Interactions of Rh(III)-dihydrido-bis(phosphine) complexes with semicarbazones

Article abstract of DOI:10.1021/ic0489185

Interaction of cis,trans,cis-[Rh(H)₂(PR₃) ₂(acetone)₂]PF₆ complexes (R = aryl or R ₃ = Ph₂Me, Ph₂Et) under H₂ with E-semicarbazones gives the Rh(III)-dihydr

Full text of DOI:10.1021/ic0489185

Inorg. Chem. 2005, 44, 1482−1491
Interactions of Rh(III)
Semicarbazones
−Dihydrido−Bis(phosphine) Complexes with
Maria B. Ezhova,† Brian O. Patrick,† Kapila N. Sereviratne,† Brian R. James,*,† Francis J. Waller,‡ and
Michael E. Ford‡
Department of Chemistry, UniVersity of British Columbia,
VancouVer, British Columbia V6T 1Z1, Canada, and Air Products & Chemical Inc.,
Allentown, PennsylVania 18195-1501
Received August 6, 2004
Interaction of cis,trans,cis-[Rh(H)2(PR3)2(acetone)2]PF6 complexes (R
E-semicarbazones gives the Rh(III) dihydrido bis(phosphine) semicarbazone species cis,trans-[Rh(H)2(PR3)2-
(R′′)C N(H)CONH2 ]PF6, where R and R′′ are Ph, Et, or Me. The complexes are generally characterized
by elemental analysis, 31P 1H NMR, 1H NMR, and IR spectroscopies, and MS. X-ray analysis of three PPh3
) aryl or R3 ) Ph2Me, Ph2Et) under H2 with
−
−
−
{R
′
dNs
}
′
{
}
complexes reveals chelation of E-semicarbazones by the imine-N atom and the carbonyl-O atom. In contrast, the
corresponding reaction of [Rh(H)2(PPhMe2)2(acetone)2]PF6 with acetophenone semicarbazone gives the ortho-
metalated-semicarbazone species cis-[RhH(PPhMe2)2{o-C6H4(Me)CdN−N(H)CONH2}]PF6. The X-ray structure of
E-propiophenone semicarbazone is also reported. Rhodium-catalyzed, homogeneous hydrogenation of semicar-
bazones was not observed even at 40 atm H2.
Scheme 1. Formation of the Orthometalated Semicarbazone
Introduction
Complexesa
As part of our long term interest in catalyzed homogeneous
hydrogenation of imine derivatives, we recently reported on
the room temperature (∼20 °C), 1:1 reaction of cis-[Rh-
(PR3)2(solvent)2]PF6 complexes with E-semicarbazones
(R ) aryl or R3 ) Ph2Me; solvent ) acetone, MeOH).1 When
the semicarbazone contained a Ph group on the imine-C
atom, the product was the RhIII hydrido-orthometalated
species [RhH(PR3)2{o-C6H4(R′)sCdNsN(H)CONH2}]PF6
containing trans-PR3 ligands, where R′ is Me or Et (see I in
Scheme 1).1 The PPh3 complex with R′ ) Me was structur-
ally characterized, including location of the hydride, which
had not been reported previously for an orthometalated
semicarbazone complex. For a semicarbazone containing no
Ph group, the product was a RhI-(η2-semicarbazone) species,
exemplified by [Rh(PPh3)2{Et(Me)CdNsN(H)CONH2}]PF6
with the semicarbazone coordinated via the imine-N and
carbonyl-O atoms.1
a S ) solvent, R′ ) Me or Et.
ate cis,trans,cis (c,t,c)-[Rh(H)2(PR3)2(solvent)2]PF6, and the
subsequent removal of H2 to give cis-[Rh(PR3)2(solvent)2]-
PF6 species;2,3 these systems have been used to catalyze
hydrogenation of imines.4,5 The several modes of coordina-
tion of semicarbazones were also reviewed in one of our
publications,1 including the type shown as I in Scheme 1,
containing two fused, five-membered rings.
(2) Shapley, J. R.; Schrock, R. R.; Osborn, J. A. J. Am. Chem. Soc. 1969,
91, 2816.
(3) Marcazzan, P.; Ezhova, M. B.; Patrick, B. O.; James, B. R. C. R.
Chim. 2002, 5, 373 (J. A. Osborn issue).
Our publication1 included introductory material describing
the well-known chemistry of [Rh(COD)(PR3)2]PF6 to gener-
(4) (a) Blaser, H.-U.; Malan, C.; Pugin, B.; Spindler, F.; Steiner, H.; Studer,
M. AdV. Synth. Catal. 2003, 345, 103. (b) Kobayashi, S.; Ishitani, H.
Chem. ReV. 1999, 99, 1069. (c) James, B. R. Catal. Today 1997, 37,
209.
(5) (a) Marcazzan, P.; Patrick, B. O.; James, B. R. Organometallics 2003,
22, 1177. (b) Marcazzan, P.; Abu-Gnim, C.; Seneviratne, K. P.; James,
B. R. Inorg. Chem. 2004, 43, 4820.
* To whom correspondence should be addressed. E-mail: brj@
chem.ubc.ca. Fax: (604) 822-2847.
† University of British Columbia.
‡ Air Products & Chemical Inc.
(1) Ezhova, M. B.; Patrick, B. O.; James, B. R.; Waller, F. J.; Ford, M.
E. Russ. Chem. Bull., Int. Ed. 2003, 52, 2707.
1482 Inorganic Chemistry, Vol. 44, No. 5, 2005
10.1021/ic0489185 CCC: $30.25
© 2005 American Chemical Society
Published on Web 02/09/2005

Rh(III)-Dihydrido-Bis(phosphine) Complexes
δH -20.72 dt, JRhH ) 25.3, JPH ) 15.0); 2b (δP 44.82, d, JRhP
)
In studies aimed at the catalytic hydrogenation of semi-
carbazones, this current paper describes interaction of these
substituted imines with the dihydrides c,t,c-[Rh(H)2(PR3)2-
(acetone)2]PF6 under H2. The products depend on the nature
of R and are either (i) the Rh(III)-dihydrido-bis(phos-
phine)-η2-N,O-semicarbazone species such as cis,trans (c,t)-
[Rh(H)2(PR3)2{Ph(R′)CdN-N(H)CONH2}]PF6, where R )
Ph or R3 ) Ph2Me or Ph2Et, and R′ ) Me or Et; or (ii) the
orthometalated species [RhH(PR3)2{o-C6H4(Me)CdNsN(H)-
CONH2}]PF6 with cis-phosphines when R ) PhMe2. The
semicarbazones are all of E-geometry, as exemplified in
Scheme 1.
117; δH -20.79 dt, JRhH ) 25.0, JPH ) 15.0); 2c (δP 43.27, d,
JRhP ) 118; δH -20.93 dt, JRhH ) 25.5, JPH ) 15.3); 2d (δP 40.66,
d, JRhP ) 116; δH -20.98 dt, JRhH ) 26.6, JPH ) 15.5); 2e (δP
42.73, d, JRhP ) 119; δH -20.54 dt, JRhH ) 24.96, JPH ) 15.3); 2f
(δP 39.32, d, JRhP ) 116; δH -21.70 dt, JRhH ) 25.2, JPH ) 15.9);
2g (δP 24.09, d, JRhP ) 114; δH -21.31 dt, JRhH ) 27.0, JPH
16.8); 2h (δP 27.57, br d, JRhP ) 131; δH -17.45 m).
cis,trans-[Rh(H)2(PPh3)2{PhC(Me)dNsN(H)C(O)NH2}]PF6
(3a). [Rh(COD)(PPh3)2]PF6 (1a) (21.6 mg, 0.025 mmol) was reacted
with 1 atm H2 in acetone (0.6 mL) at room temperature for 2.5 h.
During this time, the solution color changed from orange to pale
yellow when 2a is formed. E-Acetophenone semicarbazone (4.34
mg, 0.025 mmol) was then added; after ∼15 min at room
temperature, 3a is fully formed. All volatile compounds (H2, solvent,
and cyclooctane) were removed under vacuum at room temperature,
and the residue was dissolved in CH2Cl2 (∼0.5 mL). Addition of
hexanes or Et2O (∼3 mL) precipitated an off-white solid, that was
collected and dried under vacuo overnight. Yield 19.0 mg (80%).
