Treatment of [(v4-CsHlz)RuH(NH2NMe2)3]PF6 (C8HlZ = cycloocta-1,5-diene) with cyclopentadienylthallium in refluxing acetone affords the novel cyclopentadienyl-ruthenium(I1) complex [ (q5-C5H5)Ru-(v4-CsHlz)H] (1). Reaction of 1 with halogenating agents (CC14, CH2Brz, CH31) in pentane gives the halo complexes [(v5-C5H5)Ru(v4-C8Hl2)X] (2-4; X = C1, Br, I), while halide metathesis on 2 using either NaBr or NaI in methanol provides alternative routes to 3 and 4, respectively. The substitution of the cycloocta-1,5-diene and/or chloro ligands in 2 in a range of solvents and under mild reaction conditions is a rapid and facile process. Mono-and bidentate ligands [CO, PPh3, PMe3, 1,2-bis(diphenylphosphino)ethane, P(OMe)3, PPhzH, MeNC, t-BuNC, 2,6-MezC6H3NC, CN(CH2)6NC, 3,4,7,8-Me4-1,lO-phenanthroline] and the dienes (buta-1,3-diene, 2,3-dimethylbuta-1,3-diene, 1-methyl-4-(methoxycarbonyl)buta-l,3-diene, bicyclo[2.2.l]hepta-2,5-diene) substitute the cycloocta-1,5-diene ligand in 2, in ethanol, acetone, or tetrahydrofuran solutions to give neutral products of the general type [ (v5-C5H5)RuL2C1]. Polyolefins (cyclohepta-173,5-triene, cycloocta-l,3,5-triene, cyclooctatetraene) and aromatics (benzene, hexamethylbenzene, indene, benzyl chloride, triphenylamine) react with 2 in refluxing ethanol solution to give, following anion exchange with NH4PF6, salts of the general formulation [ (v5-C5H5)RuL ]PF& Sodium tetraphenylborate C6H5BPh3)]. Cyclopentadienylsodium reacts with 2 in tetrahydrofuran at room temperature giving ruthenocene, while sodium hydrotris( 1-pyrazoly1)borate (NaHBpz3) with 2 in ethanol yields the unusual "metallocene" [ (v5-C5H5)Ru(HBpz3)]. These compounds are all obtained in high yield and have been characterized by a combination of elemental analysis and spectroscopic methods (IR and 'H and 13C NMR spectroscopy).reacts directly with 2 in refluxing ethanol to give the zwitterionic 7 1 -arene complex [(v5-C5H,)Ru(v6-

Cyclodimerization of t w o molecules of phenylacetylene at the ruthenium(i1) centre in Ru(q-C8Hl2)Br] = cyclo-octa-l,5-diene) gives the novel ruthenacyclopentatriene [(q-C4HS)Ru(C4Ph2H2)BrJ characterized by 1H and 13C n.m.r. spectroscopy and by X-ray analysis; the triene undergoes facile 'oxidative addition' with donor ligands L (e.g. morpholine, trimethyl phosphite, dimethylphenylphosphine) in a bimolecular reaction involving an associative mode of activation t o give the ruthenacyclopentadienes [ ( T ~-C ~H ~) R U ( L ) ( C ~P ~~H ~) B ~] .

Since the pioneering work of Charles Nicolle in 1909 [see Gross (1996) Proc Natl Acad Sci USA 93:10539-10540] most medical officers and scientists have assumed that body lice are the sole vectors of Rickettsia prowazekii, the aetiological agent of louse-borne epidemic typhus (LBET). Here we review the evidence for the axiom that head lice are not involved in epidemics of LBET. Laboratory experiments demonstrate the ability of head lice to transmit R. prowazekii, but evidence for this in the field has not been reported. However, the assumption that head lice do not transmit R. prowazekii has meant that head lice have not been examined for R. prowazekii during epidemics of LBET. The strong association between obvious (high) infestations of body lice and LBET has contributed to this perception, but this association does not preclude head lice as vectors of R. prowazekii. Indeed, where the prevalence and intensity of body louse infections may be high (e.g. during epidemics of LBET), the prevalence and intensity of head louse infestations is generally high as well. This review of the epidemiology of head louse and body louse infestations, and of LBET, indicates that head lice are potential vectors of R. prowazekii in the field. Simple observations in the field would reveal whether or not head lice are natural vectors of this major human pathogen.

Solvation shells surrounding complex inorganic anions have not been extensively studied and are often mentioned with an amorphous picture in mind. We use a computational model previously validated against experimental results and ab initio quantum calculations (Lienke, A.; Klatt, G.; Robinson, D.; Koch, K. R.; Naidoo, K. J. Inorg.Chem. 2001, 40, 2352-2357) to investigate the nature of the hydration shells about simple platinum group metal chloro complexes ([PtCl(6)](2-), [RhCl(6)](3-), [PtCl(4)](2-), and [PdCl(4)](2-)). Our simulations show that the hydration shells surrounding these complexes are symmetric and take on familiar geometric forms. We find that only the [RhCl(6)](3-) complex has a clearly defined second hydration shell while the [PtCl(6)](2-), [PtCl(4)](2-), and [PdCl(4)](2-) second hydration shells are more diffuse.