Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(amine)2I2

Inorganica Chimica Acta 357 (2004) 2218–2230

www.elsevier.com/locate/ica

Multinuclear NMR study and crystal structures of complexes

of the types cis- and trans-Pt(amine)₂I₂

*

Fernande D. Rochon , Viorel Buculei

D ꢀe partement de chimie, Universit ꢀe du Qu ꢀe bec ꢁa Montr ꢀe al, C.P. 8888, Succ. Centre-ville, Montreal, Que., Canada H3C 3P8

Received 16 July 2003; accepted 2 October 2003

Available online 4 February 2004

Abstract

Complexes of the types cis- and trans-Pt(amine)2I2 were studied by spectroscopic methods, especially by multinuclear NMR

spectroscopy. In ¹⁹⁵Pt NMR, the cis diiodo compounds with primary amines were observed between )3342 and )3357 ppm in

acetone, while the trans compounds were found between )3336 and )3372 ppm. For the secondary amines, the chemical shifts were

1

13

observed at lower ﬁelds. In H NMR, the trans complexes were observed at higher ﬁelds than the cis compounds, while in C NMR,

1

2

195

1

3

195

the reverse was observed. The J( Pt– H) and J( Pt– H) coupling constants are larger for the cis compounds (ave. 67 and 45 Hz,

1

3

2

195

13

3

195

13

respectively) than for the trans isomers (ave. 59 and 38 Hz). In C NMR, the values of J( Pt– C) and J( Pt– C) were also

found to be larger for the cis complexes (ave. 17 and 39 Hz versus 11 and 28 Hz). There seems to be a slight dependence of the pKa

values of the protonated amines or the proton aﬃnity in the gas phase with the d(Pt) chemical shifts. The crystal structures of eight

diiodo complexes were determined. These compounds are cis-Pt(CH3NH2)2I2, cis-Pt(n-C4H9NH2)2I2, cis-Pt(Et2NH)2I2, trans-Pt(n-

C3H7NH2)2I2, trans-Pt(iso-C3H7NH2)2I2, trans-Pt(n-C4H9NH2)2I2, trans-Pt(t-C4H9NH2)2I2 and trans-Pt(Me2NH)2I2. The Pt–N

bond distances located in trans position to the iodo ligands were compared to those located in trans position to the amines. The Pt–

N bond in cis-Pt(Et2NH)2I2 are much longer than the others, probably caused by the steric hindrance of the two very bulky ligands

located in cis positions.

Keywords: Crystal structures; Platinum; Amines; NMR; Iodo ligands; IR

1

. Introduction

Several earlier studies on the mechanism of action of

cisplatin have been reported [7–11]. Most of the early

work postulated that the main species present in the

cells were the aqua-hydroxo species. More recently,

House and co-workers [12–20] have published a series

of papers on the hydrolysis of cisplatin in diﬀerent

chloride concentrations. They calculated, with various

rate constants, the proportion of the diﬀerent species

inside the cells and in the plasma. At pH 7.4 and

The anti-tumor complex cisplatin, cis-Pt(NH3)2Cl2,

has been known for several decades. Its chemistry has

been studied by many authors. The compound is now

one of the most widely used anti-cancer drug. A good

review of the inﬂuence of structure on the activity of Pt

drugs has been published [1]. It has been observed that

when NH₃is replaced by primary amines, the anti-

tumor activity can sometimes increase, especially for

cyclic amines [2–5], but these compounds have generally

a more limited activity spectrum. Furthermore, some of

the most active complexes with amines are too insoluble

to be useful anti-cancer drugs [6].

ꢀ

[Cl ] ¼ 0.1 M (concentration in the plasma), the main

species are cis-Pt(NH3)2Cl2 (68%), cis-Pt(NH3)2(OH)Cl

þ

ꢀ

(24%) and cis-[Pt(NH3)2(H2O)Cl] (7%). At [Cl ] ¼

0.004 M (concentration inside the cell), the main spe-

cies are cis-Pt(NH3)2Cl2 (31%), cis-Pt(NH3)2(OH)Cl

þ

(

32%), cis-[Pt (NH ) (H O)Cl]

(28%) and cis-

[Pt(NH ) (H O)(OH)] (7%). The method used by

3

þ

2

*

3

2

Corresponding author. Tel.: +1-514987-3000x4896; fax: +1-514-

87-4054.

E-mail address: rochon.fernande@uqam.ca (F.D. Rochon).

these authors to detect the diﬀerent species did not

permit the observation of oligomeric species, which are

9

0

doi:10.1016/j.ica.2003.10.039

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2219

known to exist. Indeed, it has been shown, mainly by

1

2.1. Crystallographic measurements and structure resolu-

tion

⁹⁵Pt NMR and crystallographic methods, that at

neutral pH, several hydroxo-bridged oligomers are

formed [21–27]. Some of these species have been found

to be toxic for humans and may be partly responsible

for the toxicity of cisplatin [28,29]. Therefore, it seems

important to study the hydrolysis reactions of the Pt

complexes at neutral pH, prior to the development of

new anti-tumor agents.

The crystals were selected after examination under a

polarizing microscope for homogeneity. The unit cell

parameters were obtained by least-squares reﬁnement of

the angles 2h, x and v for well-centered reﬂections on a

Siemens P4 diﬀractometer using graphite-monochroma-

ꢂ

tized Mo Ka radiation (k ¼ 0:71073 A). The data collec-

The objective of this project was to study the hy-

drolysis reactions of the complexes cis and trans diamine

Pt(II) complexes, which will be the subject of a sub-

sequent paper. The starting materials are usually the

dihalo complexes, which have been known for a long

time and most of them have been characterized mainly

by IR spectroscopy. A few dichloro and diiodo diamine

complexes have also been characterized by NMR tech-

tions were done at room temperature using the XSCANS

program [39]. The background time to scan time ratio was

0.5. The crystal data and the experimental details are lis-

ted in Tables 1 and 2. All the calculations were done using

the SHELXTL system [39]. The coordinates of the Pt atoms

were determined from Patterson map calculations or by

direct methods and the positions of all the other non-

hydrogen atoms were found by the usual Fourier meth-

1

2

niques (mainly H), in DMF or DMSO [30–36], solvents

ods. The reﬁnement of the structures was done on F_o

which are known to react with these complexes.

In this paper, we report a systematic and detailed study

of the multinuclear ( H, ¹³C and ¹⁹⁵Pt) NMR spectra of

the complexes cis- and trans-Pt(amine) I in acetone-d

using all the reﬂections. The H atoms were ﬁxed at their

calculated positions (riding model) with Ueq ¼ 1:2 (or 1.5

for methyl groups) ꢁ Ueq of the C atom to which they are

bonded. The intensity data were corrected for absorption

(Gaussian integration for crystals I and VII and semi-

empirical for the others) and for the eﬀects of Lorentz and

polarization. In cis-Pt(nBuNH2)2I2 (II) one butyl chain is

disordered while in trans-Pt(tBuNH2)2I2 (VII) there are

two positions for all the terminal CH3 groups. The re-

ﬁnement of the scale factor, coordinates and anisotropic

temperature factors of all the non-hydrogen atoms con-

verged to the R and wR values shown in Tables 1 and 2.

1

2

6

(

the compounds decompose in CDCl ), a solvent which is

3

relatively inert. Complexes with diﬀerent amines were

studied. Amines cannot accept electron density from the

metal. Therefore, the r bonds should cause a deshielding

eﬀet on the ligand and a shielding eﬀect on the metal. The

strength of the r bond should be related to the pKa value

of the protonated ligand or the proton aﬃnity of the li-

gand, although few of the latter values have been re-

ported in the literature. We also report in this paper, the

crystal structures of eight diiodo complexes in an attempt

to gain information on the nature of the Pt–amine bond

and on the relative trans inﬂuence of the ligands. The

results were compared to those obtained recently on

similar dipyridine complexes [37,38].

1

2

The most intense residual peaks were found in the close

environment of the Pt atom.

2.2. Synthesis

2 2

2.2.1. cis-Pt(amine) I

These complexes were synthesized by a modiﬁed

version of DharaÕs method [40]. An excess of amine

(Pt:amine ¼ 4.6) was used and added very slowly. The

mixture was stirred for 6–8 h. The precipitate was ﬁl-

tered, washed with water and ethanol and dried. For the

amine tBuNH2, the cis compound does not form. A

brown compound, probably the iodo-bridged dimer was

obtained. For Et2NH, a brown product was also formed

and ¹⁹⁵Pt NMR has shown the presence of the iodo-

bridged dimers (70%) and another compound, which

was assumed to be cis-Pt(Et NH) I (30%).

2

. Experimental

K2[PtCl4] was obtained from Johnson Matthey and

was recrystallized in water before use. The amines were

bought from Aldrich. CD3COCD3 and 1.101DMF-d7

were purchased from CDN Isotopes.

