The anion of a phenyltris(alkylamino)phosphonium (PhTAP) salt as a chelating ligand: Synthesis and X-ray crystal structure of a 16-electron ruthenium(II) organometallic complex

Article abstract of DOI:10.1021/om970819u

The phosphonium salt [PhP(NHⁱPr)₃]Br has been synthesized, and the ligand properties of its deprotonated forms have been investigated. Treatment of its dilithiate Li₂[PhP(Nⁱ-Pr)₃] with the dimer [(η-p-cymene)RuCl₂]₂ provides the unsaturated 16-electron cation [(η-p-cymene)Ru{η²-(ⁱPrN)₂PPh(NH ⁱPr)}]⁺ which adds cyanide and carbon monoxide (reversibly) and has been structurally characterized as its tetraphenylborate salt.

Full text of DOI:10.1021/om970819u

Organometallics 1998, 17, 551-555
551
Th e An ion of a P h en yltr is(a lk yla m in o)p h osp h on iu m
(P h TAP ) Sa lt a s a Ch ela tin g Liga n d : Syn th esis a n d X-r a y
Cr ysta l Str u ctu r e of a 16-Electr on Ru th en iu m (II)
Or ga n om eta llic Com p lex
Philip J . Bailey,* Keith J . Grant, and Simon Parsons
Department of Chemistry, The University of Edinburgh, The King’s Buildings,
West Mains Road, Edinburgh EH9 3J J , U.K.
Received September 16, 1997
The phosphonium salt [PhP(NHiPr)3]Br has been synthesized, and the ligand properties
of its deprotonated forms have been investigated. Treatment of its dilithiate Li2[PhP(Ni-
Pr)3] with the dimer [(η-p-cymene)RuCl2]2 provides the unsaturated 16-electron cation [(η-
p-cymene)Ru{η2-(iPrN)2PPh(NHiPr)}]+ which adds cyanide and carbon monoxide (reversibly)
and has been structurally characterized as its tetraphenylborate salt.
The chemistry of complexes containing tripod ligands
continues to provide new and exciting examples of
structure and reactivity in coordination and organome-
tallic chemistry.1 The ability of a tripod ligand to
effectively provide a coordination pocket to encapsulate
a metal center allows both the steric shielding of the
remaining coordination sites at the metal and a strict
control over the stereochemistry of these sites, which
F igu r e 1.
provide three homotopic coordination sites for substrate
coordination opposite the ligand.3
may be finely adjusted by choice of donor atom substit-
uent(s). The implications of orders of rotational sym-
metry higher than two for controlling the stereochem-
istry of ligand transformations in stoichiometric and
catalytic processes has recently been attracting increas-
ing attention.2 Our interest in developing new ligands
for asymmetric catalysis by octahedral metal complexes
has lead us to consider ways in which tripod ligands
may be used to reduce their symmetry to C3 and thus
The majority of tripodal ligands contain a bridgehead
atom linked to the three donor atoms via mono- or
diatomic arms. However, systems which may be re-
garded as a third structural type in which the three
donor atoms are directly bonded to the bridgehead only
rarely behave as tripodal ligands. Perhaps the best
known examples of this type of coordination are tet-
rahydroborate, which is known to coordinate in an η3-
mode in complexes such as [M(BH4)4] (M ) Zr, Hf),4 and
(1) (a) Schrock, R. R. Acc. Chem. Res. 1997, 30, 9 and references
therein. (b) Menge, W. M. P. B.; Verkade, J . G. Inorg. Chem. 1991, 30,
4628. (c) Cummins, C. C.; Schrock, R. R.; Davis, W. M. Inorg. Chem.
1994, 33, 1448. (d) Ge, P.; Haggerty, B. S.; Rheingold, A. L.; Riordan,
C. G. J . Am. Chem. Soc. 1994, 116, 8406. (e) Canary, J . W.; Allen, C.
S.; Castagnetto, J . M.; Wang, Y. J . Am. Chem. Soc. 1995, 117, 8484.
(f) Nomura, K.; Schrock, R. R.; Davis, W. M. Inorg. Chem. 1996, 35,
3695. (g) Kernbach, U.; Ramm, M.; Luger, P.; Fehlhammer, W. P.
Angew. Chem, Int. Ed. Engl. 1996, 35, 310. (h) Friedrich, S.; Gade, L.
H.; Li, W. S.; McPartlin, M. Chem. Ber. 1996, 129, 1287. (i) Memler,
H.; Kauper, U.; Gade, L. H.; Stalke, D.; Lauher, J . W. Organometallics
1996, 15, 3637. (j) Freidrichs, S.; Memler, H.; Gade, L. H.; Li, W. S.;
Scowen, I. J .; McPartlin, M.; Housecroft, C. E. Inorg. Chem. 1996, 35,
2433. (k) Lah, M. S.; Chun, H. Inorg. Chem. 1997, 36, 1782. (l) Findeis,
B.; Contel, M.; Gade, L. H.; Laguna, M.; Concepcion, M.; Scowen, I. J .;
McPartlin, M. Inorg. Chem. 1997, 36, 2386.
