Intramolecular C-H and N-H transfer by ruthenium(II) amidophosphine complexes

5440

Organometallics 2005, 24, 5440-5454

Intramolecular C-H and N-H Transfer by

Ruthenium(II) Amidophosphine Complexes

Michael D. Fryzuk,* Michael J. Petrella, and Brian O. Patrick

Department of Chemistry, University of British Columbia, 2036 Main Mall,

Vancouver, BC, Canada, V6T 1Z1

Received July 8, 2005

The formation of ruthenium amidophosphine complexes was accomplished by the addition

of [P₂N₂]Li₂(Diox) (where P₂N₂is PhP(CH₂SiMe₂NSiMe₂CH₂)₂PPh and Diox is 1,4-dioxane)

to [RuCl₂(cod)]_xto generate [P₂N₂]Ru(cod), or to RuCl₂(PPh₃)₃to generate [P₂NNH]Ru(C₆H₄-

PPh₂). In the former complex, the Ru(II) center is in an octahedral environment perched

above the P₂N₂macrocycle having two formally anionic amido donors; in the latter complex,

there is only one amido ligand with the other as an amine donor where the proton originates

from the cyclometalated triphenylphosphine group. Reaction of the tridentate amidophos-

phine ligand precursor [NPN]Li₂(THF)₂(where NPN is PhP(CH₂SiMe₂NPh)₂) with [RuCl₂-

(cod)]_xresults in the formation of two diastereomeric complexes of the formula [NPNH]Ru(η³:

η²-C₈H₁₁), wherein the cyclooctadiene ligand has been deprotonated by the ancillary ligand

to generate a cyclooctadienyl unit. These Ru(II) complexes are five-coordinate with a bidentate

PN ligand and a dangling amine unit. The diastereomers are in equilibrium, as shown by

variable-temperature NMR studies. The fluxional process that interconverts diastereomers

involves proton transfer from the dangling amine arm to the amido unit, a process that

equilibrates the two ends of the tridentate NPN ligand on the chemical time scale.

Deprotonation of the amine arm by MN(SiMe₃)₂generates a series of ruthenate complexes

of the formula [M(THF)]([NPN]Ru(η³:η²-C₈H₁₁)), where M ) Li or Na. Addition of Me₃SiCl

results in the formation of new diastereomers that contain silylated dangling arms, and

these diastereomers do not interconvert.

Introduction

between the transition metal hydride and the coordi-

nated amine ligand.^11-17A critical component of this

mechanism is the formation of an intermediate ruthe-

nium amide complex that heterolytically cleaves dihy-

drogen to regenerate the catalytically active species and,

thereby, close the cycle. This last step, the heterolytic

cleavage of H₂by a ruthenium amide (Ru-NR₂) unit, was

first demonstrated in our laboratory utilizing the mixed-

donor [PNP] (where [PNP] ) N(SiMe₂CH₂PPh)₂) ligand

set.¹⁸

While a single amide unit is all that is required for

the bifunctional mechanism, we were interested in

examining the effect of two amido donors coordinated

to ruthenium(II). With the late transition elements,

anionic amido donors are often quite reactive and can

engage in intramolecular proton transfer and migratory

insertion.^19-21Previous work from our laboratory has

In recent years 18-electron ruthenium(II) complexes

incorporating phosphine and amine ligands have been

employed as precursors for the catalytic asymmetric

reduction of prochiral ketone and imine substrates.^1-9

For example, complexes of the type trans-Ru(binap)Cl₂-

(diamine) and corresponding hydride derivatives are

among the most active catalyst precursors for the

hydrogenation of polar substrates and display remark-

able chemoselectivity for preferential reduction of polar

CdO or CdN functionalities over nonpolar CdC groups.¹⁰

A widely accepted proposal, labeled the “metal-ligand

bifunctional mechanism”, involves a cooperative effort

* To whom correspondence should be addressed. E-mail: fryzuk@

chem.ubc.ca.

(1) Abbel, R.; Abdur-Rashid, K.; Faatz, M.; Hadzovic, A.; Lough Alan,

J.; Morris, R. H. J. Am. Chem. Soc. 2005, 127, 1870.

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Lough, A. J.; Morris, R. H. J. Am. Chem. Soc. 2002, 124, 15104.

(3) Abdur-Rashid, K.; Fedorkiw, T.; Lough, A. J.; Morris, R. H.

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Chem. Soc. 2001, 123, 7473.

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Terada, M.; Noyori, R. J. Am. Chem. Soc. 1998, 120, 1086.

(8) Ohkuma, T.; Hattori, T.; Ooka, H.; Inoue, T.; Noyori, R. Org.

Lett. 2004, 6, 2681.

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2000, 122, 6510.

(10) Ohkuma, T.; Ooka, H.; Ikariya, T.; Noyori, R. J. Am. Chem.

Soc. 1995, 117, 10417.

(13) Noyori, R. Adv. Synth. Catal. 2003, 345, 15.

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2001, 73, 227.

(15) Yamakawa, M.; Ito, H.; Noyori, R. J. Am. Chem. Soc. 2000, 122,

1466.

(16) Ohkuma, T.; Ooka, H.; Yamakawa, M.; Ikariya, T.; Noyori, R.

J. Org. Chem. 1996, 61, 4872.

(17) Ohkuma, T.; Ooka, H.; Hashiguchi, S.; Ikariya, T.; Noyori, R.

J. Am. Chem. Soc. 1995, 117, 2675.

(18) Fryzuk, M. D.; Montgomery, C. D.; Rettig, S. J. Organometallics

1991, 10, 467.

Publication on Web 09/22/2005

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5441

Table 1. Selected Bond Lengths and Angles in [P₂N₂]Ru(η²:η²-C₈H₁₂) (1)

atom

distance (Å)

Ru(1)

C(13)

N(1)/N(1)*

P(1)/P(1)*

C(13)/C(13)*

C(14)/C(14)*

C(14)

2.223(2)

2.3908(7)

2.200(3)

2.202(3)

1.386(4)

atom

angle (deg)

atom

angle (deg)

P(1)

N(1)

P(1)

N(1)

Ru(1)

P(1)*

N(1)*

N(1)

N(1)*

C(13)

C(13)*

C(14)

152.18(4)

92.91(12)

75.88(6)

N(1)

P(1)

Ru(1)

C(14)*

C(13)

C(13)*

C(14)

C(14)*

C(13)*

C(14)*

90.59(10)

83.98(8)

116.39(8)

120.34(8)

80.40(8)

90.15(16)

90.51(17)

P(1)

84.99(6)

P(1)

C(13)

C(14)

158.62(10)

92.40(10)

163.67(9)

detailed the synthesis of two amidophosphine ligand

precursors that each have two amido units attached to

one or two phosphine moieties, that is, [NPN]Li₂(THF)₂

([NPN] ) PhP(CH₂SiMe₂NPh)₂; THF ) tetrahydrofu-

ran) and [P₂N₂]Li₂(Diox) ([P₂N₂] ) [PhP(CH₂SiMe₂-

NSiMe₂CH₂)₂PPh]; Diox ) 1,4-dioxane), respectively.^22,23

In this paper, we report the coordination chemistry of

these two multidentate ligands with two Ru(II) precur-

sors. We have already published the reaction of one of

these precursor complexes with H₂and examined its

ability to hydrogenate imines and ketones.²⁴

in hexanes, it can be purified from the more soluble dark

colored impurities by rinsing the crude product mixture

with hexanes.

The solid-state molecular structure of 1 as determined

by a single-crystal X-ray diffraction study is shown in

Figure 1, with selected bond lengths and angles high-

lighted in Table 1. The complex adopts a distorted

octahedral geometry in which the amido donors of the

[P₂N₂] ligand set and the olefin donors of the cyclo-

octadiene ligand lie in an equatorial plane. The phos-

phine ligands occupy the corresponding axial positions

with a P(1)-Ru(1)-P(1)* angle of 152.18(4)°. The com-

pound exhibits C₂symmetry in the solid state.

Results and Discussion

The smaller N-Ru-N bite angle of 92.91(12)° com-

pared to the larger P-Ru-P bite angle of 152.18(4)° is

consistent with the previously observed binding of the

[P₂N₂] ligand in which the amide donors are typically

cis while the phosphines are located approximately

trans to one another. Similar to [P₂N₂] complexes of the

early transition metals,^25,26the ruthenium center in 1

is perched on, rather than nested in, the macrocycle.

The room-temperature ¹H NMR spectrum of complex

1 in toluene-d₈is indicative of a C_2vsymmetric solution

structure. For instance, the [P₂N₂] ligand in 1 gives rise

to two resonances for the silyl methyl protons at δ 0.4

and 0.5. These correspond to the silyl methyl groups

directed to the “top” and “bottom” of the ligand (where

top refers to the side of the ligand to which the metal is

bound). If the C₂symmetry evident in the solid-state

molecular structure of 1 was maintained in solution,

four silyl methyl proton resonances would be expected.

In addition, there is a single peak present for the four

vinyl protons of the cyclooctadiene ligand and a broad

Synthesis and Characterization of [P₂N₂]Ru

Complexes. The reaction of colorless [P₂N₂]Li₂(Diox)²³

with [RuCl₂(cod)]_xgenerates a dark yellow-brown solu-

tion from which [P₂N₂]Ru(η²:η²-C₈H₁₂) (1) can be isolated

in 73% yield (eq 1). Compound 1 is the first ruthenium

complex of the [P₂N₂] ligand that has been prepared;

[P₂N₂] complexes of some early transition metals have

previously been investigated.^25,26Due to the fact that

the yellow diamido species 1 is only moderately soluble

(19) Fryzuk, M. D.; Montgomery, C. D. Coord. Chem. Rev. 1989, 95,

1.

(20) Watson, L. A.; Coalter, J. N., III; Ozerov, O.; Pink, M.; Huffman,

J. C.; Caulton, K. G. New J. Chem. 2003, 27, 263.

(21) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G. Acc.

Chem. Res. 2002, 35, 44.

(22) Fryzuk, M. D.; Johnson, S. A.; Patrick, B. O.; Albinati, A.;

Mason, S. A.; Koetzle, T. F. J. Am. Chem. Soc. 2001, 123, 3690.

(23) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. J. Chem. Soc., Chem.

Commun. 1996, 2783.

(24) Fryzuk, M. D.; Petrella, M. J.; Coffin, R. C.; Patrick, B. O. C.

