Synthesis, characterization, and protonation reactions of Ar-BIAN and Ar-BICAT diimine platinum diphenyl complexes

FULL PAPER

DOI: 10.1002/ejic.200900975

Synthesis, Characterization, and Protonation Reactions of Ar-BIAN and

Ar-BICAT Diimine Platinum Diphenyl Complexes

Jerome Parmene,^[a]Alexander Krivokapic,^[a]and Mats Tilset*^[b]

Keywords: Platinum / Hydride ligands / Arene ligands / N ligands / C–H

Pt^IIdiphenyl complexes (N–N)PtPh₂[N–N = diimines Ar–

N=C(An)C=N–Ar with Ar = substituted aryl groups] have

ture is raised. A second protonation and rapid benzene elimi-

nation produces the dicationic Pt^IIspecies (N–N)Pt-

(NCMe)₂at approximately 50 °C. Protonation of (N–N)-

1

2+

been prepared and characterized by H, ¹³C, and ¹⁹⁵Pt NMR

spectroscopy. The ¹⁹⁵Pt NMR spectroscopic data establish the

electronic influence exerted by substituents at the backbone

of the diimine ligand system to the metal center. When com-

pared to diimines Ar–N=CMe–CMe=N–Ar, the electron-

withdrawing ability of the Ar-BIAN ligand and the electron-

donating ability of the O,O-heterocyclic Ar-BICAT systems

are demonstrated. Trends in ¹⁹⁵Pt NMR chemical shifts sug-

gest that electronic tuning of the metal center is better

achieved through variations of the diimine backbone substit-

uents rather than variation of the substituents at the N-Aryl

groups. Protonation of (N–N)PtPh₂in dichloromethane/aceto-

nitrile at –78 °C furnishes the corresponding Pt^IVhydrides

(N–N)PtPh₂H(NCMe)⁺. The Pt^IVhydrides liberate benzene

with the formation of (N–N)PtPh(NCMe)⁺when the tempera-

PtPh₂in the absence of acetonitrile results in the clean forma-

tion of (N–N)PtPh(η²-C₆H₆)⁺at temperatures that depend on

the steric hindrance provided by the alkyl substituents at the

diimine N-aryl groups. These findings support the notion that

the metal is the kinetically preferred site of protonation. The

results qualitatively agree with a recent mechanistic study of

protonation-induced reactions of (diimine)PtPh₂complexes

that bear simple methyl substituents at the diimine back-

bone. Several compounds have been crystallographically

characterized. All complexes have the expected square

planar environment at the metal. Modest variations in the

metric parameters suggest that the Ar-BICAT system has a

weaker trans influence than the Ar-BIAN and Ar-DAB sys-

tems.

been intensely investigated to gain further insight into the

C–H activation mechanisms. In this respect, the most com-

monly studied diimine-ligand systems (Scheme 1) are those

of the DAB (1,4-diaza-1,3-butadiene) type^[15–21]and the

bpy and bipym systems studied by Puddephatt^[22–25]and

Periana.^[12,26–31]

Introduction

Shortly after Garnett and Hodges first reported that

acidic solutions of Pt^IIsalts in D₂O were capable of affect-

ing H/D exchange into aromatic hydrocarbons in 1967,^[1,2]

Shilov extended this reaction to aliphatic hydrocarbons, in-

cluding methane.^[3,4]These early reports of aromatic and

aliphatic hydrocarbons C–H activation have been highly in-

fluential for the organometallic chemistry community since

then. The tremendous industrial and technological implica-

tions of effective catalytic C–H activation and functionali-

zation processes have motivated intense research efforts. A

wide variety of experimental and theoretical investigations

have been published which have helped elucidate the under-

lying mechanism of what is commonly referred to as “Shi-

lov chemistry”^[4–6]and other C–H activating schemes.^[7–12]

Model systems more amenable to spectroscopic monitoring

than the original Pt salts in aqueous media were needed,

and the Bercaw group first reported that a tmeda-Pt^IIcom-

plex was capable of activating C–H bonds.^[13,14]Variously

substituted diimine-Pt^IIalkyl and aryl complexes have

Scheme 1.

[a] Department of Chemistry, University of Oslo,

P. O. Box 1033 Blindern, 0315 Oslo, Norway

[b] Centre for Theoretical and Computational Chemistry, Depart-

ment of Chemistry, University of Oslo,

Recent efforts of ours have focused on gaining insight

into aromatic C–H activation reactions by looking at a cru-

cial step in the microscopic reverse, i.e. the protonation of

Pt^IIaryl complexes.^[15,32]Of particular relevance for this

P. O. Box 1033 Blindern, 0315 Oslo, Norway

E-mail: mats.tilset@kjemi.uio.no

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J. Parmene, A. Krivokapic, M. Tilset

1

FULL PAPER

contribution, we have recently^[32]conducted detailed kinetic complexes were characterized by H, ¹³C, and ¹⁹⁵Pt NMR

and mechanistic studies of a protonation-induced sequence spectroscopy as well as elemental analysis. Complexes 1a–f

of reactions that occur from (N–N)PtPh₂with N–N repre- showed ¹⁹⁵Pt signals with chemical shifts in the range δ

senting the DAB-type ligand Ar–N=CMe-CMe=N–Ar; Ar –2770 to –2851; the chemical shift of 1g appears at δ –3384

= 2,6-Me₂C₆H₃. Here, low-temperature protonation in ppm. Within the series 1a–1c, which are 2,6-dimethyl-sub-

CH₂Cl₂/MeCN cleanly yielded the Pt^IVhydride (N–N)- stituted at Ar and where the substituents within the series

PtPh₂H(NCMe)⁺which upon heating eliminated benzene change only at the para position of Ar, the ¹⁹⁵Pt chemical

to furnish benzene and (N–N)PtPh(NCMe)⁺in a reaction shift increases (to less negative values) with increasing

for which initial MeCN dissociation was rate limiting. On Hammett σ_psubstituent parameters.^[53]Similarly, within the

the other hand, protonation of (N–N)PtPh₂in CH₂Cl₂in series 1d–1f, which are 2,6-unsubstituted and where changes

the absence of acetonitrile cleanly furnished (N–N)PtPh(η²- occur at the meta and para positions, there is a trend of

C₆H₆)⁺which, upon addition of acetonitrile, underwent increasing chemical shifts with increasing Σ(σ_m+ σ_p). Thus,

substitution of benzene by acetonitrile in an associative pro- there appears to be a normal substituent electronic effect –

cess. In order to expand the scope of our studies, we have higher

now turned our attention to non-DAB diimine ligands.

δ values with increasing electron-withdrawing

power – of the Ar substituents on the ¹⁹⁵Pt NMR chemical

The closely related Ar-BIAN [Ar-BIAN = bis(arylimino)- shifts in compounds that may be readily compared.

acenaphthene, see Scheme 1] ligand system, pioneered by Furthermore, the Ar-BIAN and Ar-BICAT ligand systems

the Elsevier group,^[33–40]has been explored with respect to appear to have a significant effect on the Pt electronic prop-

many catalytic processes, including olefin oligomerization erties, as seen in a comparison of ¹⁹⁵Pt chemical shifts for

and polymerization^[41–45]and olefin/CO copolymeriza- 1a–1g with those for the corresponding Ar-DAB com-

tion.^[46]The Ar-BIAN system is a highly stable, rigid biden- plexes.^[15]The ¹⁹⁵Pt NMR signals for the Ar-BIAN series

tate spectator ligand with interesting electronic proper- occur at approximately 280 ppm higher (less negative)

ties.^[47,48]Elsevier and co-workers suggested that Ar-BIAN chemical shift values compared to those of the correspond-

ligands may act as stronger σ-donors toward the metal ing compounds in the DAB series. This suggests that the

when compared to bpy, and also proposed that the rigid Ar-BIAN ligands are more electron withdrawing than the

Ar-BIAN ligands are rather comparable to open chain R- similarly substituted Ar-DAB ligands, which may be attrib-

DAB analogues in electronic properties, which would be the uted to a greater π acceptor capacity for the extended π

case if the diimine system in the Ar-BIAN ligands is elec- systems of the BIAN ligands.^[54]On the other hand, the

tronically isolated from and has no conjugation with the ¹⁹⁵Pt NMR signal of the Ar-BICAT ligated complex 1g is

naphthalene backbone.^[35]The capacity of this ligand type seen at a more than 500 ppm lower (more negative) chemi-

to support many oxidation states has been amply demon- cal shift value than that of the corresponding Ar-BIAN

strated; for example, Pt Ar-BIAN complexes have been re- complex and thence is located at even more negative chemi-

ported in oxidation states ranging from Pt^0[35]via Pt^II[45]to cal shifts, by about 300 ppm, than the Ar-DAB complexes.

Pt^IV.^[38]Ar-BIAN Pt complexes have found uses in catalytic The catecholate bridge at the backbone therefore appears

hydrosilylation of styrene^[49]and some complexes have to exert a considerable electron donating power towards the

interesting photophysical properties.^[50–52]Surprisingly to metal, transmitted through the diimine ligand core. In sum-

us, to the best of our knowledge no reports have appeared mary, approximate chemical shifts for the Pt^IIdiphenyl

on the use of Ar-BIAN ligand systems in studies of reac- complexes are –2800 for BIAN, –3050 for DAB, and –3380

tions of relevance to C–H bond activation.

for BICAT ligand systems.

In this contribution, we present the synthesis and spec-

troscopic and structural characterization of a series of new

(diimine)Pt^IIcomplexes where the diimine is Ar-BIAN with

Ar = 2,6-Me₂C₆H₃, 2,4,6-Me₃C₆H₂, 4-Br-2,6-Me₃C₆H₂,

3,5-Me₂C₆H₃, 4-MeC₆H₄, and 4-CF₃C₆H₄. In addition, we

report the novel bis(arylimino) catechol-based ligand sys-

tem Ar-BICAT, see Scheme 1. A qualitative description of

the protonation reactions of the corresponding (diimine)-

PtPh₂complexes is also included and discussed in view of

existing knowledge of related reactions.

Results and Discussion

Scheme 2.

Synthesis and Characterization of Metal Complexes: The

air- and moisture-stable platinum complexes 1a–g

Further support for the apparent electronic effect pro-

(Scheme 2) were prepared in good yields by stirring a solu- vided by the diimine backbone structure, as inferred from

tion of (Me₂S)₂PtPh₂and the diimine ligand at ambient the ¹⁹⁵Pt NMR chemical shifts, were obtained from infrared

temperature by adaptation of published procedures.^[15]The ν(CO) spectra of (diimine)PtPh(CO)⁺complexes which

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Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

1

were synthesized by protonolysis of the corresponding (di- tom” non-equivalence was not observed, and the H NMR

imine)PtPh₂complexes in trifluoroethanol under CO. This signals appeared more broadened – possibly indicating

is an adaptation of a published procedure for generation somewhat slowed rotation at –78 °C. This suggest less se-

of (Ar-DAB)PtMe(CO)⁺complexes (see also Experimental vere steric repulsions between the N-aryl methyl protons

section).^[20]The IR ν(CO) spectra of the Ar-BIAN, Ar- and the catechol backbone.

