Rearrangements of phosphinoimines to phosphine-imines in ruthenium chelate complexes

Article abstract of DOI:10.1039/c2dt30505d

Thermal reaction of 1:1 mixtures of the RuCl₂(PPh ₃)₃ and phosphinoimine R₂PNCPh₂ (R = Ph, iPr, Me) at 140 °C results in isolation of the dimeric species [RuCl(μ-Cl)(PPh₃)(C₆H₄(PPh ₂)C(Ph)NH)]₂ (R = Ph 1, iPr 2, Me 3) containing phosphine-imine chelating ligands. Subsequent reaction of 1 and 3 with one equivalent of pyridine at room temperature give RuCl₂(PPh ₃)(py)(C₆H₄(PR₂)C(Ph)NH) (R = Ph 4, Me 5). Excess pyridine reacts with 2 to give a mixture of the cis and trans-isomers of RuCl₂(py)₂(C₆H ₄(PiPr₂)C(Ph)NH) 6 and 7 respectively. Treatment of 5 with excess PPh₃ affords RuCl₂(PPh₃) ₂(C₆H₄(PMe₂)C(Ph)NH) 8. Aspects of the mechanism of the thermal rearrangements of the phosphinoimine to the phosphine-imine ligands are considered and the isolation of RuCl ₂(Ph₂PNCPh₂)(SIMes)(CHPh) 9 and RuCl ₂(PPh₃)₂(HNC(Ph)C₆H₄) 10 provide support for a proposed mechanism involving a intermediate containing a Ru-bound metallated aryl-imine fragment.

Full text of DOI:10.1039/c2dt30505d

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PAPER
Rearrangements of phosphinoimines to phosphine–imines in ruthenium
chelate complexes†
Christopher C. Brown and Douglas W. Stephan*
Received 2nd March 2012, Accepted 12th June 2012
DOI: 10.1039/c2dt30505d
Thermal reaction of 1 : 1 mixtures of the RuCl2(PPh3)3 and phosphinoimine R2PNvCPh2 (R = Ph, iPr,
Me) at 140 °C results in isolation of the dimeric species [RuCl(μ-Cl)(PPh3)(C6H4(PPh2)C(Ph)NH)]2
(R = Ph 1, iPr 2, Me 3) containing phosphine–imine chelating ligands. Subsequent reaction of 1 and 3
with one equivalent of pyridine at room temperature give RuCl2(PPh3)(py)(C6H4(PR2)C(Ph)NH)
(R = Ph 4, Me 5). Excess pyridine reacts with 2 to give a mixture of the cis and trans-isomers of
RuCl2(py)2(C6H4(PiPr2)C(Ph)NH) 6 and 7 respectively. Treatment of 5 with excess PPh3 affords
RuCl2(PPh3)2(C6H4(PMe2)C(Ph)NH) 8. Aspects of the mechanism of the thermal rearrangements of the
phosphinoimine to the phosphine–imine ligands are considered and the isolation of RuCl2(Ph2PNvCPh2)-
(SIMes)(CHPh) 9 and RuCl2(PPh3)2(HNvC(Ph)C6H4) 10 provide support for a proposed mechanism
involving a intermediate containing a Ru-bound metallated aryl-imine fragment.
Introduction
A variety of ligands containing P–N bonds have found wide
spread use in coordination chemistry and catalysis. For example,
high oxidation state P(V)–N bonded ligands such as phosphini-
mines (R3PNR′), and phosphinimides (R3PN−) (Scheme 1) have
been used to prepare a large range of main group and transition
metal-based derivatives as well as in early transition metal based
catalysts for olefin polymerization.1–4 P(III)–N aminophosphine
ligands of the form (R2N)3P, 5,6 (R′2NPR2)7–10 and (R′2N)2PR11
(Scheme 1) are readily prepared and have been employed in
coordination chemistry and a variety of metal mediated trans-
formations. While these ligands are most commonly monoden-
Scheme 1 Various Binding modes of P–N Ligands.
tate via P-metal binding, ligands of the form (R′HNPR2) have
also been shown to be readily deprotonated forming PNM three
membered rings.
