Preparation of (1,4,7-triazacyclononane)Rh(hydrocarbyl)3 compounds and their derivatives. Strong donor labilization of RhC1 bonds toward alkylation and preparation of unusually stable alkyl hydride complexes of rhodium

Article abstract of DOI:10.1021/om960623e

(tacn)Rh(R)₃ compounds (tacn=1,4,7-triazacyclononane; R=Me, Et, Ph, vinyl) have been prepared in 65-86% yields by treatment of (tacn)RhCl₃·H₂O with more than a 7-fold molar quantity of RLi in THF, followed by protonation by methanol. The product before protonation is (Li₃tacn)RhR₃ (Li₃tacn = 1,4,7-trilithio-1,4,7-triazacyclononane) which can be isolated. The alkylation is complete in a few minutes to a couple of hours, depending on R, which compares with 3-4 days for CnRhCl₃ with MeLi (Cn = 1,4,7-trimethyl-1,4,7-triazacy-clononane) and suggests that the presumably first-formed (Li₃tacn)RhCl₃ is highly activated toward Cl^- dissociation by the strong donor effect of the three LiNR₂ groups in the rhodium coordination sphere. Protonation of (Li₃tacn)RhR₃ by methanol gives the neutral products (tacn)RhR₃. X-ray structure determinations of (tacn)RhEt₃ and (tacn)RhPh₃ have been carried out. Protonolysis of (tacn)RhR₃ (R = Me, Et, Ph) by 2 HSO₃CF₃ (HOTf) affords (tacn)-RhR(OTf)₂. Dissolution of the latter in D₂O gives [(tacn)RhR(D₂O)₂](OTf)₂, which on standing for up to 2 days undergoes H/D exchange of the two NH groups trans to the aqua ligands. Treatment of (tacn)RhR(OTf)₂ with 1 equiv of PMe₃ followed by NaBH₄ or KBH₄ yields a mixture of [(tacn)Rh(H)R(PMe₃)](OTf) and [(tacn)Rh(H)₂(PMe₃))](OTf) which is separated by benzene extraction. Counterion exchange has been carried out where R = Me and Et with Na{B[C₆H₃-3,5-(CF₃)₂]₄} (NaBAr^F₄) yielding [(tacn)Rh(H)R(PMe₃)](BAr^F₄). Heating of [CnRh-(H)Et(PMe₃)IX (X = OTf or BAr^F₄), [(tacn)Rh(H)Et(PMe₃)]X, and [(tacn)Rh(H)Me(PMe₃)]X in C₆D₆ leads to formation of [(Cn/tacn)Rh(D)(C₆D₅)(L)]XL)]X in high yield in all cases. The half-lives of these cleanly first-order reactions at 80 °C are 1 min, 1.2 h, and 7.3 h, respectively, illustrating alkyl hydride thermal stabilities unprecedented in rhodium chemistry.

Full text of DOI:10.1021/om960623e

434
Organometallics 1997, 16, 434-441
P r ep a r a tion of
(1,4,7-tr ia za cyclon on a n e)Rh (h yd r oca r byl)3 Com p ou n d s
a n d Th eir Der iva tives. Str on g Don or La biliza tion of
Rh Cl Bon d s tow a r d Alk yla tion a n d P r ep a r a tion of
Un u su a lly Sta ble Alk yl Hyd r id e Com p lexes of Rh od iu m
Renjie Zhou, Chunming Wang, Yonghan Hu, and Thomas C. Flood*
Department of Chemistry, University of Southern California,
Los Angeles, California 90089-0744
Received J uly 29, 1996X
(tacn)Rh(R)3 compounds (tacn ) 1,4,7-triazacyclononane; R ) Me, Et, Ph, vinyl) have been
prepared in 65-86% yields by treatment of (tacn)RhCl3‚H2O with more than a 7-fold molar
quantity of RLi in THF, followed by protonation by methanol. The product before protonation
is (Li3tacn)RhR3 (Li3tacn ) 1,4,7-trilithio-1,4,7-triazacyclononane) which can be isolated.
The alkylation is complete in a few minutes to a couple of hours, depending on R, which
compares with 3-4 days for CnRhCl3 with MeLi (Cn ) 1,4,7-trimethyl-1,4,7-triazacy-
clononane) and suggests that the presumably first-formed (Li3tacn)RhCl3 is highly activated
toward Cl- dissociation by the strong donor effect of the three LiNR2 groups in the rhodium
coordination sphere. Protonation of (Li3tacn)RhR3 by methanol gives the neutral products
(tacn)RhR3. X-ray structure determinations of (tacn)RhEt3 and (tacn)RhPh3 have been
carried out. Protonolysis of (tacn)RhR3 (R ) Me, Et, Ph) by 2 HSO3CF3 (HOTf) affords (tacn)-
RhR(OTf)2. Dissolution of the latter in D2O gives [(tacn)RhR(D2O)2](OTf)2, which on standing
for up to 2 days undergoes H/D exchange of the two NH groups trans to the aqua ligands.
Treatment of (tacn)RhR(OTf)2 with 1 equiv of PMe3 followed by NaBH4 or KBH4 yields a
mixture of [(tacn)Rh(H)R(PMe3)](OTf) and [(tacn)Rh(H)2(PMe3)](OTf) which is separated by
benzene extraction. Counterion exchange has been carried out where R ) Me and Et with
Na{B[C6H3-3,5-(CF3)2]4} (NaBArF ) yielding [(tacn)Rh(H)R(PMe3)](BArF ). Heating of [CnRh-
4
4
(H)Et(PMe3)]X (X ) OTf or BArF4), [(tacn)Rh(H)Et(PMe3)]X, and [(tacn)Rh(H)Me(PMe3)]X
in C6D6 leads to formation of [(Cn/tacn)Rh(D)(C6D5)(L)]X in high yield in all cases. The
half-lives of these cleanly first-order reactions at 80 °C are 1 min, 1.2 h, and 7.3 h,
respectively, illustrating alkyl hydride thermal stabilities unprecedented in rhodium
chemistry.
In tr od u ction
hydrocarbyl hydrides of rhodium, three of which, [(tacn)-
Rh(H)R(PMe3)]+ (R ) Me, Et, Ph), are prepared and
characterized herein. These alkyl hydride complexes
are even more stable than the previously reported
[CnRh(H)Me(PMe3)]+.1c
When the initial investigations into the organome-
tallic chemistry of “Cn”RhIII (Cn ) 1,4,7-trimethyl-1,4,7-
triazacyclononane)1 were conducted, the assumption
was made that tertiary amines were necessary to allow
the incorporation of alkyl groups at rhodium via the
usual highly basic reagents such as RLi, RMgX, and R2-
Mg. We have recently found that this assumption is
unwarranted, as alkylations of (tacn)RhCl3 (tacn )
1,4,7-triazacyclononane) proceed rapidly and in good
yields with several organolithium reagents. In fact, the
alkylations are faster and cleaner than the correspond-
ing reactions of CnRhCl3, leading us to suppose that the
intermediate (1,4,7-trilithio-1,4,7-triamidocyclononane)-
RhCl3 is highly activated toward halide dissociation by
the strongly basic triamido trianion ligand. This ver-
satile preparation of rhodium trihydrocarbyl complexes
provides a convenient route for the preparation of
Resu lts
P r ep a r a tion of (ta cn )Rh R3. Wieghardt2 reported
the synthesis of (tacn)RhCl3‚H2O by heating a methanol-
DMSO solution of tacn and RhCl3‚nH2O at 90 °C, and
this procedure generally affords 70-80% yields of the
air-stable, yellow compound. This is then treated with
an excess of RLi or ArLi in THF, followed by addition
of methanol to yield the trihydrocarbyl complexes 1a -d
(Scheme 1). These alkylations can be examined conve-
niently by NMR spectroscopy in THF-d8. Reaction with
MeLi is complete in 2 h at ambient temperature, and
that with EtLi, in 5 min. On a synthetic scale, THF
was added to a solid mixture of (tacn)RhCl3‚H2O and a
7-8-fold molar quantity of RLi at -78 °C, to avoid
excess exotherm, and the solution was allowed to warm
to room temperature. These were run for somewhat
X Abstract published in Advance ACS Abstracts, J anuary 1, 1997.
(1) (a) Wang, L.; Flood, T. C. J . Am. Chem. Soc. 1992, 114, 3169.
(b) Wang, L.; Lu, R. S.; Bau, R.; Flood, T. C. J . Am. Chem. Soc. 1993,
115, 6999. (c) Wang, C.; Ziller, J . W.; Flood, T. C. J . Am. Chem. Soc.
1995, 117, 1647. (d) Wang, L.; Wang, C.; Bau, R.; Flood, T. C.
Organometallics 1996, 15, 491. (e) Wang, L.; Sowa, J . R.; Wang, C.;
Lu, R. S.; Gassman, P. G.; Flood, T. C. Organometallics 1996, 15, 4240.
(f) Zhen, H.; Wang, C.; Hu, Y.; Flood, T. C. Submitted for publication.
(2) Wieghardt, K.; Schmidt, W.; Nuber, B.; Prinkner, B.; Weiss, J .
Chem. Ber. 1980, 113, 36.
