m-Terphenylphosphines: Synthesis, structures and coordination properties

Article abstract of DOI:10.1016/j.ica.2009.03.034

A series of m-terphenylphosphines TerphPCl₂, TerphPH₂ and TerphPMe₂ (Terph = 2,6-Mes₂C₆H₃-, 2,6-(4-t-BuC₆H₄)₂C₆H ₃-, 2,6-(3,5-Me₂

Full text of DOI:10.1016/j.ica.2009.03.034

Inorganica Chimica Acta 362 (2009) 3465–3474
Contents lists available at ScienceDirect
Inorganica Chimica Acta
journal homepage: www.elsevier.com/locate/ica
m-Terphenylphosphines: Synthesis, structures and coordination properties
Bryan Buster a, Armando A. Diaz a, Tillman Graham a, Rabiyah Khan a, Masood A. Khan a,
Douglas R. Powell a, Rudolf J. Wehmschulte b,
*
a Department of Chemistry and Biochemistry, University of Oklahoma, 620 Parrington Oval, Room 208, Norman, OK 73019, United States
b Department of Chemistry, Florida Institute of Technology, 150 W. University Blvd., Melbourne, FL 32901, United States
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 9 January 2009
Received in revised form 17 March 2009
Accepted 24 March 2009
Available online 31 March 2009
A series of m-terphenylphosphines TerphPCl2, TerphPH2 and TerphPMe2 (Terph = 2,6-Mes2C6H3–, 2,6-(4-
t-BuC6H4)2C6H3–, 2,6-(3,5-Me2C6H3)2C6H3–, 2,6-(2,6-Et2C6H3)2C6H3–, and 2,6-(2,6-i-Pr2C6H3)2C6H3–;
Mes = 2,4,6-Me3C6H2–) was prepared and fully characterized. The structural investigation by X-ray crys-
tallography and density functional theory revealed significant distortions in the environment of the ipso
carbon and phosphorus centers. These can be traced back to steric interactions and repulsions of the
chlorine and methyl substituents on phosphorus with one of the flanking arenes of the m-terphenyl sub-
stituents. The primary phosphine 2,6-Mes2C6H3PH2, 6, and the dimethylphosphine 2,6-(3,5-Me2C6H3)2
C6H3PMe2, 9, readily form complexes with the Cl2Ru(p-cymene) complex fragment, whereas the larger
phosphine 2,6-Mes2C6H3PMe2, 8, does not. Heating of the complexes TerphPR2Ru(Cl2)(p-cymene) 11
and 12 and the mixture of 8 and {(p-cymene)RuCl2}2 lead to expulsion of the p-cymene ligand and intra-
molecular g6 coordination of one of the flanking arene rings to the ruthenium center to afford the
Keywords:
Phosphine
Ruthenium complex
Bulky ligand
X-ray crystal structure
Density functional theory
NMR
Chelate complex
Intramolecular coordination
Arene complex
complexes Cl2RuP(H2)C6H3-2-
C6H3-2-
6-(3,5-Me2C6H3)-6-(3,5-Me2C6H3), 15. All complexes were characterized by NMR spectroscopy
and complexes 14 and 15 also by X-ray crystallography.
g g
6-Mes-6-Mes, 13, Cl2RuP(Me2)C6H3-2- 6-Mes-6-Mes, 14, and Cl2RuP(H2)-
g
Ó 2009 Elsevier B.V. All rights reserved.
1. Introduction
{(p-cymene)RuCl2}2, and the X-ray crystal structures of two repre-
sentative complexes were determined.
Organophosphorous compounds bearing large substituents
have been successfully applied to stabilize unusual oxidation states
or coordination environments [1–3]. In recent years, sterically
encumbered electron-rich trialkyl- and biphenyldialkylphosphines
have been employed as supporting ligands in various catalyzed C–
C, C–N or C–O coupling reactions [4,5]. A relatively new class of
bulky substituents are m-terphenyls [6,7]. During our work on
unsymmetrical 9-phosphafluorenes, which were prepared by facile
intramolecular C–H activation in m-terphenyldichlorophosphines
TerphPCl2 [8,9], we have obtained several X-ray crystal structures
of these precursors. Since these compounds featured relatively
large distortions of the C–Cipso–P angles, we then prepared the re-
lated methyl or hydrogen substituted compounds TerphPMe2 and
TerphPH2 and determined the structures of two of these to better
understand the reasons for these distortions. The experimental
data have been supported by quantum mechanical calculations.
In addition, the coordination properties of selected phosphines
TerphPMe2 and TerphPH2 were probed by their interactions with
2. Experimental
2.1. General procedures
All work was performed under anaerobic and anhydrous condi-
tions by using either modified Schlenk techniques or an Innovative
Technologies or Vacuum Atmospheres drybox. Solvents were
freshly distilled under N2 from sodium, potassium or sodium/
potassium alloy and degassed twice prior to use. n-Butyllithium
(1.6 M in hexanes), methyllithium (1.5 M in Et2O), methylmagne-
sium bromide (2.6 M in THF), and PCl3 were obtained from com-
mercial suppliers. 2,6-Et2C6H3Br [10], 2,6-(2,6-i-Pr2C6H3)2C6H3I
[11], 2,6-Mes2C6H3PCl2, 1 [12,13], 2,6-(4-t-BuC6H4)2C6H3PCl2, 2
[14], 2,6-(3,5-Me2C6H3)2C6H3PCl2, 3 [8], and 2,6-Mes2C6H3PH2, 6
[12], were synthesised according to literature methods. NMR spec-
tra were recorded on a Varian Mercury 300 MHz, a Varian Unity
Plus 400 MHz or a Bruker Avance 400 MHz spectrometer, and 1H
NMR chemical shift values were determined relative to the resid-
ual protons in C6D6 or CDCl3 as internal reference (d = 7.15 or
7.27 ppm). 13C NMR spectra were referenced to the solvent signal
(d = 128.0 or 77.0 ppm) and 31P NMR spectra were referenced to
* Corresponding author. Tel.: +1 321 674 7659; fax: +1 321 674 8951.
E-mail address: rwehmsch@fit.edu (R.J. Wehmschulte).
0020-1693/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2009.03.034

Table 1
Crystal data and structural refinement for compounds 1, 3, 4, 6, 7, 9, 10, 14 and 15.
