John C. Bollinger

Coordinated carbenes from electron-rich olefins on RuHCl(PPr3i)2

Dehydrohalogenation of RuH2Cl2L2 (L=PPr3i) gives (RuHClL2)2, shown to be a halide-bridged dimer by X-ray crystallography; the fluoride analog is also a dimer. (RuHClL2)2 reacts with N2, pyridine and C2H4 (L′) to give RuHClL′L2, but with vinyl ether and vinyl amides, H2CCH(E) [E=OR, NRC(O)R′] such olefin binding is followed by isomerization to the heteroatom-substituted carbene complex L2HClRuC(CH3)(E). The reaction mechanism for such rearrangement is established by DFT(B3PW91) computations, for C2H4 as olefin (where it is found to be endothermic), and the structures of intermediates are calculated for H2CC(H)(OCH3) and for cyclic and acyclic amide-substituted olefins. It is found, both experimentally and computationally, that the amide oxygen is bonded to Ru, with a calculated bond energy of approximately 9 kcal mol−1 for an acyclic model. Less electron-rich vinyl amides or amines form η2-olefin complexes, but do not isomerize to carbene complexes. Calculated ΔE values for selected ‘‘ competition’’ reactions reveal that donation by both Ru and the heteroatom-substituted X are necessary to make the carbene complex L2HClRuC(X)(CH3) more stable than the olefin complex L2HClRu(η2-H2CCHX). This originates in part from a diminished endothermicity of the olefin→carbene transformation when the sp2 carbon bears a π-donor substituent. The importance of a hydride on Ru in furnishing a mechanism for this isomerization is discussed. The compositional characteristics of Schrock and Fischer carbenes are detailed, it is suggested that reactivity will not be uniquely determined by these characteristics, and these new carbenes RuHCl[C(X)CH3]L2 are contrasted to Schrock and Fischer carbenes.

Synthesis and structure of [(μ3-I)(μ3-WSe4){Ag(PMe2Ph)}3]

Reaction of [NPr 4 ] 2 [WSe 4 ] with [Ag(PMe 3 )I] 4 in CH 3 CN followed by addition of PMe 2 Ph affords the title compound, (μ 3 -iodo)(μ 3 -tetraselenidotungstide)tris(dimethylphenylphosphinesilver), [(μ 3 -I)(μ 3 -WSe 4 ){AgC 8 H 11 P)} 3 ] [systematic name: tris(dimethylphenylphosphine)-2κP,3κP,4κP-μ 3 -iodo-2:3:4κ 3 I-tri-μ 3 -selenido-1:2:3κ 3 Se; 1:2:4κ 3 Se; 1:3:4κ 3 Se-selenido-1κSe-trisilvertungsten], a neutral cubane cluster. The compound was characterized by a single-crystal X-ray structure determination

R-Group reversal of isomer stability for RuH(X)L2(CCHR) s. Ru(X)L2(CCH2R): access to four-coordinate ruthenium carbenes and carbynes

NaOPh converts equimolar RuHClL2(CCHR) (L = PPr3i and PCy3) first to RuH(OPh)L2(CCHR), but then, only for R = H, these isomerize to the more stable carbynes Ru(OPh)L2(C–CH3); the rate of isomerization is slowed considerably by THF. RuH(OPh)L2(CCHR) can also be synthesized by reaction of RuCl2L2[CH(CH2R)] with 2 NaOPh; again, only when R = H does the hydrido vinylidene isomerize to the carbyne. While phenoxide converts RuCl2L2(CHPh) to Ru(OPh)L2(CPh), ia the observable intermediates RuCl2−n(OPh)nL2(CHPh), alkoxides OBut and OAdamantyl cause phosphine displacement to give the four-coordinate carbenes Ru(OR)2L(CHPh). DFT (B3PW91) calculations show these d6 species have a traditional cis-divacant octahedral structure with trans OR groups.

Copper clusters built on bulky amidinate ligands: spin delocalization via superexchange rather than direct metal-metal bonding.

Entry into a new class of tetra- and dicopper clusters was assisted by a fine steric tuning of bulky amidinate ligands that provide spin-delocalizing superexchange pathways in class III mixed-valence clusters, the properties of which are best understood without invoking metal-metal bonding.

Molecular engineering of two-dimensional π-conjugation: expected and unexpected photophysical consequences of a simple particle-in-a-box approach

A highly modular and convergent synthetic route was devised to construct a series of planar π-conjugated molecules with systematically varied structural dimensions and electronic characteristics. High-yielding triple Schiff base condensation reactions between π-extended bulky anilines and 1,3,5-triformylphloroglucinol furnished a series of pseudo C3-symmetric tris(N-salicylideneamine)s displaying intense absorptions at λmax = 445–475 nm and emissions at λmax = 470–504 nm. X-Ray crystallographic studies revealed that intricate hydrogen-bonding networks sustain the planar conjugation of these discotic molecules, the HOMO–LUMO gaps of which decrease with increasing conjugation area. This reduction in excitation energy is accompanied by a nearly 4-fold enhancement in emission quantum yield (ΦF). Past a structural threshold, however, increasing conjugation area leads to either (i) decrease in ΦF or (ii) development of localized electronic transitions. These findings provide a well-defined structural window for future elaboration of this emerging family of dynamic 2-D conjugation, the luminescence properties of which have already been shown to reversibly change in response to external stimuli.