S0276-7333(96)00623-1 CCC: $14.00 © 1997 American Chemical Society

(1,4,7-triazacyclononane)Rh(hydrocarbyl)3 Compounds
Organometallics, Vol. 16, No. 3, 1997 435
Sch em e 1
F igu r e 1. Molecular structure (50% probability) of the
(tacn)RhEt3 (1b) heavy atoms.
longer times than the NMR experiments had indicated
in order to ensure completion (see Experimental Sec-
tion), but it is important not to let them go for much
longer times (e.g., 8 h), as this results in reduced yields.
The initial product is the tris(lithium amide) 2 of which
2a (R ) Me) and 2b (R ) Et) have been isolated by
evaporation of THF, extraction of excess RLi from the
residue with ether or pentane, and then extraction of
the product from the residue by (further) treatment with
ether. Removal of the solvent under vacuum gave pale
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for (ta cn )Rh Et3 (1b) a n d (ta cn )Rh P h 3
(1c)
(tacn)RhEt3 (1b)
Rh-N(1)
Rh-N(2)
Rh-N(3)
Rh-C(7)
Rh-C(9)
Rh-C(11)
2.209(3)
2.199(4)
2.192(4)
2.057(4)
2.047(5)
2.047(5)
N(1)-Rh-N(2)
N(2)-Rh-N(3)
N(1)-Rh-N(3)
C(7)-Rh-C(9)
C(9)-Rh-C(11)
C(7)-Rh-C(11)
78.8(1)
79.3(1)
79.0(1)
86.8(2)
87.8(2)
87.1(2)
1
yellow (Li3tacn)RhR3, 2a ,b (Scheme 1). The H and 13C
(tacn)RhPh3 (1c)
Rh-N(1)
Rh-N(2)
Rh-N(3)
Rh-C(11)
Rh-C(21)
Rh-C(31)
2.226(4)
2.200(4)
2.220(4)
2.025(4)
2.052(4)
2.022(4)
N(1)-Rh-N(2)
N(2)-Rh-N(3)
N(1)-Rh-N(3)
C(11)-Rh-C(21)
C(21)-Rh-C(31)
C(11)-Rh-C(31)
78.4(1)
78.9(1)
78.5(1)
88.9(2)
92.4(2)
94.6(2)
NMR spectra of 2b, for example, are distinctly different
from those of 1b (see Experimental Section), and
analysis of the lithium content of solid 2b yielded a
value of 5.69% (calcd, 6.18%). Protonation of lithium
amides 2 is carried out in THF at room temperature
with an excess of methanol, and solvent removal and
product extraction with methylene chloride or benzene
gives 65-86% yields of tris(hydrocarbyls) (tacn)RhR3 (1;
R ) Me (a ), Et (b), Ph (c), Vi (d ); Scheme 1), which are
all air and water stable and of considerable thermal
stability. For example, 1b is unaltered after 20 h in
benzene-d6 at 80 °C in a sealed tube.
unidentate ligands.1c,d,f An average N-Rh-N bond
angle of 79° clearly indicates that the tacn ligand is
moved away from the metal along the molecular 3-fold
axis (not a crystallographic axis) to the same extent as
the Cn ligand does in its CnRhR3 complexes. The
average Rh-N distance of 2.20 Å is slightly but probably
significantly shorter than in the CnRhR3 complexes
which average 2.23 Å. Presumably this is the difference
between secondary and tertiary Rh-N lengths. The
Rh-C distances average 2.05 Å and the C-Rh-C
angles average 87°, values indistinguishable from Cn-
RhMe3 and [N,N′,N′′-tris(neohexyl)triazacyclononane]-
RhMe3.1d In the case of CnRhMe3, the slightly acute
C-Rh-C angle was attributed to steric congestion
between the Rh-methyl and the N-methyl groups.
Since there are no N-Me groups in 1b, this explanation
for CnRhMe3 is unlikely, and an alternate explanation
is not clear to us.
Solution of the X-ray diffraction data of 1c generated
the structure shown in Figure 2. Table 1 lists some of
its bond parameters. As expected, structural features
of the (tacn)Rh moiety are very similar to those of 1b.
A priori, because of the sp2 carbon hybridization of the
phenyl groups in 1c, one might expect the Rh-C
distances to be shorter in 1c than in 1b, and because of
the differing trans influences of phenyl and ethyl, one
might expect the Rh-N distances in 1c to be slightly
longer than those in 1b. These expectations are con-
sistent with the bond lengths in the two structures,
except that the differences are of about the same size
as 3σ and so must be regarded as only suggestive. Our
attempts to prepare CnRhPh3 have failed, so comparison
to the Cn system is not possible. Two notable features
of the 1c structure are that there is a rather large
variation in the C-Rh-C angles (94.6-88.9°), and the
mutually trans Rh-C(21) and Rh-N(2) lengths are
All of the tris(hydrocarbyls) 1 show broad and/or
complex 1H NMR patterns for the tacn CH protons
between δ 2.3 and 3.0 and broad NH singlets which are
characteristically between δ 3.2 and 4.0 ppm in DMSO-
d6 or CD3CN. In THF the spectrum of 1b shows two
broad singlets for the amine CH at δ 2.65 and 3.00, and
the NH resonances are moved upfield underneath the
peak at 3.00. In most solvents, protons on carbon
bonded to rhodium (R-CH) are moved upfield from
alkane values and, for example, are at δ -0.58 for RhMe
and 0.32 for the RhEt methylenes in DMSO-d6. All
three vinyl CH protons are rhodium coupled in 1d , but
only the R-carbon is rhodium coupled in the 13C spec-
trum. Benzene-d6 has a unique effect on the proton
spectrum of 1b, showing the amine CH resonances as
two sharp but complex second-order multiplets at δ 1.47
and 2.23 and the NH peaks upfield at δ 1.85. In
addition, the methylene of the rhodium ethyl group is
downfield at δ 1.15 ppm. The tris(N-methyl) complexes
CnRhR3 (R ) Me, Et;1d R ) Vi1f), analogues of 1, show
1
the same distinct H NMR behavior in benzene solvent.
Str u ctu r e Deter m in a tion s of (ta cn )Rh Et3 (1b)
a n d (ta cn )Rh P h 3 (1c). Slow evaporation of a meth-
ylene chloride solution of 1b resulted in formation of
light yellow single crystals. Figure 1 shows a labeled
molecular drawing of 1b, and Table 1 lists selected bond
parameters. The structure of the (tacn)Rh moiety shows
features essentially the same as those of the tri-N-
methylated CnRh molecules that bear three strong-field

436 Organometallics, Vol. 16, No. 3, 1997
Zhou et al.
Sch em e 3
F igu r e 2. Molecular structure (50% probability) of the
(tacn)RhPh3 (1c) heavy atoms.
Sch em e 2
stoichiometry, we assign the exchange to the NH groups
trans to the aqua ligands; apparently the NH trans to
the hydrocarbyl does not H/D exchange with the solvent
under conditions of simple dissolution at room temper-
ature, but we have not checked for possible pH or
temperature dependence of the exchange.
P r ep a r a tion of Alk yl Hyd r id es. One equivalent
of trimethylphosphine in THF displaces triflate from
3a -c and forms [(tacn)RhR(PMe3)(OTf)](OTf), 5a -c
(Scheme 3); 5a ,b were isolated, while 5c was prepared
only in situ. An excess of PMe3 must be avoided since
disubstitution giving [(tacn)RhR(PMe3)2](OTf)2 occurs
very readily. This is in contrast to the analogue
CnRhMe(OTf)2, which forms only [CnRhMe(PMe3)(OTf)]-
(OTf) even with an excess of PMe3.1c Reduction of 5 to
hydrocarbyl hydride 6 was attempted with LiBHEt3,
LiBH(secBu)3, and LiAlH(O-t-Bu)3, but these gave com-
plex mixtures that may come from reaction of the basic
hydride with the NH bonds of the tacn ligand. Treat-
ment of the salt 5 with NaBH4 or KBH4 in THF
generates a mixture of [(tacn)Rh(H)R(PMe3)](OTf), 6a -
c, and [(tacn)Rh(H)2(PMe3)](OTf), 7 (Scheme 3). The
amount of 7 is highly variable: 10-50% with NaBH4
and 60-95% with KBH4. We have been unable to
determine the source of this variability. Hydrocarbyl
hydride 6 is sparingly soluble in benzene, while dihy-
dride 7 is quite insoluble, so that separation of the two
is possible although tedious. The benzene extraction
also serves to separate 6 from insoluble excess NaBH4
or KBH4. Fortunately, dihydride 7 is inert to most of
the chemistry that we wish to examine with the alkyl
hydrides, and so moderate amounts can be tolerated in
the sample. In some cases, it serves as a useful NMR
internal standard. Small amounts of colored impurity
are removed from 6a ,b and 7 by counterion exchange
with Na{B[C6H3-3,5-(CF3)2]4} (NaBArF4) in chloroben-
longer and shorter, respectively, than the other two
pairs. These differences probably reflect the strong
steric interaction of the three bulky phenyl groups.
