Coordinatively diverse ortho -phosphinoaniline complexes of ruthenium and isolation of a putative intermediate in ketone transfer hydrogenation catalysis

Article abstract of DOI:10.1021/ic100165t

Amine-functionalized mono- and diphosphines have been used to prepare a series of ruthenium complexes which exhibit a variety of coordination modes depending on the number of donors possessed by the ligands, the degree of amine methylation, the solvent system used, and the oxidation state of the metal. Reactions of the monophosphinoanilines, Ph₂PAr or Ph ₂PAr′ (Ar = o-C₆H₄NHMe, Ar′ = o-C₆H₄NMe₂), with 0.5 equiv of [RuCl(μ-Cl)(η⁶-p-cymene)]₂ in dichloromethane result in the formation of [RuCl₂(η⁶-p-cymene)(P- Ph₂PAr)] or [RuCl(η⁶-p-cymene)(P,N-Ph ₂PAr′)]Cl, respectively. In refluxing methanol, [RuCl ₂(η⁶-p-cymene)(P-Ph₂PAr)] gradually undergoes chloride ion dissociation to afford the P,N-chelate, [RuCl(η⁶-p-cymene)(P,N-Ph₂PAr)]Cl. This chelate can then be deprotonated to afford the amido complex, [RuCl(η⁶-p- cymene)(P,N-Ph₂PAr^-)] (Ar^- = o-C ₆H₄NMe^-), which is an active ketone transfer hydrogenation catalyst. Reactions of the diphosphines, Ar₂PCH ₂PAr₂ (mapm) or Ar′₂PCH ₂PAr′₂ (dmapm) with 0.5 equiv of [RuCl(μ-Cl)( η⁶-p-cymene)]₂ result in the formation of [RuCl ₂(P,P′,N,N′-mapm)] or [RuCl(η⁶-p-cymene) (P,P′-dmapm)]Cl, respectively, in which increased methyl substitution in the latter actually inhibits amine coordination with retention of the p-cymene fragment. Reaction of mapm with 1 equiv of [Ru(CO)₄(η ²-C₂H₄)] in dichloromethane initially produces [Ru(CO)₄(P-mapm)] which, over a 24 h period with exposure to ambient light, is completely converted to the P,P′-chelate, [Ru(CO) ₃(P,P′-mapm)], by photodissociation of carbon monoxide. The same reaction with 2 equiv of [Ru(CO)₄(η²-C ₂H₄)] generates a mixture of [Ru₃(CO) ₁₀(μ-P,P′-mapm)] and the mononuclear P,P′-chelate. The trinuclear complex can also be synthesized by direct reaction of mapm with 1 equiv of [Ru₃(CO)₁₂].

Full text of DOI:10.1021/ic100165t

4288 Inorg. Chem. 2010, 49, 4288–4300
DOI: 10.1021/ic100165t
Coordinatively Diverse ortho-Phosphinoaniline Complexes of Ruthenium and
Isolation of a Putative Intermediate in Ketone Transfer Hydrogenation Catalysis
Lindsay J. Hounjet, Matthias Bierenstiel,† Michael J. Ferguson,‡ Robert McDonald,‡ and Martin Cowie*
Department of Chemistry, University of Alberta, Edmonton, Alberta, Canada T6G 2G2.
†Present Address: Department of Chemistry, Cape Breton University, Sydney, Nova Scotia, Canada, B1P 6L2.
‡X-ray Crystallography Laboratory, University of Alberta
Received January 26, 2010
Amine-functionalized mono- and diphosphines have been used to prepare a series of ruthenium complexes which exhibit
a variety of coordination modes depending on the number of donors possessed by the ligands, the degree of amine
methylation, the solvent system used, and the oxidation state of the metal. Reactions of the monophosphinoanilines,
Ph2PAr or Ph2PAr0 (Ar = o-C6H4NHMe, Ar0 = o-C6H4NMe2), with 0.5 equiv of [RuCl(μ-Cl)(η6-p-cymene)]2 in
dichloromethane result in the formation of [RuCl2(η6-p-cymene)(P-Ph2PAr)] or [RuCl(η6-p-cymene)(P,N-Ph2PAr0)]Cl,
respectively. In refluxing methanol, [RuCl2(η6-p-cymene)(P-Ph2PAr)] gradually undergoes chloride ion dissociation to
afford the P,N-chelate, [RuCl(η6-p-cymene)(P,N-Ph2PAr)]Cl. This chelate can then be deprotonated to afford the amido
complex, [RuCl(η6-p-cymene)(P,N-Ph2PAr-)] (Ar- = o-C6H4NMe-), which is an active ketone transfer hydrogenation
catalyst. Reactions of the diphosphines, Ar2PCH2PAr2 (mapm) or Ar02PCH2PAr02 (dmapm) with 0.5 equiv of [RuCl-
(μ-Cl)(η6-p-cymene)]2 result in the formation of [RuCl2(P,P0,N,N0-mapm)] or [RuCl(η6-p-cymene)(P,P0-dmapm)]Cl,
respectively, in which increased methyl substitution in the latter actually inhibits amine coordination with retention of
the p-cymene fragment. Reaction of mapm with 1 equiv of [Ru(CO)4(η2-C2H4)] in dichloromethane initially produces
[Ru(CO)4(P-mapm)] which, over a 24 h period with exposure to ambient light, is completely converted to the P,P0-
chelate, [Ru(CO)3(P,P0-mapm)], by photodissociation of carbon monoxide. The same reaction with 2 equiv of
[Ru(CO)4(η2-C2H4)] generates a mixture of [Ru3(CO)10(μ-P,P0-mapm)] and the mononuclear P,P0-chelate. The
trinuclear complex can also be synthesized by direct reaction of mapm with 1 equiv of [Ru3(CO)12].
Introduction
character of the phosphine is coupled with the σ-donor
character of the amine.5,6 The hybrid electronic characteristics
of ruthenium P,N-complexes have been exemplified by their
highly variable stereochemistries8-13 and such complexes have
found many applications as catalysts for (transfer) hydro-
genation,11-16 hydroformylation,17,18 hydrosilylation,19,20
and terminal alkyne homocoupling21 reactions.
Hybrid ligands, which contain more than one type of
donor functionality, have attracted much recent interest.1-5
The incorporation of two or more different donor groups can
result in coordinatively diverse complexes because of the
steric and electronic asymmetries6 that are introduced by the
mixed-donor ligands upon coordination. Furthermore, when
the differing donor atoms are electronically diverse hard and
soft combinations, the additional aspect of hemilability7 can
come into play. P,N-Ligands bearing soft phosphine and
hard amine donors can provide a unique electronic environ-
ment for the metal center, in which the weakly π-acidic
(8) Dabb, S. L.; Messerle, B. A.; Smith, M. K.; Willis, A. C. Inorg. Chem.
2008, 47, 3034–3044.
(9) Ziessel, R.; Toupet, L.; Chardon-Noblat, S.; Deronzier, A.; Matt, D.
J. Chem. Soc., Dalton Trans. 1997, 3777–3784.
(10) Costella, L.; Del Zotto, A.; Mezzetti, A.; Zangrando, E.; Rigo, P.
J. Chem. Soc., Dalton Trans. 1993, 3001–3008.
(11) Braunstein, P.; Graiff, C.; Naud, F.; Pfaltz, A.; Tiripicchio, A. Inorg.
Chem. 2000, 39, 4468–4475.
*To whom correspondence should be addressed. E-mail: martin.cowie@
ualberta.ca. Fax: 01 7804928231. Phone: 01 7804925581.
(1) Braunstein, P.; Naud, F. Angew. Chem., Int. Ed. 2001, 40, 680–699.
(2) Slone, C. S.; Weinberger, D. A.; Mirkin, C. A. Prog. Inorg. Chem.
1999, 48, 233–350.
(12) Yang, H.; Alvarez-Gressier, M.; Lugan, N.; Mathieu, R. Organo-
metallics 1997, 16, 1401–1409.
€
(13) Dahlenburg, L.; Kuhnlein, C. J. Organomet. Chem. 2005, 690, 1–13.
(14) Braunstein, P.; Naud, F.; Rettig, S. J. New J. Chem. 2001, 25, 32–39.
(15) Rahman, M. S.; Prince, P. D.; Steed, J. W.; Hii, K. K. Organo-
metallics 2002, 21, 4927–4933.
(3) Werner, H. Dalton Trans. 2003, 3829–3837.
(4) Lindner, E.; Pautz, S.; Haustein, M. Coord. Chem. Rev. 1996, 155,
145–162.
(5) Espinet, P.; Soulantica, K. Coord. Chem. Rev. 1999, 193-195, 499–
556.
(6) Guiry, P. J.; Saunders, C. P. Adv. Synth. Catal. 2004, 346, 497–537.
(7) Jeffrey, J. C.; Rauchfuss, T. B. Inorg. Chem. 1979, 18, 2658–2666.
(16) Bacchi, A.; Balordi, M.; Cammi, R.; Elviri, L.; Pelizzi, C.; Picchioni,
F.; Verdolino, V.; Goubitz, K.; Peschar, R.; Pelagatti, P. Eur. J. Inorg. Chem.
2008, 4462–4473.