1c
3
4
6
8
9
10
14
15 ꢀ CDCl3
Empirical formula
Formula weight
T (K)
Wavelength (Å)
Crystal system
Space group
a (Å)
C24 H25 Cl1.91 I0.05 P0.95 C22H21Cl2P
C26H29Cl2P
443.36
98(2)
0.71073
monoclinic
P2(1)/n
7.5113(3)
14.6869(7)
20.6494(9)
90
92.5510(10)
90
2275.74(17)
4
1.294
0.366
C24H27
P
C26H31
P
C24H27
346.43
100(2)
0.71073
monoclinic
P2(1)/c
10.3378(4)
24.3603(10)
8.1965(3)
90
104.4470(10)
90
1998.87(13)
4
1.151
0.141
P
C52H58P2
744.92
173(2)
0.71073
monoclinic
P2(1)/c
11.213(4)
16.355(4)
23.544(7)
90
94.32(3)
90
4305(2)
4
1.149
0.135
C26H31Cl2PRu
546.45
293(2)
0.71073
monoclinic
Pc
19.122(7)
8.207(3)
15.917(6)
90
96.929(9)°
90
2479.7(16)
4
1.464
0.923
C25H28Cl5PRu
637.76
99(2)
0.71073
monoclinic
P2(1)/n
8.9261(10)
27.417(3)
10.8952(12)
90
103.636(2)
90
2591.2(5)
4
1.635
1.196
416.44
98(2)
387.26
98(2)
346.43
173(2)
0.71073
orthorhombic
Cmc2(1)
23.20(2)
13.165(11)
6.567(5)
90
90
90
2006(3)
4
1.147
374.48
120(2)
0.71073
orthorhombic
P2(1)2(1)2(1)
7.7542(8)
14.7337(14)
19.0484(19)
90
90
90
2176.2(4)
4
1.143
0.71073
triclinic
P1
0.71073
monoclinic
P2(1)/c
10.2237(6)
23.8919(13)
8.2733(5)
90
104.4120(10)
90
1957.3(2)
4
ꢀ
8.824(2)
8.939(2)
15.867(4)
77.595(6)
76.772(6)
61.812(5)
1065.5(4)
2
b (Å)
c (Å)
a
(°)
b (°)
c
(°)
V (Å3)
Z
Dcalc (mg/m3)
1.298
1.314
l(Mo K
a
) (mmꢁ1
)
0.437
0.415
0.140
0.134
F(0 0 0)
436
808
936
744
808
744
1600
1120
1288
Crystal size (mm3)
Crystal color and habit
2hmax (°)
0.32 ꢂ 0.24 ꢂ 0.18
colorless prism
26.00
6063
255
0.0328
0.0973
1.004
0.366
0.28 ꢂ 0.26 ꢂ 0.20 0.46 ꢂ 0.36 ꢂ 0.22 0.48 ꢂ 0.28 ꢂ 0.12 0.36 ꢂ 0.24 ꢂ 0.22 0.38 ꢂ 0.24 ꢂ 0.12 0.42 ꢂ 0.38 ꢂ 0.32 0.24 ꢂ 0.20 ꢂ 0.12 0.26 ꢂ 0.18 ꢂ 0.16
colorless prism
27.49
4451
colorless plate
27.50
5205
colorless plate
25.02
1410
colorless prism
27.50
4982
colorless plate
27.50
4575
orange prism
24.01
6722
red prism
28.33
11751
558
0.0181
0.0499
1.028
red rod
27.50
5924
Number of observations
Number of variables
230
266
125
252
232
495
295
a
R1 [I > 2
r(I)]
0.0411
0.1154
1.009
0.0384
0.0954
1.034
0.0500
0.1280
1.037
0.0355
0.0968
1.047
0.0370
0.1043
1.036
0.0817
0.1826
1.015
0.0215
0.0545
1.113
0.525
b
wR2 [I > 2
r(I)]
Goodness-of-fit on F2
Largest difference of peak (e Åꢁ3
)
0.553
1.281
0.177
0.546
0.389
0.737
0.573
P
P
a
b
c
R1
=
||Fo| ꢁ |Fc||/ |Fo|.
P
P
wR2 = ( w||Fo| ꢁ |Fc||2/ w|Fo|2)1/2
.
Contains 5% 2,6-Mes2C6H3I.

B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
3467
external 85% H3PO4. Mass spectra were recorded with a JEOL Accu-
TOF direct analysis in real time (DART) spectrometer or on a Micro-
mass Q-ToF (ESI) spectrometer. UV/vis spectra for compound 10
were collected with an Agilent 8453 spectrophotometer. Melting
points were determined in Pyrex capillary tubes (sealed under
nitrogen) with a Mel-Temp apparatus and are uncorrected.
microcrystalline solid (1.11 g). Concentration of the mother liquor
and subsequent cooling to ꢁ30 °C for 1 week gave a second batch
of small crystals (0.25 g). Yield: 1.36 g, 38%. M.p. 128–131 °C. 1H
NMR (300 MHz, C6D6): d 7.24 (t, J = 7.8 Hz, p-H(Dep), 2H), 7.07
(d, J = 7.8 Hz, m-H(Dep), 4H), 7.04 (t, J = 7.5 Hz, p-H, 1H), 6.90 (dd,
J = 7.5 Hz, JHP = 3.0 Hz, m-H, 2H), 2.49 (dq, J = 15 Hz, 7.5 Hz, CH2,
4H), 2.36 (dq, J = 15 Hz, 7.5 Hz, CH2, 4H), 1.06 (t, 7.5 Hz, CH3,
12H). 131C{1H} NMR (75.45 MHz, C6D6): d 146.29 (d, JCP = 28.9 Hz),
142.63 (d, JCP = 2.6 Hz, o-C(Dep)), 137.55 (d, JCP = 8.3 Hz), 134.65 (d,
JCP = 73.0 Hz, i-C), 131.85 (p-C), 131.19 (d, JCP = 1.1 Hz, m-C), 129.02
(p-C(Dep)), 125.64 (m-C(Dep)), 28.02 (CH2CH3), 15.22 (CH2CH3).
2.2. 2,6-(2,6-Et2C6H3)2C6H3I
This compound was prepared in analogy to the literature
[15,16] starting with 2,6-Et2C6H3I, and it was purified by crystalli-
zation from ethanol. Yield: 47%. M.p. 102–103 °C. 1H NMR
(400 MHz, C6D6): 7.26 (t, J = 7.6 Hz, p0-H, 2H), 7.12 (d, J = 7.6 Hz,
m0-H, 4H), 7.03 (t, J = 7.6 Hz, p-H, 1H), 6.8 (d, J = 7.6 Hz, m-H, 2H),
2.47 (dq, J = 14.8 Hz, 7.4 Hz, CH2, 4H), 2.38 (dq, J = 14.8 Hz, 7.4 Hz,
CH2, 4H), 1.12 (t, CH3, 12H), 7.4 Hz. 13C{1H} NMR (100.57 MHz,
C6D6): 146.97, 144.11, 141.42, 128.77, 128.51, 127.90, 126.04
(m0-C), 109.69 (C-I), 27.03 (CH2), 15.10 (CH3).
31P{1H} NMR (121.47 MHz, C6D6):
d 160.2. MS (DART): m/z
443.133 (M+H+). Anal. Calc. for C26H30Cl2P+: 443.146.