The infrared spectra were measured from 4000 to 280

ꢀ

1

cm as KBr pellets using a Perkin–Elmer 783 grating

spectrometer. The decomposition points were measured

on a Fisher-Johns instrument and are not corrected. The

NMR spectra were measured on a Varian Gemini 300BB

in CD3COCD3. For comparison purposes, a few spectra

were repeated in DMF-d6. The ﬁelds were 300.075, 75.462

and 64.311 MHz, respectively, for H, ¹³C and ¹⁹⁵Pt. The

2

2 2

cis-Pt(MeNH ) I : Yield ¼ 86%, m.p. ¼ 138–203 °C

2

2 2

ꢀ

1

(dec). IR (cm ): m(N–H) 3265s, 3195s, 3115w, m(C–H)

2963s, 2925m, d(N–H) 1580s, 1565s, d(C–H) 1475s,

1453m, 1396s, 1380s, m(C–N) 1280s, 1195s, 1170s, m(Pt–N)

470w, 420m, other bands: 1338m, 1025m, 925w, 880m,

1

acetone peak was used as an internal standard for H (2.04

ppm) and ¹³C (29.8 ppm). The external reference used for

740m, 355m. NMR (d (ppm)): H: NH 4.459s+d,

2

195

3

J( Pt–NH) ¼ 69 Hz, H 2.628t+dt, J ¼ 6.3 Hz,

1

95

3

195

13

2

195

Pt was K[Pt(DMSO)Cl ] (in D O), adjusted at )2998

J( Pt–H ) ¼ 49 Hz, C: C 33.792, J( Pt–C ) ¼ 21

3

2

1

ppm from K [PtCl ] (d(Pt) ¼ 0 ppm).

Hz.

2

6

2220

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

Table 1

Crystallographic data for crystals I–IV

Crystal

I

II

III

IV

Name

cis-Pt(MeNH

Pt

2

)

2

I

2

cis-Pt(nBuNH

2

)

2

I

2

cis-Pt(Et

H

2

NH)

Pt

2

I

2

2 2 2

trans-Pt(nPrNH ) I

C H I N Pt

6 18 2 2

Chemical formula

Molecular weight

Space group

C

2

H

10

I

2

N

2

C

8

H

22

595.17

I

2

N

2

Pt

C

8

22

I

2

N

2

511.01

P2 =c (No. 14)

595.17

P2 =n (No. 14)

567.11

1

C2=c (No. 15)

24.477(5)

8.979(2)

24.232(5)

114.468(10)

4847(2)

12

1

Pc (No. 7)

8.958(3)

7.748(2)

9.571(2)

90.16(2)

664.3(3)

2

ꢂ

a (A)

6.928(2)

8.021(3)

16.236(5)

99.02(2)

891.0(5)

4

9.060(3)

13.151(4)

13.024(4)

105.62(3)

1494.5(8)

4

ꢂ

b (A)

ꢂ

c (A)

b (°)

Volume (A )

ꢂ

3

Z

ꢀ3

q_c_a_l_c(g cm

)

3.809

2.447

12.478

2.645

2.835

ꢀ

1

l(Mo KaÞ (cm

F ð000Þ

)

22.594

880

1888

13.491

1072

13 390

15.168

504

7544

3216

14 526

Measured reﬂections

Independent reﬂections (Rint

)

1742 (0.0442)

1291

3802 (0.1044)

2271

3426 (0.0640)

2802

3906 (0.0851)

3207

Observed reﬂections ðI > 2rðIÞÞ

R

wR

S

1

ðF > 2rðIÞÞ

0.0399

0.1144

1.056

0.0699

0.1816

1.072

0.0542

0.1304

1.083

0.0440

0.1187

1.067

2

(all data)

P

2

c

2

o

2

1=2

R1 ¼ ðjFo ꢀ FcjÞ=jFoj, wR2 ¼ ½ ðwðF_oꢀ F Þ Þ= ðwðF Þ Þꢂ

.

Table 2

Crystallographic data for crystals V–VIII

Crystal

V

VI

VII

VIII

Name

trans-Pt(isoPrNH

Pt

2

)

2

I

2

trans-Pt(nBuNH

Pt

2

)

2

I

2

trans-Pt(tBuNH

Pt

2

)

2

I

2

2 2 2

trans-Pt(Me NH) I

Chemical formula

Molecular weight

Space group

C

6

H

18

567.11

I

2

N

2

C

8

H

22

595.17

I

2

N

2

C

8

H

22

595.17

I

2

N

2

4 14 2 2

C H I N Pt

539.06

P2 =n (No. 14)

P2 =c (No. 14)

1

P2 =c (No. 14)

1

P2 =n (No. 14)

1

ꢂ

a (A)

11.805(2)

12.312(2)

9.252(2)

98.72(2)

1329.1(4)

4

10.346(3)

16.092(4)

9.903(3)

110.26(2)

1546.7(8)

4

8.841(3)

9.131(2)

19.785(5)

97.16(2)

1584.6(7)

4

8.2029(13)

7.0033(9)

10.2556(14)

112.329(11)

544.98(13)

2

ꢂ

b (A)

ꢂ

c (A)

b (°)

Volume (A )

ꢂ

3

Z

ꢀ3

q_c_a_l_c(g cm

)

2.834

2.556

2.495

3.285

18.479

ꢀ

1

l(Mo KaÞ (cm

F ð000Þ

)

15.162

1008

9243

13.035

1072

13859

12.723

1072

14106

472

4085

Measured reﬂections

Independent reﬂections (Rint

)

3532 (0.0587)

2592

3548 (0.1057)

2743

3645 (0.0399)

3009

1071 (0.0465)

1017

0.0283

Observed reﬂections ðI > 2rðIÞÞ

R

wR

1

ðF > 2rðIÞÞ

0.0407

0.0917

1.052

0.0417

0.0925

1.044

0.0307

0.0653

1.054

2

(all data)

0.0698

1.058

S

P

2

c

2

o

2

1=2

R1 ¼ ðjFo ꢀ FcjÞ=jFoj; wR2 ¼ ½ ðwðF_oꢀ F Þ Þ= ðwðF Þ Þꢂ

.

cis-Pt(EtNH2)2I2: Yield ¼ 82%, m.p. ¼ 130–196 °C

2950s, 2920m, 2840m, d(N–H) 1565s, d(C–H) 1460m,

1440m, 1385w, m (C–N) 1205m, 1095m, other bands:

1320w, 1045m, 980m, 945m, 885w, 748w, 700m, 645w,

560w. NMR (d (ppm)): H: NH 4.462s+d, ²J(¹⁹⁵Pt–

ꢀ

1

(

2

1

dec.). IR (cm ): m(N–H) 3200s, 3150w, m(C–H) 2900m,

870m, 2830m, d(N–H) 1580w, d(C–H) 1465s, 1420m,

395m, m(C–N) 1270s, 1220m, 1135m, 1080s, m(Pt–N)

95w, 450w, other bands: 1015s, 895s. NMR (d (ppm)):

1

3

4

1

NH) ¼ 68 Hz, H 2.935tt, J ¼ 7.5, 7.2 Hz, H 1.711tq,

1

2

195

3

2

3

13

H: NH 4.455s+d, J( Pt–NH) ¼ 68 Hz, H 3.022tq,

J ¼ 7.5, 7.2 Hz, H 0.930t, J ¼ 7.2 Hz, C: C 49.683,

1

3

195 3 195

1

3

13

J ¼ 7.5 Hz, 6.9 Hz, H2 1.270t, J ¼ 7.2 Hz, C: C1

J( Pt–C1) ¼ 17 Hz, C2 25.156, J( Pt–C2) ¼ 45 Hz,

2

195

3

195

4

2.747, J( Pt–C1) ¼ 18 Hz, C2 16.823, J( Pt–C2) ¼

C3 11.222.

8 Hz.

cis-Pt(nBuNH2)2I2: Yield ¼ 91%, m.p. ¼ 117–169 °C

ꢀ

1

cis-Pt(nPrNH2)2I2: Yield ¼ 88%, m.p. ¼ 129–192 °C

(dec.). IR (cm ): m(N–H) 3245s, 3210s, 3110w, m(C–H)

2965s, 2920w, 2890w, d(N–H) 1586s, 1577s, 1568s,

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3240m, 3200s, 3120m, m(C–H)

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2221

d(C–H) 1455m, 1396m, 1380m, m(C–N) 1225s, 1205s,

KauﬀmanÕs method [41], except for Et2NH and

tBuNH2. A large excess of amine (amine:Pt ¼ 20) was

added very slowly to K2[PtI4] and the yellow mixture

was stirred for several days until a colorless solution

was obtained. With a few ligands, slight heating was

necessary. The solution was concentrated until a white

precipitate was observed. The latter was ﬁltered and

washed with very cold water and dried. The compound

[Pt(amine)4]I2 was suspended in ethanol and the mix-

ture was heated (40–50 °C) with stirring until a dark

yellow solution was obtained. The solution was ﬁltered

and the ﬁltrate was left in air several hours to con-

centrate until crystallization was complete. The pre-

cipitate was ﬁltered, recrystallized in ethanol, washed

with water and then with cold ethanol and ﬁnally

dried. For the ligands Me NH and secBuNH , the

1

085s, 1065s, m(Pt–N) 485w, other bands: 1365m, 1035s,

8

85w, 805w, 725m, 680w, 565w, 385w. NMR (d (ppm)):

1

2

195

H: NH 4.443s+d, J( Pt–NH) ¼ 65 Hz, H1 2.978tt,

3

195

3

J ¼ 7.5, 7.2 Hz, J( Pt–H1) ¼ 43 Hz, H2 1.682tt, J ¼

3

7

.5, 6.9 Hz, H 1.380tq, J ¼ 7.5, 7.2 Hz, H 0.908t,

3

4

3

13

2

195

J ¼ 7.2 Hz, C: C 47.679, J( Pt–C ) ¼ 18 Hz, C

1

2

3

195

3

4.050, J( Pt–C ) ¼ 43 Hz, C 20.344, C 13.970.

