Infrared spectra of metallacyclopropane, insertion, and dihydrido complex products in reactions of laser-ablated group 6 metal atoms with ethylene molecules

Reactions of laser-ablated group 6 metal atoms with ethylene have been investigated. The insertion and dihydrido products (MH-CHCH(2) and MH(2)-C(2)H(2)) are identified from reactions of W and Mo with ethylene isotopomers, whereas products in the Cr spectra are assigned to the insertion and metallacyclopropane (M-C(2)H(4)) complexes. Our experiments with CH(2)CD(2) show that the dihydrido complex is formed by beta-hydrogen transfer in the insertion complex because the MHD-CHCD isotopic product is favored. The present matrix infrared spectra and DFT computational results support the general trend that the higher oxidation-state complexes become more stable on going down the group 6 column. Unlike the cases of group 4 and 5 metals, binary metal hydride (MH(x)) absorptions are not observed in the infrared spectra, suggesting that the H(2)-elimination reactions of ethylene by group 6 metals are relatively slow, consistent with previous gas-phase reaction dynamics studies.     

Infrared spectra of HC[triple bond]C-MH and M-eta2-(C2H2) from reactions of laser-ablated group- 4 transition-metal atoms with acetylene

Reactions of laser-ablated group 4 transition-metal atoms with acetylene have been carried out. The ethynyl metal hydrides (HC[triple bond]C-MH) and corresponding pi complexes (M-eta(2)-(C2H2)) are identified in the matrix infrared spectra. The observed M-H and C-M stretching absorptions show that oxidative C-H insertion readily occurs during codeposition and photolysis afterward. The absorptions from the pi complex, on the other hand, are relatively weak in the original deposition spectrum but increase dramatically in the process of annealing. The vinylidene complex, another plausible product, is not identified in this study. The observed spectra and DFT calculations both show that the back-donations from the group 4 metals to the antibonding pi* orbital of C2H2 are extensive such that the group 4 metals form unusually strong pi complexes. Thus, it is the formation of two Ti-C bonds in the group 4 systems than leads to the stronger bonding than that in the group 8 systems. While bonds form, the Ti atom is weakly bound to C2H2, and we still refer to it as a pi complex. Evidence of relativistic effects is also observed in frequency trends for the Ti, Zr, and Hf products.     

Sequential C-H activation and dinuclear insertion of ethylene promoted by a diiridium complex

Two ethylene molecules, bonded to different metal atoms of a diiridium(I) complex, can be converted into a bridging 3-butenyl-1-yl ligand and a terminal hydride. Such transformation is initiated by an ethylene C-H activation step and followed by an insertion of the second ethylene into a bridging vinyl ligand. This result illustrates the potentiality of diiridium(I) complexes to promote and support reaction sequences of alkene functionalization through C-H activation.     

Preparation and properties of metallacyclobutanes of nickel and palladium

Bis(phosphine)-3,3-dimethylnickela- and palladacyclobutanes have been prepared by intramolecular C-H insertion reaction of the corresponding dineopentyl metal complexes. Nickelacyclobutane complexes decompose when heated thereby undergoing competitive carbon-carbon bond cleavage to give isobutene and ethylene, with reductive elimination affording 1,1-dimethylcyclopropane and skeletal isomeri-zation of the metallacyclic ring yielding 3-methyl-1-butene, whereas the palladium analog gave no significant amounts of CC bond cleavage products.Added phos-phine was seen to have an effect on CC bond scission of nickelacyclobutane complexes. Nickelacyclobutane complexes in solution are thought to be in equilibrium with olefin-coordinated nickel-carbene complex on the basis of available experimental evidence from hydrogenolysis, carbene-trap reactions with olefins and reaction with carbon monoxide     

CX_2(X=H,F,Cl)与甲基异丙基醚C-H键插入反应的理论研究

用从头计算方法在MP2 /6 31G(d)水平上研究了CX2 (X =H ,F ,Cl)与甲基异丙基醚的C -H键插入反应。CCl2 与甲基异丙基醚两个不同的α C的C -H键插入势垒分别为 117.2kJ/mol (甲基 )和 2 0 .6kJ/mol (异丙基 )。CF2 与异丙基α C的C -H键上插入势垒为 12 0 .0kJ/mol,在插入甲基上C -H键时会引起C -O键的断裂。CH2 的插入反应则不需要势垒。对CX2 与二甲醚、甲乙醚、甲基异丙基醚、甲基苄基醚上各种不同的C -H键插入势垒进行了比较 ,甲基和苯基都促使其毗邻的C -H键更容易被CX2 所插入     

