Oxidative addition of carbon-chloride bonds to rhodium(I) complexes containing terdentate nitrogen ligands. X-ray analyses of rhodium(I) chloride and rhodium(III) chloromethyl complexes

Article abstract of DOI:10.1021/om9607614

Potentially terdentate hemilabile 2,6-bis(R²-carbaldimino)pyridine and 2,6-bis(R²-ethylidyneimino)pyridine ligands (2,6-(C(R¹)=NR²)₂C₅H₃N; R¹ = H, R² = i-Pr

Full text of DOI:10.1021/om9607614

Organometallics 1997, 16, 887-900
887
Oxid a tive Ad d ition of Ca r bon -Ch lor id e Bon d s to
Rh od iu m (I) Com p lexes Con ta in in g Ter d en ta te Nitr ogen
Liga n d s. X-r a y An a lyses of Rh od iu m (I) Ch lor id e a n d
Rh od iu m (III) Ch lor om eth yl Com p lexes
Hendrikus F. Haarman,† J an M. Ernsting,† Mirko Kranenburg,†
Huub Kooijman,‡ Nora Veldman,‡ Anthony L. Spek,‡
Piet W. N. M. van Leeuwen,† and Kees Vrieze*,†
J . H. van’t Hoff Research Instituut, Laboratorium voor Anorganische Chemie, Universiteit van
Amsterdam, Nieuwe Achtergracht 166, 1018 WV Amsterdam, The Netherlands, and Bijvoet
Centre for Biomolecular Research, Vakgroep Kristal- en Structuurchemie, Universiteit Utrecht,
Padualaan 8, 3584 CH Utrecht, The Netherlands
Received September 3, 1996X
Potentially terdentate hemilabile 2,6-bis(R2-carbaldimino)pyridine and 2,6-bis(R2-ethyli-
dyneimino)pyridine ligands (2,6-(C(R1)dNR2)2C5H3N; R1 ) H, R2 ) i-Pr (1), t-Bu (2),
cyclohexyl (3), p-anisyl (4); R1 ) Me, R2 ) p-anisyl (5), i-Pr (6)) have been used to prepare
in high yields the novel and highly nucleophilic complexes [RhCl(2,6-(C(R1)dNR2)2C5H3N)]
(R1 ) H, R2 ) i-Pr (7), t-Bu (8), cyclohexyl (9), p-anisyl (10); R1 ) Me, R2 ) p-anisyl (11),
i-Pr (12)) with [RhCl(alkene)2]2 (alkene ) ethene, cyclooctene) as starting material. X-ray
analyses of 7, 8, and 12 show severe steric interactions between the R2 group and the
equatorial chloride atom, leading to out-of-plane bending of the chloride atom. The angle
between the NsNsN plane and the RhsCl axis is 5.34(16)° for 7, 11.73(11)° for 8, and
10.04(11)° for 12. Reaction of the Rh(I) complexes with CH2Cl2, CHCl3, benzyl chloride,
and R,R-dichlorotoluene led to Rh(III) complexes by CsCl bond rupture. The RhsC bonds
of the chloromethyl complexes [RhCl2(CH2Cl)(2,6-(C(R1)dNR2)2C5H3N)] (R1 ) H, R2 ) i-Pr
(13), cyclohexyl (15)) are all short (2.052(5)-2.059(3) Å), while the CsCl bonds (range 1.728-
(4)-1.790(5) Å) are rather long, which indicates the contribution of a RhdCH2+Cl- resonance
form. In solution all Rh(III) complexes exist as one isomer with the ligand bonded in a
terdentate fashion (both H and 13C NMR), except for the complexes [RhCl2(R3)(2,6-(C(Me)dN-
1
i-Pr)2C5H3N)] (R3 ) CH2Cl (18), CH2Ph (24), CHClPh (27), Cl (33)), which all contain two
interconverting isomers; one five-coordinate Rh(III) isomer has a ligand which coordinates
in a bidentate manner, while the other six-coordinate isomer has a ligand which coordinates
in a terdentate fashion, as evidenced by low-temperature NMR measurements. Molecular
modeling has shown that the formation of the five-coordinate Rh(III) species is caused by
the axial ligands, which force the equatorial Cl atom into the NsNsN plane, resulting in
an increased steric interaction of R2 and R1. Reaction of the chloromethyl and dichloromethyl
complexes 13-21 in boiling water with oxygen gave the trichloride complexes [RhCl3(2,6-
(C(R1)dNR2)2C5H3N)] (R1 ) H, R2 ) i-Pr (28), t-Bu (29), cyclohexyl (30), p-anisyl (31); R1 )
Me, R2 ) p-anisyl (32), i-Pr (33)), while the chlorotolyl complex [RhCl2(CHClPh)(2,6-
(C(Me)dN-i-Pr)2C5H3N)] 27 gave the complex 33, benzaldehyde, and H2O2.
In tr od u ction
bonylation reactions homogeneously catalyzed by pal-
ladium and platinum complexes.7-14 Oxidative addition
is also a general synthetic method for formation of
carbon-metal σ-bonds.15
The oxidative addition of carbon halides to low-valent
metal complexes is of paramount interest. It is a key
step in a number of industrially important catalytic
processes, such as the carbonylation of methanol to
acetic acid1,2 catalyzed by rhodium and HI, for which
the kinetics have been elucidated largely by the work
of Maitlis et. al.3-6 Another example is the oxidative
addition of aryl halides in the cross-coupling and car-
To elucidate the mechanism of the oxidative addition
of carbon-halide bonds, a considerable amount of work
(5) Haynes, A.; Mann, B. E.; Gulliver, D. J .; Morris, G. E.; Maitlis,
P. M. J . Am. Chem. Soc. 1991, 113, 8567.
(6) Hickey, C. E.; Maitlis, P. M. J . Chem. Soc., Chem. Commun.
1984, 1609.
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Engl. 1989, 28, 1386.
(8) Herrmann, W. A.; Brossmer, C.; Priermeier, T.; O¨ fele, K. J .
Organomet. Chem. 1994, 481, 97.
* To whom correspondence should be adressed.
† Universiteit van Amsterdam.
‡ Universiteit Utrecht.
X Abstract published in Advance ACS Abstracts, February 1, 1997.
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S0276-7333(96)00761-3 CCC: $14.00 © 1997 American Chemical Society

888 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
has been focused on zerovalent palladium and platinum
complexes.16-23 Many kinetic studies have been carried
out on Ir(I) complexes, e.g. trans-[IrX(CO)L2] (X )
halide, L ) phosphine).17 It has become clear that no
single mechanism holds for oxidative-addition reactions.
In general three different mechanisms (oxidative inser-
tion, backside nucleophilic SN2 substitution, and radical
pathways) have been observed, depending on the reac-
tants and the conditions of the reaction.15-23 A recent
article on oxidative-addition reactions involving [IrCl-
(CO)L2], MeI, H2, and O2 illustrates the difficulty of
obtaining clear insight into the mechanisms of these
reactions.24
When we restrict ourselves to oxidative additions of
carbon halide substrates to complexes of Rh(I) and Ir-
(I), it has been found that, for example, additions of
CH2X2 (X ) Cl, Br, I) are generally enhanced by
increasing the electron density on the metal atom. This
is evidenced by the oxidative addition of CH2I2 to
[RhCp*(CO)2] (Cp* ) pentamethylcyclopentadiene), af-
fording [RhI(CH2I)Cp*(CO)], while [RhCp(CO)2] (Cp )
cyclopentadiene) in contrast does not react, owing to the
smaller electron donor capacity of Cp compared to Cp*.25
The activation of dichloromethane requires even stron-
ger donor ligands.26-38 For example, reaction of [Rh-
(dmpe)2]Cl containing the strongly electron donating
Me2P(CH2)2PMe2 (ddmpe) ligands with CH2Cl2 afforded
the complex [RhCl(CH2Cl)(dmpe)2]Cl‚CH2Cl2.39 Coor-
dination of ligands with three or four nitrogen donor
atoms to Rh(I) gives also strongly nucleophilic species
that can activate dichloromethane. For example, reac-
tion of a rhodium(I) complex with a tetradentate cyclic
dioxime ligand with CH2Cl2 afforded a chloromethyl
complex.36 Reaction of [RhCl(cyclooctene)2] with the
terdentate nitrogen ligand bis(4,4-dimethyloxazolin-2-
yl)pyridine (pybox) in dichloromethane gave the corre-
sponding (chloromethyl)rhodium(III) complex [RhCl2(CH2-
Cl)(pybox)], but attempts to isolate the intermediate
nucleophilic Rh(I) complexes failed.40
Recently, articles on the stability of a series of chloro-
(chloromethyl)palladium(II) and -platinum complexes in
CDCl3 solution (both in the absence and presence of air)
were published by McCrindle et al.41 In the case of
trans-mono(chloromethyl)platinum(II) complexes it was
found that they decompose in the presence of moisture
to formaldehyde and platinum hydrides, which undergo
subsequent conversion into dichlorides.42 It was sug-
gested, in analogy to the work of van Leeuwen et al.,43
that metal-carbene intermediates may be involved.
In our laboratory we are investigating the influence
of steric and electronic properties of bi- and terdentate
nitrogen ligands on the course of a number of carbon-
carbon coupling reactions mediated by palladium
complexes.44-48 In the course of these studies we have
designed bidentate nitrogen ligands which are able to
stabilize Pd(0), Pd(II), and Pd(IV) complexes.44-48 These
results prompted us to extend our investigations to
complexes of Rh with the aim of stabilizing both Rh(I)
and Rh(III) complexes and creating very nucleophilic
Rh(I) species. In this article we describe the employ-
ment of the trinitrogen species 2,6-bis(R2-carbaldimino)-
pyridine and 2,6-bis(R2-ethylidyneimino)pyridine (2,6-
(C(R1)dNR2)2C5H3N: R1 ) H, R2 ) i-Pr (1), t-Bu (2),
cyclohexyl (3), p-anisyl (4); R1 ) Me, R2 ) p-anisyl (5),
i-Pr (6)) for the isolation of novel, very reactive Rh(I)
complexes. The use of these trinitrogen ligands makes
it possible to form stable, strongly nucleophilic Rh(I)
complexes, which undergo a fast oxidative addition of
a number of substrates containing CsCl bonds. In
addition we have studied from a structural point of view
the alkylidene character of the chloromethyl moieties
of the Rh(III) complexes.
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All experiments were performed under a dry nitrogen
atmosphere using standard Schlenk techniques. Benzene,
diethyl ether, and pentane were distilled before use from
sodium/benzophenone, dichloromethane and chloroform from
calcium hydride, and acetone from KMnO4/Na2CO3. Molecular
sieves (3 Å) were activated at 180 °C in vacuo for 24 h.
Deuteriobenzene was dried over sodium and stored under
nitrogen. Deuterated chlorinated solvents were dried with
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Leeuwen, P. W. N. M.; Vrieze, K. Inorg. Chem. 1993, 32, 5769.