DAB, and Ar-BICAT complexes with Ar = 4-MeC₆H₄ex-

As is commonly seen, Pt^IVhydrides require stabiliza-

hibited CO stretching bands at 2115.6, 2113.8, and tion^[25]by an additional axial ligand, in our case, acetoni-

2113.2 cm^–1, respectively. Whereas the differences are small, trile. When the NMR samples were heated, 2a–g gradually

these data do indeed support the notion that the electronic eliminated benzene starting at approximately –40 °C to fur-

effect of the Pt center is altered by tuning of the diimine nish the corresponding Pt^IIacetonitrile complexes 3a–g

backbone structure. The combined IR and ¹⁹⁵Pt NMR (Scheme 3), for which the spectroscopic data reveal that the

spectroscopic data allow us to confidently assert that the “top-bottom” symmetry has been restored. These com-

BICAT system is a better electron donor than the DAB plexes have been independently synthesized (vide infra).

system, whereas the BIAN system is the poorest donor of

Similar behavior involving protonation at the metal and

the three. We note that the published ν(CO) data for subsequent hydrocarbon elimination has been reported for

[16–18,55]

[15,32]

(ArN=CH–CH=NAr)PtMe(CO)⁺are approximately 4– (Ar-DAB)PtMe₂

and (Ar-DAB)PtPh₂

com-

5 cm^–1higher than those for the corresponding plexes. The formation of 2a–g is fully consistent with pro-

(ArN=CMe-CMe = NAr)PtMe(CO)⁺complexes.^[20]

tonation at Pt to give a coordinately unsaturated, five-coor-

Low-Temperature Protonation of (N–N)PtPh₂in the Pres- dinate Pt^IVhydride intermediate that is trapped by acetoni-

ence of Acetonitrile: In situ protonation of 1a–g was per- trile, in agreement with mechanistic studies on the men-

formed in NMR tubes at –78 °C with HBF₄·Et₂O (see Exp. tioned diimine-Pt dimethyl and diphenyl complexes.^[16,32]

Sect.). Protonation in the presence of [D₃]acetonitrile in

Low-Temperature Protonation of (N–N)PtPh₂in the Ab-

[D₂]dichloromethane led to the immediate formation of the sence of Acetonitrile: Protonation of 1a–g with HBF₄·Et₂O

hexacoordinate Pt^IVhydrides (N–N)PtPh₂H(NCCD₃)⁺in [D₂]dichloromethane in the presence of [D₁₀]Et₂O (see

(2a–g) (Scheme 3). The ¹H NMR spectra of these hexacoor- Experimental section) leads to the quantitative formation

dinate Pt^IVhydrides exhibit characteristic Pt–H singlets at of the Pt^IIπ-benzene complexes (N–N)Pt(C₆H₅)(η²-C₆H₆)⁺

1

δ≈–21 with the expected ¹⁹⁵Pt satellites, J(¹⁹⁵Pt-H) of ap- (4a–g, Scheme 4) at sub-ambient temperatures. The ¹H

1

proximately 1600 Hz. The H NMR spectra show that the NMR spectra of these complexes exhibit a characteristic

two halves of the diimine ligands are symmetry equivalent. singlet arising from the η²-C₆H₆ligand at approximately δ

We infer that the hydride and MeCN ligands occupy the = 7.1 (4a–f) or 6.9 (4g); the lower chemical shift value of

two apical, mutually trans, coordination sites. For the Ar- the latter may again reflect the better donor capacity of

BIAN complexes, the signals that arise from ortho and meta the BICAT system when compared to BIAN. These signals

Ar–H and Ar–Me groups (when sufficiently resolved) have exhibit a somewhat broadened base, which sometimes can

split into two sets of signals of equal intensity. Such dupli- be resolved to reveal broadened ¹⁹⁵Pt satellites where the

cation is not seen for any other signals. This phenomenon is broadening is presumed to arise from spin relaxation

most likely due to restricted rotation around the N–C(aryl) caused by chemical shift anisotropy.^[56–58]Compounds 1a–

bond, where the rotational barrier is imposed by the nearby c underwent facile protonation at –30 °C, in the sense that

ortho protons at the BIAN skeleton. This renders the aryl the reaction was complete by the time that an NMR spec-

hydrogens or methyl groups located at the “top” (hydride trum could be recorded. At this temperature the products

side, see Scheme 3) and “bottom” (MeCN side) of the 4a–c are only partially stable, as slow liberation of benzene

square plane chemically non-equivalent. Such a hindrance is seen. At temperatures of –50 °C and below, the proton-

to rotation was also observed with Ar-DAB complexes.^[15]ations of the Ar-BIAN complexes 1a–c (which are 2,6-Me₂

In the case of the Ar-BICAT complex 2g, such “top-bot- substituted at Ar) were surprisingly slow (30 min or more

Scheme 3.

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J. Parmene, A. Krivokapic, M. Tilset

FULL PAPER

was required for complete reaction), compared to the corre-

In the case of the BICAT complex 1g, protonation to

sponding Ar-DAB complexes (complete reaction by the furnish 4g is immediate at –78 °C. Monitoring of this prod-

time NMR spectra could be recorded).^[15]The slower pro- uct showed no degradation after more than 1 h at that tem-

tonation of these Ar-BIAN complexes than of analogously perature. Decomposition and liberation of benzene was ob-

substituted Ar-DAB complexes with comparable steric served from approximately –60 °C, indicating that the BI-

requirements may be a result of the poorer electron donat- CAT ligand appears to activate the neutral complex toward

ing power of the Ar-BIAN system, as inferred from IR and protonation (as might be expected for a better donor li-

¹⁹⁵Pt NMR spectroscopic data in a previous paragraph. By gand), and the π-benzene complex toward benzene loss,

contrast, compounds 1d–f (2,6-unsubstituted at Ar) were when compared to the BIAN systems.

immediately protonated even at –70 °C, and the corre-

Protonation of 1a–g in the Presence of Acetonitrile at Am-

sponding benzene complexes 4d–f started to slowly lose bient Temperature: Treatment of the (N–N)PtPh₂complexes

benzene already at –50 °C. The Pt-containing products of 1a–g with triflic acid (TfOH) or HBF₄·Et₂O in acetonitrile

these reactions have not been identified. The differences in at ambient temperature led to rapid conversion to the corre-

reactivity between the a–c and d–f series presumably arise sponding monophenyl solvento cations (N–N)PtPh-

from the steric influence of the substituents at Ar in the Ar- (NCMe)⁺(3a–g, Scheme 3). The BF₄salts of 3a–g were

–

BIAN ligands. Since the Ar groups are expected to be more isolated and characterized spectroscopically as well as by

or less perpendicularly oriented with respect to the Pt coor- elemental analysis and, in some cases, by X-ray diffraction

dination plane, the 2,6-Me₂substituents will cause a con- (vide infra). The C_2vsymmetry of the precursors 1a–g was

gestion of the space immediately above and below the coor- clearly broken in 3a–g as evidenced by the two sets of sig-

dination plane. Thus, protonation by the external acid will nals arising from the two halves of the diimine ligands. The

be inhibited in these complexes. On the other hand, the η²- coordinated acetonitrile ligands in the isolated compounds

benzene complexes will be stabilized by the 2,6-dimethyl 3a–g were seen as NMR singlets at δ = 2.06–2.21 ppm; for

4

groups because the displacement of benzene (and other hy- complexes 3a and 3g, a J(¹⁹⁵Pt-H) coupling of 10.3 and

drocarbons) from these and related diimine-Pt complexes 13.9 Hz respectively were seen in this signal. Species 3 are

has been demonstrated to be associative reactions.^[32,59,60]

presumed to form by protonation at Pt with concomitant

elimination of benzene, as reported for Ar-DAB ana-

logues.^[15,32]

Quantitative production of benzene was seen when the

protonation reactions were monitored by NMR spec-

troscopy (done for 1a, e, and g). Complexes 3 were also

generated by addition of acetonitrile to solutions of pre-

formed π-benzene complexes (N–N)Pt(C₆H₅)(π-C₆H₆)⁺

4

(done for 4a, e, and g). Substitution of benzene by acetoni-

trile occurred within approximately 15 min to an extent of

approximately 10% already at –70 °C for 4a and 4e, and

even at –78 °C for 4g. These are temperatures at which the

π-benzene species are stable in the absence of acetonitrile,

clearly consistent with the notion that the substitution of

benzene by acetonitrile occurs associatively.

Scheme 4.

Protonation of 1a–f in the Presence of Acetonitrile at Ele-

vated Temperatures: Treatment of the (Ar-BIAN)PtPh₂

It has been demonstrated that the kinetically preferred complexes 1a–f with triflic acid (TfOH) in acetonitrile at

site of protonation is the Pt center for (Ar-DAB)PtMe₂50 °C overnight led to clean conversion to the correspond-

2+

complexes.^[17,18]We have recently presented experimental ing dicationic Pt^IIspecies (Ar-BIAN)Pt(NCMe)₂(5a–f,

evidence that this is also the case for (Ar-DAB)PtPh₂ana- Scheme 5) which were characterized spectroscopically and,

logues,^[32]a scenario that had already been predicted by in part, by elemental analysis. The triflate salt of 5b was in

DFT calculations.^[61]The distinct difference in protonation addition characterized by X-ray crystallography (vide in-

rates between 1a–c and 1d–f may indirectly support the no- fra).

tion of a metal-centered protonation followed by a rapid

C(phenyl)/H reductive coupling to furnish the π-benzene li-

gand: A metal-based protonation in which the acid ap-

proaches from above or below the coordination plane

should be considerably inhibited by the 2,6-Me₂-substituted

aryl groups. On the other hand, a ligand-centered proton-

ation might be less dependent on the nature of these substit-

uents, especially if the putative approach of the acid

towards the phenyl ligand occurs more or less in the coordi-

nation plane.

Scheme 5.

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Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

Double protonation of diimine Pt dimethyl complexes to

Certain key features are common to all structurally char-

furnish related dicationic species has been reported pre- acterized compounds. They all have the square-planar envi-

viously to occur when (Ar-DAB)PtMe₂complexes are ronment that is expected around Pt^II. The deviations from

treated with TfOH or BF₃in trifluoroethanol.^[21]Complex the least-squares planes defined by the central Pt atom and

5b appears to be the first structurally characterized (di- the four Pt-bonded atoms are in the range of 0.0–0.057 Å

2+

imine)Pt(NCMe)₂complex. We recently have reported for Pt and 0.001–0.052 Å for the attached C or N atoms

that an analogous double protonation of an (Ar-DAB)- (further details on the metric parameters can be found in

PtPh₂complex occurs with TfOH, but not with HBF₄, in the respective crystallographic cif files, see Experimental

MeCN at temperatures above ambient.

part). The sum of the four cis L–Pt–LЈ angles around plati-

The C_2vsymmetry of the precursor 1a–f was clearly pre- num is 360Ϯ0.3° for all compounds. The acenaphthene

served as evidenced by the observation of one set of signals backbone lies in the coordination plane defined by Pt, N1

arising for the two halves of the diimine ligands. The coor- and N2. The backbone plane of the BICAT ligand as de-

dinated acetonitrile ligands in the isolated compounds 5a– fined by the catechol ring is only slightly bent from the co-

b and 5d–e appeared as singlets at δ = 2.24–2.37 with no ordination plane by a 7.6° angle. The rather slight deviation

discernible ⁴J(¹⁹⁵Pt-H) couplings. Compounds 5c and 5f from coplanarity suggests that electronic communication

were characterized in situ due to decomposition during at- between the backbone skeleton and the diimine-metal

tempted purification. We surmise that the Pt^IIspecies 5 are structure may occur through the ligand π system.

produced by two successive protonation/benzene elimi-

Some interesting differences may be found, to be dis-

nation sequences but have made no attempts at investiga- cussed in the following paragraph, when comparisons are

ting the finer details of the underlying reaction mechanism. made between neutral, monocationic, and dicationic species

X-ray Crystal Structures: Crystals of 1a, 1b, 1e, 1g, 3a, on one side, and between BIAN, BICAT, and DAB ligated

3b, 5a, and 5b were subjected to structure determinations systems of same charge on the other.

by X-ray crystallography. Selected bond lengths and angles

are summarized in Table 1. Figure 1 shows ORTEP draw- the three neutral Ar-BIAN complexes 1a, 1b, and 1e. The

ings of all solid-state structures. corresponding chelate bite angles average 77.7°. In the

The Pt–N(diimine) bond lengths average 2.120 Å for

Table 1. Selected bond lengths and angles for 1a, 1b, 1e, 1g, 3a, 3b, and 5b.