R. Chim. 2002, 5, 451.

Figure 1. ORTEP representation (thermal ellipsoids

shown at 50% probability) of the solid-state molecular

structure of [P₂N₂]Ru(η²:η²-C₈H₁₂) (1). The silyl methyl

groups of the [P₂N₂] ligand have been omitted for clarity.

(25) Fryzuk, M. D.; Love, J. B.; Rettig, S. J. Organometallics 1998,

17, 846.

(26) Fryzuk, M. D.; Johnson, S. A.; Rettig, S. J. Organometallics

1999, 18, 4059.

5442 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

signal for the eight methylene protons. The ¹³C{¹H}

NMR spectrum at this same temperature is also con-

sistent with complex 1 exhibiting C_2vsymmetry in

solution. Two resonances for the silyl methyl carbon

nuclei are observed and only one peak for the [P₂N₂]

methylene carbon nuclei is present; no coupling to the

³¹P nucleus could be resolved. The cyclooctadiene ligand

has a single vinylic carbon resonance at δ 70.0 and a

single methylene carbon resonance at δ 25.0.

two compounds in hydrocarbon solvents. Isolation of 2

was successfully accomplished by the addition of 2

equivalents of anhydrous CuCl; this generates an

insoluble “CuCl(PPh₃)” oligomeric complex³⁰that is

more easily removed by filtration.

The high symmetry of complex 1 in solution as

1

evidenced by the H and ¹³C{¹H} NMR data is due to

the conformationally flexible nature of the [P₂N₂] ligand.

The C_2vsymmetry can be rationalized via a twisting

motion of the [P₂N₂] ligand in 1 about the amido

nitrogen atoms of the macrocycle that is fast on the

NMR time scale.

1

A variable-temperature H NMR study of complex 1

was undertaken, and the effect of temperature on the

vinylic proton resonances of the cyclooctadiene ligand

in 1 was monitored. As the temperature is lowered, the

singlet at δ 2.80 that is observed at room temperature

begins to broaden until decoalescence occurs at 234 K.

At the low-temperature limit (198 K) two signals are

present at δ 2.6 and 3.0, each integrating to two vinyl

protons. Also at 198 K four signals are present for the

silyl methyl groups of the [P₂N₂] ligand between δ 0.3

and 0.8. The broad peak for the cyclooctadiene methyl-

ene protons collapses to four singlets and the [P₂N₂]

methylene protons remain as two peaks. Although the

resolution at this temperature was not adequate to

provide coupling constants, the features present in the

low-temperature limiting spectrum are consistent with

C₂symmetry, as observed in the solid state. A line-shape

analysis of the methylene protons of the cyclooctadiene

ligand from 212 to 243 K combined with an Arrhenius

plot of the resulting rate constants provided an activa-

tion barrier of 18.6 ( 1.6 kcal mol^-1for the twisting

motion of the [P₂N₂] framework within complex 1 (see

Supporting Information).

The reaction of RuCl₂(PPh₃)₃with the [P₂N₂] ligand

precursor did not afford the expected diamidodiphos-

phine ruthenium(II) complex [P₂N₂]Ru(PPh₃)₂. Rather,

the compound isolated was the product of ortho-meta-

lation of one of the triphenylphosphine ligands, [P₂-

NNH]Ru(C₆H₄PPh₂) (2), as shown in eq 2. The propen-

sity for the PPh₃ligand to ortho-metalate is well known

not only for complexes of ruthenium(II)^18,27but for other

metals as well.^28,29Previous studies in the Fryzuk

laboratory have shown that the related species [PNP]-

RuCl(PPh₃), where [PNP] represents N(SiMe₂CH₂-

PPh₂)₂, suffers a similar fate upon addition of trieth-

ylphosphine, resulting in the formation of [PNHP]RuCl-

(C₆H₄PPh₂).¹⁸

Diagnostic of complex 2 is the ³¹P{¹H} NMR spec-

trum, which shows a doublet (at δ 25.8) and a triplet

(at δ -11.8) for the ancillary phosphine donors of the

[P₂NNH] ligand set and the (C₆H₄)PPh₂ligand, respec-

tively (²J_PP) 31 Hz). These signals integrate in the ratio

2:1. An upfield shift for the ³¹P nucleus of the (C₆H₄)-

PPh₂ligand has been observed in other complexes that

incorporate an ortho-metalated triphenylphosphine

ligand.³¹The equivalency of the phosphorus centers in

the [P₂NNH] ligand is consistent with the proposed

structure, which has C_ssymmetry.

1

The room-temperature 500 MHz H NMR data are

also consistent with the proposed structure of complex

2 shown in eq 2. Four resonances for the silylmethyl

groups of the [P₂NNH] ligand set are observed between

δ 0.40 and 0.60 in accordance with a mirror plane of

symmetry contained within the equatorial plane of the

octahedral coordination geometry of 2. The ligand

methylene protons give rise to two sets of overlapping

resonances consisting of a second-order AA′BX pattern.

A singlet at δ 2.8 has been ascribed to the amino proton

(N-H). The aromatic protons of the ortho-metalated

triphenylphosphine and [P₂N₂] phosphorus phenyl sub-

stituents occur as overlapping resonances between δ 6.5

and 8.2.

Single crystals of [P₂NNH]Ru(C₆H₄PPPh₂) (2) suitable

for an X-ray diffraction study were grown by the slow

evaporation of a saturated pentane solution. The solid-

state molecular structure of 2 as determined by X-ray

crystallography is shown in Figure 2, with selected bond

lengths and bond angles detailed in Table 2. Complex

2 crystallizes with two crystallographically distinct but

structurally related molecules in the asymmetric unit,

in addition to one molecule of n-pentane. The following

structural discussion will be concerned with only one

of the molecules for the sake of brevity.

Stirring a solution containing an equimolar mixture

of [P₂N₂]Li₂(Diox) and RuCl₂(PPh₃)₃in toluene results

in the formation of an orange-brown solution within 3

h. Removal of LiCl is accomplished by filtration; how-

ever, separation of 2 from free triphenylphosphine

proved difficult due to the similar solubilities of these

The geometry of complex 2 was found to be distorted

octahedral with the two phosphine donors of the [P₂-

NNH] ligand occupying the axial positions; these are

pinched back from an ideal trans disposition giving a

(27) Pez, G. P.; Grey, R. A.; Corsi, J. J. Am. Chem. Soc. 1981, 103,

7528.

(30) Cotton, F. A.; Wilkinson, G. Advanced Inorganic Chemistry: A

Comprehensive Text, 4th ed.; John Wiley and Sons: New York, 1980;

pp 804-805.

(31) Cole-Hamilton, D. J.; Wilkinson, G. J. Chem. Soc., Dalton

Trans. 1977, 797.

(28) McKinney, R. J.; Knobler, C. B.; Huie, B. T.; Kaesz, H. D. J.

Am. Chem. Soc. 1977, 99, 2988.

(29) Jones, W. D.; Rosini, G. P.; Maguire, J. P. Organometallics 1999,

18, 1754.

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5443

Table 2. Selected Bond Lengths and Bond Angles in [P₂NNH]Ru(C₆H₄PPh₂) (2)

atom

distance (Å)

atom

distance (Å)

Ru(1)

C(26)

N(2)

P(3)

2.034(5)

Ru(1)

N(1)

P(1)

2.3565(13)

2.414(4)

0.73(6)

2.260(4)

N(1)

2.2989(13)

2.3248(13)

H(101)

P(2)

N(2)

2.404

atom

angle (deg)

atom

angle (deg)

C(26)

N(2)

C(26)

N(2)

P(3)

Ru(1)

N(2)

P(3)

P(2)

P(1)

99.66(18)

68.39(14)

167.65(12)

93.96(14)

86.15(11)

97.51(5)

P(3)

P(2)

C(26)

N(2)

P(3)

P(2)

P(1)

N(1)

Ru(1)

H(101)

P(1)

N(1)

N(2)

93.02(5)

168.67(5)

178.48(18)

79.33(17)

112.55(13)

87.12(11)

84.99(11)

137.72

C(26)

N(2)

93.80(14)

84.41(11)

P(1)-Ru(1)-P(2) angle of 168.67(5)°. The ortho-meta-

lated triphenylphosphine ligand as well as the amide

and amine ligands all lie in the plane of the octahedron

with a combined equatorial angle of 359.93°. The N(1)-

Ru(1)-N(2) bond angle of 79.33(17)° is quite small in

comparison to complex 1, which has a N-Ru-N bond

angle of approximately 92°. It is likely that this smaller

bond angle in 2 is a consequence of an intramolecular

hydrogen-bonding interaction between the amino proton

and the amido nitrogen atom (vide infra). The ruthe-

nium-amido bond length, Ru(1)-N(2), of 2.260(4) Å is

similar to that found in 1, while the ruthenium-amine

bond length, Ru(1)-N(1), is longer at 2.414(4) Å as

expected; this latter bond distance is longer than that

found in related systems.^18,20As expected, the amido

nitrogen N(2) is essentially planar, with the sum of the

angles being 358.1°, while the geometry around the

amine nitrogen N(1) is distorted slightly away from

planar, with the sum of the angles (excluding the H

atom) being 350.9° (Si(2)-N(1)-Si(1), 127.2(3)°; Si(2)-

N(1)-Ru(1), 109.4(2)°; Si(1)-N(1)-Ru(1), 114.3(2)°).

The Ru-P bond distances (2.3248(13) and 2.3565(13)

Å) for the [P₂NNH] ligand of complex 2 are slightly

elongated compared to P(3) of the metalated triphen-

ylphosphine (2.2989(13) Å). Presumably this structural

feature is due to the high trans influence of phosphines

relative to that of amides. This difference, however, is

not as significant as that observed in the isoelectronic

species [PNHP]RuCl(C₆H₄PPh₂).¹⁸In this complex, the

phosphine donors of the tridentate ligand are displaced

2.3945 Å on average from the Ru(II) center, whereas

the Ru-P distance for the metalated triphenylphos-

phine ligand is 2.2545 Å. These distances are compa-

rable to those found in RuCl₂(PPh₃)₃,³²in which the two

mutually trans triphenylphosphine ligands exhibit Ru-P

distances of 2.374(6) and 2.388(7) Å, while the remain-

ing phosphine (trans to an open site) is located 2.230(8)

Å from the metal. The shorter Ru-P distances for the

phosphine donors of the [P₂NNH] ligand in 2 may be

the result of a “macrocyclic effect”.³³The longer Ru(1)-

P(3) distance in complex 2, on the other hand, may be

a consequence of minimizing steric interactions with the

[P₂NNH] ligand set.