Acid Clea va ge of Rh -C Bon d s. As is the case with
CnRhMe3,1d (tacn)RhR3 complexes (1a -c; R ) Me, Et,
Ph) undergo Rh-C cleavage with 2 equiv of triflic acid
(HOS(O)2CF3, HOTf) to afford (tacn)RhR(OTf)2, 3a -c
(Scheme 2). Triethyl 1b generates a complex mixture
when treated with just 1 equiv of acid. CnRhEt3 and 1
equiv of HOTf forms CnRh(π-CH2dCH2)(OTf),3 but
apparently the tacn analogue is not stable. Trivinyl 1d
protonates at the vinyl methylene in the presence of 1
equiv of acid to form a cationic alkylidene complex which
undergoes subsequent rearrangement to [(tacn)Rh-
(CHdCH2)(η3-CH2CHCHMe)](OTf). This latter chem-
istry using CnRh(Vi)3 has been reported elsewhere.1f
The (tacn)RhR(OTf)2 compounds, 3a -c, dissolve in D2O
to form materials assigned the structures [(tacn)RhR-
(D2O)2](OTf)2, 4a -c (Scheme 2), which are all indefi-
nitely stable in solution. The NH proton resonances of
the tacn ligand of all three diaqua complexes show a
clear pattern of two broad singlets at δ 5.65-5.86 and
5.90-6.35 ppm, with a 1:2 intensity ratio typical of
materials with Cs symmetry. Gradually over a period
of hours, the two-proton peak at lower field disappears,
while the single-proton peak remains unchanged for
much longer periods. Half-lives for exchange are slighly
dependent on the hydrocarbyl ligand; t1/2 for 4a (Me) )
24 h and 4b (Et) ) 10 h, while the exchange of 4c (Ph)
is complete in less than 6 h. On the basis of the
zene. The -BArF salts are designated 8a ,b and 9 to
4
distinguish them from the triflate salts. In any event,
preparation of pure alkyl hydrides can be achieved, but
mixtures of 6 and 7 are suitable for most purposes.
Complexes 8a ,b, 6c, and 9 have been fully character-
ized, including combustion analysis and/or high-resolu-
1
tion mass spectroscopy. In the H NMR spectra of 6/8
the hydride resonance appears between δ -16.7 and
-18.1 ppm (dd, J RhH ∼ 28 Hz, J PH ∼ 36 Hz), P(CH3)3 is
a doublet (J PH ∼ 9-10 Hz) between δ 1.2 and 1.4 ppm,
and NH appears as three broad singlets (the metal is
chiral) between δ 4.7 and 5.8 ppm. 31P{1H} NMR
resonances are doublets (J RhP ∼ 136-145 Hz) between
(3) Wang, C.; Flood, T. C. Unpublished results.

(1,4,7-triazacyclononane)Rh(hydrocarbyl)3 Compounds
Organometallics, Vol. 16, No. 3, 1997 437
Ta ble 2. Ra te of Rea ction of Rh od iu m Alk yl
Hyd r id e Ca tion s a t 80 °C in Ben zen e-d 6 (L ) P Me3)
compd
rate const (s-1
)
half-life (min)
[CnRh(H)Me(L)]+ a
[CnRh(H)Et(L)]+ b
[(tacn)Rh(H)Me(L)]+
[(tacn)Rh(H)Et(L)]+
2.67((0.20) × 10-4
2.65((0.02) × 10-5
1.60((0.03) × 10-4
43
≈1
436
72
≈1 × 10-2
F igu r e 3. Schematic representation of the symmetry
properties of amido ligands in potential overlap with the
rhodium center. Lithium counterions have been omitted
for clarity. See the text and note 6.
a
b
Reference 1c. Rate constant at 56 °C is 1.97((0.03) × 10-4
s-1 (t1/2 ) 59 min).
δ 10.4 and 12.9 ppm, and off-resonance decoupling
reveals a doublet of doublets for 6/8 and a doublet of
triplets for 7/9, confirming the dihydride structure of
the last. As anticipated, the 13C{1H} NMR spectra of
6/8 show six tacn ligand resonances because of the metal
chirality. The ethyl group R-carbon of 6b/8b appears
at δ -0.29 (dd, J RhC ) 26 Hz, J PC ) 11 Hz).
All three alkyl hydrides are stable enough for analysis
by fast atom bombardment mass spectroscopy. Using
FAB, signals at the masses of the intact cations are
strong, and in the case of the phenyl hydride 6c, it is
the strongest signal. Also evident in each case is the
mass corresponding to the ion [(tacn)Rh(PMe3)]+ from
which the neutral hydrocarbon has been lost.
Th er m olysis of Alk yl Hyd r id es. The relative
stability (thermodynamic and kinetic) of metal alkyls
is of current interest. We recently reported1c the
preparation and some chemistry of [CnRh(H)Me(PMe3)]+.
Its thermolysis in benzene results in loss of methane
and the oxidative addition of the solvent to form [CnRh-
(H)Ph(PMe3)]+ essentially quantitatively. For purposes
of comparison, we have also prepared the ethyl deriva-
tive [CnRh(H)Et(PMe3)]+, and it, 6a , and 6b all react
with benzene at 80 °C to give high yields of the
corresponding phenyl hydride complex. Half-lives for
all of these reactions are given in Table 2. An estimate
is given for [CnRh(H)Et(PMe3)]+ because its reaction
was too fast at 80 °C to obtain a reliable value by NMR.
The results shown in Table 2 clearly illustrate a
substantial enhancement in stability for methyl over
ethyl complexes and for tacn-ligated materials over the
Cn analogues.
CoX]2+ and related systems.4bc Brown and co-workers4d
delineated the importance of “cis effects” in carbonyl
complexes such as (CO)5MnX. For example, the rate
ratio is 108 for CO substitution cis to the ligand X in
Cr(CO)5X between X ) Cl- and X ) PPh3 and 1010
between X ) Cl- and X ) CO.4e Since the early work
of Brown, others have provided examples of the cis lone
pair effect in other organometallic systems.5 It is
generally argued that strong π-electron pair donation
of a ligand such as an amido group in a 5-coordinate,
16-electron fragment would cause the metal center to
assume a trigonal bipyramidal geometry with the amido
nitrogen and its lone pair lying in the equatorial plane.
This would situate the plane of the amido group
perpendicular to the equatorial plane of the TBP as in
structure I (Figure 3).6 It is difficult to see how the
5-coordinate, chloride-dissociated intermediate II could
assume such an analogous geometry because the con-
straints of the tacn chelate would require two of the
nitrogens to be equatorial and yet the N-Rh-N angle
probably could not open very much from the ca. 80°
characteristic of the octahedral tacn complexes. In
addition, the nitrogen centers could not rotate and
flatten in the same way as in I. Nevertheless, although
spacial overlap with metal orbitals is expected to be
poor, the electron pair is of π-symmetry with respect to
the N-Rh axis and so some overlap with π-symmetry
metal orbitals can still occur, and linear combinations
of the three nitrogen lone pairs give considerable
flexibility to the amido lone pairs for symmetry match-
ing for π donation. Thus, the two unidentate ligands
in the 5-coordinate intermediate could also reorganize
to optimize stabilization of the coordinative unsatura-
tion of the metal center. These last two effects are
pictured in hypothetical structure III, where two nitro-
gens and a third ligand form a “Y”-shaped equatorial
array about the metal with a π-symmetry linear com-
bination of their lone pairs available for approximately
equatorial-plane donation. Last, the field effects from
Discu ssion
For some time we had assumed that in order to
prepare (triamine)RhR3 via (triamine)RhCl3 and reac-
tive metallohydrocarbyls, the triamine ligand must
contain only tertiary amines: certainly trianions such
as (Li3tacn)RhCl3 or (Li3tacn)RhR3 (2) must be unstable.
Nevertheless, we decided to attempt reaction of MeLi
with (tacn)RhCl3, which bears a trisecondary amine, and
observed that the reaction is actually very clean and
faster than reaction of MeLi with CnRhCl3. Although
solid 2 can be isolated, so far attempts to obtain
crystallographic quality crystals have failed. We as-
sume that three lithium ions are critical to the stability
of (Li3tacn)RhX3 (X ) halide or hydrocarbyl) and it is
probable that they are tightly paired in THF solution.
Given the fact that species such as 2 are stable, it is not
surprising that the alkylation should proceed so well.
The notion that basic lone pairs on ligands labilize a
complex toward dissociation of another ligand dates
back to 1937.4a The phenomenon of π-symmetry lone
pairs labilizing mutually cis ligands has been studied
in detail in classical coordination chemistry, particularly
in the context of base-catalyzed hydrolysis of [(NH3)5-
(4) (a) Garrick, F. J . Nature 1937, 139, 507. (b) Basolo, F.; Pearson,
R. G. Mechanisms of Inorganic Reactions, 2nd ed.; Wiley: New York,
1967. (c) Tobe, M. L. Acc. Chem. Res. 1970, 3, 377. (d) Lichtenberger,
D. L.; Brown, T. L. J . Am. Chem. Soc. 1978, 100, 366. (e) Atwood, J .
D.; Brown, T. L. J . Am. Chem. Soc. 1976, 98, 3160.
(5) (a) Bryndza, H. E.; Fong, L. K.; Paciello, R. A.; Tam, W.; Bercaw,
J . E. J . Am. Chem. Soc. 1987, 109, 1444. (b) Davey, R. D.; Hall, M. B.