(2) (a) Burk, M. J .; Harlow, R. L. Angew. Chem, Int. Ed. Engl. 1990,
29, 1462. (b) Ward, T. R.; Venanzi, L. M.; Albinati, A.; Lianza, F.;
Gerfin, T.; Gramlich, V.; Tombo, G. M. R. Helv. Chim. Acta 1991, 74,
983. (c) Burk, M. J .; Feaster, J . E.; Harlow, R. L. Tetrahedron:
Asymmetry 1991, 2, 569. (d) Nugent, W. A. J . Am. Chem. Soc. 1992,
114, 2786. (e) Tokar, C. J .; Kettler, P. B.; Tolman, W. B. Organome-
tallics 1992, 11, 2737. (f) Adolfsson, H.; Warnmark, K.; Moberg, C. J .
Chem. Soc., Chem. Commun. 1992, 1054. (g) LeCloux, D. D.; Tolman,
W. B. J . Am. Chem. Soc. 1993, 115, 1153. (h) LeCloux, D. D.; Tokar,
C. J .; Osawa, M.; Houser, R. P.; Keys, M. C.; Tolman, W. B. Organo-
metallics 1994, 13, 2855. (i) Nugent, W. A.; Harlow, R. L. J . Am. Chem.
Soc. 1994, 116, 6142. (j) Hammes, B. S.; Ramos-Maldonado, D.; Yap,
G. P. A.; Liable-Sands, L.; Rheingold, A. L.; Young, V. G., J r.; Borovik,
A. S. Inorg. Chem. 1997, 36, 3210. (k) Bolm, C.; Kadereit, D.; Valacchi,
M. Synlett 1997, 687.
the trimethylenemethane (TMM) ligand [C(CH2)3]2-
,
which commonly occurs in an η4-coordination mode and
may be included in this category (Figure 1).5 Some time
ago we recognized that such tripodal ligands, possessing
approximately tetrahedral donor atoms bearing one
bulky substituent, could be effective in the role we have
identified since the two possible arrangements of the
substituents around the coordinated ligand would pro-
vide the required chiral complexes with C3 symmetry
(Figure 2). Furthermore, the anticipated rigidity of such
a metal-ligand unit and the proximity of the stereo-
genic centers to the catalytically active site are expected
to provide effective stereocontrol over processes occur-
ring at the metal center.
With the aim of developing a new ligand system of
this type, we have recently been considering the system
(3) Bailey, P. J .; Blake, A. J .; Kryszczuk, M.; Parsons, S.; Reed, D.
J . Chem. Soc., Chem. Commun. 1995, 1647.
(4) (a) Bird, P. H.; Churchill, M. R. J . Chem. Soc., Chem. Commun.
1967, 403. (b) Broach, R. W.; Chuang, I. S.; Marks, T. J .; Williams, J .
M. Inorg. Chem. 1983, 22, 1081.
(5) J ones, M. D.; Kemmitt, R. D. W. Adv. Organomet. Chem. 1987,
27, 279.
S0276-7333(97)00819-4 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 01/23/1998

552 Organometallics, Vol. 17, No. 4, 1998
Bailey et al.
an investigation of the coordination of such a ligand with
a ruthenium(II) arene fragment.
Resu lts a n d Discu ssion
The phosphonium salt [PhP(NHiPr)3]Br was synthe-
sised by the in-situ preparation of [PhPBrCl2]Br from
PhPCl2 followed by its condensation with isopropyl-
amine.13 The crystalline salt was pure by elemental
analysis and NMR (1H, 13C, and 31P), and these data
closely correspond to those previously reported; how-
ever, its melting point of 215 °C differs very significantly
from the published value of 138-140 °C.13,14 Treatment
of the finely ground salt in THF (in which it is largely
insoluble) with 3 mol equiv of n-butyllithium provides
a yellow solution which, when treated with 3 mol equiv
of MeI, provided the trimethylated phosphonium cation
[PhP{N(Me)iPr}3]+.15 Furthermore, it was established
that the starting salt [PhP(NHiPr)3]Br remained un-
changed on treatment with MeI under the same condi-
tions. These observations, therefore, strongly suggest
that the yellow solution contains the dilithiate Li2[PhP-
(NiPr)3], which was used in subsequent reactions with-
out further characterization.
F igu r e 2. Formation of C3-symmetric octahedral com-
plexes by tripod ligands in which the donor atoms are
directly bonded to the bridgehead atom.
