Properties of the polyhydride anions [WH5(PMe 2Ph)3]- and [ReH4(PMePh 2)3]- and periodic trends in the acidity of polyhydride complexes

Article abstract of DOI:10.1021/ic062037b

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 K_a 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 pK_α^THF 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 pK_α ^THF for ReH₅(PMePh₂)₃ can be estimated as greater than the pK_α^THF of 38 for HNPh₂ and less than the pK_α^THF 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 _α^THF 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 pK_α^THF values from 30 to 44 on going from phenyl-substituted to alkyl-substituted phosphine ligands whereas MH_x(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 _α^THF 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.

Full text of DOI:10.1021/ic062037b

Inorg. Chem. 2007, 46, 4392−4401
-
Properties of the Polyhydride Anions [WH5(PMe2Ph)3] and
-
[ReH4(PMePh2)3] and Periodic Trends in the Acidity of Polyhydride
Complexes
Justin G. Hinman, Alan J. Lough, and Robert H. Morris*
Department of Chemistry, UniVersity of Toronto, 80 St. George Street, Toronto, Ontario M5S 3H6,
Canada
Received October 24, 2006
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 Ka of polyhydride complexes in THF, approximately corrected for ion
THF
pairing, are determined by NMR in order to better understand the periodic trends of metal hydrides. The pKR
(WH6(PMe2Ph)3/[WH5(PMe2Ph)3]-) is 42
of
±
THF
4 according to the equilibrium set up by reacting WH6(PMe2Ph)3 with
THF
[K(2,2,2-crypt)][ReH6(PCy3)2]. The pKR
for HNPh2 and less than the pKR
for ReH5(PMePh2)3 can be estimated as greater than the pKR
of 38
of 41 for ReH7(PCy3)2. Reaction of the phosphazene base P4-tBu with ReH7-
THF
(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 pKR
of [HP4-tBu]+ is found to be 40
THF
THF
±
4. In general, neutral complexes MHx(PR3)n (M
)
W, Re, Ru, Os, Ir; n
)
3, 2) studied to date have pKR
+
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 pKR
of 30
±
4. The equilibrium constant for the similar
THF
deprotonation reaction with [K(18-crown-6)][{ReH2(PMePh2)2}2(µ-H)3] confirmed this value.
Introduction
trends across periods. The practical applications of this
knowledge include the rational design of electrocatalysts for
dihydrogen evolution2 and the design of catalysts for polar
bond hydrogenation3-7 and dehydrogenation.8
A characteristic property of transition metal hydride
complexes is their reactivity as acids as well as bases. The
determination of acid dissociation constants helps to sys-
tematize and understand this reactivity. Some trends are
emerging for the acidity of hydride complexes on going down
groups of transition metals.1 However, little is known about
Tetrahydrofuran (THF) is an excellent solvent for studying
the widest range of transition metal hydride complexes.9-11
The pKRTHF values can range from 0 for protonated THF to
over 50 for deprotonated THF. The acidity of a wide range
* To whom correspondence should be addressed. E-mail: rmorris@
chem.utoronto.ca. Tel. and fax: 1-416-9786962.
(1) Curtis, C. J.; Miedaner, A.; Raebiger, J. W.; DuBois, D. L. Organo-
metallics 2004, 23, 511-516.
(2) Wilson, A. D.; Newell, R. H.; McNevin, M. J.; Muckerman, J. T.;
Rakowski-DuBois, M.; DuBois, D. L. J. Am. Chem. Soc. 2006, 128,
358.
(3) Kimmich, B. F. M.; Fagan, P. J.; Hauptman, E.; Marshall, W. J.
Bullock, R. M. Organometallics 2005, 24, 6220.
(4) Casey, C. P.; Vos, T. E.; Singer, S. W.; Guzei, I. A. Organometallics
2002, 21, 5038.
(5) Ogo, S.; Kabe, R.; Hayashi, H.; Harada, R.; Fukuzumi, S. Dalton
Trans. 2006, 4657.
4392 Inorganic Chemistry, Vol. 46, No. 11, 2007
10.1021/ic062037b CCC: $37.00
© 2007 American Chemical Society
Published on Web 01/26/2007

Polyhydride Anions
of C-H,12-16 Si-H,17 N-H,18-21 P-H,9,22 and O-H23-25
acids in THF has been evaluated.
conjugate bases strong enough to be completely protonated
by acetonitrile, such as the anionic hydrides of our study.9
However, there are difficulties in accounting for referenc-
MA
Kd
{M+, A-} y z M+ + A-
(1)
(2)
ing and for ion-pairing effects. For example the pKTHF value
THF 26
of CH2(CN)2 has been reported as 12 (pKip
)
and 23
[M + ][A- ]
[{M +, A- }]
(pKRTHF).9 Streitwieser and co-workers,27,28 Antipin and co-
workers,29,30 Leito and co-workers,18 and our lab9 have
accounted for ion-pairing by the use of dissociation constants
for cation-anion ion pairing in THF (eqs 1 and 2). The use
of acetonitrile (MeCN) as a solvent would avoid most ion-
pairing problems in acid-base studies.1,31-42 However it is
not useful for acids with values of pKaMeCN > 34 that have
MA
Kd
)
The 1:1 ion-pair dissociation constants, Kd (eq 2), are
determined by conductivity measurements or are estimated
theoretically by use of the Fuoss model of ion-pairs43 or other
methods. Recently, the Fuoss model has been shown to be
quite inaccurate when applied to certain ion-pairing in THF.22
Our lab introduced a pKRTHF expression as an approxima-
tion of the free ion pKaTHF acidity and reported a ladder scale
of over 70 cationic and neutral acids, with acidities ranging
from pKRTHFof ([HPEtPh2]+/PEtPh2) ) 5.3 to pKRTHF of (IrH5-
(PiPr3)2/[cis-IrH4(PiPr3)2]-) ) 44.9,44 The scale is based on
linked acid-base equilibria constants that are determined by
(6) Clapham, S. E.; Hadzovic, A.; Morris, R. H. Coord. Chem. ReV. 2004,
248, 2201.
(7) Guan, H.; Iimura, M.; Magee, M. P.; Norton, J. R.; Zhu, G. J. Am.
Chem. Soc. 2005, 127, 7805.
(8) Schlaf, M. Dalton Trans. 2006, 4645.
(9) Abdur-Rashid, K.; Fong, T. P.; Greaves, B.; Gusev, D. G.; Hinman,
J. G.; Landau, S. E.; Lough, A. J.; Morris, R. H. J. Am. Chem. Soc.
2000, 122, 9155.
(10) Peterson, T. H.; Golden, J. T.; Bergman, R. G. Organometallics 1999,
18, 2005.
(11) Gusev, D. G.; Hubener, R.; Burger, P.; Orama, O.; Berke, H. J. Am.
Chem. Soc. 1997, 119, 3716.
(12) Streitwieser, A., Jr. Acc. Chem. Res. 1984, 17, 353.
(13) Stratakis, M.; Wang, P. G.; Streitwieser, A. J. Org. Chem. 1996, 61,
3145.
(14) Streitwieser, A.; Wang, G. P.; Bors, D. A. Tetrahedron 1997, 53,
10103.
(15) Wang, D. Z. R.; Streitwieser, A. Can. J. Chem. 1999, 77, 654.
(16) Greco, J. B.; Peters, J. C.; Baker, T. A.; Davis, W. M.; Cummins, C.
C.; Wu, G. J. Am. Chem. Soc. 2001, 123, 5003.
(17) Korogodsky, G.; Bendikov, M.; Bravo-Zhivotovskii, D.; Apeloig, Y.
Organometallics 2002, 21, 3157.
THF
1H and 31P NMR measurements and is anchored to pKR
) pKaaq ) 9.7 for [HPCy3][BPh4]/PCy3 and 12 for picric
THF
acid/picrate.9,18-20 The pKR
of an unknown acid can be
determined from reaction of the acid or conjugate base with
a known reference base or acid to give Keq (eq 3), and eq 4
can be used to solve for KRTHF(HA1/A1 ) or KRTHF(HA2/A2 ).
In the case of unknown Kd values, this approach provides
the least uncertainty, especially when ions have similar
properties on each side of eq 3.
-
-
(18) Kaljurand, I.; Rodima, T.; Pihl, A.; Maemets, V.; Leito, I.; Koppel, I.
A.; Mishima, M. J. Org. Chem. 2003, 68, 9988.
(19) Leito, I.; Rodima, T.; Koppel, I. A.; Schwesinger, R.; Vlasov, V. M.
J. Org. Chem. 1997, 62, 8479-8483.
Keq
HA1 + {M+, A2 } y z HA2 + {M+, A1 }
(3)
(4)
-
-
-
Kd KRTHF (HA1/A1
)
MA2
(20) Rodima, T.; Kaljurand, I.; Pihl, A.; Maemets, V.; Leito, I.; Koppel, I.
A. J. Org. Chem. 2002, 67, 1873.
Keq
)
MA1
(21) Kaljurand, I.; Ku¨tt, A.; Soova¨li, L.; Rodima, T.; Ma¨emets, V.; Leito,
I.; Koppel, I. A. J. Org. Chem. 2005, 70, 1019.
Kd
KRTHF (HA2/A-2 )
(22) Streitwieser, A.; McKeown, A. E.; Hasanayn, F.; Davis, N. R. Org.