Compound

1a

1b

1e

1g

3a

3b

5b

Bond lengths

Pt1 N1

Pt1 N2

Pt1 N3

Pt1 N4

Pt1 C31

Pt1 C37

N1 C1

N2 C2

C1 C2

2.115(2)

2.138(2)

–

2.122(2)

2.107(2)

–

2.1180(19)

–

2.001(2)

–

1.290(3)

–

2.1427(17)

2.1492(17)

–

2.014(3)

2.111(3)

1.969(3)

–

2.010(3)

–

1.300(4)

1.286(4)

1.488(4)

–

2.014(3)

2.115(3)

1.965(3)

–

2.011(4)

–

1.301(5)

1.286(5)

1.490(5)

–

2.027(5)

1.997(5)

1.997(7)

1.983(6)

–

2.002(3)

2.020(3)

1.287(4)

1.291(4)

1.489(4)

–

1.994(3)

1.998(3)

1.282(3)

1.288(3)

1.487(4)

–

1.991 (2)

1.988 (2)

1.280(3)

1.279(3)

1.478(3)

–

1.308(4)

1.281(4)

1.494(4)

–

C1 C1

1.482(4)

Bond angles

N1 Pt1 N2

N1 Pt1 C31

N2 Pt1 C37

C31 Pt1 C37

Pt1 N1 C1

Pt1 N2 C2

C1 N1 C22

C2 N2 C13

C13 N1 C1

N1 Pt1 N3

N2 Pt1 N3

N3 Pt1 C31

77.86(10)

93.04(11)

95.54(11)

93.50(12)

114.3(2)

113.0(2)

118.5(2)

118.9(2)

–

77.62(8)

97.13(9)

95.73(9)

89.52(10)

113.89(17)

114.47(18)

118.8(2)

120.2(2)

–

77.68(11)

97.40(9)

–

87.53(13)

114.06(15)

–

76.75(7)

97.85(7)

97.93(7)

87.38(8)

114.12(14)

113.75(13)

120.30(18)

120.17(17)

–

79.76(11)

97.05(12)

–

80.08(12)

97.89(14)

–

114.1(3)

112.1(2)

117.0(3)

122.5(3)

–

171.33(13)

91.81(13)

90.36(14)

80.76(19)

–

113.3(4)

114.3(4)

122.2(5)

118.2(5)

–

174.6(2)

95.3(2)

–

114.5(2)

112.3(2)

118.5(3)

121.7(3)

–

172.51(12)

93.11(12)

89.93(13)

–

118.46(19)

–

Torsion angles

C1 N1 C22 C27

C2 N2 C13 C18

C1 N1 C13 C18

C36 C31 Pt1 N1

C42 C37 Pt1 N2

87.5(4)

–84.3(4)

–

71.5(2)

–53.4(3)

104.1(3)

–84.4(3)

–

120.9(2)

–72.1(3)

–

130.8(3)

–135.7(3)

–

90.8(2)

–95.2(2)

82.3(5)

–93.9(5)

–

52.9(3)

–

100.5(4)

–105.0(4)

75.7(8)

–80.0(9)

–

63.8(3)

58.7(2)

–

127.2(3)

–

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Figure 1. ORTEP drawings of (N–N)Pt^IIcomplexes 1a, 1b, 1e, 1g, 3a–b, and 5b. 50% probability ellipsoids are shown (hydrogen atoms

are removed for clarity. In 5b there are two molecules in the asymmetric unit, but only one is shown for clarity).

monocationic complexes 3a and 3b the Pt–N(diimine) dis- and 3b (2.011 Å); a modest change in the same direction

tances average 2.064 Å whereas the bite angles are 79.2°. was seen in the Ar-DAB systems.^[15]When the three ligand

Finally, in the dicationic complex 5b, the average Pt–N(di- systems Ar-BIAN, Ar-BICAT, and Ar-DAB are com-

imine) distance is 2.009 Å whereas the bite angle is 80.8°. pared for (diimine)PtPh₂compounds, it is noteworthy that

Thus, Pt–N(diimine) bonds are, as might be expected, the Pt–N(diimine) bond lengths decrease from Ar-BICAT

shortened when the positive charge increases, and this (2.146) Å via Ar-BIAN (2.120 Å) to Ar-DAB (2.103 Å).

bond shortening has the consequence of slightly increas- The average Pt–C(phenyl) bond lengths show less varia-

ing the ligand bite angle. The replacement of a phenyl tion but tend to decrease in the opposite order, i.e. from

ligand by MeCN might also contribute to the bite angle Ar-DAB (2.011 Å) via Ar-BIAN (2.003 Å) to Ar-BICAT

increase. For the previously reported^[15](Ar-DAB)PtPh₂(1.990 Å). Although variations in metric parameters are

and (Ar-DAB)PtPh(NCMe)⁺systems, a similar trend modest, the data may suggest that the Ar-BICAT system

towards Pt–N(diimine) bond shortening (from 2.103 Å to has a somewhat weaker trans influence than the Ar-BIAN

2.053 Å) and chelate bite angle opening (from 75.8 to and Ar-DAB systems. There appears to be no significant

77.7°) is also seen when the neutral and charged systems differences in the C=N and C–C bond lengths of the li-

are compared. The average Pt–C(phenyl) bond lengths in gand backbone when the neutral complexes of Ar-BIAN,

neutral Ar-BIAN complexes 1a, 1b, and 1e (2.003 Å) are Ar-DAB, and Ar-BICAT ligands are compared. In the

slightly shorter than in the two cationic counterparts 3a neutral Ar-BIAN complexes 1a–1e, the N–Pt–N bite an-

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Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

Table 2. Crystallographic data for 1a, 1b, 1e, 1g, 3a, 3b, and 5b.

Compound

Formula

1a

1b

1e

1g

3a

3b

5b

C₄₀H₃₄N₂Pt C₄₂H₃₈N₂Pt C₃₈H₃₀N₂Pt·

C₃₄H₂₈N₂O₂Pt· C₃₆H₃₂N₃PtBF₄· C₃₈H₃₆N₃PtBF₄· C₃₄H₂₈N₄Pt(CF₃SO₃)₂

2CH₂Cl₂

879.62

black

1.5CH₂Cl₂

819.10

red

2CH₂Cl₂

958.43

red

CH₂Cl₂

901.55

red

Formula weight

Color

737.8

green

765.87

black

985.84

red

Crystal system

Space group

triclinic

P1

monoclinic

P2₁/n

monoclinic

C2/c

monoclinic

C2/c

triclinic

P1

monoclinic

P2₁/c

monoclinic

C2/c

¯

a [Å]

b [Å]

c [Å]

α

7.7564(15)

9.6428(18)

21.685(4)

85.280(3)

79.733(3)

87.308(3)

1589.7(5)

2

10.9971(6)

24.7328(15)

12.5147(7)

90

95.378(2)

90

16.250(6)

23.643(9)

9.052(3)

90

93.499(4)

90

26.9288(10)

16.3437(6)

18.4914(13)

90

128.35

90

12.470(4)

13.713(4)

13.834(4)

64.476(3)

88.788(3)

67.244(3)

1938.2(10)

2

16.7874(18)

13.0774(14)

17.1024(18)

90

92.5320(10)

90

45.443(7)

15.064(2)

23.998(4)

90

110.685(2)

90

β

γ

V [Å³]

3388.9(3)

4

3471(2)

4

6382.7(6)

8

3750.9(7)

4

15369(4)

16

Z

T [K]

105

103

105

F(000)

732

1528

1736

3224

944

1784

7742

Radiation

λ

Mo-K_α

0.71073 Å

θ range [°]

Reflection measured

Unique reflections

1.9 to 28.4

14164

7260

1.7 to 28.3

27077

8357

1.52 to 27.56

14136

3985

1.57 to 28.74

27916

7718

1.66 to 28.60

17664

8986

1.96 to 27.13

30983

8269

1.60 to 27.12

64440

16927

Number of data/restraint/param. 6484/0/388

6140/0/406

1.1030

3595/0/214

1.0330

6291/0/395

1.1257

7672/0/460

1.1055

6175/0/451

1.0015

13564/472/961

1.221

Goodness of fit, F

1.0775

R₁, w R₂[IϾ3 σ (I)]

0.027, 0.03

1.47, –1.26

0.020, 0.022

1.33, –0.95

0.0208, 0.0225 0.0162, 0.0169

1.06, –0.77 0.80, –0.50

0.0286, 0.0296

1.07, –0.97

0.0263, 0.0289

2.07, –0.88

0.0545*, 0.1481*

5.956, –1.177

Largest diff. peak [eÅ^–3]

* Refined on F². Values are for R₁, w R₂[IϾ2 σ (I)].

gle is rather constant at 77.62–77.86° but undergoes a sizes the steric hindrance imposed by the 2,6-dimethyl-sub-

slight decrease to 76.75° in Ar-BICAT complex 1g and a stituted N-aryl groups: The perpendicular orientation of

further decrease to 75.47–75.88° in the previously pub- these N-aryl groups with respect to the coordination plane

lished^[15]Ar-DAB complexes.

causes the methyl groups to sterically block the access to Pt

In the cationic compounds 3a and 3b, the Pt–N(aceton- from above and below the coordination plane. This has a

itrile) distances (1.967 Å) are shorter than the average Pt– pronounced effect on the qualitative protonation rates and

N(diimine) distances (2.064 Å) by approximately 0.1 Å. The on the stabilities of the Pt^IIπ-benzene complexes, as dis-

Pt–N1 bond lengths trans to MeCN [2.014(3) Å] are signifi- cussed earlier.

cantly shorter than the Pt–N2 bond lengths trans to phenyl

Mechanistic Issues: Scheme 6 summarizes the current

(2.113 Å) by approximately 0.1 Å, clearly as a result of the view of the mechanisms that operate for protonation-in-

greater trans influence of the phenyl compared to the aceto- duced benzene eliminations from (diimine)PtPh₂com-

nitrile ligand. In the dicationic complex 5b, the average Pt– plexes.^[32]

N(acetonitrile) distance of 1.997 Å is slightly longer than in

We have reported that (Ar-DAB)PtMe₂complexes un-

the monocationic species 3a and 3b. It remains to be seen dergo protonation with the metal center as the kinetically

whether these changes in bond lengths and angles correlate preferred site of attack.^[18]Recent DFT calculations suggest

with relative chemical reactivities that are under investiga- that this also holds true for protonation of (Ar-

tion in our group.

DAB)PtPh₂complexes,^[61]a conclusion that has been

The phenyl ligands and the N-aryl groups of the diimines supported by recent kinetic studies in our group.^[32]Simi-

are twisted away from planarity with the Pt coordination larly, the formation of Pt^IVhydrides (Ar-BIAN)-

plane, as inferred from the torsion angles in Table 2. The PtPh₂H(NCMe)⁺and (Ar-BICAT)Ph₂H(NCMe)⁺by pro-

aryl groups are twisted out of the coordination plane by tonation of square-planar Pt^IIprecursors is in agreement

83° and 77–82°, respectively, in complexes 1a and 1b which with a metal-centered protonation.

are 2,6-dimethyl-substituted at the aryl. The corresponding

The π-benzene complexes 4a–c, sterically shielded at Pt

twist angles are 64.5° and by 51–54° in complexes 1e and by the 2,6-Me₂substituents at the N-aryl groups, are

1g, respectively, which are not 2,6-dimethyl-substituted. The formed at approximately –30 °C by protonation with HBF₄

torsion angles of the phenyl groups with respect to the co- in dichloromethane. Formation of the corresponding com-

ordination plane span 59–78° in compounds 1a and 1b and plexes 4d–f, sterically less shielded, occurs at much lower

61–86° in 1e and 1g. These differences reflect the increased temperatures, approximately –60 °C. The consequential dif-

steric demands of the 2,6-dimethyl-substituted systems and ference in protonation rates between 1a–c and 1d–f sup-

appear to be a common feature for N,NЈ-diaryl-substituted ports the notion of a metal-centered protonation followed

(N–N)PtX₂complexes where similar trends in dihedral by a rapid phenyl-C/H reductive coupling to furnish the π-

angles have been reported.^{[15,36,44,45,54,60,62–67]}This empha- benzene ligand: A metal-based protonation in which the

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Scheme 6.

acid approaches from above or below the coordination π-benzene complex is an intermediate in the elimination of

plane should be considerably inhibited by the 2,6-Me₂-sub- benzene from 3a, as discussed in our recent contribution.^[32]

stituted aryl groups, leading to a great difference between

1a–c and 1d–f. By contrast, a ligand-centered protonation

might be less dependent on the nature of these substituents,

especially if the approach of the acid towards the phenyl

ligand occurs more or less in the coordination plane: The

Conclusions

expected difference between 1a–c and 1d–f will be less strik-

ing.

