Synthesis and characterisation of 2,2-bis(hydroxymethyl)-1,3-diselenolato metal(II) complexes bearing various phosphanes

FULL PAPER

DOI: 10.1002/ejic.200900824

Synthesis and Characterisation of 2,2-Bis(hydroxymethyl)-1,3-diselenolato

Metal(II) Complexes Bearing Various Phosphanes^[‡]

Tobias Niksch,^[a]Helmar Görls,^[a]Manfred Friedrich,^[a]Raija Oilunkaniemi,^[b]

Risto Laitinen,^[b]and Wolfgang Weigand*^[a]

Dedicated to Prof. Wolfdieter A. Schenk on the occasion of his 65th birthday

Keywords: Steric demand / Selenolato ligands / Phosphane ligands / Hydrogen bonds / X-ray diffraction

An improved synthesis of 4,4-bis(hydroxymethyl)-1,2-di-

selenolane and the complexation properties of the corre-

sequently, several group-10 metal complexes with P–M–P

angles (bite angles) in the range from 71–108° are investi-

sponding diselenolato dianion to group-10 metals are re- gated. The use of the sterically demanding bridging phos-

ported. We describe an efficient and straightforward pro-

cedure that bypasses the isolation of the malodorous and air-

sensitive diselenol and starts with the diselenide and an ap-

propriate group-10 metal complex bearing phosphane and

chlorido ligands. A series of complexes with various mono-

and bidentate phosphanes is prepared and characterised by

multinuclear NMR spectroscopy, mass spectrometry, and ele-

mental analysis. Furthermore, the structure of most com-

plexes is studied by single-crystal X-ray diffraction to estab-

lish their supramolecular arrangement in the solid state. Con-

phane 4,5-bis(diphenylphosphanyl)-9,9-dimethylxanthene,

which exhibits a large bite angle yields a mixture of a di- and

trinuclear complex. While the platinum-containing com-

plexes are proven to be rather stable, the palladium and

nickel analogues tend to decompose. Especially, the nickel

complexes were found to be sensitive against oxidation. This

circumstance leads to the formation of the so far unknown

1,8-bis(diphenylphosphanyl)naphthalene monooxide, the

formation and structure of which could be confirmed from

NMR spectroscopic data and single-crystal X-ray diffraction.

nols has mainly been concerned with mono-^[6a]and dinu-

clear^[6b]complexes of monodentate selenols. Information

Introduction

Almost a century ago the first metal complexes of organo- of bis(phosphane) platinum-group metal complexes

selenium compounds were reported. In 1911 Fritzmann of bidentate organoselenium derivatives is rather sparse and

prepared the first selenoether platinum(II) complexes,^[1a]is mainly concerned with Pt^IIcomplexes of diselenols

and some years later the corresponding palladium(II) ana- bearing aromatic fragments in the bridging moieties^[7]and

logues.^[1b]Since that time the chemistry of selenium-con- complexes of diselenocarbonate derivatives^[8]or diselenol-

taining ligands has developed rapidly. In particular those enes.^[9]Regarding Pd^{II [8a,9d,10]}and Ni^{II [9a,11]}bis(phos-

complexes are of great interest in means of catalytic applica- phane) complexes with bidentate organoselenium ligands,

tions^[2]and as precursors for electronic devices.^[3]Beyond information is even sparser. Likewise, most of these com-

this, attention is paid to their biological activities as they plexes contain diselenocarbonate^{[8a,10a,10b,11d,11e]}or diselen-

are promising antitumor agents.^[4]A huge variety of seleno- olene^{[9a,9d,10c–10g,11c–11e]}derivatives.

ether complexes of group-10 metals has been reported dur-

More than twenty years ago, Schmidt and Hoffmann

have reported the thus far only application of alkyldiselen-

ols in complexes of the type [ML₂(Se,SeЈ-SeRSe)] (where M

= Ni, Pd, Pt; L = phosphane, R = alkyl spacer).^[12]They

ing the last decades.^[5]Though the ligand chemistry of sele-

[‡] Determination of the Steric Demand of Bidentate Phosphanes

Using X-ray Crystal Structure Data, Part 1. Part 2: T. Niksch, also succeeded in the synthesis of the 1,3-diselenolato-2-

H. Görls, W. Weigand, Eur. J. Inorg. Chem. 2010, 95–105,

thiapropane and 1,3-diselenolato-2-selenapropane deriva-

following paper.

tives, carrying a sulfur or selenium atom in the bridging

alkyl group, respectively. This elaborate preparation de-

manded reduction of the polymeric starting materials in li-

quid ammonia. Whereas the diselenium analogue of me-

thanedithiol is unknown, Khanna et al. have reported the

crystal structure of [Pt(PPh₃)₂(CH₂Se₂)] that was prepared

by the reaction of oligomeric [Pt(PPh₃)₂(µ-Se)]_nwith dichlo-

[a] Institut für Anorganische und Analytische Chemie, Friedrich-

Schiller-Universität Jena,

August-Bebel-Str. 2, 07743 Jena, Germany

Fax: +49-3641-948102

E-mail: wolfgang.weigand@uni-jena.de

[b] Department of Chemistry, University of Oulu,

P. O. Box 3000, 90041 Oulu, Finland

Supporting information for this article is available on the

WWW under http://dx.doi.org/10.1002/ejic.200900824.

74

Eur. J. Inorg. Chem. 2010, 74–94

Steric Demand of Bidentate Phosphanes, Part 1

romethane.^[13]Applying a similar reaction, Yeo et al. were

able to obtain [Pt(PPh₃)₂(η²-Se₂C₂O₂-Se,SeЈ)] by the reac-

tion of [Pt₂(PPh₃)₄(µ-Se)₂] and oxalyl chloride.^[14]

In this work, we report a simple and efficient method for

the preparation of the [ML₂{(SeCH₂)₂C(CH₂OH)₂}] (M =

Ni, Pd, Pt; L = mono- or ½-bidentate phosphane) com-

plexes from the corresponding diselenide and the appropri-

ate precursor [MCl₂L₂]. This straightforward approach cir-

cumvents the need to isolate the malodorous and oxygen

sensitive diselenols and affords the complexes in good yields

in a one-pot reaction. All products were identified and

characterised by multinuclear NMR spectroscopy (¹H, ¹³C,

³¹P, ⁷⁷Se, ¹⁹⁵Pt NMR), mass spectrometry and elemental

analysis. For further investigations, the compounds were

additionally studied by single-crystal X-ray structure analy-

sis, when feasible.

Scheme 1. Synthesis of 4,4-bis(hydroxymethyl)-1,2-diselenolane (2).

a) First synthesis of 2 reported from Bergson in 1958.^[16]b) Im-

proved procedure for the synthesis of 2 via 5,5-bis(bromomethyl)-

2,2-dimethyl-1,3-dioxane (1).

Results and Discussion

I. 4,4-Bis(hydroxymethyl)-1,2-diselenolane (2)

It is well known that the diselenolane system tends to

polymerise, e.g. the unsubstituted 1,2-diselenolane and the

3-methyl-substituted analogue both form a polymeric gum

in the solid state.^[15]In this work, we utilised 4,4-bis(hy-

droxymethyl)-1,2-diselenolane (2), because it is a stable

compound that is easy to handle. It was first reported to be

produced in a very poor yield by the reaction of 2,2-bis-

(iodomethyl)propane-1,3-diol with dilithium diselenide,

Li₂Se₂(path a in Scheme 1).^[16]We were able to improve the

synthesis by starting from 2,2-bis(bromomethyl)propane-

1,3-diol (see path b in Scheme 1). Selenium was introduced

by using potassium selenocyanate, KSeCN, which substi-

tutes the bromine in alkyl bromides to give the correspond-

ing alkyl selenocyanates. The twofold substitution required

a long reaction time and harsh reaction conditions. It also

proved necessary to protect the hydroxy groups as the ketale

1 to obtain a good conversion. The reaction of 1 with

KSeCN was carried out in boiling acetone for 14 days, af-

fording the crude diselenocyanated product, which was re-

duced with sodium borohydride in ethanolic solution. The

diselenol was easily oxidised by oxygen followed by acidic

deprotection of the hydroxy groups. The overall yield of

cyclic diselenide 2 over two steps was 69%.

due to the ring strain, forcing the lone pairs of the selenium

atoms in eclipsed conformation.^[20]

Due to the presence of two hydroxy groups and two sele-

nium atoms in compound 2, there are some interesting as-

pects concerning its molecular structure and the supra-

molecular arrangement in the solid state. On the one hand

the hydroxy functions might link molecules and build up a

network via hydrogen bonds, while on the other hand non-

bonding interactions between the selenium atoms might in-

fluence the arrangement of 2 in the solid state. There are

several compounds known, showing close intermolecular

Se···Se distances,^[21]that are remarkably shorter than the

sum of the van der Waals radii of 4.0 Å.^[22]For some com-

pounds these chalcogen–chalcogen interactions are most

determinant for their arrangement in the solid state, as for

instance can be seen in the work of Werz and Gleiter.^[21f–21l]

As shown in Figure 1 short intermolecular Se···Se distances

might be characterised as interactions between occupied

p(Se) orbitals and empty σ*(Se-R⁴) orbitals.^{[21h,21j,21l,23]}

1

The H NMR spectrum of 2 exhibits resonances at δ =

4.76 (OH), 3.46 (CH₂OH) and 3.17 (CH₂Se) ppm, with the

Figure 1. Short intermolecular selenium–selenium distances deriv-

ing from interaction of occupied p and unoccupied σ* orbitals.

2

last resonance showing typical ⁷⁷Se satellites with J_H,Se

=

15.4 Hz. The coupling to ⁷⁷Se is also seen in the

¹³C{¹H} NMR spectrum, in which the signal of the methyl-

The molecular structure of 2 exhibits an interesting inter-

ene group next to the diselenide bridge appears at δ = play of these effects (Figures 2 and 3). Regarding the hydro-

35.6 ppm as a singlet with ⁷⁷Se satellites (¹J_C,Se= 66.2 Hz). gen-bonding^[24]network, only intermolecular hydrogen

1

The coupling constants to H and ¹³C are in good agree- bonds were present. A closer look reveals that four mole-

ment with those reported for alkyl diselenides.^[17]In ad- cules are connected through four hydrogen bonds building

dition to that, the presence of selenium in 2 allows its spec- an almost perfect square (Figure 2, middle). Thus the mole-

troscopic investigation via ⁷⁷Se NMR techniques. The sele- cules are aligned in a double-chain-like structure. Concern-

nium atoms of 2 show resonance at δ = 270.0 ppm that is ing selenium selenium interactions, we found a huge net-

typical for five-membered cyclic diselenides.^[18]The strong work of close contacts (Figure 2, right), arranging all sele-

downfield shift compared to acyclic diselenides^[19]might be nium atoms in separated layers with a thickness of less then

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Figure 2. Left: molecular structure of 4,4-bis(hydroxymethyl)-1,2-diselenolane (2) in the crystal. Centre: view along the b-axis, displaying

intermolecular hydrogen-bonding system. Right: Se···Se interactions in the crystal (all other atoms have been omitted). All ellipsoids are

drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths [Å] and angles

[°]: Se1–Se2 2.3743(7), Se1–C1 1.959(5), Se2–C2 1.972(5), O2···O1ⁱ2.687 (intrastrand hydrogen bonds), O2···O1ⁱⁱ2.686 (interstrand hydro-

gen bonds), Se2···Se2Ј 3.358 (dashed lines), Se1···Se2Ј 3.677 (dotted lines); C1–Se1–Se2 91.36(13), C2–Se2–Se1 92.19(13), O1ⁱⁱ···O2···O1ⁱ

88.92 (upper left and lower right corner of the quadrangular hydrogen bridging system), O2···O1ⁱ···O2ⁱⁱⁱ91.08 (upper right and lower left

corner); i: x, –y, –0.5 + z; ii: –x, y, 1.5 – z; iii: –x, –y, 1 – z.