Lett. 2005, 7, 1259.
In the case where the reaction of a neutral acid and a
neutral base is being used to provide an equilibrium constant
(23) Coetzee, J. F.; Deshmukh, B. K.; Liao, C.-C. Chem. ReV. 1990, 90,
827.
THF
Keq (eq 5), the KR
for either (HB)+ or (HA) can be
(24) Barro´n, D.; Barbosa, J. Anal. Chim. Acta 2000, 403, 339.
(25) Casey, C. P.; Singer, S. W.; Powell, D. R.; Hayashi, R. K.; Kavana,
M. J. Am. Chem. Soc. 2001, 123, 1090.
(26) Antipin, I. S.; Gareyev, R. F.; Vedernikov, A. N.; Konovalov, A. I. J.
Phys. Org. Chem. 1994, 7, 181.
calculated from eq 6 by using either KRTHF(HB+/B) or KR
-
THF
(HA/A-) as a reference. When Kd has to be estimated, this
approach gives a larger uncertainty.22
(27) Krom, J. A.; Petty, J. T.; Streitwieser, A. J. Am. Chem. Soc. 1993,
115, 8024.
(28) Kaufman, M. J.; Gronert, S.; Streitwieser, A. J. Am. Chem. Soc. 1988,
110, 2829.
(29) Antipin, I. S.; Gareev, R. F.; Ovchinnikov, V. V.; Konovalov, A. I.
Dokl. Akad. Nauk. SSSR. 1989, 304, 135.
(30) Antipin, I. S.; Gareyev, R. F.; Vedernikov, A. N.; Konovalov, A. I. J.
Phys. Org. Chem. 1994, 7, 181.
Keq
HA + B y z {HB+, A-}
KRTHF (HA/A- )
(5)
(6)
Keq
)
KdHBA KRTHF (HB+/B)
(31) Kristja´nsdo´ttir, S. S.; Moody, A. E.; Weberg, R. T.; Norton, J. R.
Organometallics 1988, 7, 1983.
(32) Kristja´nsdo´ttir, S. S.; Loendorf, A. J.; Norton, J. R. Inorg. Chem. 1991,
30, 4470.
(33) Kristja´nsdo´ttir, S. S.; Norton, J. R. In Transition Metal Hydrides:
Recent AdVances in Theory and Experiment; Dedieu, A., Ed.; VCH:
New York, 1992; Chapter 9, p 309.
(34) Weberg, R. T.; Norton, J. R. J. Am. Chem. Soc. 1990, 112, 1105 and
references therein.
In the case where a cationic acid reacts with an anionic
base to give an equilibrium (eq 7), eq 8 can be used to
calculate KR
THF
THF
(HB+/B) when KR
(HA/A-) is used as a
(39) Ciancanelli, R.; Noll, B. C.; DuBois, D. L.; Rakowski Dubois J. Am.
Chem. Soc. 2002, 124, 2984.
(40) Ellis, W. W.; Miedaner, A.; Curtis, C. J.; Gibson, D. H.; DuBois, D.
L. J. Am. Chem. Soc. 2002, 124, 1926.
(41) Curtis, C. J.; Miedaner, A.; Ellis, W. W.; DuBois, D. L. J. Am. Chem.
Soc. 2002, 124, 1918.
(42) Berning, D. E.; Noll, B. C.; DuBois, D. L. J. Am. Chem. Soc. 1999,
121, 11432.
(35) Ellis, W. W.; Raebiger, J. W.; Curtis, C. J.; Bruno, J. W.; DuBois, D.
L. J. Am. Chem. Soc. 2004, 126, 2738.
(36) Ellis, W. W.; Ciancanelli, R.; Miller, S. M.; Raebiger, J. W.; Rakowski
Dubois, M.; DuBois, D. L. J. Am. Chem. Soc. 2003, 125, 12230.
(37) Curtis, C. J.; Miedaner, A.; Ciancanelli, R.; Ellis, W. W.; Noll, B. C.;
Rakowski Dubois, M.; DuBois, D. L. Inorg. Chem. 2003, 42, 216.
(38) Price, A. J.; Ciancanelli, R.; Noll, B. C.; Curtis, C. J.; DuBois, D. L.;
Rakowski Dubois, M. Organometallics 2002, 21, 4833.
(43) Fuoss, R. M. J. Am. Chem. Soc. 1958, 80, 5059.
(44) Landau, S. E.; Groh, K. E.; Lough, A. J.; Morris, R. H. Inorg. Chem.
2002, 41, 2995.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4393

Hinman et al.
Unity 400 MHz spectrometers. 31P NMR spectra were acquired on
a Varian Gemini 300 MHz or a Varian Mercury 300 MHz
spectrometer operating at 121 MHz for 31P. 1H NMR spectra were
referenced indirectly to TMS via solvent peaks; 31P NMR spectra
were referenced to external 85% H3PO4 or to internal P(OMe)3/
C6D6. Equilibrium constants were determined by gated 1H de-
coupled 31P NMR in nondeuterated THF, employing 90° pulses
and a recycling time (D1 + AT) of 46 s.
reference and vice versa.
Keq
-
-
{HB+, BPh4 } + {M+,A-} y z {M+, BPh4 } + HA + B
(7)
KRTHF (HB+/B)Kd
Kd
HBBPh4
MA
Keq
)
(8)
MBPh4
Kd
KRTHF (HA/A-)
Infrared spectra were acquired on a Nicolet Magna-IR spec-
trometer 550 or a Perkin-Elmer Paragon 500 FT-IR spectrometer.
Elemental analyses were performed by Guelph Chemical Labo-
ratories, Guelph Canada, except for the analysis of [K(1,10-diaza-
18-crown-6)][WH5(PMe2Ph)3], which was performed by Oneida
Research Services, Inc., Whitesboro, NY.
Single-crystal X-ray diffraction data were collected using a
Nonius Kappa-CCD diffractomer with Mo KR radiation (λ )
0.71073 Å). The CCD data were integrated and scaled using the
Denzo-SMN package. The structures were solved and refined using
SHELXTL V5.1. Refinement was by full-matrix least-squares on
F2 using all data (negative intensities included). Hydride atoms were
located and refined with isotropic thermal parameters.
Some strengths of the NMR method for the construction
of acidity scales are that it is easy to implement and provides
an accurate equilibrium constant from the species present
when they have characteristic 1H and 31P resonances. It also
provides a means of detecting side reactions; if they occur,
that may not be detected by methods like UV-vis spectros-
copy. Some weaknesses include the higher sample concen-
trations needed compared with UV-vis spectroscopy and
the difficulty in accounting for ion pairing, solvation, and
hydrogen bonding in this low dielectric constant solvent.
THF
Thus the values of pKR
reported here are not thermody-
The following compounds were prepared by literature methods:
ReOCl3(PPh3)2,49 WCl4(PMe2Ph)3,50 WH6(PMe2Ph)3,51[HNEt3]-
[BPh4],9 [K(2,2,2-crypt)][OP(OEt)2NPh],9 ReH7(PCy3)2,9 [K(2,2,2-
crypt)][ReH6(PCy3)2],9,47 ReH3(PMe2Ph)4,9 [ReH4(PMe2Ph)4][BPh4],9
ReCl3(PMePh2)3,52 ReH5(PMePh2)3,53 and [K(18-crown-6)][{ReH2-
(PMePh2)2}2(µ-H)3].48 The compounds 18-crown-6, 1,10-diaza-18-
crown-6, KH, LiAlH4, 2,2,2-crypt, and Re metal powder were
purchased from the Aldrich Chemical Co. KH was obtained as a
suspension in mineral oil; the salt was filtered and washed with
hexanes under a nitrogen atmosphere prior to use. Strem Chemical
Company supplied PMePh2, PMe2Ph, PCy3, and WCl6, Fluka
Laboratory Chemicals supplied P2-tBu (2 M in THF) and [HP4-t-
Bu][BF4], and Chem. Service, Inc., provided OP(OEt)2NHPh.
Nitrogen (prepurified grade) and argon gases (ultrahigh purity grade)
were obtained from Matheson Gases Canada. Hydrogen gas (grade
4.0) was obtained from BOC Gases Canada and used without further
purification.
namically accurate pKa values but are nevertheless useful in
estimating the relative acidity of compounds in THF.
An objective of the current work is to study the basicity
of anionic polyhydrides and the acidity of their conjugate
acid form MHx+1(PR3)n in order to discover periodic trends
in their acid-base properties and to probe the interesting
phenomenon of hydridic-protonic MH‚‚‚HN bonding.45 The
polyhydride anions [MHx(PR3)n]- have hydrogen-accepting
hydrides pointed in opposite directions and so the introduc-
tion of cations such as [K(1,10-diaza-18-crown-6)]+ ([K(H-
NQNH)]+) with divergent hydrogen bond donor N-H groups
should encourage the self-assembly of chain structures.
Indeed this is the case for [K(HNQNH)]+[IrH4(PiPr3)2]-,44
[K(HNQNH)]+[MH5(PiPr3)2]-, M ) Ru, Os,46 [K(HNQNH)]+-
i
[ReH6(PR3)2]-, R ) Me, Pr,47 and [K(HNQNH)]+[{ReH2-
(PMePh2)2}2(µ-H)3]-.48 Here, we examine whether such
structures can form with polyhydrides that have three
phosphine ligands per metal.
