Synthesis of Sterically Demanding Secondary Phosphides and Diphosphanes and Their Utilization in Small-Molecule Activation

Diphosphanes and Their Utilization in Small-Molecule Activation

Article

Synthesis of Sterically Demanding Secondary Phosphides and

Jonas Bresien, Yannic Pilopp, Axel Schulz,* Lilian Sophie Szych, Alexander Villinger,

and Ronald Wustrack

Cite This: https://dx.doi.org/10.1021/acs.inorgchem.0c01934

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sı Supporting Information

ABSTRACT: Sterically demanding secondary potassium phos-

phides (4) were synthesized and investigated. Reaction with

halophosphanes (5) yields diphosphanes (6), whereas reaction

with CS yields phosphanyl dithioformates (10). These can be

further converted to the corresponding phosphanyl esters of

dithioformic acid R P−C(S)S−PR (8). One of these thioesters

(

8) was found to undergo a migration reaction, resulting in the

formation of a phosphanylthioketone with an additional

phosphanylthiolate group (9), which was used as a chiral ligand

in gold coordination chemistry. The phosphanyl migration

reaction was investigated by spectroscopic and theoretical

methods, revealing a ﬁrst-order reaction via a cyclic transition

state. All species mentioned were fully characterized.

INTRODUCTION

Scheme 1. Activation of CS by Phosphorus-Containing

■

Compounds, Yielding Phosphanyl Derivatives of

In recent years, metal-free activation of small molecules has

taken on an increasingly central role in inorganic molecular

chemistry. Numerous phosphorus-based compounds have

proven to be of relevance in this ﬁeld during the last

28,29

Dithioformic Acid

−9

decades.

Of particular interest is the activation of small

molecules such as CO and CS , which can serve as building

10−19

blocks for synthetic applications.

In the past, some

examples for the activation of CS with phosphorus-based

0−22

compounds have been published.

We recently reported

the reaction of CS₂with phosphorus-centered biradicals,

yielding bicyclic compounds, and Dielmann et al. reported

the activation of CS by highly electron-rich tertiary

phosphanes. Furthermore, a few phosphorus-containing

frustrated Lewis pairs [consisting of sterically demanding

Lewis acid (LA) and Lewis base (LB)] were reported to

activate CS , forming, e.g., adducts such as LB−C(S)−S−

5−27

LA.

The formation of similar, rare structural motives was

recently reported by Masuda et al. and Grubba et al.

Conversion of diphosphanes with CS yielded phosphanyl

derivatives of dithioformic acid, where CS is inserted between

8,29

both P atoms.

Besides the steric situation, the electronic

properties of the investigated phosphanes seem to be of

relevance for their reaction behavior because this kind of

reactivity has only been reported for (partially) N-substituted

phosphanes (Scheme 1).

Received: June 30, 2020

During our research on the reactivity of sterically demanding

phosphorus compounds, we found that the terphenyl

substituent [Ter = 2,6-bis(2,4,6-trimethylphenyl)phenyl] is a

XXXX American Chemical Society

Inorg. Chem. XXXX, XXX, XXX−XXX

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Article

suitable ligand for stabilizing reactive bonding situations,

without completely diminishing the reactivity of the stabilized

KH is almost insoluble in typical organic solvents, complete

deprotonation of 3 in tetrahydrofuran (THF) takes up to

10 days with stirring at room temperature. The resulting

secondary potassium phosphides 4 are deep-red and highly air-

and moisture-sensitive compounds, with the latter property

indicating high nucleophilicity and basicity of the compounds.

Therefore, the in situ use of 4 after decanting from excess KH

was found to be advantageous. The completeness of the

1,32

species.

work.

Thus, this substituent is used in the course of this

To the best of our knowledge, no examples for the activation

of CS by exclusively C-substituted diphosphanes are known to

date. Yet, the phosphanyl esters of dithioformic acid display

interesting structural motives. Because they are potentially

ambidentate ligands, binding through either S or P atoms to a

metal center, these species are of interest for their use in

coordination chemistry. Thus, in this work, a novel synthetic

route toward arbitrarily substituted phosphanyl esters of

dithioformic acid is presented. Therefore, terphenyl-stabilized

phosphanyl dithioformates were synthesized, which thereafter

were converted with secondary halophosphanes to form the

desired R P−C(S)S−PR species.

deprotonation reaction can easily be veriﬁed by P NMR

spectroscopy. The products show singlet resonances with

chemical shifts of 23.9 ppm (4a) and −23.6 ppm (4b) in

THF-d .

4a can be crystallized from THF at room temperature in the

form of small red crystals. 4a crystallizes in the monoclinic

space group P 2 with four formula units per cell (Figure 1).

RESULTS AND DISCUSSION

Synthesis of Bulky Secondary Phosphides. Conversion

■

of secondary metal phosphides with secondary halophosphanes

is a well-known synthetic route to access (dissymmetric)

diphosphanes. Frequently occurring side products in these

syntheses are, e.g., alternative coupling products, which might

be the result of in situ metal−halogen exchange reac-

4,33−35

tions.

For the terphenyl-stabilized phosphanes used

throughout this work (1 and 3a−3e; Scheme 2), the increased

Scheme 2. Deprotonation of Terphenylphosphane 1 and

Conversion to Secondary Phosphanes 3 via the Addition of

Alkyl Bromides and of Secondary Phosphanes in THF,

Yielding the Corresponding Potassium Phosphides 4

Figure 1. Molecular structure of 4a in the single crystal. Ellipsoids set

at 50% probability (123 K). Selected bond length (Å) and angles

(

deg): P1−C1 1.847(3); P1−C2 1.887(3); K1···P1 3.2164(11); C1−

P1−C2 101.92(14).

