Alkyl carbon-nitrogen reductive elimination from platinum(IV)-sulfonamide complexes

Article abstract of DOI:10.1021/ja069191h

Platinum(IV) complexes containing monodentate sulfonamide ligands, fac-(dppbz)PtMe₃(NHSO₂R) (dppbz = o-bis(diphenylphosphino) benzene; R = p-C₆H₄(CH₂)₃CH ₃ (1a), p-C₆H₄CH₃ (1b), CH ₃ (1c)), have been synthesized and characterized, and their thermal reactivity has been explored. Compounds 1a-c undergo competitive C-N and C-C reductive elimination upon thermolysis to form N-methylsulfonamides and ethane, respectively. Selectivity for either C-N or C-C bond formation can be achieved by altering the reaction conditions. Good yields of the C-N-coupled products were observed when the thermolyses of 1a-c were conducted in benzene-d ₆. In contrast, exclusive C-C reductive elimination occurred upon thermolysis of 1a,b in nitrobenzene-d₅. When the thermolyses of 1a were performed in the presence of sulfonamide anion NHSO₂R ^- in benzene-d₆, ethane elimination was completely inhibited and C-N reductive elimination products were formed in high yield. Mechanistic studies support a two-step reaction pathway involving initial dissociation of NHSO₂R^- from the platinum center, followed by nucleophilic attack of this anion on a methyl group of the resulting five-coordinate platinum(IV) cation to form MeNHSO₂R and (dppbz)-PtMe₂. C-C reductive elimination to form ethane occurs directly from the five-coordinate Pt(IV) cation.

Full text of DOI:10.1021/ja069191h

Published on Web 08/02/2007
Alkyl Carbon-Nitrogen Reductive Elimination from
Platinum(IV)-Sulfonamide Complexes
Andrew V. Pawlikowski, April D. Getty, and Karen I. Goldberg*
Contribution from the Department of Chemistry, UniVersity of Washington, P.O. Box 351700,
Seattle, Washington 98195-1700
Received December 21, 2006; E-mail: goldberg@chem.washington.edu
Abstract: Platinum(IV) complexes containing monodentate sulfonamide ligands, fac-(dppbz)PtMe3(NHSO2R)
(dppbz ) o-bis(diphenylphosphino)benzene; R ) p-C6H4(CH2)3CH3 (1a), p-C6H4CH3 (1b), CH3 (1c)), have
been synthesized and characterized, and their thermal reactivity has been explored. Compounds 1a-c
undergo competitive C-N and C-C reductive elimination upon thermolysis to form N-methylsulfonamides
and ethane, respectively. Selectivity for either C-N or C-C bond formation can be achieved by altering
the reaction conditions. Good yields of the C-N-coupled products were observed when the thermolyses
of 1a-c were conducted in benzene-d6. In contrast, exclusive C-C reductive elimination occurred upon
themolysis of 1a,b in nitrobenzene-d5. When the thermolyses of 1a were performed in the presence of
sulfonamide anion NHSO2R- in benzene-d6, ethane elimination was completely inhibited and C-N reductive
elimination products were formed in high yield. Mechanistic studies support a two-step reaction pathway
involving initial dissociation of NHSO2R- from the platinum center, followed by nucleophilic attack of this
anion on a methyl group of the resulting five-coordinate platinum(IV) cation to form MeNHSO2R and (dppbz)-
PtMe2. C-C reductive elimination to form ethane occurs directly from the five-coordinate Pt(IV) cation.
extremely scarce.6,7 Hillhouse has reported oxidatively induced
C(sp3)-N reductive eliminations from Ni(II) complexes that
Introduction
Amines and their derivatives are widely used in the chemical
industry as dyes, surfactants, pharmaceutical agents, and
specialty chemicals. As a result, the development of new, facile
synthetic procedures for the formation of carbon-nitrogen bonds
is the subject of much current research.1 One prominent example
that has emerged over the past decade is the synthesis of
aromatic amines from aryl halides and primary or secondary
amines catalyzed by Pd(II) or Ni(II) complexes, developed by
the groups of Hartwig2 and Buchwald.3 Detailed mechanistic
studies of these C-N bond-forming reactions support aryl C-N
reductive elimination from the M(II) center as the critical
product release step of the catalytic cycle.2,3 A number of other
C-N reductive elimination reactions have been reported in
recent years from low-valent, late transition metal centers such
as Pd(II)4 or Ru(II),5 all involving sp2-hybridized carbon atoms.
Examples of C(sp3)-N reductive elimination, a potentially
important reaction step in the formation of alkyl amines, are
proceed upon a one-electron oxidation to Ni(III). Such reactions
with Ni(II) metallacycles produced cyclic amines in high
yields,6,7 but reactions of acyclic complexes produced tertiary
amines in low yields.6 Closely related to C(sp3)-N reductive
elimination reactions, intramolecular nucleophilic attack of an
amino group on axial alkyl groups attached to Rh(III) porphyrin
complexes to form pyrrolidines has recently been documented.8
Since many catalytic systems involve oxidative addition of
substrate to a d8 metal complex followed by reductive elimina-
tion from a d6 center later in the cycle,9 the examination of
C-N bond forming reductive elimination from high-valent d6
metal complexes could play a crucial role in the rational
development of novel catalysts and catalytic amination reactions.
(4) (a) Paul, F.; Patt, J.; Hartwig, J. F. J. Am. Chem. Soc. 1994, 116, 5969. (b)
Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1995, 117, 4708. (c) Guram,
A. S.; Rennels, Buchwald, S. L. Angew. Chem., Int. Ed. 1995, 34, 1348.
(d) Driver, M. S.; Hartwig, J. F. J. Am. Chem. Soc. 1997, 119, 8232. (e)
Wagaw, S.; Rennels, R. A.; Buchwald, S. L. J. Am. Chem. Soc. 1997, 119,
8451. (f) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2090. (g) Mann,
G.; Hartwig, J. F.; Driver, M. S.; Fernandez-Rivas, C. J. Am. Chem. Soc.
1998, 120, 827. (h) Carbayo, A.; Cuevas, J. V.; Garcia-Herbosa, G. J.
Organomet. Chem. 2002, 658, 15. (i) Yamashita, M.; Cuevas Vicario, J.
V.; Hartwig, J. F. J. Am. Chem. Soc. 2003, 125, 16347.
(1) (a) Brunet, J. J.; Neibacker, D.; Niedercorn, F. J. Mol. Catal. 1989, 49,
235. (b) Lawrence, S. A. Amines: Synthesis, Properties and Applications;
Cambridge University Press: New York, 2004.
(2) (a) Hartwig, J. F. Angew. Chem., Int. Ed. 1998, 37, 2046. (b) Hartwig, J.
F. Acc. Chem. Res. 1998, 31, 852. (c) Hartwig, J. F. Pure Appl. Chem.
1999, 71, 1417. (d) Hartwig, J. F. In Handbook of Organopalladium
Chemistry for Organic Synthesis; Negishi, E. I., Ed.; Wiley-Interscience:
New York, 2002; Vol. 1, p 1051. (e) Hartwig, J. F. Synlett 2006, 1283. (f)
Shekhar, S.; Ryberg, P.; Hartwig, J. F.; Mathew, J. S.; Blackmond, D. G.;
Strieter, E. R.; Buchwald, S. L. J. Am. Chem. Soc. 2006, 128, 3584. (g)
Hartwig, J. F. Inorg. Chem. 2007, 46, 1936.
(3) (a) Wolfe, J. P.; Wagaw, S.; Marcoux, J.-F.; Buchwald, S. L. Acc. Chem.
Res. 1998, 31, 805. (b) Yang, B. H.; Buchwald, S. L. J. Organomet. Chem.
1999, 576, 125. (c) Muci, A. R.; Buchwald, S. L. Top. Curr. Chem. 2002,
219, 131. (d) See ref 2f.
(5) Abbenhuis, H. C. L.; Pfeffer, M.; Sutter, J.-P.; de Cian, A.; Fischer, J.; Ji,
H. L.; Nelson, J. H. Organometallics 1993, 12, 4464.
(6) Koo, K.; Hillhouse, G. L. Organometallics 1995, 14, 4421.
(7) (a) Koo, K.; Hillhouse, G. L. Organometallics 1996, 15, 2669. (b) Lin, B.
L.; Clough, C. R.; Hillhouse, G. L. J. Am. Chem. Soc. 2002, 124, 2890.
(8) Sanford, M. S.; Groves, J. T. Angew. Chem., Int. Ed. 2004, 43, 588.
(9) (a) Crabtree, R. H. The Organometallic Chemistry of the Transition Metals,
4th ed.; John Wiley & Sons: New York, 2005. (b) Parshall, G. W.; Ittel,
S. D. Homogeneous Catalysis: The Applications and Chemistry of Catalysis
by Soluble Transition Metal Complexes, 2nd ed.; Wiley-Interscience: New
York, 1992.
