One-Dimensional Coordination Polymers of Dihydrobis(1,2,4-triazol-1-yl)borate Ruthenium(II) Complex

Abstract

Increasing interest in coordination and organometallic polymers lies in the various intriguing properties of welldesigned inorganic polymer materials. A variety of attempts have been made to synthesize multidentate ligands which can bridge various metal centers. Ambidentate poly(triazolyl)borate ligands [HnB(tz)4-n] − (n = 1 and 2, tz = 1,2,4triazol-1-yl) are good candidates for multidimensional network topologies. It was revealed that both the exodentate (4-position) and endodentate (2-position) nitrogen atoms of the triazolyl rings have comparable electron density to coordinate competitively to metal centers from the theoretical calculation and the N NMR study. It was frequently observed that the poly(triazolyl)borate ligands induce metal ions to form multidimensional coordination polymers through the coordinations of exodentate N atoms whose electron density is higher than the endodentate N atoms. However, in the case of [HB(tz)3] −, tridentate chelated monomers M[η-HB(tz)3]2 (M = Fe, Co, Cu and Zn) are exclusively isolated, and these results are explained by a combination of chelate and kinetic effect. Discrete Ag and Cu complexes bearing a bidentate dihydrobis(1,2,4triazolyl)borate through endodentate coordination such as Cu(L)n[η-H2B(tz)2] (L = aryl phosphines, n = 1 or 2), Ag(L)2[η-H2B(tz)2] (L = aryl phosphines), Ag(dppf)[ηH2B(tz)2] (dppf = 1,10-bis(diphenylphosphino)ferrocene) and their polymeric derivatives were recently reported. In these cases, however, the dihydrobis(1,2,4-triazolyl)borate ligands coordinate to the same type of ions to constitute 1D homometallic polymer networks. In order to develop efficient heterometallic polymeric systems whose physicochemical properties can be systematically tuned, we are pursuing to prepare discrete mononuclear complexes bearing anionic dihydrobis(1,2,4-triazolyl)borate ligands through endodentate coordinations instead of exodentate coordinations. Discrete complexes having a ligand (or ligands) through a bidentate coordination of the two endodentate N atoms could potentially serve as metalloligands for the engineering of 1D modular structure through additional coordinations of the exodentate N atoms to two other transition metal moieties. Recently we were able to prepare discrete mononuclear Fe[HB(tz)3]2·ClO4 and Ag(L)(PPh3) (L = hydrotris(3,5-dimethyl-4-(4-pyridyl)pyrazolyl)borate) to use them as building blocks for novel 3D or 2D functional networks. On the other hand, the reaction between Mn(TPP)·ClO4 and K[H2B(tz)2] only afforded a discrete mononuclear Mn(TPP)(H2O)[η-H2B(tz)2] instead of 1D polymeric structures because of a steric bulk of TPP ligand (TPP is 5,10,15,20-tetraphenylporphine). Here we report a new metalloligand having a dihydrobis(1,2,4-triazolyl)borate, RuH(CO)(PPh3)2[η-H2B(tz)2] (1) and its successful applications to 1D supramolecular systems through self-assembly. Because 1 might have catalytic activities for the hydrogenation of ketones and aldehydes under hydrogen atmosphere, the 1D polymers of 1 could be used as recyclable heterogeneous catalysts. The compound 1 was obtained in good yield from the reaction of RuHCl(CO)(PPh3)3 10 with K[H2B(tz)2] 2 (Figure 1). The compound 1 was fully characterized by H and P{H} NMR, IR, and elemental analysis. A triplet resonance signal of the hydride ligand from H NMR and a singlet peak of two P atoms from P{H} NMR clearly indicate that the proposed structure of 1 which is an ideal geometry as a metalloligand. The entire coordination environment is same to the crystallographically characterized RuH(CO)[P(p-Tolyl)3]2[η-H2B(tz)2] and RuH(CO)(AsPh3)2[η-H2B(pz)2] (pz is pyrazol-1-yl). Unlike other insoluble dihydrobis(triazolyl)borate derivatives, the monomer 1 shows a good solubility in halogenated hydrocarbon solvents. The reactions of 1 with 1 or 2 equivalent Cu(OAc)2·H2O afford well-defined 1D heterometallic polymers {[Cu2(OAc)4][1][Cu(η-OAc)2][1]}n (2) and {[1][Cu2(OAc)4]·(CH2Cl2)2}n (3), respectively, which contain lantern-type dicopper moieties, Cu2(OAc)4. 12 Single crystal x-ray crystallographic studies of 2 and 3 confirm the