Thioether, dinitrogen, and olefin complexes of (PNP)Rh: Kinetics and thermodynamics of exchange and oxidative addition reactions

Article abstract of DOI:10.1021/om700563k

A variety of (PNP)Rh-L complexes (where L = organic sulfide or sulfoxide, dinitrogen, or tertbutylethylene) have been synthesized by trapping transient (PNP)Rh (1) in situ. Equilibrium studies established the relative affinity of the (PNP)Rh fragment (1) for various L in the following ofder (of decreasing affinity): Ph₂SO > SBu₂ⁿ > SPhMe > dibenzothiophene > SPh₂ > benzothiophene > SPr ₂¹ > thiophene ≈ SBu^tMe > SBu ₂^s ≈ H₂C=CHCMe₃ ? SBu ₂^t. Dinitrogen reacted with 1 to yield a mixture of terminal and bridging N₂ complexes and was found to bind more strongly than SPr₂ⁱ. Reaction of (PNP)Rh(SPr ₂ⁱ) (10) with PhHal led to the corresponding oxidative addition products (PNP)Rh(Ph)(Hal) (Hal = Cl, 18a; Hal = Br, 18b; Hal = I, 18c). The relative rates of oxidative addition of PhHal to 10 were found to be in the order PhI > PhBr > PhCl. Kinetic studies of the reaction of 10 with PhBr were consistent with the reaction proceeding via reversible dissociation of SPr₂ⁱ, followed by irreversible addition of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph₂) in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh]₂(N₂) (19a) and (PNP)Rh(H₂C=CHCMe₃) (21) were determined using X-ray crystallography. Approximately squareplanar geometry about Rh was registered.

Full text of DOI:10.1021/om700563k

6066
Organometallics 2007, 26, 6066-6075
Articles
Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh: Kinetics
and Thermodynamics of Exchange and Oxidative Addition
Reactions
Sylvain Gatard, Chengyun Guo, Bruce M. Foxman, and Oleg V. Ozerov*
Department of Chemistry, Brandeis UniVersity, MS 015, 415 South Street, Waltham, Massachusetts 02454
ReceiVed June 8, 2007
A variety of (PNP)Rh-L complexes (where L ) organic sulfide or sulfoxide, dinitrogen, or tert-
butylethylene) have been synthesized by trapping transient (PNP)Rh (1) in situ. Equilibrium studies
established the relative affinity of the (PNP)Rh fragment (1) for various L in the following order (of
decreasing affinity): Ph2SO > SBun2 > SPhMe > dibenzothiophene > SPh2 > benzothiophene > SPri2
> thiophene ≈ SButMe > SBus2 ≈ H2CdCHCMe3 . SBut2. Dinitrogen reacted with 1 to yield a mixture
of terminal and bridging N2 complexes and was found to bind more strongly than SPri2. Reaction of
(PNP)Rh(SPri2) (10) with PhHal led to the corresponding oxidative addition products (PNP)Rh(Ph)(Hal)
(Hal ) Cl, 18a; Hal ) Br, 18b; Hal ) I, 18c). The relative rates of oxidative addition of PhHal to 10
were found to be in the order PhI > PhBr > PhCl. Kinetic studies of the reaction of 10 with PhBr were
consistent with the reaction proceeding via reversible dissociation of SPri2, followed by irreversible addition
of PhBr. Evidence for a similar dissociative mechanism for the conversion of 10 to (PNP)Rh(S(O)Ph2)
in a ligand exchange reaction was also discovered. Solid-state structures of [(PNP)Rh]2(N2) (19a) and
(PNP)Rh(H2CdCHCMe3) (21) were determined using X-ray crystallography. Approximately square-
planar geometry about Rh was registered.
and examples of well-defined OA of aryl halides to Rh are
rare.5-8 Recently, we reported that a rigid PNP pincer ligand9,10
supports a system where reactions of oxidative addition (OA)
of aryl halides to RhI and C-C reductive elimination from RhIII
can be studied in a well-defined fashion (Scheme 1).11a Our
experiments demonstrated critical importance of the generation
of unobserved12 unsaturated (PNP)Rh (1), which rapidly un-
dergoes OA reactions with aryl halides.11a
Introduction
Oxidative addition (OA)1 of aryl halides to complexes of
zerovalent Pd and other group 10 metals has received a great
deal of attention, due to the importance of the OA step in the
rich catalytic coupling chemistry.2,3 The analogous Rh-catalyzed
coupling chemistry of aryl halides is only beginning to emerge,4
* Corresponding author. E-mail: ozerov@brandeis.edu.
(1) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition
Metals, 3rd ed.; Wiley-Interscience: New York, 2001; pp 149-173. (b)
van Leeuwen, P. W. N. M. Homogeneous Catalysis: Understanding the
Art; Kluwer Academic Publishers: Dordrecht, Boston, London, 2004; pp
271-298, 387-402.
(7) (a) de Pater, B. C.; Zijp, E. J.; Fruhauf, H.-W.; Ernsting, J. M.;
Elsevier, C. J.; Vrieze, K.; Budzelaar, P. H. M.; Gal, A. W. Organometallics
2004, 23, 269. (b) Grushin, V. V.; Alper, H. Organometallics 1991, 10,
1620. (c) Labinger, J. A.; Osborn, J. A.; Coville, N. J. Inorg. Chem. 1980,
19, 3236. (d) Mureinik, R. J.; Weitzberg, M.; Blum, J. Inorg. Chem. 1979,
18, 915. (e) Abeysekera, A. M.; Grigg, R.; Trocha-Grimshaw, J.; Viswanatha,
V. J. Chem. Soc., Perkin Trans. 1 1977, 1395.
(8) (a) Semmelhack, M. F.; Ryono, L. Tetrahedron Lett. 1973, 31, 2967.
(b) Willems, S. T. H.; Budzelaar, P. H. M.; Moonen, N. N. P.; de Gelder,
R.; Smits, J. M. M.; Gal, A. W. Chem.sEur. J. 2002, 8, 1310. (c) Grushin,
V. V.; Marshall, W. J. J. Am. Chem. Soc. 2004, 126, 3068. (d) Macgregor,
S. A.; Roe, D. C.; Marshall, W. J.; Bloch, K. M.; Bakhmutov, V. I.; Grushin,
V. V. J. Am. Chem. Soc. 2005, 127, 15304.
(9) (a) Liang, L.-C.; Lin, J.-M.; Hung, C.-H. Organometallics 2003, 22,
3007. (b) Winter, A. M.; Eichele, K.; Mack, H.-G.; Potuznik, S.; Mayer,
H. A.; Kaska, W. C. J. Organomet. Chem. 2003, 682, 149. (c) Fan, L.;
Foxman, B. M.; Ozerov, O. V. Organometallics 2004, 23, 326.
(10) (a) Liang, L.-C. Coord. Chem. ReV. 2006, 250, 1152. (b) Ozerov,
O. V. In The Chemistry of Pincer Compounds; Morales-Morales, D., Jensen,
C., Eds.; Elsevier: Amsterdam, 2007; pp 287-309.
(11) (a) Gatard, S.; C¸ elenligil-C¸ etin, P R.; Guo, C.; Foxman, B. M.;
Ozerov, O. V. J. Am. Chem. Soc. 2006, 128, 2808. (b) We previously
showed that 1 is converted to (PNP)Rh(η2-C2H4) in the presence of Et2O.11a
(12) A related three-coordinate (PNP*)Co species (where PNP* ) [(But2-
PCH2SiMe2)2N], the Fryzuk-type PNP ligand) has been recently character-
ized: Ingleson, M.; Fan, H.; Pink, M.; Tomaszewski, J.; Caulton, K. G. J.
Am. Chem. Soc. 2006, 128, 1804.
(2) Negishi, E. I., Ed. Handbook of Organopalladium Chemistry for
Organic Synthesis; Wiley-Interscience: New York, 2002.
(3) (a) Hartwig, J. F. Synlett 1997, 329. (b) Hartwig, J. F. Acc. Chem.
Res. 1998, 31, 852. (c) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37,
2046. (d) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2001, 219, 131.
(e) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem.
Res. 1998, 31, 805.
(4) (a) Lewis, J. C.; Wu, J. Y.; Bergman, R. G.; Ellman, J. A. Angew.
Chem., Int. Ed. 2006, 45, 1589. (b) Yanagisawa, S.; Sudo, T.; Noyori, R.;
Itami, K. J. Am. Chem. Soc. 2006, 128, 11748. (c) Wang, X.; Lane, B. S.;
Sames, D. J. Am. Chem. Soc. 2005, 127, 4996. (d) Ueura, K.; Satoh, T.;
Miura, M. Org. Lett. 2005, 7, 2229. (e) Lewis, J. C.; Wiedemann, S. H.;
Bergman, R. G.; Ellman, J. A. Org. Lett. 2004, 6, 35. (f) Bedford, R. B.;
Limmert, M. E. J. Org. Chem. 2003, 68, 8669. (g) Ishiyama, T.; Hartwig,
J. J. Am. Chem. Soc. 2000, 122, 12043.
(5) (a) Several examples of C-F activation by Rh complexes are
known.5b-f (b) Aizenberg, M.; Milstein, D. Science 1994, 265, 359. (c)
Aizenberg, M.; Milstein, D. J. Am. Chem. Soc. 1995, 117, 8674. (d) Young,
R. J., Jr.; Grushin, V. V. Organometallics 1999, 18, 294. (e) Yang, H.;
Gao, H.; Angelici, R. Organometallics 1999, 18, 2285. (f) Noveski, D.;
Braun, T.; Neumann, B.; Stammler, A.; Stammler, H.-G. Dalton Trans.
2004, 4106.
(6) Grushin, V. V.; Alper, H. Chem. ReV. 1994, 94, 1047.
10.1021/om700563k CCC: $37.00 © 2007 American Chemical Society
Publication on Web 11/03/2007

Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh
Organometallics, Vol. 26, No. 25, 2007 6067
Scheme 1
allowed synthesis of 11-15. Compound 16 was prepared by
reacting 10 with Ph2SO. Compounds 6, 8-12, and 16 were
isolated as air-sensitive orange solids. Compounds 7 and 13-
15 were not isolated and were only characterized by solution
NMR methods in situ. In all of these methods, the (PNP)Rh
intermediate is presumably generated and then captured by L.
After all, we have previously shown that C-C elimination
generates 1,11,13 and dehydrochlorination has been used to
generate (PCP)Rh and (PCP)Ir fragments in situ.14,15 The
mechanism of the ligand exchange at (PNP)Rh will be discussed
later in this Article.