0.9 Å (based on atom positions). The intermolecular Se···Se

distances are 3.36 Å and 3.68 Å and hence significantly

shorter than the sum of the van der Waals radii and even

shorter than most of the reported selenium–selenium inter-

actions (for some examples see ref.^[21]). The value of 3.36 Å

is even shorter than the interstrand distances in elemental

grey selenium, which is reported to be 3.43 Å.^[25]Figure 3

displays the view along the c-axis, clearly showing the sepa-

rated selenium layers that are connected through hydrogen

bonds, building a three-dimensional network.

Figure 3. View along the c-axis of the crystal structure of 2 showing

the three-dimensional supramolecular arrangement due to strong

intermolecular Se Se interactions and hydrogen bonds. For the sake

of clarity a ball-and-stick model is displayed, while hydrogen atoms

and solvent molecules have been omitted.

Figure 4. Summary of the investigated mono- and bidentate phos-

phanes and their systematic names. The abbreviations used in the

text are given in parentheses.

II. [PtCl₂(4-dppdbf)₂] (3), [MCl₂(dppn)] {M = Ni (4), Pd

(5), Pt (6)}, [PdCl₂(dppn)·PdCl₂] (7) and [PtCl₂(xantphos)]

(8)

The phosphanes investigated in this work and their ab-

The platinum complex cis-[PtCl₂(4-dppdbf)₂] (3) involv-

breviations are summarised in Figure 4. Important NMR ing the sterically demanding 4-dppdbf, was easily prepared

spectroscopic data, coupling constants and P1–M–P2 from [PtCl₂(cod)] in almost a quantitative yield and high

angles for compounds 2–29 are outlined in Table 1. The selectivity. The ³¹P{¹H} NMR spectrum shows a singlet

1

main emphasis in this work involves the influence of the with typical ¹⁹⁵Pt satellites at δ = 9.7 ppm. The J_P,Ptcou-

bite angle of the phosphane and the spheric crowding at the pling constant of 3742 Hz is consistent with a cis-configura-

metal centre.

tion of dichloridodiphosphaneplatinum(II) that has been

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Eur. J. Inorg. Chem. 2010, 74–94

Steric Demand of Bidentate Phosphanes, Part 1

Table 1. NMR spectroscopic data, coupling constants and P1–M–P2 angles of compounds 2–29. For the correlation between ring size

and ³¹P NMR shifts see ref.^[26]

1

Compound ³¹P shift /ppm ⁷⁷Se shift /ppm^[a]

¹⁹⁵Pt shift /ppm^[a]J_{P, Pt}/Hz^[b]

Further coupling constants /Hz

P1–M–P2 angle /°

2

270.0^[c]

3^[d]

4

9.7

39.4

24.5

3742

103.36(4)

91.18(5)

90.37(5)

5

6

86.58(8)

92.20(7)

100.87(8)

94.62(5)

94.98(6)

7^[d]

8

5.5

9.8

3312

–4329.8

–4620.0

–4798.6

–4840.9^[c]

–4848.3^[c]

–4655.4^[c]

–4364.0

–4787.3

–4748.0

–4758.4

–4685.9^[c]

–4816.6

–4833.6

–4891.8

–4786.4

3694

2694

2491

2897

2967

2315

2442

2721

2736

2652

2573

2783

2846

2886

2952

9

–26.1

–63.5

22.0

16.0

–49.6

34.5

47.9

–1.9

8.1

–36.0

–33.2

60.0

66.1

–20.5

–47.9

–42.6

–25.2

12.4

39.7

27.9

33.2

64.9

61.1

8.8

10

11a/11b

12

13

14

15

16

17

18

19

20

21^[e]

24

25

26

27

28

29

47.7 (²J_{P, Se}), 167.3 (¹J_Pt,Se

48.5 (²J_{P, Se}

32.7 (²J_{P, Se}

33.8 (²J_{P, Se}

)

99.13(5), 97.03(8)

)

73.05(7)

71.71(4)

85.33(11)

87.81(8)

91.98(8)

88.36(10)

95.06(8)

101.21(6)

53.2 (²J_{P, Se}

45.0 (²J_{P, Se}

40.6 (²J_{P, Se}), 220.9 (¹J_Pt,Se

45.4 (²J_{P, Se}

43.8 (²J_{P, Se}

39.6 (²J_{P, Se}

49.7 (²J_{P, Se}

29.6, 50.2 (²J_P,Se

33.7, 40.8 (²J_P,Se

48.6 (²J_{P, Se}

48.7, 54.2 (²J_P,Se

8.9 (²J_{P, P}

)

13.7

1.2

)

15.1

19.8

49.2

13.5

20.9

59.9

–10.3, 39.4

107.65(5), 100.61(6)/101.69(8)^[f]

96.99(6)

)

85.84(7), 85.42(7)^[g]

93.0

134.7

24.9

)

99.34(6)

87.58(8)

)

[a] If not mentioned otherwise, the shifts derive from HMBC NMR spectra. [b] Coupling constant determined from ³¹P{¹H} NMR

spectroscopy. [c] Shift deriving from directly measured ⁷⁷Se{¹H} or ¹⁹⁵P{¹H} NMR spectrum. [d] Due to the poor solubility no ¹⁹⁵Pt

resonance could be detected. [e] All NMR spectroscopic data were obtained from solutions of expected 21, while single-crystal X-ray

analysis revealed the composition of complexes 22 and 23. [f] The first two values were taken from the molecular structure of 22, the last

from that of 23, respectively. [g] The values belong to two symmetry-independent molecules.

reported to exhibit coupling Ͼ3000 Hz.^[27]The single-crys-

tal X-ray structure of 3 confirmed the formation of cis-iso-

mer (Figure 5). Due to the presence of two dibenzofuran

moieties, the P1–Pt–P2 angle of 103.36(4)° is ca. 3.5° larger

than the corresponding angle in [PtCl₂(PPh₃)₂] [99.12(3)°

and 99.93(4)° for two symmetry-independent molecules^[28]].

Additionally, intramolecular π–π stacking interactions be-

tween the two dibenzofuran moieties were seen in 3. The

average distance of the planes of the rings marked with A

and B (see Figure 5) is ca. 3.22 Å and the ring centroids are

shifted 1.01 Å against each other indicating typical face-to-

face π–π stacking interaction.^[29]

As chelating phosphane with a bite angle close to 90°

and a rigid backbone, dppn^[30]attracted our attention.

While [PdCl₂(dppn)] (5)^[30a]and [PtCl₂(dppn)] (6)^[30a,31]

have been prepared in the past, their nickel analogue

[NiCl₂(dppn)] (4) is not previously known. It could be pre-

cipitated as orange solid by stirring equimolar amounts of

dppn and Ni^IICl₂·6H₂O in ethanol under exclusion of oxy-

Figure 5. Molecular structure of [PtCl₂(4-dppdbf)₂] (3) in the crys-

tal. Ellipsoids are drawn at 50% probability level, hydrogen atoms

gen. Its ³¹P{¹H} NMR spectrum shows a resonance at δ =

and solvent molecules have been omitted for clarity. Selected bond

lengths [Å] and angles [°]: Pt–P1 2.2546(11), Pt–P2 2.2411(10), Pt–

Cl1 2.3544(11), Pt–Cl2 2.3627(10); P1–Pt–P2 103.36(4), Cl1–Pt–

Cl2 87.24(4). The average distance between the planes of the phenyl

rings marked A and B is 3.22 Å, while the shift of the two rings is

39.4 ppm.

Single crystals of 4 suitable for X-ray structure analysis

were grown from a concentrated dichloromethane solution.

Its molecular structure together with those of isomorphic

Pd and Pt complexes 5 and 6 is displayed in Figure 6. All about 1.01 Å.

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W. Weigand et al.

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complexes show a twofold axis of rotation through atoms

C5, C6 and the corresponding metal atom. The bite angle

(P1–M–P1A) of dppn differs only slightly depending on the

metal [91.18(5)°, 90.37(5)° and 92.20(7)° for Ni, Pd and Pt,

respectively]. The out-of-plane displacement of the two

phosphorus atoms, however, increases with the metal atom

becoming heavier, as can be seen from the torsion angles

(P1–C1···C1A–P1A) that are 33.68°, 34.31° and 35.03° for

4, 5 and 6, respectively.

Figure 7. Molecular structure of [PdCl₂(dppn)·PdCl₂] (7) in the

crystal. Ellipsoids are drawn at 50% probability level, hydrogen

atoms and solvent molecules have been omitted for clarity. Selected

bond lengths [Å] and angles [°]: Pd1–P1 2.234(2), Pd1–P2 2.232(2),

Pd1–Cl1 2.422(2), Pd1–Cl2 2.400(2), Pd2–Cl1 2.340(2), Pd2–Cl2

2.312(2), Pd2–Cl3 2.295(2), Pd2–Cl4 2.277(2); P1–Pd1–P2 86.58(8),

Cl1–Pd1–Cl2 82.49(7), Cl1–Pd2–Cl2 86.20(8), Cl3–Pd2–Cl4

91.23(8), P1–C1···C9–P2 9.89.

Figure 6. Molecular structure of [MCl₂(dppn)] [M = Ni (4), Pd (5)

and Pt (6)] in the crystal. Ellipsoids are drawn at 50% probability

level, hydrogen atoms and solvent molecules have been omitted for

clarity. Selected bond lengths [Å] and angles [°] (the first value re-

fers to the Ni, the second to the Pd and the third one to the Pt

analogue): M–P1 2.1529(9), 2.2276(10), 2.2195(4), M–Cl 2.2088(9),

2.3651(10), 2.3618(14); P1–M–P1A 91.18(5), 90.37(5), 92.20(7), Cl–

M–ClA 91.57(5), 90.33(5), 88.19(7), C1–P1–M 122.15(12),

121.25(13), 119.82(19), P1–C1···C1A–P1A 33.68, 34.31, 35.03.

Surprisingly a small amount of [PdCl₂(dppn)·PdCl₂] (7)

was obtained during the preparation of 5, as verified by

single-crystal X-ray structure analysis (see Figure 7). The

attempts to separate 7 from 5 by column chromatography

or fractional crystallisation were unfortunately not success-

ful, as were attempts to synthesise this compound or its

platinum analogue from the appropriate [M₂Cl₆]^2–precur-

sor.^[32]Instead, compounds 5 or 7 and some amount of pre-

cipitated MCl₂were obtained for palladium and platinum,

respectively (see Scheme 2). The small excess of free PdCl₂

forming 7 might be present in the reaction mixture as impu-

rity or it could have been generated from the precursor

[PdCl₂(NCPh)₂].