2.4. 2,6-(2,6-i-Pr2C6H3)2C6H3PCl2, 5
A solution of n-BuLi (1.6 M in hexanes, 5 mL, 8.0 mmol) was
added to a solution of 2,6-(2,6-i-Pr2C6H3)2C6H3I (3.80 g, 7.2 mmol)
in hexanes (50 mL) at 0 °C. After about 1 h a fine colorless precip-
itate began to form. The mixture was slowly warmed to room tem-
perature and stirred for an additional 2 h. The precipitate was
collected on a sintered glass frit and dried in vacuo to give 2.34 g
of product which was identified as almost pure 2,6-(2,6-i-
Pr2C6H3)2C6H3Li by 1H NMR spectroscopy. A small amount of ben-
zene insoluble material was assumed to be LiI. A suspension of this
solid in hexanes (40 mL) was added dropwise (20 min) to a solu-
tion of freshly distilled PCl3 in hexanes at ꢁ78 °C. The mixture
was kept at that temperature for 30 min and then allowed to
slowly warm to room temperature. During warm-up the suspen-
sion changed color to orange. After stirring at room temperature
overnight the mixture was filtered, and the volatile material was
removed from the filtrate in vacuo. The resulting pale yellow
viscous oil solidified after 2 h at room temperature. It was
identified as a 3:1 mixture of 2,6-(2,6-i-Pr2C6H3)2C6H3PCl2 and
2.3. 2,6-(2,6-Et2C6H3)2C6H3PCl2, 4
A solution of 2,6-(2,6-Et2C6H3)2C6H3I (3.81 g, 8.1 mmol) in hex-
anes (60 mL) was treated with n-BuLi (1.6 M in hexanes, 5.45 mL,
8.7 mmol) at 0 °C, whereupon the color changed to yellow. The
reaction mixture was warmed to room temperature and stirred
overnight. The volatile material was distilled from the yellow sus-
pension. The remaining pale yellow solid was suspended in hex-
anes (50 mL), cooled to ꢁ78 °C, and freshly distilled PCl3
(0.76 mL, 8.7 mmol) was added via syringe. The mixture was
slowly warmed to room temperature and stirred for another
10 h. The precipitated colorless solid was collected on a sintered
glass frit, dissolved in toluene (40 mL) and filtered. The resulting
pale yellow solution was concentrated under reduced pressure to
ca. 5 mL and cooled to ꢁ30 °C for 2 days to give a pale yellow
Table 2
Experimental and calculated (in parentheses) bond distances (Å) and angles (°) for the m-terphenylphosphines TerphPX2 1–9.
1a
2b
3
4
5
6
7
8
9
X = Cl
X = Cl
X = Cl
X = Cl
X = Cl
X = H
X = H
X = Me
X = H
P–CTerph
P–X
1.847(3)
(1.863)
2.0556(10)
(2.114)
2.0666(11)
(2.115)
98.77(5)
(101.3)
105.53(9)
(104.0)
101.28(9)
(102.9)
130.2(2)
(129.7)
109.87(19)
(110.6)
1.837(2)
(1.859)
2.0612(9)
(2.108)
2.0723(9)
(2.131)
100.11(4)
(101.5)
104.53(7)
(104.5)
101.93(7)
(102.7)
128.2(2)
(128.3)
111.4(2)
(111.2)
118.9(2)
(119.4)
358.5
1.8591(17)
(1.858)
2.0583(6)
(2.108)
2.0785(7)
(2.138)
99.24(3)
(101.4)
104.46(5)
(104.5)
102.08(6)
(102.9)
127.92(13)
(128.5)
111.39(12)
(111.1)
117.08(9)
(119.4)
356.39
1.8451(15)
(1.864)
2.0592(5)
(2.114)
2.0695(5)
(2.116)
100.04(2)
(101.1)
103.35(5)
(103.6)
102.64(5)
(103.5)
128.83(11)
(129.4)
111.41(10)
(111.0)
1.816(5)
(1.860)
1.33(6)
(1.418)
1.33(6)
(1.418)
116(6)
(94.8)
100(3)
(98.4)
100(3)
(98.3)
120.5(2)
(120.3)
120.5(2)
(120)
118.9(4)
(119.5)
359.9
1.8602(13)
(1.881)
1.8500(13)
(1.864)
1.885(2)
(1.869)
98.23(8)
(97.5)
109.87(6)
(109.4)
99.49(8)
(102.3)
128.44(10)
(128.1)
113.24(10)
(113.9)
1.8662(11)
(1.884)
1.8499(13)
(1.875)
1.8530(12)
(1.875)
94.37(6)
(94.7)
105.61(5)
(103)
103.10(5)
(102.4)
123.09(8)
(121.4)
119.80(8)
(120.9)
(1.864)
(2.104)
(2.122)
(100.7)
(105.6)
(101.5)
(130.5)
(109.9)
(119.6)
(360)
(1.867)
(1.420)
(1.420)
(94.7)
X–P–X
X–P–CTerph
(97.0)
(97.0)
Cortho–Cipso–P
(120.4)
(120.3)
(119.2)
(359.9)
Cortho–Cipso– Cortho
119.9(2)
(119.7)
359.97
119.74(13)
(119.6)
359.98
118.31(12)
(117.8)
359.99
117.08(9)
(117.7)
359.97
P
(angles at Cipso
)
(360.0)
(358.9)
2.800
(2.820)
2.957
(359.0)
2.859
(2.810)
2.984
(360)
(359.8)
(359.8)
(360)
XꢀꢀꢀH
(3.101)
163.7
(3.077)
160.4
Dihedral angle Cmeta–Cortho–Cipso–P
178.4
177.6
178.7
175.2
177.4
(176.8)
178.1
(177.0)
(162.3)
166.3
(164.6)
(162.5)
163.2
(164.9)
(176.6)
179.3
(177.2)
(179.2)
(179.5)
(176.1)
178.7
(176.1)
(175.5)
(175.5)
(176.2)
175.0
(177.3)
(171.2)
176.8
(171.1)
a
X-ray data from Ref. [13].
