The First Coordination Polymers Based on 1,3‐Diphosphaferrocenes and 1,1′,2,3′,4‐Pentaphosphaferrocenes

Abstract

Phosphaferrocenes in combination with coinage metal salts proved to be excellent building blocks in supramolecular chemistry for the buildup of oligomeric and polymeric assemblies. The synthesis of a series of novel phosphaferrocenes containing the 1,3‐P₂C₃ iPr₃ and/or the 1,2,4‐P₃C₂ iPr₂ ligand is described herein. The self‐assembly processes of the 1,3‐diphospha‐, 1,2,4‐triphospha‐, and 1,1′,2,3′,4‐pentaphosphaferrocenes with Cu^I halides led to the formation of 1D or 2D polymers. With [Cp*Fe(η⁵‐P₂C₃ iPr₃)] (Cp* = η⁵‐C₅Me₅), infinite chains are formed, whereas with [(η⁵‐P₃C₂ iPr₂)Fe(η⁵‐P₂C₃ iPr₃)] 1D ladderlike structures are obtained. These are the first polymers containing such a di‐ and pentaphosphaferrocene, respectively. On the other hand, the use of [Cp*Fe(η⁵‐P₃C₂ iPr₂)] leads to the construction of 2D networks with intact sandwich complexes, which is uncommon for this class of complexes.

Introduction

The year 2016 marks the 50th anniversary of 2,4,6‐triphenylphosphabenzene, and until now the fundamental interest in main group heterocycles is unabated.1 According to the isolobal principle, the formal substitution of methine moieties in aromatic rings (e.g., benzene, cyclopentadienide) by substituent‐free phosphorus atoms is possible. The resulting derivatives of Cp^– are also capable of acting as η⁵ ligands for the synthesis of sandwich complexes, classified as phosphametallocenes. Among them, the phosphaferrocenes containing iron and one to six P atoms are the most popular representatives. First labeled as “laboratory curiosity”,2 their widespread potential in catalysis and supramolecular chemistry soon was recognized. Contrary to their all‐carbon analogue, the lone pairs of the phosphorus atoms make them excellent building blocks towards Lewis acidic metal salts. We especially use Cu^I halides as linker molecules, since they show great versatility in combination with phosphaferrocenes.

The 1,2,3,4,5‐pentaphosphaferrocene [Cp*Fe(η⁵‐P₅)] (Cp* = η⁵‐C₅Me₅), for instance, is capable of building up polymeric3 or, depending on the applied conditions, even spherical coordination compounds.4 These sensitive self‐assembly processes also depend on the substitution patterns of the phosphaferrocenes. Especially 1,2,4‐triphosphaferrocenes [Cp^RFe(η⁵‐P₃C₂R′₂)] (Cp^R = Cp, Cp*, Cp″′; Cp″′ = η⁵‐C₅H₂ tBu₃; R′ = tBu, Ph, Mes) have been synthesized and studied extensively concerning their coordination potential (Figure 1, a–c).5 Thereby, special attention is paid to the influence of the substitution pattern on the coordination behavior towards Cu^I halides. For example, the 1,2,4‐triphosphaferrocenes [Cp^RFe(η⁵‐P₃C₂ tBu₂)] (Cp^R = Cp, Cp*) form dimeric (Figure 1, a) and oligomeric products with stoichiometric amounts of CuX (X = Cl, Br, I), and in one case a 2D polymer with an excess of CuI.6 The last‐named example is the only coordination polymer containing an intact 1,2,4‐triphosphaferrocene complex. On the other hand, an astonishing fragmentation and rearrangement process to form a tetraphosphabutadiene ligand can be observed with the Cp″′ complex [Cp″′Fe(η⁵‐P₃C₂ tBu₂)] (Figure 1, b).7

Figure 1.

Selected examples of coordination products of 1,2,4‐triphosphaferrocenes with Cu^I halides (a–c) and a 1,1′,2,3′,4‐pentaphosphaferrocene with a {W(CO)₅} fragment (d).

Furthermore, especially the R′ group at the phospholyl ligand profoundly affects its reactivity. Thus, enhancement of the steric bulk at the phospholyl ring results in completely different reactivity: The combination of the mesityl‐substituted phosphaferrocene [Cp*Fe(η⁵‐P₃C₂Mes₂)] with CuX (X = Cl, Br, I) entails fragmentation of the sandwich complex. The split‐off [P₃C₂Mes₂]^– ligand serves as building block for the formation of oligomeric and polymeric assemblies (Figure 1, c).8

Therefore, large substituents at the Cp^R or phospholyl ligand lead to a higher instability of the phosphaferrocenes with respect to fragmentation. Encouraged by these results, we were particularly interested in decreasing the steric demand of the R′ group in the phospholyl ligand, which has been neglected so far. For this purpose, the smaller iPr substituent moved into our focus. The less bulky ligand may enhance the stability of the corresponding phosphaferrocenes and thus allow coordination chemistry without fragmentation and rearrangement processes. The common synthetic route for the preparation of [P₃C₂R′₂]^– starts from the corresponding phosphaalkene5d or phosphaalkyne9 and is accompanied by the formation of [P₂C₃R′₃]^– as a byproduct (Scheme 1).

Scheme 1.

Established synthesis of 1,3‐di‐ and 1,2,4‐triphospholyl moieties.

Concerning the iPr group, Nixon et al. showed that treating a mixture of the phosphaalkynes iPrC≡P and tBuC≡P with sodium results in the formation of nine differently substituted 1,3‐di‐ and 1,2,4‐triphospholyl ligands.9 Though several derivatives of 1,3‐diphospholyl ligands were synthesized by this method, no comprehensive coordination studies involving these heterocycles are known in the literature. Merely a few phosphaferrocenes are structurally characterized: two 1,3‐diphosphaferrocenes [Cp^RFe(η⁵‐P₂C₃R′₃)],5f,10 four 1,1′,3,3′‐tetraphosphaferrocenes [(η⁵‐P₂C₃R′₃)₂Fe],11 and one 1,1′,2,3′,4‐pentaphosphaferrocene [(η⁵‐P₃C₂ tBu₂)Fe(η⁵‐P₂C₃ tBu₃)].12 In addition, the last‐named sandwich complex has been used for coordination of a {W(CO)₅} fragment (Figure 1, d)13 and a ligand‐transfer reaction.14 Furthermore, Nixon et al. described mass‐spectrometric evidence of the iPr derivatives of these three phosphaferrocenes among a mixture of more than 20 different sandwich complexes.9 No supramolecular assemblies based on phosphaferrocenes containing a 1,3‐diphospholyl ligand are known.

