348
Organometallics 1986, 5, 348-355
Accurate cell dimensions and crystal orientation matrix were determined on a CAD4 diffractometer by a least-squarea treatment of 25 reflections with 0 in the range 10-15'. The intensities of reflections with h, -13 to +13, k, -21 to +21, and 1,0 to +13, with 2' < 0 < 20' were measured by the w-26 method using graphite-monochromatized Mo K a radiation. The intensities of three reflections chosen as standards were monitored every 0.83 h and showed no evidence of crystal decay. The intensities of 8060 reflections were measured of which 7318 were unique after averaging. Of these 6234 and I > 3u(I) and were used in the structure solution and refinement. Data were corrected18 for Lorentz and polarization effects and later for absorption. The crystal used for the data collection measured 0.10 X 0.20 X 0.43 mm; the maximum and minimum values of the transmission coefficients are 0.601 and 0.311, respectively. S t r u c t u r e Solution a n d Refinement. The coordinates of the three Pt atoms were deduced from a three-dimensional Patterson function computed with data which had not been corrected for absorption; the remaining non-hydrogen atoms of the cation and anions were located from neccessive rounds of structure factor and difference electron density maps. Initial isotropic full-matrix refinement of the atoms was followed by five cycles in which the non-phenyl atoms were allowed anisotropic vibration. A difference map computed at this stage showed clearly that acetone of solution had been entrapped in the crystal lattice; maxima consistent with many of the hydrogen atoms of the structure were also present. The composition of the unit cell having now been established, the data were corrected for absorption. In the final rounds of full-matrix calculations the solvate 0 and C atoms and the phenyl C atoms were allowed isotropic vibration, all other non-hydrogen atoms were allowed to vibrate anisotropically, and the 66 hydrogens of the cation were positioned (18) All calculations were made on a PDP-11/73 computer using the SDP-PLUS system, (B.A.Frenz and Associates, Inc., College Station, TX 77840, and Enraf-Nonius, Delft, Holland).
on geometrical grounds (C-H = 0.95 A) and included in the calculation (with an overall Bi, of 5.0 A') but not refined. The acetone of solvation is very loosely held in the lattice (average B , for acetone atoms 18 A2), and no allowance was made for the six acetone hydrogens. Refinement converged with R = CllFol - IFcll/CIFoI = 0.035 and R, = (xw(lFol- lFc1)2/~wlFo12)1/2 = 0.046 for the 6234 observed reflections; R = 0.044 for all reflections. The number of variables in the final rounds of refinement was 557, and the "goodness of fit" value was 1.50. The maximum shift/error ratios were 0.02 for the x coordinate of atom C93 and 0.01 for the Biso parameter of atom C103. A final difference map computed at the end of the refinement calculations had three maxima greater than 0.3 e A-3 (0.6-1.3 e A-3) near the Pt atoms but no chemically significant features. In the refinement calculations, scattering factors and anomalous dispersion corrections were taken from ref 19; the weighting scheme was of the form w = 1/[2(F0) 0.05
+
(F,2)1.
Principal dimensions for the structure are summarized in Table I. Table I1 lists the final fractional coordinates of the non-hydrogen atoms with their estimated standard deviations. Tables of all bond lengths and angles, thermal parameters, calculated hydrogen coordinates, and mean plane data and a structure factor listing are available as supplementary material.
Acknowledgment. Financial support from N.S.E.R.C. G.F. a n d R.J.P. is gratefully acknowledged.
(Canada) t o
Supplementary Material Available: Tables of all bond lengths and angles, thermal parameters, calculated hydrogen coordinates, and mean plane data and a listing of structure amplitudes (87 pages). Ordering information is given on any current masthead page. ~~~~
(19) "International Tables for X-ray Crystallography";The Kynoch Press, Birmingham, England, 1974; Vol. IV.
Metallocyclic Palladium( I I ) Complexes Possessing Six- and Seven-Membered Rings:' Synthesis and Structural Characteristics George R. Newkome,' Garry E. Kiefer, Yves A. Frere,2aMasayoshi Onishi,2bVinod K. Gupta, and Frank R. Fronczek Department of Chemistry, Louisiana State University, Baton Rouge, Louisiana 70803- 1804 Received June 10, 1985
T h e syntheses of several new cyclometalated Pd(I1) complexes, which contain either phenanthroline
or bipyridine moieties, are described. These complexes achieve partial coordination to the metal core via an sp3 carbon anionic bond(s) and form fused cyclic ring systems with overall cis geometry. The dipyridyl ethylenic and ketonic ligands undergo facile cyclometalation to generate the symmetric 5.7.5 and 5.6.5 complexes, respectively; in contrast, the potentially tetracoordinate 6.5.6 ligand systems available with phenanthroline and bipyridine yielded only a single C-Pd bond. The single-crystal X-ray structural analyses of selected complexes have afforded insight into the molecular features responsible for precluding generation of dual C-Pd bonds in the 6.5.6 system.