Scheme 2. The reaction of dppn with preformed [Pd₂Cl₆]^2–and

[Pt₂Cl₆]^2–ions.^[32]

[PtCl₂(xantphos)] (8) is obtained by reacting 4,5-bis(di-

phenylphosphanyl)-9,9-dimethylxanthene (xantphos) that

exhibits a large bite angle with an equimolar amount of

[PtCl₂(cod)] in dichloromethane for 12 h. The equivalent

phosphorus atoms show a resonance at δ = 9.8 ppm and a

1

coupling constant of J_P,Pt= 3694 Hz. The platinum atom

is clearly distracted from the main plane of the xanthene

moiety (see Figure 8). The angle between the planes

through the atoms P1, P2, C2, C12 and P1, P2, Pt, Cl1, Cl2

is about 86.8° and thus shows the platinum atom bound to

be almost perpendicular to the xanthene moiety. The plati-

num atom shows a significantly distorted square-planar co-

ordination with the P1–Pt–P2 angle being enlarged to

100.87(8)°.

Figure 8. Molecular structure of 8 in the crystal. Ellipsoids are

drawn at 50% probability level, hydrogen atoms and solvent mole-

cules have been omitted for clarity. Selected bond lengths [Å] and

angles [°]: Pt–P1 2.253(2), Pt–P2 2.264(2), Pt–Cl1 2.354(2), Pt–Cl2

2.348(2); P1–Pt–P2 100.87(8), Cl1–Pt–Cl2 86.83(8), P1–Pt–Cl1

85.71(8), P2–Pt–Cl2 85.17(8); the dihedral angle between the least-

squares planes (P1, P2, C2, C12) and (P1, P2, Pt, Cl1, Cl2) is 86.8°.

78

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Eur. J. Inorg. Chem. 2010, 74–94

Steric Demand of Bidentate Phosphanes, Part 1

III. [ML₂{(SeCH₂)₂C(CH₂OH)₂}] (M = Ni, Pd, Pt; L =

mono- or ½ bidentate phosphane) (9–21 and 24–28)

spectra. Indirect methods were performed on the determi-

nation of ⁷⁷Se and ¹⁹⁵Pt NMR spectra (¹H ⁷⁷Se HMBC and

¹H ¹⁹⁵Pt HMBC NMR, respectively), reducing the accumu-

lation time significantly. The obvious disadvantage of these

indirect methods is the loss of information on small cou-

pling constants due to the enlarged half width of the reso-

nances.

General

Metal(II) phosphane complexes bearing selenolato li-

gands are generally prepared by the oxidative addition of

metal(0) phosphane complex fragments to diselenides (for

some examples, see refs.^[7b,7d,33]), or by substitution of labile

ligands at the metal, e.g. halides, by a deprotonated selenol

species (as exemplified in ref.^[34]). As the isolation of mal-

odorous and unstable selenols normally is often inevitable

in the second method, the oxidative addition seems to be

preferable. The preparation of diselenolato diphosphane

M^IIcomplexes is, however, a straightforward one-pot syn-

thesis that circumvents the isolation of the bad smelling se-

lenols.

Therefore, the air- and moisture-stable diselenide 2 was

placed in a Schlenk vessel and dissolved in ethanol under

argon giving a red-coloured solution. The addition of an

excess sodium borohydride, NaBH₄, resulted in a clear and

colourless solution indicating that the diselenide is com-

pletely reduced to the corresponding diselenolate dianion.

The excess NaBH₄was destroyed by the dropwise addition

of dilute hydrochloric acid before potassium carbonate,

K₂CO₃, was added to deprotonate the diselenol again. The

appropriate dichloridodiphosphanemetal(II) complex was

added as a suspension in acetone, chloroform, dichloro-

methane or ethanol. The reaction mixture slowly turned

yellow due to the formation of the desired complexes. The

reaction proceeds faster in chloroform or dichloromethane

suspensions due to the higher solubility of [MCl₂L₂]. Com-

mon workup procedures and column chromatography gave

complexes 9–28 as yellow to orange air- and moisture-stable

solids, which slowly decomposed in chlorinated solvents.

The reaction conditions and the summary of the synthe-

sised complexes are shown in Scheme 3.

[PtL₂{(SeCH₂)₂C(CH₂OH)₂}] (L = PMe₃, PTA, PPh₃,

4-dppdbf) (9–12)

The ³¹P{¹H} NMR spectrum of 9 exhibits a single reso-

nance at δ = –26.1 ppm with the anticipated ¹⁹⁵Pt satellites.

1

The J_P,Ptcoupling constant shows a value of 2694 Hz and

is expectedly smaller than that in [PtCl₂(PMe₃)₂] (¹J_P,Pt

=

3481 Hz) due to the higher trans influence of selenium in 9

compared to that of chlorine in [PtCl₂(PMe₃)₂]. The cou-

pling to ⁷⁷Se over two bonds was not resolved in the

³¹P{¹H} NMR spectroscopy.

The ¹H ⁷⁷Se HMBC NMR spectrum exhibited a high or-

der multiplet at δ = –36 ppm. The indirect HMBC NMR

method, however, could not resolve the splittings. Second-

order quartet accompanied by ¹⁹⁵Pt satellites were expected

for the ⁷⁷Se resonance in a similar fashion to that reported

by Risto et al.^[34a,34b]in the ¹²⁵Te NMR spectra of the Te-

containing cis-Pt complexes. We therefore also recorded the

direct ⁷⁷Se NMR spectrum. Unfortunately, the directly

measured ⁷⁷Se NMR spectrum also yielded only unresolved

multiplets probably due to smaller coupling constants be-

tween ⁷⁷Se and ³¹P compared to those between ¹²⁵Te and

³¹P. The ¹H ¹⁹⁵Pt HMBC NMR spectrum gave a triplet

1

centred at –4620 ppm with J_Pt,P= 2706 Hz in agreement

with that obtained from the ³¹P{¹H} NMR spectrum.

The spectroscopic data are consistent with the molecular

structure of complex 9 that was determined by single-crys-

tal X-ray diffraction (see Figure 9). The platinum atom

shows a distorted square-planar coordination with two cis-

phosphorus and two cis-selenium atoms. The P1–Pt–P2 an-

gle is almost 2° smaller than that in cis-[PtCl₂(PMe₃)₂],^[35]

while the Se1–Pt–Se2 angle [91.090(17)°] is only slightly

larger than 90°. Furthermore, the high trans influence of

selenium is seen in the relatively long platinum–phosphorus

bond lengths of 2.2726(13) Å and 2.2756(13) Å compared

to the average of 2.24 Å in [PtCl₂(PMe₃)₂].^[35]In the crystal

there is a very short contact between a hydroxy group of

one molecule and the central platinum atom of another (see

Figure 9). The intermolecular oxygen···platinum distance is

3.38 Å, with the oxygen atom located in an apical position

above the square-planar coordination plane of platinum.

These interactions align the molecules in a chain-like struc-

ture along the b-axis throughout the crystal as shown in

Figure 9.

Complex 10 involves the sterically little demanding phos-

phane PTA. The most interesting property of complexes

bearing this ligand is their improved solubility in protic sol-

vents, especially water.^[36]This peculiarity requires the puri-

Scheme 3. Synthesis of complexes 9–21 and 24–28 applying an one-

pot procedure starting with 2. For details see Supporting Infor-

mation.

The presence of various NMR active nuclei in complexes fication of 10 to be adjusted, as common aqueous workup

9–28 enables manifold NMR investigations, namely the re- procedures cannot be applied. Therefore, 10 was purified by

cording of ¹H, ¹³C{¹H}, ³¹P{¹H}, ⁷⁷Se and ¹⁹⁵Pt NMR extracting the crude product with chloroform using a

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Figure 9. Left: molecular structure of 9 in the crystal. Right: part of a chain of 9 in the crystal, caused by hydrogen bonds between

oxygen and platinum atoms. Ellipsoids are drawn at 50% probability level, hydrogen atoms have been omitted for clarity. Selected bond

lengths [Å] and angles [°]: Pt–P1 2.2726(13), Pt–P2 2.2756(13), Pt–Se1 2.4708(5), Pt–Se2 2.4576(5), O1···Ptⁱ3.38; P1–Pt–P2 94.62(5), Se1–

Pt–Se2 91.090(17), P1–Pt–Se1 84.96(4), P2–Pt–Se2 87.36(4), O1ⁱ···Pt–P1 88.22, O1ⁱ···Pt–P2 86.63, O1ⁱ···Pt–Se1 89.32, O1ⁱ···Pt–Se2 92.27;

i: 2.5 – x, 0.5 + y, z.

Soxhlet extractor. However, 10 is poorly soluble in chlori- another complex [d(O···N) = 2.90 Å] and the other hydroxy

nated solvents, so the extraction of 150 mg took about 12 h. group showing a close contact to the oxygen of solvent

Another possibility for the purification seems to be the ex- dmso molecule [d(O···O) = 2.78 Å]. These interactions ar-

traction of the crude product with dmso, to separate it from range 10 in chains along the b-axis of the crystal.

inorganic salts. The addition of hexane or methanol precipi-

The complex 11 that contains triphenylphosphane was

tated 10 in low purity. Even after several repetitions the easily prepared according to the developed procedure de-

product thus obtained did not gave satisfying elemental scribed above. The purification of the crude product by col-

analysis.

umn chromatography using a dichloromethane/ethyl acetate

The ³¹P{¹H} NMR spectrum of 10 displays the expected mixture as eluent gave 11 as ethyl acetate solvate. Interest-

resonance at δ = –63.5 ppm (¹J_P,Pt= 2491 Hz) and the ⁷⁷Se ingly, even in solution the solvent molecules are bound

resonance at δ = –33.2 ppm. The ¹⁹⁵Pt{¹H} NMR spectrum through hydrogen bonds to the hydroxy groups of 11, as

exhibited a triplet at δ = –4799 ppm (¹J_Pt,P= 2490 Hz). deduced from H and ¹³C{¹H} NMR spectra and verified

1

Suitable crystals for X-ray structure determination were ob- by NOE NMR experiments. However, the use of other el-

tained by slow diffusion of methanol into a concentrated uents (dichloromethane/ethanol, 80:20) gave non-solvated

dmso solution of 10 at room temp. during several weeks. crystals of 11 (assigned 11a) in analytical purity.

The molecular structure of 10 and the packing of the com-

The ³¹P{¹H} NMR spectrum of compound 11 showed a

plexes in the crystal are shown in Figure 10. The square- resonance at δ = 22.0 ppm exhibiting ¹⁹⁵Pt and ⁷⁷Se satel-

1

2

planar coordination sphere around the platinum atom is lites. The J_P,Ptcoupling constant is 2897 Hz and the J_P,Se

similar to that in 9 with the P1–Pt–P2 angle being 94.98(6)° is 47.7 Hz. These values are in good agreement with com-

and the opposite Se1–Pt–Se2 angle being 90.49(2)°. Both parable complexes known from literature, but the assign-

hydroxy groups are involved in the formation of hydrogen ment whether the coupling between ³¹P and ⁷⁷Se is a matter

bonds, one linking to a nitrogen atom of the PTA ligand of of cis- or trans-coupling is ambiguous.^{[7b,7d,8e,8f,37]}The ⁷⁷Se

Figure 10. Left: molecular structure of 10 in the crystal. Right: part of the chain of 10 in the crystal, due to intermolecular hydrogen

bonds. Ellipsoids are drawn at 50% probability level, hydrogen atoms and non-coordinated solvent molecules have been omitted for

clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.2663(15), Pt–P2 2.2703(16), Pt–Se1 2.4578(7), Pt–Se2 2.4588(6), O1···OS 2.78

[hydrogen bond to solvent (dmso)], O2···N3ⁱ2.90; P1–Pt–P2 94.98(6), Se1–Pt–Se2 90.49(2), P1–Pt–Se1 86.25(4), P2–Pt–Se2 88.34(4); i:

1 – x, –0.5 + y, 0.5 – z.

