David G. Churchill

Carbonyl abstraction reactions of Cp*Mo(PMe3)3H with CO2, (CH2O)n, HCO2H, and MeOH: the synthesis of Cp*Mo(PMe3)2(CO)H and the catalytic decarboxylation of formic acid

Abstract Cp*Mo(PMe3)3H undergoes carbonyl abstraction reactions with a variety of reagents, including CO2, (CH2O)n, HCO2H, and MeOH to yield Cp*Mo(PMe3)2(CO)H. The reaction between Cp*Mo(PMe3)3H and HCO2H has been studied by 1H-NMR spectroscopy, which indicates that the initial interaction involves protonation of the molybdenum center to give [Cp*Mo(PMe3)3H2][HCO2]; upon heating to 80xa0°C, however, [Cp*Mo(PMe3)3H2][HCO2] is converted to the carbonyl complex Cp*Mo(PMe3)2(CO)H. In the presence of excess HCO2H, Cp*Mo(PMe3)2(CO)H reacts further to yield Cp*Mo(PMe3)2(CO)(η1-O2CH); the latter complex undergoes decarboxylation at 80xa0°C and regenerates Cp*Mo(PMe3)2(CO)H. Thus, Cp*Mo(PMe3)2(CO)H serves as a catalyst for the decomposition of HCO2H to CO2 and H2. Although the formate complex Cp*Mo(PMe3)2(CO)(η1-O2CH) has not been isolated, the molecular structure of the acetate derivative Cp*Mo(PMe3)2(CO)(η1-O2CMe) has been determined by X-ray diffraction.

Tris(mercaptoimidazolyl)hydroborato complexes of cobalt and iron, [TmPh]2M (M=Fe, Co): structural comparisons with their tris(pyrazolyl)hydroborato counterparts

Abstract The tris(mercaptophenylimidazolyl)borate iron and cobalt complexes [TmPh]2M (M=Fe, Co) have been synthesized by reaction of [TmPh]Tl with MI2. Structural characterization by X-ray diffraction demonstrates that the potentially tridentate [TmPh] ligand binds through only two sulfur donors in these ‘sandwich’ complexes and that the ‘tetrahedral’ metal centers supplement the bonding by interactions with the two B–H groups. Comparison of the structures of [TmPh]2M (M=Fe, Co) with the related tris(pyrazolyl)borate [TpPh]2M counterparts indicates that the tris(mercaptoimidazolyl) ligand favors lower primary coordination numbers in divalent metal complexes. The trivalent complexes, {[TpPh]2Fe}[ClO4] and {[pzBmMe]2Co}I, however, exhibit octahedral coordination, with the ligands binding using their full complement of donor atoms.

Synthesis and structural characterization of 2-mercapto-1-tert-butylimidazole and its Group 12 metal derivatives (HmimtBu)2MBr2 (M = Zn, Cd, Hg)

Abstract2-Mercapto-1-tert-butylimidazole (HmimtBu) and its Group 12 metal complexes (HmimtBu)2 MBr2 (M = Zn, Cd, Hg) have been readily prepared and structurally characterized. Whereas the former displays a dimeric structure in the solid state with two S ⋅ ⋅ ⋅ H–N interactions linking each pair of molecules, the four-coordinate complexes exhibit distorted tetrahedral geometries with the S–M–S angles in the range 103.2–135.2○. The average M–Br bond lengths are 2.401, 2.567, and 2.688 Å for M = Zn, Cd, and Hg, respectively, and the corresponding average M–S bond distances are 2.350, 2.540, and 2.467 Å. The average C–S bond length for all the complexes (1.72 Å) is only ca. 0.02 Å longer than the corresponding value in the free ligand. HmimtBu is orthorhombic, space group Pbca, a = 10.1571(5) Å, b = 9.7906(5) Å, c = 17.6616(9) Å, V = 1756.34(15) Å3, Z = 8; (HmimtBu)2ZnBr2 is monoclinic, space group C2/c, a = 17.187(3) Å, b = 8.9908(17) Å, c = 15.560(3) Å, β = 117.206(3)○, V = 2138.3(7) Å3, Z = 4; (HmimtBu)2CdBr2 is triclinic, space group Pn

A non-classical hydrogen bond in the molybdenum arene complex [η6-C6H5C6H3(Ph)OH]Mo(PMe3)3: evidence that hydrogen bonding facilitates oxidative addition of the O–H bond

{bar 1}

Iron(II)-promoted amidoglycosylation and amidochlorination of an allal C3-azidoformate

n, a = 7.4625(6) Å, b = 9.6149(9) Å, c = 31.020(3) Å, α = 93.485(2)○, β = 94.579(2)○, γ = 103.872(2)○, V = 2146.6(3) Å3, Z = 4; (HmimtBu)2HgBr2 is monoclinic, space group P21/c, a = 6.8908(6) Å, b = 10.2397(9) Å, c = 29.859(3) Å, β = 94.364(2)○, V = 2100.7(3) Å3, Z = 4.

Synthesis and molecular structure of bis(pyrazolyl)(3,5-di-tert-butylpyrazolyl)hydroborato thallium: ahetero-tris(pyrazolyl)- hydroborato ligand derived from two different pyrazoles

Although the marine alkaloids halichlorine (1) and the pinnaic acids 2, which contain a quinolizidine ring system, exhibit considerable structural homology, they act upon different biological targets (VCAM-1 and cPLA2, respectively). Quinolizidines can exist as cisoid or transoid invertomers. In the recently reported total synthesis of (+)-halichlorine, it was determined by NMR that advanced intermediates 3 and 4, containing the spiroquinolizidine core, exhibit the transoid conformation, while the macrolactone-containing halichlorine has the cisoid conformation. We conclude that constraints imposed upon closure of the macrolactone ring force adoption of the cisoid conformation. The major conformational reorganization upon macrolactonization has implications for the design of pharmacophors and anticipated structure-activity relationships in their action on biological targets.

The syntheses, structures and reactivity of bis(tert-butylcyclopentadienyl)molybdenum derivatives: nitrogen alkylation of an η2-acetonitrile ligand and influence of the chalcogen on the barrier to inversion of chalcogenoether adducts

Mo(PMe3)6 reacts with 2,6-Ph2C6H3OH to give the eta 6-arene complex [eta 6-C6H5C6H3(Ph)OH]Mo(PMe3)3 which exhibits a non-classical Mo...H-OAr hydrogen bond; DFT calculations indicate that the hydrogen bonding interaction facilitates oxidative addition of the O-H bond to give [eta 6,eta 1-C6H5C6H3(Ph)O]Mo(PMe3)2H.

Synthesis and molecular structures of a pair of tris(imidazolyl)phosphine cobalt–perchlorate complexes, {[PimPri2]Co(OClO3)}[ClO4] and {[PimPri2]Co(OH2)(HOMe)(OClO3)}[ClO4]

The tris(2-mercapto-1-mesitylimidazolyl)borate ligand, [TmMes]–, has been used to synthesize {[TmMes]Zn(HOMe)}+, a stable monomeric tetrahedral zinc–methanol complex which resembles the proposed alcohol intermediate in the catalytic cycle of the mechanism of action of liver alcohol dehydrogenase.