€€
€
(17) Moreno, M. A.; Haukka, M.; Jaaskelainen, S.; Vuoti, S.; Pursiainen,
J.; Pakkanen, T. A. J. Organomet. Chem. 2005, 690, 3803–3814.
r
pubs.acs.org/IC
Published on Web 04/05/2010
2010 American Chemical Society

Article
Hybrid P,N-chelate complexes which exhibit hemilability are
Inorganic Chemistry, Vol. 49, No. 9, 2010 4289
Ar atmosphere using standard Schlenk techniques. The reagents,
[Ru3(CO)12], [RuCl(μ-Cl)(η6-p-cymene)]2 (1), and triethylamine
were purchased from Strem Chemicals. Isopropanol (>99%,
distilled over Mg turnings and stored under Ar), acetophenone
of particular interest in homogeneous catalysis by low-valent,
late-metal complexes12,14 in which the labile amine can be
readily displaced by the catalytic substrate and, after completion
of the metal-mediated transformation, can facilitate decom-
plexation of the modified substrate by recoordination, thereby
stabilizing the catalyst. Recently, we demonstrated how the rate
of hemilabile, internal ligand exchange processes within ortho-
phosphinoaniline complexes of rhodium(I) can be varied by
exploiting steric requirements of the amines via the degree of
N-methyl substitution.22
In the current study, we illustrate how the degree of
N-methylation and the number of available phosphine and
amine donors substantially diversifies the coordination be-
havior of these ligands at ruthenium, but surprisingly, does
not give rise to observable hemilability in the compounds
studied. A further motivation for the study of incompletely
substituted amines as donors to ruthenium stems from the
well-documented “N-H effect,”23 in which the amine can be
deprotonated by the addition of an external base to generate
amido-ruthenium complexes, many of which function as
catalytic intermediates for the (transfer) hydrogenation
of polar substrates, particularly ketones.23,24 Recently,
Stradiottoetal. reportedefficient “non-N-H”iridium-based
transfer hydrogenation catalysts bearing an o-N,N-dimethyl-
anilinylphosphine ligand,25 while Pelagatti et al. also demon-
strated transfer hydrogenation using the same ligand within a
ruthenium complex.16 Ruthenium complexes possessing
other types of NMe2-containing donor ligands have also
been shown to act as catalysts for ketone transfer hydro-
genation reactions.26,27 Such examples serve to illustrate the
catalytic utility of completely N-substituted ortho-phosphino-
aniline complexes. Interestingly, P,N-ligated ruthenium(II)-
arene complexes have also received attention as selective
anticancer agents.28
˚
(99%, deoxygenated and stored under Ar over 5 A molecular
sieves), and potassium tert-butoxide (resublimed and stored
under Ar), used for transfer hydrogenation catalysis, were
purchased from Aldrich. Ethylene was purchased from
Matheson Tri-Gas. Diphenyl(o-N,N-dimethylanilinyl)phosphine
(Ph2PAr0),29 bis(di(o-N,N-dimethylanilinyl)phosphino)methane
(dmapm),30 diphenyl(o-N-methylanilinyl)phosphine (Ph2PAr),22
and bis(di(o-N-methylanilinyl)phosphino)methane (mapm)22 were
prepared as previously reported. NMR spectra were recorded on
Varian Inova-400, -500 or Varian Unity-500 spectrometers oper-
ating at 399.8, 498.1, or 499.8 MHz, respectively, for 1H, at 161.8,
201.6, or 202.3 MHz, respectively, for 31P and at 100.6, 125.3, or
125.7 MHz, respectively, for 13C nuclei. J values are given in hertz
(Hz) and overlapping or unresolved aromatic 1H signals, observed
in the typical 6-8 ppm range, and 13C{1H} signals, found between
80-120 ppm, respectively, are not reported. Spectroscopic data for
all metal complexes (2a-c, 3b, 4, 5, 6a, 6b, and 7) are provided in
Table 1. Solution phase infrared spectra (KBr cell) were recorded
on a FT-IR Bomem MB-100 spectrometer. Elemental analyses
were performed by the Microanalytical Laboratory of the Uni-
versity of Alberta. Electrospray ionization mass spectra were run
on a Micromass Zabspec spectrometer in the departmental MS
facility. In all cases, the distribution of isotope peaks for the
appropriate parent ion matched very closely that calculated
from the formulation given. Conductivity measurements were
carried out under inert conditions on 10-3 M solutions of
[RuCl2(η6-p-cymene)(P-Ph2PAr)] (2a), [RuCl(η6-p-cymene)-
(P,N-Ph2PAr)]Cl (2b), [RuCl(η6-p-cymene)(P,N-Ph2PAr-)]
(2c), [RuCl(η6-p-cymene)(P,N-Ph2PAr0)]Cl (3b), [RuCl(η6-p-
cymene)(P,P0-dmapm)]Cl (4), and [RuCl2(P,P0,N,N0-mapm)]
(5) in dry nitromethane using a Yellow Springs Instrument
Model 31 conductivity bridge. For these species the molar
conductivities were determined as Λ = 6, 59, 23, 79, 62, and
7 cm2 Ω-1 mol-1, respectively.
Preparation of Metal Complexes. (a). Dichloro(η6-p-cymene)-
(diphenyl(o-N-methylanilinyl)phosphine)ruthenium(II), [RuCl2(η6-
p-cymene)(P-Ph2PAr)] (2a). Method i. In a 50 mL Schlenk flask
under anhydrous conditions and Ar atmosphere, [RuCl(μ-Cl)-
(η6-p-cymene)]2 (1) (109 mg, 178 μmol) and Ph2PAr (104 mg,
356 μmol) were dissolved in 15 mL of benzene at ambient
temperature. The resulting red solution was stirred at ambient
temperature for 30 min, and a bright red precipitate formed. The
solvent was then removed in vacuo, and the red solid was washed
with 15 mL of n-pentane. The solid was then dried in vacuo
producing an orange-red powder (219 mg, 91% yield, found: C,
Experimental Section
General Comments. All solvents were deoxygenated, dried
(using appropriate drying agents), distilled before use, and
stored under nitrogen. All reactions were performed under an
ꢀ
(18) Drommi, D.; Nicolo, F.; Arena, C. G.; Bruno, G.; Faraone, F.;
Gobetto, R. Inorg. Chim. Acta 1994, 221, 109–116.
(19) Zhu, G.; Terry, M.; Zhang, X. J. Organomet. Chem. 1997, 547, 97–
101.
€
(20) Tuttle, T.; Wang, D.; Thiel, W.; Kohler, J.; Hofmann, M.; Weis, J.
62.24; H, 6.10; N, 2.04%. Calcd for [C29H32Cl2NPRu] C6H6: C,
3
Dalton Trans. 2009, 5894–5901.
62.22; H, 5.67; N, 2.07%). Although the crystal structure determi-
nation indicated no solvent inclusion, the sample used for elemen-
tal analysis was non-crystalline, and H NMR analysis of this
(21) Slugovc, C.; Doberer, D.; Gemel, C.; Schmid, R.; Kirchner, K.;
Winkler, B.; Stelzer, F. Monatsh. Chem. 1998, 129, 221–233.
(22) Hounjet, L. J.; Bierenstiel, M.; Ferguson, M. J.; McDonald, R.;
Cowie, M. Dalton Trans. 2009, 4213–4226.
1
sample in CD2Cl2 (obtained at approximately the same time as the
elemental analysis) verified the benzene content. Single crystals
suitable for X-ray crystallographic analysis were obtained by
dissolving the complex, under Ar atmosphere, in a minimum
volume of benzene and layering the solution with anhydrous
n-pentane in an NMR tube. HRMS (ESI): m/z 598.0760 [M þ
H]þ. Calcd for C29H33Cl2NPRu: m/z 598.0766.
(23) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. Rev.
2004, 248, 2201–2237.
(24) (a) Noyori, R.; Ohkuma, T. Angew. Chem., Int. Ed. 2001, 40, 40–73.
(b) Haack, K.-J.; Hashiguchi, S.; Fujii, A.; Ikariya, T.; Noyori, R. Angew. Chem.,
Int. Ed. Engl. 1997, 36, 285–288. (c) Yamakawa, M.; Ito, H.; Noyori, R. J. Am.
Chem. Soc. 2000, 122, 1466–1478.
(25) Lundgren, R. J.; Stradiotto, M. Chem.;Eur. J. 2008, 14, 10388–
10395.
(26) Lundgren, R. J.; Rankin, M. A.; McDonald, R.; Schatte, G.;
Stradiotto, M. Angew. Chem., Int. Ed. 2007, 46, 4732–4735.
(27) Standfest-Hauser, C.; Slugovc, C.; Mereiter, K.; Schmid, R.; Kirchner,
K.; Xiao, L.; Weissensteiner, W. J. Chem. Soc., Dalton Trans. 2001, 2989–
2995.
Method ii. Using dichloromethane rather than benzene, the
product did not spontaneously precipitate, but was obtained
in excellent yield by precipitation with ether and subsequent
(29) Fritz, H. P.; Gordon, I. R.; Schwarzhans, K. E.; Venanzi, L. M.
J. Chem. Soc. 1965, 5210–5216.
(28) (a) Renfrew, A. K.; Phillips, A. D.; Egger, A. E.; Hartinger, C. G.;
Bosquain, S. S.; Nazarov, A. A.; Keppler, B. K.; Gonsalvi, L.; Peruzzini, M.;
Dyson, P. J. Organometallics 2009, 28, 1165–1172. (b) Bugarcic, T.; Habtemariam,
A.; Deeth, R. J.; Fabbiani, F. P. A.; Parsons, S.; Sadler, P. J. Inorg. Chem. 2009, 48,
9444–9453.
(30) Jones, N. D.; Meessen, P.; Smith, M. B.; Losehand, U.; Rettig, S. J.;
Patrick, B. O.; James, B. R. Can. J. Chem. 2002, 80, 1600–1606.
(31) Cooke, J.; Berry, D. E.; Fawkes, K. L. J. Chem. Educ. 2007, 84, 115–
118.

4290 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4291
workup. However, satisfactory elemental analyses and X-ray
quality single crystals could not be obtained owing to facile
solvent loss.
red solution was stirred at ambient temperature for 10 min until it
had turned orange in color. The solvent volume was reduced to
approximately 1 mL in vacuo, and 10 mL of n-pentane was added
with stirring resulting in an immiscible, red oil which was allowed
to settle from the yellow solution. The supernatant was removed
via syringe, and the oily residue was dried in vacuo producing an
orange powder (115 mg, 79% yield). HRMS (ESI) found: m/z
827.2724 for [M]þ. Calcd for [C43H56ClN4P2Ru]: m/z 827.2707.
Single crystals suitable for X-ray crystallographic analysis were
obtained by dissolving the complex, under Ar atmosphere, in a
minimum volume of CH2Cl2 and layering the solution with
anhydrous n-pentane in an NMR tube.
(b). Dichloro(η6-p-cymene)(diphenyl(o-N-methylanilinyl)-
phosphine)ruthenium(II), [RuCl(η6-p-cymene)(P,N-Ph2PAr)]Cl (2b).