X-ray data from Ref. [14].
b

3468
B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
2,6-(2,6-i-Pr2C6H3)2C6H3I. Pure product was obtained after recrys-
tallization from hexanes (15 mL) at ꢁ20 °C in form of large (2–
3 mm) pale yellow crystals. Yield: 1.15 g, 32% based on 2,6-(2,6-
i-Pr2C6H3)2C6H3I. M.p. 172–3 °C. 1H NMR (400.13 MHz, C6D6): d
7.30 (t, J = 7.7 Hz, p-H(Dipp), 2H), 7.15 (d, J = 7.7 Hz, m-H(Dipp),
4H), 7.07 (m, p- and m-H, 3H), 2.76 (sept, J = 6.8 Hz, CH(CH3)2),
4H), 1.29 (d, J = 6.8 Hz, CH(CH3)2, 12H), 1.00 (d, J = 6.8 Hz, CH(CH3)2,
12H). 13C{1H} NMR (100.61 MHz, C6D6): d 147.26 (d, JPC = 2.2 Hz, o-
C(Dipp)), 145.69 (d, JPC = 28.7 Hz), 136.50 (d, JPC = 8.4 Hz), 136.05
(d, JPC = 72.6 Hz, i-C), 132.04 (p-C(Dipp) or m-C), 130.85 (p-C),
129.47 (p-C(Dipp) or m-C), 123.06 (m-C(Dipp)), 31.52 (CH(CH3)2),
25.69 (CH(CH3)2), 22.78 (CH(CH3)2). 31P{1H} NMR (145.78 MHz,
C6D6): d 157.6. MS (DART): m/z 499.184 (M+H+). Anal. Calc. for
C30H38Cl2P+: 499.208.
C6D6): 7.25 (s, o-H(Xyl), 4H), 7.22 (dd (A part of A2BX system),
J = 8.1 Hz, JHP = 1.8 Hz, 2H), 7.12 (B part of A2BX system),
J = 8.1 Hz, 1H, 6.81 (s, p-H(Xyl), 2H), 2.18 (s, m-CH3, 12H), 0.79
(d, JHP = 5.4 Hz, P-CH3, 6H). 13C{1H} NMR (75.45 MHz, C6D6):
148.1, 144.32, 137.71, 129.91, 128.96, 127.96, 127.03, 21.56 (m-
CH3), 16.53 (d, JCP = 15.8 Hz, P-CH3). 31P{1H} NMR (121.47 MHz,
C6D6): ꢁ32.7. MS(ESI) in CH3CN solution: m/z 347.2 (M+H+).
2.8. [2,6-(2,6-Et2C6H3)2C6H3P]2, 10
A solution of 4 (1.00 g, 2.2 mmol) in THF (20 mL) was added to
Mg turnings (0.11 g, 4.5 mmol), which had been activated by stir-
ring in THF (20) in the presence of one small crystal of naphtha-
lene. After stirring the mixture at room temperature for 14 h a
color change to pale orange was observed. As the color deepened
to dark red/purple after two more hours the mixture was filtered
through a medium porosity glass frit to give a clear orange solu-
tion. The solvent was removed under reduced pressure and the res-
idue was extracted with hexanes (60 mL). The insoluble material
was allowed to settle, and the orange supernatant liquid was dec-
anted. Concentration to 2–3 mL and cooling at ꢁ30 °C for 5 d affor-
ded large orange plates of 10. Yield: 0.21 g, 25%. M.p. color
intensified to bright red around 140 °C, did not melt below
260 °C. 1H NMR (300 MHz, C6D6): 7.19 (t, J = 7.5 Hz, p-H(Dipp),
4H), 7.00 (t, J = 8.1 Hz, p-H, 2H), 7.00 (t, J = 7.5 Hz, m-H(Dipp),
8H), 6.89 (d, J = 8.1 Hz, m-H, 4H), 2.17 (m, CH2, 18H), 1.013 (t,
CH3, 24H). 13C{1H} NMR (75.45 MHz, C6D6): 143.66 (d,
JCP = 16.4 Hz), 143.66 (s), 141.69 (o-C(Dipp)), 140.82, 129.51,
128.65, 125.56 (m-C(Dipp)), 27.18 (CH2), 14.85 (CH3). 31P{1H}
2.5. 2,6-(4-t-BuC6H4)2C6H3PH2, 7
A solution of 2 (1.81 g, 4.1 mmol) in Et2O (50 mL) was added
slowly to a suspension of LiAlH4 (0.40 g, 10.5 mmol) in Et2O at
0 °C. The mixture was allowed to warm to room temperature and
was stirred overnight. After filtration of the resulting cloudy reac-
tion mixture through a medium porosity glass frit the solvent was
distilled off the clear colorless filtrate under reduced pressure, and
the remaining colorless solid was extracted with hexanes (60 mL).
Concentration to 10 mL and cooling at ꢁ28 °C overnight afforded 7
as thin colorless needles (0.79 g). A second crop (0.21 g) was ob-
tained after concentration to 3 mL and cooling to ꢁ28 °C for 2 days.
Yield: 65%. M.p. 125–127 °C. 1H NMR (400 MHz, C6D6): 7.43 (d,
J = 8.2 Hz, o- or m-H (4-t-BuC6H4), 4H): 7.31 (d, J = 8.2 Hz, o- or
m-H (4-t-BuC6H4), 4H), 7.23 (dd, J = 7.2 Hz, JHP = 2.2 Hz, m-H, 2H),
7.13 (t, J = 7.2 Hz, p-H, 1H), 3.69 (d, JHP = 211.2 Hz, P-H, 2H), 1.23
(s, p-C(CH3)3). 13C{1H} NMR (100.57 MHz, C6D6): 150.38, 147.41
(d, JPC = 8.3 Hz), 140.81, 129.39 (d, JPC = 14.1 Hz), 129.04, 127.46,
125.70, 34.57 (C(CH3)3), 31.44 (CH3). 31P NMR (161.90 MHz,
C6D6): ꢁ132.0 (t, JPH = 211 Hz).
NMR (121.47 MHz, Cꢁ6D1 6): 500.6. UV/Vis (hexanes):
e (259 nm
ꢁ1
(sh)) = 11 070 cm
M
;
e
(372 nm) = 7920 cmꢁ1 Mꢁ1
;
e
(478 nm) = 440 cmꢁ1 Mꢁ1
.
2.9. (2,6-Mes2C6H3PH2)RuCl2(p-cymene), 11
A Schlenk flask was charged with 6 (0.34 g, 1.0 mmol), {(p-cym-
ene)RuCl2}2 (0.28 g, 0.45 mmol) and toluene (5 mL). The reaction
mixture was stirred overnight to afford a red solution with a fine
red-orange solid suspended in it. The solid was dissolved by a brief
heating with a heat gun, and the resulting deep red-orange solu-
tion was left standing for 7 h at room temperature during which
time red-orange crystals formed. Overnight storage at ꢁ20 °C gave
some additional crystals. Yield: 0.53 g, 85%. M.p. slight gas evolu-
tion at 160 °C, melts at 186–188 °C. 1H NMR (400.13 MHz, CDCl3):
d 7.52 (td, J = 7.6 Hz, JHP = 1.2 Hz, p-H, 1H), 7.09 (dd, J = 7.6 Hz,
JHP = 2.9 Hz, m-H, 2H), 7.00 (s, m-H(Mes), 4H), 5.46 (d,
JHP = 368.2 Hz, PH), 4.70 (d, AB system, J = 5.8 Hz, m-H(cy), 2H),
4.67 (d, AB system, J = 5.8 Hz, o-H(cy), 2H), 2.49 (sept, J = 6.9 Hz,
CH(CH3)2(cy), 1H), 2.34 (s, p-CH3, 6H), 2.14 (s, o-CH3, 12H), 2.00
(s, p-CH3(cy), 3H), 1.06 (d, J = 6.9 Hz, CH(CH3)2(cy), 6H). 13C{1H}
NMR (100.62 MHz, CDCl3): d 146.86 (d, JPC = 8.3 Hz, o-C), 137.99
p-C(Mes)), 137.86 (d, JPC = 4.3 Hz, i-C(Mes)), 131.10 (p-C), 129.92
(d, JPC = 7.1 Hz, m-C), 128.95 (m-C(Mes)), 123.45 (d, JPC = 47.1 Hz,
i-C), 107.67 (i-C(cy)), 103.89 (p-C(cy)), 86.01 (d, JPC = 4.0 Hz, m-
C(cy)), 84.66 (o-C(cy)), 30.31 (CH(CH3)2(cy)), 22.28 (CH(CH3)2(cy)),
21.52 (o-CH3), 21.32 (p-CH3), 18.11 (p-CH3(cy)). 31P NMR
(161.97 MHz, CDCl3): d ꢁ58.2 (t, JHP = 368.2 Hz).
