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The structures and reactivity of metal hydride complexes dissolved in tetrahydrofuran (THF) are studied. The acidity of these complexes involving different metals shows an increase according to the position of metals in the periodic table.

A variety of monomeric, anionic rhenium hydride salts are conveniently synthesized by the deprotonation of neutral polyhydride complexes by use of a strong base, such as KH. Studies have shown that analogous anionic dimers with other phosphine ligands such as P(p-C6H4F)(sub 3) and PMe(sub 3) can be prepared.

Acidity scales for phosphorus compounds in tetrahydrofuran are examined.

The new anionic complexes [K(18-crown-6)][WH5(PMe2Ph)3], [K(1,10-diaza-18-crown-6)][WH5(PMe2Ph)3), [K(2,2,2-crypt)][ReH4(PMePh2)3], and [K(1,10-diaza-18-crown-6)][ReH4(PMePh2)3] were prepared by reaction of KH/crown or KH/crypt with the appropriate neutral polyhydride WH6(PMe2Ph)3 or ReH5(PMePh2)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 Kα 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(PMe2Ph)3/[WH5(PMe2Ph)3]-) is 42 ± 4 according to the equilibrium set up by reacting WH6(PMe2Ph)3 with [K(2,2,2-crypt)][ReH6(PCy3)2]. The pKαTHF 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]+(ReH6(PCy3)2]- whereas reaction with WH6(PMe2Ph)3 gave an equilibrium with [HP4-tBu]+[WH5(PMe2Ph)3]-. From these and a related equilibrium, the pKαTHF of [HP4-tBu]+ is found to be 40 ± 4. In general, neutral complexes MHx(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 pKαTHF of 30 ± 4. The equilibrium constant for the similar deprotonation reaction with [K(18-crown-6)][{ReH2(PMePh2)2}2(μ-H)3] confirmed this value. [ABSTRACT FROM AUTHOR]

Characterizes the anionic polyhydride dimer {ReH[sub 2](PMePh[sub 2])[sub 2]}[sub 2{mu-H)[sub 3]][sup -]. Synthesis of the dimer; Effect of certain ligands on the dimer; Reaction of the dimer with potassium hydride.