A series of new diimine platinum diphenyl complexes has

been synthesized and subjected to protonation reactions

In our recent study of the protonation of (Ar-DAB)PtPh₂that are of relevance for our on-going investigation of

(Ar = 2,6-Me₂C₆H₄),^[32]one issue that was discussed was mechanistic aspects of Pt-mediated C–H activation reac-

whether the protonation of the neutral Pt^IIcomplex in the tions, which in the past has focused on Ar-DAB supporting

presence of acetonitrile to give (Ar-DAB)PtPh₂H(NCMe)⁺ligands. Thus, the well-known Ar-BIAN diimine structures

was a stepwise process, involving initial protonation fol- have been used, and a novel Ar-BICAT diimine ligand has

lowed by rapid capture of the putative five-coordinate inter- been synthesized. Spectroscopic features of the Ar-BIAN,

mediate (Ar-DAB)PtPh₂H⁺by acetonitrile, or a concerted Ar-BICAT, and Ar-DAB systems have been compared and

process involving simultaneous protonation and acetonitrile suggest that the donor capacity of the ligands decrease in

coordination. The same question is relevant here. We note the order Ar-BICAT Ͼ Ar-DAB Ͼ Ar-BIAN. Further-

that the series of complexes 1a–c are protonated rather more, crystallographic data suggest that the trans influence

slowly in dichloromethane, requiring temperatures as high of the ligands increases in the order Ar-BICAT Ͼ Ar-BIAN

as approximately –30 °C for protonation to occur and fur- Ͼ Ar-DAB. (N–N)PtPh₂complexes based on the Ar-BIAN

nish the π-benzene complexes 4a–c at reasonable rates. By and Ar-BICAT ligands were subjected to protonation reac-

contrast, protonation of 1a–c in dichloromethane contain- tions, as an extension of recently reported work on the ki-

ing acetonitrile proceeds rapidly even at –70 °C to produce netics of an (Ar-DAB)PtPh₂complex.^[32]Very approximate

2a–c. The considerable difference in protonation rates un- assessments of the rates of protonation and the ensuing re-

der these different conditions is certainly consistent with an actions lead to some tentative conclusions regarding the in-

acetonitrile-assisted protonation event, i.e. a scenario that fluence of the ligands on the reactivity patterns. First of all,

bypasses the five-coordinate species as discrete intermedi- the behavior of all the systems were quite similar in that the

ates. Alternative explanations should however be consid- entire sequence of reactions proceeded in two well-defined

ered, in particular because solvent medium effects may protonation/benzene elimination steps, nicely separated in

strongly influence the kinetics and thermodynamics of the onset temperatures, independently of the diimine structure.

proton transfer.

Spectroscopic data suggest that variations of the diimine

The π-benzene complex 4a appears to be thermally more backbone, i.e. BIAN vs. DAB vs. BICAT, constitute a more

robust in the absence of acetonitrile than the Pt^IVhydrido- powerful way to tune the electronic properties of the ligand

diphenyl complex 3a is in the presence of acetonitrile. system than variations of the N-aryl substituents within a

Whereas 4a decomposes by benzene elimination at approxi- given backbone series. However, regardless of the backbone

mately –30 °C, 3a undergoes benzene elimination at –50 °C structure, the rate of protonation appears to be primarily

without observation of the more robust 4a as an intermedi- controlled by steric factors, best modulated by the presence

ate. The addition of acetonitrile to a solution of 4a leads to or absence of ortho substituents at the N-aryl groups. More

benzene substitution already at –70 °C by what is believed details on the influence of the diimine backbone on related

to be an associative process.^{[15,19,32,60,61]}It is likely that the processes will be addressed in forthcoming reports.

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Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

cause of the limited long-term thermal instability of Ph₂Pt(SMe₂)₂

in our hands, this compound was frequently used without purifica-

tion.

Experimental Section

General Considerations: Deuteriated solvents were used as received

without further drying (CD₂Cl₂, [D₁₀]Et₂O, CD₃CN). NMR spec-

tra were recorded with Bruker DPX200, DPX300, and DRX500

instruments. For low-temperature NMR spectroscopic experi-

ments, the temperature calibration was done using a thermocouple

situated inside a thin glass tube that was inserted into an NMR

tube with methanol. ¹H NMR chemical shifts (δ) are reported in

ppm relative to TMS using the residual proton resonances of the

solvent as a reference (δ = 1.94 in CD₃CN, 5.32 in CD₂Cl₂). In

signal assignments, the terms ArH_o,m,pdenotes protons in the o, m,

p positions of the diimine N-aryl substituents (relative to N-at-

tached carbon), PhH_o,m,pdenotes the o, m, p protons of the Pt-

phenyl ligands, and AnH_o,m,pdenotes protons in the o, m, p posi-

tions of the BIAN skeleton (relative to attachment point of the

Ar-BICAT with Ar = 4-MeC₆H₄: To a solution of pyrocatechol

(277 mg, 2.51 mmol) in THF (20 mL) was added NaH (181 mg,

7.6 mmol). After 45 min and the end of gas evolution, the resulting

solution was added dropwise to a solution of ArЈN=C(Cl)–

C(Cl)=NArЈ (640 mg, 2.10 mmol) in THF (40 mL), upon which

a progressive green coloration appeared. The mixture was stirred

overnight at room temperature. Solid ammonium chloride (400 mg,

7.5 mmol) was added and the mixture was stirred for an additional

15 min. After filtration, the solution was concentrated, and the re-

sulting solid was stirred in pentane for 1 h. The extracts were evap-

orated to give a white solid (450 mg, 63%) that was sufficiently

1

pure (ca. 95% by H NMR) for the following coordination at Pt.

The ligand itself revealed difficult to purify due to decomposition

on silica gel (attempted purification of the ligand by chromatog-

raphy on silica, filtration through Celite, or extraction were unsuc-

cessful). ¹H NMR (200 MHz, CD₂Cl₂): δ = 7.24 (br., 8 H, ArH_o,m),

7.10–7.07 (m, AAЈBBЈ pattern, 4 H, catechol-H), 2.39 (s, 6 H,

ArMe) ppm. ¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 139.4, 135.9,

129.7, 124.9, 123.7, 116.8, 98.9, 21.2 ppm. EI-MS: m/z (%) = 342

(62) [M⁺], 327 (22), 225 (100).

1

five-membered ring). 2D H,¹H-COSY and H,¹H-NOESY NMR

spectroscopic experiments were recorded on the Bruker DPX300

spectrometer equipped with a 5 mm QNP probe to help the assign-

1

ments of H NMR signals. ¹⁹F NMR shifts (δ) are reported using

CCl₃F as an internal reference. ¹⁹⁵Pt NMR shifts (δ) are referenced

according to the 2001 IUPAC “unified scale” recommendation with

Ξ = 21.496784 for 1.2  Na₂PtCl₆in D₂O.^{[68] 195}Pt NMR spectra

were acquired with a 20 ms acquisition time and a 500 ms relax-

ation time between pulses. Backward linear prediction to recalcu-

late the 50 first points of the FID gave good baselines (Bruker

settings: ME-mod = LPbc, ncoef = 200, Lpbin = 130, TDOFF =

50). IR spectra were recorded with a Perkin–Elmer Spectrum One

spectrometer. Elemental analyses were performed by Mikro Kemi

AB, Uppsala, Sweden. Mass spectra were recorded on a Waters

Micromass Q-TOF2W instrument. MS data are given as m/z val-

ues.

General Procedure for Preparation of (Ar–BIAN)PtPh₂(1a–f) and

(Ar-BICAT)PtPh₂(1g): The complexes (diimine)PtPh₂were pre-

pared from Ph₂Pt(SMe₂)₂and the appropriate diimine ligand by

adapting a literature procedure.^[15]A mixture of Ph₂Pt(SMe₂)₂(ca.

300 mg, 63 mmol) and the diimine (ca. 250 mg, 63 mmol) was

stirred overnight at room temperature in toluene (15 mL). The

solution was concentrated and dichloromethane (ca. 15 mL) was

added. The solution was filtered, and concentrated again. The re-

sulting solid was washed with pentane and dried in air to afford

the desired complex as a deep green solid in 63–92% yields.

X-ray Crystallographic Structure Determinations: Crystals of 1a, 1b,

1e, 1g, 3a–b, and 5b were grown from dichloromethane/pentane.

The crystals were mounted on glass fibers with perfluoropolyether.

The data were collected at 105 K using graphite-monochromated

Mo-K_αradiation on a Siemens 1K SMART CCD diffractometer

(1a and 1b) or a Bruker Apex II diffractometer (1e, 1g, 3a,b and

5b). Data collection method: ω-scan, range 0.3°, crystal to detector

distance 5 cm. Data reduction and cell determination were carried

out with the SAINT and XPREP programs.^[69]Absorption correc-

tions were applied by the use of the SADABS program.^[70]All the

structures were solved using the Sir92^[71]or Sir97^[72]programs and

refined on F using the program Crystals.^[73]The non-hydrogen

atoms were refined with anisotropic thermal parameters; the H

atoms were all located in a difference map, but those attached to

carbon atoms were repositioned geometrically. The H atoms were

initially refined with soft restraints on the bond lengths and angles

to regularize their geometry (C–H in the range 0.93–98 Å) and iso-

tropic ADPs [U(H) in the range 1.2–1.5ϫU_eqof the adjacent

atom], after which they were refined with riding constraints. Se-

lected crystallographic data for these complexes are listed in

Table 2.

(2,6-Me₂C₆H₃-BIAN)PtPh₂(1a): From Ph₂Pt(SMe₂)₂(300 mg,

0.63 mmol) and the corresponding diimine (246 mg, 0.63 mmol);

yield 380 mg (82%); green microcrystals. ¹H NMR (200 MHz,

CD₂Cl₂): δ = 8.21 (d, J = 8.0 Hz, 2 H, AnH_p), 7.40 (dd, J = 7.2,

7.1, J = 7.2 Hz, 2 H, AnH_m), 7.08 (br., 6 H, ArH_m,p), 7.03 [d, J =

3

6.6; J(¹⁹⁵Pt-H) = 54.2 Hz, 4 H, PhH_o], 6.79 (d, J = 7.3 Hz, 2 H,

AnH_o), 6.62–6.45 (m, 6 H, PhH_m,p), 2.30 (s, 12 H, ArMe) ppm.

¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 145.3, 137.6, 130.0, 128.4,

126.9, 125.8, 122.6, 121.5, 98.9, 98.8, 17.8 ppm. ¹⁹⁵Pt{¹H} NMR

(107 MHz, CD₂Cl₂): δ = –2770 ppm. C₄₀H₃₄N₂Pt (737.79): calcd.

C 65.12, H 4.64, N 3.80; found C 64.92, H 4.54, N 3.84.

(2,4,6-Me₃C₆H₂-BIAN)PtPh₂(1b): From Ph₂Pt(SMe₂)₂(500 mg,

1.05 mmol) and the corresponding diimine (438 mg, 1.05 mmol);

yield 705 mg (87%); green microcrystals. ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.20 (d, J = 8.4 Hz, 2 H, AnH_p), 7.40 (dd, J = 7.4,

3

7.3 Hz, 2 H, AnH_m), 7.01 [dd, J = 7.2, 1.4, J(¹⁹⁵Pt-H) = 66.6 Hz,

4 H, PhH_o], 6.86 (br. s, 4 H, ArH_m), 6.82 (d, J = 7.2 Hz, 2 H,

AnH_o), 6.59 (br. t, J = 7.2 Hz, 4 H, PhH_m), 6.50 (tt, J = 7.0, 1.4 Hz,

2 H, PhH_p), 2.32 (s, 6 H, ArMe_p), 2.23 (s, 12 H, ArMe_o) ppm.

¹³C{¹H} NMR (125 MHz, CD₂Cl₂): δ = 171.5, 143.0, 137.8, 136.6,

132.5, 130.0, 129.9, 129.0, 128.8, 125.7, 122.6, 121.5, 21.0, 17.7

ppm. ¹⁹⁵Pt{¹H} NMR (107 MHz, CD₂Cl₂): δ = –2777 ppm.