31P{1H}NMR: δ 41.74 (d, JRhP ) 119), -143.2 (septet, PF6-). 1H
)
Experimental Section
General. Reactions of the Rh systems were performed under
Ar using standard Schlenk and/or glovebox techniques. All non-
deuterated solvents (reagent grade) were dried over CaH2 or Na,
distilled under N2, stored over sodium/benzophenone ketyl in a
vacuum, and vacuum distilled directly into a reaction vessel.
Deuterated solvents were dried according to standard procedures6
and stored under Ar or under vacuum.
NMR spectra were recorded at room temperature in acetone-d6
(unless noted otherwise) on Bruker AC200 and Bruker AV300
spectrometers, with residual protons of deuterated solvents (1H,
relative to external SiMe4), and external P(OMe)3 (31P{1H}, δP )
141.00 vs 85% aq H3PO4) being used as references; J values are
given in Hz. IR spectra (KBr pellets) were recorded in cm-1 on an
ATI Mattson Genesis FT-IR spectrometer. Low resolution mass
spectral data were measured on a Kratos Concept IIHQ LSIMS
instrument (using thioglycerol or 3-nitro-benzyl alcohol as matrix),
and are given as m/z with relative % intensities. Microanalyses were
performed by Mr. P. Borda in this department.
Materials. Phosphines and RhCl3‚3H2O were purchased, re-
spectively, from Strem Chemicals and Colonial Metals, Inc. H2
(Praxair, Extra Dry) was purified by passage through an Englehard
“Deoxo” catalyst. Acetone-, acetophenone-, propiophenone-, and
butanone-semicarbazone were synthesized as the E-isomer by the
standard condensation reaction of the appropriate ketone with
semicarbazide in H2O/EtOH at room temperature.7 We reported
recently 1H and 13C NMR, IR, and MS data for the last three
mentioned semicarbazones,1 and presented here for reference
purposes are some spectroscopic data for acetone semicarbazone,
Me2CdNN(H)C(O)NH2. 1H NMR (δ, acetone-d6): 1.90 (s, CH3),
1.93 (s, CH3), 2.76 (s, NH2), 8.55 (s, NH). IR: 1686 (νCdO), 1580
(νCdN). MS: 115 ([M]+, 45%,), 100 ([M - 15]+, 20%), 72
([(Me)2CdNNH2]+, 100%), 57 ([(Me)2CdNH]+, 65%).
NMR: δ -20.48 (ddt, 1H, Rh-H, JHH ) 11.4, JPH ) 13.9, JRhH
19.2), -17.02 (ddt, 1H, Rh-H, JHH ) 11.4, JPH ) 16.3, JRhH
)
)
19.2), 1.94 (s, 3H, CH3), 2.84 (br s, 2H, NH2), 6.85 (d, 2H,
dCPho-H, JHH ) 8), 7.09 (pseudo-t, 2H, JHH ) 8, dCPhm-H), 7.3-
7.65 (m, 32H, arom + NH). MS: 889 (6%), 804 ([M - 2H -
PF6]+, 7%), 760 ([Rh(PPh3)2(PhC(Me)dNsNH)]+, 2%), 627 ([Rh-
(PPh3)2]+, 100%), 287 ([RhdPPh2]+, 45%). IR: 2187 (νRh-H), 2129
(νRh-H), 1671 (νCdO), 1542 (νCdN). Anal. Calcd for C45H43N3OF6P3-
Rh: C, 56.79; H, 4.55; N, 4.42. Found: C, 56.98; H, 4.61; N, 4.76.
Compound 3a is formed similarly from a mixture of 1a and the
semicarbazone under H2, while the reaction can also be carried out
in MeOH or CH2Cl2. Use of 2 or more equivs of the semicarbazone
gave the same product.
Analogous complexes (4, 5, and 6, respectively) were formed
with propiophenone-, acetone-, and butanone-semicarbazone
using the same precursor system (1a, 2a) and the above procedure
in acetone at room temperature.
cis,trans-[Rh(H)2(PPh3)2{PhC(Et)dNsN(H)C(O)NH2}] PF6
(4). Compound 1a (50.6 mg, 0.057 mmol) and propiophenone
semicarbazone (11.0 mg, 0.057 mmol) were used in this synthesis.
Yield 41.5 mg (75%). 31P{1H}NMR: δ 41.72 (d, JRhP ) 120),
1
-143.2 (septet, PF6-). H: δ -20.65 (ddt, 1H, Rh-H, JHH ) 11.7,
JPH ) 13.2, JRhH ) 19.2), -17.13 (ddt, 1H, Rh-H, JHH ) 11.7,
JPH ) 16.1, JRhH ) 18.6), 0.72 (t, 3H, JHH ) 7.7, CH3), 2.33 (q,
2H, JHH ) 7.7, CH2), 2.83 (br s, 2H, NH2), 6.65 (d, 2H, JHH ) 8.0,
dCPho-H), 7.15 (pseudo-t, 2H, JHH ) 8.0, dCPhm-H), 7.45-7.6
(m, 32H, arom + NH). MS: 820.1 ([M - PF6]+, 80%), 818
([M - 2H - PF6]+, 100%), 626.9 ([Rh(PPh3)2]+, 100%). IR: 2083
(νRh-H), 1656 (νCdO), 1536. (νCdN). Anal. Calcd for C46H45N3OF6-
P3Rh (4)‚0.1CH2Cl2: C, 56.82; H, 4.68: N, 4.32. Found: C, 56.83;
H, 4.54; N, 4.21.
The [Rh(COD)(PR3)2]PF6 complexes [R3 ) Ph3 (1a), Ph2(C6H4-
p-Me) (1b), (C6H4-p-Me)3 (1c), (C6H4-p-OMe)3 (1d), (C6H4-p-F)3
(1e); Ph2Et (1f), Ph2Me (1g), PhMe2 (1h)], isolated according to a
literature method,2 were reacted with H2 in acetone at room
temperature to form in situ the corresponding c,t,c-[Rh(H)2(PR3)2-
Complex 4 is not stable in acetone; over 24 h, increasing amounts
(up to ∼20%) of a new species (4a) are formed. 31P{1H}NMR: δ
1
(acetone)2]PF6 (2a-h) species.2,3 The 31P{1H} and high-field H
42.56 (d, JRhP ) 110); -143.2 (septet, PF6-). H NMR: δ -20.15
1
NMR data for isolated 1a-h, and for in situ 2a-h were: 1a (δP
27.03, d, JRhP ) 145); 1b (δP 26.69, d, JRhP ) 146); 1c (δP 24.43,
d, JRhP ) 145); 1d (δP 26.96, d, JRhP ) 146); 1e (δP 25.56, d,
(ddt, 1H, Rh-H, JHH ) 11.3, JPH ) 15.2, JRhH ) 20.6), -16.48
(ddt, 1H, Rh-H, JHH ) 11.3, JPH ) 15.2, JRhH ) 17.9), 0.3 (t, 3H,
JHH ) 7.6, CH3), 2.65 (q, 2H, JHH ) 7.6, CH2). It was difficult to
JRhP ) 147); 1f (δP 21.47, d, JRhP ) 143); 1g (δP 12.25, d, JRhP
)
1
assign the other H signals of 4a.
144); 1h (δP -2.41, d, JRhP ) 145). 2a (δP 45.43, d, JRhP ) 118;
cis,trans-[Rh(H)2(PPh3)2{Me2CdNsNHC(O)NH2}]PF6 (5).
Compound 1a (16.6 mg, 0.018 mmol) and acetone-semicarbazone
(2.17 mg, 0.018 mmol) were used. Yield 12.3 mg (78%). 31P{1H}
(6) Gordon, A. J.; Ford, R. A. The Chemist’s Companion; John Wiley &
Sons: New York, 1972; p 429.
(7) Doyle M. P.; Mungall, W. S. Experimental Organic Chemistry; John
Wiley & Sons: New York, 1980; p 268.
NMR: δ 44.06 (d, JRhP ) 117), -143.2 (septet, PF6-). H NMR:
1
δ -20.5 (ddt, 1H, Rh-H, JHH ) 11.6, JPH ) 15.2; JRhH ) 21.4),
Inorganic Chemistry, Vol. 44, No. 5, 2005 1483

Ezhova et al.
