A meta-stable heterobimetallic mixed-valence ion, [Fe(II),Ru(III)], is formed by the one-electron oxidation of Cp*(dppf)RuH {1, dppf ) 1,1′-bis(diphenylphosphino)ferrocene, Cp* ) pentamethylcyclopentadienide}. A remarkable stability toward one-electron oxidation is revealed by the cyclic voltammetry of 1 which contains two reversible oxidations at +0.073 and +0.541 V and a quasireversible oxidation at +0.975 V (vs NHE) assigned to Ru(III/II), Ru(IV/III), and Fe(III/II), respectively. The isolable Ru(III) metal hydride, [Cp*(dppf)RuH]PF 6 (1 + ), is characterized by a NIR absorption at 912 nm ( ) 486 M -1 cm -1 ) assigned to an intervalence transfer band and a series of atom transfer reactions yielding the even electron derivatives [Cp*(dppf)RuXH]PF 6 (X ) H, Cl, Br, I). A crystallographically determined Fe-Ru distance of 4.383(1) Å in 1 is consonant with the classification of 1 + as a weakly coupled, Type II mixed-valence ion (H ab ) 627 cm -1 , R 2 ) 3.3 × 10 -3 ). This is the first reported example of a mixed-valence bimetallic complex containing the widely used dppf ligand. The ability of 1 to serve as a heterobimetallic catalyst for the reduction of methyl viologen with H 2 makes it a unique functional model of [NiFe] hydrogenase enzymes.

The nicotinamide coenzymes consumed in alcohol dehydrogenase catalyzed enantioselective reduction of ketones are expensive and thus require recycling. We have demonstrated that ruthenium(II) and rhodium-(III) complexes are effective catalysts for the reduction of nicotinamide coenzymes with hydrogen, under conditions that are appropriate for in situ coupling with enzymatic reductions.

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COMMUNICATIONS results for each T1 atom. For TI4 the shortest TILT1 distance in the cluster is part of this approximately linear arrangement (T12-T14-C4 169.1 "), The triangle T11, T12, TI3 can be compared with a recently calculated triplumbane (H,Pb), , for which a paddle wheel arrangement of the substituents with Pb-Pb distances longer than a Pb-Pb single bond was obtained as the energy minimum. [' 71 The bonding in this triangle is best described similarly to that in tetrakis[bis(trimethylsilyl)methyl]distannene from Lappert et aI.['*] by a Lewis acid-base interaction between three plumbanediyl (H,Pb) or thalliumdiyl (RT1) fragments through their lone pair of electrons and their empty p orbital, which in contrast to the dimeric Sn compound with a nonclassical Sn -Sn double bond results in a cyclic trimer. The atom TI4 is located above the T1, triangle with, however, significantly longer TI-T1 distances, which might indicate only very weak TI-TI bonding interactions. Thus, in addition to the cryoscopically determined molar mass of 1 in solution, the crystal structure analysis clearly confirms weaker element-element bonding than in the analogs with the lighter elements Ga and In. The TI-C bond lengths of 238 pm (to TII, T12 and T13) and 233 pm (T14-C4) are longer than the values in compounds with trivalent T1 atoms (av 215 pm).[t91 Experimenial SrctionA solution of LiC(SiMe,), 2 T H F (2.13 g, 5.58 mmol) [131 in toluene (25 mL) was added dropwise to a cooled ( -40 C) suspension of sublimed cyclopentadienylthallium(r) (1 -58 g, 5.87 mmol) in toluene (25 mL) under argon. The solution was slowly allowed to warm to 0 -C and the solvent rapidly evaporated at room temperature. The residue WAS treated with pentane (10 mL) and filtered. The red-violet filtrate was evaporated to dryness, diisopropyl ether was added, and the solution quickly cooled to -50 C Compound 1 crystallized as pyrophoric, extremely sensitive, almost black crystals. which appeared deep red-violet in thin layers. Yield: 1.58 g ( 6 5 % ) . Decomposition at 65 'C (under argon). Molar mass (determined cryoscopically in benzene) [gmol-'1: found 413; calcd 435.96 (for the monomer) 'H NMR (C,D,): d = 0.13; '"C NMR (C,D,): 6 = 6.6 (SiMe,), 30.5 (TIC). IR (Nujoi; Cs-Br):i.[cm ' ] = 1 2 5 0 m B C H , ; 1 1 6 9~, 1 1 1 3 v w , 1 0 9 3 v w , 1 0 4 4~, 1 0 0 9 m ; 8 8 3 v s , 850 vs, 766 s. 745 ni. 723 s pCH,(Si); 673 s. 665 s vJiC; 640 m, 61 1 m v$iC; 525 vs. 465 m vTI,C,. 363 w. 312 w 6SiC. UV/Vis (pentane): i . , , ,[nm] (Ige) = 215 (3.7). 245 (3.8). 320 (sh. 3 0). 380 (sh, 2.7). 515 (2.7).