Introduction Up t o this point, our interest in metallocyclic palladium(I1) complexes has been limited primarily to 2,2'-bipyridine- and 1,lo-phenanthroline-based ligands capable of forming a cis 5.5.5-cumulated ring ~ y s t e m . ~These C z 5 5 5 cumulated r i n g system
(1) Chemistry of Heterocyclic Compounds series. Part 121. (2) (a) On leave from Centre de Recherche sur lea Macromolecules, Strasbourg, France, 1982-1983. (b) On leave from Nagasaki University, Nagasaki, Japan, 1982-1983. (3) Newkome, G. R.; Puckett, W. E.; Kiefer, G. E.; Gupta, V. K.; Fronczek, F. R.; Pantaleo, D. C.; McClure, G. L.; Simpson, J. B. Deutsch, W. A. Inorg. Chem. 1985, 24, 811.
0276-7333/86/2305-0348$01.50/0
prototypes were designed specifically for the encapsulation of square-planar transition-metal ions and, with t h e exception of t h e phenanthroline derivatives, have demonstrated a propensity for generating very stable tetradentate complexes in which partial coordination is achieved via sp3 0 1986 American Chemical Society
Organometallics, Vol. 5, No. 2, 1986 349
Metallocyclic Palladium(II) Complexes Scheme I
-7 R = C02Me
4 =phenonthroline L!?
5;dipyridine
\
MeCN
R
R
/ \
R
R
R
R R
B C-Pd bonds. The evidence suggests that the 5.5.5 bis C-Pd bonded phenanthroline complex cannot be prepared due to the rigidity imposed by the 5,6-bridge which prevents angular distortions necessary for C-Pd bonding to occur on both sides of the molecule. To overcome this problem, we envisioned a simple homologation of the 2,g-alkyl substituents, thereby introducing sufficient flexibility to promote the proper alignment required for C-Pd bond formation. In order to incorporate a greater variety of metals into our general approach to cyclometalation, the syntheses of new ligands that can accommodate mutable coordination geometries have been deemed necessary. Thus, we herein report the preparation and preliminary complexation studies on several new ligands capable of forming bis C-Pd bonded complexes possessing 5.6.5-, 5.75, and 6.5.6-fused tricyclic ring systems. Overall augmentation of the ligand bite has been accomplished via insertion of an ethano or carbonyl bridging unit between two pyridine rings. Results a n d Discussion
1. Substituent Homologation. Synthesis of 4 was accomplished by generating the anion of 1,1,2,2-tetracarbomethoxyethane (3)4 with NaH in THF followed by the addition of 2,9-bis(chloromethyl)-l,l0-phenanthroline (l).5 A more efficient method for the preparation of 5 proved to be our standard K2C0,/DMF procedure? from which ligand 5 was isolated (>80%) without extensive chromatographic procedures and crystallized to afford an analytical sample. The 'H N M R of 5 was surprising in that the nonequivalent methyl ester protons appear as a single spike at 6 3.73; however, upon formation of the PdClz adduct 8, the methyl groups demonstrate the anticipated disparate behavior with two distinct singlets (6 3.60, 3.86) appearing. Hence, the syn conformation of adduct 8 has (4) Newkome, G. R.; Gupta, V. K.; Fronczek, F. R. Acta Crystallogr., Cryst. Struct. Commun. 1983, C39,113. (5) Newkome, G. R.;Kiefer, G. E.; Puckett, W. E.; Vreeland, T. J . Org. Chem. 1983,48, 5112.
Sect. C
R
R R
R
2
a pronounced influence upon the molecular environment on the NMR time scale. Complexation of 4 proceeded smoothly by using PdClz and anhydrous KZCO3in CH3CN (Scheme I), whereas the bipyridine analogue gave inconsistent yields of monometalated complex 9 and normally required longer reaction times. The addition of AgN03 did not facilitate biscyclometalation although production of the intermediary monometalated complex was accelerated. Further, chloride/nitrate ligand exchange to produce complex 7 was confirmed by NMR with a noticeable upfield shift of the methylene signals (6 4.10 and 4.24) as well as an upfield shift (A6 = 0.16) for the remaining methine proton. The nitrate ligand may, therefore, relieve some of the unfavorable steric interactions since the methylene and methine protons of 7 are, on the average, closer to the chemical shift of the free ligand than those observed in complex 6. The sluggish reactivity of 5 and low yields of the Cmetalated bipyridine complex 9 are uncharacteristic in view of previous studiesF6where cyclometalation occurred rapidly under identical conditions. These observations are best rationalized in terms of the stereochemical congestion introduced by multiple methoxycarbonyl substituents juxtaposed in the immediate vicinity of the coordination sphere. Thus, even initial formation of the N-bonded palladium adduct is retarded and decreased yields of the mono C-Pd bonded complex are a direct consequence. 2. Central Bishomologation. Ligand 16 was prepared in a fashion s i m i to that reported by Baker et al.' Thus, treatment of 1,2-bis(6-methyl-2-pyridyl)-1,2-ethylene (10) with peracetic acid gave di-N-oxide 11, which underwent smooth rearrangement with acetic anhydride to afford diester 12. Following transesterification with absolute EtOH and anhydrous KzC03, the ethylene bridge was catalytically hydrogenated by using PtOz to give (60%)diol 14. Reduction of the ethylene moiety at this stage precludes the possibility of acetate rearrangement to the (6) Puckett, W. E. Ph.D. dissertation, 1983. (7) Baker, W.;Buggle, K. M.; McOmie, J. F.; Watkins, D. A. M. J.
Chem. SOC.1968,3594.