Scheme 2
Scheme 3
All of the compounds 6-16 displayed time-averaged C2V
symmetry by NMR at ambient temperature.16 This is the highest
possible symmetry for a PNP complex. A single doublet 31P-
{1H} resonance (1JRh-P ) 133-148 Hz) was observed for each
compound in the δ 36-48 ppm region. The high symmetry even
for complexes of unsymmetrical sulfides implies fast rotation
about the Rh-S bond and also fast inversion at S.17 IR data are
often used to distinguish between the O-bound and the S-bound
modes in sulfoxide complexes.18 In the case of 16, the IR data
were ambiguous because of overlapping bands in the region of
interest. It seems most likely, however, that Ph2SO in 16 is
bound through the sulfur because of the perceived better soft-
soft match with an electron-rich RhI center. Indeed,19 O-bound
sulfoxide complexes of RhI have only been encountered in cases
where (a) O-binding is enforced by a chelate20 or (b) the
complex is cationic.21
We also propose coordination through sulfur for compounds
13-15. Coordination via the π-system would lead to more
upfield 13C resonances of the aromatic system (as compared to
free thiophene (T), benzothiophene (BT), or dibenzothiophene
In our previous report, we used C-C reductive elimination
from (PNP)Rh(Ph)(Me) (2) or (PNP)RhPh2 (3) to generate 1 in
situ.11a This is not entirely convenient for the following reasons.
Complexes 2/3 are not stable enough to be isolated and thus
only afford the in situ approach to the generation of 1. The in
situ production of 1 by the path outlined in Scheme 1 requires
the utilization of a methyl- or phenyllithium or Grignard reagent,
and thus normally would take place in the presence of the
solvent11b in which the RLi or RMgX is available, not to mention
the possible excess of the reagent. We sought to access 1 in a
different fashion, and the ligand dissociation path (Scheme 2)
appeared sensible and straightforward. The requirements for L
in Scheme 2 can be outlined as follows: (1) L must form a
complex that is isolable; (2) L should not bind to Rh too strongly
so that dissociation of L (and thus access to 1) is kinetically
retarded; (3) OA of the substrate (e.g., aryl halide) must be
thermodynamically favorable over coordination of L; (4) L must
not be reactive with the products of reactions of 1 with substrates
(e.g., aryl halides); and (5) L must be easily removable upon
workup. In the present work, we concentrate on thioethers and
related organosulfur compounds as L, but also compare them
to N2 and the bulky olefin H2CdCHCMe3.
(13) We have not observed the putative (PNP)RhMe2 in the reactions of
4 with MeMgCl, although ethane and, ostensibly, (PNP)Rh are produced.
We speculate that MeMgCl may preferentially attack the Me group of 4
via a direct SN2 mechanism. Similarly, while PhLi reacts with 4 to produce
detectable quantities of 2, the amount of the toluene coupling product (ca.
50%) formed in the time of mixing (<10 min) is inconsistent with the
known11a and relatively slow rate of C-C elimination from 2. SN2 attack
of PhLi on 4 is also plausible.
(14) Nemeh, S.; Jensen, C.; Binamira-Soriaga, E.; Kaska, W. C.
Organometallics 1983, 2, 1442.
(15) (a) Gottker-Schnetmann, I.; Brookhart, M. J. Am. Chem. Soc. 2004,
126, 9330. (b) Gottker-Schnetmann, I.; White, P.; Brookhart, M. J. Am.
Chem. Soc. 2004, 126, 1804. (c) Gottker-Schnetmann, I.; White, P. S.;
Brookhart, M. Organometallics 2004, 23, 1766.
(16) Commercial SBus2 comes as a mixture of rac- and meso-forms (in
ca. 1:1 ratio). Strictly speaking, this mixture forms two diastereomeric
products upon complexation with (PNP)Rh that do not interconvert.
However, most of the NMR resonances of these diastereomeric Rh
complexes are indistinguishable from each other, and the mixture appears
to be of 1:1 ratio as well. For simplicity, here we treat this mixture of
diastereomers as one compound (6). Furthermore, for the rac-diastereomer
of 6, C2V symmetry is not possible. However, the deviation is not practically
apparent by NMR.
(17) Thioether ligands have been shown to undergo rapid pyramidal
inversion at sulfur: Abel, E. W.; Bhargava, S. K.; Orrell, K. G. Prog. Inorg.
Chem. 1984, 32, 1.
(18) James, B. R.; Morris, R. H.; Reimer, K. J. Can. J. Chem. 1977, 55,
3927 and references within.
(19) For some relevant examples, see the following references: (a) James,
B. R.; Morris, R. H. Can. J. Chem. 1980, 58, 399. (b) Dorta, R.; Rozenberg,
H.; Shimon, L. J. W.; Milstein, D. Chem.-Eur. J. 2003, 9, 5237. (c) Dorta,
R.; Shimon, L. J. W.; Rozenberg, H.; Milstein, D. Eur. J. Inorg. Chem.
2002, 1827.
(20) (a) Iretskii, A. V.; Kagan, G. B. Russ. J. Gen. Chem. 1997, 67,
331. (b) Alcock, N. W.; Brown, J. M.; Evans, P. L. J. Organomet. Chem.
1988, 356, 233.
(21) (a) James, B. R.; Morris, R. H.; Reimer, K. J. Can. J. Chem. 1977,
55, 2353. (b) Uson, R.; Oro, L. A.; Ciriano, M. A.; Lahoz, F. J.; Bello, M.
C. J. Organomet. Chem. 1982, 234, 205. (c) Valderrama, M.; Ganz, R.;
Sariego, R. Transition Met. Chem. 1983, 8, 160. (d) Dorta, R.; Rozenberg,
H.; Milstein, D. Chem. Commun. 2002, 710.
Results and Discussion
Synthesis of (PNP)Rh(SR′R′′) Complexes 6-15 and of
(PNP)Rh(S(O)Ph2) (16). Several different routes were used to
prepare (PNP)Rh(L) complexes (Scheme 3). Addition of PhLi
to (PNP)Rh(Me)(Cl) (4) in the presence of excess of L cleanly
produced compounds 6-9 in <24 h at 22 °C. Analogously,
addition of MeMgCl to 4 in the presence of excess of L was
used to synthesize 10. Dehydrochlorination of (PNP)Rh(H)(Cl)
(5) with NaOBut in the presence of L also served well and

6068 Organometallics, Vol. 26, No. 25, 2007
Gatard et al.
Scheme 4
Scheme 5
(DBT), Scheme 3).22 This was not observed for compounds 13-
15; on the contrary, a downfield shift (relative to free T, BT,
DBT) was observed for the R-C of the coordinated thiophene.
These data are consistent with those for other S-bound thiophenes
reported in the literature.23
Scheme 6
step in the thiolation of aryl halides.25 The example of 9/17
presented here is unusual in that the thermodynamics are
perfectly balanced and the kinetic barrier is modest so that
observation of both forms in equilibrium is possible.
Reversible C-S Oxidative Addition. Thermolysis of a pure
sample of 9 (or of 10 with SPh2) at 65 °C for 18 h generated a
1:1 mixture of RhI complex 9 and the RhIII C-S oxidative
addition product 17 (Scheme 4). 17 was prepared independently
(at ambient temperature) from (PNP)Rh(Ph)(Br) (18b), PhSH,
and NaOBut. Thermolysis of 17 (65 °C, 18 h) also led to a 1:1
mixture of 9 and 17. In contrast, no evidence for the formation
of C-S oxidative addition products was observed in any of the
experiments involving thermolysis of 8.
Synthesis of Dinitrogen Complexes. Mixing 4 with MeMgCl
under an N2 atmosphere in PhF resulted in the formation of a
single product [(PNP)Rh]2(µ-N2) (19a) after 10 min at room
temperature. 19a could be isolated in the pure form. Under N2,
19a slowly establishes an equilibrium with the terminal dini-
trogen complex 19b. Thus, thermolysis of a pure sample of 19a
under N2 (3 d, 65 °C) in C6D6 in a J. Young NMR tube resulted
in conversion to a 5:95 mixture of 19a:19b (NMR evidence).
Removing the overhead N2 gas and allowing the solution to
stand for 3 d under argon increased the ratio in favor of 19a to
50:50. In contrast, thermolysis (65 °C, 1 d) of 19a under argon
did not lead to any change in the composition of the solution.
These results are consistent with the assigned identity of 19a
as the bridging N2 complex (N2-poor) and 19b as the terminal
N2 complex (N2-rich). The structure of 19a was investigated
by an X-ray diffraction study in the solid state (vide infra).
Both 19a and 19b displayed maximal symmetry in the
ambient-temperature NMR spectra (C2V for each PNP fragment).
The 31P NMR chemical shifts for 19a and 19b were very similar
The identity of 17 was deduced on the basis of the solution
NMR data. The following distinct NMR features associated with
the Rh-bound Ph group in 17 are similar to the analogous
features of the previously characterized (PNP)Rh(Ph)(Cl) (18a),
(PNP)Rh(Ph)(Br) (18b), and (PNP)Rh(Ph)(I) (18c).11a The 13C-
{1H} resonance of the Rh-bound carbon of the Ph group displays
telltale coupling to both Rh and the two phosphorus nuclei (δ
140.5 ppm, doublet of triplets, JRh-C ) 38 Hz, JP-C ) 9 Hz).
Because of the slow rotation about the Rh-C bond, the Rh-
bound Ph group in 17 gives rise to (a) five 1H resonances, four
of them broad (slow exchange of the ortho- and meta-positions,
resolved at -50 °C) and one a sharp triplet (para-CH) at 22
°C; and (b) five 13C NMR resonances besides the Rh-bound
ipso-C (vide supra), four of which are broad. One of the four
as were the corresponding 1JRh-P values (19a, δ 51.1, 1JRh-P
)
i
resonances of the Pr CH3 groups of the PNP ligand is shifted
139 Hz; 19b, δ 52.4, 1JRh-P ) 137 Hz). The similarities in these
data and the apparent small difference in free energies are
reminiscent of the analogous bridging and terminal (PCP)Rh
complexes described by Milstein et al. (20a/20b, Scheme 5).26
Similar interconversion between bridging and terminal dinitro-
gen PCP complexes of iridium has also been studied.27
characteristically upfield to ca. 0.4 ppm in the 1H NMR spectrum
(presumably, this is due to the selective influence of the ring
current effect of the Rh-Ph group on a specific pair of Me
groups). Unlike 9, which is orange, 17 is green, similar in color
to 18a/b.
Cleavage of C-S bonds in various thiophenes by RhI
complexes has been studied by Jones et al. in the context of
homogeneous models for hydrodesulfurization.24 We saw no
evidence of C-S OA with T, BT, or DBT in the present study.
On the other hand, C-S reductive elimination is a requisite
Synthesis of (PNP)Rh(H2CdCHBut) (21). Complex 21 was
prepared analogously to the synthesis of 10 by treatment of 4
with MeMgCl in the presence of H2CdCHCMe3 (Scheme 6).