[C(NR)3]2- as an isoelectronic analogue of the TMM
ligand.3,6 However, although we have found 1,2,3-
substituted guanidines and their anions to be flexible
monodentate,7 chelating,8 and bridging ligands,9 we
have yet to observe the desired tripodal coordination of
all three nitrogen atoms to a single metal. Given the
strong preference of the TMM ligand to adopt this
coordination mode,10 we were initially unsure of the
reasons for this difference in behavior. However, we
now consider the situation to be a result principally of
the geometric changes in the metal-ligand system
brought about by substituting carbon by nitrogen.11 On
coordination to a metal center, the planar, “cross-
conjugated” TMM dianion undergoes a so-called “um-
brella” distortion in which the ligand typically distorts
by 12° from planarity toward the metal.12 This distor-
tion clearly involves a loss of conjugation across the
ligand. The apparent absence of an equivalent coordi-
nation mode of the [C(NR)3]2- ligand suggests that the
energy gained by M-L bond formation is insufficient
to compensate for the distortion involved in coordination
of the ligand. The smaller size of nitrogen compared to
carbon means that, for a given metal, the distortion from
planarity required for η3-coordination of a C(N)3 ligand
is greater than that for a C(C)3 ligand. Coupled with
the stability of the η2-chelating coordination mode,
which contrasts with the rarity of a similar mode for
the TMM ligand, we believe that it is this factor which
accounts for the failure of the [C(NR)3]2- ligand to adopt
our desired η3-tripodal coordination.
In an attempt to prepare a complex of the new ligand
coordinated through all three nitrogen atoms the dimer
[(η-p-cymene)RuCl2]2 was treated with 2 mol equiv of
the PhTAP dianion, which gave a dark blue/green
solution of a product to which we assign the formula
[(η-p-cymene)Ru{(iPrN)3PPh}] (1). Despite careful ex-
clusion of air, it proved very difficult to isolate this
product uncontaminated by its deep purple decomposi-
tion product [(η-p-cymene)Ru{η2-(iPrN)2PPh(NHiPr)}]+
(2). In the absence of a clean sample of the primary
product, we have, therefore, characterized this stable
complex. We were initially unsure whether the decom-
position was due to oxidation or hydrolysis; however,
cyclic voltametry of the cationic purple product, isolated
as its tetraphenylborate salt, failed to reveal a reduction
process at a potential characteristic for a Ru(III)/Ru(II)
couple, but rather a reduction wave at -1.66 V vs
ferrocene was observed which we assign to a Ru(II)/
Ru(I) couple. We, therefore, conclude that neutral 1 is
strongly basic and that the formation of the cationic
deep purple product 2 is due to protonation by water.
This is further confirmed by the observation that the
deep blue/green color of 1 is regenerated by treatment
of 2 with n-butyllithium in THF solution. That the
purple 2 contained Ru(II) was confirmed by the obser-
vation of a sharp unshifted 1H NMR spectrum which
showed, in addition to signals due to the aromatic
groups present, the presence of three independent
isopropyl groups on the ligand and a signal at 2.97 ppm
which may be assigned to an N-H proton. These data,
therefore, suggest a complex containing the ligand as a
Recognition of these problems with TMM analogues
has lead us to consider ligands based on tetrahedral
systems. Such ligands should avoid the problems
associated with ligand distortion on coordination since
they effectively have the above distortion built in. We
have identified the dianions [PhP(NR)3]2-, derived by
the triple deprotonation of the phenyltris(alkylamino)-
phosphonium (PhTAP) cations [PhP(NHR)3]+, as pos-
sible ligands fulfilling these criteria, and here we report
(6) (a) Bailey, P. J .; Mitchell, L. A.; Raithby, P. R.; Rennie, M.-A.;
Verhorevoort, K.; Wright, D. S. J . Chem. Soc., Chem. Commun. 1996,
1351. (b) Bailey, P. J .; Gould, R. O.; Harmer, C. N.; Pace, S.; Steiner,
A.; Wright, D. S. Chem. Commun. 1997, 1161.
(7) Bailey, P. J .; Grant, K. J .; Mitchell, L. A.; Pace, S.; Parsons, S.;
Stewart, L. J . J . Chem. Soc., Dalton Trans. 1997, 4263.
(8) Bailey, P. J .; Mitchell, L. A.; Parsons, S. J . Chem. Soc., Dalton
Trans. 1996, 2839.
(9) Bailey, P. J .; Bone, S.; Mitchell, L. A.; Parsons, S.; Taylor, K.;
Yellowlees, L. J . Inorg. Chem. 1997, 36, 867.
(10) Only a very few examples of complexes in which the trimeth-
ylenemethane ligand does not adopt a symmetrical η4-coordination are
known, see: (a) Su, C.-C.; Chen, J .-T.; Lee, G.-H.; Wang, Y. J . Am.
Chem. Soc. 1994, 116, 499. (b) Herberich, G. E.; Kreuder, C.; Englert,
U. Angew. Chem., Int. Ed. Engl. 1994, 33, 2465. (c) Bazan, G. C.;
Rodriguez, G.; Cleary, B. P. J . Am. Chem. Soc. 1994, 116, 2177. (d)
Watanabe, S.; Kurosawa, H. Organometallics 1997, 16, 3601.
(11) Bailey, P. J .; Rankin, D. W. H.; Smart, B. Unpublished results.
(12) (a) Almenningen, A.; Haaland, A.; Wahl, K. Acta Chem. Scand.
1969, 13, 1145. (b) Churchill, M. R.; Gold, K. Inorg. Chem. 1969, 8,
401. (c) Churchill, M. R.; DeBoer, B. G. Inorg. Chem. 1973, 12, 525.