The structure in the single crystal clearly shows intramolecular

coordination of K1 by the P1 atom [K1···P1 = 3.2164(11) Å;

∑

r_v_d_W(K···P) = 4.55 Å ], as well as by the aromatic ring

system of one mesityl group, which is part of the Ter

occurrence of various unidentiﬁed side products was noted

when using lithium bases such as nBuLi to access the desired

metal phosphides. This has been reported previously for

substituent [average K1···C distance = 3.23 Å; ∑r_v_d_W(K···C) =

4.45 Å ]. Intermolecular coordination of K1 by the C3′ and

C4′ atoms (average K1···C′ distance = 3.11 Å) results in the

formation of a 3D chain structure of 4a within the single

crystal.

31,36

sterically demanding phosphanes.

Even variation of the

reaction conditions (temperature and solvent) did not improve

the selectivity. Thus, in subsequent reactions for the synthesis

of metal phosphides, potassium hydride was used, for which we

could observe very selective reaction behavior in terms of

deprotonation and, furthermore, in terms of the reactivity of

the isolated potassium phosphides.

Synthesis of Diphosphanes. The investigated diphos-

phanes were obtained within minutes by the reaction of a

stirred suspension of the previously synthesized secondary

potassium phosphides 4 via the addition of secondary

chlorophosphanes 5 at room temperature (Scheme 3). We

isolated dissymmetric diphosphane species 6a−6h, which

could be fully characterized and crystallized in the case of

6b, 6c, 6e, 6g, and 6h (Figure 2). All species were obtained in

good yield, and the amount of side products formed during

syntheses (3a/3b) was not signiﬁcant. Diphosphane scram-

bling reactions yielding symmetric species were not observed.

The chemical shifts of the P1 and P2 atoms within these

diphosphane species are very similar in some cases. An

A variety of bulky terphenyl-stabilized secondary phos-

phanes 3 can be synthesized by conversion of the previously

37−39

reported terphenylpotassium phosphide 2

with primary or

secondary alkyl bromides (Scheme 2). The synthesis of 3c has

been reported on a diﬀerent route before, using nickel

phosphanido complexes. The desired products 3 can be

isolated in good yield and purity. However, the deprotonation

of sterically demanding secondary phosphanes such as 3a and

3b turned out to be quite challenging. Because the chosen base

assignment was made by means of H-coupled P NMR

Inorg. Chem. XXXX, XXX, XXX−XXX

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Article

Scheme 3. Conversion of Secondary Potassium Phosphides with Secondary Chlorophosphanes to Diphosphanes

Figure 2. Molecular structures of 6b, 6c, 6e, 6g, and 6h (from left to right) in the single crystal and the corresponding P−P bond lengths. Ellipsoids

set at 50% probability (123 K; for 6e, 173 K). Selected structural parameters and data can be found in the SI .

spectra and, if additionally required, by use of quantum-

chemical calculations (Table S3). The structural parameters of

Scheme 4. Reactivity of Diphosphanes 6a−6g toward H O

and CS₂

b, 6c, and 6e in the single crystal reveal that the P−P bond

lengths of all C-substituted species are in the range of the sum

of the covalent radii of a P−P bond [2.23 Å; cf. ∑r (P−P) =

cov

.22 Å]. Slightly longer P−P bonds (2.28−2.29 Å) were

found for the partly N-substituted species 6g and 6h (Table

S3). In all crystallized species, the terphenyl substituents show

a noticeable deformation of the bond angles, which may be

attributed to the sterically crowded situation in these

diphosphanes.

Reactivity of Diphosphanes. C-Substituted Species.

Reactivity investigations on the C-substituted diphosphanes

a−6f revealed that these species are stable in an aqueous

benzene solution for several days at room temperature. The

treatment of 6a−6f with a large excess of CS (approximately

0 equiv) did not lead to any observable reaction upon stirring

for two weeks, not even under reﬂuxing conditions.

N-Substituted Species. In contrast to the C-substituted

species (vide supra), the reaction of the partly N-substituted

diphosphane 6g with water yielded the secondary phosphane

these interesting species, also enabling the isolation of species

in which the P1 and P2 atoms are variously substituted.

General Synthetic Route. According to our results, a

stepwise synthesis of the target compound 8 starting from the

potassium phosphide 4a is indeed possible (Scheme 5).

3a and cyclic oxophosphane 7a as products within a few hours,

which could be identiﬁed via NMR spectroscopy (Scheme

). This reactivity is consistent with documented observa-

tions for similar species. The reaction of 6g with an excess (3

Therefore, 4a was reacted in the ﬁrst step with CS to form

equiv) of CS at room temperature yielded the expected

the bulky potassium phosphanyl dithioformate 10. The

corresponding phosphanyl ester of dithioformic acid 8d.

reaction behavior of 4a toward CS is in accordance with

NMR spectroscopy revealed that full conversion was reached

after 2 weeks of stirring (Scheme 4). This reaction behavior of

previously reported reactions of bulky group 1 phosphides with

44−47

small molecules.

the N-substituted diphosphane 6g toward CS is in good

Species 10 can be isolated in quantitative yield in the form of

28,29

accordance with previously reported observations.

a pale-red, ﬁne powder. The P NMR shift of 55.3 ppm in

47−49

The product 8d could be isolated, fully characterized, and

crystallized, and a discussion of the analytical parameters can

be found below. Because the synthesis of 8 via conversion of

THF-d is in the range of comparable compounds.