9
10382
J. AM. CHEM. SOC. 2007, 129, 10382-10393
10.1021/ja069191h CCC: $37.00 © 2007 American Chemical Society

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
Scheme 1
Notably, however, examples of C-N reductive elimination
reactions from high-valent d6 metals such as Pt(IV), Pd(IV),
Ir(III), or Rh(III)8 are exceedingly rare.
hydroxo dimers with amines.14 Thus, the reactions of the
monomeric Pt(IV)-hydroxo complex fac-(dppbz)PtMe3(OH)15
with aniline and various sulfonamides were investigated. The
reaction with aniline did not produce a significant amount of
the desired Pt(IV)-anilido complex, and rapid reduction to Pt-
(II) was observed. Notably, however, the condensation reaction
of fac-(dppbz)PtMe3(OH) with an excess of sulfonamide, H2-
NSO2R, in THF at room temperature allowed isolation of the
Pt(IV)-sulfonamide complexes fac-(dppbz)PtMe3(NHSO2R) (R
) p-C6H4(CH2)3CH3 (1a), p-C6H4CH3 (1b), CH3 (1c)) (Scheme
1). Compounds 1a-c are unusual in that relatively few high
oxidation state, late transition metal complexes containing
monodentate amido ligands have been reported.13,16
Our group has previously reported C(sp3)-O and C(sp3)-I
reductive elimination reactions from d6 Pt(IV) complexes of the
type fac-L2PtMe3X (L2 ) bis(diphenylphosphino)ethane (dppe),
o-bis(diphenylphosphino)benzene (dppbz); X ) OAr, OC(O)R,
I).10,11 Herein we report related Pt(IV)-amido complexes and
investigations of their thermal reactivity. The Pt(IV)-sulfona-
mide complexes fac-(dppbz)PtMe3(NHSO2R) (R ) p-C6H4(CH2)3-
CH3 (1a), p-C6H4CH3 (1b), CH3 (1c)) have been synthesized
and characterized. Alkyl C-N reductive elimination from 1a-c
is observed upon thermolysis, and N-methylsulfonamides are
formed in good yields. The reactions reported here are not only
rare examples of alkyl C-N coupling reactions mediated by a
metal center6-8 but also represent the first examples of directly
observed alkyl C-N reductive elimination from a high-valent,
late transition metal center. The C-N coupling reactions to form
alkylsulfonamide linkages may also be useful in organic
synthesis, as the sulfonyl moiety can function as an amine-
protecting group, with deprotection to yield primary or second-
ary amines.12
The Pt(IV)-sulfonamide complexes 1a-c were isolated as
white, air-stable solids in 60-65% yield and were characterized
1
by H and 31P NMR spectroscopy. Compound 1a was also
characterized by X-ray crystallography. The ORTEP diagram
of 1a is shown in Figure 1, and selected bond lengths and angles
are presented in Table 1.17
The Pt-C and Pt-P bond lengths are comparable to related
fac-L2PtMe3X (L2 ) dppe, dppbz; X ) I, OAr, OC(O)R)
complexes (Pt-Ctrans to P ) 2.09-2.10 Å, Pt-Ctrans to X ) 2.06-
2.08 Å, Pt-P ) 2.35-2.38 Å).10,11 The Pt-N bond length of
2.199(4) Å is the longest reported Pt(IV)-N bond length for
structurally characterized monomeric Pt(IV)-amide complexes
(Pt-N ) 2.06-2.15 Å),13,18 presumably as a result of the strong
trans effect of the apical methyl ligand coupled with the poor
donating ability of the sulfonamide ligand.19
Results
Synthesis and Characterization of fac-(dppbz)PtMe3-
(NHSO2R) (R ) p-C6H4(CH2)3CH3, p-C6H4CH3, CH3) (1a-
c). To date there are very few reported examples of Pt(IV)
complexes containing monodentate amido ligands.13 Our initial
attempts to prepare Pt(IV) complexes, fac-L2PtMe3X, where X
) amido, were modeled after the successful preparation of
similar aryloxide complexes (X ) OAr).10 However, metathesis
reactions of fac-(dppbz)PtMe3X (X ) I, OAc, O2CCF3) with
amide salts such as KNHPh, KNPh2, KNHSO2(p-C6H4CH3),
or LiNC5H10 resulted in either immediate reduction of the
platinum to produce (dppbz)PtMe2 or the formation of the
desired Pt(IV)-amido complex occurred at a comparable rate
to the reduction of the platinum such that isolation of the Pt-
(IV)-amido species was not practical.
1
The H and 31P{1H} NMR data for 1a-c confirm that a
similar structure with a facial arrangement of the three methyl
(14) (a) Ruiz, J.; Martinez, M. T.; Vicente, C.; Garcia, G.; Lopez, G.; Chaloner,
P. A.; Hitchcock, P. B. Organometallics 1993, 12, 4321. (b) Driver, M.
S.; Hartwig, J. F. J. Am. Chem. Soc. 1996, 118, 4206. (c) Driver, M. S.;
Hartwig, J. F. Organometallics 1997, 16, 5706. (d) Ruiz, J.; Rodriguez,
V.; Lopez, G.; Casabo, J.; Molins, E.; Miravitlles, C. Organometallics 1999,
18, 1177. (e) Li, J. J.; Li, W.; James, A.; Holbert, T.; Sharp, T.; Sharp, P.
R. Inorg. Chem. 1999, 38, 1563. (f) Getty, A. D.; Goldberg, K. I.
Organometallics 2001, 20, 2545.
(15) Smythe, N. A. Reactivity Studies of Platinum(IV) Hydroxide and Methoxide
Complexes and the Study of Pincer Palladium(II) Complexes as Potential
Catalysts for Olefin Epoxidation. Ph.D. Thesis, University of Washington,
Seattle, WA, 2004.
A more successful strategy was based on the reported
syntheses of bridging Pd(II)- and Pt(II)-amido complexes via
the reaction of the analogous bridging Pd(II)- and Pt(II)-
(16) (a) Bryndza, H. E.; Tam, W. Chem. ReV. 1988, 88, 1163. (b) Fryzuk, M.
D.; Montgomery, C. D. Coord. Chem. ReV. 1989, 95, 1. (c) Glueck, D. S.;
Winslow, L. J. N.; Bergman, R. G. Organometallics 1991, 10, 1462. (d)
Kaplan, A. W.; Ritter, J. C. M.; Bergman, R. G. J. Am. Chem. Soc. 1998,
120, 6828. (e) Fulton, J. R.; Holland, A. W.; Fox, D. J.; Bergman, R. G.
Acc. Chem. Res. 2002, 35, 44. (f) Kanzelberger, M.; Zhang, X.; Emge, T.
J.; Goldman, A. S.; Zhao, J.; Incarvito, C.; Hartwig, J. F. J. Am. Chem.
Soc. 2003, 125, 13644. (g) Rais, D.; Bergman, R. G. Chem.sEur. J. 2004,
10, 3970. (h) Zhao, J.; Goldman, A. S.; Hartwig, J. F. Science 2005, 307,
1080.
(10) (a) Williams, B. S.; Holland, A. W.; Goldberg, K. I. J. Am. Chem. Soc.
1999, 121, 252. (b) Williams, B. S.; Goldberg, K. I. J. Am. Chem. Soc.
2001, 123, 2576.
(11) (a) Goldberg, K. I.; Yan, J.; Winter, E. L. J. Am. Chem. Soc. 1994, 116,
1573. (b) Goldberg, K. I.; Yan, J.; Breitung, E. M. J. Am. Chem. Soc. 1995,
117, 6889.
(12) Greene, T. W.; Wuts, P. G. M. ProtectiVe Groups in Organic Synthesis,
3rd ed.; John Wiley & Sons: New York, 1999; p 603.
(13) (a) Muller, G.; Riede, J.; Beyerle-Pfnur, R.; Lippert, B. J. Am. Chem. Soc.
1984, 106, 7999. (b) Renn, O.; Lippert, B.; Albinati, A.; Lianza, F. Inorg.
Chim. Acta 1993, 211, 177.
(17) Complete X-ray crystallographic data are provided in the Supporting
Information.
(18) (a) Campbell, C. J.; Castineiras, A.; Nolan, K. B. J. Chem. Soc., Chem.
Commun. 1995, 19, 1939. (b) Koz’min, P. A.; Surazhskzyz, M. D.;
Baranovskii, I. B. Russ. J. Inorg. Chem. 2001, 9, 1342.
(19) Becker, J. J.; White, P. S.; Gagne, M. R. Inorg. Chem. 1999, 38, 798.
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10383

A R T I C L E S
Pawlikowski et al.
Figure 2. First-order kinetic plot of thermolysis of 1a ([1a]0 ) 5 mM) in
C6D6 at 100 °C.
sulfonamide product, H2NSO2(p-C6H4(CH2)3CH3) (5a) and a
small amount of methanol (<5%) were also observed in the
1
thermolysis reaction of 1a. Integration of the H NMR signal
for the methyl groups of 2 relative to an internal standard
indicated 69% conversion to 2, the platinum product of C-N
coupling. However, 3a, the organic product of C-N coupling,
was formed in only 48% yield. The additional sulfonamide
product 5a was produced in 18% yield. Thus, the sum of the
yields of the organic sulfonamides 3a and 5a (66%) is equivalent
to the amount of 2 that formed. The identities of the organic
sulfonamide products were confirmed by comparison of their
1H NMR spectra to those of authentic samples. Integration of
the N-H signal of Pt(II)-sulfonamide 4a indicated 29%
conversion to 4a, the Pt product of C-C reductive elimination.
The Pt(II) species 2 and 4a were the only products observed
by 31P{1H} NMR, and their identities were confirmed by
comparison of their spectral data to that of independently
synthesized complexes. Thus, 98% of the Pt is accounted for
in the products (69% 2 and 29% 4a). Similar reactivity and
product ratios were observed for 1b (65% yield of 2 and 35%
yield of 4b, 65% total yield of sulfonamides 3b + 5b). During
the thermolysis of 1c in C6D6, the methylsulfonamide product
3c precipitated from solution preventing accurate integration
and determination of yields.
Figure 1. ORTEP diagram of fac-(dppbz)PtMe3(NHSO2(p-C6H4(CH2)3-
CH3)) (1a). Thermal ellipsoids are shown at the 50% probability level.