C₄₂H₄₀N₂Pt (767.86): calcd. C 65.70, H 5.25, N 3.65; found C

65.25, H 5.0, N 3.75.

CCDC-737961 (for 1a), -737962 (for 1b), -737963 (for 1e), -737964

(for 1g), -737965, (for 3a) -737966 (for 3b), -737967 (for 5b) contain

the supplementary crystallographic data for this paper. These data

can be obtained free of charge from The Cambridge Crystallo-

graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

(4-Br-2,6-Me₂C₆H₂-BIAN)PtPh₂(1c): From Ph₂Pt(SMe₂)₂

(300 mg, 0.63 mmol) and the corresponding diimine (344 mg,

0.63 mmol); yield 443 mg (78%); green microcrystals. ¹H NMR

(300 MHz, CD₂Cl₂): δ = (d, J = 8.2 Hz, 2 H, AnH_p), 7.46 (dd, J =

8.3, 7.3 Hz, 2 H, AnH_m), 7.22 (br. s, 4 H, ArH_m), 7.01 [dd, J = 7.5,

Synthetic Procedures

The Ar-BIAN ligands,^[36,62,74]the Ar-BICAT precursor^[75]

ArЈN=C(Cl)–C(Cl)=NArЈ with ArЈ = 4-MeC₆H₄, and Ph₂Pt-

[76]

(SMe₂)₂

were prepared according to published procedures. Be-

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J. Parmene, A. Krivokapic, M. Tilset

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3.3, J(¹⁹⁵Pt-H) = 70.8 Hz, 4 H, PhH_o], 6.96 (d, J = 7.1 Hz, 2 H,

AnH_o), 6.64 (br. t, J = 7.0 Hz, 4 H, PhH_m), 6.56 (tt, J = 7.2, 2.4 Hz,

2 H, PhH_p), 2.27 (s, 12 H, ArMe) ppm. ¹³C{¹H} NMR (75 MHz,

CD₂Cl₂): δ = 171.5, 144.3, 141.3, 137.4, 132.7, 131.6, 131.1, 130.5,

3

(100 µL) and CD₂Cl₂(200 µL) was then carefully layered on top of

the solution of 1 in CD₂Cl₂and the tube with contents was main-

tained at –78 °C in a dry ice/acetone bath without mixing of the

layers. This procedure was used to minimize premature protonation

128.7, 126.1, 122.8, 121.9, 119.9, 17.7 ppm. ¹⁹⁵Pt{¹H} NMR of the Pt complex 1. The tube was shaken to mix the layers immedi-

(107 MHz, CD₂Cl₂): δ = –2750 ppm. C₄₀H₃₄Br₂N₂Pt (897.60): ately before it was transferred to the pre-cooled NMR probe at the

calcd. C 53.52, H 3.82, N 3.12; found C 53.30, H 3.65, N 3.20.

desired temperature. The low-temperature ¹H NMR spectra indi-

cated clean conversion of compounds 1 into the corresponding Pt^IV

hydrides 2. No traces of the Pt^IIspecies (N-N)PtPh(NCCD₃)⁺(3)

were seen.

(3,5-Me₂C₆H₃-BIAN)PtPh₂(1d): From Ph₂Pt(SMe₂)₂(300 mg,

0.63 mmol) and the corresponding diimine (246 mg, 0.63 mmol);

yield 422 mg (91%); green microcrystals. ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.18 (d, J = 7.7 Hz, 2 H, AnH_p), 7.42 (dd, J = 7.2,

7.2 Hz, 2 H, AnH_m), 7.23 (d, J = 7.2 Hz, 2 H, AnH_o), 6.97 [dd, J

= 8.1, 1.4, ³J(¹⁹⁵Pt-H) = 71.8 Hz, 4 H, PhH_o], 6.87 (br. s, 2 H,

ArH_p), 6.70 (br. s, 4 H, ArH_o), 6.65 (br. t, J = 7.5 Hz, 4 H, PhH_m),

6.53 (tt, J = 7.2, 1.5 Hz, 2 H, PhH_p), 2.21 (s, 12 H, ArMe) ppm.

¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 138.9, 137.8, 129.9, 129.4,

128.8, 126.1, 123.8, 121.7, 120.3, 21.2 ppm. ¹⁹⁵Pt{¹H} NMR

(107 MHz, CD₂Cl₂): δ = –2849 ppm. C₄₀H₃₄N₂Pt (737.79): calcd.

C 65.12, H 4.64, N 3.80; found C 64.85, H 4.70, N 3.90.

–

(2,6-Me₂C₆H₃-BIAN)PtPh₂H(NCCD₃)⁺BF₄(2a·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 8.24 (d, J = 8.3 Hz, 2 H, AnH_p),

7.56 (t, J = 7.8 Hz, 2 H, AnH_m), 7.19 (t, J = 7.6 Hz, 2 H, ArH_p),

7.13 (d, J = 7.5 Hz, 2 H, ArH_m), 7.06 (d, J = 7.3 Hz, 2 H, ArH_m),

6.89–6.60 (m, 8 H, PhH_o,pand AnH_o), 6.61 (t, J = 7.6 Hz, 4 H,

PhH_m), 2.19 (s, 6 H, ArMe), 2.00 (s, 6 H, ArMe), –20.89 [s, ¹J(¹⁹⁵Pt-

H) = 1598 Hz, 1 H, PtH] ppm.

–

(2,4,6-Me₃C₆H₂-BIAN)PtPh₂H(NCCD₃)⁺BF₄

(2b·BF₄):

¹H

NMR (500 MHz, CD₂Cl₂, –78 °C): δ = 8.23 (d, J = 8.2 Hz, 2 H,

AnH_p), 7.55 (t, J = 7.9 Hz, 2 H, AnH_m), 6.86 (s, 2 H, ArH_m), 6.80

(s, 2 H, ArH_m), 6.80–6.68 (m, 8 H, AnH_o, PhH_o,p), 6.62 (br. t, J =

7.5 Hz, 4 H, PhH_m), 2.28 (s, 6 H, ArMe), 2.12 (s, 6 H, ArMe), 1.93

(4-MeC₆H₄-BIAN)PtPh₂(1e): From Ph₂Pt(SMe₂)₂(264 mg,

0.56 mmol) and the corresponding diimine (200 mg, 0.56 mmol);

yield 270 mg (68%); green microcrystals. ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.18 (d, J = 8.2 Hz, 2 H, AnH_p), 7.40 (t, J = 7.2 Hz,

2 H, AnH_m), 7.12 (app d, J = 7.8 Hz, 6 H, ArH and AnH_o), 6.98

(d, J = 8.3 Hz, 4 H, ArH), 6.92 [dd, J = 8.3, 1.3, ³J(¹⁹⁵Pt-H) =

40.1 Hz, 4 H, PhH_o], 6.62 (br. t, J = 6.9 Hz, 4 H, PhH_m), 6.54 (tt,

J = 7.3, 1.4 Hz, 2 H, PhH_p), 2.39 (s, 6 H, ArMe) ppm. ¹³C{¹H}

NMR (75 MHz, CD₂Cl₂): δ = 138.2, 137.5, 129.9, 129.5, 129.4,

126.2, 123.8, 122.3, 121.6, 21.2 ppm. ¹⁹⁵Pt{¹H} NMR (107 MHz,

CD₂Cl₂): δ = –2851 ppm. C₃₈H₃₂N₂Pt (711.75): calcd. C 64.12, H

4.53, N 3.94; found C 64.00, H 4.20, N 4.00.

1

(s, 6 H, ArMe), –20.99 [s, J(¹⁹⁵Pt-H) = 1605 Hz, 1 H, PtH] ppm.

–

(4-Br-2,6-Me₂C₆H₂-BIAN)PtPh₂H(NCCD₃)⁺BF₄(2c·BF₄): ¹H

NMR (500 MHz, CD₂Cl₂, –78 °C): δ = 8.28 (d, J = 8.3 Hz, 2 H,

AnH_p), 7.61 (t, J = 7.8 Hz, 2 H, AnH_m), 7.31 (s, 2 H, ArH_m), 7.22

(s, 2 H, ArH_m), 6.92 (d, J = 7.4 Hz, 2 H, AnH_o), 6.84–6.70 (m, 6

H, PhH_o,p), 6.66 (br. t, ³J = 7.4 Hz, 4 H, PhH_m), 2.18 (s, 6 H,

ArMe), 1.97 (s, 6 H, ArMe), –20.90 [s, ¹J(¹⁹⁵Pt-H) = 1593 Hz, 1 H,

Pt-H] ppm.

(3,5-Me₂C₆H₃-BIAN)PtPh₂H(NCCD₃)⁺BF₄(2d·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 8.22 (d, J = 8.3 Hz, 2 H, AnH_p),

7.58 (t, J = 7.9 Hz, 2 H, AnH_m), 7.27 (d, J = 7.3 Hz, 2 H, AnH_o),

7.00–6.83 (m, 6 H, PhH_oand ArH_o), 6.75 (br. t, J = 7.2 Hz, 2 H,

PhH_p), 6.69–6.64 (m, 6 H, PhH_mand ArH_o), 6.51 (s, 2 H, ArH_p),

–

(4-CF₃C₆H₄-BIAN)PtPh₂(1f): From Ph₂Pt(SMe₂)₂(370 mg,

0.78 mmol) and the corresponding diimine (365 mg, 0.78 mmol).

The product was purified by chromatography on silica with dichlo-

romethane/pentane (1:1). Yield 370 mg (92%); green microcrystals.

¹H NMR (200 MHz, CD₂Cl₂): δ = 8.24 (d, J = 8.1 Hz, 2 H, AnH_p),

7.54 (d, J = 8.3 Hz, 4 H, ArH_m), 7.44 (d, J = 7.2, 7.2 Hz, 2 H,

AnH_m), 7.20 (app d, J = 7.5 Hz, 6 H, AnH_oand ArH_o), 6.86 [dd,

J = 8.0, 1.6, ³J(¹⁹⁵Pt-H) = 64.7 Hz, 4 H, PhH_o], 6.67–6.55 (m, 6 H,

PhH_m,p) ppm. ¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 141.4, 137.7,

130.8, 129.7, 128.0, 126.5, 126.3, 124.0, 123.0, 122.1 ppm. ¹⁹F

NMR (188 MHz, CD₂Cl₂): δ = –62.57 ppm. ¹⁹⁵Pt{¹H} NMR

(107 MHz, CD₂Cl₂): δ = –2782 ppm. C₃₈H₂₄F₆N₂Pt (817.68):

calcd. C 55.82, H 2.96, N 3.43; found C 55.70, H 3.00, N 3.50.

1

2.18 (s, 6 H, ArMe), 2.10 (s, 6 H, ArMe), –21.46 [s, J(¹⁹⁵Pt-H) =

1608 Hz, 1 H, PtH] ppm.

–

(4-MeC₆H₄-BIAN)PtPh₂H(NCCD₃)⁺BF₄(2e·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 8.22 (d, J = 8.3 Hz, 2 H, AnH_p),

7.56 (t, J = 7.9 Hz, 2 H, AnH_m), 7.14–7.09 (m, 6 H, ArH and

AnH_o), 6.95 (d, J = 7.9 Hz, 2 H, ArH), 6.93–6.84 (m, 6 H, ArH

and PhH_o), 6.76 (t, J = 7.3 Hz, 2 H, PhH_p), 6.62 (t, J = 7.5 Hz, 4

1

H, PhH_m), 2.33 (s, 6 H, ArMe), –21.37 [s, J(¹⁹⁵Pt-H) = 1608 Hz,

1 H, PtH] ppm.

(4-MeC₆H₄-BICAT)PtPh₂(1g): The diimine (350 mg, 1 mmol) was

added to a toluene suspension of Ph₂Pt(SMe₂)₂(485 mg, 1 mmol)

and stirred overnight under inert atmosphere. Filtration and con-

centration gave a red mixture that was purified by chromatography

on silica with dichloromethane/pentane (1:1). Yield 488 mg (69%);

red microcrystals. ¹H NMR (300 MHz, CD₂Cl₂): δ = 7.19 and 7.11

(two m, AAЈBBЈ pattern, 2 H each, catechol-H), 6.98 (br. d, J =

8.3 Hz, 4 H, ArH), 6.92–6.86 (m, 8 H, ArH and PhH_o), 6.57–6.53

(m, 6 H, PhH_m,p), 2.30 (s, 3 H, ArMe) ppm. ¹³C NMR (75 MHz,

CD₂Cl₂): δ = 140.9, 138.3, 138.2, 138.0, 137.4, 128.7, 126.7, 126.2,

124.0, 121.5, 117.4, 21.1 ppm. ¹⁹⁵Pt{¹H} NMR (107 MHz,

CD₂Cl₂): δ = –3384 ppm. C₃₄H₂₈N₂O₂Pt·H₂O (709.69): calcd. C

57.54, H 4.26, N 3.96; found C 57.65, H 4.17, N 4.10.