Inorg. Chem. 1989, 28, 3524. (c) Fryzuk, M. D.; Montgomery, C. D.
Coord. Chem. Rev. 1989, 95, 1. (d) Riehl, J . F.; J ean, Y.; Eisenstein,
O.; Pelissier, M. Organometallics 1992, 11, 729. (e) J ohnson, T. J .;
Huffman, J . C.; Caulton, K. G. J . Am. Chem. Soc. 1992, 114, 2725.
(6) Although the lithium ions have been omitted from Figure 3 for
clarity, they are almost certainly tightly associated in solution as well
as in the solid. However, wherever the lithium ions are located, they
will have no effect on the symmetry of overlap of the nitrogen lone
pairs with the rhodium center. In addition, while the coulombic
stabilization of the anion by the cations must be critically important,
the bonding is probably essentially completely ionic, and so the lithium
cations can relocate to accommodate the redistribution of negative
charge within the rhodium complex. Thus, they probably have
minimal effects on the extent of charge redistribution by orbital overlap
of the nitrogens with rhodium.

438 Organometallics, Vol. 16, No. 3, 1997
Zhou et al.
three facial, anionic nitrogen ligands are difficult to
estimate; they could be influential in ejecting an anionic
ligand from the metal. In any event, it is clear that the
amido groups are not without effect, since substitution
is so much faster for (tacn)RhCl3 than CnRhCl3. These
substitutions afford a general entry into the organo-
Rh(tacn) system.
In general, alkyl hydride complexes of rhodium have
been much less stable to alkane loss than their iridium
analogues. For example, loss of methane from Cp*Ir-
(H)Me(PMe3) requires temperatures in excess of 150
°C,7e while Cp*Rh(H)Me(PMe3) loses methane at -17
°C.7b Cp*Rh(H)Et(PMe3) was prepared below -60 °C
and loses ethane at -30 °C.7f On the other hand, the
anionic ligand tris(2,3-dimethylpyrazolyl)borate (tpb*)
seems to impart greater stability to rhodium alkyl
hydrides: (tpb*)Rh(CO)(H)Me persists at room temper-
ature for hours,7g and (tpb*)Rh(CN-t-Bu)(H)Me loses
methane at 23 °C with t1/2 ) 5.6 h.7k Thus, the half-
life for methane loss of ca. 7 h at 80 °C exhibited by
[(tacn)Rh(H)Me(PMe3)]+, 6a , is a remarkable stability
for a rhodium alkyl hydride. This particular stability
for the [(tacn)Rh(H)R(PMe3)]+ series places them in a
range where they are stable enough for convenient
synthesis and characterization and yet reactive enough
to study under conditions where the chemistry is more
likely to remain relatively clean and free of decomposi-
tion to catalytic impurities. Thus, synthetic and mecha-
nistic investigations of (tacn)Rh(H)R(X) with hydrocar-
byl ligands R intended to address specific questions with
assorted neutral and anionic ligands X are the objects
of our continuing efforts.
A pleasant surprise regarding the (tacn)Rh system in
general is that while solubilities of analogous (tacn)Rh
and CnRh molecules are frequently somewhat different
and solubility for either type of molecule is often quite
limited, nevertheless, the solubility of the (tacn)Rh
species are not generally diminished in aromatic and
polar organic solvents compared to the CnRh congeners.
Another encouraging finding is that, contrary to our
initial concern that (tacn)Rh alkyls might eliminate
alkane by protonolysis from the rather acidic intra-
molecular N-H bonds, to date we have seen no indica-
tions of intramolecular RH elimination. Perhaps this
is not surprising in view of the effective precedent1b of
[CnRhMe(H2O)2]2+ being stable indefinitely at ambient
temperature in aqueous solution. Of course, we now
know that [(tacn)RhR(H2O)2]2+, 4a -c, are all similarly
stable in water, and the hydrocarbyl groups are cer-
tainly less likely to react with the intramolecular NH
protons than with the much more acidic protons of
coordinated water.
Exp er im en ta l Section
The most obvious mechanisms for H/D exchange of
the N-H groups in [(tacn)RhR(D2O)2]2+, 4a -c, in D2O
(Scheme 2) are (a) ionization of the N-H bond of the
intact complex and (b) dissociation of an amine center
from the rhodium in the otherwise intact ion long
enough to undergo normal proton exchange with the
deuterated solvent. Useful information is available
from a previously reported1b X-ray structure determi-
nation of the closely related [CnRhMe(H2O)2]2+, wherein
a large difference in trans influence of the strong-field
methyl group and weak-field aqua ligands on the Rh-N
bond distances is evident. Lengths for the Rh-N bonds
trans to H2O are 2.04(2) and 2.07(2) Å, while that trans
to methyl is 2.21(1) Åsdifferences of ca. 7%! Assuming
that the structure of [(tacn)RhR(D2O)2]2+, 4, would
possess the same differences and taking the shorter
bonds to be stronger and therefore slower to dissociate,
the Rh-N dissociation explanation for H/D exchange
in 4b seems very unlikely. On the other hand, a
substantially stronger Rh-N bond could reasonably be
expected to render the N-H bond more acidic and
therefore faster to exchange by an ionization mecha-
nism.
Gen er a l Meth od s. All reactions involving organometallic
compounds, unless otherwise mentioned, were carried out
under an atmosphere of N2 or Ar purified over reduced Cu
catalyst (BASF R3-11) and Aquasorb. Flamed-out glassware
and standard vacuum line, Schlenk, and N2-atmosphere box
techniques were employed. Benzene, ether, hexanes, pen-
tanes, and THF were distilled from purple solutions of sodium/
benzophenone, and CH2Cl2 were distilled twice from CaH2.
Elemental analyses were performed by Galbraith Laboratories,
Knoxville, TN. High-resolution FAB MS were recorded at the
Mass Spectroscopy Facility of the University of California at
Riverside. NMR chemical shifts are reported in parts per
million (δ) downfield from tetramethylsilane for 1H and 13C.
Ma ter ia ls. Concise preparations of tacn, Cn, and CnRhCl3
10
have recently been published.1d NaBArF
and EtLi11 were
4
literature preparations. Et2Mg was prepared from EtMgBr
by the standard dioxane method,12 and ViLi was prepared from
SnVi4.13 PhLi, MeLi, EtMgBr, MeMgBr, SnVi4, all other
reagents, and all solvents were commercial materials.
(ta cn )Rh Cl3‚H2O.2 A solution of tacn (2.20 g, 17.1 mmol)
in 17 mL of methanol was added dropwise to a stirred solution
of RhCl3‚3H2O (4.49 g, 17.1 mmol) in 80 mL of DMSO (dried
over 3 Å molecular series) at RT (room temperature). The color
of the solution changed to light red. After a few minutes,
heating was commenced at 90 °C for 2 h, during which a
copious yellow precipitate formed. The supernatant was
decanted, and the precipitate was washed with DMSO (2 ×
30 mL), water (3 × 30 mL), ethanol (3 × 30 mL), and ether (3
× 30 mL), and air-dried to yield 4.4 g of yellow solid (72%).
The product was too insoluble to obtain spectra.
The thermolysis of alkyl hydride complexes of the late
transition metals is now a well-known method for the
generation of reactive metal species capable of re-adding
C-H bonds of alkanes,7 arenes,7b-e,g,k,8 and alkenes.7b,d,9
(7) (a) Wax, M. J .; Stryker, J . M.; Buchanan, J . M.; Kovac, C. A.;
Bergman, R. G. J . Am. Chem. Soc. 1984, 106, 1121. (b) J ones, W. D.;
Feher, F. J . J . Am. Chem. Soc. 1984, 106, 1650. (c) J ones, W. D.; Feher,
F. J . J . Am. Chem. Soc. 1985, 107, 620. (d) Wenzel, T. T.; Bergman,
R. G. J . Am. Chem. Soc. 1986, 108, 4856. (e) Buchanan, J . M.; Stryker,
J . M.; Bergman, R. G. J . Am. Chem. Soc. 1986, 108, 1537. (f) Periana,
R. A.; Bergman, R. G. J . Am. Chem. Soc. 1986, 108, 7332. (g) Ghosh,
C. K.; Graham, W. A. G. J . Am. Chem. Soc. 1987, 109, 4726. (h)
Harper, T. G. P.; Shinomoto, R. S.; Deming, M. A.; Flood, T. C. J . Am.
Chem. Soc. 1988, 110, 7915. (i) Harper, T. G. P. Ph.D. Thesis, U. of
Southern California, Los Angeles, CA, 1989. (j) Shinomoto, R. S.;
Desrosiers, P. J .; Harper, T. G. P.; Deming, M. A.; Flood, T. C. J . Am.
Chem. Soc. 1990, 112, 704. (k) J ones, W. D.; Hessell, E. T. J . Am.
Chem. Soc. 1993, 115, 554.
(ta cn )Rh Me3 (1a ). THF (60 mL) was slowly added to a
stirred mixture of (tacn)RhCl3‚H2O (0.40 g, 1.1 mmol) and solid
(9) (a) Stoutland, P. O.; Bergman, R. G. J . Am. Chem. Soc. 1988,
110, 5732. (b) Ghosh, C. K.; Hoyano, J . K.; Krentz, R.; Graham, W. A.