(13) de la Fuente, G. F.; Huheey, J . E. Phosphorus, Sulfur Silicon
Relat. Elem. 1993, 78, 23.
(14) The phosphonium salt [PPh(NHiPr)3]Br has been crystallo-
graphically characterized (monoclinic, space group C2/c, a ) 14.485-
(3) Å, b ) 9.213(3) Å, c ) 29.213(5) Å; â ) 99.24(2)°, R1 ) 0.0531) and
full details are provided in the Supporting Information.
(15) [PhP{N(Me)iPr}3]I: 1H NMR (250 MHz, CDCl3, 20 °C, TMS) δ
i
) 7.7 (mult, 5H, Ph), 3.5 (mult, 3H, Pr-CH), 2.72 (d, J P-H ) 12 Hz,
9H, CH3), 1.22 (d, J ) 9 Hz, 18H, iPr-CH3); MS (+ FAB) m/ z 324 (100)
[M+].

A 16-Electron Ru(II) Phosphonium Complex
Organometallics, Vol. 17, No. 4, 1998 553
Sch em e 1. Ch ela tin g Bis(a m id e) Sta biliza tion of
16-Electr on Ru (II) F r om Ref 18
corresponding N-Ru-N angle in the complex contain-
ing the chelating guanidine monoanion [(η-p-cymene)-
Ru{η2-(iPrN)2C(NHiPr)}Cl],16 the difference attributable
to the larger size of phosphorus. The angle N(1)-P-
N(2) is distorted by ca. 15° from tetrahedral (94.01(14)°),
while the remaining angles at P are correspondingly
expanded. The puckering of the N(1)-P-N(2)-Ru
plane is slight [13.9(3)°] but not negligible, indicating
the possibility of a small pseudo π-allyl contribution to
the M-L bonding, although the Ru-P separation of 2.71
Å suggests that this is unlikely to be significant. The
angle between the planes defined by the p-cymene ring
and the atoms N(1), Ru(1), and N(2) is 91.0°, indicating
negligible pyramidalization of the ruthenium center,
consistent with the PhTAP ligand acting as a π-donor.17
Although 2 is an unusual example of a 16-electron
Ru(II) complex containing an η-bonded arene ligand, it
is not unique, and a comparison with the other known
example of such a system is of interest. Noyori has
found that KOH treatment of the system [(η-p-cymene)-
Ru{(S,S)-TsDPEN)}Cl] ((S,S)-TsDPEN ) (1S,2S)-N-p-
toluenesulphonyl-1,2-diphenylethylenediamine) results
in elimination of one of the acidic NH2 protons and the
Cl- ligand and formation of a stable neutral 16-electron
species, which is also deep purple in color.18 This
process may be reversed by treatment with triethylam-
monium chloride (Scheme 1). The 16-electron complex
is a highly effective catalyst for the asymmetric transfer
hydrogenation of ketones and is readily converted into
the yellow active hydrido species by treatment with
isopropyl alcohol, the reducing agent used in this
process. In contrast to these observations, 2 is unaf-
fected by treatment with sources of chloride (PPh4Cl)
or HCl (NEt3HCl). It would, therefore, appear that the
PhTAP-derived chelating ligand is more effective at
stabilizing the ruthenium unsaturation by π-donation
from the coordinated amido nitrogen atoms than is the
TsDPEN ligand. This is perhaps as would be predicted
if the amido substituents in the two ligand systems are
compared. The resulting increased electron density at
the ruthenium in 2 is illustrated by its reactivity with
π-acceptor ligands. Passing a stream of carbon mon-
oxide through a CH2Cl2 solution of 2 leads to the rapid
bleaching of the purple color of the solution to yellow.
This solution shows a sharp absorption in the infrared
at 1993 cm-1 attributable to the coordinated CO ligand,
a surprisingly low frequency for a cationic complex, and
a further illustration of the strong π-donor character of
the PhTAP-derived ligand. Allowing this solution to
F igu r e 3. Thermal ellipsoid plot of the structure of the
cation in [(η-p-cymene)Ru{η2-(iPrN)2PPh(NHiPr)}][BPh4]
(2).
