Yaw Kai Yan

Tricarbonylrhenium(I) complexes of phosphine-derivatized amines, amino acids and a model peptide: structures, solution behavior and cytotoxicity

Abstract Modified Mannich reactions of amines, amino acids and a model peptide with Ph2PH and CH2O gave bis(diphenylphosphinomethyl)amines (Ph2PCH2)2NR [R=Ph (1), CH2CH2OH (2), CH2COOCH2Ph (3), CH2CONHCH2COOCH2Ph (4), CH2COOH (5)] and (Ph2PCH2)2NCH2CH2N(CH2PPh2)2 (6). Reaction with [ReBr3(CO)3]2− under mild conditions led to [ReBr(CO)3]{(Ph2PCH2)2NR} [R=Ph (7), CH2CH2OH (8), CH2COOCH2Ph (9), CH2CONHCH2COOCH2Ph (10), CH2COOH (11)] and [ReBr(CO)3(Ph2PCH2)2NCH2]2 (12). All new complexes have been characterized by NMR and IR spectroscopy and for 7, 9 and 10, single-crystal X-ray diffraction analyses. Electrospray mass spectrometric studies show that the rhenium–phosphine chelates are very stable, especially in neutral methanolic solution. Hydrolysis of the ester and amide linkages slowly occur in acidic and basic solutions over several weeks; displacement of the bromide ligand also occurs in basic medium. Cytotoxicity testing of 7–10 and 12 showed that all the complexes are active against specific tumor cell lines, especially MCF-7 breast cancer and HeLa-S3 suspended uterine carcinoma.

Substituted metal carbonylsXVIII. rhenium 1,1′-bis(diphenylphosphino)ferrocene (DPPF) complexes derived from [Re2(CO)9]. Crystal structures of two isomorphous pentametallic [M2(CO)9]2(μ-dppf) (M Mn, Re) and trimetallic Re2(CO)9(dppfO) complexes

Abstract Amine oxide-assisted decarbonylation of Re2(CO)10 in the presence of 1,1′-bis(diphenylphosphino)ferrocene (dppf) produces, under different conditions, [Re2(CO)9]2 (μ-dppf) (1), Re2(CO)9(1-dppf) (5) and its oxidation product Re2(CO)9(1-dppfO) (7). 1 undergoes an oxidative bridge-scission with Me3NO to give 7. X-ray crystallographic analysis of 1 and [Mn2(CO)9]2(μ-dppf) (2), included for comparison, revealed that the two molecules are isomorphous, each taking the form of an open and “linear” tetranuclear complex supported alternately by M M bonds and a “half eclipsed” dppf bridge. Complex 7, which is trimetallic, consists of dppf (mono)oxide coordinated to [Re2(CO)9] through the phosphine site. X-ray Photoelectron Spectra revealed the existence of the chemically inequivalent Re and P sites within the same molecule. The chemically distinct Re centres in 1, 5, 7 and Re2(CO)9(CH3CN) are differentiable by their Re(4f7/2) and Re(4f5/2) binding energies.

Synthesis, X-ray structures, and cytotoxicity of rhenium(I) carbonyl 2-(dimethylamino)ethoxide complexes

Abstract The complexes [Re(η2-Me2NCH2CH2O)(CO)3(μ-OH)Re(η2-Me2NCH2CH2OH)(CO)3] (1) and [Re3(μ3-OH)(μ-OH)2(μ-OCH2CH2NMe2H)(CO)9] (2) have been synthesised and characterised by single-crystal X-ray diffraction analysis. Complex 1 exists as hydrogen-bonded dimers in the solid state and in solution. Proton NMR, 1H–1H COSY and NOESY spectroscopic studies showed that the structure of 1 is static in solution, and that only one of the many possible geometric isomers of 1 exists. The hydrogen atom on the ammonio nitrogen of 2 is involved in intramolecular NH⋯O hydrogen-bonding with a bridging OH group. Complexes 1 and 2 were shown to be potent in suspended tumour cell lines in suppressing growth but were more selective in inhibiting the growth of cultures from solid tumours. The compounds [NBun4][ReO4] and [NEt4]2[ReBr3(CO)3] were also very active against the suspended cell lines and selective against solid tumours. All the compounds tested are inactive against normal cells.

