929685-40-5Relevant academic research and scientific papers
Properties of the polyhydride anions [WH5(PMe 2Ph)3]- and [ReH4(PMePh 2)3]- and periodic trends in the acidity of polyhydride complexes
Hinman, Justin G.,Lough, Alan J.,Morris, Robert H.
, p. 4392 - 4401 (2008/10/09)
The new anionic complexes [K(18-crown-6)][WH5(PMe 2Ph)3], [K(1,10-diaza-18-crown-6)][WH5(PMe 2Ph)3], [K(2,2,2-crypt)][ReH4(PMePh 2)3], and [K(1,10-diaza-18-crown-6)][ReH 4(PMePh2)3] were prepared by reaction of KH/crown or KH/crypt with the appropriate neutral polyhydride WH 6(PMe2Ph)3 or ReH5(PMePh 2)3. The rate of deprotonation of the rhenium hydride in THF is much greater for the reaction involving crypt compared with that of crown. The structure of [ReH4(PMePh2)3] - is distorted pentagonal bipyramidal as determined by an X-ray diffraction study of the crypt salt. No hydridic-protonic M-H...HN bonding is detected between the hydrides of the anionic hydrides and the amino hydrogens of the cations [K(1,10-diaza-18-crown-6)]+ suggesting that stronger M-H...K interactions are present. Acid dissociation constants Ka of polyhydride complexes in THF, approximately corrected for ion pairing, are determined by NMR in order to better understand the periodic trends of metal hydrides. The pKαTHF of (WH6(PMe 2Ph)3/[WH5(PMe2Ph)3] -) is 42 ± 4 according to the equilibrium set up by reacting WH6(PMe2Ph)3 with [K(2,2,2-crypt)][ReH 6(PCy3)2]. The pKα THF for ReH5(PMePh2)3 can be estimated as greater than the pKαTHF of 38 for HNPh2 and less than the pKαTHF of 41 for ReH7(PCy3)2. Reaction of the phosphazene base P4-tBu with ReH7-(PCy3)2 gave an equilibrium with [HP4-tBu]+[ReH 6(PCy3)2]_ whereas reaction with WH6(PMe2Ph)3 gave an equilibrium with [HP 4-tBu]+[WH5(PMe2Ph) 3]-. From these and a related equilibrium, the pK αTHF of [HP4-tBu]+ is found to be 40 ± 4. In general, neutral complexes MH x(PR3)n (M = W, Re, Ru, Os, Ir; n = 3, 2) studied to date have pKαTHF values from 30 to 44 on going from phenyl-substituted to alkyl-substituted phosphine ligands whereas MHx(PR3)n+ (M = Re, Fe, Ru, Os, Co, Rh, Ni, Pd, Pt; n = 4, 3), including diphosphine ligands ((PR3) 2 = PR2-PR2), have values from 12 to 23. From the equilibrium established from the reaction of [HP2- tBu][BPh4] and [K(2,2,2-crypt)]-[OP(OEt)2NPh], [HP2-tBu]+ was calculated to have a pK αTHF of 30 ± 4. The equilibrium constant for the similar deprotonation reaction with [K(18-crown-6)][{ReH 2(PMePh2)2}2(μ-H)3] confirmed this value.
