Pt(II) and Pt(IV) amido, aryloxide, and hydrocarbyl complexes: Synthesis, characterization, and reaction with dihydrogen and substrates that possess C-H bonds

ARTICLE

pubs.acs.org/IC

Pt(II) and Pt(IV) Amido, Aryloxide, and Hydrocarbyl Complexes:

Synthesis, Characterization, and Reaction with Dihydrogen and

Substrates that Possess CꢀH Bonds

Joanna R. Webb,^†Colleen Munro-Leighton,^{^}Aaron W. Pierpont,^‡Joshua T. Gurkin,^{^}T. Brent Gunnoe,*^,†

Thomas R. Cundari,*^,‡Michal Sabat,^§,†Jeﬀrey L. Petersen,^||and Paul D. Boyle^{^}

^†Department of Chemistry, University of Virginia, Charlottesville, Virginia 22904, United States

^‡Department of Chemistry, Center for Advanced Scientiﬁc Computing and Modeling (CASCaM), University of North Texas, Denton,

Texas 76203, United States

^§Nanoscale Materials Characterization Facility, Department of Materials Science and Engineering, University of Virginia, Charlottesville,

Virginia 22904, United States

C. Eugene Bennett Department of Chemistry, West Virginia University, Morgantown, West Virginia, 26506

^{^}Department of Chemistry, North Carolina State University, Raleigh, North Carolina 27695, United States

S Supporting Information

b

ABSTRACT: The Pt(II) amido and phenoxide complexes

(^tbpy)Pt(Me)(X), (^tbpy)Pt(X)₂, and [(^tbpy)Pt(X)(py)][BAr⁰₄]

(X = NHPh, OPh; py = pyridine) have been synthesized and

characterized. To test the feasibility of accessing Pt(IV) com-

plexes by oxidizing their Pt(II) precursors, the previously

reported (^tbpy)Pt(R)₂(R = Me and Ph) systems were oxidized

with I₂to yield (^tbpy)Pt(R)₂(I)₂. The analogous reaction with

(^tbpy)Pt(Me)(NHPh) and MeI yields the corresponding

(^tbpy)Pt(Me)₂(NHPh)(I) complex. Reaction of (^tbpy)Pt-

(Me)(NHPh) and phenylacetylene at 80 ꢀC results in the

formation of the Pt(II) phenylacetylide complex (^tbpy)-

Pt(Me)(CtCPh). Kinetic studies indicate that the reaction

of (^tbpy)Pt(Me)(NHPh) and phenylacetylene occurs via a

pathway that involves [(^tbpy)Pt(Me)(NH₂Ph)][TFA] as a

catalyst. The reaction of H₂with (^tbpy)Pt(Me)(NHPh) ulti-

mately produces aniline, methane, ^tbpy, and elemental Pt. For

this reaction, mechanistic studies reveal that 1,2-addition of dihydrogen across the PtꢀNHPh bond to initially produce

(^tbpy)Pt(Me)(H) and free aniline is catalyzed by elemental Pt. Heating the cationic complexes [(^tbpy)Pt(NHPh)(py)][BAr⁰₄]

and [(^tbpy)Pt(OPh)(py)][BAr⁰₄] in C₆D₆does not result in the production of aniline and phenol, respectively. Attempted

synthesis of a cationic system analogous to [(^tbpy)Pt(NHPh)(py)][BAr⁰₄] with ligands that are more labile than pyridine (e.g.,

NC₅F₅) results in the formation of the dimer [(^tbpy)Pt(μ-NHPh)]₂[BAr⁰₄]₂. Solid-state X-ray diﬀraction studies of the complexes

(^tbpy)Pt(Me)(NHPh), [(^tbpy)Pt(NH₂Ph)₂][OTf]₂, (^tbpy)Pt(NHPh)₂, (^tbpy)Pt(OPh)₂, (^tbpy)Pt(Me)₂(I)₂, and (^tbpy)Pt-

(Ph)₂(I)₂are reported.

’ INTRODUCTION

to systems with empty dπ orbitals), imparting nucleophilic and

basic reactivity.^{2,3,12,13,18ꢀ21}Such reactive ligands positioned

adjacent to Lewis acidic metal centers provide an opportunity

to activate relatively unreactive organic substrates.

In order to identify the factors that control transformations of

MꢀX moieties (X = NR₂, OR; M = high d-electron count transition

metal), well-deﬁned systems with varied oxidation states, ligand

sets, metal centers, and coordination environments must be

Late transition metal centers with high d-electron counts

bearing heteroatomic ligands (e.g., amido, alkyl/aryloxo, hydroxo,

imido, or oxo ligands) exhibit diverse reactivity.^1ꢀ5Such systems have

been implicated in metal-mediated reactions such as oleﬁn and alkyne

hydroamination, oleﬁn insertions, aryl amination, aryl etheration, and

CꢀH bond activation.^2,4,6ꢀ17The range of reactivity of these systems

has been attributed, at least in part, to the disruption of ligand-to-

metal π bonding.³Limiting ligand-to-metal π donation by using late

transition metals with high d-electron counts serves to localize

negative charge density on the heteroatomic ligand (i.e., compared

Received: January 24, 2011

Published: March 28, 2011

r

2011 American Chemical Society

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Inorganic Chemistry

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bond length of 2 is 2.005(2) Å. With a PtꢀN3ꢀC20ꢀC21

dihedral angle of 9.0(4)ꢀ, the amido lone pair is approximately

aligned for donation into the π* orbitals of the phenyl ring

(Figure 2). Consequently, the N_amidoꢀC_phenylbond length for

complex 2 is 1.357(4) Å. Cowan and Trogler et al. reported the

crystal structure for trans-PtH(NHPh)(PEt₃)₂with a Pt(II)ꢀN

bond distance longer than that of 2 {2.125(5) versus 2.005(2) Å}

and a shorter N_amidoꢀC_phenylbond than that of 2 {1.343(8) versus

1.357(4) Å}.¹⁷Gomez et al. reported a monomeric Pt(II)-substi-

tuted amido complex, trans-[PtCl{NH(p-IC₆H₄)}(PEt₃)₂], with a

PtꢀN bond distance of 2.006(4) Å.²⁶

Figure 1. ORTEP diagram (50% probability) of (^tbpy)Pt(Me)(NHPh)

(2) (most hydrogen atoms omitted for clarity). Selected bond lengths

(Å): Pt1ꢀN1 2.077(2), Pt1ꢀN2 2.026(2), Pt1ꢀC1 2.040(3), Pt1ꢀN3

2.005(2), N3ꢀC20 1.357(4). Selected bond angles (deg):

N3ꢀPt1ꢀC1 89.25(11), N2ꢀPt1ꢀC1 97.26(11), N3ꢀPt1ꢀN1

94.55(9), N2ꢀPt1ꢀN1 78.91(9), Pt1ꢀN3ꢀC20 126.1(2).

Figure 2. View of complex 2 showing that the amido orientation likely

allows overlap of the N3 lone pair with the π* system of the phenyl ring.

The synthesis of [(^tbpy)Pt(NH₂Ph)₂][OTf]₂(3) was accom-

plished by combining excess aniline with the previously reported

(^tbpy)Pt(OTf)₂complex (eq 3).²⁵Complex 3 is characterized by

a broad singlet at 7.65 ppm, which integrates for four protons,

due to the amine-NH₂as well as resonances due to symmetry-

accessed.^22,23Herein, we report the synthesis and characterization of

neutral and cationic Pt(II) and Pt(IV) complexes with NHR or OR

ligands bearing the bidentate ligand 4,4⁰-di-tert-butyl-2,2⁰-dipyridyl

(^tbpy), including solid-state X-ray diﬀraction studies and details of

the reactivity of these complexes with substrates that possess

covalent bonds (i.e., HꢀH and CꢀH). Portions of this work have

been previously communicated.²⁴

equivalent pyridyl groups of the bpy ligand in the H and ¹³C

NMR spectra. The solid-state structure of complex 3 has been

determined from a single-crystal X-ray diﬀraction study. Com-

plex 3 displays no hydrogen bonding between the anilido protons

and triﬂate counterions. The PtꢀN_aminebond lengths are

2.070(6) and 2.065(6) Å (Figure 3) and, thus, are elongated

by ∼0.06ꢀ0.07 Å relative to the PtꢀN_amidobond distance of 2.

Vedernikov et al. reported a monomeric Pt(II) aniline complex,

(dpms)Pt(Ph)(NH₂Ph) {dpms = di(2-pyridyl)methanesulfonate},

with a PtꢀN_aminebond length of 2.066(3) Å.²⁷Radlowski et al.

reported a Pt(II) complex with two chelating amine ligands with the

lengths of the four PtꢀN bonds between 2.023(9) and 2.073(9) Å.²⁸

t

1

’ RESULTS AND DISCUSSION

Synthesis and Characterization of Pt(II) Complexes. The

labile nature of the trifluoroacetate (TFA) ligand of the pre-

viously reported complex (^tbpy)Pt(Me)(TFA)²⁵allows coordi-

nation of aniline to afford [(^tbpy)Pt(Me)(NH₂Ph)][TFA] (1)

1

(eq 1). A singlet with Pt satellites (²J_PtꢀH= 70 Hz) in the H

NMR spectrum at 0.84 ppm and one at ꢀ10.4 ppm (¹J_PtꢀC= 774

Hz) in the ¹³C NMR spectrum confirm the presence of the

methyl ligand. Deprotonation with 1 equiv of Na[N(SiMe₃)₂]

cleanly provides the corresponding amido complex, (^tbpy)

Pt(Me)(NHPh) (2) (eq 2), with a significant upfield shift of

the NH resonance from 7.72 ppm for 1 to 3.99 ppm for

1

complex 2. The downfield region of the H NMR spectrum of

complex 2 is consistent with N_amidoꢀC_phenylbond rotation that

is rapid on the NMR time scale with one resonance each for the

ortho and meta positions of the amido phenyl group. For 2, the

methyl group resonates as a singlet (1.85 ppm) with Pt satellites

(²J_PtꢀH= 84 Hz) in the ¹H NMR spectrum and ꢀ14.2 ppm (¹J_PtꢀC

= 813 Hz) in the ¹³C NMR spectrum. Complex 2 has been

characterized by single-crystal X-ray diffraction and exhibits a pseudo

square planar coordination sphere (Figure 1). The PtꢀN_amido

Deprotonation of both amine ligands of complex 3 with 2

equiv of Na[N(SiMe₃)₂] provides the corresponding bis-amido

complex (^tbpy)Pt(NHPh)₂(4) (eq 4). Consistent with complexes

1 and 2, upon deprotonation of complex 3 the NH resonance shifts

upﬁeld from 7.65 to 3.80 ppm. Complex 4 is also characterized by

equivalent ^tbpy resonances in the ¹Hand¹³CNMRspectra.Complex

4 crystallizes as a monomeric complex from a solution of methylene

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t

inequivalent pyridyl groups of the bpy ligand. The amido NH

resonates as a broad singlet at 4.06 ppm, which is slightly

downﬁeld of the NH resonance of complex 4 (3.80 ppm).

Phenoxide analogs of complexes 2 and 4 with bpy (bpy =2,2⁰-

bipyridyl) as the supporting ligand have been reported.^29,30The

published procedure for (bpy)Pt(Me)(OPh) was used to synthesize

the ^tbpy version.²⁹Addition of excess phenol to a benzene solution of

(^tbpy)Pt(Me)₂³¹results in the precipitation of (^tbpy)Pt(Me)(OPh)

(6) (eq 6). As reported by van Koten and co-workers for

(bpy)Pt(Me)(OPh), excess phenol is necessary to drive the

reaction to completion, and 1 equiv of phenol is present in the

isolated solid for 6 (conﬁrmed by ¹H and ¹³C NMR spectroscopy

as well as elemental analysis). The methyl ligand of complex 6

resonates as a singlet at 1.00 ppm with Pt satellites (²J_PtꢀH= 82

Hz) in the ¹H NMR spectrum and at ꢀ14.2 ppm (¹J_PtꢀC= 826

Hz) in the ¹³C NMR spectrum.