In a 50 mL three-necked, round-bottom flask with an attached reflux
condenser under anhydrous conditions and Ar atmosphere, [RuCl-
(μ-Cl)(η6-p-cymene)]2 (1) (224 mg, 365 μmol) and Ph2PAr (213 mg,
731 μmol) were stirred in 10 mL of refluxing methanol (at 70 °C) for
2 h over which time the dark red slurry turned to a bright orange
solution. The solvent was removed in vacuo, and the viscous residue
was dissolved in 5 mL of tetrahydrofuran. After the addition of
15 mL of diethyl ether, a yellow precipitate formed which was then
separated from the supernatant by filtration and dried in vacuo
producing a yellow powder (380 mg, 87% yield, found: C, 58.09; H,
5.71; N, 2.12. Calcd for [C29H32Cl2NPRu]: C, 58.29; 5.40; 2.34%).
Although the crystal structure indicates tetrahydrofuran inclusion, a
(f). Dichloro(bis(di(o-N-methylanilinyl)phosphino)methane)-
ruthenium(II), [RuCl2(P,P0,N,N0-mapm)] (5). In a 50 mL Schlenk
flask under anhydrous conditions and Ar atmosphere, [RuCl-
(μ-Cl)(η6-p-cymene)]2 (1) (105 mg, 194 μmol) and mapm (194 mg,
388 μmol) were cooled to -78 °C (acetone/dry ice bath) and
10 mL of dichloromethane was added. The red-orange slurry
was stirred for 5 min before warming to ambient temperature
over 15 min. The solvent volume was reduced to approximately
1 mL in vacuo; then 10 mL of n-pentane was added to the
solution, with stirring, resulting in an orange-yellow precipitate.
The solution was filtered under argon, and the solids were washed
with 10 mL of n-pentane, then dried in vacuo. The solid was
dissolved in 5 mL of dichloromethane, and the solution was
layered with 15 mL of n-pentane and left unstirred for 3 h
producing orange-yellow crystals suitable for X-ray crystallo-
graphic analysis (282 mg, 95% yield, found: C, 49.78; H, 5.08;
1
non-crystalline sample was analyzed here. H NMR analysis in
CD2Cl2 (obtained at approximately the same time as the elemental
analysis) was used to verify solvent content. Single crystals suitable
for X-ray crystallographic analysis were obtained by slow evapora-
tion from a 1:1 solution of tetrahydrofuran and diethyl ether. HRMS
(ESI): m/z 562.0993 [M]þ. Calcd for C29H32ClNPRu: m/z 562.0999.
(c). Dichloro(η6-p-cymene)(diphenyl(o-N-methylanilido)-
phosphine)ruthenium(II), [RuCl(η6-p-cymene)(P,N-Ph2PAr-)] (2c).
In a 50 mL Schlenk flask under anhydrous conditions and Ar
atmosphere, 10 mL of benzene was added to compound 2b (381mg,
638 μmol) resulting in yellow slurry. A 10-fold excess of triethyl-
amine (0.89 mL, 6.4 mmol) was added to the slurry while stirring,
resulting in an opaque, black-red mixture, to which was then added
10 mL of deoxygenated water. After stirring the mixture for 5 min,
the layers were allowed to separate, and the organic layer was
transferred to a 50 mL Schlenk tube via cannula under Ar. The
solvent and residual triethylamine were removed in vacuo, then
5 mL of tetrahydrofuran was added to the dark residue followed by
30 mL of diethyl ether which resulted in the formation of a
precipitate from the dark solution. The solid was collected by
filtration, washed with 15 mL of n-pentane, and dried in vacuo
producing chocolate-colored microcrystals (256 mg, 72% yield,
found: C, 61.98; H, 5.60; N, 2.43. Calcd for [C29H31ClNPRu]: C,
62.08; H, 5.57; N, 2.50%). Single crystals suitable for X-ray crystallo-
graphic analysis were obtained by dissolving the complex, under Ar
atmosphere, in a minimum volume of tetrahydrofuran and layering
the solution with anhydrous n-pentane in a Schlenk tube. HRMS
(ESI): m/z 526.1227 [M - Cl]þ. Calcd for C29H31NPRu: m/z
526.1232.
N, 7.48%. Calcd for [C29H34Cl2N4P2Ru] 0.5CH2Cl2: C, 49.55;
3
H, 4.93; N, 7.84%). HRMS (ESI) found: m/z 637.0985 for
[M - Cl]þ. Calcd for [C29H34ClN4P2Ru]: m/z 637.0985.
(g). Tricarbonyl(bis(di(o-N-methylanilinyl)phosphino)methane)-
ruthenium(0), [Ru(CO)3(P,P0-mapm)] (6b). A 100 mL hexane
solution of [Ru(CO)4(η2-C2H4)] was prepared photolytically with
the use of [Ru3(CO)12] (42 mg, 66 μmol) and an ethylene purge.31
Under anhydrous conditions and Ar atmosphere, the solution was
transferred, via cannula, to a prepared 250 mL Schlenk flask
containing mapm (90 mg, 180 μmol). The pale-yellow slurry was
stirred for 5 min then 10 mL of dichloromethane was added. The
resulting solution was stirred for 2 h, eventually turning orange in
color, and was left exposed to ambient light overnight. Solvents
were removed in vacuo, and the resulting orange solid was then
washed with 10 mL of n-pentane. The product was then dried in
vacuo and isolated as an orange powder (110 mg, 89% yield,
found: C, 55.71; H, 5.12; N, 7.80%. Calcd for [C32H34N4O3P2Ru]:
C, 56.06; H, 5.00; N, 8.17%). IR (CH2Cl2 solution cell): νCO 2004
(s), 1932 (s) and 1912 (s) cm-1. HRMS (ESI) found: m/z 687.1220
for [M þ H]þ. Calcd for [C32H35N4O3P2Ru]: m/z 687.1222. Single
crystals suitable for X-ray crystallographic analysis were obtained
by dissolving the complex, under Ar atmosphere, in a minimum
volume of CH2Cl2 and layering the solution with anhydrous
n-pentane in an NMR tube.
(d). Dichloro(η6-p-cymene)(diphenyl(o-N,N-dimethylanilinyl)-
phosphine)ruthenium(II), [RuCl(η6-p-cymene)(P,N-Ph2PAr0)]Cl
(3b). The orange powder was prepared in a manner similar to
that of part (a, Method ii) using [RuCl(μ-Cl)(η6-p-cymene)]2 (1)
(104 mg, 169 μmol) and Ph2PAr0 (104 mg, 339 μmol) and was
isolated as an orange powder (200 mg, 96% yield, found: C,
55.37; H, 5.54; N, 2.22. Calcd for [C30H34Cl2NPRu] 2H2O:
(h). Decacarbonyl(bis(di(o-N-methylanilinyl)phosphino)methane)-
triruthenium(0,0,0), [Ru3(CO)10(μ-P,P0-mapm)] (7). Method i. A
125 mL n-pentane solution of [Ru(CO)4(η2-C2H4)] was prepared
photolytically with the use of [Ru3(CO)12] (48 mg, 75 μmol) and an
ethylene purge.31 Meanwhile, a solution of mapm (52 mg, 104 μmol)
in 5 mL of dichloromethane was prepared under Ar atmosphere. In
complete darkness, the mapm solution was then transferred to the
solution of [Ru(CO)4(η2-C2H4)] by cannula, and the resulting solu-
tion was heated to 50 °C with a water bath while stirring under a brisk
flow of Ar to remove the solvents. The red solid residue was then
dissolved, in the dark, in 20 mL of dichloromethane and stirred for 5 h
under a very slight flow of Ar. The solvent volume was then reduced
to approximately 5 mL in vacuo, and 25 mL of n-pentane was added
resulting in the formation of a yellow precipitate in a bright red
solution. The precipitate was allowed to settle, and the red super-
natant was removed by cannula. The remaining solid was then dried
in vacuo and isolated as an orange-red powder (34 mg, 42% yield,
3
C, 55.64; H, 5.91; N, 2.16%). Although the crystal structure
indicates 1 equiv of H2O and 2 equiv of CH2Cl2 per formula unit,
a non-crystalline sample was analyzed here which was exposed to
1
air before analysis. H NMR analysis in CDCl3 (obtained at
approximately the same time as the elemental analysis) was used
to verify water and dichloromethane content. HRMS (ESI)
found: m/z 576.1158 for [M]þ. Calcd for [C30H34ClNPRu]: m/z
576.1155. Single crystals suitable for X-ray crystallographic
analysis were obtained by slow evaporation from a saturated
dichloromethane solution.
(e). Dichloro(η6-p-cymene)(bis(di(o-N,N-dimethylanilinyl)-
phosphino)methane) ruthenium(II), [RuCl(η6-p-cymene)(P,P0-
dmapm)]Cl (4). In a 50 mL Schlenk flask under anhydrous
conditions and Ar atmosphere, [RuCl(μ-Cl)(η6-p-cymene)]2 (1)
(52 mg, 85 μmol) and dmapm (94 mg, 169 μmol) were dissolved in
10 mL of dichloromethane at ambient temperature. The initially

4292 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.
found: C, 43.86; H, 3.79; N, 4.34%. Calcd for [C39H34N4O10P2Ru3]
0.5C5H12 0.5CH2Cl2: C, 43.40; H, 3.56; N, 4.82%). IR (CH2Cl2
Scheme 1
3
3
solution cell): νCO 2079 (m), 2060 (m), 2020 (sh), 2008 (s), 1996 (sh)
and 1955 (m) cm-1. Single crystals suitable for X-ray crystallographic
analysis were obtained by dissolving the complex, under Ar atmo-
sphere, in a minimum volume of CH2Cl2 and layering the solution
with anhydrous n-pentane in an NMR tube.
Method ii. In a 100 mL Schlenk tube under anhydrous
conditions and Ar atmosphere, [Ru3(CO)12] (133 mg, 208 μmol)
and mapm (104 mg, 208 μmol) were dissolved in 25 mL of
tetrahydrofuran by stirring the mixture for 10 min at ambient
temperature. The initially orange solution was then stirred for
24 h under a very slight flow of Ar, eventually turning bright red
in color. The solvent volume was reduced to approximately
5 mL in vacuo, and the solution was then left unstirred and
layered with 40 mL of n-pentane. After 3 h an orange precipitate
had developed, and the supernatant was removed by cannula
transfer. The product was then dried in vacuo and isolated as an
orange-red powder (151 mg, 67% yield).