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Steric Demand of Bidentate Phosphanes, Part 1

nuclei show resonance at δ = 60.0 ppm and the ¹⁹⁵Pt{¹H} molecular assemblies of 11a and 11b caused by a system of

NMR spectrum reveals a triplet with ⁷⁷Se satellites at δ = intra- and intermolecular hydrogen bonds are different due

–4841 ppm (¹J_Pt,P= 2897 Hz; ¹J_Pt,Se= 167.3 Hz). The spec- to solvent molecules in case of 11b.

troscopic data are in good agreement with values known

Complex 11a crystallises in the chiral space group

P2₁2₁2₁. Due to strong intra- and intermolecular hydrogen

from literature.^{[7b,37a,37b,38]}

The molecular structures of 11a and 11b (assigned to the bonds between the hydroxy groups [d(O1···O2) = 2.65 Å

ethyl acetate solvate) revealed some interesting aspects con- and 2.77 Å, respectively] the molecules arrange into a

cerning their supramolecular arrangement in the crystal chain-like structure along the a-axis of the crystal. This

(see Figures 11 and 12, respectively). The bond lengths and alignment can be described as a pseudo-helical arrangement

angles of 11a and 11b are comparable, with the P1–Pt–P2 with two molecules in a turn. Even more impressive is the

angle being 99.13(5)° and 97.03(8)°, respectively. The supra- molecular structure of 11b. It crystallises in the tetragonal

Figure 11. Left: molecular structure of 11a in the crystal. Right: part of the double chain of 11a in the crystal, caused by intra- and

intermolecular hydrogen bonds. Ellipsoids are drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted

for clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.2893(14), Pt–P2 2.3032(13), Pt–Se1 2.4551(5), Pt–Se2 2.4647(6), O1···O2

2.65 (intramolecular), O1···O2ⁱ2.77 (intermolecular); P1–Pt–P2 99.13(5), Se1–Pt–Se2 89.70(2), P1–Pt–Se1 87.10(4), P2–Pt–Se2 83.90(4);

i: –0.5 + x, 0.5 – y, –1 – z.

Figure 12. Left: molecular structure of 11b in the crystal. Right: supramolecular assembly of 11b caused by intra- and intermolecular

hydrogen bonds (view along the c-axis of the crystal). Ellipsoids are drawn at 50% probability level, hydrogen atoms and non-coordinated

solvent molecules have been omitted for clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.292(2), Pt–P2 2.288(2), Pt–Se1

2.4654(10), Pt–Se2 2.4565(10), O1···O2 3.25 (intramolecular), O1···O2ⁱ2.74 (intermolecular), O2···O1E 2.70 [hydrogen bond to solvent

molecule (ethyl acetate)], O1···O1ⁱⁱ5.26; P1–Pt–P2 97.03(8), Se1–Pt–Se2 90.57(3), P1–Pt–Se1 83.45(6), P2–Pt–Se2 88.92(6); symmetry

operations for the tetrameric units (clockwise, starting from the lower left corner): i: 1 + y, 1.5 – x, 0.5 – z; ii: 2.5 – x, 0.5 – y, z; iii: 1.5 –

y, –1 + x, 0.5 – z.

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space group P4₂/n, in which four molecules form a tetra- to obtain single crystals suitable for crystal structure deter-

meric unit through a complex hydrogen-bonding network. mination to verify the structural deductions based on NMR

The intermolecular oxygen···oxygen distances are 2.74 Å spectroscopy.

between two hydroxy groups and 2.70 Å between a hydroxy

group and an ethyl acetate molecule. The tetramers, ac-

companied by four ethyl acetate molecules, align along the

[PtL₂{(SeCH₂)₂C(CH₂OH)₂}] (L = ½ dppm, ½ dppma,

½ dppe, ½ dppbe) (13–16)

fourfold axis of rotation (see Figure 12). The stacking of

The influence of the bite angle of bidentate phosphanes

these tetrameric units along the c-axis results in the forma- on the coordination geometry was explored by utilising bi-

tion of a hydrophilic channel throughout the crystal, which dentate phosphanes of varying bite angles. The magnitude

is partly filled with dichloromethane molecules. The small- of the bite angle was adjusted by one or more spacer atoms

est diameter of the channel determined by two opposite between the two phosphorus atoms. 1,1-Bis(diphenylphos-

oxygen atoms is about 5.3 Å.

phanyl)methane should reveal a very small bite angle, re-

The P–Pt–P angle is expected to be wider in 12 contain- sulting in a strongly distorted coordination sphere of the

ing the monodentate phosphane 4-dppdbf than in 11 as central metal atom. The ¹J_P,Ptcoupling constant of 2315 Hz

1

guessed by an increase of J_P,Ptby 70 Hz to 2967 Hz (δ = in 13 is expectedly smaller than those in 11 and 12. Analo-

2

16.0 ppm). The two-bond coupling to the selenium nuclei is gously, the J_P,Secoupling constant is decreased to 32.7 Hz

comparable to 11 (²J_P,Se= 48.5 Hz). The resonances of the from ca. 48 Hz found in both 11 and 12. The molecular

⁷⁷Se (δ = 66.1 ppm) and ¹⁹⁵Pt nuclei (δ = –4848 ppm) as structure of 13 shown in Figure 13 verifies that the P1–Pt–

derived from HMBC NMR spectra are in good agreement P2 angle is only 73.05(7)° and that the opposite Se1–Pt–Se2

with the other compounds. Unfortunately, we were not able angle is clearly widened from the right angle to 93.46(3)°.

Figure 13. Left: molecular structure of 13 in the crystal. Right: dimeric unit of 13 in the crystal, displaying intramolecular O···O hydrogen

bonds and intermolecular O···Se hydrogen bonds. Ellipsoids are drawn at 50% probability level, hydrogen atoms and solvent molecules

have been omitted for clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.245(2), Pt–P2 2.2713(17), Pt–Se1 2.4422(7), Pt–Se2

2.4537(8), O1···O2 3.30, O2···Se2ⁱ3.33; P1–Pt–P2 73.05(7), Se1–Pt–Se2 93.46(3), P1–Pt–Se1 92.41(5), P2–Pt–Se2 101.09(5); i: –x, 1 – y,

2 – z.

Figure 14. Left: molecular structure of 14 in the crystal. Right: part of the chains of 14 in the crystal, caused by intramolecular O···O

hydrogen bonds and intermolecular O···Se hydrogen bonds. Ellipsoids are drawn at 50% probability level, hydrogen atoms have been

omitted for clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.384(8), Pt–Se1 2.4522(3), P1–N1 1.698(3), N1–C16 1.472(6),

O1···O1A 3.17, O1···Se1ⁱ3.36; P1–Pt–P1A 71.71(4), Se1–Pt–Se1A 92.480(15), P1–Pt–Se1 98.51(2); i: x, 0.5 – y, 0.5 – z.

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Steric Demand of Bidentate Phosphanes, Part 1

Figure 15. Left: molecular structure of 15 in the crystal. Right: dimeric unit of 15 in the crystal, displaying intra- and intermolecular

hydrogen bonding. Ellipsoids are drawn at 50% probability level, hydrogen atoms and non-coordinated solvent molecules have been

omitted for clarity. Selected bond lengths [Å] and angles [°]: Pt–P1 2.264(3), Pt–P2 2.248(3), Pt–Se1 2.4520(13), Pt–Se2 2.4621(12), O1···O2

3.27 (intramolecular), O2···O2ⁱ2.79 (intermolecular), O1···OS1 2.94, O2···OS1 3.31, O2ⁱ···OS1 3.11 [hydrogen bonds to solvent molecule

(thf)]; P1–Pt–P2 85.33(11), Se1–Pt–Se2 92.10(4), P1–Pt–Se1 93.00(7), P2–Pt–Se2 89.57(8); i: 2 – x, 1 – y, 1 – z.

Therefore, the platinum atom is coordinated strongly dis- –4748 ppm for the ¹⁹⁵Pt nuclei (¹J_P,Ptis 2721 Hz for 15 and

torted from square planarity. This fact is even more appar- 2736 Hz for 16). The molecular structures are very similar

ent as the P1–Pt–Se1 and P2–Pt–Se2 angles have consider- (see Figures 15 and 16). Both complexes crystallise as sol-

ably different values of 93.46(3) and 101.09(5)°, respectively, vates. Complex 15 forms dimeric units, linked by two thf

further reducing the symmetry at the platinum centre. These molecules through branched hydrogen bonds (see Fig-

differences can be explained from the molecular structure, ure 15). The bite angle of dppe in 15 is 85.33(11)° and the

exposing the creation of dimeric units by formation of hy- corresponding angle in 16 is 87.81(8)°.

drogen bonds between hydroxy groups [d(O1···O2) =

3.30 Å] of 13. Furthermore, close contacts between an oxy-

gen atom of one complex and a selenium atom of another

molecule were detected. The distance is d(O2···Se2) =

3.33 Å and thus clearly shorter than the sum of the van der

Waals radii.

The bite angle of the phosphane was further decreased

by replacing the methylene bridge in dppm with a methyl-

amine moiety (dppma).^[39]Both, the ³¹P and the ¹⁹⁵Pt reso-

nances of 14 [δ(P) = 34.5 ppm, δ(Pt) = –4364 ppm] are sig-

nificantly shifted downfield compared to that of 13 [δ(P) =

–49.6 ppm and δ(Pt) = –4655 ppm (¹J_Pt,P= 2440 Hz),

1

respectively]. The H ⁷⁷Se HMBC NMR spectrum showed

a multiplet at δ = –47.9 ppm and that is close to that of the

dppm-containing complex 13. The molecular structure and

the supramolecular arrangement of 14 in the crystal are

shown in Figure 14. Unexpectedly, the molecules have a

twofold axis of rotation along the quaternary carbon atom

of the diselenolato ligand, the platinum and nitrogen atom

Figure 16. Molecular structure of 16 in the crystal. For the sake of

clarity only one conformation is shown, ellipsoids are drawn at

and the carbon atom of the methyl group (space group

Pnna). Compared to 13 the P1–Pt–P1A angle is expectedly

further reduced to 71.71(4)°, distorting the coordination

sphere at the platinum atom strongly from square planarity.

The intramolecular hydrogen bonds between the hydroxy

groups [d(O1···O1A) = 3.17 Å] and the intermolecular con-

tacts between a hydroxy oxygen and a selenium atom of the

adjacent molecule [d(O1···Se1) = 3.36 Å] link the complexes

into a continuous chain.

50% probability level, hydrogen atoms and solvent molecules have

been omitted for clarity. Selected bond lengths [Å] and angles [°]:

Pt–P1 2.248(2), Pt–P2 2.235(2), Pt–Se1 2.4426(9), Pt–Se2

2.4572(10); P1–Pt–P2 87.81(8), Se1–Pt–Se2 92.28(3), P1–Pt–Se1

90.30(6), P2–Pt–Se2 89.60(6).