G. J . Am. Chem. Soc. 1989, 111, 5480. (c) Struck, G. E. Ph.D. Thesis,
U. of Southern California, Los Angeles, CA, 1994.
(10) Nishida, H.; Takada, N.; Yoshimura, M.; Sonoda, T.; Kobayashi,
H. Bull. Chem. Soc. J pn. 1984, 57, 2600. Brookhart, M.; Grant, B.;
Volpe, A. F. Organometallics 1992, 11, 3920.
(11) Furniss, B. S.; Hannaford, A. J .; Smith, P. W. G.; Tatchell, A.
R. Vogel’s Textbook of Practical Organic Chemistry, 5th ed.; Longman
Scientific & Technical: Essex, U.K., 1989; p 443.
(12) Strohmeier, W.; Seifert, F. Chem. Ber. 1961, 94, 2356.
(13) Seyferth, D.; Weiner, M. J . Chem. Soc. 1961, 3583.
(8) Desrosiers, P. J .; Shinomoto, R. S.; Flood, T. C. J . Am. Chem.
Soc. 1986, 108, 7964.

(1,4,7-triazacyclononane)Rh(hydrocarbyl)3 Compounds
Organometallics, Vol. 16, No. 3, 1997 439
halide-free CH3Li (0.250 g 11.2 mmol) in a -78 °C bath. The
mixture was allowed to warm to RT, and after 3 h of stirring
a clear yellow solution was obtained. The solvent was evapo-
rated under vacuum, and the residue was washed with ether
(3 × 40 mL) to extract excess CH3Li, each time decanting by
cannula. The residue was dried under vacuum to give a white
solid. The material assigned the structure (Li3tacn)RhMe3 (2a )
exhibited the following spectra. 1H NMR (DMSO-d6, 360
MHz): δ -0.58 (d, J RhH ) 2.0 Hz, RhCH3), 2.4-2.85 (m, NCH2).
13C NMR (DMSO-d6, 90 MHz): δ -6.58 (dq, J RhC ) 34 Hz,
J CH ) 119 Hz, RhCH3), 47.12 (t, J CH ) 134 Hz, NCH2). For
protonation of the amido groups, the solid (Li3tacn)RhMe3 was
dissolved in 70 mL of THF and 3.0 mL of MeOH (excess) was
added with stirring. Stirring was continued for 20 min, and
then the volatiles were removed under vacuum to give a cream-
colored solid. The solid was extracted with CH2Cl2 (3 × 30
mL), and the extract was filtered and evaporated to yield a
light yellow solid (0.20 g, 65%). 1H NMR (DMSO-d6, 360
MHz): δ -0.58 (d, J RhH ) 2.6 Hz, RhCH3), 2.46-2.78 (m,
NCH2), 3.67 (brs, NH). 13C{1H} NMR (DMSO-d6, 90 MHz): δ
-6.57 (d, J RhC ) 34 Hz, RhCH3), 47.22 (NCH2). Anal. Calcd
for C9H24N3Rh: C, 38.99; H, 8.73; N, 15.16. Found: C, 38.52;
H, 8.82; N, 14.45.
(ta cn )Rh Vi3 (1d ). THF (40 mL) was slowly added to a
stirred mixture of (tacn)RhCl3‚H2O (0.25 g, 0.70 mmol) and
solid vinyllithium (0.23 g, 7.0 mmol) in a -78 °C bath. The
mixture was allowed to warm to RT, and after 20 min a clear
light brown solution had formed. After an additional 1 h of
stirring, 1.5 mL of MeOH was added resulting in evolution of
gas and formation of solids. The mixture was stirred for 30
min, the volatiles were removed under vacuum, and the
residue was extracted with CH2Cl2 (2 × 40 mL). The extract
was filtered, and the solvent was removed under vacuum to
give a light yellow solid (0.19 g, 86%). 1H NMR (DMSO-d6,
250 MHz): δ 2.38-2.97 (m, NCH2), 3.98 (br s, NH), 4.95 (ddd,
J H
) 3.6 Hz, J H ) 18 Hz, J RhH ) 1.8 Hz, RhCHdCHHa
H
H
c
a
b
a
a
cis to Rh), 5.30 (ddd, J H
) 10 Hz, J RhH ) 3.5 Hz,
H
b
c
b
RhCHdCHHb trans to Rh), 7.60 (ddd, J RhH ) 1.6 Hz,
c
RhCHcdCH2). 13C{1H} NMR (DMSO-d6, 63 MHz): δ 47.06
(NCH2), 113.64 (dCH2), 172.20 (d, J RhC ) 39 Hz, RhCHd).
Anal. Calcd for C12H24N3Rh: C, 46.01; H, 7.72. Found: C,
45.42; H, 7.69. FAB mass spectrum: Calcd for [C12H24N3Rh]-
H+, m/e 314.1104; found, m/e 314.1088 (92%) (5 ppm). Also
observed, m/e ) 288 (52%) [MH+ - C2H2].
(ta cn )Rh Me(OTf)2 (3a ). A 3.30-mL portion of a 0.245 N
solution of HOTf (0.81 mmol) in ether was slowly added to a
stirred solution of 0.12 g (0.43 mmol) of (tacn)RhMe3 in 90 mL
of CH2Cl2 in a -78 °C bath. After 5 min at -78 °C, the
solution was allowed to warm, and after 40 min at RT a
voluminous light-orange precipitate had formed. The super-
natant was decanted by cannula, and the precipitate was
washed with CH2Cl2 (3 × 20 mL) and dried under vacuum to
give a light orange solid (0.21 g, 91%). Anal. Calcd for
C9H18N3F6O6S2Rh: C, 19.82; H, 3.33; N, 7.71. Found: C,
19.95; H, 3.18; N, 7.73. NMR spectra were recorded in D2O
solvent, hence they are of [(ta cn )Rh Me(D2O)2](OTf)2 (4a -
d4). 1H NMR (D2O, 360 MHz): δ 1.54 (d, J RhH ) 2.1 Hz,
RhCH3), 2.67-3.49 (m, NCH2), 5.86 (br s, 1H, NH), 6.35 (br s,
(ta cn )Rh Et3 (1b). The procedure was the same as for
(tacn)RhMe3 using 0.38 g of (tacn)RhCl3‚H2O (1.1 mmol), 0.38
g of EtLi (8.4 mmol), and 40 mL of THF. After 45 min at RT
the THF was removed under vacuum and the residue was
extracted with pentane (4 × 40 mL) to remove excess EtLi.
Protonation was carried out in 40 mL THF with 2 mL of
MeOH. This residue was extracted with benzene (3 × 40 mL),
and a light-yellow solid (0.25 g 74%) was obtained. Slow
evaporation of a CH2Cl2 solution of the product gave single
crystals suitable for crystallography. 1H NMR (DMSO-d6, 360
MHz): δ 0.32 (dq, J RhH ) 2.8 Hz, J HH ) 8 Hz, RhCH2), 0.78 (t,
RhCH2CH3), 2.53-2.82 (m, NCH2), 3.19 (brs, NH). 1H NMR
(C6D6, 360 MHz): δ 1.15 (dq, RhCH2), 1.32 (t, RhCH2CH3),
1.42-1.56 (m, NCH2), 1.85 (br s, NH), 2.20-2.27 (m, NCH2).
1H NMR (THF-d8, 360 MHz): δ 0.48 (dq, RhCH2), 0.84 (t,
RhCH2CH3), 2.65 (brs, 6H, NCH2), 3.00 (br s, 9H, NCH2 and
NH). 13C{1H} NMR (DMSO-d6, 63 MHz): δ 9.20 (d, J RhC ) 36
Hz, RhCH2), 18.16 (RhCH2CH3), 47.09 (NCH2). Anal. Calcd
for C12H30N3Rh: C, 45.14; H, 9.47; N, 13.16. Found: C, 45.13;
H, 9.33; N, 12.83.
2H, NH). 13C{1H} NMR (D2O, 90 MHz): δ -3.64 (d, J RhC
)
24 Hz, RhCH3), 46.23, 51.47, 53.31 (3s, NCH2). The downfield
NH proton peak at δ 6.35 disappeared with an approximate
half-time of 24 h.