X-ray Structure Determinations. (a). General Procedures.
Crystals were grown via slow diffusion of n-pentane into a
benzene (2a) or CH2Cl2 (2c, 3b, 4, 5, 6b, 7) solution of the
compound, or diffusion of ether into a THF (2b) solution of the
compound. Data were collected using either a Bruker APEX-II
CCD detector/D8 diffractometer32 with the crystals cooled to
-100 °C (2a, 2b, 2c, 4, 7) or a Bruker SMART 1000 CCD
detector/PLATFORM diffractometer with the crystals cooled
to -80 °C (3b, 5, 6b); all data were collected using Mo KR
by solid potassium tert-butoxide (t-BuOK, 8.0 mg, 71 μmol),
which was added to the reaction flask under a light stream of Ar
(trxn = 0 min) and resulted in darkening to a red-brown solution.
The molar composition of the reaction mixture at this point
was [Ru]: t-BuOK: acetophenone: i-PrOH = 1:4:1,000:10,000.
Aliquots were withdrawn at trxn = 0, 5, 60, and 120 min which
were immediately filtered through columns containing 2 cm of
acidic alumina atop 2 cm of Florisil (to remove catalyst) and
collected in vials which were quickly capped. Each sample was
˚
radiation (λ = 0.71073 A). The data were corrected for absorp-
tion through Gaussian integration from indexing of the crystal
faces (2a, 2b, 2c, 3b, 7) or through use of a multiscan model
(SADABS32) (4, 5, 6b). Structures were solved using Patterson
search/structure expansion (DIRDIF-200833) (2a), direct methods
(SHELXS-9734) (2b, 2c, 3b, 6b, 7), or direct methods/structure
expansion (SIR9735) (4, 5). Refinements were completed using the
program SHELXL-97.34 Hydrogen atoms were assigned positions
based on the sp2 or sp3 hybridization geometries of their attached
carbon or nitrogen atoms, and were given thermal parameters 20%
greater than those of their parent atoms. See Supporting Informa-
tion for a listing of crystallographic experimental data and for
selected bond lengths and angles for all structures.
1
analyzed by H NMR analysis (CDCl3) within 10 min of its
withdrawal from the reaction mixture. GC-EI-MS analysis was
carried out on the filtered samples after 10-fold volumetric
dilution with dichloromethane. Conversion percentages, turn-
over numbers, and frequencies determined from acetophenone
and 1-phenylethanol signals in both 1H NMR and GC-EI-MS
analyses were mutually consistent.
(b). Special Refinement Conditions. (i) 3b: Distances invol-
ving hydrogens of the solvent water molecules were assigned
Results and Discussion
˚
(a). Monophosphinoaniline Complexes. (i). Diphenyl-
(o-N-methylanilinyl)phosphine. The monophosphinoani-
line ligand, Ph2PAr (Ar = o-C6H4NHMe) reacts with
0.5 equiv of [RuCl(μ-Cl)(η6-p-cymene)]2 (1), under mild
conditions in dichloromethane to produce the neutral
complex, [RuCl2(η6-p-cymene)(P-Ph2PAr)] (2a), in which
the chloro-bridged dimer has been cleaved by coordina-
tion of the phosphine donor while the amine functionality
remains uncoordinated and pendent (Scheme 1). The
31P{1H} NMR spectrum of 2a displays the expected
fixed idealized values during refinement (d(O-H) = 0.85 A;
˚
d(H H) = 1.39 A). (ii) 5: The Cl-C distances within the
solvent CH2Cl2 molecule were restrained to be equal (within
3 3 3
˚
0.03 A) during refinement. (iii) 7: Distances within the dis-
ordered solvent n-pentane and CH2Cl2 molecules were subject
to the following restraints during refinement: d(C-C)n-pentane
=
=
˚
1.53(1) A; d1,3(C C)
˚
= 2.50(1) A; d(Cl-C)CH Cl
n-pentane
3 3 3
2
2
˚
1.80(1); d(Cl Cl)CH Cl = 2.87(1) A.
3 3 3
2
2
Ketone Transfer Hydrogenation Catalysis. In a 50 mL three-
necked, round-bottom flask with an attached reflux condenser
under anhydrous conditions and Ar atmosphere, [RuCl(η6-p-
cymene)(P,N-Ph2PAr-)] (2c, 10.0 mg, 17.8 μmol) was dissolved
in isopropanol (i-PrOH, 13.6 mL, 178 mmol). The mixture was
heated to 90 °C for 1.0 min while stirring which resulted in an
orange-brown solution. Acetophenone (2.08 mL, 17.8 mmol)
was then added to the refluxing mixture followed immediately
1
singlet at δP 28.2 while the H NMR spectrum shows a
doublet at δH 2.81, representing the NMe protons having
3JHH = 5.0 Hz because of coupling with the amine
hydrogen (δH 5.47, q/br). The phosphorus chemical shift
of 2a is similar to that of the non-N-methylated analogue,
[RuCl2(η6-p-cymene)(P-Ph2PC6H4NH2)] (δ 28.9), re-
ported by Pelagatti et al.16 Moreover, the N-methyl signal
of 2a has a chemical shift similar to that of the free Ph2PAr
ligand (δH 2.84) suggesting that the amine is not coordi-
nated. The methyl protons of the isopropyl group of 2a are
all represented by a doublet at δH 1.39, displaying vicinal
(32) Programs for diffractometer operation, unit cell indexing, data
collection, data reduction, and absorption correction were those supplied
by Bruker.
(33) Beurskens, P. T.; Beurskens, G.; de Gelder, R.; Smits, J. M. M;
Garcia-Granda, S.; Gould, R. O. DIRDIF-2008 program system; Crystallo-
graphy Laboratory, Radboud University : Nijmegen, The Netherlands, 2008.
(34) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112–122.
(35) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, G. L.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Polidori, G.; Spagna, R. J. Appl.
Crystallogr. 1999, 32, 115–119.
coupling with the adjacent methine proton (3JHH
=
7.0 Hz). The 13C{1H} NMR spectrum of 2a shows signals
for the aliphatic carbons, which were identified between

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4293
Figure 1. ORTEP diagrams showing [RuCl2(η6-p-cymene)(P-Ph2PAr)] (2a, left), [RuCl(η6-p-cymene)(P,N-Ph2PAr)]Cl (2b, center), and [RuCl(η6-p-
cymene)(P,N-Ph2PAr-)] (2c, right). Gaussian ellipsoids for all non-hydrogen atoms are depicted at the 20% probability level. Hydrogen atoms, where
included, are shown artificially small.
δC 30.9 and 18.1 by gradient heteronuclear single quan-
tum coherence (GHSQC) analysis.
the monodentate complex against chelation of the amine by
orienting the lone pair on nitrogen away from the metal.
Once formed, the chelate complex 2b is never observed to
revert back to 2a. Chelation in 2b results in a significant
downfield shift of the 31P resonance to δP 53.4 because of
the effect of the five-membered ring38 as also reported for
the non-N-methylated analogue.16 The 1H NMR spectrum
shows a broad signal at δH 10.8 representing the deshielded
amine hydrogen which becomes quite acidic upon coordi-
nation of the amine to the cationic ruthenium center; the
doublet N-methyl proton resonance found at δH 3.52 (with
3JHH = 4.4 Hz) is also shifted downfield from that of 2a.
The chirality of 2b is made evident by two distinct signals
representing diastereotopic methyl groups of the isopropyl
moiety at δH 1.33 and 1.31 each of which appears as a
doublet because of vicinal coupling (3JHH = 7.0 Hz) with
the methine hydrogen. The 13C{1H} NMR spectrum of 2b
shows a strongly deshielded N-methyl carbon resonance at
δC 76.7 because of its geminal relationship to the formally
cationic ruthenium center. The molar conductivity of 2b is
Λ = 59 cm2 Ω-1 mol-1, consistent with a 1:1 electrolyte.
The X-ray structure of 2b (Figure 1, middle) shows a
strong hydrogen bond between the outer-sphere chloride
anion (Cl(2)) and the coordinated amine hydrogen
The solid state structure of complex 2a (Figure 1, left)
displays a hydrogen bond between one of the inner-sphere
chlorides and the pendent amine hydrogen, for which the
˚
resulting H(N1)-Cl(1) distance of 2.43 A is significantly
shorter than a normal van der Waals separation of
3.05 A.36 An analysis of the structural parameters within
˚
complex 2a reveals that the Ru-Cl(1) bond is slightly
˚
longer than Ru-Cl(2) (2.4258(4) vs 2.4035(3) A) presum-
ably because of its interaction with the pendent amine
hydrogen. The previously reported structure of the non-
N-methylated analogue of 2a, [RuCl2(η6-p-cymene)-
(P-Ph2P(o-C6H4NH2)], also shows a similar hydrogen
bond.16
Interestingly, while the N-methyl, methine, and aryl-
methyl carbon resonances of 2a appear as sharp singlets,
the signals for the methyl carbons of the isopropyl group
(δC 22.0), as well as some aromatic carbon signals, are
broad. Such broadening suggests fluxionality that we
propose results from the intramolecular hydrogen bond
involving the amine hydrogen and a chloro ligand being
weak enough to allow for facile enantiomerization via
movement from one chloro ligand to the other, yet strong
enough to render some carbon environments pseudodias-
tereotopic on the NMR time scale. A 13C{1H} NMR
spectroscopic analysis carried out at -80 °C supports this
hypothesis as two sharp signals representing the isopropyl
methyl carbons are now observed at this temperature
at δC 24.3 and 19.6. The molar conductivity of 2a is Λ =
6cm2 Ω-1 mol-1, consistent with a non-conducting complex.
