Several chromium complexes supported by a chelating N-heterocyclic carbene ligand have been prepared in an attempt to study their ability to catalyze the polymerization of ethylene. LCrCl 3 (THF) (3) (L ) 1,1′-methylene-3,3′-di-2,6-diisopropylphenylimidazole-2,2′-diylidene (2)) was found to polymerize ethylene when activated by either excess methylaluminoxane (MAO) or excess Et 2 AlCl. Chloride abstraction from 3 with Na + BARF -(BARF ) tetrakis(3,5-di-trifluoromethylphenyl)borate) yielded a dinuclear, chloridebridged product, [(LCrCl) 2 (µ-Cl) 3 ] + BARF -(4). In a similar fashion, reaction of 3 with 3.0 equiv of AlMe 3 gave the dinuclear, chloride-bridged alkyl cation [(LCrMe) 2 (µ-Cl) 3 ] + AlX 4 -(X ) Me, Cl) (5), which is isostructural to 4. A triaryl complex was also prepared by reaction of 2 with CrPh 3 (THF) 3 , giving LCrPh 3 (6) in good yield. Similarly, a series of alkyl and aryl chloride complexes of the form LCrRCl 2 (THF) (R ) Me (7a), Ph (7b), tolyl (7c)) have also been made from the appropriate CrRCl 2 -(THF) 3 starting material. Further treatement of 7a with Na + BARFresulted in the formation of the BARFsalt of complex 5. Complexes 3-6 and 7a-c catalyze the polymerization of ethylene when activated by MAO. Preliminary studies with Cr(II) have shown that LCrX 2 (THF) (X ) Cl (8a), Br (8b)) does not polymerize ethylene upon activation by either MAO or alkylaluminum reagents. Complexes 3-6, 7c, and 8b have been structurally characterized by X-ray diffraction methods.

Addition of N(SiMe 3 ) 2 anion equivalents to i PrNdCdN i Pr followed by reaction with YCl 3 generated the dimeric complex {[(Me 3 Si) 2 NC(N i Pr) 2 ] 2 Y(µ-Cl)} 2 (2). Complex 2 has proven to be an excellent starting material for preparation of a series of hydrocarbyl and amido products, 5), and [(Me 3 Si) 2 NC(N i Pr) 2 ] 2 YC(CH 3 ) 3 ( 6). Definitive evidence for the molecular structures of 2, 3, 5, and 6 is provided through singlecrystal X-ray analyses, which are presented. These results provide the first reported examples of organoyttrium complexes supported by a guanidinate ligand.

RuCl 2 (dcypb)(CO)] 2 2 (dcypb ) 1,4-bis(dicyclohexylphosphino)butane) was prepared in high yield via phosphine exchange between dcypb and RuCl 2 (CO)(PPh 3 ) 2 (DMF) (1). Reaction of 2 with 8 equiv of KBH s Bu 3 affords [fac-RuH 3 (CO)(dcypb)] -(3), stabilized by interactions with a K + counterion and an intact KBH s Bu 3 molecule in the third coordination sphere. Substantial ion pairing accounts for the stability and high hydrocarbon solubility of 3. Complex 3 effects reduction of benzophenone under unprecedentedly mild conditions, at 1 atm of H 2 in refluxing 2-propanol. It is also active for ortho functionalization of benzophenone under 20 atm of ethylene. Stoichiometric experiments reveal facile formation of orthometalated RuH(CO)[OC(C 6 H 4 )(Ph)](dcypb) (5), an intermediate proposed in both types of catalysis. The catalytic activity of isolated 5 supports this hypothesis in the case of hydrogenation but not of Murai catalysis. The X-ray crystal structures of 3 and 5 are reported.

Three dinuclear complexes [{mer-Ru(NH3)3(bpy)}2(μ-L)][ClO4]4, where L = 2,5-dimethyl- (Me2dicyd2-), 2,5-dichloro- (Cl2dicyd2-), and unsubstituted 1,4-dicyanamidobenzene dianion (dicyd2-), have been synthesized and characterized by magnetic resonance, electrochemical, and electronic absorption spectroscopic techniques. A crystal structure of [{mer-Ru(NH3)3(bpy)}2(μ-dicyd)][ClO4]4·3H2O showed dicyd2- to be approximately planar with the cyanamido groups in an anti configuration. Crystal structure data are space group = P1̄, with a, b, and c equal to 12.5613(1), 12.8738(1), and 16.3267(2) Å, respectively, α, β, and γ equal to 76.756(1), 83.893(1), and 69.053(2)°, respectively, V = 2399.28(4) Å3, and Z = 2. The structure was refined using 6112 independent reflections with I > 2.5σ(I) to a final R factor of 0.0568. The strongly coupled mixed-valence complexes [{mer-Ru(NH3)3(bpy)}2(μ-L)]3+ where L = Me2dicyd2-, dicyd2-, and Cl2dicyd2- had decreasing comproportionation constants of 1.3 × 107, 9.3 × 106, and 3.5 × 105, respectively, which are consistent with a hole transfer superexchange mechanism for metal−metal coupling. The mixed-valence properties of these complexes together with analogous systems were compared in the context of a transformation from a localized to a delocalized mixed-valence state.