Herein, we report on the straightforward synthesis and characterization of a series of partly hitherto unknown phosphaferrocenes containing the iPr‐substituted phospholyl ligands 1,3‐[P₂C₃ iPr₃] and 1,2,4‐[P₃C₂ iPr₂]. The 1,3‐di‐, 1,2,4‐tri‐, and 1,1′,2,3′,4‐pentaphosphaferrocene were further used as building blocks in coordination chemistry with Cu^I halides. Reactions with the 1,2,4‐triphosphaferrocene allowed the isolation of novel 2D polymeric networks. On the other hand, the use of [Cp*Fe(η⁵‐P₂C₃R′₃)] and [(η⁵‐P₃C₂ tBu₂)Fe(η⁵‐P₂C₃ tBu₃)] led to the formation of 1D chains, which are the first coordination polymers containing this type of di‐ and pentaphosphaferrocenes, respectively.

Results and Discussion

Synthesis and Characterization of the Phosphaferrocenes

The preparation of the phospholyl salts K[P₂C₃ iPr₃] (1a) and K[P₃C₂ iPr₂] (1b) was carried out analogously to the tBu derivative5d,15 starting from the corresponding phosphaalkene Me₃SiO(iPr)C=P(SiMe₃)16 and KP(SiMe₃)₂ (cf. Scheme 1 for R = iPr).17 In contrast, Nixon et al. treated the phosphaalkyne with elemental sodium to obtain the sodium derivatives of 1a and 1b among other products.9 Interestingly, the product distribution of 1a and 1b turned out to be temperature‐dependent. According to ³¹P{¹H} NMR spectroscopy after 1 d of heating at 50 °C, the ratio 1a/1b is about 1:1. After isolation of this first crop of product the remaining mother liquor was heated for a further day to favor the formation of 1b (1a/1b = 0.75:1). When the reaction mixture was finally heated to reflux at 100 °C, the last crop of the isolated off‐white powder solely contained the triphospholyl salt 1b. Therefore, a selective synthesis of 1b at least is feasible. Since both salts are needed for the subsequent reaction, the initial solution was heated to 75 °C for 3 d instead to give 1a and 1b in approximately 1:1 ratio.

The ³¹P{¹H} NMR spectrum of the isolated product in [D₈]thf shows a singlet at δ = 159.6 ppm, which can be assigned to 1a (cf. Na[P₂C₃ iPr₃]: δ = 155.0 ppm).9 Surprisingly, for 1b a doublet of doublets at δ = 247.6 ppm (² J _PP = 51.6 and 45.1 Hz) and a pseudodoublet (δ = 244.7 ppm) with a merged coupling constant of ² J _PP = 49.0 Hz were observed for the isolated and the adjacent phosphorus atoms, respectively. For comparison, previously reported derivatives [1,2,4‐P₃C₂R₂]^– all show a (slightly low‐field shifted) doublet and triplet with a similar coupling constant (R = Mes:5a δ = 266.4, 261.7 ppm, ² J _PP = 38 Hz; R = Ph,5a δ = 274.4, 253.9 ppm, ² J _PP = 43 Hz; R = tBu:5b δ = 256, 248 ppm, ² J _PP = 49 Hz). For Na[P₃C₂ iPr₂], a slight high‐field shift compared to 1b was observed (δ = 241.6 and 246.6 ppm, ² J _PP = 48 Hz).9

For the subsequent synthesis of the novel 1,3‐diphosphaferrocene [Cp*Fe(η⁵‐P₂C₃ iPr₃)] (2) and 1,2,4‐triphosphaferrocene [Cp*Fe(η⁵‐P₃C₂ iPr₂)] (3) we also referred to the established strategy for the tBu derivative.5k Thus, solutions of FeBr₂(dme) and LiCp* in thf were added to a mixture of 1a and 1b in thf at –50 °C (Scheme 2), and an immediate color change from orange to deep reddish brown resulted. ³¹P{¹H} and ¹H NMR spectroscopic investigations of the crude reaction mixture revealed signals corresponding to 2 and 3, but also signals of small amounts of byproducts. These included [Cp*₂Fe], the 1,1′,3,3′‐tetraphosphaferrocene [(η⁵‐P₂C₃ iPr₃)₂Fe] (4), the 1,1′,2,3′,4‐pentaphosphaferrocene [(η⁵‐P₃C₂ iPr₂)Fe(η⁵‐P₂C₃ iPr₃)] (5), and the 1,1′,2,2′,4,4′‐hexaphosphaferrocene [(η⁵‐P₃C₂ iPr₂)₂Fe] (6). The sandwich complexes 5 and 6 were already reported but only characterized by mass spectrometry in a mixture of more than 20 phosphaferrocenes.9

Scheme 2.

Synthesis of phosphaferrocenes 2–6.

The phosphaferrocenes were separated by an elaborate column‐chromatographic workup. A yellow band of [Cp*₂Fe], followed by a green fraction of a mixture of 4, 5, and 6 was eluted with hexane. With a slightly more polar eluent (hexane/toluene = 10:1) a red band of a mixture of 2 and 3 was obtained. For the isolation of the pure phosphaferrocenes, further column‐chromatographic workup of the green and red fractions is necessary (see Supporting Information and Exp. Section). In this way, analytically pure compounds 2, 3, and 5 were obtained.

All phosphaferrocenes were identified by their characteristic chemical shifts and multiplicity in the ¹H and ³¹P{¹H} NMR spectra. Compared to those of 1a and 1b, the P atoms show a significant high‐field shift of more than 100 ppm in the corresponding ³¹P{¹H} NMR spectra, which is a usual trend in phosphaferrocene chemistry.5a,5f,12,18 In contrast to 1b and in analogy to known 1,2,4‐triphospholyl derivatives, the P₃C₂ rings all show a doublet and a triplet for the isolated and adjacent phosphorus atoms on coordination to iron, respectively (² J _PP = 43.8 Hz in 3, 42.0 Hz in 5, and 38.0 Hz in 6) (Table 1). On the other hand, a singlet is obtained for the P₂C₃ ligands. In addition, multiplets in the range of δ = 2.2–3.1 ppm in the ¹H NMR spectra can be assigned to the methine groups, whereas all methyl groups show doublets (³ J _HH = 6.1–6.7 Hz) with chemical shifts between 1.0 and 1.7 ppm (for detailed assignment, see Exp. Section). In ferrocenes containing the 1,3‐diphospholyl ring, two sets of signals are observed for the CH units (integral ratio: 1:2) and three for the CH₃ groups (1:1:1). For the 1,2,4‐triphospholyl moieties in 3, 5, and 6, one multiplet (CH) and two doublets (CH₃) per ring are monitored.

Table 1.

³¹P{¹H} chemical shifts δ [ppm] of 2–5 in C₆D₆ at room temperature and of 6 in CD₂Cl₂ at 193 K.

