Inorg. Chem. 1982, 21, 3090-3094
3090
pseudo-first-order conditions with excess reductant ([Cl-] = M) was 0.94 M). The perchlorate salt ([Co,], = 5 X dissolved in water and was mixed with solutions containing hydrogen ions ([H+] = 0.1-0.9 M), chromous ions ([Cr(II)] = 0.02-0.04 M), and chloride ions. The reaction products were [(H20)&rCll2+, [CO(OH,)~]~+, and the free ligand Me3[9]aneNj in its protonated form. Kinetic data are given in Table V. The rate law (eq 2) is independent of [H+] and first order kobsd
=
kCr [Cr2+1
(2)
in [Cr2+]at constant [Cl-1. This is taken as further evidence that no bridge-cleavage processes occur in acidic solution. The cation [(Me3[9]aneN3)2C02(OH)3]3+ is reduced by the strong reductant [(H20)5CrCl]+via an outer-sphere process. It is noted that there is no experimental evidence for the reduction of a protonated species as has been proposed in ref 28. In contrast to the simple rate law eq 2 a considerably more complex expression is found for the reduction of the [([9]aneN,),C0,(0H)~]~+cation by [Cr(OH2)6]2+in the [H'] range 0.05-0.3 M (eq 3). The details of this work will be kabd
=U
+ b[H+]
c[H+][Cr(II)]
From space-fillingmodels (structure A) it can be shown that
(3)
described elsewhere.30 It is not obvious why the equilibrium eq 1 is shifted completely to the left-hand side when 1,4,7-. trimethyl-l,4,7-triazacyclononaneis the ligand L and why a value of K = 11 f 2 M-' (20 OC, p = 1.0 M) is found for the analogous complex with the nonmethylated ligand 1,4,7-triazacyclononane.6 (30) Chaudhuri, P.; Wieghardt, K.,unpublished results. (31) Thewalt, U.Z . Anorg. Allg. Chem. 1975,412, 29.
A
with Me3[9]aneN3being the ligand the product, a diaquabis(p-hydroxo) species cannot be formed because a sterically demanding CH3 group of each ligand will interfere with the steric demands of the respective aqua ligand. The same explanation may account for the unreactivity of the corresponding complexes of chromium(II1) and of rhodium( 111) toward acid-catalyzed OH-bridge cleavage. Acknowledgment. Financial support of this research by the Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie is gratefully acknowledged. Registry No. [Crz(Me3[9]aneN3)2(0H)3]13-3H20, 81898-05-7; Cr( Me3[9]aneN3)C13, 8 1915-50-6; [ Cr2(Me, [9]aneN,)2(OH)3](CIO4),, 8 1915-52-8; [Q( Me, [91aneN,),( OH),] (ClO4),,8 1898-07-9; [Rh2(Me3[9]aneN3)z(OH),](C104)3r 81898-09-1; [Rhz(Me,[9]aneN3)2(0H)3]13,8 1898-10-4. Supplementary Material Available: Listings of observed and calculated structure factors and anisotropic thermal parameters for [(Me3[9]aneN3)2Crz(OH),]13~3Hz0 (10 pages). Ordering information is given on any current masthead page.
Contribution from the Science Research Laboratory, 3M Central Research Laboratory, St. Paul, Minnesota 55 101, and the Department of Chemistry, University of Minnesota, Minneapolis, Minnesota 55455
Structure and Properties of a Palladium Methoxide Derivative, Pd2(p-CH30)2(F,acac)2. Reactions of Palladium Bis( hexafluoroacetylacetonate) with Aliphatic Alcohols A. R. SIEDLE* and L. H. PIGNOLET Received November 17, 1981 Palladium bis(hexafluoroacetylacetonate), Pd(F6acac)*, reacts with methanol at room temperature to produce P d 2 ( p CH30)2(F6acac)z. Crystal data: P&/C; u = 8.945 (4), b = 7.149 (6), c = 29.36 (1) A; @ = 93.89 (3)'; V = 1873 A3; 2 = 4. The molecule is a dimer with two methoxy groups bridging two nearly planar palladium atoms which are also attached to two g2-F6acacligands. The Pd202ring is folded along the vector passing through the bridging oxygen atoms so that the dihedral angle between the PdOz planes is 26'. In the ring, d(Pd-O), is 1.996 (7) A and d(Pd-Pd) is 2.984 (1) A. At ca. 100 OC, the palladium methoxide decomposes to palladium metal, Pd(F6acac)2,methanol, methyl formate, and dimethoxymethane. Pd(F6acac)2 and 1-propanol react in the presence of oxygen to form propyl propionate, propionaldehyde, and propyl trifluoroacetate. The complex [(Cs0s)2Pd] was prepared from croconate(2-) and Pd( F6acac)'.