Related bidentate ligands that combine phosphine and imine
donors have also been studied. In 1978 Rauchfuss14 reported an
Another class of P–N ligands are based on the direct link of
early synthesis of such a chelate ligand although it was not until
phosphine and imine fragments. Such phosphinoimines
(R2PNvCR′2) ligands have received lesser attention,12 although
the 1990’s that this class of ligands found important applications
in late transition metal polymerization catalysts.15–41 Typical
Igau and co-workers13 have recently reported interesting Ru-
syntheses of bidentate phosphine–imine ligands involve the for-
complexes in which the ligands Ph2PNvCPhR (R = H, Ph)
mation of the phosphine donor with a pendant aldehyde func-
(Scheme 1) bind only via P. Interestingly ligands R2PNvCPh-
tionality. This is followed by a condensation with an amine. In
(NiPr2) (R = Ph, iPr) are shown to bind either in a monodentate
this paper, we report a unusual preparation of Ru–phosphine–
fashion through P or in a tethered fashion involving binding
imine complexes via the thermal rearrangement of phosphino-
through P and via π-arene interaction involving the imino-phenyl
imine precursors. The nature of the resulting complexes is
ring (Scheme 1).
reported and the mechanism of the rearrangement is considered.
Department of Chemistry, University of Toronto, 80 St George St,
Toronto, Ontario M5S3H6, Canada. E-mail: dstephan@chem.utoronto.ca;
Experimental section
Tel: +01-416-946-3294
†Electronic supplementary information (ESI) available: NMR data and
General data
CIF for all structural studies have been deposited. CCDC
869893–869900. For ESI and crystallographic data in CIF or other elec-
tronic format see DOI: 10.1039/c2dt30505d
All preparations were done under an atmosphere of dry, O2-free
N2 employing both Schlenk line techniques and a MBraun inert
This journal is © The Royal Society of Chemistry 2012
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atmosphere glove box. Solvents (pentane, toluene and CH2Cl2)
were purified employing a Grubbs’ type column systems manu-
factured by Innovative Technology. Pentane and toluene were
stored over potassium while the remaining solvents were stored
over molecular sieves (4 Å). Molecular sieves (4 Å) were pur-
chased from Aldrich Chemical Company and dried at 140 °C
under vacuum for 24 h prior to use. CD2Cl2 was dried over
CaH2, vacuum-transferred into a storage flask with a Teflon stop-
collected by filtration and dried in vacuo. X-ray quality crystals
were grown from the slow evaporation of a pyridine solution.
1
4: Yield: 93%. H NMR (CD2Cl2): 9.93 (br), 9.65 (br, NH),
8.50–8.86 (br), 7.01–7.70 (m); 31P{1H} NMR (CD2Cl2): 44.5
2
2
(d, JP–P = 33 Hz), 43.3 (d, JP–P = 33 Hz); 13C{1H} NMR
(CD2Cl2):149.7, 138.4, 136.6, 135.7, 134.6, 134.0, 130.8, 130.3,
129.3, 128.7, 127.6, 127.4, 127.1, 123.7; EA: Calc. for
C53H45N2P2Cl2Ru: C, 65.60; H, 4.59; N,3.19; found: C, 60.26;
H, 4.81; N,3.29.
1
cock, and degassed accordingly. H, 13C, and 31P NMR spectra
1
were recorded on a Varian NMR System 400 MHz or a Bruker
5: Yield: 89%. H NMR (CD2Cl2): 9.51 (br, 1H, NH), 9.05,
1
2
Avance III 400 MHz spectrometer at 298 K. H and 13C NMR
8.86, 8.63, 8.09, 6.88–7.52, 1.97 (d, JH–H = 8.8 Hz, 3H, CH3),
2
spectra were referenced to SiMe4 using the residual solvent peak
impurity of the given solvent. 31P NMR spectra are referenced to
85% H3PO4. Chemical shifts are reported in ppm and coupling
constants in Hz as absolute values. Combustion analyses were
performed in house employing a Perkin Elmer CHN Analyzer.