Figure 3. ORTEP diagram (50% probability) of [(^tbpy)Pt(NH₂Ph)₂]

[OTf]₂(3) (most hydrogen atoms and the OTf counterions are omitted

for clarity). Selected bond lengths (Å): PtꢀN1 2.008(5), PtꢀN2

2.015(5), PtꢀN3 2.070(6), PtꢀN4 2.065(6), N3ꢀC19 1.468(8),

N4ꢀC25 1.474(9). Selected bond angles (deg): N1ꢀPtꢀN2 80.9(2),

N1ꢀPtꢀN4 95.4(3), N2ꢀPtꢀN3 95.2(2), N4ꢀPtꢀN3 88.4(3),

PtꢀN4ꢀC25 117.8(4), PtꢀN3ꢀC19 116.5(4).

Heating a solution of complex 4 in THF with excess phenol to

80 ꢀC yields (^tbpy)Pt(OPh)₂(7) in 95% yield (eq 7). Unlike

complex 6, excess phenol can be removed from complex 7 by rinsing

with copious amounts of hot hexanes. Complex 7 is characterized by

aryl and ^tbpy resonances consistent with symmetry-equivalent pyridyl

andphenoxide groups in the ¹H and ¹³C NMR spectra. The solid-

state structure of complex 7 has been determined by a single-

crystal X-ray diﬀraction study (Figure 5). Complex 7 possesses a

pseudosquare planar coordination geometry with angles around

the platinum center falling in the range of 80.8(2)ꢀ94.5(2)ꢀ.

The PtꢀO bond lengths (PtꢀO1 2.014(4) Å and PtꢀO2

2.001(4) Å) are similar to the analogous bond length of

2.001(5) Å for the PtꢀO bond of (bpy)Pt(Me)(OPh).²⁹

Yamamoto and co-workers reported the solid-state structure

for the Pt(II) phenoxide complex cis-(PMe₃)₂Pt(Me)(OPh),

which has a PtꢀO bond length of 2.153(9) Å, signiﬁcantly longer

than those of complex 7.³²

Figure 4. ORTEP diagram (50% probability) of (^tbpy)Pt(NHPh)₂(4)

(most hydrogen atoms omitted for clarity). Selected bond lengths (Å):

PtꢀN1 2.024(4), PtꢀN2 2.014(4), PtꢀN3 1.995(4), PtꢀN4 1.984(5),

N3ꢀC19 1.362(6), N4ꢀC25 1.371(7). Selected bond angles (deg):

N4ꢀPtꢀN3 92.5(2), N3ꢀPtꢀN2 93.28(2), N4ꢀPtꢀN1 94.8(2),

N2ꢀPtꢀN1 79.35(2), PtꢀN4ꢀC25 129.2(4), PtꢀN3ꢀC19 130.7(4).

chloride and hexanes. Selected bond distances and angles and

the structure of 4 are shown in Figure 4. The PtꢀN4_anilidobond

length for complex 4 is 1.984(5) Å, which is 0.081 Å shorter than

the PtꢀN4_aminebond length of the dicationic aniline complex 3. The

PtꢀN4_anilidobond length for 4 is also shorter than the 2.005(2) Å for

the PtꢀN_anilidobond of complex 2. Indeed, the N3ꢀC19 bond

length of complex 4 is 1.371(1) Å, which is shorter than 1.474(9) Å

for the NꢀC bond distance of the dicationic aniline complex 3.

Oxidation to Pt(IV). Examples of monomeric Pt(IV) amido

complexes are limited. Most reported Pt(IV) amido complexes have

the amido incorporated into a chelating/bridging ligand or contain

electron-deficient sulfonamide ligands.^33ꢀ37Recently, our group

The reaction of complex 4 with 1 equiv of HCl at room tem-

perature yields (^tbpy)Pt(NHPh)(Cl) (5) and free aniline (eq 5).

The ¹H NMR spectrum of 5 reveals resonances due to

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Table 1. Selected Crystallographic Data and Collection Parameters for (^tbpy)Pt(Me)(NHPh) (2), [(^tbpy)Pt(NH₂Ph)₂][OTf]₂

(3), (^tbpy)Pt(NHPh)₂(4), and (^tbpy)Pt(OPh)₂(7)

(^tbpy)Pt(Me)(NHPh) (2)

[(^tbpy)Pt(NH₂Ph)₂][OTf]₂(3)

(^tbpy)Pt(NHPh)₂(4)

(^tbpy)Pt(OPh)₂(7)

formula

mol wt

cryst syst

space group

a, Å

C₂₅H₃₂N₃Pt

569.63

C₃₆H₄₆F₇N₄O₆PtS₂

1022.98

C₃₀H₃₆N₄Pt

647.72

C₃₄H₄N₂O₃Pt

721.79

triclinic

P1

triclinic

P1

triclinic

P1

9.3230(4)

11.6735(5)

11.7514(5)

87.448(2)

73.626(2)

67.519(2)

1130.92(8)

2

12.6369(8)

13.5447(4)

14.7681(4)

114.171(1)

100.285(1)

96.691(1)

2217.88(17)

2

8.607(1)

12.698(2)

13.618(2)

72.474(3)

72.801(3)

87.372(3)

1354.2(4)

2

9.0551(3)

11.7591(4)

14.6718(5)

96.155(1)

102.157(1)

90.426(1)

1517.69(9)

2

b, Å

c, Å

R, deg

β, deg

γ, deg

V, Å³

Z

D_calcd, Mg m^ꢀ3

total reﬂns

unique

R

1.673

1.532

1.588

1.579

40 326

24 550

18 198

10 064

9335

12811

9512

4421

0.0316

0.0548

0.0529

0.0251

R_w

0.0605

0.1577

0.0860

0.0684

Figure 5. ORTEP diagram (50% probability) of (^tbpy)Pt(OPh)₂(7).

Selected bond lengths (Å): PtꢀN2 1.988(4), PtꢀN1 1.994(4), PtꢀO2

2.001(4), PtꢀO1 2.014(4). Selected bond angles (deg): N2ꢀPtꢀN1

80.75(2), N1ꢀPtꢀO2 91.30(2), N2ꢀPtꢀO1 94.51(2), O2ꢀPtꢀO1

93.45(2), PtꢀO1ꢀC19 124.3(3), PtꢀO2ꢀC25 127.3(3).

Figure 6. ORTEP diagram (50% probability) of (^tbpy)Pt(Me)₂(I)₂

(8). Selected bond lengths (Å): PtꢀN1 2.168(4), PtꢀC1 2.183(5),

PtꢀI1 2.640(1), PtꢀI2 2.652(1). Selected bond angles (deg):

N1ꢀPtꢀN1⁰75.5(2), N1ꢀPtꢀC1 101.1(2), C1ꢀPtꢀC1⁰82.2(3),

N1ꢀPtꢀI1 91.0(1), C1ꢀPtꢀI1 88.1(2), N1ꢀPtꢀI2 89.9(1),

C1ꢀPtꢀI2 91.0(2), I1ꢀPtꢀI2 178.8(2).

Table 2. Summary of Ptꢀmethyl Coupling Constants and

Anilido Chemical Shifts

¹J_PtꢀC

²J_PtꢀH

δ_NH

reported the preparation and characterization of the Pt(IV) amido

complex (NCN)Pt(Me)₂NHPh {NCN = 2,6-(pyrazolyl-CH₂)₂-

C₆H₃}.³⁸We desired to prepare Pt(IV) complexes with amido and

aryloxo ligands. We first tested oxidation of (^tbpy)Pt hydrocarbyl

(Hz)

(ppm)

[(^tbpy)Pt(Me)(NH₂Ph)][TFA] (1)

(^tbpy)Pt(Me)(NHPh) (2)

[(^tbpy)Pt(NH₂Ph)₂][OTf]₂(3)

(^tbpy)Pt(NHPh)₂(4)

(^tbpy)Pt(NHPh)(Cl) (5)

(^tbpy)Pt(Me)(OPh)-HOPh (6)

(^tbpy)Pt(Me)₂(I)₂(8)

(^tbpy)Pt(Me)₂(NHPh)(I)(10)

(^tbpy)Pt(Me)(CCPh) (11)

[(^tbpy)Pt(NHPh)(py)][BAr⁰₄] (12)

[(^tbpy)Pt(μ-NHPh)]₂[BAr⁰₄]₂(14)

774^c

813^b

70^a

84^a

7.72^a

3.99^a

7.65^c

3.80^a

4.06^a

complexes with I₂.³⁹

The reaction of (^tbpy)Pt(Me)₂³¹in benzene with iodine cleanly

produces the Pt(IV) complex (^tbpy)Pt(Me)₂(I)₂(8) (eq 8). Com-

plex 8 exhibits a downﬁeld shift from 2.12 to 3.21 ppm in the ¹H

NMR spectrum for the methyl resonance compared to its Pt(II)

analogue as well as a decrease in the ²J_PtꢀH(86 Hz compared to 73

Hz). The PtꢀH coupling constant of 73 Hz for 8 is similar to the

70.4 Hz coupling constant reported by Templeton et al. for

Tp⁰PtPh₂Me (Tp⁰= hydridotris(3,5-dimethylyprazolyl)borate).⁴⁰

The ¹³C NMR spectrum of 8 reveals a ¹J_PtꢀCof 506 Hz, similar to

¹J_PtꢀCof 515 Hz for the closely related Pt(IV)ꢀmethyl complex

826^b

506^c

630, 642^a

87^b

73^a

70^a

81^a

2.90^d

2.75^c

^aC₆D₆. ^bAcetone-d₆. ^cCDC1₃. ^dCD₂Cl₂.

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Table 3. Selected Crystallographic Data and Collection Para-

meters for (^tbpy)Pt(Me)₂(I)₂(8) and (^tbpy)Pt(Ph)₂(I)₂(9)

(¹bpy)Pt(Me)₂(I)₂(8)

(¹bpy)Pt(Ph)₂(l)₂(9)

formula

mol wt

cryst syst

space group

a, Å

C₂₀H₃₀N₂PtI₂

747.35

orthorhombic

Pnma

C₃₉H₄₃I₂N₂Pt

988.64

tetragonal

P42₁c

17.074(1)

14.267(1)

20.097(2)

90

22.3179(3)

15.1244(2)

90

b, Å

c, Å

R, deg

β, deg

90

γ, deg

V, Å³

90

Figure 7. ORTEP diagram (50% probability) of (^tbpy)Pt(Ph)₂(I)₂(9).

Selected bond lengths (Å): PtꢀC25 2.045(6), PtꢀC19 2.054(7),

PtꢀN1 2.162(5), PtꢀN2 2.173(5), PtꢀI1 2.6481(5), PtꢀI2

2.6598(5). Selected bond angles (deg): C25ꢀPtꢀC19 87.3(2),

C25ꢀPtꢀN1 97.8(2), C19ꢀPtꢀN2 99.3(2), N1ꢀPtꢀN2 75.6(2),

C25ꢀPtꢀI1 90.79(2), C19ꢀPtꢀI1 92.68(2), N1ꢀPtꢀI1 85.72(1),

N2ꢀPtꢀI1 90.20(1), C25ꢀPtꢀI2 93.49(2), C19ꢀPtꢀI2 91.14(2),

N1ꢀPtꢀI2 90.12(1), N2ꢀPtꢀI2 85.13(1).

4895.5(7)

8

7533.3(2)

8

Z

D_calcd, Mg m^ꢀ3

total reﬂns

unique reﬂns

R

2.028

1.743

31 526

5791

56 514

6514

0.0487

0.1332

0.0232

0.0783

R_w

(^tbpy)Pt(Me)₂(Br)₂.⁴¹The solid-state structure of complex 8

has been determined by a single-crystal X-ray diﬀraction study

(Figure 6). The structure reveals trans iodide ligands with PtꢀI

bond distances of 2.640(1) and 2.652(1) Å. The unit cell contains

two independent half-molecules, which each lie on a mirror plane

passing through the corresponding Pt and pair of I atoms. The

bond lengths and angles do not vary substantially between the

two molecules. Only one molecule has been shown in Figure 6.

conversion or decomposition to multiple products after ∼20 h at

room temperature. In contrast to the reaction of 2 with I₂,

the reaction of complex 2 with a slight excess of iodomethane

in benzene results in clean conversion to (^tbpy)Pt(Me)₂

1

(NHPh)(I) (10) (eq 10). The H NMR spectrum of 10 reveals

two methyl resonances that are shifted signiﬁcantly downﬁeld (2.24

and 4.77 ppm) compared to complex 2 (1.85 ppm) as well as a

downﬁeld shift for the amido NH resonance from 3.99 ppm for 2 to

4.77 ppm for 10. In comparison, the amido NH signal for

(NCN)Pt(Me)₂(NHPh), also a 6-coordinate d⁶anilido complex,

is observed at 2.88 ppm.³⁸In addition, the conversion of 2 to 10

results in a decrease of ²J_PtꢀHfor the PtꢀCH₃group from 84 to 70

Hz for both methyl resonances. The ¹³C NMR spectrum of 10 also

reveals a downﬁeld shift for the methyl resonances (ꢀ14.2 ppm for

complex 2 versus 13.8 and ꢀ0.4 ppm for 10) and a decrease in

coupling constant with ¹J_PtꢀC=813Hzforcomplex2versus ¹J_PtꢀC

=

630 and 642 Hz for complex 10. The ¹H and ¹³C NMR spectra are

consistent with a trans orientation of either the methyl/iodide or the

methyl/anilido ligands, as depicted in eq 10.