350 Organometallics, Vol. 5, No. 2, 1986
Newkome et al. Scheme I1
AcOH
Ac20
H202 CH3
\
CH3
CH3
/
0 0
OAc
CH3
Ac
I v' m' -I1
12 -
K2CO3 EtOH
SOCI,
CI
R02 H2
OH
CI
OH
HO
-
-
14
"4 R
16 -
R
/(R
(8) Newkome, G. R.;Puckett, W. E.; Kiefer, G. E.; Gupta, V. K.; Xia, Y.-J.; Coriel, M.; Hackney, M. A. J. Org. Chem. 1982, 47, 4116. (9) Taylor, H. C. R. Ph.D. dissertation, 1983. (10) (a) Offermann, W.; Vtgtle, F. J. Org. Chem. 1979, 44, 710. (b) Newkome, G. R.; Kiefer, G. E.; Xia, Y. J.; Gupta, V. K. Synthesis 1984, 676.
13
R
R
bridging methylene carbons. Subsequent treatment with S0Cl2 afforded 15, which was immediately transformed into the desired 16 with dimethyl malonate and K2C03in DMF (Scheme 11). Preparation of the bis C-Pd bonded complex 17 was readily accomplished (85%) from 16 under standard cond i t i o n ~(PdCI2/CH3CN/K2CO3). ~ Unlike the phenanthroline and bipyridine models, cyclometalation was extremely rapid and complete within 1 h with or without added AgN03. Numerous attempts at isolating the monometalated species were fruitless owing to the facile C-metalation reaction. Notably, 17 was unusually resistant to typical chemical degradation as evidenced by its prolonged stability in aqueous alcoholic solutions; under similar conditions, the 5.5.5 bipyridine and phenanthroline 5.5 cyclopalladated complexes3showed signs of decomposition. 3. Central Monohomologation. Insertion of a ketonic moiety between the two pyridine rings (e.g., dipyridyl ketone) permitted minimal expansion of the ligand bite and access to a 5.6.5 tricyclic tetradentate complex. Ligand 21 was synthesized starting from 2-bromo-6-methylpyridine ( by initial lithium-halogen exchange (BuLi) in THF at low temperature (-90 "C), followed by a double addition-elimination of the organolithium intermediate on ethyl chlor~formate.~ The ketone 19 was transformed in moderate yield to the symmetrical bis[6-(bromomethyl)-Bpyridyl] ketone (20) under standard NBS conditions.1° Treatment of 20 with diethyl malonate in DMF/K2C03gave (10% from 19) the desired ligand 21 which was transformed into the bkmetalatd 5.6.5 complex 22 with PdCl,.(C&,CN), and NaOEt in dry THF (Scheme 111). The reaction conditions were not optimized, and
HO
kPd& R
R
17 Scheme 111
u'9J I
18 -
I
CH,
CH,
19 -
-
KZC03
DMF HzC(COzEtl2
F1
FI
R=COgt
PdCIZ(PhCNl2 NoOEt/lHF
Pd R
I
R
R 22 -
,
R
R
R 21 -
further synthetic modifications to the complexation procedure were not made due to our inability to increase the yields of the very unstable bromomethyl intermediate 20. Introduction of a carbonyl unit between the pyridine rings expands the ligand "bite" to a more favorable disposition but diminishes the initial N-ligandophilicity via electron withdrawal from the already electron-deficient rings. This choice still allows the convenience of a wellstudied"J2 ligand fragment within our tetradenate framework. The expanded 5.6.5 geometry of 21 is well-suited for the preparation of the bismetalated complex, since this ring system is well documented with related tetraamine liga n d ~ This . ~ ~ring size combination may be preferred over our initial 5.5.5 system, which imposes considerable bond angle deformation of the central metal. The diminished N-electron density may reduce preliminary N-complexa(11) Newkome, G. R.;Sauer, J. D.; McClure, G. L. Tetrahedron Lett. 1973, 1599. (12) Newkome, G. R.; Taylor, H. C. R.;Fronczek, F. R.; Delord, T. J.; Kohli, D. K. J. Am. Chem. SOC.1981, 103, 7376. (13) (a) Omae, I. Chem. Rev. 1979, 79, 287. (b) Ros, R.;Renaud, J.; Roulet, R.J. Organomet. Chem. 1974, 77, C4. (c) Holton, R. A. J. Am. Chem. SOC. 1977,99,8083. (d) Schwarzenbach, D.; Pinkerton, A.; Chapius, G.; Wenger, J.; Ros, R.;Roulet, R. Inorg. Chim. Acto 1977,25,255.
Organometallics, Vol. 5, No. 2, 1986 351
Metallocyclic Palladium(II) Complexes
C23
d
'b c 3 3
Figure 1. ORTEP drawing of 6.