2

3

4

cis-Pt(isoPrNH2)2I2: Yield ¼ 83%, m.p. ¼ 142–177 °C

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3200m, 3115s, 3080s, m(C–H)

2

1

950s, 2925m, 2880m, d(N–H) 1590m, 1575s, d(C–H)

460m, 1390s, 1375s, m(C–N) 1275m, 1255s, after 1155s

120s, 1075s, m(Pt–N) 450m, other bands: 1340m, 940m,

30m, 795s, 780m, 600m, 395w. NMR (d (ppm)):

8

1

2

195

H: NH 4.383s+d,

3

J( Pt–NH) ¼ 66 Hz, H₁

3

13

3

.553thept, J ¼ 7.2, 6.9 Hz, H 1.356d, J ¼ 6.9 Hz, C:

2

195

3

195

C1 49.774, J( Pt–C1) ¼ 13 Hz, C2 23.987, J( Pt–

C2) ¼ 30 Hz.

trans complexes were isolated by concentration in air

of the colorless aqueous solutions.

cis-Pt(isoBuNH2)2I2: Yield ¼ 87%, m.p. ¼ 119–142 °C

trans-Pt(MeNH2)2I2: Yield ¼ 76%, m.p. ¼ 175–218 °C

ꢀ

1

ꢀ1

(

dec). IR (cm ): m(N–H) 3250s, 3210s, 3110m, m(C–H)

(dec.). IR (cm ): m(N–H) 3240s, 3205s, 3125m, m(C–H)

2

1

4

7

4

955s, 2865m, d(N–H) 1565s, d(C–H) 1470s, 1390m,

370m, m(C–N) 1200s, 1170m, 1120s, 1080w, m(Pt–N)

50w, other bands: 1315w, 1005s, 945m, 890w, 825w,

2955s, 2920m, 2870m, d(N–H) 1575s, d(C–H) 1452m,

1390m, 1375m, m(C–N) 1275m, 1238s, 1215s, 1145w,

1115s, 1075m, m(Pt–N) 465w, other bands: 1325m,

1030m, 965w, 900w, 825w, 770w, 605w, 345w. NMR (d

1

15s, 590m, 395w, 370w. NMR (d (ppm)): H: NH

2

195

3

1

2

195

.425s+d, J( Pt–NH) ¼ 66 Hz, H1 2.823dt, J ¼ 7.2,

(ppm)): H: NH 3.920s+d, J( Pt–NH) ¼ 61 Hz, H1

3

3 3 195 13

6

.9 Hz, H2 1.930thept, J ¼ 6.9, 6.6 Hz, H3 0.965d,

2.468t+dd, J ¼ 6.3 Hz, J( Pt–H1) ¼ 35 Hz, C: C1

2 195

3

13

2

195

J ¼ 6.6 Hz, C: C1 55.405, J( Pt–C1) ¼ 18 Hz, C2

34.733, J( Pt–C1) ¼ 15 Hz.

hidden by the solvent, C3 20.162.

cis-Pt(secBuNH2)2I2: Yield ¼ 76%, m.p. ¼ 110–141 °C

trans-Pt(EtNH2)2I2: Yield ¼ 69%, m.p. ¼ 188–217 °C

ꢀ

1

(dec.). IR (cm ): m(N–H) 3235s, 3190s, 3110m, m(C–H)

2965s, 2925m, 2860w, d(N–H) 1563s, d(C–H) 1460m,

1386m, 1375m, 1368m, m(C–N) 1230m, 1155s, 1100s,

1055m, m(Pt–N) 433w, other bands: 932m, 805m, 735m,

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3240m, 3195s, 3120m, m(C–H)

2

1

960s, 2930m, 2870m, d(N–H) 1570s, d(C–H) 1465s,

385m, 1365m, m(C–N) 1230m, 1140w, 1115s, 1065w,

1

m(Pt–N) 430w, other bands: 1030w, 965w, 895w, 815w,

595w, 385w. NMR (d (ppm)): H: NH 3.951s+d,

1

2

195

3

7

75w, 725w, 598w. NMR (d (ppm)): H: NH 4.369s+d,

J( Pt–NH) ¼ 58 Hz, H1 2.842tq, J ¼ 7.2, 6.9 Hz, H2

2

195

3

3 13 2 195

J( Pt–NH) ¼ 67 Hz, H1 3.309ttq, J ¼ 7.2, 6.9, 6.6 Hz,

1.200t, J ¼ 7.2 Hz, C: C1 43.748, J( Pt–C1) ¼ 12

3 195

3

H2 1.493dq, J ¼ 6.9, 6.6 Hz, H

0

1.370d, J ¼ 6.3 Hz, H3

Hz, C2 16.929, J( Pt–C2) ¼ 36 Hz.

2

3

13

0

.938t, J ¼ 7.2 Hz, C: C1 55.132 and 55.071, C2 31.257

trans-Pt(nPrNH2)2I2: Yield ¼ 58%, m.p. ¼ 185–209 °C

3

195

ꢀ1

and 31.090, J( Pt–C ) ¼ 32 and 32 Hz, C

0

20.830 and

2

(dec.). IR (cm ): m(N–H) 3240m, 3210s, 3125m, m(C–H)

2

0.693, J(¹⁹⁵Pt–C

3

) ¼ 25 and 23 Hz, C 10.646.

2960s, 2920m, 2860w, d(N–H) 1573s, d(C–H) 1465m,

1450m, 1375w, m(C–N) 1218s, 1195w, 1095m, other

bands: 1315m, 1050m, 1008m, 965w, 600w, 405w. NMR

2

0

2

3

cis-Pt(Me NH) I : Yield ¼ 92%, m.p. ¼ 132–158 °C

2

2 2

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3180s, m(C–H) 2900m, 2870s,

1

2

195

2

1

830s, d(C–H) 1460s, 1455s, 1430m, 1390m, m(C–N)

130m, 1105s, 1065m, m(Pt–N) 495m, 465m, other bands:

(d (ppm)): H: NH 3.931s+d, J( Pt–NH) ¼ 59 Hz, H1

3

2.765tt, J ¼ 7.5, 6.9 Hz, H2 1.649tq, J ¼ 7.5, 7.2 Hz, H3

1

2

195

3

13

2

195

005s, 885s. NMR (d (ppm)): H: NH 4.920s+d, J( Pt–

0.912t, J ¼ 7.2 Hz, C: C1 50.700, J( Pt–C1) ¼ 10 Hz,

NH) ¼ 70 Hz, H1 2.793d+dd, J ¼ 5.7 Hz, J(¹⁹⁵Pt–

3

C2 25.004, J( Pt–C2) ¼ 36 Hz, C3 11.253.

3 195

1

3

2

195

H ) ¼ 43 Hz, C: C 43.870, J( Pt–C ) ¼ 14 Hz.

trans-Pt(nBuNH ) I : Yield ¼ 61%, m.p. ¼ 131–176 °C

1

2 2 2

ꢀ

1

cis-Pt(Et NH) I : This compound was not obtained

2

(dec.). IR (cm ): m(N–H) 3200s, 3120s, 3060s, m(C–H)

2945s, 2920s, 2860m, d(N–H) 1568s, 1550s, d(C–H)

1413s, 1405m, m(C–N) 1235w, 1210m, 1110m, 1065m,

m(Pt–N) 445w, other bands:1322m, 1020w, 972m, 945w,

2 2

pure. The product of the reaction contained 70% of the

1

iodo-bridged dimers. NMR (d (ppm)): H: NH

2

195

3

4

.604s+d, J( Pt–NH) ¼ 68 Hz, H1 3.119tq, J ¼ 7.2,

3 13 2 195

1

6

.9 Hz, H2 1.358t, J ¼ 6.9 Hz, C: C1 50.487, J( Pt–

890w, 732m, 710m, 597w. NMR (d (ppm)): H: NH

3

195

2

195

3

C1) ¼ 13 Hz, C2 14.683, J( Pt–C2) ¼ 34 Hz.