A preparation similar to that for complex 8 was used for

the synthesis of (^tbpy)Pt(Ph)₂(I)₂(9) from the reaction of

(^tbpy)Pt(Ph)₂with iodine (eq 9). The solid-state structure of

complex 9 was determined by a single-crystal X-ray diﬀraction study

(Figure 7). The structure reveals trans iodide ligands and phenyl

ligands that are rotated 47ꢀ (N2ꢀPtꢀC19ꢀC20 dihedral angle)

out of the square plane containing the ^tbpy ligand. It is unclear

whether trans iodide complexes 8 and 9 are thermodynamic

products or kinetic products that undergo fast isomerization.

Reactivity with H₂and Substrates that Possess CꢀH

Bonds. Selective functionalization of CꢀH bonds is an impor-

tant class of transformations because of the broad applicability to

organic synthesis.⁴²In general, the functionalization of CꢀH

bonds requires two steps, CꢀH activation and CꢀX bond

formation. Early transition metalꢀimido systems initiate CꢀH

activation of hydrocarbons by 1,2-addition across metalꢀimido

bonds to produce amido hydrocarbyl products.^43ꢀ47For these

reactions, detailed studies have established the importance of

CꢀH coordination to the metal center and polarized MdNR

bonds to facilitate the 1,2-addition reaction.^43,45ꢀ47Although

CꢀH activation has been demonstrated, CꢀN bond formation

With the successful conversion of Pt(II)ꢀhydrocarbyl complexes

to Pt(IV) bis-iodide systems, the oxidation of complex 2 with I₂was

attempted. In separate experiments, reactions of complex 2 with

either 1 equiv or excess I₂in various solvents (e.g., chloroform,

acetone, acetonitrile, and nitromethane) resulted in incomplete

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via reductive coupling with these early metal complexes has not

been observed, to our knowledge. Extension of the 1,2-addition

reaction to late transition metal systems bearing formally anionic

heteroatomic ligands might allow incorporation into a catalytic

cycle for controlled CꢀH activation and functionalization.

However, few late transition metal systems have demonstrated

1,2-CH-addition, and a more detailed understanding of the

factors that control the reaction are needed.^{12ꢀ14,16,22,48ꢀ50}

Figure 8. Plot of [2] versus time for the reaction of 2 with 0.112 M

phenylacetylene at 80 ꢀC (R²= 0.99).

The basic and nucleophilic character of amido or alkoxide ligands

coordinated to late transition metal systems in low oxidation states

has been demonstrated. Previously, our group reported that TpRu-

(L)₂(X) {X = OH, NH₂, NH^tBu, NHPh; L = PMe₃, P(OMe)₃}

complexes possess nucleophilic anilido and hydroxo ligands. For

example, TpRu(L)₂(NHPh) reacts with malononitrile (pK_a≈ 24 in

THF)⁵¹at room temperature to form the ion pair [TpRu(L)₂-

NH₂Ph][HC(CN)₂]. TpRu(L)₂(NHPh) does not react with phe-

nylacetylene (pK_a≈ 28 in DMSO)⁵²at room temperature, but upon

heating at 80 ꢀC free aniline and the phenylacetylide complexes

TpRu(L)₂(CtCPh) are formed (see below).⁵³The combination of

Figure 9. Plot of k_obsversus concentration of phenylacetylene for

conversion of (^tbpy)Pt(Me)(NHPh) (2) and phenylacetylene to aniline

and (^tbpy)Pt(Me)(CtCPh) (11).

t

TpRu(L)₂(NHR) (R = H or Bu) with phenylacetylene at room

temperature results in the formation of a Ruꢀamine/acetylide ion

pair, [TpRu(L)₂(NH₂R)][CtCPh].⁵³Thus, substitution of the

t

amido phenyl substituent with H or Bu results in a more basic

analysis. The resonance at 3.99 ppm for the amido NH of 2 is

replaced by a broad resonance at 2.78 ppm characteristic of the free

aniline NH₂resonance along with downﬁeld resonances consistent

with the phenyl group of free aniline. In addition, the resonance for

the phenylacetylene HꢀCtCPh is absent in the ¹H NMR

spectrum, and resonances at 103.0 and 100.6 ppm in the ¹³C

NMR spectrum are consistent with a phenylacetylide ligand. The

reaction proceeds without observation of an amineꢀacetylide ion

pair. As discussed above, trans-[(DMPE)₂Ru(H)(NH₂)] and

amido ligand. Bergman and co-workers reported that the pa-

rent amidoruthenium complex trans-[(DMPE)₂Ru(H)(NH₂)]

{DMPE = 1,2-bis(dimethylphosphinoethane)} reacts at room tem-

perature with phenylacetylene to release ammonia and form the

phenylacetylide complex.¹⁹At low temperature, the initial amido/

acetylide ion pair is observed before conversion to the phenylacety-

lide complex. The parent amido complex is also suﬃciently basic to

deprotonate triphenylmethane (pK_a= 30.6 in DMSO) to form an

equilibrium between the parent amido complex/triphenylmethane

and the Ruꢀamine/triphenylmethide ion pair.¹⁹Related Ru(II) and

Fe(II) parent amido complexes demonstrate similar acid/base

reactivity.^21,54Perhaps more germane here, two-coordinate Cu(I)

complexes with amido, alkoxide, and sulﬁde ligands exhibit nucleo-

philic character at the heteroatomic ligand.^55ꢀ57

In order to delineate metal-based eﬀects, including d-electron

count and coordination geometry, similar studies were extended to

the Pt(II) systems discussed above. The Pt(II) systems are d⁸and

square planar versus d⁶Ru(II) octahedral systems. The square planar

geometry provides access to an empty p orbital perpendicular to the

square plane, which could facilitate substrate coordination. Also,

Pt(II) possesses increased electronegativity versus Ru(II) (χ = 1.513

for Pt(II) and 1.434 for Ru(II) on the Pauling scale).⁵⁸

To directly compare the reactivity of the Pt(II) anilido

systems with the systems discussed above, complex 2 was

reacted with phenylacetylene. Heating a C₆D₆solution of

(^tbpy)Pt(Me)(NHPh) (2) with phenylacetylene at 80 ꢀC results

in a reaction that is complete after ∼8 h (eq 11). The ¹H NMR

spectrum of the reaction mixture reveals the formation of

free aniline and the corresponding phenylacetylide complex,

(^tbpy)Pt(Me)(CtCPh) (11), which has been isolated and char-

acterized by ¹H and ¹³C NMR spectroscopy as well as elemental

t

TpRu(L)₂(NHR) (R = H or Bu) react with phenylacetylene at

room temperature^19,53but TpRu(L)₂(NHPh) only reacts with

phenylacetylene at 80 ꢀC (see above).

Initial kinetic studies gave inconsistent rates for the reaction of

complex 2 with phenylacetylene. For example, using two diﬀer-

ent batches of complex 2 resulted in rates diﬀering by ∼20%,

indicating the possibility that an impurity was catalyzing the

reaction. Monitoring the reaction of 2 with excess phenylacety-

lene at 80 ꢀC (¹H NMR) and plotting [2] versus time reveals a

linear dependence, which is indicative of a zero-order depen-

dence on complex 2 (Figure 8). Pseudo-ﬁrst-order reactions of

complex 2 and excess phenylacetylene concentrations (based on

2) were run at 80 ꢀC. A plot of k_obsversus phenylacetylene

concentration reveals that at 0.445 M phenylacetylene the

reaction rate begins to saturate (Figure 9).

With a zero-order dependence on complex 2 for the rate of

conversion of 2 and phenylacetylene to 11, the possibility that

the reaction is catalyzed by a precursor to complex 2 was

considered. A series of reactions of complex 2, phenylacetylene,

and varied concentrations of [(^tbpy)Pt(Me)(NH₂Ph)][TFA]

(1), the precursor to complex 2, were performed to investigate

this possibility. A plot of k_obsversus equivalents of [(^tbpy)-

Pt(Me)(NH₂Ph)][TFA] (1) reveals a linear increase in the rate

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reform the putative catalyst [(^tbpy)Pt(Me)(NH₂Ph)][TFA]

(1). Alternatively, [(^tbpy)Pt(Me)(η²-PhCtCH)][TFA] could

rearrange to a vinylidene complex, [(^tbpy)Pt(Me)(dCdCPhH)]-

[TFA],⁵⁹prior to deprotonation. No intermediates are observed

by ¹H NMR spectroscopy for the conversion of complex 2 and

phenylacetylene to complex 11. Similar results were reported by

our group for the conversion of TpRu(L)₂(NHPh) {L = PMe₃or

P(OMe)₃} and phenylacetylene to TpRu(L)₂(CtCPh) and

aniline.⁵³Kinetic results were consistent with the TpRu(PMe₃)₂-

(OTf) complex, a precursor to TpRu(PMe₃)₂(NHPh), catalyz-

ing the conversion of the anilido complex to TpRu(PMe₃)₂-

(CtCPh). A similar mechanism to that in Scheme 1 was

proposed to proceed through a Ruꢀvinylidene intermediate.

In this case, the Ruꢀvinylidene complex was identiﬁed in the

reaction mixture.⁵³In addition, for the reaction of TpRu-

(PMe₃)₂NHPh and phenylacetylene, the formation of the

Fischer carbene Tp(PMe₃)₂RudC(CH₂Ph)(NHPh), presum-

ably from reaction of aniline and the Ruꢀvinylidene complex, is

observed. An analogous carbene complex {i.e., [(^tbpy)(Me)Ptd

C(CH₂Ph)(NHPh)]^þ} is not observed in the Pt-based

reaction.

Our group and others have reported the activation of RꢀH

(R = aryl or H) bonds with late transition metal hydroxide and

amido complexes via net 1,2-addition of RꢀH across the

metalꢀheteroatom bond.^{12ꢀ16,22,24,49,50,60}From a coordinated

hydrocarbon species, it has been suggested that the presence of

the basic lone pair on the heteroatomic ligand might provide an

inherent kinetic advantage to CꢀH activation compared to a

metalꢀalkyl complex; however, there are no reports of CꢀH

activation with a metal center bearing both an alkyl and a

heteroatomic ligand to provide a direct comparison.^12,22,50The

synthesis of complex 2 provides a system with both an alkyl and a

heteroatomic ligand and could provide an internal competition

for CꢀH activation and allow a direct comparison of CꢀH

activation rates (i.e., CꢀH activation across the PtꢀNHPh bond

versus the PtꢀCH₃bond). However, previously reported Pt(II)

systems that perform CꢀH activation typically require the

generation of a three-coordinate reactive species.^61ꢀ63Thus,

we considered that the coordination of a CꢀH bond by complex

2 and CꢀH activation was not likely and chose to study H₂

activation as a model. We anticipated that the reaction of

complex 2 with H₂could result in coordination of dihydrogen

to form a ﬁve-coordinate intermediate, HꢀH activation across

the methyl or anilido ligands, methane or amine dissociation, and

formation of the corresponding Ptꢀhydride complexes

(Scheme 2).

Figure 10. Plot of k_obsversus equivalents of complex 1 for conver-

sion of complex 2 and phenylacetylene to aniline and complex 11

(R²= 0.98).