Figure 2. ORTEP drawing of 17.
tion when compared to 4 or 16 but does not prohibit formation of the C-Pd bonds. The majority of the known cyclometalated complexes have exploited the five-membered metallocyclic ring structure.6 The five-membered chelate ring has been shown to enhance the stability of organometallic complexes by virtue of the favorable bond angles formed with respect to the transition-metal coordination sphere. There are examples of six-membered chelate ring structures,13 whereas larger metallocyclic ring systems are less common. Our previous report of a six-membered cyclopalladated trans complex (23) was the first example of a totally
methyl-l,10-phenanthroline.16Thus, the relatively undistorted bond lengths are supportive of a complex, which is free of any geometrical constraints imposed via cyclometalation. In contrast, the previously reported complex 243 exhibits an unusually long Pd-N bond (2.225A) on the non C-Pd-bonded side, which is indicative of the increased strain inherent in the five-membered chelate ring
R
25
23
characterized, expanded chelate ring structure incorporating both the N-donor atom and an sp3 C-Pd bond.14 Similarly, the complexes reported herein are the first examples of cis geometry within fused tetradentate 6.5.6, 5.7.5, and 5.6.5 cumulated ring systems, which possess the equivalent bonding mode. Although the "five-membered chelate ring theory"16 is a useful and valid criterion for assessing the stability of latent transition-metal complexes, it should not be used as an exclusive guide for the design and synthesis of potential ligands. In fact, these five-membered chelates can actually become a hindrance to cyclometalation if other conformational restraints exist. Obviously, the probability of forming the C-Pd bond with excessively large chelate rings is remote; however, with judicious ligand design, it seems likely that the occurrence of cyclometalated complexes with six-, seven-, and possibly eight-membered chelate rings could become more frequent. 4. X-ray Structural Analysis. The structure of 6 is depicted in Figure 1. The Pd-N1 and Pd-N2 bond distances are 2.064 (5) and 2.153 (5) A,respectively, which are surprisingly close to the average Pd-N bond length (2.064 A) determined for the PdClz adduct of 2,9-di(14) Newkome, G. R.; Puckett, W. E.; Gupta, V. K.; Fronczek, F. R. Organometallics 1983, 2, 1247. (15) Matauda, S.; Kikkawa, S.;Omae, I. Kogyo Kagaku Zasshi 1966, 69, 646 [Chem. Abstr. 1966, 65,18612el. (16) Newkome, G. R.; Gupta, V. K.; Kiefer, G. E.; Fronczek, F. R.; Xia, -Y.; Watkins, S. F. Inorg. Chem., submitted for publication.
24 -
The symmetric arrangement of the ligating atoms around the palladium core in 6 is also supportive of the unperturbed bonding in the coordination sphere. Nonetheless, generation of the second C-Pd bond was not possible and can be attributed to the steric bulk of the ester groups. Close inspection of Figure 1 reveals that if the second C-Pd bond were to form, the terminal ester groups of the 2- and 9-alkyl substituents would overlap. Thus, it is clear that the steric requirements of the substituents on the methine carbon must be considerably reduced over the present case in order to permit formation of the bismetalated complex. The structure of 17 is depicted in Figure 2. Bond angles in the Pd coordination sphere are considerably distorted from ideal (90%) with N1-Pd-C1 and N2-Pd-C16 being 79.7 and 78.3O, respectively, averaged over the two independent molecules of the asymmetric unit. In addition, the average Nl-Pd-N2 angle in the seven-membered ring is 101.2O, which is noticeably larger than those observed in previous ~ t u d i e s .The ~ pyridine rings are not coplanar with the dihedral angle between the best planes defining the two rings being 132.3' in one of the independent molecules, and 138.9' in the other. Table IV summarizes the bond lengths and angles in the immediate coordination sphere of 6 and 17 for comparative purposes. Conclusion The purpose of the work described herein was to determine the feasibility of synthesizing cyclopalladated complexes containing a variety of ring sizes with overall cis geometry. We have demonstrated that the six-membered chelate ring is not unique to trans complexes alone and can be incorporated into cis complexes which exhibit stability comparable to the five-membered analogues. In addition, variations in the ligand "bite" achieved via in-