[PtL₂{(SeCH₂)₂C(CH₂OH)₂}] (L = ½ dppp, ½ dppn)

(17, 18)

In complexes 15 and 16 the spacer between the two phos-

The complexes 17 and 18 involve dppp and the naphthyl-

phorus atoms of the diphosphane is composed by two car- bearing dppn, respectively, and contain a spacer of three

bon atoms. The phosphorus atoms in both complexes show carbon atoms between the two phosphorus donors. The ³¹

P

an identical resonance at δ = 47.9 ppm. The respective resonances are observed at δ = –1.9 and 8.1 ppm with ¹J_P,Pt

HMBC NMR spectra yielded signals at δ = –42.6 and = 2652 and 2573 Hz, for compounds 17 and 18, respec-

1

–25.2 ppm for the ⁷⁷Se nuclei and at δ = –4787 and tively. The increased value of J_P,Ptin 17 compared to that

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Figure 17. Left: molecular structure of 17 in the crystal. Right: part of the chains of 17 built by intra- and intermolecular hydrogen

bonds. Ellipsoids are drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond

lengths [Å] and angles [°]: Pt–P1 2.268(2), Pt–P2 2.266(2), Pt–Se1 2.4652(9), Pt–Se2 2.4652(8), O1···O2 2.69, O2···Se1ⁱ3.46, O2···Ptⁱ3.89;

P1–Pt–P2 91.98(8), Se1–Pt–Se2 91.69(3), P1–Pt–Se1 87.39(6), P2–Pt–Se2 88.91(5); i: x, 0.5 – y, –0.5 + z.

in 18 indicates a larger bite angle in dppp than in dppn.

As shown in Figure 17, complex 17 forms intramolecular

Both the ⁷⁷Se and ¹⁹⁵Pt resonances of 18 are also shifted [d(O1···O2) = 2.69 Å] hydrogen bonds. In addition, there

downfield due to the presence of the naphthalene bridge, are intermolecular hydrogen bonds between a hydroxy

appearing at δ = 39.7 ppm for selenium (17: δ = 12.4 ppm) group and one selenium atom and the platinum centre of

and at δ = –4686 ppm for platinum (17: δ = –4758 ppm).

an adjacent molecule. The distances d(O2···Se1) = 3.46 Å

The molecular structures of 17 and 18 show the expected and d(O2···Pt) = 3.89 Å are still below the sum of the van

differences in the bite angle (see Figures 17 and 18). The der Waals radii and indicate weak interactions. Complex 18

P1–Pt–P2 angle in 17 is 91.98(8)°, while the analogous an- crystallises as a thf solvate, with each hydroxy group form-

gle in 18 is only 88.36(10)° due to the rigid backbone in ing a hydrogen bond to the oxygen of a thf molecule

dppn. The coordination sphere of the metal centre in both [d(O1···OS1) = 2.85 Å and d(O2···OS2) = 2.80 Å].

complexes is close to square planarity. Additionally, the di-

hedral angle between the phosphorus atoms at the naphtha-

[PtL₂{(SeCH₂)₂C(CH₂OH)₂}] (L = ½ dppb, ½ dppo-

lene moiety is found to be as small as 0.45°, arranging it

xyl) (19, 20)

with the atoms surrounding the platinum centre almost per-

fectly coplanar. Therefore, the dppn ligand serves well for

The complexes 19 and 20, bearing the bidentate phos-

phanes dppb and dppo-xyl, both contain a spacer of four

the formation of complexes close to perfect square-planar

atoms. While the dppo-xyl moiety should result in a rather

coordination.

rigid conformation of the metallacycle, the corresponding

compound containing the dppb ligand is expected to be

more flexible. The NMR spectroscopic data of both com-

pounds are comparable considering the shifts of the reso-

nances, being δ = 13.7 and 1.2 ppm for the ³¹P, δ = 27.9

and 33.2 ppm for the ⁷⁷Se and δ = –4817 and –4834 ppm

for the ¹⁹⁵Pt nuclei, for 19 and 20, respectively. A first evalu-

ation of the bite angle can be obtained from the phosphorus

1

platinum coupling constants. For 19 and 20 J_P,Ptwere de-

termined to be 2783 and 2847 Hz, respectively, surpassing

all values of the aforementioned complexes bearing biden-

tate phosphanes. Consequently, the bite angle is expected

to be enlarged in 19 and 20.

As shown in Figure 19 the dppb bridge of 19 seems to

be quite flexible, resulting in a bite angle of 95.06(8)° and

hence is in agreement with the expectations. In the crystal,

19 arranges in dimeric units built via intra- and intermo-

lecular hydrogen bonds. Both hydroxy groups form triple-

branched hydrogen bonds. Two close contacts are observed

between oxygen atoms from hydroxy groups [d(O1···O2) =

3.37 Å, intramolecular; d(O1···O1) = 2.78 Å, intermo-

lecular] and one strong hydrogen bond to chlorine from

cocrystallised chloroform, only 2.69 Å [d(O2···Cl)] long.

The supramolecular alignment of 20 is comparable to 19,

Figure 18. Molecular structure of 18 as thf solvate in the crystal.

Ellipsoids are drawn at 50% probability level, hydrogen atoms have

been omitted for clarity. Selected bond lengths [Å] and angles [°]:

Pt–P1 2.243(3), Pt–P2 2.248(3), Pt–Se1 2.4548(11), Pt–Se2

2.4582(11), O1···OS1 2.85, O2···OS2 2.80 [hydrogen bonds to sol-

vent molecules (thf)]; P1–Pt–P2 88.36(10), Se1–Pt–Se2 91.09(4),

P1–Pt–Se1 90.77(8), P2–Pt–Se2 89.55(7), P1–C6···C14–P2 0.45.

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Steric Demand of Bidentate Phosphanes, Part 1

Figure 19. Left: molecular structure of 19 in the crystal. Right: dimeric unit of 19 formed via intra- and intermolecular hydrogen bonds.

Ellipsoids are drawn at 50% probability level, hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles [°]:

Pt–P1 2.284(2), Pt–P2 2.263(2), Pt–Se1 2.4430(9), Pt–Se2 2.4737(9), O1···O2 3.37 (intramolecular hydrogen bond), O1···O2ⁱ2.78, O1···O1ⁱ

3.09 (intermolecular hydrogen bonds), O2···Cl1 2.69 [hydrogen bond to solvent molecule (chloroform)]; P1–Pt–P2 95.06(8), Se1–Pt–Se2

91.25(3), P1–Pt–Se1 87.77(6), P2–Pt–Se2 85.88(6); i: – x, 4 – y, –z.

Figure 20. Left: molecular structure of 20 in the crystal. Right: dimeric unit of 20 in the crystal, displaying intra- and intermolecular

hydrogen bonding. Ellipsoids are drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted for clarity.

Selected bond lengths [Å] and angles [°]: Pt–P1 2.2564(18), Pt–P2 2.2682(17), Pt–Se1 2.4672(7), Pt–Se2 2.4614(8), O1···O2 3.40 (intramo-

lecular hydrogen bond), O1···O2ⁱ2.85, O2···O2ⁱ3.34 (intermolecular hydrogen bonds); P1–Pt–P2 101.21(6), Se1–Pt–Se2 90.87(2), P1–Pt–

Se1 85.38(5), P2–Pt–Se2 84.55(5); i: 1 – x, –y, 1 – z.

just varying in the shape of the branched hydrogen bonds δ = 15.1 ppm (¹J_P,Pt= 2886 Hz) displaying also ⁷⁷Se satel-

without involvement of solvent molecules (Figure 20). In- lites (²J_P,Se= 39.6 Hz) and the HMBC NMR spectra exhib-

stead three oxygen···oxygen contacts are monitored, one ited resonances at δ = 64.9 and –4892 ppm for ⁷⁷Se and

short intermolecular distance being d(O1···O2) = 2.85 Å ¹⁹⁵Pt, respectively. However, the elemental analysis and

and one intra- and intermolecular contact each [d(O1···O2) mass spectrum of the solid product were not consistent with

= 3.40 Å and d(O2···O2) = 3.34 Å, respectively]. Most inter- the composition of 21 nor did it match with any amount of

esting is the rigidity of the o-xylene bridging moiety, ex- cocrystallised solvent.

panding the P1–Pt–P2 angle to 101.21(6)° and thus clearly

distorting the platinum centre from a square-planar coordi-

nation. This enlargement is at the expense of the P–Pt–Se

angles, which are reduced to 85.38(5)° and 84.55(5)°,

whereas the bite angle of the diselenolato ligand is deter-

mined to 90.87(2)°.

The observed carbon content is 5% smaller than that

calculated for 21. Furthermore, the product contained 9.9%

of chlorine that should not be present in 21. The mass spec-

trum showed the parent ion at m/z = 2298 with the isotopic

pattern consistent with the presence of two platinum and

two selenium atoms. The base peak was observed at m/z =

1131 and was inferred to be due to a doubly charged posi-

tive ion indicating a mass of 2262 g/mol. Therefore, the dif-

ference between the parent ion and the base peak seems to

equal HCl or chlorine. Hence, in the solid state some species

must have been formed containing at least two platinum

centres.

Attempted Synthesis of [Pt{(SeCH₂)₂C(CH₂OH)₂}-

(xantphos)] (21)

4,5-Bis(diphenylphosphanyl)-9,9-dimethylxanthene is a

diphosphane with a spacer of five atoms. The complex for-

mation, however, led to surprising results. The

Upon crystallisation, a mixture of two types of crystals

³¹P{¹H} NMR spectrum showed the expected resonance at was obtained and their investigation exposed two different

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W. Weigand et al.

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molecular structures, neither being the expected complex

21. One of them showed a doubly charged complex cation

bearing two platinum-phosphane moieties and only one di-

selenolato ligand with chloride counterions (22, see Fig-

ure 21). Comparable complexes have been prepared by

Singhal et al. from the reaction of [ML₂(SeR)₂] (L = ½

bidentate phosphane) and metal(II) phosphane frag-

ments.^[34c]Each selenium atom in 22 acts as µ-bridging do-

nor between the two platinum centres. Both platinum atoms

show a strongly distorted square-planar coordination envi-

ronment. Xantphos showed two clearly differing bite angles

of 107.65(5)° and 100.61(6)° at Pt1A and Pt1B, respectively.

The expansion of the P–Pt–P angles is at the expense of a

decrease of the Se–Pt–Se angles, which measure

77.501(19) Å and 78.032(19) Å for Pt1A and Pt1B, respec-

tively. The coordination planes are hinged at the bridging

selenium atoms with the angle between the least-squares

planes involving the platinum centres (P1A, P2A, Pt1A,

Se1, Se2 and P1B, P2B, Pt1B, Se1, Se2) is 144.09°. Another

evidence for the asymmetry of 22 in the crystal is seen in

the arrangement of the two xanthene moieties indicated by

the dihedral angles between the mean planes of the plati-

num atoms and the planes through the phosphorus and

ipso-carbon atoms of the according xanthene. While this

angle is determined to 165.0° at Pt1A, arranging the xan-

thene group almost in the platinum plane, the analogous

angle at Pt1B measures 83.5°, locating it more perpendicu-

lar. One of the chloride counterions is bound by a hydrogen

bond to the hydroxy groups with the distances between

chlorine and oxygen of 3.03 Å and 3.10 Å. The second chlo-

ride ion shows a close contact of 3.24 Å to Pt1B and ex-

panding the coordination sphere of the platinum atom to a

pseudo-square pyramid. Consequently, the platinum atom

deviates from the least-squares plane by 0.2 Å towards the

chloride ion.