10 is

sensitive to air and moisture but can be stored under inert-gas

conditions for months.

Conversion of 10 with secondary chlorophosphanes 5

selectively aﬀorded the desired phosphanyl esters of

diphosphanes with CS seems to be not a universal route, we

were curious to ﬁnd a diﬀerent synthetic approach to access

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Article

Scheme 5. Synthesis of Phosphanyl Dithioformate 10a and the Subsequent Addition of 5, Yielding 8a−8d, and Migration

Reaction for 8a in Solution, Resulting in the Formation of 9

Figure 3. Molecular structures of 8b (left), 8c (middle left), 8d (middle right), and 9a (right) in the single crystal. Ellipsoids set at 50% probability

(123 K). Top view on the P1−C1−S1 planes. Selected structural data are listed in Table 1.

dithioformic acid 8a−8d. Compounds 8b−8d can be isolated

as pure, crystalline materials and were unequivocally identiﬁed

by NMR spectroscopy and X-ray structure elucidation in the

solid state.

This stepwise synthesis route is advantageous over the

previously mentioned one starting from diphosphanes. It oﬀers

the possibility of synthesizing arbitrarily substituted species,

not necessarily bearing N-substituted P atoms. Furthermore,

the stepwise synthesis yielding 8d is signiﬁcantly faster than the

time-consuming synthesis starting from the diphosphane 6g.

Compound 8d can be synthesized in high purity on both

synthesis routes.

8b−8d and 9a could be isolated in the form of deeply

colored crystals from concentrated n-hexane solutions at room

temperature (8b−8d, deep red; 9a, dark green). While 8b, 8c,

and 9a crystallize in monoclinic space groups (8b and 8c,

crystallizes in the triclinic space group P1

units per unit cell. The most prominent structural feature of

b−8d is the approximately planar P1−C1(S1)−S2 unit

Figure 3 and Table 1, dihedral angle da3). The C1−S1 bond

/c; 9a, P2

/n) with four formula units per unit cell, 8d

with two formula

(

Table 1. Selected Structural Parameters of 8b−8d in the

Single Crystal (Figure 3)

Interestingly, while 8b−8d are stable toward isomerization,

parameter

a directly undergoes a R P migration reaction within a few

C1−S1

S2−P2

1.625(1)

2.1924(4)

128.53(7)

124.78(7)

102.49(4)

165.78(4)

−19.03(8)

174.1(1)

1.624(1)

2.1373(4)

127.94(6)

126.94(6)

105.44(3)

154.66(3)

−23.06(7)

−177.2(1)

1.643(1)

2.3207(4)

125.30(6)

127.00(6)

105.41(4)

175.40(4)

−5.12(9)

days of storage in solution, yielding 9a. The migration is

III

accompanied by a formal oxidation of one P atom from P to

P1−C1−S1

S1−C1−S2

C1−S2−P2

P . Because of this migration, it was impossible to fully

characterize or crystallize compound 8a. Thus, 8a was

identiﬁed by a comparison of its ³¹P NMR signals to those

of 8b−8d and the results of theoretical calculations (Table S4).

The migration product 9a can be regarded as phosphanylth-

ioketone with an additional neighboring phosphanylthiolate

group. To the best of our knowledge, this structural motive is

unknown so far.

Heating 8b and 8c to 100 °C in toluene does not lead to any

speciﬁc (migration) reaction: 8b decomposes unspeciﬁcally,

and 8c is stable under these conditions.

da1

da2

da3

−179.4(1)

Bond lengths in angstroms and angles in degrees. da1 = ∠P2−S2−

C1−P1 dihedral angle. da2 = ∠P2−S2−C1−S1 dihedral angle. da3

∠P1−C1−S1−S2 dihedral angle.

length in 8b−8d are in the range of a CS bond [∑r (C−

cov

S) = 1.78 Å; ∑r (CS) = 1.61 Å]. For 8b and 8c, the S2−

cov

Structure Elucidation. Compounds 8b−8d exhibit the

P2 bond length is in the range of a single bond [∑r (P−S) =

cov

expected signals of the CS moiety in their C NMR spectra

2.14 Å; ∑r (PS) = 1.96 Å]. However, the S2−P2 bond

cov

1 13

[

8b: dd, 239.9 ppm, J( P C) = 16 and 60 Hz; 8c: dd, 245.1

in 8d [2.3207(4) Å, Table 1] is signiﬁcantly longer than a P−S

31 13

ppm, J( P C) = 22 and 61 Hz; 8d: dd, 248.3 ppm, J( P C)

12 and 59 Hz], as well as CS absorption bands (8b: 1059

bond, probably for steric reasons.

The migration product 9a exhibits a signal of the CS moiety

at 253.7 ppm in its C NMR spectrum [dd, J( P C) = 24

and 60 Hz] and a CS absorption band (983 cm ) as well as

−

−1

31 13

cm ; 8c : 1072 cm ; 8d : 1061 cm ) in their IR spectra [see

4,29

−1

the Supporting Information (SI) for details].

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−

−1

Figure 4. UV−vis spectra of 8b (c = 0.033 mg mL , red), 8c (c = 0.05 mg mL , gray), 8d (c = 0.025 mg mL , purple), and 9a (c = 0.02 mg

−1

mL , green) in hexane and 11 (vide infra, c = 0.025 mg mL , yellow) in benzene at room temperature (for absorption maxima, see Table S6).