3.910s+d, J( Pt–NH) ¼ 58 Hz, H1 2.805tt, J ¼ 7.5, 6.9

3

Hz, H2 1.621tt, J ¼ 7.5, 7.2 Hz, H3 1.367tq, J ¼ 7.5, 7.2

3

13

2

195

2

.2.2. trans-Pt(amine)₂I₂

These compounds were synthesized from the tetra-

Hz, H 0.902t, J ¼ 7.2 Hz, C: C 48.575, J( Pt–

4

1

3

195

C ) ¼ 12 Hz, C 33.837, J( Pt–C ) ¼ 34 Hz, C 20.284,

1

2

3

substituted compounds [Pt(amine) ]I₂similarly to

4

C 13.939.

4

2222

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

trans-Pt(isoPrNH2)2I2: Yield ¼ 82%, m.p. ¼ 220–233 °C

trans-Pt(Et2NH)2I2: Yield ¼ 59% (contained 30% of

the cis isomer), m.p. ¼ 152–176 °C (dec.). NMR (d

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3240m, 3200s, 3100m, m(C–H)

1

2

195

2

1

8

3

6

960s, 2930m, 2830w, d(N–H) 1582s, 1565s, d(C–H)

465m, 1390m, 1366m, m(C–N) 1232s, 1153m, 1095m,

065m, m(Pt–N) 435m, other bands: 1040w, 930m, 860w,

(ppm)): H: NH 4.285s+d, J( Pt–NH) ¼ 60 Hz, H1

3 3 13

2.968tq, J ¼ 7.5, 6.9 Hz, H2 1.327t, J ¼ 6.9 Hz, C: C1

2

195

3

195

53.750, J( Pt–C1) ¼ 9 Hz, C2 15.199, J( Pt–C2) ¼

1

05m, 755w, 590w, 385w. NMR (d (ppm)): H: NH

22 Hz.

2

195

3

.896s+d, J( Pt–NH) ¼ 60 Hz, H 3.415thept, J ¼ 7.2,

1

3

13

2

195

.6 Hz, H 1.282d, J ¼ 6.6 Hz, C: C 51.428, J( Pt–

2

1

3

195

C1) ¼ 11 Hz, C2 24.412, J( Pt–C2) ¼ 22 Hz.

3

. Results and discussion

trans-Pt(isoBuNH2)2I2: Yield ¼ 74%, m.p. ¼ 123–

ꢀ

1

44 °C (dec.). IR (cm ): m(N–H) 3260s, 3225m, 3120w,

3

.1. Synthesis

m(C–H) 2960s, 2950m, 2870m, d(N–H) 1577s, d(C–H)

1

475m, 1465m, 1390m, 1370m, m(C–N): 1212w, 1200s,

167m, 1120s, 1080w, m(Pt–N) 445w, other bands:

335m, 1307m, 1015s, 808w, 600w, 395w. NMR (d

Complexes of the type cis-Pt(amine)2I2 with

amine ¼ methylamine (MeNH ), ethylamine (EtNH ),

2

1

2

195

n-propylamine (nPrNH ), n-butylamine (nBuNH ), iso-

2

(

2

ppm)): H: NH 3.862s+d, J( Pt–NH) ¼ 59 Hz, H

1

3

propylamine (isoPrNH ), iso-butylamine (isoBuNH ),

2

.633dt, J ¼ 7.5, 6.9 Hz, H2 1.928thept, J ¼ 6.9, 6.6

3 13 2 195

sec-butylamine (secBuNH₂) and dimethylamine

Me2NH) were synthesized by a modiﬁed DharaÕs

method [40]. A slight excess of the amine was used to

Hz, H3 0.931d, J ¼ 6.6 Hz, C: C1 56.376, J( Pt–

C1) ¼ 14 Hz, C2-hidden by the solvent, C3 20.071.

trans-Pt(secBuNH2)2I2: Yield ¼ 74%, m.p. ¼ 132–

(

ꢀ

1

maximize the yields, which varied between 76% and

1

48 °C (dec.). IR (cm ): m(N–H) 3240s, 3200s, 3165m,

9

diethylamine (Et NH) produced the iodo-bridged di-

2%. Similar reactions with t-butylamine (tBuNH2) and

m(C–H) 2955s, 2930m, 2870w, d(N–H) 1575s, d(C–H)

2

1

455s, 1378w, m(C–N) 1275w, 1235s, 1215s, 1150w,

mers I(amine) Pt(l-I) Pt(amine)I. The product obtained

2

115s, 1070m, m(Pt–N) 465w, other bands: 1325w,

1

with Et NH contained also about 30% of another

compound which we have assigned to cis-Pt(Et NH) I .

2

030m, 960w, 900w, 770w, 600w. NMR (d (ppm)): H:

3

2

2 2

NH 3.908 and 3.828, H1 3.214ttq, J ¼ 7.2, 6.6, 6.3 Hz

3

The ligand t-butylamine is too bulky to form a cis

compound.

The equivalent trans-Pt(amine)₂I₂complexes were

prepared by two diﬀerent methods. For the most steri-

and 3.206ttq, J ¼ 7.2, 6.6, 6.3 Hz, H2 1.448dq, J ¼ 7.5,

3

7

.2 Hz and 1.451dq, J ¼ 7.2, 6.9 Hz, H20 1.288d,

3

13

J ¼ 6.6 Hz, H3 0.929t, J ¼ 7.2 Hz, C: C1 56.665,

2

195

3

195

J( Pt–C ) ¼ 10 Hz, C 31.029, J( Pt–C ) ¼ 28 Hz,

1

2

3

195

cally demanding amines (tBuNH₂and Et NH), the

0

21.270, J( Pt–C₂

trans-Pt(Me NH) I : Yield ¼ 80%, m.p. ¼ 194–211 °C

0

) ¼ 21 Hz, C 10.281.

2

C₂

3

compounds were prepared from the reaction of the

iodo-bridged dimers with a large excess of amine in

water. Slight heating is necessary to reduce the time of

reaction

2

2 2

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3170s, 3075s, m(C–H) 2980m,

2910m, d(N–H) 1570s, d(C–H) 1445s, 1415m, m(C–N)

1273s, 1255s, 1080s, 1065s, m(Pt–N) 475m, other bands:

1325w, 1035s, 1010s, 980s, 775s, 755m, 730s, 695w. NMR

IðamineÞPtðl-IÞ PtðamineÞI þ 2amine

2

1

2

195

(

2

4

d (ppm)): H: NH 4.439s+d, J( Pt–NH) ¼ 62 Hz, H1

!

²^t^r^aⁿ^s^-^P^t^ð^a^mⁱⁿ^e^Þ2^I

3

195

13

2

.630d+dd, J ¼ 6.6 Hz, J( Pt–H ) ¼ 37 Hz, C: C

1

2

195

6.374, J( Pt–C ) ¼ 10 Hz.

The iodo-bridged dimers were synthesized by the re-

ported method [42] or as mentioned above. The other

trans compounds were prepared from the tetrasubsti-

tuted intermediates similarly to KauﬀmanÕs method [41]

1

The transtBuNH and Et NH compounds were syn-

2

thesized from the iodo-bridged dimer as described above

for the synthesis of the cis isomers. An excess of amine

(

amine:Pt ¼ 15) was added to the dimers suspended in

H2O

K ½PtI ꢂ þ 4 amine ! ½PtðamineÞ ꢂI

water and heated until the brown color changed to

bright yellow. The precipitate was ﬁltered, recrystallized

in ethanol, washed with water and then with cold eth-

2

4

2

ꢀ

2KI

!

trans-PtðamineÞ I # þ2 amine

2

anol and ﬁnally dried. The Et NH compound contained

2

2 2

For Me NH and secBuNH , the colorless aqueous so-

3

0% of the cis isomer.

trans-Pt(tBuNH2)2I2: Yield ¼ 71%, m.p. ¼ 171–192 °C

lutions were concentrated until precipitation of the trans

compounds occurred. For the six other amines, the

tetrasubsituted complexes were dissolved in ethanol and

the solutions were heated until precipitation occurred.

ꢀ

1

(

dec.). IR (cm ): m(N–H) 3240s, 3210s, 3135m, m(C–H)

2

1

970s, 2925m, 2890w, d(N–H) 1578s, d(C–H) 1460w,

440m, 1380m, m(C–N) 1235s, 1075s, other bands:

2 4

The yields (from K [PtCl ]) are lower than those for the

1

345m, 1035s, 885w, 820m, 600w. NMR (d (ppm)): H:

cis compounds due to the diﬃculty to obtain the tetra-

substituted compound in quantitative yields, especially

for the bulkier amines. They varied between 59%

2

195

13

NH 4.197s+d, J( Pt–NH) ¼ 58 Hz, H 1.450s, C: C₁

1

5.420, ²J(¹⁹⁵Pt–C ) ¼ 9 Hz, C₂32.608, J(¹⁹⁵Pt–

3

5

1

C ) ¼ 17 Hz.