-17.05 (ddt, 1H, Rh-H, JHH ) 11.6, JPH ) 14.0, JRhH ) 17.6),
1.39 (s, 3H, CH3), 1.49 (s, 3H, CH3), 2.81 (br s, 2H, NH2), 7.43-
7.52 (m, 14H, arom + NH), 7.60-7.72 (m, 17H, arom). MS: 744
([M - PF6]+, 5%), 627 ([Rh(PPh3)2]+, 100%). IR: 2066 (νRh-H),
1671 (νCdO), 1543 (νCdN). Anal. Calcd for C40H41N3OF6P3Rh
(5)‚0.5CH2Cl2: C, 52.20; H, 4.55: N, 4.51. Found: C, 52.17; H,
4.62; N, 4.36.
cis,trans-[Rh(H)2(PPh3)2{Et(Me)CdN-NHC(O)NH2}]PF6 (6).
Compound 1a (18.4 mg, 0.021 mmol) and butanone-semicarba-
zone (2.7 mg, 0.021 mmol) were used. Yield 13.1 mg (70%).
31P{1H} NMR: δ 43.42 (d, JRhP ) 118), -143.2 (septet, PF6-).
1H NMR: δ -20.28 (ddt, 1H, Rh-H, JHH ) 11.3, JPH ) 15.0;
JRhH ) 21.0), -16.50 (ddt, 1H, Rh-H, JHH ) 11.4; JPH ) 15.0;
JRhH ) 17.3), 0.34 (t, 3H, CH3CH2, JHH ) 7.5), 1.49 (s, 3H,
CH3Cd), 2.13 (m, 2H, CH3CH2), 2.85 (br s, 2H, NH2), 7.4-7.55
(m, 19H, arom + NH), 7.55-7.7 (m, 12H, arom). MS: 758
([M - PF6]+, 18%), 627 ([Rh(PPh3)2]+, 65%), 307 (31%), 285
(16%), 154 (100%), 136 (64%). IR: 2047 (νRh-H), 1667 (νCdO),
1544 (νCdN). Anal. Calcd for C41H43N3OF6P3Rh (6)‚Me2CO: C,
54.95; H, 5.14; N, 4.37. Found: C, 54.87; H, 5.05; N, 4.52.
After ∼20 days in acetone, 6 is partially (∼40%) converted to
6a. 31P{1H} NMR: δ 43.57 (d, JRhP ) 118), -143.2 (septet, PF6-).
1H NMR: δ -20.48 (ddt seen as m, 1H, Rh-H), -16.55 (ddt seen
as m, 1H, Rh-H, overlapping with hydride of 6), 0.66 (t, 3H,
JRhH ) 19.5), 1.91 (s, 3H, CH3C), 2.83 (br s, 2H, NH2), 3.84 (s,
18H, OCH3), 6.95-7.05 (m, 12H, arom), 7.15 (pseudo-t, JHH
)
7.74, 2H, dCPhm-H), 7.25-7.55 (m, 16H, arom + NH). MS: 986.2
([M - PF6]+, 100%). A satisfactory elemental analysis could not
be obtained.
cis,trans-[Rh(H)2(P(C6H4-p-F)3)2{(Ph(Me)CdNsNHC(O)-
NH2}]PF6 (3e). Compound 1e (19.7 mg, 0.020 mmol) and the
semicarbazone (3.52 mg, 0.020 mmol) were used. Yield 15.5 mg
(73.5%). 31P{1H} NMR: δ 39.30 (d, JRhP ) 119), -143.2 (septet,
PF6-). H NMR: δ -20.36 (ddt, 1H, Rh-H, JHH ) 11.5, JPH
)
1
13.7, JRhH ) 19.4), -17.03 (ddt, 1H, Rh-H, JHH )11.5, JPH )16.1,
JRhH ) 18.9), 2.10 (s, 3H, CH3), 2.91 (br s, 2H, NH2), 6.92 (d, 2H,
JHH ) 8.0, dCPho-H), 7.17 (pseudo-t, 2H, JHH ) 8.0, dCPhm-H),
7.25-7.65 (m, 26H, arom + NH). MS: 912 ([M - PF6]+, 9%),
735 ([Rh(P(C6H4-p-F)3)2]+, 100%), 596 (25%), 323 (60%). IR:
2062 (νRh-H), 1669 (νCdO), 1588 (νCdN). Anal. Calcd for C45H36N3-
OF12P3Rh: C, 51.01; H, 3.52; N, 3.97. Found: C, 50.70; H, 3.60;
N, 4.08.
cis,trans-[Rh(H)2(PPh2Et)2{Ph(Me)CdNsNHC(O)NH2}]-
PF6 (3f). Compound 1f (20.0 mg, 0.025 mmol) and the semicar-
bazone (4.50 mg, 0.025 mmol) were used in this in situ synthesis.
31P{1H} NMR: δ 38.14 (d, JRhP ) 116), -143.2 (septet, PF6-).
1H NMR: δ -21.33 (ddt, 1H, Rh-H, JHH ) 11.9, JPH ) 15.2,
JRhH ) 20.9), -17.81 (ddt, 1H, Rh-H, JHH ) 11.9, JPH ) 15.5,
JRhH ) 20.0), 0.97 (pseudo-pentet, 6H, CH3CH2P, JHH ) 7.5,
JPH ) 9.1), 1.77 (s, 3H, CH3C)), 2.11 (m, 2H, CH3CH2P), 2.41
(m, 2H, CH3CH2P), 3.48 (br s, 2H, NH2), 7.04 (d, 2H, JHH ) 6.8,
dCPho-H), 7.25 (pseudo-t, 2H, JHH ) 6.9, dCPhm-H), 7.34-7.66
(m, 22H, arom + NH).
JHH ) 7.6, CH3CH2), 1.54 (s, 3H, CH3Cd), 1.71 (q, 2H, JHH
7.6, CH3CH2).
)
From the c,t,c-[Rh(H)2(PR3)2(acetone)2]+ precursors (2b-2g),
prepared analogously in situ in acetone, the dihydrido-acetophe-
none semicarbazone complexes were isolated (3b-e) or formed in
situ (3f, 3g). Reaction of 2h with acetophenone semicarbazone gave
the isolated hydrido-orthometalated complex 8.
cis,trans-[Rh(H)2(PPh2Me)2{PhC(Me)dNsNHC(O)NH2}]-
PF6 (3g). Compound 1g (10.0 mg, 0.013 mmol) and PhC-
(Me)dNsN(H)CONH2 (2.35 mg, 0.013 mmol) were placed in an
NMR tube equipped with a J-Young valve, and then ∼0.6 mL of
dry, degassed acetone-d6 was condensed into this tube. The resulting
solution was exposed to 1 atm of H2 at room temperature, and after
2 h ∼45% of 1g had reacted to form 3g: 31P{1H} NMR: δ 21.44
cis,trans-[Rh(H)2(PPh2C6H4-p-Me)2{Ph(Me)CdNsNHC(O)-
NH2}]PF6 (3b). Compound 1b (15.3 mg, 0.017 mmol) and
acetophenone-semicarbazone (3.00 mg, 0.017 mmol) were used
here. Yield 11.6 mg (70.5%). 31P{1H} NMR: δ 41.08 (d, JRh-P
)
120), -143.2 (septet, PF6-). H NMR: δ -20.5 (ddt, 1H, Rh-H,
JHH ) 11.7; JPH ) 13.2; JRhH ) 19.7), -17.05 (ddt, 1H, Rh-H,
JHH ) 11.7, JPH ) 15.6, JRhH ) 19.1), 1.90 (s, 3H, CH3Cd), 2.38
(s, 6H, p-CH3), 2.85 (br s, 2H, NH2), 6.88 (d, 2H, JHH ) 7.5,
dCPho-H), 7.09 (pseudo-t, 2H, JHH ) 8.0, dCPhm-H), 7.25-7.6
(m, 30H, arom + NH). MS: 931 (70%), 832 ([M - PF6 - 2H]+,
7.5%), 655 ([Rh(PPh2C6H4-p-Me)2]+, 100%). IR: 2064 (νRh-H),
1670 (νCdO), 1538 (νCdN). Anal. Calcd for C51H55N3OF6P3Rh: C,
57.62; H, 4.84; N, 4.29. Found: C, 57.40; H, 4.84; N, 4.50.
cis,trans-[Rh(H)2(P(C6H4-p-Me)3)2{Ph(Me)CdNsNHC(O)-
NH2}]PF6 (3c). Compound 1c (21.2 mg, 0.022 mmol) and the
semicarbazone (3.89 mg, 0.022 mmol) were used. Yield 16 mg
1
(d, JRhP ) 114), -143.2 (septet, PF6-). H NMR: δ -20.99 (ddt,
1
1H, Rh-H, JHH ) 11.9, JPH ) 17.3, JRhH ) 21.5), -17.81 (ddt, 1H,
Rh-H, JHH ) 11.9, JPH ) 16.1, JRhH ) 21.5), 1.91 (s, 3H, CH3C),
1.48 (br s, 6H, P-CH3), 7.1-7.5 (m, 26H, arom + NH).