Selected Kohn−Sham orbitals (right) of 8b (top) and 9a (bottom). Top view on the P1−C1−S1 planes. Structures optimized at PBE0-D3/def2-

SVP.

Figure 5. Left: UV−vis spectroscopic monitoring of the migration reaction from 8a to 9a in n-hexane at room temperature (time progression

indicated by colors: from dark blue to yellow, with the ﬁrst and last spectra depicted in black). Middle: P NMR spectra (in C D ) of the migration

reaction at t = 0 h (blue), t = 30 h (black), and t = 104 h (red). Right: Migration reaction monitored by P NMR spectroscopy in C D

concentration of the starting material, blue; concentration of the product, red); k_N_M_R_,_b_e_n_z_e_n_e= 8.52(7) × 10 s ; k

−

−1

−6 −1

= 4.75(4) × 10

NMR,n‑hexane

see the SI for further information).

−

a P−S absorption band (703 cm ) in its IR spectrum (see the

SI for details).

of compounds of the structure type 8 exhibit absorption

maxima that are centered at smaller wavelength (between 300

and 390 nm; see Table S6 for detailed values).

In the single crystal, the migration product 9a has a S2−P2

bond length of 1.9537(4) Å, which is in the typical range for

The P1−C1−S1 angle with 121.67(6)° is

comparable to the corresponding ones in compounds 8b−8d

The calculated absorption maxima are in good agreement

with the experimentally observed maxima (Table S6).

Accordingly, the intense colors of the compounds are caused

by n → π* transitions [formally highest occupied molecular

orbital (HOMO)−lowest unoccupied molecular orbital

(LUMO) transitions; Figure 4]. For 8b as well as for 9a, the

HOMO describes delocalized, mainly nonbonding electrons at

the P1 and S1 atoms and in 9a also at the S2 atom. In both

structures, the LUMO mainly describes the π* orbital of the

CS bond.

50,51

P −S bonds.

(Figure 3).

Spectroscopic Investigations on the R P Migration

Reaction. The mechanism of the migration reaction from 8a

to 9a was investigated in detail by quantum-chemical

calculations (vide infra) and also by UV−vis and NMR

spectroscopy to identify a reaction mechanism and possible

intermediates.

Because species 8b−8d and 9a are intensely colored (8b−

d, red/purple; 9a, dark green), UV−vis spectra of the

compounds were measured. The diﬀerent absorption of the

two structure types 8 and 9 in n-hexane is distinctly visible in

the UV−vis spectra (Figure 4) of the substances. The

spectrum of compound 9a exhibits a broad and intense

maximum that is centered at 453 nm (fwhm = 90 nm). Spectra

Because 8a and 9a show noticeably diﬀerent absorption

maxima (Table S6), it was possible to investigate the kinetics

of the migration reaction using time-resolved UV−vis

spectroscopy. The UV−vis spectra in n-hexane at room

temperature clearly display the reaction progress of the

migration: While the absorption maxima at

λ_m_a_x_,₁(8a) = 345 nm and λ_m_a_x_,₂(8a) = 386 nm decrease, a

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Scheme 6. Schematic View of the Energy Diagram (Gas Phase) of the Migration Reaction Mechanism from 8 to 9

The intermediates for species b−d are omitted for clarity.

noticeable increase of absorption can be observed for

λ_m_a_x_,₁(9a) = 453 nm (Figure 5). The existence of an isosbestic

point at λ_i_s_o= 416 nm indicates that, during the considered

reaction period (approximately 100 h), no secondary reactions

reaction step leads to a rotamer (INT2a) of the product 9a via

cyclic transition state TS2a and is the rate-determining step

(RDS) of the migration reaction. INT2a then relaxes to the

ﬁnal product 9a via C−P bond rotation. Because the equilibria

related to internal single-bond rotations are very fast in

comparison with the RDS, the overall rate of the reaction

approximately depends on the energy diﬀerence between 8 and

TS2 (S86). Thus, for derivatives 8b−8d, only transition states

TS2b−TS2d were computed to estimate the reaction rates,

showing larger energy diﬀerences (ΔG°) and thus slower

reaction rates in agreement with the experimental observation.

The agreement between experimentally estimated (n-hexane,

occurred (Figure 5). The migration reaction was found to be

a ﬁrst-order reaction at ambient temperature (k = 4.64(1)

UV−vis

−

−1

10 s ) with a half-life of about 42 h.

P NMR spectroscopy is also well-suited to study the

migration reaction because the staring material 8a and product

a contain P atoms with clearly distinguishable chemical shifts

Figure 5). NMR spectroscopic investigations in n-hexane and

C D at room temperature could verify the ﬁrst-order reaction

(

= 4.75(4) × 10⁻s ; k

−1

103.4 kJ mol ; benzene, 101.9 kJ mol ) and calculated (n-

−1

mechanism [k

.52(7) × 10 s ].

NMR,n‑hexane

NMR,benzene

−

−1

hexane, 108.4 kJ mol ; benzene, 107.6 kJ mol ) energy

diﬀerences is reasonable. Moreover, the investigated reaction

mechanism is a monomolecular reaction. Hence, it agrees with

the experimentally observed reaction of ﬁrst order.