The product was isolated in 62% yield upon workup. 21 displays
C1 symmetry in its NMR spectra. The two inequivalent 31P
nuclei form an AB system with a coupling constant (JPP ) 328
Hz) characteristic of trans-disposed phosphines. The olefinic
resonances of the coordinated H2CdCHCMe3 appear at 4.43,
(22) Rao, K. M.; Day, C. L.; Jacobson, R. A.; Angelici, R. J. Inorg.
Chem. 1991, 30, 5046.
(23) (a) Benson, J. W.; Angelici, R. J. Organometallics 1992, 11, 922.
(b) Hachgenei, J. W.; Angelici, R. J. Organometallics 1989, 8, 14. (c) Choi,
M.-G.; Angelici, R., J. J. Am. Chem. Soc. 1989, 111, 8754. (d) Goodrich,
J. D.; Nickias, P. N.; Selegue, J. P. Inorg. Chem. 1987, 26, 3424. (e)
Paneque, M.; Poveda, M. L.; Salazar, V.; Taboada, S.; Carmona, E.;
Gutierrez-Puebla, E.; Monge, A.; Ruiz, C. Organometallics 1999, 18, 139.
(24) (a) Maresca, O.; Maseras, F.; Lledos, A. New J. Chem. 2004, 28,
625. (b) Myers, A. W.; Jones, W. D. Organometallics 1996, 15, 2905. (c)
Dong, L.; Duckett, S. B.; Ohman, K. F.; Jones, W. D. J. Am. Chem. Soc.
1992, 114, 151. (d) Jones, W. D.; Dong, L. J. Am. Chem. Soc. 1991, 113,
559.
(25) (a) Kondo, T.; Mitsudo, T. Chem. ReV. 2000, 100, 3205. (b)
Fernandez-Rodriguez, M. A.; Shen, Q.; Hartwig, J. F. J. Am. Chem. Soc.
2006, 128, 2180 and references within.
(26) Cohen, R.; Rybtchinski, B.; Gandelman, M.; Rozenberg, H.; Martin,
J. M. L.; Milstein, D. J. Am. Chem. Soc. 2003, 125, 6532.
(27) (a) Ghosh, R.; Kanzelberger, M.; Emge, T. J.; Hall, G. S.; Goldman,
A. S. Organometallics 2006, 25, 5668. (b) Lee, D. W.; Kaska, W. C.; Jensen,
C. M. Organometallics 1998, 17, 1.

Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh
Organometallics, Vol. 26, No. 25, 2007 6069
Scheme 7
Table 1
no.
L
L′
K
1
2
3
4
5
6
7
8
9
SPri2
SPri2
SPri2
SPri2
SPri2
SPri2
SPri2
SPri2
SPri2
SPri2
SPhMe
StBu2
CH2dCHCMe3
StBuMe
T
BT
SPh2
<10-4
0.2(1)
0.4(1)
0.4(1)
3(1)
10(2)
33(5)
48(10)
63(5)
400(100)
0.004(1)
DBT
SPhMe
SnBu2
S(O)Ph2
SsBu2
10
11
in free N2, signifying only modest back-donation into the π*-
orbitals of the dinitrogen ligand.28
Figure 1. ORTEP drawing29 (80% probability ellipsoids) of 19a
showing selected atom labeling. Hydrogen atoms and all methyl
groups are omitted for clarity. Selected bond distances (Å) and
angles (deg) follow: N2-N3, 1.1191(17); Rh1-N2, 1.9035(12);
Rh1-N1, 2.0358(12); Rh1-P1, 2.2818(4); Rh1-P2, 2.2808(4);
Rh1-N2-N3, 178.16(12); P1-Rh1-N2, 82.18(4); P2-Rh1-N2,
81.98(4); N1-Rh1-N2, 179.52(5); P1-Rh1-P2, 163.623(14).
The two Rh-C distances in 21 are different, with the distance
to the carbon bearing a tert-butyl substituent being greater by
ca. 0.05 Å (likely for steric reasons). The C-C distance of
1.360(7) Å in the coordinated olefin is indicative of modest
back-donation into the π*-orbital of H2CdCHBut. This C-C
distance is at the lower end of the range for olefin complexes,
similar to other RhI olefin complexes.30
Equilibrium Studies. To determine the comparative ther-
modynamic affinity of the (PNP)Rh fragment (1) for various
ligands, we measured equilibrium constants (K) for a series of
ligand exchange reactions. Equilibrium constants were measured
for the reactions generically depicted in Scheme 7. To establish
equilibrium, the solutions of reactants in C6D6 were heated in
a J. Young tube by placing them into an oil bath at 65 °C until
the observed ratios ceased to change. The concentrations were
measured using NMR after cooling of the sample. Because the
reactions do not involve a change in the number of particles,
we assume that the ∆Srxn values are negligible and and therefore
so is ∆Grxn; thus the relative order of the values of K should be
independent of temperature. Three experiments with different
starting ratios of reactants were performed for each determina-
tion of K. No decomposition was detected by NMR. The results
are presented in Table 1.
The equilibrium constant for a reaction of 10 with N2 was
not measured because of the uncertainty in the N2 concentra-
tion.31 However, addition of 1 atm of N2 (ca. 100 µmol) to a J.
Young tube containing a solution of 31 mmol of 10 in 0.7 mL
of C6D6 and subsequent thermolysis in a closed tube (65 °C, 1
d) led to the formation of predominantly 19a/19b. Because the
concentration of N2 in C6D6 would be rather small, this is
indicative of greater affinity of (PNP)Rh toward N2 (or toward
NtN-Rh(PNP) for the case of 19a) than for SPri2.
Figure 2. ORTEP drawing29 (50% probability ellipsoids) of 21
showing selected atom labeling. Hydrogen atoms and all methyl
groups are omitted for clarity. Selected bond distances (Å) and
angles (deg) follow: Rh1-C27, 2.132(5); Rh1-C28, 2.189(5);
Rh1-P1, 2.3220(19); Rh1-P2, 2.2964(14); Rh1-N1, 2.062(4);
C27-Rh1-C28, 36.7(2); C27-Rh1-P1, 97.64(16); C28-Rh1-
P1, 110.42(14); C27-Rh1-P2, 96.65(15); C28-Rh1-P2, 92.72-
(14); P1-Rh1-P2, 155.64(5); C27-Rh1-N1, 161.04(17); C28-
Rh1-N1, 160.64(17); P1-Rh1-N1, 80.69(11); P2-Rh1-N1,
79.40(11).
1
2.88, and 2.78 ppm in the H NMR spectrum, within a typical
region for olefin complexes.
Structures of 19a and 21. Structures of 19a and 21 were
determined in the course of X-ray diffraction studies on
appropriate single crystals (Figures 1 and 2). In both compounds,
the environment about all Rh centers is approximately square
planar, with deviations primarily attributable to the geometric
constraints of the PNP ligands. The metrics relating to the PNP
ligands in these compounds are unremarkable. The Rh-Ndinitrogen
distance in 19a of 1.9035(12) Å is markedly shorter than the
corresponding distance in the closely related 20a,26 presumably
a reflection of a weaker trans-influence of the amido ligand in
19a as compared to the aryl ligand in 20a. Despite the greater
proximity of the N2 ligand to Rh in 19a, the N-N distance in
19a of 1.1191(17) Å is only slightly longer than that in 20a
(1.108(3) Å).26 These distances are close to the N-N distance
For bis(hydrocarbyl) sulfides, the trend that emerged from
our studies indicated that steric considerations played a primary
role in the relative strength of binding of various L to (PNP)-
Rh. Increasing the size of the substituents on S (be that alkyl
or aryl) led to weaker binding.32,33 Di-tert-butylsulfide was by
far the most weakly binding L. Accurate equilibrium constant
(29) (a) ORTEP plots were created using Ortep-3 for Windows. Farugia,
L. J. Appl. Crystallogr. 1997, 30, 565. (b) 3D-rendering was done using
Persistence of Vision Ray Tracer (POV-Ray), available at http://www-
.povray.org/.
(30) Cohen, S. A.; Auburn, P. A.; Bercaw, J. E. J. Am. Chem. Soc. 1983,
105, 1136.
(31) For treatment of N2 concentration for equilibrium constant calcula-
tion, see ref 27a (Goldman) and references within.
(32) For discussion of steric effects in dialkylsulfides, see: (a) Shi, T.;
Elding, L. I. Inorg. Chem. 1996, 35, 5941. (b) Tracey, A. A.; Eriks, K.;
Prock, A.; Giering, W. P. Organometallics 1990, 9, 1399.
(28) For reviews on the chemistry of dinitrogen complexes, see the
following: (a) MacKay, B. A.; Fryzuk, M. D. Chem. ReV. 2004, 104, 385.
(b) Shaver, M. P.; Fryzuk, M. D. AdV. Synth. Catal. 2003, 345, 1061. (c)
Fryzuk, M. D.; Johnson, S. A. Coord. Chem. ReV. 2000, 200-202, 379.

6070 Organometallics, Vol. 26, No. 25, 2007
Gatard et al.
Figure 3. (A) Pseudo first-order decay of 10 in the presence of four concentrations of SPri2 (0.22-0.88 M). (B) Pseudo first-order decay
of 10 in the presence of four concentrations of PhBr (0.22-0.88 M). (C) Inverse dependence of kobs on the concentration of SPri2. (D)
Positive dependence of kobs on the concentration of PhBr.
Scheme 8
determination in a reaction involving SPri2 versus SBus2 was
not possible due to overlap of resonances in the NMR spectra.
This equilibrium constant was estimated at ca. 0.2 (favoring
binding of SPri2) from the data in lines 8 and 11 of Table 1.
For the thiophenic ligands T, BT, and DBT, an opposite trend
was observed. DBT was found to bind more strongly than BT,
which in turn was found to bind more strongly than T. A similar
trend has been previously reported.23a,c Binding of the metal to
S in a thiophene presumably disrupts the aromaticity of the five-
membered cycle. This becomes less of a loss for the fused BT
and DBT, and so DBT binds most strongly despite being the
largest of the three.34
Diphenylsulfoxide was found to bind most strongly of all
ligands studied. Specifically, it displayed a K of an order of
magnitude higher than the corresponding sulfide Ph2S. tert-
Butylethylene was found to bind comparably to the moderately
bulky dialkylsulfides.
Kinetics of Oxidative Addition of PhHal to 10. As we
to aryl halides. The generic mechanistic situation in our case is
fully analogous to the oxidative addition of aryl halides to (Q-
expected, 10 cleanly reacted with aryl halides to produce the
phos)-Pd0-(Q-phos) (22) investigated in detail by Barrios-
C-Hal oxidative addition products with release of free SPri2.