	δ [ppm] (P2C3)	δ [ppm] (P3C2)	2 J PP [Hz]
1a	161.4 (s)
1b		247.6 (dd), 244.7 (pseudo‐d)	51.6, 45.1, 49.0
2	–2.8 (s)	–	–
3	–	29.7 (t), 49.6 (d)	43.8
4	6.7 (s)	–	–
5	15.0 (s)	46.9 (t), 53.7 (d)	42.0
6	–	46.2 (d), 69.3 (t)	38.0

In the FD mass spectra the molecular‐ion peaks are observed for all complexes 2–6, albeit with low intensity for 4. In addition, the structures of 2, 4, and 5 were confirmed by X‐ray structural analyses (see below).

Molecular Structures of 2, 4, and 5

Crystals of 2, 4, and 5 suitable for X‐ray structural analysis were obtained by layering toluene solutions with CH₃CN and storing at –28 °C (Figure 2). Compound 2 crystallizes in the monoclinic space group P2₁/c, 4 in the triclinic space group P , and 5 in three monoclinic polymorphic modifications (P2₁, P2₁/n, for details see Supporting Information and Table 3). All molecular structures can be described as sandwich complexes with η⁵‐coordinated ligands in an eclipsed conformation. The tetraphosphaferrocene 4 forms the most “perfect” sandwich complex with an interplanar angle of 0.27(5)° and a (P₂C₃ iPr₃)_centroid–Fe–(P₂C₃ iPr₃)_centroid angle of 179.84(2)°. These distortions are slightly more pronounced in 2 [3.33(7)° and 177.09(3)°] and 5 [3.57(7)° and 177.25(3)°] (Figure 2). The interplanar angles are comparable to those of the tBu‐substituted 1,2,4‐triphosphaferrocenes [Cp^RFe(η⁵‐P₃C₂ tBu₂)] (2.2° for Cp^R = Cp; 0.1° for Cp^R = Cp″′)7,5d and much smaller than that in the tilted [Cp*Fe(η⁵‐P₃C₂Mes₂)] derivative (12.2°).5a Thus, dissociation of the cyclopentadienyl19 or the phospholyl ligand8 is rather unlikely.

Figure 2.

Molecular structures of the phosphaferrocenes 2, 4, and 5. H atoms are omitted for clarity.

Table 3.

Crystallographic data for 2, 4, 5, 5′, 5″, and 2‐Br.

	2	4	5	5′	5″	2‐Br
Formula	C22H36FeP2	C24H42FeP4	C20H35FeP5	C20H35FeP5	C20H35FeP5	C24H39Br2Cu2FeNP2 ·0.75(CH3CN)
FW	418.30	510.31	486.18	486.18	486.18	777.04
Crystal system, space group	monoclinic, P21/c	triclinic, P	monoclinic, P21	monoclinic, P21/n	monoclinic, P21/n	monoclinic, C2/c
T [K]	123(2)	123(1)	123(1)	123(2)	126(3)	123(2)
a, b, c [Å]	9.1532(2), 33.9928(5), 14.0171(2)	11.8344(3), 13.0807(4), 14.2363(4)	9.6056(1), 16.9567(2), 14.3763(2)	9.5449(1), 15.9135(2), 15.1917(1)	13.6464(4), 12.1784(2), 28.7527(8)	25.4093(5), 19.3055(2), 15.7888(3)
α, β, γ [°]	90, 90.330(1), 90	67.789(3), 69.866(3), 77.591(2)	90, 92.825(1), 90	90, 94.664(1), 90	90, 90.183(2), 90	90, 126.781(3), 90
V [Å3]	4361.25(13)	1906.47(11)	2338.76(5)	2299.87(4)	4778.4(2)	6203.2(3)
Z	8	3	4	4	8	8
F(000)	1792	816	1024	1024	2048	3124
Radiation	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α
μ [mm–1]	6.93	7.19	8.42	8.56	8.25	9.39
Habit	orange plate	red‐brown block	green block	green plate	green rod	yellow plate
T min., T max.	0.226, 0.677	0.296, 0.430	0.412, 0.655	0.317, 0.732	0.282, 0.824	0.382, 0.706
R int	0.047	0.029	0.027	0.054	0.042	0.040
(sin λ/θ)max [Å–1]	0.624	0.595	0.595	0.624	0.596	0.597
R[F 2 > 2σ(F 2)], wR(F 2), S	0.037, 0.106, 1.04	0.030, 0.079, 0.90	0.036, 0.097, 1.11	0.026, 0.069, 0.99	0.029, 0.055, 0.80	0.029, 0.075, 1.05
No. of reflections	8422	6639	7064	4626	8317	5508
Δρ max., Δρ min. [e Å–3]	0.71, –0.47	0.44, –0.38	0.86, –0.33	0.49, –0.45	0.64, –0.31	0.97, –0.48

Within the coordinated di‐ and triphospholyl rings, all bond lengths lie between those of a single and a double bond and thus confirm the aromaticity of this ligand (Table 2; sums of covalent radii: C–C: 1.50 Å; C–P: 1.86 Å; P–P: 2.22 Å; C=C: 1.34 Å; C=P: 1.69 Å; P=P: 2.04 Å).20

Table 2.

Selected bond lengths [Å] within the phospholyl rings in 2, 4, 5, 5′, and 5″. Ranges of bond lengths are given if more than one bond is present in the asymmetric unit.

	Ligand	P–P	P–C	C–C
2	P2C3	–	1.761(2)–1.784(2)	1.424(2)–1.426(3)
4	P2C3	–	1.770(2)–1.789(2)	1.425(3)–1.430(3)
5	P2C3	–	1.759(5)–1.790(6)	1.438(7)–1.440(7)
	P3C2	2.121(2)–2.134(2)	1.746(5)–1.777(5)	–
5′	P2C3	–	1.763(1)–1.786(1)	1.419(2)
	P3C2	2.126(1)	1.759(2)–1.769(2)	–
5″	P2C3	–	1.756(3)–1.794(3)	1.441(4)–1.445(3)
	P3C2	2.119(1)–2.121(1)	1.761(3)–1.772(3)	–

Diphosphaferrocene 2 as Building Block

Although 1,3‐diposphaferrocenes have been known since 1990,10 they have not yet been used for the formation of supramolecular assemblies. However, the separate and therefore opposite positions of the phosphorus atoms in the ring are predestinated for the buildup of 1D coordination polymers. Hence, diffusion experiments of 2 with CuX (X = Br, I) were carried out and led to the crystallization of [{Cp*Fe(μ₃,η^5:1:1‐P₂C₃ iPr₃)}Cu₂(μ‐Br)₂(CH₃CN)]_n ·0.75n(CH₃CN) (2‐Br) and [{Cp*Fe(μ₃,η^5:1:1‐P₂C₃ iPr₃)}Cu₂(μ‐I)₂(CH₃CN)_0.5]_n ·0.5n(CH₃CN) (2‐I), respectively (Scheme 3).

Scheme 3.

1,3‐Diphosphaferrocene‐derived coordination polymers 2‐Br and 2‐I.

