Synthesis, characterization, and acidity of ruthenium dihydrogen complexes with 1,4,7-triazacyclononane, 1,4,7-trimethyl-1,4,7-triazacyclononane, and hydrotris (pyrazolyl)borato ligands

Article abstract of DOI:10.1021/om9710374

Protonation of [^RCnRuH(L)(L′)]⁺ (^RCn = 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-triazacyclononane; L,L′ = (PPh₃)₂, dppe, and CO,PPh₃) produced the corresponding dicationic dihydrog

Full text of DOI:10.1021/om9710374

2052
Organometallics 1998, 17, 2052-2059
Syn th esis, Ch a r a cter iza tion , a n d Acid ity of Ru th en iu m
Dih yd r ogen Com p lexes w ith 1,4,7-Tr ia za cyclon on a n e,
1,4,7-Tr im eth yl-1,4,7-tr ia za cyclon on a n e, a n d
Hyd r otr is(p yr a zolyl)bor a to Liga n d s
Siu Man Ng, Yi Qun Fang, and Chak Po Lau*
Department of Applied Biology & Chemical Technology, The Hong Kong Polytechnic
University, Hung Hom, Kowloon, Hong Kong, China
Wing Tak Wong
Department of Chemistry, The University of Hong Kong, Pokfulam Road, Hong Kong, China
Guochen J ia*
Department of Chemistry, The Hong Kong University of Science and Technology,
Clear Water Bay, Kowloon, Hong Kong, China
Received November 24, 1997
Protonation of [RCnRuH(L)(L′)]+ (RCn ) 1,4,7-triazacyclononane and 1,4,7-trimethyl-1,4,7-
triazacyclononane; L,L′ ) (PPh3)2, dppe, and CO,PPh3) produced the corresponding dicationic
dihydrogen complexes [RCnRu(H2)(L)(L′)]2+. Protonation of TpRuH(dppe) (Tp ) hydrotris-
(pyrazolyl)borato) yielded the new monocationic dihydrogen complex [TpRu(H2)(dppe)]+. The
acidity of the dihydrogen complexes [RCnRu(H2)(L)(L′)]2+ and monocationic dihydrogen
complexes [TpRu(H2)(L)(L′)]+ (L,L′ ) dppe, (PPh3)2, CH3CN,PPh3, and CO,PPh3) has been
studied. It was found that the dicationic complexes are more acidic than their monocationic
Tp and Cp counterparts. [MeCnRu(H2)(CO)(PPh3)]2+ was found to be more acidic than
[HCnRu(H2)(CO)(PPh3)]2+, probably due to the stronger H-H interaction in the latter complex.
It is also noted that triazacyclononane and hydrotris(pyrazolyl)borato dihydrogen complexes
with pseudo aqueous pKa values well above that of H3O+ can be deprotonated by H2O to
form the corresponding monohydride complexes in organic/aqueous mixed solvents. It is
believed that deprotonation of the dihydrogen ligands in these complexes is assisted by strong
solvation of H+ by H2O.
In tr od u ction
During the past few years, there have been numerous
efforts in defining the factors affecting the acidity of
dihydrogen complexes, especially dihydrogen complexes
of the types [Cp′Ru(H2)(PP)]+ (Cp′ ) Cp, Cp*; PP )
diphosphines),5,6 [MH(H2)(PP)2]+ (M ) Fe, Ru, Os; PP
) diphosphines),7,8 [MCl(H2)(PP)2]+ (M ) Fe, Ru, Os;
PP ) diphosphines),8,9 and [M(L)(H2)(PP)2]2+ (M ) Fe,
Ru, Os; PP ) diphosphines; L ) CO, CH3CN).8,10
Deprotonation of dihydrogen ligands with various bases
Knowledge about the acidity of dihydrogen complexes
may help to understand mechanisms of stoichiometric
and/or catalytic reactions involving heterolytic cleavage
of dihydrogen bond1 and to design new catalytic proc-
esses. The most interesting examples involving hetero-
lytic cleavage of dihydrogen reported recently include
intramolecular protonation of alkyl ligands by dihydro-
gen ligands in the hydrogenation reactions,2 intramo-
lecular protonation of vinylidene ligands by dihydrogen
ligands to form carbyne complexes,3 and transition
metal catalyzed H/D exchange reactions.4
(5) (a) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc. 1990, 112,
5166. (b) Chinn, M. S.; Heinekey, D. M. J . Am. Chem. Soc. 1987, 109,
5865.
(6) (a) J ia, G.; Lough, A. J .; Morris, R. H. Organometallics 1992,
11, 161. (b) J ia, G.; Morris, R. H. J . Am. Chem. Soc. 1991, 113, 875.
(c) J ia, G.; Morris, R. H.; Schweitzer, C. T. Inorg. Chem. 1991, 30, 593.
(d) J ia, G.; Morris, R. H. Inorg. Chem. 1990, 29, 581.
(7) Cappellani, E. P.; Drouin, S. D.; J ia, G.; Maltby, P. A. Morris,
R. H.; Schweitzer, C. T. J . Am. Chem. Soc. 1994, 116, 3375.
(8) Rocchini, E.; Mezzetti, A.; Ru¨egger, H.; Burckhardt, U.; Gram-
lich, V.; Del Zotto, A.; Martinuzzi, P.; Rigo, P. Inorg. Chem. 1997, 36,
711.
(9) (a) Maltby, P. A.; Schlaf, M.; Steinbeck, M.; Lough, A. J .; Morris,
R. H.; Klooster, W. T.; Koetzle, T. F.; Srivastava, R. C. J . Am. Chem.
Soc. 1996, 118, 5396. (b) Chin, B.; Lough, A. J .; Morris, R. H.;
Schweitzer, C. T.; D’Agostino, C. Inorg. Chem. 1994, 33, 6278.
(10) Schlaf, M.; Lough, A. J .; Maltby, P. A.; Morris, R. H. Organo-
metallics 1996, 15, 2270.
(1) (a) Crabtree, R. H. Angew. Chem., Int. Ed. Engl. 1993, 32, 789.
(b) Heinekey, D. M.; Oldham, W. J ., J r. Chem. Rev. 1993, 93, 913. (c)
J essop, P. G.; Morris, R. H. Coord. Chem. Rev. 1992, 121, 155.
(2) Bianchini, C.; Meli, A.; Peruzzini, M.; Frediani, P.; Bohanna, C.;
Esterrelas, M. A.; Oro, L. A. Organometallics 1992, 11, 138.
(3) Espuelas, J .; Esteruelas, M. A.; Lahoz, F. J .; Oro, L. A.; Ruiz, N.
J . Am. Chem. Soc. 1993, 115, 4683.
(4) See for examples: (a) Albeniz, A. C.; Heinekey, D. M.; Crabtree,
R. H. Inorg. Chem. 1991, 30, 3632. (b) Lau, C. P.; Cheng, L. Inorg.
Chim. Acta 1992, 195, 133. (c) Lau, C. P.; Cheng, L. J . Mol. Catal.
1993, 84, 39. (d) Kubas, G. J .; Burns, C. J .; Khalsa, G. R. K.; Van Der
Sluys, L. S.; Kiss, G.; Hoff, C. D. Organometallics 1992, 11, 3390. (e)
J essop, P. G.; Morris, R. H. Inorg. Chem. 1993, 32, 2236.
S0276-7333(97)01037-6 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/17/1998

Ruthenium Dihydrogen Complexes
Organometallics, Vol. 17, No. 10, 1998 2053
have been reported for other complexes,11 for example,
[IrH(H2)(bq)(PPh3)2]+ (bq ) 7,8-benzoquinolinate) by
BuLi, [Os(H2)(NH3)5]2+ by NaOMe, and [Os(H2)(CO)-
(bpy)(PPh3)2]2+ by Et2O. These studies show that
acidity of dihydrogen complexes can vary widely de-
pending on ligands and metals.
reported,14a,b,i and the isostructural complexes
[RCnRu(H2)(L)(L′)]2+ are virtually unknown. While pKa
values of complexes of the type [(C5R5)Ru(H2)(L)(L′)]+
have been reported,5,6 that of the isostructural Tp and
RCn complexes have not been well studied. We report
here the synthesis and properties of some ruthenium
complexes supported by 1,4,7-triazacyclononane and
1,4,7-trimethyl-1,4,7-triazacyclononane ligands and the
acidity of [RCnRu(H2)(L)(L′)]2+ and [TpRu(H2)(L)(L′)]+.
