David C. R. Hockless

Cylindricines A and B, novel alkaloids from the ascidian clavelina cylindrica

Abstract The ascidian Clavelina cylindrica, which was collected in Tasmania, has yielded two novel alkaloids, cylindricine A, rel-(3R, 4R, 5S, 7aR, 11aR)-3-chloromethyl-5-hexyl-perhydro-pyrrolo-[2,1-j]quinolin-7-one, (12), and cylindricine B, rel-(3S, 5R ,6S ,8aR ,12aR)-3-chloro-6-hexyl-perhydropyrido[2,1-j]quinoline-8-one, (13). Cylindricine B is the first example of the new pyrido-[2,1-j]-quinoline ring system while cylindricine A is the first pyrrolo[2, 1-j]quinoline known from nature. Single crystal X-ray studies support the assignment of the two alkaloids.

Trifluoromethanesulfonic anhydride–4-(N,N-dimethylamino)pyridine as a reagent combination for effecting Bischler–Napieraiski cyclisation under mild conditions: application to total syntheses of the Amaryllidaceae alkaloids N-methylcrinasiadine, anhydrolycorinone, hippadine and oxoassoanine

A combination of triflic anhydride and 4-(N,N-dimethylamnino)pyridine effects Bischler–Napieraiski cyclisation of β-phenethytearbamates and β-phenethylamides under very mild conditions.

Organometallic complexes for nonlinear optics. Part 27. Syntheses and optical properties of some iron, ruthenium and osmium alkynyl complexes

The syntheses of the alkynyl complexes M(4-CCC6H4NO2)(dppe)(η-C5H5) [M=Fe (1), Ru (2), Os (3)], Os(4-CCC6H4NO2)(PPh3)2(η-C5H5) (4) and Ru(4-CCC6H4NO2)(CO)2(η-C5H5) (5) are reported. Structural studies reveal a decrease in RuC(1) distance on proceeding from 5 to 2, consistent with greater back-donation of electron density to the alkynyl ligand from the more electron-rich metal center in 2. Electrochemical data show that the MII/III couple for the dicarbonyl complex 5 is at a significantly more positive potential than that of the related diphosphine complex 2, consistent with ligand variation modifying the electron richness and hence donor strength of the metal center. Time-dependent density functional calculations on model complexes M(4-CCC6H4NO2)(PH3)2(η-C5H5) (M=Fe, Ru, Os) have been employed to assign the intense low-energy optical transition in these complexes as MLCT in character, the higher energy band being phenyl–phenyl* in nature. Molecular quadratic optical nonlinearities have been measured using the hyper-Rayleigh scattering procedure at 1064 nm. β values vary as Fe≤Ru≤Os for metal variation and CO<phosphines for co-ligand variation, the latter consistent with the variation in donor strength of the metal center inferred from electrochemical and crystallographic data. The observed trend in β on metal variation follows the trend in backbonding energies calculated by DFT.

Organometallic complexes for nonlinear optics. 14. Syntheses and second-order nonlinear optical properties of ruthenium, nickel and gold σ-acetylides of 1,3,5-triethynylbenzene: X-ray crystal structures of 1-(HC≡C)-3,5-C6H3(trans-C≡CRuCl(dppm)2)2 and 1,3,5-C6H3(C≡CAu(PPh3))3

The complexes 1-(HC≡C)-3,5-C 6 H 3 [M] 2 ([M] = trans -C≡CRuCl(dppm) 2 ( 1 ), C≡CNi(PPh 3 )( η 5 -C 5 H 5 ) ( 2 )) and 1,3,5-C 6 H 3 (C≡CAu(PPh 3 )) 3 ( 3 ) have been prepared by extensions of well-established σ -acetylide synthetic methodologies, and 1 and 3 have been structurally characterized. Steric restrictions preclude coordination of three trans -RuCl(dppm) 2 or Ni(PPh 3 )( η 5 -C 5 H 5 ) moieties about the central 1,3,5-triethynylbenzene unit, a problem which the smaller Au(PPh 3 ) group does not experience. The quadratic optical nonlinearities at 1.06 μ m have been investigated by hyper-Rayleigh scattering with the C 2v symmetry complexes 1 and 2 having significantly larger β HRS than their monometallic [M]C≡CPh ([M] = trans -RuCl(dppm) 2 ( 4 ) and Ni(PPh 3 )( η 5 -C 5 H 5 ) ( 5 )) counterparts. The D 3h symmetry octopolar complex 3 has a similar nonlinearity to its dipolar monometallic analogue Au(C≡CPh)(PPh 3 ) ( 6 ). Complexes 1 , 2 and 3 have λ max similar to 4 , 5 and 6 (i.e., no loss of optical transparency is observed), but have significantly larger oscillator strengths for the important optical transitions.

