IR and Raman characterization of the zincocenes (eta(5)-C5Me5)2Zn2 and (eta(5)-C5Me5)(eta(1)-C5Me5)Zn

The measured Raman and IR spectra of solid, polycrystalline bis(pentamethylcyclopentadienyl)dizinc, (eta(5)-C5Me5)2Zn2, 1, and bis(pentamethylcyclopentadienyl)monozinc, (eta(5)-C5Me5)(eta(1)-C5Me5)Zn, 8, are reported in some detail. The IR spectra of the vapors of 1 and 8 each trapped in a solid Ar matrix at 12 K confirm the essentially molecular character of the solids. The experimental results have been interpreted with particular reference (i) to the corresponding spectra of (68)Zn-enriched samples of the compounds, and (ii) to the spectra simulated by density functional theory (DFT) calculations at the B3LYP level. The marked differences of structure of 1 and 8 contrast with the relatively close similarity of their vibrational spectra, disparities being revealed only on detailed scrutiny, including the effects of (68)Zn enrichment, and primarily at wavenumbers below 1000 cm(-1). The Zn-Zn stretching motion of 1 features not as a single, well-defined mode identifiable with intense Raman scattering but in several normal modes which respond in varying degrees to (68)Zn substitution. A stretching force constant of 1.42 mdyne A(-1) has been estimated for the Zn-Zn bond of 1.     

Condensed metallaborane clusters: synthesis and structure of Fe2(CO)6(eta5-C5Me5RuCO)(eta5-C5Me5Ru)B6H10

Mild pyrolysis of (eta5-C5Me5Ru)2B6H12 with Fe2(CO)9 yields the 12 skeletal electron pair (sep) Fe2(CO)6(eta5-C5Me5RuCO)(eta5-C5Me5Ru)B6H10 cluster; the title compound represents a novel class of hybrid multiple cluster in which a Fe2B2 tetrahedron has been fused to a ruthenaborane substrate.     

On the origin of dinitrogen hydrogenation promoted by [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2)

The origin of the hydrogenation of the dinitrogen ligand in [(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2) has been investigated by a combined computational and experimental study. Density functional theory calculations on the zirconocene dinitrogen complex demonstrate significant imido character in the zirconium nitrogen bonds, arising from effective pi-back-bonding from the low-valent zirconium and the side-on bound N2 ligand. The twisted ground-state structure of the N2 complex is a key requirement for nitrogen hydrogenation, as calculations on the model complex [(eta5-C5H5)2Zr]2(mu2,eta2,eta2-N2) reveal reduced overlap as the dihedral angle between the zirconocene wedges approaches 0 degrees . Experimentally, isotopic labeling studies on the microscopic reverse are consistent with a 1,2-addition mechanism for nitrogen hydrogenation.     

Reductive activation of carbon-fluorine bonds in perfluoroalkyl ligands: an unexpected route to the only known tetrafluorobutatriene transition metal complex: Ir(eta 5-C5Me5)(PMe3)(2,3-eta 2 -CF2[double bond]C[double bond]C[double bond]CF2)

Six-electron reduction of the perfluoro-sec-butyl ligand in Cp*Ir(PMe3)I(C4F9) with sodium naphthalenide affords the first known example of a transition metal complex of tetrafluorobutatriene, Cp*Ir(PMe3)(C4F4). The free ligand is a highly unstable compound. The compound has been completely characterized by a single-crystal X-ray diffraction study; the center coordinated double bond shows significant elongation, and the flanking fluoroalkenes show significant shortening, as compared to the dimensions in the free ligand.     

