Preparation and structural characterization of a series of ternary palladium(II) binuclear complexes containing triazolopyrimidinate bridges

Abstract

The reaction of the [Pd(H₂O)₂(L–L)][NO₃]₂ electrophiles (L–L = ethane-1,2-diamine 1, propane-1,3-diamine 2, or 2,2′-bipyridine 3) with 4,7-dihydro-5-methyl-7-oxo[1,2,4]triazolo[1,5-a]pyrimidine (Hmtpo) in 1∶1 molar ratio, in aqueous media (pH 7–8), yielded palladium(II) binuclear complexes of general formula [Pd₂(µ-mtpo-N³,N⁴ )₂(L–L)₂][NO₃]₂. The compounds have been structurally characterized by one- and two-dimensional ¹H and ¹³C NMR spectroscopy and single-crystal X-ray diffraction (1 and 3). The crystal structures of both compounds show that the Pd atoms are located in nearly square-planar PdN₄ environments. Two mtpo ligands arranged in a head-to-tail orientation bridge the two metal centres, giving rise to short intermetallic contacts. The Pd · · · Pd separation appears to be modulated by the interactions between the auxiliary ligands L–L in adjacent co-ordination planes. Thus, substitution of ethane-1,2-diamine by planar 2,2′-bipyridine is responsible for a shortening of the intermetallic separation from 3.225(1) Å in compound 1 to 3.034(1) Å in 3. The NMR data suggest that the structures are preserved in solution.

References

1. (a) K. J. Barnham, C. J. Bauer, M. I. Djuran, M. A. Mazid, T. Rau and P. J. Sadler, Inorg. Chem., 1995, 34, 2826; (b) K. Uchida, A. Toyama, Y. Tamura, M. Sugimura, F. Mitsumori, Y. Furukawa, H. Takeuchi and I. Harada, Inorg. Chem., 1989, 28, 2067; (c) S. Schuvachittanont and R. van Eldik, Inorg. Chem., 1994, 33, 895; (d) T. G. Appleton, D. R. Bedgood and J. R. Hall, Inorg. Chem., 1994, 33, 3834.
2. B. Lippert, Prog. Inorg. Chem., 1989, 37, 1; O. Renn, A. Albinati and B. Lippert, Angew. Chem., Int. Ed. Engl., 1990, 29, 84.
3. K. Umakoshi, A. Ichimura, I. Kinoshita and S. Ooi, Inorg. Chem., 1990, 29, 4005.
4. W. Micklitz, G. Müller, B. Huber, J. Riede, F. Rashwan, J. Heinze and B. Lippert, J. Am. Chem. Soc., 1988, 110, 7084.
5. M. Krumm, B. Lippert, L. Randaccio and E. Zangrando, J. Am. Chem. Soc., 1991, 113, 5129; M. Krumm, E. Zangrando, L. Randaccio, S. Menzer and B. Lippert, Inorg. Chem., 1993, 32, 700.
6. R. Cini, F. P. Fanizzi, F. P. Intini, L. Maresca and G. Natile, J. Am. Chem. Soc., 1993, 115, 5123.
7. J. A. Bailey, M. G. Hill, R. G. Marsh, V. M. Miskowski, W. P. Schaefer and H. B. Gray, Inorg. Chem., 1995, 34, 4591.
8. T. Kawamoto, Y. Nagasawa, H. Kuma and Y. Kushi, Inorg. Chem., 1996, 35, 2427.
9. J. J. Novoa, G. Aullón, P. Alemany and S. Alvarez, J. Am. Chem. Soc., 1995, 117, 7169.
10. L. S. Hollis and S. J. Lippard, J. Am. Chem. Soc., 1981, 103, 1230.
11. M. Grehl and B. Krebs, Inorg. Chem., 1994, 33, 3877.
12. T. V. O'Halloran and S. J. Lippard, J. Am. Chem. Soc., 1983, 105, 3342; Inorg. Chem., 1989, 28, 1289.
13. J. A. R. Navarro, M. A. Romero, J. M. Salas, M. Quirós, J. El Jaraoui Bahraoni and J. Molina, Inorg. Chem., 1996, 35, 7829.
14. J. A. R. Navarro, M. A. Romero, J. M. Salas and M. Quirós, unpublished work.
15. H. Hohmann and R. van Eldik, Inorg. Chim. Acta, 1990, 174, 87.
16. G. M. Sheldrick, SHELXTL PLUS, Program for the solution of crystal structures, Release 34, Siemens Analytical X-Ray Instruments, Madison, WI, 1989.
17. W. Micklitz, W. S. Sheldrick and B. Lippert, Inorg. Chem., 1990, 29, 211.
18. M. Krumm, I. Mutikainen and B. Lippert, Inorg. Chem., 1991, 30, 884.
19. A. J. Bondi, J. Phys. Chem., 1964, 68, 441.
20. C.-L. Yao, L.-P. He, J. D. Korp and J. L. Bear, Inorg. Chem., 1988, 27, 4389.
21. H. Engelking, S. Karentzoupolos, G. Reusmann and B. Krebs, Chem. Ber., 1994, 127, 2355.
22. G. Aullón, P. Alemany and S. Alvarez, Inorg. Chem., 1996, 35, 5061.
23. R. G. Miller, R. D. Stauffer, D. R. Fahey and D. R. Parnell, J. Am. Chem. Soc., 1970, 92, 1511.
24. A. Albinati, P. S. Pregosin and F. Wombacher, Inorg. Chem., 1990, 29, 1812; G. Frommer, F. Lianza, A. Albinati and B. Lippert, Inorg. Chem., 1992, 31, 2434.