A series of low-valent ruthenium complexes bearing 2,6-bis(imino)pyridyl ("[N 3 ]") ligands has been synthesized and characterized. Reduction of [N 3 ) with hydridosilanes in an arene solvent such as toluene yields new 18eη 6 -arene complexes [κ 2 -N 3 ]Ru(η 6 -MeC 6 H 5 ), 2a,b,c, in which the [N 3 ] ligand is bidentate and only one imine group is coordinated to the metal. The arene ligand can be displaced with dinitrogen in non-arene solvents to yield the binuclear, four-coordinate, formally Ru(0) complexes {[N 3 ]Ru} 2 (μ-N 2 ), 3a,b,c. Pyrophoric complex 3c is a rare example of a structurally characterized Ru(0) dinitrogen complex. Treatment of low-valent complexes 2 or 3 with donor ligands generates five-coordinate complexes [N 3 xyl ]RuL 1,2 (L 1,2 =C 2 H 4 , 4a; L 1,2 =PMe 3 , 5a; L 1,2 =CO, 6a; L 1 =PMe 3 , L 2 =CO, 7a). Complexes 2a, 3c, 5a, 6a, and 7a are diamagnetic and have been structurally characterized by single-crystal X-ray diffraction methods. New six-coordinate Ru(II) complexes [N 3 xyl ]RuCl 2 (L) (L=PMe 3 , CO) were also isolated and structurally characterized. The infrared data, observed geometrical parameters, and reactivity patterns of the formally Ru(0) centers suggest varying degrees of electron delocalization to the "non-innocent" bis(imino)pyridyl, but probably not to the extent implied by the valence tautomeric [N 3 ] 2-/Ru(II) canonical form. Although the [N 3 ] -/Ru(I) representation may portray the electron distribution more accurately than "Ru(0)", the inherent odd electron counts on both ligand and metal;and requisite antiferromagnetic coupling;provides little in the way of "useful" distinctions or predictive value for the low-valent [N 3 ]Ru(L) 2 complexes with strong-field co-ligands such as CO and PMe 3. These five-coordinate adducts seem to be adequately described as Ru(0) complexes of the neutral [N 3 ] ligand. However, "non-innocent" valence tautomeric canonical forms such as [N 3 ] -/Ru þ may be more applicable to the four-coordinate dinitrogen complexes {[N 3 ]Ru} 2 (μ-N 2 ).

A series of silylamido complexes of zirconium, Cp2Zr(X)(N'BuSiMejH) (X = H, I, Br, Cl, F; 1-5), have been prepared. These complexes exhibit agostic 3-Si-H interactions with the metal center and have been characterized by spectroscopic and structural methods. Spectroscopic evidence for the interaction of the Si-H cr-bond with zirconium include (1) abnormally large upfield chemical shifts for the silicon hydride and silicon nuclei in the 'H and 29Si NMR spectra, (2) unusually small values of the silicon-hydrogen coupling constants (17sih)i and (3) iow-energy Si-H stretching frequencies in the infrared spectra. AH of the spectroscopic data also establish a clear trend for the strength of the nonclassical Zr-H-Si interaction in Cp2Zr(X)(N'BuSiMe2H): X = H > I > Br > Cl > F. This ordering directly reflects the relative electrophilicity of the zirconium center. The molecular structures of the hydride and chloride derivatives 1 and 4 as determined by single-crystal X-ray diffraction studies are also consistent with coordination of the Si-H bond to the metal center. In particular, short Zr-Si distances and acute Zr-N-Si angles point to a severe bending of the silyl group toward zirconium, and the location of the amido group near the center of the metallocene equatorial wedge is consistent with a Cp2ML3 coordination environment, not the Cp2ML2 geometry implied by the formula Cp2Zr(NR2)(X).

A new catalytic route for the formation of arene−silicon bonds based on the transfer dehydrogenative coupling of triethylsilane with an arene (Ar−X:  X = −CF3, −F, −H, −CH3, −Cl, −Br) in the presence of 3,3-dimethylbut-1-ene (tBu-ethylene) is reported. Rhodium and ruthenium catalysts (η5-C5Me5)Rh(H)2(SiEt3)2 and (η6-arene)Ru(H)2(SiEt3)2 and their corresponding dimeric chloride precursors not only catalyze the coupling of Et3SiH with an arene but additionally promote the dimerization of Et3SiH producing a carbosilane, Et3Si−CHMe−SiEt2H.

