Irmi E. Buys

Models of surface-confined metallocene derivatives

Abstract The silsesquioxane [((C6H11)7Si7O9)(OH)3] (LH3) was reacted with [M(C5H5)2Cl2] (M = Ti, Zr, Hf) and with [Ti(C5H5)Cl3]. The reaction with [Ti(C5H5)Cl3] produced [Ti(C5H5)L], whereas the reaction with [Ti(C5H5)2Cl2] produced a mixture of [Ti(C5H5)L]n. (n = 1, 2) as determined by NMR spectroscopy. Only [Ti(C5H5)L] could be isolated from the mixture. The reaction with [M(C5H5)2Cl2] (M = Zr, Hf) produced oligomeric species which contained no cyclopentadienyl ligands and which were formulated as containing trimeric [M3L4Cl]− anions on the basis of analytical and spectroscopic data.

Photochemical reactions of [cis-Fe(H)2(Me2PCH2CH2PMe2)2] with thiophenes: insertion into C–H and C–S bonds

Photolysis of [cis-Fe(H)2(dmpe)2][dmpe = 1,2-bis(dimethylphosphino)ethane] in the presence of simple thiophenes gives products formed by insertion of the iron centre into both C–H and C–S bonds; the crystal structure of [[graphic omitted]H)(dmpe)2] is a planar ‘ferrathiacycle’ but bond lengths and 1H NMR spectroscopy indicate that this ring is best described as a localised diene structure rather than a ‘ferrathiabenzene’ with delocalised π-system.

Models of the active sites of zinc containing enzymes: The crystal structures of two bis(tripod)zinc(II) complexes

Abstract Attempts to prepare complexes of the type [Zn(tripod)L]x+, where L is a uni-negative anion, yielded only bis(tripod)zinc(II) complexes. The crystal structures of two of these bis(tripod)zinc(II) complexes, bis(tris(pyrazolyl)methane)zinc(II) nitrate (1) and bis(tris(pyridine)methanol)zinc(II) nitrate-4-hydrate (II) are described The geometries about the zinc atoms are close to octahedral and average ZnN distances are 2.136 and 2.148 A for I and II, respectively. There are no significant interligand interactions which might mitigate against the formation of the bis(tripod)zinc(II) complexes. The reasons for the preference for these complexes over those sought are discussed.

Synthesis and characterisation of nitrile complexes of iron

Abstract The reaction of cis-[FeH2(DMPE)2] (DMPE = 1,2-bis(dimethylphosphino)ethane) (1a) and trans-[FeCl2(DMPE)2] (7a) with acetonitrile, cyanocyclopropane, benzonitrile, p-bromobenzonitrile and terephthalonitrile and reaction of trans-[FeCl2(DEPE)2] (DEPE = 1,2-bis(diethylphosphino)ethane) (7b) with acetonitrile, cyanocyclopropane and benzonitrile in methanol solution resulted in a series of nitrile chloride complexes trans-[FeCl(N≡C-R)(PP)2]+ and bis-nitrile complexes trans-[Fe(N≡C-R)2(PP)2]2+ of iron. All of the complexes have been characterised spectroscopically and four bis-nitrile complexes have been characterised crystallographically. Crystals of trans-[Fe(N≡CCH3)2(DMPE)2][2PF6] (3a) are monoclinic, space group P2/c, with a = 8.697(3), b = 9.165(5), c = 20.026(5) A, β = 107.54(3)°, Z= 2 and R = 0.058 (2300 F values). Crystals of trans-[Fe(N≡CC3H5)2(DEPE)2][2BF4] (4b) are monoclinic, space group P21/n, with a = 11.146(1), b = 15.396(2), c = 11.810(2) A, β = 111.06(1)°, Z = 2 and R = 0.050 (3011 F values). Crystals of trans-[Fe(N≡CPh)2(DMPE)2][2PF6] (5a) are monoclinic, space group P21/n, with a = 11.006(2), b = 12.351(3), c = 13.650(4) A, β = 93.60(2)°, Z = 2 and R = 0.035 (2650 F values). Crystals of trans-[Fe(p-N≡CC6H4Br)2(DMPE)2][2PF6][0.5KPF6] (6a) are tetragonal, space group I4¯c2, with a = b = 20.015(6), c = 21.610(3) A, β = 90.00°, Z = 8 and R = 0.049 (2235 F values).

