The first η2-CH2Cl2 adduct of Ru(II):[RuH(η2-CH2Cl2)(CO)(P(t)Bu2Me)2][BAr'4] (Ar' = 3,5-C6H3(CF3)2) and its RuH(

Full text of DOI:10.1021/ja970240n

7398
J. Am. Chem. Soc. 1997, 119, 7398-7399
The First η2-CH2Cl2 Adduct of
Ru(II):[RuH(η2-CH2Cl2)(CO)(PtBu2Me)2][BAr′4]
(Ar′ ) 3,5-C6H3(CF3)2) and Its
+
RuH(CO)(PtBu2Me)2 Precursor
Dejian Huang, John C. Huffman, John C. Bollinger,
Odile Eisenstein,* and Kenneth G. Caulton*
Department of Chemistry and Molecular Structure Center
Indiana UniVersity, Bloomington, Indiana 47405-4001
LSDSMS UMR 5636, UniVersite´ de Montpellier 2
34095 Montpellier Cedex 5, France
ReceiVed January 27, 1997
Figure 1. ORTEP drawing of the intimate ion pair [RuH(CO)(CH2-
Cl2)(PtBu2Me)2]BAr′4. Only the CH2Cl2 hydrogens are shown. Cl14-
Ru1-C2 ) 125.4 and 171.6°.
The quest for the ideal noncoordinating solvent, like that for
the ideal noncoordinating anion1 has fallen upon hard times in
that a sufficiently potent Lewis acid will find nucleophilicity
+
in even the weakest of nucleophiles. Thus, Si(iPr)3 interacts
partial decomposition. The reaction solution therefore was
centrifuged, and the solution was decanted and layered with
pentane. Crystals were obtained after the solution was kept 2
days at -20 °C. Proton NMR of this complex at 25 °C in CD2-
Cl2 shows two virtual triplets for diastereotopic tBu, one virtual
triplet for the PCH3 protons and a triplet at -19 ppm for the
Ru hydride. Proton chemical shifts show a single BAr′4
environment, and 31P{1H} and 19F NMR each give a sharp
singlet. Attempts to detect the coordinated CD2Cl2 by 13C{1H}
NMR at -90 °C were not successful, indicating that even at
this temperature the coordinated CD2Cl2 undergoes rapid
exchange with free CD2Cl2.
A well-formed single crystal from CH2Cl2/pentane used for
X-ray study of [RuH(CO)L2][BAr′4]‚2CH2Cl2 (L ) PtBu2Me)
shows14 the unit cell to contain one CH2Cl2 molecule in the
lattice, in the general region of the Ar′ rings and the other CH2-
Cl2 donating both chlorines to Ru(II), to complete a six-
coordinate octahedral geometry about the metal (Figure 1). The
Ru/Cl distances are long (2.74 Å) and the C-Cl distances
(1.756(27) Å) are not lengthened from those in free CH2Cl2.
The Cl-Ru-Cl angle is quite acute (63°). This “salt” is
sufficiently soluble in benzene to obtain NMR spectra, which
is probably because the BAr′4 anion interacts in a pairwise
space-filling manner with the cation: two phenyl rings adopt
an atypical rotational conformation about their B-C(ipso) bonds
to form a crevice, into which the CH2Cl2 ligand fits like a knife
edge. This directs each (acidic) dichloromethane hydrogen
toward the center of a phenyl ring, to form a hydrogen bond to
the arene π-system (the distances from dichloromethane hy-
drogens to the centers of phenyl rings are 2.71 Å). Thus, even
in the solid state, an intimate ion pair is formed.
with toluene,2 CH4 interacts with Cr(CO)5,3 HB(C6F5)3- interacts
with Cp*2ZrH+,4 and halocarbon solvents (CH2Cl2) have been
shown to bind in a bidentate manner to Ag(I)5 and monodentate
in [(iPr3P)2PtH(η1-CH2Cl2)][BAr′4]6 and [Cp*Ir(PMe3)(CH3)(η1-
CH2Cl2)][BAr′4].7 Indeed, this has led Strauss to suggest a
redefinition of the concept of coordinative unsaturation (i.e.,
not simply having a 16-valence electron count).8 We report
here our efforts to make and isolate a 14-electron species for
metals earlier in the transition series than Cu+, Ag+, or Au+
(which often show 14-electron counts) and the consequent first
observation of CH2Cl2 as a bidentate ligand9 to a single platinum
group metal ion.
10
Reaction of RuHF(CO)L2 (L ) PtBu2Me) with 1 equiv of
Me3SiOTf produces quantitatively RuH(OTf)(CO)L2.11 The
latter undergoes metathesis with 1 equiv of NaBAr′4 (Ar′ )
3,5-C6H3(CF3)2)12 in CH2Cl2 at room temperature to give
[RuH(CO)(CH2Cl2)L2][BAr′4]13 in quantitative yield in 5 min.