Hydrogen atoms, disorder in the butyl chain, and molecules of THF and
ether have been omitted for clarity.
Table 1. Selected Bond Lengths and Angles in the Crystal
Structure of 1a
bond lengths (Å)
bond angles (deg)
Pt-C(1)
2.092(5)
2.108(5)
2.108(5)
2.199(4)
2.3569(13)
2.3659(13)
1.583(4)
1.439(4)
1.439(4)
C(1)-Pt-C(3)
88.6(2)
84.5(2)
88.5(2)
Pt-C(2)
Pt-C(3)
Pt-N(1)
Pt-P(1)
C(1)-Pt-C(2)
C(3)-Pt-C(2)
C(3)-Pt-N(1)
C(2)-Pt-N(1)
C(1)-Pt-P(2)
C(3)-Pt-P(2)
N(1)-Pt-P(2)
C(1)-Pt-P(1)
C(2)-Pt-P(1)
N(1)-Pt-P(1)
P(1)-Pt-P(2)
C(1)-Pt-N(1)
C(3)-Pt-P(1)
C(2)-Pt-P(2)
Pt-N(1)-S(1)
88.40(19)
92.53(18)
93.85(15)
92.28(15)
89.13(12)
90.77(16)
95.39(15)
92.42(12)
83.75(4)
175.85(18)
175.94(15)
178.17(15)
130.3(3)
Pt-P(2)
N(1)-S(1)
S(1)-O(1)
S(1)-O(2)
Kinetic studies were performed in C6D6 at 100 °C to
investigate the mechanism of C-N reductive elimination from
1a. When the concentration data of 1a as a function of time are
subjected to a first-order kinetic treatment (ln([1a]t/[1a]0) vs t),
it is seen that the plots are not linear (Figure 2). While the initial
data appear linear through ca. 25% conversion, the plots curve
downward, indicating that the reaction accelerates with time.
The slope of the line through the early reaction times (25%
conversion) gives an initial rate constant of kobs ) 1.1 × 10-5
s-1. At the end of the reaction the kobs value approaches 1.0 ×
ligands is maintained in solution. Only one resonance with Pt
satellites is observed in the 31P NMR spectra of 1a-c, indicating
two equivalent phosphorus atoms. In the 1H NMR spectra, the
Pt-bound methyl groups give rise to a triplet and a virtual triplet
with Pt satellites in a 1:2 ratio; the signal for the axial methyl
3
group (0.32 ppm, 3H, JP-H ) 7.5 Hz, 2JPt-H ) 67 Hz for 1a)
is shifted upfield from the equatorial methyl groups (1.89 ppm,
6H, 3JP-H ) 7.0 Hz, 2JPt-H ) 60 Hz). The chemical shifts and
coupling constants for the Pt-bound methyl groups are compa-
rable with the values reported for other fac-L2PtMe3X com-
plexes.10,11,15 The chemical shifts of the protons on the Pt-bound
sulfonamide moiety are similar to the free sulfonamide H2-
NSO2R, with the exception that the N-H protons of 1a-c are
shifted upfield by almost 2 ppm. For example, the N-H proton
of 1a resonates at 1.77 ppm and the N-H protons of H2NSO2(p-
C6H4(CH2)3CH3) resonate at 3.57 ppm in C6D6.
Thermolysis of 1a. Products from both C-N reductive
elimination ((dppbz)PtMe2 (2) and MeNHSO2(p-C6H4(CH2)3-
CH3) (3a)) and C-C reductive elimination (ethane and (dppbz)-
PtMe(NHSO2(p-C6H4(CH2)3CH3)) (4a)) were observed upon
thermolysis of 1a at 100 °C in C6D6 (Scheme 2). An additional
10-4 s-1
.
Compound 1a was also thermolyzed at 100 °C in the polar
solvent nitrobenzene-d5. Exclusive C-C reductive elimination
to form ethane and (dppbz)PtMe(NHSO2(p-C6H4(CH2)3CH3))
(4a) was observed under these conditions. This reaction was
extremely fast at 100 °C; therefore, only an estimate of the rate
was possible (kobs ) 4 × 10-3 s-1). It should be noted, however,
that the reaction in nitrobenzene-d5 is 2 orders of magnitude
faster than the thermolysis in C6D6.
Effect of Added Sulfonamides. The downward curve of the
plot of ln([1a]t/[1a]0) vs time in C6D6 (Figure 2) suggests that
a product of thermolysis could be responsible for the acceleration
of the reaction. To investigate this possibility, the thermolysis
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10384 J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
Scheme 2
of 1a was carried out in the presence of added C-N coupled
product 3a. Thermolysis of 1a in C6D6 at 100 °C in the presence
of 1-4 equiv of 3a still resulted in curved first-order plots, but
the curvature was much less pronounced. Thermolysis of 1a
with a large excess of 3a (pseudo-first-order conditions, 9 mM
1a, 150 mM 3a) resulted in linear first-order kinetic behavior,
with kobs ) 3.6 × 10-4 s-1 (Figure 3).
of 1a (9 mM) with 17 equiv of 3a added, as compared to 29%
and 69% without added 3a. Notably, sulfonamide 5a was not
observed as a product of thermolysis when 3a was added, and
the amount of 3a produced was consistent with the amount of
2 that formed.
The addition of sulfonamide 5a to the reaction had an even
greater accelerative effect than the addition of 3a on the
thermolysis of 1a. When the thermolysis of 1a in C6D6 at
100 °C was carried out with 4.1 equiv of added 5a, the reaction
was complete in less than 1 h and occurred so quickly that only
an estimate of the rate constant was possible (kobs ≈ 1 × 10-3
s-1). The greater accelerative effect that sulfonamide 5a has on
the rate of thermolysis of 1a provides an explanation for the
observation that the kobs(final) for thermolysis of 1a alone (9.6
× 10-5 s-1) was greater than the kobs(initial) for thermolysis
with 1.2 equiv of added 3a (5.5 × 10-5 s-1), as 5a is formed
as a byproduct in 18% yield during the thermolysis of 1a.20
Effect of Added Sulfonamide Anion. The thermolysis of
1a in C6D6 ([1a]0 ) 5 mM) was also studied in the presence of
sulfonamide anion, added as [K-18-crown-6][NHSO2(p-
C6H4(CH2)3CH3)] (6a). The crown ether was employed to
increase the solubility of the potassium salt of the sulfonamide
in the nonpolar benzene solvent. Sulfonamide salt concentrations
ranged from 1.5 to 15 mM. In each case, at the conclusion of
the thermolysis, the Pt(II) product of C-N coupling, (dppbz)-
Values of kobs(initial) and kobs(final) were extrapolated from
the data in Figure 3, kobs(initial) from the slope of the lines
through the first 30% conversion and kobs(final) from the slope
of the lines through the final 30% conversion. The values of
k
obs(initial) and kobs(final) are provided in Table 2 for runs with
and without added 3a. These results are consistent with the
observed nonlinear first-order kinetic behavior of the thermolysis
of 1a and support the proposal that production of 3a during the
thermolysis of 1a leads to acceleration of the reaction.
Despite the faster reaction rate, the yields of the Pt(II)
products 2 and 4a in these reactions were roughly comparable
to the yields obtained upon thermolyses of 1a without added
3a, with only a small increase in C-C coupling (ca. 5%) at the
expense of C-N coupling. For example, 4a was formed in a
35% yield and 2 was formed in a 64% yield upon thermolysis
1
PtMe2 (2), was detected in >95% yield (as determined by H
NMR) and was the only product observed by 31P NMR. Notably,
ethane and (dppbz)PtMe(NHSO2(p-C6H4(CH2)3CH3)) (4a), the
expected products of C-C reductive elimination, were not
observed in these reactions.
Kinetic plots of ln([1a]t/[1a]0) versus time for the thermolyses
carried out in C6D6 at 100 °C in the presence of 6a still exhibited
downward curvature indicating acceleration of the reactions as
the reactions progressed. However, the degree of curvature was
significantly less than that found for the reactions without added
6a. In addition, the degree of curvature of the plots decreased
with higher concentrations of 6a. An overlay plot of two kinetic
experiments with concentrations of 6a that differ by nearly an
order of magnitude (1.5 mM vs 12 mM) clearly shows that the
initial rate of reaction is not affected by the concentration of
6a (Figure 4). The first-order plot of thermolysis of 1a with
the highest concentration of added 6a (12 mM) appeared linear
Figure 3. First-order kinetic plots for the thermolysis of 1a in C6D6 at
100 °C with added 3a (b ) 17 mM [1a]0, 20 mM [3a]0; 2 ) 9 mM [1a]0,
32 mM [3a]0; 9 ) 9 mM [1a]0, 150 mM [3a]0).
Table 2. Rate Constants for Thermolysis of 1a in C6D6 at 100 °C,
with and without Added 3a
1
1
equiv of 3a
kobs(initial) (104 s-
)
kobs(final) (104 s-
)
0
0.11
0.55
1.0
0.96
1.3
1.9
1.2
3.6
17
N/A
3.6
(20) The unsubstituted sulfonamide 5a is not observed during the thermolysis
of 1a with added 3a.
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10385

A R T I C L E S
Pawlikowski et al.
mM, 1.08 equiv). After 25 h, complete sulfonamide exchange
was evident, resulting in an equilibrium mixture of 1b, 6a, 1a,
and 6b (Scheme 3). Overlap of signals in the 1H NMR prevented
an accurate determination of the equilibrium constant. A small
amount (∼5%) of the Pt(II) product 2, resulting from C-N
reductive elimination, was also observed to form at this
temperature during the 25 h period.