'-
Introduction T h e electron-withdrawing effect of the four trifluoromethyl groups in palladium bis( hexafluoroacetylacetonate), Pd(F6acac),, leads to strong metal-centered acceptor behavior in this fluorinated organometallic compound. Facile displacement of chelating and oxygen- and carbon-bonded F6acac groups is the source of an extensive acid-base chemistry as illustrated by our previous characterization of 1:1, 2: 1, 3: 1, and 4:l adducts of Pd(F6acac), with molecular Lewis basis14 and 2:1 adducts with solid donors such as silica and a l ~ m i n a . ~ . ~
'To whom correspondence should be addressed at 3M Central Research Laboratory.
Since the hexafluoroacetylacetonate anion is a good leaving group, Pd(F6acac)' is a useful reagent in cy~lometallation~ and p-diketonate exchange reactionss and in the synthesis of highly colored (02-formazanyl)palladiumcompound^.^ The present paper extends the synthetic chemistry of Pd(F,acac), and (1) A. R. Sidle and L. H. Pignolet, Inorg. Chem., 20, 1849 (1981). (2) A. R.Sidle, R. A. Newmark, A. A. Kruger, and L. H. Pignolet, Inorg. Chem., 20, 3399 (1981). (3) A. R.Sidle, L.H. Pignolet, and R. A. Newmark, J . Am. Chem. Soc., 103, 4947 (1981). (4) A. R. Sidle and L. H. Pignolet, Inorg. Chem., 21, 135 (1982). (5) A. R.S i d e and R. A. Newmark, J. Am. Chem. Soc., 103,1240 (1981). (6) A. R. Sidle, P. M . Sperl, and T.W. Rusch, Appl. Surf. Sci., 6, 149 (1980). (7) A. R. Sidle, J . Organomet. Chem., 208, 115 (1981). (8) A. R. Sidle, Inorg. Chem., 20, 1318 (1981). (9) A. R.Sidle and L. H. Pignolet, Inorg. Chem., 20, 1318 (1981).
0020-1669/82/ 1321-3090%01.25/0 0 1982 American Chemical Society
Pd2(p-cH 3 0 ) 2 (F6acac) 2
Inorganic Chemistry, Vol. 21, No. 8, 1982 3091
F14A describes the preparation, structure, and reactivity of a novel F9A palladium alkoxide, Pd2(p-CH30)2(F6acac)2,and the reaction of P d ( F , a ~ a c )with ~ simple aliphatic alcohols. Results and Discussion Synthesis and Spectroscopic Properties of Pd2(pCH30)2(F,acac),. Attempts to effect displacement of F,acac- from Pd(F,acac), by methoxide salts in a variety of solvents led to the decomposition of the starting material and the formation of palladium metal. However, solutions of Pd(F,acac), in -x methanol deposited, upon standing at room temperature, rust-colored crystals of Pd2(p-CH30)2(F6aca~)2 (1). A similar FBB WF13C reaction employing CD30D was used to prepare Pd,(pCD,O),(F,~C~C)~ (2). The yield, based on Pd(F,acac), conFigure 1. ORTEP drawing of the molecular structure of Pd2(pCH30)2(F,aca~)~ showing the labeling scheme. Ellipsoids are drawn sumed, is 71%, but the conversion is only 40%. Efforts to with 30% probability boundaries. increase the conversion by increasing the reaction time or temperature resulted in the formation of metallic palladium as a byproduct. Solid 1 may be stored for at least several months at -20 OC but gradually decomposes at room temperature. Differential scanning calorimetry revealed a rapid and complete decomposition (vide infra) beginning at 93 'C. 1 is insoluble in methanol or acetone, and dimethyl sulfoxide solutions were unstable. The most useful solvent found was carbon tetrachloride. Characterization of the new palladium methoxide compounds was achieved by elemental analyses and by vibrational spectroscopy. The infrared spectrum of 1 showed strong bands at 1610, 1600, 1270, 1230, and 1160 cm-' due to the hexafluoroacetylacetonate ligand. A medium intensity band at 1010 cm-', assigned to the C-0 stretching in the p-CH,O group, shifts to 985 cm-' in 2 due to the increased reduced mass of the bridging group. A 1430-cm-' absorption is attributed to a symmetrical methyl deformation mode, but is 2, this band is obscured by strong CF, peaks. Bands at 2830 and 2490 cm-' may be assigned to symmetric and asymmetric Figure 2. ORTEP stereoview