The orange complex is highly sensitive to the air. Moreover,
filtration of the reaction mixture through Celite also causes
* Corresponding authors: caulton@indiana.edu; eisenst@lsd.univ-
mntp2.fr.
(1) Strauss, S. H. Chem. ReV. 1993, 93, 927.
(2) Lambert, J. B.; Zhang, S.; Stern, C. L.; Huffman, J. C. Science 1993,
260, 1917. Cacare, F.; Attina, M.; Fornarini, S. Angew. Chem., Int. Ed.
Engl. 1995, 34, 654.
(3) Brookhart, M.; Chandler, W.; Kessler, R. J.; Liu, Y.; Pienta, N.;
Santini, C.; Hall, C.; Perutz, R.; Timney, J. A. J. Am. Chem. Soc. 1992,
114, 3802.
(4) Yang, X.; Stern, C. L.; Marks, T. J. Angew. Chem., Int. Ed. Engl.
1992, 31, 1375.
(5) (a) Colsman, M. R.; Newbound, T. D.; Marshall, L. J.; Noirot, M.
D.; Miller, M. M.; Wulfsberg, G. P.; Frye, J. S.; Anderson, O. P.; Strauss,
S. H. J. Am. Chem. Soc. 1990, 112, 2349. (b) Seggen, D. M. V.; Hurlburt,
P. K.; Anderson, O. P.; Strauss, S. H. J. Am. Chem. Soc. 1992, 114, 10995.
(6) Butts, M. D.; Scott, B. L.; Kubas, G. J. J. Am. Chem. Soc. 1996,
118, 11831.
(7) Arndtsen, B. A.; Bergman, R. G. Science 1995, 270, 1970.
(8) Strauss, S. H. Chemtracts: Inorg. Chem. 1994, 6, 1.
(9) (a) Kulawiec, R. J.; Crabtree, R. H. Coord. Chem. ReV. 1990, 99,
89. (b) Peng, T.; Winter, C. H.; Gladysz, J. A. Inorg. Chem. 1994, 33,
2534.
(10) Poulton, J. T.; Sigalas, M. P.; Folting, K.; Streib, W. E.; Eisenstein,
O.; Caulton, K. G. Inorg. Chem. 1994, 33, 1476.
The carbonyl stretching frequency (1951 cm-1) in CD2Cl2 is
much higher than that of RuH(OTf)(CO)L2 (1923 cm-1),
revealing much weaker π-donor ability of the metal in the
former. Upon standing in vacuum for 12 h, a CH2Cl2-free
complex is obtained. Elemental analysis of that solid supports
the solvent-free form.15 Furthermore, the much higher CO
stretching frequency (1971 cm-1) of this solid than that in CD2-
Cl2 solution also substantiates even lower electron density of
the metal center, consistent with the solvent-free (i.e., ligand
(11) Synthesis of RuH(OTf)(CO)L2: RuHF(CO)L2 (2.0 g, 4.3 mmol)
was dissolved in dry diethyl ether (30 mL). To the solution was added
Me3SiOTf (0.83 mL, 43 mmol) slowly via a syringe; exothermic reaction
occurred immediately (which caused reflux of the solvent if the addition
rate is fast). The solution color changed to bright yellow. After the addition
(5 min), the solution was stirred for 10 min and the volatiles were removed
in vacuo. The residue was recrystallized from diethyl ether (-40 °C) to
yield yellow needles, 2.2 g (92%). Anal. Calcd for C20H43F3O4P2RuS: C,
(13) Spectroscopic data for [RuH(η2-CD2Cl2)(CO)L2][BAr′4]: 1H NMR
(CD2Cl2, 20 °C): δ 7.70 (br, s, 8H, BAr′4-), 7.50 (br, s, 4H, BAr′4-), 1.54
(vt, N ) 4.8 Hz, 6H, PCH3), 1.30 (vt, N ) 14.4 Hz, 18H, PtBu), 1.13 (vt,
N ) 13.2 Hz, 18H, PtBu). -19.4 (br, t, JPH ) 17 Hz, 1H, Ru-H). 31P{1H}
NMR (CD2Cl2, 20 °C): 49 (s). 19F NMR (CD2Cl2, 20 °C): 62.0 (s). IR
(CD2Cl2, cm-1): ν(CO) ) 1951.
(14) Crystallographic data for C53H58BCl4F24OP2Ru (-170 °C): a )
13.639(1) Å and c ) 34.558(3) Å with Z ) 4 in space group P41212. R(F)
) 0.0462 for 1845 data with F > 2.33σ(F) and a fully anisotropic refinement
model with idealized hydrogens. A crystallographic C2 axis passes through
Ru and B; consequently, the hydride and CO ligands are disordered.