Effect of Added Water. Thermolysis samples were prepared
using dry solvents under rigorously air-free conditions with
oven-dried NMR tubes that were flame-sealed under vacuum.
It was noted, however, that although no water was detected in
1
the H NMR spectra of 1a in C6D6 prior to thermolysis, trace
amounts of water were observed after heating. For this reason,
the effect of additional water on the thermolysis reactions was
probed and the thermolysis of 1a was carried out in undried
C6D6 rather than in C6D6 that had been vacuum transferred from
sodium. Integration of the H2O resonance in the 1H NMR
spectrum prior to thermolysis indicated an approximate 1:1 ratio
of water to 1a. In this thermolysis reaction with water present,
the C-C reductive elimination pathway was the dominant
decomposition pathway, with 64% formation of (dppbz)PtMe-
(NHSO2(p-C6H4(CH2)3CH3)) (4a) and 33% formation of (dp-
Figure 4. First-order kinetics plots for thermolysis of 1a ([1a]0 ) 5 mM)
in the presence of 6a in C6D6 at 100 °C (2 ) 1.5 mM [6a]; 9 ) 12 mM
[6a]).
through at least 30% conversion, and the slope of the line
through these points gave an estimate of the initial rate constant
for C-N reductive elimination of kobs(C-N) ) 8.3 × 10-6 s-1
.
This value agrees closely with the kobs(initial)) 1.1 × 10-5 s-1
when no 6a was added and both C-C and C-N reductive
elimination reactions were observed.
The yield of the organic product of C-N coupling (3a) was
challenging to establish in the presence of excess sulfonamide
anion. Sulfonamide 3a reacts with the added 6a to form an
equilibrium mixture with H2NSO2(p-C6H4(CH2)3CH3) (5a) and
[K-18-crown-6] [N(Me)SO2(p-C6H4(CH2)3CH3)] (7a), as shown
in eq 1. This equilibration has been verified in independent
experiments wherein 3a and 6a were combined in C6D6 solvent.
1
pbz)PtMe2 (2) as observed by H and 31P NMR. Despite the
33% yield of 2, the C-N-coupled sulfonamide product 3a
formed in a modest 15% yield. The yield of H2NSO2(p-
C6H4(CH2)3CH3) (5a) was 20% in this reaction, making 5a the
dominant organic sulfonamide product. Notably, the yield of
methanol increased to 17%. Again, the sum of the yields of 3a
and 5a are equivalent to the amount of 2 formed. An additional
thermolysis reaction was carried out in which water (0.006
mmol) was added to a sample of 1a (0.004 mmol) in dry C6D6
(0.4 mL) via vacuum transfer, and the results were nearly
identical. Although kinetics data were not recorded for the
thermolyses of 1a with additional water, these reactions
qualitatively occurred much faster than thermolyses of 1a in
dry C6D6 and reached completion within 8 h.
MeNHSO R
H NSO R
2 2
[K-18-crown-6][NHSO R]
+
h
+
2
2
3a
5a
6a
[K-18-crown-6][N(Me)SO2R]
(1)
7a
R ) p-C6H4(CH2)3CH3
1
The H NMR spectrum of a prepared mixture of 3a and 6a
in C6D6 shows only one broad N-H resonance for 3a, 5a, and
6a together, along with a single N-methyl resonance arising from
the methyl groups on 3a and 7a. The remaining resonances in
the 1H NMR spectrum result from the protons on the aryl rings
and n-butyl chains of 3a, 5a, 6a, and 7a, and these signals
overlap with one another making integration of resonances
corresponding to each individual compound impossible. The
total amount of 3a and 7a present after thermolysis was
determined by integration of the N-bound methyl resonance,
and these products together were consistently formed in 70%
yield. A third sulfonamide product, Me2NSO2(p-C6H4(CH2)3-
CH3) (8a), was produced in 10% yield. Sulfonamide 8a is not
involved in the exchange reaction (eq 1) and can be quantified
by integration of its distinct N-Me resonance (δ 2.27) in the
1H NMR spectrum. The value of the integral of the combined
N-H resonance (3a, 5a, and 6a) upon completion of the
thermolysis equals the sum of the integrals of the N-H-
containing species (1a and 6a) prior to thermolysis, indicating
that sulfonamide mass balance is maintained.
Synthesis and Reactivity of fac-(dppbz)PtMe3(N(Me)SO2-
(p-C6H4(CH2)3CH3)) (9a). Compound 9a, the N-methyl ana-
logue of 1a, was prepared in situ by the deprotonation of 1a
with KH in THF followed by addition of iodomethane and
filtration to remove the KI precipitate (Scheme 4). The 1H NMR
data for 9a are similar to that for 1a, with the exception of the
N-H resonance, which is replaced by an N-Me singlet
resonance at 2.76 ppm, broadened at the base due to Pt-H
coupling (3JPt-H ≈ 11 Hz). The absence of this peak in the
spectrum of 9a-d3, prepared by the addition of CD3I rather than
CH3I, supports the assignment of the N-Me resonance.
Compound 9a was unstable in solution at room temperature
and decomposed slowly overnight upon standing in benzene or
THF to the Pt(II) products (dppbz)PtMe2 (2) (ca. 75%) and
(dppbz)PtMe(N(Me)SO2(p-C6H4(CH2)3CH3)) (ca. 25%), as ob-
served by 31P NMR. The organic products of this decomposition
were ethane, methane, and an unusual sulfonamide dimer, CH2-
(N(Me)SO2(p-C6H4(CH2)3CH3))2 (10a).21 The known Pt(IV)-
hydride fac-(dppbz)PtMe3H22 was detected as a transient
1
intermediate (31P NMR, 25 ppm; H NMR Pt-H, -8.2 ppm,
A crossover experiment provided evidence that sulfonamide
anion exchange at the Pt(IV) center occurs at lower temperatures
than reductive elimination from complexes 1a,b. The tolylsul-
fonamide complex 1b (12.3 mM) was heated at 85 °C in C6D6
in the presence of the n-butylbenzenesulfonamide salt 6a (13.3
1JPt-H ) 687 Hz).
(21) Sekera, A.; Rumpf, P. C. R. Acad. Sci. 1965, 260, 2252.
(22) Crumpton-Bregel, D. M.; Goldberg, K. I. J. Am. Chem. Soc. 2003, 125,
9442.
9
10386 J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
Scheme 3
Scheme 4
if incorporated as the product forming step in catalytic reactions,
the discovery of new examples of this reactivity in model
systems provides a tremendous opportunity to gain understand-
ing of the mechanism of such couplings and how to promote
them. The results of previously reported mechanistic studies of
alkyl C-I and alkyl C-O reductive eliminations from Pt(IV)
complexes fac-L2PtMe3X (L2 ) dppe, dppbz; X ) iodide,
carboxylate, or aryloxide) support a common two-step mech-
anism for both C-O and C-I bond formation.10,11 In the first
step, dissociation of X- from the Pt(IV) center forms the cationic
five-coordinate intermediate [L2PtMe3]+. An SN2 nucleophilic
attack by X- on a Pt-bound methyl group of this intermediate
forms the C-X-coupled product and the Pt(II) species L2PtMe2.
An analogous mechanism for the C-N reductive elimination
from 1 (path D, Scheme 6) is considered here, as well as three
additional possible mechanisms (Scheme 6).
Attempts to prepare 9a via a condensation route similar to
that shown in Scheme 1 were unsuccessful. When fac-(dppbz)-
PtMe3(OH) was allowed to react with an excess of 3a in C6D6,
compound 9a was detected in small amounts at early reaction
times but rapidly decomposed to the same products mentioned
above. The Pt(IV)-hydride fac-(dppbz)PtMe3H was also ob-
served in these reactions as an intermediate decomposition
product by both 31P and H NMR.
1
Path A is presented as a two-step mechanism in Scheme 6,
but the two steps could also occur simultaneously. In the first
step, sulfonamide anion acts as a nucleophile to attack a methyl
group of the six-coordinate Pt(IV) starting complex to form the
methylsulfonamide product 3a and an anionic, five-coordinate
Pt(II) intermediate. Loss of sulfonamide anion from this
intermediate affords the Pt(II) product (dppbz)PtMe2 (2). This
mechanism should exhibit a direct first-order dependence upon
[NHSO2R-]. However, the rate of C-N reductive elimination
from 1a was found to be independent of the concentration of
added sulfonamide anion in direct conflict with this pathway.
None of the remaining mechanistic pathways should show a
dependence on sulfonamide anion concentration. In path B,
dechelation of one end of the dppbz ligand affords a neutral
five-coordinate intermediate which then undergoes C-N bond
formation to form 3a, followed by recoordination of the
phosphine ligand to form 2. A similar mechanism has been
reported for C-C reductive elimination from (dppe)PtMe4,22
and it was recently proposed that the mechanism of C(sp2)-O
reductive elimination from Pd(IV) complexes containing cy-
clometalated pyridine ligands proceeds through a neutral five-
coordinate intermediate formed by the dissociation of a pyridyl
nitrogen of a bidentate ligand.26 Direct reductive elimination
of CH3I from neutral, five-coordinate Rh(III) pincer complexes
was also recently reported.27
Heating a solution of the N-methylsulfonamide complex 9a
in C6D6 at 100 °C for only 30 min resulted in complete
1
conversion to (dppbz)PtMe2 (2), as observed by 31P and H
NMR spectroscopy. Integration of the Pt-Me signal of 2 in
the 1H NMR spectrum indicated >93% conversion to this
product. The only organic products of this reaction identified
in the 1H NMR spectrum were the sulfonamide dimer 10a (40%
yield),23 methane, and dimethylsulfonamide 8a (30-40% yield)
(Scheme 5). Compound 8a is the sulfonamide product resulting
from C-N reductive elimination from 9a. In contrast to the
slow room-temperature decomposition, no products resulting
from C-C reductive elimination are observed upon thermolysis.