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for th e Ca tion in
[(η-p-cym en e)Ru {η2-(iP r N)2P P h (NHiP r )}][BP h 4] (2)
N1-Ru
N2-Ru
P-N1
2.011(3)
2.017(3)
1.620(3)
1.608(3)
1.616(3)
1.801(3)
1.477(4)
1.476(4)
1.480(5)
71.76(11)
94.01(14)
P-N1-Ru
96.10(14)
96.26(13)
115.6(2)
115.7(2)
113.5(2)
113.6(2)
104.8(2)
124.0(2)
125.8(2)
122.9(3)
13.9(3)
P-N2-Ru
N1-P-N3
N2-P-N3
N1-P-C41
N2-P-C41
N3-P-C41
P-N1-C11
P-N2-C21
P-N3-C31
P-N1-Ru-N2
P-N2
P-N3
P-C41
N1-C11
N2-C21
N3-C31
N1-Ru-N2
N1-P-N2
monoanion with the third nitrogen present as an
-NHiPr group. Whether this third nitrogen is bonded
to the metal is unclear, however, in the absence of such
coordination, a 16-electron Ru(II) complex results. The
fact that the complex is a cation precludes the presence
of a further anionic ligand, and since there is no
evidence in the NMR spectrum for any other organic
group which may be coordinated to the metal and the
FAB mass spectrum shows a molecular ion at m/ z )
517 consistent with the formulation of the complex as
[(η-p-cymene)Ru{(iPrN)2(NHiPr)PPh}]+, it appears that
2 is either an unusual example of a 16-electron Ru(II)
organometallic complex or contains the monoanionic
ligand in the desired η3-coordination mode.
An X-ray crystal structure analysis of 2[BPh4] shows
that it is in fact a 16-electron complex with the ligand
in an η2-chelating coordination mode with the -NHiPr
group remaining uncoordinated. Apart from the η-bond-
ed p-cymene, no other ligands are present. A thermal
ellipsoid plot of the structure of 2 is shown in Figure 3,
and significant bond lengths and angles are given in
Table 1. The two Ru-N bond distances do not differ
significantly (2.017(3) and 2.011(3) Å), and the P-N
bond distances are also not significantly different, with
the bond to the uncoordinated nitrogen N(3) (1.616(3)
Å) perhaps surprisingly lying between the values for the
two coordinated nitrogens (1.608(3) and 1.620(3) Å). The
chelating angle at Ru (N(1)-Ru-N(2)) is 71.76(11)°,
which compares with a value of 62.07(7)° for the
(16) Bailey, P. J .; Elliot, M.; Parsons, S. Unpublished results.
(17) J ohnson, T. J .; Folting, K.; Streib, W. E.; Martin, J . D.; Huffman,
J . C.; J ackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995,
34, 488.
(18) Haack, K.-J .; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R.
Angew. Chem., Int. Ed. Engl. 1997, 36, 285.

554 Organometallics, Vol. 17, No. 4, 1998
Bailey et al.
stand under a nitrogen atmosphere leads to rapid
regeneration of the purple color, and within 10 min at
room temperature, the IR absorption of the CO complex
has disappeared. Attempted crystallization of the CO
complex under an atmosphere of CO led to slow conver-
sion to secondary products which could be followed by
31P NMR, a total of six signals being observed after a
period of 1 week. In an attempt to prepare a stable
derivative of 2, the coordination of various other π-ac-
ceptor ligands was investigated. Both triphenylphos-
phine and triphenyl phosphite remained uncoordinated,
although it is reasonable to assume that the bulk of the
PhTAP ligand might be responsible for this. However,
treatment of a methanol solution of 2 with potassium
cyanide instantly gave a stable yellow solution display-
ing a sharp ν(CtN) mode at 2102 cm-1. A single signal
at 34.6 ppm in the 31P NMR spectrum of this solution
showed it to be uncontaminated by other products. The
high solubility of this neutral complex in all solvents
has so far prevented us from obtaining crystals suitable
for crystallography. The stability of this cyanide com-
plex compared with that of CO is perhaps unsurprising
given the involatile nature of the ligand, however, it is
probable that the additional ionic component of the
M-CN bond adds to the stability. The donor strength
of the PhTAP ligand is further indicated by the low
value of the CtN stretching frequency, which is due to
considerable back-bonding from the metal and, thus,
indicates high electron density at the metal in 2. In
contrast to Noyori’s complex, 2 shows no reactivity
toward isopropyl alcohol or, taking account of the
difference in charge between the two complexes, sodium
isopropoxide. This may presumably be attributed to the
electronic differences between the two complexes, al-
though, as noted above, steric effects may be significant
in 2.
To our knowledge there have been only two previous
reports of complexes containing ligands of the general
type [RP(NR′)2NR′2]-, although in both of these cases
the ligand was derived from an aminobis(imino)phos-
phorane [(NR)2PNR2] and not from a phosphonium salt.
The complex [(η3-C3H5)Ni{η2-RP(NR′)2NR′2}]-, (R )
allyl, R′ ) SiMe3) has been shown to be an effective
catalyst for ethene19 and 1-alkene20 polymerization, and
its palladium analogue has been structurally character-
ized.19 However, in the current context, the behavior
of the complexes [(CO)nMn{η2-RP(NR′)2NR′2}]- (R ) Br,
R′ ) SiMe3, n ) 3, 4; R ) OPh, R′ ) SiMe3, n ) 3) are
of greater interest.21 The tetracarbonyl complex with
R ) Br shows a reversible loss of a carbonyl ligand
generating a 16-electron Mn(I) species, while substitu-
tion of Br by phenoxide provides a tricarbonyl complex
which shows no tendency to coordinate CO to attain an
18-electron configuration. The ability of these ligands
to stabilize formally unsaturated species has, therefore,
been observed previously, and it would seem that such
behavior could develop into a general feature of their
chemistry. There is a clear relationship between these
ligands and the extensively studied phosphoniobis-
(methanide) ligands [R2P(CH2)2]-.22 However, no ten-
dency for these ligands to stabilize formally unsaturated
metal complexes has been noted, and this is presumably
a reflection of the absence of electrons in π-symmetry
orbitals on the carbon donor atoms.
