title: Synthesis and structure of the incomplete cuboidal clusters [W3Se4H3(dmpe)3]+, [W3Se4H(3-x)(OH)x(dmpe)3]+ and [W3Se4(OH)3(dmpe)3]+, and the mechanism of the acid-assisted substitution of the coordinated hydrides.
abstract: The novel incomplete cuboidal cluster [W3Se4H3(dmpe)3](PF6), [1](PF6), has been prepared by reduction of [W3Se4Br3(dmpe)3](PF6) with LiBH4 in THF solution. The trihydroxo complex [W3Se4(OH)3(dmpe)3](PF6), [2](PF6), was obtained by reacting [W3Se4Br3(dmpe)3](PF6) with NaOH in MeCN-H2O solution. The complexes [1](PF6) and [2](PF6) were converted to their BPh4- salts by treatment with NaBPh4. Recrystallisation of [1](BPh4) in the presence of traces of water affords the mixed dihydride hydroxo complex [W3Se4H2(OH)(dmpe)3](BPh4). The crystal structures of [1](BPh4), [2](BPh4) and [W3Se4H2(OH)(dmpe)3](BPh4) have been resolved. Although the [1]+ trihydride does not react with an excess of halide salts, reaction with HX leads to [W3Se4X3(dmpe)3]+ (X = Cl, Br). The kinetics of this reaction has been studied at 25 degrees C in MeCN-H2O solution (1:1, v/v) and found to occur with two consecutive kinetic steps. The first step is independent of the nature and concentration of the X(-) anion but shows a first order dependence on the concentration of acid (k1 = 12.0 mol(-1) dm(3) s(-1)), whereas the second one is independent of the nature and concentration of both the acid and added salts (k2 = 0.024 s(-1)). In contrast, the reaction of [2]+ with acids occurs in a single step with kobs = 0.63 s(-1)(HCl) and 0.17 s(-1)(HBr). These kinetic results are discussed on the basis of the mechanism previously proposed for the reactions of the analogous [W3S4H3(dmpe)3]+ cluster, with special emphasis on the effects caused by the change of S by Se on the rate constants for the different processes involved.
authors.affiliation: Departamento de Ciencia de los Materiales e Ingeniería Metalúrgica y Química Inorgánica, Facultad de Ciencias, Universidad de Cádiz, Apartado 40, Puerto Real, 11510, Cádiz, Spain. manuel.basallote@uca.es
authors.forename: Manuel G
authors.initials: MG
authors.lastname: Basallote
authors.forename: Francisco
authors.initials: F
authors.lastname: Estevan
authors.forename: Marta
authors.initials: M
authors.lastname: Feliz
authors.forename: M
authors.initials: M
authors.lastname: Jesús Fernández-Trujillo
authors.forename: Dora A
authors.initials: DA
authors.lastname: Hoyos
authors.forename: Rosa
authors.initials: R
authors.lastname: Llusar
authors.forename: Santiago
authors.initials: S
authors.lastname: Uriel
authors.forename: Cristian
authors.initials: C
authors.lastname: Vicent
mesh_terms: D000143:Acids / Q000737:chemistry; D018360:Crystallography, X-Ray; D007700:Kinetics; D008956:Models, Chemical; D008958:Models, Molecular; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry; D012643:Selenium / Q000737:chemistry*; D013696:Temperature; D014414:Tungsten / Q000737:chemistry*
chemical_list: D000143:Acids; D009942:Organometallic Compounds; D012643:Selenium; D014414:Tungsten