The slightly diﬀerent rate constants in n-hexane and C D

can be explained by solvent eﬀects. Benzene stabilizes the

transition state (vide infra) and therefore accelerates the

migration reaction. Possible intermediates of this migration

As mentioned before, the migration reaction is associated

III

reaction could be observed by neither UV−vis nor P NMR

spectroscopy, which might be due to a short lifetime or a low

concentration of the intermediates in the reaction solution

compared to the concentrations of the starting material and

product.

with a change of the formal oxidation state of P2 from P to

P , while the C1 atom is formally being reduced from C to

C . Hence, the migration process could be considered an

internal redox reaction.

Coordination Chemistry of 9a. The migration product 9a

was studied as a ligand in gold coordination chemistry in order

to exemplarily prove its coordination ability. It was of special

interest to determine whether coordination occurs via the P

and/or S atom of 9a. Indeed, the addition of a green solution

Computations on the R P Migration Reaction. To better

understand the mechanism of the migration reaction from 8a

to 9a, computations were performed at the PBE0-D3/def2-

SVP level of theory (for computational details, see also the SI ).

The migration yielding 9a is an exergonic process (Δ G° =

of 9a in THF to (SMe )AuCl at room temperature led to an

−

37.4 kJ mol ). After rotation of the P(iPr) moiety around

immediate change of color to an intensely dark orange.

Crystallization from n-hexane by slow evaporation gave

complex 11 (Figure 6) in good yield. The gold complex 11

the C1−S2 bond (resulting in intermediate INT1a; Scheme

), P2 can perform a nucleophilic attack at C1. This S 2-type

Inorg. Chem. XXXX, XXX, XXX−XXX

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The preparation of arbitrarily substituted phosphanyl esters

of dithioformic acid 8 by a new general synthetic route is

reported. This new route starts from phosphanyl dithiofor-

mates 10, which are converted with secondary chlorophos-

phanes, selectively yielding the target structures.

On one occasion (R = iPr), a R P migration within the

phosphanyl ester, which is initiated by the nucleophilic attack

of P2 at the C1 atom, was observed. The migration results in

the formation of a phosphanylthioketone with an additional

neighboring phosphanylthiolate group 9a. Theoretical and

experimental studies of the migration reaction revealed a ﬁrst-

order reaction with a formal three-membered cyclic transition

state. Moreover, this migration process can be regarded as an

internal redox process. All other studied phosphanyl esters 8

did not undergo such an isomerization process because of a

larger activation barrier.

Compound 9a further proved to be a suitable ligand for

stabilization of gold(I) species, coordinating via the P and S

atoms.

In future studies, other small molecules should be activated

with phosphides to further investigate the properties of

sterically demanding secondary potassium phosphides.

Figure 6. Molecular structure of 11 in the single crystal. Ellipsoids set

at 50% probability (123 K). Selected bond length (Å) and angles

(

deg): P2−S2 1.9506(5); P1−Au1 2.2299(5); Cl1···H2′ 2.8436(5);

C)H1···Au 2.7107(6); S2···Au1 3.3559(6); P1−Au1−Cl1

70.760(13); P1−C1−P2−S2 −41.90(7).

was fully characterized, and X-ray analysis revealed the

presence of a P/S-bound AuCl complex, as depicted in Figure

EXPERIMENTAL SECTION

■

. While the P1 atom in 9a shows an NMR shift of 139.2 ppm,

All manipulations were carried out under oxygen- and moisture-free

conditions under argon using standard Schlenk or drybox techniques,

if not stated otherwise. All starting materials were produced using

it is signiﬁcantly high-ﬁeld-shifted to 84.6 ppm in 11. The same

phenomenon can be observed for the P2 atom (9a, 73.8 ppm;

11, 40.5 ppm). 11 crystallizes in the triclinic space group P1

(

modiﬁed) literature procedures. The reactants and solvents were

with two formula units per cell. X-ray structure elucidation

revealed a puckered ﬁve-membered Au−P−C−P−S ring

exhibiting a P1−C1−P2−S2 unit in 11 that is no longer

planar as in 9a because the S2 atom is noticeably bent out of

the plane [∠P1−C1−P2−S2 dihedral angle = −41.90(7)°]. It

is well-known that gold(I) complexes tend to prefer a linear

geometry, but for electronic and steric reasons, the P1−Au1−

obtained from commercial sources and thoroughly dried and puriﬁed.

If not stated otherwise, experiments and crystallization attempts were

carried out at room temperature [298(2) K]. The removal of solvents

as well as evaporation of substances in vacuo was carried out at 1 ×

−

10 mbar, if not stated otherwise.

Caution! KH is highly reactive and can react vigorously with air/

moisture! Appropriate safety precautions should be taken (inert gas

storage/handling, proper/immediate destruction of accruing excess, etc.).

Further information on the synthesis of precursors, experimental

procedures, data acquisition and processing, and puriﬁcation of

starting materials and solvents and a full set of analytical data for each

compound as well as computational details can be found in the SI.

Synthesis of Compounds. Synthesis of Secondary Phosphanes

3−55

Cl1 angle in 11 is decreased to 170.76(1)°.

Complex 11 is

further stabilized by intramolecular agostic interactions: The

(

C)H1···Au1 bond length of 2.7107(6) Å [∑r_v_d_W(H···Au) =

.1 Å] is in the shorter range of previously reported (C)H···

7−60

Au agostic interactions.