1
40.06; H, 7.23. Found: C, 40.40; H, 6.95. H NMR (C6D6, 25 °C): 1.48
(vt, N ) 5.1, PCH3), 1.13 (vt, N ) 13, 18H, PC(CH3)3), 1.00 (vt, N ) 13,
18H, PC(CH3)3), -24.7 (t, JPH ) 19 Hz, 1H, Ru-H) ppm. 31P{1H} NMR
(C6D6, 25 °C): 56.4 ppm. 19F NMR (C6D6, 25 °C): -76.6 ppm. IR
(C6D6): ν(CO) ) 1923 cm-1
.
(12) Brookhart, M.; Grant, B.; Volpe, J. Organometallics 1992, 11, 3920.
S0002-7863(97)00240-0 CCC: $14.00 © 1997 American Chemical Society

Communications to the Editor
J. Am. Chem. Soc., Vol. 119, No. 31, 1997 7399
ligands. Making the structure more planar, for instance, would
result in the occurrence of a low-lying LUMO, z2. Making the
structure more tetrahedral would create a d splitting of two
orbitals lower in energy than the other three, which is inap-
propriate for low-spin d6 complexes. [RuH(CO)L2]+ thus has
two empty orbitals which are symmetric and antisymmetric with
respect to the plane bisecting the H-Ru-C angle. These two
orbitals are adapted to make bonds to the two Cl atoms of CH2-
Cl2 or to two agostic C-H bonds. The dissociation energy for
loss of CH2Cl2 (based on DFT/Becke 3LYP calculations on
Ru(H)(CO)(CH2Cl2)(PH3)2+) is calculated to be 22.2 kcal/mol,
which is in accord with the facile loss of dichloromethane under
vacuum. The C-Cl bonds are calculated to be negligibly
stretched (1.80 Å) with respect to free CH2Cl2 (1.77 Å). The
Ru-Cl bond trans to H is longer (2.89 Å) than that trans to
CO (2.67 Å), in accord with the relative trans influence of H
and CO, and their average value is close to the experimental,
2.74 Å. The H-Ru-CO angle (85°) is not significantly
modified by binding to CH2Cl2. The experimental and calcu-
lated Cl-Ru-Cl angles are almost identical (63 and 64°,
respectively). This good agreement between several experi-
mental and calculated geometrical parameters allows reliance
on the calculated hydride position; crystallographic disorder
prevents experimental determination.
Figure 2. ORTEP drawing of [RuH(CO)(PtBu2Me)2]+. Only the
hydrogens of the agostic methyl groups are shown. The (undetected)
hydride ligand points toward the viewer.
loss) form. The 1H NMR of the solid in CD2Cl2 does not show
a signal of the CH2Cl2 (CH2Cl2 in CD2Cl2 is a singlet at 5.34
ppm, while CDHCl2 is a triplet at 5.33 ppm); this supports the
claim that CH2Cl2 removal is complete. CH2Cl2 is not essential
in the synthesis since the same CH2Cl2-free solid can also be
obtained by executing the synthesis in C6H5F layered with
pentane.
An X-ray diffraction study of the CH2Cl2-free material16
(Figure 2) shows no interaction of either the lattice C6H5F or
the BAr′4 anion with the coordination complex cation. The
The structure of this complex is especially interesting in that
the 14-electron species only rather weakly binds dichlo-
romethane, without reacting further (e.g., oxidative addition);
the weak bonding is in agreement with the poor basicity
(nucleophilicity) of CH2Cl2. The structure observed for
+
RuH(CO)L2 ion has thus been authentically “isolated”, al-
though the cation in the crystal is disordered around a center of
symmetry, which limits the quantitative features which we can
learn about structure. The phosphines bend toward one another
+
RuH(CO)(CH2Cl2)L2 is thus associated with strong Lewis
acidic properties and weak reducing ability of the Ru(H)(CO)-
t
( P-Ru-P ) 166.3(5)°), and for each phosphine, one Bu
+
L2 moiety.
group bends inward, toward Ru ( Ru-P-C ) 100.3(5) and
Since CH2Cl2 is a very poor base, the M-ClCH2Cl dative
bond has always been presumed to be weak and labile. The
only previous reports on structurally characterized bidentate
CH2Cl2 complexes (of Ag(I)) show that the structure of
coordinated CH2Cl2 only slightly deforms from that of free CH2-
Cl2. The other common feature is that all CH2Cl2 complexes
are cationic. In contrast, Waters et al. reported an Ru3 cluster
with a bridging CH2Cl2.19 The CH2Cl2 is bound tightly to the
three Ru by donating four lone pairs (two from each Cl), and
thus, significant structural change of this CH2Cl2 is observed.
t
96.4(5)° compared to 119.7(8) and 116.4(8)° for the second -
Bu groups). As a result, there are two short Ru-CH3(tBu)
distances (2.74(2) and 2.85(2) Å) which speak for the 14-
electron cation RuH(CO)(PtBu2Me)2+ forming two agostic inter-
actions to methyl C-H bonds. This gives Ru‚‚‚H(CH3)
distances of approximately 2.17 Å. The authentic 14-electron
species is thus too electron deficient to exist when L ) PtBu2-
Me.
