,
NH), 2.29 (m, 2H, CH2), 2.11 (m, 2H, CH2), 1.36 (d, J ) 6.1, 6H,
dNCHMe2), 1.29 (d, J ) 6.1, 6H, dNCHMe2), 0.95 (d, J ) 6.4,
[PhP(C{NCy}{NHCy})CH2-]2 (1b). Compound 1b was syn-
thesized using a procedure analogous to that described for 1a, using
[PhP(Li{THF}2)CH2-]2 (0.500 g, 0.92 mmol), CyNdCdNCy
(0.380 g, 1.83 mmol), and [HNEt3][Cl] (0.250 g, 1.83 mmol).
Recrystallization of the crude white product from hexane at -30
°C afforded pure 1b. Yield: 0.280 g, 61%. Anal. Calc for
C40H60N4P2 (658.43): C 72.92, H 9.18, N 8.50. Found: C 73.02,
1
H 9.16, N 8.53. H NMR (300 MHz): mixture of meso-{Esyn
:
Esyn} and meso-{Esyn:Zanti} δ 7.72 (m, o-C6H5), 7.50 (m, o-C6H5),
7.12-7.00 (m, m- and p-C6H5), 4.27 (m, NCH), 4.16 (m, NH),
4.06 (m, NCH), 3.75 (d, J ) 7.2, NH), 3.68 (d, J ) 7.2, NH), 3.28
(m, NCH), 3.23 (m, NCH), 2.82 (m, CH2), 2.69 (m, CH2), 2.40
(m, NCH), 2.30 (m), 2.20 (m, NCH), 2.03-0.71 (m, Cy-CH2);
mixture of rac-{Esyn:Esyn} and rac-{Esyn:Zanti} δ 7.78 (m, o-C6H5),
7.63 (m, o-C6H5), 7.08-6.99 (m, m- and p-C6H5), 4.25 (m, NCH),
4.15 (m, NH), 4.08 (m, NCH), 3.79 (d, J ) 7.0, NH), 3.72 (d,
J ) 7.2, NH), 3.29 (m), 3.11 (m, NCH), 2.83 (m), 2.44 (m), 2.31
(m), 2.21 (m), 1.97-0.82 (m, Cy-CH2). 31P NMR (121 MHz):
meso-{Esyn:Esyn} δ -28.7 (s); rac-{Esyn:Esyn} δ -29.0 (s); meso-
{Esyn:Zanti} δ -14.5 (d, J ) 41.0 Hz), -26.9 (d, J ) 41.0 Hz);
rac-{Esyn:Zanti} δ -14.9 (d, J ) 33.5 Hz), -26.1 (d, J )
33.5 Hz).
[PhP(C{NiPr}2AlMe2)CH2-]2 (2a). A 0.20 mL portion of a
solution of AlMe3 (2.0 M in hexanes, 0.40 mmol) was added
dropwise via syringe to a solution of [PhP(C{NiPr}{NHiPr})CH2-
]2 (0.100 g, 0.20 mmol) in hexane (∼15 mL). The resultant clear,
colorless solution was stirred at ambient temperature for 15 h. The
volatiles were removed in vacuo to afford a crude white solid.
Analytically pure samples were obtained by crystallization from
hexane at -30 °C. Yield: 0.084 g, 76%. Anal. Calc for C32H54N4-
Al2P2 (610.34): C 62.93, H 8.91, N 9.17. Found: C 62.91, H 8.84,
N 8.99. 1H NMR (300 MHz): meso δ 7.36 (m, 2H, o-C6H5), 7.03
(t, J ) 7.4, 2H, m-C6H5), 6.92 (d, J ) 7.5, 1H, p-C6H5), 3.95 (sept,
J ) 6.2, 2H, CHMe2), 2.56 (m, 1H, CH2), 2.45 (m, 1H, CH2), 1.08
(d, J ) 6.3, 6H, CHMe2), 0.91 (d, J ) 6.0, 6H, CHMe2), -0.20 (s,
6H, AlMe2); rac δ 7.34 (m, 2H, o-C6H5), 7.05-6.89 (m, 3H, m-,
p-C6H5), 3.95 (br sept, 2H, CHMe2), 2.52 (m, 2H, CH2), 1.10 (d,
J ) 6.9, 6H, CHMe2), 0.90 (d, J ) 6.0, 6H, CHMe2), -0.22 (s,
6H, AlMe2). 31P NMR (121 MHz): meso δ -27.6 (s); rac δ -29.0
(s).