Structural features of the four-membered ring of the

metallacycle are typical of other such rings found in the

literature. For instance, the C-Ru-P angle of 68.39-

(14)° measured in 2 is similar to that found in the

ruthenate complex K[RuH₂(C₆H₄PPh₂)(PPh₃)₂]²⁷(67.6-

(3)°), as well as the related species [PNHP]RuCl(C₆H₄-

PPh₂) (68.24(8)°).¹⁸In the ruthenate complex, the Ru-C

distance is 2.098(11) Å, whereas in the tridentate

[PNHP] complex it is observed to be 2.054(3) Å. In 2, a

slightly shorter Ru-C distance of 2.034(5) Å was found.

This trend in bond distances is in accordance with the

trans influence differences between PPh₃, Cl, and amine

donors³⁴in the respective complexes. The ruthenium-

amine bond length in complex 2 is likewise lengthened

(2.414(4) Å) by the high trans influence of the ortho-

metalated aryl group.

An interesting feature evident in the solid-state

molecular structure of complex 2 is the presence of a

hydrogen bond between the amine proton (H(101)) and

the amido nitrogen (N(2)). A similar bonding interaction

was also evident between the amine and chloride

ligands in the complex [PNHP]RuCl(C₆H₄PPh₂), as well

as in other complexes of rhodium and iridium that also

(32) Hoffman, P. R.; Caulton, K. G. J. Am. Chem. Soc. 1975, 97,

4221.

Figure 2. Solid-state molecular structure (ORTEP rep-

resentation, 50% thermal ellipsoid probability) of [P₂NNH]-

Ru(C₆H₄PPh₂) (2) as determined by X-ray crystallography.

The silylmethyl groups of the [P₂NNH] ligand have been

omitted for clarity.

(33) Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M.

Advanced Inorganic Chemistry: A Comprehensive Text, 6th ed.; John

Wiley and Sons: Toronto, 1999; pp 29-30.

(34) Miessler, G. L.; Tarr, D. A. Inorganic Chemistry, 3rd ed.;

Prentice Hall: Upper Saddle River, NJ, 2004; p 439.

5444 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

Scheme 1

macrocyclic [P₂N₂] ligand onto Ru(II) via reaction with

[RuCl₂(cod)]_xgenerates the species [P₂N₂]Ru(η²:η²-

C₈H₁₂) (1). Thus it was anticipated that the outcome of

the reaction between the tridentate [NPN] ligand pre-

cursor [NPN]Li₂(THF)₂(where [NPN] is PhP(CH₂SiMe₂-

NPh)₂) with [RuCl₂(cod)]_xwould be the formation of the

diamidophosphine complex [NPN]Ru(η²:η²-C₈H₁₂), as

shown in eq 3. That this was not the isolated product

from this reaction was immediately apparent upon

inspection of the room-temperature ¹H NMR spectrum

(Figure 3). Just the sheer number of peaks present

implied the existence of more than one species (each of

low symmetry) in solution, and furthermore, the broad-

ened resonances were indicative of a fluxional process

1

occurring in solution. The H NMR spectra at 298 and

245 K are shown in Figure 3. However, elemental

analysis of the red crystalline solid that was isolated

from this reaction is consistent with the formulation of

the expected product, [NPN]Ru(η²:η²-C₈H₁₂), suggesting

that the isolated products were structurally related

isomers of this species.

incorporate this tridentate ligand system.³⁵The NH‚‚‚

N distance of 2.404 Å in complex 2 is shorter than the

expected van der Waals contact distance of 2.7 Å

between these two nuclei.³⁶Also indicative of the

presence of a bonding interaction between the hydrogen

and amido nitrogen atom is the fact that the amine

hydrogen lies nearly in the plane of N(1), N(2), and Ru-

(1) illustrated by the Ru(1)-N(1)-H(101)-N(2) torsion

angle of -15.1°, thus minimizing the NH‚‚‚N separation.

The mechanism of the observed ortho-metalation to

form 2 is unknown. However, one might have expected

that transfer of the ortho-hydrogen atom to the amido

donor would result in cis-disposed amine and σ-aryl

ligands in the product. In fact, the solid-state data show

that the amine ligand is located trans to the ortho-

metalated carbon atom. One rationalization for this may

be that the reaction of the [P₂N₂] ligand with RuCl₂-

(PPh₃)₃is not kinetically controlled and that the forma-

tion of complex 2 proceeds under thermodynamic con-

trol. The position of the donors in the equatorial plane

may be governed by electronics and arranged according

to the relative trans influences of phosphine, amine,

aryl, and amide ligands. The known trans influence

decreases in the order PPh₃> C₆H₅> amine,³⁴sug-

gesting that the amido ligand in 2 may exhibit the

weakest trans influence. Scheme 1 depicts a plausible

reaction pathway for the formation of the isolated

species 2. Activation of the ortho C-H bond of the PPh₃

would result in a cis disposition of the N-H and the

σ-bound aryl group in the kinetic product. It is specu-

lated that the amine donor in the kinetic product

dissociates, undergoes inversion at nitrogen, and reco-

ordinates, allowing for an intramolecular hydrogen-

bonding interaction with the coordinated amido ligand.

Subsequent transfer of the amino proton to the amide

nitrogen atom generates the observed complex 2. A

similar rearrangement was proposed to occur upon

ortho-metalation in the complex [PNHP]RuCl(C₆H₄-

PPh₂).¹⁸

As portrayed in eq 4, the products that are formed in

the reaction between the [NPN] ligand precursor and

[RuCl₂(cod)]_xare a pair of diastereomers. Transfer of

an allylic C-H atom of the cyclooctadiene ligand to one

of the amido donors of the [NPN] ligand occurs, gener-

ating a mixture of the two species exo- and endo-[NPNH]-

Ru(η³: η²-C₈H₁₁) (exo-3 and endo-3, respectively). The

activation of an allylic C-H bond of a coordinated

cyclooctadiene moiety resulting in the formation of a

Synthesis, Characterization, and Reactivity of

exo- and endo-[NPNH]Ru(η³:η²-C₈H₁₁) (exo-3 and

endo-3). As already discussed, the incorporation of the

(35) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. J. Am. Chem. Soc.

1987, 109, 2803.

(36) Joesten, M. D.; Schaad, L. J. Hydrogen Bonding; Marcel

Dekker: New York, 1974.

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5445

Figure 3. 500 MHz ¹H NMR spectrum of the mixture of complexes 3 in toluene-d₈at 298 K (upper spectrum) and 245 K

(lower spectrum).

cyclooctadienyl ruthenium(II) complex has previously

been reported.^37,38The terms “exo” and “endo” are used

to distinguish the two diastereomers, and they refer to

the orientation of the amino sidearm of the [NPNH]

ligand set with respect to the methylene unit bridging

the olefin and allyl donor groups of the cyclooctadienyl

ligand. In the endo diastereomer the pendant amino

ligand and the bridging methylene unit are oriented

toward the same “side” of the metal, whereas in the exo

isomer, the amino ligand is positioned to the opposite

face of the metal and points away from the bridging

methylene unit.

crystallography and variable-temperature one- and two-

dimensional NMR spectroscopy (¹H, ¹³C{¹H}, and ³¹P-

{¹H}) in addition to reactivity studies all provided

valuable clues about this system.

The solid-state structural identification of the dias-

tereomer endo-3 provided the first insight into the

details of the reaction of the [NPN] ligand precursor

with [RuCl₂(cod)]_x. The solid-state molecular structure

is shown in Figure 4; pertinent bond lengths and angles

can be found in Table 3. Transfer of an allylic C-H atom

of the cyclooctadiene ligand to an amido nitrogen atom

is clearly evident from the solid-state molecular struc-

ture, which shows the η³-allyl, η²-olefin coordination

mode adopted by the cyclooctadienyl ligand. The pro-

tonated sidearm of the [NPNH] ligand is also apparent,

and it does not coordinate to the metal center. The

amino proton (H43) was located and refined isotropi-

cally. The complex exhibits a five-coordinate, distorted

trigonal bipyramidal geometry at ruthenium (with the

allyl donor occupying two coordination sites and the

The identification and characterization of the diaster-

eomers exo-3 and endo-3, as well as an understanding

of the dynamic behavior of these two species in solution,

proved to be challenging. Techniques including X-ray

(37) Ashworth, T. V.; Chalmers, A. A.; Liles, D. C.; Meintjies, E.;

Singleton, E. Organometallics 1987, 6, 1543.

(38) Wiles, J. A.; Lee, C. E.; McDonald, R.; Bergens, S. H. Organo-

metallics 1996, 15, 3782.

5446 Organometallics, Vol. 24, No. 22, 2005

Table 3. Selected Bond Lengths and Angles in endo-[NPNH]Ru(η³: η²-C₈H₁₁) (endo-3)

Fryzuk et al.

atom

distance (Å)

atom

distance (Å)

Ru(1)

C(25)

N(1)

2.019(2)

2.3024(6)

2.300(3)

2.332(2)

2.187(2)

2.169(2)

2.195(2)

1.354(4)

C(29)

C(30)

N(1)

N(2)

N(1)

N(2)

N(1)

C(30)

C(31)

C(7)

C(19)

Si(1)

Si(2)

H(43)

1.408(4)

1.411(4)

1.430(3)

1.392(3)

1.734(2)

1.727(2)

3.419

P(1)

C(25)

C(26)

C(29)

C(30)

C(31)

C(26)

atom

angle (deg)

atom

angle (deg)

P(1)

N(1)

Ru(1)

N(1)

87.32(6)

163.35(7)

162.61(7)

95.22(7)

83.98(7)

103.09(7)

97.09(9)

90.06(9)

N(1)

Ru(1)

N(1)

C(29)

C(30)

C(31)

Si(1)

C(7)

147.35(9)

170.65(9)

142.72(9)

124.3(1)

123.6(2)

112.2(2)

68.2(1)

C(25)

C(26)

C(29)

C(30)

C(31)

C(25)

C(26)

N(1)

Ru(1)

Si(1)

C(29)

N(1)

Ru(1)

C(7)

