2992
Inorg. Chem. 1986, 25, 2992-3000
Support for this proposal is suggested by the reaction of matters. Somehow asymmetric phosphorus donor coordination Rh2(02CCF3)4with excess P(OMe)3. This reaction was studied to the rhodium dimer polarizes the Rh-Rh bond and cleaves earlier, but difficulties in obtaining good N M R spectra were carboxylate bridges leading to formation of Rh(1) complexes that encountered. The reaction of Rh2(02CCF3)4with 10 equiv of coordinate only the phosphorus donors and Rh(II1) complexes P(OMe), yields a pale yellow solid of empirical formula Rhthat coordinate two phosphines and the CF3C02-ions. (02CCF3)2(P(OMe)3)3.However, we suggested5 that the complex Experimental Section was most likely Rh(P(OMe)3)4+Rh(02CCF3)4(P(OMe)3)2-, Rh2(02CCF3)4, RhAOzCCF3)4(PPhA Rh2(02CCF,),(P(OPh)3)2, four-coordinate Rh(1) and six-coordinate Rh(II1) species, reRh2(0,CCH2CH2CH3)4(PPh3)2,and Rh(02CCF3),(P(OMe),), were 'H) and I9F N M R spectra spectively. The previously reported 31P{ synthesized as described previously.s Rh,(O,CCF,),(PCy,), was preof this species were more complex than expected. This was pared by dropwise addition of a toluene solution of PCy, (2 equiv, Aldprobably due to interconversion between Rh complexes over time rich) to a toluene solution of Rh2(O2CCF,),. Removal of solvent by while in solution at room temperature. In this study, a CDC13 pumping and recrystallization from toluene gave brown Rh2solution of the P(OMe)3 complex was frozen at -70 "C and held (O,CCF,),(PCy,),. IR (cm-I): u,,,(C02) 1663 (Nujol), 1710 w, 1660 a t that temperature except when N M R spectra were obtained. m (CHCI,). 19FNMR (CDCI,, 27 C, ppm relative to CFCI,): -72.73, -74.51, -75.42, -75.92 (1:1:2:1). Anal. Calcd for Rh2C44H66P2F120s: The 31P(1H) N M R spectrum obtained in this manner showed two C, 43.36; H, 5.46; P, 5.08. Found: C, 45.53; H, 5.49; P, 5.23. Following sharp doublets in a 2:l area ratio over the temperature range -50 the above procedure but using excess PCy, ( I O equiv) and Rh2(02CCF,), to +20 O C . No significant changes in either chemical shift or in 1:l toluene/acetonitrile led to a solution color change from brown to coupling constants were seen. The signals appeared a t 135.0 f pale yellow after heating at 40 OC for 30 min. Removal of solvent by 0.5 ppm (relative to 85% H 3 P 0 4 ) ,J = 181.5 f 0.1 Hz, and at pumping and recrystallization from 1:1 CH2C12/hexaneafforded a pale 89.5 f 0.5 ppm, J = 132.5 f 0.5 Hz. The 19Fspectrum showed yellow solid. IR (cm-I, Nujol): u(CN) 2260 m; uarY(CO2)1735 s, 1680 a single sharp peak a t -75.33 ppm a t room temperature. Rhs; u(CF,) 1180 s, 1140 s; 6(C02) 725 s. Anal. Calcd for Rh(02CCF3)4(P(OMe)3)yis an AX2 spin system as the trans isomer, C, 49.17; H, 6.75; N , 2.61; P, 5.76; (O~CCF,)(P(C~H,I),)(CH,CN): showing a doublet in the X region, and would show a single I9F C:H:N:P = 22:36:1:1. Found: C, 53.69; H, 7.40; N, 2.84: P, 6.50; C:H:N:P = 22.0:36.2:1.0:1.0. The product is contaminated with PCy, signal for four equivalent monodentate CF3C02- ligands (IR and complexes thereof, giving the high % C, % H, and % P. v,,,,(C02) a t 1720 cm-l in CHCI3). Rh(P(OMe)3)4+is an AX4 NMR spectra were recorded on a Nicolet NT-300 instrument operspin system and also shows a 31Pdoublet. Over time, and probably ating at a field of 7 T. "P(lH] (121.5 MHz) sample were in CDCI, in as a result of O2 and/or light, other Rh species could come about. 