Manganese Complexes of 1,3,5-Triaza-7-phosphaadamantane (PTA): The First Nitrogen-Bound Transition-Metal Complex of PTA Brian J. Frost,* Carolyn M. Bautista, Rongcai Huang, and Jason Shearer* Department of Chemistry, MS 216, UniVersity of NeVada, Reno, NeVada 89557 Received February 24, 2006 The structures of two manganese(II) complexes of 1,3,5-triaza-7- phosphaadamantane (PTA) reveal the first transition-metal com- plexes of PTA in which the metal preferentially coordinates to a nitrogen and not the phosphorus of PTA. The coordination environment about the manganese was probed using X-ray crystallography (solid state) and EXAFS spectroscopy (solution). The air-stable, water-soluble, heterocyclic phosphine 1,3,5- triaza-7-phosphaadamantane (PTA) 1 has received a great deal of attention in recent years as a ligand for aqueous-phase catalysis. 2-4 We have been interested in the coordination chemistry of PTA and, specifically, the requirements for nitrogen versus phosphorus coordination. 5,6 PTA preferen- tially coordinates metals through the soft phosphorus center, while the harder amine functionalities are the preferred sites of alkylation and protonation, 4 which can be rationalized utilizing hard soft acid base (HSAB) theory. In the 3 decades since the discovery of PTA, no examples of PTA binding to a metal through nitrogen, leaving an uncoordinated phos- phorus, have been observed. 4 Darensbourg et al. described a transient intermediate tentatively identified as [Ni(PTA) 6-n (H 2 O) n ] 2+ and reported as possibly containing a nitrogen- bound PTA based upon the blue color of the complex. 7 Peruzzini et al. reported the first definitive transition-metal complex bound through a nitrogen of PTA; nitrogen coor- dination to silver was observed in a ruthenium-bound PTA complex (i.e., nitrogen coordination after metal coordination of the phosphorus). 8 We more recently reported the first coordination complex of PTA in which only the nitrogen of PTA was bound to a hard Lewis acid (boron); the addition of BH 3 to PTA resulted in the formation of a coordination complex (PTA-BH 3 ) in which the borane was bound to nitrogen, leaving an uncoordinated phosphorus atom. 5 Herein we present experimental data on the first nitrogen- coordinated PTA transition-metal complexes. Complexes 1 and 2 were synthesized using a procedure published for the hexamethylenetetraamine (HMT) manganese complex. 9 The manganese salt (MnCl 2 ‚4H 2 O or MnBr 2 ‚4H 2 O) was dissolved in a 1:1 acetone/ethanol (v/v) solution and added to a solution of PTA dissolved in an equal volume of ethanol and acetone (Scheme 1). Precipitation of the product with hexanes yielded * To whom correspondence should be addressed. E-mail: Frost@ chem.unr.edu (B.J.F.), shearer@chem.unr.edu (J.S.). (1) (a) Daigle, D. J.; Pepperman, A. B., Jr.; Vail, S. L. J. Heterocycl. Chem. 1974, 11, 407-408. (b) Daigle, D. J. Inorg. Synth. 1998, 32, 40-45. (2) For example, see: (a) Mebi, C. A.; Frost, B. J. Organometallics 2005, 24, 2339-2346. (b) Akbayeva, D. N.; Gonsalvi, L.; Oberhauser, W.; Peruzzini, M.; Vizza, F.; Brueggeller, P.; Romerosa, A.; Sava, G.; Bergamo, A. Chem. Commun. 2003, 264-265. (c) Bolano, S.; Gonsalvi, L.; Zanobini, F.; Vizza, F.; Bertolasi, V.; Romerosa, A.; Peruzzini, M. J. Mol. Catal. A 2004, 224, 61-70. (d) Kova ´cs, J.; Todd, T. D.; Reibenspies, J. H.; Joo ´ , F.; Darensbourg, D. J. Organometallics 2000, 19, 3963-3969. (e) Joo ´, F.; Laurenczy, G.; Karady, P.; Elek, J.; Nadasdi, L.; Roulet, R. Appl. Organomet. Chem. 2000, 14, 857- 859. (f) Laurenczy, G.; Joo ´, F.; Nadasdi, L. Inorg. Chem. 2000, 39, 5083-5088. (g) Darensbourg, D. J.; Joo ´, F.; Kannisto, M.; Katho, A.; Reibenspies, J. H.; Daigle, D. J. Inorg. Chem. 1994, 33, 200- 208. (h) Krogstad, D. A.; Cho, J.; DeBoer, A. J.; Klitzke, J. A.; Sanow, W. R.; Williams, H. A.; Halfen, J. A. Inorg. Chem. Acta 2006, 359, 136-148. (i) Joo ´, F.; Nadasdi, L.; Benyei, A. C.; Darensbourg, D. J. J. Organomet. Chem. 1996, 512, 45-50. (j) Joo ´, F.; Laurenczy, G.; Nadasdi, L.; Elek, J. Chem. Commun. 1999, 971-972. (k) Dyson, P. J.; Ellis, D. J.; Henderson, W.; Laurenczy, G. AdV. Synth. Catal. 2003, 345, 216-221. (3) Darensbourg, D. J.; Decuir, T. J.; Reibenspies, J. H. In Aqueous Organometallic Chemistry and Catalysis; Horva ´th, I. T., Joo ´ , F., Eds.; High Technology; Kluwer: Dordrecht, The Netherlands, 1995; pp 61- 80. (4) Phillips, A. D.; Gonsalvi, L.; Romerosa, A.; Vizza, F.; Peruzzini, M. Coord. Chem. ReV. 2004, 248, 955-993 and references cited therein. (5) Frost, B. J.; Mebi, C. A.; Gingrich, P. W. Eur. J. Inorg. Chem. 2006, 1182-1189. (6) Frost, B. J.; Miller, S. B.; Rove, K. O.; Pearson, D. M.; Korinek, J. D.; Harkreader, J. L.; Mebi, C. A.; Shearer, J. Inorg. Chem. Acta 2006, 359, 283-288. (7) Darensbourg, D. J.; Robertson, J. B.; Larkins, D. L.; Reibenspies, J. H. Inorg. Chem. 1999, 38, 2473-2481. (8) Lidrissi, C.; Romerosa, A.; Saoud, M.; Serrano-Ruiz, M.; Gonsalvi, L.; Peruzzini, M. Angew. Chem., Int. Ed. 2005, 44, 2568-2572. (9) Tang, Y.-C.; Sturdivant, J. H. Acta Crystallogr. 1952, 5, 74-82. Scheme 1. Synthesis of Mn(OH2)2PTA2X2, Where X ) Cl (1) or Br (2) Inorg. Chem. 2006, 45, 3481-3483 10.1021/ic060322p CCC: $33.50 © 2006 American Chemical Society Inorganic Chemistry, Vol. 45, No. 9, 2006 3481 Published on Web 04/06/2006