Addition of C-Cl Bonds to Rh Complexes
Organometallics, Vol. 16, No. 5, 1997 889
molecular sieves (3 Å) and stored under nitrogen. The 1H and
The complexes could be recrystallized by slow diffusion of
diethyl ether into a saturated dichloromethane solution at
room temperature. Isolated yields of the other compounds are
in the range 80-90%.
Anal. Calcd for C14H21Cl3N3Rh (13): C, 38.16; H, 4.81; N,
9.54. Found: C, 38.22; H, 4.86; N, 9.62. Anal. Calcd for
13C NMR spectra were recorded on
a Bruker AMX 300
spectrometer. The spectra were indirectly referenced to TMS
using residual solvent signals. Fast atom bombardment (FAB)
mass spectrometry was carried out by the Institute for Mass
Spectroscopy of the University of Amsterdam using a J EOL
J MS SX/SX102A four-sector mass spectrometer, coupled to a
J EOL MS-7000 data system. The samples were loaded in a
matrix solution (nitrobenzyl alcohol) onto a stainless steel
probe and bombarded with xenon atoms with an energy of 3
keV. During the high-resolution FABMS measurements a
resolving power of 5000 (10% valley definition) was used. CsI
and/or glycerol was used to calibrate the mass spectrometer.
Elemental analyses were carried out by Dornis und Kolbe,
Mikroanalytisches Laboratorium, Mu¨lheim a.d. Ruhr, Ger-
many and by our institute.
[RhCl(cyclooctene)2]2,49 [RhCl(C2H4)2]2,50 2,6-pyridinedicar-
boxaldehyde,51 and the 2,6-bis(R2-carbaldimino)pyridine and
2,6-bis(R2-ethylidyneimino)pyridine ligands52 (1-6) were syn-
thesized according to literature procedures. The ligands were
purified by either sublimation or crystallization depending on
the ligand. p-Anisidine, isopropyl-, tert-butyl-, and cyclohexy-
lamine, 2,6-diacetylpyridine, benzyl chloride, and R,R-dichlo-
rotoluene were obtained from Aldrich and used after purifi-
cation. Hoekloos oxygen 4.8 was used.
Syn t h esis of [R h Cl(2,6-(C(R1)dNR2)2C5H 3N)] (7-12).
The following synthesis of the Rh(I) compound [RhCl(2,6-
(C(H)dN-i-Pr)2C5H3N)] (7) is representative for the method
used. Both [RhCl(cyclooctene)2]2 and [RhCl(C2H4)2]2 can be
used as starting materials. Complexes 10 and 11 are insoluble
in benzene.
To a solution of 0.20 g of [RhCl(cyclooctene)2]2 (0.27 mmol)
in 15 mL of C6H6 was added a solution of 0.13 g of the ligand
1 (0.55 mmol) in 15 mL of C6H6 heated to reflux for 30 min,
giving a very dark green solution. The reaction mixture was
concentrated to a small volume, and pentane was added, after
which fast crystallization occurred. The deposit was filtered
off, washed with pentane (3 × 2 mL), and dried in vacuo. The
product could be recrystallized from a small volume of benzene
at 7 oC as block-shaped, green crystals. Yield: 0.15 g (0.43
mmol), 78% of pure product. Yields of the other compounds
are in the range 80-90%.
C
22H21Cl3N3O2Rh (16): C, 46.46; H, 3.72; N, 7.38. Found: C,
45.37; H, 3.72; N, 7.15. Accurate elemental analyses of 14 and
17 could not be obtained, due to cocrystallization of irregular
amounts of solvent. Elemental analyses of 15 and 18 were
not carried out, because the spectroscopic data (1H and 13C
NMR) for 15 and 18 are very similar to those for 13 and 16.
FAB+ (m/z obsd, calcd) 14 (C16H25Cl3N3Rh - Cl) 432.0485,
432.0473; 15 (C20H29Cl3N3Rh - H), 518.0355, 518.0397; 16
(C22H21Cl3N3O2Rh - Cl) 532.0021, 532.0058; 17 (C24H25Cl3N3O2-
Rh + H) 596.0118, 596.0138; 18 (C16H25Cl3N3Rh-H) 466.0014,
466.0084.
Syn t h esis of [R h Cl2(CHCl2)(2,6-(C(R1)dNR2)2C5H3N)]
(19-21). A representative method is given for complex [RhCl2-
(CHCl2)(2,6-(C(H)dN-i-Pr)2C5H3N)] (19). A 0.12 g portion of
7 (0.34 mmol) was dissolved in 40 mL of CHCl3 at -60 oC.
The green solution was warmed to room temperature. After
8 h the solution had turned yellow-orange. The reaction
mixture was concentrated to a minimum volume, and cooling
gave the product analytically pure as block-shaped crystals.
Isolated yield: 0.11 g (0.22 mmol), 65%. The yields of the other
compounds are about 70-80%.
Anal. Calcd for C14H20Cl4N3Rh (19): C, 35.40; H, 4.25; N,
8.85. Found: C, 35.46; H, 4.29; N, 8.78. Elemental analysis
of 21 did not give very satisfactory results, owing to solvent
incorporation. Elemental analysis of 20 was not carried out,
since the spectroscopic data (1H and 13C NMR) for 20 are very
similar to those for 19.
FAB+ (m/z obsd, calcd) 19 (C14H20Cl4N3Rh + Na) 495.9328,
495.9357; 20 (C16H24Cl4N3Rh + H) 501.9820, 501.9850; 21
(C16H24Cl4N3Rh + Na) 523.9669, 523.9670.
Syn th esis of [Rh Cl2(CH2C6H5)(2,6-(C(R1)dNR2)2C5H3N)]
(22-24). The synthesis of the complex [RhCl2(CH2C6H5)(2,6-
(C(H)dN-i-Pr)2C5H3N)] (22) is presented as an example. To
a green acetone solution (10 mL) of 0.055 g of 7 (0.15 mmol)
was added 0.023 mL of benzyl chloride (0.025 g, 0.20 mmol)
was added at -96 °C. The reaction mixture was warmed to
room temperature and stirred for 6 h, during which the color
changed to orange. Acetone was evaporated in vacuo and the
sticky residue was washed with benzene (3 × 2 mL) and
pentane (3 × 2 mL). The yellow powder obtained was dried
in vacuo. Isolated yield: 0.059 g (0.12 mmol), 80%. Other
compounds had yields varying from 70-85%.
Elemental analysis of 22-24 did not give very satisfactory
results, owing to solvent incorporation. However, FAB mea-
surements clearly established the composition of the products
formed. FAB+(m/z obsd, calcd) 22: (C20H26Cl2N3Rh - HCl)
446.0903, 446.0863; 23 (C22H30Cl2N3Rh - Cl) 474.1159,
474.1176; 24 (C22H30Cl2N3Rh - Cl) 474.1108, 474.1176.
Syn th esis of [Rh Cl2(CHClP h )(2,6-(C(R1)dNR2)2C5H3N)]
(25-27). A representative synthesis is given for complex
[RhCl2(CHClPh)(2,6-(C(H)dN-i-Pr)2C5H3N)] (25). To a green
acetone solution (10 mL) of 0.14 g of 7 (0.39 mmol) was added
0.09 mL of R,R-dichlorotoluene (0.1 g, 0.7 mmol) at -96 °C.
The reaction mixture was warmed to room temperature and
was stirred for an additional 4 h at this temperature, during
which the color changed to yellow. Acetone was evaporated
in vacuo, leaving a sticky residue that was washed with
benzene (3 × 5 mL) and pentane (3 × 5 mL). The yellow
powder obtained was dried in vacuo. Yield: 0.14 g (0.31
mmol), 79%. The yields of the other compounds are in the
range of 80-90%.
Anal. Calcd for C13H19ClN3Rh (7): C, 43.90; H, 5.39; N,
11.81. Found: C, 43.74; H, 5.30; N, 11.66. Anal. Calcd for
C
23H23ClN3O2Rh (11): C, 53.97; H, 4.53; N, 8.21. Found: C,
53.88; H, 4.59; N, 8.18. Anal. Calcd for C15H23ClN3Rh (12):
C, 46.95; H, 6.05; N, 10.95. Found: C, 46.84; H, 6.10; N, 11.06.
The spectroscopic data (1H and 13C NMR) for 9 are very similar
to those for 7, 11, and 12, and therefore, no elemental analyses
were carried out. Elemental analysis of 8 and 10 did not give
very satisfactory results, owing to solvent incorporation.
However, FAB measurements of 8 clearly established the
composition of the formed product. Complex 10 gave problems
in the FAB apparatus, and no information could be obtained.
FAB+ (m/z obsd, calcd) 8: (C15H23ClN3Rh-Cl) 348.0870,
348.0940; 9, C19H27ClN3Rh 435.0886, 435.0941.
Syn t h esis of [R h Cl2(CH2Cl)(2,6-(C(R1)dNR2)2C5H3N)]
(13-18). As an example the synthesis is given for complex
[RhCl2(CH2Cl)(2,6-(C(H)dN-i-Pr)2C5H3N)] (13). A 0.14 g amount
of 7 (0.39 mmol) was dissolved in 30 mL of dichloromethane
at -96 oC. The dark green solution was warmed to room
temperature and stirred for 16 h. The solvent was evaporated
in vacuo, leaving a sticky solid. The solid was washed with
benzene (3 × 5 mL) and pentane (3 × 5 mL). The orange
powder was dried in vacuo. Yield: 0.17 g (0.37 mmol) 94%.
(49) van der Ent, A.; Onderdelinden, A. L. Inorg. Synth. 1990, 28,
90.
Anal. Calcd for C20H25Cl3N3Rh (25): C, 46.49; H, 4.88; N,
8.13. Found: C, 47.59; H, 4.92; N, 7.95. Elemental analysis
of 26 and 27 did not give very satisfactory results, owing to
solvent incorporation. 27 gave problems in the FAB+ ap-
paratus and no information could be obtained.
(50) Cramer, R. Inorg. Synth. 1990, 28, 86.
(51) Matsumoto, I.; Yoshizaw, J . J pn. Patent 7,202,093; Chem. Abstr.
1972, 76, 126801.
(52) Lavery, A.; Nelson, S. M. J . Chem. Soc., Dalton Trans. 1985,
1053.