(ta cn )Rh Et(OTf)2 (3b). The procedure was the same as
for 3a , using 5.0 mL of a 0.245 N solution of HOTf (1.2 mmol)
in ether and 0.21 g (0.64 mmol) of (tacn)RhEt3 in 70 mL of
CH2Cl2. The precipitate was washed with CH2Cl2 (3 × 20 mL)
and dried under vacuum to yield a light orange solid (0.35 g,
88%). In DMSO-d6, both the 1H and 13C NMR spectra
correspond to a chiral molecule and so are assigned the
monosolvate structure [(tacn)RhEt(DMSO)(OTf)](OTf). 1H
NMR (DMSO-d6, 360 MHz): δ 1.13 (t, J HH ) 8 Hz, RhCH2CH3),
2.06-2.20 (m, RhCH2), 2.75-3.31 (m, NCH2), 5.68, 6.12, 6.90
(Li3ta cn )Rh Et3 (2b). The initial product from reaction of
(tacn)RhCl3‚H2O and EtLi in the preparation of 1b above was
extracted with pentane to remove excess EtLi. The residue
was then extracted with ether to separate 2b from insoluble
salts. The ether was removed and the product dried under
vacuum. 1H NMR (THF-d8, 360 MHz): δ -0.15 (dq, J RhH
2.2 Hz, J HH ) 7 Hz, RhCH2), 1.02 (t, RhCH2CH3), 2.58 (br s,
)
(3 br s, NH). 13C{1H} (DMSO-d6, 63 MHz): δ 15.22 (d, J RhC
)
NCH2). 13C{1H} NMR (THF-d8, 90 MHz): δ -1.50 (d, J RhC
)
21 Hz, RhCH2), 16.74 (RhCH2CH3), 42.70, 48.88, 49.40, 49.51,
51.44, 56.08 (5s, NCH2). Anal. Calcd for C10H20N3F6O6S2Rh:
C, 21.48; H, 3.60; N, 7.51. Found: C, 21.45; H, 2.91; N, 7.22.
FAB mass spectrum from H2O/glycerin volatilized [(tacn)-
Rh(Et)(OTf)]+: Calcd for [C9H20N3F3O3SRh]+, m/e 410.0233;
found, m/e 410.0229 (16%) (1 ppm). Also observed, m/e ) 382
(11%) [M+ - C2H4]. Dissolution in D2O afforded [(ta cn )Rh Et-
(D2O)2](OTf)2 (4b-d4). 1H NMR (D2O, 360 MHz): δ 1.08 (t,
J HH ) 8 Hz, RhCH2CH3), 2.61 (dq, J RhH ) 2.5 Hz, J HH ) 8 Hz,
RhCH2), 3.02-3.48 (m, NCH2), 5.65 (br s, 1H, NH), 5.90 (br s,
2H, NH). 13C{1H} NMR (D2O, 90 MHz): δ 12.52 (d, J RhC ) 23
Hz, RhCH2), 15.78 (RhCH2CH3), 45.89, 51.42, 53.10 (3s, NCH2).
The downfield NH proton peak at δ 5.90 disappeared with an
approximate half-time of 10 h.
29 Hz, RhCH2), 14.48 (RhCH2CH3), 59.65 (NCH2). Anal.
Calcd for C12H27N3Li3Rh: Li, 6.18. Found: Li, 5.69.
(ta cn )Rh P h 3 (1c). The procedure was the same as for
(tacn)RhMe3 using 0.30 g of (tacn)RhCl3‚H2O (0.84 mmol), 0.71
g of PhLi (8.4 mmol), and 50 mL of THF. After 45 min at RT
the THF was removed under vacuum and the residue was
extracted with pentane (4 × 40 mL) to remove excess PhLi,
and protonation was carried out in 30 mL THF with 2.5 mL
of MeOH. This residue was extracted with CH2Cl2 (2 × 50
mL), and a light yellow solid (0.31 g 80%) was obtained. Slow
evaporation of a CH2Cl2 solution of the product gave light
yellow crystals suitable for crystallography. 1H NMR (DMSO-
d6, 250 MHz): δ 2.44-2.52 (m, 6H, NCH2), 2.80-2.92 (m, 6H,
NCH2), 4.45 (br s, NH), 6.54-7.34 (m, RhC6H5). 13C{1H} NMR
(DMSO-d6, 90 MHz): δ 47.91 (NCH2), 118.50 (Ph), 124.58 (2C,
Ph), 139.99 (2C, Ph), 169.70 (d, J RhC ) 40 Hz, Ph). Anal. Calcd
for C24H30N3Rh: C, 62.20; H, 6.52; N, 9.07. Found: C, 62.88;
H, 6.29; N, 8.59. FAB mass spectrum from CH2Cl2-nitro-
benzyl alcohol-NaCl matrix volatilized [(tacn)RhPh3Na]+:
Calcd for [C24H30N3Rh]Na+, m/e 486.1392; found, m/e 486.1373
(1.7%) (4 ppm). Also observed, m/e ) 462 (3.5%) [M+ - H],
386 (4%) [M+ - C6H5], 309 (15%) [M+ - C12H10].
(ta cn )Rh P h (OTf)2 (3c). The procedure was the same as
for 3a , using 3.1 mL of a 0.201 N solution of HOTf (0.63 mmol)
in ether and 0.15 g (0.32 mmol) of (tacn)RhPh3 (1c) in 70 mL
of CH2Cl2. The precipitate was washed with CH2Cl2 (3 × 20
mL) and dried under vacuum to yield a light orange solid (0.18
g, 92%). Anal. Calcd for C14H20N3F6O6S2Rh: C, 27.69; H, 3.32;
N, 6.92. Found: C, 27.56; H, 3.17; N, 6.89. In DMSO-d6, both
1
the H and 13C NMR spectra correspond to a chiral molecule
and so are assigned the monosolvate structure [(tacn)RhPh-

440 Organometallics, Vol. 16, No. 3, 1997
Zhou et al.
(DMSO)(OTf)](OTf). 1H NMR (DMSO-d6, 360 MHz): δ 2.24-
3.54 (m, NCH2), 3.61, 6.72 (2 br s, NH), 7.10-7.63 (m, RhC6H5
+ 1NH). 13C{1H} NMR (DMSO-d6, 62 MHz): δ 44.62, 49.35,
50.11 (2C), 51.93, 55.66 (5 s, NCH2), 124.71 (Ph), 128.5 (2C,
Ph), 135.19 (2C, Ph), 148.83 (d, J RhC ) 29 Hz, ipso-C).
Dissolution in D2O afforded [(ta cn )Rh P h (D2O)2](OTf)2 (4c-
d4). 1H NMR (D2O, 360 MHz): δ 2.39-3.53 (m, NCH2), 6.04
(br s, 1H, NH), 6.26 (br s, 2H, NH), 7.25-7.50 (m, RhC6H5).
The downfield NH proton peak at δ 6.26 disappeared com-
pletely within 6 h.
[(ta cn )Rh Et(OTf)(P Me3)](OTf) (5b). PMe3 (68 µL, 0.65
mmol) was added to a stirred solution of (tacn)RhEt(OTf)2 (0.38
g, 0.62 mmol) in 40 mL of THF in a -78 °C bath. After 5
min, the mixture was allowed to warm to RT. After 20 min
the mixture became cloudy, and stirring was continued for an
additional 2 h. The solution was filtered, and the solvent was
evaporated under vacuum to yield a yellow solid (0.36 g, 90%).
In the NMR solvent DMSO-d6, 5b undergoes solvolysis to
[(tacn)RhEt(DMSO)(PMe3)](OTf)2 over the period of 2 h. 1H
NMR (DMSO-d6, 360 MHz, after 2 h): δ 1.06-1.10 (m, 5H,
RhCH2CH3), 1.53 (d, J PH ) 11 Hz, PCH3), 2.83-3.21 (m,
NCH2), 5.93, 6.01, 6.19 (3 br s, NH). 13C{1H} (DMSO-d6, 90
MHz): δ 10.40 (dd, J RhC ) 7 Hz, J PC ) 21 Hz, RhCH2), 13.52
(d, J PC ) 34 Hz, PCH3), 16.77 (RhCH2CH3), 46.55, 49.70, 51.25,
53.44, 54.75, 54.80 (6 s, NCH2). 31P{1H} (DMSO-d6, 145
Rh(H)Et(PMe3)](OTf) (6b, 18 mg, 0.034 mmol), NaBArF (29
4
mg, 0.033 mmol), and C6H5Cl (15 mL) was stirred at RT for 3
h. The solution was filtered, and the solvent was removed
under vacuum to yield white solid 8b (36 mg, 90%). 1H NMR
(DMSO-d6, 360 MHz): δ -18.07 (dd, J RhH ) 28 Hz, J PH ) 36
Hz, RhH), 0.78-0.93 (m, 5H, RhCH2CH3), 1.34 (d, J PH ) 9 Hz,
PCH3), 2.58-2.80 (m, NCH2), 4.76, 4.92, 5.54 (3 br s, NH). 13C-
{1H} NMR (DMSO-d6, 90 MHz): δ -0.29 (dd, J RhC ) 26 Hz,
J PC ) 11 Hz, RhCH2), 17.25 (d, J PC ) 32 Hz, PCH3), 19.64
(RhCH2CH3), 46.18, 47.18, 48.47, 48.98, 49.91, 50.06 (NCH2);
anion resonances as in 8a above. 31P{1H} (DMSO-d6, 145
MHz): δ 12.38 (d, J RhP ) 145 Hz). Anal. Calcd for C43H42
-
N3F24PBRh: C, 42.99; H, 3.52; N, 3.50. Found: C, 42.38; H,
3.16; N, 3.50. FAB mass spectrum: Calcd for [C11H30N3PRh]+,
m/e 338.1232; found, m/e 338.1232 (11%). Also observed, m/e
) 308 (36%) [M+ - C2H6].