Cyclopentadienyls,12 hydrotris(pyrazolyl)borates,13,14
and 1,4,7-triazacyclononane derivatives (RCn)15,16 are
very useful ligands in organometallic chemistry and
homogeneous catalysis. The three ligands are similar
in that they all coordinate to metals in a facial geometry
and are formally 6e donors on ionic model. They are
different in their π-accepting ability, with cyclopenta-
dienyls being the strongest and 1,4,7-triazacyclononane
derivatives the weakest. It is therefore expected that
the three ligands should show differences in stabilizing
dihydrogen ligands and in affecting the acidity of the
resulting dihydrogen and hydride complexes. However,
such comparison has not been made yet. Despite that
numerous complexes of the formula [(C5R5)RuH2(L)-
(L′)]+ (L,L′ ) neutral ligands such as monophosphines,
diphosphines, CO, solvent molecules) are known,5,6,17
only a few [TpRu(H2)(L)(L′)]+ complexes have been
Resu lts a n d Discu ssion
Syn th esis a n d Ch a r a cter iza tion of [RCn (H2)(L)-
(L′)]2+ Com plexes. The dihydrogen complexes [RCnRu-
(H2)(L)(L′)]2+ (5-8) were synthesized by protonation of
the corresponding monohydride complexes 1-4 with
HBF4‚Et2O or CF3SO3H (eq 1).
(11) See for example: (a) Lough, A. J .; Park, S.; Ramchandran, R.;
Morris, R. H. J . Am. Chem. Soc. 1994, 116, 8356. (b) Schlaf, M.; Lough,
A. J .; Morris, R. H. Organometallics 1993, 12, 3808. (c) Crabtree, R.
H.; Lavin, M. J . Chem. Soc., Chem. Commun. 1985, 794. (d) Crabtree,
R. H.; Lavin, M.; Bonneviot, L. J . Am. Chem. Soc. 1986, 108, 4032. (e)
Baker, M. V.; Field, L. D.; Young, D. J . J . Chem. Soc., Chem. Commun.
1988, 546. (f) Van Der Sluys, L. S.; Miller, M. M.; Kubas, G. J .; Caulton,
K. G. J . Am. Chem. Soc. 1991, 113, 2513. (g) Bicnchini, C.; Perez, P.
J .; Peruzzini, M.; Zanobini, F.; Vacca, A. Inorg. Chem. 1991, 30, 279.
(h) Sellman, D.; Ka¨ppler, J .; Moll, M. J . Am. Chem. Soc. 1993, 115,
1830. (i) Mudalige, D. C.; Rettig, S. J .; J ames, B. R.; Cullen, W. R. J .
Chem. Soc., Chem. Commun. 1993, 830. (j) Bianchini, C.; Linn, K.;
Masi, D.; Peruzzini, M.; Polo, A.; Vacca, A.; Zanobini, F. Inorg. Chem.
1993, 32, 2366. (k) Heinekey, D. M.; Luther, T. A. Inorg. Chem. 1996,
35, 4396. (l) Heinekey, D. M.; Voges, M. H.; Barnhart, D. M. J . Am.
Chem. Soc. 1996, 118, 10792.
The starting monohydride complexes [MeCnRuH(dppe)]-
CF3SO3 (3)16d and [MeCnRuH(CO)(PPh3)]PF6 (4)16d are
known compounds. The monohydride complex [HCnRuH-
(PPh3)2]BF4 (1) was prepared by reacting HCn with
RuHCl(PPh3)3 in the presence of NaBF4. We have
attempted to prepare the analogous complex [MeCnRuH-
(PPh3)2]BF4 by using MeCn in place of HCn. However,
the preparation was not successful and some intractable
materials were obtained. Failure of the reaction is
probably due to large steric interaction between tri-
phenylphosphine and the sterically more demanding
MeCn ligand. The complex [HCnRuH(CO)(PPh3)]BF4 (2)
was prepared by refluxing a mixture of HCn and RuHCl-
(CO)(PPh3)3 in 2-methoxyethanol, followed by precipita-
tion with NaBF4. A similar procedure has been used
previously for the preparation of [MeCnRuH(CO)(PPh3)]-
PF6 (4).16d
The new monohydride complexes can be readily
characterized by their NMR, IR, and elemental analysis.
The structure of complex 1 has also been confirmed by
X-ray diffraction. The molecular structure of the cation
[HCnRuH(PPh3)2]+ is shown in Figure 1. Crystal-
lographic details and selected bond distances and angles
are given in Tables 1 and 2, respectively.
(12) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 2nd ed.; J ohn Wiley & Sons: New York, 1994.
(13) Reviews on Tp complexes: (a) Trofimenko, S. Chem. Rev. 1993,
93, 943. (b) Trofimenko, S. Prog. Inorg. Chem. 1986, 34, 115. (c)
Trofimenko, S. Chem. Rev. 1972, 72, 497. (d) Trofimenko, S. Acc. Chem.
Res. 1971, 4, 17.
(14) For recent work on tris(pyrazolyl)borato dihydrogen complexes,
see for example: (a) Chen, Y. Z.; Chan, W. C.; Lau, C. P.; Chu, H. S.;
Lee, H. L.; J ia, G. Organometallics 1997, 16, 1241. (b) Chan, W. C.;
Lau, C. P.; Chen, Y. Z.; Fang, Y. Q.; Ng, S. M.; J ia, G. Organometallics
1997, 16, 34. (c) Bohanna, C.; Esteruelas, M. A.; Go´mez, A. V.; Lo´pez,
A. M.; Mart´ınez, M.-P. Organometallics 1997, 16, 4464. (d) Eckert, J .;
Albinati, A.; Bucher, U. E.; Venanzi, L. M. Inorg. Chem. 1996, 35, 1292.
(e) Vicente, C.; Shul’pin, G. G.; Moreno, B.; Sabo-Etienne, S.; Chaudret,
B. J . Mol. Catal. A: Chem. 1995, 98, L5. (f) Moreno, B.; Sabo-Etienne,
S.; Chaudret, B.; Rodriguez, A.; J alon, F.; Trofimenko, S. J . Am. Chem.
Soc. 1995, 117, 7441. (g) Moreno, B.; Sabo-Etienne, S.; Chaudret, B.
J . Am. Chem. Soc. 1994, 116, 2635. (h) Heinekey, D. M.; Oldham, W.
J ., J r. J . Am. Chem. Soc. 1994, 116, 3137. (i) Halcrow, M. A.; Chaudret,
B.; Trofimenko, S. J . Chem. Soc., Chem. Commun. 1993, 465. (j)
Bucher, U. E.; Lengweiler, T.; Nanz, D.; von Philipsborn, W.; Vernanzi,
L. M. Angew. Chem., Int. Ed. Engl. 1990, 29, 548.
(15) Flood’s notation is adopted with slight modification: HCn )
1,4,7-triazacyclononane; MeCn ) 1,4,7-trimethyl-1,4,7-triazacyclononane.
(16) For recent work on RCn complexes, see for example: (a) Yang,
S. M.; Chen, M. C. W.; Cheung, K. K.; Che, C. M.; Peng, S. M.
Organometallics 1997, 16, 2819. (b) Wang, L.; Sowa, J . R., J r.; Wang,
C.; Lu, R. S.; Gassman, P. G.; Flood, T. C. Organometallics 1996, 15,
4240. (c) Wang, L.; Wang, C.; Bau, R.; Flood, T. C. Organometallics
1996, 15, 491. (d) Yang, S. M.; Cheng, W. C.; Peng, S. M.; Cheung, K.
K.; Che, C. M. J . Chem. Soc., Dalton Trans. 1995, 2955. (e) Yang, S.
M.; Cheng, W. C.; Cheung, K. K.; Che, C. M.; Peng, S. M. J . Chem.
Soc., Dalton Trans. 1995, 227. (f) Wang, C.; Ziler, J . W.; Flood, T. C.