A series of octahedral ruthenium silyl hydride complexes, cis-(PMe(3))(4)Ru(SiR(3))H (SiR(3) = SiMe(3), 1a; SiMe(2)CH(2)SiMe(3), 1b; SiEt(3), 1c; SiMe(2)H, 1d), has been synthesized by the reaction of hydrosilanes with (PMe(3))(3)Ru(eta(2)-CH(2)PMe(2))H (5), cis-(PMe(3))(4)RuMe(2) (6), or (PMe(3))(4)RuH(2) (9). Reaction with 6 proceeds via an intermediate product, cis-(PMe(3))(4)Ru(SiR(3))Me (SiR(3) = SiMe(3), 7a; SiMe(2)CH(2)SiMe(3), 7b). Alternatively, 1 and 7 have been synthesized via a fast hydrosilane exchange with another cis-(PMe(3))(4)Ru(SiR(3))H or cis-(PMe(3))(4)Ru(SiR(3))Me, which occurs at a rate approaching the NMR time scale. Compounds 1a, 1b, 1d, and 7a adopt octahedral geometries in solution and the solid state with mutually cis silyl and hydride (or silyl and methyl) ligands. The longest Ru-P distance within a complex is always trans to Si, reflecting the strong trans influence of silicon. The aptitude of phosphine dissociation in these complexes has been probed in reactions of 1a, 1c, and 7a with PMe(3)-d(9) and CO. The dissociation is regioselective in the position trans to a silyl ligand (trans effect of Si), and the rate approaches the NMR time scale. A slower secondary process introduces PMe(3)-d(9) and CO in the other octahedral positions, most likely via nondissociative isomerization. The trans effect and trans influence in 7a are so strong that an equilibrium concentration of dissociated phosphine is detectable (approximately 5%) in solution of pure 7a. Compounds 1a-c also react with dihydrogen via regioselective dissociation of phosphine from the site trans to Si, but the final product, fac-(PMe(3))(3)Ru(SiR(3))H(3) (SiR(3) = SiMe(3), 4a; SiMe(2)CH(2)SiMe(3), 4b; SiEt(3), 4c), features hydrides cis to Si. Alternatively, 4a-c have been synthesized by photolysis of (PMe(3))(4)RuH(2) in the presence of a hydrosilane or by exchange of fac-(PMe(3))(3)Ru(SiR(3))H(3) with another HSiR(3). The reverse manifold - HH elimination from 4a and trapping with PMe(3) or PMe(3)-d(9) - is also regioselective (1a-d(9)() is predominantly produced with PMe(3)-d(9) trans to Si), but is very unfavorable. At 70 degrees C, a slower but irreversible SiH elimination also occurs and furnishes (PMe(3))(4)RuH(2). The structure of 4a exhibits a tetrahedral P(3)Si environment around the metal with the three hydrides adjacent to silicon and capping the P(2)Si faces. Although strong Si...HRu interactions are not indicated in the structure or by IR, the HSi distances (2.13-2.23(5) A) suggest some degree of nonclassical SiH bonding in the H(3)SiR(3) fragment. Thermolysis of 1a in C(6)D(6) at 45-55 degrees C leads to an intermolecular CD activation of C(6)D(6). Extensive H/D exchange into the hydride, SiMe(3), and PMe(3) ligands is observed, followed by much slower formation of cis-(PMe(3))(4)Ru(D)(Ph-d(5)). In an even slower intramolecular CH activation process, (PMe(3))(3)Ru(eta(2)-CH(2)PMe(2))H (5) is also produced. The structure of intermediates, mechanisms, and aptitudes for PMe(3) dissociation and addition/elimination...

Ru(0) complexes of bis(imino)pyridine ligands, [eta2-N3]Ru(eta6-Ar) and {[N3]Ru}2(mu-N2), where Ar = C6H6 or C6H5Me and [N3] = 2,6-(MesN=CMe)2C5H3N, react with N-heterocyclic silicon(IV) compounds to yield Ru(II) silylene complexes of the type [N3]Ru(X)(Cl){Si(NN)} (X = H, Cl, and Si(NN) = N,N'-bis(neopentyl)-1,2-phenylenedi(amino)silylene). The activation of two groups on the silane occurs in a stepwise fashion: initial oxidative addition of a Si-X bond, followed by 1,2-migration (alpha-elimination) of the Si-Cl group to the metal. Reversible dissociation from the Ru(II) center leads to free silylene, which can be preferentially trapped with Ru(0) complexes to generate a zero-valent silylene complex, [N3]Ru(N2){Si(NN)}, which also contains a terminal dinitrogen ligand.