[(ta cn )Rh (H)P h (P Me3)](OTf) (6c). Meth od A. [(tacn)-
Rh(H)Et(PMe3)]OTf (25 mg, 0.051 mmol) and 5 mL of C6H6
were sealed in a 9-mm, medium-walled glass tube, and the
sample was heated at 80 °C for 10 h. The tube was opened,
and the solution was filtered and the solvent evaporated under
vacuum to yield tan, solid 6c (24 mg, 87%). 1H NMR (DMSO-
d6, 360 MHz): δ -16.75 (dd, J PH ) 35 Hz, J RhH ) 28 Hz, RhH),
1.20 (d, J PH ) 10 Hz, PCH3), 2.67-3.10 (m, NCH2), 5.07, 5.51,
5.56 (3 br s, NH), 6.73-6.82 (m, 3H, C6H5), 7.34-7.36 (m, 2H,
C6H5). 13C{1H} (DMSO-d6, 90 MHz): δ 17.22 (d, J PC ) 34 Hz,
PCH3), 46.16, 48.13, 48.56, 49.12, 49.67, 50.22 (NCH2), 120.86
(Ph), 126.12 (2C, Ph), 128.31 (2C, Ph), 145.87 (d, J RhC ) 33
MHz): δ 6.08 (d, J RhP ) 121 Hz). Anal. Calcd for C13H29
-
N3F6O6S2PRh: C, 24.57; H, 4.60; N, 6.61. Found: C, 24.29;
H, 4.85; N, 6.54.
Hz, Ph). 31P{1H} (DMSO-d6, 145 MHz): δ 10.46 (d, J RhP
)
[(ta cn )Rh (H)Me(P Me3)]OTf (6a ). PMe3 (28 µL, 0.28
mmol) was added to a stirred solution of (tacn)RhMe(OTf)2
(0.15 g, 0.28 mmol) in 30 mL of THF in a -78 °C bath. After
10 min the mixture was allowed to warm to RT. After the
mixture was stirred for an additional 2.5 h, a small sample of
the [(tacn)Rh(OTf)Me(PMe3)](OTf) (5a ) was removed for mass
136 Hz). FAB mass spectrum: Calcd for [C15H30N3PRh]+, m/e
386.1232; found, 386.1227 (93%) (2 ppm). Also observed, m/e
) 308 (58%) [M+ - C6H6].
Meth od B. PMe3 (20 µL, 0.20 mmol) was added to a stirred
solution of (tacn)RhPh(OTf)2 (3c) (0.12 g, 0.20 mmol) in 30 mL
of THF at -78 °C. The mixture was stirred for 10 min and
then allowed to warm to RT. After being stirred for an
additional 2.5 h, the solution was transferred by cannula to a
Schlenk flask containing 15.0 mg of NaBH4 (0.40 mmol), and
this was stirred for 3 h. Some brown precipitate was removed
by filtration, and the solvent was removed under vacuum to
yield a brown solid. The solid was extracted with C6H6 (3 ×
40 mL), and solvent removal gave a tan solid (75 mg, 71%).
Spectra were as in method A above.
spectral analysis. FAB mass spectrum: Calcd for [C11H27
-
N3F3O3PSRh]+, m/e 472.0518; found, m/e 472.0491 (100%) (6
ppm). Also observed, m/e ) 457 (8%) [M+ - CH3] and 396
(78%) [M+ - PMe3]. The rest of the THF solution of 5a was
transferred by cannula to a Schlenk flask containing 15 mg of
NaBH4 (0.40 mmol) (or KBH4 could be used), and this was
stirred for 3 h. Some brown precipitate was removed by
filtration, and the solvent was evaporated under vacuum to
yield a tan solid (0.12 g), which was a 9:1 mixture of 6a and 7
(ca. 90% of the two) and some residual NaBH4. Spectra of the
cation of 6a in DMSO-d6 were identical to those of 8a given
below.
[(ta cn )Rh (H)2P Me3]X (7/9). THF (25 mL) was added to a
mixture of [(tacn)RhEt(PMe3)(OTf)](OTf) (5b, 0.10 g, 0.57
mmol) and KBH4 (10 mg, 0.19 mmol), and the mixture was
stirred at RT for 3 h. The solution was filtered, and the solvent
was removed under vacuum to give a mixture of crude brown
solid 7 and some 6b. This mixture was transferred to a 9-mm,
medium-walled glass tube which contained 5.0 mL of C6H6.
The tube was sealed under vacuum and heated at 80 °C for
10 h to convert the small amount of 6b all to 6c which is more
benzene soluble. The tube was opened, the supernatant was
decanted by cannula, and the precipitate was washed with
C6H6 (2 × 10 mL) and dried under vacuum to give tan, solid
[(tacn)Rh(H)2PMe3](OTf) (7, 55 mg, 76%). A mixture of
[(tacn )Rh (H)Me(P Me3)](BAr F4) (8a). A mixture of [(tacn)-
RhMe(H)(PMe3)](OTf) (80 mg, 0.17 mmol), NaBArF (13 mg,
4
0.15 mmol), and C6H5Cl (15 mL) was stirred at RT for 3 h.
The solution was filtered, and the solvent was removed under
vacuum to yield off-white, solid 8a (0.15 g, 75%). 1H NMR
(DMSO-d6, 360 MHz): δ -17.67 (dd, J RhH ) 27 Hz, J PH ) 36
Hz, RhH), -0.23 (dd, J PH ) 4.0 Hz, J RhH ) 2.3 Hz, RhCH3),
1.31 (d, J PH ) 10 Hz, PCH3), 2.51-3.20 (m, NCH2), 4.92, 5.12,
5.76 (3 br s, NH). 13C{1H} (DMSO-d6, 90 MHz): δ -14.34 (dd,
J RhC ) 27 Hz, J PC ) 12 Hz, RhCH3), 17.20 (d, J PC ) 33 Hz,
PCH3), 45.05, 46.82, 47.86, 48.74, 48.95, 49.37 (6 s, NCH2).
Anion (-BArF4) resonances: δ 117.67 (C4), 123.98 (q, J FC ) 273
Hz, CF3), 128.46 (q, J FC ) 30 Hz, C3), 134.04 (C2), 160.92 (1:
1:1:1 q, J BC ) 49 Hz, C1). 31P{1H} (DMSO-d6, 145 MHz): δ
12.85 (d, J RhP ) 139 Hz). FAB mass spectrum volatilized [M+
- H]: Calcd for [C10H27N3PRh]+, m/e 323.0998; found, 323.0996
(85%). Also observed, m/e ) 308 (27%) [M+ - CH4].
[(tacn)Rh(H)2PMe3](OTf) (55 mg, 0.12 mmol), NaBArF (101
4
mg, 0.11 mmol), and C6H5Cl (15 mL) was stirred at RT for 3
h. The solution was filtered and the solvent was removed
under vacuum to yield white, solid 9 (124 mg, 93%). 1H NMR
(DMSO-d6, 360 MHz): δ -17.38 (dd, J PH ) 35 Hz, J RhH ) 25
Hz, RhH), 1.34 (d, J PH ) 10 Hz, PCH3), 2.62-2.84 (m, NCH2),
5.34 (br s, 2H, NH), 6.12 (br s, 1H, NH), 7.60-7.70 (br s,
BArF4). 13C{1H} (DMSO-d6, 90 MHz): δ 20.78 (d, J PC ) 33
Hz, PCH3), 48.60, 48.74, 49.29 (NCH2); anion resonances as
in 8a . 31P{1H decoupled, RhH coupled} (DMSO-d6, 145
MHz): δ 10.81 (dt, J RhP ) 131 Hz, J HP ) 26 Hz). Anal. Calcd
for C41H38N3F24PBRh: C, 41.97; H, 3.26; N, 3.58. Found: C,
41.83; H, 3.03; N, 3.50.
[(ta cn )Rh (H)Et(P Me3)]OTf (6b). A mixture of THF (20
mL), [(tacn)RhEt(OTf)(PMe3)](OTf) (5b, 0.10 g, 0.15 mmol),
and NaBH4 (20 mg, 0.26 mmol) (or KBH4 could be used) was
stirred at RT for 3 h. The solution was filtered, and the solvent
was removed under vacuum. The solid residue was extracted
with benzene (5 × 40 mL), and the benzene was removed
under vacuum to yield tan, solid 6b (48 mg, 63%). Spectra of
the cation of 6b in DMSO-d6 were identical to those of 8b
below.
Cn Rh Et3. An ether solution of Et2Mg (30 mL of 0.48 N,
7.2 mmol) was slowly added to a mixture of CnRhCl3 (1.1 g,
2.6 mmol) and 60 mL THF at -78 °C. The cold bath was
removed, and the mixture was stirred at RT for 2 h. Then 5
[(ta cn )Rh (H)Et(P Me3)][BAr F4] (8b). A mixture of [(tacn)-

(1,4,7-triazacyclononane)Rh(hydrocarbyl)3 Compounds
Organometallics, Vol. 16, No. 3, 1997 441
Ta ble 3. Selected Cr ysta llogr a p h ic Da ta for 1b,c
mL of MeOH was added to the clear yellow-brown solution to
destroy excess Et2Mg. The solvents were removed under
vacuum, and the solid residue was extracted with ether (3 ×
30 mL). Evaporation of the ether gave a light yellow solid (0.35
g, 37%). 1H NMR (C6D6, 500 MHz): δ 1.22 (dq, J RhH ) 3.6
Hz, J HH ) 8 Hz, RhCH2), 1.50 (dt, J RhH ) 1.8 Hz, J HH ) 8 Hz,
RhCH2CH3), 1.56-1.63 (m, 6H, NCH2), 2.02-2.10 (m, 6H,
NCH2), 2.21 (s, NCH3). 13C{1H} NMR (C6D6, 125 MHz): δ 8.40
(d, J RhC ) 40 Hz, RhCH2), 16.27 (RhCH2CH3), 48.41 (NCH3),
57.14 (NCH2). DEI mass spectrum: Calcd for [C15H36N3Rh]+,
m/e 361.1964; found, m/e 361.1962 (1.3%) (1 ppm). Also
observed, m/e ) 302 (11%), [CnRh(C2H4)]+.