Scheme 1. Possible Reaction Pathway for Conversion

of (^tbpy)Pt(Me)(NHPh) (2) and Phenylacetylene to

(^tbpy)Pt(Me)(CCPh) (11) and Aniline Catalyzed by

Impurity Complex 1

The reaction of complex 2 with H₂(room temperature)

produces free ^tbpy ligand, CH₄, and aniline after approximately

12 h. At 45 psi of H₂, the formation of an intermediate complex,

(^tbpy)Pt(Me)(H), is observed by ¹H NMR spectroscopy after 7 h

(Scheme 3). For (^tbpy)Pt(Me)(H), a hydride resonance is

observed at ꢀ14.8 ppm in the ¹H NMR spectrum (singlet with

Pt satellites, ¹J_PtꢀH= 1575 Hz) as well as a new methyl resonance

at 2.21 ppm (singlet with Pt satellites, ²J_PtꢀH= 83 Hz). Our group

and others have previously reported the 1,2-addition of H₂across

metalꢀheteroatom bonds.^64ꢀ69For example, the ﬁve-coordinate

(PCP)Ru(CO)(NH₂) [PCP = 2,6-(CH₂P^tBu₂)₂C₆H₃] complex

reacts with H₂at room temperature to give (PCP)Ru(CO)(H) and

ammonia.⁶⁸Mechanistic studies suggest a pathway that involves

coordination of H₂, 1,2-addition across the Ruꢀamido bond to yield

(PCP)Ru(CO)(H)(NH₃), and ammonia dissociation. Fryzuk et al.

reported a similar 1,2-H,H addition reaction with a Ru(II) complex

of formation of (^tbpy)Pt(Me)(CtCPh) (11) (Figure 10). The

reaction rate is ﬁrst order in 1. In principle, extrapolation of

the linear regression for this plot to the y intercept should provide

the intrinsic rate of the reaction of complex 2 and phenylacety-

lene in the absence of complex 1. However, the deviation in the y

intercept is too large to draw a reasonable conclusion about the

intrinsic rate.

These results are consistent with trace amounts of the

Ptꢀamine complex 1 catalyzing the conversion of the anilido

complex 2 and phenylacetylene to the phenylacetylide complex

11 and aniline. Scheme 1 shows a possible reaction pathway that is

catalytic in 1. Starting with 1, aniline/phenylacetylene ligand

exchange would produce [(^tbpy)Pt(Me)(η²-PhCtCH)][TFA].

Deprotonation of [(^tbpy)Pt(Me)(η²-PhCtCH)][TFA] by

(^tbpy)Pt(Me)(NHPh) (2) would produce complex 11 and

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Scheme 2. Possible Reaction Pathways for Reaction of Complex 2 with Dihydrogen

bearing a chelating amido ligand.⁶⁶Morris et al. demonstrated that

Scheme 3. Proposed Reaction Sequence for Reaction of

Complex 2 with Dihydrogen

the reaction of H₂with a Ru(II) amido complex produces a

dihydrogen complex in which the HꢀH bond is intermediate

between dihydrogen and protic-hydridic bonding.⁷⁰Goldberg,

Kemp, et al. reported the activation of dihydrogen across Pd-

(II)ꢀOR (R = H or CH₃) complexes via a σ-bond metathesis-type

transition state to produce ROH and a Pd(II)ꢀH complex.⁶⁷Thus,

reaction of H₂with 2 via a similar mechanism would involve

coordination of H₂to give (^tbpy)Pt(Me)(NHPh)(η²-H₂), followed

by 1,2-H,H addition to give (^tbpy)Pt(Me)(NH₂Ph)(H),and aniline

dissociation to form free NH₂Ph and (^tbpy)Pt(Me)(H). Free

^tbpy, methane, and Pt(s) would then be formed by subsequent

decomposition. However, after monitoring multiple reactions

(¹H NMR spectroscopy) of the same concentration of 2 with H₂

at room temperature over a period of 8 h, plots of [2] versus time

reveal inconsistent induction periods (Figure 11, plot A) as well

as varied rates (Table 4). The observation of an induction period

led us to consider that Pt(s) is serving as a heterogeneous

catalyst.⁷¹

As an initial probe, a standard Hg test was used to suppress

reactivity from in situ Pt(s) formation.⁷¹Elemental mercury was

added to a solution of 2 in C₆D₆followed by pressurization with

H₂. The reaction was monitored (¹H NMR spectroscopy) over

7 h. The addition of elemental mercury results in complete

suppression of reactivity (Figure 11, plot B). Next, a solution of 2

pressurized with H₂was allowed to react until conversion of 2

and visible Pt(s) formation was observed. The reaction solution

was then decanted to leave the solid, and a fresh solution of 2 in

C₆D₆was added to the original NMR tube, pressurized with H₂.

For this fresh solution with “generated” Pt(s), a plot of [2] versus

time revealed a line for the conversion of 2 and H₂without an

induction period, indicative of a reaction with a zero-order

dependence on complex 2 (Figure 11, plot C). Maitlis’ test⁷²

was performed by monitoring the reaction through the induction

period and the beginning of the reaction. The reaction tube was

then vented, the solution ﬁltered through Celite, and the ﬁltrate

placed in a clean NMR tube, pressurized with H₂, and monitored

(¹H NMR spectroscopy) for ∼2 h. Figure 11 (plot D) shows that

after removal of the Pt(s), there is a second induction period.

As additional conﬁrmation, 10 wt % Pt on activated carbon was

added to a solution of 2 before pressurization with H₂. Following

the addition of H₂, the reaction reached 50% conversion after

5 min and reached completion in less than 1 h.

by an intramolecular proton transfer through a four-centered

transition state. The proposed pathway of H₂addition across the

PtꢀNHPh bond of complex 2 is diﬀerent than the proposed

mechanism for the Pd(II) hydroxide and methoxide complexes

reported by Goldberg, Kemp et al.⁶⁷To probe the source of these

diﬀerences, we employed DFT calculations (B3LYP, double-ζ-

plus-polarization pseudopotential basis sets) using 2,2⁰-bipyri-

dine (bpy) as a model for the ^tbpy ligand. The overall reaction

of (bpy)Pt(Me)(NHPh) (2⁰) and H₂to give (bpy)Pt(Me)(H)

and free aniline is calculated to be exothermic by 6 kcal/mol.

However, this reaction is calculated to occur with an enthalpy

of activation of 45 kcal/mol (Scheme 4). In contrast, the

previously calculated enthalpy of activation barrier for H₂addi-

tion across the PdꢀOH bond of (PCP⁰)Pd(OH) {PCP⁰= 2,6-

bis-(CH₂PMe₂)₂C₆H₃} to give (PCP⁰)Pd(H) and water is 21.0

kcal/mol, despite the similar overall reaction enthalpy (ꢀ4 kcal/

mol).⁶⁷The calculated reaction enthalpy and H₂activation

barrier for the corresponding Pdꢀmethoxide complex (PCP⁰)Pd

(OMe) are similar to those of the hydroxyl analogue (ꢀ3 and

24 kcal/mol, respectively).⁶⁷

Although the calculations reveal a substantial diﬀerence in

the activation barrier for HꢀH bond cleavage by the (PCP⁰)Pd

(OH)/(OMe) and (^tbpy)Pt(Me)(NHPh) systems, the source of

the diﬀerence is not obvious. In order to probe these diﬀerences,

we performed calculations by varying the ligand X, metal, and

ancillary ligand (PCP versus bpy). Systematic changes reveal an

impact on the enthalpy of activation by ∼5ꢀ10 kcal/mol for

each alteration. Scheme 5 provides an overview of the calcula-

tions for each variation, and Figure 12 provides key bond

distances for all of the calculated transition states. No correlations

that would lead us to conﬁdently invoke trends based on early versus

late transition states could be found among the calculated transition

state metrics and the activation barriers (or calculated enthalpies).

For hydrogenolysis of (PCP)Pd(OH), Goldberg, Kemp et al.

reported a mechanism that involves coordination of H₂followed

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Figure 11. Plots monitoring [2] versus time for conversion of 2 and H₂to free ^tbpy, aniline, methane, and Pt(s): (A) 200 psi of H₂at room temperature,

(B) elemental Hg added at the beginning of reaction, (C) fresh solution of 2 added to a tube with “generated” Pt(s), and (D) reaction solution ﬁltered to

remove Pt(s) after initial induction period (plot started after 14 400 s reaction time).

Table 4. Summary of Experimental Trials for Reaction of

Complex 2 and H₂

Scheme 4. Calculated Reaction Enthalpy (DFT, B3LYP) and

Enthalpy of Activation for Reaction of Complex 2⁰with H₂

experiment

induction period (s)

rate^a(s^ꢀ1

)

1

2

3

4

4800

6000

9600

4200

2.0 ꢁ 10^ꢀ6

2.6 ꢁ 10^ꢀ6

3.0 ꢁ 10^ꢀ6

2.2 ꢁ 10^ꢀ6

^aRate after the induction period.

One major diﬀerence between (PCP⁰)Pd(OH) and (bpy)Pt

(Me)(NHPh) may be the aﬃnity for H₂coordination and,

hence, activation of H₂. Consistent with this suggestion, our

calculations reveal that H₂does not form a stable bond with

complex 2. Attempts to isolate a bound H₂adduct of complex 2

were not successful. Geometry optimizations converged to

stationary points in which H₂and complex 2 are well separated.

This is potentially explained by the anticipated decrease in

electrophilicity of Pt relative to Pd. When the metal center

of (bpy)Pt(Me)(NHPh) is substituted with Pd to give

(bpy)Pd(Me)(NHPh), although the overall ΔH becomes less

favorable by 2.6 kcal/mol, there is a decrease in the enthalpy of

activation of 7.4 kcal/mol. Variation of the ligand X and ancillary

ligand also impacts the activation barrier signiﬁcantly. For

example, replacing the anilido ligand in (bpy)Pt(Me)(NHPh)

with NHMe or OMe decreases the activation barrier from 45.5 to

37.4 or 40.1 kcal/mol. The calculated activation barrier from

(bpy)Pd(Me)(OMe) is 33.2 kcal/mol, and substitution of bpy

and the methyl ligand with PCP⁰to give (PCP⁰)Pd(OMe) lowers

the barrier by 9.2 to 24.0 kcal/mol.

In addition to metal electrophilicity, steric and electronic

contributions from the heteroatomic ligand play a crucial role

in the elevated barriers. Figure 13 displays the calculated transi-

tion state for HꢀH activation by complex 2. In order for

the amido lone pair to orient to receive H^þfrom a coordinated

H₂, which is positioned approximately above the Pt square plane

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Scheme 5. Overview of Calculations (enthalpies in kcal/mol for the activation barrier and overall transformation) with

Systematic Variation of the Ligand X, Metal, and Ancillary Ligand (bpy versus PCP) for Reaction of the MetalꢀHeteroatom

a

Complexes with H₂

^aPh* = phenyl group modeled by the universal force ﬁeld, enthalpies at 1 atm, 298.15 K.

Figure 12. Overview of calculated transition state active sites (bond lengths in Angstroms) with systematic variation of metal (Pt vs Pd), activating

ligand (NMe vs OMe vs NPh vs NPh*), and ancillary ligand (bpy vs PCP) for reaction of the metalꢀheteroatom complexes in Scheme 5 with H₂.

in the apical position, the amido lone pair must be aligned

approximately perpendicular to the Pt square plane. This or-

ientation places the phenyl group in close proximity to either the

Me ligand or the ^tbpy ligand, which provides a steric inhibition to

H₂activation. In addition, the solid-state structure suggests that

the amido lone pair is aligned for donation into the phenyl π*

system (Figure 2). However, for the lone pair to align perpendi-

cular to the Pt square plane, the phenyl substituent must rotate

perpendicular to the amide plane, breaking C_ipsoꢀN conjuga-

tion. The calculated transition state reveals longer bond lengths

of 1.46 Å for the C_ipsoꢀN bond versus 1.39 Å (calculated, 1.36 Å

experimental) in complex 2. Thus, stabilization of the anilido

lone pair into the phenyl π* system is negated, resulting in an

electronic inhibition to H₂activation. These results may indicate

the critical role that the lone pair on the ꢀNHR and ꢀOR

ligands plays in the activation of HꢀH and CꢀH bonds.^12,22,50,60

For some of the calculated transition states, the bond distance

between Pt and the incipient PtꢀH is longer (>2.4 Å) than is

expected for a 1,2-addition; however, for these complexes there is

no evidence of an H₂adduct that would precede the addition

reaction. We believe that the unexpectedly long PtꢀH bond

distances are a result of this facet of the reaction, which perhaps

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example, although direct CꢀH activation with TpRu(PMe₃)₂-

(X) (X = OH, NHPh) was not accessible, H/D exchange was

observed into the hydroxide and anilido-NH ligands.^12,13

It is possible that CꢀD activation of C₆D₆was not observed

for complex 12 because pyridine is bound too tightly to the metal

center. Abstraction of the chloride ligand from complex 5 with

AgBAr⁰₄in the presence of more weakly coordinating solvents (e.

g., THF or pentaﬂuoropyridine) or a noncoordinating solvent

results in the formation of the dimer [(^tbpy)Pt(μ-NHPh)]₂-

t

[BAr⁰₄]₂(14) (eq 14). Complex 14 exhibits three aryl bpy

t

resonances and one Bu bpy resonance integrating for 36

protons. Heating complex 14 in benzene (C₆D₆, 120 ꢀC) results

in no change in the ¹H NMR spectrum.