Compound 2‐Br crystallizes as orange platelets in the monoclinic space group C2/c, whereas 2‐I crystallizes in the orthorhombic space group P2₁2₁2₁ (for crystallographic data see Table 3 for 2‐Br and Table 4 for 2‐I). The X‐ray structural analyses revealed that, in both 2‐Br and 2‐I, 1D chains are formed from moieties of 2 linked by {Cu₂(μ‐X)₂} four‐membered rings (Figure 3, for bond lengths see Supporting Information).

Table 4.

Crystallographic data for 2‐I, 3‐Cl, 3‐Cl′, 3‐Br, 5‐Br, and 5‐I.

	2‐I	3‐Cl	3‐Cl′	3‐Br	5‐Br	5‐I
Formula	C24H39Cu2FeI2NP2	C18H29Cl2Cu2FeP3	C18H29Cl2Cu2FeP3	C18H29Br2Cu2FeP3 ·0.15(C7H8)	C20H35Br3Cu3FeP5 ·0.5(C7H8)	C20H35Cu2FeI2P5
FW	840.23	592.15	592.15	694.89	962.59	867.06
Crystal system, space group	orthorhombic, P212121	monoclinic, P21/c	orthorhombic, Pbca	monoclinic, P21/c	triclinic, P	monoclinic, P21/n
T [K]	123(1)	123(2)	123(2)	123(2)	123(2)	123(1)
a, b, c [Å]	11.1640(2), 14.2254(2), 37.2743(4)	8.4412(1), 16.8393(2), 17.2062(2)	16.6294(3), 16.8479(3), 16.9793(3)	8.6057(1), 16.8865(1), 17.7057(1)	9.5046(2), 10.6841(2), 16.5146(2)	8.9909(3), 31.8655(12), 48.0476(18)
α, β, γ [°]	90, 90, 90	90, 100.823(1), 90	90, 90, 90	90, 99.799(1), 90	76.978(1), 78.518(1), 85.863(1)	90, 93.688(3), 90
V [Å3]	5919.62(15)	2402.25(5)	4757.10(15)	2535.46(4)	1600.55(5)	13737.1(9)
Z	8	4	8	4	2	20
F(000)	3280	1200	2400	1374	946	8400
Radiation	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α	Cu‐K α
μ [mm–1]	23.04	10.77	10.21	11.95	12.61	26.43
Habit	yellow plate	red cube	red prism	purple prism	green prism	green‐brown plate
T min., T max.	0.055, 0.424	0.403, 0.562	0.189, 0.433	0.254, 0.433	0.212, 0.533	0.302, 0.669
R int	0.042	0.049	0.034	0.028	0.021	0.115
(sin λ/θ)max. [Å–1]	0.597	0.624	0.624	0.596	0.596	0.624
R[F 2 > 2σ(F 2)], wR(F 2), S	0.019, 0.047, 1.03	0.029, 0.074, 0.98	0.035, 0.088, 0.95	0.023, 0.054, 1.07	0.020, 0.049, 1.05	0.060, 0.148, 0.78
No. of reflections	10506	4828	4622	4485	5643	27095
Δρ max., Δρ min. [e Å–3]	0.87, –0.62	0.41, –0.73	0.74, –0.65	0.58, –0.39	0.68, –0.45	1.92, –1.79

Figure 3.

Section of the polymeric structures of 2‐Br and 2‐I. iPr groups and H atoms are omitted for clarity.

The bending of the strands is caused by the position of the phosphorus atoms within the P₂C₃ five‐membered ring and the tetrahedral coordination environment of some of the copper ions. The latter makes the difference between the iodine and the bromine derivative: At first, they differ in their numbers of acetonitrile ligands, coordination of which leads to expansion of the environment of the copper center from trigonal planar to tetrahedral. In 2‐Br, every second Cu atom is affected and thus all {Cu₂(μ‐Br)₂(CH₃CN)} rings are similar. On the contrary, the iodine analogue 2‐I contains fewer acetonitrile ligands, and only every fourth Cu atom is four‐coordinated.

Consequently, the {Cu₂(μ‐I)₂} and {Cu₂(μ‐I)₂(CH₃CN)} units are perpendicular to each other. This results in a different undulation of the chains. Furthermore, the phosphaferrocene units in 2‐Br are oriented upwards and downwards in alternation. In contrast, this change in direction occurs only after every second moiety of 2 in 2‐I (Figure 3). Unfortunately, an unambiguous reason for this different coordination mode of CH₃CN cannot be given, but it may be attributable to the “outlier position” of CuI in coordination chemistry.21 The coordination motif of {Cu₂(μ‐X)₂} rings is known and has already been observed for several assemblies,21 also with complexes of P_n ligands.3,22

Once crystallized, both compounds 2‐Br and 2‐I are insoluble in common solvents; therefore, characterization in solution could not be carried out. Only the slightly yellow‐orange mother liquor could be used for NMR spectroscopic and mass spectrometric investigations. In the negative‐ion ESI spectra only peaks assigned to copper halide fragments up to [Cu₅Br₆]^– for 2‐Br and [Cu₄I₅]^– for 2‐I were found. On the contrary, the positive‐ion ESI spectra showed peaks for ferrocene‐containing fragments with the largest at m/z = 1043.3 ([{Cp*Fe(P₂C₃ iPr₃)}₂Cu₂Br]⁺) for 2‐Br and at m/z = 712.0 ([{Cp*Fe(P₂C₃ iPr₃)}Cu₂I(CH₃CN)]⁺) for 2‐I. In the ³¹P{¹H} NMR spectra of the mother liquors of 2‐Br and 2‐I, small singlets for the P₂C₃ ligand at δ = 14.3 and 15.9 ppm were observed, respectively. Since no significant broadening of the signal due to coordination of the P atoms to Cu (nuclear spin I = 3/2) is recognizable, it can most likely be attributed to the free complex 2.

Triphosphaferrocene 3 as Building Block

To study the influence of the smaller iPr substituents in comparison to the Mes and tBu derivatives, also the 1,2,4‐triphosphaferrocene 3 was used for consecutive reactions. Layering experiments of 3 with CuX (X = Cl, Br) lead to the formation of the 2D polymeric compounds [{Cp*Fe(μ₄,η^5:1:1:1‐P₃C₂ iPr₂)}Cu₂(μ‐Cl)₂]_n (3‐Cl) and [{Cp*Fe(μ₄,η^5:1:1:1‐P₃C₂ iPr₂)}Cu₂(μ‐Br)₂]_n ·0.15n(C₇H₈) (3‐Br), respectively (Scheme 4).

Scheme 4.

1,2,4‐triphosphaferrocene‐derived coordination polymers 3‐Cl and 3‐Br.

Both products crystallize as isomorphous compounds in the monoclinic space group P2₁/c (crystallographic data: Table 4). In addition, compound 3‐Cl is polymorphous and also crystallizes in the orthorhombic space group Pbca (3‐Cl′).