2

(Et NH) and 82%.

2

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2223

The decomposition points of the compounds

Pt(amine)2I2 are shown in Section 2. In general, the cis

complexes start to decompose at lower temperatures

than the corresponding trans compounds. A few cis

complexes probably isomerize to the trans isomer as the

temperature is increased. Thermal isomerization of the

cis complexes with MeNH , EtNH and nBuNH has

already been reported [43,44]. All the diido complexes

were characterized by IR (except cis and trans-

Pt(Et2NH)2I2 which were not obtained pure) and mul-

tinuclear NMR spectrocopies.

band) symmetries are considered for the cis and trans

complexes, respectively [53]. The energy of the m(Pt–N)

vibrations seems to be dependent on the halo ligand.

For example, for the cis-Pt(NH3)2X2 complexes, the two

1

bands were reported at 520 and 508 cm for X ¼ Cl

1

[47,49], at 513 and 499 cm for X ¼ Br [48] and at 491

1

and 477 cm for X ¼ I [48]. Our values are also slightly

2

lower than those of a few published dichloro com-

pounds [45,46] and a few diido complexes with more

crowded ligands [36].

3.3. NMR

3

.2. IR spectroscopy

The NMR spectra of all the complexes Pt(amine)₂I₂

were measured in CD COCD . Although several com-

3 3

The main IR bands are listed in Section 2. The

spectra of the disubstituted complexes have shown the

pounds are soluble in normal CHCl , they decompose

3

presence of two or three bands in the stretching m(N–H)

region at slightly lower energies (3075–3260 cm ) than

quite rapidly to produce iodine. Attempts to purify

CDCl3 were not successful. We also encountered similar

problems with CD2Cl2. DMSO reacts quite rapidly with

these compounds and was rapidly eliminated. DMF re-

acts more slowly, but since our ¹³C NMR spectra were

accumulated for at least overnight, we have found that

deuterated acetone was the best solvent, even if it is not a

very inert solvent. In order to determine if solvolysis could

occur in acetone, the spectra of cis- and trans-

Pt(amine)2I2 (amine ¼ EtNH2 and sec BuNH2) were re-

corded in CD3COCD3 in the presence of 0, 2, 5 and 10

meq of KI. But no diﬀerence was observed in the spectra

measured with and without KI. We have also veriﬁed if

the cis complexes could isomerize to the trans compounds

as reported for a few dichloro complexes [54]. The NMR

spectra of fresh solutions of the cis complexes were iden-

tical after one week of standing in CD3COCD3.

ꢀ

1

in the free amines. The deformation bands d(N–H) were

ꢀ

1

also observed at lower frequencies (1560–1585 cm ) in

the coordinated ligands. The vibration frequencies of the

Pt–N bonds were assigned based on published works

[

36,45–52]. These bands are usually weak and are quite

diﬃcult to assign. Some of these vibrations might also

couple with others, which increases the assignment dif-

ﬁculties. Attempts have been made to interpret these

vibrations and the results are shown in Table 3, along

with some published results. All the trans compounds

have shown only one band, while one or two bands are

reported for the cis complexes. This is in agreement with

group theory, when idealized C₂_v(2 bands) and D₂_h(1

Table 3

t(Pt–N) vibrations (cm ¹) for the complexes cis- and trans-PtL2X2 and

ꢀ

195

3

.3.1. Pt NMR

The d(Pt) chemical shifts of all the compounds are

some examples from the literature

Complex

cis

trans

Ref.

listed in Table 4. The signals of the cis diiodo complexes

with primary amines were observed between )3342 and

)3357 ppm and between )3345 and )3372 ppm for the

trans analogues. The Dd between the two isomers are

very small. These results are quite surprising, since in the

pyridine (Ypy) series, the diﬀerence between the cis and

trans isomers were larger. The cis diiodo pyridine com-

plexes were observed in CDCl3 between )3199 and

m

s

m

as

m

as

Pt(NH

3

)

2

Cl

2

517

23

508

507

509

538

[47]

[49]

[51]

[50]

[48,50]

[48]

[45]

[46]

[36]

5

06

05

Pt(NH

3

)

2

Br

2

513

491

565

595

495

578

568

585

499

477

506

502

498

518

3

I

2

Pt(MeNH

2

)

2

Cl

2

Pt(cycloPrNH

2

)

2

Cl

2

)

3312 ppm, while the trans analogues were observed at

Pt(MeNH

Pt(EtNH

2

)

2

I

2

485

498

lower ﬁeld, between )3122 and )3264 ppm [37], with Dd

values (cis–trans) ꢃ )70 ppm. Our results on amine

complexes show Dd (cis–trans) values between )10 and

18 ppm. We have repeated these spectra several times

and the results were always almost identical (ꢄ2 ppm).

For isoPrNH2 and secBuNH2, the cis complexes were

observed at slightly higher ﬁelds than the trans isomers

as expected. For the other ligands, the trans compounds

were observed at higher ﬁelds (although the Dd values

are not very large) which is contrary to all published

values on similar compounds. With ligands capable of

2

)

2

I

2

2 2 2

Pt(cycloBuNH ) I

Pt(cycloPeNH

2

)

2

I

2

530

500

478

420

450

2 2 2

Pt(2-adamNH ) I

Pt(Me

Pt(MeNH

Pt(EtNH

Pt(nBuNH

2

NH)

2

I

2

502

470

495

485

2

)

2

465

433

445

435

445

465

475

2

)

2

I

2

2 2

) I

Pt(isoPrNH )

Pt(isoBuNH ) I

2

I

2

450

430

465

2 2 2

Pt(secBuNH

2 2 2

) I

Pt(Me NH)

2

I

2

495

2224

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

Table 4

Table 5

1

95

195

Chemical shifts d( Pt) and Ddðdcis–dtransÞ (ppm) of the complexes

PtL2I2 in CD3COCD3

PtL2X2 in the literature

L

PA

914

pK

a

cis

trans

Dd

Complex

Pt(NH

cis

trans

Dd

Ref.

a

MeNH

2

10.62

10.63

)3342

)3360

)3348

)3368

)3353

)3363

)3345

)3372

)3336

)3322

18

24

14

25

13

3

)

2

I

2

)3264

)3198

)3327

)3330

)3327

)3364

)3333

)3302

)3346

)3387

)3389

[31]

[32]

a

c

)

3324

)3354

3328

c

EtNH

2

930

Pt(MeNH

Pt(EtNH

Pt(Me NH)

2

)

2

I

2

[36]

a

c

)

2

)

2

I

2

c

nPrNH

nBuNH

isoPrNH

isoBuNH

secBuNH

2

933

924

10.69

10.61

10.63

10.72

10.56

)3350

)3349

)3352

)3357

)3346

2

I

2

[36]

c

2

Pt(1-adam)

Pt(2-adam)

2

I

2

)3331

)33

c

2

)7

15

2

[36]

c

2

Pt(cpa)

Pt(cba)

2

I

2

c

2

)10

13

2

[36]

a

c

)

3309,

a

Pt(cba)(2-adam)I

Pt(MeNH )(1-Me-

adam)I

Pt(py)

Pt(Ypy)

Pt(NH

2

)3358

)3336

)29

)53

c

)3321 (65%)

2

[36]

(

35%)

2

a

tBuNH

Me NH

Et NH

2

10.68

10.73

11.04

)3369

)3057

)3128

2

I

2

)3199

)3235

)2104

)2100

)2097

)2222

)2188

)2224

)2215

)2235

)2184

)2230

)2242

)2014

)2009

)3133

)3161

)2101

)66

)74

)3

1

[37,38]

a;b

2

)3247

)3302

)190

)174

2

I

2

ðdave

Þ

[31,38] [37]

b

c

2

3

)

2

Cl

2

[30]

[32]

c

a

In DMF-d7.

See text.

d

b

[35]

c

Pt(MeNH

Pt(Me NH)

Pt(isoPrNH

Pt(C

Pt(cba)

Pt(1-adam)

Pt(2-adam) Cl

2

)

2

Cl

2

[36]

c

2

Cl

)2181

)2130

)7

c

)

2

Cl

2

[36]

[34]

accepting p-electrons like sulfoxides, the cis compounds

are observed at lower ﬁelds, since the p-bonding is much

more eﬃcient in the cis geometry compared to the trans

isomer. The cis compounds are also more stable than the

trans analogues in the sulfoxide system. But amines

cannot accept back p-donation and the trans amine

compounds are thermodynamically more stable. Pyri-

d

a

6

H11NH

2

)

2

)85

c

2

Cl

2

[36]

c

2

Cl

2

)2141

)2193

)43

)37

[36]

c

2

c

Pt(1-Meadam)

2

Cl

2

[36]

a

Pt(py)

2

Cl

Pt(Ypy) Cl

2

)1960

)1957

)54

)52

[37]

a

2

ðdave

Þ

a

ꢅ

CDCl3.

dine ligands contain empty p orbitals capable of

c

DMF-d7.