Metallaboranes of the Early Transition Metals: Direct Synthesis and Characterization of [{(eta5-C5Me5)Ta}2BnHm] (n=4, m=10; n=5, m=11), [{(eta5-C5Me5)Ta}2B5H10(C6H4CH3)], and [{(eta5-C5Me5)TaCl}2B5H11

Reaction of [Cp*TaCl4] (Cp*=eta5-C5Me5) with a sixfold excess of LiBH(4)thf followed by BH3thf in toluene at 100 degrees C led to the isolation of hydrogen-rich metallaboranes [(Cp*Ta)2B4H10] (1), [(Cp*Ta)2B5H11] (2), [(Cp*Ta)2B5H10(C6H4CH3)] (3), and [(Cp*TaCl)2B5H11] (4) in modest yield. Compounds 1-3 are air- and moisture-sensitive but 4 is reasonably stable in air. Their structures are predicted by the electron-counting rules to be a bicapped tetrahedron (1), bicapped trigonal bipyramids (2, 3), and a nido structure based on a closo dodecahedron 4. Yellow tantalaborane 1 has a nido geometry with C2v symmetry and is isostructural with [(Cp*M)2B4H8] (M=Cr and Re); whereas 2 and 3 are C3v-symmetric and isostructural with [(Cp*M)2B5H9] (M=Cr, Mo, W) and [(Cp*ReH)2B5Cl5]. The most remarkable feature of 4 is the presence of a hydride ligand bridging the ditantalum center to form a symmetrical tantalaborane cluster with a long Ta--Ta bond (3.22 A). Cluster 4 is a rare example of electronically unsaturated metallaborane containing four TaHB bonds. All these new metallaboranes have been characterized by mass spectrometry, 1H, 11B, and 13C NMR spectroscopy, and elemental analysis, and the structural types were unequivocally established by crystallographic analysis of 1-4.     

Electron paramagnetic resonance and spectroscopic characteristics of electrogenerated mixed-valent systems [(eta 5-C5Me5)M(mu-L)M(eta 5-C5Me5)]+ (M = Rh, Ir; L = 2,5-diiminopyrazines) in relation to the radicals [(eta 5-C5Me5)ClM(mu-L)MCl(eta 5-C5Me5)]+ and [(eta 5-C5Me5)M(mu-L)MCl(eta 5-C5Me5)]2+

Electrochemical reduction of the dinuclear [(eta 5-C5Me5)ClM(mu-L)MCl(eta 5-C5Me5)]2+ ions (M = Rh, Ir; L = 2,5-bis(1-phenyliminoethyl)pyrazine (bpip) and 2,5-bis[1-(2,6-dimethylphenyl)iminoethyl]pyrazine (bxip)) proceeds via the paramagnetic intermediates [(eta 5-C5Me5)ClM(mu-L)MCl(eta 5-C5Me5)]+ (L = bpip) or [(eta 5-C5Me5)M(mu-L)MCl(eta 5-C5Me5)]2+ (L = bxip) and [(eta 5-C5Me5)M(mu-L)M(eta 5-C5Me5)]+. Whereas the first is clearly a radical species with a small g anisotropy, the chloride-free cations are distinguished by structured intervalence charge transfer (IVCT) bands in the near-infrared region and by rhombic electron paramagnetic resonance features between g = 1.9 and g = 2.3, which suggests considerable metal participation at the singly occupied MO. Alternatives for the d configuration assignment and for the role of the bisbidentate-conjugated bridging ligands will be discussed. The main difference between bpip and bxip systems is the destabilization of the chloride-containing forms through the bxip ligand for reasons of steric interference.     

Theoretical study of the mechanism of hydrogenation of side-on coordinated dinitrogen activated by Zr binuclear complexes ([(eta5-C5Me4H)2Zr]2(mu2,eta2,eta2-N2))

The reaction mechanism of the reduction of dinitrogen coordinated side-on to a binuclear Zr complex, [(eta(5)-C(5)Me(4)H)(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) (T1), was investigated theoretically using a model complex, [(eta(5)-C(5)H(5))(2)Zr](2)(mu(2),eta(2),eta(2)-N(2)) (A1), employing density functional theory calculations. The effectiveness of A1 in describing T1 was confirmed by comparing the structures, distributions of charge, and frontier molecular orbitals. Our calculations showed that A1 has a twisted structure, resembling that of T1, which results in similar properties. The calculations for A1 and its derivatives on H(2) addition clearly explain the reaction mechanism and the reaction path that T1 follows, as well as the experimentally required reaction conditions. The immediate reaction of the first and second H(2) additions produces [(eta(5)-C(5)Me(4)H)(2)ZrH](2)(mu(2),eta(2),eta(2)-N(2)H(2)) (T2), and this is explained by the barrier heights of the reaction, which were calculated to be 20.4 and 10.9 kcal/mol, respectively. The latter barrier was below that of A1 + 2H(2). Complex T2 may be the initial complex for further H(2) addition under proper conditions, or it could lose one H(2) molecule followed by H migration from the Zr site to the N site. Both reactions are expected to occur, because of the closeness of the barrier heights (25.1 and 36.5 kcal/mol, respectively). Gentle warming is required for further H(2) additions, which can be understood from the energetics as well. The high reactivity of T1 with H(2) has been discussed by the comparison of the calculation of A1 and another complex with different ligands, presenting an interesting indication on the effects of the ligands. These theoretical results and discussion explaining the experiment should provide insight into the nature of the hydrogenation mechanism.     