5-mm tubes coaxial in 12-mm tubes, the latter containing P(OMe), in The chemistry of transition-metal phosphite complexes is comCDCI, as an external chemical shift reference (140.0 ppm relative to 85% plicated, and a variety of species are known for cobaltI2 and other H3PO4). I9F (282.3 MHz) samples were in 5-mm tubes containing 1neta1s.l~ For rhodium, Rh(P(OMe)3)5+ and R h ( 0 P CFCI, as an internal reference. (OMe),)(P(OMe),), have been reported.I4-l5 In the system Acknowledgment. Financial assistance in the purchase of the reported here, the Rh-Rh bond in Rh2(02CCF3), probably is N M R instrument used in this study a t the University of Florida cleaved asymmetrically by P(OMe)3 to give a phosphite-coorand support for this research by the N S F are acknowledged. dinated Rh(1) species and a Rh(II1) species containing all the James R. Rocca is thanked for his assistance in obtaining the CF3C02- ligands. This type of reaction also occurs with phosN M R spectra. phines, although oxidation to phosphine oxides complicates Registry No. Rh2(02CCH2CH,CH3)4(PPh3)2, 90968-08-4; Rh2(0,CCF,)4(P(OPh)3)2, 77966-17-7; Rh2(O2CCF,),(PPh,), (class I), (12) Muetterties, E. L.; Bleeke, J. R.; Yang, Z.-Y.; Day, V. W. J . Am. Chem. 77966-16-6; Rh2(O,CCF3),(PPh,), (class HI), 102745-66-4; Rh,SOC.1982, 104, 2940. (O2CCF3),(PCy,), (class I), 83398-63-4; Rh2(O2CCF3),(PCy,), (class (13) Choi, H. W.; Muetterties, E. L. J. Am. Chem. SOC.1982, 104, 153. HI), 102745-67-5; [Rh(0,CCF,)4[P(OMe)3]2]-[Rh(P(OMe),),l+, (14) Meakin, P.; Jesson, J. P. J . Am. Chem. SOC.1973, 95, 7272. 102745-69-7; Rh(O2CCF,)(P(C6H,l),)(CH,CN), 102745-70-0; Rh2(IS) Hitchcock, P. B.; Klein, S. 1.; Nixon, J. F. J . Orgunomet. Chem. 1983, (02CCF3),, 31 126-95-1. 241, C9.
Contribution from the Department of Chemistry, University of the Witwatersrand, Johannesburg, South Africa
Small Macrocyclic Ligands with Mixed Nitrogen- and Oxygen-Donor Atoms Vivienne J. Thom, M. Salim Shaikjee, and Robert D. Hancock* Received September 1 I I985 The stability of some of the complexes of the metal ions Cu2', Ni2', Znzt, Cd2+,Pb2+,CaZt, and Hg2+with the ligands 9-aneN20 (1 -oxa-4,7-diazacyclononane),12-aneN30 (1 -oxa-4,7,1O-triazacyclododecane), 12-ane( 1 ,4)N2O2(1,4-dioxa-7,1 O-diazacyclododecane), 13-aneN30 (I-oxa-4,7,1 I-triazacyclotridecane),1 3-aneN202(1,4-dioxa-7,1 I-diazacyclotridecane), HEEN (1-oxa-4,7diazaheptane), ODEN (4-oxa-1,7-diazaheptane), DHEEN ( I , lO-dioxa-4,7-diazadecane),and 12-aneN4 (1,4,7, IO-tetraazacyclododecane) are reported. It is shown that addition of neutral oxygen donors to existing amine ligands leads to an increase in complex stability for large metal ions (e& Pb2+,Ca2+)and a decrease for small