352 Organometallics, Vol. 5, N o . 2, 1986
atom Pd
c1
01 02
03 04 05 06 07 08 09 010 011 012
013 014 015 016 N1 N2
c1
c2 c3 c4 c5 C6 c7 C8 c9 c10 c11 a
X
Y
t
0.49051 (8) 0.4170 (3) 0.2637 (7) 0.2241 (7) 0.2231 (6) 0.0989 (6) 0.1934 (6) 0.3473 (6) 0.4963 (6) 0.5939 (6) 1.0159 (7) 0.9190 (7) 0.9987 (7) 0.8321 (6) 0.6382 (7) 0.7148 (7) 0.9266 (7) 0.9746 (6) 0.5101 (7) 0.6226 (7) 0.4586 (8) 0.4533 (9) 0.5016 (10) 0.5587 (9) 0.5630 (9) 0.6210 (9) 0.6808 (9) 0.7455 (10) 0.7567 (10) 0.6928 (9) 0.6128 (10)
0.33696 (6) 0.1755 (2) 0.4393 (5) 0.2787 (5) 0.4110 (6) 0.3912 (5) 0.2011 (5) 0.1362 (5) 0.3287 (5) 0.2658 (5) 0.1513 (5) 0.1964 (6) 0.3656 (6) 0.3501 (5) 0.0070 (5) 0.0136 (5) 0.0313 (5) 0.1924 (5) 0.4889 (5) 0.3806 (5) 0.5400 (7) 0.6403 (7) 0.6840 (8) 0.6343 (7) 0.5343 (7) 0.4775 (7) 0.5223 (7) 0.4679 (8) 0.3746 (8) 0.3322 (7) 0.6744 (8)
0.24845 (6) 0.2563 (2) -0.0965 (5) -0.0968 (4) 0.1839 (4) 0.0285 (5) 0.0670 (5) 0.0274 (5) -0.0193 (4) 0.1074 (4) 0.4629 (5) 0.5660 (5) 0.4553 (6) 0.3172 (5) 0.2081 (5) 0.3697 (5) 0.2580 (5) 0.2593 (5) 0.2670 (5) 0.3973 (5) 0.2016 (6) 0.2305 (7) 0.3273 (7) 0.3987 (7) 0.3659 (6) 0.4333 (6) 0.5338 (7) 0.5956 (8) 0.5572 (7) 0.4575 (7) 0.5017 (7)
N e w k o m e e t al. Table I. Coordinates for 6 B or B(eq)*, B or B(eq)*, A2 atom X Y z A2 2.68 (2)* C12 0.6711 (10) 0.6238 (8) 0.5646 (7) 4.2 (2) 4.17 (7)* C13 0.4096 (9) 0.4941 (7) 0.0953 (7) 3.4 (2) 5.2 (2)* C14 0.3192 (8) 0.3900 (7) 0.0600 (6) 3.0 (2) 4.3 (2)* C15 0.3930 (8) 0.3080 (7) 0.0972 (6) 2.8 (2) C16 0.7040 (9) 0.2293 (7) 4.8 (2)* 3.4 (2) 0.4168 (7) C17 0.8324 (9) 0.2191 (7) 4.6 (2)* 0.4006 (6) 3.2 (2) C18 0.7968 (9) 4.2 (2)* 0.1423 (7) 0.3017 (6) 3.2 (2) c19 0.2675 (9) 0.3744 (7) -0.0524 (7) 4.4 (2)* 3.9 (2) 4.2 (2)* c20 0.2087 (9) 0.3964 (7) 0.1000 (7) 3.3 (2) 4.1 (2)* c21 0.2993 (9) 0.2108 (7) 0.0652 (7) 3.4 (2) 5.0 (2)* c22 0.4957 (9) 0.0538 (6) 0.3018 (7) 3.2 (2) 0.1923 (13) 6.4 (2)* C23 0.2554 (10) -0.2021 (8) 6.5 (4)* C24 -0.0080 (11) 0.3945 (10) 0.0604 (9) 5.8 (2)* 6.5 (4)* 4.1 (2)* C25 0.2672 (12) 0.0010 (9) 0.0395 (8) 6.5 (4)* 5.4 (2)* C26 0.6957 (11) 0.2595 (9) 0.0700 (8) 5.7 (3)* 5.6 (2)* 0.4863 (7) C27 0.9254 (10) 0.1878 (7) 4.2 (3)* C28 5.6 (2)* 0.9007 (9) 0.3198 (7) 0.3946 (7) 3.7 (3)* 4.5 (2)* C29 0.7134 (10) 0.0466 (7) 0.2997 (7) 4.0 (3)* 2.9 (2) C30 0.9060 (10) 0.1139 (8) 0.2728 (7) 4.0 (3)* 2.9 (2) C31 1.1156 (12) 0.1265 (10) 0.5404 (9) 7.2 (4)* C32 0.3093 (9) 6.0 (4)* 3.0 (2) 0.8799 (12) 0.4494 (8) c33 3.9 (2) 8.5 (5)* 0.5486 (14) -0.0833 (11) 0.1906 (11) c34 4.3 (2) 1.0829 (11) 0.1751 (10) 0.2329 (9) 6.5 (4)* 0.1401 (9) 3.8 (2) 01A 0.2556 (11) 0.8025 (9) 11.3 (4) 3.1 (2) C1A 0.8163 (13) 0.1691 (12) 9.9 (5) 0.1702 (16) C2A 0.8804 (14) 3.1 (2) 10.6 (5) 0.0830 (17) 0.1357 (13) C3A 0.7238 (15) 3.5 (2) 0.1297 (19) 0.2118 (14) 12.1 (6) 0.0265 (18) OClB 4.6 (2) 0.4479 (22) 0.4754 (19) 16.1 (9) C2Ba 4.1 (2) 0.1069 (23) 0.5160 (30) 0.5405 (22) 8.5 (9) C3B" 0.3378 (39) -0.0114 (32) 0.4003 (30) 3.3 (2) 12.9 (13) 4.5 (3)
Populeition =
atom Pd Pd' 01 02 03 04 05 06 07 08 01' 02' 03'
04' 05' 06' 07' 08' N1 N2 N1' N2'
c1 c2
c3 c4 c5 C6 c7 C8 c9 c10 c11 c12
C13 C14
x
Y
0.66659 (7) 0.38683 (6) 1.0660 (7) 1.0007 (6) 0.8666 (8) 0.8387 (6) 0.8822 (6) 0.7820 (6) 0.4519 (6) 0.5312 (6) -0.0165 (6) 0.0588 (6) 0.1686 (6) 0.1935 (6) 0.2070 (6) 0.2924 (6) 0.5274 (6) 0.6195 (6) 0.6539 (7) 0.4826 (7) 0.3802 (6) 0.5849 (6) 0.8732 (8) 0.9029 (10) 0.7765 (10) 0.7880 (12) 0.6583 (13) 0.5354 (13) 0.5289 (11) 0.3932 (13) 0.3313 (13) 0.3648 (10) 0.2775 (11) 0.3032 (11) 0.4195 (10) 0.5055 (8)