Additionally, weak S2···Au1

interactions in 11 are indicated by a short distance of

a−3e. Alkyl bromide [2 mmol; iPrBr, 0.246 g; nBuBr, 0.274 g; EtBr,

.3559(6) Å [∑r_v_d_W(S···Au) = 3.5 Å]. Intermolecular

0.218 g; iBuBr, 0.274 g; 2-phenylethyl bromide (EtPhBr), 0.370 g] is

added dropwise to a solution of terphenylpotassium phosphide (2

mmol, 0.768 g) in THF (15 mL). The resulting colorless suspension

is stirred for 2 h. All volatile components are removed in vacuo, the

remaining white solids are extracted with n-hexane, and the resulting

suspension is ﬁltered. The solvent of the ﬁltrate is evaporated, yielding

the product as a colorless solid. If necessary, the product can be

hydrogen bonding can be observed between the Cl1 atom

and one meta-H atom of the mesityl group at the neighboring

Ter substituent H2′, resulting in a 3D chainlike structure in the

solid state. The corresponding distance Cl1···H2′ is 2.8436(5)

Å [∑r (H,Cl) = 3.2 Å]. In 11, the asymmetrically

vdW

substituted P1 atom is coordinated to Au , which makes this

crystallized overnight from n-hexane or CH Cl /CH CN. Yield: R =

iPr, 95% (1.90 mmol, 0.74 g); R = nBu, 85% (1.70 mmol, 0.68 g); R

type of metal complex interesting for catalytic purposes.

Further investigations on the catalytic activity as well as

coordination reactions of 11 are planned.

Et, 39% (0.78 mmol, 0.29 g); R = iBu, 44% (0.87 mmol, 0.35 g);

R = EtPh, 76% (1.52 mmol, 0.69 g). 3a. Mp: 120.0 °C. Elem anal.

Calcd (found): C, 83.47 (84.59); H, 8.56 (8.79). P NMR (C D ,

CONCLUSIONS

98.1 K, 500.13 MHz): δ −36.8 (br dd, J( P, H) = 229 Hz,

■

31 1

J( P, H) = 17 Hz, PH). 3b. Mp: 110.4 °C. Elem anal. Calcd (found):

C, 83.54 (83.94); H, 8.76 (8.68). P NMR (C D , 300.0 K, 101.26

The ﬁndings on the reaction behavior of sterically demanding

terphenyl-substituted diphosphanes are consistent with the

previously published results (vide ante). The partly N-

substituted diphosphane 6g recently synthesized by us could

MHz): δ −70.9 (d, J( P, H) = 220 Hz, PH). 3c. Mp: 116.5 °C.

Elem anal. Calcd (found): C, 84.29 (83.98); H, 7.35 (8.14). P NMR

(

C D , 300.0 K, 101.26 MHz): δ −63.4 (dt, J( P, H) = 220 Hz, J =

be converted with CS , selectively yielding the phosphanyl

2.3 Hz, PH). 3d. Mp: 131.2 °C. Elem anal. Calcd (found): C, 83.54

ester of dithioformic acid. In contrast to that, the synthesized

83.05); H, 8.76 (9.31). P NMR (C D , 298.2 K, 121.51 MHz): δ

6 6

sterically demanding C-substituted diphosphanes 6a−6f

−

39.3 (m, J( P, H) = 219 Hz, PH), −44.3 (m, J( P, H) = 219 Hz,

31 1

showed no reactivity toward an excess of CS , even under

J( P, H) = 20 Hz PH). 3e. Mp: 115.2 °C. Elem anal. Calcd (found):

reﬂuxing conditions, indicating that the reactions of the

C, 85.30 (85.42); H, 7.83 (7.94). P NMR (C D , 300.0 K, 101.26

6 6

diphosphanes with CS are kinetically forbidden.

MHz): δ −72.3 (br d, J( P, H) = 219 Hz, PH).

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

Article

Synthesis of Secondary Phosphides 4a and 4b. A solution of

secondary phosphane (1 mmol; iPrTerPH, 0.388 g; nBuTerPH, 0.403

g) in THF (10 mL) is added to KH (4 mmol, 0.160 g). The resulting

suspension is stirred for 2 weeks, and an increase of the pressure in

the ﬂask due to hydrogen formation must be prevented using a

pressure relief valve. Afterward, the solution is separated from KH by

decantation, and the highly sensitive product is directly used in situ to

prevent decomposition. Note: The product might still contain traces

of KH, and this should be considered with respect to diﬀerent

substrates. The product is extremely sensitive, and the equipment

needs to be thoroughly dried to prevent product decomposition. If the

product should be obtained without traces of KH, the reaction

mixture can be ﬁltered in a glovebox using syringe ﬁlters (pore size:

(8.349); N 4.56 (4.522). P NMR: (THF-d , 298.2 K, 121.51 MHz):

δ = −26.8 (br.d, J( P, P) = 213 Hz, 1P, TerPH); 121.8 (br.d,

1J( P, P) = 213 Hz, 1P, (NCH CH N)P).

Synthesis of Phosphanyl Dithioformate 10a. A solution of the

potassium phosphide iPrTerPK (1 mmol, 0.426 g) in THF (10 mL) is

slowly added to a stirred excess of CS (2 mmol, 0.152 g). The

resulting orange-to-pale-red suspension is ﬁltered to remove traces of

potassium hydride from the starting material and the solvent of the

ﬁltrate evaporated, yielding the desired product in the form of a pale-

red powder. Yield: 95% (0.95 mmol, 0.48 g). 10a. Mp: 260.0 °C.

Elem anal. Calcd (found): C, 66.89 (66.13); H, 6.42 (6.92); S, 12.73

(

11.64). P NMR (C D , 299.2 K, 202.48 MHz): δ 55.3 (br d,

6 6

J( H, P) = 15 Hz, P).