Figure 13. Calculated transition state for activation of H₂by complex 2.

Most H atoms omitted for clarity.

closely resembles deprotonation of “free” dihydrogen and, hence,

the substantial activation barriers.

Three-coordinate Pt(II) systems are known to activate CꢀH

bonds.^61ꢀ63Recently, our group reported the catalytic activation

of aromatic CꢀH bonds with [(^tbpy)Pt(Ph)(L)][BAr⁰₄] [L =

labile ligand; Ar⁰= 3,5-(CF₃)₂C₆H₃].⁷³To test the viability of

performing CꢀH activation with analogous heteroatomic sys-

tems, complexes of the type [(^tbpy)Pt(X)(L)]^þ(X = NHPh,

OPh; L = pyridine, THF, NC₅F₅) were targeted.

’ SUMMARY AND CONCLUSIONS

When complex 4 is reacted with 1 equiv of HBAr⁰₄in the

presence of pyridine, the production of free aniline and [(^tbpy)-

Pt(NHPh)(py)][BAr⁰₄] (py = pyridine) (12) is observed

(eq 12). Conversion from the neutral complex 4 to cationic 12

results in an upﬁeld shift of the NH resonance from 3.8 (C₆D₆) to

2.90 ppm (CD₂Cl₂) in the ¹H NMR spectrum. The correspond-

ing cationic phenoxide complex [(^tbpy)Pt(OPh)(py)][BAr⁰₄]

(13) was prepared in a similar fashion (eq 13).

Herein, we report the preparation of neutral and cationic

Pt(II) anilido and phenoxide systems and studied their reactions

with H₂and substrates that possess CꢀH bonds. Salient points

include:

(1) The 1,2-addition of CꢀH and HꢀH bonds across Pt-

(II)ꢀX bonds is not accessible from four-coordinate

(^tbpy)Pt(X)(Y) or [(^tbpy)Pt(X)(L)]^þsystems. For the

activation of H₂by (^tbpy)Pt(Me)(NHPh), which we

studied computationally and experimentally, several as-

pects appear to preclude access to the 1,2-addition

reaction via initial H₂coordination to give ﬁve-coordinate

(^tbpy)Pt(Me)(NHPh)(H₂) followed by HꢀH addition

across the PtꢀNHPh bond to give (^tbpy)Pt(Me)

(NH₂Ph)(H). Our studies suggest the factors that con-

tribute to the substantial activation barrier (calculated

ΔH^‡= 45 kcal/mol) include ancillary ligand identity,

decreased Pt electrophilicity (compared, for example, to a

related Pd system), and steric constraints. For example, in

order for the amido lone pair to orient perpendicular to

the square plane to receive H^þfrom coordinated H₂, the

phenyl group is placed in close proximity to either the

methyl or ^tbpy ligand, providing a steric inhibition to H₂

activation. In addition, the DFT calculations suggest that

simple coordination of H₂to (^tbpy)Pt(Me)(NHPh) is

not favorable, and the strongly donating anilido and

methyl ligands likely play a role here.

Complexes 12 and 13 were heated in C₆D₆(100 ꢀC) and

monitored for the production of aniline and phenol, respectively.

After heating for 72 h, aniline or phenol production was not

observed. Careful monitoring of the NH resonance (2.90 ppm)

of 12 also revealed no H/D exchange. To test the thermody-

namic accessibility of the CꢀH activation reaction, the reverse

reaction was attempted. Heating (24 h, 100 ꢀC)

[(^tbpy)Pt(Ph)(NC₅F₅)][BAr⁰₄] and 1 equiv of pyridine with

either aniline or phenol in dichloromethane-d₂results in con-

version to 12 or 13, respectively (Scheme 6). These results

indicate that the benzene CꢀH activation reactions are not

thermodynamically favorable, but kinetic access to H/D ex-

change into the NH of complex 12 was still a possibility. For

(2) Four-coordinate (^tbpy)Pt(X)(Y) complexes can provide

net activation of acidic CꢀH bonds (e.g., phenylacetylene);

however, the reaction is catalyzed by an impurity and

likely does not proceed by a 1,2-CH-addition pathway.

Thus, even for “activated” CꢀH bonds, the 1,2-CH-

addition process via a ﬁve-coordinate intermediate does

not appear to be facile.

(3) Elemental platinum serves as a catalyst for the 1,2-

addition of H₂across a PtꢀNHPh bond. To our knowl-

edge, this is the ﬁrst report of a heterogeneous catalyst

activating covalent bonds toward addition across a

metalꢀheteroatom bond and provides a caveat to

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Scheme 6. Reaction of [(^tbpy)Pt(Ph)(NC₅F₅)][BAr⁰₄] with Aniline and Phenol to Form Complexes 12 and 13

mechanistic conclusions for related reactions in the

absence of kinetic data.^74,75

characterization details of NaBAr⁰₄,⁷⁸HBAr⁰₄,⁷⁹AgBAr⁰₄,⁸⁰(^tbpy)Pt-

(Me)₂,³¹(^tbpy)Pt(Me)(TFA),²⁵(^tbpy)Pt(OTf)₂,²⁵and (^tbpy)Pt(Ph)₂

81

have been previously reported. Phenylacetylene was passed through a

column of activated alumina prior to use.

(4) Similar to CꢀH activation by related Pt(II) systems with

hydrocarbyl or halide ligands,^{61ꢀ63,76,77}the 1,2-addition

of CꢀH bonds from 3-coordinate [(^tbpy)Pt(X)]^þcom-

plexes could be feasible. However, [(^tbpy)Pt(X)(py)]^þ

complexes did not activate CꢀH bonds, perhaps because

pyridine is too tightly bound. For the anilido complex,

attempts to replace pyridine with less strongly donating

ligands resulted in the formation of a μ-NHPh binuclear

complex. This system did not activate CꢀH bonds, which

is likely due to the inability to access the desired 3-co-

ordinate Pt(II) cations.

These results suggest that the key factor for observing 1,2-CH-

addition across MꢀX bonds of d⁸systems is access to coordina-

tively unsaturated systems (i.e., 3-coordinate). Given the ability

of “X” ligands (e.g., OR, NHR) to bridge electrophilic metals, this

will likely require a subtle steric balance that promotes coordi-

native unsaturation but does not inhibit hydrocarbon

coordination.

[(^tbpy)Pt(Me)(NH₂Ph)][(TFA)] (1). (^tbpy)Pt(Me)(TFA) (0.058

g, 0.099 mmol) (TFA = O₂CCF₃) was dissolved in toluene (5 mL) in a

pressure tube. After addition of aniline (0.027 mL, 0.30 mmol), the tube

was sealed and heated to 90 ꢀC for 24 h. After removal of volatiles in

vacuo, the resulting residue was reconstituted in THF and filtered

through Celite. The filtrate was reduced in vacuo to a residue. After

dissolution in methylene chloride (∼ 1 mL), the addition of hexanes

resulted in the formation of a yellow precipitate, which was collected and

dried in vacuo (0.056 g, 83% yield). ¹H NMR (C₆D₆, δ): 9.42 (d, 1H,

³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 8.45, 8.30 (each a d, each 1H, ⁴J_H3ꢀH5= 2

Hz, ^tbpy 3/3⁰), 8.26 (d, 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.88 (d, 2H,

³J_HH= 7 Hz, aniline-ortho), 7.72 (br s, 2H, PtꢀNH₂Ph), 7.04ꢀ6.98 (m,

t

3

3H, overlap of aniline-meta and bpy 5/5⁰), 6.80 (t, 1H, J_HH= 7 Hz,

aniline-para), 6.67 (dd, 1H, ³J_H_t_5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰),

1.19, 1.06 (each a s, each 9H, bpy ^tBu), 0.84 (s with Pt satellites, 3H,

²J_PtꢀH= 70 Hz, PtꢀCH₃). ¹³C{¹H} NMR (CD₂Cl₂, δ): 164.6, 164.2,

150.3, 149.2, 142.8, 129.7, 126.5, 125.9, 124.7, 124.1, 120.4, 119.7, 118.6,

115.3 (each a s, ^tbpy aromatic and anilido-phenyl carbons), 36.3 {s, ^tBu-

C(CH₃)₃, one signal missing presumably due to coincidental overlap},

’ EXPERIMENTAL SECTION

t

30.5, 30.4 {each a s, Bu-C(CH₃)₃}, ꢀ10.4 (singlet with Pt satellites,

¹J_PtꢀC= 774 Hz, Pt-CH₃); Note: carbons of O₂CCF₃were not located.

¹⁹F NMR (C₆D₆, δ): ꢀ74.5 (s, O₂CCF₃). Anal. Calcd for

C₂₇H₃₄F₃N₃O₂Pt: C, 47.37; H, 5.01; N, 6.14. Found: C, 46.82; H,

4.94; N, 5.97.

General Methods. All procedures were performed under anaero-

bic conditions in a nitrogen-filled glovebox or using standard Schlenk

techniques. Glovebox purity was maintained by periodic nitrogen purges

and monitored by an oxygen analyzer (O₂< 15 ppm for all reactions).

Benzene, toluene, and tetrahydrofuran were purified by distillation over

sodium/benzophenone. Pentane was distilled over P₂O₅prior to use.

Diethyl ether and pyridine were distilled over CaH₂prior to use.

Hexanes and methylene chloride were purified by passage through a

column of activated alumina. Benzene-d₆, chloroform-d₁, acetone-d₆,

and methylene chloride-d₂were degassed via three freezeꢀpumpꢀthaw

cycles and stored under nitrogen atmosphere over 4 Å molecular sieves.

Tetrahydrofuran-d₈was used as received in glass ampules packed under

dinitrogen. Aniline was dried over CaH₂, vacuum distilled, and stored

under a nitrogen atmosphere over 4 Å molecular sieves. All other

(^tbpy)Pt(Me)(NHPh) (2). In a round-bottom flask, a yellow

homogeneous solution of [(^tbpy)Pt(Me)(NH₂Ph)][TFA] (1) (0.045 g,

0.066 mmol) in ∼15 mL of benzene was prepared. Upon addition of a

THF solution of Na[N(SiMe₃)₂] (0.066 mL, 0.066 mmol), a color

change to deep green was observed. The resulting mixture was stirred for

2 h and then filtered through Celite. The filtrate was reduced in vacuo to

a green solid (0.032 g, 85% yield). A crystal suitable for an X-ray

diffraction study was grown by slow evaporation of a diethyl ether

1

solution of 2. H NMR (C₆D₆, δ): 9.37, 8.97 (each a d, each 1H,

³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.40ꢀ7.28 (m, 6H, overlap of ^tbpy 3/3⁰with

4

3

1

anilido-ortho and ꢀmeta), 6.65 (tt, 1H, J_HH= 7 Hz, J_HH= 2 Hz,

reagents were used as purchased from commercial sources. H and

anilido-para), 6.46, 6.42 (each a dd, each 1H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5

=

¹³C NMR spectra were acquired using Varian Mercury spectrometers

operating at 300 (¹H NMR) and 75 MHz (¹³C NMR) and are

referenced to tetramethylsilane using residual proton signals or the

¹³C resonances of the deuterated solvent. ¹⁹F NMR spectra were

acquired using a Varian Mercury spectrometer operating at 282 MHz

with C₆F₆(ꢀ163.0 ppm) as the external standard. All NMR spectra

were acquired at room temperature unless otherwise noted. Thick-

walled high-pressure glass NMR tubes with a PV-ANV Teflon valve

(maximum pressure rating 200 psi) were purchased from Wilmad-

Labglass and used for all 200 psi H₂experiments. Tubes were charged

with H₂using a stainless steel gas pressure line (maximum pressure

rating 3000 psi) connected directly to the gas cylinder. Elemental

analyses were performed by Atlantic Microlabs, Inc. Synthetic and

2 Hz, ^tbpy 5/5⁰), 3.99 (br s, 1H, PtꢀNHPh), 1.85 (s with Pt satellites,

3H, ²J_PtꢀH= 84 Hz, PtꢀCH₃), 0.95, 0.89 (each a s, each 9H, ^tbpy ^tBu).