Landeros and Hartwig in 2005 (Scheme 8).36
We were interested in the mechanism of this transformation
To gain insight into the mechanism, we investigated the
and set out to investigate it by means of kinetic studies.
kinetics of oxidative addition of PhBr to 10 as a function of
Particularly, the issue in question is whether addition of aryl
both [PhBr] and [SPri2] under pseudo first-order conditions.
halide occurs prior to, in concert with, or following the
Kinetic data were obtained by monitoring the disappearance of
dissociation of SPri2. Oxidative addition of alkyl halides to four-
10 by 31P NMR in C6D6 at 65 °C. In the first set of experiments
coordinate d8 metal centers via an (associative) SN2 mechanism
(Figure 3A), the concentration of PhBr was kept approximately
is well-documented.35 However, this mechanism is not available
constant (0.22 M) while the concentration of SPri2 was varied
(0.22-0.88 M). In the second set of experiments (Figure 3B),
(33) For a general discussion of cone angles, see: (a) Tolman, C. A. J.
Am. Chem. Soc. 1970, 92, 2956. (b) Tolman, C. A. Chem. ReV. 1977, 77,
the concentration of SPri2 was kept constant (0.88 M) while
313. (c) Bunten, K. A.; Chen, L.; Fernandez, A. L.; Poe¨, A. J. Coord. Chem.
varying the concentration of PhBr (0.22-0.88 M). The plots
ReV. 2002, 233-234, 41.
(34) Harris, S. Organometallics 1994, 13, 2628.
of ln[10] versus time were linear over 3 half-lives. Figure 3C
(35) Collman, J. P.; Hegedus, L. S.; Norton, J. R.; Finke, R. G. Principles
and Applications of Organotransition Metal Chemistry; University Science
Books: Mill Valley, CA, 1987; p 306.
(36) Barrios-Landeros, F.; Hartwig, J. F. J. Am. Chem. Soc. 2005, 127,
6944.

Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh
Organometallics, Vol. 26, No. 25, 2007 6071
Scheme 9
clearly shows that the observed pseudo first-order rate constant
(kobs) is inversely proportional to the concentration of SPri2. On
the other hand, Figure 3D clearly shows the linear dependence
of 1/kobs on the concentration of 1/[PhBr], indicating positive
dependence of the reaction rate on [PhBr].
The combination of positive dependence on [PhBr] and
inverse dependence on [SPri2] is only consistent with a mech-
anism that involves reversible dissociation of SPri2 followed
by irreversible addition of PhBr (Scheme 8).36 In other words,
dissociation of SPri2 produces (PNP)Rh (1), which subsequently
can either re-coordinate SPri2 or undergo addition of PhBr.
Importantly, addition of PhBr occurs only after loss of SPri2.
This reaction follows (qualitatively) the same rate law as the
addition of PhCl to 22.36 However, in the latter study, addition
of PhBr was faster, and the reaction did not display inverse
dependence on [Q-phos] and thus followed an apparently
different rate law. However, that still can be construed as the
same mechanism as the difference amounts simply to the much
greater k2 for PhBr. The addition of PhI to 22 was reported to
proceed even faster and by an associative mechanism.36 We have
not performed scrupulous kinetic studies for aryl halides other
than PhBr, but we have determined that, qualitatively, the rate
of oxidative addition increases in the series PhCl < PhBr <
PhI. For instance, in reactions of 10 with 3 equiv of PhI, PhBr,
or PhCl at 65 °C in C6D6, the conversions to the corresponding
OA products after 1 h, as measured by 31P{1H} NMR, were as
follows: (18c, 95%) > (18b, 85%) > (18a, 45%).
Oxidative Addition of PhBr to 10, 19a/b, and 21. The
activation energy for dissociation of L from (PNP)Rh(L) can
be roughly equated to the Rh-L bond dissociation energy.37 In
essence, we have measured the differences among the latter in
our equilibrium studies (vide supra). If we assume the same
mechanism for OA reactions of various (PNP)Rh(L) with, for
instance, PhBr, then the rate of the reaction should increase with
decreasing strength of binding of L. Toward this end, we used
31P NMR to monitor the reactions of PhBr with 10, 19a/b, and
21 at 65 °C in C6D6. The relative rates for the OA reaction
were as follows, based on the observed conversions after 40
min: 21 (95%) > 10 (85%) > 19a/b (4%). These results are
consistent with the relative affinities of (PNP)Rh for the three
ligands (vide supra) in the order H2CdCHBut < SPri2 < N2.
Kinetics of the Conversion of 10 to 16. To investigate
whether ligand exchange in (PNP)Rh(L) systems occurs by a
mechanism similar to that of OA of PhBr, we set out to probe
the dependence of the rate of conversion of 10 to 16 as a
function of [SPri2] and [Ph2SO]. We selected this pair of ligands
primarily because the reaction can be practically considered
irreversible for the purposes of this investigation (K ) 400, vide
supra). We observed faster conversion to 16 in the presence of
higher concentration of [Ph2SO] when [SPri2] was kept constant
and, conversely, slower conversion to 16 in the presence of
higher concentration of [SPri2] when [Ph2SO] was kept constant.
These experiments qualitatively demonstrate that the rate of the
forward reaction depends positively on [Ph2SO] and inversely
on [SPri2]. No evidence of five-coordinate RhI compounds
(putative intermediates in an associative exchange pathway) was
detected, including in a separate experiment where 10 was
treated with 50 equiv of SPri2. Although our qualitative findings
do not allow one to paint a definitive mechanistic picture, they
are consistent with the displacement of SPri2 in 10 by Ph2SO
to give 16 proceeding similarly to OA of PhBr (Scheme 8),
that is, reversible dissociation of SPri2, followed by effectively
irreversible coordination of Ph2SO (Scheme 9). It seems likely
that these findings might apply to other ligands in this study.
Summary
We have prepared a series of complexes (PNP)Rh(L) where
L is an organic sulfide, dinitrogen, or an olefin. The relative
affinity of (PNP)Rh (1) for various organic sulfides is guided
primarily by steric factors. On the other hand, the affinity for
(PNP)Rh (1) increases in the following series thiophene <
benzothiophene < dibenzothiophene, which is ascribed to
electronic effects. (PNP)Rh(SPh2) (9) exists in observable
equilibrium with its C-S oxidative addition form (PNP)Rh-
(Ph)(SPh) (17) at 65 °C. The (PNP)Rh(L) complexes generate
the fleeting (PNP)Rh species 1 in situ via dissociation of L and
serve well as synthons for 1 in oxidative addition reactions with
aryl halides. The reaction of (PNP)Rh(SPri2) (10) with PhBr
was determined to proceed via reversible dissociation of SPri2
followed by irreversible addition of PhBr. Displacement of SPri2
in 10 with Ph2SO to give (PNP)Rh(Ph2SO) (16) proceeds by
an analogous mechanism.
Experimental Section
General Considerations. Unless specified otherwise, all ma-
nipulations were performed under an argon atmosphere using
standard Schlenk line or glovebox techniques. Toluene, ethyl ether,
THF, pentane, and isooctane were dried and deoxygenated (by
purging) using a solvent purification system38 by MBraun and stored
over molecular sieves in an Ar-filled glovebox. C6D6 was dried
over and distilled from NaK/Ph2CO/18-crown-6 and stored over
molecular sieves in an Ar-filled glovebox. Fluorobenzene, chlo-
robenzene, bromobenzene, iodobenzene, and CD2Cl2 were dried,
then distilled or vacuum transferred from CaH2 and stored over
molecular sieves in an Ar-filled glovebox. Liquid dialkyl sulfides
were degassed prior to use and stored over molecular sieves in an
Ar-filled glovebox. (PNP)Rh(Me)(Cl) (4),39 (PNP)Rh(H)(Cl) (5),39
and (PNP)Rh(Ph)(Br) (18b)11a were prepared according to modified
published procedures. All other chemicals were used as received
from commercial vendors. PhLi was used as a 2 M solution in
Bu2O; MeMgCl was used as a 3.1 M solution in THF. NMR spectra
were recorded on a Varian iNova 400 (1H NMR, 399.755 MHz;
13C NMR, 100.518 MHz; 31P NMR, 161.822 MHz; 19F NMR,
1
376.104 MHz) spectrometer. For H and 13C NMR spectra, the
residual solvent peak was used as an internal reference. 31P NMR
spectra were referenced externally using 85% H3PO4 at 0 ppm.
Synthesis of (PNP)Rh(SBus2) (6). 4 (40.0 mg, 0.068 mmol) was
treated with SsBu2 (13 µL, 0.074 mmol) in C6D6 (0.7 mL) in a J.
Young NMR tube followed by addition of PhLi (36.0 µL, 0.074
mmol). After 24 h at ambient temperature, the solution was
evaporated to dryness, and the residue was passed through a plug
of silica gel with Et2O as eluent. The resultant ether solution was
(37) There is some debate in the literature pertaining to this approxima-
tion: (a) Zhang, S.; Dobson, G. R. Inorg. Chim. Acta 1991, 181, 103. (b)
Asali, K. J.; Awad, H. H.; Kimbrough, J. F.; Lang, B. C.; Watts, J. M.;
Dobson, G. R. Organometallics 1991, 10, 1822. (c) Bryndza, H. E.;
Domaille, P. J.; Paciello, R. A.; Bercaw, J. E. Organometallics 1989, 8,
379. (d) Klassen, J. K.; Selke, M.; Sorensen, A. A.; Yang, G. K. J. Am.
Chem. Soc. 1990, 112, 1267.
(38) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(39) (a) Ozerov, O. V.; Guo, C.; Papkov, V. A.; Foxman, B. M. J. Am.
Chem. Soc. 2004, 126, 4792. (b) Weng, W.; Guo, C.; Moura, C. P.; Yang,
L.; Foxman, B. M.; Ozerov, O. V. Organometallics 2005, 24, 3487.

6072 Organometallics, Vol. 26, No. 25, 2007
Gatard et al.
evaporated to dryness to yield an orange solid residue. This residue
was dissolved in Et2O and placed in the freezer at -35 °C to afford
6 by precipitation. Yield: 18 mg (39%). NMR data for 6 follow.16
1H NMR (C6D6): δ 7.72 (d, 2H, 8 Hz, Ar-H of PNP), 6.99 (s,
2H, Ar-H of PNP), 6.78 (d, 2H, 8 Hz, Ar-H of PNP), 2.65 (m,
2H, SCH), 2.48 (m, 4H, SCHCH2), 2.25 (s, 6H, Ar-CH3 of PNP),
2.25 (m, 4H, CHMe2), 1.40 (app. quartet (dvt), 12H, 8 Hz, CHMe2),
1.34 (d, 6H, 8 Hz, SCHCH3), 1.16 (app. quartet (dvt), 12H, 8 Hz,
CHMe2), 0.85 (m, 6H, SCHCH2CH3). 13C{1H} NMR (C6D6): δ
163.3 (vt, 10 Hz, C-N of PNP), 131.2 (s, CAr of PNP), 131.0 (s,
CAr of PNP), 123.2 (vt, 18 Hz, CAr of PNP), 122.6 (vt, 3 Hz, CAr
of PNP), 115.6 (vt, 5 Hz, CAr of PNP), 50.2 (s, SCH), 31.5, 31.4
(two s, SCHCH2), 24.3 (vt, 9 Hz, CH(CH3)2), 21.1 (s, SCHCH3),
20.7 (s, Ar-CH3), 19.7, 17.4 (two s, CH(CH3)2), 11.6 (two s,
SCHCH2CH3). 31P{1H} NMR (C6D6): δ 41.0 (d, 146 Hz, P(Pri)2).