CD2Cl2.

DMSO.

accepting electron density from platinum. This back-

donation will reduce the electron density on the metallic

center, resulting in a deshielding in the Pt chemical

shifts. For pyridine ligands, it does not seem very im-

portant, since the trans compounds are observed at

lower ﬁelds than the cis as mentioned above.

A few results on diiodo complexes were reported by

our research group several years ago on some cis di-

amine complexes, and also with slightly more bulky

amines (mainly adamantanamine derivatives) [36].

These have been measured in DMF and some of the

results are shown in Table 5. All these compounds were

synthesized as to produce cis compounds. The more

bulky ligands showed two signals in ¹⁹⁵Pt NMR and we

have assumed partial isomerization of the cis to the trans

complexes. Based on data published in the literature, we

had suggested that the resonance of the cis isomers were

at higher ﬁelds than the corresponding trans compounds

b

d

Pt(secBuNH ) I showed one signal at )3322 ppm, while

2

2 2

the cis compound showed two peaks ()3309 and )3321

ppm), indicating that some isomerization has taken place.

If we compare the values in DMF with those in

CD3COCD3, the values in DMF were observed at slightly

lower ﬁelds than those in acetone (12–37 ppm). But all the

cis compounds were observed in DMF at lower ﬁelds than

the corresponding trans isomers. The Dd (cis–trans) vary

between 13 and 25 ppm. The diﬀerence seems to be slightly

more important in DMF (ave. Dd 21 ppm) than in

CD COCD (ave. Dd 7 ppm) for these three amines.

3

For the secondary amine Me2NH, the diﬀerence be-

tween the cis and trans isomers is much larger and is as

expected. The cis compound is observed at higher ﬁeld

and the Dd (cis–trans) is )190 ppm. For Et2NH, a

similar value (Dd ¼ ꢀ174 ppm) was observed, although

we were not certain of the identiﬁcation of the cis

compound as discussed above.

(

Dd (cis–trans) between )29 and )53 ppm). But these

assignments might have been inverted. DMF is a rea-

sonably good solvent to isomerize such compounds,

especially those with bulkier ligands.

For comparison purposes, we have remeasured our cis

and trans MeNH2, EtNH2 and secBuNH2 compounds in

DMF. The chemical shifts are shown in Table 4 along

with our results in CD3COCD3. With MeNH2, and

EtNH2 in DMF, there was only one signal for the cis and

trans compounds. The ¹⁹⁵Pt NMR spectrum of trans-

There are not many ¹⁹⁵Pt NMR data in the literature

on Pt(amine)2X2 (X ¼ Cl or I) systems. These data are

shown in Table 5. For the chloro system, the chemical

shifts of cis- and trans-Pt(NH3)2Cl2 have been reported

in DMF [30,32,33]. The data are identical for the two

isomers. The cis compound was also reported at )2097

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2225

ppm in DMSO [35] ppm. For NH2(CH2)5CH3, (X ¼ Cl)

the diﬀerence is larger, )2215 (cis in DMSO) and )2130

ppm (trans in CDCl3) [34], although the solvents are

diﬀerent. In the iodo system, the chemical shift of cis-

Pt(NH3)2I2 was reported in DMF at )3198 ppm [32]

and at )3264 ppm in CDCl₃[31], but no data are

available for the trans isomer. The other studies [36–38]

have been discussed above.

seems to be a linear relationship as expected, but the

dispersion around the straight line is fairly large. Fur-

thermore, some of the amines in the list are quite diﬀerent

in bulkiness. For the two secondary amines, the d(Pt)

values are more diﬀerent, but more data are needed to

conﬁrm the linear relationship.

The basicity of a ligand can also be evaluated by its

proton aﬃnity in the gas phase. There are not many

such values available in the literature. Fig. 4 shows the

d(Pt) versus the published proton aﬃnity of the amines

[60–64]. The linear relationship is much better and seems

to indicate that the proton aﬃnity value in the gas phase

is a better basicity indicator than the pKa values. The

latter are measured in a solvent which usually partici-

pates in the reaction and the results depend on many

factors like the bulkiness around the protonated atom.

The ¹⁹⁵Pt chemical shifts depend on many factors and

can be described by modiﬁed versions of RamseyÕs

equation [55–57]. One of the factor is the metallic char-

acter of the diﬀerent d orbitals of the platinum atom.

Therefore, the chemical shifts can give information of the

degree of covalency of the bonding between the metal and

the ligands. Strong r-donors should increase the electron

density on the metal resulting in a shielding in ¹Pt NMR.

The basicity of the ligands can be evaluated by the pKa

values of the protonated amines. We have attempted to

correlate the pKa values [58,59] with the ¹⁹⁵Pt NMR sig-

nals. Figs. 1 and 2 show the relation between d(Pt) versus

pKa values for the cis and trans primary amine com-

pounds, respectively. Fig. 3 shows a few results on sec-

ondary amines. For the primary amines, the maximum

95

1

13

3.3.2. H and C NMR

1

13

The H and C NMR signals are listed in Section 2

with the proposed assignments. No free ligand was de-

tected in the spectra. The NMR spectra of the free amines

were also measured and compared with those of the

complexes. Three of the ligands are commercially avail-

able as aqueous solutions, since they are gases at room

temperature. The chemical shifts of the free amines vary

diﬀerence in pK and in d(Pt) values are very small and the

a

experimental errors are not negligible. Therefore, there

-

3000

3050

3100

-

3340

3345

3350

3355

trans

MeA

Me2NH

Et2NH

secBuA

-3150

-3200

-3250

-3300

nBuA

isoPrA

nPrA

cis

Me2NH

EtA

Et

2

NH

11.1

isoBuA

10.75

-

3350

1

0.7

10.75

10.8

10.85 10.9

pKa

10.95

11

11.05

3360

1

0.5

10.55

10.6

10.65

pKa

10.7

10.8

Fig. 3. d(¹⁹⁵Pt) vs pKa of the protonated amines for cis- and trans-

PtL2I2 (L ¼ secondary amine).

Fig. 1. d(¹⁹⁵Pt) vs pKa of the protonated amines for cis-PtL2I2

L ¼ primary amine).

(

-

3330

3340

3350

3360

-

3330

3340

3350

3360

3370

3380

MeA

secBuA

cis

nBuA

nPrA

isoPrA

EtA

trans

MeA

nBuA

nPrA

tBuA

EtA

-3370

tBuA

isoBuA

10.75

-

3380

9

10.5

10.55

10.6

10.65

pKa

10.7

10.8

10

915

920

925

AP (kJ/mole)

930

935

940

Fig. 2. d(¹⁹⁵Pt) vs pKa of the protonated amines for trans-PtL2I2

L ¼ primary amine).

Fig. 4. d(¹⁹⁵Pt) vs proton aﬃnity (PA) of the amines for cis- and trans-

PtL2I2.

(

2226

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

13

with the solvents. For example, the chemical shift of

MeNH2 is observed at 2.927 ppm in CD3COCD3 (con-

taining water from the dissolved amine) and at 2.245 ppm

in pure D2O. Therefore, the spectra of the three aqueous

amineswere notrecorded in pure acetone. Forthis reason,

it is diﬃcult to discuss the Dd values (d_c_o_m_p_l_e_x–d_a_m_i_n_e).

Furthermore, acetone is not an inert solvent for amines.

We have measured the H and ¹³C NMR spectra of the

free amines in CD3COCD3, CDCl3, and D2O and calcu-

lated the Dd values. In acetone (complexes and free am-

ines), these values are not very informative, but in CDCl3

or D2O (complex in acetone, amine in CDCl3 or D2O), the

values decrease as the distance from the bonding atom

In ¹³C NMR, the ²J(¹⁹⁵Pt– C) and ³J(¹⁹⁵Pt– C)

coupling constants are also shown in Table 6. The ³J

values (cis: ave. 38 Hz, trans: ave. 27 Hz) are similar to

those observed in similar complexes [37,66,67]. For

secBuNH, the ³J(¹⁹⁵Pt– H) coupling constant on the

terminal C atom is smaller (cis: 24 Hz, trans: 21 Hz) than

1

3

195

1

the other J( Pt– H) constant (cis: 32 Hz, trans: 28

2

1

Hz). The J are much smaller than expected, probably

because of inadequate orientation of the orbitals. The

average values are 17 Hz (cis) and 11 Hz (trans).

The ligand sec-butylamine is a chiral molecule. Its

complexes have shown a single resonance in ¹⁹⁵Pt

1

NMR. In H NMR, the trans isomer has shown two

1

increase, as expected [65]. In H NMR, the Dd values are

smaller for the trans isomers, indicating that they are more

series of peaks, while only one was observed for the cis

complex. Surprisingly in ¹³C NMR, the reverse was

observed. The cis isomer has shown two series of

peaks, while only one series of signals was observed for

the trans compound. The separation between the two

series becomes negligible as the distance from the

bonding atom increases.

shielded upon coordination than the cis compounds. In

1

3

C NMR, the Dd values are smaller for the cis isomers,

indicating that the latter are more shielded upon coordi-

nation than the corresponding trans compounds.