On occasion repeated attempts to obtain satisfactory EA for Ru
complexes resulted in good N and H analyses but consistently
low C analysis. This was attributed to formation metal-carbides
during combustion. In these cases, NMR data for the pure
samples have been deposited in the SI. All common organic
reagents were purified by conventional methods unless otherwise
noted. The compounds R2PNvCPh2 (R = Ph, iPr, Me) were pre-
pared by literature methods.42,43 All other reagents were purchased
from Aldrich and were used as received. RuCl2(py)(SIMes)-
(CHPh) was purchased from the Aldrich Chemical Co. and
RuCl2(PPh3)3 was prepared according to a literature procedure.44
0.78(d, JH–H = 9.5 Hz, 3H, CH3); 31P{1H} NMR (CD2Cl2):
2
2
48.6 (d, JP–P = 34 Hz,), 31.2(d, JP–P = 34 Hz); 13C{1H} NMR
(CD2Cl2): 175.40, 175.3, 153.8, 150.2, 140.2, 137.2, 136.8,
136.6, 136.5, 136.1, 134.4, 134.3, 133.4, 133.3, 132.5, 132.1
131.4 131.3 130.4 129.5, 129.5, 129.0, 128.0, 126.8, 126.0,
125.9, 124.0, 123.6, 123.6, 18.3 (d), 9.79 (d). EA: Calc. for
C33H36N2P2Cl2Ru: C, 60.48; H, 4.81; N, 3.71; found: C, 57.60;
H, 4.56; N,3.87.
Synthesis of cis-RuCl2(py)2(C6H4(PiPr2)C(Ph)NH) 6 and
trans-RuCl2(py)2(C6H4(PiPr2)C(Ph)NH) 7
To a suspension of the dimer 2 in CH2Cl2 (2.5 mL) was added
(2.5 mL) pyridine. The solution was stirred at room temperature
for 2 h and subsequently filtered through Celite. Pentane
(15 mL) was added to precipitate the product which was collect
by filtration and dried in vacuo. Yield of 6 and 7: 92%. Ratio
6 : 7 = 73 : 27. 6: 1H NMR (CD2Cl2): 12.33 (br, 1H, NH),
2
7.44–7.74 (8) 2.62–2.76 (m, 2H, CH(CH3)2), 0.97 (dd, JP–H
=
Synthesis of [RuCl(μ-Cl)(PPh3)(C6H4(PR2)C(Ph)NH)]2
(R = Ph 1, iPr 2, Me 3)
2
2
13.6, JH–H = 7.2 Hz, 6H, CH(CH3)2), 0.85 (dd, JP–H = 14.4,
2JH–H = 7.2 Hz, 6H, CH(CH3)2); 31P{1H} NMR (CD2Cl2): 59.6;
13C{1H} NMR (CD2Cl2): 141.5, 134.0, 133.9, 131.0, 130.9,
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. Following combination of 5 mL
bromobenzene solutions of RuCl2(PPh3)3 (480 mg, 0.50 mmol)
and Ph2PNvCPh2 (183 mg, 0.50 mmol), the mixture was
heated overnight at 140 °C in a Schleck bomb sealed with a
teflon tap. The initial brown colour changed to red and afforded
a red precipitate. The hot solution was filtered and the precipitate
washed with bromobenzene (3 × 10 mL) and pentane (3 ×
10 mL). This product was very poorly soluble, precluding
characterization by NMR spectroscopy. However X-ray quality
crystals of 1 (and 3) were grown from the slow cooling of a satu-
rated bromobenzene solution at 140 °C.
1: Yield: 69%. EA: Calc. for C48H40NP2Cl2Ru: C, 61.52; H,
4.21; N, 1.46. Found: C, 61.60; H, 4.30; N, 1.48. 2: Yield: 48%.
EA: Calc. for C34H32NP2Cl2Ru: C, 60.67; H, 4.79; N, 2.08.
Found: C, 59.30; H, 5.10; N, 2.09. 3: Yield: 85%. EA: Calc. for
C28H31NP2Cl2Ru: C, 58.67; H, 4.63; N, 2.07. Found: C, 58.13;
H, 5.13; N, 2.32.