C(31)

olefin donor one coordination site). Within the trigonal

bipyramid, the amide and the allyl moieties lie within

the trigonal plane, while the phosphine and olefin

ligands occupy the axial positions. The P(1)-Ru(1)-

C(25) and P(1)-Ru(1)-C(26) bond angles are 163.35-

(7)° and 162.61(7)°, respectively, indicating a nearly

trans disposition between the phosphine and olefin

donor groups. The allyl moiety of the cyclooctadienyl

ligand is symmetrically bound to ruthenium with an

average Ru-C_allylbond distance of 2.184 Å.

coordinate complexes cis-Ru(H)(PMe₃)₄(NHPh)³⁹and

Ru(η⁶-C₆Me₆)(PMe₃)(Ph)(NHPh)⁴⁰bearing the anilido

ligand have ruthenium to nitrogen distances of 2.160-

(6) and 2.121(3) Å, respectively. The shorter Ru-N bond

length in the five-coordinate endo-3 can be attributed

to delocalization of the amido nitrogen lone pair to a

vacant metal d-orbital. Also consistent with the exist-

ence of a π-bonding interaction is the planar, sp²-

hydridized geometry displayed by the amido nitrogen

atom (sum of angles ) 360°); planarity of the amido unit

necessarily occurs to maximize π-bonding with the

metal center. This planarity, however, could also arise

from similar π-interactions existing between the amide

nitrogen atom and the neighboring silicon atom or

phenyl ring. The bond distance (1.430(3) Å) from the

amido nitrogen (N(1)) to the phenyl ipso carbon (C(7))

of the amido moiety is longer than that of aniline (1.398

Å), suggesting minimal π-delocalization into the amido

aromatic ring in complex endo-3. In an earlier report,

an inverse correlation between Ru-N and N-C_ipsobond

distances in ruthenium(II) phenyl amido systems had

been noted.⁴¹

Although 3 may be considered an unsaturated, 16-

electron species, the presence of the π-donating amido

ligand can also result in a formal 18-electron configu-

ration at the metal center. An indication of a π-bonding

interaction can be portrayed structurally by a short

metal-nitrogen bond distance as well as a trigonal

planar coordination geometry at the amido nitrogen

atom.¹⁹In the case of endo-3 the ruthenium amide (Ru-

(1)-N(1)) bond length is 2.019(2) Å. In contrast, the

coordinatively saturated species [P₂N₂]Ru(η²:η²-C₈H₁₂)

(1) has a Ru-N bond length of 2.223(2) Å. The six-

Theoretical calculations^42,43have shown that a dia-

magnetic d⁶ML₅complex distorts away from the Jahn-

Teller active trigonal bipyramidal structure to generate

either a square pyramid or a distorted trigonal bipyra-

mid type geometry. These two extreme geometries were

found to be very close in energy, and the preference for

one over the other comes from a subtle balance of the

σ- and π-properties of the ligands. When one of the

ligands is a π-donor, a distorted trigonal bipyramidal

geometry is observed^44-47with this ligand located op-

posite the acute angle in the equatorial plane of the

(39) Hartwig, J. F.; Andersen, R. A.; Bergman, R. G. Organometallics

1991, 10, 1875.

(40) Boncella, J. M.; Eve, T. M.; Rickman, B.; Abboud, K. A.

Polyhedron 1998, 17, 725.

(41) Jayaprakash, K. N.; Gunnoe, T. B.; Boyle, P. D. Inorg. Chem.

2001, 40, 6481.

(42) Rachidi, I. E. I.; Eisenstein, O.; Jean, Y. New J. Chem. 1990,

14, 671.

(43) Riehl, J. F.; Jean, Y.; Eisenstein, O.; Pelissier, M. Organome-

tallics 1992, 11, 729.

(44) Johnson, T. J.; Folting, K.; Streib, W. E.; Martin, J. D.; Huffman,

J. C.; Jackson, S. A.; Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1995,

34, 488.

Figure 4. Solid-state molecular structure (ORTEP depic-

tion shown at 50% thermal ellipsoid probability) of endo-

[NPNH]Ru(η³: η²-C₈H₁₁) (endo-3) as determined by X-ray

diffraction. The amino proton (H43) was refined isotropi-

cally.

(45) Bickford, C. C.; Johnson, T. J.; Davidson, E. R.; Caulton, K. G.

Inorg. Chem. 1994, 33, 1080.

(46) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.;

Eisenstein, O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476.

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5447

Figure 5. J-modulated ¹³C{¹H} NMR spectrum for endo-3 and exo-3 obtained at 245 K in toluene-d₈highlighting the

cyclooctadienyl carbon resonances. The CH resonances point up and the CH₂resonances point down. The spectral range

indicated is from δ 110 for C₂(exo) to δ 25 for C₈(endo).

molecule. Such a geometry permits the formation of a

partial double bond between an empty metal d-orbital

and the lone pair of the π-donor, which is manifested

as a shortening in the M-X bond and, in the case of a

single-face π-donor, a preferred orientation to maximize

orbital overlap. No such π-interaction can occur in the

square pyramidal structure since all of the appropriate

symmetry-adapted d-orbitals are filled.

The observed geometry of endo-3 in the solid state

coincides well with the theoretical predictions and on

the basis of orbital symmetry allows for amide-to-

ruthenium multiple bonding to take place. The P(1)-

Ru(1)-N(1)-Si(1) dihedral angle of -5.8(1)° indicates

that the plane of the amide donor is perpendicular to

the equatorial plane of the molecule, and this allows for

maximal overlap of the filled amido lone pair orbital (p_y)

with the empty d_xymetal orbital. Complex 3 can

therefore be regarded as a “π-stabilized” unsaturated

complex.

As already mentioned, the room-temperature ¹H

NMR spectrum of 3 indicates the presence of (at least)

two species in solution, and furthermore, the number

of resonances observed suggests that these complexes

are of low symmetry. The characterization of endo-3 in

the solid state shows that it is chiral, exhibiting C₁

symmetry. By examination of the spectra in more detail,

it was determined that there were two species in

solution, in equilibrium with each other and displaying

similar types of environments for the cyclooctadienyl

resonances and the ancillary ligand. The room-temper-

ature ¹H NMR spectrum of a bulk sample of 3 consists

of many broadened resonances, which hampered peak

assignments (see Figure 3). The ³¹P{¹H} NMR spectrum

at the same temperature contains one peak at δ 33.0.

Cooling the sample, however, results in two singlets in

the ³¹P{¹H} NMR spectrum in the ratio 2:1, establishing

the presence of two species (one major and one minor)

in solution. It was not possible to determine which

diastereomer is the major or minor species; therefore,

in the following discussion concerning the variable-

temperature NMR studies it is assumed that endo-3 is

the major isomer in solution.

Interestingly, identical NMR spectra (¹H and ³¹P{¹H})

are obtained whether a single crystal of endo-3 is

employed for the NMR investigations or a bulk pow-

dered sample. This suggests that a dynamic equilibrium

exists between the two species in solution. At 245 K the

fluxional process responsible for the interconversion of

the two species is slow enough to allow for the identi-

fication of endo-3 and exo-3 as the two complexes in

solution. Full characterization of these two isomers was

based on low-temperature ¹H, ³¹P{¹H}, and ¹³C{¹H}

NMR data. In addition, two-dimensional homo- and

heteronuclear correlation experiments allowed for the

complete assignment of the resonances attributed to

1

both of the diastereomers. A collection of the H and

¹³C assignments for the cyclooctadienyl ligand of iso-

mers endo-3 and exo-3 is given in the Supporting

Information, together with data for other complexes

containing this ligand. The labeling convention used for

assignment of NMR peaks corresponding to the cyclo-

octadienyl ligand that will be used in the following

discussion is shown in the Experimental Section.

The J-modulated ¹³C{¹H} NMR spectrum obtained at

245 K (shown in Figure 5) identifies the presence of 10

CH and six CH₂resonances for the cyclooctadienyl

ligand, consistent with an η³-allyl, η²-olefin coordination

mode for each isomer. Complex endo-3 contains two

doublets at δ 108.1 (²J_PC) 10.5 Hz) and 61.4 (²J_PC

)

6.5 Hz) in the ¹³C{¹H} NMR spectrum that have been

ascribed as the olefinic bound carbon atoms C₂and C₁,

respectively; these show a two-bond coupling with the

trans-located phosphine donor. The allyl carbon reso-

nances occur at δ 71.6 (C₆), 61.6 (C₅), and 35.6 (C₇). For

these latter peaks no scalar coupling to the ³¹P nucleus

could be resolved; a much smaller coupling would be

expected due to the cis orientation between these two

donor groups. These data agree with the solid-state

structure, which shows that the olefin and phosphine

donors are trans-disposed to one another.

The 500 MHz ¹H NMR spectrum of endo-3 shows four

silyl methyl and four methylene proton resonances of

the [NPNH] ligand, indicating that the asymmetry of

(47) Fryzuk, M. D.; MacNeil, P. A.; Rettig, S. J. Organometallics

1986, 5, 2469.

5448 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

Figure 6. Region of the 500 MHz ¹H{³¹P} NMR spectrum of isomers endo-3 and exo-3 highlighting the downfield shifted

cyclooctadienyl proton resonances at 245 K in toluene-d₈.

the complex is maintained in solution. In addition, all

11 cyclooctadienyl protons are inequivalent and give rise

to 11 coupled resonances. The olefinic protons are

shifted furthest downfield at δ 4.25 (H_b) and 4.23 (H_a),

respectively. The terminal allyl proton resonances are

found at δ 4.20 (H_e) and 2.85 (H_g), whereas the central

allyl proton (H_f) is significantly upfield shifted at δ 1.64.