Experimental and theoretical study on the structure and formation mechanism of [C6H5Cu(m)]- (m = 1-3)

The important intermediate phenyl-copper metal complexes [C(6)H(5)Cu(m)]- (m = 1-3), which are produced from the reactions between copper metal clusters formed by laser ablation and the benzene molecules seeded in argon carrier gas, are studied by photoelectron spectroscopy(PES) and density functional theory (DFT). Their structures and bonding patterns are investigated, which results in the conclusion that C(6)H(5) groups bond perpendicularly on copper clusters through Cu-C sigma bond. The formation mechanism of these complexes has been studied at B3LYP//6-311G(d, p)/Lanl2dz level. Direct insertion reaction between [Cu(m)]- and C(6)H(6) yields intermediate complex [C(6)H(5)Cu(m)H]-, and then eliminates the H atom, or releases the H atom to other neutral Cu atoms or anionic Cu ions via H abstraction reaction. The first step is the rate-limiting step with C-H activation and cleavage, and H abstraction by neutral Cu atom is the most energetically favorable pathway for the final step. Moreover, the complex [C(6)H(5)Cu(2)]- is ascertained to be easier to be generated than [C(6)H(5)Cu(3)]- and [C(6)H(5)Cu]-, which are in excellent agreement with the experimental results.     

Intramolecular C-H insertion reactions of (eta(5)-cyclopentadienyl)dicarbonyliron carbene complexes: scope of the reactions and application to the synthesis of (+/-)-sterpurene and (+/-)-pentalenene

(eta(5)-Cyclopentadienyl)dicarbonyliron carbene complexes, [(eta(5)-C(5)H(5))(CO)(2)Fe=CHR](+)BF(4)(-), are generated as reactive intermediates from thioether derivatives, (eta(5)-C(5)H(5))(CO)(2)FeCH(R)SPh, by S-alkylation with trimethyloxonium tetrafluoroborate and loss of thioanisole. The carbene complexes undergo intramolecular C-H insertion into appropriately situated side chains to form cyclopentane derivatives. The reaction has been developed into a general procedure employing cycloalkanones as scaffolds bearing the iron carbene moieties and the side chains at C(2) and C(3), respectively. The products of the intramolecular insertion reactions are substituted bicyclo[n.3.0]alkanones. The scope and limitations of the reaction are described. The reaction is applied to a total synthesis of sterpurene and to a formal synthesis of pentalenene. Overall, this approach to cyclopentane annulation complements the related metal-catalyzed insertion reactions of diazocarbonyl compounds, which are also believed to occur via metal carbene complexes.     

Infrared Spectra of CH(3)-MH through Methane Activation by Laser-Ablated Sn, Pb, Sb, and Bi Atoms

Methane activation has been carried out by laser-ablated Sn, Pb, Sb, and Bi atoms. All four metals generate the insertion complex (CH(3)-MH), but subsequent H-migration from C to M to form CH(2)-MH(2) and CH-MH(3) complexes is not observed. Our previous and present experimental and computational results indicate that the higher oxidation state complexes become less favored with increasing atomic mass in groups 14 and 15, which is opposite the general trend found for transition metals. The C-H bond insertion evidently occurs during reaction on sample condensation, and the product dissociates on broad-band photolysis afterward. The insertion complex contains a near right angle C-M-H moiety because of high p contribution from the metal center to the C-M and M-H bonds unlike many transition-metal analogues. The computed methylidene structures for these main group metals are not agostic possibly because of the absence of valence d-orbitals.     