J . Am. Chem. Soc. 1995, 117, 1647. (g) Cheng, W. C.; Yu, W. Y.;
Cheung, K. K.; Che, C. M. J . Chem. Soc., Dalton Trans. 1994, 57. (h)
Cheng, W. C.; Yu, W. Y.; Cheung, K. K.; Che, C. M. J . Chem. Soc.,
Chem. Commun. 1994, 1063. (i) Wang, L.; Lu, R. S.; Bau, R.; Flood, T.
C. J . Am. Chem. Soc. 1993, 115, 6999. (j) Wang, C.; Flood, T. C. J .
Am. Chem. Soc. 1992, 114, 3169. (k) Sun, N. Y.; Simpson, S. J . J .
Organomet. Chem. 1992, 434, 341.
The structure could be described as a distorted
octahedron with the hydride trans to N(2). The distor-
tion can be attributed to the coordination geometry of
(17) (a) de los R´ıos, I.; Tenorio, M. J .; Padilla, J .; Puerta, M. C.;
Valerga, P. Organometallics 1996, 15, 4565. (b) Lemke, F. R.; Bram-
mer, L. Organometallics 1995, 14, 3980. (c) Conroy-Lewis, F. M.;
Simpson, S. J . J . Chem. Soc., Chem. Commun. 1986, 506. (d) Conroy-
Lewis, F. M.; Simpson, S. J . J . Chem. Soc., Chem. Commun. 1987,
1675. (e) Wilczewski, T. J . Organomet. Chem. 1989, 361, 219. (f) Chinn,
M. S.; Heinekey, D. M.; Payne, N. G.; Sofield, C. D. Organometallics
1989, 8, 1824. (g) Klooster, W. T.; Koetzle, T. F.; J ia, G.; Fong, T. P.;
Morris, R. H.; Albinati, A. J . Am. Chem. Soc. 1994, 116, 7677.

2054 Organometallics, Vol. 17, No. 10, 1998
Ng et al.
plexes 5-8 (eq 1). The dihydrogen complex [HCnRu-
(H2)(PPh3)2](BF4)2 (5), isolated as yellow solid by addi-
tion of Et2O to a CH2Cl2 solution of [HCnRuH(PPh3)2]BF4
acidified with slightly excess HBF4‚Et2O, was contami-
nated by small amount of aquo complex [HCnRu(H2O)-
(PPh3)2](BF4)2. Apparently, the aquo complex was
formed by displacement of η2-H2 in 5 by adventitious
water in the solvents. Similar contamination problem
was encountered in the preparation of the dihydrogen
complex [MeCnRu(H2)(dppe)](CF3SO3)2 (7). But it will
be seen (vide infra) that, in the absence of acid, water
acts as a base to deprotonate the η2-H2 in 5 or 7. The
dihydrogen complexes 5 and 7 are stable in the solid
state at room temperature, but in solution, the η2-H2
ligand is displaced by strongly coordinating solvent such
as acetonitrile. The very acidic CO-containing dihydro-
gen complexes 6 and 8 are unstable with respect to loss
of H2, both in the solid state and in solution, at room
temperature. These complexes were prepared by acidi-
fication at -30 °C with excess HBF4‚Et2O and were
characterized in situ with NMR spectroscopy.
F igu r e 1. Molecular structure of the cation [HCnRuH-
(PPh3)2]+.
Ta ble 1. Cr ysta l Da ta a n d Refin em en t Deta ils for
[HCn Ru H(P P h 3)2]BF 4‚2CH2Cl2
The existence of the η2-H2 moieties in complexes 5-8
was confirmed by variable-temperature T1 measure-
ments and the observation of large 1J (HD) coupling
constants for the corresponding isotopomers which were
prepared by acidification of 1-4 with DBF4 or CF3SO3D.
In particular, the 1J (HD) coupling constants for the
isotopomers were observed in the range of 29.4-31.8
Hz, and T1(min) values, in the range of 12-24 ms at
formula
C44H47BCl4F4N3P2Ru
fw
1009.51
color and habit
red blcok
cryst dimens (mm)
0.22 × 0.23 × 0.29
cryst syst
space group
a, Å
orthorhombic
P212121 (No. 19)
10.598(1)
b, Å
20.046(1)
c, Å
21.973(1)
4668.1(4)
V, Å3
1
400 MHz. The changes in the J (HD) and T1(min) are
Z
d
4
rather small especially in view of the fact that the
electronic properties of the ligands have been changed
drastically. It is also interesting to note that the 1J (HD)
for [HCnRu(HD)(CO)(PPh3)]2+ (31.8 Hz) is slightly large
than that of [MeCnRu(HD)(CO)(PPh3)]2+ (30.0 Hz), but
the T1(min) for [HCnRu(H2)(CO)(PPh3)]2+ (14 ms) is
slightly longer than that of [MeCnRu(H2)(CO)(PPh3)]2+
(12 ms). The shorter T1(min) for [MeCnRu(H2)(CO)-
(PPh3)]2+ is undoubtedly caused by the extra relaxation
due to the methyl groups.19
calcd, g cm-3
1.436
F(000)
2060.00
radiation
Mo KR (λ ) 0.710 73 Å)
µ(Mo KR), cm-1
T, °C
6.83
25.0
diffractometer
2θmax, deg
Marresearch image plate scanner
3.0-50.0
ω
5
28 766
4741
3178 (F > 3.0σ(F))
interimage scaling
scan type
exposure (min)
no. of reflns collcd
no. of unique reflns
no. of obsd reflns
abs corr
Complexes 5-8 provide additional examples of di-
cationic dihydrogen complexes. In contrast to the
abundance of isolable monocationic dihydrogen com-
plexes, well characterized dicationic dihydrogen com-
plexes are still very limited in numbers. Reported
dicationic dihydrogen complexes were mainly those of
no. of params refined
final R indices (obsd data), %
goodness of fit
data-to-param ratio
largest diff peak, e Å-3
largest diff hole, e Å-3
328
R ) 7.2, Rw ) 9.9
3.41
9.69
0.63
-0.52
the osmium complexes such as [Os(H2)(NH3)5]2+ 20a
[Os(H2)(en)2(L)]2+ 20b trans-[Os(H2)(dppe)2(CH3CN)]2+ 10
[Os(H2)(CO)(bpy)(PPh3)2]2+ (bpy ) 2,2′-dipyridyl),11k
[Os(H2)(CO)(bpy)2]2+ 11k and [Os(H2)(CO)(dppp)2]2+.8 Di-
,
the HCn ligand. The N-Ru-N angles and Ru-N bond
distances in complex 1 are very similar to those ob-
,
,
served for related complexes such as
(PMe3)(P(OMe)3(CtCPh)]PF6,16a MeCnRu(PMe3)(η3-PhC3-
CHPh)]PF6,16a MeCnRuH(η4-COD)]PF6,16e
and
MeCnRu(η5-C8H11)]PF6.16e The bond Ru-N(2) (2.30(1)
[
MeCnR-
,
[
cationic dihydrogen complexes of other metals are
[
limited to trans-[Fe(H2)(L)(dppe)2]2+ (L ) CO, CNH)21
[
and [Ru(H2)(CO)(dppp)2]2+ 8
.
Å) is slightly longer than Ru-N(1) (2.20(1) Å) and Ru-
N(3) (2.19(1) Å), presumably due to the trans influence
of the hydride ligand. The P(1)-Ru-P(2) angle (96.4°)
is smaller than that observed for CpRuH(PPh3)2
(101.4°)18a and comparable to that observed for CpRuH-
(PMe3)2.18b,c
Syn t h esis a n d Ch a r a ct er iza t ion of [Tp R u (H2)-
(L)(L′)]+ Com plexes. The dihydrogen complexes [TpRu-
(H2)(PPh3)2]BF4 (14) and [TpRu(H2)(CH3CN)(PPh3)]BF4
(15) were recently synthesized by us from protonation
reactions of the corresponding monohydride complexes
with HBF4‚Et2O.14b With similar strategy, the new
Protonation of the monohydride complexes 1-4 with
HBF4‚Et2O or CF3SO3H produced the dihydrogen com-
(19) Desrosiers, P. J .; Cai, L.; Lin, Z.; Richards, R.; Halpern, J . J .