Although the Pt(II) product 2 was consistently formed in >90%
yield, the total yield of the organic products 10a and 8a only
accounted for approximately 80% of the sulfonamide moiety.
1
However, no additional resonances were observed in the H
NMR spectrum after thermolysis and no additional products
were detected by GC/MS.
Compound 9a-d3 was thermolyzed under the same conditions,
and selective deuterium incorporation into the identified organic
products was observed. The partially deuterated dimer (RO2-
SN(CH3))CD2(N(CD3)SO2R) (10a-d5) was formed, along with
CH3D as the only isotopomer of methane and CH3N(CD3)SO2R
(8a-d3) (R ) p-C6H4(CH2)3CH3) (Scheme 5). Again, the only
Pt product observed was 2.
In pathway C, C-N reductive elimination occurs directly
from the coordinatively saturated starting material 1a. Direct
Discussion
Mechanism of C-N Reductive Elimination from 1a. There
are very few examples of reductive elimination reactions to form
carbon(sp3)-heteroatom bonds from metal centers.6-8,10,11,24,25
However, since this could potentially be a very powerful reaction
(25) (a) Luinstra, G. A.; Labinger, J. A.; Bercaw, J. E. J. Am. Chem. Soc. 1993,
115, 3004. (b) Hutson, A. C.; Lin, M.; Basickes, N.; Sen, A. J. Organomet.
Chem. 1995, 504, 69. (c) Luinstra, G. A.; Wang, L.; Stahl, S. S.; Labinger,
J. A.; Bercaw, J. E. J. Organomet. Chem. 1995, 504, 75. (d) Stahl, S. S.;
Labinger, J. A.; Bercaw, J. E. Angew. Chem., Int. Ed. 1998, 37, 2180. (e)
Vedernikov, A. N.; Binfield, S. A.; Zavalij, P. Y.; Khusnutdinova, J. R. J.
Am. Chem. Soc. 2006, 128, 82.
(23) The dimer 10a contains two sulfonamide moieties and forms from 2 equiv
of the starting material 1a.
(24) Matsunaga, P. T.; Hillhouse, G. L. J. Am. Chem. Soc. 1993, 115, 2075.
(26) Dick, A. R.; Kampf, J. W.; Sanford, M. S. J. Am. Chem. Soc. 2005, 127,
12790.
(27) Frech, C. M.; Milstein, D. J. Am. Chem. Soc. 2006, 128, 12434.
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10387

A R T I C L E S
Scheme 5
Pawlikowski et al.
Scheme 6
reductive elimination from six-coordinate Pt(IV) is feasible but
appears to be quite rare. In virtually all studies of reductive
elimination to form C-H, C-C, and C-X bonds from Pt(IV)
or Pd(IV), the formation of five-coordinate intermediates prior
to the reductive coupling has been indicated.10,11,22,26-28 Notably,
however, in the study of C-H reductive elimination to form
methane from fac-L2PtMe3H (L2 ) dppe, dppbz), mechanistic
investigations supported a direct pathway, one without prelimi-
nary ligand dissociation.22
In path D, dissociation of NHSO2R- from 1a occurs to form
a cationic five-coordinate intermediate. Nucleophilic attack by
the dissociated sulfonamide anion at a methyl group on the five-
coordinate Pt(IV) cation generates sulfonamide 3a and (dpp-
bz)PtMe2 (2). This pathway is analogous to the accepted
mechanism for C-O and C-I reductive elimination from the
closely related Pt(IV) complexes fac-L2PtMe3X (L2 ) dppe,
dppbz; X ) iodide, carboxylate, or aryloxide).10,11 Although
path D requires NHSO2R- to act as a nucleophile to form the
C-N bond in the rate-determining step, the rate of the reductive
elimination reaction should be independent of [NHSO2R-].29
While paths B-D are not expected to show dependence on
sulfonamide anion concentration, only path D should be
significantly affected by added sulfonamide product 3a. The
sulfonamide product 3a can act as a Lewis acid to facilitate the
dissociation of NHSO2R- from 1a. Acetic acid and phenols were
found to act in this manner and accelerate C-O reductive
elimination from fac-L2PtMe3(OR) (R ) C(O)Me, Ar) com-
plexes.10 Indeed, added sulfonamide 3a was shown to accelerate
the C-N reductive elimination reaction from 1a. Thus, reductive
elimination to form 3a would be expected to accelerate as more
(28) (a) Brown, M. P.; Puddephatt, R. J.; Upton, C. E. E. J. Chem. Soc., Dalton
Trans. 1974, 2457. (b) Roy, S.; Puddephatt, R. J.; Scott, J. D. J. J. Chem.
Soc., Dalton Trans. 1989, 2121. (c) Hill, G. S.; Yap, G. P. A.; Puddephatt,
R. J. Organometallics 1999, 18, 1408. (d) Byers, P. K.; Canty, A. J.; Crespo,
M.; Puddephatt, R. J.; Scott, J. D. Organometallics 1988, 7, 1363. (e) Aye,
K. T.; Canty, A. J.; Crespo, M.; Puddephatt, R. J.; Scott, J. D.; Watson, A.
A. Organometallics 1989, 8, 2709. (f) Canty, A. J. Acc. Chem. Res. 1992,
25, 83. (g) van Asselt, R.; Rijnberg, E.; Elsevier, C. J. Organometallics
1994, 13, 706. (h) Markies, B. A.; Canty, A. J.; Boersma, J.; van Koten,
G. Organometallics 1994, 13, 2053. (i) Ducker-Benfer, C.; van Eldik, R.;
Canty, A. J. Organometallics 1994, 13, 2412. (j) Canty, A. J. In
ComprehensiVe Organometallic Chemistry, 2nd ed.; Puddephatt, R. J., Ed.;
Pergamon: New York 1995; Vol. 9, Chapter 5. (k) Kruis, D.; Markies, M.
A.; Canty, A. J.; Boersma, J.; van Koten, G. J Organomet. Chem. 1997,
532, 235. (l) Canty, A. J.; Hoare, J. L.; Davies, N. W.; Traill, P. R.
Organometallics 1998, 17, 2046. (m) Canty, A. J.; Hoare, J. L.; Patel, J.;
Pfeffer, M.; Skelton, B. W.; White, A. H. Organometallics 1999, 18, 2660.
(n) Bayler, A.; Canty, A. J.; Edwards, P. G.; Skelton, B. W.; White, A. H.
J. Chem. Soc., Dalton Trans. 2000, 3325. (o) Puddephatt, R. J. Angew.
Chem., Int. Ed. 2002, 41, 261. (p) Procelewska, J.; Zahl, A.; Liehr, G.;
van Eldik, R.; Smythe, N. A.; Williams, B. S.; Goldberg, K. I. Inorg. Chem.
2005, 44, 7732.
(29) The rate law for the C-N reductive elimination reaction pathway shown
in Scheme 7 (also path D, Scheme 6) simplifies to the following: rate )
k
C-N[1a], where kC-N ) (k1k2)/(k2 + k-1). This rate law is independent of
[NHSO2R-]. See ref 10.
9
10388 J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
Scheme 7
3a is produced, and such behavior is clearly evident in the
downward curvature of the first-order kinetic plots of the
reaction. While such accelerative behavior is expected if the
reaction proceeds by path D, it is difficult to rationalize the
accelerative effect of methylsulfonamide 3a on the rate of
reaction for either the phosphine dissociation mechanism (path
B) or direct reductive elimination from 1a (path C).
Note that while a hydrogen-bonding interaction between the
methylsulfonamide product 3a and the sulfonamide moiety of
1a would be expected to facilitate sulfonamide dissociation from
1a, such an interaction should also be expected to decrease the
nucleophilicity of the resulting sulfonamide anion. The overall
acceleration in the C-N reductive elimination results from a
larger influence of the hydrogen bonding on the preequilibrium
step. This is similar to the observation of a positive F value for
the overall C-O reductive elimination of methyl aryl ethers
from fac-L2PtMe3(OR) which results from the sum of a large
positive equilibrium F value for OAr- dissociation and a smaller
negative kinetic F value for nucleophilic attack at the C(sp3)
by the OAr- group.10b
The mechanism in path D is also supported by the results of
the sulfonamide anion-exchange reaction. It was shown that the
exchange of sulfonamide anion is significantly more rapid than
the C-N reductive elimination. Complete exchange with
added sulfonamide was observed (i.e., equilibrium was reached)
at 85 °C, 15 °C lower than the temperature at which reductive
elimination was studied (Scheme 3). Sulfonamide anion ex-
change by an associative mechanism at Pt(IV) seems unlikely,
and thus, this result supports the kinetic viability of sulfonamide
dissociation as a preequilibrium first step under the reaction
conditions.
When the thermolysis of 1a is carried out without added
sulfonamide anion, carbon-carbon coupling to form ethane is
competitive with the C-N reductive elimination to produce 3a.