metal ions (e.g. Cu2+,Zn2+). This occurs whether the added oxygen donors are part of hydroxyalkyl groups, as in the addition of hydroxyethyl groups to en (ethylenediamine) to give DHEEN or the addition of ethereal oxygens that are part of a macrocyclic ring to en to give 12-ane(1,4)N202.It is found that the macrocyclic effect in mixed-donor ligands is much smaller than in the all-nitrogen-donor analogues. Thus, the increase in complex stability (the macrocyclic effect) in passing from DHEEN to 12-aneN202,for example, is much smaller than in passing from TRIEN (1,4,7,1O-tetraazadecane)to 12-aneN4. This is discussed in terms of ligand-related contributions to the macrocyclic effect, such as steric hindrance to the solvation of the free ligand. A feature of these ligand-related effects is that a metal ion such as Cazt, which ordinarily shows little affinity for ligands containing only nitrogen donors, will still form a complex of some stability with a ligand such as 12-aneN4,with log K, at 25 OC in 0.1 M NaNO, of 3.1. I
An interesting feature of macrocyclic chemistry is the fact that the oxygen-donor macrocycles complex strongly only with the alkali- and alkaline-earth-metal ions, plus a few large metal ions such as Pb2+ and Hg2+. In contrast, the nitrogen-donor macro-
cycles appear to complex well only with the transition-metal and post-transition-metal ions, such as Co3+,Ni2+,Cu2+,Zn2+,or Cd2+. A few metal ions such as Pb2+ and Hg2+ appear able to bond well to both classes of macrocycle. An obvious area for investigation
0020-1669/86/1325-2992$01.50/00 1986 American Chemical Society
Inorganic Chemistry, Vol. 25, No. 17, 1986 2993
Small Macrocyclic Ligands H
13-ane N,
13-ana NO ,
13- anc N,O,
H 18- ane
- N,O,
12-one N,
12-aneN30
I
I
15 - a n a
- N,O,
B H P - 1 8 - a n e - N,O,
12-ane(l,4)N2O,
IZ-one(l, 7)N,02
""2
H
9-anaNS
9-one N,O
2.3.2 - T E T
TRlEN
HEEN
ODEN
H
I
DHEEN
BAEDOE
Figure 2. Structures of the oxygen-nitrogen mixed-donor macrocycles reported in this paper, together with those of their all-nitrogen-donor macrocyclic analogues and those of their open-chain analogues. 14-ana-N, (cyclam)
Ni2+ > Cd2+ > Zn2+ > Pb2+. (3) Contributions to the stability of complexes of N-donor macrocycles that are ligand related, such as steric hindrance to solvation of the N donors in the macrocyclic cavity, mean that metal ions such as Ca", which ordinarily show no affinity for N-donor ligands, can form complexes of considerable stability with ligands such as 12-aneN4. (4) Replacing nitrogen by oxygen donors in macrocyclic ligands leads to a drop in complex stability. For large ionically bound metal ions such as Pb2+, the rate of falloff in complex stability is lower, so that complexes of some stability are still observed when all the nitrogens have been replaced by oxygens; Le., crown ethers
(44) Hancock, R. D.; McDougall, G. J. J . Am. Chem. SOC.1980, 102, 6551-6553.
(45) Tho,, V. J.; Hancock, R. D. J . Chem. SOC.,Dalton Trans. 1985, 1877-1880.
(46) Hart, S . M.; Boeyens, J. C. A,; Hancock, R. D. Inorg. Chem. 1983,22,
982-986.