Synthesis of (PNP)Rh(SPri2) (10). 4 (809.0 mg, 1.40 mmol)
was treated with SPri2 (222 µL, 1.53 mmol) in fluorobenzene (10
mL) in a Teflon stoppered gastight round-bottom flask. The reaction
mixture was stirred for 10 min at ambient temperature, and MeMgCl
(493 µL, 1.53 mmol) was added. After being stirred for 10 min,
the solution was filtered through Celite, then passed through a short
column of silica, and then filtered through Celite again. The resultant
solution was evaporated to dryness to yield an orange solid residue.
This residue was dissolved in Et2O and placed in the freezer at
1
-35 °C to afford 10 by precipitation. Yield: 478 mg (53%). H
NMR (C6D6): δ 7.70 (d, 2H, 9 Hz, Ar-H of PNP), 6.98 (s, 2H,
Ar-H of PNP), 6.77 (d, 2H, 8 Hz, Ar-H of PNP), 2.64 (septet,
2H, 6 Hz, SCHMe2), 2.25 (s, 6H, Ar-CH3 of PNP), 2.25 (m, 4H,
CHMe2), 1.37 (app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.37 (d,
12H, 6 Hz, SCHMe2), 1.17 (app. quartet (dvt), 12H, 8 Hz, CHMe2).
13C{1H} NMR (C6D6): δ 163.3 (vt, 10 Hz, C-N of PNP), 131.2
(s, CAr of PNP), 130.9 (s, CAr of PNP), 123.2 (vt, 18 Hz, CAr of
PNP), 122.5 (vt, 3 Hz, CAr of PNP), 115.6 (vt, 5 Hz, CAr of PNP),
44.0 (s, SCHMe2), 25.1 (s, SCH(CH3)2), 24.4 (vt, 15 Hz, CH-
(CH3)2), 20.7 (s, Ar-CH3), 19.7, 17.5 (two s, CH(CH3)2). 31P{1H}
NMR (C6D6): δ 40.9 (d, 105 Hz). Anal. Calcd for C32H54-
NRhP2S: C, 58.94; H, 8.21. Found: C, 59.15; H, 8.37.
N.B.: Commercial SsBu2 is a 1:1 mixture of rac- and meso-
1
isomers. Some, but not all, of their H and 13C NMR resonances
are distinguishable. Data for this mixture follow. 1H NMR (C6D6):
δ 2.54 (sextet, 2H, 7 Hz, SCH), 1.50 (m, 2H, SCHCHaHb), 1.40
(m, 2H, SCHCHaHb), 1.15 (2 d are overlapping, 6H, 7 Hz,
SCHCH3), 0.91 (t, 3H, 8 Hz, SCHCH2CH3), 0.90 (t, 3H, 8 Hz,
SCHCH2CH3). 13C{1H} NMR (C6D6): δ. 40.4 (s, SCH), 30.4, 30.3
(two singlets, SCHCH2), 21.5 (two singlets, SCHCH3), 11.7, 11.3
(two singlets, SCHCH2CH3).
Synthesis of (PNP)Rh(SBun ) (11). 5 (30.0 mg, 0.053 mmol)
2
was treated with SBun2 (9.3 µL, 0.053 mmol) in C6D6 (0.7 mL) in
a J. Young NMR tube followed by NaOtBu (7.6 mg, 0.079 mmol).
After 10 min, the solution was treated with water (1.5 mL) and
then evaporated to dryness, and the residue was extracted with ether
and filtered through Celite. The filtrate was evaporated to dryness
to yield an orange solid residue. This residue was triturated three
times with toluene (3 × 1 mL) and dried to give 11 that was >95%
Synthesis of (PNP)Rh(SBut2) (7). 4 (20.0 mg, 0.034 mmol) was
treated with tert-butyl sulfide (18.5 µL, 0.103 mmol) in C6D6 (0.7
mL) in a J. Young NMR tube followed by addition of PhLi (19.0
µL, 0.038 mmol). After 24 h at ambient temperature, 7 was observed
1
1
by H and 31P{1H} NMR and characterized in solution in situ. H
NMR (C6D6): δ 7.56 (d, 2H, 8 Hz, Ar-H of PNP), 6.99 (s, 2H,
Ar-H of PNP), 6.73 (d, 2H, 8 Hz, Ar-H of PNP), 2.33 (m, 4H,
CHMe2), 2.23 (s, 6H, Ar-CH3 of PNP), 1.51 (app. quartet (dvt),
12H, 8 Hz, CHMe2), 1.43 (s, 18H, SC(CH3)3), 1.21 (app. quartet
(dvt), 12H, 8 Hz, CHMe2). 31P{1H} NMR (C6D6): δ 36.6 (d, 148
Hz).
1
pure by NMR. Yield: 27 mg (90%). H NMR (C6D6): δ 7.78 (d,
2H, 9 Hz, Ar-H of PNP), 7.04 (s, 2H, Ar-H of PNP), 6.79 (d,
2H, 8 Hz, Ar-H of PNP), 2.47 (t, 4H, 8 Hz, SCH2), 2.26 (s, 6H,
Ar-CH3 of PNP), 2.26 (m, 4H, CHMe2), 1.70 (q, 4H, 8 Hz,
SCH2CH2), 1.42 (app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.30
(sextet, 4H, 8 Hz, SCH2CH2CH2), 1.22 (app. quartet (dvt), 12H, 8
Hz, CHMe2), 0.85 (t, 6H, 8 Hz, SCH2CH2CH2CH3). 13C{1H} NMR
(C6D6): δ 163.5 (vt, 10 Hz, C-N of PNP), 131.4 (s, CAr of PNP),
131.0 (s, CAr of PNP), 123.1 (vt, 18 Hz, CAr of PNP), 122.8 (vt, 3
Hz, CAr of PNP), 115.6 (vt, 5 Hz, CAr of PNP), 42.9 (s, SCH2),
31.4 (s, SCH2CH2), 25.1 (vt, 9 Hz, CH(CH3)2), 22.5 (s, SCH2-
CH2CH2), 20.6 (s, Ar-CH3), 19.9, 17.9 (two singlets, CH(CH3)2),
13.9 (s, SCH2CH2CH2CH3). 31P{1H} NMR (C6D6): δ 43.2 (d, 145
Hz).
Synthesis of (PNP)Rh(StBuMe) (12). This was synthesized
analogously to the preparation of 11 from 5 (23.0 mg, 0.040 mmol),
NaOtBu (4.27 mg, 0.044 mmol), and StBuMe (6 µL, 0.044 mmol).
Yield: 0.011 g (43%). 1H NMR (C6D6): δ 7.73 (d, 2H, 8 Hz, Ar-H
of PNP), 7.07 (s, 2H, Ar-H of PNP), 6.77 (d, 2H, 8 Hz, Ar-H of
PNP), 2.24 (s, 6H, Ar-CH3 of PNP), 2.24 (m, 4H, CHMe2), 1.93
(s, 3H, S-CH3), 1.41 (app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.17
(app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.16 (s, 9H, SC(CH3)3).
13C{1H} NMR (C6D6): δ 163.7 (vt, 10 Hz, C-N of PNP), 131.4
(s, CAr of PNP), 131.1 (s, CAr of PNP), 123.1 (vt, 18 Hz, CAr of
PNP), 122.8 (vt, 3 Hz, CAr of PNP), 115.9 (vt, 6 Hz, CAr of PNP),
44.5 (s, SC(CH3)3), 29.7 (s, SC(CH3)3), 25.2 (m, SCH3), 22.7 (vt,
6 Hz, CH(CH3)2), 20.6 (s, Ar-CH3), 19.9, 18.1 (two singlets, CH-
(CH3)2). 31P{1H} NMR (C6D6): δ 41.0 (d, 146 Hz).
Synthesis of (PNP)Rh(SPhMe) (8). This was synthesized
analogously to the preparation of 6 from 4 (40.0 mg, 0.068 mmol),
PhLi (38 µL, 0.076 mmol), and thioanisole (9 µL, 0.076 mmol).
Yield: 0.025 g (58%). 1H NMR (C6D6): δ 7.83 (d, 2H, 9 Hz, Ar-H
of PNP), 7.76 (d, 2H, 8 Hz, SC6H5), 7.02 (t, 2H, 8 Hz, SC6H5),
7.01 (s, 2H, Ar-H of PNP), 6.88 (t, 1H, 8 Hz, p-SC6H5), 6.80 (d,
2H, 8 Hz, Ar-H of PNP), 2.39 (s, 3H, SCH3), 2.23 (s, 6H, Ar-
CH3 of PNP), 2.16 (m, 4H, CHMe2), 1.22 (app. quartet (dvt), 12H,
8 Hz, CHMe2), 1.15 (app. quartet (dvt), 12H, 8 Hz, CHMe2). 13C-
{1H} NMR (C6D6): δ 163.6 (vt, 10 Hz, C-N of PNP), 142.9 (s,
S-i-C6H5), 131.6 (s, CAr of PNP), 131.1 (s, CAr of PNP), 129.1 (s,
SC6H5), 127.3 (s, SC6H5), 126.5 (s, S-p-C6H5), 123.1 (vt, 3 Hz,
CAr of PNP), 122.8 (vt, 18 Hz, CAr of PNP), 115.7 (vt, 5 Hz, CAr
of PNP), 26.8 (t, 4 Hz, SCH3), 25.1 (vt, 15 Hz, CH(CH3)2), 20.6
(s, Ar-CH3), 19.3, 18.0 (two singlets, CH(CH3)2). 31P{1H} NMR
(C6D6): δ 43.6 (d, 142 Hz). Anal. Calcd for C33H48NRhP2S: C,
59.97; H, 7.26. Found: C, 60.45; H, 7.37.
Synthesis of (PNP)Rh(SPh2) (9). This was synthesized analo-
gously to the preparation of 6 from 4 (40.0 mg, 0.068 mmol), PhLi
(38.0 µL, 0.076 mmol), and diphenyl sulfide (12.8 µL, 0.076 mmol).