Am. Chem. Soc. 1991, 113, 4173.
(18) (a) Smith, K. T.; Rømming, C.; Tilset, M. J . Am. Chem. Soc.
1993, 115, 8681. (b) Lemke, F. R.; Brammer, L. Organometallics 1995,
14, 3980. (c) Brammer, L.; Klooster, W. T.; Lemke, F. R. Organo-
metallics 1996, 15, 1721.
(20) (a) Harman, W. D.; Taube, H. J . Am. Chem. Soc. 1990, 112,
2261. (b) Li, Z. W.; Taube, H. J . Am. Chem. Soc. 1991, 113, 8946.
(21) Forde, C. E.; Landau, S. E.; Morris, R. H. J . Chem. Soc., Dalton
Trans. 1997, 1663.

Ruthenium Dihydrogen Complexes
Organometallics, Vol. 17, No. 10, 1998 2055
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles (d eg) for [HCn Ru H(P P h 3)2]BF 4‚2CH2Cl2
Interatomic Distance
Ru-P(1)
Ru-N(2)
2.286(4)
2.30(1)
Ru-P(2)
Ru-N(3)
2.270(4)
2.19(1)
Ru-N(1)
Ru-H
2.20(1)
1.8(2)
Intramolecular Angles
P(1)-Ru-P(2)
P(1)-Ru-N(3)
P(2)-Ru-N(2)
N(1)-Ru-N(2)
N(2)-Ru-N(3)
96.4(1)
172.8(4)
110.8(4)
78.2(6)
P(1)-Ru-N(1)
93.8(4)
95(5)
90.6(3)
79.0(5)
154(6)
P(1)-Ru-N(2)
P(2)-Ru-N(1)
P(2)-Ru-H
N(1)-Ru-H
N(3)-Ru-H
102.2(4)
164.5(4)
85(6)
82(6)
83(6)
P(1)-Ru-H
P(2)-Ru-N(3)
N(1)-Ru-N(3)
N(2)-Ru-H
76.9(5)
dihydrogen complexes [TpRu(H2)(dppe)]BF4 (13) and
[TpRu(H2)(CO)(PPh3)]BF4 (16) were prepared (eq 2).
Acid ity of th e Dih yd r ogen Com p lexes. We have
attempted to rank the relative acidity of the dihydrogen
complexes. A useful approach to do so is to measure
the pseudo aqueous pKa values.6-10 In this approach,
equilibrium constants for the reactions of LnMH (pre-
cursors to dihydrogen complexes) and an acid with
known aqueous pKa value are determined in nonaque-
ous solutions. The pseudo aqueous pKa of the dihydro-
gen complexes are then calculated in reference to the
aqueous pKa of the acid. The pseudo aqueous pKa
values of 5, 7, 13, 14, and 15 were estimated by studying
1
the equilibrium shown in eq 3 with H NMR in CD2Cl2,
using the hydride complexes RuHCl(dppe)2, CpRuH-
(PPh3)2, and CpRuH(dppm) as the bases. The pseudo
aqueous pKa values of [RuCl(H2)(dppe)2]+,9b [CpRuH2-
(PPh3)2]+,6b and [CpRu(H2)(dppm)]+ 6b have been deter-
mined previously in CD2Cl2 using a similar method. The
equilibrium mixture could be conveniently obtained by
protonation
Like 5 and 7, the isolated 13 was contaminated by a
small amount of aquo complex [TpRu(H2O)(dppe)]BF4.
It should be mentioned that the CO-containing dihy-
drogen complex 16 is unstable with respect to loss of
H2 at room temperature; therefore, the acidification had
to be carried out at -30 °C and 16 was not isolated but
was studied in situ.
[LnRu(H2)]n+ + L′nMH S [LnRuH](n-1)+ + L′nMH2
+
(3)
with a limited amount of HBF4‚Et2O of a mixture of
[LnRuH](n-1)+ and L′nMH. All the equilibria were
obtained at room temperature, except in the case of
[TpRu(H2)(CH3CN)(PPh3)]+, which was carried out at
-30 °C. The relative concentrations of the dihydrogen
complexes and the metal hydrides in equilibrium were
estimated from integrations of the upfield hydride
signals in the 1H NMR spectra, and therefore, the
equilibrium constants can be estimated on the basis of
the known pKa values of L′nMH2+. The pseudo aqueous
pKa value of the Tp carbonyl dihydrogen complex [TpRu-
(H2)(CO)(PPh3)]BF4 (16) was determined in a similar
manner at -80 °C, using [HCnRu(H)(CO)(PPh3)]BF4 (2)
as the base.
The existence of the η2-H2 moiety in [TpRu(H2)(dppe)]-
BF4 (13) was confirmed by observation of a T1(min)
value of 14 ms for 13 and a large 1J (HD) coupling
constant of 32.5 Hz for the corresponding isotopomer
[TpRu(HD)(dppe)]BF4, which was prepared by acidifica-
tion of 9 with DBF4. Similarly, the existence of the η2-
H2 moiety in 16 is evidenced by short T1(min) of this
1
complex and large J (HD) coupling constant (33.3 Hz)
of the corresponding isotopomer [TpRu(HD)(CO)(PPh3)]-
BF4.
Com p a r ison of th e Abilities of Cp-, Tp -, a n d RCn
in Sta bilizin g Dih yd r ogen Com p lexes. Although
R
Cp-, Tp-, and Cn are isoelectronic and all adopt facial
The pKa values of the RCn carbonyl dihydrogen
complexes 6 and 8 could not be estimated by use of eq
geometry, their abilities to stabilize dihydrogen ligands
are different. For example, while [CpRuH2(PPh3)2]+ is
a classical dihydride complex, both [TpRu(H2)(PPh3)2]+
and [HCnRu(H2)(PPh3)2]2+ are molecular dihydrogen
complexes. Subtle differences in the Tp and RCn
complexes are also noted. Although the RCn dihydrogen
complexes 5-8 are dicationic and the Tp dihydrogen
complexes 13-16 are monocationic,1J (HD) couplings of
the isotopomers of the RCn complexes are consistently
smaller than those of the Tp counterparts. This is
probably the result of RCn being better σ-donors than
Tp and the latter being able to act as π-accepting ligand.
+
3 because they are much more acidic than the L′nMH2
complexes. The pKa values of 6 and 8 were estimated
by studying the protonation reactions of 2 and 4 with
HBF4‚Et2O (eq 4) using 1H NMR at -80 °C. The
[RCnRuH(CO)(PPh3)]PF6 + HBF4‚Et2O S
[RCnRu(H2)(CO)(PPh3)](PF6)(BF4) + Et2O (4)
relative molar concentrations of HBF4‚Et2O, Et2O, the
ruthenium carbonyl hydrides and the carbonyl dihy-
drogen complexes were estimated on the basis of the
1H NMR integrations. The pKa values of 6 and 8 were
estimated to be -1.3 and -2.6, respectively, taking the
pKa of HBF4‚Et2O as -2.4.22 Details on the acidity
measurements are summarized in Table 3.
1
In consonance with the trends in J (HD) couplings, we
have observed that the η2-H2 ligands in the Tp com-
plexes 13-16 are much more readily displaced by water
in the absence of H2 pressure than those in 5-8.
Reactions of these complexes with water warrant fur-
ther discussion later.
(22) Perdoncin, G.; Seorrano, G. J . Am. Chem. Soc. 1977, 99, 6983.