A competing C-C reductive elimination was also observed with
C-X reductive elimination from the Pt(IV) complexes fac-L2-
PtMe3X (L2 ) dppe, dppbz; X ) iodide, carboxylate, or
aryloxide). In these systems, the C-C coupling occurs from
the same cationic five-coordinate intermediate as the C-X
coupling.10,11 The complete inhibition of the C-C coupling
reaction in the presence of added sulfonamide anion implies
a similar mechanism for ethane production from 1a. The
results of the kinetic and mechanistic studies described above
are all fully consistent with the mechanism shown in Scheme 7
for C-N and C-C reductive elimination from 1a. Initial
dissociation of sulfonamide anion occurs to form the intermedi-
ate five-coordinate Pt(IV) cation I. Nucleophilic attack by
NHSO2R- at a methyl group of I forms the C-N-coupled
product 3a and the Pt(II) product 2. C-C reductive elimination
of ethane occurs directly from I, and the resulting unsaturated
Pt(II) species is trapped by NHSO2R- to yield 4. In the presence
of added NHSO2R-, C-C reductive elimination from I is
inhibited as the rate of nucleophilic attack on intermediate I
(k2[NHSO2R-][I]) becomes larger than that of C-C coupling
(k3[I]).
The mechanism shown in Scheme 7 also provides a rationale
for the observed solvent dependence of the product distribution.
Although C-N reductive elimination from 1 is favored in the
nonpolar solvent C6D6, use of the polar solvent nitrobenzene-
d5 enhances the C-C coupling pathway and no C-N coupling
is observed. The polar solvent nitrobenzene should favor the
formation of the five-coordinate cationic intermediate, the first
step in both pathways. However, the second step of C-N
reductive elimination should be less favored in polar solvents
as the charged intermediates are partially neutralized in the
transition state. As a result, the rate of the C-C reductive
elimination reaction increases more significantly with the
polarity of the solvent than that of C-N reductive elimination
and C-C reductive elimination is the exclusive pathway in the
very polar nitrobenzene solvent. Similar solvent effects were
seen in the product distributions and relative rates of C-O and
C-C couplings from fac-L2PtMe3(OR) complexes.10
Finally, the competitive mechanism depicted in Scheme 7 is
also consistent with the faster rates of reactions observed for
thermolyses of 1a carried out with added sulfonamide 3a and
with added water. Both of these additives can act as Lewis acids
to promote the first step of both C-N and C-C reductive
eliminationsthe dissociation of NHSO2R-. While this interac-
tion of sulfonamide 3a with the sulfonamide anion would be
expected to slow the second step of C-N reductive elimination
(the nucleophilic attack of NHSO2R- on the Pt(IV)-Me of I),
the larger contribution to the equilibrium first step results in a
faster C-N reductive elimination (see above). In contrast, the
C-C reductive elimination only experiences the increase
in the rate of the first step and so the C-C reductive elimination
rate might be expected to increase more than the C-N reductive
elimination rate. Indeed, a small increase in the amount
of C-C-coupled product (from 29% to 35%) was observed
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10389

A R T I C L E S
Scheme 8
Pawlikowski et al.
at the expense of C-N-coupled product in the presence of 17
equiv of 3a. The effect of the added water on the product
ratio was more dramatic, as C-C reductive elimination in-
creased from 29% to 64% in the presence of 1 equiv of H2O.
There was relatively little C-N coupling to produce 3a (15%)
as the major sulfonamide containing product was 5a, consistent
with protonation of the dissociated sulfonamide anion by the
water.
poses to the same products as 9a, with deuterium partially
incorporated into 8a and 10a to form 8a-d3 and 10a-d5 (Scheme
5). CH3D is the only isotopomer of methane that is observed,
consistent with the formation of fac-(dppbz)PtMe3D by â-deu-
teride elimination. Support for the formation of the reactive
deuterated sulfonylimine intermediate is provided by the
incorporation of deuterium into the methylene bridge of dimer
10a-d5. That one methyl group of both products 8a and 10a
remains undeuterated is consistent with the proposed nucleo-
philic attacks on the five-coordinate Pt cation (Scheme 8).
It is noteworthy that the classical mechanism for â-hydride
elimination requires the presence of a vacant coordination site
cis to the metal alkyl, alkoxide, or alkylamine.9a However, there
is evidence in related Pt(IV) systems to support that the rigid
ancillary dppbz ligand is not likely to dissociate under the
thermolysis conditions.22 Thus, the absence of facile access to
an empty coordination site cis to the sulfonamide ligand in 9a
appears in conflict with a proposal of â-hydride elimination.
However, examples of nonclassical â-hydride elimination reac-
tions for transition metal alkoxides have been reported.31-33 The
data from two of these systems are consistent with dissociation
of the alkoxide to generate the open site that accommodates
the transfer of the hydride from the alkoxide to the metal.32,33
A similar mechanism is proposed for this Pt(IV) system where
considerable evidence for dissociation of the sulfonamide anion
has been presented. The observation of fac-(dppbz)PtMe3H as
an intermediate is consistent with this proposal.
Decomposition of 9a. Compound 9a, the N-methyl derivative
of 1a, was less stable in C6D6 solution than 1a, and complete
decomposition of 9a to the Pt(II) compound 2 was observed
within 30 min upon thermolysis at 100 °C, forming dimethyl-
sulfonamide 8a from C-N reductive elimination, as well as
the sulfonamide dimer 10a and methane as organic products
(Scheme 5). Slow room-temperature decomposition of 9a
formed the same products in addition to small amounts of ethane
and (dppbz)PtMe(N(Me)SO2(p-C6H4(CH2)3CH3)), the products
of C-C reductive elimination from 9a. Monitoring the room-
temperature decomposition of 9a by 1H and 31P NMR allowed
for the observation of the Pt(IV)-hydride fac-(dppbz)PtMe3H22
as an intermediate. Compound 9a differs from 1a in that it is
susceptible to â-hydride elimination because of the methyl group
on nitrogen. â-hydride elimination is a common decomposition
pathway for late-metal alkylamides.16a â-hydride elimination
from 9a would form the N-sulfonylimine species H2CdNSO2-
(p-C6H4(CH2)3CH3), which was not directly observed, and Pt-
(IV)-hydride fac-(dppbz)PtMe3H, which was observed and is
known to react further under these conditions to form the
observed products of methane and (dppbz)PtMe2 (2).22 The
terminal methylene carbon of the N-sulfonylimine is expected
to be highly electrophilic,30 and reaction with methylsulfonamide
anion N(Me)SO2R- would form the new anion 11a. Nucleo-
philic attack on a Pt(IV) methyl group by anion 11a can then
form the observed sulfonamide dimer 10a (Scheme 8).
Isotopic labeling experiments provide support for this unusual
decomposition pathway. The labeled compound 9a-d3 decom-
Formation of Additional Sulfonamide Products. Ther-
molysis of 1a in C6D6 in the presence of the sulfonamide salt
6a produces sulfonamides 3a and 5a, with formation of
dimethylsulfonamide 8a in small amounts as well. The formation
of 8a can be rationalized by the equilibrium shown in eq 1.
Reaction of methylsulfonamide product 3a with the anion of
6a forms H2NSO2(p-C6H4(CH2)3CH3) (5a) and the methylsul-
fonamide anion of 7a (eq 1). The methylsulfonamide anion of
(31) Ritter, J. C. M.; Bergman, R. G. J. Am. Chem. Soc. 1998, 120, 6826.
(32) Blum, O.; Milstein, D. J. Organomet. Chem. 2000, 593-594, 479.
(33) Farad, C. M.; Ozerov, O. V. Inorg. Chim. Acta 2007, 360, 286.
(30) Bharatam, P. V.; Kaur, A.; Kaur, D. Tetrahedron 2002, 58, 10335.
9
10390 J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
Experimental Section
7a can nucleophilically attack a methyl group on the five-
coordinate intermediate to form 8a and 2, as proposed in the
top reaction in Scheme 8 for the formation of Me2NSO2(p-
C6H4(CH2)3CH3) upon thermolysis of 9a.
General Comments. Unless otherwise noted, all manipulations were
carried out under a nitrogen atmosphere in a drybox or using standard
vacuum-line techniques. Tetrahydrofuran, benzene, benzene-d6, toluene,
and diethyl ether were transferred under vacuum from sodium/
benzophenone. Pentane was transferred from CaH2. Iodomethane
(Strem) was dried with and stored under 4 Å molecular sieves. KH
was purchased from Aldrich as a suspension in oil and was filtered
under nitrogen and washed with hexanes prior to use. o-Bis(diphe-
nylphosphino)benzene (Strem) was stirred with KH in THF and then
recrystallized from THF/pentane. The Pt(IV) compounds fac-(dppbz)-
PtMe3(O2CCF3)10 and fac-(dppbz)PtMe3(OH)15 were prepared as previ-
ously described. 4-n-Butylbenzenesulfonamide and 4-n-butylbenzene-
sulfonyl chloride were purchased from Alfa Aesar and used as received.
All other reagents and solvents were purchased from Alrich and used
as received. NMR spectra were recorded using Bruker DRX 499, AV
500, AV 301, or DPX 200 spectrometers. 1H NMR spectra were
referenced to residual proton peaks in the deuterated solvent, and
chemical shifts (δ) are reported in ppm relative to tetramethylsilane.
31P{1H} NMR spectra were referenced to an external standard of 85%
H3PO4.
Notably, the dimethylsulfonamide product 8a is only observed
during thermolysis of 1a in the presence of added sulfonamide
salt 6a. Thermolysis of 1a alone produces only the expected
product 3a and the unsubstituted sulfonamide 5a as the organic
sulfonamide products. Small amounts of methanol (<5%) also
formed upon thermolysis of 1a. The yields of 3a and 5a together
equaled the amount of the corresponding Pt(II) product 2 that
was formed. In these reactions, adventitious water in the NMR
could be responsible for the formation of 5a and of the methanol.