Figure 21. Molecular structure of 22 in the crystal. Ellipsoids are

drawn at 50% probability level, hydrogen atoms and solvent mole-

cules have been omitted for clarity. Selected bond lengths [Å] and

angles [°]: Pt1A–P1A 2.3349(14), Pt1A–P2A 2.3450(16), Pt1A–Se1

2.4766(6), Pt1A–Se2 2.4739(6), Pt1B–P1B 2.3021(15), Pt1B–P2B

2.3046(16), Pt1B–Se1 2.4632(6), Pt1B–Se2 2.4600(6), O1···Cl1 3.10,

O2···Cl1 3.03, Pt1B···Cl2 3.24; P1A–Pt1A–P2A 107.65(5), Se1–

Pt1A–Se2 77.501(19), P1A–Pt1A–Se2 88.50(4), P2A–Pt1A–Se1

85.85(4), P1B–Pt1B–P2B 100.61(6), Se1–Pt1B–Se2 78.032(19),

P1B–Pt1B–Se1 90.25(4), P2B–Pt1B–Se2 88.60(4); the dihedral an-

gle between the platinum mean planes (P1A, P2A, Pt1A, Se1, Se2)

and (P1B, P2B, Pt1B, Se1, Se2) is 144.09°.

The second crop of crystals gave the molecular structure

shown in Figure 22 (complex 23). It shows a doubly posi-

tive-charged trinuclear complex cation with two chloride

counterions. It can be described as two molecules of 21

linked by a platinum atom. The platinum centres are

bridged by selenolato ligands. The cation of 23 is symmetric

and the central platinum atom is located at the centre of

inversion. The Se1–Pt2–Se2 angle is 83.91(3)°, the Se1–Pt2–

Se2A angle is 96.09(3)°.

The bite angle of the xantphos ligand in 23 involving the

coordination to Pt1 is 101.69(8)° and the opposite Se1–Pt1–

Se2 angle is decreased to 81.00(3)°. The angle between the

least-squares planes of the platinum atoms is 130.14° (pla-

nes through atoms P1, P2, Pt1, Se1, Se2 and Se1, Se2, Pt2,

Se1A, Se2A). The dihedral angle between the platinum co-

ordination plane and the xanthene moiety has a value of

81.4° again arranging it perpendicular. The platinum–sele-

Figure 22. Molecular structure of 23 in the crystal. Ellipsoids are

drawn at 50% probability level, hydrogen atoms and solvent mole-

cules have been omitted for clarity. Selected bond lengths [Å] and

angles [°]: Pt1–P1 2.287(2), Pt1–P2 2.285(2), Pt1–Se1 2.4919(8),

Pt1–Se2 2.4890(9), Pt2–Se1 2.4202(8), Pt2–Se2 2.4181(8), O1···Cl1

3.05, O2···Cl1 3.28; P1–Pt1–P2 101.69(8), Se1–Pt1–Se2 81.00(3),

P1–Pt1–Se1 87.45(5), P2–Pt1–Se2 88.38(6), Se1–Pt2–Se2 83.91(3),

Se1–Pt2–Se2A 96.09(3); the dihedral angle between the least-

squares planes (P1, P2, Pt1, Se1, Se2) and (Se1, Se2, Pt2, Se1A,

Se2A) is 130.14°.

nium bond lengths at the central Pt atom are significantly droxy groups, showing oxygen chlorine contacts of 3.05 Å

shorter [d(Pt2–Se1) = 2.4202(8) Å and d(Pt2–Se2) = and 3.28 Å.

2.4181(8) Å] than the corresponding bonds involving the

The elemental analysis can be explained in terms of a 1:1

phosphane coordinated platinum atom Pt1 [d(Pt1–Se1) = mixture of 22 and 23 together with three equivalents of sol-

2.4919(8) Å and d(Pt1–Se2) = 2.4890(9) Å]. The two chlo- vent chloroform. The m/z = 2298 in the mass spectrum can

ride counterions are linked by hydrogen bonds to the hy- be assigned to (23)⁺upon loss of one Cl^–, and the base

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Steric Demand of Bidentate Phosphanes, Part 1

peak at m/z = 1131 to (23)²⁺upon loss of both Cl^–anions. [PtL₂{(SeCH₂)₂C(CH₂OH)₂}] (L = ½ dppf) (24)

Still unsettled remains the fact that no evidence for the con-

Dppf serves as an example for a diphosphane with a

stitution of 22 and 23 can be obtained from phosphorus,

large bite angle, resulting in the stable complex 24. The

¹J_P,Ptof the complex 24 obtained from the ³¹P{¹H} NMR

selenium and platinum NMR spectra. As the selenium

atoms in 22 and 23 are magnetically equivalent each and

spectrum is 2952 Hz and indicates a wide P1–Pt–P2 angle.

The HMBC NMR spectra gave the ⁷⁷Se and ¹⁹⁵Pt reso-

nances at δ = 61.6 and –4786 ppm, respectively. Single crys-

tals that were suitable for X-ray structure determination

were grown by diffusion of hexane into a concentrated chlo-

roform solution. The molecular structure shows the bite an-

gle of dppe of 96.99(6)° and the Se1–Pt–Se2 angle of

90.53(3)° (see Figure 23). The molecules of 24 are linked

into dimeric units by hydrogen bonding. Close inter- and

intramolecular oxygen···oxygen contacts are in the range of

2.8 to 3.4 Å. The complex 24 slowly decomposes in chlori-

nated solvents after several days, as indicated from the col-

our of the solution and NMR spectra.

their signal appears as multiplet, no hint for the struc-

ture can be expected. The ³¹P{¹H} NMR and ¹H ¹⁹⁵Pt

HMBC NMR spectra of 21 should differ remarkably from

the spectra of 23 as additional coupling to the central plati-

num atom can be expected. However none of the expected

splittings was detected.

A proposed reaction mechanism for the formation of 22

and 23 is shown in Scheme 4. The desired complex 21 might

react with one equivalent of 8 giving 22, which might form

23 on reaction with another molecule of 21 with elimination

of xantphos. Repeated experiments gave comparable analyt-

ical results, thus it must be concluded that complex 21 is

not stable. It is assumed that the instability is due to the

large bite angle of xantphos.

[ML₂{(SeCH₂)₂C(CH₂OH)₂}] (M = Pd, Ni; L =

½ dppe, ½ dppn, ½ dppf) (25–28)

The effect of the metal centre on the bite angle and sta-

bility of the complexes was explored by preparing Pd^IIor

Ni^IIcomplexes that are analogues to the Pt^IIcomplexes de-

scribed above. The complex 25 is the palladium analogue

of 15 with the bidentate dppe ligand. The ³¹P{¹H} NMR

spectrum showed a resonance at δ = 49.2 ppm with two

sets of satellites due to the coupling to two magnetically

inequivalent ⁷⁷Se nuclei. The two phosphorus atoms exhibit

different magnitudes to cis- and trans-coupling (²J_P,Se

=

29.6 and 50.1 Hz). This is in good agreement with reported

values, though the assignment to cis- and trans-coupling

cannot be made.^{[7b,7d,13,34c,34e,37d,37e]}The ¹H ⁷⁷Se HMBC

NMR showed a broad resonance at δ = 8.8 ppm.

Crystals suitable for structure analysis were obtained by

slow diffusion of hexane into a concentrated chloroform/

methanol solution. There are two symmetry-independent

molecules (A and B) of 25 in the asymmetric unit, as shown

in Figure 24. The bond lengths and angles are comparable

to the platinum analogue 15. The bite angle of the dppe

ligand is 85.84(7)° and 85.42(7)° for A and B, respectively.

Scheme 4. Proposed formation of complexes 22 and 23 from 21

[where the bridged selenium ligand is 2,2-bis(hydroxymethyl)-1,3-

diselenolatopropane, the phosphane moiety is xantphos].

Figure 23. Left: molecular structure of 24 in the crystal. Right: dimeric unit of 24 formed via intra- and intermolecular hydrogen bonds.

Ellipsoids are drawn at 50% probability level, hydrogen atoms have been omitted for clarity. Selected bond lengths [Å] and angles [°]:

Pt–P1 2.2792(17), Pt–P2 2.2918(18), Pt–Se1 2.4527(7), Pt–Se2 2.4586(7), O1···O2 3.39 (intramolecular hydrogen bond), O1···O2ⁱ2.83,

O2···O2ⁱ2.96 (intermolecular hydrogen bonds); P1–Pt–P2 96.99(6), Se1–Pt–Se2 90.53(3), P1–Pt–Se1 88.12(5), P2–Pt–Se2 84.41(5); i: 1 –

x, y, 1.5 – z.

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Figure 24. Left: molecular structure of one of the two symmetry-independent molecules of 25 in the crystal. Right: supramolecular

arrangement of the independent molecules A and B in the crystal with intra- and intermolecular hydrogen bonds. Ellipsoids are drawn

at 50% probability level, hydrogen atoms and non-coordinated solvent molecules have been omitted for clarity. Selected bond lengths [Å]

and angles [°], the first value is assigned to molecule A, the second to B, respectively: Pd–P1 2.280(2)/2.2640(18), Pd–P2 2.2724(18)/

2.2799(19), Pd–Se1 2.4518(8)/2.4437(9), Pd–Se2 2.4573(9)/2.4536(9), O1A···O2Aⁱ2.77, O1Bⁱⁱ···O2Bⁱⁱⁱ2.68, O2A···OS 2.71, O2Bⁱⁱⁱ···OS 2.76

[hydrogen bonds to solvent molecule (methanol)]; P1–Pd–P2 85.84(7)/85.42(7), Se1–Pd–Se2 93.09(3)/92.94(3), P1–Pd–Se1 92.88(5)/

85.19(5), P2–Pd–Se2 88.54(5)/96.74(5); i: –1 – x, –y, 1 – z; ii: 1 + x, 0.5 – y, 0.5 + z; iii: –1 – x, –0.5 + y, 1.5 – z.

The respective Se1–Pd–Se2 angles are widened to 93.09(3)° are slightly shorter than the corresponding platinum–sele-

and 92.94(3)°. The P1–Pd–Se1 and P2–Pd–Se2 angles were nium bonds of 2.4527(7) Å and 2.4586(7) Å in 24. The

significantly different, one being enlarged to 92.88(5)°/ metal–phosphorus bonds of 2.3391(19) Å and 2.3187(17) Å

96.74(5)° and the other diminished to 88.54(5)°/85.19(5)° are longer in 27 than in 24 [d(Pt–P) = 2.2792(17) Å and

for A/B, respectively. The independent molecules form di- 2.2918(18) Å]. The bite angle of dppf in 27 is 99.34(6)° and

meric units (each A/A and B/B) due to hydrogen bonding therefore is enlarged by more than 2° compared to that in

[d(O1A/B···O2A/B) = 2.77 Å and 2.68 Å for A and B, 24. The supramolecular assembly of the dppf-bearing 27 is

respectively]. They also align into a double chain-like struc- comparable to that of 13, containing the dppm moiety (see

ture linked by hydrogen bonds to solvent methanol [d(O2A/ Figures 25 and 13). Dimeric units are formed through inter-

B···OS) = 2.71 Å and 2.76 Å for A and B, respectively]. The molecular hydrogen bonds between a hydroxy group of one

intermolecular hydrogen bonds show oxygen···oxygen dis- molecule and a selenium atom of a neighbouring one. The

tances of 2.77 Å for A and 2.68 Å for B, respectively, the oxygen···selenium distance is determined to 3.27 Å [cf.

distances to the oxygen atom of methanol are 2.71 Å and d(O···Se) = 3.33 Å in 13]. Like in many of the complexes

2.76 Å. We note that 25 decomposes in thf solution within described in this work, an intramolecular hydrogen bond

two or three days, as indicated by its NMR spectra.

between the two hydroxy groups of each molecule is de-

The ³¹P{¹H} resonance of complex 26 (δ = 13.5 ppm) tected [d(O1···O2) = 2.69 Å].