6H, NHCHMe2), 0.88 (d, J ) 6.4, 6H, NHCHMe2); meso-{Esyn
:
Z
anti} δ 7.65 (m, 4H, o-C6H5), *, 4.58 (m, 1H, dNCH {Esyn}),
4.25 (sept, J ) 6.5, 1H, NHCH {Esyn}), 3.97 (m, 1H, NHCH
{Zanti}), 3.84 (m, 1H, NH {Zanti}), 3.58 (d, J ) 7.2, 1H, NH {Esyn}),
3.36 (sept, J ) 6.1, 1H, dNCH {Zanti}), 2.74 (m, 1H, CH2), 2.63
(m, 1H, CH2), 2.21 (m, 1H, CH2), 2.04 (m, 1H, CH2), 1.36 (d, J )
6.1, 3H, dNCHMe2 {Esyn}), 1.34 (d, J ) 6.3, 3H, dNCHMe2
{Zanti}), 1.29 (d, J ) 6.1, 3H, dNCHMe2 {Esyn}), 1.22 (d, J ) 6.2,
3H, dNCHMe2 {Zanti}), 0.95 (d, J ) 6.4, 3H, NHCHMe2 {Esyn}),
0.91 (d, J ) 6.3, 3H, NHCHMe2 {Zanti}), 0.88 (d, J ) 6.4, 3H,
NHCHMe2 {Esyn}), 0.44 (d, J ) 6.3, 3H, NHCHMe2 {Zanti}); rac-
{Esyn:Esyn} δ 7.42 (m, 4H, o-C6H5), *, 4.59 (m, 2H, dNCH), 4.25
(sept, J ) 6.5, 2H, NHCH), 3.56 (d, J ) 6.8, 2H, NH), 2.22 (m,
4H, CH2), 1.38 (d, J ) 6.1, 6H, dNCHMe2), 1.29 (d, J ) 6.1, 6H,
dNCHMe2), 0.98 (d, J ) 6.5, 6H, NHCHMe2), 0.90 (d, J ) 6.5,
6H, NHCHMe2). rac-{Esyn:Zanti} δ 7.71 (m, 2H, o-C6H5), 7.57 (m,
2H, o-C6H5), *, 4.58 (m, 1H, dNCH {Esyn}), 4.25 (sept, J ) 6.5,
1H, NHCH {Esyn}), 3.97 (m, 1H, NHCH {Zanti}), 3.94 (m, 1H, NH
[PhP(C{NCy}2AlMe2)CH2-]2 (2b). Compound 2b was syn-
thesized using a procedure analogous to that described for 2a, using
[PhP(C{NCy}{NHCy})CH2-]2 (0.100 g, 0.15 mmol) and AlMe3
(0.15 mL of a 2.0 M solution in hexane, 0.30 mmol). Recrystal-
lization of the crude white product from hexane at -30 °C afforded
pure 2b. Yield: 0.070 g, 58%. Anal. Calc for C44H70N4Al2P2
(770.47): C 68.55, H 9.15, N 7.27. Found: C 68.67, H 9.21, N
7.18. 1H NMR (300 MHz): meso δ 7.41 (m, 2H, o-C6H5), 7.03 (t,
J ) 7.3, 2H, m-C6H5), 6.94 (d, J ) 7.3, 1H, p-C6H5), 3.61 (m, 2H,
NCH), 2.63 (m, 2H, CH2), 1.93-0.91 (m, 20H, Cy-CH2), -0.14
(s, 6H, AlMe2). 31P NMR (121 MHz): meso δ -28.1 (s); rac δ
-30.5 (s).
(11) Rettig, M. F.; Wing, R. M.; Wiger, G. R. J. Am. Chem. Soc. 1981,
103, 2980. Kistner, C. R.; Hutchinson, J. H.; Doyle, J. R.; Storlie, J. C.
Inorg. Chim. Acta 1963, 2, 1255.

2474 Organometallics, Vol. 25, No. 10, 2006
Mansfield et al.
PtCl2([PhP(C{NiPr}{NHiPr})CH2-]2) (3a). A clear colorless
solution of [PhP(C{NiPr}{NHiPr})CH2-]2 (1a, 0.100 g, 0.20 mmol)
in toluene (∼10 mL) was added dropwise to a stirred suspension
of PtCl2(COD) (0.075 g, 0.20 mmol) in toluene (∼10 mL). Filtration
from a small amount of particulate matter, followed by removal of
the volatiles under reduced pressure, afforded 3a as a crude white
solid. Analytically pure samples were obtained by crystallization
from THF at -30 °C. Yield: 0.11 g, 35%. Anal. Calc for C28H44N4-
Cl2P2Pt (763.21): C 43.98, H 5.80, N 7.33. Found: C 44.06, H
δ 42.4 (J ) 3372 {Zanti}), 32.0 (J ) 3479 {Esyn}). 195Pt (107
MHz): meso-{Esyn:Zanti} δ - 4540 (dd, J ) 3372, 3479); rac-
{Zanti:Zanti} δ -4594 (t, J ) 3380); meso-{Zanti:Zanti} δ -4608
(t, J ) 3382).