1
129.9, 129.7, 129.1, 126.7, 26.2, 26.0, 16.8, 16.5. 7: H NMR
(CD2Cl2): 11.04 (br, 1H, NH), 7.44–7.74 (8) 2.78–2.89 (m, 2H,
CH(CH3)2), 1.00–1.10 (m, 12H, CH(CH3)2); 31P{1H} NMR
(CD2Cl2): 57.5. EA (for 6/7): Calc. for C29H34N3Cl2Ru·1/
2CH2Cl2 from crystallization: C, 52.88; H, 5.27; N, 6.27. Found:
C, 52.51; H, 5.30; N, 6.59.
Synthesis of RuCl2(PPh3)2(C6H4(PMe2)C(Ph)NH) 8
To a toluene (10 mL) solution of 5 (47 mg, 0.05 mmol), was
added PPh3 (12 mg, 0.07 mmol). The solution was stirred over-
night. The solution was dried in vacuo, washed with 5 mL of
diethyl ether. Yield: 85%. 1H NMR (CD2Cl2): 7.67–7.77(m,
2
39H), 6.10 (br, 1H), 1.02 (d, JH–H = 8.8 Hz, 6H); 31P{1H}
2
2
NMR (CD2Cl2): 27.5 (t, JP–P = 27.5 Hz, 1P), 24.5 (d, JP–P
=
27.5 Hz, 2P); 13C{1H} NMR (CD2Cl2): 137.4, 137.3, 134.5,
134.4, 134.1, 133.8, 133.6, 129.5, 129, 128.7, 128.6, 128.5,
128.3, 127.9, 127.0, 126.9, 126.8, 126.3, 18.8, 8.3; EA: Calc.
for C51H46NP3Cl2Ru: C, 62.53; H, 4.70; N,1.28. Found:
C, 62.86; H, 5.35; N, 1.06. X-ray quality crystals were grown
from cooling a saturated bromobenzene solution.
Synthesis of RuCl2(PPh3)(py)(C6H4(PR2)C(Ph)NH)
(R = Ph 4, Me 5)
These compounds were prepared in a similar fashion and thus
only one preparation is detailed. To a suspension of 1 in CH2Cl2
(2.5 mL) was added (2.5 mL) pyridine. The solution was stirred
at room temperature for 2 h and filtered through Celite. Pentane
(15 mL) was added to precipitate the product which was
Synthesis of RuCl2(SIMes)(CHPh)(iPr2PNvCPh2) 9
A CH2Cl2 solution (5 mL) of 2 (30 mg, 1 mmol, 1 eq) was
added to a CH2Cl2 solution (5 mL) of RuCl2(py)(SIMes)(CHPh)
9432 | Dalton Trans., 2012, 41, 9431–9438
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(73 mg, 1 mmol, 1 eq). The reaction was stirred for 2 h while the
brown reaction mixture changed to deep green. Pentane (10 mL)
was added and the reaction mixture was cooled to −35 °C. Over-
night green crystals were formed. (Yield: 70 mg, 0.86 mmol,
86%). 1H NMR (CD2Cl2): 19.13(s, 1H, RuvCH), 7.76–7.94(br,
2H, Ph), 7.16–7.40(11H, m, Ph), 6.87–6.94(m, 4H, Ph),
6.22–6.49(br, 2H, Ph), 4.03(t, 2H, J = 9.9Hz, CH2), 3.87(t, 2H,
J = 9.9Hz, CH2), 2.62(s, 6H, CH3), 2.23(s, 9H, CH3), 2.02(s,
3H, CH3), 0.54–0.62(m, 6H, CH(CH3)2), 0.30–0.50(br, 6H, CH
(CH3)2) 31P{1H} NMR (CD2Cl2) 89.8 13C{1H} NMR (CD2Cl2):
301.7–302.3(m, Ruv(CH), 220.8, 219.9, 171.1, 170.9, 151.3,
140.5, 140.4, 139.4, 138.9, 138.0, 137.5, 137.2, 135.2, 132.0,
129.7, 129.7, 128.9, 128.0, 127.8, 52.2, 51.9, 26.7, 21.1, 21.09,
20.2, 18.9, 18.6, 18.2; EA: Calc. for C51H46NP3Cl2Ru:
C, 62.53; H, 4.70; N,1.28. Found: C, 62.86; H, 5.35; N, 1.06.