2056 Organometallics, Vol. 17, No. 10, 1998
Ta ble 3. Acid ity Mea su r em en ts of Dih yd r ogen Com p lexes in CD2Cl2
Ng et al.
a
M(H2)
B
Keq
pKa(M(H2))
[HCnRu(H2)(PPh3)2](BF4)2 (5)
RuHCl(dppe)2
Et2O
RuHCl(dppe)2
Et2O
CpRuH(dppm)
CpRuH(dppm)
CpRuH(PPh3)2
[HCnRuH(CO)(PPh3)]+
31.6
4.5
-1.3
3.8
-2.6
7.6
7.9
8.9
-0.6
[HCnRu(H2)(CO)(PPh3)](BF4)2 (6)
0.07b
[
[
MeCnRu(H2)(dppe)2](CF3SO3)2 (7)
166
MeCnRu(H2)(CO)(PPh3)](PF6)(CF3SO3) (8)
1.56b
[TpRu(H2)(PPh3)2]BF4 (13)
[TpRu(H2)(dppe)]BF4 (14)
[TpRu(H2)(CH3CN)(PPh3)]BF4 (15)
[TpRu(H2)(CO)(PPh3)]BF4 (16)
0.303
0.179
0.277c
0.498b
a
pKa values (on the pseudo aqueous scale) of the dihydrogen complexes are estimated by means of the equation pKa(M(H2)) ) pKeq
+
pKa(HB+); Keq is the equilibrium constant of eq 3 or the reciprocal of the equilibrium constant of eq 4. At -80 °C. c -30 °C.
b
Ta ble 4. Sp ectr oscop ic P r op er ties a n d Acid ities of Hyd r id e Com p lexes
c
complexes
T1(min), msa (temp)
1J (HD), Hz
d(HH), Åb
pKa
ref
[HCnRu(H2)(PPh3)2](BF4)2 (5)
20 (250 K)
14 (248 K)
24 (266 K)
12 (224 K)
14 (230 K)
21 (240 K)
16 (231 K)
12 (224 K)
29.4
31.8
29.4
31.0
32.5
32.0
33.0
33.3d
0.93
0.89
0.93
0.92
0.88
0.89
0.87
0.86
4.5
-1.3d
3.8
this work
this work
this work
this work
this work
this work
this work
this work
6b
[HCnRu(H2)(CO)(PPh3)](BF4)2 (6)
[
[
MeCnRu(H2)(dppe)](CF3SO3)2 (7)
MeCnRu(H2)(CO)(PPh3)(PF6)(CF3SO3) (8)
-2.6d
7.9
[TpRu(H2)(dppe)]BF4 (13)
[TpRu(H2)(PPh3)2]BF4 (14)
[TpRu(H2)(CH3CN)(PPh3]BF4 (15)
[TpRu(H2)(CO)(PPh3)]BF4 (16)
[CpRuH2(PPh3)2]+
7.6
8.9e
-0.6d
8.3
[CpRu(H2)(dppm)]+
21.9
20.9
24.9
1.05
1.07
1.00
7.1
6b
6b
6b
[Cp*Ru(H2)(dppm)]+
18 (220 K)
9.2f
7.0
[CpRu(H2)(dppe)]+
a
b
1
At 400 MHz. Calculated on the basis of J (HD) values as described in ref 9a. c pKa values were determined in CD2Cl2 but reported
on the pseudo aqueous scale. Determined at -80 °C. e Determined at -30 °C. f Determined in THF.
d
Com m en ts on th e Acid ity. It should be stressed
that the pseudo aqueous pKa values of complexes 5-8
and 13-16 are obtained on the basis of the assumption
that the differences in the pKa values of the dihydrogen
complexes and the reference acids are the same in water
and CD2Cl2. Since the assumption has not been con-
firmed yet, the pseudo aqueous pKa values of the
complexes may be different from the true aqueous pKa
values and should not be treated too seriously. How-
ever, the pseudo aqueous pKa values can still provide
valuable information in the trend of the acidity of the
complexes. For comparison, the pseudo aqueous pKa
values of the new dihydrogen complexes and related
[(η5-C5R5)RuH2(L)(L′)]+ complexes are listed in Table 4.
To see the effect of H-H bonding on the acidity, the
T1(min) and r(HH) for the dihydrogen complexes and
1J (HD) for the HD isotopomers are also listed if avail-
able. The hydrogen-hydrogen separations, r(HH), were
calculated according to an empirical equation (eq 5)9a
acidic than the analogous monocationic Tp complex
[TpRu(H2)(CO)(PPh3)]+ (pKa ) -0.6) but to a smaller
extent. Several highly acidic dicationic dihydrogen
complexes have been reported; for example, the di-
cationic dihydrogen complex trans-[Os(H2)(dppe)-
(CH3CN)]2+ has a pseudo aqueous pKa value close to
-2.10 The complex [Os(H2)(CO)(bpy)(PPh3)2]2+ can be
deprotonated by diethyl ether.11k The dicationic dihy-
drogen complexes [M(H2)(CO)(dppp)2]2+ (M ) Ru, Os)
were reported to have pKa values close to -6.8 It should
be mentioned that dicationic dihydrogen complexes are
not necessarily stronger acids than monocationic com-
plexes; for example, [Os(H2)(NH3)5]2+ was reported to
be a weak acid and is stable to moderately strong base
such as NaOMe. The high pKa value of this complex is
probably due to the strong electron-donating effect of
the NH3 ligands.20a
Within the HCn, MeCn, and the Tp dihydrogen complex
series, substitution of phosphine group for CO leads to
a 5-8 unit decrease in the pKa value. The observation
is very similar to that observed for [RuCl(H2)(L)(PMP)]+
(L ) CO, PPh3).24 The same trend has also been
observed for classical hydride complexes. For example,
MnH(CO)5 has a pKa(CH3CN) of 15.125 vs 20.4 for MnH-
(CO)(PPh3),26 CpCrH(CO)3 has a pKa(CH3CN) of 13.327
vs 21.8 for CpCrH(CO)2(PPh3),28 and HCo(CO)4 has a
pKa of 8.325 vs 15.4 for HCo(CO)3(PPh3).25 These
observations may indicate that the inductive effect of
the ligands is very important in determining the acidity
of the dihydrogen complexes.
r(HH) ) 1.42 - 0.0167J (HD)
(5)
that shows a linear relationship between J (HD) and
r(HH) in a wide variety of η2-H2 complexes whose J (HD)
values fall in the range 7-35 Hz. An essentially
identical linear relationship is also predicted by quan-
tum chemical calculation for complexes of the type
[Os(NH3)4L(H2)]2+ for a wide range of trans ligands L.23
It can be seen from Table 4 that isostructural and
monocationic Tp and Cp ruthenium dihydrogen com-
plexes have similar acidity. The dicationic RCn dihy-
drogen complexes 5 and 7 are significantly more acidic
than their Tp and Cp analogues (by 3-4 pKa units
difference). The carbonyl-containing RCn dihydrogen
complexes [MeCnRu(H2)(CO)(PPh3)]2+ (pKa ) -2.6) and
[HCnRu(H2)(CO)(PPh3)]2+ (pKa ) -1.3) are also more
(24) J ia, G.; Lee, H. M.; Williams, I. D.; Lau, C. P.; Chen, Y. Z.
Organometallics 1997, 16, 3941.
(25) Moore, E. J .; Sullivan, J . M.; Norton, J . R. J . Am. Chem. Soc.
1986, 108, 2257.
(26) Kristja´nsdo´ttir, S. S.; Moody, A. E.; Weberg, R. T.; Norton, J .
R. Organometallics 1988, 7, 1983.
(27) J ordan, R. F.; Norton, J . R. J . Am. Chem. Soc. 1982, 104, 1255.
(28) Parker, V. D.; Handoo, K. L.; Roness, F.; Tilset, M. J . Am. Chem.
Soc. 1991, 113, 7493.
(23) Hush, N. S. J . Am. Chem. Soc. 1997, 119, 1717.

Ruthenium Dihydrogen Complexes
Organometallics, Vol. 17, No. 10, 1998 2057
be suggested by the general trend in the acidity of
classic hydride complexes. Morris et al. has recently
proposed that the dramatic reduction of the pKa value
of trans-[RuCl(H2)(dppe)2]+ vs that of trans-[RuH(H2)-
(dppe)2]+ could be attributed to a lower H-H bond
strength in the former. The high acidity of the trihy-
dride complex [RuH3(dppf)2]+ (dppf ) 1,1′-bis(di-
phenylphosphino)ferrocene) compared to that of [RuH-
(H2)(dppe)2]+ is also in accord with this idea.9b
Rea ction s of Dih yd r ogen Com p lexes w ith Wa -
ter . We have recently discussed the roles of the
dihydrogen complexes [TpRu(H2)(PPh3)2]+ (14) and
[TpRu(H2)(CH3CN)(PPh3)]+ (15) in olefin hydrogenation
reactions.14b It was noted that their catalytic activities
are greatly enhanced when the reactions were per-
formed in THF/H2O mixed solvents instead of anhy-
drous THF. The enhancement effect is attributed to
deprotonation of η2-H2 by H2O to generate the active
metal hydride species. The deprotonation reaction with
water has been demonstrated with NMR study with
complex 14. It is somewhat surprising to find out in
the present study that the pseudo aqueous pKa values
of complexes 14 (7.6) and 15 (8.9) are significantly
higher than that of H3O+ (-1.74).31 As H2O is a very
weak base, it is not expected that H2O should be basic
enough to deprotonate the dihydrogen complexes.