Yield: 25 mg (51%). 1H NMR (C6D6): δ 7.84 (d, 2H, 9 Hz, Ar-H
of PNP), 7.78 (d, 4H, 8 Hz, SC6H5), 7.01 (s, 2H, Ar-H of PNP),
6.96 (t, 4H, 8 Hz, SC6H5), 6.88 (t, 2H, 8 Hz, p-SC6H5), 6.80 (d,
2H, 8 Hz, Ar-H of PNP), 2.22 (s, 6H, Ar-CH3 of PNP), 1.88 (m,
4H, CHMe2), 1.17 (2 app. quartets (dvt) are overlapping, 24H, 8
Hz, CHMe2). 13C{1H} NMR (C6D6): δ 163.6 (vt, 10 Hz, C-N of
PNP), 139.6 (s, S-i-C6H5), 131.6 (s, CAr of PNP), 131.5 (s, SC6H5),
131.1 (s, CAr of PNP), 129.3 (s, SC6H5), 127.3 (s, S-p-C6H5), 123.3
(vt, 18 Hz, CAr of PNP), 123.3 (vt, 18 Hz, CAr of PNP), 115.8 (vt,
5 Hz, CAr of PNP), 24.9 (vt, 12 Hz, CH(CH3)2), 20.6 (s, Ar-CH3),
19.4, 17.9 (two singlets, CH(CH3)2). 31P{1H} NMR (C6D6): δ 43.6
(d, 142 Hz, P(Pri)2).
Synthesis of (PNP)Rh(T) (13). 5 (40.0 mg, 0.070 mmol) was
treated with thiophene (6.20 µL, 0.078 mmol) in C6D6 (0.7 mL) in
a J. Young NMR tube followed by NaOtBu (7.5 mg, 0.078 mmol).
13 was characterized in situ by NMR spectroscopy. 1H NMR
(C6D6): δ 7.80 (d, 2H, 9 Hz, Ar-H of PNP), 7.10 (br s, 2H, SCH),
6.98 (s, 2H, Ar-H of PNP), 6.79 (br s, 2H, SCHCH), 6.79 (d, 2H,
6 Hz, Ar-H of PNP), 2.19 (s, 6H, Ar-CH3 of PNP), 1.94 (m, 4H,
CHMe2), 1.13 (app. quartet (dvt), 24H, 8 Hz, CHMe2). 13C{1H}
NMR (C6D6): δ 163.7 (vt, 10 Hz, C-N of PNP), 133.3 (s, SCH),

Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh
Organometallics, Vol. 26, No. 25, 2007 6073
131.8 (s, CAr of PNP), 131.4 (s, CAr of PNP), 126.4 (s, SCHCH),
123.8 (vt, 3 Hz, CAr of PNP), 122.5 (vt, 18 Hz, CAr of PNP), 115.6
(vt, 5 Hz, CAr of PNP), 25.2 (vt, 11 Hz, CH(CH3)2), 20.5 (s, Ar-
CH3), 19.0, 18.3 (two s, CH(CH3)2). 31P{1H} NMR (C6D6): δ 47.9
(d, 133 Hz).
Yield: 60 mg (92%). 1H NMR (CD2Cl2, -50 °C): δ 8.20 (br d, 8
Hz, 1H, C6H5), 7.76 (d, 2H, 8 Hz, Ar-H of PNP), 7.50 (d, 2H, 8
Hz, SC6H5), 7.06-6.98 (three triplets are overlapping, 3H, SC6H5),
6.97 (d, 2H, 8 Hz, Ar-H of PNP), 6.91 (s, 2H, Ar-H of PNP),
6.68 (t, 1H, 8 Hz, C6H5), 6.61 (t, 1H, 8 Hz, C6H5), 6.41 (br d, 8
Hz, 1H, C6H5), 6.29 (t, 1H, 8 Hz, C6H5), 2.48 (br m, 2H, CHMe2),
2.39 (br m, 2H, CHMe2), 2.22 (s, 6H, Ar(PNP) -CH3), 1.08 (br
app. quartet (dvt), 6H, 8 Hz, CHMe2), 1.01 (br app. quartet (dvt),
6H, 8 Hz, CHMe2), 0.80 (br app. quartet (dvt), 6H, 8 Hz, CHMe2),
0.12 (br app. quartet (dvt), 6H, 8 Hz, CHMe2). 13C{1H} NMR (CD2-
Cl2, -50 °C): δ 160.0 (vt, 10 Hz, C-N of PNP), 148.2 (t, JC-Rh
) 6 Hz, S-i-C6H5), 141.3 (s, Ar-C), 140.5 (dt, JC-P ) 9 Hz, JC-Rh
) 38 Hz, i-C6H5), 134.6, 134.1 (two s, 2C, Ar-C), 132.9, 131.4
(s, 2C, CAr of PNP), 127.7 (s, Ar-C), 126.6 (s, Ar-C), 126.1 (s,
Ar-C), 125.8 (vt, 3 Hz, CAr of PNP), 123.9 (s, Ar-C), 122.6 (s,
Ar-C), 118.3 (vt, 18 Hz, CAr of PNP), 117.5 (vt, 6 Hz, CAr of
PNP), 25.9 (vt, 11 Hz, CH(CH3)2), 23.9 (vt, 13 Hz, CH(CH3)2),
20.26, 20.16 (two s, 2C, Ar-CH3), 19.4 (br s, CH(CH3)2), 17.2-
16.5 (seven br s, 7C, CH(CH3)2). 31P{1H} NMR (CD2Cl2): δ 37.7
(d, 108 Hz).
Synthesis of (PNP)Rh(BT) (14). 5 (40.0 mg, 0.070 mmol) was
treated with benzothiophene (10.4 mg, 0.078 mmol) in C6D6 (0.7
mL) in a J. Young NMR tube followed by NaOtBu (7.5 mg, 0.078
1
mmol). 14 was characterized in situ by NMR spectroscopy. H
NMR (C6D6): δ 8.03 (br d, 1H, SC8H6), 7.81 (d, 2H, 8 Hz, Ar-H
of PNP), 7.44 (br d, 1H, SC8H6), 7.15-6.89 (other SC8H6
resonances overlapped with C6D5H and free benzothiophene
resonances, 4H), 6.96 (s, 2H, Ar-H of PNP), 6.80 (d, 2H, 8 Hz,
Ar-H of PNP), 2.21 (s, 6H, Ar-CH3 of PNP), 2.07 (m, 4H,
CHMe2), 1.10 (app. quartet (dvt), 24H, 8 Hz, CHMe2). 13C{1H}
NMR (C6D6): δ 163.6 (vt, 10 Hz, C-N of PNP), 147.5 (s, SC8H6),
140.0 (s, SC8H6), 134.8 (s, SC8H6), 131.7 (s, CAr of PNP), 131.4
(s, CAr of PNP), 125.2 (s, SC8H6), 124.8 (s, SC8H6), 124.6 (s,
SC8H6), 124.3 (s, SC8H6), 123.7 (vt, 3 Hz, CAr of PNP), 123.5 (s,
SC8H6), 122.5 (vt, 18 Hz, CAr of PNP), 115.5 (vt, 5 Hz, CAr of
PNP), 25.1 (vt, 10 Hz, CH(CH3)2), 20.5 (s, Ar-CH3), 19.0, 18.2
(two s, CH(CH3)2). 31P{1H} NMR (C6D6): δ 46.1 (d, 135 Hz).
Synthesis of (PNP)Rh(DBT) (15). 5 (40.0 mg, 0.070 mmol)
was treated with dibenzothiophene (14.3 mg, 0.078 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube followed by NaOtBu (7.5 mg,
0.078 mmol). 15 was characterized in situ by NMR spectroscopy.
1H NMR (C6D6): δ 8.11 (d, 2H, 8 Hz, SC12H8), 7.82 (d, 2H, 8 Hz,
Ar-H of PNP), 7.72 (d, 2H, 8 Hz, SC12H8), 7.21-7.15 (other
SC12H8 resonances overlapped with C6H6 and free dibenzothiophene
resonances, 4H), 6.94 (s, 2H, Ar-H of PNP), 6.81 (d, 2H, 8 Hz,
Ar-H of PNP), 2.21 (s, 6H, Ar-CH3 of PNP), 2.03 (m, 4H,
CHMe2), 1.07 (app. quartet (dvt), 24H, 8 Hz, CHMe2). 13C{1H}
NMR (C6D6): δ 163.5 (vt, 10 Hz, C-N of PNP), 145.7 (s, SC12H8),
136.4 (s, SC12H8), 131.7 (s, CAr of PNP), 131.4 (s, CAr of PNP),
126.8 (s, SC12H8), 125.8 (s, SC12H8), 124.6 (s, SC12H8), 123.7 (vt,
3 Hz, CAr of PNP), 123.5 (s, SC12H8), 122.6 (vt, 18 Hz, CAr of
PNP), 121.7 (s, SC12H8), 115.5 (vt, 5 Hz, CAr of PNP), 24.8 (vt, 10
Hz, CH(CH3)2), 20.5 (s, Ar-CH3), 18.9, 18.0 (two s, CH(CH3)2).
31P{1H} NMR (C6D6): δ 46.0 (d, 136 Hz).
Observation of Interconversion of 9 and 17. Experiment A.
9 (20.0 mg) was dissolved in 0.7 mL of C6D6 in a J. Young NMR
tube, and the solution was heated at 65 °C for 18 h. Experiment
B. 17 (20.0 mg) was dissolved in 0.7 mL of C6D6 in a J. Young
NMR tube, and the solution was heated at 65 °C for 18 h.
Experiment C. 10 (0.020 g, 0.031 mmol) was treated with diphenyl
sulfide (15.6 µL, 0.092 mmol) in C6D6 (0.7 mL) in a J. Young
NMR tube. The solution was heated at 65 °C for 24 h. In all three
experiments, a 1:1 mixture of 9:17 was observed following the
thermolyses.
Synthesis of (PNP)Rh(µ-N2)Rh(PNP) (19a) and (PNP)Rh(η1-
N2) (19b). A solution of 4 (30 mg, 0.051 mmol) in C6D6 (0.7 mL)
in a J. Young NMR tube was degassed by freeze-pump-thaw
techniques, and the tube was back-filled with N2. Next, the tube
was taken into an argon glovebox, opened, and MeMgCl (18 µL,
0.057 mmol) was added. After 10 min at ambient temperature, 19a
was the only compound observed by 31P{1H} NMR (>95%). The
solution was degassed again by freeze-pump-thaw techniques,
and the tube was back-filled with N2. After 18 h at ambient
temperature, a 7:3 mixture of 19a:19b was observed by 31P{1H}
NMR. The resulting solution was filtered through a plug of silica.
The filtrate was evaporated to dryness to yield an orange solid
residue. The residue contained 19a:19b in a 7:3 ratio and was >95%
pure (NMR evidence). A small sample of pure 19a was obtained
by recrystallization from an ether solution of 19a/b at -35 °C.