X-ray quality crystals were grown from cooling a saturated
bromobenzene solution.
fixed at 1.20 times the isotropic temperature factor of the C-atom
to which they are bonded. The H-atom contributions were calcu-
lated, but not refined. The locations of the largest peaks in the
final difference Fourier map calculation as well as the magnitude
of the residual electron densities in each case were of no chemi-
cal significance.
Results and discussion
Heating a 1 : 1 mixture of the RuCl2(PPh3)3 and R2PNvCPh2
(R = Ph, iPr, Me) overnight at 140 °C results in isolation of red
precipitates that were very poorly soluble. The products were
washed with dichloromethane and pentane to give products
which were insoluble and thus could not be characterized by
NMR spectroscopy. Elemental analysis of each of these products
were consistent with the empirical formulation as RuCl(μ-Cl)-
(PPh3)(C6H4(PR2)C(Ph)NH) (R = Ph 1, iPr 2, Me 3). X-ray
quality crystals of 1 were obtained by slow cooling of the reac-
tion mixture from 140 °C. The crystallographic study of 1
confirmed the dimeric nature, i.e. [RuCl(μ-Cl)(PPh3)-
(C6H4(PPh2) C(Ph)NH)]2 (Scheme 2, Fig. 1). The crystal struc-
tures of 1 reveal that this species is a symmetric dimer with the
two Ru centres bridged by two chloride atoms (Table 1).
Synthesis of RuCl2(PPh3)2(HNv(C(Ph)C6H4) 10
To a 1,2-dichloroethane (20 mL) solution of RuH(PPh3)3Cl
(290 mg, 0.30 mmol) was added benzophenone imine (60 mg,
0.33 mmol). The solution was heated overnight in a Schlenk
flask at 70 °C, The solution was removed in vacuo, washed with
The bridging Ru–Cl distances are 2.4761(10)
Å and
2.4720(10) Å with a Cl–Ru–Cl angle of 91.03(4)°. The terminal
Ru–Cl distance was found to be 2.4409(11) Å. Trans to the brid-
ging Cl atoms are the P atoms of the phosphine–imine ligand
and Ph3P. The Ru–P distances were determined to be 2.2489(11)
Å and 2.3078(12) Å, respectively. Perpendicular to the bridging
Ru2Cl2 plane is the N of the imine-phosphine ligand and an
additional chloride. The Ru–N distance was found to be 2.013(4)
Å. The bite angle for the phosphine–imine chelate is 86.49(10)°.
X-ray characterization of 3 revealed a structure similar to 1
(Fig. 2). While the metric parameters were similar to those in 1,
the Ru–P distances in the phosphine–imine chelate were found
to be 2.2192(4) Å, reflecting the stronger donor character of the
PMe2 fragment in comparison to the PPh2 unit in 1. This feature
50 mL of diethyl ether and 50 mL of pentane. Yield: 71%, μeff
=
1.20 BM, X-ray quality crystals were grown from a layered solu-
tion of dichloromethane and cyclohexane. EA: Calc. for
C49H40NP2Cl2Ru: C, 67.12; H, 4.60; N, 1.60. Found: C, 67.03;
H, 5.03; N, 1.77.
X-ray crystallography
Crystals were coated in Paratone-N oil in the glove-box,
mounted on a MiTegen Micromount and placed under an N2
stream, thus maintaining a dry, O2-free environment for each
crystal. The data were collected on a Bruker Apex II diffracto-
meter employing Mo Kα radiation (λ = 0.71073 Å). Data collec-
tion strategies were determined using Bruker Apex software and
optimized to provide >99.5% complete data to a 2θ value of at
least 55°. The data were collected at 150( 2) K for all crystals.
The frames were integrated with the Bruker SAINT software
package using a narrow-frame algorithm. Data were corrected for
absorption effects using the empirical multi-scan method
(SADABS). Non-hydrogen atomic scattering factors were taken
from the literature tabulations.45 The heavy atom positions were
determined using direct methods employing the SHELXTL
direct methods routine. The remaining non-hydrogen atoms were
located from successive difference Fourier map calculations. The
refinements were carried out by using full-matrix least squares
techniques on F, minimizing the function ω (Fo − Fc)2 where the
2
2
weight ω is defined as 4Fo /2σ (Fo ) and Fo and Fc are the
observed and calculated structure factor amplitudes, respectively.