Cn Rh Et(OTf)2. A 1.6 mL portion of a 0.651 N HOTf
solution in ether (1.0 mmol) was slowly added to a stirred
solution of 0.20 g (0.55 mmol) of CnRhEt3 in 60 mL of CH2Cl2
at -78 °C. The mixture was allowed to warm and was stirred
at RT for 40 min. The precipitate was collected, washed with
CH2Cl2 (3 × 20 mL), and dried under vacuum to give light
orange, solid CnRhEt(OTf)2 (0.27 g, 84%). Anal. Calcd for
compd
(tacn)RhEt3 (1b) (tacn)RhPh3 (1c)‚
MeOH
empirical formula
color; habit
cryst size (mm)
cryst system
space group
a (Å)
C
12H30N3Rh
C25H34N3ORh
pale yellow, stable
colorless, stable
0.50 × 0.40 × 0.50 0.40 × 0.45 × 0.50
monoclinic
P21/n (No. 14)
8.244(2)
13.143(2)
13.462(2)
90.00
triclinic
P1h (No. 2)
8.041(2)
10.998(2)
13.723(2)
69.17(2)
81.02(2)
85.65(2)
1120.1(4)
2
b (Å)
c (Å)
R (deg)
â (deg)
98.28(2)
90.00
1443.4(5)
γ (deg)
V (Å3)
molecules per unit cell (Z) 4
fw
319.30
1.469
45.0
527.51
1.469
45.0
calcd density (g cm-3
2θ(max) (deg)
reflcns collcd
reflcns used
)
3374
3545
2291 [F > 4σ(F)] 2749 [F > 4σ(F)]
145
R(F) ) 0.0342
R(wF) ) 0.0374
C
13H26N3F6O6S2Rh: C, 25.96; H, 4.36; N, 6.99. Found: C,
no. of params refined
final agreement factors
290
25.79; H, 4.44; N, 6.82. FAB mass spectrum from H2O/glycerin
volatilized [CnRh(Et)(OTf)]+: Calcd for [C12H26N3F3O3SRh]+,
m/e 452.0702; found, m/e 452.0720 (22%) (4 ppm). Also
observed, m/e ) 424 (66%) [M+ - C2H4].
R(F) ) 0.0352
R(wF) ) 0.0402
0.710 73 Å), µ(Mo KR) ) 11.65 cm-1, F(000) ) 672) were
collected in the range 2.0 < 2θ < 45° on a Syntex P4
diffractometer by the ω-scan method. The 2291 independent
reflections (of 3374 measured) for which I > 4σ(I) were
corrected for Lorentz and polarization effects. The structure
was solved by Patterson methods and refined by least-squares
methods. Hydrogen atoms were included in calculated posi-
tions in a riding mode. Refinement converged at a final R )
3.42 (Rw ) 3.74) with allowance for the thermal anisotropy of
all non-hydrogen atoms. Selected distances and angles are
given in Table 1.
[Cn Rh (H)Et(P Me3)](OTf). PMe3 (26 µL, 0.25 mmol) was
added to a mixture of CnRhEt(OTf)2 (0.15 g, 0.25 mmol) and
30 mL of THF at -78 °C, and the mixture was allowed to warm
to RT. After the mixture was stirred for 15 min at RT, NaBH4
(10 mg, 0.26 mmol) was added to the clear yellow solution,
and the new mixture was stirred for 3 h. The solution was
filtered, and the solvent was removed under vacuum to yield
a tan solid (0.12 g, 82%). 1H NMR (THF-d8, 500 MHz): δ
-19.50 (dd, J RhH ) 30 Hz, J PH ) 38 Hz, RhH), 1.10-1.26 (m,
RhCH2), 1.49 (d, J RhP ) 9 Hz, PCH3), 2.69, 2.89, 2.97 (3s,
NCH3), 2.81-3.20 (m, NCH2). 13C{1H} NMR (THF-d8, 125
MHz): δ 12.50 (dd, J RhC ) 23 Hz, J PC ) 8 Hz, RhCH2), 18.60
(d, J PC ) 32 Hz, PCH3), 23.20 (RhCH2CH3), 51.68, 53.61, 54.63
(3s, NCH3), 58.06, 58.15, 59.56, 59.95, 61.10, 63.25 (6s, NCH2).
31P{1H} NMR (THF-d8): δ 0.61 (d, J RhP ) 153 Hz, PMe3).
[Cn Rh (H)Et(P Me3)](BAr F 4). A mixture of [CnRh(H)Et-
(PMe3)](OTf) (0.10 g, 0.19 mmol), NaBArF4 (0.15 g, 0.17 mmol),
and 25 mL of C6H5Cl was stirred at RT for 3 h. The solution
was filtered and the solvent was removed under vacuum to
yield a light brown solid (0.19 g, 90%). The NMR spectra were
identical to those reported for [CnRh(H)Et(PMe3)](OTf) above.
FAB mass spectrum: Calcd for [C14H36N3PRh]+, m/e 380.1702;
found, m/e 380.1710 (27%) (2 ppm). Also observed, m/e ) 350
(100%) [M+ - C2H6].
X-r a y Str u ctu r e Deter m in a tion of (ta cn )Rh P h 3‚CH3-
OH (1c‚CH3OH). Complex 1c was crystallized from CH2Cl2
as light yellow blocks, and a single crystal suitable for data
collection was mounted on a glass fiber in a random orienta-
tion. Selected crystallographic and refinement data are given
in Table 3. Complete data are given in the Supporting
Information. Three-dimensional, room-temperature X-ray
data (Mo KR radiation (λ ) 0.710 73 Å), µ(Mo KR) ) 7.84 cm-1
,
F(000) ) 516) were collected in the range 2.0 < 2θ < 45° on a
Syntex P4 diffractometer by the ω-scan method. The 2749
independent reflections (of 3545 measured) for which I >
4σ(I) were corrected for Lorentz and polarization effects. The
structure was solved by Patterson methods and refined by
least-squares methods. Methanol molecules were found par-
tially populated in two unique positions (four per unit cell).
Refinement of their populations resulted in a total content of
ca. one solvent molecule per rhodium. Hydrogen atoms were
included in calculated positions in riding mode. Refinement
converged at a final R ) 3.52 (Rw ) 4.02) with allowance for
the thermal anisotropy of all non-hydrogen atoms. Selected
interatomic distances and angles are given in Table 1.
Kin etics. A solution of the rhodium alkyl hydride salt,
typically ca. 5 mg (4 µmol) in C6D6 in a 5-mm NMR tube, was
freeze-pump-thaw degassed, and the tube was sealed. The
samples were heated in an oil bath at 80 °C, and the progress
of their reactions was followed by NMR at RT. Disappearance
of [(tacn)Rh(H)Me(PMe3)](BArF4) (8a ) was followed by moni-
toring the RhCH3 1H NMR peak relative to the BArF
-
4
resonances. The reaction exhibited clean, first-order kinetics
over 4 half-lives with a rate constant of 2.65((0.02) × 10-5
s-1 and R2 ) 0.999. The conversion of [(tacn)Rh(H)Et(PMe3)]-
(BAF4) (8b) to [(tacn)Rh(D)(C6D5)(PMe3)](BArF4) (8c-d6) was
followed by 31P NMR by monitoring the RhP(CH3)3 peaks of
the reactant and product. The reaction exhibited clean, first-
order kinetics over 4 half-lives with a rate constant of 1.60-
((0.03) × 10-4 s-1 and R2 ) 0.997.
Ack n ow led gm en t. This work was supported by the
National Science Foundation (Grant CHE 93-17570).
We thank Prof. Robert Bau for guidance in the X-ray
crystallographic work and Dr. Timothy La for experi-
mental assistance.
X-r a y Str u ctu r e Deter m in a tion of (ta cn )Rh Et3 (1b).
Complex 1b was crystallized from CH2Cl2 as colorless blocks,
and a single crystal suitable for data collection was mounted
on a glass fiber in a random orientation. Selected crystal-
lographic and refinement data are given in Table 3. Complete
data are given in the Supporting Information. Three-
dimensional, -100 °C X-ray data (Mo KR radiation (λ )
Su p p or tin g In for m a tion Ava ila ble: Complete crystal-
lographic data for 1b,c, including tables of X-ray parameters,
positional and thermal parameters, and bond distances and
angles (9 pages). Ordering information is given on any current
masthead page.
OM960623E