The question of whether the ligand dianions [Ph-
(NR)3]2- are capable of displaying an η3-coordination
mode as we wish still remains to be answered. Clearly,
in the present case, what we assume to be the neutral
complex [(η-p-cymene)Ru{(iPrN)3PPh}] (1) may contain
the ligand in an η2- or η3-mode. If the third nitrogen is
coordinated, its high basicity suggests that its interac-
tion with the metal is not strong and the available
evidence would seem to suggest that it is in fact
uncoordinated. Whether this is due to electronic or
steric effects is a moot point, however, inspection of
molecular models suggests that it is possible that
excessive steric interaction between the isopropyl groups
on the ligand and the alkyl groups on the η-bonded
arene could prevent coordination of the third nitrogen.
Exp er im en ta l Section
All reactions and manipulations were carried out under an
atmosphere of dry, oxygen-free nitrogen using standard Schlenk
techniques and solvents which were distilled from the ap-
propriate drying agents under nitrogen immediately prior to
use. The dimer [(η-p-cymene)RuCl2]2 was prepared according
to the literature,23 while the phosphonium salt [PhP(NHiPr)3]-
Br was prepared by modification of a literature procedure as
described below.13 NMR spectra were recorded on a Bruker
AC 250 spectrometer, mass spectra on a Kratos MS50 TC
instrument in positive-ion FAB mode using 3-nitrobenzyl
alcohol as the matrix and CsI as calibrant, and infrared spectra
on a Perkin-Elmer Paragon instrument. Electrochemical
measurements were performed using GPES, version 4, soft-
ware run on a personal computer connected to an Antilab
system via an PSTAT 10 potentiostat. Cyclic voltammetry was
performed using a standard three-electrode configuration with
platinum working (0.5 mm diameter disc) and counter elec-
trodes and a Ag/AgCl reference electrode, which gave the CpFe/
CpFe+ couple at 0.58 V. All measurements were made in a
nitrogen-purged solution of CH2Cl2/0.5M [n-Bu4N][BF4].
P r ep a r a tion of [P h P (NHiP r )3]Br . To a 500 cm3 round-
bottomed flask fitted with a reflux condenser and a pressure
equalizing dropping funnel was added a solution containing 5
cm3 of PPhCl2 (6.59 g, 36.8 mmol) in 100 cm3 of CHCl3. To
this solution was added dropwise a solution of 1.89 cm3 of Br2
(5.89 g, 36.8 mmol) in 20 cm3 of CHCl3. The resulting bright
yellow precipitate of [PhPCl2Br]Br was allowed to stir for 30
min, and then a solution containing 19 cm3 of isopropylamine
(13.19 g, 0.223 mol) in 100 cm3 of CHCl3 was added dropwise
over a period of 30 min. As the exothermic reaction proceeded,
the precipitate dissolved to give a yellow solution which
became colorless once all of the amine had been added. The
resulting solution was finally heated to reflux for 2 h. Separa-
tion of the product from isopropylammonium bromide was
achieved by column chromatography on silica, eluting with
CHCl3/CH3OH (3:1). Crystallization of the product from MeCN
provided 6.3 g of large colorless crystals (47%).14 M.p: 215
°C. Anal. Calcd for C15H29BrN3P: C, 49.7; H, 8.01; N, 11.6.
Found: C, 51.1; H, 8.35; N, 11.85. 1H NMR (250 MHz, CDCl3,
20 °C, TMS): δ 8.1 (mult, 2H, Ph), 7.45 (mult, 3H, Ph), 5.43
(19) Keim, W.; Appel, R.; Storeck, A.; Kru¨ger, C.; Goddard, R. Angew.
Chem., Int. Ed. Engl. 1981, 20, 116.
(20) Mo¨hring, V. M.; Fink, G. Angew. Chem., Int. Ed. Engl. 1985,
24, 1001.
(21) Scherer, O. J .; Kerth, J .; Sheldrick, W. S. Angew. Chem., Int.
Ed. Engl. 1984, 23, 156.
(22) (a) Schmidbaur, H. Acc. Chem. Res. 1975, 8, 62. (b) Schmidbaur,
H. Pure Appl. Chem. 1978, 50, 19. (c) Kaska, W. C. Coord. Chem. Rev.
1983, 48, 1. (d) Grohmann, A.; Schmidbaur, H. Comprehensive Orga-
nometallic Chemistry II; Pergamon: Oxford, 1995; Vol. 3, pp 19-31.
(23) Bennett, M. A.; Smith, A. K. J . Chem. Soc., Dalton Trans. 1974,
233.