890 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
FAB+ (m/z obsd, calcd) 25 (C20H25Cl3N3Rh + Na) 538.0098,
538.0060; 26 (C22H29Cl3N3Rh -Cl) 508.0807, 508.078.
Syn th esis of [Rh Cl3(2,6-(C(R1)dN-R2)2C5H3N)] (28-33).
The synthesis of the complex [RhCl3(2,6-(C(H)dN-i-Pr)2C5H3N)]-
(28) is given as an example. A green benzene solution (10 mL)
of 7 (0.12 g, 0.33 mmol) was exposed to Cl2 gas, giving a yellow-
orange deposit. This deposit was washed with benzene (3 ×
3 mL) and pentane (3 × 3 mL) and dried in vacuo, giving 0.12
g of pure 28 (0.28 mmol), yield 83%. The yields of the other
complexes are in the range 70-90%.
Anal. Calcd for C13H19Cl3N3Rh (28): C, 36.60; H, 4.49; N,
9.85. Found: C, 36.54; H, 4.55; N, 9.82. Elemental analysis
of 33 did not give very satisfactory results, owing to solvent
incorporation. Elemental analyses of 29-32 were not carried
out, because the spectroscopic data (1H and 13C NMR) for 29-
32 are very similar to those for 28 and FAB measurements of
29, 30 and 33 clearly established the composition of the formed
products. 31 and 32 gave problems in the FAB+ apparatus,
and no information could be obtained.
structures were determined, although the orthorhombic modi-
fication diffracted rather poorly; only 16% of the intensity data
in the θ ) 25° region were above the 2.5σ(I) level due to severe
solvent disorder.
Crystals suitable for X-ray diffraction were glued to the tip
of a glass fiber and transferred into the cold nitrogen stream
of an Enraf-Nonius CAD4-T diffractometer on a rotating
anode. Broad, highly structured reflection profiles of varying
width were observed for the complex 7m on o, which is indicative
of a crystal consisting of several slightly misaligned individu-
als. The A-vector method58 was used to calculate for each
reflection the ψ angle for which the minimal profile width could
be expected. For all structures accurate unit cell parameters
and an orientation matrix were determined by least-squares
fitting of the setting angles of a set of well-centered reflections
(SET459). Reduced-cell calculations did not indicate higher
lattice symmetry.60 Crystal data and details on data collection
and refinement are collected in Table 1 for complexes 12, 13,
and 15 and in the Supporting Information for complexes 7m on o
,
7or th o, and 8. All data were collected at 150 K using Mo KR
radiation and a graphite monochromator.
FAB+ (m/z obsd, calcd) 28 (C13H19Cl3N3Rh + Na) 447.9655,
447.9590; 29 (C15H23Cl3N3Rh - Cl): 418.0303, 418.0316; 30
(C16H25Cl3N3Rh - HCl) 418.0337, 418.0317; 33 (C15H23Cl3N3-
Rh + H) 454.0075, 454.0084.
Data were corrected for Lp effects and for the observed
linear decay of the reference reflections. For complex 13 the
standard deviations of the intensities as obtained by counting
statistics were increased according to an analysis of the excess
variance of the reference reflections: σ2(I) ) σ2cs(I) + (0.03I)2.61
An analytical absorption correction, based on Gaussian inte-
gration techniques (ABSORB62), was applied for the complex
7or th o; empirical absorption correction was applied for com-
pounds 8, 12, 13, and 15 (DIFABS63). No absorption correction
Rea ction of 13-27 w ith H2O a n d O2. The reaction of
complex 13 is representative. Complex 13 (0.0893 g, 0.20
mmol) was heated in 10 mL of H2O at 100 °C for 1 h, while
oxygen was bubbled through. Water and volatile products
were evaporated in vacuo, and the residue was washed with
diethyl ether (3 × 2 mL) and dried in vacuo. An orange-yellow
1
product was obtained. The H NMR spectrum of the product
was applied for the complex 7m on o
.
1
was identical with the H NMR spectrum of 28. The yield is
The structures were solved by automated Patterson methods
and subsequent difference Fourier techniques (DIRDIF-9264).
Compound 13 was refined on F by full-matrix least-squares
techniques (SHELX7665). All other structures were refined on
F2 using full-matrix least-squares techniques (SHELXL-9366);
no observance criterion was applied during refinement on F2.
Hydrogen atoms were included in the refinement on calculated
positions, riding on their carrier atoms. All methyl hydrogen
atoms were refined in a rigid group, allowing for rotation
around the C-C bonds.
The asymmetric unit of 15 contains two independent
molecules, both of which display conformational disorder in
the chloromethyl moiety. A disorder model consisting of two
positions for the Cl atom and the methylene hydrogen atoms
was introduced in both independent molecules. The site
occupation factor of the major disorder component was refined
to 0.844(4) and 0.843(5) for 15a and 15b, respectively.
A difference Fourier study of 7or th o revealed a large number
of residual density peaks (∼2.4 e Å-3) in two sets of symmetry-
related interlocking channels, both running parallel to the ab
plane. No discrete solvent model could be refined. The
BYPASS procedure,67 as implemented in the program PLA-
TON,68 was used to take this electron density into account.
After the application of BYPASS the refinement became more
stable. A total of 54 electrons was found in each of the two
quantitative. In this manner complexes 14-21 and 25-27
could be converted into the corresponding complexes 28-33.
Complexes 22-24 could not be converted.
Id en tifica tion of Ben za ld eh yd e a n d H2O2 fr om Rea c-
tion of 27 w ith H2O a n d O2. In 10 mL of water 27 (0.084 g,
0.16 mmol) was dissolved in air at 100 °C. The reaction
mixture was cooled to room temperature. The volatile prod-
ucts were distilled in vacuo, and the distillate was extracted
1
with CDCl3 (2 × 0.5 mL). The H NMR of the extract showed
only benzaldehyde as a product, as concluded from comparison
with the spectrum of a sample of benzaldehyde. The amount
of H2O2 was determined by iodometry,53-55 which showed the
formation of H2O2 in 80-90% yield.
Com p u ta tion a l Deta ils. All calculations were performed
using CAChe WorkSystem software56 on an Apple Power
Macintosh 9500 equipped with 2 CAChe CXP coprocessors.
The molecular mechanics calculations were performed using
the augmented MM2 force field.57 Block-diagonal Newton-
Raphson was used as the optimization method. As imput
geometry an octahedral Rh center was used, and the N-Rh,
Cl-Rh, and C-Rh bonds and the Rh-C-Cl angle were fixed
at the values found in the X-ray crystal structures of 12 and
15. The obtained structure was optimized fully. An optimized
map search was performed to investigate the steric interac-
tions around the Rh center. The torsion angles C(7)-C(6)-
N-Rh and Cl(eq)-Rh-R3 (R3 ) Cl, CH2Cl, CHCl2, CH2Ph,
CH(Ph)Cl) were rotated stepwise (15° at a time).
(58) Duisenberg, A. J . M. Acta Crystallogr. 1983, A39, 211.
(59) de Boer, J . L.; Duisenberg, A. J . M. Acta Crystallogr. 1984, A40,
C410.
(60) Spek, A. L. J . Appl. Crystallogr. 1988, 21, 578.
(61) McCandlish, L. E.; Stout, G. H.; Andrews, L. C. Acta Crystallogr.
1975, A31, 245.
X-r a y Str u ctu r e Deter m in a tion of 7, 8, 12, 13, a n d 15.
Crystals of complex 7 were obtained in two different shapes
(from different batches), which turned out to be an ortho-
rhombic modification (7or th o, plate-shaped crystals) and a
monoclinic modification (7m on o, block-shaped crystals). Both
(62) Spek, A. L. ABSORB Program for absorption correction; Utrecht
University: Utrecht, The Netherlands, 1983; p 283.
(63) Walker, N.; Stuart, D. Acta Crystallogr. 1983, A39, 158.
(64) Beurkens, P. T.; Admiraal, G.; Beurkens, G.; Bosman, W. P.;
Garcia-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF Program System: Technical Report of the Crystallographic
Laboratory; University of Nijmegen: Nijmegen, The Netherlands, 1992.
(65) Sheldrick, G. M. SHELX76 Program for Crystal Structure
Determination; University of Cambridge: Cambridge, England, 1976.
(66) Sheldrick, G. M. SHELXL93. Program for Crystal Structure
Refinement; University of Go¨ttingen: Go¨ttingen, Germany, 1993.
(67) van der Sluis, P.; Spek, A. L. Acta Crystallogr. 1990, A46, 194.
(68) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(53) Milas, N. A. Encyclopedia of Chemical Technology; Inter-
science: New York, 1951; Vol. 7, p 727.
(54) Vogel, A. I. A Textbook of Qualitative Inorganic Analysis, 3rd
ed.; Wiley: New York, 1961; p 343.
(55) Barbaro, P.; Bianchini, C.; Frediani, P.; Meli, A.; Vizza, F. Inorg.
Chem. 1992, 31, 1523.
(56) CAChe Worksystem version 3.7, CSI, 18700 N. W. Walker Road,
Building 92-01, Beaverton, OR 97006.
(57) Burkert, U.; Allinger, N. L. Molecular Mechanics; American
Chemical Society: Washington, DC, 1982.

Addition of C-Cl Bonds to Rh Complexes
Ta ble 1. Cr ysta llogr a p h ic Da ta for 12, 13, a n d 15
12 13
Organometallics, Vol. 16, No. 5, 1997 891
15
C20H29Cl3N3Rh
Crystal Data
C14H21Cl3N3Rh
formula
mol wt
cryst syst
space group
a, Å
C15H23ClN3Rh
383.73
orthorhombic
P212121 (No. 19)
9.5744(4)
10.9998(6)
440.60
520.73
monoclinic
C2/c (No. 15)
28.461(2)
9.0062(6)
15.309(2)
116.479(10)
3512.4(6)
1.666
monoclinic
P21/c (No. 14)
16.7524(11)
18.3617(10)
15.3835(10)
110.336(5)
4437.1(5)
1.559
b, Å
c, Å
16.0668(6)
â, deg
V, Å3
1692.10(13)
1.506
D
Z
calc, g cm-3
4
8
8
F(000)
784
1776
14.1 (Mo KR)
0.03 × 0.20 × 0.38
2128
µ, cm-1
11.6 (Mo KR)
0.3 × 0.5 × 0.5
11.3 (Mo KR)
0.2 × 0.4 × 0.4
cryst size, mm
Data Collection
θ
min, θmax, deg
2.2, 27.5
11.38, 13.62 (21 rflns)
1.5, 27.5
10.02, 13.99 (25 rflns)
1.1, 27.5
11.42, 13.97 (25 rflns)
SET4 θmin, θmax deg
scan type
∆ω, deg
horiz, vert, aperture, mm
X-ray exposure, h
linear instability, %
ref rflns
ω
ω/2θ
ω/2θ
0.62 + 0.35 tan θ
0.80 + 0.35 tan θ
0.77 + 0.35 tan θ
2.30 + 1.15 tan θ, 4.00
3.23, 4.00
2.68, 4.00
11
2
38
6
59
1
062, 251, 324h
2h2h4, 42h3, 73h2
4h5h2, 3h2h5, 24h3
data set
-12 to +11, -14 to +14, -20 to 0 -36 to +36, -11 to 0, -19to +19 -21 to +20, -23 to 0, 0 to -19
total no. of data
total no. of unique data
Rint
7865
3881
0.016
8866
4020
0.131
15 319
10155
0.011
no. of obsd data
abs corr range
no crit applied
0.89, 1.16 (DIFABS)
3334 (I > 2.5σ(I))
0.67, 1.46 (DIFABS)
no crit applied)
0.90, 1.08 (DIFABS)
Refinement
no. of refined params
final R1a
187
203
495
0.0172 (3784I > 2σ(Ι))
0.0419
0.0481 (3334I > 2.5σ(Ι))
0.0274 (8825 I > 2σ(Ι))
0.0634
final wR2b
c
final Rw
0.0653
goodness of fit
1.10
4.36
1.03
w-1 d
σ2(F2) + (0.0242P)2 + 0.23P
-0.01(3)
σ2(F2) + 0.001999F2
σ2(F2) + (0.0251P)2 + 6.11P
Flack x param
(∆/σ)av, (∆/σ)max
0.000, 0.002
0.009, 0.060
-1.62, 1.42 (near Rh)
0.013, 0.519
-0.87, 0.86 (near Rh)
min and max residual density, e Å-3 -0.22, 0.32 (near Rh)
a
b
2
d
R1 ) ∑||Fo| - |Fc||/∑|Fo|. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
c Rw ) [∑[w(||Fo| - |Fc||)2]/∑[w(Fo2)]]1/2
.
P ) (Max (Fo2, 0) + 2Fc2)/3.
channel systems, which had a volume of 330 Å3 each. The
channels are probably filled with benzene, which was used in
crystallization.
PLATON68 and PLUTON;73 all calculations were performed
on a DECstation 5000 cluster.
The data set for 7or th o did not allow for anisotropic refine-
ment of the non-hydrogen atoms, except for the Rh atom. The
non-hydrogen atoms of all other structures were refined with
anisotropic thermal parameters, except for the minor disorder
component Cl atoms in 13. Hydrogen atoms of 13 were refined
with one overall isotropic thermal parameter amounting to
0.034(4) Å2. The hydrogen atoms of the other compounds were
refined with a fixed isotropic thermal displacement parameter
related to the value of the equivalent isotropic displacement
parameter of their carrier atoms by a factor of 1.5 for the
methyl hydrogen atoms and 1.2 for the other hydrogen atoms.
The Flack x parameters,69 derived during the final structure
factor calculation of 7m on o, 8, and 12, indicate correctly
assigned absolute structures. The data set of 7or th o did not
produce a reliable value for the x parameter.
Resu lts
Gen er a l Con sid er a t ion s. The numbers of the
synthesized compounds and the numbering used for the
NMR identification are given in Tables 2 and 3, respec-
tively. The NMR data have been collected in Table 4
(1H NMR) and Table 5 (13C NMR).
Syn th esis of [Rh Cl(2,6-(C(R1)dNR2)2C5H3N)] (7-
12). The novel complexes [RhCl(2,6-(C(R1)dNR2)2-
C5H3N)] (R1 ) H, R2 ) i-Pr (7), t-Bu (8), cyclohexyl (9),
p-anisyl (10); R1 ) Me, R2 ) p-anisyl (11), i-Pr (12)) were
prepared by a ligand displacement reaction in benzene
from [RhCl(cyclooctene)2]2 or [RhCl(C2H4)2]2 (Scheme 1,
for the numbering of the complexes, see Table 2). For
complete conversion the reaction mixture was heated
to reflux in benzene for 30 min, after which the Rh(I)
complexes crystallized from the warm benzene solu-
tions.
Compound 13 was refined using neutral atom scattering
factors taken from Cromer and Mann70 with anomalous
dispersion corrections from Cromer and Liberman.71 Neutral
atom scattering factors and anomalous dispersion corrections
used in the other refinements were taken from ref 72.
Geometrical calculations and illustrations were performed with
1H NMR (Table 4) is an excellent tool to determine
the geometry of the compounds, as in most cases the
signals are sufficiently separated. Coordination of the
(69) Flack, H. D. Acta Crystallogr. 1983, A39, 876.
(70) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1968, A24, 321.
(71) Cromer, D. T.; Liberman, D. J . Chem. Phys. 1970, 53, 1891.
(72) Wilson, A. J . C. International Tables for Crystallography;
Kluwer Academic: Dordrecht, The Netherlands, 1992; Vol. C.
(73) Spek, A. L. PLUTON Molecular Graphics Program; Utrecht
University: Utrecht, The Netherlands, 1995.

