Scott Kassel

Syntheses and structures of mono-thiocyanate complexes of cadmium(II) and lead(II) containing bulky nitrogen based polydentate ligands

Abstract The reaction of [Cd2(thf)5](BF4)4 with two equiv. of Tl[HB(3-Butpz)3] (pz=pyrazolyl ring) produces the intermediate {[HB(3-Butpz3]Cd}[BF4] that reacts with potassium thiocyanate to yield [HB(3-Butpz)3]Cd(NCS) (1). The solid state structure shows that the sterically demanding 3-tert-butyl groups enforce the formation of a tetrahedral, monomeric complex, the first four-coordinate cadmium(II)-thiocyanate complex to be structurally characterized. The decomposition of this compound produced [(ButHpz)2Cd(NCS)2]n (2) as shown by X-ray crystallography. It was not possible to form a lead(II) complex analogous to 1, but using less sterically demanding ligands allowed the preparation of {[HB(3,5-Me2pz)3]Pb(μ-NCS)}2 (3), and {[HB(pz)3]Pb(μ-NCS)}n (4). The former has a dimeric structure with both μ-NCS-S,N and μ-NCS-S,S bridging SCN− ligands and the latter has a infinite 2-D layered array in which three nonequiv. {[HB(pz)3]Pb}+ groups sandwich a layer of SCN− ligands. Using neutral 2,6-pyridyl-diimine ligands (pydim) having bulky 2,6-dimethylphenyl substituents, parallel complexes of both metals were prepared. The cadmium complex, [(pydim)Cd (NCS)]2[BF4]2 (5) is dimeric with normal μ-NCS-S,N bridging groups. The structure of the lead(II) analog, [(pydim)Pb(NCS)][BF4] (6) is monomeric with an N-bound, isothiocyanate ligand and a four-coordinate lead(II). The structure of 6 is very different from 5, presumably because of the stereoactive lone pair on lead(II).

Synthesis and x-ray crystallographic analysis of 4,6-di-O-acetyl-2,3-dideoxy-α-d-threo-hexopyranosyl cyanide

The glycopyranosyl cyanide 4,6-di-O-acetyl-2,3-dideoxy-α-D-threo-hexopyranosyl cyanide has been synthesized from tri-O-acetyl-D-galactal by reaction with trimethylsilyl cyanide in the presence of boron trifluoride diethyl etherate followed by catalytic hydrogenation. The synthesis provides the α-anomer stereoselectively, the structure of which was assigned based on 2D NMR techniques and x-ray crystallography.

An Investigation Into Rigidity-Activity Relationships in bisQAC Amphiphilic Antiseptics

Twenty‐one mono‐ and biscationic quaternary ammonium amphiphiles (monoQACs and bisQACs) were rapidly prepared in order to investigate the effects of rigidity of a diamine core structure on antiseptic activity. As anticipated, the bioactivity against a panel of six bacteria including methicillin‐resistant Staphylococcus aureus (MRSA) strains was strong for bisQAC structures, and is clearly correlated with the length of non‐polar side chains. Modest advantages were noted for amide‐containing side chains, as compared with straight‐chained alkyl substituents. Surprisingly, antiseptics with more rigidly disposed side chains, such as those in DABCO‐12,12, showed the highest level of antimicrobial activity, with single‐digit MIC values or better against the entire bacterial panel, including sub‐micromolar activity against an MRSA strain.

Crystal structures of fac-tri­carbonyl­chlorido­(6,6′-dihy­droxy-2,2′-bi­pyridine)­rhenium(I) tetra­hydro­furan monosolvate and fac-bromido­tricarbon­yl(6,6′-dihy­droxy-2,2′-bi­pyridine)­manganese(I) tetra­hydro­furan monosolvate

The structures of two facially coordinated Group VII metal complexes, fac-[ReCl(6,6′-dihydroxy-2,2′-bipyridine)(CO)3]·C4H8O and fac-[MnBr(6,6′-dihydroxy-2,2′-bipyridine)(CO)3]·C4H8O, are reported. These complexes are relevant to catalysis for CO2 reduction.