(4-CF₃C₆H₄-BIAN)PtPh₂H(NCCD₃)⁺BF₄(2f·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 8.27 (d, J = 8.3 Hz, 2 H, AnH_p),

7.62 (d, J = 8.5 Hz, 2 H, ArH), 7.60 (t, J = 7.9 Hz, 2 H,AnH_m),

7.55 (d, J = 8.3 Hz, 2 H, ArH), 7.35 (d, J = 7.9 Hz, 2 H, ArH),

7.17 (d, J = 7.3 Hz, 2 H, AnH_o), 7.10 (d, J = 8.0 Hz, 2 H, ArH),

–

6.84 [d, J = 7.5, J(¹⁹⁵Pt-H) = 60.3 Hz, 4 H, PhH_o], 6.75 (br. t, J

3

= 7.3 Hz, 2 H, PhH_p), 6.60 (br. t, J = 7.4 Hz, 4 H, PhH_m), –21.15

1

[s, J(¹⁹⁵Pt-H) = 1592 Hz, 1 H, PtH] ppm.

(4-MeC₆H₄-BICAT)PtPh₂H(NCCD₃)⁺BF₄(2g·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 7.21–7.19 (m, 2 H, catechol-H),

7.11–7.09 (m, 2 H, catechol-H), 6.95 (br. d, J = 7.9 Hz, 4 H, ArH),

6.82–6.79 (m, 8 H, ArH and PhH_o), 6.74 (br. t, J = 7.5 Hz, 2 H,

PhH_p), 6.59 (br. t, J = 7.9 Hz, 4 H, PhH_m), 2.23 (s, 6 H, ArMe),

–

General Procedure for in Situ Generation of (N–N)PtPh₂H-

(NCCD₃)⁺(2a–g) as BF₄^–Salts: The appropriate (N–N)PtPh₂com-

plex 1 (ca. 4 mg, 5 µmol) was dissolved in CD₂Cl₂(400 µL) and

kept under inert atmosphere at –78 °C in an NMR tube. A pre-

made mixture of HBF₄·Et₂O (5 µL, ca. 40 µmol) in CD₃CN

1

–21.61 [s, J(¹⁹⁵Pt-H) = 1594 Hz, 1 H, PtH] ppm.

General Procedure for the Synthesis of (N–N)PtPh(NCMe)⁺(3a–g)

–

as BF₄Salts: HBF₄·Et₂O (22 µL, 0.16 mmol) was added dropwise

1390

www.eurjic.org

Eur. J. Inorg. Chem. 2010, 1381–1394

Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

to a stirred solution of (N–N)PtPh₂(ca. 100 mg, depending on the

diimine, 0.14 mmol) in acetonitrile at 0 °C under an argon atmo-

sphere. The solution was stirred and gradually warmed to ambient

temperature. After 1 h the solvent was removed under vacuum, and

the resulting red-orange solid was washed several times with ether.

The product was recrystallized from a dichloromethane solution

layered with ether.

(75 MHz, CD₂Cl₂): δ = 144.4, 140.8, 139.9, 135.5, 133.0, 132.5,

131.2, 130.5, 129.7, 126.3, 125.6, 124.7, 120.5, 119.2, 21.5, 21.1, 3.7

ppm. ¹⁹F NMR (188 MHz, CD₂Cl₂): δ = –153.04, –153.10 (¹⁰BF₄

–

and ¹¹BF₄) ppm. ¹⁹⁵Pt NMR (107 MHz, CD₂Cl₂): δ = –3216 ppm.

C₃₆H₃₂BF₄N₃Pt (788.54): calcd. C 54.8, H 4.1, N 5.3; found C 53.8,

H 4.3, N 5.7. ESI MS: m/z = 701.1 [M⁺].

–

(4-MeC₆H₄-BIAN)PtPh(NCMe)⁺BF₄^–(3e·BF₄): From 1e (100 mg,

1

(2,6-Me₂C₆H₃-BIAN)PtPh(NCMe)⁺BF₄

(3a·BF₄): From 1a

–

0.14 mmol). Yield 58 mg (54%). H NMR (300 MHz, CD₂Cl₂): δ

(113 mg, 0.15 mmol). Yield 88 mg (73%). ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.35 (d, J = 7.1 Hz, 1 H, AnH_p), 8.33 (d, J = 7.1 Hz,

1 H, AnH_p), 7.64 (dd, J = 8.3, J = 8.3 Hz, 1 H, AnH_m), 7.54 (dd,

J = 8.3, J = 8.3 Hz, 1 H, AnH_m), 7.44 (br., 3 H, ArH), 7.22 (t, J

= 8.3 Hz, 1 H, ArH_p), 7.16 (d, J = 7.0 Hz, 1 H, AnH_o), 7.09 (d, J

= 7.7 Hz, 2 H, ArH_m), 6.89–6.87 (m, 2 H, PhH_o), 6.74–6.71 (m, 3

H, PhH_m,p), 6.69 (d, J = 7.2 Hz, 1 H, AnH_o), 2.50 (s, 6 H, ArMe),

2.24 (s, 6 H, ArMe), 2.06 [s, ⁴J(Pt-H) = 10.3 Hz, 3 H, NCMe] ppm.

¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 148.2, 142.2, 135.1, 133.7,

133.0, 132.2, 130.5, 130.4, 140.0, 129.6, 129.4, 129.1, 127.0, 125.6,

125.5, 125.2, 124.9, 18.0, 17.9, 3.2 ppm. ¹⁹F NMR (188 MHz,

= 8.30 (d, J = 8.2 Hz, 1 H, AnH_p), 8.28 (d, J = 7.8 Hz, 1 H, AnH_p),

7.62 (t, J = 7.8 Hz, 1 H, AnH_m), 7.57–7.45 (m, 6 H, AnH_o,mand

ArH), 7.11 (d, J = 8.0 Hz, 2 H, ArH), 6.93–6.85 (m, 5 H, ArH,

AnH_oand PhH_o), 6.74–6.72 (m, 3 H, PhH_m,p), 2.57 (s, 3 H, ArMe),

2.36 (s, 3 H, ArMe), 2.20 (br. s, 3 H, NCMe) ppm. ¹³C{¹H} NMR

(75 MHz, CD₂Cl₂): δ = 178.6, 171.4, 147.9, 142.4, 142.0, 140.5,

139.7, 135.8, 133.1, 132.5, 132.2, 130.9, 130.7, 130.2, 129.6, 127.2,

126.2, 125.9, 125.5, 125.1, 124.5, 122.8, 121.9, 21.4, 21.6, 3.8 ppm.

–

¹⁹F NMR (188 MHz, CD₂Cl₂): δ = –152.88, –152.93 (¹⁰BF₄and

¹¹BF₄) ppm. ¹⁹⁵Pt NMR (107 MHz, CD₂Cl₂): δ = –3216 ppm.

–

C₃₄H₂₈BF₄N₃Pt (760.49): calcd. C 53.7, H 3.7, N 5.5; found C 51.3,

H 3.8, N 5.1. ESI MS: m/z = 673.1 [M⁺].

–

CD₂Cl₂): δ = –153.02, –153.07 (¹⁰BF₄and ¹¹BF₄) ppm. ¹⁹⁵Pt

NMR (107 MHz, CD₂Cl₂): δ = –3170 ppm. C₃₆H₃₂BF₄N₃Pt

(788.54): calcd. C 54.8, H 4.1, N 5.3; found C 54.0, H 4.3, N 5.3.

ESI MS: m/z = 701.1 [M⁺].

(4-CF₃C₆H₄-BIAN)PtPh(NCMe)⁺BF₄^–(3f·BF₄): From 1f (100 mg,

–

1

0.12 mmol). Yield 60 mg (56%). H NMR (300 MHz, CD₂Cl₂): δ

= 8.34 (d, J = 6.8 Hz, 1 H, AnH_p), 8.32 (d, J = 7.0 Hz, 1 H, AnH_p),

8.06 (d, J = 8.4 Hz, 2 H, ArH), 7.82 (d, J = 6.2 Hz, 2 H, ArH),

7.64 (dd, J = 7.5, 8.2 Hz, 1 H, AnH_m), 7.58–7.51 (m, 3 H, AnH_m

and ArH), 7.39 (d, J = 7.3 Hz, 1 H, AnH_o), 7.24 (d, J = 8.3 Hz, 2

H, ArH), 6.92 (d, J = 8.3 Hz, 1 H, AnH_o), 6.86–6.84 (m, 2 H,

PhH_o), 6.72–6.70 (m, 3 H, PhH_m,p), 2.21 (s, 3 H, NCMe) ppm.

¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 135.5, 133.7, 133.1, 132.3,

129.9, 127.9, 127.6, 127.0, 126.3, 125.9, 125.6, 124.8, 124.0, 123.0,

3.8 ppm. ¹⁹F NMR (188 MHz, CD₂Cl₂): δ = –62.65 (s, Ar-CF₃),

(2,4,6-Me₃C₆H₂-BIAN)PtPh(NCMe)⁺BF₄(3b·BF₄): From 1b

(100 mg, 0.13 mmol). Yield 90 mg (85%). ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.35 (d, J = 7.9 Hz, 1 H, AnH_p), 8.33 (d, J = 7.6 Hz,

1 H, AnH_p), 7.64 (dd, J = 7.4, 7.3 Hz, 1 H, AnH_m), 7.54 (dd, J =

7.5, 7.2 Hz, 1 H, AnH_m), 7.24 (br. s, 2 H, ArH_m), 7.18 (d, J =

7.2 Hz, 1 H, AnH_o), 6.89 (br. s, 2 H, ArH_m), 6.89–6.85 (m, 2 H,

PhH_o), 6.75–6.72 (m, 4 H, AnH_oand PhH_m,p), 2.47 (s, 3 H, Ar-

Me_p), 2.45 (s, 6 H, ArMe_o), 2.30 (s, 3 H, ArMe_p), 2.16 (s, 6 H,

ArMe_o), 2.07 (s, 3 H, NCMe) ppm. ¹³C{¹H} NMR (75 MHz,

CD₂Cl₂): δ = 178.9, 148.0, 140.2, 139.9, 139.4, 139.1, 135.3, 133.5,

132.8, 130.4, 130.3, 130.1, 129.9, 129.6, 128.8, 126.9, 125.7, 125.5,

124.9, 21.2, 21.1, 17.9, 17.2, 3.2 ppm. ¹⁹F NMR (188 MHz,

–

–63.02 (s, Ar-CF₃), –152.35 and –152.40 (¹⁰BF₄and ¹¹BF₄) ppm.

¹⁹⁵Pt NMR (107 MHz, CD₂Cl₂): δ = –3240 ppm. C₃₄H₂₂BF₁₀N₃Pt

(868.43): calcd. C 47.0, H 2.6, N 4.8; found C 46.2, H 2.7, N 4.9.

ESI MS: m/z = 781.0 [M⁺].

CD₂Cl₂): δ = –153.11, –153.16 (¹⁰BF₄and ¹¹BF₄) ppm. ¹⁹⁵Pt

NMR (107 MHz, CD₂Cl₂): δ = –3164 ppm. C₃₈H₃₆BF₄N₃Pt

(816.60): calcd. C 55.9, H 4.4, N 5.2; found C 55.0, H 4.5, N 5.0.

ESI MS: m/z = 729.1 [M⁺].