After 2 days, 1g was no longer present, but most of 3g had
“decomposed” to a species with δP 33.82 (dd, JRhP ) 180, JPP
)
64) and 37.11 (dd, JRhP ) 193, JPP ) 64), considered to be [Rh-
1
(PPh2Me)2{PhC(Me)dNsN(H)CONH2}]PF6 (7). No hydride H
NMR signals were seen. An MS of this solution showed peaks at
680 ([M - PF6]+, 3%), 503 ([Rh(PPh2Me)2]+, 7%), and 154
(100%).
(70.2%). 31P{1H} NMR: δ 39.85 (d, JRhP ) 119), -143.2 (septet,
[Rh(H)(PPhMe2)2{o-C6H4C(Me)dNsNHC(O)NH2}]PF6 (8).
The procedure to generate 8 was identical to the one used for the
preparation of 3a, but with the reactants 1h (36.1 mg, 0.057 mmol)
and PhC(Me)dNNHC(O)NH2 (10.1 mg, 0.057 mmol). The product
solution was then treated with Et2O (∼1 mL), when an oily layer
became evident. The acetone/ether solution was decanted from the
oil and pumped to dryness. The residue was redissolved in a C6H6
(15 mL)/CH2Cl2 (2 mL) mixture, and the solution concentrated to
precipitate a light yellow solid. Yield 11.5 mg (28.7%). 31P{1H}
NMR (in situ): δ 20.94 (dd, JRhP ) 129.9, JPP ) 32), 21.10 (dd,
1
PF6-). H NMR: δ -20.59 (ddt, 1H, Rh-H, JHH ) 12.6, JPH
)
)
15.9, JRhH ) 19.7), -17.13 (ddt, 1H, Rh-H, JHH ) 12.6, JPH
16.0; JRhH ) 19.1), 1.48 (s, 3H, CH3Cd), 2.31 (s, 6H, p-CH3),
2.40 (s, 12H, p-CH3), 6.92 (d, 2H, JHH ) 7.5, dCPho-H), 7.12
(pseudo-t, 2H, JHH ) 7.7, dCPhm-H), 7.2-7.7 (m, 26H, arom +
NH). MS: 888 ([M - 2H - PF6]+, 10%), 711 ([Rh(P(C6H4-p-
Me)3)2]+, 100%). IR: 2092 (νRh-H), 1661 (νCdO), 1600 (νCdN). Anal.
Calcd for C51H55N3OF6P3Rh (3c)‚1.5H2O: C, 57.63; H, 5.50; N,
3.95. Found: C, 57.50; H, 5.25; N, 3.83.
JRhP ) 122, JPP ) 32), -143.2 (septet, PF6-). H NMR (in situ):
1
cis,trans-[Rh(H)2(P(C6H4-p-OMe)3)2{Ph(Me)CdNsNHC(O)-
NH2}]PF6 (3d). Compound 1d (18.7 mg, 0.018 mmol) and the
semicarbazone (3.13 mg, 0.018 mmol) were used. Yield 12.3 mg
δ -18.7 (ddd, 1H, Jtrans-PH ) 20.1, Jcis-PH ) 15.7, JRhH ) 32.2,
Rh-H), 1.16 (d, 3H, JPH ) 10.7, PCH3), 1.43 (d, 3H, JPH ) 10.7,
PCH3), 1.69 (d, 3H, JPH ) 11.7, PCH3), 1.81 (d, 3H, JPH ) 11.7,
PCH3), 2.60 (s, 3H, CH3C). MS: 655 (10%), 592 ([M - Me -
F6]+, 6%), 556 ([M - PF6]+, 15%), 379 ([Rh(PPhMe2)2]+ 100%).
(61.8%). 31P{1H} NMR: δ 37.57 (d, JRhP ) 119), -143.2 (septet,
PF6-). H NMR: δ -20.63 (ddt, 1H, Rh-H, JHH ) 10.5, JPH
)
1
16.1, JRhH ) 19.7), -17.2 (ddt, 1H, Rh-H, JHH ) 10.5, JPH ) 16.4,
1484 Inorganic Chemistry, Vol. 44, No. 5, 2005

Rh(III)-Dihydrido-Bis(phosphine) Complexes
Table 1. Crystallographic Data for Propiophenone Semicarbazone and the Complexes [Rh(H)2(PPh3)2(Ph(Me)CdN-NHC(O)NH2)]PF6 (3a),
[Rh(H)2(PPh3)2(Ph(Et)CdNsNHC(O)NH2)]PF6 (4), and [Rh(H)2(PPh3)2(Me2CdNsNHC(O)NH2)]PF6 (5)
propiophenone
semicarbazone
3aa
4‚2CH2Cl2
5‚Me2CO
formula
fw
C10H13N3O
191.23
C45H43N3OF6P3Rh
951.64
C48H49N3OF6 Cl4P3Rh
1135.56
0.35 × 0.20 × 0.10
triclinic
P1h (No. 2)
12.7688(6)
14.4322(8)
14.842(1)
97.986
104.637
98.751
2570.1(3)
2
C43H47N3O2F6P3Rh
947.68
cryst size (mm3)
cryst syst
space group
a, Å
0.50 × 0.20 × 0.10
orthorhombic
Pccn (No. 56)
17.885(2)
15.005(3)
7.4444(8)
90.00
90.00
90.00
1998(1)
8
1.271
0.40 × 0.20 × 0.20
0.25 × 0.15 × 0.15
triclinic
triclinic
P1h (No. 2)
12.9890(3)
14.1950(5)
14.732(1)
67.437(2)
77.667(2)
70.973(3)
2359.1(2)
2
P1h (No. 2)
12.6183(9)
12.7951(5)
14.244(1)
79.465(2)
73.471(2)
83.606(3)
2163.3(2)
2
b, Å
c, Å
R (deg)
â (deg)
γ (deg)
V, Å3
Z
D
calc (g cm-3
)
1.340
5.23
0.052
1.467
6.93
0.044
1.455
µ (cm-1
)
0.86
0.050
Rint
0.044
total reflns
18044
20165
23670
19061
unique reflns
no. variables
2774
139
0.065; 0.091
0.034; 0.042
17.70
8987
554
0.066; 0.124
0.046; 0.117
16.22
11351
651
0.067; 0.109
0.039; 0.048
17.44
9042
543
0.056; 0.089
0.032; 0.041
16.65
R, Rw (F2, all data)
R, Rw (F, I > nσ(I))b
refln/param ratio
GOF
1.04
1.06
1.26
1.13
a An unresolved molecule of CH2Cl2 that was not modeled was also present in the lattice. b n ) 2 for 3a, and 3 for the other structures.
Anal. Calcd for C25H33N3OP3F6Rh (8)‚0.6C6H6: C, 45.91; H, 4.93;
N, 5.62. Found: C, 45.84; H, 5.61; N, 5.29.
The non-H atoms were refined anisotropically, while the H atoms
attached to the Rh and the N atoms were refined isotropically, and
the other H atoms were included in fixed positions. All calculations
were performed using the teXsan crystallographic software pack-
age.11 One region in the asymmetric unit cell of 3a contained large
residual electron density peaks consistent with a CH2Cl2 molecule.
Subsequent refinements (as CH2Cl2), however, proved to be
unsatisfactory, as this region appears to be only partially occupied,
the solvent molecule being significantly disordered. As a result,
the SQUEEZE function12 found in PLATON13 was employed. The
atoms of the disordered solvent molecule were removed, and a
refinement was carried out, resulting in large, unassigned residual
peaks in the void space. SQUEEZE then identifies any void spaces
in the unit cell, uses the original data to find unassigned electron
density peaks in these spaces, and then produces a new, “corrected”
data set that eliminates this residual electron density from the spaces,
leaving the remainder of the structure unchanged, but containing a
void space (i.e., no atoms or residual electron density). This new
data set is used in subsequent refinements. SQUEEZE calculated
electron density equivalent to 27 electrons (or slightly more than
one-half of a CH2Cl2 molecule) in a void space of 338 Å3. The
refinement improved from R1 ) 0.065 with the partially modeled
CH2Cl2 molecule (and from R1 ) 0.096 with no solvent modeled)
to 0.046.
Attempted Hydrogenation of Acetophenone-Semicarbazone.