The X‐ray structural analyses revealed 2D networks with a meshlike construction (Figure 4). Similar to 2‐X (X = Br, I), the phosphaferrocenes are linked by four‐membered {Cu₂(μ‐X)₂} rings (for bond lengths see Supporting Information). However, in 3‐Cl and 3‐Br the presence and coordination of three P atoms lead to extension of the polymer in two dimensions (Figure 4).

Figure 4.

Section of the polymeric structures of 3‐Cl and 3‐Br. a) Top view, Cp* and iPr ligands are omitted for clarity. b) Side view, H atoms are omitted for clarity.

Notably, all copper ions attached to the isolated P atom of the P₃C₂ ring show a trigonal‐planar environment, whereas any other Cu center is tetrahedrally coordinated. Again, adjacent phosphaferrocene units in 3‐Cl and 3‐Br are oriented upwards and downwards (Figure 4, b). The meshes therefore form layers separated by the Cp* ligands and, in the case of 3‐Br, provide enough space for a solvent molecule embedded between these layers.

Remarkably, 3‐Cl and 3‐Br are the first polymeric compounds containing triphosphaferrocenes and CuX (X = Cl, Br) despite many trials. Previous findings all demonstrate that fragmentation reactions of the phosphaferrocene occur7,8 or dimeric6a and oligomeric6b compounds are formed. Only the use of CuI yields a coordination polymer in combination with [Cp*Fe(η⁵‐P₃C₂ tBu₂)].6b A meaningful comparison can be drawn to pentaphosphaferrocene‐containing polymers bearing the cyclo‐P₅ unit in a 1,2,4‐coordination mode. This type is known for all halides in the 2D networks [{Cp*Fe(μ₄,η^5:1:1:1‐P₅)}(CuX)]_n (X = Cl, Br, I). In these networks, the structural motif differs and the P atoms are linked by simple {CuX} units as opposed to {Cu₂(μ‐X)₂} (X = Cl, Br) rings in 3‐Cl and 3‐Br.

Since the 1D polymers 2‐Br and 2‐I are already insoluble, it is not surprising that also the 2D networks 3‐Cl and 3‐Br cannot be dissolved in any common solvent. Nonetheless, the mother liquors are still slightly colored, and hence they were analyzed by ESI mass spectrometry and ³¹P{¹H} NMR spectroscopy. However, for 3‐Cl no signal in the respective NMR spectrum could be obtained, whereas in the ³¹P{¹H} NMR spectrum of the mother liquor of 3‐Br small signals of the P₃C₂ ligand at δ = 11.4 ppm (d, ² J _PP = 46 Hz, 2P) and δ = 22.7 ppm (t, ² J _PP = 46 Hz, 1P) were observed, again most probably belonging to the free complex 3. Similar to 2‐Br and 2‐I, in the negative‐ion ESI mass spectra [Cu_n–1X_n]^– units were detected with n ≤ 4 for X = Cl and n ≤ 6 for X = Br. The largest peaks in the positive‐ion ESI spectra at m/z = 1541.4 and 1573.5 are assigned to [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₄Cl₃]⁺ and [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₆Br₅]⁺, respectively (for smaller fragments see Exp. Section).

Pentaphosphaferrocene 5 as Building Block

Since no supramolecular assemblies containing pentaphosphaferrocenes of the type [(η⁵‐P₃C₂R₂)Fe(η⁵‐P₂C₃R₃)] are mentioned in the literature, also the reactivity of 5 towards Cu^I halides was investigated. Diffusion experiments of solutions of 5 in CH₂Cl₂ or toluene and CuX (X = Br, I) in CH₃CN led to the formation of green prisms of [{(μ₃,η^5:1:1‐P₃C₂ iPr₂)Fe(μ,η^5:1‐P₂C₃ iPr₃)}Cu₃(μ‐Br)(μ₃‐Br)(μ₄‐Br)]_n ·0.5n(C₇H₈) (5‐Br) and strongly intergrown plates of [{(μ,η^5:1‐P₃C₂ iPr₂)Fe(μ,η^5:1‐P₂C₃ iPr₃)}Cu₂(μ₃‐I)₂]_n (5‐I), respectively (Scheme 5).

Scheme 5.

1,1′,2,3′,4‐Pentaphosphaferrocene‐derived coordination polymers 5‐Br and 5‐I.

Due to the simpler structure, 5‐I is described first. It crystallizes in the monoclinic space group P2₁/n and shows a 1D linear polymer formed by a {CuI} double strand with the sandwich complex 5 acting as a 1,1′‐chelating ligand (Figure 5 right, for crystallographic details and bond lengths see Table 4 and Supporting Information). The regular structure of this ladder is formed by iodine atoms, all of which have a μ₃ coordination mode, and tetrahedrally coordinated Cu atoms.

Figure 5.

Section of the polymeric structures of 5‐Br (left) and 5‐I (right). iPr groups and solvent molecules are omitted for clarity.

The 1D polymer 5‐Br crystallizes as a solvate in the triclinic space group P and shows a similar ladderlike scaffold (Table 4). The moieties of 5 also act as chelating ligands, though the coordination via three P atoms (two from the tri‐ and one from the diphospholyl ligand) leads to a 1,2,1′ connectivity. As a consequence, the {CuBr} double strand is bent at the positions of the triphospholyl ligand and a stairlike arrangement results with the bromide ligands in a μ, μ₃, or even μ₄ mode.

Similar structural motifs are already known for the hexaphosphaferrocene‐containing polymers [{Fe(μ,η^5:1‐P₃C₂ tBu₂)₂}{Cu(μ₃‐X)}₂]_x (X = Cl, Br, I) and [{Fe(μ,η^5:1‐P₃C₂ tBu₂)(μ₃,η^5:1:1‐P₃C₂ tBu₂)}Cu₃(μ‐I)(μ₃‐I)₂(CH₃CN)]_x.23 In these compounds, the sterically demanding tBu groups lead to a sinusoidal distortion of the strands, which is not the case for 5‐Br and 5‐I.

The characterization of the polymers 5‐Br and 5‐I in solution was again limited to the mother liquor. This time, only in the ³¹P{¹H} NMR spectrum were signals corresponding to 5‐I observed, which can be assigned to the free complex 5. Yet, they are slightly shifted to high field (δ = 9.5 ppm (s, 2 P, P₂C₃), 30.8 ppm (d, ² J _PP = 43.2 Hz, 2 P, P₃C₂), 46.9 (t, ² J _PP = 43.6 Hz, 1 P, P₃C₂). In the negative‐ and positive‐ion ESI mass spectra of this solution, a variety of different fragments were detected (for details, see Exp. Section). Among them, the largest peak appears at m/z = 1078.3 for [Cu₅I₆]^– and 1796.9 for [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}₂Cu₅I₄]⁺, respectively.