892 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
Ta ble 2. Nu m ber in g of Syn th esized Com p ou n d s
a n d Liga n d s
The symmetric square-planar geometry is clear from
the equivalency of the hydrogen and carbon atoms with
and without the prime (′) mark.
ligand
R1
R2
Molecu la r Geom etr y a n d Cr ysta l Str u ctu r e of 7,
8, a n d 12. The structural features of 7, 8, and 12 are
similar and are described here together. Two crystal
forms of 7, which are orthorhombic (7or th o) and mono-
clinic (7m on o) forms were determined. Because the
crystal structure of 7m on o has been determined more
accurately, only the structural data for 7m on o is given
in the Supporting Information. An ORTEP drawing of
12 along with the adopted numbering scheme is shown
in Figure 1. Selected bond distances and angles for 12
are given in Table 6, while selected bond distances
and angles for 8 are given in the Supporting Informa-
tion.
1
2
3
4
5
6
H
H
H
H
CH3
CH3
i-Pr
t-Bu
cyclohexyl
p-anisyl
p-anisyl
i-Pr
complex
R1
R2
R3
7
8
9
10
11
12
H
H
H
H
CH3
CH3
i-Pr
t-Bu
cyclohexyl
p-anisyl
p-anisyl
i-Pr
13
14
15
16
17
18
H
H
H
H
CH3
CH3
i-Pr
CH2Cl
CH2Cl
CH2Cl
CH2Cl
CH2Cl
CH2Cl
The structure determinations show that 7m on o, 8, and
12 are mononuclear, distorted-square-planar rhodium
complexes with the three N atoms of the nitrogen ligand
and a chloride atom coordinated to the Rh(I) atom. The
deviation of the rhodium atom from the least-squares
plane through N(1)-N(2)-N(3) increases from 0.024-
(1) Å for 7m on o to 0.073(1) Å for 12 and to 0.100(1) Å for
8. Also, the angle between the Rh-Cl(1) bond and the
N(1)-N(2)-N(3) plane, (φ; see Figure 2) increases from
5.34(16)° for 7m on o to 10.04(9)° for 12 and to 11.73(11)°
for 8. The comparable N(2)-Rh-N(3) angles of 158.08-
t-Bu
cyclohexyl
p-anisyl
p-anisyl
i-Pr
19
20
21
H
H
CH3
i-Pr
t-Bu
i-Pr
CHCl2
CHCl2
CHCl2
22
23
24
H
H
CH3
i-Pr
t-Bu
i-Pr
CH2Ph
CH2Ph
CH2Ph
25
26
27
H
H
CH3
i-Pr
t-Bu
i-Pr
CHClPh
CHClPh
CHClPh
(13), 157.56(8), and 158.30(6)° for the complexes 7m on o
,
8, and 12, respectively, are distorted from the ideal
angle of 180° and are in the same range as those found
for other metal 2,6-bis(R2-ethylidyneimino)pyridine (R2
) alkyl, aryl) complexes.74-76 The Rh-N and Rh-Cl
bond lengths of the complexes 7m on o and 8 and the Rh-
N(2) and Rh-N(3) bond lengths of the complex 12 are
comparable to the lengths of the Rh-N and the equato-
rial Rh-Cl bonds in the Rh(III) chloromethyl complexes
13 and 15 (see Tables 6-8), while both the Rh-N(1)
and the Rh-Cl bond lengths of the complex 12 are
slightly shorter than those found in the Rh(III) chlo-
romethyl complexes 13 and 15 (see Tables 6-8). The
N(2)-C(6) and N(3)-C(10) bond lengths of the com-
plexes 7m on o and 8 are not different from the C-N bond
lengths in the Rh(III) complexes 13 and 15, while the
N(2)-C(6) and N(3)-C(10) bond lengths of complex 12
are longer than the C-N bond lengths in the Rh(III)
complexes 13 and 15 (Tables 6-8).
Ster ic In ter a ction s in 7, 8, a n d 12. Intramolecular
distances between several substituents in 7, 8, and 12
were compared to the van der Waals radii, to analyze
possible steric interactions. In Figure 3 a space-filling
model of the X-ray structure of complex 12 is shown, in
which the interaction between the chloride atom and
the i-Pr substituents is evident. The chloride atom is
pressed out of the plane of the molecule by the i-Pr
groups. The distances between the hydrogen atoms of
the i-Pr group and the chloride in 12 are between 2.613-
(4) and 2.666(11) Å, which are 0.28-0.34 Å shorter than
the sum of the van der Waals radii. In 7, the values
are respectively 2.777(6) and 2.932(16) Å and 0.02-0.17
Å for the monoclinic modification and 2.66(5) and 2.90-
28
29
30
31
32
33
H
H
H
H
CH3
CH3
i-Pr
t-Bu
cyclohexyl
p-anisyl
p-anisyl
i-Pr
Cl
Cl
Cl
Cl
Cl
Cl
Ta ble 3. Nu m ber in g for NMR Id en tifica tion
R1
R2
R3
C(9)H2Cl
C(5)H3
(6)
(7)
(7′)
C(9)HCl2
(7)
(6)
(7)
(7)
(11′) (12′)
(10)
(6)
(7)
(7)
H2C(9)
(13)
(7)
(7)
(7)
(11) (12)
(11′) (12′)
(10)
(7′) (7′)
(6)
OC(8)H3
HClC(9)
(13)
(6)
(7) (7)
(11) (12)
ligand for the complexes 7-12 can be inferred from the
chemical shift differences of H(2), H(4), and H(5) when
compared to H(2), H(4), and H(5) of the free ligands 1-6.
Pyridine coordination is clear from the 1.5 ppm high-
field shift of H(2). The imine coordination is apparent
from a high-field shift of 0.3 ppm for H(4). For com-
3
plexes 7-10 a J Rh-H coupling constant on H(4) was
observed of about 3.5-3.9 Hz. For complexes 11 and
12 the imine coordination is obvious from a high-field
shift of 1.2 ppm for H(5). In the 13C NMR spectra the
high-field shift of C(4) and the 2J Rh-C coupling constant
on C(1) are indicative of coordination of the ligand. 13C
NMR spectra could not be measured for complexes 10
and 11 because of their low solubility.
(74) Alyea, E. C.; Ferguson, G.; Restivo, R. J . Inorg. Chem. 1975,
14, 2491.
(75) Blake, A. J .; Lavery, A. J .; Hyde, T. I.; Schro¨der, M. J . Chem.
Soc., Dalton Trans 1989, 965.
(76) Nishiyama, H.; Kondo, M.; Nakamura, T.; Itoh, K. Organome-
tallics 1991, 10, 500.

Addition of C-Cl Bonds to Rh Complexes
Organometallics, Vol. 16, No. 5, 1997 893
Ta ble 4. 1H NMR Da ta a (p p m ) of Liga n d s a n d Com p ou n d s
no.
H(2)
H(3)
7.79
H(4)/H(5)
H(9)b
other
1c
2d
3d
4d
5c
6c
7e
8e
9e
8.03
8.01
7.98f
8.25f
8.27
8.06
6.54
6.54
6.61
6.69
6.80i
6.52
7.88
7.93
7.87
8.44
8.36
8.39
8.67
2.37
2.40
H(6), 3.66 [sept, 2H]; H(7), 1.29 [d, 12H]
H(7), 1.31 [s, 18H]
7.79
7.77f
7.92f
7.89
7.68
7.65
7.74
7.68
7.69
7.78
7.69
8.07
H(6), 3.3 [m, 2H]; H(7), 1.1-2.0 [multi, 20H]
H(7), 6.97 and 7.36 [both d, 8H]; H(8), 3.86 [s, 6H]
H(7), 6.84 and 6.95 [both d, 8H]; H(8), 3.84 [s, 6H]
H(6), 3.93 [sept, 2H]; H(7), 1.24 [d, 12H]
H(6), 4.60 [sept, 2H]; H(7), 1.65 [d, 12H]
H(7), 1.90 [s, 18H]
H(6), 4.35 [m, 2H]; H(7), 1.1-2.4 [multi, 20H]
H(7), 7.99 and 6.80 [both d, 8H]; H(8), 3.28 [s, 6H]
H(7), 6.80i and 7.43 [both d, 8H]; H(8), 3.27 [s, 6H]
H(6), 4.48 [sept, 2H]; H(7), 1.98 [d, 12H]
H(6), 4.5 [m, 2H]; H(7), 1.55 [t, 12H]
8.02 (3.8)f
8.10 (3.9)f
8.02 (3.8)f
8.31 (3.5)f
1.10
10e
11e
12e
13d
14d
15d,g
16d
17d
18d
1.07
8.19 (3.2)f
4.47 (3.2)
4.93 (3.3)
4.42 (2.8)
4.33 (3.1)
4.31 (3.2)
4.6i
8.10-8.14i 8.10-8.14i
H(7), 1.72 [s, 18H]
8.06
8.14 (2.6)f
H(6), 4.06 [m, 2H]; H(7), 1.1-2.6 [m, 24 H]
H(7), 6.94 and 7.70 [d, 8H]; H(8), 3.86, [s, 3H]
H(7), 6.93 and 7.3 [br, 8H]; H(8), 3.83 [s, 6H]
H(6), 4.6i [br, 2H]; H(7), 1.57 [d, 6H], 1.64 [br, 6H]
H(6), 5.47 [sept, 1H], 4.36 [sept, 1H], 4.36 [sept, 2H];
H(7), 1.4-1.6 [m, 12H]
7.98-8.11i
8.02
7.98-8.11i 8.20 (3.3)f
8.23
8.11
2.56
2.67
7.84
18d,h,j 7.82,k 7.89k, 7.90 8.13,l 8.17 2.73,m 2.63,m 2.63 4.55 (3.2),
4.72 (3.3)
19d
20d
21d
7.91
7.99
7.87
8.14
8.21
8.17
8.22, 8.25
8.17 (3.4)f
8.11 (3.4)f
2.69
6.96k (3.3)
7.35k (3.6)
7.14k (3.5)
H(6), 4.64 [s, 2H]; H(7), 1.55[dd, 12H]
H(7), 1.67 [s, 18H]
H(6), 4.95 [br s 2H]; H(7), 1.57 [d, 6H], 1.62 [d, 6H]
H(6), 5.13 [sept, 1H], 4.29 [m, 1H]; H(6), 4.29 [m, 2H];
H(7) andH(7), 1.56-1.43 [m, 24H]
H(6), 4.56 [m, 2H]; H(7), 1.60 [d, 6H], 1.43 [d, 6H]; H(11),
6.54 [d, 2H]; H(12), 6.82 [t, 2H]; H(13), 6.94 [t, 1H]
H(7), 1.80 [s, 18H]; H(11), 6.49 [d, 2H]; H(12), 6.70 [t, 2H];
H(13), 6.85 [t, 1H]
H(6), 4.9 [br, 2H]; H(7), 1.68 [br dd, 12H]; H(11),
6.41 [d, 2H]; H(12), 6.70 [t, 2H]; 7.05 [t, 1H]
H(6), 5.57 [sept, 1H], 4.43 [sept, 1H]; H(7), 1.80
[d, 3H], 1.74 [d, 2H], 1.71 [d, 2H], 1.64 [d, 2H];
H(6), 4.43 [sept, 2H]; H(7), 1.57 [d, 6H], 1.50 [d, 6H];
H(11,12,13,11,12,13), 6.32-6.8 [m, 10H]
H(6), 4.75 [sept, 1H], 3.79 [sept, 1H]; H(7), 1.65 [d, 3H], 1.62
[d, 3H], 1.42 [d, 3H], 0.87 [d, 3H]; H(11,12,13), [br. 5H]
H(6), 4.63 [sept, 1H], 3.67 [sept, 1H]; H(7), 1.55 [m, 6H],
1.33 [d, 3H], 0.84 [d, 3H]; H(11), 7.26 [ho d, 1H],
6.67 [d, 1H]; H(12), 7.06 [m, 2H]; H(13), 6.96 [ho t, 1H]
H(7), 1.78 [s, 9H], 1.08 [s, 9H]; H(11,12,13), 7.08 [br, 5H]
21d,j,t 7.96,k 7.86,k 8.03
2.69,m 2.61,m 2.74 7.03k (3.5),
6.88k (3.2)
22d
23d
24d
7.58
7.39
7.37
7.84
7.96 (2.6)f
7.95 (3.5)f
2.68
3.36 (3.3)
4.06 (3.4)
3.64
7.70
7.73
24d,n,j 7.37, 7.39
7.74, 7.72
2.60, 2.53, 2.53
3.50 (3.2),
3.79 (3.2)
25d
7.88,k 7.70k
7.91,k 7.70k
8.04
8.03
8.21k (3.2),f
7.73k (3.0)f
8.22k (3.2),f
7.74k (3.2)f
6.53k (4.3)
6.42k (4.3)
25d,o
26d
27d
7.97k7.91k
8.18
8.08k (3.4),f
7.93k (3.0)f
2.70,m 2.42m
6.87k (4.3)
6.66k (3.6)
7.83,p 7.62q
8.06r
H(6), 4.9 [br, 1H], 4.70 [sept, 1H]; H(7), 1.72 [d, 3H],
1.69 [d, 3H], 1.47 [br d, 3H], 0.73 [br 3H]; H(11,12,13),
7.03 [br, 5H]
27d,n,j 7.98,k 7.82,k
8.21, 7.79
2.64,m 2.34,m
6.64 (4.5),
6.30 (4.3)
H(6), 4.45 [sept, 1H], 5.3u [1H]; H(7), 1.81 [br d, 3H], 1.48
[d, 3H], 1.22 [d, 3H], 0.12 [d, 3H]; H(11), 7.44 [d, 1H],
7.05i [d, 1H]; H(12), 7.05i [m, 2H]; H(13), 6.54 [ho t, 1H];
H(6), 4.34 [br, 2H]; H(7), 1.66-1.56 [br m,12H]; H(11),
7.81 [m, 2H]; H(12), 6.45 [m, 2H]; H(13), 6.60 [ho t, 1H]
H(6), 4.33 [sept, 2H]; H(7), 1.55 [d, 12H]
7.61,k 7.12k
2.69,m 2.34m
28s
29s
30d
31s
32s
33d
8.23
8.27
7.95
8.38
8.42
7.95
8.38
8.42
8.15
8.50
8.52
8.22
8.58 (2.4)f
8.47 (2.2)f
8.13(2.6)f
8.56 (2.8)f
2.80
H(7), 1.60 [s, 18 H]
H(6), 4.32 [br t, 2H]; H(7), 2.4-0.9 [m, 20 H]
H(7), 7.78 [d, 4H], 7.30 [d, 4H]; H(8), 3.99 [s, 6H]
H(7), 7.38 [d, 4H], 7.08 [d, 4H]; H(8), 3.95 [s, 6H]
H(6), 4.4 [br, 2H]; H(7), 1.65 [br d, 6H], 1.56 [br s, 6H]
H(6), 4.36 [sept, 2H]; H(7), 1.65 [d, 12H]; H(6), 5.73
[sept, 1H], 4.36 [sept, 1H]; H(7), 1.60 [d, 6H], 1.50 [d, 6H]
H(6), 4.64 [sept, 2H]; H(7), 1.54 [d, 12H]
2.72
33d,t,j 2.26,k 7.99,k 7.93k 8.01, 8.23
2.75, 2.85,m 2.75m
33s
8.36
8.49
2.94
a
Unless otherwise specified, the spectra were recorded at room temperature at 300.13 MHz. Assignments: H(2), d, 2H; H(3), t, 1H;
3
H(4), s, 2H or with J Rh-H (Hz), d, 2H; H(5), s, 6H. Abbreviations: s ) singlet, d ) doublet, t ) triplet, dd ) double doublet, sept ) septet,
m ) multiplet, br ) broad, ho ) higher order. The atoms with the (prime) mark will not be mentioned if they have the same chemical
b 2
d
shift as the atoms without the (prime) mark. If they have different values, both shifts will be given.
J
in Hz. c CDCl3. CD2Cl2.
Rh-H
e C6D6.
J
(Hz). 263 K. 230 K. Complicated by other signals. Values for the bidentate isomer in italics. d, 1H. dd, 1H. s,
f 3
g
h
i
j
k
l
m
Rh-H
3H. 223 K. o 218 K. br d, 1H. br, 1H. br t, 1H. D2O. 183 K. Complicated by solvent signal.
n
p
q
r
s
t
u
(16) Å and 0.29-0.05 Å for the orthorhombic modifica-
tion. In 12 the shortest distance between the hydrogen
atoms of the R1 methyl substituent (see Figure 1; the
hydrogen atoms on C(11) and C(15)) and the i-Pr
hydrogen atoms is 2.036(16) Å, which is 0.36 Å shorter
than the sum of the van der Waals radii. Also, the
distance of 2.052(11) Å between the meta hydrogen atom
of the pyridine ring and the methyl substituent is 0.35
Å shorter than the sum of the van der Waals radii.
CsCl Act iva t ion b y [R h Cl(2,6-(C(R 1)dNR 2)2-
C5H3N)] (7-12). The nucleophilicity of the complexes
7-12 was studied by reaction with dichloromethane,
chloroform, benzylchloride, R,R-dichlorotoluene and chlo-
robenzene (Scheme 2, see Table 2 for numbering of the
complexes). The C-Cl bond of chlorobenzene could not
be activated.
Ch lor om et h yl Com p lexes [R h Cl2(CH 2Cl)(2,6-
(C(R1)dNR2)2C5H3N)] (13-18). The chloromethyl com-