[K(18-crown-6)][WH5(PMe2Ph)3]. THF (5 mL) was added to
WH6(PMe2Ph)3 (353 mg, 0.584 mmol), KH (65 mg, 1.62 mmol),
and 18-crown-6 (153 mg, 0.584 mmol) under Ar. The solution
turned deep red and was stirred for 3 h at ambient temperature.
The excess potassium hydride was filtered from solution and washed
with THF (3 mL). The solvent was removed from the combined
filtrate by vacuum, yielding [K(18-crown-6)][WH5(PMe2Ph)3] as
a deep red-purple microcrystaline solid which was then washed
with hexanes (2 × 5 mL) and dried in vacuo. Yield: 440 mg
(83.3%). Anal. Calcd: C, 47.69; H, 6.89. Found: C, 48.04; H, 6.52.
1H NMR (C6D6) δ: 8.21-7.00 (m, Ph, 15H), 3.17 (s, CH2, 24H),
Experimental Section
Unless otherwise stated, all manipulations and reactions were
carried out under ultrahigh purity argon or prepurified nitrogen using
Schlenk and glovebox techniques. All solvents were distilled under
argon over appropriate drying agents. THF, toluene, diethyl ether,
and hexanes were dried and distilled from sodium metal and
benzophenone indicator. CH2Cl2 was refluxed and distilled over
calcium hydride, and ethanol and methanol were refluxed and
distilled over iodine-activated magnesium turnings. CDCl3, CD2Cl2,
C6D6, and THF-d8 were obtained from Cambridge Isotope Labo-
ratories and dried by storing over molecular sieves (3-Å beads,
8-12 mesh, Aldrich Chemical Co.).
2
2.04 (d, J(1H,31P) ) 6 Hz, PMe2, 18H), -4.22 (br, WH, 5H).
1
31P{1H} NMR(C6D6) δ: -3.23 (s; d J(183W, 31P) ) 171.2 Hz).
[K(1,10-diaza-18-crown-6)][WH5(PMe2Ph)3]. A procedure simi-
lar to the preparation of [K(18-crown-6)][WH5(PMe2Ph)3] was
employed with the following quantities: THF (3 mL), WH6(PMe2-
Ph)3 (280 mg, 0.463 mmol), KH (30 mg, 0.75 mmol), and 1,10-
diaza-18-crown-6 (122 mg, 0.465 mmol). Yield: 362 mg (86.5%).
Anal. Calcd C, 47.79; H, 7.13; N, 3.10. Found: C, 47.81; H, 7.02;
1H NMR spectra were acquired on Varian Gemini 200 MHz,
Varian Gemini 300 MHz, Varian Mercury 300 MHz, or Varian
(45) Morris, R. H. In Recent AdVances in Hydride Chemistry; Peruzzini,
M., Poli, R., Eds.; Elsevier: Amsterdam, 2001; p 1.
(46) Abdur-Rashid, K.; Gusev, D.; Lough, A. J.; Morris, R. H. Organo-
metallics 2000, 19, 834.
1
N, 3.34. H NMR (C6D6) δ: 8.00-6.99 (m, Ph, 15H), 3.06 (br,
(49) Johnson, N. P.; Lock, C. J. L.; Wilkinson, G. Inorg. Synth. 1969, 9,
(47) Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Can. J. Chem. 2001,
79, 964.
(48) Hinman, J. G.; Abdur-Rashid, K.; Lough, A. J.; Morris, R. H. Inorg.
Chem. 2001, 40, 2480.
145.
(50) Chatt, J.; Heath, G. A.; Richards, R. L. J. Chem. Soc., Dalton Trans.
1974, 2074.
(51) Crabtree, R. H.; Hlatky, G. G. Inorg. Chem. 1984, 23, 2388.
4394 Inorganic Chemistry, Vol. 46, No. 11, 2007

Polyhydride Anions
1
CH2, 8H), 3.00 (br, CH2, 8H), 2.15 (br, CH2, 8H), 1.83 (s, PMe3,
as a white powder. Yield: 1.12 g (97.8%). H NMR (C6D6) δ:
18H), 0.64 (s, NH, 2H), -4.36 (m, WH, 5H). 31P{1H} NMR(C6D6)
2.72 (d, 3J(31P, 1H) ) 9.9 Hz, 54 H), 1.85 (d, 4J(31P, 1H) ) 0.9 Hz,
1
2
δ: 0.03 (s; d J(183W, 31P) ) 165.2 Hz). IR (Nujol): νNH 3283
9 H). 31P {1H} NMR (THF) δ: 3.85 (d, J(31P, 31P) ) 18.1 Hz, 3
cm-1; νWH 1798, 1769, 1735 cm-1
.
P), -26.19 (qrt, J(31P-31P) ) 18.1 Hz, 1 P).
2
THF
[HP4-tBu][BPh4]. THF (4 mL) was added to the P4 base (175
mg, 0.276 mmol) and [HNEt3][BPh4] (114 mg, 0.270 mmol), and
the solution was stirred for 12 h at ambient temperature. The solvent
was removed by vacuum, and the resulting white residue was
filtered and washed with diethyl ether (5 mL) to yield [HP4-tBu]-
[BPh4] as a white powder. Yield: 220 mg (85%). Anal. Calcd: C,
57.92; H, 8.88; N, 19.09. Found: C, 57.87; H, 9.14; N, 18.60. 1H
NMR (CD2Cl2) δ: 7.5-6.9 (m, BPh4, 20 H), 2.69 (m, NMe2, 54
pKR
Determination of WH6(PMe2Ph)3 Relative to ReH7-
(PCy3)2. An NMR tube charged with WH6(PMe2Ph)3 (10 mg, 0.016
mmol), [K(2,2,2-crypt)][ReH6(PCy3)2] (20 mg, 0.017 mmol), and
THF (0.65 mL) under Ar was periodically shaken over the course
of 3 h. The NMR spectra were recorded. The solution immediately
turned from colorless to red. The spectrum was checked by use of
NMR again after 8 h, and no further changes were detected. 31P-
{1H gated} NMR δ: 64.7 (s, I ) 29.4, [ReH6(PCy3)2]-), 47.2 (s,
1
I ) 11.4, ReH7(PCy3)2) -0.9 (s, I ) 7.9; d J(183W, 31P) ) 165.1
H), 2.13 (br d, J(31P, H) 6 Hz, NH, 1H), 1.34 (s, Bu, 9H). 31P-
{1H} NMR (CD2Cl2) δ: 13.45 (d, J(31P, 31P) ) 49.8 Hz, 3P),
2
1
t
Hz, [WH5(PMe2Ph)3]-), -4.1 (s, I ) 48.9; d, 1J(183W, 31P) ) 75.0
Hz, WH6(PMe2Ph)3).
2
2
-22.73 (qrt, J(31P, 31P) ) 49.8 Hz, 1 P).
[K(2,2,2-crypt)][ReH4(PMePh2)3]. THF (5 mL) was added to
ReH5(PMePh2)3 (0.245 g, 0.309 mmol), 2,2,2-crypt (0.116 g, 0.308
mmol), and KH (0.040 g, 1.0 mmol). The solution turned deep red
after 45 min and was stirred for an additional 4 h at room
temperature. Excess KH salts were filtered from solution, and the
solvent was removed from the filtrate by vacuum. The resulting
orange residue was washed with hexanes (6 mL) and dried in vacuo
to yield [K(2,2,2-crypt)][ReH4(PMePh2)3]. Yield: 0.260 g (69.7%).
Anal. Calcd: C, 56.74; H, 6.60; N, 2.32. Found: C, 56.10; H, 6.41;
N, 2.36. 1H NMR (C6D6) δ: 7.62-6.82 (m, 30 H, Ar-H), 3.48 (s,
12 H, CH2), 3.44 (t, 12 H, CH2), 2.44 (t, 12 H, CH2), 1.68 (s,
A1. pKRTHF Determination of [HP4-tBu]+. Method 1. An NMR
tube charged with P4-tBu (9 mg, 0.014 mmol), ReH7(PCy3)2 (11
mg, 0.015 mmol), and THF (0.65 mL) under Ar was periodically
shaken over the course of 3 h, and the 31P NMR spectrum was
recorded. Another spectrum was collected after 8 h, and no further
changes were detected. 31P{1H gated} NMR (THF) δ: 63. 5 (s, I
) 14.7, [ReH6(PCy3)2]-), 45.7 (s, I ) 3.8, ReH7(PCy3)2), 10.7 (d,
I ) 52.7, 2J(31P, 31P) ) 49.8 Hz, [HP4-tBu]+), -25.7 (qrt, I ) 20.43,
2J(31P, 31P) ) 49.8 Hz, [HP4-tBu]+), 3.0 (d, I ) 5.22, 2J(31P, 31P))
18.1 Hz, P4).
A2. Method 2. An NMR tube charged with WH6(PMe2Ph)3 (16
mg, 0.026 mmol), P4-tBu (16 mg, 0.025 mmol), and THF (0.65
mL) under Ar was periodically shaken over the course of 3 h. The
31P NMR spectrum was recorded. Another spectrum was recorded
after 8 h, and no further changes were detected. The solution was
observed to immediately change from colorless to red. 31P{1H
2
9 H, PMe), -7.91 (qrt, J(31P1H) ) 17.4 Hz, 4H, ReH). 31P{1H}
NMR (C6D6) δ: 11.41 (s). IR (Nujol): νReH 1949 (s), 1930
(s) cm-1
.