Conclusions

The di‐ and triphospholyl salts 1a/b bearing rather small iPr groups were synthesized starting from the phosphaalkene. By subsequent reaction with FeBr₂ and LiCp* a series of mainly novel phosphaferrocenes 2–6 containing two, three, four, five or six phosphorus atoms could be synthesized and isolated.

Since no supramolecular assemblies were known for a 1,3‐diphospha‐ or 1,1′,2,3′,4‐pentaphosphaferrocene, their coordination behavior towards Cu^I halides was studied. Both building blocks form 1D polymers, yet with different structures. Whereas with 2 as a ditopic linker infinite chains (2‐Br, 2‐I) are obtained, the self‐assembly of 5 with CuX (X = Br, I) leads to ladderlike structural motifs (5‐Br, 5‐I) in which 5 acts as a chelating ligand. The obtained products are the first coordination polymers containing 1,3‐di‐ and 1,1′,2,3′,4‐pentaphosphaferrocenes, respectively.

Furthermore, previous results have shown that 1,2,4‐triphosphaferrocenes tend to form di‐ and oligomeric products with intact sandwich complexes or polymeric products, albeit with fragmented and/or rearranged moieties of the building block. On the contrary, by using the iPr‐substituted compound 3, isolation of 2D networks 3‐Cl and 3‐Br is possible. Hence, the additional phosphorus atom in combination with small iPr substituents enables the phosphaferrocene 3 to act as tridentate planar linking unit that is predestined for the formation of 2D sheets. Both compounds contain intact units of 3 and therefore are the second and third representative of a triphosphaferrocene‐based polymer. Furthermore, they show an unprecedented meshlike structure.

Experimental Section

General: All reactions were performed under an inert atmosphere of dry nitrogen or argon with standard vacuum, Schlenk, and glove‐box techniques. Solvents were purified, dried, and degassed prior to use by standard procedures. Me₃SiO(iPr)C=P(SiMe₃),16 K[P(SiMe₃)₂],17 and FeBr₂(dme)24 were synthesized according to the reported procedures. Commercially available chemicals were used without further purification. Solution NMR spectra were recorded with a Bruker Avance 300 or 400 spectrometer. The ESI‐MS spectra were recorded with a ThermoQuest Finnigan MAT TSQ 7000 mass spectrometer, and EI‐MS spectra were measured with a Finnigan MAT 95 mass spectrometer. Elemental analyses were performed with a Vario EL III apparatus.

Synthesis of 1a/b: A suspension of K[P(SiMe₃)₂] (2.40 g, 0.11 mol) in a mixture of toluene (20 mL) and Et₂O (10 mL) was added to a solution of the phosphaalkene Me₃SiO(iPr)C=P(SiMe₃) (5.5 g, 0.022 mol) in toluene (10 mL). An immediate color change from yellow to orange‐red was observed. The reaction mixture was heated to 75 °C for 3 d. After cooling to room temp. the off‐white powder was collected by filtration, washed with toluene (2 × 10 mL), and dried in vacuo to give 1a and 1b as a 1:1 mixture (1.35 g, 5.32 mmol, 48 %). Analytical data of 1a: ¹H NMR ([D₈]thf): δ = 1.33 (d, ³ J _HH = 6.8 Hz, 12 H, CH₃‐adjacent), 1.37 (d, ³ J _HH = 6.8 Hz, 6 H, CH₃‐isolated), 3.28 (m, 2 H, CH‐adjacent), 3.44 (m, 1 H, CH‐isolated) ppm. ³¹P{¹H} NMR ([D₈]thf): δ = 161.44 (s, 2 P) ppm. Analytical data of 1b: ¹H NMR ([D₈]thf): δ = 1.43 (d, ³ J _HH = 6.8 Hz, 12 H, CH₃), 3.79 (m, 2 H, CH) ppm. ³¹P{¹H} NMR ([D₈]thf): δ = 247.60 (dd, ² J _PP = 51.6, 45.1 Hz, 1 P, P_isolated), 244.72 (pseudo‐d, ² J _PP = 49.0 Hz, 2 P, P_adjacent) ppm.

Synthesis of Phosphaferrocenes 2–6: FeBr₂(dme) (2.0 g, 6.5 mmol) and a mixture of 1a and 1b (1:1, 1.7 g, 6.5 mmol) were dissolved in thf (200 mL) at –40 °C. An immediate color change from yellow‐orange to dark red occurred. A suspension of LiCp* (930 mg, 6.5 mmol) in thf (50 mL) was added subsequently. The reaction mixture was warmed to room temp. and the solvent removed under reduced pressure. Afterwards, the residue was dissolved in toluene, the solution filtered through Celite, and the solvent again removed. The solid was adsorbed on silica and loaded onto a column filled with silica (50 cm × 3 cm). By using hexane as eluent, a yellow band of [Cp*₂Fe] could be eluted, followed by a green fraction containing the hexaphosphaferrocene 6, the pentaphosphaferrocene 5, and the tetraphosphaferrocene 4 (70 mg, ca. 3 %, calculated by means of the average molar weight). By switching to a hexane/toluene mixture (10:1) a red band of the triphosphaferrocene 3 and the diphosphaferrocene 2 (440 mg, ca. 17 %, calculated by means of the average molar weight) could be eluted. To separate 2 and 3 or 4, 5, and 6, the solvent of the respective fraction must be removed and a further chromatographic workup is needed (50 cm × 3 cm). Unfortunately, the products cannot be eluted as separate bands with hexane as eluent; therefore, several fractions must be collected. The first fraction gives pure 2, the last pure 3, and the intermediate ones give mixtures with different molar ratios (for an NMR spectrum, see the Supporting Information). Furthermore, elemental analysis could not be carried out, since the phosphaferrocenes are oily solids at room temp. and crystals obtained at lower temperature start melting when warmed to room temp. Therefore, standard solutions were prepared for following reactions.