894 Organometallics, Vol. 16, No. 5, 1997
Ta ble 5. 13C NMR Da ta a (p p m ) for Liga n d s a n d Com p ou n d s
Haarman et al.
no.
C(1)
C(2)
C(3)
C(4)
C(9)b
other
1c
2d
3d
4d
5c
6c
7e
8e
9e
155.1
156.0
155.6
155.8
156.8
156.4
122.6
137.5
159.6
C(6), 61.9; C(7), 24.5
C(6), 58.5; C(7), 30.0
C(6), 70.3; C(7), 25.3, 26.4, 35.0
C(6), 144.3, 159.9; C(7),115.2, 123.5; C(8), 56.2
C(5), 16.7; C(6), 144.3, 156.3; C(7),114.8, 121.4; C(8), 56.0
C(5), 13.1; C(6), 51.3; C(7), 23.2
C(6), 63.0; C(7), 22.7
122.0
122.4
123.0
122.7
120.8
122.6
124.1
122.5
124.2
128.9
127.7
126.9
127.5i
137.6
137.5
137.9
137.3
136.3
122.5
121.8
122.5
121.6
140.7
139.2
138.7
138.4
156.8
159.9
158.6
167.9
163.5
155.8
154.8
159.9
162.7
165.1
163.2
163.3
175.4
155.4 (3)b
155.1 (3)b
155.6 (3)b
156.4 (3)b
157.5
C(6), 66.1; C(7), 29.6
C(6), 70.6; C(7), 25.5, 25.6, 33.3
C(5), 15.6; C(6), 58.6; C(7), 22.4
C(6), 64.7; C(7), 24.5, 25.3
12e
13d
14d
41.9 (27)
39.3 (27)
40.3 (27)
42.5(28)
156.0
C(6), 70.0; C(7), 29.8
15d,f 155.9
C(6), 70.3; C(7), 26.0, 26.1, 33.2 34.5
C(5),19.3; C(6) and C(7), 114.3, 127.5,i 139.3, 160.0;
C(8),56.2
17d
17d,k 157.0
18d
157.2
123.5
139.0
138.0
176.1
172.0
42.7 (29)
40.6 (28)
C(5), 20.3; C(6) and C(7), 113.8, 114.7, 127.8, 128.4,
139.4, 159.9; C(8), 58.4
158.1
126.3h
C(5) and C(7), 18.2-22.5;i C(6), 59.8
C(5) and C(7), 17.8-22.8;i C(6), 60.1, 56.7, 60.8
18d,g,j 158.3, 157.3, 126.2, 127.4, 138.6, 138.8 174.1, 171.6, 40.6 (28),
157.7
127.4
127.6
172.2
161.4
40.9 (28)
26.7 (20)
22d,l 155.8
136.8
137.9
136.2
C(6), 63.3; C(7), 25.6, 23.7; C(10), 146.5; C(11,12),
128.4, 127.7; C(13), 126.1
23d,l 156.9
24d,l 157.7
128.0
124.4
i
163.4
171.2
22.9 (18)
C(6), 71.4; C(7), 31.8; C(10), 147.8; C(11,12), 129.2, 129.9;
C(13), 128.0
m
C(5),m C(6), 22.1, 23.0; C(10), 147.1; C(11,12), 128.7, 127.6;
C(13), 125.7
24d,n,j 157.8, 157.0,
136.6, 136.7 172.8, 170.8, 22.9 (20),
171.4 21.1 (20)
C(5), 22.3, 17.8; C(5), 18.0; C(6) and C(6), 23.6, 23.2, 22.6,
22.1, 21.4, 20.8 C(11,12,11,12),i 128.8, 127.7, 127.5,
126.6, 125.4, 124.6
157.2
a
b 1
Unless otherwise specified, the spectra were recorded at room temperature at 75.48 MHz.
J
in Hz, given in parentheses. c CDCl3.
Rh-C
CD2Cl2. e C6D6. f 263 K. 230 K. Broad. Complicated by other signals. Values for the second isomer given in italics. 200 K. 50.32
MHz. Not visible. 226 K.
d
g
h
i
j
k
l
m
n
Ta ble 6. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 12
Sch em e 1. Rea ction of th e Liga n d s 1-6 w ith
[Rh Cl(a lk en e)2]2 (Alk en e ) Cycloocten e, Eth en e)
To Yield th e Rh (I) Com p lexes 7-12a
Rh(1)-Cl(1)
Rh(1)-N(1)
Rh(1)-N(2)
Rh(1)-N(3)
2.3488(5)
1.8962(16)
2.0612(18)
2.0644(18)
N(2)-C(6)
N(3)-C(10)
C(5)-C(10)
C(1)-C(6)
1.305(3)
1.313(2)
1.455(3)
1.456(3)
Cl(1)-Rh(1)-N(1) 172.19(5) N(1)-Rh(1)-N(3)
79.37(7)
Cl(1)-Rh(1)-N(2) 100.82(5) N(2)-Rh(1)-N(3) 158.30(6)
Cl(1)-Rh(1)-N(3) 100.87(4) N(2)-C(6)-C(1) 115.36(19)
N(1)-Rh(1)-N(2) 79.19(7) N(3)-C(10)-C(5) 115.33(17)
a
For the sake of clarity the R1 and R2 substituents have
been omitted for the complexes 7-12.
F igu r e 2. Side-view drawing of 12, showing the chloride
bending out of the N(1)-N(2)-N(3) plane. The angle
between Rh(1)-Cl(1) and N(1)-N(2)-N(3) ()φ) is 10.04-
(9)°. Hydrogen atoms have been omitted for clarity.
virtually quantitative oxidative addition of dichlo-
romethane had taken place. The reaction is not revers-
ible, since in deuteriodichloromethane the RhsCH2Cl
moiety remained intact. Sometimes side products [RhCl3-
(2,6-(C(R1)dNR2)2C5H3N)] (28-33) in the range of 1-10%
yield have been observed owing to a reaction of the
chloromethyl moiety, when insufficient care was taken
to exclude water and oxygen (vide infra).
F igu r e 1. ORTEP68 drawing (50% probability level) of 12.
The hydrogen atoms have been omitted for clarity.
plexes 13-18 have been prepared by dissolving the
Rh(I) complexes 7-12 in dichloromethane at low tem-
perature (-96 °C) followed by warming to room tem-
perature, during which the color changed from dark
green to light orange. It appeared that a clean and
Characteristic of the chloromethyl complexes 13-18
is the proton signal of the chloromethyl moiety H(9) at
2
δ 4.31-4.93 with a J Rh-H coupling constant of 2.8-3.3