Macropolyhedral boron-containing cluster chemistry. The unique nido-five-vertex-<B2>-nido-ten-vertex conjuncto structure of [(eta5-C5Me5)2Rh2B11H15] via an unexpected cluster-dismantling

B16H20 and [RhCl2(eta5-C5Me5)]2 with tmnd give [(eta5-C5Me5)2Rh2B11H15], which has an unprecedented thirteen-vertex macropolyhedral cluster core based on a nido ten-vertex {MB9} subcluster and a nido five-vertex {MB4} subcluster fused with their open-face {B2} edges in common.     

Reductive reactivity of the organolanthanide hydrides, [(C5Me5)2LnH]x, leads to ansa-allyl cyclopentadienyl (eta(5)-C5Me4CH2-C5Me4CH2-eta(3))2- and trianionic cyclooctatetraenyl (C8H7)3- ligands

The reductive reactivity of lanthanide hydride ligands in the [(C5Me5)2LnH]x complexes (Ln = Sm, La, Y) was examined to see if these hydride ligands would react like the actinide hydrides in [(C5Me5)2AnH2]2 (An = U, Th) and [(C5Me5)2UH]2. Each lanthanide hydride complex reduces PhSSPh to make [(C5Me5)2Ln(mu-SPh)]2 in approximately 90% yield. [(C5Me5)2SmH]2 reduces phenazine and anthracene to make [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C12H8N2) and [(C5Me5)2Sm]2(mu-eta(3):eta(3)-C10H14), respectively, but the analogous [(C5Me5)2LaH]x and [(C5Me5)2YH]2 reactions are more complicated. All three lanthanide hydrides reduce C8H8 to make (C5Me5)Ln(C8H8) and (C5Me5)3Ln, a reaction that constitutes another synthetic route to (C5Me5)3Ln complexes. In the reaction of [(C5Me5)2YH]2 with C8H8, two unusual byproducts are obtained. In benzene, a (C5Me5)Y[(eta(5)-C5Me4CH2-C5Me4CH2-eta(3))] complex forms in which two (C5Me5)(1-) rings are linked to make a new type of ansa-allyl-cyclopentadienyl dianion that binds as a pentahapto-trihapto chelate. In cyclohexane, a (C5Me5)2Y(mu-eta(8):eta(1)-C8H7)Y(C5Me5) complex forms in which a (C8H8)(2-) ring is metalated to form a bridging (C8H7)(3-) trianion.     

Formation of two isomeric closo-[(eta5-C5H5)FePC2B8H10] phosphadicarbaborane analogues of ferrocene via isolable eta1-bonded complexes of the [7-[(eta5-C5H5)Fe(CO)2]-(eta1-nido-PC2B8H10)] type