A 16-Electron Ru(II) Phosphonium Complex
Organometallics, Vol. 17, No. 4, 1998 555
(dd, J H-H ) 9.8 Hz, J P-H ) 15.5 Hz, 3H, NH), 3.30 (mult, 3H,
CH), 1.10 (d, 18H, CH3). 13C{1H} NMR (62.9 MHz, CDCl3, 20
°C, TMS): δ 132.9 (d, J P-C ) 2.8 Hz), 132.3 (d, J P-C ) 11.3
Hz), 128.6 (d, J P-C ) 14 Hz), 126.0 (d, J P-C ) 144 Hz), 42.7
(s), 24.55 (s). 31P NMR (101.2 MHz, CDCl3, 20 °C, H3PO4): δ
yellow, and after 1 h of stirring, the solvent was removed in
vacuum. Extraction of the residue with pentane gave a bright
yellow solution from which only an oil could be obtained by
concentration and cooling. IR (pentane): ν(CtN) 2102 cm-1
.
1H NMR (250 MHz, CDCl3, 20 °C, TMS): δ 7.8 (m, 2H, Ph),
29.7. MS (+ FAB): m/ z: 281 (100) [M+], 223 (30) [M+
-
7.4 (m, 3H, Ph), 5.2 (m, 4H, Ar-CH), 3.9 (br, 1H, NH), 3.32
NHiPr], 166 (31) [M+ - 2NHiPr].
(sept, J ) 8.6 Hz, 1H, Pr-CH), 3.23 (sept, J ) 7.9 Hz, 1H,
i
i
P r ep a r a t ion
of [(η-p -cym en e)R u {η2-(iP r N)2P P h -
iPr-CH), 2.96 (sept, J ) 7.8 Hz, 1H, Pr-CH), 2.76 (sept, J )
(NHiP r )}][BP h 4]. To a suspension of 454 mg of finely ground
[PhP(NHiPr)3]Br (1.25 mmol) in THF (30 cm3) at -78 °C was
added 1.5 cm3 of a 2.5 M solution of n-BuLi in hexane (3.75
mmol). On warming to room temperature, the salt dissolved
and a pale yellow solution was formed. The solution was
stirred at room temperature for a further 15 min and recooled
to -78 °C. To the solution was added 380 mg of [(η-p-cymene)-
RuCl2]2 (0.621 mmol), and the mixture was allowed to warm
to room temperature and stir for 1 h. The solvent was removed
from the resulting deep blue/green solution under vacuum, and
the residue was dissolved in wet methanol, resulting in a deep
purple solution to which 450 mg of NaBPh4 (1.32 mmol) was
added. After the mixture was stirred for 30 min, the methanol
was removed under vacuum and the residue was washed with
ether (2 × 10 cm3) to remove the last traces of methanol. The
residue was dissolved in CH2Cl2 (5 cm3), and the solution was
passed through a short (10 cm) column of silica by eluting with
CH2Cl2. The deep purple band was collected, the solvent
removed under vacuum, and the product crystallized from hot
methanol to yield 671 mg (64%) of purple/black crystals in
three crops. Anal. Calcd for C49H61BN3PRu: C, 70.7; H, 7.09;
N, 5.05. Found: C, 71.1; H, 7.25; N, 4.99. 1H NMR (250 MHz,
CDCl3, 20 °C, TMS): δ 7.6-6.8 (mult, 25H, Ph), 5.55 (mult,
(AB)2, J A-B ) 6.3 Hz, 4H, arene-CH), 3.45 (sept, J ) 6.8 Hz,
1H, CH), 3.31 (sept, J ) 6.8 Hz, 1H, CH), 2.97 (s, br, 1H, NH),
2.91 (sept, J ) 5.9 Hz, 1H, CH), 2.50 (sept, J ) 6.3 Hz, 1H,
7.8 Hz, 1H, Pr-CH), 2.15 (s, 3H, arene-CH3), 1.21 (d, J ) 8.6
i
i
i
Hz, 6H, Pr-CH3), 1.12 (d, J ) 7.9 Hz, 6H, Pr-CH3), 1.04 (d, J
) 7.8 Hz, 6H, Pr-CH3), 0.93 (d, J ) 7.8 Hz, 6H, Pr-CH3). 31P
NMR (101.2 MHz, CDCl3, 20 °C, H3PO4): δ 34.6. MS (+
FAB): m/ z 543 (100) [M+], 517 (84) [M+ - CN], 280 (43) [M+
- CN - {Ru(p-cymene)}].