Hydrogenation of the semicarbazone (∼ 0.1 M) was attempted using
a solution of [Rh(COD)(PPh3)2]PF6 (∼10-3 M) at room temperature
under 1-40 atm H2, the Rh precursor having been pretreated with
1 atm H2 prior to addition of the semicarbazone to form c,t,c- [Rh-
(H)2(PR3)2(solvent)2]PF6 (in acetone and MeOH) or [(Ph3P)Rh(µ-
PhPPh2)]2[PF6]2 in CH2Cl2.2,3 The experiments at ambient conditions
and at high pressure were carried out with stirring in a Schlenk
tube, and a small-scale Parr autoclave, respectively. After 24 h,
the volatile fraction (distilled under vacuum) of the product mixture,
and the residue (after dissolution in DMSO-d6), were analyzed by
GC (on a Hewlett-Packard instrument; HP-17 (25 m), T1 ) 80 °C,
1
t1 ) 3 min, R ) 20 °C/min, T2 ) 220 °C, t2 ) 15 min) and H
NMR; no hydrogenation products (from CdN or CdO reduction)
or hydrogenolysis products (e.g., Ph(Me)CHNH2) were detected,
and most of the semicarbazone was recovered.
X-ray Crystallographic Analysis. Colorless, prism crystals of
cis,trans-[Rh(H)2(PPh3)2PhC(Me)dN-N(H)C(O)NH2}]PF6 (3a),
cis,trans-[Rh(H)2(PPh3)2{PhCs(Et)dNsN(H)C(O)NH2}] PF6 (4),
and cis,trans-[Rh(H)2(PPh3)2{Me2CdNsNHC(O)NH2}]PF6 (5)
were grown by slow evaporation of solutions of the complexes in
1:1 hexane/CH2Cl2 (3a, 4) or 1:1 hexane/acetone (5); a crystal of
propiophenone-semicarbazone was grown from an EtOH solution.
Measurements on the crystals were made at 173(1) K (for 3a, 5)
or 198(1) K (for 4 and the semicarbazone) on a Rigaku/ADSC CCD
with graphite monochromated Mo KR radiation (0.71069 Å). Some
crystallographic data and principle parameters from the refinement
of the crystals are given in Table 1. The final unit cell parameters
were based on 11 063 reflections for 3a, 13 307 reflections for 4,
11 509 reflections for 5, and 9066 reflections for the semicarbazone,
with 2θ in the general range 4.1-60.1°. The data were collected
and processed using the d*TREK program,8 and the structure was
solved by direct methods9 and expanded using Fourier techniques.10
Complex 4 crystallized with 2 CH2Cl2 molecules per asymmetric
unit, one having chlorine atoms disordered over two sites with
relative populations refined to 0.90 and 0.10; the semicarbazone
(9) Altomare, A.; Burla, M. C.; Cammalli, G.; Cascarano, M.; Giacovazzo,
C.; Guagliardi, A.; Moliterni, A. G. G.; Poidori, G.; Spagna, A. J.
Appl. Crystallogr. 1999, 32, 115.
(10) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.; de
Gelder, R.; Israel, R.; Smits J. M. M. The DIRDIF-94 Program System;
Technical Report of the Crystallography Laboratory; University of
Nijmegen: The Netherlands, 1994.
(11) teXsan: Crystal Structure Analysis Package; Molecular Structure
Corporation; The Woodlands, TX, 1985 and 1992.
(12) SQUEEZE: Sluis, P. v.d.; Spek, A. L. Acta Crystallogr. 1990, A46,
194.
(8) d*TREK: Area Detector Software, version 4.13; Molecular Structure
Corporation, The Woodlands, TX, 1996-1998.
(13) Spek, A. L. PLATON: A Multipurpose Crystallographic Tool; Utrecht
University: Utrecht, The Netherlands, 1998.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1485

Ezhova et al.
ethyl group of 4 was also disordered, the two fragments being
distributed equally over two sites.
Results and Discussion
The [Rh(COD)(PR3)2]PF6 (1a-h) and c,t,c-[Rh(H)2-
(PR3)2(acetone)2]PF6 (2a-h) Complexes. Although the
reactivity of [Rh(COD)(PPh3)2]PF6 with H2 to give c,t,c-[Rh-
(H)2(PPh3)2(solvent)2]PF6 has been thoroughly investigated,2,3
listed in the Experimental Section are some in situ 31P{1H}
1
and the high-field H NMR data for analogous systems
containing other phosphine ligands; data are given for the
bis(acetone) species with R3 ) Ph3 (2a), Ph2(C6H4-p-Me)
(2b), (C6H4-p-Me)3 (2c), (C6H4-p-OMe)3 (2d), (C6H4-p-F)3
(2e), Ph2Et (2f), Ph2Me (2g), and PhMe2 (2h). For 2a-e,
the δP doublets appear between 46 and 40 ppm, while species
with the more basic phosphines, PPh2Me (2g) and PPhMe2
(2h), not unreasonably show a more upfield shift (at δP 24
and 27, respectively); a similar trend is seen for 1a-f vs 1g
and 1h, and is also evident within the corresponding cis-
[Rh(PR3)2(solvent)2]+ species.1 (The data for 2f and 1f,
containing Ph2Et, surprisingly are closer to, but are at the
higher field end of, those of the tris(arylphosphine) systems.)
As expected, the JRhP values for the trans-phosphine species
2 (114-131 Hz) are always less than for the corresponding
cis-phosphine species 1 (143-145 Hz).1,3,5,14
Figure 1. ORTEP diagram of the cis,trans-[Rh(H)2(PPh3)2{PhC-
(Me)dNsN(H)C(O)NH2}]+ cation of 3a, with 50% probability thermal
ellipsoids.
Qualitatively, the rate of reaction of 1 with H2 at room
temperature to fully form 2 decreases when an electron-
withdrawing p-fluorine is substituted into PPh3 (t1/2 ∼3 h vs
∼0.5 h), this being consistent with a rate-determining
oxidative addition of H2 to 1 or to the presumed intermediate
[Rh(PR3)2(acetone)2]+ species. However, in apparent con-
tradiction, the presence of a more basic phosphine, such as
PPh2Me (vs PPh3) also decreases the rate of formation of 2
(t1/2 ∼1 h), and this is thought to be due to an increase in
the rate of loss of H2 from the dihydride, as 2g decomposes
(on removing the H2 atmosphere) to [Rh(PPh2Me)2(acetone)2]-
PF6 relatively rapidly (t1/2 ∼1 h) compared to the 2a-e
systems. Correspondingly, reaction of the most basic PPhMe2
species (1h) with H2 is the slowest (t1/2 ∼10 h), and the 2h
product now exhibits a broadened doublet (δP 27.6), implying
again perhaps a faster “off-rate”; indeed, 2h loses H2 more
rapidly (t1/2 ∼0.5 h) than does 2g. Quantitative kinetic data
are required for a more detailed understanding of the overall
reaction of 1 to generate 2, where steric effects appear to
play a role.
Dihydrido-Bis(phosphine)-Semicarbazone Rh(III)
Complexes: cis,trans-[Rh(H)2(PR3)2(η2-N,O-semicarba-
zone)]PF6 (3a-g, 4-6). The in-situ 2a species reacts in a
few minutes with E-acetophenone-semicarbazone in acetone
at room temperature to form in high yield the dihydrido-
semicarbazone complex 3a, which is air-stable in solution
or in the solid state even in the absence of H2; the reaction
is simple replacement of the acetone by the chelating
semicarbazone still in the E-configuration, and the species
has trans-PPh3 ligands and cis-hydrides (Scheme 2).