The reaction of nido-[7,8,9-PC(2)B(8)H(11)] (1) with [[CpFe(CO)(2)](2)] (Cp=eta(5)-C(5)H(5) (-)) in benzene (reflux, 3 days) gave an eta(1)-bonded complex [7-Fp-(eta(1)-nido-7,8,9,-PC(2)B(8)H(10))] (2; Fp=CpFe(CO)(2); yield 38 %). A similar reaction at elevated temperatures (xylene, reflux 24 h) gave the isomeric complex [7-Fp-(eta(1)-nido-7,9,10-PC(2)B(8)H(10))] (3; yield 28 %) together with the fully sandwiched complexes [1-Cp-closo-1,2,4,5-FePC(2)B(8)H(10)] 4 a (yield 30%) and [1-Cp-closo-1,2,4,8-FePC(2)B(8)H(10)] 4 b (yield 5%). Compounds 2 and 3 are isolable intermediates along the full eta(5)-complexation pathway of the phosphadicarbaborane cage; their heating (xylene, reflux, 24 h) leads finally to the isolation of compounds 4 a (yields 46 and 52%, respectively) and 4 b (yields 4 and 5%, respectively). Moreover, compound 3 is isolated as a side product from the heating of 2 (yield 10%). The structure of compound 4 a was determined by an X-ray structural analysis and the constitution of all compounds is consistent with the results of mass spectrometry and IR spectroscopy. Multinuclear ((1)H, (11)B, (31)P, and (13)C), two-dimensional [(11)B-(11)B]-COSY, and (1)H[(11)B(selective)] magnetic resonance measurements led to complete assignments of all resonances and are in excellent agreement with the structures proposed.     

Macropolyhedral boron-containing cluster chemistry. Ligand-induced two-electron variations of intercluster bonding intimacy. Structures of nineteen-vertex [(eta5-C5Me5)HIrB18H19(PMe2Ph)] and the related carbene complex [(eta5-C5Me5)HIrB18H19[C(NHMe)2]

Addition of PMe2Ph to fused-cluster syn-[(eta5-C5Me5)IrB18H20] 1 to give [(eta5-C5Me5)HIrB18H19(PMe2Ph)] 3 entails a diminution in the degree of intimacy of the intercluster fusion, rather than retention of inter-subcluster binding intimacy and a nido-->arachno conversion of the character of either of the subclusters. Reaction with MeNC gives [(eta5-C5Me5)HIrB18H19[C(NHMe)2]] 4 which has a similar structure, but with the ligand now being the carbene [:C(NHMe)2], resulting from a reductive assembly reaction involving two MeNC residues and the loss of a carbon atom.     

Experimental and molecular dynamics simulation study of the sublimation and vaporization energetics of iron metalocenes. crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)

The standard molar enthalpies of sublimation of ferrocene, 1,1'-dimethylferrocene, decamethylferrocene, ferrocenecarboxaldehyde and alpha-methylferrocenemethanol, and the enthalpy of vaporization of N,N-dimethyl(aminomethyl)ferrocene, at 298.15 K, were determined by Calvet-drop microcalorimetry and/or the Knudsen effusion method. The obtained values were used to assess and refine our previously developed force field for metallocenes. The modified force field was able to reproduce the deltasubHdegreesm and deltavapHdegreesm values of the test-set with an accuracy better than 5 kJ.mol-1, except for decamethylferrocene, in which case the deviation between the calculated and experimental deltasubHdegreesm values was 16.1 kJ.mol-1. The origin of the larger error found in the prediction of the sublimation energetics of decamethylferrocene, and which was also observed in the estimation of structural properties (e.g., density and unit cell dimensions), is discussed. Finally, the crystal structures of Fe(eta5-C5H4CH3)2 and Fe[(eta5-(C5H5)(eta5-C5H4CHO)] at 293 and 150 K, respectively, are reported.     

Novel hetero-bimetallic metalla-macrocycles based on the bis-1-pyridyl ferrocene [Fe(eta 5-C5H(4)-1-C5H4N)2] ligand. Design,synthesis and structural characterization of the complexes [Fe(eta 5-C5H(4)-1-C5H4N)2](AgI)2(2+)/(CuII)2(4+)/(ZnII)2(4+)

The bidentate sandwich ligand [Fe(eta 5-C5H(4)-1-C5H4N)2] has been prepared, structurally characterized and employed in the preparation of the novel supramolecular heterobimetallic metalla-macrocycles [Fe(eta 5-C5H(4)-1-C5H4N)2]Ag2(NO3)(2).1.5H2O, [Fe(eta 5-C5H(4)-1-C5H4N)2]Cu2(CH3COO)(4).3H2O and [Fe(eta 5-C5H(4)-1-C5H4N)2]Zn2Cl4.