¹³C{¹H} NMR (acetone-d₆, δ): 163.2, 162.6, 149.2, 148.9, 129.2, 128.9,

125.2, 124.8, 121.8, 120.6, 116.7, 110.3 (each a s, ^tbpy and NH-phenyl

carbons, two signals missing presumably due to coincidental overlap),

36.5 (s, ^tBu-C(CH₃)₃, one signal missing presumably due to coinciden-

tal overlap), 30.5, 30.3 (each a s, ^tBuC(CH₃)₃), ꢀ14.2 (singlet with Pt

1

satellites, J_PtꢀC= 813 Hz, Pt-CH₃). Anal. Calcd for C₂₅H₃₃N₃Pt: C,

52.62; H, 5.83; N, 7.36. Found: C, 53.31; H, 5.88; N, 7.37.

[(^tbpy)Pt(NH₂Ph)₂][OTf]₂(3). A homogeneous solution of

(^tbpy)Pt(OTf)₂(0.042 g, 0.056 mmol) in methylene chloride (5 mL)

was prepared. Upon addition of aniline (0.020 mL, 0.22 mmol) an

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immediate color change from yellow to green was observed. After

stirring for 30 min, the volatiles were removed in vacuo. Reconstitution

in THF followed by addition of hexanes resulted in the precipitation of a

green solid. The solid was collected by filtration through a fine-porosity

frit and washed with hexanes (2 ꢁ 5 mL) and diethyl ether (2 ꢁ 5 mL)

(0.041 g, 78% yield). A crystal suitable for an X-ray diffraction study was

grown by slow diffusion of a THF solution of 3 layered with hexanes. ¹H

NMR (CDCl₃, δ): 8.50 (d, 2H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.92 (d, 2H,

⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 7.69 (d, 4H, ³J_HH= 8 Hz, aniline-ortho), 7.65

(br s, 4H, aniline NH₂), 7.54 (dd, 2H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz,

^tbpy 5/5⁰), 7.25ꢀ7.22 (m, 6H, overlap of aniline-meta and -para), 1.40

phenol-para), 3.79 (br s phenol-OH), 1.45, 1.43 (each a s, each 9H, ^tbpy

^tBu), 1.00 (singlet with Pt satellites, ²J_PtꢀH= 82 Hz, PtꢀCH₃). ¹³C{¹H}

NMR (acetone-d₆, δ): 171.1, 164.3, 163.4, 156.9, 155.6, 151.1, 147.6,

129.6, 128.5, 128.2, 124.7, 124.4, 121.4, 120.1, 119.8, 119.4, 115.5, 113.5

(each a s, ^tbpy, phenoxy, and 1 equiv of H-bonded phenol carbons), 36.6

t

(s, Bu-C(CH₃)₃, one signal missing presumably due to coincidental

t

overlap), 30.5, 30.2 {each a s, Bu-C(CH₃)₃}, ꢀ14.2 (singlet with Pt

1

satellites, J_PtꢀC= 826 Hz, Pt-CH₃). Anal. Calcd for C₂₅H₃₂N₂OPt

3

C₆H₆O: C, 55.93; H, 5.75; N, 4.21. Found: C, 56.46; H, 5.78; N, 4.19.

Note: 1 equiv of phenol confirmed by ¹H NMR.

(^tbpy)Pt(OPh)₂(7). (^tbpy)Pt(NHPh)₂(4) (0.140 g, 0.216 mmol)

and THF (10 mL) were combined in a thick-walled glass pressure tube.

After the addition of phenol (0.083 g, 0.88 mmol), the tube was sealed

with a PTFE screw cap. The mixture was heated at 80 ꢀC for ∼12 h in a

temperature-controlled oil bath. After cooling to room temperature, the

solvent was reduced in vacuo to ∼1 mL. The addition of hexanes

resulted in the precipitation of a green solid. The solid was collected by

filtration through a fine-porosity frit and washed with hot hexanes (5 ꢁ

2 mL) to remove excess phenol (0.134 g, 95% yield). A crystal suitable

for an X-ray diffraction study was grown by slow diffusion of a THF

t

(s, 18H, bpy Bu). ¹³C{¹H} NMR (CDCl₃, δ): 167.1, 156.2, 150.5,

138.6, 130.1, 128.1, 125.6, 124.7, 120.5 (each a s, ^tbpy and NH-phenyl

carbons), 120.4 (q, ¹J_CꢀF= 318 Hz, O₃SCF₃), 36.3 (s, ^tBu C(CH₃)₃),

t

30.2 (s, Bu C(CH₃)₃). ¹⁹F NMR (282.2 MHz, CDCl₃, δ): ꢀ78.6 (s,

O₃SCF₃). Anal. Calcd for C₃₂H₃₈F₆N₄O₆PtS₂: C, 40.55; H, 4.04; N,

5.91. Found: C, 40.82; H, 3.97; N, 5.88.

(^tbpy)Pt(NHPh)₂(4). [(^tbpy)Pt(NH₂Ph)₂][OTf]₂(3) (0.089 g,

0.093 mmol) was dissolved in benzene (5 mL) to give a green solution.

Upon addition of Na[N(SiMe₃)₂] (0.19 mL, 0.19 mmol) a blue-green

mixture was observed. After 2 h, the blue suspension was filtered through

Celite and the filtrate was reduced to dryness. Reconstitution in minimal

THF and addition of hexanes gave a fine blue precipitate, which was

collected by filtration through a fine-porosity frit and washed with

hexanes (2 ꢁ 10 mL) (0.020 g, 71% yield). A crystal suitable for an X-ray

diffraction study was grown by slow diffusion of a methylene chloride

1

solution layered with hexanes. H NMR (acetone-d₆, δ): 8.88 (d, 2H,

³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 8.55 (d, 2H, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 7.80

(dd, 2H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 7.15 (d, 4H, ³J_HH

=

8 Hz, phenoxy-ortho), 6.89 (t, 4H, ³J_HH= 8 Hz, phenoxy-meta), 6.36 (t,

2H, ³J_HH= 8 Hz, phenoxy-para), 1.44 (s, 18H, ^tbpy ^tBu). ¹³C{¹H} NMR

(THF-d₈, δ): 169.8, 164.4, 149.4, 128.9, 128.6, 124.9, 120.9, 120.1, 114.9

(each a s, ^tbpy and phenoxy carbons), 36.8 {s, ^tBu-C(CH₃)₃}, 30.4 {s,

^tBu-C(CH₃)₃}. Anal. Calcd for C₃₀H₃₄N₂O₂Pt: C, 55.46; H, 5.27; N,

4.31. Found: C, 54.85; H, 5.57; N, 3.76.

1

solution of 4 layered with hexanes. H NMR (C₆D₆, δ): 9.32 (d, 2H,

³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.30ꢀ7.25 (m, 8H, overlap of anilido-ortho

t

and -meta), 7.18ꢀ7.16 (m, 2H, overlap of solvent and bpy 3/3⁰),

6.69ꢀ6.62 (m, 2H, anilido-para), 6.32 (dd, 2H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5

= 2 Hz, ^tbpy 5/5⁰), 3.80 (br s, 2H, PtꢀNHPh), 0.89 (s, 18H, ^tbpy ^tBu).

¹³C{¹H} NMR (THF-d₈, δ): 163.6, 160.1, 158.5, 151.5, 128.9, 124.8,

120.6, 116.9, 111.6 (each a s, ^tbpy aryl and NH-phenyl carbons), 36.7 (s,

^tBu C(CH₃)₃), 30.4 (s, ^tBu C(CH₃)₃). Anal. Calcd for C₃₀H₃₆N₄Pt: C,

55.63; H, 5.60; N, 8.65. Found: C, 55.76; H, 5.72; N, 8.42.

(^tbpy)Pt(Me)₂(I)₂(8). In a round-bottom flask, (^tbpy)Pt(Me)₂

(0.069 g, 0.14 mmol) and iodine (0.038 g, 0.15 mmol) were combined in

∼15 mL of benzene. After stirring for 18 h, the solvent was removed in

vacuo and the product was dried (0.082 g, 73% yield). A crystal suitable

for an X-ray diffraction study was grown by slow diffusion of a THF

solution layered with pentane. ¹H NMR (C₆D₆, δ): 8.34 (d, 2H, ³J_H5ꢀH6

= 6 Hz, ^tbpy 6/6⁰), 7.94 (d, 2H, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 6.76 (dd, 2H,

³J_H5ꢀH6= 6, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 2.63 (s with Pt satellites, 6H,

²J_PtꢀH= 73 Hz, PtꢀCH₃), 1.04 (s, 18H, ^tbpy ^tBu). ¹³C NMR (CDCl₃,

δ): 164.0, 154.9, 147.7, 124.4, 120.5 (each a s, ^tbpy aryl resonances), 35.7

(^tbpy)Pt(NHPh)(Cl) (5). In a Schlenk flask, (^tbpy)Pt(NHPh)₂(4)

(0.032 g, 0.048 mmol) was prepared as a blue-green solution in benzene

(5 mL). The addition of HCl (1.0 M diethyl ether solution, 0.048 mL,

0.048 mmol) resulted in a color change to deep green. After stirring for 1

h, the volatiles were reduced in vacuo to approximately 1 mL, and

hexanes were added to give a blue solid. The solid was collected by filtration

through a fine-porosity frit and washed with hexanes (2 ꢁ 10 mL) and

diethyl ether (2 ꢁ 10 mL) (0.021 g, 75% yield). ¹H NMR (C₆D₆, δ): 9.53,

9.27 (each a d, each 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.39ꢀ7.21 (m, 6H,

overlap of anilido-ortho and -meta and ^tbpy 3/3⁰), 6.68ꢀ6.62 (m, 2H, overlap

of anilido-para and ^tbpy 5), 6.33 (dd, 1H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz,

^tbpy 5⁰), 4.06 (br s, 1H, PtꢀNHPh), 0.99, 0.91 (each an s, each 9H, ^tbpy

^tBu). ¹³C{¹H} NMR (THF-d₈, δ): 164.2, 163.9, 161.6, 159.9, 151.05, 150.2,

129.2, 128.8, 125.0, 124.9, 121.0, 120.8, 117.5, 112.4 (each a s, ^tbpy and NH-

phenyl carbons), 36.8, 36.7 (each a s, ^tBu-C(CH₃)₃), 30.5, 30.4 (each a s, ^tBu-

C(CH₃)₃). Anal. Calcd for C₂₄H₃₀ClN₃Pt: C, 48.77; H, 5.12; N, 7.11.

Found: C, 48.48; H, 5.08; N, 6.98.

t

{s, Bu-C(CH₃)₃}, 30.7 {s, Bu-C(CH₃)₃}, ꢀ14.7 (s with Pt satellites,

¹J_PtꢀC= 506 Hz, Pt-CH₃). Anal. Calcd for C₂₀H₃₀I₂N₂Pt: C, 32.14; H,

4.05; N, 3.75. Found: C, 32.38; H, 4.01; N, 3.70.