.45 μm), and the solvent is evaporated under atmospheric pressure

Synthesis of Phosphanyl Esters of Dithioformic Acid 8b and 8c.

The chlorophosphane ClP(R ) (1 mmol; ClP(Ph) , 0.221 g;

ClP(tBu) , 0.181 g) is added dropwise to a stirred solution of

phosphanyl dithioformate (1 mmol, 0.503 g) in THF (10 mL). The

resulting suspension is stirred for 10 min; afterward, the solvent is

removed in vacuo. The resulting intensely colored precipitate is

extracted with n-hexane (8 mL) and ﬁltered. The ﬁltrate is

concentrated in vacuo, yielding a slightly viscous oily residue, from

which the desired products crystallize. The supernatant is removed

and discarded, and the crystals are washed with small amounts of n-

hexane and dried in vacuo. Yield: R = Ph, 53% (0.53 mmol, 0.34 g);

R = tBu, 32.5% (0.33 mmol, 0.20 g). 8b. Mp: 118.5 °C. Elem anal.

Calcd (found): C, 74.04 (74.07); H, 6.52 (6.27); S, 9.88 (9.48).

NMR (THF-d , 297.8 K, 101.27 MHz): δ 20.7 (br d, 1P, J( P, H) =

2 Hz, P(Ph) ), 51.5 (m, 1P, iPrPTer). 8c. Mp: 130.5 °C. Elem anal.

Calcd (found): C, 71.02 (69.78); H, 8.28 (7.95); S, 10.53 (11.78).

over a few days, yielding the desired product in the form of a slightly

oily solid. Yield: R = iPr, 80% (0.80 mmol, 0.34 g); R = nBu, 83%

(

0.83 mmol, 0.36 g). Because of the extremely high sensitivity of the

samples of 4a and 4b, it was not possible to obtain an accurate

elemental analysis; all other analytical data as well as the reported

reaction behavior prove the successful synthesis of the desired

products. 4a. Mp: 273 °C. P NMR (THF-d , 300.0 K, 101.26

MHz): δ 23.9 (m, PK). 4b. Mp: 172 °C (dec). P NMR (THF-d₈,

98.5 K, 121.51 MHz): δ −23.6 (s, P).

Synthesis of Diphosphanes 6a−6f. Chlorophosphane (1 mmol;

iPr PCl, 0.152 g; Ph PCl, 0.221 g; tBu PCl, 0.181 g) is slowly added

to a stirred solution of potassium phosphide (1 mmol; iPrTerPK,

.426 g; nBuTerPK, 0.441 g) in THF (10 mL). The resulting

colorless suspension is stirred for 1 h, and subsequently all volatile

components are removed in vacuo. The remaining white solids are

extracted with n-hexane, and the resulting suspension is ﬁltered,

yielding a colorless solution as the ﬁltrate. The desired products can

P NMR (THF-d , 298.2 K, 121.51 MHz): δ 63.8 (m, 1P, iPrPTer),

77.3 (m, 1P, P(tBu)₂).

be crystallized overnight from a concentrated solution. Yield: R = iPr,

Synthesis of Phosphanyl Esters of Dithioformic Acid 8d. Method

1. A solution of potassium dithioformate [iPrTerPCS K (10a); 1

R = iPr, 59% (0.59 mmol, 0.30 g); R = iPr, R = Ph, 54% (0.54

mmol, 0.31 g); R = iPr, R = tBu, 48% (0.48 mmol, 0.26 g); R =

nBu, R = iPr, 55% (0.55 mmol, 0.29 g); R = nBu, R = Ph, 67% (0.67

mmol, 0.503 g) in THF (10 mL) is added slowly at 298 K to a stirred

solution of 1,3-di-tert-butyl-2-chloro-1,3,2-diazaphospholidine (1

mmol, 0.237 g) in THF (3 mL). The resulting turbid red suspension

is stirred for 10 min and subsequently ﬁltered. The solvent of the

ﬁltrate is evaporated, the solid residue is extracted with n-hexane and

ﬁltered, and the ﬁltrate is concentrated in vacuo, yielding purple

crystals of the desired product overnight at 298 K. Yield: 48.0% (0.48

mmol, 0.32 g).

Method 2. CS (3 mmol, 0.23 g) is added to a solution of

diphosphane 6g (1 mmol, 0.59 g). The resulting yellowish solution is

stirred for 2 weeks, whereupon the color changes to purple. The

reaction can be traced using P NMR spectroscopy. After

approximately 2 weeks, all volatile components are removed in

vacuo and the resulting precipitate is solved in n-hexane (10 mL). The

product can be crystallized overnight after removal of approximately 8

mL of the solvent in vacuo. Yield: 40.0% (0.40 mmol, 0.26 g).

mmol, 0.39 g); R = nBu, R = tBu: 72% (0.72 mmol, 0.39 g). 6a. Mp:

6.6 °C. Elem anal. Calcd (found): C, 78.54 (77.79); H, 9.19 (7.79).

31 31

P NMR (C D , 298.8 K, 121.5 MHz): δ −12.2 (d, J( P, P) = 353

31 31

Hz, 1P, iPrTerP), 1.6 (d, J( P, P) = 353 Hz, 1P, (iPr) P). 6b. Mp:

95.6 °C. Elem anal. Calcd (found): C, 81.79 (81.34); H, 7.39 (7.81).