The signals of the amine groups in the complexes

could be detected in CD3COCD3. Furthermore, an ap-

2

195

1

proximate value of the J( Pt– H) coupling constants

could be calculated and are shown in Table 6. These

vary between 65 and 70 Hz (ave. 67 Hz) for the cis

compounds and between 58 and 62 Hz (ave. 59 Hz) for

3.4. Crystal structures and the trans inﬂuence

The crystal structures of three cis (crystals I–III) and

ﬁve trans diamine complexes (crystals IV–VIII) were de-

termined. The crystallographic details are shown in Ta-

bles 1 and 2. The crystallographic results were compared

with those obtained on the diiodo complexes with pyri-

dine ligands [37]. The data on pyridine derivatives seemed

to indicate that the trans inﬂuence of the chloro ligand is

3

195

1

the trans isomers. A few J( Pt– H) coupling constants

were also observed. The average values are 45 Hz for the

cis compounds and 36 Hz for the trans complexes.

Therefore, these coupling constants are larger in the cis

isomers as observed in other related compounds [37].

Table 6

Coupling constants with ¹⁹⁵Pt of the complexes

2

195

1

3

195

1

2

195

13

3

195

13

Amine

MeNH

Isomer

J( Pt– H)

J( Pt– C)

2

cis

69

61

49

35

21

15

trans

EtNH

2

cis

68

58

18

12

48

36

trans

nPrNH

2

cis

68

59

17

10

45

36

trans

nBuNH

2

cis

trans

65

58

43

18

12

43

34

isoPrNH

2

cis

trans

66

60

13

11

30

22

isoBuNH

2

cis

trans

66

59

18

14

secBuNH

2

cis

67

32, 24

28, 21

trans

10

9

tBuNH

2

trans

58

17

Me NH

2

cis

trans

70

62

43

37

14

10

Et

2

NH

2

cis

68

60

13

9

34

22

trans

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2227

larger than the one of pyridine, although the diﬀerence

might be small. The trans inﬂuence of the iodo ligand

seemed much larger than the one of the chloro ligand. The

order of the trans inﬂuence series was found to be [37]

larger, although the diﬀerence might not appear signiﬁ-

cant. The average Pt–N bond distance in the trans com-

ꢂ

plexes is 2.062 A. In the cis isomers, the bonds are very

ꢂ

similar for crystals I and II (ave. 2.054 A), but it is very

ꢀ

diﬀerent in crystal III. The latter crystal contains two

bulky secondary amines (Et NH) located in cis position

I ꢆ Cl > py

2

195

For the dipyridine isomers, the diﬀerence in d( Pt)

between the two isomers is greater for the diiodo com-

plexes (average 65 ppm) than for the dichloro complexes

(

45 ppm) [37]. McFarlane [68] has proposed for the cis

195

2 2

and trans isomers of the type PtL X , that Dd( Pt) is

greater when the ligands L and X are far from each

other in the trans inﬂuence series, since the energy dif-

ference (DE terms in Ramsey equation) between the two

isomers would be larger. Contrary to the trans eﬀect

series which is relatively well known, the trans inﬂuence

series is not known with certainty. In order to compare

the results obtained in the pyridine system with the di-

amine system, we have studied several diamine com-

plexes by X-ray diﬀraction methods.

The crystal structures of the cis diiodo complexes

with MeNH2 (I), nBuNH2 (II) and Et2NH (III) and of

the trans compounds containing the ligands nPrNH2

(

IV), isoBuNH2 (V), nBuNH2 (VI), tBuNH2 (VII) and

Me NH (VIII) were determined. In cis-Pt(nBuNH ) I

2

2 2 2

(

II), there are two independent molecules, one is located

Fig. 6. Labeled diagram of cis-Pt(Et2NH)2I2 (III).

on a twofold axis, while the second is in general posi-

tion. In trans-Pt(MeNH2)2I2 (VIII), the Pt atom is

located on an inversion centre. Labeled diagrams of a

few structures are shown in Figs. 5–8.

The Pt–I and Pt–N bond distances are listed in Table 7.

The Pt–I like the Pt–Cl bond distances usually do not vary

very much with the trans ligand, but the Pt–N bond dis-

tances are usually more sensitive to its trans ligand. The

Pt–I average bond distance in the cis structures (in trans

ꢂ

position to an amine) is 2.598 A, while it is 2.604 A in the

trans isomers (trans to iodide). The latter seems slightly

Fig. 7. Labeled diagram of trans-Pt(isoPrNH2)2I2 (V).

Fig. 8. Labeled diagram of trans-Pt(tBuNH2)2I2 (VII). The terminal

methyl groups are disordered on two positions.

Fig. 5. Labeled diagram of cis-Pt(MeNH2)2I2 (I).

2228

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

Table 7

Selected bond distances (A) for the complexes Pt(amine)2X2

ꢂ

Complex

Pt–N

Pt–I

cis-Pt(MeNH

2

)

2

I

2

(I)

(II)

2.047(12), 2.070(10)

2.042(18), 2.042(18)

2.5938(13), 2.5973(13)

2.604(2), 2.604(2)

2.595(2), 2.596(2)

2.5967(13), 2.6011(13)

2.594(2), 2.599(2)

2.6049(9). 2.6062(9)

2.5972(9), 2.5977(9)

2.6098(7), 2.6072(7)

2.6104(6)

cis-Pt(nBuNH

2

)

2

I

2

.059(21), 2.054(18)

cis-Pt(Et NH)

2

I

2

(III)

2.112(10), 2.113(10)

2.024(8), 2.096(9)

2.054(6), 2.069(6)

2.051(7), 2.058(8)

2.068(6), 2.062(5)

2.070(5)

trans-Pt(nPrNH

2

)

2

I

2

(IV)

(V)

trans-Pt(isoPrNH

trans-Pt(nBuNH

trans-Pt(tBuNH

trans-Pt(Me NH)

)

2

I

2

)

2

I

2

(VI)

(VII)

(VIII)

2 2 2

) I

2

I

2

to each other, resulting in very long Pt–N bonds

(

sition to a primary amine is similar to the one in trans

position to a chloro ligand

ꢂ

2.113(10) A). Therefore, these distances are not only

inﬂuenced by its trans ligand, but also by the substituents

on the N donor atoms. In trans-Pt(Et2NH)(NH@

C(NEt2)2) I2 [69], the Pt–N bond was also longer (2.095(9)

ꢀ

I > Cl ꢃ Amines > Ypy

These results support the previous discussion on the

1

95

ꢂ

Pt chemical shifts observed in NMR. This trans in-

ﬂuence series might explain why the NMR chemical

shifts d(Pt) of cis- and trans-Pt(amine) are quite

similar, while the ones of cis and trans-Pt(Ypy) are

A), although the bulkiness is slightly reduced in a trans

compound. In the iodo-bridged dimer (Et2NH)IPt(l-

I)2Pt(Et2NH)I [70], the Pt–N bonds are normal (2.065(9)

2 2

I

ꢂ

A), probably because the steric hindrance is reduced by

2 2

I

very diﬀerent. In the chloro analogues, the amine com-

plexes have identical chemical shifts, while the pyridine

compounds have slightly diﬀerent d(Pt). The crystallo-

graphic results seem to support the suggestion of

McFarlane [68] mentioned above.

the smaller angle inside the four-membered ring, which

increases the other angles. The cis ligand is also mono-

atomic. The inﬂuence of the bulkiness of the amine can

also be seen by comparing the results on the crystals

containing nBuNH2 (VI) and tBuNH2 (VII). The Pt–N

The crystal structure of cis-Pt(MeNH2)2Cl2 was re-

ported [72]. Two crystallographic forms were observed.

In form A, the two MeNH2 ligands are located on the

same side of the Pt plane, while form B contains three

types of units. Two of these look like form A, while in

the third unit, one of the methyl groups is above the

plan, while the other one is located below the Pt plane.

Fig. 5 shows the diagram of the diiodo analogue

(crystal I). The two methyl groups are located on

diﬀerent sides of the Pt plane.

It is interesting to observe that a few trans crystals

were obtained from the isomerization of the cis isomers

during the recrystallizing process in organic solvents.

Therefore, this method is an eﬀective alternate method

to synthesize trans compounds, especially with sterically

more demanding ligands.

and Pt–I bonds are slightly longer in the tBuNH2 crystal

ꢂ

2.054(8) and 2.5974(9) A for VI and 2.065(6) and

(

2

ꢂ

.6085(7) A for VII). In the reported structure trans-

ꢂ

Pt(tBuNH ) Cl , the average Pt–N bond was 2.047(6) A

2

[

71]. In trans-Pt(Me NH) I (VIII), the Pt–I bonds are the

2 2 2

ꢂ

longest observed in this study, (2.6104(6) A). The pres-

ence of two methyl groups on the bonding atom probably

increases this distance. The Pt–N bonds are also slightly

ꢂ

long (2.070(5) A. These values are identical to those ob-

served in trans-Pt(tBuNH2)2I2 (VII), another bulky

amine. These results seem to indicate that the bulkiness of

the amine is an important factor in the Pt–N bond dis-

tances, probably more important than its trans inﬂuence.