[K(1, 10-diaza-18-crown-6)][ReH4(PMePh2)3]. THF (5 mL)
was added to ReH5(PMePh2)3 (155 mg, 0.196 mmol), 1,10-diaza-
18-crown-6 (51 mg, 0.194 mmol), and KH (25 mg, 0.62 mmol).
The solution was heated to 68 °C for 24 h, and the solution turned
from colorless to red-orange. Excess KH was filtered from the
solution, and the solvent was removed by vacuum from the filtrate.
The red-orange residue was washed with diethyl ether (20 mL)
and dried in vacuo to yield [K(1,10-diaza-18-crown-6)][ReH4-
2
gated} NMR δ: 8.2 (d, I ) 29.89, J(31P, 31P) ) 49.8 Hz, [HP4-
2
tBu]+), -28.2 (quartet, J(31P, 31P) ) 49.8 Hz, [HP4-tBu]+), 0.33
2
(d, I ) 11.8, J(31P, 31P) ) 18.1 Hz, P4-tBu), -4.8 (s, I ) 26.95;
d 1J(183W, 31P) ) 165.1 Hz, [WH5(PMe2Ph)3]-), -8.1 (s, I ) 20.72;
1
d, J(183W, 31P) ) 75.0 Hz, WH6(PMe2Ph)3).
A3. Method 3. An NMR tube charged with [K(18-crown-6)]-
[WH5(PMe2Ph)3] (23 mg, 0.024 mmol), [HP4-tBu][BPh4] (23 mg,
0.024 mmol), and THF (0.65 mL) under Ar was periodically shaken
over the course of 3 h, and the NMR spectra were recorded. The
solution was checked again after 5 h, and no further changes were
1
(PMePh2)3] as an orange powder. Yield: 50 mg (23%). H NMR
(THF-d8) δ: 7.85-6.95 (m, 30 H, Ar-H), 3.65 (t, 8 H, CH2), 3.60
(t, 8 H, CH2), 2.40 (s, 8 H, CH2), 1.85 (s, 9 H, PMe), 0.85 (s, 2H,
NH), -7.77 (qrt, 2J(31P, 1H)) 17.8 Hz, 4 H, ReH). IR (neat): νRe-H
1988 (s), 1924 (s), 1884(s); νNH 3291 (m) cm-1
.
2
detected. 31P{1H gated} NMR : 8.8 (d, I ) 39.0, J(31P, 31P) )
Attempted Reaction of ReH5(PMePh2)3 with [K(2,2,2-crypt)]-
[NPh2]. An NMR tube charged with ReH5(PMePh2)3 (5 mg, 0.006
mmol), [K(2,2,2-crypt)][NPh2] (6 mg, 0.01 mmol), and THF (0.65
mL) under N2 was flame-sealed and heated to 45 °C for 72 h. The
colorless solution analyzed by 31P NMR showed only ReH5-
(PMePh2)3.
Attempted Reaction of [K(2,2,2-crypt)][ReH4(PMePh2)3] and
ReH7(PCy3)2. An NMR tube charged with ReH7(PCy3)2 (12 mg,
0.016 mmol), [K(2,2,2-crypt)][ReH4(PMePh2)3] (23 mg, 0.019
mmol), and THF (0.65 mL) under N2 was sealed and periodically
shaken for 48 h at room temperature. The red solution analyzed by
31P NMR showed ReH7(PCy3)2, [K(2,2,2-crypt)][ReH4(PMePh2)3],
and a trace amount of ReH5(PMePh2)3 presumably due to trace
amounts of H2O present in the THF.
P4-tBu. THF (6 mL) was added to [HP4-tBu][BF4] (1.30 g, 1.80
mmol), KH (0.35 g, 8.75 mmol), and 2,2,2-crypt (10 mg, 0.027
mmol). The suspension was heated to 60 °C for 6 h and then stirred
at room temperature for 48 h. The solvent was removed by vacuum
from the resulting white powder, and the neutral P4 base was
extracted with hexanes (3 × 10 mL). The solvent was removed by
vacuum from the combined hexane extracts to yield P4-tBu base
2
49.8 Hz, [HP4-tBu]+), -27.53 (qrt, J(31P, 31P) ) 49.8 Hz, [HP4-
tBu]+), 1.2 (d, I ) 1.52, 2J(31P, 31P)) 18.1 Hz, P4-tBu), -4.6 (s, I
1
) 42.9; d J(183W, 31P) ) 165.1 Hz, [WH5(PMe2Ph)3]-), -7.3 (s,
1
I ) 3.7; d, J(183W, 31P) ) 75.0 Hz, WH6(PMe2Ph)3).
Reaction of P4-tBu and Triphenylmethane. An NMR tube
charged with P4-tBu (30 mg, 0.047 mmol), triphenylmethane (10
mg, 0.041mmol), and THF (0.65 mL) under Ar was sealed and
periodically shaken, and the solution remained colorless for several
days. 31P NMR δ: 12.28 (br, I ) 39.6), 4.82 (br, I ) 39.4), -25.0
(br, I ) 21.06).
Preparation of [HP2-tBu][BPh4]. A solution of P2-tBu in THF
(0.30 mL of 2.0 M, 0.60 mmol) was added to [HNEt3][BPh4] (250
mg, 0.593 mmol) in THF (4 mL). The solution was stirred at
ambient temperature for 12 h, and the solvent was removed by
vacuum. The resulting white powder was washed with diethyl ether/
hexanes (3 mL:3 mL) and filtered. Yield: 346 mg (84%). Anal.
Calcd: 66.37; H, 8.79; N, 14.26. Found: C, 66.82; H, 8.95; N,
1
14.13. H NMR (CD2Cl2) δ: 7.40-6.80 (BPh4, 20 H), 2.69 (d,
1
3
1
3J(31P, H) ) 11 Hz, 18 H, NMe2), 2.67 (d, J(31P, H) ) 11 Hz,
NMe2, 12 H), 2.31 (br d, J(31P, H) ) 51 Hz, NH, 1 H), 1.33 (s,
2
1
Inorganic Chemistry, Vol. 46, No. 11, 2007 4395

Hinman et al.
Table 1. Crystal Data and Structure Refinement for
[K(2,2,2-crypt)][ReH4(PMePh2)3]
temp, K
150(1)
wavelength, Å
cryst syst
space group
0.71073
monoclinic
P2(1)/n
unit cell dimens
a, Å
26.6572(3)
b, Å
13.7512(2)
c, Å
31.9934(4)
90
102.6630(10)
90
11442.5(3)
Figure 1. Proposed ion pairing of (a) [K(1,10-diaza-18-crown-6)]-
[WH5(PMe2Ph)3] and (b) [K(1,10-diaza-18-crown-6)][ReH4(PMePh2)3].
R, deg
â, deg
γ, deg
V, Å3
(PMePh2)2}2(µ-H)3]-), 16.36 (d, 2J(31P, 31P) ) 64.1 Hz, I ) 19.9),
Z
8
2
8.40 (d, J(31P, 31P) ) 64.1 Hz, I ) 18.0).
density (calcd), Mg/m3
abs coeff, mm-1
F(000)
1.401
2.329
4976
X-ray Structural Analysis of [K(2,2,2-crypt)][ReH4(PMePh2)3].
Crystals suitable for X-ray crystallography were grown by slow
diffusion of hexanes into a THF solution of the salt. The crystal
data are listed in Table 1. The hydride ligands were located and
refined isotropically.
cryst size, mm
θ range for data collection, deg
index ranges
0.34 × 0.26 × 0.16
2.57 to 27.47
0 e he 34, 0 e k e 17,
-41 e l e 40
74 078
26 070 [R(int) ) 0.080]
99.5
multiscan
reflns collected
indep reflns
completeness to θ ) 27.47°, %
abs correction
Results and Discussion
Synthesis of [K(Q)][WH5(PMe2Ph)3] (Q ) 18-crown-6
and 1,10-diaza-18-crown-6) and pKRTHF Determination of
WH6(PMe2Ph)3. WH6(PMe2Ph)3 was prepared by the reduc-
tion of the known WCl4(PMe2Ph)3 complex using NaH2Al-
(OCH2CH2OMe)2 as described by Crabtree and Hlatky.51
Caulton and co-workers previously observed the penta-
hydride K[WH5(PMe2Ph)3] in solution by NMR when
treating WH6(PMe2Ph)3 with KH in THF.54 For our study,
[K(Q)][WH5(PMe2Ph)3] (Q ) 18-crown-6 and 1,10-diaza-
18-crown-6) were both prepared in high yield by treating
WH6(PMe2Ph)3 with KH in the presence of the respective
crown-Q. Both the 18-crown-6 and 1,10-diaza-18-crown-6
salts were isolated as extremely air sensitive, microcrystalline
red-purple solids, and both are soluble in THF and benzene.