also shows two sets of ⁷⁷Se satellites, giving similar cis- and

The palladium complexes 25–27 are less stable than their

trans-coupling constants (²J_P,Se= 33.7 and 40.8 Hz). The platinum analogues. This trend continues with the nickel

³¹P{¹H} NMR spectrum of 27 revealed a resonance at δ = complexes that are quite unstable. The dppe-containing

20.9 ppm with only one pair of ⁷⁷Se satellites (²J_P,Se

=

nickel(II) complex 28 readily starts to decompose in chlori-

48.6 Hz). The ⁷⁷Se chemical shifts are found at δ = 93.0 nated solvents, the main products being dppe-dioxide and

and 134.7 ppm for 26 and 27, respectively. Thus, the ⁷⁷Se 2. Apparently, some inorganic nickel species are also devel-

resonance of 26 is shifted downfield more than 50 ppm oped, as indicated by the green colour of the aqueous solu-

compared to the platinum analogue 18, while the downfield tions. Nonetheless, we were able to obtain 28 in analytical

shift of 27 compared to the corresponding platinum com- purity. Its ³¹P{¹H} NMR spectrum again exhibits a single

plex 24 is even larger (Ͼ70 ppm). The deshielding of the resonance at δ = 59.9 ppm with two sets of ⁷⁷Se satellites

selenium nuclei might be explained by a better π-acceptor due to the aforementioned inequivalence (²J_P,Se= 48.8 and

ability of palladium compared with platinum because of a 54.2 Hz). The ¹H ⁷⁷Se HMBC NMR spectrum showed a

better overlap of the orbitals of selenium and palladium. multiplet at δ = 24.9 ppm in which the coupling constants

Unfortunately no crystals suitable for single-crystal X-ray could not be resolved.

structure determination of 26 could be obtained, as the

Crystals suitable for single-crystal X-ray structure deter-

compound decomposed in thf solutions within two days mination were obtained by diffusion of hexane into a con-

(the crystals of the platinum analogue 18 could only be centrated chloroform solution of 28 under non-inert condi-

grown from thf solutions).

tions. As shown in Figure 26, the crystals included a half

On the other hand, suitable crystals of 27 were grown equivalent of dppe dioxide, which was generated by the de-

from concentrated chloroform solution (see Figure 25). The composition of 28. The bite angle of dppe in the Ni^IIcom-

palladium–selenium bonds of 2.4453(8) Å and 2.4287(9) Å plex is 87.58(8)° and the opposite Se1–Ni–Se2 angle is wid-

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Steric Demand of Bidentate Phosphanes, Part 1

Figure 25. Left: molecular structure of 27 in the crystal. Right: dimeric unit of 27 formed via intermolecular hydrogen bonds. Ellipsoids

are drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted for clarity. Selected bond lengths [Å] and

angles [°]: Pd–P1 2.3391(19), Pd–P2 2.3187(17), Pd–Se1 2.4453(8), Pd–Se2 2.4287(9), O1···O2 2.69, O1···Se1ⁱ3.27; P1–Pd–P2 99.34(6),

Se1–Pd–Se2 90.29(3), P1–Pd–Se1 85.97(5), P2–Pd–Se2 85.85(5); i: 1 – x, 1 – y, 1 – z.

Figure 26. Left: molecular structure of 28 in the crystal. Right: arrangement of the dimeric units of 28 and hydrogen bridging to cocrystal-

lised dppe dioxide. Ellipsoids are drawn at 50% probability level, hydrogen atoms and solvent molecules have been omitted for clarity.

Selected bond lengths [Å] and angles [°]: Ni–P1 2.1467(19), Ni–P2 2.152(2), Ni–Se1 2.2977(12), Ni–Se2 2.3081(13), O1···O2ⁱ2.66 (intermo-

lecular hydrogen bonds), O1···OP1 2.61 (hydrogen bonds to cocrystallised dppe dioxide); P1–Ni–P2 87.58(8), Se1–Ni–Se2 96.02(5), P1–

Ni–Se1 87.43(6), P2–Ni–Se2 89.43(6); i: –x, 1 – y, 1 – z.

ened to 96.02(5)° consistent with the distorted square- reaction was additionally carried out in dry and degassed

planar coordination. The intermolecular hydrogen bonds diethyl ether using lithium alumininum hydride to reduce

between two molecules of 28 are 2.66 Å and the 2 to the diselenolato species (see Supporting Information,

oxygen···oxygen distance between the hydroxy groups and procedure B). Upon addition of 4 dissolved in thf, the col-

the dppe dioxide is 2.61 Å. In consequence of the cocrystal- our again changed to deep red and lightened very quickly.

lisation of dppe dioxide, a chain-like structure is formed, The ³¹P{¹H} NMR spectrum only showed resonances due

with dimeric units of 28 linked by the phosphane dioxide to 29 and a small amount of dppn dioxide. Therefore, no

involving hydrogen bonds.

further attempts to purify the crude products were made.

The synthesis of [Ni(dppn){(SeCH₂)₂C(CH₂OH)₂}] was

also attempted by direct oxidative addition of 2 to a freshly

prepared zero-valent nickel complex [Ni(cod)(dppn)] (see

Attempted Synthesis of [Ni(dppn){(SeCH₂)₂C(CH₂OH)₂}]

All attempts to synthesise the nickel analogue of 18 and Supporting Information, procedure C) that was prepared

26 following the established procedure failed due to the fast from [Ni(cod)₂] in toluene in order to circumvent the re-

decomposition of the complex. The desired compound duction step. Even under an argon atmosphere at –24 °C

might be rapidly formed, as indicated by the deep red col- this unstable dark green, almost black solid decomposed

our of the reaction mixture that fast lightened to orange. within two weeks. According to the ³¹P{¹H} NMR,

After common workup procedures and purification using [Ni(dppn)₂] might be formed. It further decomposed to ele-

column chromatography, 2 was obtained in almost a quan- mental nickel and free dppn. Unfortunately, the decomposi-

titative yield. The second fraction yielded the dppn mono- tion of the Ni⁰complex proceeds faster than the oxidative

oxide 29. As the ethanol might act as an oxygen donor, the addition to the diselenide or the formation of 29.

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Characterisation of dppn Monooxide 29

complexes 13–20 and 24. Hence, a rough estimation of the

bite angle from the J_P,Ptcoupling constant is justified. The

1

Contrary to earlier reports,^[30a]dppn is not air-stable but

is easily oxidised to form the appropriate dioxide, without

detectable amounts of the monooxide 29. On the other

hand, we noted that 29 is surprisingly insensitive to further

oxidation by oxygen in air. Because only the monosulfide

and the related monoselenide have been reported,^[40]we in-

vestigated the spectroscopic properties of 29 and its molecu-

lar structure. The ¹H and ¹³C{¹H} NMR spectroscopic data

of 29 are in good agreement with those reported for the

monosulfide and monoselenide of dppn. The ³¹P nuclei

showed resonance at δ = –10.3 and 39.4 ppm, assigned to

the unoxidised and oxidised phosphorus atom, respectively.

Both resonances are split into doublets because of the cou-

pling between the two phosphorus nuclei (⁴J_P,P= 8.9 Hz).

The molecular structure of 29 (see Figure 27) showed the

distance between the unoxidised phosphorus atom and oxy-

gen to be 2.98 Å and thus expectedly shorter than the corre-

sponding phosphorus···selenium distance of 3.41 Å in

dppnSe.^[40a]The torsion angle P1–C1···C9–P2 has a value

of 31.25° and is larger than the corresponding angle in the

monoselenide that is 28.87°.

linear fit possesses a coefficient of correlation of 0.80. It

must be noted that the coupling constants are based on

solution data, while the bite angles were taken from the

solid state arrangement of the respective complexes.

1

Figure 28. Relationship between the bite angle and the J_P,Ptcou-

pling constant for diphosphane diselenolato platinum(II) com-

plexes 13–20 and 24. The dashed line represents the linear fit with

a coefficient of determination of 0.80.

Conclusions

During our investigation of the influence of the bite an-

gle of bidentate phosphanes towards their steric demand we

determined the molecular structures of some dichlorido-

phosphanemetal(II) complexes and prepared the sterically

demanding monodentate phosphane 4-dppdbf, which,

upon reaction with [PtCl₂(cod)], yielded the appropriate cis-

complex 3. Furthermore, we improved the synthesis of 4,4-

bis(hydroxymethyl)-1,2-diselenolane 2 using a two-step syn-

thesis starting from 2,2-bis(bromomethyl)propane-1,3-diol.

The molecular structure of 2 revealed an interesting supra-

molecular assembly caused by the interplay of a hydrogen-

bonding network and rather strong chalcogen–chalcogen

interactions.

To study the complexation behaviour of the dianion of

the air- and moisture-stable 1,2-diselenolane 2 towards

group-10 metals, an efficient and straightforward one-pot

procedure was established that circumvents the isolation of

the malodorous and air-sensitive diselenol. Compound 2

was reduced in situ by sodium borohydride in protic media

followed by the addition of an appropriate dichloridophos-

phanemetal(II) yielding complexes of the type

[ML₂{(SeCH₂)₂C(CH₂OH)₂}] (M = Ni, Pd, Pt; L = mono-

or ½ bidentate phosphane) (9–28) in good yields. The plati-

num complexes proved to be rather stable, showing slow

decomposition only in chlorinated solvents after several

weeks. By contrast, the palladium complexes also decom-

posed in thf, and the nickel complexes proved to be sensitive

against oxidation.

Figure 27. Molecular structure of 29 in the crystal. Upper right

corner: view along the plane of the naphthalene ring, displaying

the distortion of the two phosphorus atoms. Ellipsoids are drawn

at 50% probability level, hydrogen atoms and solvent molecules

have been omitted for clarity. Selected bond lengths [Å] and angles

[°]: P1–O1 1.4875(16), P1–C1 1.827(2), P2–C9 1.843(2), P2···O1

2.98; P1–C1···C9–P2 31.25.

We conclude that the oxygen atom of 29 can only come

from small traces of air or the hydroxy groups of the sele-

nium ligand itself. Since utmost care was taken to attain

inert conditions, the hydroxy group of [(SeCH₂)₂C-

(CH₂OH)₂]^2–either as a free ligand or coordinated in

[Ni(dppn){(SeCH₂)₂C(CH₂OH)₂}], or the solvent in inter-

action with the nickel centre oxidises one of the phosphorus

atoms of the dppn moiety to form 29 and possibly leading

to the decomposition of the nickel(0) complex.

1

Relationship between Bite Angle and J_P,PtCoupling

Constant

The number of complexes reported, allows proving the

All complexes were characterised by multinuclear NMR

assumed relationship between the bite angle and the magni- spectroscopy (¹H, ¹³C{¹H}, ³¹P{¹H}, ⁷⁷Se{¹H} and

1

tude of J_P,Pt. As shown in Figure 28 a linear correlation is ¹⁹⁵Pt{¹H}, where appropriate), mass spectrometry and ele-

recognisable for diphosphane diselenolato platinum(II) mental analysis. Phosphorus and platinum NMR spec-

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Steric Demand of Bidentate Phosphanes, Part 1

39.5 ppm). ³¹P{¹H}, ⁷⁷Se{¹H} and ¹⁹⁵Pt{¹H} NMR spectra were

recorded using 85% H₃PO₄(δ = 0.0 ppm) and concentrated SeO₂

in D₂O (δ = –1302.6 ppm) solutions and saturated K₂PtCl₄in 1 

NaCl (δ = –1628.0 ppm) D₂O solution as external references,

respectively. The ⁷⁷Se chemical shifts are reported relative to neat

Me₂Se [δ(Me₂Se) = δ(SeO₂) + 1302.6 ppm],^[42]while the ¹⁹⁵Pt reso-

troscopy particularly proved to be useful for the prediction

of bite angles from J_P,Ptcoupling constants. The

1

³¹P{¹H} NMR spectra of some complexes also showed two

sets of ⁷⁷Se satellites due to cis- and trans-coupling to the

selenium nuclei. The magnetic non-equivalence of the two

phosphorus atoms in the case of one NMR active selenium

atom results in further splitting of the selenium resonances

in the ⁷⁷Se{¹H} NMR spectra resulting in unresolved high-

order multiplets.