Synthesis and characterization of ethylbis(2-pyridylethyl)amineruthenium complexes and two different types of C-H bond cleavage at an ethylene arm

Ruthenium complexes bearing ethylbis(2-pyridylethyl)amine (ebpea), which has flexible -C(2)H(4)- arms between the amine and the pyridyl groups and coordinates to a metal center in facial and meridional modes, have been synthesized and characterized. Three trichloro complexes, fac-[Ru(III)Cl(3)(ebpea)] (fac-[1]), mer-[Ru(III)Cl(3)(ebpea)] (mer-[1]), and mer-[Ru(II)Cl(3){η(2)-N(C(2)H(5))(C(2)H(4)py)═CH-CH(2)py}] (mer-[2]), were synthesized using the Ru blue solution. Formation of mer-[2] proceeded via a C-H activation of the CH(2) group next to the amine nitrogen atom of the ethylene arm. Reduction reactions of fac- and mer-[1] afforded a triacetonitrile complex mer-[Ru(II)(CH(3)CN)(3)(ebpea)](PF(6))(2) (mer-[3](PF(6))(2)). Five nitrosyl complexes fac-[RuX(2)(NO)(ebpea)]PF(6) (X = Cl for fac-[4]PF(6); X = ONO(2) for fac-[5]PF(6)) and mer-[RuXY(NO)(ebpea)]PF(6) (X = Cl, Y = Cl for mer-[4]PF(6); X = Cl, Y = CH(3)O for mer-[6]PF(6); X = Cl, Y = OH for mer-[7]PF(6)) were synthesized and characterized by X-ray crystallography. A reaction of mer-[2] in H(2)O-C(2)H(5)OH at room temperature afforded mer-[1]. Oxidation of C(2)H(5)OH in H(2)O-C(2)H(5)OH and i-C(3)H(7)OH in H(2)O-i-C(3)H(7)OH to acetaldehyde and acetone by mer-[2] under stirring at room temperature occurred with formation of mer-[1]. Alternative C-H activation of the CH(2) group occurred next to the pyridyl group, and formation of a C-N bond between the CH moiety and the nitrosyl ligand afforded a nitroso complex [Ru(II)(N(3))(2){N(O)CH(py)CH(2)N(C(2)H(5))C(2)H(4)py}] ([8]) in reactions of nitrosyl complexes with sodium azide in methanol, and reaction of [8] with hydrochloric acid afforded a corresponding chloronitroso complex [Ru(II)Cl(2){N(O)CH(py)CH(2)N(C(2)H(5))C(2)H(4)py}] ([9]).     

Migratory insertion of [B(C6F5)2] into C-H bonds: CO promoted transfer of the boryl fragment

The reaction of (eta(5)-C5H5)Fe(CO)2B(C6F5)2 with CO has been shown to proceed via ligand substitution at the metal with accompanying transfer of the boryl fragment (via C-H insertion) to the Cp ring, thereby generating the zwitterion [eta(5)-C5H4B(C6F5)2H]Fe(CO)3 in quantitative yield.     

Infrared spectra of CH3-MH, CH3-M, and CH3-MH- prepared via methane activation by laser-ablated Au, Ag, and Cu atoms

Methane activation by laser-ablated, excited Group 11 metal atoms has been carried out, leading to generation of CH(3)-MH, CH(3)-M, and CH(3)-MH(-), which are identified in the product infrared spectra on the basis of isotopic shifts and correlation with DFT calculated frequencies. The products reveal that C-H insertion by excited Au, Ag, and Cu readily occurs, and subsequent hydride-detachment or electron addition also follows. Each type of product has similar photochemical properties regardless of the metal. DFT computed energies reveal facile hydride dissociation and high electron affinities for the insertion complexes. The methyl metal species have the shortest C-M bonds, consistent with their highest calculated effective bond order, and the CH(3)-MH complexes have higher electron affinities than the metal atoms.     

Matrix isolation investigation of the photochemical reaction of methyl-substituted benzenes with CrCl2O2

The matrix isolation technique, combined with infrared spectroscopy, has been used to characterize the products of the photochemical reactions of toluene, m-, o-, and p-xylene, mesitylene, and hexamethylbenzene with CrCl2O2. While initial twin jet deposition of the reagents led to no visible changes in the recorded spectra, strong product bands were noted following irradiation with light of lambda > 300 nm. The irradiation was shown to lead to oxygen atom transfer, forming complexes between methylcyclohexadienone derivatives and CrCl2O. With the xylenes and mesitylene, di- and trimethylphenols, complexed to CrCl2O, were also observed, respectively. This latter result arises from C-H bond activation and oxygen atom insertion into a C-H bond. The identification of the complexes was further supported by isotopic labeling (2H) and by density functional calculations at the B3LYP/6-311G++(d,2p) level. Product distributions were rationalized by an analysis of the electron density distribution.     