The protons of the methylene unit bridging the olefin

and allyl groups (H_hand H_h′) are observed as multiplets

at δ 2.70 and 2.00. The remaining methylene proton

environments of the cyclooctadienyl ligand are located

at δ 2.63 (H_c), 1.58 (H_c′), 2.18 (H_d), and 1.50 (H_d′). The

two-dimensional ¹H-¹H COSY and ¹H-¹³C HMQC data

aided in the assignment of the cyclooctadienyl proton

environments. The amino proton of the dissociated

sidearm of the [NPNH] ligand occurs as a singlet at δ

6.63.

same coordination mode adopted by the cyclooctadienyl

ligand in both species. For exo-3, the olefinic protons

exist furthest downfield at δ 4.68 (H_a) and 3.92 (H_b) with

the two terminal allyl protons at δ 3.50 (H_e) and 3.37

(H_g). Although the central allyl proton (H_f) is obscured

by neighboring peaks, its presence at δ 1.50 was

confirmed by ¹H-¹H and ¹H-¹³C correlation experi-

ments. The significant upfield shift of this proton also

occurs for isomer endo-3. To further assist in the

characterization of isomer exo-3, a simulation of the spin

system of the cyclooctadienyl proton environments was

performed. The calculated coupling constants, tabulated

in the Supporting Information, are similar to those

obtained for other complexes known to contain a η³,η²-

cyclooctadienyl ligand bound to ruthenium(II).³⁷An

asymmetric solution structure for exo-3 is also apparent

from the four silyl methyl and four methylene proton

environments of the [NPNH] ligand set. The amino

proton occurs at δ 6.35, shifted 0.28 ppm upfield from

the amino proton of endo-3.

Inspection of the ¹³C resonances for the cyclooctadi-

enyl carbon nuclei of the minor isomer shows that they

are only slightly shifted with respect to endo-3, sug-

gesting a very similar coordination mode adopted by this

1

Analysis of the variable-temperature H NMR data

ligand. Furthermore, two doublets at δ 110.0 (²J_PC

)

confirmed the existence of an equilibrium between the

species endo-3 and exo-3 in solution. Integration of the

amino proton resonance for each of the diastereomers

at various temperatures gave relative concentrations of

the two isomers and allowed for the evaluation of the

equilibrium constants according to K ) [endo-3]/[exo[3].

A van’t Hoff plot permitted the determination of the

following thermodynamic parameters for the equilibri-

um process: ∆H° ) 0.93 ( 0.10 kcal mol^-1and ∆S° )

1.62 ( 0.20 eu (see Supporting Information).

Figure 7 shows the N-H region of the two-dimensional

EXSY spectrum obtained at room temperature (500

MHz, t_mix) 400 ms) for the mixture of endo-3 and exo-3

in toluene-d₈. A positively phased cross-peak between

11.3 Hz) and 65.3 (²J_PC) 5.8 Hz) indicate that the

phosphine donor is located trans to the olefin moiety, a

feature that was also evident in the ¹³C{¹H} NMR

spectrum of endo-3. These data are consistent with exo-3

as the second species in solution.

The ¹H NMR data also support the formulation of the

second species in solution as diastereomer exo-3. Figure

6 shows a region of the 500 MHz ¹H{³¹P} NMR

spectrum highlighting the downfield-shifted cycloocta-

dienyl resonances for both diastereomers. In addition

to exhibiting a similar trend in the chemical shift of the

proton environments, both endo-3 and exo-3 display

similar coupling patterns, which is consistent with the

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5449

Scheme 2

may be the result of an electrostatic attraction between

these two nuclei. A hydrogen-bonding interaction was

evident in the solid-state structure of the complex [P₂-

NNH]Ru(C₆H₄PPh₂) (2), with a NH‚‚‚N distance of 2.404

Å.

The variable-temperature ¹H NMR data also permit-

ted a kinetic investigation into the mechanistic details

for the process that interconverts isomers endo-3 and

exo-3. Line-shape analysis of the N-H resonances al-

lowed for the rate constants to be determined at several

temperatures and used in an Eyring plot to calculate

the activation parameters of ∆H^q) 16 ( 1 kcal mol^-1

and ∆S^q) 4 ( 4 eu for this process (see Supporting

Information).

Support for the proposed six-coordinate transition

state shown in Scheme 2 comes from the structure of

the stable and isolable lithium-ruthenate complexes.

The addition of 1 equiv of LiN(SiMe₃)₂to an equilibrium

mixture of endo-3 and exo-3 in toluene generates a

hydrocarbon insoluble lithium-ruthenate complex, which

upon addition of THF, results in the formation of [Li-

(THF)]([NPN]Ru(η³: η²-C₈H₁₁)) (4), as shown in Scheme

3. The synthesis of the sodium-ruthenate complex is

analogous to that of 4 but employs NaN(SiMe₃)₂as the

base (see Supporting Information).

Figure 8 shows the solid-state molecular structure of

complex 4 as determined by a single-crystal X-ray

diffraction study. The solid-state structure of the sodium-

ruthenate complex can be found in the Supporting

Information. Selected bond lengths and angles for the

lithium-ruthenate are given in Table 4.

Figure 7. N-H region of the 2-D EXSY spectrum for the

mixture of endo-3 and exo-3. Obtained at 298 K in toluene-

d₈, 500 MHz, and a mixing time of 0.4 s.

sites in a 2D-EXSY spectrum indicates that these nuclei

are in chemical exchange, providing further evidence

for the dynamic equilibrium that exists in solution. No

cross-peaks were observed between the amino protons

and any of the cyclooctadienyl proton resonances,

indicating that the N-H proton does not get incorporated

into the cyclooctadienyl ligand. Cross-peaks were also

observed for resonances associated with the cycloocta-

dienyl ligand; however, due to the fact that these peaks

were broadened and overlapping at 298 K, they could

not be assigned to specific proton environments. The

[NPNH] silyl methyl and methylene resonances between

isomers also gave rise to positively phased cross-peaks

as would be expected.

The interconversion of the two diastereomers endo-3

and exo-3 requires inversion of chirality at the phos-

phorus atom. The mechanism proposed for this process

involves the direct transfer of the N-H proton from one

arm of the [NPNH] ligand to the other via the transition

state that is illustrated in Scheme 2. Shifting of the

phosphine ligand to the “bottom” of the metal and the

close approach of the amine sidearm to the ruthenium

center allows for the N-H proton to reside in a bridging

position between both nitrogen atoms. Transfer of this

proton from one arm to the other followed by dissocia-

tion of the resulting amine ligand and finally coordina-

tion of the phosphine back to the site trans to the olefin

donor acts to invert the chirality of the phosphorus

atom. A related transition state has been postulated for

aryloxide/phenol proton exchange in a pentamethylcy-

clopentadienyl nickel(II) system.⁴⁸

Inspection of the solid-state molecular structure of

complex 4 shows that the η³-allyl, η²-olefin coordination

mode of the cyclooctadienyl ligand has been maintained

and that the [NPN] ligand is bound to the ruthenium

in a facial manner. The amido donors bridge the lithium

and ruthenium centers, forming a “LiN₂Ru” core. Com-

plex 4 is six-coordinate at ruthenium and exhibits C₁

symmetry in the solid state. Deviations from ideal

octahedral coordination geometry arise due to con-

straints imposed by the chelating [NPN] ligand as well

as the cyclooctadienyl ligand. For example, the P(1)-

The solid-state molecular structure of complex endo-3

shows that the amino hydrogen atom is pointed toward

the amido nitrogen atom. Although the distance be-

tween the two nuclei (3.419 Å) is too long to be

considered a hydrogen bond, the observed orientation

(48) Holland, P. L.; Andersen, R. A.; Bergman, R. G.; Huang, J.;

Nolan, S. P. J. Am. Chem. Soc. 1997, 119, 12800.

5450 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

Scheme 3

Figure 8. ORTEP representation (50% thermal ellipsoid

probability) of the solid-state molecular structure of [Li-

(THF)]([NPN]Ru(η³: η²-C₈H₁₁)) (4) as determined by X-ray

diffraction. The [NPN] ligand silyl methyl groups have been

omitted for clarity and only the ipso carbon atoms of the

amido phenyl rings are shown.

Ru(1)-C(31) and N(2)-Ru(1)-C(31) bond angles (163.77-

(7)° and 110.04(8)°, respectively) show that the terminal

allyl carbon atom, C(31), is bent away from its ideal

apical position. In addition, atom C(31) is approximately

0.18 Å further displaced from the metal center than are

C(29) and C(30) of the allyl donor. An unsymmetrical

coordination mode for the cyclooctadienyl ligand in

related ruthenium(II) systems has previously been

reported.³⁷The bis-amide-bridged “LiN₂Ru” core is

asymmetric, containing one shorter (2.275(2) Å) and one

longer (2.364(2) Å) ruthenium to nitrogen distance; the

amido to lithium distances are equivalent within ex-

perimental error. The Ru-N bond lengths in 4 are

longer than that found in endo-3 (2.019(2) Å). Coordi-

native saturation at the ruthenium center does not allow

for π-donation from the amido lone pair of electrons, and

consequently both the amide donors exhibit a pseudo-

tetrahedral coordination geometry.⁴⁹The lithium atom

in complex 4 adopts a planar, three-coordinate geometry

with a molecule of THF completing its coordination

sphere.

The asymmetry of 4 evident in the solid state is

maintained in solution, which suggests a rigid solution

structure. To support this, the ¹³C{¹H} NMR spectrum

contains four resonances for the silyl methyl carbon

atoms and eight resonances for the inequivalent cy-

clooctadienyl carbon nuclei. Once again, the J-modu-

lated ¹³C{¹H} spectrum confirmed the η³:η²-coordination

mode of the cyclooctadienyl ligand, as in complex 3. The

greatest variation in peak positions occurs for the

ruthenium-bound carbon nuclei. The central allyl carbon

(C₆), for instance, is shifted downfield from ca. δ 71.0

in endo-3 and exo-3 to δ 100.5 in complex 4. The olefin

carbon atom, C₂, experiences an upfield shift of similar

magnitude from ca. δ 110.0 (in endo-3 and exo-3) to δ

67.8.