The synthetic routes to the salts [K(18-crown-6)][WH5-
(PMe3)3],[Na(15-crown-5)][WH5(PMe3)3],and[WH5(PMe3)3-Li+]4
are known, and their structures have been previously discus-
sed.55-57 The broad multiplet detected in the hydride region
of the room temperature 1H NMR spectra for [K(Q)][WH5-
(PMePh2)3] (Q ) 1,10-diaza-18-crown-6 and 18-crown-6)
max and min transm
refinement method
data/restraints/param
GOF on F2
final R indices [I > 2σ(I)]
R indices (all data)
largest diff peak and hole, e Å-3
0.7069 and 0.5047
full-matrix least-squares on F2
26 070 / 0 / 1291
1.030
R1 ) 0.0523, wR2 ) 0.0871
R1 ) 0.0951, wR2 ) 0.0979
1.176 and -1.061
tBu, 9H). 31P {1H} NMR (THF) δ: 17.35 (d, J(31P, 31P) ) 67.8
2
2
Hz, 1 P), 9.69 (d, J(31P, 31P) ) 67.8 Hz, 1 P).
31P NMR Spectra of [HP2-tBu][BPh4]/P2-tBu mixtures. NMR
tubes were charged with the amounts of P2-tBu, [HP2-tBu][BPh4],
and THF (0.65 mL) listed in the Supporting Information. Unlike
mixtures of P4-tBu and [HP4-tBu]+, where distinct chemical shifts
for both the acid and base forms are observed in solution, mixtures
of P2-tBu and [HP2-tBu]+ in solution are in fast exchange on the
NMR time scale and two averaged chemical shifts are observed.
Linear calibration lines were determined between each of the
phosphorus chemical shifts and the mole fraction of P2-tBu/[HP2-
tBu]+ and between the J(31P, 31P) coupling and the mole fraction
2
of P2-tBu/[HP2-tBu]+. The 2J(31P, 31P) coupling gave the best
correlation, having a line of best fit with R2 ) 0.999, likely due to
the fact that the coupling is independent of small referencing
errors.
1
is consistent with the H NMR spectra of related [WH5-
(PMe3)3]- and [WH5(PMe2Ph)3]- salts.54,55 The infrared NH
stretching frequency of the [K(1,10-diaza-18-crown-6)]-
[WH5(PMe2Ph)3] at 3283 cm-1 is similar to that of [K(1,10-
diaza-18-crown-6)][BPh4] at 3287 cm-1.46 This suggests that
there is no significant WH‚‚‚HN hydridic-protonic interac-
tion in the [K(1,10-diaza-18-crown-6)][WH5(PMe2Ph)3] salt.
B1. pKRTHF Determination of [HP2-tBu]+. Method 1. An NMR
tube was charged with [HP2-tBu][BPh4] (15 mg, 0.022 mmol),
[K(2,2,2-crypt)][OP(OEt)2NPh] (15 mg, 0.023 mmol), and THF
(0.65 mL). The tube was sealed under Ar and periodically shaken
over the course of 5 h, and the NMR spectrum was recorded. It
was checked again after 8 h, and no further changes were noted.
1
The H NMR chemical shift of the NH moiety at δ ) 0.64
is low and would also suggest the absence of an WH‚‚‚HN
interaction in benzene-d6 solution. The X-ray structure of
the similar [K(18-crown-6)][WH5(PMe3)3] complex shows
that the metal cation interacts with the hydrides and forms
ion pairs with relatively short K-W distances of 3.660(1)
Å.55 This may suggest that the K+ is forming an ion pair
with the tungsten hydride anion as shown in Figure 1 and
cannot form significant WH‚‚‚HN hydridic-protonic hy-
drogen bonds.
31P{1H gated} NMR δ: 15.80 (d, J(31P, 31P) ) 56.4 Hz, I )
2
21.0, [HP2-tBu]+/P2-tBu), 6.12 (d, 2J(31P, 31P) ) 56.4 Hz, I ) 18.5,
[HP2-tBu]+/P2-tBu), 4.07 (s, I ) 22.8, OP(OEt)2NHPh/[OP-
(OEt)2NPh]-).
B2. Method 2. An NMR tube was charged with [HP2-tBu][BPh4]
(16 mg, 0.023 mmol), [K(18-crown-6)][{ReH2(PMePh2)2}2(µ-H)3]
(35 mg, 0.024 mmol), and THF (0.65 mL). The tube was sealed
under Ar and periodically shaken, and after 8 h an NMR spectrum
was recorded. The NMR spectrum was checked again after 20 h,
and no further changes were detected. 31P NMR{1H gated} δ: 12.36
(s, I ) 17.2, {ReH2(PMePh2)2}2(µ-H)4), 18.08 (s, I ) 45.0, [{ReH2-
Attempts to obtain X-ray quality crystals of [K(1,10-diaza-
18-crown-6)][WH5(PMe2Ph)3] have been unsuccessful.
4396 Inorganic Chemistry, Vol. 46, No. 11, 2007

Polyhydride Anions
Table 2. Ion Pair Radii Used to Calculate Kd
just a few hours. The analogous deprotonation reaction with
KH in the presence of 1,10-diaza-18-crown-6 was found to
require 24 h of reflux to go to completion. This demonstrates
the catalytic enhancement of the rate of deprotonation by
the addition of 2,2,2-crypt. The air sensitive, red-orange
[K(2,2,2-crypt)][ReH4(PMePh2)3] salt was isolated in 70%
yield and is soluble in THF but insoluble in toluene, diethyl
ether, and hexanes.
ion-pair
radius, Å
formula
[WH5(PMe2Ph)3]-
[ReH6(PCy3)2]-
[OP(OEt)2NPh]-
[{ReH2(PMePh2)2}2(µ-H)3]-
[BPh4]-
2.0
3.0
3.0
4.3
4.4
4.7
3.3
4.2
2.0
5.0
[HP4-tBu]+
[HP2-tBu]+
The structure for [K(2,2,2-crypt)][ReH4(PMePh2)3] as
determined by X-ray crystallography is shown in Figure 2.
[K(2,2,2-crypt)][ReH4(PMePh2)3] crystallized with two very
similar molecules in the unit cell. Selected bond lengths and
angles are listed in Table 4. The geometry around rhenium
is distorted pentagonal bipyramidal with a pair of axial
phosphorus atoms P(2A) and P(3A). The angle of P(2A)-
Re(A)-P(3A) is 163.58(4)°, bent toward the smaller hydride
ligands. The ReH bond distances range from 1.52(4) to
1.70(4) Å and are typical of such bonds. The Re-P bond
distances, ranging from 2.301(1) to 2.355(1) Å, are typical
of Re-P bonds. The 1H NMR spectrum of [K(2,2,2-crypt)]-
[ReH4(PMePh2)3] shows a quartet in the hydride region at δ
[ReH4(PMe2Ph)4]+
[K(18-crown-6)]+
[K(2,2,2-crypt)]+
The equilibrium constant of eq 9, as calculated from 31P-
{1H, inverse gated decoupled} NMR data, was used in eq 4
to calculate the pKRTHF value of 42 for WH6(PMe2Ph)3. The
ion pair radii used to estimate Kd from the Fuoss equation
were based on the K‚‚‚W distance determined for the related
[K(18-crown-6)][WH5(PMe3)3] complex (Table 2). The Keq
and Kd values used to calculate pKR
Table 3.
THF
are listed in
) -7.91, J(31P, H) ) 17.4 Hz, due to rapid exchange
between the hydride ligands. The 31P{1H} NMR spectrum
shows a singlet at δ ) 11.41, consistent with three equivalent
phosphines.
Keq
2
1
WH6(PMe2Ph)3 + [K(2,2,2-crypt)][ReH6(PCy3)2] y z
[K(2,2,2-crypt)][WH5(PMe2Ph)3] + ReH7(PCy3)2 (9)
The pKRTHF of 42 for WH6(PMe2Ph)3 makes this one of the
least acidic phosphine-containing transition metal hydride
complexes measured to date.
When hydridic and protonic groups form a nonclassical
hydrogen bond, the 1H NMR chemical shift of the hydridic
hydrogen is usually shifted slightly upfield and the protonic
hydrogen is shifted slightly downfield. However, the hy-
dride 1H NMR signal of [K(1,10-diaza-18-crown-6)][ReH4-
(PMePh2)3] is shifted slightly downfield with δ(ReH) )
-7.71 from the analogous [K(2,2,2-crypt)]+ salt (δ(ReH) )
-7.91), and the NH proton chemical shift of 0.85 ppm is
comparable to that for the [K(1,10-diaza-18-crown-6)][BPh4]
salt (1.00 ppm), which contains no hydridic-protonic
interactions. This suggests that there is negligible nonclassical
hydrogen bonding between the NH of the 1,10-diaza-18-
crown-6 and the [ReH4(PMe2Ph)3]- anion. Attempts to obtain
X-ray quality crystals of the [K(1,10-diaza-18-crown-6)]+
salt have been unsuccessful.