i
i
X-r a y Cr ysta llogr a p h y. Crystals of 2 were grown from a
saturated methanol solution by slow cooling to -20 °C. Crystal
data. C49H61BN3PRu, M ) 834.86, monoclinic, a ) 9.897(2)
Å, b ) 28.024(5) Å, c ) 16.213(3) Å, â ) 102.86(2)°, V ) 4383.9-
(14) Å3 (from 48 reflections, 14° < θ < 15° measured at (ω, λ
) 0.710 73 Å), space group P21/n, Z ) 4, Dc ) 1.265 g cm-3
,
F(000) ) 1760, purple lath, 0.51 × 0.27 × 0.12 mm3, T ) 150-
(2) K, µ(Mo KR) ) 0.430 mm-1. Intensity data were collected
in the range 5° < 2θ < 50° using ωθ scans with on-line profile
fitting24 on a Stoe Stadi-4 diffractometer equipped with an
Oxford Cryosystems low-temperature device.25 Following data
reduction and the application of an absorption correction based
on æ-scans (Tmin ) 0.438; Tmax ) 0.480), the structure was
solved by direct methods (SIR92)26 and refined by full-matrix
least-squares against F2 (SHELXTL).27 H atoms attached to
C were placed in calculated positions and subsequently allowed
to ride on their parent atoms; the H atom attached to N3 was
located in a difference synthesis and refined freely. All non-H
atoms were modeled with anisotropic displacement param-
eters, and the refinement converged to a conventional R1 of
4.33% (based on F and 6047 data with F > 4σ(F)) with wR2 )
9.26% (based on F2 and all 7631 data used during refinement)
for 501 parameters. The final difference map extrema were
+0.49 and -0.39 e Å3.
i
CH), 1.93 (s, 3H, arene-CH3), 1.31 (d, J ) 6.8 Hz, 6H, Pr-
i
CH3), 1.30 (d, J ) 6.8 Hz, 6H, Pr-CH3), 1.07 (d, J ) 5.9 Hz,
6H, iPr-CH3), 1.01 (d, J ) 6.3 Hz, 6H, iPr-CH3). 13C{1H} NMR
(62.9 MHz, CDCl3, 20 °C, TMS): δ 164.4 (d, J B-C ) 8.2 Hz,
B-Ph), 136.2 (B-Ph), 133.1 (d, J P-C ) 2.9 Hz, Ph), 130.2 (d,
J P-C ) 9.8 Hz, Ph), 129.2 (d, J P-C ) 12.1 Hz, Ph), 127.0 (Ph),
125.3 (q, J B-C ) 2.6 Hz, B-Ph), 121.5 (B-Ph), 96.8 (Ar-CH),
84.8 (Ar-CH), 81.7 (Ar-CH), 79.5 (Ar-CH), 47.47 (iPr-CH),
47.42 (iPr-CH), 431.7 (iPr-CH), 26.3 (d, J P-C ) 9.3 Hz, iPr-CH3),
Ack n ow led gm en t. We are grateful to the Engineer-
ing and Physical Science Research Council (EPSRC) for
provision of a 4-circle diffractometer and The Lever-
hulme Trust (fellowship to K.J .G.), The Royal Society,
and The Nuffield Foundation for financial support. Drs.
L. J . Yellowlees and A. Brown are thanked for carrying
out the electrochemical studies and David Coventry for
additional work.
i
i
25.7 (d, J P-C ) 4.6 Hz, Pr-CH3), 25.1 (d, J P-C ) 3.9 Hz, Pr-
i
i
CH3), 20.2 (Ar-CH3, Pr-CH3), 15.1 (Ar-CH3, Pr-CH3). 31P
NMR (101.2 MHz, CDCl3, 20 °C, H3PO4): δ 49.6. MS (+
FAB): m/ z 517 (23) [M+], 281 (100) [M+ - Ru(p-cymene)].
Rea ction of [(η-p-cym en e)Ru {η2-(iP r N)2P P h (NHiP r )}]-
[BP h 4] (2) w ith CO. A slow stream of CO was passed
through a deep purple solution containing 150 mg (0.18 mmol)
of 2 in 20 cm3 of CH2Cl2. Within 30 s the solution had changed
color to pale yellow. The solution was stable under an
atmosphere of CO, but under nitrogen it reverted back to the
deep purple color over a period of 10 min, and this cycle could
be repeated. The infrared spectrum of the yellow solution
showed a strong absorption at 1993 cm-1. Characterization
of this species was hampered by its decomposition to further
products over longer periods under a CO atmosphere.
Su p p or tin g In for m a tion Ava ila ble: X-ray crystallo-
graphic files, in CIF format, for compound 2 and thermal
ellipsoid plot for [PhP(NHiPr)3]Br are available through the
Internet only. Cyclic voltammogram of compound 2 (1 page).
See any current masthead page for ordering and Internet
access instructions.
OM970819U
(24) Clegg, W. Acta Crystallogr. 1981, A37, 22.
(25) Cosier, J .; Glaser, A. M. J . Appl. Crystallogr. 1986, 19, 105.
(26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G.; Giaco-
vazzo, C.; Guagliardi, A.; Polidori, G. J . Appl. Crystallogr. 1994, 27,
435.
(27) Sheldrick, G. M. SHELXTL; Siemens Analytical X-ray
Instruments: Madison, WI, 1995.
Rea ction of [(η-p-cym en e)Ru {η2-(iP r N)2P P h (NHiP r )}]-
[BP h 4] (2) w ith CN-. To a solution containing 2 (150 mg,
0.18 mmol) in 20 cm3 of methanol was added KCN (13 mg,
0.019 mmol). The solution rapidly changed color to bright