2.6. 2,6-Mes2C6H3PMe2, 8
A solution of MeMgBr in Et2O (2.8 mL, 8.4 mmol, 3.0 M) was
added dropwise to a solution of 1 in hexanes (70 mL) at ꢁ78 °C.
The reaction mixture was slowly warmed to room temperature
and stirred overnight. Filtration, concentration to 25–30 mL under
reduced pressure and crystallization at ꢁ28 °C for 3 d afforded col-
orless crystals suitable for X-ray diffraction (0.69 g). A second crop
was obtained from the concentrated mother liquor (0.31 g). Yield:
1.00 g, 78%. M.p. 147–149 °C. 1H NMR (300 MHz, C6D6): 7.12 (t,
J = 7.5 Hz, p-H, 1H), 6.84 (s, m-H(Mes), 4H), 6.84 (dd, J = 7.5 Hz,
JHP = 1.8 Hz, m-H, 2H), 2.20 (s, p-Me, 6H), 2.15 (s, o-Me, 12H),
0.78 (d, J = 4.8 Hz, PMe, 6H). 13C{1H} NMR (100.57 MHz, C6D6):
146.15 (d, JCP = 13.7 Hz), 139.91, 136.76, 136.12 (o-C(Mes)),
129.86 (d, JCP = 2.3 Hz, m-C), 128.79 (p-C), 128.46 (m-C(Mes)),
21.34 (d, JCP = 3.0 Hz, o-Me), 21.16 (p-Me), 13.6 (d, JCP = 20.7 Hz,
PMe). 31P{1H} NMR (121.47 MHz, C6D6): ꢁ36.4. MS(FAB): m/z
391.1 (M+O+H+, 37%), 375.1 (M+H+, 44%), 374.1 (M+, 14.2%),
359.1 (M+ꢁMe, 100%).
2.7. 2,6-(3,5-Me2C6H3)2C6H3PMe2, 9
A solution of 3 (0.92 g, 2.4 mmol) in hexanes (45 mL) was trea-
ted with MeMgBr (2.6 M solution in THF, 1.8 mL, 4.7 mmol) at
ꢁ78 °C. The mixture was warmed to room temperature and stirred
overnight. The resulting colorless cloudy reaction mixture was fil-
tered through a medium porosity glass frit, and the solvent was re-
moved under reduced pressure. Recrystallization of the colorless
solid from hexanes (20 mL) at ꢁ40 °C for 2 days afforded colorless
crystals of 9. Yield: 0.55 g, 68%. M.p. 96–98 °C. 1H NMR (300 MHz,
2.10. (2,6-(3,5-Me2C6H3)2C6H3PMe2)RuCl2(p-cymene), 12
A solution of 9 (0.19 g, 0.55 mmol) in benzene (10 mL) was
added to {(p-cymene)RuCl2}2 (0.17 g, 0.28 mmol), and the suspen-
sion was stirred for 1 h at room temperature. The orange micro-
crystalline solid was isolated. Yield: 0.26 g, 72%. M.p. 340–350 °C
(dec). 1H NMR (300.07 MHz, CDCl3):
d
7.33 (td, J = 7.5 Hz,
JHP = 2.3 Hz, p-H, 1H), 7.20 (dd, J = 7.6 Hz, JHP = 2.4 Hz, m-H, 2H),

B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
3469
7.07 (s, broad, w1/2 = 8.3 Hz, o-H, 4H), 7.01 (s, p-H(3,5-Me2C6H3),
2H), 5.24 (d, o- or m-H(cy), J = 5.4 Hz, 2H), 4.99 (d, o- or m-H(cy),
J = 5.4 Hz, 2H), 2.69 (sept, J = 6.9 Hz, CH(CH3)2(cy), 1H), 2.39 (s,
m-CH3, 12H), 1.94 (s, p-CH3(cy), 3H), 1.21 (d, JHP = 10.8 Hz,
P(CH3)2, 6H), 1.07 (d, J = 6.9 Hz, CH(CH3)2(cy), 6H). 13C{1H} NMR
130.34, 127.82, 126.92 (d, JCP = 13.8 Hz), 111.95 (d, JCP = 2.9 Hz),
91.94 (d, JCP = 15.2 Hz), 21.58 (m-CH3), 19.07 (m-CH3), 17.30 (d,
JCP = 32.3 Hz, P(CH3)2). 31P{1H} NMR (121.47 MHz, C6D6): 46.6.
MS(ESI) in CH3CN solution: m/z 541.01 M+Na+, 483.05 MꢁClꢁ; cor-
rect isotope pattern.
(75.45 MHz, CDCl3):
d 147.39 (d, JCP = 11.0 Hz), 142.16 (d,
JCP = 2.4 Hz), 136.74, 131.73 (d, JCP = 7.7 Hz), 129.28, 128.20,
127.99 (d, JCP = 3.6 Hz), 105.55, 95.87, 88.22 (d, JCP = 4.9 Hz, o-or
m-C(cy)), 84.69 (d, JCP = 4.8 Hz, o- or m-C(cy)), 30.29 (CH(CH3)2),
22.10 (CH(CH3)2), 21.52 (m-CH3), 19.50 (d, JCP = 30.3 Hz, P(CH3)2),
18.45 (CH3(cy)). 31P{1H} NMR (121.47 MHz, CDCl3): d 13.7.