Preparation of ReH5(PMePh2)3 and [K(Q)][ReH4-
(PMePh2)3] (Q ) 2,2,2-crypt or 1,10-diaza-18-crown-6)
Complexes. The precursor ReCl3(PMePh2)3 has been pre-
pared by Cotton and Luck by treatment of ReCl5 with
PMePh2.58 In this study, ReCl3(PMePh2)3 was prepared in
quantitative yield by substitution and reduction of ReOCl3-
(PPh3)2 with PMePh2, in a similar method to the one
described by Chatt et al.52 ReH5(PMePh2)3 was prepared by
hydride addition to ReCl3(PMePh2)3 using LiAlH4 followed
by ethanol addition, similar to the method used by Douglas
and Shaw to prepare ReH5(PMe2Ph)3.53
The first report of the deprotonation of a ReH5(PR3)3 (PR3
) tertiary phosphine) by Caulton and co-workers in 198954
described the treatment of ReH5(PMePh2)3 with KH in THF
to produce the salt K[ReH4(PMePh2)3] that was observed by
1H NMR. It was also noted that deprotonation of ReH5(PMe2-
Ph)3 was particularly slow compared with other similar metal
hydrides and the reaction required reflux for 24 h to go to
completion.54 We found that the addition of 2,2,2-crypt
significantly increased the rate of deprotonation of ReH5-
(PMePh2)3 in THF so that complete conversion occurred after
The IR spectrum of [K(1,10-diaza-18-crown-6)][ReH4-
(PMePh2)3] also suggests the absence of such an interaction;
the NH stretch is observed at 3291 cm-1, and this is
consistent with the ν(NH) stretch data for [K(1,10-diaza-
18-crown-6)][BPh4]. Potassium-hydride-rhenium inter-
actions are suspected to be stronger than hydridic-
protonic interactions in this case as shown in Figure 1b, as
previously discussed for [K(1,10-diaza-18-crown-6)]-
[WH5(PMe2Ph)3] and the Re, Os, and Ir complexes men-
tioned above. The bulkiness of the three PR3 groups may
prevent MH‚‚‚HN bonding with the [K(1,10-diaza-18-crown-
6)]+ cation.
(52) Chatt, J.; Leigh, G. J.; Mingos, D. M. P.; Paske, R. J. J. Chem. Soc.
A 1968, 2636.
(53) Douglas, P. G.; Shaw, B. L. Inorg. Synth. 1977, 17, 64.
(54) Alvarez, D.; Lundquist, E. G.; Ziller, J. W.; Evans, W. J.; Caulton,
K. G. J. Am. Chem. Soc. 1989, 111, 8392.
(55) Bandy, J. A.; Berry, A.; Green, M. L. H.; Prout, K. J. Chem. Soc.,
Chem. Commun. 1985, 1462.
(56) Barron, A. R.; Hursthouse, M. B.; Motevalli, M.; Wilkinson, G. J.
Chem. Soc., Chem. Commun. 1986, 81.
The pKRTHF for ReH5(PMePh2)3 can be estimated as greater
THF
THF
than the pKR
of 38 for HNPh2 and less than the pKR
of 41 for ReH7(PCy3)2. This is based on the evidence that
[K(2,2,2-crypt)][NPh2] was not basic enough to deprotonate
ReH5(PMePh2)3 and [K(2,2,2-crypt)][ReH4(PMePh2)3] could
not deprotonate ReH7(PCy3)2.
(57) Berry, A.; Green, M. L. H.; Brandy, J. A.; Prout, K. J. Chem. Soc.,
Dalton Trans. 1991, 2185.
(58) Cotton, F. A.; Luck, R. L. Inorg. Chem. 1989, 28, 2181.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4397

Hinman et al.
THF
Table 3. The Keq and Kd Values Used To Calculate pKR
time to reach
equilibrium
acid
base
Keq
Kd/10-5
WH6(PMe2Ph)3
[K(Z)][ReH6(PCy3)2]a
<3 h
<4h
0.26
5 {[K(Z)]+,[ReH7(PCy3)2]-}
2 {[K(Z)]+,[WH5(PMe2Ph)3]-}
4 {[HP4-tBu]+,
a
t
ReH7(PCy3)2
P4 Bu
2.0 × 103 (1/M)
1.3 × 102 (1/M)
5 × 10-6 (M)
[ReH6(PCy3)]-}
b
t
WH6(PMe2Ph)3
P4 Bu
<4 h
<4 h
1 {[HP4-tBu]+,
[WH5(PMe2Ph)3]-}
[HP4-tBu][BPh4]
[K(Q)][WH5(PMe2Ph)3]b
[K(Z)][OP(OEt)2NPh]c
11 {[HP4-tBu]+, [BPh4]-}
0.003 {[K(Q)]+, [WH5(PMe2Ph)3]-}
1 { [K(Q)]+, [BPh4]-}
[HP2 Bu][BPh4]
<5 h
<6 h
2.3 × 10-3 (M)
4.2 × 10-3 (M)
4 {[HP2-tBu]+, [BPh4]-}
5 {[K(Z)]+, [OP(OEt)2NPh]-}
13 { [K(Z)]+, [BPh4]-}
4 {HP2-tBu]+, [BPh4]-}
1 {[K(Q)]+, [{ReH2(PMePh2)2}2(-H)3]-}
1 {[K(Q)]+, [BPh4]-}
t
t
[HP2 Bu][BPh4]
[K(Q)]
[{ReH2(PMePh2)2}2(µ-H)3]d
a pKRTHF(ReH7(PCy3)2) ) 41, Z ) 2,2,2-crypt. pKR
(WH6(PMe2Ph)3) ) 42, Q ) 18-crown-6. c pKR
(OP(OEt)2NHPh) ) 32. d pKR
b
THF
THF
THF
{ReH2(PMePh2)2}2(µ-H)4 ) 32.
Table 4. Select Bond Lengths (Å) and Angles (deg) for
[K(2,2,2-crypt)][ReH4(PMePh2)3]
Re(1A)-H(1)
1.52(4)
1.63(4)
1.65(4)
1.65(4)
2.301(1)
2.326(1)
2.353(1)
70(2)
153(2)
136(2)
139(2)
69(2)
67(2)
98(1)
84(1)
93(1)
83(1)
87(1)
83(1)
90(1)
Re(1B)-H(8)
1.62(4)
1.68(4)
1.69(4)
1.70(4)
2.310(1)
2.311(1)
2.355(1)
68(2)
153(2)
138(2)
135(2)
67(2)
72(2)
91(1)
83(1)
92(1)
86(1)
90(1)
79(1)
96(1)
Re(1A)-H(2)
Re(1B)-H(7)
Re(1A)-H(3)
Re(1B)-H(5)
Re(1A)-H(4)
Re(1B)-H(6)
Re(1A)-P(2A)
Re(1B)-P(3B)
Re(1A)-P(3A)
Re(1B)-P(2B)
Re(1A)-P(1A)
Re(1B)-P(1B)
H(1)-Re(1A)-H(2)
H(1)-Re(1A)-H(4)
H(2)-Re(1A)-H(4)
H(1)-Re(1A)-H(3)
H(2)-Re(1A)-H(3)
H(4)-Re(1A)-H(3)
H(1)-Re(1A)-P(2A)
H(2)-Re(1A)-P(2A)
H(4)-Re(1A)-P(2A)
H(3)-Re(1A)-P(2A)
H(1)-Re(1A)-P(3A)
H(2)-Re(1A)-P(3A)
H(4)-Re(1A)-P(3A)
H(3)-Re(1A)-P(3A)
H(8)-Re(1B)-H(7)
H(8)-Re(1B)-H(5)
H(7)-Re(1B)-H(5)
H(8)-Re(1B)-H(6)
H(7)-Re(1B)-H(6)
H(5)-Re(1B)-H(6)
H(8)-Re(1B)-P(3B)
H(7)-Re(1B)-P(3B)
H(5)-Re(1B)-P(3B)
H(6)-Re(1B)-P(3B)
H(8)-Re(1B)-P(2B)
H(7)-Re(1B)-P(2B)
H(5)-Re(1B)-P(2B)
H(6)-Re(1B)-P(2B)
Figure 2. Structure of one of the molecules (A) of [K(2,2,2-crypt)][ReH4-
(PMePh2)3] in the unit cell.
83(1)
79(1)
Basicities of P4-tBu and P2-tBu in THF. The phosphazene
base chemistry has been well studied and previously
discussed by Schwesinger.59-61 In the present study the
neutral P4-tBu base (Figure 3) was isolated as a white powder
in quantitative yield by treatment of commercially available
[HP4-tBu][BF4] with KH and a catalytic amount of 2,2,2-
crypt in THF (eq 10). Schwesinger previously reported that
treatment of [HP4-tBu][BF4] with NaH resulted in decom-
position of the phosphazene base;59 however, there was no
evidence for any decomposition products in this reaction
using KH. The neutral P4-tBu base is extremely moisture
sensitive, and this may have been the cause of the decom-
position described previously.
P(2A)-Re(1A)-P(3A) 163.58(4) P(3B)-Re(1B)-P(2B) 159.60(4)
H(1)-Re(1A)-P(1A)
H(2)-Re(1A)-P(1A)
H(3)-Re(1A)-P(1A)
H(4)-Re(1A)-P(1A)
81(1)
151(1)
74(1)
H(8)-Re(1B)-P(1B)
H(7)-Re(1B)-P(1B)
H(5)-Re(1B)-P(1B)
H(6)-Re(1B)-P(1B)
80(1)
148(1)
73(1)
141(1)
145(1)
P(2A)-Re(1A)-P(1A) 95.07(4)
P(3A)-Re(1A)-P(1A) 101.22(4) P(2B)-Re(1B)-P(1B) 104.03(4)
P(3B)-Re(1B)-P(1B) 96.28(4)
tBu][BPh4] salt was prepared in quantitative yield by treating
the P4-tBu base with [HNEt3][BPh4] in THF (eq 11). The 1H
NMR spectrum for [HP4-tBu][BPh4] was similar to that
previously reported for [HP4-tBu][BF4].60 31P{1H} NMR data
for both [HP4-tBu]+ and the neutral P4-tBu have not previ-
ously been reported. The neutral base shows two signals: a
doublet for the three PA at δ ) 3.85 (2J(31P, 31P) ) 18.1 Hz)
and a quartet for PB at δ ) -26.19 (2J(31P, 31P) ) 18.1 Hz).