0.49610 (4) 0.09243 (4) 0.6361 (4) 0.4963 (3) 0.6240 (4) 0.6896 (4) 0.6028 (4) 0.7038 (3) 0.6017 (4) 0.6501 (3) -0.0280 (3) 0.1130 (3) -0.0851 (4) -0.1089 (4) 0.0416 (4) -0.0766 (4) -0.0534 (4) 0.0016 (3) 0.4372 (4) 0.4176 (4) 0.1100 (4) 0.1818 (4) 0.5462 (5) 0.4726 (6) 0.4355 (6) 0.4011 (7) 0.3732 (8) 0.3761 (8) 0.4121 (7) 0.4240 (7) 0.3553 (8) 0.3619 (6) 0.3076 (6) 0.3066 (7) 0.3632 (6) 0.4182 (5)
Table 11. Coordinates for 17 B or B(eq)*, z A= atom X 3.60 (2)* C15 0.6299 (8) 0.23321 (4) C16 3.03 (1)* 0.6624 (8) 0.22399 (4) C17 0.9884 (9) 6.7 (2)* 0.3171 (5) 4.6 (1) 0.8610 (9) C18 0.3166 (3) 1.1162 (10) c19 0.1004 (4) 6.6 (2)* 0.8181 (11) c20 5.7 (I) 0.2308 (4) c21 0.7888 (8) 0.4558 (4) 5.4 (2)* 0.5367 (8) c22 4.6 (1) 0.4112 (3) 0.8968 (10) 5.9 (2)* C23 0.4039 (4) 0.4321 (10) 4.7 (1) C24 0.2959 (3) 0.1740 (8) 0.2429 (4) C1' 4.9 (2)* 0.1321 (8) C2' 4.2 (1) 0.2715 (3) 0.2470 (8) C3' 0.0544 (3) 4.9 (2)* 0.2246 (9) C4' 5.2 (1) 0.1854 (4) 0.3393 (9) 5.1 (2)* c5' 0.4054 (3) 0.4745 (9) 4.9 (1) C6' 0.3625 (4) 0.4928 (8) C7' 5.5 (2)* 0.2554 (4) 0.6375 (9) 4.7 (1) C8' 0.3907 (3) 0.6732 (10) C9' 4.8 (2) 0.1041 (4) 0.6813 (8) C10' 4.3 (2) 0.2657 (4) C11' 0.7893 (9) 3.2 (1) 0.0971 (4) 0.7981 (9) C12' 0.2888 (4) 3.5 (1) 0.7041 (9) C13' 0.2116 (5) 3.9 (2) 0.5934 (8) C14' 5.2 (2) 0.1431 (6) 0.4821 (9) 5.2 (2) '215' 0.0776 (6) 0.4182 (8) C16' 7.4 (3) -0.0103 (7) 0.0645 (8) C17' 8.7 (3) -0.0606 (8) 0.1776 (8) 8.1 (3) C18' -0.0375 (8) -0.0502 (10) C19' 6.8 (3) 0.0503 (7) 0.2077 (11) C20' 0.0846 (7) 8.9 (3)* 0.2939 (9) C21' 9.9 (4)* 0.1231 (9) C22' 0.5230 (8) 5.9 (2) 0.2159 (6) C23' 0.1728 (11) 6.2 (2) 0.2548 (6) C24' 6.6 (3) 0.7169 (10) 0.3342 (7) 01w -0.001 (2) 5.2 (2) 0.3859 (6) 3.9 ( 2 ) 0.3482 (5)
Estimated standard deviations in the least significant digits are shown in parentheses
B or B(eq)*, Y
2
A2
0.4826 (5) 0.5592 (5) 0.5674 (5) 0.6227 (5) 0.5050 (6) 0.7652 (5) 0.6217 (5) 0.6041 (5) 0.7683 (6) 0.7081 (6) 0.0314 (5) 0.0825 (5) 0.0960 (5) 0.0929 (5) 0.0985 (5) 0.1087 (5) 0.1152 (5) 0.1329 (6) 0.2265 (6) 0.2331 (5) 0.2968 (5) 0.3045 (6) 0.2535 (6) 0.1915 (5) 0.1363 (5) 0.0530 (5) 0.0326 (5) -0.0587 (5) 0.1186 (6) -0.1955 (5) 0.0073 (5) -0.0059 (5) -0.1259 (6) -0.0574 (6) 0.742 (1)
0.4000 (5) 0.3585 (5) 0.2868 (5) 0.1736 (5) 0.3857 (7) 0.2009 (7) 0.4118 (5) 0.3562 (5) 0.4616 (7) 0.3053 (6) 0.1727 (5) 0.1063 (5) 0.0539 (5) -0.0335 (5) -0.0760 (5) -0.0321 (5) 0.0553 (5) 0.1083 (5) 0.1636 (6) 0.2573 (5) 0.3127 (5) 0.3972 (6) 0.4303 (6) 0.3734 (5) 0.4050 (5) 0.3388 (5) 0.2328 (5) 0.1297 (5) 0.3248 (6) 0.1536 (7) 0.3714 (5) 0.3207 (5) 0.3884 (6) 0.3837 (6) 0.960 (1)
3.7 (2) 3.4 (2) 4.2 (2) 4.5 (2) 6.2 (3)* 6.3 (3)* 3.4 (2) 3.8 (2) 6.4 (3)* 6.1 (3)* 3.0 (2) 3.3 (2) 3.2 (2) 4.0 (2) 4.5 (2) 4.3 (2) 3.5 (2) 4.5 (2)* 5.4 (2)* 4.0 (2) 4.5 (2) 4.8 (2) 4.7 (2) 3.9 (2) 4.3 (2) 3.4 (2) 3.1 (2) 3.4 (2) 5.6 (3)* 6.8 (3)* 4.0 (2) 3.6 (2) 6.4 (3)* 5.8 (3)* 31 (1)*
Organometallics, Vol. 5, No. 2, 1986 353
Metallocyclic Palladium(II) Complexes
Table 111. Crystal Data and Data Collection Parameters 6
triclinic pi 11.298 (2) 13.932 (3) 14.778 ( 5 ) 99.06 (2) 109.03 (2) 97.44 (2) 2130 (2) 1.491
cryst system space group a, A
b, A
c,
A
a , deg P, deg Yt deg
v, A3
d, g ~ m - ~ 2, formulas/cell temp, "C p(Mo Ka),cm-' crystal size, mm color: min relative transmissn, % 28 limits, deg scan rates, degmin-' precision max scan time, s unique data obsd data variables
2
28 5.6 0.20 X 0.24 X 0.44 orange 85.10 2-43 0.69-10 I z 250(4 90 4883 2798 395 0.048 0.055 0.61
R Rw m w residual, e A-3
Table IV. Bond Lengths (A) and Angles (deg) in Complexes 6 and 17 17
6
atoms Pd-N1 Pd-N2 Pd-C15 Pd-Cl
dist, A 2.064 ( 5 ) 2.153 ( 5 ) 2.090 (6) 2.329 (2)
atoms Pd-N1 Pd-N2 Pd-C1 Pd-C16
angle, deg 80.4 (2) 95.0 (2) 159.3 (2) 168.4 (2) 96.2 (1) 91.8 (2)
atoms N1-Pd-N2 N1-Pd-C1 N1-Pd-C16 N2-Pd-Cl N2-Pd-C16 C1-Pd-C16
17
6
atoms N1-Pd-N2 N1-Pd-C15 N1-Pd-C1 N2-Pd-Cl5 N2-Pd-Cl C15-Pd-C1
dist. A 2.112 ( 5 ) 2.184 ( 5 ) 2.108 (5) 2.090 ( 5 ) angle, deg 101.2 (2) 79.7 (2) 170.8 (2) 165.3 (2) 78.3 (2) 103.1 (2)