Reactions of [Pt2(μ-S)2(PPh3)4] with Group 6 and 7 metal carbonyls; crystal structure of the apparently unsaturated heterometallic complex [Pt2Re(μ3-S)2(PPh3)4(CO)3]+

Abstract Reaction of [Pt2(μ-S)2(PPh3)4] (1) with a mixture containing [Re2(CO)10], Me3NO·2H2O and MeOH at room temperature affords an oxidative methoxylation complex, [Pt2Re2(μ-OMe)2(μ3-S)2(PPh3)4(CO)6] (2), and a PtRe heterometallic salt, [Pt2Re(μ3-S)2(PPh3)4(CO)3]+[Re3(μ3-OMe)(μ-OMe)3(CO)9]− (3a). The core of the cation of 3a comprises a {Pt2ReS2} trigonal bipyramidal ‘cluster’ with weak PtRe bonding interactions and an apparently unsaturated Re(I) atom. The [BF4]− salt of this cation, 3b, can be prepared by the reaction of 1 with [Re(CO)5(H2O)][BF4], and the Mn analogue, [Pt2Mn(μ3-S)2(PPh3)4(CO)3][BF4] (4), can be similarly synthesised using [Mn(FBF3)(CO)5]. Addition of 1 to [M(I)2(CO)3(NCMe)2] (M=Mo, W) is accompanied by iodide migration to give the salts [Pt2M(μ3-S)2I(PPh3)4(CO)4][M(I)3(CO)4] (M=Mo, 5; W, 6a). With [Mo(CO)4(NCMe)2], 1 undergoes reductive carbonylation and desulfurization to give [Pt2(μ-S)(PPh3)3(CO)] (7). The above reactions represent the first examples of 1 as a metalloligand towards carbonyl complexes of the less electron-rich transition metals, and demonstrate that addition reactions of 1 can be complicated by ligand dissociation, ligand migration, or reductive desulphurization. The crystal structures of compounds 3a and 3b were determined.

Substituted metal carbonyls: XXII . Synthesis of 1,1′-bis(diphenylphosphino)ferrocene-bridged complexes with two heterometallic AuM (M Mn and Re) bonds

Abstract AU 2 Cl 2 (μ-1,1′-bis(diphenylphosphino)ferrocene (dppf) reacts with Na[M(CO) 5 ] to give [AuM(CO) 5 ] 2 (μ-dppf) (M  Re ( 1 ); M  Mn ( 2 )) in 45% and 71% yields respectively. Both 1 and 2 represent pentametallic structures with a dppf metalloligand bridging between two heterometallic fragments which consist of AuM bonds. The X-ray photoelectron spectroscopic data suggested polarization of the Au δ+ Re δ- bonds in 1 . Contrary to 1 , (CO) 9 Re 2 (μ-dppf)AuCl ( 3 ), which is synthesized from Re 2 (CO) 9 (dppf- P ) and AuCl(Me 2 S) in 65% yield, shows binding energies typical of Au I and Re 0 . Reaction between Au 2 Cl 2 (μ-dppf) and K 2 Pd(CN) 4 resulted in no MM bond but ligand displacement to give Au 2 (CN) 2 (μ-dppf) ( 4 ) (yield, 8%) as the only isolable product.

Methoxylation of the Re–Re bond in [Re2(CO)10] by methanol under ambient conditions

Addition of 1,1′-bis(diphenylphosphino)ferrocene (dppf) to an ‘activated mixture’ containing [Re2(CO)10] and Me3NO·2H2O in thf–MeOH (2 : 1) in the molar ration 1.0 : 1.0 : 2.4 at 25 °C gives [Re2(µ-OMe)2(CO)6(µ-dppf)] in 34% yield. The molecular structure was determined by X-ray diffraction analysis: monoclinic, space group P21/n, a= 13.646(1), b= 18.440(2), c= 17.850(4)A, β= 97.69(1)°, final R 0.030 for 3992 observations. It contains two tricarbonylrhenium(I) moieties bridged by dppf and two methoxo ligands. The cp–Fe–cp (cp =η-C5H5) axis of dppf makes a projection of 53.5° onto the Re–Re axis.

Rhenium(I) methoxo carbonyl complexes containing tetraphosphine or triphosphine ligands; facile separation and X-ray crystallographic studies of d/l- and meso-[{Re2(μ-OMe)2(CO)6}2(μ,μ′-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetra-phosphadecane)]