Despite handling of the samples under rigorously air- and
moisture-free conditions, trace amounts of water are observed
1
in the H NMR spectra of 1a upon heating. The first step of
the mechanism of reductive elimination from 1a is the dissocia-
tion of NHSO2R- from the platinum center to form the five-
coordinate intermediate. Any water in the sample could assist
in the dissociation and react with the dissociated anion to form
5a and hydroxide anion. Reaction of the hydroxide anion with
the five-coordinate intermediate would form 2 and methanol.
Consistent with this proposal, the yields of both methanol and
sulfonamide 5a increased significantly upon addition of water
to the thermolysis reactions.
Synthesis of fac-(dppbz)PtMe3(NHSO2R) (1a-c). The Pt(IV)-
sulfonamide complexes were prepared from fac-(dppbz)PtMe3(OH) and
the corresponding sulfonamide in THF. For 1a, fac-(dppbz)PtMe3(OH)
(75.8 mg, 0.108 mmol) and excess 4-n-butylbenzenesulfonamide (47.5
mg, 0.223 mmol) were dissolved in 10 mL of dry THF. The solution
was stirred overnight. MgSO4 was added as a drying agent and the
reaction mixture stirred for 10 min and then filtered through a Teflon
syringe filter. The solvent was removed from the filtrate under vacuum,
and the oily solid residue was washed with cold Et2O (2 × 5 mL) to
remove excess sulfonamide. The remaining white solid was dried under
vacuum overnight and recrystallized from THF/pentane to afford 1a
in a 65% isolated yield (63 mg). 1b,c were prepared by analogous
Conclusions
The novel Pt(IV)-sulfonamide complexes fac-(dppbz)PtMe3-
(NHSO2R) (R ) p-C6H4(CH2)3CH3, p-C6H4CH3, CH3) (1a-c)
were prepared from fac-(dppbz)PtMe3(OH) and the correspond-
ing sulfonamide in THF at room temperature. These complexes
undergo C-N reductive elimination upon thermolysis in C6D6
to form methylsulfonamides 3a-c in high yield. C-C coupling
also occurs to form ethane and Pt(II)-sulfonamides 4a-c in
lower yield. High selectivity for the C-N reductive elimination
pathway can be achieved by addition of sulfonamide anion to
the thermolysis reactions. These C-N reductive elimination
reactions represent the first examples of directly observed
thermal C(sp3)-N reductive elimination. Mechanistic studies
of the thermolysis of 1a support a two-step reaction pathway
of initial dissociation of NHSO2R- from the metal center to
form a cationic five-coordinate intermediate, followed by
nucleophilic attack by NHSO2R- on a methyl group of this
intermediate to form the products. This mechanism is analogous
to the mechanisms for C-O and C-I reductive eliminations
reported from similar Pt(IV) complexes.10,11 Thus, an apparently
general mechanism for C(sp3)-I, C(sp3)-O, and C(sp3)-N
reductive elimination from Pt(IV) has been identified. Also
significant is that the second step of this mechanism, the
nucleophilic attack of the X group on the alkyl group of a five-
coordinate d6 metal, is similar to that observed in C-O and
C-X bond-forming reactions at Pt(IV)10,11,25 and at Rh(III).8
Thus, in all these cases, the rare alkyl C-X coupling step occurs
via a common mechanism of nucleophilic attack of the
heteroatom group at a high-valent d6 five-coordinate alkyl
species. This apparent generality of the mechanism of alkyl
carbon-heteroatom bond formation from high-valent d6 metal
centers should be of significant use in the design of catalysts
for organic transformations relying on the challenging formation
of an alkyl carbon-heteroatom bond.
procedures. 1a: 1H NMR (C6D6) δ 0.32 (t w/Pt satellites, 3H, 3JP-H
)
7.5, 2JPt-H ) 67, Pt-CH3 trans to N), 0.84 (t, 3H, 3JH-H ) 7.3, -CH2-
CH2CH2CH3), 1.20 (m, 2H, -CH2CH2CH2CH3), 1.42 (m, 2H, -CH2CH2-
3
CH2CH3), 1.77 (br s, 1H, NH), 1.89 (vt w/Pt satellites, 6H, JP-H
)
2
3
7.0, JPt-H ) 60, Pt-CH3 cis to N), 2.45 (t, 2H, JH-H ) 7.7, -CH2-
CH2CH2CH3), 6.8-8.0 (m, 24H, protons of phosphine and sulfonamide
aryl rings, unresolved); 31P{1H} NMR (C6D6) δ 17.9 (s w/Pt satellites,
1JPt-P ) 1028). 1b: 1H NMR (THF-d8) δ -0.09 (t w/Pt satellites, 3H,
3JP-H ) 7.5, 2JPt-H ) 66, Pt-CH3 trans to N), 1.23 (vt w/Pt satellites,
6H, 3JP-H ) 7.0, 2JPt-H ) 60, Pt-CH3 cis to N), 1.33 (s w/Pt satellites,
2
1H, JPt-H ) 1.5, NH), 2.30 (s, 3H, p-C6H4CH3)), 7.0-7.7 (m, 24H,
protons of phosphine aryl rings and p-tolyl group, unresolved); 31P-
{1H} NMR (THF-d8) δ 15.9 (s w/Pt satellites, JPt-P ) 1030). 1c: 1H
1
3
2
NMR (THF-d8) δ -0.10 (t w/Pt satellites, 3H, JP-H ) 7.3, JPt-H
)
65, Pt-CH3 trans to N), 1.27 (vt w/Pt satellites, 6H, 3JP-H ) 6.5, 2JPt-H
) 60, Pt-CH3 cis to N), 2.33 (s, 3H, HNSO2CH3), 7.2-7.8 (m, 20H,
protons of phosphine aryl rings, unresolved) (signal for the NH proton
of the Pt-NHSO2Me group coincident with residual protio THF in
the deuterated solvent (δ 1.4)); 31P{1H} NMR (THF-d8) δ 16.3 (s w/Pt
1
satellites, JPt-P ) 1044).
X-ray Crystal Structure of 1a. Colorless crystal prisms of 1a were
grown by slow diffusion of diethyl ether into a THF solution of 1a at
-35 °C. Crystallographic data for 1a were collected at the University
of Washington X-ray crystallography laboratory (Table 3). A crystal
of 1a was mounted on a glass capillary with oil. All hydrogen atoms
were located using a riding model. All non-hydrogen atoms were refined
anisotropically by full-matrix least squares. The data was integrated
and scaled using hkl-SCALEPACK.
Synthesis of fac-(dppbz)PtMe3(N(Me)SO2(p-C6H4(CH2)3CH3))
(9a). Compound 1a (4 mg, 0.004 mmol) was weighed into an NMR
tube equipped with a Teflon valve, and an excess of solid KH was
added. A small stirbar was also added to the tube. THF was vacuum
transferred and the suspension stirred for 2 days. The solution gradually
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10391

A R T I C L E S
Pawlikowski et al.
preparation of N-methylbenzenesulfonamide.35 n-Butylbenzenesulfonyl
chloride (1.64 g, 7.04 mmol) was reacted with an excess of a 40%
w/w solution of methylamine in water (3.2 mL, 35.7 mmol). The
reaction mixture was heated on a steam bath for 15 min. The product
was extracted three times with 15 mL portions of CH2Cl2. The organic
fractions were combined, washed with water (3 × 5 mL) and then dried
over MgSO4. The solvent was removed in vacuo by rotary evaporation
to yield the product as a clear oil. Yield: 1.45 g, 90%. 1H NMR
(C6D6): δ 0.81 (t, 3H, 3JH-H ) 7.3, -CH2CH2CH2CH3), 1.13 (m, 2H,
-CH2CH2CH2CH3), 1.32 (m, 2H, -CH2CH2CH2CH3), 2.06 (d, 3H,
Table 3. X-ray Diffraction Data for 1a
empirical formula
fw
C47H55.87NO3P2PtS
971.88
T (K)
130(2)
wavelength (Å)
cryst descriptn
space group
0.710 73
colorless prism
triclinic, P1h
unit cell dimens (Å, deg)
a ) 10.8090(4)
b ) 14.5820(5)
c ) 14.6140(6)
R ) 100.0110(14)
â ) 101.9370(14)
γ ) 91.6000(15)
2214.41(14)
2, 1.458
3
N-CH3), 2.28 (t, 2H, JH-H ) 7.7, -CH2CH2CH2CH3), 3.82 (s, 1H,
3
NH), 6.86 (d, 2H, JH-H ) 8.0, aryl protons ortho to sulfonamide),
V (Å3)
3
7.77 (d, 2H, JH-H ) 8.0, aryl protons meta to sulfonamide).
Z, F (mg/m3)
M (mm-1
F(000)
)
3.328
985.7
6a. 4-n-Butylbenzenesulfonamide (53.5 mg, 0.251 mmol) and 18-
crown-6 (67 mg, 0.253 mmol) were dissolved in THF, and an excess
of KH was added. The reaction mixture was stirred for 2 h and then
filtered through glass wool and diatomaceous earth. The solvent was
removed under vacuum, and the white crystalline product was recrystal-
lized from THF/pentane. Yield: 97 mg, 75%. 1H NMR (C6D6): δ 0.82
(t, 3H, 3JH-H ) 7.3, -CH2CH2CH2CH3), 1.20 (m, 2H, -CH2CH2CH2-
CH3), 1.45 (m, 2H, -CH2CH2CH2CH3), 2.44 (t, 2H, 3JH-H ) 7.6, -CH2-
CH2CH2CH3), 2.67 (s, 1H, NH), 3.35 (br s, 24H, crown ether protons),
7.03 (d, 2H, 3JH-H ) 8.0, aryl protons ortho to sulfonamide), 8.48 (d,
cryst size (mm)
reflcns for indexing
θ range (deg)
0.46 × 0.24 × 0.17
689
2.15-28.32
-12 e h e 14
-19 e k e 18
-18 e l e 19
16 628, 10 376
99.10
index ranges
reflcns collcd, unique
completeness to θ (%)
abs corr
refinement method
goodness of fit on F2
R1
semiempirical from equivalents
full-matrix least squares on F2
S ) 0.973
3
2H, JH-H ) 8.0, aryl protons meta to sulfonamide).