of the molecule. methyl C-H stretching modes, respectively. These shift to 2070 and 2320 cm-I in 2, but the shift in v, is about 100 cm-' surrounding oxygen atoms and are displaced by 0.077 (1) and smaller than expected. The hexafluoroacetylacetonate u ~ - ~0.027 (1) A, respectively, from the least-squares planes which occurs at 3140 cm-I in 1 and at 3200 cm-' in 2. Overall, the contain 0 1 , 0 2 , 0 5 , 0 6 and 0 1 , 0 2 , 0 3 , 0 4 . A table of effect on the infrared spectra of replacing p-CH30 by p-CD,O weighted least-squares planes is available as supplementary in Pd2(p-CH30)2(F,acac)2parallel that seen in the gas-phase material. The molecular geometry is shown in Figures 1 and spectra of alcohols and in high-resolution energy loss spectra 2, and selected distances and angles are given in Table I. The of C H 3 0 groups on Cu(lOO).'o four corresponding 0-Pd-0 angles around Pd 1 and Pd2 are The 'H NMR spectrum of Pd2(p-CH30)2(F6a~a~)2 in the same within experimental error and exemplify the pseucarbon tetrachloride contained two singlets at 6 2.41 and 6.14 do-twofold symmetry of the molecular structure. The F,acac in a 3:l ratio due respectively to the C H 3 0 and F6acac groups. chelate bite angles [05-Pd146 = 94.1 (2) and 03-Pd2-04 The 6.14 ppm resonance is also observed in 2, indicating that = 94.9 (2)O] are somewhat large compared with those found deuterium exchange between CD30D and the F6acac proton in other structures which contain the (F,acac)Pd moiety.'V2 has not occurred to a significant extent, a point of importance The Pdl-01-Pd2 and Pdl-02-Pd2 angles are 97.1 (2) and in our subsequent pyrolysis studies. The 19FNMR spectrum 96.5 (2)O, respectively, and the 01-Pdl-02 and 01-Pd2-02 comprised a sharp singlet at 75.0 ppm. The NMR data esangles are 79.4 (2) and 80.2 (2)'. The 01.-02 distance [2.56 tablish that 1 is a symmetrical aggregate, [Pd(1) A] is considerably shorter than the separations between (OCH,)(F,acac)], with n L 2, since the compound corre03-04 [2.93 (1) A] and 05-.06 [2.93 (1) A], and the sponding to n = 1 would be coordinatively unsaturated. Osdistance between palladium atoms is 2.984 (1) A. This dismometric and mass spectroscopic molecular weight determitance and the overall geometry of the Pd202ring argue against nations were inconclusive due to thermal instability but were any significant metal-metal bonding in 1. The Pd202ring is suggestive of a dimer. So that the palladium alkoxide could folded along the 01-02 vector so that the dihedral angle be more thoroughly characterized, a single-crystal X-ray between the Pd 1,01,02 and Pd2,O 1,02 planes is 26'. The structure determination was carried out. two halves of the molecule which are related by the pseudoDescription of the Structure. Crystalline Pd,(p-CH,O),twofold axis are each approximately planar; however, packing (F,acac), consists of discrete molecular units. The shortest forces are responsible for slight deviations. For example, the intermolecular contact is between fluorine atoms (F8B-F9A dihedral angle between the least-squares planes which contain = 2.87 (1) A) and is not unusually short. The mixed alkoxide 05,06,ClO,Cll,C12 and 01,02,05,06 is 10.5'. The dihehexafluoroacetylacetonate is clearly a dimer with bridging dral angle between the corresponding pseudo-C2-relatedplanes methoxy groups and terminal, bidentate oxygen-bonded F6acac [03,04,C5,C6,C7 and 01,02,03,04] is only 1.6'. ligands. The two palladium atoms, Pdl and Pd2, are in apThe four Pd-0 distances in the Pd202unit range from 1.982 proximately square-planar environments comprised by the four (7) to 2.005 (7) A. The avera e distance involving the bridging methoxy group is 1.996 (7) , and d(Pd-O),, involving the F,acac ligands has the same value within experimental error (10) E. A. Sexton, Surf. Sci., 88,299 (1979).