Table 4. Selected Bond Lengths and Angles in the Complexes [Li(THF)]([NPN]Ru(η³: η²-C₈H₁₁)) (4)

atom

distance (Å)

atom

distance (Å)

Ru(1)

N(1)

2.275(2)

2.364(2)

2.2944(6)

2.179(2)

2.176(2)

2.364(2)

2.180(2)

2.224(2)

2.004(5)

N(2)

O(1)

N(1)

N(2)

N(1)

N(2)

C(29)

C(30)

C(33)

Li(1)

C(7)

C(19)

Si(1)

Si(2)

C(30)

C(31)

C(34)

2.010(5)

1.956(5)

1.410(3)

1.414(3)

1.745(2)

1.729(2)

1.424(4)

1.396(4)

1.384(4)

N(2)

P(1)

C(29)

C(30)

C(31)

C(33)

C(34)

Li(1)

atom-atom-atom

angle (deg)

atom-atom-atom

angle (deg)

N(1)-Ru(1)-N(2)

N(1)-Ru(1)-P(1)

N(2)-Ru(1)-P(1)

N(1)-Ru(1)-C(29)

N(1)-Ru(1)-C(31)

N(1)-Ru(1)-C(33)

N(1)-Ru(1)-C(34)

N(2)-Ru(1)-C(29)

N(2)-Ru(1)-C(31)

N(2)-Ru(1)-C(33)

N(2)-Ru(1)-C(34)

P(1)-Ru(1)-C(29)

86.49(7)

87.12(5)

84.28(5)

97.13(9)

100.97(8)

156.22(8)

167.14(9)

175.46(9)

110.04(8)

83.52(8)

98.12(9)

98.60(7)

P(1)-Ru(1)-C(31)

P(1)-Ru(1)-C(33)

P(1)-Ru(1)-C(34)

163.77(7)

113.17(7)

81.44(8)

66.6(1)

62.87(9)

88.8(1)

92.1(1)

78.9(1)

104.8(2)

84.5(2)

82.0(2)

C(31)-Ru(1)-C(29)

C(31)-Ru(1)-C(33)

C(31)-Ru(1)-C(34)

C(29)-Ru(1)-C(33)

C(29)-Ru(1)-C(34)

N(1)-Li(1)-N(2)

Li(1)-N(1)-Ru(1)

Li(1)-N(2)-Ru(1)

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5451

1

The H NMR spectrum of 4 shows four silyl methyl

temperature (from 200 to 360 K) shows that the two

species are not in equilibrium since no change in product

ratios could be discerned. These results provide further

evidence for the mechanism depicted in Scheme 2 for

the interconversion of the diastereomers of species 3.

As was expected, the bulky trimethylsilyl group is not

exchanged between the two isomers, and consequently,

they remain independent of one another.

resonances, four ligand methylene resonances, 11 in-

equivalent cyclooctadienyl proton resonances, and three

sets of ortho, meta, and para phenyl proton resonances

for the [NPN] phenyl groups. This number of peaks is

consistent with a C₁symmetric structure in solution.

The changes in chemical shifts of the cyclooctadienyl

protons (as compared to endo-3 and exo-3) mirror those

of the carbon nuclei to which they are attached (see

Supporting Information).

The characterization of endo-5 and exo-5 was based

1

on solution NMR studies. The ¹³C{¹H} and H NMR

As shown in Scheme 3, the equilibrium mixture of

endo-3 and exo-3 can be regenerated by the stoichio-

metric addition of NEt₃‚HCl to the ruthenate complex

4. Utilizing the deuterium-labeled acid (NEt₃‚DCl) in

the above reaction allows for selective deuteration at

the amine nitrogen atom, which verified the assignment

data were diagnostic for these two isomers and showed

remarkable similarities to the corresponding low-tem-

perature spectra of the diastereomeric mixture of endo-3

and exo-3. The coupling of the ³¹P nucleus to the olefinic

carbon atoms indicates a trans disposition between the

phosphine and olefin donors in these complexes. In

endo-5, for example, C₁occurs as a doublet at δ 61.6

(²J_PC) 6.3 Hz), and likewise C₂appears as a doublet

at δ 107.6 (²J_PC) 10.6 Hz). Complex endo-3 shows very

similar resonances for these two nuclei, with nearly

identical coupling constants (6.5 and 10.5 Hz, respec-

tively). A similar trend is observed for exo-5 and exo-3.

The ¹³C chemical shifts of the remaining cyclooctadienyl

carbon nuclei are only slightly shifted, suggesting that

a very similar coordination mode is adopted by this

ligand for the related endo and exo isomers of complexes

3 and 5.

Both the endo and exo isomers of complex 5 have four

ligand silyl methyl proton resonances; the ligand meth-

ylene resonances for both isomers overlap with the

cyclooctadienyl resonances and occur between ca. δ 1.0

and 1.5. The terminal amino silyl methyl (N-SiMe₃)

signal for endo-5 occurs as a singlet at δ 0.15 and

integrates for nine protons. For the isomer exo-5 this

resonance appears as a singlet at δ 0.12. The remaining

phosphine, amine, and amido phenyl resonances occur

at expected positions between δ 6.8 and 7.7. The ³¹P-

{¹H} NMR spectrum contains two singlets at δ 32.9 and

32.3 for complexes endo-5 and exo-5, respectively.

1

of the N-H resonance in the H NMR spectrum of the

diastereomers endo-3 and exo-3.

In analogy with the above example, in which the basic

behavior of the lithium-ruthenate complex toward NEt₃‚

HCl regenerates the equilibrium mixture of endo-3 and

exo-3, the reaction of Me₃SiCl with 4 was examined.

Addition of an excess of chlorotrimethylsilane (Me₃SiCl)

to a solution of 4 in toluene results in a change in color

from orange to red over a period of 24 h. After workup,

the two diastereomers endo- and exo-[NPN(SiMe₃)]Ru-

(η³:η²-C₈H₁₁) (endo-5 and exo-5, respectively) could be

isolated as an extremely moisture-sensitive solid. The

two isomers are formed in approximately 50% yield

each; attempts to separate the two complexes via

crystallization proved impossible.

Summary and Conclusions

The synthesis of ruthenium(II) complexes that incor-

porate the mixed-donor macrocyclic [P₂N₂] and triden-

tate [NPN] ligand sets is described. The reaction of

[P₂N₂]Li₂(Diox) with [RuCl₂(cod)]_xgenerates the diami-

dodiphosphine complex [P₂N₂]Ru(η²:η²-C₈H₁₂) (1), which

at room temperature displays C_2vsymmetry in solution;

however, cooling the solution results in a C₂symmetric

complex consistent with the solid-state X-ray structure.

The reaction between the dilithium salt of the [P₂N₂]

ligand with RuCl₂(PPh₃)₃yields the species [P₂NNH]-

Ru(C₆H₄PPh₂) (2), in which ortho-metalation of the

triphenylphosphine ligand occurs. The solid-state mo-

lecular structure of 2 shows that there is an intra-

molecular hydrogen-bonding interaction involving the

amine proton and amide nitrogen atom of the [P₂NNH]

ligand. The position of amine proton in the coordination

sphere suggests that this product results from thermo-

dynamic rather than kinetic control.

1

Unlike the room-temperature H NMR spectrum for

endo-3 and exo-3, which is comprised of broadened

peaks, the H NMR spectrum (at 298 K) for complexes

endo-5 and exo-5 contains well-resolved resonances for

all proton environments, implying that the two species

do not exhibit any fluxionality. In fact, examination of

the ¹H and ³¹P{¹H} NMR spectra as a function of

1

The ligand [NPN]Li₂(THF)₂reacts with [RuCl₂(cod)]_x

to give an equilibrium mixture of endo-3 and exo-3. The

diastereomers of 3 are formed via deprotonation of the

cyclooctadiene moiety by the [NPN] ligand; transfer of

the resulting amino proton between the [NPNH] side-

(49) (a) Conner, D.; Jayaprakash, K. N.; Gunnoe, T. B.; Boyle Paul,

D. Inorg. Chem. 2002, 41, 3042. (b) Conner, D.; Jayaprakash, K. N.;

Wells, M. B.; Manzer, S.; Gunnoe, T. B.; Boyle, P. D. Inorg. Chem.

2003, 42, 4759.

5452 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

of [RuCl₂(cod)]_x(0.324 g, 1.16 mmol) in 10 mL of THF. The

mixture was stirred at room temperature for 3 h, yielding a

yellow-brown solution. The mixture was evaporated to dryness

in vacuo, and the resulting solid was extracted into 20 mL of

toluene and filtered through Celite. The solvent was removed

until a thick oily residue remained. Addition of hexanes (10

mL) caused a yellow solid to precipitate from the solution. The

solid was collected on a frit and washed with hexanes until

the dark impurities were removed. The remaining solid was

dried under vacuum to yield [P₂N₂]Ru(η²:η²-C₈H₁₂) (1) (0.628

g, ∼70%). X-ray quality crystals were obtained by the slow

evaporation of the hexanes rinsings and contained 1 equiv of

cocrystallized hexane. ¹H NMR (C₆D₆, 298 K, 500 MHz): δ 0.40

and 0.50 (s, SiCH₃, 24H total), 0.95 and 1.42 (m (br), P-CH₂,

8H total), 1.82 (m, cyclooctadiene -CH₂, 8H), 2.80 (s (br),

cyclooctadiene -CH, 4H), 7.12 (m, overlapping, PPh-para, 1H),

7.20 (m, PPh-meta, 4H), (m, PPh-ortho, 4H). ³¹P{¹H} NMR

(C₆D₆, 298 K, 202.5 MHz): δ 44.5 (s). ¹³C{¹H} NMR (C₆D₆, 298

K, 125.8 MHz): δ 7.0 and 9.0 (s, SiCH₃), 25.0 (s (br),

cyclooctadiene -CH₂), 28.0 (s (br), P-CH₂), 70.0 (s, cycloocta-

diene -CH), 127.5 (s, overlapping, PPh-para), 128.5 (s, PPh-

arms establishes the observed equilibrium. Deprotona-

tion of co-ligands would appear to be a common occur-

rence in ruthenium(II) systems containing the [NPN]

and [P₂N₂] ligand sets. Formation of the ruthenate

complex [Li(THF)]([NPN]Ru(η³: η²-C₈H₁₁)) (4) is ac-

complished by the addition of LiN(SiMe₃)₂to a mixture

of endo-3 and exo-3. The ruthenate species is nonflux-

ional in solution, as evidenced by the NMR data.

Complex 4 reacts with acidic compounds to regenerate

an equilibrium mixture of endo-3 and exo-3 or with

chlorotrimethylsilane to give the two independent,

nonfluxional diastereomers endo- and exo-[NPN(SiMe₃)]-

Ru(η³:η²-C₈H₁₁) (endo-5 and exo-5, respectively).

Experimental Section

General Procedures. Unless otherwise stated, all ma-

nipulations were performed under a dry, oxygen-free atmo-

sphere of dinitrogen or argon by means of standard Schlenk

or glovebox techniques (Vacuum Atmospheres HE-553-2 glove-

box equipped with a MO-40-2H purification system and a -40

°C freezer). Toluene and hexanes were purchased in anhydrous

form from Aldrich and deoxygenated by passage through a

tower containing Q-5 catalyst and further dried by passage

through a tower containing alumina under a positive pressure

of dinitrogen. Anhydrous THF was predried by refluxing over

CaH₂and then distilled under argon from sodium benzophe-

none ketyl. Anhydrous diethyl ether was stored over sieves

and distilled from sodium benzophenone ketyl under argon.