F igu r e 2. 31P NMR spectra of [MeCnRuH(CO)(PPh3)]+ and
[HCnRuH(CO)(PPh3)]+ in CD2Cl2 at -35 °C (top) and
([MeCnRuH(CO)(PPh3)]+ and [HCnRuH(CO)(PPh3)]+) +
HBF4‚Et2O in CD2Cl2 at -80 °C (bottom).
To see if deprotonation by water would also occur on
other dihydrogen complexes with pseudo aqueous pKa
values significantly higher than that of H3O+, we have
tested the reactivities of complexes [TpRu(H2)(dppe)]+
(13, pKa ) 7.9), [HCnRu(H2)(PPh3)2]2+ (5, pKa ) 4.5),
and [MeCnRu(H2)(dppe)]2+ (7, pKa ) 3.8) toward water.
It is well established that the acidity of hydride
complexes are strongly influenced by the metals as well
as auxiliary ligands.29,30 With a few exceptions, the
acidity of isostructural classic hydride complexes de-
creases as ligands become more electron-donating and
as the metal is replaced successively by heavier metals
in the same group. The relative acidities of most of the
complexes studied in this work are consistent with the
trend. However, exception is observed for complexes 6
and 8. It might be expected that complex 8 should be
less acidic than complex 6 because MeCn is more
electron-donating than HCn, as reflected from the
1J (HD) coupling constants of the corresponding iso-
topomers of complexes 6 and 8. In fact, complex 8 was
found to be more acidic than complex 6 on the basis of
the equilibrium study as described before. The more
acidic nature of complex 8 compared to complex 6 is
further supported by the fact that the complex
[HCnRuH(CO)(PPh3)]+ is preferentially protonated when
a mixture of [HCnRuH(CO)(PPh3)]+ and [MeCnRuH(CO)-
(PPh3)]+ was treated with a limited amount of HBF4‚OEt2
(see Figure 2).
In the absence of H2 pressure, like complex 14, H2O
displaced the η2-H2 ligand in 13 to give [TpRu(H2O)-
(dppe)]+. The reaction took a different route under H2
pressure in CD2Cl2/H2O biphasic medium. When 50-
100 µL of H2O was added to a 0.4 mL CD2Cl2 solution
of 13 in a Wilmad pressure-valved NMR tube, phase
separation occurred. The 1H NMR spectrum of the
CD2Cl2 phase showed that some of the η2-H2 was
displaced by H2O via simple ligand substitution reac-
tion. But after the tube was pressurized with 15 atm
of H2, most of the dihydrogen complex was re-formed;
partial deprotonation of η2-H2 by H2O took place, as
evidenced by the appearance of the ruthenium hydride
1
signal in the H NMR spectrum.
The dihydrogen complexes 5 and 7 are more stable
with respect to loss of H2 at room temperature; thus,
deprotonation studies with H2O can be carried out in
the absence of H2 atmosphere in CD2Cl2. It was shown
that the dihydrogen complexes were deprotonated com-
pletely to form the monohydride complexes. The ob-
servation is probably not surprising, as complexes 5 and
7 are more acidic than their Tp analogues.
Deprotonation of η2-H2 in complexes 5, 7, 13, and 14,
which have pseudo aqueous pKa values above 3, in
biphasic conditions, is probably due to the strong
solvation of H+ by H2O. It is also likely that the
difference in the pKa values of the dihydrogen complexes
in aqueous solution may not be as large as the pseudo
aqueous pKa values may imply.
It is not apparent why the MeCn complex 8 is more
acidic than the HCn complex 6. It is possible that the
H-H bond strength in 6 and 8 may play some role in
determining the relative acidity. The more electron-
donating MeCn ligand in 8 renders the H-H interacton
weaker than that in complex 6 which contains the less
donating HCn ligand, and the weaker H-H interaction
may make a dihydrogen complex more acidic than may
(29) Kristja´ndo´ttir, S. S.; Norton, J . R. In Transition Metal Hydrides;
Dedieu, A., Ed.; VCH: Weinheim, FRG, 1992.
(30) (a) Angelici, R. J . Acc. Chem. Res. 1995, 28, 51. (b) Pearson, R.
G. Chem. Rev. 1985, 85, 41.
(31) Ritchie, C. D. Physical Organic Chemistry, The Fundamental
Concept, Marcel Dekker: New York, 1990; p 238.

2058 Organometallics, Vol. 17, No. 10, 1998
Ng et al.
borate (0.66 g, 6 mmol) was added, and the resulting mixture
was filtered to afford the crude product which was washed with
ethanol and diethyl ether. It was then extracted with 20 mL
of dichloromethane, and the solvent of the extract was removed
to yield a white solid. Yield: 0.44 g (27%). Anal. Calcd for
C25H31BN3OF4PRu: C, 49.36; H, 5.14; N, 6.91. Found: C,
49.10; H, 5.23; N, 6.78. IR (KBr, cm-1): ν(CO) 1920 (vs), ν(Ru-
H) 1997 (w). 1H NMR (400 MHz, CD2Cl2): δ -12.83 (d, 1H,
2J (HP) ) 28.8 Hz, Ru-H), 2.81 (s, 1H, N-H), 2.45-3.40 (m,
12H, NCH2), 3.90 (s, 1H, N-H), 5.12 (s, 1H, N-H), 7.34-7.58
(m, 15H of PPh3). 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 68.1
(s). FAB MS (m/z): 522, [M]+.
Tp R u H(d p p e) (12). A 1,4-dioxane solution (100 mL) of
TpRuH(PPh3)2 (0.50 g, 0.60 mmol) and dppe (0.30 g, 0.75
mmol) was stirred under nitrogen at 100 °C for 16 h. The
solution was cooled and concentrated to about 5 mL. Diethyl
ether (10 mL) was added to give a yellow solid, which was
filtered out. The solid was washed with diethyl ether and then
dried under vacuum. Yield: 0.35 g (82%). Anal. Calcd for
C35H35BN6P2Ru: C, 58.89; H, 4.94; N, 11.78. Found: C, 58.88;
H, 5.10; N, 11.54. IR (KBr, cm-1): ν(Ru-H) 1909 (w), ν(B-
H) 2470 (br). 1H NMR (400 MHz, CD2Cl2): δ -14.23 (t, 1H,
2J (HP) ) 28.0 Hz, Ru-H), 2.09-2.49 (m, 4H, CH2CH2), 5.34
[t, 1H, H(pz)], 5.58 (d, 1H, H(pz)], 5.90 [t, 2H, H(pz′)], 7.03 [d,
2H, H(pz′)], 7.47 [d, 1H, H(pz)], 7.61 [d, 2H, H(pz′)] (pz )
pyrazolyl group trans to hydride, pz′ ) pyrazolyl groups trans
to dppe; all coupling constants for pyrazolyl proton resonances
were about 2 Hz); 6.86, 6.98, 7.13, 7.35, 7.89 (m, 20 H of dppe
phenyl groups). 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 90.0
(s). FAB MS (m/z): 714, [M]+.
Con clu sion
We have synthesized and characterized the first
dihydrogen complexes supported by triazacyclononane
ligands. These complexes are also new members of the
still very small family of dicationic dihydrogen com-
plexes. Triazacyclononane ligands seem to have similar
properties as the hydrotris(pyrazolyl)borates in stabiliz-
ing dihydrogen ligands. The dicationic RCn dihydrogen
complexes are more, and in some cases significantly
more, acidic than their hydrotris(pyrazolyl)borato and
cyclopentadienyl analogues, which are monocationic.