While 2a is indefinitely stable in dichloromethane solu-
tion, the compound can be converted to the cationic P,N-
chelated isomer, [RuCl(η6-p-cymene)(P,N-Ph2PAr)]Cl (2b)
in refluxing methanol within hours (Scheme 1). Faraone
et al. have shown that protic solvents kinetically enhance
amine coordination in a similar complex by providing
strong hydrogen bond donors to facilitate the dissociation
of a chloro ligand.37 Although the solid-state structure of 2a
(vide supra) clearly depicts a hydrogen bond between the
pendent amine hydrogen and a chloro ligand, it appears
that, rather than promoting chloride ion dissociation, this
intramolecular hydrogen bond actually appears to stabilize
˚
(H(1N); 2.16 A), which is consistent with the extensive
deshielding of this proton observed spectroscopically,
while also clearly illustrating the diastereotopicity of the
isopropyl methyl groups of the p-cymene ligand, consis-
tent with the observation of two distinct signals for these
groups in both the 1H and 13C{1H} NMR spectra.
The acidic amine hydrogen of 2b is readily deprotonated
to give the corresponding amido complex, [RuCl(η6-p-
cymene)(P,N-Ph2PAr-)] (2c, Ar- = o-C6H4NMe-;
Scheme 1). Addition of 10 equiv of triethylamine to a
slurry of 2b in benzene resulted in immediate darkening to
an opaque, black-red mixture from which the triethyl-
ammonium chloride byproduct was easily removed by
aqueous extraction, yielding 2c as a brown, microcrystalline
solid. Spectroscopic analysis of 2c shows the phosphorus
resonance at δP 59.3, which is shifted even further down-
field from that of 2b. Interestingly, the 1H NMR spectrum
of 2c in CD2Cl2 shows broad signals at ambient tempera-
ture and, notably, the proton signals for the two diaster-
eotopic isopropyl methyl groups of the p-cymene unit
(36) Zefirov, Y. V.; Zorkii, P. M. Russ. Chem. Rev. 1989, 58, 421–440.
(37) Arena, C. G.; Calamia, S.; Faraone, F.; Graiff, C.; Tiripicchio, A. J.
Chem. Soc., Dalton Trans. 2000, 3149–3157.
(38) Garrou, P. E. Chem. Rev. 1981, 81, 229.

4294 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.
Scheme 2. Enantiomerization of 2c via Coordinatively Unsaturated
Intermediate 2d
suggesting some degree of π-donation to ruthenium
which could also be reflected in the short Ru-N bond
(vide supra).
(ii). Diphenyl(o-N,N-dimethylanilinyl)phosphine. Pelagatti
et al. have reported that reaction of the N,N-dimethyl
analogue, Ph2PAr0, with 0.5 equiv of 1 initially results in
the pendent, monodentate complex, [RuCl2(η6-p-cymene)-
(P-Ph2PAr0)] (3a) analogous to 2a, which over time in
dichloromethane converted to the P,N-chelated species,
[RuCl(η6-p-cymene)(P,N-Ph2PAr0)]Cl (3b),16 in which the
amine has replaced a chloro ligand at ruthenium to generate a
cationic complex analogous to 2b (see Scheme 3). In our
hands, however, the intermediate 3a was never observed.
Despite our best efforts to exclude moisture from reaction
mixtures, the hygroscopic intermediate 3a readily sequesters
adventitious water, as is observed by 1H NMR spectroscopy,
elemental analysis, and X-ray crystallography of 3b (which
showed the presence of water in the unit cell), which appears
to facilitate chelation by hydrogen-bonding assisted chloride
ion abstraction.16,37 Unfortunately very little characterization
of the intermediate 3a is given in the report of this compound
beyond the 31P{1H} NMR chemical shift; the other spectro-
scopic data given for this compound16 appear to be those of
3b, as shown by comparison with our data. The apparent ease
with which intermediate 3a is able to undergo chelation under
mild conditions contrasts the protic, forcing conditions
necessary to promote chelation in 2a. Presumably, the intra-
molecular hydrogen bond between the amine hydrogen and a
chloro ligand in 2a (Figure 1) renders the pendent amine
more inert to chelation (vide supra), while the more nucleo-
philic N,N-dimethylanilinyl group of 3a rapidly displaces a
chloro ligand to generate the cationic, chelated product, 3b.37
Coordination of the N,N-dimethylanilinyl group is favored
despite the increased steric bulk of this group compared with
the N-methyl analogue.
coalesce at 40 °C. Such fluxional behavior implies that a
rapid enantiomerization process is occurring in solution,
presumably by chloride ion dissociation to generate the
cationic, coordinatively unsaturated intermediate, [Ru-
(η6-p-cymene)(P,N-Ph2PAr-)]Cl (2d, Scheme 2), followed
by recoordination of the chloride ion on the opposite face
of the chelate ring, resulting in stereoinversion at ruthe-
nium. A fluxional process involving stereoinversion at
nitrogen seems less likely since such a mechanism would
involve two diastereoisomers which should produce two
signals in the 31P{1H} NMR spectrum. Futhermore, the
X-ray structure of 2c, discussed below, reveals nearly
perfect planarity of the amido nitrogen, suggesting that
lone pair inversion is not a likely cause for the observed
fluxionality. The conductivity of complex 2c was found to
be Λ = 23 cm2 Ω-1 mol-1, which is intermediate between
that of a neutral species and a 1:1 electrolyte, supporting
the equilibrium shown in Scheme 2. Pellagatti reports a
computationally determined energy difference between
two species, that are structurally analogous to 2c and 2d,
of only ΔG = 2.9 kcal/mol, with the cationic, coordina-
tively unsaturated complex (similar to 2d) being less
stable.16 Our variable temperature NMR analysis of 2c
indicates that its enantiomerization, at the coalescence
temperature of the proton signals for the methyl groups
of the isopropyl moiety (Tcoal = 40 °C), occurs with a rate
constant of kcoal = 95 s-1, corresponding to an energy
barrier of ΔGq (313 K) = 15 kcal/mol.39
The 31P{1H} NMR spectrum of 3b shows a singlet at δP
47.5 (CD2Cl2) which is shifted significantly downfield
from those of 2a or 3a16 and is again consistent with the
presence of a five-membered chelate ring.38 The P,N-
chelation mode of 3b is demonstrated by 1H NMR
spectroscopy which shows two distinct, relatively down-
field singlets (δH 4.04 and 3.50) for the diastereotopic
N-methyl groups, a result of the stereogenic center
created at ruthenium upon coordination of the amine.
The asymmetry of 3b is also made evident by two distinct
doublet resonances for the methyl protons of the p-cymene
isopropyl group (δH 1.26 and 1.35, 3JHH = 7.0 Hz), as well
as four chemically distinct aromatic p-cymene proton
signals between δH 7.32 and 5.18, which were identified
by gradient correlation spectroscopic (GCOSY) analysis.
By contrast with 2a, the 13C{1H} NMR spectrum of 3b
shows two sharp singlets for the methyl carbons of the
isopropyl groups at δC 22.3 and 20.7 and relatively de-
shielded N-methyl resonances at δC 65.2 and 58.4, consis-
tent with amine coordination to a formally cationic
ruthenium center. The molar conductivity of 3b is Λ =
79 cm2 Ω-1 mol-1, characteristic of a 1:1 electrolyte. The
p-cymene ligands of the monophosphinoaniline complexes
remain coordinated and are not displaced, even in the
presence of an excess of the ligands Ph2PAr and Ph2PAr0,
respectively. This presumably reflects the strong binding
affinity of the η6-p-cymene ligand and is apparently not the
result of any inherent instability of the presumed products,
A representation of the amido complex 2c is shown in
Figure 1 (right), confirming the spectroscopic character-
ization of this species. The three structures depicted in
Figure 1 clearly illustrate the transition of the complex
with the Ph2PAr ligand in a monodentate, P-bound
coordination mode (2a), to the P,N-chelate (2b), to the
amido species (2c). The η6-p-cymene unit appears normal
in all of the monophosphinoaniline complexes with rela-
tively small deviations in Ru-Carene bond lengths. Com-
pound 2c has a significantly shorter Ru-N bond length
˚
˚
(2.086(2) A) than that of 2b (2.172(2) A) owing presum-
ably to both the decreased steric demand of the deproto-
nated donor and the greater basicity of the formally
anionic amido nitrogen in 2c which strengthens the Ru-N
bond. The three atoms bound to the amido nitrogen atom
of 2c (Ru, C(17), C(12)) are arranged in an approximate
trigonal plane as is evident from the sum of the three angles
about nitrogen (358.0°) and can be compared to the sum
of the same three angles (341.0°) in 2b containing the
pyramidal nitrogen. The planarity of the amido group
illustrates the strong sp2 character of the nitrogen atom
(39) Bain, A. D. Prog. Nucl. Magn. Reson. Spectrosc. 2003, 43, 63–103.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4295
Scheme 3
is also an efficient catalyst for the transfer hydrogenation
of acetophenone from isopropanol to produce 1-phenyl-
ethanol and acetone. Although this reaction has already
been studied using the N,N-dimethyl complex, 3b, as well
as the non-N-methylated analogue, [RuCl(η6-p-cymene)-
(P,N-Ph2P(o-C6H4NH2))]Cl (2e), as catalysts,16 we sought
to compare the catalytic activity of the N-methylamido
compound, 2c, with those previously reported. Not
surprisingly perhaps, under similar conditions the N-methyl-
amido complex, 2c, exhibits a catalytic activity inter-
mediatebetweenthemoreactivenon-N-methylated complex,
2e, and the less active N,N-dimethyl complex, 3b16 (Table 2).
In principle, compound 2c could function as a transfer
hydrogenation catalyst in the absence of base, via the
Noyori bifunctional mechanism23,24 whereby the amido
species is converted into the catalytically active amine-
hydride by Hþ/H- transfer from isopropanol. However,
Entry 7 shows that 2c is inactive as a catalyst in the
absence of base. This suggests that an amido-hydride
species, generated from 2c via chloride replacement by
isopropoxide followed by β-hydride elimination, may be
the catalytically active species. However, this possibility
remains to be tested. It should also be noted that a related
NMe2-containing complex, which cannot function by the
bifunctional mechanism, has also been shown to require
base, yet the derived hydride species was found to be
inactive as a catalyst.26 Another possible mechanism that
needs to be investigated is the Meerwein-Ponndorf-
Verley-Oppenauer mechanism in which simultaneous
coordination of both the alkoxide and the ketone to the
metal leads to direct transfer of the β-hydrogen on the
alkoxide to the ketone without the formation of a hydrido
complex.23,42,43
Figure 2. ORTEP diagram of one of two crystallograþphically indepen-
dent molecules of [RuCl(η6-p-cymene)(P,N-Ph2PAr0)] (cation of 3b).