–

(4-MeC₆H₄-BICAT)PtPh(NCMe)⁺BF₄

(3g·BF₄): From 1g

(100 mg, 0.15 mmol). Yield 89 mg (83%). ¹H NMR (200 MHz,

CD₂Cl₂): δ = 7.43 (br., 4 H, ArH), 7.31–7.20 (m, 3 H, catechol-H),

7.14–7.08 (m, 1 H, catechol-H), 6.95 (br. d, J = 7.9 Hz, 2 H, ArH),

6.87 (br. d, J = 8.1 Hz, 2 H, ArH), 6.83–6.78 (m, 2 H, PhH_o), 6.69–

6.63 (m, 3 H, PhH_m,p), 2.47 (s, 3 H, ArMe), 2.26 (s, 3 H, ArMe),

(4-Br-2,6-Me₂C₆H₂-BIAN)PtPh(NCMe)⁺BF₄(3c·BF₄): From 1c

(100 mg, 0.11 mmol). Yield 71 mg (68%). ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.41 (d, J = 8.4 Hz, 1 H, AnH_p), 8.38 (d, J = 8.4 Hz,

1 H, AnH_p), 7.69 (dd, J = 8.3, 8.3 Hz, 1 H, AnH_m), 7.62 (br. s, 2

H, ArH_m), 7.60 (dd, J = 8.3, 8.3 Hz, 1 H, AnH_m), 7.24 (br. s, 2 H,

ArH_m), 7.21 (d, J = 7.1 Hz, 1 H, AnH_o), 6.86–6.77 (m, 6 H, AnH_o

and PhH_o,m,p), 2.49 (s, 6 H, ArMe), 2.21 (s, 6 H, ArMe), 2.19 (br.

s, 3 H, NCMe) ppm. ¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 178.9,

172.7, 148.4, 141.5, 134.9, 134.2, 133.5, 132.4, 132.3, 132.1, 131.5,

130.6, 130.5, 127.3, 125.6, 125.2, 125.1, 124.9, 122.6, 122.2, 17.9,

17.8, 3.5 ppm. ¹⁹F NMR (188 MHz, CD₂Cl₂): δ = –152.61, –152.65

–

4

2.08 [s, J(¹⁹⁵Pt-NCMe) = 13.9 Hz, 3 H, NCMe] ppm. ¹⁹F NMR

–

(188 MHz, CD₂Cl₂): δ = –152.15, 152.20 (¹⁰BF₄^–and ¹¹BF₄) ppm.

ESI MS: m/z = 655.2 [M⁺].

General Procedure for in situ Generation of (N–N)PtPh(η²-C₆H₆)⁺

–

(4a–g) as BF₄Salts: The appropriate (N-N)PtPh₂complex (ca.

5 mg, 7 µmol) was dissolved in CD₂Cl₂(400 µL) and kept under

an inert atmosphere at –78 °C in an NMR tube. A pre-made mix-

ture of HBF₄·Et₂O (5–10 µL) in [D₁₀]Et₂O (80 µL) and CD₂Cl₂,

for a total volume of 300 µL, was then carefully layered on top of

the solution of 1 in CD₂Cl₂and the tube with contents was main-

tained at –78 °C in a dry ice/acetone bath without mixing of the

layers. This procedure was used to minimize premature protonation

of the Pt complex 1. The tube was shaken to mix the layers immedi-

ately before it was transferred to the pre-cooled NMR probe at the

desired temperature. The low-temperature ¹H NMR spectra indi-

cated clean conversion of compounds 1a–g into the corresponding

Pt^IIphenyl π-benzene complexes 4a–g.

–

(¹⁰BF₄and ¹¹BF₄) ppm. ¹⁹⁵Pt NMR (107 MHz, CD₂Cl₂): δ =

–3177 ppm. C₃₆H₃₀BBr₂F₄N₃Pt (946.33): calcd. C 45.7, H 3.2, N

4.4; found C 44.7, H 3.2, N 4.2. ESI MS: m/z = 857.9, 859.9 [M⁺].

(3,5-Me₂C₆H₃-BIAN)PtPh(NCMe)⁺BF₄

(3d·BF₄): From 1d

–

(100 mg, 0.14 mmol). Yield 82 mg (76%). ¹H NMR (300 MHz,

CD₂Cl₂): δ = 8.30 (d, J = 8.2 Hz, 1 H, AnH_p), 8.28 (d, J = 8.1 Hz,

1 H, AnH_p), 7.62 (dd, J = 7.4, 8.2 Hz, 1 H, AnH_m), 7.52 (dd, J =

7.5, 8.3 Hz, 1 H, AnH_m), 7.47 (d, J = 7.1 Hz, 1 H, AnH_o), 7.24 (br.

s, 1 H, ArH_p), 7.15 (br. s, 2 H, ArH_o), 7.02 (d, J = 7.1 Hz, 1 H,

(2,6-Me₂C₆H₃-BIAN)PtPh(η²-C₆H₆)⁺BF₄(4a·BF₄): ¹H NMR

–

AnH_o), 6.93 (br. s, 1 H, ArH_p), 6.89–6.86 (m, 2 H, PhH_o), 6.77– (500 MHz, CD₂Cl₂, –35 °C): δ = 8.29 (d, J = 8.3 Hz, 1 H, AnH_p),

6.71 (m, 3 H, PhH_m,p), 6.61 (br. s, 2 H, ArH_o), 2.50 (s, 6 H, ArMe),

8.24 (d, J = 8.4 Hz, 1 H, AnH_p), 7.51 (t, J = 7.9 Hz, 1 H, AnH_m),

7.46 (t, J = 7.9 Hz, 1 H, AnH_m), 7.40–7.37 (m, 3 H, ArH), 7.07 (s,

2.20 (s, 6 H, ArMe), 2.19 (s, 3 H, NCMe) ppm. ¹³C{¹H} NMR

Eur. J. Inorg. Chem. 2010, 1381–1394

www.eurjic.org

1391

J. Parmene, A. Krivokapic, M. Tilset

FULL PAPER

6 H, C₆H₆), 7.02 (t, J = 7.6 Hz, 1 H, ArH_p), 6.92 (d, J = 6.7 Hz, 2

H, ArH_m), 6.74 (br. d, J = 7.0 Hz, 2 H, PhH_o), 6.52–6.36 (m, 5 H,

AnH_oand PhH_m,p), 2.29 (s, 6 H, ArMe), 2.20 (s, 6 H, ArMe) ppm.

2.24 (s, 6 H, NCMe) ppm. ¹³C{¹H} NMR (125 MHz, CD₂Cl₂): δ

= 136.2, 131.6, 131.1, 130.5, 127.4, 18.0, 3.0 ppm. ¹⁹F NMR

(188 MHz, CD₂Cl₂): δ = –78.83 ppm. ¹⁹⁵Pt NMR (107 MHz,

CD₂Cl₂): δ = –2391 ppm. C₃₄H₃₀F₆N₄O₆PtS₂(963.82): calcd. C

42.4, H 3.1, N 5.8; found C 43.7, H 3.6, N 6.2. ESI MS: m/z =

332.6 [M²⁺], 312.0 [M²⁺– MeCN].

(2,4,6-Me₃C₆H₂-BIAN)PtPh(η²-C₆H₆)⁺BF₄(4b·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –35 °C): δ = 8.28 (d, J = 8.3 Hz, 1 H, AnH_p),

8.23 (d, J = 8.4 Hz, 1 H, AnH_p), 7.55 (t, J = 8.2 Hz, 1 H, AnH_m),

7.46 (t, J = 8.1 Hz, 1 H, AnH_m), 7.16 (s, 2 H, ArH_m), 7.05 (s, 6 H,

C₆H₆), 6.68 (br. s, 4 H, ArH_mand PhH_o), 6.57 (d, J = 8.2 Hz, 1

–

(2,4,6-Me₃C₆H₂-BIAN)Pt(NCMe)₂²⁺(TfO^–)₂[5b·(TfO^–)₂]: From 1b

(100 mg, 0.13 mmol) and TfOH (40 µL, 0.46 mmol). Yield 102 mg

H, AnH_o), 6.46–6.38 (m, 4 H, AnH_oand PhH_m,p), 2.42 (s, 3 H, (79%). ¹H NMR (300 MHz, CD₂Cl₂): δ = 8.44 (d, J = 8.2 Hz, 2

ArMe_p), 2.25 (s, 6 H, ArMe_o), 2.14 (s, 3 H, ArMe_p), 2.12 (s, 6 H,

ArMe_o) ppm.

H, AnH_p), 7.70 (dd, J = 7.8, 7.7 Hz, 2 H, AnH_m), 7.24 (br. s, 4 H,

ArH_m), 7.08 (d, J = 7.3 Hz, 2 H, AnH_o), 2.46 (br. s, 12 H, ArMe_o),

2.45 (s, 6 H, ArMe_p), 2.34 (s, 6 H, NCMe) ppm. ¹³C{¹H} NMR

(75 MHz, CD₂Cl₂): δ = 182.1, 152.4, 145.8, 141.9, 138.7, 135.8,

132.3, 130.8, 130.5, 127.1, 122.7, 21.3, 18.0, 3.6 ppm. ¹⁹F NMR

(188 MHz, CD₂Cl₂): δ = –78.85 ppm. ¹⁹⁵Pt NMR (107 MHz,

CD₂Cl₂): δ = –2391 ppm. C₃₆H₃₄F₆N₄O₆PtS₂(991.88): calcd. C

43.6, H 3.5, N 5.7; found C 43.3, H 3.5, N 5.3. ESI MS: m/z =

346.6 [M²⁺], 326.0 [M²⁺– MeCN].

(4-Br-2,6-Me₂C₆H₂-BIAN)PtPh(η²-C₆H₆)⁺BF₄

(4c·BF₄): ¹H

–

NMR (500 MHz, CD₂Cl₂, –35 °C): δ = 8.33 (d, J = 8.4 Hz, 1 H,

AnH_p), 8.28 (d, J = 8.4 Hz, 1 H, AnH_p), 7.58–7.49 (m, 4 H, AnH_m

and ArH_m), 7.10 (s, 6 H, C₆H₆), 7.06 (s, 2 H, ArH_m), 6.74 (br., 2

H, PhH_o), 6.62 (d, J = 6.4 Hz, 1 H, AnH_o), 6.57–6.55 (m, 2 H,

AnH_oand PhH_p), 6.49 (br. t, J = 7.1 Hz, 2 H, PhH_m), 2.24 (s, 6

H, ArMe), 2.17 (s, 6 H, ArMe) ppm.

(4-Br-2,6-Me₂C₆H₂-BIAN)Pt(NCCD₃)₂²⁺(TfO^–)₂[5c·(TfO^–)₂]: On

top of a solution of 1c (8 mg, 9 µmol) in [D₂]dichloromethane

(400 µL) was layered 50 µL of [D₂]dichloromethane. Then a pre-

mixed solution of TfOH (3 µL, 0.035 mmol) in [D₃]acetonitrile

(200 µL) was added, and the tube was shaken and kept overnight

–

(3,5-Me₂C₆H₃-BIAN)PtPh(η²-C₆H₆)⁺BF₄(4d·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –55 °C): δ = 8.27 (d, J = 7.3 Hz, 1 H, AnH_p),

8.23 (d, J = 7.4 Hz, 1 H, AnH_p), 7.55 (t, J = 7.5 Hz, 1 H, AnH_m),

7.46 (t, J = 7.7 Hz, 1 H, AnH_m), 7.18 (s, 1 H, ArH_p), 7.12 (s, 6 H,

C₆H₆), 7.08 (s, 2 H, ArH_o), 6.77 (d, J = 9.4 Hz, 1 H, AnH_o), 6.71

(s, 1 H, ArH_p), 6.64 (d, J = 7.7 Hz, 1 H, AnH_o), 6.40 (s, 2 H,

ArH_o), 6.30–6.22 (m, 5 H, PhH_o,m,p), 2.44 (s, 6 H, ArMe), 2.06 (s,

6 H, ArMe) ppm.

1

at 50 °C at which point a bright orange solution was obtained. H

NMR (300 MHz, CD₂Cl₂): δ = 8.43 (d, J = 8.1 Hz, 2 H, AnH_p),

7.70 (dd, J = 8.2, 8.2 Hz, 2 H, AnH_m), 7.59 (br. s, 4 H, ArH_m),

7.07 (d, J = 7.3 Hz, 2 H, AnH_o), 2.46 (s, 12 H, ArMe) ppm.