In the final cycles of each refinement, all non-hydrogen atoms
were assigned anisotropic temperature factors in the absence of
disorder or insufficient data. In the latter cases atoms were
treated isotropically. C–H atom positions were calculated and
allowed to ride on the carbon to which they are bonded assuming
a C–H bond length of 0.95 Å. H-atom temperature factors were
Scheme 2 Synthesis of 1–8.
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confirmed the geometries of these pseudo-octahedral complexes.
In the case of 6 (Fig. 4(a)), the trans-Ru–Cl distances were
found to range from 2.414(2) Å to 2.436(2) Å in the two mol-
ecules in the asymmetric unit. The cis pyridine ligands result in
Ru–N distances average 2.165(5) Å. The Ru–N and Ru–P dis-
tances for the imino-phosphine chelate average 1.990(5) Å and
2.267(2) Å, while the N–Ru–P angle was found to be 86.1(2)°.
In the other isomer 7 (Fig. 3(b)), the cis-Ru–Cl distances were
found to be 2.447(1) Å and 2.511(1) Å. This marked difference
is a result of the corresponding trans N and P atoms, respect-
ively. The trans-pyridine ligands give rise to Ru–N distances of
2.123(4) Å. Interestingly the metric parameters for the phos-
phine–imine chelate in 7 do not differ significantly from that in
6 as the Ru–N distance in the chelate ligand in 7 is 1.991(3) Å
while the Ru–P distance is 2.261(1) Å with a N–Ru–P bite angle
of 87.7(1)°.
Treatment of 5 with excess PPh3 afforded the new species 8 in
85% yield. This species exhibited a doublet and a triplet in the
31P{1H} NMR spectrum at 27.5 and 24.5 ppm with a P–P coup-
ling of 27.5 Hz. These data suggest the formulation of 8 as
RuCl2(PPh3)2(C6H4(PMe2)C(Ph)NH) in which two PPh3 ligands
are cis to the P of the phosphine–imine chelate (Scheme 2).
X-ray crystallographic data for 8 confirmed this formulation with
a geometry (Fig. 5) that was analogous to that of 7. The two
phosphine ligands adopt trans position axial to the NPRuCl2
plane. The Ru–P distances for the axial phosphines are 2.396(1) Å
and 2.400(1) Å. The Ru–Cl distances in 8 were found to be
2.4658(11) Å and 2.4963(11) Å, while the Ru–P and Ru–N dis-
tances associated with the imino-phosphine ligand are found to
be 2.015(4) Å and 2.2493(13) Å, respectively. The correspond-
ing bite angle of the N–P chelate of 84.4(1)° is smaller than in 7,
presumably a result of the increased steric demands of the axial
ligands.
In considering the mechanism of the rearrangement of the
phosphinoimine ligands leading to 1–8, it is reasonable to specu-
late that the initial binding is monodentate via P. Such binding
results from the reaction of the phosphinoimine ligand
Ph2PNvCPh2 with the alkylidene complex RuCl2(PPh3)-
(SIMes)(CHPh) affording the analog formulated as
RuCl2(Ph2PNvCPh2)(SIMes)(CHPh) 9. While the coordinated
phosphorus results in a 31P{1H} NMR signal at 89.8 ppm, the
most defining spectroscopic features of 9 are the 1H NMR signal
at 19.13 ppm and 13C resonance centered at 302.0 ppm attribu-
table to the alkylidene moiety. X-ray crystallographic data for 9
confirmed the five coordinate Ru centre with Ru–Cl distances of
2.3719(7) Å and 2.4043(7) Å (Fig. 6). The carbene Ru–C dis-
tances is 2.087(2) Å while the Ru-alkylidene fragment gives rise
to a Ru–C distance of 1.830(3) Å. The phosphinoimine binds to
Ru via P and occupies the position trans to the N-heterocyclic
carbene ligand with a Ru–P distance of 2.3826(7) Å and a P–N
distance of 1.680(2) Å. Analogous monodentate binding
of phosphinoimine ligands was observed by Igau et al.13 in the
Ru-complexes RuCl2(MeC6H4iPr)(iPr2PNvCPh2) (R = Ph, H).