Water can deprotonate RCn and Tp dihydrogen com-
plexes with pseudo aqueous pKa values significantly
larger than that of H3O+, probably due to strong
solvation of H+ by H2O.
Exp er im en ta l Section
All reactions were carried out under a dry N2 atmosphere
using Schlenk techniques. All solvents were distilled and
degassed prior to use. Dichloromethane and acetonitrile were
distilled from calcium hydride; tetrahydrofuran, diethyl ether,
and hexane were distilled from sodium benzophenone ketyl.
1,4,7-Triazacyclononane and 1,4,7-trimethyl-1,4,7-triaza-
cyclononane were prepared as reported.32 The complexes
RuHCl(CO)(PPh3)3,33 MeCnRuCl3,34 MeCnRuH(dppe)]CF3SO3,16d
[
[
MeCnRuH(CO)(PPh3)]PF6,16d TpRuH(PPh3)2,14b [TpRu-
(H2)(PPh3)2]BF4,14b TpRuH(CH3CN)(PPh3),14b [TpRu(H2)-
(CH3CN)(PPh3)]BF4,14b and TpRuH(CO)(PPh3)14a were synthe-
sized according to literature methods. HBF4‚Et2O was pur-
chased from Fluka and was used as received.
Dih yd r ogen Com p lexes a n d Th eir Isotop om er s. The
carbonyl dihydrogen complexes 6, 8, and 16 are unstable with
respect to loss of H2 at room temperature. It is also difficult
to obtain dihydrogen complexes 5, 7, and 13 in pure form
because they are usually contaminated by their corresponding
aquo complexes. The dihydrogen complexes were therefore
only characterized in situ.
Infrared spectra were obtained from a Nicolet Magna 750
FT IR spectrophotometer. 1H NMR spectra were taken on a
Bruker DPX 400 spectrometer. Chemical shifts were refer-
enced to the residue peaks of the deuterated solvents. 31P{1H}
NMR spectra were recorded on a Bruker DPX 400 spectrom-
eter at 161.70 MHz. 31P chemical shifts were externally
referenced to 85% H3PO4. T1 relaxation measurements were
carried out in CD2Cl2 at 400 MHz by the inversion-recovery
method using a standard 180-τ-90 pulse sequence. FAB MS
was carried out with a Finnigan MAT 95S mass spectrometer
using 3-nitrobenzyl alcohol as matrix. Elemental analyses
were performed by M-H-W Laboratories, Phoenix, AZ.
[HCn Ru H(P P h 3)2]BF 4 (1). A mixture of RuHCl(PPh3)3
(0.50 g, 0.54 mmol), 1,4,7-triazacyclononane (0.20 g, 1.55
mmol), and NaBF4 (0.10 g, 0.91 mmol) in 100 mL of THF was
stirred under nitrogen for 2 h. The mixture was filtered
through Celite, and the filtrate was concentrated to about 5
mL. Diethyl ether (10 mL) was added to precipitate out a
yellow solid which was filtered out. The solid was washed with
diethyl ether and vacuum-dried at room temperature. Yield:
0.36 g (79%). Anal. Calcd for C42H46BN3F4P2Ru: C, 59.86;
H, 5.50; N, 4.99. Found: C, 59.10; H, 5.73; N, 5.03. IR (KBr,
cm-1): ν(Ru-H) 1958 (w). 1H NMR (400 MHz, CD2Cl2): δ
The complexes [HCnRu(H2)(PPh3)2](BF4)2 (5), [MeCnRu(H2)-
(dppe)](CF3SO3)2 (7), and [TpRu(H2)(dppe)]BF4 (13) were
prepared as follows. In a typical experiment, a sample (10
mg) of a metal hydride was loaded into a 5 mm NMR tube,
which was then capped with a rubber septum. The tube was
evacuated and then filled with nitrogen for three cycles.
Dichloromethane-d2 (0.4 mL) was added to dissolve the sample,
followed by addition of 5 µL of HBF4‚Et2O or CF3SO3H. The
solution was immediately analyzed by NMR spectroscopy.
[HCn Ru (H2)(P P h 3)2](BF 4)2 (5). 1H NMR (400 MHz, CD2-
Cl2): δ -9.04 [br, 2H, Ru-(H2)], 2.35-4.29 (m, 2H, N-H and
12H NCH2), 5.84 (s, 1H, N-H), 7.26-7.44 (m, 30H of PPh3).
31P{1H} NMR (161.70 MHz, CD2Cl2): δ 39.5 (s). T1 (400 MHz,
CD2Cl2), ms (temperature): 22 (273 K), 21 (263 K), 20 (253
K), 20 (243 K), 21 (233 K), 23 (223 K), 27 (213 K), 34 (203 K).
A ln T1 vs 1000/T plot gave a T1(min) of 20 ms at 250 K.
[
MeCn Ru (H2)(d p p e)](CF 3SO3)2 (7). 1H NMR (400 MHz,
CD2Cl2): δ -9.79 [br, 2H, Ru-(H2)], 1.93 (m, 2H, NCH2), 2.56-
2.69 (m, 4H, PCH2), 2.79-2.81 (m, 6H, NCH2), 7.48-7.62 (m,
20H of PPh3). 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 7.4 (s).
T1 (400 MHz, CD2Cl2), ms (temperature): 29 (313 K), 27 (303
K), 26 (293 K), 25 (283 K), 25 (273 K), 24 (263 K), 25 (253 K),
26 (243 K), 28 (233 K), 31 (223 K), 37 (213 K), 47 (203 K). A ln
T1 vs 1000/T plot gave a T1(min) of 24 ms at 266 K.
[Tp Ru (H2)(d p p e)]BF 4 (13). 1H NMR (400 MHz, CD2Cl2):
δ -9.28 [br, 2H, Ru-(H2)], 2.82-2.96 (m, 4H, PCH2), 5.25 [t,
1H, H(pz)], 5.52 [d, 1H, H(pz)], 6.09 [t, 2H, H(pz′)], 6.82 [d,
2H, H(pz′)], 7.51 [d, 1H, H(pz)], 7.79 [d, 2H, H(pz′)] (pz )
pyrazolyl group trans to H2, pz′ ) pyrazolyl groups trans to
dppe; all coupling constants for pyrazolyl proton resonances
were about 2 Hz); 6.63, 7.06, 7.30, 7.53 (m, 20H of dppe phenyl
groups). 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 45.7 (s). T1
(400 MHz, CD2Cl2), ms (temperature): 22 (293 K), 20 (283 K),
18 (273 K), 17 (263 K), 15 (253 K), 14 (243 K), 14 (233 K), 13
2
-15.98 (t, 1H, J (HP) ) 38.3 Hz, Ru-H), 2.29-3.44 (m, 2H,
N-H and 12H, NCH2), 5.24 (s, 1H, N-H), 7.19-7.43 (m, 30
H of PPh3). 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 67.4 (s).
FAB MS (m/z): 756, [M - BF4]+; 494, [M - BF4 - PPh3]+.
[HCn Ru H(CO)(P P h 3)]BF 4 (2). A mixture of RuHCl(CO)-
(PPh3)3 (2.50 g, 2.69 mmol) and 1,4,7-triazacyclononane (0.50
g, 3.87 mmol) in 250 mL of 2-methoxyethanol was refluxed
under nitrogen for 18 h. The mixture was filtered, and the
filtrate was concentrated to about 40 mL. Sodium tetrafluoro-
(32) Wieghardt, K.; Chaudhuri, P.; Nuber, B.; Weiss, J . Inorg. Chem.
1982, 21, 3086.
(33) Ahmad, N.; Levison, J . J .; Robinson, S. D.; Uttley, M. F. Inorg.
Synth. 1974, 15, 48.
(34) Neubold, P.; Wieghardt, K.; Nuber, B.; Weiss, J . Inorg. Chem.
1989, 28, 459.

Ruthenium Dihydrogen Complexes
Organometallics, Vol. 17, No. 10, 1998 2059
(228 K), 15 (218 K), 16 (213 K). A T1 vs 1000/T plot gave a
T1(min) of 14 ms at 230 K.