Abstract Reaction of the activated mixture of Re2(CO)10, Me3NO and MeOH with a 1:1 mixture of rac (d/l)- and meso-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane (hptpd) yields a mixture of (d/l)- and meso-[{Re2(μ-OMe)2(CO)6}2(μ,μ′-hptpd)] 1. The diastereomers can be easily separated by selective dissolution of d/l-1 in benzene, and give clearly distinguishable 1H- and 31P-NMR spectra. The fluxional behavior of d/l-1 in solution has been studied by variable-temperature 1H- and 31P-{1H}-NMR spectroscopy. The crystal structures of both d/l- and meso-1 have been determined. Both molecules consist of two {Re2(μ-OMe)2(CO)6} moieties which are bridged by the two PCH2CH2P moieties of the hptpd ligand. Whilst the molecules of meso-1 possess crystallographic i-symmetry, those of d/l-1 do not have any crystallographic symmetry. These diastereomers therefore give clearly distinguishable Raman spectra in the solid state. Reaction of tris[2-(diphenylphosphino)ethyl]phosphine (tdppep) with the activated mixture affords the complex [{Re2(μ-OMe)2(CO)6}(μ,η2-tdppep)] 2, and the analogous reaction involving bis[2-diphenylphospinoethyl)phenylphosphine (triphos) gives [{Re2(μ-OMe)2(CO)6}(μ,μ′,η3-triphos){Re2(CO)9}] 3 and [{Re2(μ-OMe)2(CO)6}(μ,η2-triphos)] 4.

Amine-oxide-mediated oxidative methanolysis of metal–metal bonds in [MM′(CO)10] (M=Mn, Re; M′=Re) and [Os3(CO)12]: crystal structure of fac-[Re{OC(O)OMe}(CO)3(η2-dppf)]

Abstract The reaction of 1,1′-bis(diphenylphosphino)ferrocene (dppf) with a mixture of [MnRe(CO)10], MeOH and Me3NO afforded the complexes fac-[MnH(CO)3(η2-dppf)] and [Re2(μ-OMe)2(μ-dppf)(CO)6]. In the one-pot reaction of [Re2(CO)10] with Me3NO, MeOH and dppf, the major mononuclear Re species isolated was the CO2-inserted complex fac-[Re{OC(O)OMe}(CO)3(η2-dppf)], the crystal structure of which was determined. The coordination sphere of the rhenium atom is roughly octahedral, consisting of an oxygen atom from the methyl carbonate ligand, two phosphorus atoms from a chelating dppf ligand, and three carbon atoms from a facial arrangement of three terminally bonded carbonyls. Analogous Me3NO-mediated methoxylation reactions involving [Os3(CO)12] were also investigated. With a [Me3NO]:[Os3(CO)12] ratio of 2:1, the major product is [Os3(CO)10(μ-H)(μ-OMe)]. With three molar equivalents of Me3NO, significant quantities of [Os3(CO)10(μ-OMe)2] are also obtained.

Amine-oxide-mediated reactions of Re2(CO)10 with phenol and aliphatic alcohols: The formation of Re3(CO)14(μ-H) and a hydroxo-methoxo trirhenium aggregate [Me3NH]+[Re3(CO)9(μ-OH)2(μ-OMe)(μ3-OMe)]−

Abstract Oxidative decarbonylation of Re 2 (CO) 10 by Me 3 NO in a mixture of THF and phenol resulted in Re 3 (CO) 14 ( μ -H), 1 , and [Me 3 NH] + [Re 2 (CO) 6 ( μ -OPh) 3 ] − , 2 , in 30 and 17% yields respectively. In the analogous reaction in THF-MeOH mixture, a trinuclear complex, [Me 3 NH] + [Re 3 (CO) 9 ( μ -OH) 2 ( μ -OMe)( μ 3 -OMe)] − , 3 , was isolated instead. The structure of 3 was determined by single-crystal X-ray diffraction analysis: orthorhombic, space group Ama 2, a = 14.022(2), b = 18.003(5), c = 9.601(2) A, final R = 0.031 for 958 reflections. The anion contains a Re 3 triangle edge-bridged by one methoxy and two hydroxy ligands and capped by a methoxy group. No formal Re-Re bond (Re ⋯ Re 3.423 and 3.439 A is envisaged. Possible mechanisms for the formation of 1, 2 and 3 are proposed.

REDUCTIVE COUPLING OF HALOGENOTHIOPHENES AND HALOGENOTHIAZOLES CATALYSED BY PDII IN A BASIC ALCOHOL MEDIUM

A catalytic reductive coupling method has been developed whereby 2- and 3-bromo- and 2-iodothiophenes, 2-bromothiazole and 2-bromofuran are converted into their corresponding bithiophene, bithiazole and bifuran derivatives. The use of a basic alcohol medium favours the reductive coupling pathway over the hydrodehalogenation pathway, which is generally more facile when other reducing agents are used. The catalytic mechanisms are discussed. The syntheses and characterization of the proposed intermediate complexes, trans-[PdBr(C4H3S-C)(PPh3)2] 1, trans-[PdI(C4H3S-C)(PPh3)2] 2 and trans-(N,P)-[{PdBr(µ-C3H2NS-C2,N)(PPh3)}2]·½CHCl3 3 support the proposed mechanism and the catalytic results. Single-crystal X-ray crystallographic structure determinations of 2 and 3 were carried out.