An ORTEP for the cation of 3a is shown in Figure 1, and
selected bond distances and angles are given in Table 2. The
Scheme 2. Formation of the Dihydrido-Semicarbazone Complexes
3a (R ) Ph, R′ ) Ph, R′′ ) Me), 3b (R3 ) Ph2C6H4-p-Me, R′ ) Ph,
R′′ ) Me), 3c (R ) C6H4-p-Me, R′ ) Ph, R′′ ) Me), 3d (R )
C6H4-p-OMe, R′ ) Ph, R′′ ) Me), 3e (R ) C6H4-p-F, R′ ) Ph, R′′ )
Me), 3f (R3 ) Ph2Et, R′ ) Ph, R′′ ) Me), 3g (R3 ) Ph2Me, R′ ) Ph,
R′′ ) Me), 4 (R ) Ph, R′ ) Ph, R′′ ) Et), 5 (R ) Ph, R′ ) R′′ ) Me),
6 (R ) Ph, R′ ) Et, R′′ ) Me)
η2-N,O-coordination mode of a semicarbazone is very
common,15 but we are unaware of any other metal dihy-
drido-semicarbazone complexes, although a monohydridic
[OsH(CO)(PPh3)2(η2-N,O-semicarbazone derivative)]+ has
been structurally characterized.16a More common are η3-
C,N,O-semicarbazone-type species containing two fused
metallocycle rings, formed via (i) orthometalation of a Ph
substituent on the imine C atom (see Scheme 1),1,16b,c,17 or
(ii) donation from an ortho-N- or O-donor substituent on
this Ph group.18 The closest analogues of 3a-g, 4-6 are
the cis,trans-[Rh(H)2(PR3)2(N-N)]+ complexes, also con-
taining a five-membered metallocycle, where N-N is a
chelated, unsaturated (imine type) N-donor.19
(15) A search of the Chemical Abstracts database revealed that metal-
semicarbazone complexes (with ligand/metal ratios ) 1-3) are known
with ∼40 elements of the periodic table.
(16) (a) Gupta, P.; Basuli, F.; Peng, S.-M.; Lee, G.-H.; Bhattacharya, S.
Inorg. Chem. 2003, 42, 2069. (b) Basuli, F.; Peng, S.-M.; Bhattacharya,
S. Inorg. Chem. 2001, 40, 1126. (c) Pal, I.; Dutta, S.; Basuli, F.;
Goverdhan, S.; Peng, S.-M.; Lee, G.-H.; Bhattacharya, S. Inorg. Chem.
2003, 42, 4338.
(17) Ferna´ndez, A.; Lo´pez-Torres, M.; Sua´rez, A.; Ortigueira, J. M.; Pereira,
T.; Ferna´ndez, J. J.; Vila, J. M.; Adams, H. J. Organomet. Chem.
2000, 598, 1.
(14) Winter, W. J. Organomet. Chem. 1975, 92, 97.
1486 Inorganic Chemistry, Vol. 44, No. 5, 2005

Rh(III)-Dihydrido-Bis(phosphine) Complexes
Table 2. Selected Bond Distances (Å) and Angles (deg) for Propiophenone Semicarbazone and the Cations of Complexes 3a, 4, and 5 with Estimated
Standard Deviations in Parentheses
propiophenone
semicarbazonea
3a
4a
5
N1-C7
1.289(1)
1.234(1)
1.511(1)
1.481(2)
1.372(1)
1.337(1)
1.374(1)
N2-C38
O1-C37
C38-C39
C38-C40
N1-C37
N3-C37
N1-N2
Rh-P1
1.295(5)
1.255(5)
1.506(6)
1.483(6)
1.353(5)
1.327(5)
1.383(4)
2.3081(10)
2.3046(10)
1.50(4)
N3-C38
O1-C37
C38-C45A
C38-C39
N2-C37
N1-C37
N2-N3
Rh-P1
1.274(4)
1.246(3)
1.49(1)
1.488(5)
1.363(4)
1.326(4)
1.398(4)
2.3005(7)
2.3031(7)
1.52(3)
N1-C38
O1-C37
C38-C39
C38-C40
N2-C37
N3-C37
N1-N2
Rh-P1
1.283(3)
1.253(3)
1.491(4)
1.493(4)
1.353(3)
1.329(3)
1.400(3)
2.3131(7)
2.2982(7)
1.51(2)
O1-C10
C7-C8
C1-C7
N2-C10
N3-C10
N1-N2
Rh-P2
Rh-P2
Rh-P2
Rh-H51
Rh-H52
Rh-O1
Rh-H1
Rh-H1
Rh-H2
Rh-O1
Rh-N1
1.56(4)
2.233(2)
2.226(3)
Rh-H2
1.48(4)
2.226(2)
2.188(2)
1.49(3)
2.207(2)
2.187(2)
Rh-O1
Rh-N2
Rh-N3
N2-N1-C7
N1-N2-C10
C1-C7-C8
O1-C10-N2
N2-C10-N3
119.03(9)
118.08(9)
119.96(9)
120.53(9)
116.1(1)
N1-N2-C38
N2-N1-C37
116.6(3)
120.1(3)
119.3(4)
121.3(4)
116.4(4)
169.12(4)
89.89(7)
97.80(8)
74.61(10)
105.9(16)
83.1(16)
86.1(16)
87.2(16)
88.9(16)
76(2)
N2-N3-C38
N3-N2-C37
117.6(3)
118.5(3)
109.2(5)
121.4(3)
116.7(3)
163.30(3)
96.19(5)
97.26(7)
75.14(8)
101(1)
83(1)
82(1)
83(1)
89(1)
84(2)
176(1)
175(1)
N2-N1-C38
N1-N2-C37
116.0(2)
118.8(2)
117.2(2)
121.4(2)
116.2(2)
168.02(2)
93.41(5)
93.29(6)
75.41(7)
103(1)
88(1)
84(1)
84(1)
87(1)
80(1)
179(1)
176(1)
C39-C38-C40
O1-C37-N1
N1-C37-N3
P1-Rh-P2
C39-C38-C45A
O1-C37-N2
N1-C37-N2
P1-Rh-P2
P1-Rh-O1
P1-Rh-N3
O1-Rh-N3
N3-Rh-H2
P1-Rh-H1
P2-Rh-H1
P1-Rh-H2
P2-Rh-H2
H1-Rh-H2
O1-Rh-H2
N3-Rh-H1
C39-C38-C40
O1-C37-N2
N2-C37-N3
P1-Rh-P2
P1-Rh-O1
P1-Rh-N1
O1-Rh-N1
N1-Rh-H1
P2-Rh-H2
P1-Rh-H2
P2-Rh-H1
P1-Rh-H1
H1-Rh-H2
O1-Rh-H1
N1-Rh-H2
P1-Rh-O1
P1-Rh-N2
O1-Rh-N2
N2-Rh-H52
P2-Rh-H51
P1-Rh-H51
P2-Rh-H52
P2-Rh-H52
H51-Rh-H52
O1-Rh-H52
N2-Rh-H51
178.7(15)
175.6(16)
a The atom labelings for the semicarbazone and for 4 correspond to equivalent atoms.
Figure 2. Diagrams showing RhH‚‚‚HC interactions in the cations of 3a, 4, and 5; sections of the phenyl groups have been omitted for clarity.
In the distorted octahedral structure of 3a, the trans-PPh3
ligands lean towards the hydrides as indicated by the
P-Rh-P angles (169.12°) and the P-Rh-H angles (83.1-
88.9°); intramolecular RhH‚‚‚HC interactions between the
hydride and some Ph ring protons may play a role (Figure
2). Two trifurcated arrangements of the type (sp2)CH‚‚‚HRh‚‚‚
HRh between Ph ring protons of different phosphines and
the metal-hydrides are present (Table 3). These interactions
(19) (a) Iglesias, M.; Del Pino, C.; Garcio-Blanco, S.; Carrera, S. M. J.
Organomet. Chem. 1986, 317, 363. (b) Iglesias, M.; Del Pino, C.;
Nieto, J. L.; Blanco, S. G.; Carrera, S. M. Inorg. Chim. Acta 1988,
145, 91. (c) Paneque, M.; Sirol, S.; Trujillo, M.; Carmona, E.;
Gutiwrrez-Puebla, E.; Moge, M. A.; Ruiz, C.; Malbosc, F.; Serra-Le
Berre, C.; Kalck, P.; Etienne, M.; Daran, J. C. Chem.sEur. J. 2001,
7, 3868. (d) Yu, X.-Y.; Maekawa, M.; Morita, T.; Chang, H.-C.;
Kitagawa, S.; Jin, G.-X. Polyhedron 2002, 21, 1613. (e) Ghedini, M.;
Neve, F.; Lanfredi, A. M. M.; Ugozzoli, F. Inorg. Chim. Acta 1988,
147, 243.
(18) (a) Carcelli, M.; Fochi, A.; Pelagatti, P.; Pelizzi, G.; Russo, U. J.
Organomet. Chem. 2001, 626, 161. (b) Kasuga, N. C.; Sekino, K.;
Koumo, C.; Shimada, N.; Ishikawa, M.; Nomiya, K. J. Inorg. Biochem.