Synthesis of (PNP)Rh(S(O)Ph2) (16). 10 (40.0 mg, 0.062 mmol)
was treated with phenyl sulfoxide (13.7 mg, 0.068 mmol) in C6D6
(0.7 mL) in a J. Young NMR tube and heated at 65 °C for 18 h.
The resultant solution was evaporated to dryness to yield an orange
solid residue. Next, this residue was dissolved in Et2O and placed
in the freezer at -35 °C to afford 16 by precipitation. Yield: 0.025
1
1
19a. H NMR (C6D6): δ 7.67 (d, 2H, 9 Hz, Ar-H of PNP), 6.96
g (55%). H NMR (C6D6): δ 8.07 (d, 4H, 7 Hz, SC6H5), 7.77 (d,
(s, 2H, Ar-H of PNP), 6.75 (d, 2H, 9 Hz, Ar-H of PNP), 2.29
(m, 4H, CHMe2), 2.20 (s, 6H, Ar-CH3 of PNP), 1.45 (app. quartet
(dvt), 12H, 8 Hz, CHMe2), 1.21 (app. quartet (dvt), 12H, 8 Hz,
CHMe2). 13C{1H} NMR (C6D6): δ 163.5 (vt, 10 Hz, C-N of PNP),
131.9 (s, CAr of PNP), 131.6 (s, CAr of PNP), 124.3 (vt, 3 Hz, CAr
of PNP), 121.0 (vt, 18 Hz, CAr of PNP), 115.9 (vt, 5 Hz, CAr of
PNP), 25.5 (vt, 10 Hz, CH(CH3)2), 20.5 (s, Ar-CH3), 19.7 (s, CH-
(CH3)2), 18.4 (s, CH(CH3)2). 31P{1H} NMR (C6D6): δ 51.1 (d, 139
Hz). Data for 19b follow (identified in a 19a/19b mixture): 7.64
(d, 2H, 9 Hz, Ar-H of PNP), 6.90 (s, 2H, Ar-H of PNP), 6.75 (d,
2H, 9 Hz, Ar-H of PNP), 2.29 (m, 4H, CHMe2), 2.20 (s, 6H, Ar-
CH3 of PNP), 1.28 (app. quartet (dvt), 12H, 8 Hz, CHMe2), 1.11
(app. quartet (dvt), 12H, 8 Hz, CHMe2). 13C{1H} NMR (C6D6): δ
163.2 (vt, 10 Hz, C-N of PNP), 131.7 (s, CAr of PNP), 131.5 (s,
CAr of PNP), 123.9 (vt, 3 Hz, CAr of PNP), 121.0 (vt, 18 Hz, CAr
of PNP), 115.9 (vt, 5 Hz, CAr of PNP), 25.1 (vt, 10 Hz, CH(CH3)2),
20.4 (s, Ar-CH3), 19.4 (s, CH(CH3)2), 18.2 (s, CH(CH3)2). 31P-
{1H} NMR (C6D6): δ 52.4 (d, 137 Hz). IR (C6D6): νNtN 2115
2H, 8 Hz, Ar-H of PNP), 7.07 (s, 2H, Ar-H of PNP), 6.90 (2
triplets overlapped, 6H, 8 Hz, SC6H5), 6.79 (d, 2H, 8 Hz, Ar-H of
PNP), 2.19 (s, 6H, Ar-CH3 of PNP), 1.94 (m, 4H, CHMe2), 1.20
(app. quartet (dvt), 24H, 8 Hz, CHMe2). 13C{1H} NMR (C6D6): δ
162.9 (vt, 10 Hz, C-N of PNP), 153.3 (s, S-i-C6H5), 131.6 (s,
CAr of PNP), 131.3 (s, CAr of PNP), 130.4 (s, SC6H5), 129.1 (s,
SC6H5), 124.5 (s, SC6H5), 123.8 (vt, 3 Hz, CAr of PNP), 122.8 (vt,
18 Hz, CAr of PNP), 116.1 (vt, 6 Hz, CAr of PNP), 24.8 (vt, 6 Hz,
CH(CH3)2), 20.6 (s, Ar-CH3), 19.8, 18.1 (two singlets, CH(CH3)2).
31P{1H} NMR (C6D6): δ 41.0 (d, 146 Hz). Anal. Calcd for C38H50-
NORhP2S: C, 61.98; H, 6.68. Found: C, 62.20; H, 6.86.
Synthesis of (PNP)Rh(SPh)(Ph) (17). 18b (63.0 mg, 0.091
mmol) was treated with thiophenol (10.3 µL, 0.100 mmol) in
fluorobenzene (2 mL) in a Teflon stoppered gastight round-bottom
flask. The reaction mixture was stirred for 10 min at ambient
temperature, and NaOtBu (9.6 mg, 0.100 mmol) was added. After
another 10 min, the solution was treated with water (1.8 mL) and
then evaporated to dryness. The residue was extracted with Et2O
and filtered through Celite. The filtrate was evaporated to dryness
to yield a green solid residue. This residue was triturated three times
with toluene (3 × 5 mL) to give 17 that was >95% pure by NMR.
cm-1
.
Interconversion between 19a and 19b. A solution of 4 (80 mg,
0.14 mmol) in C6D6 (3 mL) in a Teflon stoppered gastight round-

6074 Organometallics, Vol. 26, No. 25, 2007
Gatard et al.
bottom flask was degassed by freeze-pump-thaw techniques, and
the flask was back-filled with N2. The reaction mixture was stirred
for 10 min at ambient temperature, and the flask was taken into an
argon glovebox, opened, and MeMgCl (49 µL, 0.15 mmol) was
added. After 10 min at room temperature, 19a was the only
compound observed by 31P{1H} NMR. The solution was then
degassed by freeze-pump-thaw techniques, and the flask was
back-filled with N2. Thermolysis of this solution during 3 d at
65 °C resulted in a conversion to a 5:95 mixture of 19a:19b (NMR
evidence). Removal of the overhead N2 gas and continued ther-
molysis (65 °C) changed the ratio to 50:50.
Reaction of (PNP)Rh(SPri2) (10) with N2 To Yield 19a and
19b. A solution of 10 (20.0 mg, 0.031 mmol) in C6D6 (0.7 mL) in
a J. Young NMR tube was degassed by freeze-pump-thaw
techniques, and the NMR tube was back-filled with N2. The sample
was placed in an oil bath, which was preheated at 65 °C. The
disappearance of 10 was monitored by 31P{1H} NMR. After 24 h
at 65 °C, a mixture of 19a (66%), 19b (17%), and 10 (17%) was
observed by 31P{1H} NMR.
of 10 was monitored by 31P{1H} NMR. In the course of the reaction,
10 was converted into 18c, 18b, or 18a, respectively. After 40 min
at 65 °C, the conversions measured by 31P{1H} NMR were as
follows: (18c, 95%), (18b, 85%), and (18a, 45%). Compound 18a
formed quantitatively after 16 h at 65 °C in C6D6.
Oxidative Addition of PhBr to 19a/b, 10, and 21. Experiment
A. A mixture of complexes 19a/b in a 7:3 ratio (27 mg, 0.049
mmol Rh) was obtained as described above from complex 4 (30.0
mg, 0.051 mmol) and MeMgCl (18.0 µL, 0.057 mmol). The mixture
was dissolved in C6D6 (0.8 mL) in a J. Young NMR tube followed
by addition of PhBr (15.6 µL, 0.154 mmol). Experiment B. 10
(22.0 mg, 0.034 mmol) was dissolved in 0.8 mL of C6D6 in a J.
Young NMR tube followed by addition of PhBr (10.3 µL, 0.102
mmol). Experiment C. 21 (21.0 mg, 0.034 mmol) was dissolved
in 0.8 mL of C6D6 in a J. Young NMR tube followed by addition
of PhBr (10.3 µL, 0.102 mmol). Thermolysis. The three NMR tubes
from experiments A, B, and C were placed into the same oil bath
that was preheated to 65 °C. In the course of the reaction, 10, 19,
and 21 were being converted into 18b; the reaction progress was
monitored by 31P{1H} NMR spectroscopy. After 40 min, the
conversions measured by 31P{1H} NMR were as follows: exp. C
(21), 95%; exp. B (10), 85%; and exp. A (19a/b), 4%.
Kinetic Study of the Reaction of (PNP)Rh(SPri2) (10) with
PhBr. Experiments with Varying Concentrations of PhBr. 10
(0.020 g, 0.031 mmol) was dissolved in C6D6 in a J. Young NMR
tube and treated with PhBr (four different experiments for four
different concentrations of PhBr: 15.6 µL, 0.155 mmol, 0.22 M;
31.2 µL, 0.310 mmol, 0.44 M; 46.8 µL, 0.465 mmol, 0.66 M; 62.4
µL, 0.620 mmol, 0.88 M) and SPri2 (90 µL, 0.620 mmol). The
total volume of each solution was 0.700 mL (by using the
appropriate amount of C6D6). All four NMR tubes were placed in
the same oil bath, which was preheated to 65 °C. The disappearance
of 10 was monitored by 31P{1H} NMR spectroscopy at regular
intervals for at least 3 half-lives and followed pseudo first-order
kinetics. Experiments with Varying Concentrations of SPri2. 10
(0.020 g, 0.031 mmol) was dissolved in C6D6 in a J. Young NMR
tube and was treated with SPri2 (four different experiments for four
different concentrations of isopropyl sulfide: 22.5 µL, 0.155 mmol,
0.22 M; 45 µL, 0.310 mmol, 0.44 M; 67.5 µL, 0.465 mmol, 0.66
M; 90 µL, 0.620 mmol, 0.88 M) and PhBr (15.6 µL, 0.155 mmol).
The total volume of each solution was 0.700 mL (by using the
appropriate amount of C6D6). The samples were placed in an oil
bath, which was preheated to 65 °C. The disappearance of 10 was
monitored by 31P{1H} NMR spectroscopy at regular intervals for
at least 3 half-lives and followed pseudo first-order kinetics. See
the Supporting Information for further details.
Synthesis of (PNP)Rh(η2-CH2dCHCMe3) (21). 4 (50 mg,
0.086 mmol) was treated with 3,3-dimethyl-1-butene (14 µL, 0.094
mmol) in C6D6 (1 mL) in a J. Young NMR tube followed by
MeMgCl (31 µL, 0.094 mmol). After 10 min, the solution was
treated with water (1.7 mL) and then evaporated to dryness, and
the residue was extracted with Et2O and filtered through Celite.
The ether solution was evaporated to dryness to yield a green solid
residue. 31P{1H} NMR analysis of this green residue revealed the
presence of (PNP)Rh(H)(Cl) 5 (δ 50.4 ppm, d, JP-Rh ) 104 Hz),
in addition to 21. This solution in C6D6 (0.7 mL) was treated with
3,3-dimethyl-1-butene (13.6 µL, 0.094 mmol) followed by NaOt-
Bu (8.2 mg, 0.086 mmol). After 10 min, the solution was treated
with water (1.6 mL) and then evaporated to dryness, and the residue
was extracted with Et2O and filtered through Celite. The ether
solution was evaporated to dryness to yield a green solid residue.