Organometallic complexes for nonlinear optics. X. Molecular quadratic and cubic hyperpolarizabilities of systematically varied (cyclopentadienyl)bis(phosphine) ruthenium σ-arylacetylides: X-ray crystal structure of Ru((E)-4,4′-C CC6H4CHC6H4NO2)(PPh3)2(η-C5H5) ☆

Abstract The complexes Ru(4,4′-C  CC6H4C6H4NO2)(PPh3)2(η-C5H5) and Ru(4,4′-C  CC6H4C  CC6H4NO2)(PPh3)2(η-C5H5) have been prepared and the latter structurally characterized; they belong to a series of organometallic donor-bridge-acceptor compounds containing (cyclopentadienyl)bis(phosphine)ruthenium(II) centres as donors, conjugated arylacetylide bridges, and nitro acceptor groups. Electrochemical data for the series of complexes Ru(C  CR)(PR′3)2(η-C5H5) (R  Ph, 4-C6H4NO2, R′  Ph, Me; R = 4,4′-C6H4C6H4NO2, (E)-4,4′-C6H4CH  CHC6H4NO2, 4,4′-C6H4C  CC6H4NO2, 4,4′-C6H4N  CHC6H4NO2, R′  Ph) are consistent with an RuII/III couple whose oxidation potentials vary strongly with chain-lengthening from one-ring to two-ring acetylide ligand, but show little variation with changes at the bridging unit of the two-ring acetylide ligand. The molecular quadratic and cubic optical nonlinearities of the series of complexes have been determined by hyper-Rayleigh scattering (HRS) and Z-scan techniques, respectively. Molecular first hyperpolarizabilities by HRS at 1064 nm are dispersively enhanced; experimental and two-level corrected data suggest an increase in nonlinearity on chain-lengthening of the bridge, in proceeding from C6H4 to C6H4C6H4 and then C6H4C  CC6H4 and C6H4CH  CHC6H4, a general trend that is reproduced by semiempirical ZINDO computations. Cubic hyperpolarizabilities by Z-scan at 800 nm are negative for complexes with nitro acceptor groups, probably a result of two-photon dispersion, with absolute values (up to 850 × 10−36 esu) large for small organometallic complexes; as with quadratic nonlinearities, cubic nonlinearities increase substantially on bridge lengthening, with little variation on phosphine substitution.

Organometallic complexes for nonlinear optics. 15. Molecular quadratic hyperpolarizabilities of trans-bis{bis(diphenylphosphino)methane}ruthenium σ-aryl- and σ-pyridyl-acetylides: X-ray crystal structure of trans-[Ru(2-CCC5H3N-5-NO2)Cl(dppm)2]

The complexes trans -[Ru(2-CCC 5 H 3 N-5-R)Cl(dppm) 2 ] [R=H ( 6 ), NO 2 ( 7 )] have been prepared and 7 has been structurally characterized; comparison with the structural study of trans -[Ru(4-CCC 6 H 4 NO 2 )Cl(dppm) 2 ] ( 3 ) reveals a decrease in Ru–C(1) distance and increase in Ru–Cl(1) distance, consistent with stronger σ -bonding by the nitropyridylalkynyl ligand in 7 compared to the nitrophenylalkynyl ligand in 3 . Electrochemical data for 3 , 6 , 7 , precursor dichloro complexes [RuCl 2 (dppm) 2 ] [ cis ( 1a ), trans ( 1b )], and related alkynyl complexes trans -[Ru(4-CCC 6 H 4 R)Cl(dppm) 2 ] [R=H ( 2 ), 4-C 6 H 4 NO 2 ( 4 ), ( E )-4-CHCHC 6 H 4 NO 2 ( 5 )] have been determined by cyclic voltammetry. Introduction of nitro substituent in progressing from 2 to 3 or 6 to 7 leads to a substantial increase in E o Ru II/III , most of which is lost on chain-lengthening the alkynyl ligand in progressing from 3 to 4 or 5 . Replacement of phenyl by pyridyl in progressing from 2 to 6 or 3 to 7 results in a 0.1 V increase in E o Ru II/III . The optical spectra of representative complexes have been examined. Introduction of a nitro substituent onto the phenylalkynyl ligand, in progressing from 2 to 3 , results in a substantial (ca. 11 000 cm −1 ) red-shift in the intense MLCT band of the Ru II –CC–Ar–NO 2 moiety. Complexes 3 , 4 and 5 exhibit sizable solvatochromic shifts, suggestive of significant optical nonlinearities. Quadratic hyperpolarizabilities for 2 – 7 were determined by hyper-Rayleigh scattering (HRS) at 1064 nm; measurements are consistent with an increase in β HRS upon incorporation of nitro substituent (progressing from 2 to 3 or 6 to 7 ), chain-lengthening the alkynyl ligand (progressing from 3 to 4 and then to 5 ) and replacing phenyl by pyridyl in progressing from 2 to 6 , general trends that are maintained with the two-level-corrected data, and which parallel shifts in λ max to low energy. The observed and two-level-corrected β HRS values for 7 are lower than expected; it is perhaps significant that λ max for 7 is close to the second-harmonic.

