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.

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.

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.

Reactivities of the dianionic guanidinate complex of [ i PrNdC(N i Pr) 2 ]Ta(NMe 2 ) 3 (1) and the monoanionic guanidinate complex Ta(NMe 2 ) 3 Cl[( i PrN) 2 CN(H) i Pr] (4) have been investigated. Reaction of 1 with Me 3 SiCl produced compound 2, Ta(NMe 2 ) 3 Cl[( i PrN) 2 CN-(SiMe 3 ) i Pr], which is proposed to arise from the addition of the Si-Cl bond across a Ta-N(guanidinate) bond of the starting material rather than one of the Ta-NMe 2 bonds. Complex 2 is the analogue of 4 in which H has been replaced by SiMe 3 . Derivatization of 2 was achieved by reaction with PhCH 2 MgCl to produce Ta(NMe 2 ) 3 (CH 2 Ph)[( i PrN) 2 CN-(SiMe 3 ) i Pr] (3). The single-crystal X-ray-determined structural features of 3 are reported and support the spectroscopic characterization of 3, and indirectly that of 2, by revealing a bidentate tetrasubstituted guanidinate monoanion and an η 1 -benzyl group. Complexes 1 and 4 insert 2,6-dimethylphenyl isocyanide (ArNC) to yield the structurally characterized complex Ta(NMe 5), which possesses one dianionic bidentate guanidinate ligand and two η 2 -iminocarbamoyl ligands derived from the insertion of ArNC into two of the Ta-NMe 2 bonds of the starting materials. The formally sevencoordinate Ta(V) center of 5 can be viewed as pseudo trigonal bipyramidal, with each of the η 2 -CdN linkages occupying a single coordination site. In the case of 4, the transformation of the guanidinate anion into its dianionic form was concomitant with insertion of ArNC. The sources of base for the deprotonation of the guanidinate ligand are likely the amido groups of a portion of the starting material.Supporting Information Available: Figures giving selected 1 H NMR spectra for 3 and X-ray diffraction data, including tables of atomic positions, thermal parameters, crystallographic data, and bond distances and angles and ORTEP drawings, for compounds 3 and 5. This material is available free of charge via the Internet at http://pubs.acs.org. OM991010F

The complexes trans- [Ru(py) 4 L 2 ] where py ) pyridine and L ) (2-chlorophenyl)-, (2,3-dichlorophenyl)-, (2,4,5-trichlorophenyl)-, (2,3,4,5-tetrachlorophenyl)-and (pentachlorophenyl)cyanamide were synthesized and characterized by electronic and 1 H NMR spectroscopies. A crystal structure of trans-[Ru(py) 4 ((2-chlorophenyl)cyanamide) 2 ] showed the expected trans coordination of the phenylcyanamide ligands. Crystal structure data: space group C2/c, with a, b, and c ) 40.6441(3), 9.2003(1), and 22.6946(2) Å, respectively, ) 116.387(1)°, V ) 7602.2(1) Å 3 , and Z ) 8. The structure was refined by using 4943 independent reflections with I > 2σ(I) to a final R factor of 0.060. Spectroelectrochemistry was used to generate the electronic absorption spectra of the Ru(III) complexes trans-[Ru(py) 4 L 2 ] + . Ru(III)-cyanamide coupling elements derived from charge transfer spectral data of the trans-[Ru(py) 4 L 2 ] + complexes were significantly larger than those of the corresponding [Ru(NH 3 ) 5 L] 2+ complexes.

Preparation and characterization of novel alkyl alkylidyne (Me3SiCH2)3W(⋮CSiMe3)(PMe3) (1a) and bis-alkylidene (Me3SiCH2)2W(CHSiMe3)2(PMe3) (1b) and studies of the exchange between alkylidyne 1a and bis-alkylidene 1b are reported. An adduct between PMe3 and alkyl alkylidyne (Me3SiCH2)3W⋮CSiMe3 (2a), (Me3SiCH2)3W(⋮CSiMe3)(PMe3) (1a), was found to undergo a rare reversible transformation to its bis-alkylidene tautomer (Me3SiCH2)2W(CHSiMe3)2(PMe3) (1b). The X-ray crystal structure of 1b has been determined. The bis-alkylidene tautomer 1b is favored in the 1a ⇌ 1b equilibrium with K eq ranging from 12.3(0.2) at 278(1) K to 9.37(0.12) at 303(1) K, giving the thermodynamic parameters for the equilibrium: ΔH° = −1.8(0.5) kcal/mol and ΔS° = −1.5(1.7) eu. The α-H exchange between 1a and 1b follows first-order reversible kinetics. The activation parameters are ΔH ⧧ = 16.2(1.2) kcal/mol and ΔS ⧧ = −22(4) eu for the forward reaction (1a → 1b) and ΔH ⧧ = 18.0(1.3) kcal/mol and ΔS ⧧ = −21(4) eu for the reverse reaction (1b → 1a). An adduct between (Me3SiCH2)3W⋮CSiMe3 and PMe2Ph, (Me3SiCH2)3W(⋮CSiMe3)(PMe2Ph) (3a), was found to undergo a similar reversible transformation to its bis-alkylidene tautomer (Me3SiCH2)2W(CHSiMe3)2(PMe2Ph) (3b). The 3a ⇌ 3b equilibrium is shifted more to the alkyl alkylidyne adduct 3a [K eq‘ = 4.65(0.11) at 303 K] than the 1a ⇌ 1b equilibrium. The forward 3a → 3b conversion in the PMe2Ph complexes is slower than the 1a → 1b conversion at 303 K, whereas the reverse 3b → 3a conversion is slightly faster than the 1b → 1a conversion.

Ru 2 (OAc) 4 ] cleanly reacts with 2-(S)-diphenylphosphinomethylpyrrolidine (PPro) and 2-(S)-diphenylphosphinomethyl-N-methylpyrrolidine (PProMe) to give trans,trans,trans-[Ru(OAc) 2 (PPro) 2 ] (2) and [Ru(OAc) 2 (PProMe) 2 ], respectively, which possess stereogenic nitrogen atoms. The latter complex exists as the cis-P,P-cis-P,N-(∆)-stereoisomer (∆-3) in THF and as the (Λ)-stereoisomer (Λ-5) with cis-P,P-trans-N,N coordination geometry in MeOH. Formation of N-based stereocenters occurs selectively, and complexes 2, 3, and 5 are present as single epimers in solution and in the solid state. Thermolysis of ∆-3 in boiling dioxane affords (∆)-and (Λ)-stereoisomers of the carbene ruthenium complex (7), due to facile dehydrogenation of the N-Me groups of the ligand.