Calculational and experimental investigations of the pressure effects on radical-radical cross combination reactions: C2H5+C2H3

Pressure-dependent product yields have been experimentally determined for the cross-radical reaction C2H5 + C2H3. These results have been extended by calculations. It is shown that the chemically activated combination adduct, 1-C4H8*, is either stabilized by bimolecular collisions or subject to a variety of unimolecular reactions including cyclizations and decompositions. Therefore the "apparent" combination/disproportionation ratio exhibits a complex pressure dependence. The experimental studies were performed at 298 K and at selected pressures between about 4 Torr (0.5 kPa) and 760 Torr (101 kPa). Ethyl and vinyl radicals were simultaneously produced by 193 nm excimer laser photolysis of C2H5COC2H3 or photolysis of C2H3Br and C2H5COC2H5. Gas chromatograph/mass spectrometry/flame ionization detection (GC/MS/FID) were used to identify and quantify the final reaction products. The major combination reactions at pressures between 500 (66.5 kPa) and 760 Torr are (1c) C2H5+C2H3-->1-butene, (2c) C2H5 + C2H5-->n-butane, and (3c) C2H3+C2H3-->1,3-butadiene. The major products of the disproportionation reactions are ethane, ethylene, and acetylene. At moderate and lower pressures, secondary products, including propene, propane, isobutene, 2-butene (cis and trans), 1-pentene, 1,4-pentadiene, and 1,5-hexadiene are also observed. Two isomers of C4H6, cyclobutene and/or 1,2-butadiene, were also among the likely products. The pressure-dependent yield of the cross-combination product, 1-butene, was compared to the yield of n-butane, the combination product of reaction (2c), which was found to be independent of pressure over the range of this study. The [1-C4H8]/[C4H10] ratio was reduced from approximately 1.2 at 760 Torr (101 kPa) to approximately 0.5 at 100 Torr (13.3 kPa) and approximately 0.1 at pressures lower than about 5 Torr (approximately 0.7 kPa). Electronic structure and RRKM calculations were used to simulate both unimolecular and bimolecular processes. The relative importance of C-C and C-H bond ruptures, cyclization, decyclization, and complex decompositions are discussed in terms of energetics and structural properties. The pressure dependence of the product yields were computed and dominant reaction paths in this chemically activated system were determined. Both modeling and experiment suggest that the observed pressure dependence of [1-C4H8]/[C4H10] is due to decomposition of the chemically activated combination adduct 1-C4H8* in which the weaker allylic C-C bond is broken: H2C=CHCH2CH3-->C3H5+CH3. This reaction occurs even at moderate pressures of approximately 200 Torr (26 kPa) and becomes more significant at lower pressures. The additional products detected at lower pressures are formed from secondary radical-radical reactions involving allyl, methyl, ethyl, and vinyl radicals. The modeling studies have extended the predictions of product distributions to different temperatures (200-700 K) and a wider range of pressures (10(-3)-10(5) Torr). These calculations indicate that the high-pressure [1-C4H8]/[C4H10] yield ratio is 1.3+/-0.1.     

Theoretical studies of molybdenum peroxo complexes [MoOn(O2)3-n(OPH3)] as catalysts for olefin epoxidation