2.14. X-ray crystallography
Crystals were removed from the Schlenk tube under a stream of
N2-gas and immediately covered with a layer of hydrocarbon oil. A
suitable crystal was selected, attached to a glass fiber, and imme-
diately placed in the low-temperature nitrogen stream. The data
for 6 and 10 were collected at 173(2) K on a Siemens P4 diffract-
ometer and those for 1, 3, 4, at 98(2), for 8 at 120(2), for 9 at
100(2), for 14 at 293(2), and for 15 at 99(2) K on a Bruker Apex dif-
2.11. Cl2RuP(H2)C6H3-2-g
6-Mes-6-Mes, 13
A suspension of 11 (0.24 g, 0.37 mmol) in benzene (10 mL) was
dissolved at 75 °C and kept at this temperature for 46 h. After cool-
ing to room temperature the red-orange solid that had precipitated
was isolated, washed with benzene (2 ꢂ 3 mL) and dried in vacuo
to afford the product as an orange mat of very fine needles. Yield:
0.09 g, 47%. M.p. > 260 °C. 1H NMR (400.13 MHz, CDCl3): d 7.80 (t,
J = 7.5 Hz, p-H, 1H), 7.56 (d, J = 7.6 Hz, m-H, 1H), 7.43 (d,
fractometer using Mo Ka (k = 0.71073 Å) radiation. The data were
corrected for Lorentz and polarization effects. Absorption correc-
tions based on a multi-scan method from equivalent reflections
were used for 1, 3, 4, 8, 9, 14, and 15. The structures were solved
by direct methods using the SHELXTL program suite, Version 5.1
[17] for 6 and 10, Version 6.12 for 3, 4, 8, 9, 14, and 15 and Version
6.14 for 1 and refined by full-matrix least-squares on F2 including
all reflections. Unless stated otherwise, all the non-hydrogen atoms
were refined anisotropically and all the hydrogen atoms were in-
cluded in the refinement with idealized parameters. The crystal
of 1 exhibited non-merohedral twinning by a rotation of 180°
J = 7.2 Hz, m-H, 1H), 6.99 (s, m-H(Mes), 2H), 5.73 (s, m-H(g6
Mes), 2H), 5.10 (d, J = 383 Hz, H-P, 2H), 2.55 (d, JHP = 4.5 Hz, p-
CH3(
6-Mes), 3H), 2.34 (s, p-CH3(Mes), 3H), 1.95 (s, o-CH3(Mes),
6H), 1.79 (s, o-CH3(
6-Mes), 6H). 13C{1H} NMR (100.62 MHz,
-
g
g
CDCl3): d 148.96, 144.55 (d, JPC = 24.6 Hz), 138.98, 135.41, 134.95,
134.91, 134.88, 133.74 (d, JPC = 2.0 Hz, p-C), 130.49 (d, JPC = 5.5 Hz,
m-C), 129.19 (m-C(Mes)), 127.14 (d, JPC = 14.1 Hz, m-C), 104.90 (d,
around the direction (0 0 1) with
a twin ratio refined to
0.4989(7). The crystal structure as refined with 100%-PCl2 con-
tained a large peak in the difference map that was about 2.1 Å from
C1. This peak was believed to be due to a small component of io-
dine in place of the PCl2 group, i.e. starting material. The occupan-
cies of the hetero atoms refined to 0.9546(8) for PCl2 and 0.0454(8)
for I. Restraints on the displacement parameters of the disordered
atoms were required. Considering the disorder and twinning pro-
blems with the structure of 1 the data discussed in the narrative
are taken from Ref. [13]. The hydrogen atom bound to P in 6
(H1) was located in the difference map and refined isotropically.
The structure of 14 contains two independent molecules, whose
metric parameters are very similar. The data discussed here are
those of molecule 1 (Ru1). Some details of the crystal data and re-
finement are given in Table 1, and selected bond distances and an-
gles are listed in Table 2. Further details can be obtained from the
Cambridge Crystallographic database under deposition numbers
715808–715816.
JPC = 0.4 Hz, (
g
6-Mes)), 103.69 (d, JPC = 15.4 Hz, (
g
6-Mes)), 98.85 (d,
g
6-Mes), 21.29 (p-CH3(Mes)),
JPC = 4.1 Hz, m-C(
g
6-Mes)), 91.46 (
20.64 (o-CH3(Mes)), 17.82 (d, JPC = 1.5 Hz, p-CH3(g
6-Mes)), 17.09
(o-CH3(
g
6-Mes)). 31P{1H} NMR (161.97 MHz, CDCl3): d ꢁ19.0.
2.12. Cl2RuP(Me2)C6H3-2-g
6-Mes-6-Mes, 14
D-8 toluene (1 mL) was added to a mixture of 8 (8 mg,
0.02 mmol) and {(p-cymene)RuCl2}2 (6 mg, 0.01 mmol) in an
NMR tube equipped with a Teflon resealable cap. The mixture
was heated at 117 °C for 24 h during which time a deep red solu-
tion formed. Cooling to room temperature afforded a red-orange
microcrystalline solid of 14. Recrystallization from CDCl3 and hex-
ane (vapor infusion) gave X-ray quality crystals. 1H NMR
(300.07 MHz, CDCl3): d 7.69 (td, J = 7.5 Hz, JHP = 2.0 Hz, p-H, 1H),
7.51 (d, J = 7.5 Hz, m-H, 1H), 7.23 (ddd, J = 7.5 Hz, J = 1.2 Hz,
HHP = 1.2 Hz), 7.01 (s, m-H(Mes), 2H), 5.63 (s, m-H(
g
6-Mes), 2H),
2.54 (d, JHP = 4.2 Hz, p-CH3(
g
6-Mes), 3H), 2.38 (s, p-CH3(Mes),
2.15. Computational methods
3H), 1.98 (s, o-CH3(Mes), 6H), 1.75 (s, o-CH3(Mes), 6H), 1.39 (d,
JHP = 12.0 Hz, P(CH3)2, 6H). 13C{1H} NMR (75.45 MHz, CDCl3): d
147.43, 144.20 (d, JCP = 18.3 Hz), 141.42 (d, JCP = 31.5 Hz), 138.79,
133.31, 135.81, 132.57 (d, JCP = 4.0 Hz), 132.30, 128.71, 127.23 (d,
JCP = 10.3 Hz), 104.25, 102.20 (d, JCP = 10.9 Hz), 99.37 (d,
JCP = 2.3 Hz), 88.66, 21.45, 21.40, 17.89, 17.11, 12.35 (d,
JCP = 22.9 Hz, P(CH3)2). 31P{1H} NMR (121.47 MHz, C6D6): 44.6.
The geometries for the compounds 1–9 were fully optimized
using B3LYP Density Functional Theory with the 6-31G basis set.
*
Vibrational frequencies were computed for each compound to con-
firm the absence of imaginary frequencies. Important geometric
data are summarized in Table 2. Figures comparing experimental
and calculated structures as well as a list of Cartesian coordinates
of the calculated structures are provided in the Supporting Infor-
mation. All computations were performed with the Spartan’04
Macintosh software.