The crystal and molecular structure of (η5-pentaphenylcyclopentadienyl) (η5-cyclopentadienyl)iron(II), 1,2,3,4,5-pentaphenylferrocene, [Fe(C5Ph5)(C5H5)]

Abstract The preparation and characterization of [Fe(C5Ph5)(C5H5)] by single-crystal X-ray diffraction are reported. The compound crystallizes from chlorobenzene as a chlorobenzene solvate. The (C5H5) ring is planar to within 0.002 A, whilst the C5 ring of the (C5Ph5) ligand is planar to within 0.004 A. The Fe—(ring centroid)_distances are both 1.652 A. The phenyl substituents of the (C5Ph5) ring are canted relative to the cyclopentadienyl frame at angles between 44.3° and 61.8°. The structure of [Fe(C5Ph5)(C5H5)] is compared with the structures of ferrocene, 1,2,3,4,5-pentamethylferrocene and 1,2,3,4,5-penta(p-tolyl) ferrocene. The synthesis and characterization of [Fe(C5Ph5)(CO)2]2 is also reported. [Fe(C5Ph5)(CO)2]2 is assigned a trans configuration on the basis of its IR spectrum.

Synthesis, properties and complexation studies on 3-amino-6,6'-dimethyl-2,2'-bipyridine

The new unsymmetrical bipyridyl ligand 6,6′-dimethyl-3-nitro-2,2′-bipyridine was prepared via coupling of 6-methyl-2-trimethylstanniopyridine and 2-chloro-6-methyl-3-nitropyridine in the presence of [Pd(PPh3)2Cl2]. Reduction of the nitro group afforded 3-amino-6,6′-dimethyl-2,2′-bipyridine (L), a model for the central subunit of the antitumour drug streptonigrin. At low temperatures, in [2H6]acetone, L is planar, held in place by a hydrogen bond from the amino group to the pyridyl nitrogen in the adjacent ring. From 1H NMR lineshape analysis the barrier to rotation about the amino–bipyridyl bond (ΔGb‡) was estimated to be ≈38 kJ mol–1 at 200 K. This value is significantly lower than the barrier to rotation about the biaryl bond connecting the aryl rings. In solution, L co-ordinates to CdII, CuI and ZnII as a bipyridyl ligand; in these complexes the chemical shift of the amino group protons shifts upfield to ca.δ 5 compared to L where they resonate at δ 6.5. The crystal structure of [(CdLCl2)2] was determined by X-ray diffraction methods and refined to a residual of 0.027 for 1895 independent observed reflections. The crystals are monoclinic, space group P21/n, a= 9.560(2), b= 16.886(2), c= 9.577(3)A, β= 118.37(2)°. The complex crystallized as a dimer in which each cadmium binds three chloride ligands and a bipyridyl ligand in a distorted trigonal-bipyramidal arrangement. The relevance of these results to the structure and properties of the antitumour drug streptonigrin is discussed.

Trisimidazole complexes of ruthenium and osmium

Abstract The preparation and characterisation of ruthenium(II) and osmium(II) complexes with the trisimidazole ligands tris(N-methylimidazol-2-yl)methanol (1a) ((mim)3COH) and tris(N-ethoxymethylimidazol-2-yl)methanol (1b) ((emim)3COH) are reported (mim = N-methylimidazol-2-yl, emim = N-ethoxymethylimidazol-2-yl). The complex [RuCl(PPh3)2((mim)3COH)+Cl−] (2) was formed by the reaction of (mim)3COH with [RuCl2(PPh3)4]. The complexes [Ru(PPh3)(CO)H((mim)3COH)+Cl−] (3a) and [Ru(PPh3)(CO)H((emim)3COH)+Cl−] (3b) were formed by the reaction of (mim)3COH or (emim)3COH (respectively) with [Ru(PPh3)3HCl(CO)]. Likewise, the reaction of (mim)3COH or (emim)3COH (respectively) with [Os(PPh3)3HCl(CO)] formed [Os(PPh3)(CO)H((mim)3COH)+Cl−] (4a) and [Os(PPh3)(CO)H((emim)3COH)+Cl−] (4b). The ruthenium monohydride complex [Ru(PPh3)(CO)H((mim)3COH)+Cl−] (3a) adds to the terminal C-H bond of phenylacetylene to form the vinyl complex [Ru(PPh3)(CO)(CH=CHPh)((mim)3COH)+Cl−] (5). The air-stable complexes were characterised by multinuclear NMR spectroscopy and 2 and 3b were characterised by X-ray crystallography. Crystals of 2, C49H46N6OP2RuCl2, M 968.87, are triclinic, space group P1¯, a = 12.011(5), b = 13.342(3), c = 16.554(6) A, α = 89.26(3)°, β = 76.94(3)°, γ = 77.43(3)°, Z = 2. Crystals of 3b, C38H44N6O5PRuCl, M 832.30, are triclinic, space group P1¯, a = 12.759(3), b = 13.017(2), c = 13.167(4) A, α = 87.65(2)°, β = 64.09(2)°, γ = 88.82(2)°, Z = 2.