PtI2([PhP(C{NCy}{NHCy})CH2-]2) (3b′). Compound 3b′ was
synthesized using a procedure analogous to that described for 3a,
using [PhP(C{NCy}{NHCy})CH2-]2 (0.10 g, 0.15 mmol) and PtI2-
(COD) (0.08 g, 0.15 mmol). Recrystallization of the crude yellow
product from toluene at -30 °C afforded pure 3b′. Yield: 0.05 g,
29%. Anal. Calc for C40H60N4I2P2Pt (1107.20): C 43.37, H 5.46,
N 5.06. Found: C 43.43, H 5.56, N 4.94. 31P NMR (121 MHz)†:
δ 57.7 (J ) 3154) 52.8 (J ) 3157), 44.7 (J ) 3209), 33.8 (J )
3198) († definitive assignment of isomers has not been possible
1
5.87, N 7.39. H NMR (500 MHz): meso-{Zanti:Zanti} δ 8.21 (m,
4H, o-C6H5), 7.55 (m, 2H, NH), *, 3.81 (sept, J ) 6.1, 2H, d
NCH), 3.48 (m, 2H, NHCH), 2.64 (m, 2H, CH2), 1.47 (m, 2H,
CH2), 1.18 (d, J ) 6.2, 6H, dNCHMe2), 1.16 (d, J ) 6.1, 6H,
dNCHMe2), 0.97 (d, J ) 6.3, 6H, NHCHMe2), 0.81 (d, J ) 6.2,
6H, NHCHMe2); meso-{Esyn:Zanti} δ 7.97 (m, 2H, o-C6H5 {Zanti}),
7.88 (m, 2H, o-C6H5 {Esyn}), 7.12 (m, 1H, NH {Zanti}), 5.31 (d br,
1H, NH {Esyn}), 4.29 (m br, 1H, dNCH {Esyn}), 4.21 (m br, 1H,
NHCH {Esyn}), 3.78 (sept, J ) 6.1, 1H, dNCH {Zanti}), 3.55 (sept,
J ) 6.5, 1H, NHCH {Zanti}), 2.64 (m, 2H, CH2), 1.47 (m, 2H, CH2),
1.37 (d br, 3H, dNCHMe2 {Esyn}), 1.09 (d br, 3H+3H, NHCHMe2
{Esyn}), 1.05 (d, 3H+3H, dNCHMe2 {Esyn} + NHCHMe2 {Zanti}),
0.98 (d, J ) 6.5, 6H, dNCHMe2 {Zanti}), 0.85 (d, J ) 6.3, 3H,
NHCHMe2 {Zanti}); rac-{Zanti:Zanti} δ 8.13 (m, 4H, o-C6H5), 7.34
(m, 2H, NH), *, 3.81 (sept, J ) 6.1, 2H, dNCH), 3.48 (sept, J )
6.8, 2H, NHCH), 2.65 (m, 2H, CH2), 1.47 (m, 2H, CH2), 1.18 (d,
J ) 6.1, 6H, dNCHMe2), 1.16 (d, J ) 6.1, 6H, dNCHMe2), 0.97
(d, J ) 6.3, 6H, NHCHMe2), 0.81 (d, J ) 6.3, 6H, NHCHMe2) [*
remaining aromatic resonances for both isomers overlap in the
region δ 7.05-6.96]. 31P NMR (202 MHz): rac-{Zanti:Zanti} δ 44.9
1
due to the complexity of the H NMR spectra arising from the
presence of the cyclohexylsubstituents; however, the resonances
at δ 52.8 and 44.7 are believed to represent two different phosphorus
environments within an asymmetric molecule due to their similar
intensities and the observation of an additional 7 Hz coupling of
unknown origin in each case).
Acknowledgment. Johnson Matthey plc is thanked for the
loan of precious metal salts, and the University of Sussex is
thanked for additional financial support.
Supporting Information Available: CIF files for 1a, 1b, meso-
2a, rac-2a, 2b, and 3b′. This material is available free of charge
via the Internet at http://pubs.acs.org.
(J ) 3380); meso-{Zanti:Zanti} δ 43.2 (J ) 3382); meso-{Esyn:Zanti
}
OM060014Z