Synthesis, structural characterization and magnetic properties of mixed-valent bis-bipyridine manganese carboxylate clusters

Abstract Procedures have been developed for the synthesis of complexes containing the cations [Mn4O2(O2CR)4(L)2]2+ (R=Me, Et, Ph) (1) and [Mn4O2(MeO)3(O2CPh)2(L)2(MeOH)]2+ (2). Treatment of the corresponding [Mn3O(O2CR)6(py)3](ClO4) complex with the ligand 1,2-bis(bipyridine-6′-yl)ethane (L) in MeCN or MeOH leads to the formation of 1 and 2, respectively. Both complexes contain [Mn4O2] cores. Complex 1 has overall antiferromagnetic coupling resulting in a S=1 spin ground state. The metal centers in the core of complex 2 are also antiferromagnetically coupled, but in this case the spin ground state is S=7/2. Complex 2 also displays an out of phase signal in the ac magnetic susceptibility study, indicating it to be a new example of single molecule magnet (SMM).

HX elimination from Ir(H)2X(PBu2tPh)2 promoted by CO coordination: assessment of X ligand influence

The coordinatively unsaturated complexes Ir(H)2X(PBu2tPh)2 [X=Cl, Br, I, N3, NCNSiMe3, NHC(O)CH3, OC(O)CF3, OSO2CF3, OC(O)CH3, SPh, OPh, F] all react within the mixing time in arene solvents to bind carbon monoxide. Subsequent reactivity of these CO adducts reductively to eliminate HX is dependent on the magnitude of the inherent destabilization caused by filled-filled repulsions between the ligand pπ orbitals and metal dπ orbitals. This destabilization is not sufficient to promote the loss of HX when X=Cl, Br, I, N3, NCNSiMe3, NHC(O)CH3 or OC(O)CF3. When X=OC(O)CH3 or SPh, metastable CO adducts are formed that ultimately lose HX. The complexes containing OPh or F quickly lose HX upon reaction with CO. The unusual iridium(I) complexes IrH(CO)2(PBu2tPh) and IrH(CO)(PBu2tPh)2 have been characterized by multinuclear NMR and IR spectroscopy. The reaction of Ir(H)2(F)(PBu2tPh)2 with CO in a glass vessel yields crystalline [Ir(H)2(CO)2(PBu2tPh)2][SiF5] and [Ir(CO)2(PBu2tPh)2][SiF5]·C6D6, both characterized by X-ray diffraction. The latter, although approximately square planar, has a C–Ir–C angle of only 162.7°. Crystallographic data (Pc at -165 °C) for [Ir(H)2(CO)2(PBu2tPh)2][SiF5], a=8.293(2), b=12.462(5), c=16.333(7) A, β=98.21(2)° with Z=2. Crystallographic data (P21/n at -172 °C) for [Ir(CO)2(PBu2tPh)2][SiF5]·C6D6, a=13.041(7), b=12.998(5), c=22.553(13) A, β=97.50(2)° with Z=4.

Bis(β-diketonate) ligands for the synthesis of bimetalliccomplexes of TiIII, VIII, MnIII andFeIII with a triple-helix structure

Addition of the bis(β-diketone) ligand L [L = 1,3-bis(3-phenyl-3-oxopropanoyl)benzene] to a suitable source of M III ions (M = Ti, V, Mn, Fe) in a L:M = 3:2 ratio gives the dinuclear products [M 2 L 3 ], which have a triple-helical structure.

Common Molecules: Bringing Research and Teaching Together through an Online Collection

The World Wide Web contains a number of collections of data files for molecules with limited usability and utility for users. We describe the design of a Common Molecules collection that provides interactive tools for 3-D visualization of molecules. Our organizational design is intuitive and our collection is large, growing, and provides not only structural information, but also historical and/or key information on the properties of the molecules in the collection. The use of the collection by students and the role of students in the development of the collection are also described.

Monoindenyl Titanium Alkyl Halides. The Synthesis and Molecular structures of (h 5 -C 9 H 7 )TiBr 3 , (h 5 -C 9 H 7 )Ti(CH 3 )Br 2 , and (h 5 -C 9 H 7 )Ti(CH 3 )Cl 2

Abstract The monoindenyl titanium tribromide (η5-C9H7)TiBr3 (1), has been prepared from the interaction of TiBr4 and Bu3SnC9H7. The monomethyl species (η5-C9H7)Ti(CH3)Br2 (2), and (η5-C9H7)Ti(CH3)Cl2 (3), have been efficiently prepared from the interaction of the trihalides with AlMe3. Complexes 1 and 2 represent rare examples of organotitanium bromides, and all three compounds are likely to be of interest in the context of homogeneous olefin polymerization catalysis. All three complexes have been characterized by 1H and 13C NMR spectroscopy and single crystal X-ray crystallography. These analyses reveal that the indenyl complexes exhibit a three-legged piano stool geometry in which the indenyl ligands are bound to the metal centers in an η5 fashion. Crystal data for 1: (T=103 K), molecular formula, C9H7TiBr3, crystal system: monoclinic, space group P21/n, with a=7.155(1), b=12.682(1), c=12.216(1) A, β=97.92°, V=1097.97 A3, Z=4; 2: (T=103 K), molecular formula, C10H10TiBr2, crystal system: triclinic, space group P1, with a=7.142(1), b=12.501(1), c=7.117(1) A, α=105.70(1), β=115.81(1), γ=88.21(1)°, V=547.91 A3, Z=2; 3: (T=110 K), molecular formula, C10H10TiCl2, crystal system: orthorhombic, space group Pcab, with a=11.539(3), b=12.593(3), c=14.327(4) A, V=2081.84 A3, Z=8.