The equilibrium geometries of the molybdenum oxo/peroxo compounds MoOn(O2)3-n and the related complexes [MoOn(O2)3-n(OPH3)] and [MoOn(O2)3-n(OPH3)(H2O)] (n = 0-3) have been calculated using gradient-corrected density-functional theory at the B3LYP level. The structures of the peroxo complexes with ethylene ligands [MoOn(O2)3-n(C2H4)] and [MoOn(O2)3-n(OPH3)(C2H4)] (n = 1, 2) where ethylene is directly bonded to the metal have also been optimized. Calculations of the metal-ligand bond-dissociation energies show that the OPH3 ligand in [MoOn(O2)3-n(OPH3)] is much more strongly bound than the ethylene ligand in [MoOn(O2)3-n(C2H4)]. This makes the substitution of phosphane oxide by olefins in the epoxidation reaction unlikely. An energy-minimum structure is found for [MoO(O2)2(OPH3)(C2H4)], for which the dissociation of C2H4 is exothermic with D0 = -5.2 kcal/mol. The reaction energies for the perhydrolysis of the oxo complexes with H2O2 and the epoxidation of ethylene by the peroxo complexes have also been calculated. The peculiar stability of the diperoxo complex [MoO(O2)2(OPH3)(H2O)] can be explained with the reaction energies for the perhydrolysis of [MoOn(O2)3-n(OPH3)(H2O)]. The first perhydrolysis step yielding the monoperoxo complex is less exothermic than the second perhydrolysis reaction, but the further reaction with H2O2 yielding the unknown triperoxo complex is clearly endothermic. CDA analysis of the metal-ethylene bond shows that the binding interactions are mainly caused by charge donation from the ligand to the metal.     

Reactions of monomeric [1,2,4-(Me3C)3C5H2]2CeH and CO with or without H2: an experimental and computational study

Addition of CO to [1,2,4-(Me3C)3C5H2]2CeH,Cp'2 CeH, in toluene yields the cis-(Cp'2Ce)2(mu-OCHCHO), in which the cis-enediolate group bridges the two metallocene fragments. The cis-enediolate quantitatively isomerizes intramolecularly to the trans-enediolate in C6D6 at 100 degrees C over 7 months. When the solvent is pentane, Cp'2Ce(OCH2)CeCp'2 forms, in which the oxomethylene group or the formaldehyde dianion bridges the two metallocene fragments. The cis-enediolate is suggested to form by insertion of CO into the Ce-C bond of Cp'2Ce(OCH2)CeCp'2, generating Cp'2CeOCH2COCeCp'2. The stereochemistry of the cis-enediolate is determined by a 1,2-hydrogen shift in the OCH2CO fragment that has the OC(H2) bond anti-periplanar relative to the carbene lone pair. The bridging oxomethylene complex reacts with H2, but not with CH4, to give Cp'2CeOMe, which is also the product of the reaction between Cp'2CeH and a mixture of CO and H2. The oxomethylene complex reacts with CO to give the cis-enediolate complex. DFT calculations on C5H5 model metallocenes show that the reaction of Cp2CeH with CO and H2 to give Cp2CeOMe is exoergic by 50 kcal mol-1. The net reaction proceeds by a series of elementary reactions that occur after the formyl complex, Cp2Ce(eta2-CHO), is formed by further reaction with H2. The key point that emerges from the calculated potential energy surface is the bifunctional nature of the metal formyl in which the carbon atom behaves as a donor and acceptor. Replacing H2 by CH4 increases the activation energy by 17 kcal mol-1.     

The role of group 14 element hydrides in the activation of C-h bonds in cyclic olefins