Deuterated benzene, tetrahydrofuran, pentane, and toluene

were dried by refluxing over sodium and potassium alloy in a

sealed vessel under partial pressure, then trap-to-trap distilled

and degassed by three freeze-pump-thaw cycles prior to use.

Nitrogen and argon were dried and deoxygenated by passage

through a column containing activated molecular sieves and

MnO. Unless otherwise stated, ¹H, ¹H{³¹P}, ²H, ³¹P{¹H},

¹³C{¹H}, ⁷Li{¹H}, and variable-temperature NMR spectra were

recorded on a Bruker AMX-500 instrument operating at 500.1

MHz for ¹H spectra, a Bruker AV-300 instrument (300.1 MHz),

or a Bruker AC-200 instrument (200.1 MHz). ¹H NMR spectra

were referenced to internal C₆D₅H (7.15 ppm) or C₇D₇H (2.09

ppm), ³¹P{¹H} NMR spectra to external P(OMe)₃(141.0 ppm

with respect to 85% H₃PO₄at 0.0 ppm), and ¹³C{¹H} NMR

spectra to ¹³CC₅D₆(128.4 ppm). All δ values are given in ppm

units. Infrared spectra were recorded on an ATI Matton

Genesis Series FTIR spectrometer as KBr pellets. Elemental

analyses were performed in the Department of Chemistry at

the University of British Columbia by Mr. P. Borda or Mr. M.

Lakha. Complexes for which elemental data are not reported

gave results outside of error limits. For this reason, these

derivatives were characterized by solution and X-ray data only.

(i) Materials. The compounds [NPN]Li₂(THF)₂,²²[P₂N₂]Li₂-

1

meta), 131.0 (s, PPh-ortho), 143.0 (s (br), PPh-ipso). H NMR

(C₆D₆, 198 K, 500 MHz): δ 0.30 to 0.60 (s, overlapping, SiCH₃,

24H total), 0.90 (s (br), P-CH₂, 2H), 1.30 (s (br), overlapping,

P-CH₂2H), 1.30 (s (br), overlapping, cyclooctadiene -CH₂, 2H),

1.90 (s, cyclooctadiene -CH₂, 2H), 2.09 (s, cyclooctadiene

-CH₂, 2H), 2.20 (s, cyclooctadiene -CH₂, 2H), 2.60 (s (br),

cyclooctadiene -CH, 2H), 3.00 (s (br), cyclooctadiene -CH,

2H), 6.80 to 7.15 (m, overlapping, PPh-meta and -para, 6H

total), 7.80 (s (br), PPh-ortho, 4H).

¹H NMR (C₇D₈, 212 K, 500 MHz): δ 2.60 and 3.0 (s (br),

cyclooctadiene -CH, 2H). Line shape analysis of the peaks at

different temperatures gave rate constants that when plotted

using the Arrhenius equation have E_a) 18.6 ( 1.6 kcal/mol

(see Supporting Information).

Despite many attempts, a satisfactory elemental analysis

could not be obtained for this material.

[P₂NNH]Ru(C₆H₄PPh₂) (2). Toluene (30 mL) was added

to a mixture of [P₂N₂]Li₂(Diox) (0.170 g, 0.268 mmol) and

RuCl₂(PPh₃)₃(0.256 g, 0.267 mmol). The initial slurry was

stirred for 3 h at room temperature, resulting in the formation

of an orange-brown solution, which was filtered to remove

insoluble LiCl. Anhydrous CuCl (0.054 g, 0.536 mmol) was

added to the solution, and the contents were stirred for 12 h.

The mixture was filtered, and the filtrate was evaporated until

approximately 2 mL of toluene remained. Addition of pentane

(10 mL) caused the deposition of [P₂NNH]Ru(PC₆H₄Ph₂) (2)

as an orange solid. The solid was collected by filtration, rinsed

with a minimum amount of pentane, and dried in vacuo to

yield 0.207 g of 2 (86%). Single crystals suitable for an X-ray

diffraction study were grown by the slow evaporation of the

pentane-soluble rinsings. There were two independent mol-

ecules in the asymmetric unit as well as a molecule of

1

cocrystallized pentane. H NMR (C₆D₆, 298 K, 500 MHz): δ

(Diox),²³[RuCl₂(cod)]_x,⁵⁰and RuCl₂(PPh₃)₃were prepared

51

0.39, 0.41, 0.58, and 0.60 (s, SiCH₃, 24H total), 1.40 (m,

overlapping, P-CH₂, 4H), 1.53 (m, overlapping, P-CH₂, 4H),

2.80 (s, N-H), 6.52-8.12 (m, P-Ph, [P₂NNH] and PC₆H₄Ph₂,

24 H total). ³¹P{¹H} NMR (C₆D₆, 298 K, 202.5 MHz): δ 25.8

(d, ²J_PP) 31 Hz, [P₂NNH], 2P), -11.8 (t, ²J_PP) 31 Hz, PC₆H₅-

Ph₂, 1P). Anal. Calcd for C₄₂H₅₇N₂P₃Si₄Ru: C, 56.28; H, 6.41;

N 3.13. Found: C, 56.11; H, 6.58; N, 3.29.

For complexes 3 through 5 the following labeling convention

is employed for assignment of the ¹H and ¹³C nuclei of the

cyclooctadienyl moiety:

according to reported literature procedures. NEt₃‚DCl was

prepared by the dropwise addition of aqueous deuterium

chloride to a solution of triethylamine in diethyl ether. The

solid was collected by filtration and dried under vacuum.

Triphenylphosphine, triisopropylphosphine, and tricyclohexyl-

phosphine (Strem Chemicals) and LiN(SiMe₃)₂, NaN(SiMe₃)₂,

NEt₃‚HCl, CuCl, and chlorotrimethylsilane (Aldrich) were used

without further purification. RuCl₃‚3H₂O was obtained on loan

from Johnson-Matthey, as well as purchased from Precious

Metals Online.

endo- and exo-[NPNH]Ru(η³:η²-C₈H₁₁) (endo-3 and exo-

3). Toluene (30 mL) was added to a mixture of [NPN]Li₂(THF)₂

(1.06 g, 1.78 mmol) and [RuCl₂(cod)]_x(0.50 g, 1.78 mmol), and

the mixture was stirred for 2 days at room temperature.

During this time the initial brown slurry turned red and a

colorless solid formed. The mixture was then filtered through

Celite and the solvent removed under reduced pressure,

[P₂N₂]Ru(η²:η²-C₈H₁₂) (1). A solution of [P₂N₂]Li₂(Diox)

(0.734 g, 1.16 mmol) in 10 mL of THF was added to a slurry

(50) Albers, M. O.; Ashworth, T. V.; Oosthuizen, E. Inorg. Synth.

1989, 26, 68.

(51) Hallman, P. S.; Stephenson, T. A.; Wilkinson, G. Inorg. Synth.

1970, 12, 237.

Ruthenium(II) Amidophosphine Complexes

Organometallics, Vol. 24, No. 22, 2005 5453

CH_hH_h′, 1H), 3.45 (m, overlapping, CH_f, 1H), 4.35 (m, CH_g,

1H), 6.58 (t, NPh-para, 1H), 6.78 (t, N′Ph-para, 1H), 7.70 (m,

NPh-meta, 2H), 7.20 (m, overlapping, NPh-ortho, 2H), 7.20 (m,

overlapping, PPh-para, 1H), 7.39 (m, N′Ph-meta, 2H), 8.05 (m,

AX, PPh-ortho, 2H), 8.30 (d, N′Ph-ortho, 2H). ³¹P{¹H} NMR

(C₆D₆, 298 K, 202.5 MHz): δ 46.8 (s). ¹³C{¹H} NMR (C₇D₈, 298

K, 125.8 MHz) selected data: δ 22.7 (s, C₈), 27.7 (s, C₄), 27.9

2

(s, C₃), 33.2 (d, C₁, ²J_PC) 6.4 Hz), 45.0 (d, C_7,J_PC) 19.2 Hz),

46.0 (d, C₅, ²J_PC) 2.1 Hz), 68.2 (d, C₂, ²J_PC) 5.8 Hz), 100.5 (s,

C₆).

The sodium congener is described in the Supporting Infor-

mation.

leaving an oily solid. A small amount of hexanes (ca. 5 mL)

was added to dissolve the solid, and the mixture was allowed

to stand in a closed vessel for 48 h, during which time complex

3 crystallizes from solution. The supernatant was decanted

and the red crystals were washed with hexanes. Yield: 0.90

g, 78%. A further crop of crystals was obtained by the slow

evaporation of the supernatant. Isomer endo-3: ¹H NMR

(C₇D₈, 245 K, 500 MHz): δ 0.08 (s, br, SiCH₃, 6H), 0.34 (s,

SiCH₃, 3H), 0.43 (s, SiCH₃, 3H), δ 0.76 (m, AA′BX, PCHH, 1H),

1.0 (m, AA′BX, PCH₂, 2H), 1.17 (m, AA′BX, PCHH, 1H), 1.50

(m, CH_dH_d′, 1H), 1.58 (m, CH_cH_c′, 1H), 1.64 (m, CH_f, 1H), 2.00

(m, CHH_h′, 1H), 2.18 (m, CH_dH_d′, 1H), 2.36 (m, CH_cH_c′, 1H),

2.70 (m, CH_hH_h′, 1H), 2.85 (m, CH_g, 1H), 4.20 (m, CH_e, 1H),

4.23 (m, CH_a, 1H), 4.25 (m, CH_b, 1H), 6.63 (s, NH, 1H), 6.82-

7.42 (m, overlapping, NPh, NHPh, and PPh,). ³¹P{¹H} NMR

(C₇D₈, 245 K, 202.5 MHz): δ 33.4 (s). ¹³C{¹H} NMR (C₇D₈, 245

K, 125.8 MHz) selected peaks: δ 25.2 (s, C₈), 30.3 (s, C₃), 32.8

Reaction of Complex 4 with NEt₃‚HCl. Addition of NEt₃‚

HCl (0.015 g, 0.109 mmol) to a solution of 4 (0.078 g, 0.108

mol) in toluene (10 mL) resulted in a change in color from

orange to red within 2 h. The mixture was filtered to remove

insoluble LiCl, and the volatile components were removed

1

under vacuum, giving a red solid. The H and ³¹P{¹H} NMR

spectra of the red solid indicate that it is a mixture of the two

diastereomers endo-3 and exo-3.