Acid ity Mea su r em en t. pKa values of 5, 7, and 13-16
were estimated by studying the equilibrium shown in eq 3.
All measurements were carried out at room temperature
except that of 15 (-30 °C) and 16 (-80 °C). In a typical
experiment, appropriate amounts of [LnRuH](n-1)+ and L′nRuH
were dissolved in CD2Cl2 in an NMR tube, and then a limited
amount of HBF4‚Et2O was added. 31P and 1H NMR spectra
were taken. Relative molar concentrations of the equilibrated
The corresponding HD isotopomers were prepared analo-
gously except that DBF4, which was prepared by mixing
HBF4‚Et2O with D2O in a volume ratio of 3:1, was used instead
of HBF4‚Et2O or CF3SO3H. The η2-HD signals were observed
after nulling the η2-H2 peaks by the inversion-recovery
method.
[HCn Ru (HD)(P P h 3)2]2+
.
1H NMR (400 MHz, CD2Cl2): δ
species were estimated from the H NMR integrations of the
hydride signals.
1
1
2
-9.06 [tt, J (HD) ) 29.4 Hz, J (HP) ) 6.3 Hz, R-(HD)].
[
MeCn Ru (HD)(d p p e)]2+
.
1H NMR (400 MHz, CD2Cl2): δ
The pKa values of the two RCn carbonyl dihydrogen com-
plexes 6 and 8 were estimated by use of the equilibrium
depicted in eq 4. In a typical experiment, an appropriate
amount of HBF4‚Et2O was added to a CD2Cl2 solution of the
metal hydride in an NMR tube. NMR spectra were recorded
at -80 °C, and the relative molar concentrations of HBF4‚
Et2O, Et2O, the metal hydride, and the dihydrogen complex
were estimated on the basis of the 1H NMR integrations.
Cr yst a llogr a p h ic An a lysis for [H Cn R u H (P P h 3)2]-
BF 4‚2CH2Cl2. Suitable crystals for X-ray diffraction study
were obtained by layering of hexane on a dichloromethane
solution of [HCnRuH(PPh3)2]BF4. A red block crystal of dimen-
sion 0.22 × 0.23 × 0.29 mm was mounted in a glass capillary
and used for X-ray structure determination. All measure-
ments were made on a Marresearch image plate scanner with
graphite monochromated Mo KR radiation. The crystal system
is orthorhombic, and the space group is P212121 (No. 19). The
data were collected at 25 °C using the ω scan technique to a
maximum 2θ value of 51.2°. A total of 4741 intensity
measurements were made using the ω scan technique. The
1
2
-9.85 [tt, J (HD) ) 29.4 Hz, J (HP) ) 8.0 Hz, Ru-(HD)].
[Tp Ru (HD)(d p p e)]+. 1H NMR (400 MHz, CD2Cl2):
δ
1
-9.34 [t, J (HD) ) 32.5 Hz), Ru-(HD)].
The CO-containing dihydrogen complexes 6, 8, and 16 were
prepared as follows. In a typical experiment, a sample (10
mg) of the metal hydride was loaded into a 5 mm NMR tube,
which was then capped with a rubber septum. The tube was
evacuated and filled with nitrogen for three cycles. Dichloro-
methane-d2 (0.4 mL) was added to dissolve the sample. The
solution was cooled to -78 °C, and 5 µL of HBF4 or CF3SO3H
was added through a microsyringe. The tube was loaded into
the NMR probe precooled to -30 °C (6 and 8) or -80 °C (16),
and the sample was immediately analyzed by NMR spectros-
copy.
[HCn Ru (H2)(CO)(P P h 3)](BF 4)2 (6). 1H NMR (400 MHz,
CD2Cl2): δ -7.25 [br, 2H, Ru-(H2)], 1.26-5.58 (m, 3H, N-H
and 12H, NCH2), 7.48-7.61 (m, 15H of PPh3). 31P{1H} NMR
(161.70 MHz, CD2Cl2): δ 45.7 (s). T1 (400 MHz, CD2Cl2), ms
(temperature): 15 (263 K), 13 (253 K), 14 (243 K), 18 (233 K),
19 (223 K), 20 (213 K). A ln T1 vs 1000/T plot gave a T1(min)
of 14 ms at 248 K.
linear coefficient, µ, for Mo KR radiation is 6.8 cm-1
. Azi-
muthal scans of several reflections indicated no need for an
absorption correction. The data were corrected for Lorentz and
polarization effects. The structure was solved by heavy-atom
Patterson methods and expanded using Fourier techniques
using the TEXSAN program package. Some non-hydrogen
atoms were refined anisotropically, while the rest were refined
isotropically. The final cycle of full-matrix least-squares
refinements was based on 3178 observed reflection (I >
3.00σ(I)) and 328 variable parameters and converged with
unweighted and weighted agreement factors R ) 7.2%, and
Rw ) 9.9% with GOF ) 3.41. The data:parameter ratio was
[
MeCn Ru (H2)(CO)(P P h 3)](P F 6)(CF 3SO3) (8). 1H NMR
(400 MHz, CD2Cl2): δ -7.63 [br, 2H, Ru-(H2)], 1.26-4.52 (m,
9H, NCH3 and 12H, NCH2), 7.41-7.66 (m, 15H of PPh3).
31P{1H} NMR (161.70 MHz, CD2Cl2): δ 32.2 (s). T1 (400 MHz,
CD2Cl2), ms (temperature): 41 (258 K), 28 (253 K), 17 (248
K), 15 (243 K), 14 (238 K), 15 (223 K), 17 (215 K), 20 (203 K).
A ln T1 vs 1000/T plot gave a T1(min) of 12 ms at 224 K.
[Tp R u (H2)(CO)(P P h 3)]BF 4 (16). 1H NMR (400 MHz,
CD2Cl2): δ -6.84 [br, 2H, Ru-(H2)], 5.89 [br, 1H, H(pz)], 6.05
[br, 1H, H(pz)], 6.31 [br, 1H, H(pz)], 6.40 [br, 1H, H(pz)], 6.66
[br, 1H, H(pz)], 7.76 [br, 2H, H(pz)], 7.85 1H, H(pz)], 7.94 [br,
1H, H(pz)]. 31P{1H} NMR (161.70 MHz, CD2Cl2): δ 45.7 (s).
T1 (400 MHz, CD2Cl2), ms (temperature): 13 (243 K), 12 (238
K), 11 (233 K), 11 (223 K), 12 (218 K), 13 (213 K), 14 (208), 47
(203 K). A ln T1 vs 1000/T plot gave a T1(min) of 12 ms at
224 K.
9.69:1 and residual electron density/hole 0.63/-0.52 e Å-3
.
Further crystallographic details and selected bond distances
and angles are given in Tables 1 and 2, respectively.
Ack n ow led gm en t. The authors acknowledge the
financial support from the Hong Kong Research Grant
Council (Earmarked Grant HKP91/94P). We thank Dr.
Hon Man Lee for measuring the acidity of complex 14.
The corresponding HD isotopomers were prepared analo-
gously except that DBF4 was used in place of HBF4‚Et2O. The
η2-HD signals were observed after nulling the η2-H2 peaks by
the inversion-recovery method.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates and equivalent isotropic displacement coefficients,
complete bond lengths and bond angles, anisotropic displace-
ment coefficients, and isotropic displacement coefficients for
[HCnRuH(PPh3)2]BF4‚2CH2Cl2 (15 pages). Ordering informa-
tion is given on any current masthead page.
[H Cn R u (H D)(CO)(P P h 3)]2+
.
1H NMR (400 MHz,
1
CD2Cl2): δ -7.29 [t, J (HD) ) 31.8 Hz, Ru-(HD)].
[
Me Cn R u (H D)(CO)(P P h 3)]2+
.
1H NMR (400 MHz,
1
CD2Cl2): δ -7.65 [t, J (HD) ) 31.0 Hz, Ru-(HD)].
[Tp Ru (HD)(CO)(P P h 3)]+. 1H NMR (400 MHz, CD2Cl2):
1
δ -6.87 [t, J (HD) ) 33.3 Hz, Ru-(HD)].
OM9710374