Agnes L. Tan

Structure-activity relationships of some indolo[3,2-c]quinolines with antimalarial activity.

The synthesis, physicochemical characterization and in vitro antimalarial activity of a series of indolo[3,2-c]quinolines (9a-f) are described. There is only a poor correlation between the activity and hydrophobicity. In contrast, 33% of the observed variation in antimalarial activity can be attributed to the size of the side chain attached to position 9 of the indoloquinoline ring. An increase in the size of this dibasic side chain generally results in a reduction in activity, suggesting that it is accommodated in a site/cavity of limited size on the receptor. More significantly, the charge on the distal nitrogen (N3) on the side chain, located 10-11 A from the quinoline N, could account for 75% of the observed variation. Since a large charge on N3 is associated with improved antimalarial activity, it is suggested that N3 is protonated and functions as a H bond donor in the drug-receptor interaction.

Stabilization of a Y-shaped CuI coordination in [CuPt2(PPh3)5(μ3-S)2]PF6 by Pt2(PPh3)4(μ-S)2 and its expansion to a pentanuclear aggregate [Cu{Pt2(PPh3)4(μ3-S)2}2]PF6. X-ray crystal structure of [CuPt2(PPh3)5(μ3-S)2]PF6

Abstract Addition of Pt 2 (PPh 3 ) 4 (μ-S) 2 , 1 , to an equimolar quantity of Cu(NO 3 )(PPh 3 ) 2 gave [CuPt 2 (PPh 3 ) 5 ( μ 3 -S) 2 ]NO 3 , 2a , which readily reacted with NH 4 PF 6 giving [CuPt 2 PPh 3 ) 5 ( μ 3 -S) 2 ]PF 6 , 2b . Further addition of a molar equivalent of 1 to 2b gave rise to a pentanuclear {CuPt 4 } complex of [Cu{Pt 2 (PPh 3 ) 4 ( μ 3 -S) 2 }]PF 6 , 3 . Complex 3 was also obtained from the direct 2:1 addition of 1 to [Cu(CH 3 CN) 4 ]PF 6 . Complexes 2 and 3 have been characterized by IR and 31 P-{ 1 H} NMR spectroscopy and in the case of 2b single crystal X-ray crystallography. The geometry of Cu I in 2b is three-coordinate and Y-shaped. It represents the first crystallographically characterized mixed-metal complex of 1 with a trigonal-planar heterometal. The unexpectedly short non-bonding CuPt distances (av.2.869(4) A) are associated with a more open {Pt 2 S 2 } butterfly core (σ 137.5(5)°). Some theoretical aspects of these geometric peculiarities are discussed.

Bis(carboxylato) complexes of platinum(II). Structural and bonding analysis of [Pt(O2CR)2(L–L)][L–L = 2PPh3, Ph2PCH2PPh2 or Fe(C5H4PPh2)2; R = Me, CF3, Pri or Ph]

Treatment of [PtCl2(L–L)][L–L = 2 PPh3, Ph2PCH2PPh2(dppm) or Fe(C5H4PPh2)2(dppf)] with Ag(O2CR)(R = Me, CF3, Pri or Ph) at room temperature generally gave [Pt(O2CR)2(L–L)] in moderate to good yields. The crystal and molecular structures of [Pt(O2CMe)2(dppf)]·H2O, [Pt(O2CPh)2(dppf)]·CH2Cl2 and [Pt(O2CCF3)2(dppm)] have been determined by single-crystal X-ray diffractometry. All these complexes show a mononuclear square-planar structure with a chelating diphosphine and two neighbouring (cis) carboxylates in a monodentate mode. These structures contrast those of the parent [Pt4(µ-O2CMe)8] and its derivative [Pt4(en)4(µ-O2CMe)4]4+(en = ethylenediamine) which are tetrameric, based on octahedral PtII, and contain bridging acetates and direct Pt–Pt bonds. Fenske–Hall molecular orbital calculations of these structures confirmed the existence of Pt–Pt bonding interactions. The presence of hard and electronegative ligands like en and acetate incurs a deficiency in σ-electron density, compared to virtually filled non-bonding orbitals; the former is alleviated by Pt–Pt bonding. d8 Complexes with ligands like phosphines possessing both σ-donating and π-accepting qualities appear to favour the usual square-planar geometry.

Heteropolymetallic aggregates from [Pd2(dppf)2(µ-S)2]. Bonding and structural analysis of [Ag2Pd2Cl2(dppf)2(µ3-S)2]·4CH2Cl2[dppf = Fe(C5H4PPh2)2]—a flat {Pd2S2} core with two AgCl ‘tails’

Nucleophilic addition of the heterometallic complex [Pd2(dppf)2(µ-S)2][dppf = 1,1′-bis(diphenylphosphino)-ferrocene] to [AgCl(PPh3)] or AgCl gave [Ag2Pd2Cl2(dppf)2-(µ3-S)2], the first example of a heteropolymetallic aggregate based on a {Pd2S2} core and whose crystal structure shows a planar {Pd2S2} ring with two protruding AgCl fragments.

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.

[Pt2(PPh3)4(μ-S)2] as a metalloligand toward main-group Lewis acids. Crystal structures and bonding analysis of two low-coordinate BiCl3 adducts—[Pt2(PPh3)4(μ3-S)2BiCl3] and [Pt2(PPh3)4(μ3-S)2BiCl2]PF6

Abstract Addition of BiCl3 to [Pt2(PPh3)4(μ-S)2] gives [Pt2(PPh3)4(μ3-S)2BiCl3], which undergoes dissociation and metathesis with NH4PF6 to give [Pt2(PPh3)4(μ3-S)2BiCl2]PF6. An X-ray single-crystal diffraction analysis established two highly distorted square-pyramidal and tetrahedral structures, respectively. The four- and five-coordination numbers are unusually low among the known BiIII halide adducts. Fenske-Hall MO analysis offers an explanation to the structural characteristics with reference to the stereochemically active lone pairs, coordination numbers, uneven BiCl and BiS lengths and the butterfly geometry of the {Pt2S2} core. These parameters are compared with those of the other intermetallics previously reported.

The Isolobal Theory and Organotransition Metal Chemistry—Some Recent Advances

Abstract Hoffmanns isolobal theory was largely credited for bridging the gap between inorganic complexes and carbon-based compounds. Recent advances have extended its applications to organotransition metal monomers and cluster molecules. Isolobal mapping is not only applicable among molecules and molecular fragments, but also significant in comparing organometallic reactions. Such advancement is likely to influence current trends in mechanistic chemistry. Through a concise review of some of the latest and more representative results, this article aims to highlight and illustrate the versatility and applicability of the theory. Coupled with the Polyhedral Skeletal Electron Pair theory, the isolobality principle provides a useful theoretical underpinning for some synthetic and structural characteristics of many organotransition metal compounds.