Inorg. Chem. 1986, 25, 3000-3006
3000
have been produced. For all the complexes of the mixed-donor macrocycles the macrocyclic effect is much smaller than is the case for the all-nitrogen-donor analogues. (5) For the tetradentate macrocycles, an increase in the number of atoms forming the macrocyclic ring is usually considered to lead to an increase in the size of the macrocyclic cavity. However, for both the all-nitrogen- and the nitrogen-oxygen mixed-donor macrocycles studied here, the results suggest that the ligands with smaller macrocyclic rings, e.g. 12-aneN4 or 12-aneN30, complex larger metal ions such as Pb2+ more strongly than do those with larger macrocyclic rings, e.g. 13-aneN, or 13-aneN30. In contrast, small metal ions such as Cu2+ show a strong preference for the macrocycles with larger macrocyclic rings. This effect does not
appear to depend on the presence of a macrocyclic ring, but is rather related to the presence of five-memkred vs. six-membered chelate rings in the complexes formed, since similar sizeselectivity patterns are observed in the open-chain analogues.
Acknowledgment. We thank the Council Research Grants Committee of the University of the Witwatersrand and the Foundation for Research Development of the Council for Scientific and Industrial Research for generous financial support for this work. Registry No. 9-aneN20, 80289-59-4; 13-aneN30, 8891 5-58-6; 13aneN202, 60350-15-4; 12-aneN30, 53835-21-5; 12-ane(I,4)N2O2, 60350-1 3-2.
Contribution from the Chemistry Department, The Ohio State University, Columbus, Ohio 43210
Structure and Dynamic Behavior in Solution of Binuclear Nickel(I1) Face-to-Face Complexes with Bis( cyclidene) Ligands Naomi Hoshino, Kenneth A. Goldsby, and Daryle H. Busch* Received February 12, I986 A series of dinickel(I1) complexes having macrotricyclic bis(cyc1idene) ligands has been prepared and characterized. N M R studies revealed a dynamic molecular motion in solution, and electrochemical investigations showed that the difference in redox couples (AI?,,*) for the two Ni-cyclidene units correlates well with the sequence of intermetallic distances.
Introduction
Scheme I
The number of synthetic model compounds for metalloproteins having more than one metal center has continuously increased and the structure types have been diversified substantially since the first report on a side-by-side example in 1970.' One advantage for such bioinorganic models is that the coordination geometry around the metal center and its surroundings can be easily controlled by ligand design; e.g., bridging two macrocyclic units into a stacked pair leads to the "face-to-face" s t r ~ c t u r e . ~ ~ ~ Face-to-face diporphyrins, whose electrochemical applications have been extensively i n v e ~ t i g a t e d , exemplify ~.~ stacked macrocyclic systems. Efforts in this area have focused on the relationships between electrocatalytic activity in the reduction of O2 to H 2 0 and structural parameters of the cobalt-containing catalyst. We have developed a distinct family of dinuclear transitionmetal complexes in which two macrocyclic units, called cyclidene rings: are joined together in a macrotricyclic ligand. The cyclidene groups have approximately face-to-face orientations, but they may be displaced with respect to a common axis or tilted with respect to that same axis. Because of the saddle shape of the cyclidene Pilkington, N. H.; Robson, R. Ausr. J . Chem. 1970, 23, 2225-2236. See for example: Collman, J. P.; Denisevich, P.; Konai, Y.; Marrocco, M.: Koval. C.: Anson. F. C. J. Am. Chem. SOC.1980.102.6027-6036. Eaton, S. S.; Eaton, G. R.; Chang, C. K. J . Am. Chem. Soc. 1985, 107, 3 177-3 184 and references therein. For example: Durand, R. R., Jr.; Bencosme, C. S.;Collman, J. P.; Anson, F. C. J . Am. Chem. SOC.1983, 105, 2710-2718. Liu, H. Y.; Abdalmuhdi, I.; Chang, C. K.; Anson, F. C. J . Phys. Chem. 1985, 89, 665-670. The cyclidene notation is based on the tetraimine macrocycle
+
4 CH30-
cy/ I
cy-J
Cl"-J
XnY I
I
rings, many of these dinucleating ligands will maintain a constant separation between the two chelated metal ions. Structure Ia indicates the bonding in the complex while structure Ib shows the 3-dimensional array of atoms. These dinuclear complexes fall
R2
R2
n = 2, [14]cyclidene n = 3, [16]cyclidene
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Ia
0 1986 American Chemical Society
Ib
