Tripodal Triamidostannates as Building Blocks in the Generation of Sn-M-Bonded Heterobimetallics (M  Fe, Ru)

Towards Covalent Photosensitizer-Polyoxometalate Dyads-Bipyridyl-Functionalized Polyoxometalates and Their Transition Metal Complexes

A triol-functionalized 2,2'-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells-Dawson- and Anderson-type feature a C-C bond as a linkage between the POM and bpy fragments. This structural motif is expected to increase the hydrolytic stability of the compounds. This is of particular relevance with respect to the application of POM-bpy metal complexes, as photocatalysts, in the hydrogen-evolution reaction (HER) in an aqueous environment. Accordingly, Rh(III) and Ir(III) complexes of the POM-bpy ligands have been prepared and characterized. These catalyst-photosensitizer dyads have been analyzed with respect to their electrochemical and photophysical properties. Cyclic and square-wave voltammetry, as well as UV/vis absorption and emission spectroscopy, indicated a negligible electronic interaction of the POM and metal-complex subunits in the ground state. However, emission-quenching experiments suggested an efficient intramolecular electron-transfer process from the photo-excited metal centers to the POM units to account for the non-emissive nature of the dyads (thus, suggesting a strong interaction of the subunits in the excited state). In-depth photophysical investigations, as well as a functional characterization, i.e., the applicability in the HER reaction, are currently ongoing.

Tris(amido)tingold Complexes in Different Oxidation States. First Structural Characterization of a Sn-Au-Au-Sn Linear Chain

The reaction of [MeSi{Me(2)SiN(Li)(p-tol)}(3)(Et(2)O)(2)] with SnCl(2) in a 1:1 molar ratio leads the tris(amido)stannate [MeSi{Me(2)SiN(p-tol)}(3)SnLi(Et(2)O)] (1), which further reacts with neutral [AuCl(PPh(3))] and anionic [PPN][AuCl(2)], PPN[AuRCl] (R = C(6)F(5), mes), and chlorogold(I) complexes yielding [Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(PPh(3))] (2) and [PPN][Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(2)] (3) and [Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(R)] (R = C(6)F(5), 4; R = mes, 5), respectively. The reaction of 1 with the dinuclear gold(II) derivative [Au(2)(CH(2)PPh(2)CH(2))(2)Cl(2)] in a 1:2 ratio affords [Au(2)(CH(2)PPh(2)CH(2))(2)(MeSi{Me(2)SiN(p-tol)}(3)Sn)(2)] (6). In a similar way but starting from PPN[Au(C(6)F(5))(3)Cl] and reacting with 1 in a 1:1 ratio, the Au(III) complex [PPN][Au(MeSi{Me(2)SiN(p-tol)}(3)Sn)(C(6)F(5))(3)] (7) has been obtained. X-ray crystal structure analyses were performed for compounds 2 and 6, establishing the Sn-Au bonds [d(Au-Sn) = 2.5651(13) and 2.6804(13) Å, respectively). Compound 6 has a nearly linear Sn-Au-Au-Sn array and features the first examples of tin-gold(II) bonds.

Stabilizing Heterobimetallic Complexes Containing Unsupported Ti-M Bonds (M = Fe, Ru, Co): The Nature of Ti-M Donor-Acceptor Bonds

The stabilization of unsupported Ti-M (M = Fe, Ru, Co) heterodinuclear complexes has been achieved by use of amidotitanium building blocks containing tripodal amido ligands. Salt metathesis of H(3)CC(CH(2)NSiMe(3))(3)TiX (1) and C(6)H(5)C(CH(2)NSiMe(3))(3)TiX (2) as well as HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)TiX (3) (X = Cl, a; Br, b) with K[M(CO)(2)Cp] (M = Fe, Ru) and Na[Co(CO)(3)(PR(3))] (R = Ph, Tol) gave the corresponding stable heterobimetallic complexes of which H(3)CC(CH(2)NSiMe(3))(3)Ti-M(CO)(2)Cp (M = Fe, 6; Ru, 7) and HC{SiMe(2)N(4-CH(3)C(6)H(4))}(3)Ti-M(CO)(2)Cp (M = Fe, 12; Ru, 13) have been characterized by X-ray crystallography. 6: monoclinic, P2(1)/n, a = 15.496(3) Å, b = 12.983(3) Å, c = 29.219(3) Å, beta = 104.52(2) degrees, Z = 8, V = 5690.71 Å(3), R = 0.070. 7: monoclinic, P2(1)/c, a = 12.977(3) Å, b = 12.084(3) Å, c = 18.217(3) Å, beta = 91.33(2) degrees, Z = 4, V = 2855.91 Å(3), R = 0.048. 12: monoclinic, I2/c, a = 24.660(4) Å, b = 15.452(3) Å, c = 20.631(4) Å, beta = 103.64(3) degrees, Z = 8, V = 7639.65 Å(3), R = 0.079. 13: monoclinic, I2/c, a = 24.473(3) Å, b = 15.417(3) Å, c = 20.783(4) Å, beta = 104.20(2) degrees, Z = 8, V = 7601.84 Å(3), R = 0.066. (1)H- and (13)C-NMR studies in solution indicate free internal rotation of the molecular fragments around the Ti-M bonds. Fenske-Hall calculations performed on the idealized system HC(CH(2)NH)(3)Ti-Fe(CO)(2)Cp (6x) have revealed a significant degree of pi-donor-acceptor interaction between the two metal fragments reinforcing the Ti-Fe sigma-bond. Due to the availability of energetically low-lying pi-acceptor orbitals at the Ti center this partial multiple bonding is more pronounced that in the tin analogue HC(CH(2)NH)(3)Sn-Fe(CO)(2)Cp (15x) in which an N-Sn sigma-orbital may act as pi-acceptor orbital.