(^tbpy)Pt(Ph)₂(I)₂(9). (^tbpy)Pt(Ph)₂(0.137 g, 0.221 mmol) and

iodine (0.061 g, 0.24 mmol) were combined in ∼20 mL of benzene in a

round-bottom flask. After stirring for 12 h, the volatiles were reduced in

vacuo to ∼1 mL. The addition of hexanes yielded an orange precipitate,

which was filtered through a plug of silica gel on a fine-porosity frit. The

solid was rinsed with 25% Et₂O/75% hexanes (v:v 3 ꢁ 3 mL) to remove

excess iodine followed by methylene chloride to elute the orange

complex from the silica gel. The filtrate was reduced to dryness in vacuo

to yield an orange solid (0.161 g, 84% yield). ¹H NMR (C₆D₆, δ): 9.12

(d, 2H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 8.71 (d, 4H, ³J_HH= 8 Hz, phenyl-

(^tbpy)Pt(Me)(OPh) HOPh (6). (^tbpy)Pt(Me)₂(0.10 g, 0.20

4

t

ortho), 7.81 (d, 2H, J_H3ꢀH5= 2 Hz, bpy 3/3⁰), 7.2ꢀ7.1 (m, 6H,

3

overlapping phenyl-meta and -para), 6.47 (dd, 2H, J_H5ꢀH6= 6 Hz,

mmol) and phenol (0.186 g, 1.97 mmol) were combined in a round-

bottom flask in benzene (∼20 mL). After stirring the red suspension for

2 h, the volatiles were reduced in vacuo to ∼1 mL. The addition of

hexanes resulted in a yellow precipitate that was collected by filtration

through a fine-porosity frit. The resulting solid was rinsed with pentane

(2 ꢁ 3 mL) and diethyl ether (3 ꢁ 3 mL) (0.092 g, 82% yield). ¹H NMR

(acetone-d₆, δ): 9.05, 8.77 (each a d, each 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/

6⁰), 8.53, 8.47 (each a d, each 1H, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 7.78, 7.63

(each a dd, each 1H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5 and 5⁰), 7.17

(t, 1H, ³J_HH= 8 Hz, phenoxy/phenol-para), 7.06ꢀ6.75 (m, 8H, overlap

of phenoxy/phenol-ortho and -meta), 6.34 (t, 1H, ³J_HH= 7 Hz, phenoxy/

⁴J_H3ꢀH5= 2 Hz, bpy 5/5⁰), 0.89 (s, 18H, bpy Bu). ¹³C{¹H} NMR

t

(C₆D₆, δ): 163.9, 155.9, 151.5, 146.2, 127.7, 126.8, 125.4, 124.3, 120.4

t

(each a s, bpy and phenyl carbons), 35.2 {s, bpy-C(CH₃)₃}, 30.3 {s,

^tbpy-C(CH₃)₃}. Anal. Calcd for C₃₀H₃₄I₂N₂Pt: C, 41.35; H, 3.93; N,

3.21. Found: C, 41.17; H, 3.83; N, 3.23.

(^tbpy)Pt(Me)₂(NHPh)(I) (10). In a round-bottom flask, (^tbpy)-

Pt(Me)(NHPh) (2) (0.112 g, 0.196 mmol) and iodomethane (15 μL,

0.240) were combined in ∼15 mL of benzene. After stirring for 2 h, a

color change from green to brown was observed, and the volatiles were

reduced in vacuo to ∼1 mL. Hexanes were added to precipitate a brown

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solid. The solid was collected by filtration on a fine-porosity frit and

washed with hexanes (2 ꢁ 3 mL) and pentane (2 ꢁ 3 mL) (0.095 g, 68%

yield). ¹H NMR (C₆D₆, δ): 9.67, 8.51 (each a d, each 1H, ³J_H5ꢀH6= 6

Anal. Calcd for C₆₁H₄₇BF₂₄N₄Pt: C, 48.91; H, 3.16; N, 3.74. Found: C,

48.49; H, 3.01; N, 3.70.

t

0

[( bpy)Pt(OPh)(py)][BAr₄] (13). In a round-bottom flask,

(^tbpy)Pt(OPh)₂(7) (0.051 g, 0.079 mmol) and pyridine (30 μL, 0.40

mmol) were combined in methylene chloride to give a green solution.

HBAr⁰₄was added, and the solution instantly turned gold. The reaction

was stirred for 12 h, and the volatiles were removed in vacuo. After

reconstitution in 5 mL of diethyl ether, the solution was transferred to a

vial. The volatiles were removed to yield a low-density dark gold solid

(0.098 g, 81%). ¹H NMR (CD₂Cl₂, δ): 8.82 (dd, 1H, ³J_H5ꢀH6= 6 Hz,

⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 8.79 (d, 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 8.06,

8.04 (each a d, each 1H, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 7.98 (t, 1H, ³J_HH= 8

Hz, OPh or py para), 7.77 (d, 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 7.74ꢀ7.66

(m, 10H, overlapping ortho-BAr⁰₄and OPh or py ortho), 7.57ꢀ7.47 (m,

7H, overlapping para-BAr⁰₄, ^tbpy 5/5⁰, and OPh or py ortho), 7.08ꢀ6.92

(m, 4H, overlapping OPh and py meta), 6.57 (t, 1H, ³J_HH= 8 Hz, OPh or

py para), 1.45, 1.42 (each a s, each 9H, ^tbpy ^tBu). ¹³C NMR (pyridine-d₅,

δ): 168.1, 167.0, 166.4, 157.6, 157.0, 149.1, 130.0, 129.4, 125.7, 124.9,

122.5, 121.8, 120.8, 119.8, 118.9, 118.6, 117.8 (each a s, ^tbpy, pyridine, and

phenoxide-phenyl carbons), 163.0 (q, ¹J_BꢀC= 50 Hz, ipso-BAr⁰₄), 134.4

t

Hz, bpy 6/6⁰), 7.78, 7.74 (each a br s, each 1H, bpy 3/3⁰), 7.4ꢀ7.2

(overlapping ortho- and meta-anilido, 4H), 7.0ꢀ6.9 (overlapping para-

t

3

4

anilido and bpy5/5⁰, 2H), 6.72 (dd, 1H, J_H5ꢀH6= 6 Hz, J_H3ꢀH5

=

t

2

2 Hz, bpy 5/5⁰), 4.77 (br s with Pt satellites, 1H, J_PtꢀH= 50 Hz,

2

PtꢀNHPh), 2.24 (s with Pt satellites, 3H, J_PtꢀH= 70 Hz, PtꢀCH₃),

1.35 (s with Pt satellites, 3H, ²J_PtꢀH= 70 Hz, PtꢀCH₃), 0.98, 0.95 (each

a s, each 9H, ^tbpy ^tBu). ¹³C{¹H} NMR (C₆D₆, δ): 163.6, 157.2, 156.2,

153.6, 149.0, 148.8, 129.5, 125.0, 124.6, 122.6, 120.4, 119.7, 117.6 (each

a s, ^tbpy aryl and anilido-phenyl carbons, one signal missing presumably

due to coincidental overlap), 35.5, 35.4 {each a s, ^tBu-C(CH₃)₃}, 30.5,

30.3 {each a s, ^tBu-C(CH₃)₃}, 13.8 (s with Pt satellites, ¹J_PtꢀC= 630 Hz,

1

Pt-CH₃), ꢀ0.4 (s with Pt satellites, J_PtꢀC= 642 Hz, Pt-CH₃). Anal.

Calcd for C₂₆H₃₆IN₃Pt: C, 43.82; H, 5.09; N, 5.90. Found: C, 43.54; H,

5.02; N, 5.63.

(^tbpy)Pt(Me)(CtCPh) (11). (^tbpy)Pt(Me)(NHPh) (2) (0.061 g,

0.11 mmol) and phenylacetylene (12 μL, 0.11 mmol) were combined in

∼5 mL of benzene in a thick-walled glass pressure tube. The homo-

geneous blue-green solution was heated at 80 ꢀC for 12 h in a

temperature-controlled oil bath. The resulting orange solution was

allowed to cool to room temperature, and the volatiles were reduced

in vacuo to ∼1 mL. The addition of hexanes resulted in the formation of

an orange precipitate. The solid was collected by filtration through a fine-

porosity frit and washed with hexanes (3 ꢁ 2 mL) (0.041 g, 66% yield).

¹H NMR (C₆D₆, δ): 9.58, 8.65 (each a d, each 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy

6/6⁰), 7.92 (d, 2H, ³J_HH= 8 Hz, phenylacetylide-ortho), 7.64, 7.58 (each

(s, ortho-BAr⁰₄), 130.2 (q, ²J_CꢀF= 31 Hz, meta-BAr⁰₄), 125.4 (q, ¹J_CꢀF

=

271 Hz, CF₃ꢀBAr⁰₄), 117.5 (s, para-BAr⁰₄), 36.5 {s, ^tBu-C(CH₃)₃, one

signal missing presumably due to coincidental overlap}, 30.1, 30.0 (each a

t

19

s, Bu-C(CH₃)₃). F NMR (pyridine-d₅, δ): ꢀ62.2 (s, BAr⁰₄CF₃).

Satisfactory elemental analysis data were not obtained. Representative

NMR spectra are provided in the Supporting Information.

[(^tbpy)Pt(μ-NHPh)]₂[BAr⁰₄]₂(14). In a round-bottom flask,

(^tbpy)Pt(NHPh)(Cl) (5) (0.063 g, 0.106 mmol) and AgBAr⁰₄(0.106

g, 0.109 mmol) were combined in THF (∼15 mL), resulting in a

homogeneous blue-green solution. After stirring for 48 h, the volatiles

were removed in vacuo. Reconstitution in THF and filtration through

Celite resulted in a brown filtrate that was reduced in vacuo to ∼1 mL.

Hexanes were added, and the resulting brown solid was collected on a

fine-porosity frit and washed with pentane (2 ꢁ 3 mL) (0.136 g, 58%

yield). ¹H NMR (CD₂Cl₂, δ): 7.93 (d, 4H, ³J_HH= 8 Hz, anilido-ortho),

7.90 (d, 4H, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 3/3⁰), 7.85 (d, 4H, ³J_H5ꢀH6= 6 Hz,

^tbpy 6/6⁰), 7.72 (br s, 16H, ortho-BAr⁰₄), 7.54 (br s, 8H, para-BAr⁰₄),

7.44 (d, 4H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 7.36 (t, 4H,

³J_HH= 8 Hz, anilido-meta), 7.19 (t, 2H, ³J_HH= 8 Hz, anilido-para), 3.83

(br s, 2H, PtꢀNHPh), 1.33 (s, 36H, ^tbpy ^tBu). ¹³C{¹H} NMR (CD₂Cl₂,

δ): 168.0, 156.6, 149.1, 148.4, 130.8, 127.0, 125.0, 124.5, 120.9 (each a s,

^tbpy and anilido-phenyl carbons), 162.3 (q, ¹J_BꢀC= 50 Hz, ipso-BAr⁰₄),

135.4 (s, ortho-BAr⁰₄), 129.4 (q, ²J_CꢀF= 31 Hz, meta-BAr⁰₄), 125.1 (q,

4

t

3

a d, each 1H, J_H3ꢀH5= 2 Hz, bpy 3/3⁰), 7.26 (t, 2H, J_HH= 7 Hz,

phenylacetylide-meta), 7.08 (t, 1H, ³J_HH= 8 Hz, phenylacetylide-para),

6.72, 6.55 (each a dd, each 1H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/

5⁰), 1.65 (s with Pt satellites, 3H, ²J_PtꢀH= 81 Hz, PtꢀCH₃), 1.10, 1.01

(each a s, each 9H, ^tbpy ^tBu). ¹³C{¹H} NMR (C₆D₆, δ): 161.3, 160.6,

158.4, 155.5, 150.5, 146.9, 132.7, 125.0, 124.6, 124.2, 120.0, 118.8 (each

t

a s, bpy aryl and acetylide-phenyl resonances, two signals missing

presumably due to coincidental overlap), 103.0, 100.6 (each a s, CtC

carbons), 35.6, 35.5 {overlapping singlets, ^tBu-C(CH₃)₃}, 30.3 {s, ^tBu-

C(CH₃)₃, one signal missing presumably to coincidental overlap},

1

ꢀ17.4 (s, Pt-CH₃). Note: Anticipated J_PtꢀCsatellites were not ob-

served due to a low signal-to-noise ratio. Anal. Calcd for C₂₇H₃₂N₂Pt: C,

55.95; H, 5.56; N, 4.83. Found: C, 55.68; H, 5.48; N, 4.71.