+
The structure of the model species RuH(CO)(PH3)2 was
optimized with DFT/Becke3LYP calculations with Cs sym-
metry.17 This four-coordinate 14-electron species was found
to have the (nonintuitive) nonplanar structure18 which is a
fragment of an octahedron (H-Ru-C ) 87°; P-Ru-P ) 173°)
with two empty sites trans to the ligands of largest trans effect.
This unusual structure is preferred because it permits the six
electrons in the d shell to be in d orbitals which are nonbonding
with respect to the ligands, or which are even stabilized by back-
donation into CO, and it also creates the largest HOMO-LUMO
gap since all empty orbitals are strongly antibonding with the
Acknowledgment. This work was supported by the National
Science Foundation and by material support from Johnson Matthey/
Aesar. We thank the NSF and the CNRS for support of the U.S./France
collaboration through an international NSF/PICS grant.
Supporting Information Available: Tables giving full crystal-
lographic details and anisotropic thermal parameters for the two
structures reported (15 pages). See any currect masthead page for
ordering or Internet access instructions.
(15) Synthesis of [RuH(CO)L2][BAr′4]: RuH(OTf)(CO)L2 (200 mg, 0.33
mmol) and NaBAr′4 (300 mg, 0.34 mmol) were mixed with CH2Cl2 (10
mL) in a test tube in an Ar-filled glovebox. The mixture was shaken for 5
min before it was centrifuged. The resulting clear solution was carefully
decanted to a Schlenk flask (also in an Ar-filled glovebox). The solution
was then layered with pentane and stored at -20 °C for 3 days. Large
orange crystals were formed, which were filtered and washed with pentane.
The solid was dried under vacuum for 12 h to obtain CH2Cl2 free form
(240 mg, 55%). Anal. Calcd for C51H55BF24OP2Ru: C, 46.57; H, 4.22.
Found: C, 46.15; H, 4.33. IR (Nujol mull, cm-1): ν(CO) ) 1971. If the
solid is dissolved in CD2Cl2, the NMR spectra are the same as the ones
described.13
(16) Crystal data for C57H59BF25OP2Ru (-170 °C): a ) 18.744(3) Å, b
) 17.870(3) Å, c ) 18.608(3) Å, and â ) 95.48(1)° with Z ) 4 in space
group C2/c. R(F) ) 0.0789 for 2133 reflections with F > 4σ(F). Agostic
hydrogens were placed in idealized (sp3) locations with C-H ) 0.96 Å
and a staggered rotational conformation; distances involving these hydrogens
are thus unreliable.
JA970240N
(17) The calculations were performed with the Gaussian 94 package.
The pseudopotential and basis sets for Ru, P, C, O, and hydride are those
of LANL2DZ. Polarization functions were added to P, C, O, and the hydride.
The hydrogens of PH3 are calculated with a minima basis set. Optimization
was carried out at the DFT (B3LYP) level. Gaussian 94. Revision D. I.:
Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Gill, P. M. W.; Johnson, B.
G.; Robb, M. A.; Cheeseman, J. R.; Keith, T.; Peterson, G. A.; Montgomery,
J. A.; Raghavachari, K.; Al-Laham, M. A.; Zakrzewski, V. G.; Ortiz, J. V.;
Foresman, J. B.; Cioslowski, J.; Stefanov, B. B.; Nanayakkara, A.;
Challacombe, M.; Peng, C. Y.; Ayala, P. Y.; Chen, W.; Wong, M. W.;
Andres, J. L.; Replogle, E. S.; Gomperts, R.; Martin, R. L.; Fox, D. J.;
Binkley, J. S.; Defrees, D. J.; Baker, J.; Stewart, J. P.; Head-Gordon, M.;
Gonzalez, C.; Pople, J. A. Gaussian, Inc.: Pittsburgh, PA, 1995.
(18) See, however: Elian, M.; Hoffmann, R. Inorg. Chem. 1975, 14,
1058. Burdett, J. K. J. Chem. Soc., Faraday Trans. 2 1974, 1599.
(19) Brown, M.; Waters, J. M. J. Am. Chem. Soc. 1990, 112, 2442.