2.13. Cl2RuP(Me2)C6H3-2-g
6-(3,5-Me2C6H3)-6-(3,5-Me2C6H3), 15
A suspension of 12 (0.03 g, 0.046 mmol) in C6D6 (2 mL) in an
NMR tube was heated at 95–100 °C for 2.5 h. Upon cooling to room
temperature a dark orange solid precipitated. Isolation and recrys-
tallization from CDCl3/petroleum ether gave X-ray quality crystals
of 15. 1H NMR (300.07 MHz, CDCl3): d 7.55 (m, m-H, 2H), 7.37 (m,
p-H, 1H), 7.15 (s, p-H(3,5-Me2C6H3), 1H), 6.99 (s, o-H(3,5-
3. Results and discussion
3.1. m-Terphenylphosphines
The new m-terphenyldichlorophosphines 2,6-(2,6-Et2C6H3)2-
C6H3PCl2, 4, and 2,6-(2,6-i-Pr2C6H3)2C6H3PCl2, 5, were prepared in
analogy to the known compounds 2,6-Mes2C6H3PCl2, 1 [12,13],
2,6-(4-t-BuC6H4)2C6H3PCl2, 2 [14], and 2,6-(3,5-Me2C6H3)2C6H3-
PCl2, 3 [8], (Eq. (1)) in good to moderate yields.
Me2C6H3), 2H), 5.94 (s, p-H(g
6-3,5-Me2C6H3), 1H), 4.59 (s, p-
H(g
6-3,5-Me2C6H3), 2H), 2.43 (s, m-CH3, 6H), 2.24 (s, m-CH3, 6H),
1.62 (d, JHP = 12.3 Hz, P(CH3)2, 6H). 13C{1H} NMR (125.69 MHz,
CDCl3): d 147.56, 139.75, 137.83, 132.41 (d, JCP = 5.8 Hz), 130.40,

3470
B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
and they correspond closely to the structures obtained and dis-
R
R
R
cussed here. In addition, energy minimized structures of 1–9 were
determined using DFT calculations. In all cases the calculated
structures mirror closely the experimental structures lending cre-
dence to the calculated structures of 5, 7, and 9 for which no exper-
imental data were obtained (Table 2). With the exception of 6 and
9 all m-terphenylphosphines display a pronounced distortion at
the ipso carbon. The phosphorus center is bent towards one of
the flanking arene rings of the m-terphenyl substituent resulting
in Cortho–Cipso–P angles ranging from 109.9° (1) to 111.4° (2–4)
for the narrow angle and 127.9° (3) to 130.2° (1) for the wide angle.
This kind of asymmetry has been previously described for terphe-
nylarsines, stibines and bismuthines [20] and was attributed to the
so-called Menshutkin interaction [21]. Whereas the latter interac-
tion can be traced back to an attraction between an electron rich
aromatic system and a Lewis acidic arsenic, antimony and bismuth
center, the data collected in this study suggest that the here ob-
served distortions are most likely due to steric influences. There
are no distortions for the primary phosphines 6 and 7 and only lit-
tle distortion for the dimethylphosphine 9. In these compounds the
plane bisecting the X–P–X angles is almost orthogonal to the plane
R
R
R
PCl2
R
- 78 ºC
- LiCl
+ PCl3
Li
ð1Þ
R
4; R = Et
5; R = iPr
They have been obtained as colorless to pale yellow moisture
sensitive crystals. The presence of lithium iodide in the m-ter-
phenyl lithium reagent should be avoided, because it leads to un-
wanted side reactions. For example, compounds 2 and 3 are
partially converted to 9-iodo-9-phosphafluorenes, and m-ter-
phenyl iodide is produced during the preparation of 1 and 5 if lith-
ium iodide is present. Reduction of 1 and 2 with LiAlH4 cleanly
afforded the primary phosphines 2,6-Mes2C6H3PH2, 6 and 2,6-(4-
t-BuC6H4)2C6H3PH2, 7 in form of moderately air sensitive, colorless
crystals. Methylation of 1 and 3 with LiMe or MeMgBr gave access
to the colorless, crystalline m-terphenyldimethylphosphines 2,6-
Mes2C6H3PMe2, 8 and 2,6-(3,5-Me2C6H3)2C6H3PMe2, 9 (Eq. (2)).
R'
R"
R'
R"
R'
R"
R'
R
R'
R
R'
R
MeLi or
MeMgBr
R
PCl2
R
R
PMe2
R
R
PH2
R
LiAlH4
ð2Þ
R
R'
R
R'
R
R'
R'
R"
R'
R"
R'
R"
6; R = R" = Me, R' = H
7; R = R' = H, R" = t-Bu
8; R = R" = Me, R' = H
9; R = R" = H, R' = Me
1; R = R" = Me, R' = H
2; R = R' = H, R" = t-Bu
3; R = R" = H, R' = Me
Compounds 6 [12] and 8 [18] have been reported previously
and had been prepared by slightly different methods than those
described here. All compounds are readily soluble in standard or-
ganic solvents. The solution NMR spectra are simple and reflect
of the central arene ring. Use of the larger 2,6-Mes2C6H3–, 2,6-(2,6-
Et2C6H3)2C6H3– and 2,6-(2,6-i-Pr2C6H3)2C6H3–substituents in com-
bination with methyl (8) and chlorine substituents (1, 4 and 5)
leads to the above mentioned significant distortions. Here, the
plane bisecting the X–P–X angles is almost parallel with the plane
of the central arene ring, and the phosphorus center is leaning
towards one of the flanking rings. The combination of the smaller
m-terphenyl substituents 2,6-(4-t-BuC6H4)2C6H3– and 2,6-(3,5-
Me2C6H3)2C6H3– with chlorine substituents (2 and 3) also resulted
in large distortions. This is most likely due to secondary HꢀꢀꢀCl con-
tacts stabilizing the ‘‘parallel” rotamer (as in 1) as opposed the
‘‘orthogonal” rotamer (see 9). The other geometrical parameters
are within their normal range. A reviewer suggested that electronic
contributions to the distortions could be manifested in an increase
in the pyramidalization of the ipso carbon caused by negative
4
the symmetry of these compounds. Long-range JPH couplings
involving the m-hydrogens of the central ring with values of 2–
3 Hz are observed for most of the compounds. The 31P NMR chem-
ical shifts are typical for each class of compounds with ca. 160 ppm
for TerphPCl2 1–5, ca. ꢁ132 ppm for TerphPH2 6 and 7 and ca.
ꢁ35 ppm for TerphPMe2 8 and 9 [19]. Reduction of 4 with magne-
sium in THF afforded the diphosphene 2,6-(2,6-Et2C6H3)2C6H3P@
PC6H3(C6H3-Et2-2,6)2-2,6, 10 as an orange crystalline solid (Eq.
(3)) (Figs. 1–6).