In these species, the Ru–P distances were found to be
2.3068(17) Å and 2.3409(6) Å respectively; very similar to that
seen in 9.
Fig. 1 POV-ray depiction of 1, hydrogen atoms are omitted for clarity.
also has an impact on the Ru–Cl distances in 3 which were
found to be slightly longer with the terminal Ru–Cl distance in 3
at 2.4462(4) Å and the bridging Ru–Cl distances of 2.4642(3) Å
and 2.4991(3) 2 Å.
Subsequent reaction of 1 with pyridine at room temperature
gave rise to a new and soluble species 4 which displays a 31P
{1H} NMR coupled resonances at 44.5 and 43.3 ppm with a
P–P coupling constant of 33 Hz. This together with the expected
1H NMR signals including a signal at 9.65 ppm which arises
from the presence of the NH fragment, are consistent with clea-
vage of the dimer and the formation of the species formulated as
RuCl2(PPh3)(py)(C6H4(PPh2)C(Ph)NH) 4 (Scheme 2). X-ray
crystallographic characterization of 4 confirmed the pseudo-octa-
hedral geometry about Ru, with the phosphine–imine chelate
and Cl atoms in one plane, while the PPh3 and pyridine ligands
adopt axial positions (Fig. 3). The Ru–N and Ru–P distances in
the phosphine–imine ligand were found to be 2.0011(15) Å and
2.2860(5) Å while the Ru–Cl bond distances trans-to these
donors were 2.4492(5) Å and 2.4776(4) Å, respectively. The
bite-angle of the chelate in 4 is 82.08(4)°. The Ru–P and Ru–N
distances of the axial PPh3 and pyridine ligands in 4 are
2.3179(5) Å and 2.173(2) Å. Treatment of 3 with pyridine
afforded the RuCl2(PPh3)(py)(C6H4(PMe2)C(Ph)NH) 5 in 89%
yield (Scheme 2). This product exhibits 1H NMR signals at
9.51 ppm and 31P{1H} NMR signals at 48.6 and 31.2 ppm with
a coupling of 34 Hz.
The analogous treatment of 2 with pyridine afforded a mixture
of two new species 6 and 7 in a combined yield of 92%. These
species exhibited singlets in the 31P{1H} NMR spectrum at 59.6
1
and 57.5 ppm in a 2 : 1 ratio. In addition resonances in the H
NMR spectrum at 12.33 and 11.04 ppm were attributable to the
NH fragment of the phosphine–imine ligand. These data suggest
the formulation of 6 and 7 as the isomers of RuCl2(py)2(C6H4-
(PiPr2)C(Ph)NH) in which the pyridine ligands are cis and trans
respectively. These compounds crystallized as blocks and
needles respectively allowing the acquisition of X-ray crystallo-
graphic data for both 6 and 7 (Scheme 2, Fig. 4). These data
The mechanism of the formation of the phosphine–imine
ligands in complexes 1–8 is an interesting point for consideration
as this reaction effects the interchange of proton and phosphide
9434 | Dalton Trans., 2012, 41, 9431–9438
This journal is © The Royal Society of Chemistry 2012

Table 1 Crystallographic data
1
3
4
6
7
8
9
10
Formula
wt
Cryst. syst.