2001, 84, 55. (c) Poleti, D.; Karanovic, L.; Leovic, V. M.; Jevtovic,
V. S. Acta Crystallogr. 2003, C59, m73.
Inorganic Chemistry, Vol. 44, No. 5, 2005 1487

Ezhova et al.
a
Scheme 3. Decomposition of 3g via Loss of H2
Table 3. Calculated RhH···HC Distances (Å)
Ha‚‚‚Hb Ha‚‚‚Hc Ha‚‚‚Hd Hb‚‚‚Hc′ Hb‚‚‚Hd′ Hb‚‚‚He
3a
4
5
1.89(5)
2.01(5)
1.92(4)
2.04
2.27
1.98
1.96
2.14
2.32
2.19
2.25
2.37
2.20
(from 1.89 to 2.32 Å) vary from strong to weak considering
the van der Waals distance between two H atoms is 2.40
Å,20,21 and are similar to interactions (H‚‚‚H ) 2.00-2.20
Å) found in a related orthometalated RhIII-azobenzene
system,20 but are stronger than those found in the hydrido-
orthometalated acetophenone-semicarbazone complex I
shown in Scheme 1.1
a rt ) room temperature.
semicarbazone, seen as a doublet and pseudo-triplet, respec-
tively, are shifted 0.5-0.6 ppm upfield in comparison to
those of the free semicarbazone,1 while signals for the Me
and NH2 protons are shifted <0.1 ppm downfield. The
assignment of the NH proton signal (for example, seen at δ
9.45 in free acetophenone semicarbazone,1 and δ 8.55 in
acetone semicarbazone) is difficult, as it appears to overlap
in the δ 7.30-7.65 region the aromatic signals of the PPh3
ligands, and that of the p-proton of the semicarbazone-Ph;
the δNH signal is included with those of these aromatic
protons (see Experimental Section), although it is impossible
to quantify the integration for 1 NH proton in the presence
of the 31 aromatic protons (30 from the two PPh3 ligands
plus the p-H of the semicarbazone-Ph). The problem of
locating δNH was encountered with all the semicarbazone
complexes.
The chelated semicarbazone within the five-membered ring
and the hydrides are essentially coplanar. The hydrides are
trans to the imine-N and O-atoms, with N-Rh-H and
O-Rh-H angles of 175.6° and 178.7°, respectively. The
N-Rh-O angle (74.61°) is close to those found in the η2-
N,O-acetophenone-semicarbazone of the cationic hydrido-
bis(phosphine) Os(II) species(74.52°),16a a cationic chloro-
bis(phosphine) Ru(II) species (76.43°),16b and the orthometa-
lated hydrido-bisphosphine-hydrido-Rh species I (Scheme
1) (73.6°).1 The H-Rh-H angle (76°) is smaller than the
corresponding angle in the cis,trans-[Rh(H)2(PR3)2(N-N)]+
complexes (89.1-90.5°),19a,b and is, in fact, closer to the
angle of other cis,trans-[Rh(H)2(PR3)2(N)2]+ species where
N is a monodentate, unsaturated N-donor.19c,d The Rh-H
bond length (1.50 Å) is in the expected range,1,19a,b,d,e and
the Rh-P bond distances are similar to those in other
complexes containing trans-PPh3 ligands.1,16c,20 The Rh-O
bond (2.233 Å) is somewhat shorter, and the Rh-N bond
(2.226 Å) somewhat longer, than those reported for I (2.310
and 2.065 Å, respectively).1 The other bond lengths and
angles within the coordinated semicarbazone agree well with
corresponding values for other metal-acetophenone-semi-
carbazones complexes.16-18 The crystallographic data given
for the free propiophenone-semicarbazone, and the chelated
form in complex 4 (see below) (Table 2), imply that the
geometry of a semicarbazone changes remarkably little upon
coordination.
Dihydrido-bis(phosphine)-acetophenone semicarbazone
complexes, 3b-e, analogous to 3a but having a p-substituent
in a phosphine-aryl ring were similarly isolated (Scheme 2),
while complexes containing an alkyl substituted phosphine,
3f and 3g, were made in situ in acetone. Their spectroscopic
data, especially the two high-field ddt 1H signals in the ranges
δH -20.3 ( 0.7 and -17.5 ( 0.3 for the hydrides, imply
the same type structure as 3a. Similarly, the 31P{1H} data
for 3b-g show doublets at δP 21-41, with JRhP values of
114-120 Hz, and there is a trend of the δP values with
phosphine basicity similar to that noted for 1a-g and 2a-
g. Again, the isolated and in situ complexes are air-stable,
although the in situ 3g decomposes very slowly and
irreversibly at room temperature with loss of H2 to the
Rh(I)-semicarbazone complex [Rh(PPh2Me)2{PhC(Me)d
NsN(H)CONH2}]PF6 (7, Scheme 3), as evidenced by the
The solid-state IR spectrum of 3a shows νRh-H,
CdN bands in the appropriate regions, and the mass spectrum
νCdO, and
ν
1
absence of H NMR hydride signals, and the ABX pattern
gives a signal for the molecular cation minus two hydrogens.
in 31P{1H} spectrum; we have recently isolated an analogous
butanone-semicarbazone complex, [Rh(PPh3)2{EtC(Me)dN-
N(H)CONH2}]PF6, which has δP values ∼20 ppm above
those for 7, but with very similar JRhP and JPP values, the
higher field δP value (δP ) 33.82 for 7) being assigned to
the P atom trans to the imine-N atom.1
1
31P{1H} and H NMR spectra of 3a in acetone-d6 show
that the solid-state structure is maintained in solution. The
δP doublet for the P atoms is seen at 41.74, in the region
found for other Rh(III) semicarbazone complexes with
phosphine ligands,1,16c and the JRhP value (119 Hz) is
1
consistent with equivalent trans-phosphines.1-3,22 The H
To give satisfactory characterization data required the
addition of 1.5 mol of H2O in the formulation for 3c, 0.1
mol of CH2Cl2 for 4, 0.5 mol CH2Cl2 for 5, 1.0 mol of
Me2CO for 6, and 0.6 mol C6H6 for 8, while a good elemental
analysis could not be obtained for 3d. Water was seen
qualitatively for 3c in the 1H NMR (δ 2.85), while the crystal
structures of 3a, 4, and 5 revealed the presence of 1 or 2
mol of solvate per molecule (Table 1). The 1H NMR signals
for the NH2 group were not seen for 3c, 3g, and 8 (see
below). These Rh-semicarbazone complexes certainly reveal
NMR data show two high-field ddt signals for inequivalent
hydrides due to coupling to the Rh, a H atom and two
equivalent P atoms, with appropriate JHH, JPH, and JRhH
values.1-3,19c,d,22 The 1H signals (in acetone-d6) for the o- and
m-protons of the Ph ring of the coordinated acetophenone
(20) Huang, L.-Y.; Aulwurm, U. R.; Heinemann, F. W.; Knoch, F.; Kisch,
H. Chem.sEur. J. 1998, 4, 1641.
(21) Xu, W.; Lough, A. J.; Morris, R. H. Inorg. Chem. 1996, 35, 1549.
(22) Partridge, M. G.; Messerle, B. A.; Field, L. D. Organometallics 1995,
14, 3527.
1488 Inorganic Chemistry, Vol. 44, No. 5, 2005

Rh(III)-Dihydrido-Bis(phosphine) Complexes
a propensity to retain solvate molecules. IR data were not
recorded for 3d or 8 because of the limited material available.
Of note, when the 1h/2h precursor (where the phosphine
is PPhMe2) was reacted with acetophenone semicarbazone,
the product isolated was the orthometalated Rh(III) complex
[Rh(H)(PPhMe2)2{o-C6H4C(Me)dNsNHC(O)NH2}]PF6 (8),
which is well characterized: the one high-field 1H NMR ddd
signal at δH -18.7, and the ABX pattern in the 31P{1H}
spectrum with appropriate JRhH, JPH, and JPP values are
consistent with the geometry shown. Complex 8 could be
formed from the initially formed dihydride species (3h, cf.
Scheme 2) with subsequent loss of H2, or directly via cis-
[Rh(PPhMe2)2(acetone)2]PF6, particularly as 2h is prone to
lose H2 (see above). We have reported elsewhere1 (see
Introduction) that cis-[Rh(PR3)2(acetone)2]PF6 species (R )
aryl or R3 ) Ph2Me) react with semicarbazones to form
orthometalated complexes with trans-phosphines (see Scheme
1); with the less bulky PPhMe2, the cis-phosphine isomer 8
is favored, and is the first example of an orthometalated
Rh(III)-hydrido-semicarbazone complex containing cis-
1
phosphines. Of note, H NMR data reveal that the four
Figure 3. ORTEP diagram of the cis,trans-[Rh(H)2(PPh3)2{PhC-
(Et)dNsN(H)C(O)NH2}]+ cation of 4, with 50% probability thermal
ellipsoids; only one of the disordered positions of the Et group is shown.
intermolecular H-bonding between the O-atom and the
H-atom of the NH2 of the neighboring semicarbazone moiety.