Nevertheless, the data on less bulky amines can give an

indication of their trans inﬂuence.

In the diiodo dipyridine series (Ypy), the Pt–N bonds

located in trans position to the iodo ligand were found

ꢂ

longer (ave. 2.052(12) A) than those in trans position to

ꢂ

pyridine (ave. 2.020(12) A) [37]. The latter value is

4. Conclusions

smaller than the corresponding distance in the diamine

series. These results indicate that the trans inﬂuence of

amines is larger than the one of pyridine ligands, al-

though it is smaller than the one of iodo ligands.

It might be comparable to the one of chloro ligands.

There are a few structures in the literature on cis- and

trans-Pt(amine)2Cl2 [54,72–76]. For example in cis-

Complexes of the type cis- and trans-Pt(amine)₂I₂

were characterized by multinuclear NMR in a relatively

inert solvent, acetone. In ¹⁹⁵Pt NMR, the diiodo com-

plexes were observed at much higher ﬁelds than the

dichloro analogues. Contrary to the pyridine analogues,

the cis and trans diiodo diamine compounds were ob-

served at similar ﬁelds. This diﬀerence was related to the

relative order of iodo, amine and pyridine ligands in the

trans inﬂuence series.

ꢂ

Pt(MeNH ) Cl , the average Pt–N bonds is 2.046 A [72],

2

ꢂ

while it is 2.057(12) A in the iodo analogue (I). These

data seem to indicate that the Pt–N bonds in trans po-

F.D. Rochon, V. Buculei / Inorganica Chimica Acta 357 (2004) 2218–2230

2229

There seems to be a dependence of the d(Pt) on the pKa

of the protonated ligand, but the dispersion about the

linear relation is quite large. The pKa values of the pro-

tonated amines were measured in water or alcohol and

they are inﬂuenced by the presence of molecules of solvent

close to the protonated site (N atom). The intrinsic bas-

icity of the amines can be evaluated from the gas phase

protonic aﬃnities or by the Hammett constants, but these

values are not easily accessible. Some results on the gas

phase protonic aﬃnities indicate a linear relationship with

the ¹⁹⁵Pt chemical shifts. As these values become more

available, they might bring further information on the

nature of the metal–amine bond.

[3] M.J. Cleare, P.C. Hydes, B.M. Malerbi, D.M. Watkins, Biochimie

0 (1978) 835.

6

[

4] P.D. Braddock, T. Connors, M. Jones, A.R. KhorHar, D.H.

Melzack, M.L. Tobe, Chem. Biol. Interact. 11 (1975) 145.

5] F.D. Rochon, R. Melanson, Acta Crystallogr., Sect. C 42 (1986)

1291.

[

[6] M. Nicolini, Platinum and Other Metal Coordination Compounds

in Cancer Chemotherapy, University of Padua, Italy, 1987.

[

7] B. Rosenberg, Biochimie 60 (1978) 859.

8] J.P. Caradonna, S.J. Lippard, Am. J. Chem. Soc. 104 (1982)

5

793.

[9] S. Mansy, G.Y.H. Chu, R.E. Duncan, S. Tobias, J. Am. Chem.

Soc. 100 (1978) 607.

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[

(1986) 4403.

11] B. Rosenberg, Cancer (1985) 2303.

[

The ³J(¹⁹⁵Pt– H) coupling constants in the

1

12] S.E. Miller, D.A. House, Inorg. Chim. Acta 173 (1990) 53.

Pt(amine) X complexes are larger for the cis isomers

2

[13] C.J. Abraham, K.J. Gerard, D.A. House, Inorg. Chim. Acta 209

(1993) 119.

2

(

might be a relatively simple method to diﬀerentiate be-

45 Hz) than for the trans compounds (36 Hz), which

[14] S.E. Miller, D.A. House, Inorg. Chim. Acta 161 (1989) 131.

2

195

1

[15] S.E. Miller, D.A. House, Inorg. Chim. Acta 166 (1989) 189.

[16] S.E. Miller, H. Wen, D.A. House, W.T. Robinson, Inorg. Chim.

tween the two diﬀerent isomers. The J( Pt– H) cou-

pling constants of the amine protons are also larger in

Acta 184 (1991) 111.

[17] S.E. Miller, D.A. House, Inorg. Chim. Acta 187 (1991) 125.

[18] S.E. Miller, K.J. Gerard, D.A. House, Inorg. Chim. Acta 190

3

195

13

the cis complexes (67 verus 59 Hz). The J( Pt– C) are

also geometry dependent. The average values are 38 and

(

1991) 135.

[19] E. Koubeck, D.A. House, Inorg. Chim. Acta 191 (1992) 103.

20] K. Hindmarsh, D.A. House, M.M. Turnbull, Inorg. Chim. Acta

57 (1997) 11.

2

7 Hz for the cis and trans compounds, respectively. The

2

_J₍195Pt– C) are small, 17 (cis) and 11 (trans) Hz.

13

[

The crystal structures of eight diiodo complexes were

determined and the results have shown that the iodo

ligand has a slightly larger trans inﬂuence than amines,

which in turn have a larger trans inﬂuence than pyridine

derivatives. This fact explained the smaller diﬀerence in

d(¹⁹⁵Pt) between the cis and trans isomers for the diiodo

diamine complexes when compared to the diiodo dipyri-

dine compounds. The Pt–N bonds in cis-Pt(Et NH) I

2

[21] R. Faggiani, B. Lippert, C.J.L. Lock, B. Rosenberg, J. Am. Chem.

Soc. 99 (1977) 777.

[

22] B. Lippert, C.J.L. Lock, B. Rosenberg, M. Zvagulis, Inorg. Chem.

7 (1978) 2971.

23] R. Faggiani, B. Lippert, C.J.L. Lock, B. Rosenberg, Inorg. Chem.

6 (1977) 1192.

1

[

1

[24] R. Faggiani, B. Lippert, C.J.L. Lock, B. Rosenberg, Inorg. Chem.

17 (1978) 1941.

2

2 2

[

25] B. Rosenberg, Cancer Chemother. Rep. 63 (1979) 1433.

26] J.A. Stanko, L.S. Hollis, J.A. Schreifels, J.D. Hoeschele, J. Clin.

Hematol. Oncol. 7 (1977) 138.

are very long caused by steric factors.

Finally, the crystal structure analysis of trans-

Pt(Me2NH)2I2, which was isolated from the isomeriza-

tion of the cis analogues in ethanol, conﬁrmed the cis

trans isomerization in organic solvents.

[

27] C.J. Boreham, J.A. Broomhead, D.P. Fairlie, Aust. J. Chem. 34

(1981) 659.

[28] J.A. Broomhead, D.P. Fairlie, M.W. Whitehouse, Chem. Biol.

Interact. 31 (1980) 113.

[29] S.K. Aggarwal, J.A. Broomhead, D.P. Fairlie, M.W. Whitehouse,

Cancer Chemother. Pharmacol. 4 (1980) 249.

5

. Supplementary material

[30] T.G. Appleton, A.J. Bailey, K.J. Barnham, J.R. Hall, Inorg.

Chem. 31 (1992) 3077.

[

31] S.J. Lippard, J. Mol. Biol. 194 (1987) 705.

32] T.G. Appleton, J.R. Hall, S.F. Ralph, Inorg. Chem. 24 (1985)

The CIF tables for the eight crystals have been de-

posited to the Cambridge Data File Centre. The deposit

numbers are: CCDC 224779–224786.

4

685.

[

33] Y. Qu, N. Farrell, M. Velsecchi, L. de Greco, S. Spinelli, Magn.

Res. Chem. 31 (1993) 920.

34] M. Motschi, P.S. Pregosin, L.M. Venanzi, Helv. Chim. Acta 62

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1979) 667.

35] S.J.S. Kerrison, P.J. Sadler, J. Chem. Soc., Chem. Commun.

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717.

[37] C. Tessier, F.D. Rochon, Inorg. Chim. Acta 295 (1999) 25.

Acknowledgements

(

The authors are grateful to the Natural Sciences and

Engineering Research Council of Canada for ﬁnancial

support of the project.

2

[

38] T.B. Ha, P. Castan, J.P. Souchard, F.L. Wimmer, J. Chem. Res.

S) (1992) 112.

(

39] XSCANS and SHELXTL (PC version 5, 1995) programs, Bruker

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Article Doi

Multinuclear NMR study and crystal structures of complexes of the types cis- and trans-Pt(amine)2I2

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