Formally, triple-bonded dimetallynes ArEEAr [E = Ge (1), Sn (2); Ar = C(6)H(3)-2,6-(C(6)H(3)-2,6-(i)Pr(2))(2)] have been previously shown to activate aliphatic, allylic C-H bonds in cyclic olefins, cyclopentadiene (CpH), cyclopentene (c-C(5)H(8)) and 1,4-cyclohexadiene, with intriguing selectivity. In the case of the five-membered carbocycles, cyclopentadienyl species ArECp [E = Ge (3), Sn (4)] are formed. In this study, we examine the mechanisms for activation of CpH and c-C(5)H(8) using experimental methods and describe a new product found from the reaction between 1 and c-C(5)H(8), an asymmetrically substituted digermene ArGe(H)Ge(c-C(5)H(9))Ar (5), crystallized in 46% yield. This compound contains a hydrogenated cyclopentyl moiety and is found to be produced in a 3:2 ratio with 3, explaining the fate of the liberated H atoms following triple C-H activation. We show that when these C-H activation reactions are carried out in the presence of tert-butyl ethylene (excess), compounds {ArE(CH(2)CH(2)tBu)}(2) [E = Ge(8), Sn(9)] are obtained in addition to ArECp; in the case of CpH, the neohexyl complexes replace the production of H(2) gas, and for c-C(5)H(8) they displace cyclopentyl product 5 and account for all the hydrogen removed in the dehydroaromatization reactions. To confirm the source of 8 and 9, it was demonstrated that these molecules are formed cleanly between the reaction of (ArEH)(2) [E = Ge(6), Sn(7)] and tert-butyl ethylene, new examples of noncatalyzed hydro-germylation and -stannylation. Therefore, the presence of transient hydrides of the type 6 and 7 can be surmised to be reactive intermediates in the production of 3 and 4, along with H(2), from 1 and 2 and CpH (respectively), or the formation of 3 and 5 from 1. The reaction of 6 or 7 with CpH gave 3 or 4, respectively, with concomitant H(2) evolution, demonstrating the basic nature of these low-valent group 14 element hydrides and their key role in the 'cascade' of C-H activation steps. Additionally, during the course of these studies a new polycyclic compound (ArGe)(2)(C(7)H(12)) (10) was obtained in 60% yield from the reaction of 1,6-heptadiene and 1 via double [2 + 2] cycloaddition and gives evidence for a nonradical mechanism for these types of reactions.     

Theoretical study on the structure and formation mechanism of [C6H5Mm]- (M=Ag, Au; m=1-3)

The structures and formation mechanisms of the important intermediate phenyl-coinage metal complexes [C(6)H(5)M(m)](-) (M==Ag, Au, m = 1-3) are investigated at B3LYP//6-311G(d, p)/Lanl2dz level using Gaussian 03 program. The adiabatic electron affinity and vertical dissociation energy of [M(m)](-) and [C(6)H(5)M(m)](-) are calculated, which are excellently coincident with the experimental determination. The C(6)H(5) group bonds on metal clusters through M--C sigma bond in the complex [C(6)H(5)M(m)](-). The complexes [C(6)H(5)M(m)](-) (M==Ag, Au; m = 2-3) are generated through a stepwise reaction. The first step is a direct insertion reaction between [M(m)](-) (M==Ag, Au, m = 1-3) and C(6)H(6,) which leads to the generation of intermediate [C(6)H(5)M(m)H](-) (m = 1-3) with the activation and cleavage of C--H bond. The second step is the neutral metal atom abstracting the H atom to yield the product [C(6)H(5)M(m)](-).     

DFT studies on the copolymerization of alpha-olefins with polar monomers: ethylene-methyl acrylate copolymerization catalyzed by a Pd-based diimine catalyst.

Gradient-corrected density functional theory has been used to study the elementary reactions for the copolymerization of ethylene with methyl acrylate catalyzed by Pd-based diimine catalysts, modeled by the generic complex N(wedge)N-Pd(n-C(3)H(7))(+), with N(wedge)N = -NHCHCHNH-. The steric effects in the real systems are discussed on the basis of the calculations for the catalyst with N(wedge)N = -NArCRCRNAr-, R = CH(3), and Ar = C(6)H(3)(i-Pr(2)) and the previous calculations on ethylene/propylene polymerization. Considerations have been given to the different possible acrylate complexes, as well as the transition states and the products (agostic complexes and the alternative chelates) for two acrylate insertion paths (1,2 and 2,1). The chelate-opening reactions have also been studied. The results revealed a strong electronic preference for the 2,1-insertion paths, with a barrier that is 4.5 kcal/mol lower than any other studied insertion pathway. In the real systems the 2,1-insertion of acrylate is preferred by 0.5 kcal/mol. The 2,1-insertion barrier calculated for the real system of 12.4 kcal/mol is in very good agreement with the experimental value of 12.1 kcal/mol. The six-member chelate is the most stable insertion product with an energy that is 21 kcal/mol lower than the kinetic insertion product. The reactions of the chelate opening by ethylene that start from the lowest energy complexes have the lowest barrier for the four-member ring (23 kcal/mol) and the highest for the six-member structure (30.4 kcal/mol). The high barrier for the opening of the six-member chelate suggests the possibility of a two-step chelate-opening mechanism. The internal barriers for the chelate-opening reactions starting from the higher energy complexes are lower then the one-step reaction that starts from the preferred complex and comparable to those of the ethylene insertion into the Pd-alkyl bond. While the chelate opening by a subsequent acrylate insertion seems to be facile for the generic catalyst, steric effects in the real catalyst are likely to decrease the acrylate pi-complexation energies and increase the insertion barriers to the extent where such a reaction becomes unfeasible.     