Spectroscopic data for 4-6 are readily assigned as for 3a.
Of interest, however, 4 and 6 in acetone-d6 very slowly
convert partially to species 4a and 6a, respectively, that
appear to be isomers, as evidenced by the 31P and 1H NMR
data. For 4a, the high-field 1H ddt and 31P{1H} doublet of 4
are simply shifted slightly (<1 ppm downfield), while more
phosphine-Me groups are inequivalent (each seen as a
doublet in the δ 1.16-1.81 region, JPH ) 10.7 or 11.7 Hz),
presumably because of restricted rotation about the Rh-P
bond; in the analogous orthometalated semicarbazone com-
plex with trans-PPh2Me ligands, the Me groups are equiva-
lent.
1
significant changes are seen in the H resonances of the Et
group: the CH3 signal is shifted 0.42 ppm upfield, and the
CH2 signal downfield by 0.32. For 6a, there are similar small
differences from the data for 6, the most significant again
being in the CH3 and CH2 resonances of the Et group (0.32
ppm downfield and 0.4 ppm upfield, respectively); the signal
of the Me at the imine-C atom shifts just 0.05 ppm downfield.
The most obvious rationale is that 4a and 6a are isomers
containing the Z-form of the imine component, but we have
been unable to isolate these isomers. We did not detect such
behavior for the other semicarbazone complexes with Me
and Ph groups on the imine-C atom, but the suspected
isomerization reactions are extremely slow, and further
studies are required to draw more definitive conclusions; it
is unlikely that the presence of an Et group is essential. An
isomerization would require rotation about the CdN bond,
and this could be promoted via η2-coordination of the imine
moiety; such a coordination mode for a simple, nonchelated
imine is unknown within Pt metal systems, although it has
been established for some chelated, R,â-unsaturated imines.24
Our initial goal in this project was catalytic hydrogenation
of the semicarbazones, but disappointingly no such catalysis
The propiophenone-, acetone-, and butanone-semicar-
bazone analogues of 3a, namely complexes 4-6 (Scheme
2), were also isolated and well characterized, including X-ray
crystallographic analysis of 4 and 5 (Figures 3 and 4,
respectively, and Table 2). The ORTEP for E-propiophe-
none-semicarbazone is presented in Figure 5, with selected
bond length and angles also given in Table 2.
Complexes 4 and 5 have octahedral distortions such as
those in 3a, and again, intramolecular RhH‚‚‚HC interactions
are evident (Figure 2, Table 3): interactions in 4 and 5 again
involve the hydrides and a Ph ring proton, while in 5 there
is also an interaction of a hydride with the proton of the
semicarbazone-Me group. The chelate rings are again
coplanar with the hydrides, and all the geometrical param-
eters are close to those of 3a. The data in Table 2 show that
the bond lengths and angles of the free and coordinated
propiophenone semicarbazone are essentially the same, and
this applies also on comparing data for 5 with those for free
acetone semicarbazone.23 (Propiophenone semicarbazone
crystallizes in an orthorhombic crystal system, while both
the acetone and benzaldehyde semicarbazones crystallize in
a monoclinic system.)23 Worth noting also is that all four
structures (3a, 4, 5, and the free ligand) show strong
(23) Naik, D. V.; Palenik, G. J. Acta Crystallogr. 1974, B30, 2396.
(24) Leifbritz, D.; Dieck, H. J. Organomet. Chem. 1976, 105, 255
Inorganic Chemistry, Vol. 44, No. 5, 2005 1489

Ezhova et al.
Figure 4. ORTEP diagram of the cis,trans-[Rh(H)2(PPh3)2{Me2CdNsN(H)C(O)NH2}]+ cation of 5, with 50% probability thermal ellipsoids.
example, 3a, and also shows no catalytic activity for
hydrogenation of the semicarbazone.1 Here there are two
fused five-membered rings rendering a high ground-state
stability. Whether η2-coordination of the CdN moiety is
essential for successful hydrogenation (as commonly required
for olefinic substrates) remains an unanswered question,5 but
if 4a and 6a are the Z-isomers of 4 and 6, respectively, then
such coordination at least within a transition state seems
feasible.
Conclusions
The studies reveal that E-semicarbazones react at room
temperature with the cis,trans,cis-[Rh(H)2(PR3)2(solvent)2]-
PF6 complexes (solvent ) Me2CO or MeOH; R ) aryl or
R3 ) Ph2Me, Ph2Et) under H2 by replacing the solvent
molecules with formation of a product with a five-membered
η2-N,O-semicarbazone ring; these are the first reported
dihydrido-semicarbazone complexes, and they are generally
air-stable, although cis,trans-[Rh(H)2(PPh2Me)2{PhC(Me)d
NsNHC(O)NH2}]PF6 slowly loses H2 irreversibly to form
[Rh(PPh2Me)2{PhC(Me)dNsNHC(O)NH2}]PF6. In con-
trast, treatment of the reactant complex, where R is the less
bulky PPhMe2, with acetophenone-semicarbazone generates
the orthometalated, hydrido-Rh(III) complex, cis-[Rh(H)-
(PPhMe2)2{o-C6H4C(Me)dNsNHC(O)NH2}]PF6. We have
reported earlier that the corresponding orthometalated hy-
drido complexes with more bulky trans-phosphines can be
synthesized by reaction of a semicarbazone with the cis-
[Rh(PR3)2(solvent)2]PF6 species. The orthometalated species
do not react with H2 to form the dihydrido species, and none
of the above-mentioned species catalyzes the hydrogenation
of acetophenone semicarbazone.
Figure 5. ORTEP diagram of E-PhC(Et)dNsN(H)C(O)NH2, with 50%
probability thermal ellipsoids.
was observed, at least for the acetophenone semicarbazone
tested with the [Rh(H)2(PPh3)2(solvent)2]+ species (2a),
including the system in MeOH, often the optimum solvent
for Rh-catalyzed hydrogenation of “standard” imines.5 The
Rh(III)-dihydride species 3a containing the five-membered,
chelated semicarbazone shows no inclination to transfer
hydrogen to the imine or carbonyl functionality, and appears
to be kinetically and thermodynamically stable; as noted, 3a
is a simple substitution product of the labile precursor 2a,
where presumably the high trans-effect of the hydride ligands
labilizes the solvent ligands, this rendering a usually clas-
sically substitution-inert Rh(III) species more labile. As noted
above, 3g (the analogue of 3a but containing PPh2Me) does
irreversibly slowly lose H2 to generate 7 (Scheme 3), and
so it is difficult to draw similar conclusions for quite closely
analogous systems. Further, we noted in the Introduction that
reaction of the [Rh(PPh3)2(solvent)2]+ with acetophenone
semicarbazone gives the orthometalated species [Rh(H)-
(PPh3)2{o-C6H4C(Me)dN-NH-C(O)NH2}]+ (I, Scheme
1);1 this species does not react with H2 to generate, for
In summary, the following types of cationic Rh-semi-
carbazone species have now been synthesized from the well-
known [Rh(H)2(PR3)2(solvent)2]+ or [Rh(PR3)2(solvent)2]+
precursors: cis-[Rh(PR3)2(η2-N,O-semicarbazone)]+, cis,-
trans,cis-[Rh(H)2(PR3)2(η2-N,O-semicarbazone)]+, and the
1490 Inorganic Chemistry, Vol. 44, No. 5, 2005

Rh(III)-Dihydrido-Bis(phosphine) Complexes
orthometalated cis- and trans-[Rh(H)(PR3)2(η3-C,N,O-semi-
carbazone-H}]+ complexes; the product formed depends on
the nature of the phosphine and the semicarbazone, but
details of the factors governing their formation and their
interconversions remain to be established.
ESTAC (Environmental Science and Technology Alliance
Canada) for financial support.
Supporting Information Available: X-ray crystallographic data
for the structures of complexes 3a, 4, and 5, and propiophenone-
semicarbazone in CIF format. This material is available free of
charge via the Internet at http://pubs.acs.org.
Acknowledgment. We thank the NSERC (Natural Sci-
ences and Engineering Research Council of Canada) and
IC0489185
Inorganic Chemistry, Vol. 44, No. 5, 2005 1491