2–

nances are referenced to PtCl₆

[δ(PtCl₆) = δ(PtCl₄) +

1628.0 ppm].^[43]The ⁷⁷Se{¹H} and ¹⁹⁵Pt{¹H} NMR spectra were

recorded either directly or indirectly using two dimensional ¹H ⁷⁷Se

1

and H ¹⁹⁵Pt HMBC NMR experiments. If not mentioned other-

In order to investigate the dependence of the bite angle wise, couplings to ⁷⁷Se were usually not fully resolved in ¹H,

¹³C{¹H}, ³¹P{¹H} and ¹⁹⁵Pt{¹H} NMR spectra due to the multi-

on the steric demand of phosphanes, most complexes were

plicity of the signals and the low natural abundance of the ⁷⁷Se

investigated by single-crystal X-ray crystallography. As we

isotope (see results and discussion section for details). Assignments

sought to cover a broad range of P–M–P angles for further

of ¹H and ¹³C signals were confirmed by two-dimensional NMR

investigations, a number of bidentate phosphanes with dif-

experiments (¹H ¹H COSY, ¹H ¹³C HSQC, ¹H ¹³C HMBC), in

ferent bite angles was utilised in the preparation of com-

some cases the coupling of protons to other heteroatoms was as-

plexes 9–28. As revealed by the molecular structures, phos-

phorus–metal–phosphorus angles range from 71° to 108°.

The complexes also show interesting supramolecular arran-

gements in the solid state due to the presence of hydroxy

signed by special decoupling experiments (¹H{³¹P}, ¹H{⁷⁷Se},

¹H{¹⁹⁵Pt} NMR). Mass spectra were performed with either a Fin-

nigan SSQ 710 (DEI, FAB) or a MAT 95 XL (ESI) instrument.

All mass spectra showed parent ions with appropriate isotopomer

groups forming a hydrogen-bonding network. A conclusion distributions. Elemental analyses have been measured with a Vario

EL III CHNS (Elementaranalysensystem GmbH Hanau) as single

determinations. Melting points were obtained using an Axiolap

microscope (Carl Zeiss Jena GmbH) equipped with heating unit

THMS 600 (Linkam) and Linkam LNP and CI 93 control units.

that is derived from the molecular structures of di- and tri-

nuclear cationic platinum(II) complexes 22 and 23 is the

instability of [Pt{(SeCH₂)₂C(CH₂OH)₂}(xantphos)]. The

instability might be due to the large bite angle of the phos-

phane or its bonding behaviour.

All compounds are stable in the presence of atmospheric oxygen

The attempt to synthesise [Ni(dppn){(SeCH₂)₂C- and moisture in the solid state. However, the final complexes show

some instability in chlorinated solvents, as indicated by NMR ex-

periments. Especially chloroform solutions show decomposition af-

ter several weeks,^[7b]while the nickel and palladium species showed

to be more labile and fast decomposed in thf as well. Additionally

the nickel-containing complexes showed to be sensitive against oxi-

dation.

(CH₂OH)₂}] led to rapid decomposition, affording the so

far unknown dppn monooxide 29 that is stable against fur-

ther oxidation by air. Compound 29 might be an interesting

mixed-donor ligand with hemilabile properties.^[40a,41]

Preparation of Starting Materials: For compounds 1,^[44]5^[30a]and

6^[30a]the literature procedures were modified considerably or were

not satisfying, therefore, the synthetic details are given in the Sup-

porting Information. PTA,^[36]4-dppdbf,^[45]dppma,^[39]dppn,^[30]

dppbe,^[46]dppo-xyl,^[47]xantphos,^[48][Ni(cod)₂],^[49][NiCl₂(dppe)],^[50]

Experimental Section

Caution! All new selenium-containing complexes are potentially

highly toxic compounds. The selenium precursors (Na₂Se₂,

KSeCN) are known to be poisonous and must be handled carefully.

All operations have to be carried out in a well-ventilated hood.

Particular care must be taken in the NaBH₄reduction step, as small

amounts of hydrogen selenide (H₂Se), and during the preparation

of 2 hydrogen cyanide (HCN) might evolve. Therefore, all gases

should be bubbled through concentrated aqueous NaOH solution.

[PdCl₂(NCPh)₂],^[51]

[PdCl₂(dppf)],^[52]

[PtCl₂(PTA)₂]^[53]

and

[PtCl₂(PPh₃)₂]^[54]were synthesised following literature procedures.

[PdCl₂(dppe)] and [PtCl₂(dppe)] were prepared in the same manner

as reported for the synthesis of [PtCl₂(PPh₃)₂]^[54]using dppe instead

of PPh₃and K₂PdCl₄or K₂PtCl₄, respectively. [PtCl₂(PMe₃)₂],^[8e]

[PtCl₂(dppm)], [PtCl₂(dppma)], [PtCl₂(dppbe)], [PtCl₂(dppn)],^[30a]

[PtCl₂(dppb)], [PtCl₂(dppo-xyl)] and [PtCl₂(dppf)] were synthesised

by suspending [PtCl₂(cod)]^[55]in dichloromethane or chloroform

and adding an equimolar amount of the phosphane. The reaction

mixture was stirred for 2 d at room temp., filtered, washed with a

small amount of chloroform and dried in vacuo.

General: All operations except for the preparation of 1 were carried

out under dry argon using standard Schlenk techniques. Solvents

were distilled prior to use, other reagents were used without further

purification. KSeCN and NaBH₄were purchased from Acros, 2,2-

bis(bromomethyl)propane-1,3-diol, 1,1-bis(diphenylphosphanyl)-

methane, 1,2-bis(diphenylphosphanyl)ethane, 1,3-bis(diphenyl-

phosphanyl)propane, 1,4-bis(diphenylphosphanyl)butane and 1,1Ј-

bis(diphenylphosphanyl)ferrocene from Aldrich, NiCl₂·6H₂O,

General Procedure for the Synthesis of Complexes 9–28: One equiva-

lent of 2 was dissolved in ethanol (6 mL) under argon. Three equiv-

K₂PdCl₄, K₂PtCl₄and silica gel (silica gel 60, 0.2–0.5 mm) from alents of NaBH₄were added with stirring, affording the solution

Merck. ¹H, ¹³C{¹H} and ³¹P{¹H} NMR spectra were recorded

with either a Bruker AVANCE 200 or 400, the ⁷⁷Se{¹H} and

¹⁹⁵Pt{¹H} NMR spectra were carried out with Bruker AVANCE

to lighten and turning colourless. After 30 min the excess of NaBH₄

was destroyed by dropwise addition of 4.0  HCl solution. Stirring

was continued for 5 min before an excess of K₂CO₃was carefully

added. A solution or suspension of the phosphane bearing met-

al(II) precursor (one equivalent) in acetone, chloroform, dichloro-

methane or ethanol (6 mL) was added at once and the mixture was

stirred at room temp. overnight, resulting in yellow to red solutions.

The solvent was removed using a rotary evaporator. Except for

compound 10 (see there), the residue was chromatographed on sil-

1

400 or Bruker DPX 400. H NMR spectra were calibrated to the

signal of the remaining protons of the solvents (CDCl₃: δ =

7.24 ppm, C₆D₆: δ = 7.15 ppm, CD₂Cl₂: δ = 5.32 ppm, [D₆]dmso:

δ = 2.49 ppm), ¹³C{¹H} NMR spectra were determined using the

signal of the solvent as internal reference (CDCl₃: δ = 77.0 ppm,

C₆D₆: δ = 128.0 ppm, CD₂Cl₂: δ = 53.8 ppm, [D₆]dmso: δ =

Eur. J. Inorg. Chem. 2010, 74–94

www.eurjic.org

91

W. Weigand et al.

FULL PAPER

ica gel, separating some unreacted 2 as less polar fraction and the

complexes as second fraction (the eluents are given in the detailed

procedures in the Supporting Information). Complexes 9–28 were

obtained in 48–86% yield.

Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_

request/cif.

Supporting Information (see also the footnote on the first page of

this article): Detailed experimental procedures, complete spectro-

scopic data of all new compounds and full X-ray crystallographic

data on all determined molecular structures.

4,4-Bis(hydroxymethyl)-1,2-diselenolane (2):^[16a]KSeCN (10.81 g,

75 mmol) was added to a solution of 1 (7.55 g, 25 mmol) in 70 mL

of acetone. To maximise the yield, the colourless reaction mixture

was heated to reflux for 14 d. During that time a mass of KBr and

a small amount of red selenium developed. Due to the precipitated

selenium and the formation of some amount of the product the

colour changed to deep red. After cooling to room temp., water

(70 mL) was added to dissolve the KBr and the solution was fil-

tered to remove the selenium. Ether (150 mL) was added and

phases were separated. The organic layer was washed with water

(3ϫ30 mL), dried with Na₂SO₄and the solvents evaporated to dry-

ness, giving a viscous deep red oil. This was dissolved in ethanol/

water (90:10, 100 mL) and cooled to 0 °C. NaBH₄(3.78 g,

100 mmol) was added in small portions during 2 h, while the solu-

tion lightened and became colourless. Evolving gases were removed

with a slight stream of argon, which was bubbled through a wash-

ing bottle with concentrated aqueous NaOH solution. After 1 h

water (30 mL) was added and the excess of NaBH₄was destroyed

by drop wise addition of 4.0  HCl solution until pH 2. The stream

of argon was removed and the solution was stirred vigorously un-

der air to aspirate as much oxygen as possible. After 12 h the clear,

deep red solution was heated to 75 °C for 4 h before an excess of

K₂CO₃was added carefully. The solution was slowly cooled to

room temp. and extracted with dichloromethane (5ϫ30 mL). The

combined organic layer was washed with water (10 mL), dried with

Na₂SO₄and the solvents evaporated in vacuo, giving crude 2 as a

brown red solid. Recrystallisation from ethanol yielded deep red

crystals. Single crystals were grown from a concentrated ethanol

solution at 7 °C; yield 4.72 g (73%); m.p. 134–135 °C (ref.^[16a]133–

Acknowledgments

Heraeus GmbH is gratefully acknowledged for a donation of

K₂PtCl₄. The authors wish to express their gratitude to one of the

referees for his helpful remarks. Furthermore we thank Prof. Dr.

Fabian Mohr, Bergische Universität Wuppertal, for donating some

amount of the PTA ligand. Additionally, we wish to thank Dr.

Reinald Fischer for the preparation of xantphos and Thomas

Weisheit for the donation of dppbe and dppo-xyl. Financial Sup-

port from Academy of Finland is gratefully acknowledged.

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Synthesis and characterisation of 2,2-bis(hydroxymethyl)-1,3-diselenolato metal(II) complexes bearing various phosphanes

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