[HP4-tBu][BF4] + KH 2,2,2-crypt8 P4-tBu + H2 + K[BF4]
(10)
(59) Schwesinger, R.; Schlemper, H.; Hasenfratz, C.; Willardet, W.;
Dambacher, T.; Breuer, T.; Ottaway, C.; Fletschinger, M.; Boele, J.;
Fritz, H.; Putzas, D.; Rotter, H. W.; Bordwell, F. G.; Satish, A. V.; Ji,
G.; Peters, E. M.; Peters, K.; Von Schnering, H. G.; Walz, L. Liebigs
Ann. Chem. 1996, 1055.
[HNEt3][BPh4] + P4-tBu f [HP4-tBu][BPh4] + NEt3
(11)
(60) Schwesinger, R.; Hasenfratz, C.; Schlemper, H.; Walz, L.; Peters, E.
M.; Peters, K.; Von, Schnering, H. G. Angew. Chem., Int. Ed. Engl.
1993, 32, 1361.
(61) Schwesinger, R.; Schlemper, H. Angew. Chem., Int. Ed. Engl. 1987,
26, 1167.
It was necessary to prepare the acid [HP4-tBu]+ with the
[BPh4]- counterion for equilibrium studies in THF in order
to minimize the effect of ion pairing. The white powder [HP4-
4398 Inorganic Chemistry, Vol. 46, No. 11, 2007

Polyhydride Anions
Schwesinger reported that the P4-tBu was in equilibrium
with triphenylmethane;59 however, few experimental details
were provided. In this study an attempt to establish an
equilibrium between P4-tBu and HCPh3 in THF indicates that
the reaction of P4-tBu and HCPh3 in THF results in a
colorless solution and detection of three broad peaks in the
31P NMR, assigned to equal amounts of [HP4-tBu]+ and the
neutral P4-tBu compound. However, the colorless solution
indicates the absence of red trityl anion [CPh3]-, which has
THF
a λmax of 502 nm.62 Because the pKR
of (HCPh3) is
estimated to be equal to or greater than 45,9 an equilibrium
between P4-tBu and HCPh3 in THF seems unlikely.
[HP2-tBu][BPh4] was obtained as a white powder in 84%
yield by treatment of the neutral P2-tBu with [HNEt3][BPh4]
(eq 11). The 1H NMR data were similar to those previously
reported for analogous ClO4- salts.61 The 31P NMR spectrum
for the neutral P2-tBu shows two doublets of equal intensity
at δ ) 12.95 and δ ) -8.87 with J(31P, 31P) ) 35.1 Hz.
2
Similarly, the [HP2-tBu][BPh4] 31P NMR spectrum shows
Figure 3. Structures of the phosphazene compounds P4-tBu, P2-tBu, [HP4-
tBu]+, and [HP2-tBu]+.
two doublets at δ ) 17.35 and δ ) 9.69 with 2J(31P, 31P) )
67.8 Hz.
The pKR
The protonated cation also shows two signals: a doublet at
THF
for [HP2-tBu]+ was determined from the
2
δ ) 13.45 (3PA, J(31P, 31P) ) 49.8 Hz) and a quartet at δ
following equilibria as detected by 31P NMR (eq 15 and eq
16).
2
) -22.73 (Pb, J(31P, 31P) ) 49.8 Hz).
The three following observed equilibria were used to
calculate pKRTHF values for [HP4-tBu]+ (eq 12, eq 13, eq 14)
(Table 2, Table 3).
[HP2-tBu][BPh4] + [K(2,2,2-crypt)][OP
Keq
(OEt)2NPh] y z P2-tBu + OP(OEt)2NHPh +
Keq
P4-tBu + ReH7(PCy3)2 y z [HP4-tBu]+[ReH6(PCy3)2]-
[K(2,2,2-crypt)][BPh4] (15)
(12)
[HP2-tBu][BPh4] + [K(18-crown-6)][{ReH2(PMePh2)2}2
Keq
P4-tBu + WH6(PMe2Ph)3 y z [HP4-tBu]+[WH5
Keq
(µ-H)3]y z P2-tBu + {ReH2(PMePh2)2}2(µ-H)4 +
(PMe2Ph)3]- (13)
[K(18-crown-6)][BPh4] (16)
[HP4-tBu][BPh4] + [K(18-crown-6)][WH5
From the Keq of eq 15 and the data in Table 2 and Table
Keq
THF
3, [HP2-tBu]+ was calculated to have a pKR
of 30 using
(PMe2Ph)3] y z P4-tBu + WH6(PMe2Ph)3 +
eq 8. The similar deprotonation reaction with [K(18-crown-
[K(18-crown-6)][BPh4] (14)
THF
6)][{ReH2(PMePh2)2}2(µ-H)3] (eq 16) confirmed the pKR
to be 30.63 However, in the reverse of eq 15, the neutral
P2-tBu did not react with OP(OEt)2NHPh in THF as
monitored by 31P NMR. It remains unclear if this is due to
By use of the equilibrium established starting with neutral
ReH7(PCy3)2 and P4-tBu, [HP4-tBu]+ was calculated to have
THF
a pKR
of 39.9 by eq 6. In comparison, the equilibrium
a kinetic effect or an effect of ion pairing. However, [K(18-
established starting with WH6(PMe2Ph)3 and P4-tBu (eq 13)
THF
crown-6)][ReH6(PPh3)2] (pKR
(ReH7(PPh3)2 ) 30)) was
gave a pKRTHF of [HP4-tBu]+ ) 39.3. However, starting with
found to be too weak a base to deprotonate [HP2-tBu][BPh4]
[HP4-tBu][BPh4] and [K(18-crown-6)][WH5(PMe2Ph)3] (eq
and give an equilibrium detectable by NMR.
Acidity and Periodic Trends. The pKR
THF
14), [HP4-tBu]+ was determined to have a pKR
value of
THF
values of
40.8 by the use of eq 8. Attempts to establish an equilibrium
by deprotonating [HP4-tBu][BPh4] with [K(2,2,2-crypt)]-
[ReH6(PCy3)2] were unsuccessful as the neutral P4-tBu base
was not detected and only a trace amount of ReH7(PCy3)2
was observed, likely due to residual water in the solvent
various neutral and cationic binary ligand complexes with
hydrides and phosphines are organized in Table 5 according
(62) Gronert, S.; Streitwieser, A., Jr. J. Am. Chem. Soc. 1988, 110, 2843.
THF
(63) The pKR
of [HP2-tBu]+ is expected to be 25 ( 1 on the basis of
t
the value for [HP2-Et]O3SMe,9,21,59 whereas that of [HP4 Bu]+ is
predicted to be about 36.21,59 The poor agreement between our
determined values and the expected values could be caused by the
use of different counteranions (BPh4- in our work vs SO3Me- in the
literature), errors in the calculation of the ion pair dissociation constants
by use of the Fuoss equation, and overestimates of the pKRTHF values
of our neutral acids with pKRTHF greater than 28 caused by cumulative
errors in making links to reference cationic acids. The cumulative error
is estimated to be about (4 (see ref 9).
reacting with [ReH6(PCy3)2]-. The differences between the
THF
three pKR
could be due to experimental error or due to
errors in the ion pairing correction, but we can assign a
pKRTHF of [HP4-tBu]+ ) 40 ( 4 accounting for the cumula-
tive error in estimating Kd values and making links to
reference cationic acids.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4399

Hinman et al.
THF
due to the H-H bond strength of the η2-dihydrogen ligand.
An exception to the decrease in acidity going down the group
is the order Pd g Ni . Pt for similar complexes of the type
[MH(diphos)2]+.64
Table 5. Selected pKR
Values for MHxLn, [MHxLn]+, and
cationic
[PtH2(L2)2]2+ Complexes
neutral
dn/dn+2
hydride
pKR
ref
hydride
pKR
ref
THF
THF
For the series of MHx(PiPr3)2 neutral third row transition
metal complexes, the acidity increases across the periodic
table from Re to Os and decreases across to Ir. The IrH5L2
complex is likely less acidic because the octahedral d6
[IrH4L2]- conjugate base contains unfavorable trans-hydride
ligands. Similarly, for the series of cationic [MHxL4]+ third
row metal hydride type complexes, the acidity increases from
Re across to Os and decreases from Os to Ir. In this series
it is likely that Os is the most acidic as the conjugate base
of [OsH3L4]+ is octahedral with the maximum ligand field
stabilization energy. Likewise, the d6 octahedral [IrH2L4]+
complex is less acidic as it loses the favorable octahedral
geometry to form the five coordinate neutral conjugate base.