Gaussian ellipsoids for all non-hydrogen atoms are depicted at the 20%
probability level. Hydrogen atoms are not shown.
[RuCl2(P,N-Ph2PAr)2] and [RuCl2(P,N-Ph2PAr0)2], since
a number of analogous species are known.8,11,40,41
The X-ray structural analysis of 3b shows the Ru-Cl
˚
bond lengths of 2.3944(6) and 2.3982(6) A which are close
˚
to that of 2b (2.3947(6) A) and the non-hydrogen-bonded
˚
chloro ligand in 2a (2.4035(3) A) (Figure 2). The Ru-P
bond lengths in the chelated complexes 2b, 2c, and 3b
˚
(each ∼2.30 A) are shorter than that of the pendent
˚
complex 2a (∼2.36 A) presumably because of the con-
straints imposed by the chelate rings. The crystal struc-
ture of 3b clearly shows the chemically distinct N-methyl
groups of the coordinated amine. A comparison of the
Ru-N bond lengths in structural analogues 2b and 3b
illustrates the steric effects of the additional N-methyl
group on the length of the Ru-N bond as that of 2b
The N,N-dimethyl complex (3b) is believed to operate
by an inner-sphere mechanism16 since amine deprotona-
tion to afford an amido species is not possible and
hemilability of the Ph2PAr0 ligand (via displacement of
the amine from ruthenium) seems more likely.22
Although the amine complex, 2b, itself was never tested
as a transfer hydrogenation catalyst, it can be assumed
that the addition of t-BuOK to reaction mixtures would
immediately deprotonate 2b to give the amido complex,
2c, since even weakly basic triethylamine instantly depro-
tonates 2b. With amido complex 2c in hand, we are
currently attempting to isolate the hydrido-amine complex,
˚
(2.172(2) A) is shorter than that of 3b (2.199(2) and
˚
2.209(2) A for the two independent molecules) despite
the stronger σ-donor character of the N,N-dimethylani-
linyl donor.
(iii). Ketone Transfer Hydrogenation Catalysis. Com-
pounds 2c and 2d are of interest since similar species were
recently proposed as intermediates involved in efficient
ketone transfer hydrogenation catalysis, likely operating
by a mechanism involving the simultaneous transfer of
protic and hydridic hydrogen atoms from reagent alcohol
to the coordinatively unsaturated amido complex (similar
to 2d) via an outer-sphere mechanism.16 Herein we have
verified that the amido species (2c) under basic conditions
(42) Vinzi, F.; Zassinovich, G.; Mestroni, G. J. Mol. Catal. 1983, 18, 359–
366.
(43) (a) Meerwein, H.; Schmidt, R. Justus Liebigs Ann. Chem. 1925, 444,
221. (b) Ponndorf, W. Z. Angew. Chem. 1926, 39, 138. (c) Verley, A. Bull. Chem.
Soc. Chim. Fr. 1925, 37, 537. (d) Oppenauer, R. V. Recl. Trav. Chim. Pays-Bas
1937, 56, 137. (e) Wilds, A. L. Org. React. 1944, 2, 178. (f) Djerassi, C. Org.
React. 1951, 6, 207.
(40) Jia, W.; Chen, X.; Guo, R.; Sui-Seng, C.; Amoroso, D.; Lough, A. J.;
Abdur-Rashid, K. Dalton Trans. 2009, 8301–8307.
(41) Rauchfuss, T. B.; Patino, F. T.; Roundhill, M. Inorg. Chem. 1975, 14,
652–656.

4296 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.
Table 2. Effects of N-methyl Substitution on Acetophenone Transfer Hydro-
Scheme 4. Syntheses of Diphosphinoaniline Complexes of Ruthenium
genation Activities
no. of
entry complex N-Me groups
trxn
(min)
conversion
(%) a
TOF
(h-1
b
)
116
216
316
4
5
6
2ec
2ec
2ed
2ce
2ce
2ce
2cd
3bc
0
0
0
1
1
1
1
2
5
37
g98
4440
g980
60
60
5
60
120
60
60
13
34
46
1560
340
230
7
816
10
100
a Determined by CG analysis. b Turnover frequency determined at the
corresponding reaction time (trxn) in column 4. c Reaction conditions: Tem-
perature =90 °C; Ru/KOH/acetophenone/i-PrOH = 1:4:1,000:128,000.
d In the absence of base. e Reaction conditions: Temperature =90 °C; Ru/
t-BuOK/acetophenone/i-PrOH = 1:4:1,000:10,000.
[RuH(η6-p-cymene)(P,N-Ph2PAr)]þ, as well as the hydri-
do-amido complex, [RuH(η6-p-cymene)(P,N-Ph2PAr-)],
to test these species as ketone transfer hydrogenation
catalysts.
that coordination of an anilinyl nitrogen could displace
the other end of the diphosphine, to give a P,N-chelated
species like 3b, on the basis that neither 31P resonance has
a chemical shift consistent with free dmapm (δP -36.0)30
or the pendent phosphines of other reported dmapm
complexes (δP -41.3 and -41.8).45 In addition, the molar
conductivity of Λ = 62 cm2 Ω-1 mol-1, which is con-
sistent with a 1:1 electrolyte in nitromethane, is incon-
sistent with dmapm functioning as a tridentate ligand in a
P,P0,N-chelation mode, through displacement of the
second chloro ligand.
The fluxionality of complex 4 is made evident by the
SST experiment and by the broad signals in both the 1H
and the 31P{1H} NMR spectra which exhibit temperature
dependent chemical shifts and line-shapes. Variable tem-
perature 31P{1H} NMR spectroscopic analysis of 4 shows
that the 6:1 ratio of the non-symmetric complex to the
Cs-symmetric P,P0-chelate between -80and 50 °C remains
relatively unchanged (even after replacing CD2Cl2 solvent
with CD3NO2), although all signals sharpen upon cooling.
Furthermore, between 50 and 80 °C, the signal belonging
to the Cs-symmetric isomer is coincidentally overlapping
with the more downfield signal of the non-symmetrical
species. Unfortunately, the variable temperature 1H NMR
analysis is not useful as a means of characterization for
compound 4 because of very broad, overlapping aromatic
and N-methyl signals over the entire temperature range
studied (-80 to 80 °C), rendering the identity of the major
solution isomer unknown.
(b). Diphosphinoaniline Complexes. In addition to the
monophosphinoanilines we were also interested in the analo-
gous diphosphines, Ar2PCH2PAr2 (Ar = o-C6H4NHMe;
mapm) and Ar02PCH2PAr02 (Ar0 = o-C6H4NMe2; dmapm),
and the effects of N-methyl substitution on the coordination
modes displayed by these ligands. Reaction of dmapm with 0.5
equiv of [RuCl(μ-Cl)(η6-p-cymene)]2 (1), shown in Scheme 4,
occurs much as observed earlier for the Ph2PAr0 ligand, in
which an inner-sphere chloride is lost to allow dmapm to bind
as a bidentate ligand, while the p-cymene ligand remains bound
to Ru. However, the product observed in the solid state,
[RuCl(η6-p-cymene)(P,P0-dmapm)]Cl (4), differs from 3 by
displaying P,P0-chelation rather than the P,N-coordination
mode observed in the monophosphine analogue.
Surprisingly, the 31P{1H} NMR spectrum of 4 actually
shows two species in solution. The expected sharp singlet
of 4, at δP -1.5, which is consistent with the structure
shown for 4 in Scheme 4, and as determined in the X-ray
structure analysis (vide infra), is in fact the minor species,
while a species displaying two broad doublets, at δP 1.5
and -15.4 (2JPP = 56 Hz), predominates in a 6:1 ratio. By
comparison, the 31P{1H} NMR spectrum of the closely
related dppm analogue displays only the expected singlet
at δP 2.7 (in CDCl3).44 The mass spectrum of 4 shows only
one predominant signal pattern consistent with that
calculated for the formulation of the cation depicted in
Scheme 4, supporting our hypothesis that the non-sym-
metrical species is an isomer of the symmetrical P,P0-
chelate observed in the solid state.
The solid state structure of 4 (Figure 3) also fails to
provide clues about the nature of the non-symmetrical
solution species, showing that the isopropyl unit of the
p-cymene fragment should not be restricted from freely
rotating about the isopropyl-aryl and ruthenium-arene
bond axes, suggesting that this particular geometry should
possess chemically equivalent phosphorus nuclei. How-
ever, dissolution of the crystalline sample in CD2Cl2 and
subsequent 31P{1H} NMR spectroscopic analysis shows
the same 6:1 concentration ratio of C1- to Cs-symmetric
isomers as discussed above. The Ru-Cl bond length in 4
A
31P{1H} spin saturation transfer (SST) experiment
was carried out on a sample of 4 in CD3NO2 at 40 °C by
irradiating the resonance at δP -15.4, resulting in a
significant reduction in the intensity of the signals at δP
1.5 and -1.5 relative to an internal standard, indicating
that all three phosphorus environments are undergoing
chemical exchange at this temperature. We have consid-
ered a couple of structures that could give rise to an
unsymmetrical species having two 31P environments but
neither seems possible. We have ruled out the possibility
(44) Jensen, S. B.; Rodger, S. J.; Spicer, M. D. J. Organomet. Chem. 1998,
556, 151–158.
(45) Dennett, J. N. L.; Bierenstiel, M.; Ferguson, M. J.; McDonald, R.;
Cowie, M. Inorg. Chem. 2006, 45, 3705–3717.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4297
Figure 4. 31P{1H} NMR spectrum of 5 in CD2Cl2. Signal 1 corre-
sponds to C2-symmetric stereoisomers; signals 2 correspond to C1-
symmetric stereoisomers.
disorder in one of the coordinated N-methylamino
groups over two diastereotopic positions with a 60:40 site
occupancy ratio representing C2- and C1-symmetric
stereoisomers, respectively. Dissolution of the crystalline
sample in CD2Cl2 and subsequent NMR spectroscopic
analyses also indicate the presence of these stereoisomers
in a ratio similar to that observed in the solid state,
confirming that these isomers co-crystallize. The 31P{1H}
NMR spectrum of 5 (Figure 4) shows a prominent singlet
at δP 13.7, attributed to the PR,P0R,NR,N0R configura-
tion (ORTEP shown later) and its corresponding enan-
tiomer. In this configuration, the phosphorus nuclei are
equivalent by a C2-symmetry axis. In addition to this signal
are two doublets at δP 17.1 and 8.4 (2JPP = 90 Hz),
attributed to the PR,P0R,NS,N0R configuration and its
corresponding enantiomer. The integrated signal intensi-
ties show that the ratio of these C2- to C1-symmetric
stereoisomers is approximately 3:2 (mol/mol) and that there
is no evidence of the other possible C1- and C2-symmetric
stereoisomers.