Synthesis and reactions of azido complexes of iron

Abstract Sodium azide reacts with FeH 2 (dmpe) 2 ({Bd1a}) [dmpe = 1,2-bis(dimethylphosphino) ethane] in methanol solution to form FeH(N 3 )(dmpe) 2 ({Bd3a}) and, finally, Fe(N 3 ) 2 (dmpe) 2 ({Bd2}). The bis(azide) complex may also be generated from FeCl 2 (dmpe) 2 ({Bd4a}) by a ligand exchange reaction. The azide ligand is easily replaced by terminal alkynes to form bisacetylide iron complexes. The X-ray crystal structure of Fe(N 3 ) 2 (dmpe) 2 ({Bd2a}) shows that the azide groups are mutually trans and that the NNN groups are essentially linear and tilted by approximately 132° with respect to the plane containing the Fe and four P atoms.

Crystal structures of [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5(SbPh3)](M = Mo or W): a comparative study of structure and bonding in [M(CO)5(EPh3)] complexes (E = P, as or Sb; M = Cr, Mo or W)

Crystal structures have been determined for [W(CO)5(PPh3)], [M(CO)5(AsPh3)] and [M(CO)5-(SbPh3)](M = Mo or W) as part of a systematic study of a series of nine [M(CO)5(EPh3)] complexes (M = Cr, Mo or W; E = P, As or Sb). Trends in bond lengths and angles are rationalised in terms of steric and electronic interactions between the bonded M(CO)5 and EPh3 fragments. Comparison is made between the solid-state geometry of the free and co-ordinated EPh3. Torsion angles defining the disposition of the EPh3 groups in relation to M(CO)5 show little variation within the [M(CO)5(EPh3)] series. For all nine complexes the EPh3 groups have propeller geometry with small deviations from symmetric C3 structures. The studies were extended to include other related [M(CO)5L] complexes. Trends in the structural parameters of 29 such compounds are related to the steric behaviour and π-acceptor capacity of the ligands L. It is shown that M–P bond dimensions are not adequately explained by hybridisation changes of the phosphorus atom in the ligand L.

Mechanism of arylation of nucleophiles by aryllead triacetates. Part 2. Support for a ligand coupling process and X-ray molecular structure of (p-methoxyphenyl)-α-methylphenacyllead (IV) diacetate

In the presence of boron trifluoride–diethyl ether complex p-methoxyphenyllead triacetate 4 and the propiophenone silyl enol ether 6 were found to undergo a rapid reaction to give (p-methoxyphenyl)-α-methylphenacyllead diacetate 9 in high yield. Analogous products, 5, 10 and 11 respectively, were formed when the silyl enol ethers of acetophenone, butyrophenone and isobutyrophenone were treated under the same conditions with aryllead compound 4. The diorganolead diacetates 9, 10 and 11 were relatively unstable, giving a number of products when heated at 60 °C in chloroform. In each case there was significant elimination of Pb(OAc)2, with formation of the product of ligand coupling, the deoxybenzoin. α-Methylphenacyl(o-prop-2-enyloxy)phenyllead diacetate 21, which was produced to probe the mechanism of the coupling reaction, behaved similarly to compound 9, giving no dihydrobenzofuran derivatives. Therefore, it would appear that aryl free radicals are most probably not produced in these thermal reactions, and a ligand-coupling mechanism is proposed.