sertion of bridging units between the heteroatom donors have proven very successful for increasing the degree of geometrical freedom in the resulting complexes. Further, incorporation of the carbonyl bridge has established that a diminished electron density on the heteroatom donor does not necessarily preclude generation of the cyclometalated species as evidenced by complex 22. Our previous work dealing with cyclometalated Pd(I1) complexes has established the type of ligand best suited for square-planar geometry in which partial coordination is via an sp3 carbon(s). Presently, we are interested in expanding this methodology to include a greater number of transition metals in various geometries. Thus, it has become necessary for us to explore new synthetic approaches to ligand design which will introduce an added degree of ligand flexibility as well as variations in the electronic character of heteroatom donors. The work described herein is representative of our initial efforts in this area which are ultimately directed toward the incorporation of two or more organometallic subunits into a macrocyclic framework. Presently we are investigating the syntheses of Pt(II), Rh(II), Rh(III), Ru(II), Ni(II), and Fe(I1) complexes of these and other ligands to be reported later.
17
triclinic Pi 9.610 (2) 16.182 (2) 16.191 (2) 101.53 (1) 96.47 (1) 99.86 (1) 2402.3 (13) 1.620 4 26 8.1 0.16 X 0.48 X 0.52 yellow-orange 82.20 2-40 0.49-10 I 25a(I) 120 4473 3811 40 1 0.045 0.047 0.69
Experimental Section All melting points were taken in capillary tubes with a Thomas-Hoover Uni-melt apparatus and are uncorrected. 'H and 13C NMR spectra were determined on an IBM-Bruker NR/80 spectrometer using CDCIBas solvent with MelSi as internal standard. Mass spectral (MS) data (70eV) were determined by Mr. D. A. Patterson on a Hewlett-Packard H P 5985 GC/mass spectrometer and reported herein as (assignment, relative intensity). Preparative thick-layer chromatography (ThLC) was performed on 20 X 40 cm glass plates coated with a 2-mm layer of Brinkmann silica gel PF-254-366. IR spectra were recorded on a Perkin-Elmer 621 grating infrared spectrophotometer. X-ray data were collected on an Enraf-Nonius CAD4 diffractometer equipped with Mo Kcu radiation (A = 0.71073 A) and a graphite monochromator, by w-28 scans of variable speed designed to measure all significant reflections with equal relative precision. Crystal data and experimental details are listed in Table 111. The crystal of 6 was sealed in a thin-walled glass capillary to prevent solvent loss. One hemisphere of data was collected for each crystal within the specified angular limits. Data reduction included corrections for background, Lorentz, and polarization effects, as well as an empirical absorption correction, based upon I) scans of reflections near x = 90°. Structures were solved by heavy-atom methods, and refinement was conducted by full-matrix least squares upon F, with data for Due which Z > la(T),using the Enraf-Nonius SDP ~ r 0 g r a m s . l ~ to the rather low quality of the available crystals and resulting low resolution of the data, full anisotropic refinement was not possible. For 6, only Pd, C1,0, and methyl carbon were anisotropic, while all other non-hydrogen atoms were refined isotropically. For 17, Pd, 0, methyl carbon, and methylene carbon of the seven-membered ring were anisotropic, while other nonhydrogen atoms were isotropic. While the crystal of 6 contained one ordered solvent molecule (acetone) in a general position, a second acetone molecule was found disordered across a center, which lies approximately a t the midpoint of the C=O bond in two half-populated orientations. Hydrogen atoms of the disordered acetone were ignored; all other hydrogen atoms were included as fixed contributions in calculated positions. Final R factors and residual electron densities are given in Table 111; coordinates are given in Tables I and 11. (17) Frenz, B. A.; Okaya, Y. "Enraf-Nonius Structure Determination Package"; Enraf-Nonius: Delft, Holland, 1982.