Et
Et
Et
PCl2
Et
Et
2 Mg
Et
Et
2
P
P
ð3Þ
Et
- 2 MgCl2
Et
Et
Et
Et
10
3.2. Structures of m-terphenylphosphines
Single crystal X-ray structures were obtained for compounds 1–
4, 6, 8, and 10. The structures of 1 [13] and 8 [18] have been re-
ported independently during the time this project has taken place,
Fig. 1. Molecular structure of 1 (50% ellipsoids).

B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
3471
*
hyperconjugation between the ipso carbon and P–X
r
-orbitals.
trend: For compounds 1, 4, 6, and 9 they range from 175.2° to
179.3°, but are much smaller for compounds 2 (163.7° and
166.3°) and 3 (160.4° and 163.2°). Considering that these distor-
tions are practically independent of the nature of the P–X substitu-
ent (X = H, Me, and Cl) and the previously stated observation that
However, a significant deviation from planarity as expressed by
the sum of the angles at the ipso carbon atoms was observed only
for compounds 2 ( (angles) = 358.5°) and 3 ( (angles) = 356.4°)
(see Table 2). The Cmeta–Cortho–Cipso–P dihedral angles mirror this
P
P
Fig. 2. Molecular structure of 3 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
Fig. 3. Molecular structure of 4 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
Fig. 4. Molecular structure of 6 (50% ellipsoids). Hydrogen atoms except of those bound to phosphorus have been omitted for clarity.

3472
B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
Fig. 5. Molecular structure of 8 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
Fig. 6. Molecular structure of 9 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
large deviations of the Cortho–Cipso–P angles correlate well with the
sizes of the m-terphenyl and P–X substituents, the observed distor-
tions are most likely due to unfavorable steric interactions. The
more pronounced distortions in 2 and 3 can be traced back to sec-
ondary HꢀꢀꢀCl contacts between the ortho-hydrogen atoms of the
flanking aromatice rings and one of the two chlorine substituents.
The structure of diphosphene 10 (Fig. 7) is very close to the ones
reported for the related {2,6-Mes2C6H3P}2 [12] and 2,6-Mes2C6-
H3P@P-Ar-P@PC6H3-Mes2-2,6 (Ar = 2,3,5,6-(4-t-BuC6H4)4C6 [22]).
The P–P bond distance in 10 with a value of 2.017(2) Å is slightly
longer than in the latter ones with values of 1.985(2) and
2.008(2) Å, respectively, but still within the typical range reported
for diphosphenes [1]. Furthermore, the orientation of the substitu-
ents is such that the central ring of one substituent is approxi-
mately coplanar with the C–P@P–C core, and the other one is
close to orthogonal to that core (angle between plane normals =
7.4° and 66.5°).
3.3. Ruthenium complexes
The reaction of 6 and 9 with {(p-cymene)RuCl(l-Cl)}2 at room
temperature afforded the complexes (2,6-Mes2C6H3PH2)RuCl2(p-
cymene), 11, and (2,6-(3,5-Me2C6H3)2C6H3PMe2)RuCl2(p-cymene),
12, in good yields as red-orange air-stable solids in analogy to lit-
erature reports [23]. Interestingly, the corresponding reaction of
Fig. 7. Molecular structure of 10 (50% ellipsoids). Hydrogen atoms have been
omitted for clarity.

B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
3473
Fig. 8. Molecular structure of 14 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
Fig. 9. Molecular structure of 15 (50% ellipsoids). Hydrogen atoms have been omitted for clarity.
the slightly larger phosphine 8 failed to give a complex, and NMR
spectra of the reaction mixture showed only the signals of the
unreacted starting materials. Refluxing of complexes 11 and 12
and of the reaction mixture of 8 and {(p-cymene)RuCl(l-Cl)}2 lead
to the elimination of p-cymene and intramolecular coordination of
1H and 13C{1H} NMR spectra show two sets of signals for the flank-
ing arene rings with the
6-coordinated one experiencing a charac-
g
teristic upfield shift. The 31P NMR resonances display a significant
downfield shift of 39.2 ppm (11–13) and 32.9 ppm (12–15) upon
intermolecular arene coordination. The structures of 14 and 15
(Figs. 8 and 9) show that the ruthenium centers lie approximately
in the same plain as the central arene rings of the ligands and the
phosphorus centers, and that they are positioned almost symmet-
rically above the coordinated flanking arene rings. The Ru–P dis-
tances in 14 and 15 are 2.2991(8) and 2.3181(4) Å and the RuꢀꢀꢀC
contacts average 2.205(63) and 2.210(63) Å and range from
2.113(2) to 2.287(2) Å and 2.1100(15) to 2.2788(15) Å, respec-
tively. Similar values have been reported for Cl2RuP(Cy)2C6H4-2-
one of the flanking arene rings of the m-terphenylphosphine li-
gand. The complexes Cl2RuP(H2)C6H3-2-
Cl2RuP(Me2)C6H3-2-
6-Mes-6-Mes, 14, and Cl2RuP(Me2)C6H3-2-
6-(3,5-Me2C6H3)-6-(3,5-Me2C6H3), 15, were obtained as air-sta-
g
6-Mes-6-Mes, 13,
g
g
ble red-orange crystalline solids, and the crystal structures of 14
and 15 were determined. There are only a few prior examples of
intramolecular arene coordination of biphenyl-2-phosphines to
the [RuCl2] fragment in the literature [24,25]. For the synthesis of
13 it is important not to exceed a reaction temperature of 70–
80 °C in order to avoid unwanted side reactions such as partial
elimination of the ligand 6 and concomitant formation of a yet un-
known species featuring the phosphide unit Ru-P(H)C6H3-Mes2-
2,6. The exact nature of the high temperature product is not yet
known and will be reported in a future contribution. The formation
of complexes 13–15 can readily be followed by NMR spectroscopy.
g
6-C6H4-2-NMe2: the Ru–P distance is 2.343(2) Å and the RuꢀꢀꢀC
contacts average 2.200(39) Å [24]. The phosphorus centers in 14
and 15 are bending towards the ruthenium centers as is indicated
by the narrow P–Cipso–Cortho angles with values of 113.41(14)° for
14 and 113.66(11)° for 15. These values are similar to that ob-
served for the free ligand 8, but differ from 9. This is due to the fact
that with the coordination of phosphorus the P-methyl groups of 9

3474
B. Buster et al. / Inorganica Chimica Acta 362 (2009) 3465–3474
rotate into the same position above one of the flanking arene rings
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Financial Support from the University of Oklahoma, the Florida
Institute of Technology, the Petroleum Research Fund adminis-
tered by the American Chemical Society and the National Science
Foundation (CHE-0718446) is gratefully acknowledged. We also
thank Prof. J. Clayton Baum at the Florida Institute of Technology
for assistance with the quantum chemical calculations.
Appendix A. Supplementary material
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.ica.2009.03.034.