Figure 3. ORTEP diagram of one of two crystallographically indepen-
dent cations of [RuCl(η6-p-cymene)(P,P0-dmapm)]Cl (4). Thermal ellip-
soids as in Figure 1.
˚
(2.3938(6) and 2.3928(6) A for the two independent
molecules) is similar to that of 3b (2.3944(6) and
˚
2.3982(6) A). However, complex 4 has slightly greater
˚
Ru-P bond lengths (between 2.3851(7) and 2.3313(6) A)
than that of 3b (2.3059(7) and 2.3005(7) A), presumably
˚
because of the greater strain of the four-membered chelate
ring in addition to the increased steric congestion at Ru in
4. Interestingly, the chelate ring of 4 is quite puckered with
Ru-P(1)-C(10)-P(2) and Ru-P(2)-C(10)-P(1) tor-
sional angles for the two independent molecules between
18.5(1)° and 22.99(9)° as the methylene unit is bent slightly
out of the plane of the ring toward the chloro ligand.
Although the monophosphinoaniline complexes dis-
cussed (vide supra) exhibit different coordination tenden-
cies depending on the degree of methyl substitution at
the amine, diverse coordination behavior at ruthenium is
even more pronounced when comparing the diphosphino-
anilines (mapm vs dmapm). Unlike the reaction described
above for dmapm, reaction of mapm with 0.5 equiv of 1
at ambient temperature in dichloromethane results in
facile displacement of the p-cymene moiety to generate
the tetradentate complex, [RuCl2(P,P0,N,N0-mapm)] (5,
Scheme 4). Both complexes 4 and 5 were synthesized in
dichloromethane solution followed by washing with
n-pentane (to remove any p-cymene that may have been
produced) and were isolated as orange powders in good
yields. Upon exposure to water or prolonged exposure to
air, samples of both 4 and 5 turn green, presumably
because of oxidative decomposition46 to yet unidentified
species. Although exposure of 5 to water or other protic
solvents could promote chloride ion displacement and
concomitant coordination of an additional amine to
generate a cationic complex, we have not yet investi-
gated this reaction. The formation of such a pentaden-
tate complex could produce numerous stereoisomers
which should be expected to complicate spectroscopic
analysis.
1
The H NMR spectrum of the C2-symmetric config-
urations of 5 shows two doublets at δH 3.06 (3JHH
=
6.0 Hz) and at 2.66 (3JHH = 4.8 Hz) representing the
pendent and coordinated N-methyl protons, respectively.
These signals exhibit vicinal coupling to the amine hydro-
gens which resonate at δH 6.01 and 6.61, respectively, and
appear as broad quartets. The methylene protons of the
diphosphine backbone produce a triplet resonance at
2
δH 4.78 with JPH = 11.6 Hz, confirming the chemical
equivalence of the neighboring phosphines. The 13C{1H}
=
NMR spectrum of 5 shows a triplet at δC 55.9 (1JPC
25 Hz) for the methylene carbon and two singlet reso-
nances at δC 47.8 and 30.6 belonging to coordinated and
pendent N-methylamino groups, respectively. The ambi-
ent temperature spectroscopic observation of two well-
defined N-methyl environments within this C2-symmetric
isomer shows no evidence for Type II hemilability,1 where-
by the pendent anilines could, in principle, reversibly dis-
place the coordinated ones, resulting in coalescence of
the N-methyl proton signals. The lack of such inherent
fluxionality at ruthenium(II) is in contrast to a similar series
of rhodium(I) complexes which were shown to display Type
1
The H spectrum of 5 is complicated since the com-
plex is formed as a mixture of stereoisomers. Single
crystal X-ray structural analysis of 5 0.5CH2Cl2 shows
1
II hemilability by H NMR spectroscopy.22 The molar
conductivity of 5 was found to be Λ = 7 cm2 Ω-1 mol-1
consistent with a non-conducting complex.
,
3
X-ray structural analysis of compound 5 reveals a
centrosymmetric unit cell with a disordered N-methyl
(46) Murray, K. S.; van den Bergen, A. M.; West, B. O. Aust. J. Chem.
1978, 31, 203–207.

4298 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.
Figure 5. ORTEP diagrams of (left) the PR,P0R,NR,N0R and (right) PR,P0R,NS,N0R configurations of [RuCl2(P,P0,N,N0-mapm)] (5). Thermal ellipsoids as
in Figure 1.
Scheme 5. Products of the Reaction between mapm and [Ru(CO)4(η2-C2H4)] in Ambient Light
group (N(3A) and C(37A), Figure 5) implying co-crystal-
lization of multiple stereoisomers (vide supra). The che-
lating geometry of the tetradentate, P,P0,N,N0-ligand at
ruthenium is, to the best of our knowledge, unique. The
strain of the four-membered chelate ring is made evident
by compression of the P(1)-C(1)-P(2) angle from the
ideal 109.5° to 91.09(9)° as well as compression of the
P(1)-Ru-P(2) angle from the ideal 90° to 72.83(2)°.
Within the five-membered P,N-chelate rings the angles
are much less distorted with angles at Ru, P, N, and C
close to the idealized values. All of the amine hydrogens
come into reasonably close contacts (between 2.31 and
analysis of 6a shows two broad quartets at δH 4.65 and
4.19 corresponding to two chemically distinct pairs of
amine hydrogens and were identified (by GCOSY ana-
lysis) as having vicinal relationships to the N-methyl
protons which resonate at δH 2.74 and 2.54, respectively.
The chemical shifts of the amine protons, which are close
to that of the free ligand (δH = 4.62)22 are consistent with
pendent amine groups. The fact that only two methyl
resonances are observed in the 1H NMR spectrum of 6a
eliminates the possibility that the kinetic product is
[Ru(CO)3(P,N-mapm)], which would be expected to
show four distinct N-methyl environments. The mono-
dentate coordination mode of 6a is analogous to that
reported by Kiel and Takats for [Ru(CO)4(P-dppm)]
(dppm = Ph2PCH2PPh2), which was found to undergo
photodissociation, resulting in release of carbon monoxide
and generating [Ru(CO)3(P,P0-dppm)].47 The methylene
proton signal of 6a, at δH 3.53, appears as a doublet of
doublets because of coupling with two chemically inequi-
valent phosphorus nuclei. Although the 31P{1H} NMR
spectrum of 6b at ambient temperature appears as a singlet
(vide supra), cooling to -80 °C results in splitting of this
singlet resonance into two broad signals at -42.0 and
-46.5, showing that the exchange of axial and equatorial
phosphorus nuclei by a Berry-pseudorotation can be
slowed to render them distinguishable at this temperature.
1H NMR analysis of 6b shows a broad quartet at δH
˚
2.47 A) with the two chloro ligands, which are less than
the sum of the van der Waals radii36 (3.05 A) and suggest
˚
weakly attractive interactions.
The reaction of mapm with [Ru(CO)4(η2-C2H4)] in
dichloromethane solution initially produces [Ru(CO)4-
(P-mapm)] (6a) which, at ambient temperature, over a 24
h period with exposure to ambient light, is completely
converted to the thermodynamic product, [Ru(CO)3-
(P,P0-mapm)] (6b, Scheme 5) by photolytic decarbonyla-
tion. The 31P{1H} NMR spectrum of the reaction mixture
after a few hours of exposure to ambient light shows two
doublets at δP 15.1 and -66.0 (d, 2JPP = 115 Hz) for the
coordinated and pendent phosphines of 6a, respectively,
while the signal for 6b shows up as a singlet at δP -41.3.
The 31P signal for the pendent end of the diphosphine of
6a has an expectedly similar chemical shift to that of the
free mapm ligand which appears at δP -60.9.22 1H NMR
(47) Kiel, G.-Y.; Takats, J. Organometallics 1989, 8, 839–840.

Article
Inorganic Chemistry, Vol. 49, No. 9, 2010 4299
Scheme 6
Figure 6. ORTEP diagram of [Ru(CO)3(P,P0-mapm)] (6b). Thermal
ellipsoids as in Figure 1.
4.95 (3JHH = 5.2 Hz) representing the amine hydrogens, a
triplet at 4.89 (2JPH = 10.0 Hz) representing the methylene
protonsanda doubletat2.59(3JHH =5.2Hz) representing
the N-methyl protons. The chemical equivalence of these
groups of protons at ambient temperature is consistent
with a fluxional process.
X-ray crystallographic analysis of 6b illustrates the pseu-
dotrigonal bipyramidal geometry at ruthenium with clearly
distinguishable axial and equatorial phosphine donors
(Figure 6). The strain of the four-membered chelate ring is
made evident by the P(1)-C(10)-P(2) and P(1)-Ru-P(2)
angles of 97.32(10)° and 71.41(2)°, respectively, which are
compressed from the idealized values of 109.5° and 90°,
respectively. The chelate ring is exceptionally planar as is
shown by the P(1)-Ru-P(2)-C(10) torsional angle of only
0.18(7)°, while the analogous torsional angles for the four-
membered chelate rings of 4 and 5 are 16.9° and 7.23(7)°,
respectively. Within the trigonal equatorial plane the angles
(113.8(1)° to 129.55(9)°) deviate slightly from the idealized
120°, with the largest angle (P(1)-Ru-C(3)) appearing to
have opened up to accommodate the pendent N(4) amine
group which projects into this plane from above in Figure 6.
As is typical for trigonal bipyramidal structures containing a
chelate, the Ru-P(2) vector is tilted from the idealized axial
orientation, owing to chelate ring strain, such that the P(2)-
Ru-C(1) angle (166.34(7)°) deviates from the idealized 180°.
