K. F. Mok

Versatile chiral palladium(II) complexes for enantiomeric purities of 1,2-diamines

Abstract An efficient NMR determination of the enantiomeric excess of C 2 -symmetric 1,2-diamines can be achieved by coordination of the bidentates to the optically active forms of the diamagnetic [dimethyl(1-(2-naphthyl)ethyl)aminato- C 2 , N ]palladium(II) units.

Thiophene-2,5-dicarboxylic acid incorporated self-assembly of one-, two- and three-dimensional coordination polymers

Six thiophene-2,5-dicarboxylic acid incorporated and self-assembled zinc(II), cobalt(II) and manganese(II) coordination polymers [Zn(Tda)(py)]n (1), [Zn(Tda)(bipy)(H2O)·1.5H2O]n (2), [Zn(Tda)(phen)(H2O)]n (3), [Co(Tda)(phen)(H2O)]n (4), [Mn(Tda)(phen)]n (5) and [Mn(Tda)(H2O)2]n (6) have been synthesised and structurally characterised. Complex 1 is characterised as a two-dimensional parallelogram with a cavity of about 10.4×10.4 A, while complexes 2 and 3 (4) are one-dimensional linear and zig-zag coordination polymers with mainly hydrogen-bonding and stacking interactions contributing to their crystal packing, respectively. Complex 5 is a two-dimensional porous sheet with alternating 16- and 8-membered rings, while complex 6 is a three-dimensional porous coordination polymer. The diverse coordination properties of thiophene-2,5-dicarboxylate make it a good building block for the construction of coordination polymers of different architectures, which are dependent on both the end-capping ligand and the coordination geometry of the metal ions. Physical and thermal properties of these complexes have also been studied.

Facile ligand transformation from bridging thio to terminal chloromethanethiolato. Bridge opening of [Pt(μ-S)(dppf)]2 by dichloromethane to give Pt(SCH2Cl)2(dppf) [dppf Fe(C5H4PPh2)2]

Abstract Reaction of PtCl 2 (dppf) or [Pt(CH 3 CN) 2 (dppf)][BF 4 ] 2 with Na 2 S gives [Pt(μ-S)(dppf)] 2 . This bridging thio complex rapidly undergoes nucleophilic attack on CH 2 Cl 2 to give [Pt 2 (μ-S)(μ-SCH 2 Cl)(dppf) 2 ]Cl, which cleanly converts into [Pt(SCH 2 Cl) 2 (dppf)] with liberation of [PtCl 2 (dppf)]. These reactions effectively complete a cycle which yields a chloromethanethiolato complex from Na 2 S and CH 2 Cl 2 via a thio complex.

A versatile and efficient approach to enantiomerically pure monodentate and bidentate P-chiral phosphines

Abstract Enantiomerically pure (R)-methylphenylvinylphosphine and the P-chiral diphosphine ligands (5R,7R)-, (5R,7S)- and (5S,7R)-[5-(methylphenylphosphino)-2,3-dimethyl-7-phenyl-7-phosphabicyclo[2.2.1]hept-2-ene] were stereospecifically obtained in high yields from the chiral palladium template controlled Diels–Alder reaction between (±)-methylphenylphosphine and 3,4-dimethylphenylphosphole.

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.

12,13,25,26-Tetraaza-2,15-dithia[3.3]phenanthrolinophane. Synthesis, conformational study and complexation reactions

Abstract 12,13,25,26-Tetraaza-2,15-dithia[3.3]phenanthrolinophane 7 was prepared from a cyclization reaction of 2,9-bis(bromomethyl)phenanthroline 3. The syn isomer of 7 was kinetically favoured while the anti isomer was the thermodynamically more stable product isolated. The macrocycle 7 formed 1:1 complexes, namely 10 and 11, respectively, with zinc(II) and cadmium(II) ions. A tetragonal-pyrimidal configuration is proposed for these complexes. A comparison of the 1H NMR spectral data of 7, 10 and 11 suggests that the complexation results in a symmetrical structure through the four nitrogen donor atoms. The sulfur atoms in the bridges do not seem to coordinate strongly to the metal ions.

Formation of [CoPt2Cl2(PPh3)4(µ3-S)2] from facile heterometallation of [Pt2(PPh3)4(µ-S)2] and its facile deheterometallation via carbonylative desulfurization to give Pt–Pt bonded [Pt2(CO)2(PPh3)2(µ-S)]

Metallation of [Pt2(PPh3)4(µ-S)2]1 with CoCl2 gave [CoPt2Cl2(PPh3)4(µ3-S)2]2 at room temperature. Treatment of 2 with CO in an autoclave resulted in a binuclear compound [Pt2(CO)2(PPh3)2(µ-S)]3, via a reductive desulfurization mechanism with the removal of the heterometal fragment and formation of a Pt–Pt bond. Complexes 2 and 3 have been characterized by single-crystal X-ray crystallography. The structure of 2 shows a trigonal-bipyramidal arrangement of a {CoPt2S2} core with non-bonding Pt–Pt and Co–Pt distance at 3.197(4) and 3.066(1)A respectively. Complex 3 contains a {Pt2S} trinagular core with two PPh3 ligands trans and two CO cis to the Pt–Pt bond [2.600(1)A]. Some theoretical aspects of the strength of the Pt–Pt bond in relation to the ligands on the {Pt2S} core are discussed.

High pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) and CuTCNQ

Abstract The high-pressure Raman studies of 7,7,8,8-tetracyanoquinodimethane (TCNQ) single crystals and polycrystalline CuTCNQ are presented in this paper. TCNQ shows a phase transition at 22 kbar, a pressure higher than reported earlier. CuTCNQ undergoes a first order phase transition at 30 kbar, which is characterized by the abrupt disappearance of all the Raman bands.

9,21,22-Triaza-2,11-dithia[3.3](2,6)pyridino(2,9)phenanthrolinophane: a five-donor macrocycle functioning as a bidentate ligand

Abstract 9,21,22-Triaza-2,11-dithia[3.3](2,6)pyridino(2,9)phenanthrolinophane 4 was prepared from a cyclization reaction of 2,6-bis(mercaptomethyl)pyridine 5 and 2,9-bis(bromomethyl)phenanthroline 6 . Results from 1 H NMR analysis are inconclusive but those derived from semi-empirical molecular orbital PM3 calculations support a preference for a syn conformation for 4 . The conformation barrier for interconversion between two syn isomers of 4 was estimated to be 36.5 kJ mol −1 on the basis of a dynamic 1 H NMR study. The manganese(II) and zinc(II) complexes of 4 were prepared and the metal to ligand ratios were found to be 1:1 and 2:1, respectively, by elemental analyses. Results from an 1 H NMR analysis of the zinc(II) complex of 4 suggest that only the two nitrogen atoms of the phenanthroline moiety participate in the co-ordination.

A Raman study of RbSnBr3

Abstract The Raman spectrum of rubidium tribromostannate, RbSnBr3, has been measured as a function of temperature between 14 and 520 K. On cooling the RbSnBr3 crystal, the low-energy portion of the spectrum undergoes marked changes, suggesting the occurrence of a structural phase transition. A low-lying wing feature appears below 170 K, while the lowest-energy lattice band is found to soften from 19.6 cm−1 at 14 K to ca. 15 cm−1 at 140 K. The results are interpreted on the basis of a tin coordination of octahedral bromide ions. The phase transition is probably displacive in character and is associated with a rotation of the SnBr6 octahedra.