[(^tbpy)Pt(NHPh)(py)][BAr⁰₄] (12). (^tbpy)Pt(NHPh)₂(4) (0.048

g, 0.074 mmol) and neat pyridine (∼20 equiv) were combined in a

thick-walled glass pressure tube. After addition of HBAr⁰₄(0.075 g,

0.074 mmol) the tube was sealed with a Teflon screw cap and the

mixture was heated at 80 ꢀC for ∼40 h in a temperature-controlled oil

bath. Upon cooling to room temperature, the volatiles were removed in

vacuo. After reconstitution in 5 mL of diethyl ether, the solution was

transferred to a vial and the volatiles were removed in vacuo to yield a

low-density brown solid (0.101 g, 91% yield). ¹H NMR (CD₂Cl₂, δ):

9.21 (d, 1H, ³J_H5ꢀH6= 6 Hz, ^tbpy 6/6⁰), 8.73 (dd, 1H, ³J_H5ꢀH6= 6 Hz,

⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 8.10, 8.04 (each a d, each 1H, ⁴J_H3ꢀH5= 2

Hz, ^tbpy 3/3⁰), 7.96 (t, 1H, ³J_HH= 8 Hz), 7.72 (br s, 8H, ortho-BAr⁰₄),

7.66 (dd, 1H, ³J_H5ꢀH6= 6 Hz, ⁴J_H3ꢀH5= 2 Hz, ^tbpy 5/5⁰), 7.55 (br s,

4H, para-BAr⁰₄), 7.50 (t, 2H, ³J_HH= 8 Hz), 6.93ꢀ6.80 (m, 7H), 6.37 (t,

1H, ³J_HH= 8 Hz), 2.90 (br s, 1H, anilido-NH), 1.45, 1.41 (each a s, each

9H, ^tbpy ^tBu). ¹³C{¹H} NMR (CD₂Cl₂, δ): 166.9, 166.8, 158.2, 157.0,

156.9, 153.6, 151.2, 148.4, 140.5, 129.6, 127.7, 125.9, 125.2, 120.9,

120.4, 116.7, 114.6 (each a s, ^tbpy, pyridine, and NH-phenyl carbons),

162.3 (q, ¹J_BꢀC= 50 Hz, ipso-BAr⁰₄), 135.4 (s, ortho-BAr⁰₄), 129.4 (q,

t

¹J_CꢀF= 272 Hz, CF₃ꢀBAr⁰₄), 118.0 (s, para-BAr⁰₄), 36.6 (s, Bu-

C(CH₃)₃), 30.2 (s, ^tBu-C(CH₃)₃). ¹⁹F{¹H} NMR (CD₂Cl₂, δ): ꢀ63.2

(BAr⁰₄-CF₃). Satisfactory elemental analysis data were not obtained.

Representative NMR spectra are provided in the Supporting

Information.

Kinetic Study of (^tbpy)Pt(Me)(NHPh) (2) and Phenylace-

tylene. Note: to ensure reproducibility, each kinetic experiment was

performed in triplicate. A representative procedure is given. A screw-cap

NMR tube was charged with 0.45 mL of C₆D₆, complex 2 (0.006 mmol,

0.0138 M), and hexamethylbenzene (5.9 ꢁ 10^ꢀ4mmol, 0.0013 M) as an

internal standard. An initial ¹H NMR spectrum was acquired. Phenylace-

tylene (5.5 μL, 0.04 mmol) was added to the tube via microsyringe. The

tube was placed in a ¹H NMR probe that was preheated to 80 ꢀC. The

reaction was monitored by ¹H NMR spectroscopy. The rate of reaction

was determined by monitoring the disappearance of complex 2 (the

resonance at 9.37 ppm was used). A linear plot of [2] versus time revealed

a zero-orderdependence on2. A representative plot is shown in Figure 8. A

plot of k_obsversus phenylacetylene equivalents is shown in Figure 9.

Kinetic study of the Reaction between (^tbpy)Pt(Me)

(NHPh) (2) and Phenylacetylene with Catalytic [(^tbpy)Pt(Me)

(NH₂Ph)][TFA] (1). Note: to ensure reproducibility, each kinetic

1

²J_CꢀF= 31 Hz, meta-BAr⁰₄), 125.1 (q, J_CꢀF= 271 Hz, CF₃ꢀBAr⁰₄),

118.0 (s, para-BAr⁰₄), 36.6 {s, ^tBu-C(CH₃)₃, one signal missing

t

presumably due to coincidental overlap}, 30.4, 30.3 (each a s, Bu-

C(CH₃)₃). ¹⁹F NMR (282.2 MHz, CD₂Cl₂, δ): ꢀ63.4 (s, BAr⁰₄CF₃).

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dx.doi.org/10.1021/ic200153n |Inorg. Chem. 2011, 50, 4195–4211

Inorganic Chemistry

ARTICLE

experiment was performed in triplicate. A representative procedure is given. A

vial was charged with a solution of complex 1in diethyl ether (51.8 μL, 5.59 ꢁ

10^ꢀ4mmol), and diethyl ether was removed in vacuo in order to obtain an

accurate concentration. The vial was then charged with 0.45 mL of C₆D₆,

complex 2 (5.59 ꢁ 10^ꢀ3mmol, 0.0124 M), and hexamethylbenzene (6.6 ꢁ

10^ꢀ4mmol, 0.0014 M). The solution was added to a screw-cap NMR tube,

and phenylacetylene (12.3 μL, 0.129 mmol) was added to the tube via

microsyringe. The tube was placed in a ¹H NMR probe that was preheated to

80 ꢀC. The reaction was monitored by ¹H NMR spectroscopy. The rate of

reaction was determined by monitoring the disappearance of complex 2 (the

resonance at 9.37 ppm was used). A plot of k_obsversus equivalents of complex

1 reveals a first-order dependence (Figure 10).

Filtration Test. A thick-walled high-pressure NMR tube with a

Teflon valve was charged with 0.45 mL of C₆D₆, complex 2 (0.0057

mmol, 0.0126 M), and hexamethylbenzene (0.0011 mmol, 0.00246 M,

as internal standard). An initial ¹H NMR spectrum was acquired. After

degassing the solution with three freezeꢀpumpꢀthaw cycles, the tube

1

was charged with H₂(∼200 psi). The reaction was monitored by H

NMR spectroscopy every 5 min for ∼5 h through the induction period

and initial stages of the reaction. After this time period, the solution was

filtered through Celite to remove Pt(s). The filtrate was added to a new

thick-walled high-pressure NMR tube with a Teflon valve, degassed with

three freezeꢀpumpꢀthaw cycles, and charged with H₂(∼200 psi).

Monitoring by ¹H NMR spectroscopy was continued for ∼2 h until the

reaction was complete. A plot of [2] versus time for the filtered solution

revealed a second induction period (Figure 11, plot D).

Reaction of (^tbpy)Pt(Me)(NHPh) (2) and H₂. A J. Young NMR

tube was charged with (^tbpy)Pt(Me)(NHPh) (2) (0.006 g, 0.011

mmol), a small crystal of hexamethylbenzene (as internal standard),

and C₆D₆(0.5 mL). An initial ¹H NMR spectrum was acquired. After

degassing the solution with three freezeꢀpumpꢀthaw cycles, the tube

Reaction with Added Pt/C. A thick-walled high-pressure NMR tube

with a Teflon valve was charged with 0.1 mL of C₆D₆, complex 2 (0.0057

mmol, 0.0126 M), hexamethylbenzene (0.0011 mmol, 0.00246 M, as internal

standard), and Pt (10% by weight) on carbon (0.001 g). An initial ¹H NMR

spectrum was acquired. After degassing the solution with three free-

zeꢀpumpꢀthaw cycles, the tube was charged with H₂(∼ 200 psi). The re-

action was ∼50% complete after ∼5 min and reached completion after ∼1 h.

Reaction of [(^tbpy)Pt(Ph)(NC₅F₅)][BAr⁰₄] with Aniline and

Phenol. In two separate experiments, [(^tbpy)Pt(Ph)(NC₅F₅)][BAr⁰₄]

(0.007 g, 0.004 mmol) and 1 equiv of pyridine were combined with 5

equiv of either aniline or phenol in CD₂Cl₂in a screw-cap NMR tube. An

initial ¹H NMR spectrum was acquired. After heating the tubes to 100 ꢀC

1

was charged with H₂(∼45 psi). The solution was monitored by H

NMR spectroscopy. After 7 h at room temperature, a new Ptꢀmethyl

resonance at 2.21 ppm (s with Pt satellites, ²J_PtꢀH= 83 Hz) was observed

1

(by H NMR spectroscopy) along with a Ptꢀhydride resonance at

1

ꢀ14.8 ppm (s with Pt satellites, J_PtꢀH= 1575 Hz). In addition,

t

resonances due to bpy of a new Pt complex were observed as well as

resonances due to free aniline. These data are consistent with the

formation of (^tbpy)Pt(Me)(H) and NH₂Ph. After 12 h, complete

t

conversion to free aniline, free methane, and free bpy was observed.

1

in a temperature-controlled oil bath for 24 h, the H NMR spectra

In addition, a black precipitate was observed, which we presume is Pt(s).

Kinetic Studies of (^tbpy)Pt(Me)(NHPh) (2) and H₂. Note: to

ensure reproducibility, each kinetic experiment was performed a mini-

mum of three times. A representative procedure is given. A thick-walled

high-pressure NMR tube with a Teflon valve was charged with 0.3 mL of

C₆D₆, complex 2 (0.004 mmol, 0.0138 M), and hexamethylbenzene (0.0004

mmol, 0.00131 M, as internal standard). An initial ¹H NMR spectrum was

acquired. After degassing the solution with three freezeꢀpumpꢀthaw cycles,

the tube was charged with H₂(∼200 psi). The reaction was monitored by ¹H

NMR spectroscopy every 10 min until complete conversion to free aniline,

methane, and ^tbpy was observed. The rate of reaction was determined by

monitoring the disappearance of complex 2 (the resonance at 9.37 ppm was

used). A plot of [2] versus time revealed an initial induction period and a

sigmoidal fit (Figure 11, plot A).

revealed the formation of complexes 12 and 13 along with free benzene.

Computational Methods. All calculations were performed with

the Gaussian 03 program suite⁸²using the B3LYP density functional^83,84

in conjunction with the CEP-31G valence basis sets and pseudopoten-

tials of Stevens et al.^85,86augmented with a set of d-polarization

functions for main group elements (exponents of 0.80 for C, N, and

O and 0.55 for P). The -31G basis set was used for H atoms.

Optimized geometries and transition states (all studied species were

singlet spin states) were veriﬁed by the presence of zero and one

imaginary frequency, respectively, in the calculated energy Hessian.

Thermochemistry was determined at 1 atm and 298.15 K using unscaled

B3LYP/CEP-31G(d) frequencies.

Mercury Test. A thick-walled high-pressure NMR tube with a Teflon

valve was charged with 0.1 mL of C₆D₆, complex 2 (0.0014 mmol, 0.0139

M), hexamethylbenzene (0.00016 mmol, 0.00162 M, as internal standard),

and a drop of elemental Hg. An initial ¹H NMR spectrum was acquired. After

degassing the solution with three freezeꢀpumpꢀthaw cycles, the tube was

’ ASSOCIATED CONTENT

S

Supporting Information. Computational details, NMR

b

spectra, and X-ray crystallographic data ﬁles. This material is

available free of charge via the Internet at http://pubs.acs.org.

1

charged with H₂(∼200 psi). The reaction was monitored by H NMR

spectroscopy every 20 min for ∼7 h (Figure 11, plot B). There was virtually

no change in the concentration of complex 2.

’ AUTHOR INFORMATION

Corresponding Author

*E-mail: tbg7h@virginia.edu (T.B.G.), t@unt.edu (T.R.C.).

Reaction of Complex 2 and H₂in the Presence of “Gen-

erated” Pt(s). A high-pressure NMR tube was charged with 0.1 mL of

C₆D₆, complex 2 (0.0014 mmol, 0.0139 M), and hexamethylbenzene

(0.00016 mmol, 0.00162 M, as internal standard). An initial ¹H NMR

spectrum was acquired. After degassing the solution with three free-

zeꢀpumpꢀthaw cycles, the tube was charged with H₂(∼200 psi). The

mixture was allowed to react for ∼3 h, at which time the formation of

Pt(s) was visible and initial conversion to (^tbpy)Pt(Me)(H) was evident.

The solution was carefully decanted, and the tube was rinsed with C₆D₆

leaving Pt(s) on the walls. The same NMR tube was charged with 0.1 mL

of fresh complex 2/hexamethylbenzene/C₆D₆solution. Again, the

solution was degassed with three freezeꢀpumpꢀthaw cycles and

charged with H₂(∼200 psi). The reaction was monitored by

¹H NMR spectroscopy every 10 min for ∼3 h. A plot of [2] versus

time revealed conversion of 2 and H₂indicative of a reaction with a zero-

order dependence on complex 2 (Figure 11, plot C).

’ ACKNOWLEDGMENT

T.B.G. acknowledges the National Science Foundation

(CHE-0848693) for ﬁnancial support of this work. T.R.C. thanks

the National Science Foundation for support (CHE-0701247)

and facilities (CHE-0741936). A.W.P. thanks the UNT Toulouse

Graduate School for a Dissertation Fellowship.

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Pt(II) and Pt(IV) amido, aryloxide, and hydrocarbyl complexes: Synthesis, characterization, and reaction with dihydrogen and substrates that possess C-H bonds

DOI: 10.1021/ic200153n

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