Addition of C-Cl Bonds to Rh Complexes
Organometallics, Vol. 16, No. 5, 1997 895
F igu r e 4. The two isomers of 18: 18a and 18b.
F igu r e 3. Space-filling model of 12 showing the steric
repulsion between the i-Pr groups and Cl(1).
Sch em e 2. Rea ction of th e Rh (I) Com p lexes 7-12
w ith R3-Cl To Yield th e Rh (III) Com p lexes 13-33a
a
For the sake of clarity the R1 and R2 substituents have
been omitted for the complexes 7-33.
F igu r e 5. ORTEP68 (50% probability level) drawing of 13.
The hydrogen atoms have been omitted for clarity.
Hz, which is in the range of reported values.31,38,77
Complexes 13-16 also show a J Rh-H coupling constant
3
Table 5) contains a bidentate ligand, because C(1) and
C(1′), C(2) and C(2′), C(4) and C(4′), and C(6) and C(6′)
are inequivalent. The shifts of C(1) and C(1′), C(2) and
C(2′), C(4) and C(4′), and C(6) and C(6′) of complex 18b
are equivalent, in accord with the terdentate coordina-
tion of the nitrogen ligand.
of about 2.6-.3 Hz on the imine H(4) hydrogen atom.
The 13C NMR spectra (Table 5) are quite difficult to
measure, owing to the low solubility of all chloromethyl
complexes and the long relaxation time of the chloro-
methyl carbon atom, which has been overcome by taking
longer D1 values. The 13C NMR spectrum of 16 could
not be measured.
The ratio between the isomers 18a and 18b is tem-
perature dependent and has been measured between
183 and 243 K in CD2Cl2. When the temperature is
lowered, the concentration of the six-coordinated Rh-
(III) isomer 18b increases with a concomitant decrease
in the concentration of the five-coordinated Rh(III)
isomer 18a . The two chloromethyl signals H(9) of 18a
at δ 4.55 ppm and H(9) of 18b at δ 4.72 ppm were chosen
as reporter signals. The thermodynamic parameters for
the equilibrium (Figure 4) are ∆H° ) 4.3 (( 0.2) kJ /
mol and ∆S° ) 17.4 (( 0.3) J /(mol K).
Molecu la r Geom etr y a n d Cr ysta l Str u ctu r e of
13. An ORTEP drawing of 13, along with the adopted
numbering scheme, is shown in Figure 5. Selected bond
distances and angles are given in Table 7. The com-
pound 13 is a mononuclear, distorted-octahedral rhod-
ium complex. In the equatorial plane a chloride atom
and the three N atoms of the terdentate 2,6-bis-
(isopropylcarbaldimino)pyridine ligand 1 are coordi-
nated to the rhodium atom with the rhodium atom
0.055(1) Å and Cl(2) atom 0.127(1) Å out of the least-
squares plane through N(1)-N(2)-N(3). The angle
between the Rh-Cl(2) bond and the N(1)-N(2)-N(3)
plane is 1.7(2)°. The N(2)-Rh-N(3) angle of 159.41-
(17)° is distorted from the ideal angle of 180° and is in
the same range as found for other metal 2,6-bis(R2-
ethylidyneimino)pyridine complexes.74-76 The chlorom-
ethyl ligand and the second chloride atom occupy the
axial positions. The Rh-C(14) distance of 2.052(5) Å
The signals of C(1), C(2), C(3), and C(4) all show a
low-field shift when compared to the corresponding
signals of the free ligand. Characteristic of the chlo-
romethyl complexes is the C(9) signal at δ 39-42 ppm
1
with a J Rh-H coupling constant of 27-29 Hz, which is
in accord with reported values.31,38,77
The signals for H(6), H(7), and H(9) of complex 18 are
broad at room temperature but sharpen at 243 K, while
at this temperature the number of signals for H(2), H(3),
and H(9) are doubled. These observations indicate the
presence of two isomers (18a and 18b). The complex 18a
(in italics in Table 4) contains a ligand which coordi-
nates in a bidentate manner, which is not uncommon
for 2,6-bis(R2-ethylidyneimino)pyridine ligands,47,78 as
may be concluded from the doublet of doublets for the
pyridine protons H(2), the two methyl signals H(5), and
the two proton signals H(6). In complex 18b the ligand
coordinates as a terdentate species, since there is only
one singlet for the methyl hydrogen atoms H(5), one
doublet for the pyridine hydrogen atoms H(2), and one
signal attributable to H(6). The signals for H(7) of
complexes 18a and 18b could not be used for further
identification, because of overlap. Low-temperature 13C
NMR spectra confirmed that complex 18a (in italics in
(77) Yoshida, T.; Ueda, T.; Adachi, T.; Yamamoto, K.; Hugushi, T.
J . Chem. Soc., Chem. Commun. 1985, 1137.
(78) Albon, J . M.; Edwards, D. A.; Moore, P. J . Inorg. Chim. Acta
1989, 159, 19.

896 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
F igu r e 6. ORTEP68 drawing (30% probability level) of 15a (left-hand side) and 15b (right-hand side). Atoms Cl(13) and
Cl(23) represent the major disorder component; atoms Cl(14) and Cl(24) represent the minor disorder component. Hydrogen
atoms have been omitted for clarity.
Ta ble 7. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 13
Ta ble 8. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d s 15a a n d 15b
Compound 15a
Rh-Cl(1)
Rh-Cl(2)
Rh-N(1)
Rh-N(2)
Rh-N(3)
Rh-C(14)
2.4974(13)
2.3646(13)
1.923(4)
2.073(4)
2.041(4)
2.052(5)
C(14)-Cl(3)
N(2)-C(6)
N(3)-C(10)
C(1)-C(6)
C(5)-C(10)
1.790(5)
1.293(7)
1.288(7)
1.467(7)
1.465(7)
Rh(1)-Cl(11)
Rh(1)-Cl(12)
Rh(1)-N(102)
Rh(1)-N(101)
Rh(1)-N(103)
2.4582(7)
2.3669(6)
1.9155(18)
2.0493(19)
2.0434(19)
Rh(1)-C(120)
C(120)-Cl(13)a
C(120)-Cl(14)b
C(113)-N(103)
2.052(3)
1.808(3)
1.668(10)
1.288(3)
Cl(11)-Rh(1)-Cl(12)
93.90(2) Cl(11)-Rh(1)-N(102) 87.50(6)
Cl(1)-Rh-Cl(2)
Cl(1)-Rh-N(2)
93.07(4)
N(3)-C(5)-C(10) 116.9(4)
Cl(11)-Rh(1)-N(101) 85.61(6) Cl(11)-Rh(1)-N(103) 91.49(6)
Cl(11)-Rh(1)-C(120) 178.84(8) Cl(12)-Rh(1)-N(102) 178.56(6)
Cl(12)-Rh(1)-N(101) 99.90(5) Cl(12)-Rh(1)-N(103) 100.09(5)
Cl(12)-Rh(1)-C(120) 85.33(8) N(101)-Rh(1)-N(102) 79.86(8)
N(101)-Rh(1)-N(103) 159.95(7) N(101)-Rh(1)-C(120) 93.67(10)
N(102)-Rh(1)-N(103) 80.19(8) N(102)-Rh(1)-C(120) 93.27(10)
N(103)-Rh(1)-C(120) 89.49(10) Rh(1)-C(120)-Cl(13)a 116.73(15)
90.06(13) Cl(1)-Rh-N(1)
86.93(13)
91.46(12)
177.61(13)
97.72(13)
79.69(18)
94.28(19)
91.01(19)
116.9(3)
Cl(1)-Rh-C(14) 178.51(16) Cl(1)-Rh-N(3)
Cl(2)-Rh-N(2)
Cl(2)-Rh-C(14)
N(1)-Rh-N(3)
N(2)-Rh-N(3)
N(3)-Rh-C(14)
N(2)-C(6)-C(1)
102.70(13) Cl(2)-Rh-N(1)
85.68(15) Cl(2)-Rh-N(3)
79.89(18) N(1)-Rh-N(2)
159.41(17) N(1)-Rh-C(14)
87.90(18) N(2)-Rh-C(14)
C(107)-N(101)
1.288(3) Rh(1)-C(120)-Cl(14)b 116.8(3)
117.4(5)
Rh-C(14)-Cl(3)
Compound 15b
Rh(2)-Cl(21)
Rh(2)-Cl(22)
Rh(2)-N(202)
Rh(2)-N(201)
Rh(2)-N(203)
2.4774(6)
2.3809(6)
1.920(2)
2.0481(19)
2.0554(19)
Rh(2)-C(220)
C(220)-Cl(23)a
C(220)-Cl(24)b
C(207)-N(201)
2.059(3)
1.728(4)
1.771(12)
1.287(3)
is shorter than the Rh-C distance of 2.161(2) Å found
for [Rh(Cl)(CH2Cl)(dmpe)2]Cl.CH2Cl2 and 2.080(6) Å
39
found for [RhCl(I)(CH2I)(CO)(PEt3)].31 The Rh-C(14)-
Cl(3) angle of 116.9(3)° is in the range observed for other
metal chloromethyl complexes (114.0(4)-120.4(5)°).79
The C(14)-Cl(3) bond of 1.790(5) Å is quite long and
falls at the high end of the 1.702(5)-1.803(8) Å range
observed for other metal chloromethyl complexes.79
Cl(21)-Rh(2)-Cl(22)
96.13(2) Cl(21)-Rh(2)-N(202) 86.37(6)
Cl(21)-Rh(2)-N(201) 90.44(5) Cl(21)-Rh(2)-N(203) 89.51(6)
Cl(21)-Rh(2)-C(220) 179.39(8) Cl(22)-Rh(2)-N(202) 177.44(5)
Cl(22)-Rh(2)-N(201) 100.73(6) Cl(22)-Rh(2)-N(203) 99.48(6)
Cl(22)-Rh(2)-C(220) 84.21(10) N(201)-Rh(2)-N(202) 79.73(8)
N(201)-Rh(2)-N(203) 159.68(8) N(201)-Rh(2)-C(220) 89.99(9)
N(202)-Rh(2)-N(203) 79.98(8) N(202)-Rh(2)-C(220) 93.28(11)
N(203)-Rh(2)-C(220) 89.93(9) Rh(2)-C(220)-Cl(23)a 118.98(18)
i
A possible steric interaction between the Pr group
and the chloromethyl moiety might be concluded from
the H(14)-H(9) distance, which is 2.375(7) Å and thus
0.03 Å shorter than would have been expected on the
basis of standard contact radii.
C(213)-N(203)
1.286(4) Rh(2)-C(220)-Cl(24)b 114.7(4)
a
b
Major disorder component. Minor disorder component.
atom is different. The angle φ (Figure 2) is reduced from
5.34(16)° in complex 7 to 1.7(2)° in complex 13.
By comparison of the molecular geometries of the
square-planar Rh(I) complex 7 and the octahedral Rh-
(III) complex 13, which both have the same ligand 1 and
a chloride atom coordinated in the equatorial plane, the
difference in oxidation state of Rh and the influence of
axial ligands in complex 13, which are a chloride atom
and a chloromethyl moiety, on the equatorial ligands
could be determined. The Rh-N bond lengths of the
coordinated ligand 1 and the Rh-Cl bond distance in
the equatorial plane are not affected by the axially
coordinated ligands or oxidation state, but the out-of-
plane bending of the equatorially coordinated chloride
Molecu la r Geom etr y a n d Cr ysta l Str u ctu r e of
15. The asymmetric unit cell of 15 contains two
independent molecules (hereafter referred to as 15a and
15b), both with disorder in the position of the chloro-
methyl group. An ORTEP drawing of both molecules
is given along with the adopted numbering in Figure 6.
Selected bond distances and angles are given in Table
8 for complexes 15a and 15b. Both independent mol-
ecules are distorted-octahedral Rh(III) complexes. The
difference between the two molecules is the conforma-
tions of the cyclohexyl group with respect to the N-C
bond. In 15b both hydrogen atoms H(6) (see Table 3)
of the cyclohexyl substituent point toward the chloro-
(79) Friedrich, H. B.; Moss, J . R. Adv. Organomet. Chem. 1991, 33,
235.