354
Organometallics, Vol. 5, No. 2, 1986
I,t-Bis(6-methyl-2-pyridyl)ethyleneDi-N-oxide (11). A mixture of 1,2-bis(6-methyl-2-pyridyl)ethylene7 (mp 208-209 OC; 10 g, 48 mmol), 30% H z 0 2(50 mL), and glacial AcOH (50 mL) was stirred at 90 "C for 4 h. Additional 30% H202(50 mL) and glacial AcOH (25 mL) were added, and the solution was stirred a t 90 "C for 12 h. The solution was cautiously concentrated, repeatedly diluted with water, and concentrated in vacuo. (Note: Explosions have been reported when 30% H20zwas used. Proceed cautiously when concentrating any solutions containing peroxides. Use no less than four reaction volumes of water to dilute the mixture when following the procedure given here.) The resulting viscous liquid was neutralized with solid NaZCO3and extracted with CHC1,. The extract was dried and concentrated to give a crude product, which was crystallized from EtOH/C6H6 as white crystals: 75%; mp 245 "C dec; (lit.7 mp 247-249 "C dec). 1,2-Bis[6-(acetoxymethyl)-2-pyridyl]ethylene (12). A solution of di-N-oxide 11 (10 g, 45 mmol) in distilled Ac20 (100mL) was refluxed for 30 min and then concentrated in vacuo. The resulting solid was dissolved in CHzClz, washed with dilute aqueous NazC03, dried over anhydrous MgSO,, and reconcentrated in vacuo. The crude product was passed through a short silica gel column eluting with CHZClz.The eluant was concentrated and the product crystallized from a small volume of EtOH to give the diester, as white needles: 6.6 g (50%);mp 133-136 "C (lit.' mp 133-134 "C). 1,2-Bis[6-(hydroxymethy1)-2-pyridyl]ethylene(13). Step A. A suspension of 1,2-bis[6-(acetoxymethyl)-2-pyridyl]ethylene (10 g, 31 m o l ) and anhydrous K&O, (14 g, 102 mmol) in absolute EtOH (200 mL) was stirred for 1 h. The mixture was filtered and concentrated in vacuo to give the enediol, which was crystallized from EtOH, as white needles: 7.1 g (95%); mp 138-140 "C (lit.7 mp 142-144 "C). Step B. 1,2-Bis[6-(hydroxymethyl)-2-pyridyl]ethylene (13) was catalytically reduced to give (27%) diol 14: mp 155-157 "C (lit.7 mp 157-159 "C). 1 f-Bis[ 6-(chloromet hy1)-2-pyridyllethane (15). To freshly distilled18SOCl, (5 mL) precooled to 0 "C was added diol 14 (1.1 g, 4.5 mmol) in small portions under nitrogen. The solution was refluxed for 1h and cooled and excess S0C12 removed in vacuo. The residue was neutralized with 10% aqueous Na2C03and then extracted with CH,C12 (5 x 50 mL). The combined organic extract was dried over anhydrous MgSO, and concentrated in vacuo to afford a light tan solid, which was crystallized from CHzC1z/C6Hlz to give the dichloride, as white crystals: 1.2 g (95%);mp 1OC-101 "C; 'H NMR 6 3.24 (s, CH2CH2,4 H, 4.60 (s, CH,Cl, 4 H), 7.05 (dd, 5-pyH, J = 7.8, 1.2 Hz, 2 H), 7.15 (dd, 3-pyH, J = 7.8, 1.2 Hz, 2 H), 7.50 (t,4-pyH, J = 7.8 Hz, 2 H); MS, m / e 280 (M', l), 279 (2), 245 (22), 244 (loo),210 (20), 209 (41), 207 (60). Bis(6-methyl-2-pyridyl) Ketone (19). To a solution of 2bromo-6-methylpyridine (19 g, 0.11 mol) in THF (150 mL) cooled to -90 "C (petroleum ether-liquid nitrogen) under argon was added BuLi (0.1 mol, 2.4 M in hexane) dropwise. The resultant solution was stirred at -90 "C for 1h, and then a solution of ethyl chloroformate (6 g, 0.05 mmol) in THF (15 mL) was added rapidly while the temperature was still maintained a t