8a. N,N-Dimethyl-4-n-butylbenzenesulfonamide was prepared as
follows: The potassium salt of 3a (5 mg) was added to an NMR tube
fitted with a Teflon valve. An excess of iodomethane (∼0.2 mL) was
added via vacuum transfer. The excess iodomethane was removed under
0.0467
wR (I > 2σ(I))
0.1147
1
turned pale yellow, and the formation of the deprotonated complex
was monitored by 31P NMR (after removal of the magnetic stirbar) by
the disappearance of the resonance for 1a (18.1 ppm, JPt-P ) 1028)
and the appearance of a new resonance at 12.2 ppm with a Pt-P
coupling of 1086 Hz. When the deprotonation was complete, excess
MeI (∼0.05 mL) was vacuum transferred into the tube. White KI
precipitate formed immediately, and the solution turned colorless. The
solution was filtered while cold, the THF was removed, and C6D6 was
added for NMR analysis. 1H NMR (C6D6): δ -0.004 (t w/Pt satellites,
vacuum following precipitation of KI, and C6D6 was added. H NMR
(C6D6): δ 0.81 (t, 3H, 3JH-H ) 7.3, -CH2CH2CH2CH3), 1.14 (m, 2H,
-CH2CH2CH2CH3), 1.32 (m, 2H, -CH2CH2CH2CH3), 2.27 (s, 6H,
3
N-CH3), 2.28 (t, 2H, JH-H ) 7.7, -CH2CH2CH2CH3), 6.87 (d, 2H,
3JH-H ) 8.0, aryl protons ortho to sulfonamide), 7.67 (d, 2H, 3JH-H
8.0, aryl protons meta to sulfonamide).
)
10a. The sulfonamide dimer CH2(N(Me)SO2(p-C6H4(CH2)3CH3))2
was prepared by modification of a literature procedure for the analogous
p-tolylsulfonamide dimer.21 HN(Me)SO2(p-C6H4(CH2)3CH3) (450 mg,
1.98 mmol) was dissolved in xylenes. A 0.140 mL volume of DMSO
(1.97 mmol) was added, followed by 10 mg of solid P2O5. The reaction
vessel was sealed with a Teflon stopcock and heated at 150 °C for 3
h. The solution was decanted into a separatory funnel and neutralized
with a 10% NaOH solution. Upon addition of the base, the product
precipitated from solution. The xylene fraction containing the precipitate
was collected and the solvent removed under vacuum. The oily white
3
2
3
3H, JP-H ) 8.0, JPt-H ) 66, Pt-CH3 trans to N), 0.86 (t, 3H, JH-H
) 7.0, -CH2CH2CH2CH3), 1.20 (m, 2H, -CH2CH2CH2CH3), 1.42 (m,
2H, -CH2CH2CH2CH3), 2.24 (vt w/Pt satellites, 6H, 3JP-H ) 6.6, 2JPt-H
3
) 60, Pt-CH3 cis to N), 2.38 (t, 2H, JH-H ) 7.6, -CH2CH2CH2-
CH3), 2.73 (br s, 3H, PtN-CH3), 6.8-8.2 (m, 24H, protons of
phosphine and sulfonamide aryl rings, unresolved). 31P{1H} NMR
1
(C6D6): δ 21.6 (s w/Pt satellites, JPt-P ) 1032).
Synthesis of (dppbz)PtMe(NHSO2(p-C6H4(CH2)3CH3)) (4a). (dp-
pbz)PtMe2 (4 mg, 0.006 mmol) was weighed into an NMR tube
equipped with a Teflon valve and dissolved in benzene. A 96 µL volume
of a 0.0621 M solution of trifluoromethanesulfonic acid in toluene
(0.006 mmol) was added via syringe, and the mixture was allowed to
react overnight. The solvent was removed in vacuo. The potassium
salt of 4-n-butylbenzenesulfonamide was added (2 mg, 0.008 mol), and
then C6D6 was vacuum transferred into the tube. The reaction was
complete after 1 h, as observed by 31P{1H} NMR. The solution was
filtered into another NMR tube to remove potassium triflate, and the
product was characterized by 1H and 31P{1H} NMR. 1H NMR (C6H6):
1
residue was dried under vacuum overnight. H NMR (C6H6): δ 0.81
(t, 6H, 3JH-H ) 7.3, -CH2CH2CH2CH3), 1.12 (m, 4H, -CH2CH2CH2-
CH3), 1.31 (m, 4H, -CH2CH2CH2CH3), 2.27 (t, 4H, 3JH-H ) 7.7, -CH2-
CH2CH2CH3), 2.75 (s, 6H, N-CH3), 4.56 (s, 2H, -NCH2N-), 6.82
3
(d, 4H, JH-H ) 8.3, aryl protons ortho to sulfonamide), 7.58 (d, 4H,
3JH-H ) 8.3, aryl protons meta to sulfonamide).
Sulfonamide Exchange Experiment. Compound 1b (3.7 mg, 0.0043
mmol) and sulfonamide salt 6a (2.4 mg, 0.0046 mmol) were weighed
into an NMR tube equipped with a Teflon valve. C6D6 was added via
vacuum transfer. The sample was heated at 85 °C in an oil bath for 3
days, quenching in an ice bath periodically for analysis by 1H and 31
P
3
δ 0.82 (t, 2H, JH-H ) 7.3, -CH2CH2CH2CH3), 0.84 (dd w/Pt
NMR. The amounts of Pt(IV) compounds 1b and 1a were monitored
2
satellites,34 3H, JPt-H ) 55, Pt-CH3), 1.16 (m, 2H, -CH2CH2CH2-
by 31P NMR (δ 18.0 ppm for 1b, 17.9 ppm for 1a), and the amounts
CH3), 1.37 (m, 2H, -CH2CH2CH2CH3), 2.33 (t, 2H, 3JH-H ) 7.6, -CH2-
1
of sulfonamide salts 6a and 6b were determined by H NMR (aryl
3
CH2CH2CH3), 4.24 (br d, JP-H ) 2.6, Pt-NH), 6.8-8.0 (m, 24H,
protons meta to sulfonamide; δ 8.34 ppm for 6b, δ 8.38 for 6a).
Although the reaction was monitored for 3 days, equilibrium was
reached after 25 h.
General Treatment of Kinetics Samples. A medium-walled NMR
tube affixed to a 14/20 joint was loaded with 3 mg (0.003 mmol) of
the Pt(IV)-sulfonamide complex 1 in the drybox. Triphenylmethane
protons of phosphine and sulfonamide aryl rings, unresolved). 31P{1H}
NMR (C6D6): δ 50.3 (s w/Pt satellites, 1JPt-P ) 1865, P trans to CH3),
1
41.2 (s w/Pt satellites, JPt-P ) 3625, P trans to NHSO2R).
Synthesis of Sulfonamides. 3a. N-Methyl-4-n-butylbenzenesulfona-
mide was prepared by a modification of a literature procedure for the
3
(34) The JP-H coupling constants could not be determined due to overlap of
the Pt-Me resonance with the CH3 resonance of the butyl chain.
(35) Banks, M. R.; Hudson, R. F. J. Chem. Soc., Perkin Trans. 2 1986, 1211.
9
10392 J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007

C−N Reductive Elimination from Pt(IV)
A R T I C L E S
(0.8 mg, 0.003 mmol) was added as an internal standard. A small
amount of benzene was added to the tube to dissolve the solids. The
tube was attached to the vacuum line with a stopcock adapter, and the
benzene was removed under vacuum. C6D6 was vacuum transferred
into the tube (0.3-0.45 mL), the solution was kept frozen in liquid
nitrogen, and the tube was flame-sealed under active vacuum.
A Neslab Exacal EX-250 HT elevated temperature bath was used
to heat the NMR tubes at 100.0 °C. The thermolyses were quenched at
various times for analysis by NMR by immersion of the tubes in cold
water or ice water, and the tubes were stored in a freezer at -23 °C
acquisitions. The thermolyses were followed for 3 half-lives, and mass
balance was confirmed after heating the reactions to completion.
Acknowledgment. This work was supported by the National
Science Foundation (CHE-0137394) with initial funding from
the Petroleum Research Fund, administered by the American
Chemical Society. The X-ray structure determination was
performed by Dr. W. Kaminsky at the University of Washington.
We thank Brietta J. Smith for synthetic contributions.
1
when not being heated. H and 31P{1H} NMR spectra were recorded
Supporting Information Available: A CIF file for fac-
(dppbz)PtMe3(NHSO2(p-C6H4(CH2)3CH3)) (1a). This informa-
tionisavailablefreeofchargeviatheInternetathttp://pubs.acs.org.
on a Bruker DRX 499 spectrometer, using a delay time of 50 s. The
reaction progress was monitored by integration of the signals of both
the axial and equatorial methyl groups of the starting compound relative
to the internal standard, averaging the integrals of three separate
JA069191H
9
J. AM. CHEM. SOC. VOL. 129, NO. 34, 2007 10393