Addition of C-Cl Bonds to Rh Complexes
Organometallics, Vol. 16, No. 5, 1997 897
methyl moiety. 15a differs from 15b only in that one of
the cyclohexyl substituents is slightly rotated around
the N-C bond in such a way that H(6) is pointed toward
the chloride atom Cl(12), which is coordinated in the
equatorial plane. In both molecules the equatorial plane
contains a chloride atom and a terdentate ligand 3. In
molecule 15a the rhodium atom lies 0.045 Å and the
chloride atom Cl(12) 0.159(1) Å out of the least-squares
plane N(101)-N(102)-N(103). The angle between the
Rh-Cl(12) bond and the N-N-N plane is 2.74(10)°. In
molecule 15b the rhodium atom is situated at 0.027(1)
Å and the chloride atom Cl(22) at 0.043(1) Å out of the
least-squares plane through N(201)-N(202)-N(203).
The angle between the Rh-Cl(22) bond and the N(201)-
N(202)-N(203) plane is 1.69(9)°. The N(101)-Rh(1)-
N(103) angle of 159.95(7)° and the N(201)-Rh(2)-
N(203) angle of 159.68(8)° are distorted from 180° by
the bite of the ligand and are in the same range as found
for other metal 2,6-bis(R2-ethylidynimino)pyridine com-
plexes.74-76 The chloromethyl ligand and a second
chloride atom occupy the axial positions. The Rh(1)-
C(120) distance is 2.052(3) Å, and the Rh(2)-C(220)
distance is 2.059(3) Å. These Rh-C distances are com-
parable to the ones found in 13. The Rh(1)-C(120)-
Cl(13) angle of 116.73(15)° and the Rh(2)-C(220)-
Cl(23) angle of 118.98(18)° are in the expected range
(114.0(4)-120.4(5)°) observed for other metal chloro-
methyl complexes.79 The C(120)-Cl(13) bond of 1.808-
(3) Å is very long with respect to the range of 1.702(5)-
1.803(8) Å for other metal chloromethyl complexes.79
The length of the C(220)-Cl(23) bond at 1.728(4) Å is
as expected.79 The large difference in distances of the
CH2Cl moieties (especially in molecule 15a , but also to
a lesser extent in molecule 15b (Table 8)) is a conse-
quence of the disorder, which is described with a limited
two-site static model. We did consider a constrained
refinement. Since the C-Cl bond lengths are not very
reliable in both cases, we have in the end chosen for a
model without an extra parameter constraint.
For the equilibrium between 21a and 21b the ther-
modynamic parameters could not be measured, owing
to the small temperature range available with CD2Cl2
as solvent.
Syn th esis of Ben zyl Com p lexes 22-24. The ben-
zylrhodium complexes 22-24 could be obtained in
nearly quantitative yield by adding benzyl chloride to
a benzene or cold acetone solution of the rhodium(I)
complexes 7, 8, and 12 respectively (Scheme 2; see Table
2 for the numbering of the complexes). No side products
were observed. Complexes 22-24 are octahedral com-
plexes with the terdentate nitrogen ligand coordinated
in the equatorial plane and the η1-benzyl ligand in the
axial position, as may be concluded from the 1H and 13C
NMR spectra. For the nitrogen ligand this may be
inferred from the equivalence of the signals H/C(2) and
H/C(2′), and H/C(4) and H/C(4′), respectively. In the
case of 22 the H/C(7) and H/C(7′) signals are inequiva-
lent, which is to be expected when the two axial ligands
are not identical. The η1-coordination of the benzyl
ligand may be inferred from the equivalency of H/C(11)
and H/C(11′) and of H/C(12) and H/C(12′). Also the
chemical shifts of H(11), H(11′), H(12), H(12′), and
H(13), which all resonate in the region between 6.4 and
6.9 ppm, demonstrate that the benzyl ligand is η1-
coordinated. An η3-benzyl coordination would have
resulted in a shift of one of the aromatic hydrogens
H(11) to 2.5-3.0 ppm.80 The hydrogen atom resonance
2
H(9) of CH2Ph lies at δ 3.36-4.06 ppm with a J Rh-H
coupling constant of 3.3-3.4 Hz, while the C(9) signal
1
at δ 22.9-26.7 ppm shows a J Rh-C coupling constant
of 18-20 Hz.
The signals of H(6), H(7), and H(9) of complex 24 are
broad at room temperature, while at 223 K these signals
sharpen with a doubling of the number of signals of
H(2), H(3), and H(9), which indicates the presence of
two isomers (24a and 24b). The complex 24a (values in
italics in Table 4) contains a bidentate ligand, as is clear
from the appearance of two methyl signals H(5) and
H(5′), two septets of H(6) and H(6′), and four doublets
of H(7). In complex 24b the ligand coordinates as a
terdentate species, since the methyl hydrogen atoms
H(5) appear as one singlet, H(6) appears as one septet,
and H(7) appears as two doublets. Also, from low-
temperature 13C NMR measurements it was confirmed
that complex 24a (values in italics in Table 5) contains
a ligand which coordinates as a bidentate species, as
evidenced by the inequivalence of the signals of C(1) and
C(1′), C(4) and C(4′), and C(5) and C(5′). The terdentate
coordination for 24b may be inferred from the presence
of one signal for C(1)/C(1′), one signal for C(4)/C(4′), and
one signal for C(5)/C(5′).
Syn th esis of Dich lor om eth yl Com p lexes 19-21.
For the synthesis of the dichloromethyl complexes 19-
21 the same procedure as for the chloromethyl com-
plexes was used (Scheme 2; see Table 2 for the num-
bering of the complexes). The reaction is virtually quan-
titative and not reversible in CDCl3, as the Rh-CHCl2
moiety remains intact. In some instances 28-33 were
observed as side products. Owing to low solubility the
1
dichloromethyl complexes could only be analyzed by H
NMR (Table 4), elemental analysis, and MS-FAB+.
Characteristic of the complexes 19-21 is the 1H NMR
2
signal of Rh-CHCl2 at δ 6.96-7.35 ppm with a J Rh-H
coupling constant of 3.3-3.6 Hz.
At room temperature the signals H(2), H(3), H(5),
H(7), and H(9) of complex 21 are sharp, that for H(6),
however, is broad. At 193 K two isomers (21a and 21b)
can be identified. In complex 21a , which is the major
isomer (90-95% abundance), the ligand coordinates as
a bidentate species, as is clear from the appearance of
two doublets for H(2) and H(2′), two methyl signals H(5)
and H(5′), two septets of H(6) and H(6′), and four
doublets of H(7). Complex 21b, which occurs in 5-10%
abundance, contains a ligand which is coordinated as a
terdentate species, since H(2) appears as one doublet
while the methyl hydrogen atom H(5) appears as one
singlet and H(6) appears as one septet.
Equilibrium constants could not be derived, owing to
overlap of the relevant signals.
Syn th esis of R-Ch lor otolyl Com p lexes 25-27.
The R-chlorotolyl complexes 25-27 could be prepared
in nearly quantitative yield by adding R,R-dichlorotolu-
ene to a benzene solution of the rhodium(I) complexes
7, 8, and 12, respectively, with no formation of side
products (Scheme 2; see Table 2 for the numbering of
the complexes). The geometry of the complexes could
(80) Brookhart, M.; Buck, R. C.; Danielson, E., III. J . Am. Chem.
Soc. 1989, 111, 567.

898 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
1
be determined by H NMR, while 13C NMR data could
not be obtained due to low solubility of the complexes
25-27.
The complexes 25-27 are octahedral, with the nitro-
gen ligand coordinated in the equatorial plane and the
η1-R-chlorotolyl ligand coordinated in an axial position,
as may be concluded from the 1H patterns of the signals.
The pyridine moiety in 25-27 is coordinated to the
metal, since H(2) and H(3) in all three cases show a low-
field shift relative to the corresponding signals of the
free ligand. The imine coordination of the ligand in 25
and 26 is clear from the 3J Rh-H coupling constant of 3.0-
3.2 Hz on both H(4) and H(4′). Complex 27 shows broad
1H NMR signals for the substituents, indicating flux-
ional behavior (see below).
F igu r e 7. Minimum-energy conformations of 18, 21, 24,
and 27.
The R-chlorotolyl ligand is η1-coordinated in com-
plexes 25 and 26, because the benzylic hydrogen atom
H(9) shows coupling with rhodium (2J Rh-H ) 4.3 Hz)
and a chemical shift varying between 6.4 and 6.8 ppm.
Compared to the benzylic hydrogen, H(9) of 22 and 23,
the benzylic hydrogens H(9) of 25 and 26 resonate at
lower field. At 218 K sharp aromatic signals H(11,12,-
13) lie in the range of 6.96-7.26 ppm, which is normal
for η1-benzyl ligands.80 At room temperature these
signals are broad. The observed fluxionality is probably
due to hindered rotation around the C(9)-C(10) bond,
which is not observed for the benzyl group in 22 and
23. This is obviously due to the larger steric bulk of
the R-chlorotolyl ligand.
Sch em e 3. Rea ction of th e Rh od iu m (III)
Com p lexes 13-21 a n d 25-27 w ith Wa ter a n d
Oxygen To Yield th e Rh od iu m (III)
Com p lexes 28-33a
a
For the sake of clarity the R1 and R2 substituents have
been omitted.
At room temperature the 1H NMR spectrum of 27
shows broad signals, indicating fluxional behavior. At
178 K in CD2Cl2 the spectrum became only partially
sharp and two complexes could be identified.
as a doublet, H(5) as a singlet, H(6) as a septet and H(7)
as a doublet. Complex 33a contains a ligand, which
coordinates in a bidentate fashion, as could be deter-
mined by the appearance of H(3) as a triplet, H(2) as
two doublets, H(5) as two methyl signals, H(6) as two
septets, and H(7) as two doublets. Equilibrium con-
stants could not be calculated, owing to overlapping
signals.
By comparison with the spectrum of 25 the terdentate
geometry of the coordinated ligand of 27b could be
confirmed by a triplet for H(3), two doublets for H(2),
two singlets for H(5), and four doublets for H(7).
The geometry of 27a could not be inferred so easily
from NMR, because even at 178 K the signals H(6) and
H(7) of 27a and 27b are broad. In analogy to complex
18 we tentatively conclude that the ligand probably is
coordinated as a bidentate species, as is indicated by
two doublets for both H(2) and H(2′) and two singlets
for H(5) and H(5′).
Molecu la r Mod elin g on Com p lexes 18, 21, 24, 27,
a n d 33. The molecular mechanics calculations on 18,
21, 24, 27, and 33 showed that the methyl group R1 on
the imine position restricts the rotation of the iPr
substituent R2. In the most likely conformation of the
i-Pr group, one of the methyls is pointing toward the
axial R3 group and the other toward the axial chloride.
The substituents on the R3 group experience a steric
interaction of the methyl of the i-Pr group (Figure 7).
Rea ctivity of Com p lexes 13-27 tow a r d Oxygen
in Boilin g Wa ter . During the synthesis of the chlo-
romethyl complexes 13-18 and the dichloromethyl
complex 19 the formation of rhodium trichloride com-
plexes 28-33 was observed in irreproducible amounts.
We have found, however, that the synthesis of the
chloromethyl complexes with freshly distilled dichlo-
romethane under exclusion of air yields no trichloride
complexes. To find out the cause of this side reaction,
the chloromethyl compounds were made to react in
boiling water with and without oxygen. Only in the
presence of water and oxygen (admitted either as the
pure gas or as air) the rhodium trichloride complexes
could be isolated (Scheme 3; see Table 2 for the
numbering of the complexes). In the absence of oxygen
no stable products were isolated and formation of
rhodium black was observed, while in the absence of
water no reaction took place.
The ratio between 27a and 27b is 0.8:1 at 178 K in
CD2Cl2, which could only be measured at this low
temperature, because at higher temperatures the spec-
tra are too broad.
Oxid a tive Ad d ition of Cl2 to 6-12. The yellow
water-soluble complexes 28-33 were synthesized in
benzene by reaction of 6-12 with Cl2 gas (Scheme 2;
see Table 2 for the numbering of the complexes). The
1
coordination of the ligand could be determined by H
NMR (Table 4) as for the complexes 7-27.
The 1H NMR of complex 33 in CD2Cl2 at 298 K
showed, in addition to sharp signals for H(3) and H(2),
also broad signals for the methyl group H(5), the i-Pr
hydrogen H(6), and the methyl groups H(7), indicating
fluxional behavior. At temperatures as high as 263 K
1
the H NMR signals started to sharpen, while at 243 K
a sharp spectrum was obtained which only slightly
changed on further cooling to 183 K. Two isomers could
be identified (33b and 33a ). Complex 33b contains a
ligand that coordinates as a terdentate species, as could
be deduced from the appearance of H(3) as a triplet, H(2)