Reaction of Complex 4 with NEt₃‚DCl. A procedure

similar to that described above for the reaction with NEt₃‚

HCl was followed: NEt₃‚DCl (0.017 g, 0.123 mmol), 4 (0.086

g, 0.119 mmol), and toluene (10 mL). The ¹H and ³¹P{¹H} NMR

spectra indicate the formation of an equilibrium mixture of

endo-3-d₁and exo-3-d₁in which deuteration at the amino site

occurs.

2

(s, C₄), 35.6 (s, C₇), 61.4 (d, C₁, J_PC) 6.5 Hz), 61.6 (s, C₅),

2

71.6 (s, C₆), 108.1 (d, C₂, J_PC) 10.5 Hz). Isomer exo-3: ¹H

NMR (C₇D₈, 245 K, 500 MHz): δ 0.09 (s, overlapping, SiCH₃,

3H), 0.28 (s, SiCH₃, 3H), 0.32 (s, overlapping, SiCH₃, 6H), 0.85

(m, overlapping, AA′BX, PCH₂, 2H), 1.0 (m, overlapping,

AA′BX, PCH₂, 2H), 1.30 (m, CH_cH_c′, 1H), 1.50 (m, overlapping,

CH_f, 1H), 1.75 (m, CH_dH_d′, 1H), 1.83 (m, CH_cH_c′, 1H), 2.15 (m,

overlapping, CH_hH_h′, 1H), 2.20 (m, CH_dH_d′, 1H), 3.09 (m,

CH_hH_h′, 1H), 3.37 (m, CH_g, 1H), 3.50 (m, CH_e, 1H), 3.92 (m,

CH_b, 1H), 4.68 (m, CH_a, 1H), 6.35 (s, NH, 1H), 6.82-7.42 (m,

endo- and exo-[NPN(SiMe₃)]Ru(η³:η²-C₈H₁₁) (endo-5

and exo-5). A 10-fold excess of chlorotrimethylsilane (0.292

g, 2.69 mmol) was added to an orange solution of 4 (0.194 g,

0.269 mmol) in toluene (30 mL). Over the period of 48 h the

solution turns red with the formation of a white solid (LiCl).

The solvent and other volatiles were removed in vacuo.

Toluene was added to the remaining solid, and the mixture

was filtered to remove insoluble byproducts. The soluble

fraction was dried under vacuum to give a mixture of endo-5

and exo-5 as a red solid material (0.17 g, 88%). Attempts to

separate the two isomers by fractional crystallization proved

unsuccessful. This material was characterized spectroscopi-

cally. Isomer endo-5: ¹H NMR (C₆D₆, 298 K, 500 MHz): δ 0.12

(s, overlapping, SiCH₃, 3H), 0.15 (s, overlapping, terminal

N-SiCH₃), 0.18 (s, overlapping, SiCH₃), 0.33 (s, SiCH₃, 3H),

0.46 (s, SiCH₃, 3H), 1.00 to 1.50 (m, overlapping, P-CH₂), 1.47

(m, CH_cH_c′, 1H), 1.52 (m, CH_f, 1H), 1.85 (m, CH_dH_d′, 1H), 2.05

(m, CHH_h′, 1H), 2.10 (m, CH_cH_c′, 1H), 2.25 (m, CH_dH_d′, 1H),

2.77 (m, CH_hH_h′, 1H), 2.90 (m, CH_g, 1H), 4.00 (m, CH_b, 1H),

4.16 (m, CH_e, 1H), 4.25 (m, CH_a, 1H), 6.80-7.45 (m, overlap-

ping, NPh, NHPh, and PPh). ³¹P{¹H} NMR (C₇D₈, 298 K, 202.5

MHz): δ 32.9 (s). ¹³C{¹H} NMR (C₇D₈, 298 K, 125.8 MHz)

selected peaks: δ 25.5 (s, C₈), 28.5 (s, C₃), 35.0 (s, C₄), 35.6 (s,

C₇), 61.6 (d, C₁, ²J_PC) 6.3 Hz), 61.8 (s, C₅), 70.1 (s, C₆), 107.6

3

overlapping, NPh, NHPh, and PPh). J_ab) 7.80 Hz, J_ah

)

3

2

7.70 Hz, J_ah′ ) 7.30 Hz, J_bc) 6.20 Hz, J_bc′ ) 6.10 Hz, J_cc′

3

) 14.60 Hz, J_cd) 7.60 Hz, J_cd′ ) 6.00 Hz, J_c′_d) 7.20 Hz,

³J_c′_d′ ) 8.60 Hz, J_dd′ ) 17.0 Hz, J_de) 5.60 Hz, J_d′_e) 5.80

Hz, ³J_ef) 8.00 Hz, ³J_fg) 9.90 Hz, ³J_gh) 7.90 Hz, ³J_gh′ ) 4.20

Hz, ²J_hh′ ) 19.30 Hz. ³¹P{¹H} NMR (C₇D₈, 245 K, 202.5 MHz):

δ 32.9 (s). ¹³C{¹H} NMR (C₇D₈, 245 K, 125.8 MHz) selected

peaks: δ 26.6 (s, C₈,), 27.0 (s, C₃), 36.3 (s, C₄), 36.5 (s, C₇),

2

3

2

64.9 (s, C₅), 65.3 (d, C₁, J_PC) 5.8 Hz), 70.8 (s, C₆), 110.0 (d,

C₂, J_PC) 11.3 Hz). IR (KBr): ν(NH) at 2945 and 2906 cm^-1

.

2

Anal. Calcd for C₃₂H₄₃N₂PRuSi₂: C, 59.69; H, 6.73; N, 4.35.

Found: C, 59.68; H, 7.09; N, 4.35.

[Li(THF)]([NPN]Ru(η³:η²-C₈H₁₁)) (4). A solution of LiN-

(SiMe₃)₂(0.064 g, 0.384 mmol) in toluene (10 mL) was added

dropwise to a toluene solution of 3 (0.247 g, 0.384 mmol) (20

mL), and the mixture was stirred at room temperature for 3

h, during which time an orange solid precipitated from the

solution. The solvent was removed under reduced pressure

until half volume, and hexanes (20 mL) was added to ensure

complete precipitation. The orange solid is insoluble in aro-

matic solvents. THF was added to a mixture of the orange solid

in toluene until it completely dissolved. Removal of the

volatiles in vacuo and addition of hexanes caused the deposi-

tion of 3 as an orange microcrystalline solid. The solid was

filtered, washed with hexanes, and dried under vacuum.

Yield: 0.255 g, 92%. X-ray quality crystals were grown by the

slow evaporation of a saturated toluene solution. ¹H NMR

(C₆D₆, 298 K, 500 MHz): δ 0.10, 0.20, 0.35, and 0.50 (s, SiCH_3,

12 total), 1.00 (m, AA′BX, PCHH, 1H), 1.07 (m, CH_cH_c′, 1H),

1.14 (m, overlapping, OCH₂CH₂, 2H), 1.18 (m, overlapping,

CH_cH_c′, 1H), 1.33 (m, CH_dH_d′, 1H), 1.44 (m, AA′BX, PCHH,

1H), 1.65 (m, AA′BX, PCHH, 1H), 1.73 (m, overlapping, AA′BX,

PCHH, 1H), 1.76 (m, CH_dH_d′, 1H), 2.17 (m, CH_a, 1H), 2.29 (m,

CH_b, 1H), 2.50 (m, CHH_h′, 1H), 3.06 (m, overlapping, OCH₂-

CH₂, 2H), 3.10 (m, overlapping, CH_e, 1H), 3.45 (m, overlapping,

2

(d, C₂, J_PC) 10.6 Hz). Isomer exo-5: ¹H NMR (C₇D₈, 298 K,

500 MHz): δ 0.12 (s, overlapping, terminal N-SiCH₃), 0.13 (s,

overlapping, SiCH₃, 3H), 0.16 (s, overlapping, SiCH₃), 0.57 (s,

SiCH₃, 3H), 0.60 (s, SiCH₃, 3H), 1.00 to 1.50 (m, overlapping,

P-CH₂), 1.43 (m, overlapping, CH_f, 1H), 1.45 (m, CH_cH_c′, 1H),

1.75 (m, CH_dH_d′, 1H), 2.08 (m, CH_cH_c′, 1H), 2.12 (m, CH_dH_d′,

1H), 2.20 (m, overlapping, CH_hH_h′, 1H), 2.95 (m, CH_hH_h′, 1H),

3.27 (m, CH_g, 1H), 3.60 (m, CH_e, 1H), 3.87 (m, CH_b, 1H), 4.50

(m, CH_a, 1H), 6.80-7.45 (m, overlapping, NPh, NHPh, and

PPh). ³¹P{¹H} NMR (C₇D₈, 298 K, 202.5 MHz): δ 32.3 (s). ¹³C-

{¹H} NMR (C₇D₈, 298 K, 125.8 MHz) selected peaks: δ 26.5

(s, C₈), 26.9 (s, C₃), 36.2 (s, C₇), 36.9 (s, C₄), 62.9 (d, C₁, ²J_PC

)

5.9 Hz), 63.7 (s, C₅), 69.9 (s, C₆), 108.1 (d, C₂, ²J_PC) 11.6 Hz).

Acknowledgment. Funding for this research was

provided by NSERC of Canada (Discovery Grant to

M.D.F.).

5454 Organometallics, Vol. 24, No. 22, 2005

Fryzuk et al.

Supporting Information Available: Crystallographic

data in CIF format for all complexes. Additional NMR data

for complexes (VT and simulation data); calculated rate

constants, equilibrium constants for selected complexes; full

experimental details for the synthesis of [Na(THF)]-

([NPN]Ru(η³:η²-C₈H₁₁)) including X-ray data and the ORTEP

diagram; experimental details for X-ray data collection and

refinement for all of the complexes. This material is available

free of charge via the Internet at http://pubs.acs.org.

OM050574I

Article Doi

Intramolecular C-H and N-H transfer by ruthenium(II) amidophosphine complexes

DOI: 10.1021/om050574i

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Article abstract of DOI:10.1021/om050574i

Full text of DOI:10.1021/om050574i

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