1 31 31

P NMR (C D , 300.0 K, 101.26 MHz): δ −24.5 (br d, J( P, P) =

31 31

70 Hz, 1P, (Ph) P), −17.6 (d sep, J( P, P) = 270 Hz, 1P,

31 1

J( P, H) = 17 Hz, iPrTerP). 6c. Mp: 175.6 °C. Elem anal. Calcd

(found): C, 78.91 (77.94); H, 9.46 (8.16). P NMR (C D , 298.2 K,

6 6

31 31

00.13 MHz): δ −1.7 (dm, J( P, P) = 395 Hz, 1P, iPrTerP), 31.2

1 31 31

(

dm, J( P, P) = 395 Hz, 1P, (tBu) P). 6d. Mp: 61.5 °C. Elem anal.

Calcd (found): C, 78.73 (78.90); H, 9.33 (9.43). P NMR (C D ,

31 31

00 K, 101.26 MHz): δ −37.8 (br d, J( P, P) = 323 Hz, 1P,

1 31 31

nBuTerP), 1.8 (dm, J( P, P) = 323 Hz, 1P, (iPr) P). 6e. Mp: 115.7

C. Elem anal. Calcd (found): C, 81.88 (80.98); H, 7.56 (8.18). P

NMR (C D , 300.0 K, 101.26 MHz): δ −36.2 (br d, J( P, P) = 217

31 31

8d. Mp: 182.1 °C. Elem anal. Calcd (found): C, 68.64 (69.18); H,

8.19 (8.08); N, 4.21 (4.21); S, 9.64 (9.45). P NMR (THF-d , 300.0

K, 101.26 MHz): δ 60.8 (m, 1P, iPrPTer), 159.9 (m, 1P,

(NCH CH N)P).

Synthesis of the Migration Product 9a. The chlorophosphane

31 31

Hz, 1P, nBuTerP), −20.3 (dt, J( P, P) = 217 Hz, J( P, H) = 7 Hz,

(

P, (Ph) P). 6f. Mp: 134.2 °C. Elem anal. Calcd (found): C, 79.08

79.41); H, 9.59 (9.65). P NMR (C D , 300.0 K, 101.26 MHz): δ

31 31

−

11.4 (br d, J( P, P) = 415 Hz, 1P, nBuTerP), 45.2 (dt, J( P, P)

415 Hz, J( P, H) = 34 Hz, 1P, (tBu) P).

ClP(iPr) (1 mmol, 0.153 g) is added dropwise to a stirred solution of

the phosphanyl dithioformate (1 mmol, 0.503 g) in THF (10 mL).

The resulting suspension is stirred for 10 min; afterward, the solvent is

removed in vacuo. The solid residue is extracted with n-hexane (10

mL), and the resulting suspension is ﬁltered. The ﬁltrate is

concentrated in vacuo to half of the initial volume (approximately 5

mL). After 4 days of storage, the product is obtained in the form of

dark-green crystals. The supernatant is transferred into a new vessel

and further concentrated, yielding equally pure crystals. Both fractions

of green crystals are combined, washed with small amounts of n-

hexane, and dried in vacuo. Yield: 31.0% (0.31 mmol, 0.18 g). 9a. Mp:

190.8 °C. Elem anal. Calcd (found): C, 70.31 (70.34); H, 7.98 (7.85);

Synthesis of Diphosphanes 6g and 6h. A solution of potassium

phosphide (1 mmol; iPrTerPK, 0.426 g; nBuTerPK, 0.441 g) in THF

10 mL) is slowly added to a stirred solution of 1,3-di-tert-butyl-2-

(

chloro-1,3,2-diazaphospholidine (1 mmol, 0.237 g) in THF (3 mL).

The resulting turbid yellow suspension is stirred for 1 h and ﬁltered.

The solvent of the ﬁltrate is evaporated, the resulting white solids are

extracted with CH Cl , and insoluble components are removed by

ﬁltration. The ﬁltrate is concentrated in vacuo, yielding crystals of the

desired product. Yield: R = iPr, 28% (0.28 mmol, 0.17 g); R = nBu,

1% (0.21 mmol, 0.13 g). 6g. Mp: 153.5 °C. Elem anal. Calcd

(

found): C, 75.48 (75.72); H, 9.24 (8.82); N, 4.76 (4.52). P NMR

THF-d , 298.2 K, 202.48 MHz): δ 4.7 (dm, J( P, P) = 229 Hz,

iPrTerP), 122.8 (br d, J( P, P) = 229 Hz, (NCH CH N)P). 6h.

31 31

S, 11.04 (11.11). P{ H} NMR (THF-d , 298.1 K, 202.48 MHz): δ

31 31

73.8 (br d, J( P, P) = 85 Hz, 1P, PS(iPr) ), 139.2 (br d, J( P, P)

6h: Mp: 124.3 °C. EA: calcd. (found) in %: C 75.71 (75.732); H 9.36

= 85 Hz, 1P, iPrPTer).

Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry

The Supporting Information is available free of charge at

Article

Synthesis of Complex 11. 9a (0.3 mmol, 0.171 g) is dissolved in

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ASSOCIATED CONTENT

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free of charge via www.ccdc.cam.ac.uk/data_request/cif , or by

emailing data_request@ccdc.cam.ac.uk , or by contacting The

Cambridge Crystallographic Data Centre, 12 Union Road,

Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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Yannic Pilopp − Institut fu

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Lilian Sophie Szych − Institut fu

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Alexander Villinger − Institut fu

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