Addition of C-Cl Bonds to Rh Complexes
Organometallics, Vol. 16, No. 5, 1997 899
The dichloromethyl complexes 20 and 21 and the
R-chlorotolyl complexes 25-27 could also be converted
to the corresponding trichloride complexes by this
method. In the case of 27 also benzaldehyde and H2O2
could be identified. The benzyl complexes 22-24 obvi-
ously could not be converted in boiling water in the
presence of oxygen to the trichloride complexes, un-
doubtedly owing to the absence of a chloride atom on
the organic fragment.
the Cl atom out of plane, rather than by dissociation of
one of the side arms, which would result in energetically
unfavorable three-coordinate 14-electron complexes.
Reaction of these Rh(I) complexes with CH2Cl2,
CHCl3, benzyl chloride, and R,R-dichlorotoluene led to
the rapid and virtually quantitative formation of Rh-
(III) complexes (Scheme 2), illustrating the high nu-
cleophilicity of the Rh(I) center and therefore, the strong
electron donor capacity of these N-N-N ligands. It was
not possible to split the C-Cl bond of chlorobenzene,
which may be rationalized by the mechanistic proposal
of Milstein10 et al., which involves as intermediate a
metal centre with sufficient open space to allow binding
of the chlorobenzene via both the chloride atom and the
ipso carbon atom of the phenyl ring. This bidentate type
geometry of chlorobenzene is impossible for the Rh(I)
complexes at hand, even when one imine side arm would
dissociate.
Discu ssion
In order to create a large electron density on Rh(I)
with concomitant stronger nucleophilic behavior we
employed hemilabile 2,6-bis(R2-carbaldimino)pyridine
and 2,6-bis(R2-ethylidyneimino)pyridine ligands (2,6-
(C(R1)dNR2)2C5H3N; for R1 and R2 see Table 2) with the
two imine groups as flexible imine side arms. In this
way the ligand, when bonded as a terdentate species,
strongly donates electronic charge, while at the same
time it is able to create easily accessible coordination
sites on the Rh(I) atom. We have been able to prepare
in high yields the complexes [RhCl(2,6-(C(R1)dNR2)2-
C5H3N)] (7-12; see Table 2) by using [RhCl(alkene)2]2
containing the easily displaceable ethene or cyclooctene
as the alkene (Scheme 1). It should be noted that use
of [RhCl(COD)]2 and [RhCl(NBD)]2 (COD ) 1, 5-cyclooc-
tadiene; NBD ) bicyclo[2.2.1]hepta-2,5-diene) as start-
ing materials gives very different reaction pathways, as
will be described elsewhere.81 Also, it is essential to use
benzene as a solvent with the rigorous exclusion of
oxygen and water.
It is of interest to note that the Rh-C(14) bonds of
13 (2.052(5) Å) and of 15a (2.052(3) Å) and the Rh-
C(220) bond of 15b (2.059(3) Å) are all rather short in
comparison to the Rh-C distances for [Rh(Cl)(CH2Cl)-
(dmpe)2]Cl‚CH2Cl2 (2.161(2) Å)39 and for [RhCl(I)(CH2I)-
(CO)(PEt3)] (2.080(6) Å),31 while the C(14)-Cl(13) bond
of 13 (1.790(5) Å) and the C(120)-Cl(13) bond of the
major disorder component of 15a (1.808(3) Å) and of 15b
(C(220)-Cl(23) ) 1.728(4) Å) are rather normal in
comparison to other metal chloromethyl complexes
(1.702(5)-1.803(8) Å).79 These observations are in line
with previous proposals that one should consider a
metal carbene RhdC+Cl- type bonding as an important
resonance form79 of the RhsCH2Cl moiety. It should
be evident that the metal carbene type bonding may
cause enhanced reactivity, as will be discussed later.
From Table 2 it is clear that a variety of imine R2
substituents may be used in combination with H or Me
as R1 on the imine C atom.
In solution the Rh(III) complexes exist as one isomer
with a ligand that coordinates as a terdentate species,
according to the 1H and 13C NMR spectra, with the
exception of the compounds 18, 21, 24, 27, and 33, which
all contain two isomers as evidenced by low-temperature
NMR measurements and which all have in common the
combined presence of an i-Pr group on the R2 position
and a Me group on the R1 position. It may be concluded
from the spectra at 243 K that the isomer 18a contains
a ligand that coordinates in a bidentate manner, while
18b contains a ligand that coordinates as a terdentate
species. The thermodynamic parameters of the equi-
librium (18b a 18a ), ∆H° ) -4.3 ((0.2) kJ /mol and ∆S°
) 17.4 ((0.3) J /(mol K), clearly indicate that we are
dealing with a low-energy intramolecular interconver-
sion mechanism with the five-coordinated isomer 18a
increasing in concentration with increasing tempera-
ture, as would be expected on the grounds of the entropy
factor. Unfortunately, it was impossible to calculate the
thermodynamic parameters of the equilibria occurring
for 21, 24, 27, and 33. Although precise concentration
measurements could not be carried out, it is clear that
in all these cases sizeable amounts of the five-coordinate
isomers are present at low temperatures. It is therefore
to be expected that at ambient temperatures the five-
coordinate Rh(III) complexes are by far the dominant
ones, while the fast exchange process makes the sub-
stituents on both imine side arms magnetically equiva-
lent.
1
In solution H and 13C spectra of the Rh(I) complexes
7-12 show that the ligands are bonded as terdentate
species with no evidence of fluxionality on the NMR
time scale.
The structures of 7, 8, 12, 13, and 15, determined by
X-ray analysis, show that the oxidation state of the
metal has no influence on the RhsN and the RhsCl
bonds in the equatorial plane. The CdN bond length,
which is elongated on π-back-donation82 is between
1.295(5) and 1.313(2) Å for the Rh(I) complexes and
between 1.286(4) and 1.293(7) Å for the Rh(III) com-
plexes. Obviously the oxidation state of the metal
influences the CdN bond length only slightly or not at
all.
Rather unexpected in the first instance was that the
chloride atom in the structures of 7, 8, and 12 is bending
out of the plane of the molecule (Figure 2). Very
interesting is the fact that the bending angle φ increases
going from 7 to 12 to 8 from 5.34(16) to 10.04(9) and to
11.73(11)°, respectively. These distortions from planar-
ity appear also to have a large influence on the Rh
chemical shifts.83 In the case of 12 we also observe
steric interactions between R2 (i-Pr) and R1 (Me) and
between the H atoms of the R1 groups (Me) and the meta
H atoms of the pyridine ring. The steric strain in the
monovalent Rh(I) complexes is relieved by bending of
(81) Haarman, H. F.; Bregman, F. R.; Ernsting, J . M.; Veldman,
N.; Spek, A. L.; Vrieze, K. Organometallics 1997, 16, 54.
(82) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21, 151.
(83) Haarman, H. F.; Kaagman, J . W. F.; Ernsting, J . M.; Wilms,
M.; Vrieze, K.; Elsevier, C. J . To be submitted for publication.
A very interesting observation is that the observed
fluxional behavior which may involve an associative or

900 Organometallics, Vol. 16, No. 5, 1997
Haarman et al.
a dissociative pathway, is dependent on the size of the
axial ligands. We observe that the temperatures at
which the fluxional process reaches the slow exchange
limit is dependent on the other axial group; i.e., they
decrease in the order Cl (T ) 263 K) > CH2Cl (T ) 243
K) > CH2Ph (T ) 223 K) . CHCl2 (T ) 193 K) >
CHClPh (T ) 178 K), in other words, with increasing
size of the other axial group, as would be expected if
steric factors play a dominant role. This point will be
elaborated in more detail below.
about 90° around the C(1)-C(4) axis. In this context it
is worthwhile noting that when R1 is a Me group but
R2 is a p-anisyl group, i.e. for complexes 17 and 32, there
is no evidence for the formation of five-coordinate Rh-
(III) species. This is understandable, as the p-anisyl
group is flat and causes less steric hindrance than an
i-Pr group.46
One might also consider electronic factors with regard
to the dissociation of the imine side arm, but it is
unlikely that these play an important role in view of
the above data. If electronic factors were dominant, we
would expect the more electron withdrawing N-p-anisyl
moiety to be less strongly bonded than the strongly
electron donating N-i-Pr group.
A serendipitous discovery was that trichloride com-
plexes 28-33 were formed as minor side products of the
reaction of 7-12 with dichloromethane or chloroform,
if insufficient care was taken to exclude air and mois-
ture. Formation of rhodium trichloride complexes has
been noted before for these substrates and has been
ascribed to one-electron pathways.31,40 Recently, Mc-
Crindle et al.41,42 showed in the case of chloro(chlorom-
ethyl)palladium(II) complexes of sulfide and amine
ligands that water and air were needed to convert the
M-CH2Cl moiety to M-Cl and formaldehyde. We have
now demonstrated that the Rh(III) complexes 13-21
and 25-27 could be converted to the trichloride com-
plexes 28-33, respectively (Scheme 3). In the case of
the reaction of 27 with water and oxygen we could
conclusively demonstrate the formation of 33, benzal-
dehyde, and H2O2, which is understandable in view of
the participation of the RhdC+Cl- resonance form to
the bonding (vide supra), as has been noted before for
Pd and Pt complexes by van Leeuwen et al.43 and
McCrindle et al.41,42 This interesting reaction will be
the subject of a separate publication.84
We have carried out six single X-ray determinations
in order to obtain more quantitative information on the
steric interactions. First, the equatorial Cl atom of the
Rh(I) complexes is increasingly forced out of the N-N-N
plane with increasing steric bulk of the R2 substituents.
Second, a particularly interesting exercise is to compare
the molecular structures of the Rh(I) complex 7 and the
Rh(III) complex 13, which both contain the same ter-
dentate-bonded N-N-N ligand, i.e. with R1 ) H and
R2 ) i-Pr. An eye-catching difference is the out-of-plane
bending of the equatorial Cl atom, which lies 0.243(1)
Å above this plane in 7 and only 0.127(1) Å in 13, but
in the latter this bending is in the direction of the CH2-
Cl fragment, indicating that of the two axial fragments
the Cl atom close to the Rh(III) atom has a greater steric
bulk than the CH2Cl fragment. The introduction of two
axial ligands in 13 pushes the equatorial Cl atom back
toward the N-N-N plane, which as a result will
increase the steric interaction between the R2 and the
R1 substituents. These latter interactions will be par-
ticularly strong when R1 is a Me group. To clarify the
steric interactions, we have carried out molecular
mechanics calculations (Experimental Section). In the
case of the rhodium trichloride complex 33 one does
observe that the rotation of the i-Pr group around the
N-C bond is hindered by interactions of the Me (R1)
substituent with the methyl groups of the i-Pr group,
which is sufficient to cause partial formation of a five-
coordinate species. In the case where one of the axial
groups is a CH2Cl or a CH2Ph fragment, there are also
steric interactions between the Cl atom or Ph group with
the i-Pr group (R2). The rotation about the Rh-C bond
is even more hindered in the case where one of the axial
groups is a CHCl2 or CHClPh fragment. These calcula-
tions nicely rationalize the observed temperature se-
quence at which the slow exchange limit is reached: it
is highest for Cl (33), lower for CH2Cl (18) and CH2Ph
(24), and the lowest for CHCl2 (21) and CHClPh (27)
(vide supra). Since in all cases the equatorial Cl atom
is sterically solidly wedged between the two axial
ligands, there is for the Rh(III) complex only one way
to relieve the steric strain, and that is by dissociation
of at least one of the side arms followed by rotation of
Ack n ow led gm en t. We thank Dr. H. W. F. Fru¨hauf
for stimulating discussions, K. Goubitz for assistance
with the crystallographic database, and M. Torres
Gomez for practical assistance. This work was sup-
ported in part (A.L.S., N.V.) by the Netherlands Foun-
dation of Chemical Research (SON) with financial aid
from the Netherlands Organization for Scientific Re-
search (NWO).
Su p p or tin g In for m a tion Ava ila ble: Further details of
the structure determinations, including tables of atomic
coordinates, bond lengths and angles, and thermal parameters,
for 7m on o, 7or th o, 8, 12, 13, and 15 (29 pages). Ordering
information is given on any current masthead page.
OM9607614
(84) Haarman, H. F.; Bregman, F. R.; van Leeuwen, P. W. M. N.;
Vrieze, K. Organometallics, in press.