Analytical Data of 2/3: Yield: 440 mg (17 %): integral ratios from ³¹P{¹H} NMR (C₆D₆): 50 % 2, 50 % 3. Analytical data of 2: ¹H NMR (C₆D₆): δ = 1.16 (d, ³ J _HH = 6.1 Hz, 6 H, iPr‐CH₃), 1.24 (d, ³ J _HH = 6.2 Hz, 6 H, iPr‐CH₃), 1.60 (d, ³ J _HH = 6.2 Hz, 6 H, iPr‐CH₃), 1.70 (s, 15 H, Cp*‐CH₃), 2.26 (br. m, 1 H, iPr‐CH), 2.38 (br. m, 2 H, iPr‐CH) ppm. ³¹P{¹H} NMR (C₆D₆): δ = –2.84 (s, P₂C₃) ppm. FD‐MS (toluene): 418.2 (M⁺). Analytical data of 3: ¹H NMR (C₆D₆): δ = 1.32 (d, ³ J _HH = 6.6 Hz, 6 H, iPr‐CH₃), 1.43 (d, ³ J _HH = 6.5 Hz, 6 H, iPr‐CH₃), 1.62 (s, 15 H, Cp*‐CH₃), 2.72 (br. m, 2 H, iPr‐CH) ppm. ³¹P{¹H} NMR (C₆D₆): δ = 29.69 (t, ² J _PP = 43.8 Hz, 1 P, P_isolated), 49.63 (d, ² J _PP = 43.8 Hz, 2 P, P_adjacent) ppm. FD‐MS (toluene): 394.3 (M⁺). Analytical data of 4/5/6: Yield: 70 mg: integral ratios from ³¹P{¹H} NMR (C₆D₆): 57 % 5, 39 % 6 and 4 % 4. Analytical data of 4: ³¹P{¹H} NMR (C₆D₆): δ = 6.7 (br. s, 4 P) ppm. FD‐MS (hexane): 510.2 (M⁺). Analytical data of of 5: ¹H NMR (C₆D₆): δ = 1.04 (d, ³ J _HH = 6.7 Hz, 6 H, iPr‐CH₃), 1.23 (d, ³ J _HH = 6.7 Hz, 6 H, iPr‐CH₃), 1.45 (d, ³ J _HH = 6.7 Hz, 6 H, iPr‐CH₃), 1.54 (d, ³ J _HH = 6.7 Hz, 6 H, iPr‐CH₃), 1.72 (d, ³ J _HH = 6.7 Hz, 6 H, iPr‐CH₃), 2.46 (br. m, 2 H, iPr‐CH), 2.59 (br. m, 1 H, iPr‐CH), 3.12 (br. m, 2 H, iPr‐CH) ppm. ³¹P{¹H} NMR (C₆D₆): δ = 15.00 (s, 2 P, P₂C₃), 46.90 (t, ² J _PP = 42.0 Hz, 1 P, P_isolated), 53.68 (d, ² J _PP = 42.0 Hz, 2 P, P_adjacent) ppm. FD‐MS (hexane): 486.1 (M⁺). Analytical data of 6: ¹H NMR (C₆D₆): δ = 1.29 (d, ³ J _HH = 6.7 Hz, 12 H, iPr‐CH₃), 1.36 (d, ³ J _HH = 6.7 Hz, 12 H, iPr‐CH₃), 2.91 (br. m, 4 H, iPr‐CH) ppm. ³¹P{¹H} NMR (C₆D₆): δ = 51.3 (br. m, 2 P, P_adjacent), 68.7 (br. m, 1 P, P_isolated) ppm. ³¹P{¹H} NMR (CD₂Cl₂, 193K): δ = 46.22 (d, ² J _PP = 34 Hz, 2 P, P_adjacent), 69.28 (t, ² J _PP = 38 Hz, 1 P, P_isolated) ppm. FD‐MS (hexane): 462.0 (M⁺).

Synthesis of 2‐Br: A solution of CuBr (24 mg, 0.16 mmol) in acetonitrile (1 mL) was layered on a solution of 2 (35 mg, 0.08 mmol) in toluene (0.5 mL) in a narrow Schlenk tube. After diffusion, small orange platelets of 2‐Br had formed. The mother liquor was decanted and the crystals were washed with CH₂Cl₂ and then dried under vacuum (5 mg, 6.7 μmol, 8 %). Analytical data of 2‐Br: ³¹P{¹H} NMR (C₆D₆ capillary, mother liquor): δ = 14.26 (s, P₂C₃) ppm. Positive‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 1043.3 [{Cp*Fe(P₂C₃ iPr₃)}₂Cu₂Br]⁺, 899.3 [{Cp*Fe(P₂C₃ iPr₃)}₂Cu]⁺, 326.1 (100) [Cp*₂Fe]⁺. Negative‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 798.3 [Cu₅Br₆]^–, 652.4 [Cu₄Br₅]^–, 510.4 [Cu₃Br₄]^–, 366.5 (100) [Cu₂Br₃]^–, 222.7 [CuBr₂]^–. [{Cp*Fe(η⁵‐P₂C₃ iPr₃)}Cu₂Br₂(CH₃CN)_1.5] (766.8 g/mol): calcd. C 39.16, H 5.32, N 2.74; found C 39.38, H 5.43, N 2.59.

Synthesis of 2‐I: A solution of CuI (32 mg, 0.17 mmol) in acetonitrile (6 mL) was layered on a solution of 2 (35 mg, 0.08 mmol) in toluene (3 mL) in a narrow Schlenk tube. After diffusion, small orange platelets of 2‐I had formed. The mother liquor was decanted and the crystals were washed with CH₂Cl₂ and then dried under vacuum (7 mg, 8.8 μmol, 10 %). Analytical data of 2‐I: ³¹P{¹H} NMR (C₆D₆ capillary, mother liquor): δ = 15.95 (s, P₂C₃) ppm. Positive‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 712.0 [{Cp*Fe(P₂C₃ iPr₃)}Cu₂I(CH₃CN)]⁺, 522.1 [{Cp*Fe(P₂C₃ iPr₃)}Cu(CH₃CN)]⁺, 326.1 (100) [Cp*₂Fe]⁺. Negative‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 888.4 [Cu₄I₅]^–, 698.5 [Cu₃I₄]^–, 506.6 [Cu₂I₃]^–, 316.6 (100) [CuI₂]^–. [{Cp*Fe(η⁵‐P₂C₃ iPr₃)}Cu₂I₂] (799.2 g/mol): calcd. C 33.06, H 4.54; found C 33.76, H 4.63.

Synthesis of 3‐Cl: A colorless solution of CuCl (30 mg, 0.30 mmol) in acetonitrile (3 mL) was layered on a red solution of 3 (36 mg, 0.09 mmol) in toluene (2 mL) in a narrow Schlenk tube. Thereby, the phase boundary turned orange and overnight small orange crystals of 3‐Cl formed. After complete diffusion, the mother liquor was decanted and the crystals were washed with hexane/toluene (3:1, 3 × 3 mL) and then dried under vacuum (17 mg, 0.03 mmol, 33 %). Analytical data of 3‐Cl: ³¹P{¹H} NMR (C₆D₆ capillary, mother liquor): no signal detectable. Positive‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z = 1541.4 [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₄Cl₃]⁺, 1441.4 [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₃Cl₂]⁺, 1384.4 [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₂Cl(CH₃CN)]⁺, 1341.7 [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₂Cl]⁺, 1541.4 [{Cp*Fe(P₃C₂ iPr₂)}₃Cu₄Cl₃]⁺. Negative‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 332.5 (5) [Cu₃Cl₄]^–, 232.7 (100) [Cu₂Cl₃]^–, 134.7 (20) [CuCl₂]^–. [{Cp*Fe(η⁵‐P₃C₂ iPr₂)}Cu₂Cl₂] (592.2 g/mol): calcd. C 36.51, H 4.94; found C 37.51, H 5.03.