Synthesis and properties of mononuclear and binuclear molybdenum complexes derived from bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone

The monomer molybdenum(VI) complex [MoO(2)(napoxlhH(2))].2H(2)O (1) has been synthesized from the reaction of MoO(2)(acac)(2) with bis(2-hydroxy-1-naphthaldehyde)oxaloyldihydrazone (napoxlhH(4)) in 1:1 molar ratio in ethanol under reflux. This complex on reaction with pyridine/3-picoline/4-picoline yielded the dimer molybdenum(VI) complexes [Mo(2)O(4)(napoxlhH(2))(2)(A)(2)].2H(2)O (A=py (2), 3-pic (3), 4-pic (4)), whereas reaction with isonicotinoylhydrazine (inhH(3)) and salicyloylhydrazine (sylshH(3)) lead to the reduction of the metal centre yielding monomeric molybdenum(V) complexes [Mo(napoxlhH(2))(hzid)].2H(2)O (where hzidH(3)=inhH(3) (5) and sylshH(3) (6)). The complexes have been characterized by elemental analyses, molecular weight determinations, molar conductance data, magnetic moment data, electronic, IR, ESR and (1)H NMR spectroscopic studies. The complexes (5) and (6) are paramagnetic to the extent of one unpaired electron. The electronic spectra of the complexes are dominated by strong charge transfer bands. In all of the complexes, the principal dihydrazone ligand has been suggested to coordinate to the metal centres in the anti-cis-configuration. The complexes (1), (5) and (6) are suggested to have six-coordinate octahedral stereochemistry around molybdenum(VI) and molybdenum(V) metal centres, respectively, while the complexes (2)-(4) are suggested to have eight coordinate dodecahedral stereochemistry around molybdenum(VI) metal centre.     

Aryl C-H amination by diruthenium nitrides in the solid state and in solution at room temperature: experimental and computational study of the reaction mechanism

Diruthenium azido complexes Ru(2)(DPhF)(4)N(3) (1a, DPhF = N,N'-diphenylformamidinate) and Ru(2)(D(3,5-Cl(2))PhF)(4)N(3) (1b, D(3,5-Cl(2))PhF = N,N'-bis(3,5-dichlorophenyl)formamidinate) have been investigated by thermolytic and photolytic experiments to investigate the chemical reactivity of the corresponding diruthenium nitride species. Thermolysis of 1b at ~100 °C leads to the expulsion of N(2) and isolation of Ru(2)(D(3,5-Cl(2))PhF)(3)NH(C(13)H(6)N(2)Cl(4)) (3b), in which a nitrogen atom has been inserted into one of the proximal aryl C-H bonds of a D(3,5-Cl(2))PhF ligand. A similar C-H insertion product is obtained upon thawing a frozen CH(2)Cl(2) solution of the nitride complex Ru(2)(DPhF)(4)N (2a), formed via photolysis at -196 °C of 1a to yield Ru(2)(DPhF)(3)NH(C(13)H(10)N(2)) (3a). Evidence is provided here that both reactions proceed via direct intramolecular attack of an electrophilic terminal nitrido nitrogen atom on a proximal aryl ring. Thermodynamic and kinetic data for this reaction are obtained from differential scanning calorimetric measurements and thermal gravimetric analysis of the thermolysis of Ru(2)(D(3,5-Cl(2))PhF)(4)N(3), and by Arrhenius/Eyring analysis of the conversion of Ru(2)(DPhF)(4)N to its C-H insertion product, respectively. These data are used to develop a detailed, experimentally validated DFT reaction pathway for N(2) extrusion and C-H functionalization from Ru(2)(D(3,5-Cl(2))PhF)(4)N(3). The diruthenium nitrido complex is an intermediate in the calculated reaction pathway, and the C-H functionalization event shares a close resemblance to a classical electrophilic aromatic substitution mechanism.