For MHxL3 neutral metal hydrides, the W and Re complexes
appear to be weakly acidic with comparable pKRTHF values;
however, further trends remain unclear until the pKRTHF for
the Os and Ir complexes are determined. The complex
[K(THF)(18-crown-6)][OsH3(PPh3)3] has recently been pre-
pared by reacting OsH4(PPh3)3 with KH/crown.65 Other
factors such as the sterics and stereochemistry of the acid/
conjugate base also contribute to the acidity of transition
metal complexes in ways that are still to be unraveled.64
d0/d2 WH6-
(PMe2Ph)3
42
this work
d2/d4 ReH5-
∼40
this work ReH4(PR3)4
16-23
9
+
(PMePh2)3
a
RuH6(PiPr3)2 38
9
9
OsH6(PiPr3)2 35
d4/d6
d6/d8
FeH3(PMe3)4
16
17
9,11
9,11
+
a
+ a
RuH4(PPh3)3 36
IrH5(PR3)2
9
44
RuH3(PMe3)4
+
40-44
OsH3(PR3)4
12-19 9,11
CoH2(dppe)2
RhH2(depx)2
IrH2(PMe3)4
PtH2-
16b
23b
>20
1b,c
39
69
70
64
+
+
+
2+
(EtXantphos)2
d8/d10 CoH(dppe)2 g38d
39
69
NiH(depe)2
PdH(depe)2
PtH(depe)2
17b
16b
22b
42
71
1
+
RhH(depx)2 51d
+
+
MeCN
a Dihydrogen complex. b Converted from pKa
with the use of the
correlation found in Fig. 2 of ref 21. c Note that this is for a dication.
d Neutral acids in THF have similar or greater values than those in MeCN
(see ref 9).
to the d electron count change upon deprotonation. One
general observation is that the monocationic polyhydrides
Conclusions
with four phosphorus donors, at least for M ) Re, Fe, Ru,
[K(18-crown-6)][WH5(PMe2Ph)3] was prepared by treat-
ment of the known WH6(PMePh2)3 with KH in the presence
of 18-crown-6. The analogous [K(1,10-diaza-18-crown-6)]+
salt was prepared similarly; however, from the IR and NMR
data it appears unlikely that there is hydridic-protonic
bonding in the ion pairs. WH6(PMe2Ph)3 was determined to
have a pKRTHF of 42 ( 4 as determined from the equilibrium
established from the reaction of [K(2,2,2-crypt)][ReH6-
(PCy3)2] with WH6(PMe2Ph)2.
THF
Os, Co, Rh, Ni, Pd, Pt, have pKR
values in the ap-
proximate range of 12-23. The neutral polyhydrides with
two or three phosphorus donors generally have pKRTHF values
in the range of 30-44 (Table 5). The high end of the ranges
generally is associated with donating trialkylphosphines and
the low end with phenyl-substituted phosphines as for the
series of ReH7(PR3)2, [ReH4(PR3)4]+, and [OsH3(PR3)4]+ type
complexes.9 We tried to deprotonate WH4(PMePh2)4 by
refluxing with excess KH and 2,2,2-crypt under Ar for 24 h
in THF but were unsuccessful in deprotonating the complex.
Apparently some neutral polyhydrides with four phosphorus
donors are even less acidic. Dubois and co-workers have
calculated from a thermodynamic cycle that the rhodium(I)
complex RhH(depx)2 of Table 5 should have a pKaMeCN of
51.69 However, there is a large contribution from the metal
since CoH(dppe)2 is calculated to be much more acidic with
a pKaMeCN value of 38.39
One general periodic trend for classical transition metal
hydride complexes that has been noted is a decrease in acidity
moving down the periodic table.33 This trend has been
demonstrated for the series of cationic hydrides [MH3L4]+,
where M ) Fe, Ru, and Os, and L ) PMe3 or PEt3 (note
that [RuH(H2)(PMe3)4]+ contains an η2-dihydrogen ligand
and is an exception in that it is not a classical metal
hydride).11 In general, an η2-dihydrogen complex is some-
what less acidic than a comparable classical polyhydride
complex. An example is the neutral η2-dihydrogen complex,
RuH2(H2)2(PiPr3)2, which less acidic than the classical hydride
OsH6(PiPr3)2 (Table 5). The reduced acidity presumably is
[K(2,2,2-crypt)][ReH4(PMePh2)3] was prepared and is the
first example of a [ReH4(L)3]- anion to be characterized by
X-ray crystallography. The analogous [K(1,10-diaza-18-
crown-6)]+ salt was also prepared; IR and 1H NMR studies
suggest that there is little or no hydridic-protonic interaction
between the ReH and the HN groups. It appears that anionic
transition metal hydrides of the type [MHx(PR3)3]- are not
suited to form chain structures with the [K(1,10-diaza-18-
crown-6)]+ NH donor. Such chains have been observed for
[MHx(PR3)2(CO)]- and [MHx(PR3)2]- anions, but three PR3
groups may prevent the close approach of the cation. The
pKRTHF of (ReH5(PMePh2)3) is estimated to be much less than
the pKRTHF of (H2/K(18-crown-6)H). It is between the values
THF
THF
of pKR
(NHPh2) ) 38 and pKR
(ReH7(PCy3)2) ) 41,
assuming that the reactions are under thermodynamic and
not kinetic control.
(64) Miedaner, A.; Raebiger, J. W.; Curtis, C. J.; Miller, S. M.; DuBois,
D. L. Organometallics 2004, 23, 2670-2679.
(65) Guilera, G.; McGrady, G. S.; Steed, J. W.; Jones, A. L. Organome-
tallics 2006, 25, 122.
4400 Inorganic Chemistry, Vol. 46, No. 11, 2007

Polyhydride Anions
THF
The salts [HP4-tBu][BPh4] and [HP2-tBu][BPh4] have been
prepared from the reaction of [HNEt3][BPh4] with the
respective neutral phosphazene base. A new route was
developed to P4-tBu by the treatment of the commercially
available [HP4-tBu][BF4] salt with KH in the presence of a
catalytic amount of 2,2,2-crypt. The pKRTHF value of ([HP4-
tBu]+) ) 40 ( 4 was determined from the equilibrium
established from the reaction of ReH7(PCy3)2 or WH6(PMe2-
Ph)3 with P4-tBu. The equilibrium established from [K(18-
crown-6)][WH5(PMe2Ph)3] and [HP4-tBu][BPh4] confirmed
the value. The pKRTHF value of ([HP2-tBu]+) ) 30 ( 4 was
determined from the equilibrium established from the reac-
tion of [HP2-tBu][BPh4] with [K(2,2,2-crypt)][PO(OEt)2NPh]
or [K(18-crown-6)][{ReH2(PMePh2)2}2(µ-H)3]. Certain mix-
diaminocyclohexane.68 The high value of pKR
tBu]+/P4-tBu) ) 40 explains this reactivity.
([HP4-
Two important generalizations resulting from this work
+
are that the cationic polyhydrides MHxL4 , at least for Re,
THF
Fe, Ru, Os, Co, Rh, Ni, Pd, and Pt, have pKR
values in
the range of 12-23 on going from phenyl-substituted to
alkyl-substituted phosphine ligands L, whereas neutral poly-
hydrides MHxLn, at least for M ) W, Re, Ru, Os, and Ir,
with n ) 3 or 2, have pKRTHF values in the range of 30-44.
The neutral complex WH4(PMePh2)4 with n ) 4 is less
acidic.
Acknowledgment. NSERC is thanked for a discovery
grant to R.H.M.
Supporting Information Available: Correlations between the
mole faction of P2-tBu base and protonated P2-tBu and their
averaged NMR properties and the crystallographic CIF file for
[K(2,2,2-crypt)][ReH4(PMePh2)3]. This material is available free
of charge via the Internet at http://pubs.acs.org.
tures did not produce the reactions expected on the basis of
THF
the pKR
values. This may be due to ion-pair phenomena
that have not been accounted for.
The pKRTHF determinations of [HP4-tBu]+ and [HP2-tBu]+
THF
allow for improved correlations between the pKR
(HB+)
IC062037B
and pKaDMSO (HB+) and pKaMeCN(HB+) scales. The correla-
THF
tions allow for estimates of pKR
values for the many
(66) Sandoval, C. A.; Ohkuma, T.; Mun˜iz, K.; Noyori, R. J. Am. Chem.
Soc. 2003, 125, 13490.
(67) Abdur-Rashid, K.; Faatz, M.; Lough, A. J.; Morris, R. H. J. Am. Chem.
Soc. 2001, 123, 7473.
(68) Abbel, R.; Abdur-Rashid, K.; Faatz, M.; Hadzovic, A.; Lough, A. J.;
Morris, R. H. J. Am. Chem. Soc. 2005, 127, 1870.
cationic and neutral acids measured in DMSO and MeCN
and allow for the prediction of many new acid-base
reactions.
The P4-tBu base has been used in place of KOtBu to
dehydrochlorinate complexes such as RuCl2((S)-binap)((S,S)-
dpen), binap ) 2,2′-bis(diphenylphosphino)-1,1′-binaphthyl,
dpen ) 1,2-diphenylethylenediamine,66 RuHCl((R)-binap)-
((R,R)-dpen),67 and RuHCl(PPh3)2((R,R)-dach), dach ) 1,2-
(69) Raebiger, J. W.; DuBois, D. L. Organometallics 2005, 24, 110.
THF
(70) IrH(PMe3)4 reacts with CH2(CN)2 (pKR
) 24) and precipitates,
see: Behr, A.; Herdtweck, E.; Herrmann, W. A.; Keim, W.; Kipshagen,
W. Organometallics 1987, 6, 2307.
(71) Raebiger, J. W.; Miedaner, A.; Curtis, C. J.; Miller, S. M.; Anderson,
O. P.; DuBois, D. L. J. Am. Chem. Soc. 2004, 126, 5502-5514.
Inorganic Chemistry, Vol. 46, No. 11, 2007 4401