Synthesis of 3‐Br: A colorless solution of CuBr (40 mg, 0.28 mmol) in acetonitrile (3 mL) was layered on a red solution of 3 (36 mg, 0.09 mmol) in toluene (2 mL) in a narrow Schlenk tube. Thereby, the phase boundary turned orange and overnight a colorless precipitate formed. Within a week, small orange crystals of 3‐Br had formed. The mother liquor was decanted and the crystals were washed with hexane/toluene (3:1, 3 × 3 mL) and CH₃CN to remove precipitated CuBr and then dried under vacuum (27 mg, 0.04 mmol, 44 %). Analytical data of 3‐Br: ³¹P{¹H} NMR (C₆D₆ capillary, mother liquor): δ = 11.38 (d, ² J _PP = 46 Hz, 2 P, P_adjacent), 22.71 (t, ² J _PP = 46 Hz, 1 P, P_isolated) ppm. Positive‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z = 1573.5 [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₆Br₅]⁺, 1507.6 [{Cp*Fe(P₃C₂ iPr₂)}Cu₈Br₇(CH₃CN)]⁺, 1431.4 [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₅Br₄]⁺, 1356.6 [{Cp*Fe(P₃C₂ iPr₂)}Cu₇Br₆(CH₃CN)]⁺, 1283.4 [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₄Br₃]⁺, 1209.6 [{Cp*Fe(P₃C₂ iPr₂)}Cu₆Br₅(CH₃CN)]⁺, 1135.5 [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₃Br₂]⁺, 985.3 [{Cp*Fe(P₃C₂ iPr₂)}₂Cu₂Br]⁺. Negative‐ion ESI‐MS (mother liquor, toluene/CH₃CN): m/z (%) = 798.1 (3) [Cu₅Br₆]^–, 654.2 (3) [Cu₄Br₅]^–, 510.4 (18) [Cu₃Br₄]^–, 366.3 (100) [Cu₂Br₃]^–, 222.5 (42) [CuBr₂]^–. [{Cp*Fe(η⁵‐P₃C₂ iPr₂)}Cu₂Br₂(CH₃CN)_0.1(C₇H₈)_0.1] (694.4 g/mol): calcd. C 32.69, H 4.37, N 0.20; found C 32.84, H 4.29, N 0.3.

Synthesis of 5‐Br: A colorless solution of CuBr (34 mg, 0.24 mmol) in acetonitrile (3 mL) was layered on a green solution of 5 (23 mg, 0.05 mmol) in CH₂Cl₂ (3 mL) in a narrow Schlenk tube. Thereby, no significant color change at the phase boundary could be observed. After diffusion, the reaction mixture was again layered with toluene. Within a few days, green prisms of 5‐Br formed. The mother liquor was decanted and the crystals were washed with hexane (3 × 3 mL) and dried in vacuo (24 mg, 0.025 mmol, 50 %). Analytical data of 5‐Br: ³¹P{¹H} NMR (mother liquor, C₆D₆ capillary): no signal detectable. Negative‐ion ESI‐MS (mother liquor, CH₂Cl₂/CH₃CN): m/z (%) = 510.4 (15) [Cu₃Br₄]^–, 366.4 (100) [Cu₂Br₃]^–, 222.5 (37) [CuBr₂]^–. [{(η⁵‐P₃C₂ iPr₂)Fe(η⁵‐P₂C₃ iPr₃)}Cu₃Br₃(C₇H₈)_0.5] (962.7 g/mol): calcd. C 29.32, H 4.08; found C 29.46, H 4.11.

Synthesis of 5‐I: A colorless solution of CuI (45 mg, 0.24 mmol) in acetonitrile (3 mL) was layered on a green solution of 5 (23 mg, 0.05 mmol) in CH₂Cl₂ (3 mL) in a very narrow Schlenk tube. Thereby, no significant color change at the phase boundary could be observed. Within two weeks, green‐brown intergrown plates of 5‐I formed. The mother liquor was decanted and the crystals were washed with hexane (3 × 3 mL) and dried in vacuo (16 mg, 0.018 mmol, 37 %). Analytical data of 5‐I: ³¹P{¹H} NMR (mother liquor, C₆D₆ capillary): δ = 9.45 (s, 2 P, P₂C₃), 30.75 (d, ² J _PP = 43.2 Hz, 2 P, P_adjacent), 46.88 (t, ² J _PP = 43.6 Hz, 1 P, P_isolated) ppm. Positive‐ion ESI‐MS (mother liquor, CH₂Cl₂/CH₃CN): m/z (%) = 1796.9 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}₂Cu₅I₄]⁺, 1690.2 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₇I₆]⁺, 1628.8 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₆I₅(CH₃CN)(CH₂Cl₂)]⁺, 1587.9 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₆I₅(CH₂Cl₂)]⁺, 1606.9 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}₂Cu₄I₃]⁺, 1543.9 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₆I₅(CH₃CN)]⁺, 1500.6 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₆I₅]⁺, 1437.2 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₅I₄(CH₃CN)₃]⁺, 1417.1 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}₂Cu₃I₂]⁺, 1395.9 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₅I₄(CH₃CN)₂]⁺, 1288.2 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₄I₃(CH₂Cl₂)₂]⁺, 1247.1 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₄I₃(CH₃CN)(CH₂Cl₂)]⁺, 1227.1 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}₂Cu₂I₁]⁺, 1206.1 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₄I₃(CH₂Cl₂)]⁺, 1120.6 [{(P₂C₃ iPr₂)Fe(P₃C₂ iPr₂)}Cu₄I₃]⁺. Negative ion ESI‐MS (mother liquor, CH₂Cl₂/CH₃CN): m/z (%) = 1078.3 (8) [Cu₅I₆]^–, 888.4 (14) [Cu₄I₅]^–, 698.4 (47) [Cu₃I₄]^–, 506.5 (78) [Cu₂I₃]^–, 316.6 (100) [CuI₂]^–. [{(η⁵‐P₃C₂ iPr₂)Fe(η⁵‐P₂C₃ iPr₃)}Cu₂I₂] (867.1 g/mol): calcd. C 27.70, H 4.07; found C 27.78, H 4.02.

Supporting Information (see footnote on the first page of this article): Supporting information for this article (details on the diffraction experiments including tables of bond lengths) is given via a link at the end of the document.

CCDC‐1415107 (for 2), ‐CCDC‐1415108 (for 4), ‐CCDC‐1415109 (for 5), ‐CCDC‐1415110 (for 5′), ‐CCDC‐1415111 (for 5″), ‐CCDC‐1415112 (for 2‐Br), ‐CCDC‐1415113 (for 2‐I), ‐CCDC‐1415115 (for 3‐Cl), ‐CCDC‐1415114 (for 3‐Cl′), ‐CCDC‐1415116 (for 3‐Br), ‐CCDC‐1415117 (for 5‐Br) and ‐CCDC‐1415118 (for 5‐I) contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.

Supporting information

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