Space group
a (Å)
b (Å)
c (Å)
C
90H78Cl12N2 P4Ru2 C66H62Cl4N2P4Ru2 C63H55Cl2N5 P2Ru C29H34Cl2N3PRu C30H34Cl4N3PRu C120H102Br3Cl4N2P6Ru2 C47H56Cl2N3PRu C49H40Cl2NP2Ru
1938.96
Monoclinic
C2/c
25.477(2)
12.7495(10)
28.088(2)
90.00
103.210(5)
90.00
8882.0(12)
4
1351.00
Triclinic
P1
1116.03
Monoclinic
P21/c
10.6627(5)
17.9387(8)
28.2348(12)
90.00
92.259(2)
90.00
5396.4(4)
4
627.53
Monoclinic
P21/n
9.0765(9)
46.734(5)
13.7877(14)
90.00
108.453(6)
90.00
5547.7(10)
8
710.44
Orthorhombic
Pbca
15.4539(12)
18.3795(15)
21.2573(16)
90.00
90.00
90.00
6037.8(8)
8
2341.53
Monoclinic
P21/n
17.1587(7)
14.9111(6)
20.5139(8)
90.00
99.453(2)
90.00
5177.3(4)
2
865.89
Monoclinic
P21/c
11.7266(7)
19.7505(14)
19.5819(14)
90.00
107.349(3)
90.00
4329.0(5)
4
876.73
Orthorhombic
P212121
12.1208(5)
14.9206(6)
22.2574(8)
90.00
90.00
90.00
4025.2(3)
4
ˉ
10.0277(4)
12.3376(5)
14.2100(5)
98.147(2)
110.240(2)
110.453(2)
1474.92(10)
1
α (°)
β (°)
γ (°)
V (Å3)
Z
d (calc) g cm–3 1.450
1.521
1.374
1.503
1.563
1.502
1.329
1.447
R (int)
0.0900
0.819
85 843
6341
0.0350
0.845
0.0365
0.495
78 203
15 702
662
0.0434
0.1084
1.036
0.1516
0.839
49 302
7009
0.0703
0.952
78 740
6424
0.0681
1.697
110 057
8777
0.0590
0.558
38 912
9734
0.0461
0.638
68 210
16 116
500
0.0321
0.0640
1.025
μ (mm–1
)
Total data
>2σ(Fo )
Variables
R (>2σ)
Rw
2
11 200
476
0.0271
0.0667
1.008
496
657
365
640
497
0.0530
0.1546
0.945
0.0661
0.1219
1.007
0.0564
0.1559
1.071
0.0480
0.1313
1.052
0.0367
0.0878
1.028
GOF

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Fig. 2 POV-ray depiction of 3, hydrogen atoms are omitted for clarity.
Fig. 4 POV-ray depictions of (a) 6, and (b) 7 hydrogen atoms are
omitted for clarity.
Fig. 3 POV-ray depiction of 4, hydrogen atoms are omitted for clarity.
fragments on the phosphinoimine ligand. This process could pro-
ceeds either via a ligand-assisted aryl C–H activation46 and
rearrangement or by the thermal access of a transient Ru(IV)-
phosphide intermediate. Some possible insight into the reaction
pathway is provided by the observation that prolonged heating of
Me2PNvCPh2 with RuCl2(PPh3)3 in an open vessel affords a
new species 10 albeit in rather low yield. While the spectro-
scopic characterization of 10 was problematic due to its para-
magnetic nature, crystallographic characterization of 10
confirmed its formulation to be RuCl2(PPh3)2(HNvC(Ph)-
C6H4). This species 10 was subsequently prepared in 71% yield
via the thermal reaction of RuH(PPh3)3Cl and benzophenone
imine in 1,2-dichloroethane. Although this infers solvent partici-
pation in the product formation, its precise role remains
unknown. The crystallographic data for 10 showed the two PPh3
adopt a trans configuration, while the two chlorides are cis to
Fig. 5 POV-ray depiction of 8, hydrogen atoms are omitted for clarity.
each other and trans to an aryl-imine chelate (Fig. 7). The Ru–P
and Ru–Cl distances are found to be 2.4115(4) Å, 2.3828(4) Å,
2.4283(4) Å and 2.3573(4) Å, respectively while the chelating
aryl-imine gives rise to Ru–C and Ru–N distances of 2.0384(16)
Å and 2.0470(13) Å while the bite angle of this chelate is
9436 | Dalton Trans., 2012, 41, 9431–9438
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Conclusion
Herein, we have prepared and characterized Ru–phosphine–
imine chelate complexes which are readily derived from the ther-
molysis of phosphinoimines with suitable Ru precursors. While
the precise details of the mechanism are not known, the role of a
transient metallated imine has been inferred. Further study of the
applications of the resulting complexes in on-going. In addition,
we are attempted to exploit this facile rearrangement to develop
phosphine–imine complex chemistry for other transition metal
systems.
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Dalton Trans., 2012, 41, 9431–9438 | 9437

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9438 | Dalton Trans., 2012, 41, 9431–9438
This journal is © The Royal Society of Chemistry 2012