Organometallic complexes for nonlinear optics VI: syntheses of rigid-rod ruthenium σ-acetylide complexes bearing strong acceptor ligands; X-ray crystal structures of trans-[Ru(C CC6H4NO2-4)2(dppm)2] and trans-[Ru(CCC6H4C6H4NO2-4,4′)2(dpppm)2]

Abstract A series of systematically-varied ‘rigid-rod’ octahedral ruthenium acetylide complexes, bearing the strong acceptor substituent -NO 2 , of general formula rans -[Ru(C  CC 6 H 4 R-4) 2 (dppm) 2 ] (R  NO 2 , C 6 H 4 NO 2 -4, C 6 H 4 CHCHC 4 CHCHC 6 H 4 NO 2 -4, ( E ) has been synthesized. X-ray structural studies of trans -[Ru(CCC 6 H 4 R-4) 2 (dppm) 2 ] (RNO 2 . C 6 H 4 NO 2 -4) confirm the trans -disposed geometry of the acetylide ligands and, for the latter, non-planarity of the biphenylene groups. The mixed acetylide ‘rigid-rod’ complex trans -[Ru(C  CPh)(CCC 6 H 4 NO 2 -4)(dppm) 2 ] has also been prepared. Semiempirical calculations employing zindo were performed on the mixed-acetylide complex, the results suggesting that the effect of trans -disposed ligands on the molecular quadratic hyperpolarizability β is not additive.

Organometallic complexes for non-linear optics VII. Cubic optical non-linearities of octahedral trans-bis{bis(diphenylphosphino)methane}ruthenium acetylide complexes; X-ray crystal structure of trans-[Ru(CCPH)(4-CCC6H4NO2)(dppm)2]

Abstract Cubic molecular optical non-linearities of a systematically varied series of octahedral bis{bis(diphenylphosphino)methane}ruthenium σ-acetylide complexes have been determined by the Z-scan technique: the influence on the non-linear response of sequential replacement of chloro by acetylide ligand in trans -[RuCl 2 (dppm) 2 ] and acetylide chain length in proceeding from 4-nitrophenyl- to 4-nitrobiphenyl- and 4-nitro-( E )-stilbenylacetylide has been studied. The first X-ray structuralstudy of an unsymmetrical bis(acetylide) complex of this type, trans -[Ru(CCPh)(4-CCC 6 H 4 NO 2 )(dppm) 2 ], is reported and confirms the trans -diposed stereochemistry of the alkynyl ligands.

A FeIII/Oxo Cubane Contained in an Octanuclear Complex of T Symmetry That Is Stable Over Five Oxidation States

Encapsulated in a protective [{Fe(pz)3 }4 ] outer layer, which provides the complex with structural stability, the octanuclear complex [Fe8 (μ4 -O)4 (μ-pz)12 Cl4 ] contains a Fe4 O4 core (see drawing) that withstands four consecutive reversible one-electron reductions. Iron-oxygen clusters are shown to possess redox properties which rival those of their better studied iron-sulfur analogues. pz=pyrazolate anion.

Hexacyanometalates as templates for heteropolynuclear complexes and molecular magnets: synthesis and crystal structure of [Fe{(CN)Cu(tpa)}6][ClO4]8·3H2O, [tpa = tris(2-pyridylmethyl)amine]

Reaction of [Fe(CN)6]3– with [Cu(tpa)(OH2)]2+ produces a bimetallic heptanuclear complex, [Fe{(CN)Cu(tpa)}6]-[ClO4]8·3H2O, which is characterised by single-crystal X-ray diffraction and shown to consist of an iron(II) centre connected by cyano bridges to six copper(II) centres forming spherical units of [Fe{(CN)Cu(tpa)}6]8+.