The 31P{1H} NMR spectrum of this green residue in C6D6 shows
only the resonance of 21. This residue was dissolved in Et2O and
placed in the freezer at -35 °C to afford 21 by precipitation.
Yield: 33 mg (62%). 1H NMR (C6D6): δ 7.53 (d, 2H, 9 Hz, Ar-H
of PNP), 6.95 (s, 2H, Ar-H of PNP), 6.85 (s, 2H, Ar-H of PNP),
6.76 (d, 2H, 8 Hz, Ar-H of PNP), 4.43 (br m, 1H, CHaHbdCHC-
(CH3)3), 2.88 (t, 1H, 8 Hz, CHaHbdCHC(CH3)3), 2.78 (d, 1H, 8
Hz, CHaHbdCHC(CH3)3), 2.34 (m, 1H, CHMe2), 2.18 (two
multiplets overlapping, 2H, CHMe2), 2.18 (s, 6H, Ar-CH3 of PNP),
2.02 (m, 1H, CHMe2), 1.31-0.90 (eight app. quartets (dvt)
overlapping, 24H, CHMe2), 1.21 (s, 9H, CHaHbdCHC(CH3)3). 13C-
{1H} NMR (C6D6): δ 162.2 (vt, 10 Hz, C-N of PNP), 131.9 (s,
C
Ar of PNP), 130.7 (s, CAr of PNP), 124.6 (vt, 18 Hz, CAr of PNP),
Influence of [Ph2SO] on the Rate of Conversion of 10 to 16.
10 (0.020 g, 0.031 mmol) was dissolved in C6D6 in a J. Young
NMR tube and was treated with Ph2SO (two different experiments
for two different concentrations of Ph2SO: 31.3 mg, 0.155 mmol,
0.22 M; 125.4 mg, 0.620 mmol, 0.88 M) and SPri2 (22.5 µL, 0.155
mmol to each experiment). The samples were placed in an oil bath,
which was preheated to 65 °C. The disappearance of 10 was
monitored by 31P{1H} NMR after 19 and 39 min. At 19 min, the
16:10 ratio for the experiment with [Ph2SO] ) 0.88 M was 75:25,
whereas for the experiment with [Ph2SO] ) 0.22 M this ratio was
50:50. At 39 min, 10 was fully converted into 16 for the experiment
with [Ph2SO] ) 0.88 M, whereas for the experiment with [Ph2SO]
) 0.22 M the 16:10 ratio was 60:40.
Reaction of 10 with Ph2SO at Ambient Temperature. 10 (17.0
mg, 0.026 mmol) was treated with Ph2SO (5.9 mg, 0.029 mmol)
in C6D6 (0.7 mL) in a J. Young NMR tube. After 40 min at ambient
temperature, 10 (>97%) and 16 (<3%) were observed by 31P{1H}
NMR. After 2 h at ambient temperature, 10 (92%) and 17 (8%)
were observed by 31P{1H} NMR.
122.0 (br vt, CAr of PNP), 115.4 (br vt, CAr of PNP), 72.3 (d, JC-Rh
) 11 Hz, CHaHbdCHC(CH3)3), 36.8 (d, JC-Rh ) 11 Hz, CHaHbd
CHC(CH3)3), 30.5 (s, CHaHbdCHC(CH3)3), 33.9 (s, C(CH3)3), 26.3
(br, CH(CH3)2), 25.8 (br, CH(CH3)2), 23.9 (br, CH(CH3)2), 23.0
(br, CH(CH3)2), 20.6 (s, Ar-CH3), 20.0-17.2 (eight s, 8C, CH-
(CH3)2). 31P{1H} NMR (C6D6): δ 43.5 (dd, JP-P ) 328 Hz, JP-Rh
) 145 Hz), 37.9 (dd, JP-P ) 328 Hz, JP-Rh ) 135 Hz).
Equilibrium Constant Determination. C6D6 solutions contain-
ing (PNP)Rh-L and L′ (see Scheme 7 and Table 1) in three
different ratios were prepared and subjected to thermolysis by
placing the J. Young tubes containing the solutions into an oil bath
preheated to 65 °C. The ratios were determined by integration of
the 31P{1H} NMR spectra. Equilibrium constants were calculated
as averages of three experiments. For details about each reaction,
see the Supporting Information.
Oxidative Addition of PhI, PhBr, and PhCl to 10. 10 (20 mg,
0.031 mmol) and PhI (10.3 µL, 0.092 mmol) or PhBr (9.3 µL, 0.092
mmol) or PhCl (9.4 µL, 0.092 mmol) were co-dissolved in 0.8 mL
of C6D6 in a J. Young NMR tube. The samples were placed in the
same oil bath, which was preheated at 65 °C. The disappearance
Attempt at Observation of a Putative Five-Coordinate RhI
Complex. (PNP)Rh(SPri2) (17.0 mg, 0.026 mmol) was treated with

Thioether, Dinitrogen, and Olefin Complexes of (PNP)Rh
Organometallics, Vol. 26, No. 25, 2007 6075
isopropyl sulfide (189 µL, 1.30 mmol) in C6D6 (0.7 mL) in a J.
Young NMR tube. After 3 days at room temperature, (PNP)Rh-
(SPri2) was the only compound observed by 31P{1H} NMR. After
7 h at 65 °C, (PNP)Rh(SPri2) was still the only compound observed
by 31P{1H} NMR.
refined using anisotropic displacement parameters; hydrogen atoms
were fixed at calculated geometric positions and allowed to ride
on the corresponding carbon atoms. The asymmetric unit contains
one dirhodium complex and one ether solvate molecule. The ether
molecule contains disordered ethyl groups. The sum of the two
disordered components was constrained to sum to 1.0; the major
component had an occupancy of 0.817(16). The final least-squares
refinement converged to R1 ) 0.0242 (I > 2σ(I), 14 881 data) and
wR2 ) 0.0624 (F2, 17 360 data, 613 parameters).
X-ray Data Collection, Solution, and Refinement for 21.
Single crystals of 21 suitable for X-ray diffraction measurements
were obtained by recrystallization from ether/pentane and were
mounted in a glass capillary. Data collection was carried out at
room temperature (low temperature apparatus was not available)
on a CAD-4 Turbo diffractometer equipped with Mo KR radiation;43
completeness was 100%. The structure was solved by direct
methods (SIR92).41 From the lack of systematic absences, the
observed metric constants, and intensity statistics, space group P1h
was chosen initially; subsequent solution and refinement confirmed
the correctness of this choice. Full-matrix least-squares refinement
was carried out using the Oxford University “Crystals for Windows”
system.42 All nonhydrogen atoms were refined using anisotropic
displacement parameters; hydrogen atoms were fixed at calculated
geometric positions and updated after each least-squares cycle. The
final least-squares refinement converged to R1 ) 0.0563 (I > 2σ-
(I), 5180 data) and wR2 ) 0.0624 (F, 6500 data, 325 parameters).
Influence of [SPri2] on the Rate of Conversion of 10 to 16.
10 (0.020 g, 0.031 mmol) was dissolved in C6D6 in a J. Young
NMR tube and was treated with SPri2 (two different experiments
for two different concentrations of isopropyl sulfide: 31.3 mg, 0.155
mmol, 0.22 M; 125.4 mg, 0.620 mmol, 0.88 M), and Ph2SO (31.3
mg, 0.155 mmol to each experiment) was added. The samples were
placed in an oil bath, which was preheated to 65 °C. The
disappearance of 10 was monitored by 31P{1H} NMR at 34 and 69
min. At 34 min, the 10:16 ratio for the experiment with [SPri2] )
0.88 M was 60:40, whereas for the experiment with [SPri2] ) 0.22
M it was 50:50. At 69 min, the 10:16 ratio for the experiment with
[SPri2] ) 0.88 M was 50:50, whereas for the experiment with [SPri2]
) 0.22 M it was 80:20.
X-ray Data Collection, Solution, and Refinement for 19a.
Single crystals of 19a suitable for X-ray diffraction measurements
were obtained by recrystallization from ether and were mounted
on a MiteGen mount using Paratone oil. All operations were
performed on a Bruker-Nonius Kappa Apex2 diffractometer, using
graphite-monochromated Mo KR radiation. All diffractometer
manipulations, including data collection, integration, scaling, and
absorption corrections, were carried out using the Bruker Apex2
software.40 Preliminary cell constants were obtained from three sets
of 12 frames. Data collection was carried out at 120 K, using a
frame time of 10 s and a detector distance of 60 mm. The optimized
strategy used for data collection consisted of φ and ω scan sets,
with 0.5° steps in ω; completeness was 99.6%. A total of 4149
frames were collected. Final cell constants were obtained from the
xyz centroids of 9054 reflections after integration.
Acknowledgment. Support of this research by the NSF
(CHE-0517798), Alfred P. Sloan Foundation (Research Fel-
lowship to O.V.O.), the donors of the Petroleum Research Fund,
Department of Energy (DE-FG02-86ER13615), and Brandeis
University is gratefully acknowledged. We also thank the
National Science Foundation for the partial support of this work
through grant CHE-0521047 for the purchase of a new X-ray
diffractometer. We are grateful to Dr. Wei Weng and Dr. Remle
C¸ elenligil-C¸ etin for the initial synthesis of 21.
From the lack of systematic absences, the observed metric
constants, and intensity statistics, space group P1h was chosen
initially; subsequent solution and refinement confirmed the cor-
rectness of this choice. The structures were solved using SIR-9241
and refined (full-matrix least-squares) using the Oxford University
“Crystals for Windows” program.42 All non-hydrogen atoms were
Supporting Information Available: Crystallographic informa-
tion for 19a and 21 in the form of CIF files, experimental details
on the equilibrium and kinetics experiments, and pictorial NMR
spectra for select compounds. This material is available free of
charge via the Internet at http://pubs.acs.org.
(40) Apex2, Version 2 User Manual, M86-E01078; Bruker Analytical
X-ray Systems: Madison, WI, June 2006.
(41) Altomare, A.; Cascarano, G.; Giacovazzo, G.; Guagliardi, A.; Burla,
M. C.; Polidori, G.; Camalli, M. J. Appl. Crystallogr. 1994, 27, 435.
(42) Betteridge, P. W.; Carruthers, J. R.; Cooper, R. I.; Prout, K.; Watkin,
D. J. J. Appl. Crystallogr. 2003, 36, 1487.
OM700563K
(43) Straver, L. H. CAD4-EXPRESS; Enraf-Nonius: Delft, The Neth-
erlands, 1992.