TFBA
1
3092 Inorganic Chemistry, Vol. 21, No. 8,1982
Siedle and Pignolet
Table I. Selected Distances and Anglef Distances, A
Pd 1-Pd 2 Pdl-01 Pd 2-0 1 Pdl-02 Pd 2-0 2 Pdl-05 Pdl-06 Pd2-03 Pd3-02
0 1-Pd 1-0 2 0 1-Pd 1-0 2 05-Pdl-06 01-Pdl-06 0 2-Pd 1-0 5 0 1-Pd 1-0 5 0 2-Pdl-06 03-Pd2-04 0 1-Pd 2-0 3 02-Pd2-04 0 1-Pd 2-0 4 0 2-Pd 2-0 3
2.984 (1) 2.001 (7) 1.982 (7) 2.005 (7) 1.994 (7) 2.003 (7) 1.999 (7) 1.986 (7) 1.984 (7)
79.4 (2) 80.2 (2) 94.1 (2) 93.1 (2) 93.0 (2) 171.4 (2) 171.5 (2) 94.9 (2) 92.9 (2) 92.0 (2) 171.9 (2) 173.0 (2)
0347 0 4 45 OS-ClO 06-C 12 Ol-Cl 0242 C5C6 C6C7 ClO-Cll Cll412
1.27 (1) 1.28 (1) 1.26 (1) 1.27 (1) 1.47 (1) 1.46 (1) 1.38 (1) 1.42 (1) 1.43 (1) 1.39 (1)
CSC8
c7c9 ClO-Cl3 C12C14 C8-Fb c 9-Fb C13-Fb C14-Fb 01-02 03-04 05-06
1.53 (1) 1.52 (1) 1.50 (1) 1.53 (1) 1.32 (2) 1.33 (2) 1.28 (2) 1.28 (2) 2.56 (1) 2.93 (1) 2.93 (1)
Angles, Deg
Pd1-05-C 10 Pdl-06-Cl2 Pd2-0347 Pd 2 - 0 4 4 5 Pdl-01-Pd2 Pd 1-0 2-Pd 2 Pdl-0141 Pd2-0141 Pd 1 - 0 2 4 2 Pd2-0 2-C 2 03-C7-C6 04CSC6
The numbers in parentheses are the esd's o f the last significant figure.
122.2 (7) 121.3 (7) 121.9 (7) 121.0 (7) 97.1 (2) 96.5 (2) 120.2 (6) 118.2 (6) 120.5 (6) 118.2 (6) 130 (1) 131 (1)
05-C1o-c11 0 6 4 12 4 1 1 034749 04C5C8 0 5 C l O - C 13 0 6 4 1 2 4 14 C5-C8-Fb C 7 4 9-Fb C1O C 13-Fb C 12-C 14-Fb F-C-~b CS-C6-C7 c 1O-C 11-C 12
130 (1) 131 (1) 111.7 (8) 112 (1) 113.9 (8) 114 (1) 111 (1) 112 (1) 114 (1) 113 (1) 106 (1) 121 (1) 121 (1)
Value is average involving all equivalent fluorine atoms.
[ 1.993 (7) A]. These Pd-O distances may be compared with 2.014 (6) and 1.996 (7) in [(bpy)Pd(F6aCaC)]F6aCaC,2, 2.099 ( 5 ) in the dichloromethane solvate of chloro[ 1-(diphenylphosphino)-3,3,3-trifluoropropen-2-olato](ethoxydiphenylphosphine)palladium" and 2.03 A in the dioxane solvate of chloro[ 1-(2-thiazolylazo)-2-naphtholato]palladium. l 2 The OzC3atoms which form the F6acac chelate rings are coplanar within experimental error, and the Pdl and Pd2 atoms are displaced 0.172 (1) and 0.063 (1) A from their respective planes. Compared with ionic F6acac in (4-ClC5H4N)4Pd(F6a~ac)2,4 where d(C-O),, is 1.23 (1) A and