–

(4-MeC₆H₄-BIAN)PtPh(η²-C₆H₆)⁺BF₄

(4e·BF₄): ¹H NMR

(3,5-Me₂C₆H₃-BIAN)Pt(NCMe)₂²⁺(TfO^–)₂[5d·(TfO^–)₂]: From 1d

(100 mg, 0.13 mmol) and TfOH (40 µL, 0.47 mmol). Yield 85 mg

(65%). ¹H NMR (300 MHz, CD₂Cl₂): δ = 8.23 (d, J = 8.2 Hz, 2

H, AnH_p), 7.62 (dd, J = 8.2, 8.1 Hz, 2 H, AnH_m), 7.40 (br. s, 4 H,

ArH_o), 7.30 (br. s, 2 H, ArH_p), 7.17 (d, J = 7.3 Hz, 2 H, AnH_o),

2.48 (s, 12 H, ArMe), 2.37 (s, 6 H, NCMe) ppm. ¹³C{¹H} NMR

(75 MHz, CD₂Cl₂): δ = 141.4, 134.4, 132.7, 128.9, 127.2, 120.2,

21.4, 3.8 ppm. ¹⁹F NMR (188 MHz, CD₂Cl₂): δ = –78.8 ppm. ¹⁹⁵Pt

NMR (107 MHz, CD₂Cl₂): δ = –2397 ppm. C₃₄H₃₀F₆N₄O₆PtS₂

(963.82): calcd. C 42.4, H 3.1, N 5.8; found C 41.3, H 3.2, N 5.4.

ESI MS: m/z = 346.6 [M²⁺], 326.0 [M²⁺– MeCN].

(500 MHz, CD₂Cl₂, –78 °C): δ = 8.25 (d, J = 8.3 Hz, 1 H, AnH_p),

8.21 (d, J = 8.4 Hz, 1 H, AnH_p), 7.54–7.49 (m, 3 H, AnH_mand 2

ArH), 7.45–7.38 (m, 3 H, AnH_mand ArH), 7.09 (br. s, 6 H, C₆H₆),

6.89 (d, J = 8.1 Hz, 2 H, ArH), 6.73–6.71 (m, 3 H, AnH_oand

ArH), 6.42 (d, J = 7.4 Hz, 1 H, AnH_o), 6.30–6.26 (m, 3 H, PhH_o,p),

6.19 (br. t, J = 7.2 Hz, 2 H, PhH_m), 2.46 (s, 3 H, ArMe), 2.18 (s, 3

H, ArMe) ppm.

–

(4-CF₃C₆H₄-BIAN)Pt(η²-C₆H₆)Ph⁺BF₄

(4f·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –55 °C): δ = 8.31 (d, J = 8.3 Hz, 1 H, AnH_p),

8.28 (d, J = 9.0 Hz, 1 H, AnH_p), 8.02 (d, J = 7.3 Hz, 2 H, ArH),

7.79 (d, J = 8.3 Hz, 2 H, ArH), 7.56 (t, J = 7.3 Hz, 1 H, AnH_m),

7.47 (t, J = 7.3 Hz, 1 H, AnH_m), 7.36 (d, J = 7.3 Hz, 2 H, ArH),

7.10–7.08 (m, 8 H, C₆H₆and 2 ArH), 6.72 (d, J = 7.7 Hz, 1 H,

AnH_o), 6.57 (d, J = 7.7 Hz, 1 H, AnH_o), 6.31–6.29 (m, 3 H,

PhH_o,p), 6.19 (t, J = 7.2 Hz, 2 H, PhH_m) ppm.

(4-MeC₆H₄-BIAN)Pt(NCMe)₂²⁺(TfO^–)₂[5e·(TfO^–)₂]: From 1e

(100 mg, 0.14 mmol) and TfOH (50 µL, 0.56 mmol). Yield 80 mg

(61%). ¹H NMR (300 MHz, CD₂Cl₂): δ = 8.35 (d, J = 8.1 Hz, 2

H, AnH_p), 7.65 (dd, J = 7.5, 7.3 Hz, 2 H, AnH_m), 7.54 (br., 8 H,

ArH), 7.21 (d, J = 7.3 Hz, 2 H, AnH_o), 2.54 (s, 6 H, ArMe), 2.29

(s, 6 H, NCMe) ppm. ¹³C{¹H} NMR (75 MHz, CD₂Cl₂): δ = 141.1,

134.5, 134.1, 131.3, 129.8, 127.1, 123.0, 21.6, 3.9 ppm. ¹⁹F NMR

(188 MHz, CD₂Cl₂): δ = –78.7 ppm. ¹⁹⁵Pt NMR (107 MHz,

CD₂Cl₂): δ = –2407 ppm. C₃₂H₂₆F₆N₄O₆PtS₂(935.77): calcd. C

41.1, H 2.8, N 6.0; found C 39.4, H 2.9, N 5.4. ESI MS: m/z =

318.5 [M²⁺], 298.0 [M²⁺– MeCN].

(4-MeC₆H₄-BICAT)Pt(η²-C₆H₆)Ph⁺BF₄(4g·BF₄): ¹H NMR

(500 MHz, CD₂Cl₂, –78 °C): δ = 7.36–7.32 (m, 4 H, ArH), 7.22–

7.17 (m, 2 H, catechol-H), 7.11 (br. d, J = 7.8 Hz, 1 H, catechol-

H), 7.04 (br. d, J = 7.9 Hz, 1 H, catechol-H), 6.90 (br. s, 6 H,

C₆H₆), 6.72 (d, J = 8.1 Hz, 2 H, ArH), 6.66 (d, J = 7.2 Hz, 2 H,

ArH), 6.25–6.21 (m, 3 H, PhH_o,p), 6.08 (br. t, J = 7.0 Hz, 2 H,

PhH_m), 2.34 (s, 3 H, ArMe), 2.07 (s, 3 H, ArMe) ppm.

–

(4-CF₃C₆H₄-BIAN)Pt(NCCD₃)₂²⁺(TfO^–)₂[5f·(TfO^–)₂]: On top of a

solution of 1f (8 mg, 0.01 mmol) in [D₂]dichloromethane (400 µL)

was layered 50 µL of [D₂]dichloromethane. Then a premixed solu-

tion of TfOH (3 µL, 0.035 mmol) in [D₃]acetonitrile (200 µL) was

added, and the tube was shaken and kept overnight at 50 °C at

which point a bright orange solution was obtained ¹H NMR

(200 MHz, CD₂Cl₂): δ = 8.37 (d, J = 8.2 Hz, 2 H, AnH_p), 8.02 (dd,

J = 9.4, 9.3 Hz, 8 H, ArH), 7.65 (dd, J = 6.8, 7.9 Hz, 2 H, AnH_m),

7.10 (d, J = 7.4 Hz, 2 H, AnH_o) ppm. ¹⁹F NMR (188 MHz,

CD₂Cl₂): δ = –62.48 (s, ArCF₃), –78.66 (s, OTf) ppm.

2+

General Procedure for Synthesis of (N–N)Pt(NCMe)₂(5a–f) as

TfO^–Salts: TfOH (ca. 150 µL, 1 mmol) was added dropwise to a

stirred solution of (N–N)PtPh₂(ca. 100 mg, 0.10 mmol) in acetoni-

trile (3 mL) under argon. The solution was heated to 50 °C and

stirred overnight. The solvent was removed under vacuum, produc-

ing an orange solid which was washed several times with ether.

(2,6-Me₂C₆H₃-BIAN)Pt(NCMe)₂²⁺(TfO^–)₂[5a·(TfO^–)₂]: From 1a

(80 mg, 0.10 mmol) and TfOH (40 µL, 0.46 mmol). Yield 78 mg

(75%). ¹H NMR (300 MHz, CD₂Cl₂): δ = 8.44 (d, J = 8.3 Hz, 2

H, AnH_p), 7.71 (dd, J = 7.4, 7.5 Hz, 2 H, AnH_m), 7.58–7.44 (m, 6

General Procedure for the Preparation and Characterization of (di-

H, ArH_m,p), 7.04 (d, J = 7.3 Hz, 2 H, AnH_o), 2.50 (s, 12 H, ArMe), imine)Pt(CO)Ph⁺BF₄(diimine = 4-MeC₆H₄-DAB, 4-MeC₆H₄-

–

1392

www.eurjic.org

Eur. J. Inorg. Chem. 2010, 1381–1394

Ar-BIAN and Ar-BICAT Diimine Platinum Diphenyl Complexes

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2004, pp. 264–282.

BIAN, 4-MeC₆H₄-BICAT): (4-MeC₆H₄-DAB)PtPh₂was prepared

according to the published procedure.^[20]These compounds were

prepared solely for IR and ¹H NMR characterization by adapta-

tion of a published procedure.^[20]HBF₄·Et₂O (3–6 µL, 0.02–

0.04 mmol) was added to a solution of (diimine)PtPh₂complex

(15–30 mg, 0.02–0.04 mmol) in trifluoroethanol (2 mL). After 18 h

under a CO atmosphere, the solution was concentrated to give an

oily residue. Part of the product was dissolved in CD₂Cl₂for NMR

characterization whereas another part was dissolved in CH₂Cl₂for

IR characterization.

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–

1

(4-MeC₆H₄-DAB)Pt(CO)Ph⁺BF₄: H NMR (200 MHz, CD₂Cl₂):

δ = 7.39 (d, J = 8.1 Hz, 2 H, ArH), 7.25 (d, J = 8.5 Hz, 2 H, ArH),

6.92–6.86 (m, 4 H, ArH, PhH_o), 6.86–6.72 (m, 3 H, ArH, PhH_p),

6.63–6.59 (m, 2 H, PhH_m), 2.46 (s, 3 H, DABMe), 2.44 (s, 3 H,

DABMe), 2.38 (s, 3 H, ArMe), 2.21 (s, 3 H, ArMe) ppm. IR

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16, 1209–1217.

˜

2

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1486.

–

(4-MeC₆H₄-BIAN)Pt(CO)Ph⁺BF₄: ¹H NMR (200 MHz, CD₂Cl₂):

δ = 8.29 (br. d, J = 8.2 Hz, 2 H, AnH_p), 7.68 (t, J = 7.4 Hz, 2 H,

AnH_m), 7.61 (d, J = 7.6 Hz, 1 H, AnH_o), 7.55 (br., 4 H, ArH), 7.51

(d, J = 7.8 Hz, 1 H, AnH_o), 7.09 (d, J = 8.6 Hz, 2 H, ArH), 7.08–

7.02 (m, 2 H, PhH_o), 6.99–6.80 (m, 3 H, PhH_m,p), 6.84 (d, J =

7.6 Hz, 2 H, ArH), 2.56 (s, 3 H, ArMe), 2.35 (s, 3 H, ArMe) ppm.

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IR (CH Cl ): ν = ν(CO) 2115.6 cm^–1.

˜

2

–

(4-MeC₆H₄-BICAT)Pt(CO)Ph⁺BF₄: ¹H NMR (200 MHz,

CD₂Cl₂): δ = 7.54 (br. d, J = 8.4 Hz, 2 H, ArH), 7.39 (br. d, J =

8.3 Hz, 2 ArH), 7.35–7.25 (m, 3 H, catechol-H), 7.19–7.16 (m, 1

H, catechol-H), 7.05–7.00 (m, 2 H, PhH_o), 6.95–6.75 (m, 7 H, ArH

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˜

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Acknowledgments

We gratefully acknowledge generous financial support from the

Norwegian Research Council (stipends to J. P. and A. K.). We

thank Prof. C. H. Gørbitz, University of Oslo, for assistance with

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Received: October 2, 2009

Published Online: February 11, 2010

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Article Doi

Synthesis, characterization, and protonation reactions of Ar-BIAN and Ar-BICAT diimine platinum diphenyl complexes

DOI: 10.1002/ejic.200900975

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