We attempted to exploit the pendent phosphine of 6a to
prepare a dinuclear ruthenium complex of the formula-
tion [Ru2(CO)x(μ-P,P0-mapm)] by reacting mapm with
2 equiv of [Ru(CO)4(η2-C2H4)] in complete darkness (to
prevent conversion of 6a to 6b). However, rather than
producing the expected binuclear complex, this reaction
generated a mixture, containing approximately equal
concentrations of [Ru3(CO)10(μ-P,P0-mapm)] (7) and
6a, the latter of which was gradually converted to 6b
upon exposure to ambient light (Scheme 6) as determined
Figure 7. ORTEP diagram of [Ru3(CO)10(μ-P,P0-mapm)] (7). Thermal
ellipsoids as in Figure 1.
simplify the 1H NMR spectrum, as does the fact that none
of the amines participate in coordination. The methylene
protons appear as a triplet at δH 4.76 while the amine
hydrogen signal appears as a relatively upfield quartet
at δH 3.94. Interestingly, the N-methyl proton signal
appears as a slightly broadened doublet because of
2.5 Hz coupling with the amine hydrogen (a typical
coupling constant in usually twice as large).22 The slight
broadening of this signal may be a consequence of the
fluxionality of the carbonyl moieties on the trinuclear
core which has been well documented within the analo-
gous dppm-bridged system.48 This fluxionality is made
evident by the 13C{1H} spectrum, which shows only a
single resonance at δC 210.9 representing all carbonyls.
The infrared spectrum of 7 in CH2Cl2 is similar to that
described for the dppm analogue48 showing multiple
1
by 31P{1H} and H NMR spectroscopy. Washing with
n-pentane easily removed 6b, allowing 7 to be purified and
crystallized for X-ray structural analysis. Complex 7 can
also be prepared more directly by reacting mapm with
1 equiv of [Ru3(CO)12] in tetrahydrofuran solution, and
the mixture produced by this method is also spectro-
scopically devoid of 6b. The 31P{1H} NMR spectrum of
7 shows only a singlet at δP 2.2, consistent with a sym-
metric bridging mode of the mapm ligand which serves to
carbonyl stretches between 2079 and 1955 cm-1
.
The solid state structure of compound 7 (Figure 7)
clearly illustrates the P,P0-bridging mode of the mapm
ligand across two ruthenium atoms, each of which pos-
sesses three terminally bound carbonyl ligands while
(48) Cotton, F. A.; Hanson, B. E. Inorg. Chem. 1977, 16, 3369–3371.

4300 Inorganic Chemistry, Vol. 49, No. 9, 2010
Hounjet et al.
sharing a bridging Ru(CO)4 unit. All Ru-Ru bond
lengths are very similar (Ru(1)-Ru(2), 2.8464(3); Ru(2)-
as well as the amido-hydrido complex [RuH(η6-p-cymene)-
(P,N-Ph2PAr-)], to test their activities in ketone transfer
hydrogenation catalysis.
˚
Ru(3), 2.8567(3); Ru(1)-Ru(3), 2.8504(3) A) despite the
presence of the bridging diphosphine across the Ru(1)-
Ru(2) bond. As is typical in such clusters, pairs of
carbonyls that are almost eclipsed when viewed along
the metal-metal bonds are actually staggered slightly to
avoid unfavorable contacts. As a result, the torsion angles
of these carbonyls about Ru-Ru bonds vary between
15.7(1)° and 20.5(1)°.
The preparation of 7, in which all amine groups were
pendent, led us to ponder whether amine coordina-
tion could be induced. Decarbonylation of 7 was attempted
by various methods including UV photolysis and carbonyl
oxidation with one or more equivalents of trimethylamine-
N-oxide. However, each of these attempts produced com-
plex mixtures of unidentified products as was observed
spectroscopically.
The previously reported dmapm analogue, [Ru(CO)3-
(P,P0-dmapm)],45 had previously been shown to act as a
useful precursor for the synthesis of the heterobimetallic
complex, [RhRuCl(CO)3(μ-CO)(μ-P,N,P0,N0-dmapm)];
however, instability of the complex was believed to result
from the substantial lability of the N,N-dimethylamino
donors of the dmapm ligand. We thought that substitut-
ing dmapm by mapm within such a bimetallic complex
might better stabilize the soft metal combination by
providing less labile N-methylamino donors. However,
an attempt to synthesize the heterobinuclear complex,
[RhRuCl(CO)3(μ-CO)(μ-P,N,P0,N0-mapm)], from 6b and
0.5 equiv of [RhCl(μ-Cl)(CO)2]2 reveals a number of
products by 31P{1H} NMR, which curiously includes
the previously reported dirhodium species, [Rh2Cl2-
(CO)2(μ-P,N,P0,N0-mapm)].22
Highly diverse coordination chemistry was observed using
the related diphosphine ligands Ar02PCH2PAr02 (dmapm)
and Ar2PCH2PAr2 (mapm). Whereas the dmapm ligand
reacted with 1 to give the P,P0-chelate, [RuCl(η6-p-cymene)-
(P,P0-dmapm)]Cl (4), in which all dimethylanilinyl groups
remained pendent, mapm reacted by displacement of the
p-cymene group to give [RuCl2(P,P0,N,N0-mapm)] (5) in
which both phosphorus and two of the N-methylanilinyl
groups are bonded to Ru, giving an unprecedented coordina-
tion mode for the ligand. Complex 4 is believed to undergo an
isomerization between a Cs-symmetric P,P0-chelate and a yet
unidentified species in solution while complex 5, which
exhibits a P,P0,N,N0-chelation mode, is prepared as a mixture
of stereoisomers. Starting from the Ru(0) precursor, [Ru-
(CO)4(η2-C2H4)], the pendent chelate complex [Ru(CO)4-
(P-mapm)] (6a) results from displacement of ethylene by
mapm which, upon exposure to ambient light for an extended
period, is eventually converted to 6b via photodissociation of
CO. Our attempts to prepare binuclear complexes of ruthe-
nium bridged by the diphosphinoanilines, although unsuc-
cessful, have resulted in the generation of the trinuclear
compound [Ru3(CO)10(μ-P,P0-mapm)] (7). None of the
complexes 6a, 6b, nor 7 are found to possess coordinated
aniline donors, and our attempts to displace carbonyl func-
tionalities from compound 7, to cleanly generate complexes
stabilized by coordinated amines, were unsuccessful, pre-
sumably reflecting the lack of affinity of the soft Ru(0) center
for the hard amine groups. Nevertheless, the pendent amines
of complexes 6b and 7 serve as potential stabilizing function-
alities in the event of coordinative unsaturation at the metal
centers.
Although the trinuclear dmapm complex, [Ru3(CO)10-
(μ-P,P0-dmapm)], analogous to 7, has not yet been synthe-
sized, it can presumably be prepared in an analogous manner
since amine coordination does not seem to have an influence
on diphosphinoaniline reactivity with ruthenium carbonyl
complexes. However, reactions of the monophosphinoani-
lines, Ph2PAr and Ph2PAr0, with [Ru(CO)4(η2-C2H4)] are
expected to result in P,N-chelates, and synthetic investiga-
tions are currently underway to confirm this proposal.
Conclusions
A number of coordination modes for ortho-phosphinoani-
line ligands at ruthenium have been reported herein and,
as was previously described in related Rh chemistry,22 the
N-methyl and N,N-dimethyl analogues can give rise to rather
different chemistries. For example, a comparison of the
reactivities of the monophosphinoaniline ligands, Ph2PAr
and Ph2PAr0 (Ar = o-C6H4NHMe; Ar0 = o-C6H4NMe2)
with [RuCl(μ-Cl)(η6-p-cymene)]2 (1), illustrates that the de-
gree of N-methyl substitution on the ligand influences the
barrier to amine coordination. While the N,N-dimethyl
complex, [RuCl2(η6-p-cymene)(P-Ph2PAr0)] (3a), rapidly
undergoes amine coordination under mild conditions to afford
the P,N-chelated [RuCl(η6-p-cymene)(P,N-Ph2PAr0)]Cl (3b),
the N-methyl analogue, [RuCl2(η6-p-cymene)(P-Ph2PAr)]
(2a), is stabilized by intramolecular hydrogen bonding in
the monodentate P-coordinated isomer and requires kinetic
assistance from a protic solvent to promote formation of
the P,N-chelate, [RuCl(η6-p-cymene)(P,N-Ph2PAr)]Cl (2b).
Compound 2b can be deprotonated to yield the amido com-
plex, [RuCl(η6-p-cymene)(P,N-Ph2PAr-)] (2c), which appears
to undergo enantiomerization in solution, presumably through
the coordinatively unsaturated species, [Ru(η6-p-cymene)-
(P,N-Ph2PAr-)]Cl (2d). Although 2c has been shown to act as
a ketone transfer hydrogenation catalyst, the mechanism
remains unclear. We are currently attempting to isolate the
amine-hydride complex, [RuH(η6-p-cymene)(P,N-Ph2PAr)]þ,
Acknowledgment. We thank the Natural Sciences and
Engineering Research Council of Canada (NSERC) and
the University of Alberta for financial support for this
research and NSERC for funding the Bruker PLAT-
FORM/SMART 1000 CCD diffractometer, the Bruker
D8/APEX II CCD diffractometer, and the Nicolet Avatar
IR spectrometer. We thank the Department’s Analytical
and Instrumentation Laboratory, NMR Spectroscopy
Laboratory, and Mass Spectrometry Facility for excep-
tional assistance, as well as Dr. Owen C. Lightbody and
Dr. Jason Cooke for helpful discussions.
Supporting Information Available: Tables of crystallographic
experimental details and selected bond lengths and angles for
compounds 2a, 2b C4H8O, 2c, 3b 2CH2Cl2,H2O, 4, 5 0.5CH2Cl2,
3
3
3
6b, and 7 0.5C5H12,0.5CH2Cl2. Atomic coordinates, interatomic
3
distances and angles, anisotropic thermal parameters, and hydrogen
parameters for these compounds in a CIF file. This material is
available free of charge via the Internet at http://pubs.acs.org.