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Phosphenium Versus Pro-Phosphide Character of P-tert-butyldicyclopropeniophosphine: Zwitterionic Palladate Complexes of a Dicationic Phosphido Ligand Cleve Dionel Mboyi, Carine Maaliki, Amelle Mankou Makaya, Yves Canac, Carine Duhayon, and Remi Chauvin* †

Laboratoire de Chimie de Coordination (LCC), CNRS, 205, route de Narbonne, F-31077 Toulouse, France Universite Toulouse III Paul Sabatier (UPS), Institut National Polytechnique (INP), Laboratoire de Chimie de Coordination (LCC), Université de Toulouse, F-31077 Toulouse, France

‡

S Supporting Information *

ABSTRACT: With the view to enhancing the unique coordinating ability of the known phenyl-tetrakis(diisopropylamino)dicyclopropeniophosphine (Ph-DCP), replacement of the phenyl substituent by a tert-butyl substituent was envisaged. Both αdicationic R-DCP phosphines, with R = Ph and tBu, were prepared in 54%−55% yield by substitution of RPCl2 with two equivalents of bis(diisopropylamino)-dicyclopropenylidene (BAC) and metathesis with NaBF4. This method is implicitly consistent with the representation of R-DCPs as BAC-phosphenium adducts. The R-DCP salts were found to coordinate hard and soft Lewis acids such as a promoted oxygen atom (in the singlet spin state) in the corresponding R-DCP oxides, and electron-rich transition-metal centers in η1-R-DCP complexes with AuCl, PtCl3−, or PdCl3−, respectively. Coordination of PhDCP with PdCl2, which is a more electron-deficient Pd(II) center, leads to pentachlorinated dinuclear complexes [(PhDCP)PdCl2]2Cl−, where the dicoordinate Cl− bridge screens the repelling pairs of positive charges from each other. The same behavior is inferred for the tBu-DCP ligand, from which addition of an excess of (MeCN)2PdCl2 was found to trigger a heterolytic cleavage of the DCP−tBu bond, releasing tBu+ and a dicationic phosphide, DCP−: the latter is evidenced as a ligand in a tetranuclear complex ion [(μ2-DCP−)Pd2Cl4]2, which, upon HCl treatment, dissociates to a doubly zwitterionic dipalladate complex. All the complexes were isolated in 82%−97% yield, and five of them were characterized by X-ray crystallography.

1. INTRODUCTION A long-standing concern in organometallic catalysis has been the development of electron-rich Lewis bases with the view to improving the stability of ligand−metal bonds by increasing the σ-donation effect, in particular by going from phosphane to Nheterocyclic carbene (NHC) ligands.1 For specific purposes, more recent efforts have been devoted to the design of electron-poor phosphane ligands giving a tradeoff between a required high Lewis acidity of the metal center and the stability of the ligand−metal bond (e.g., by playing on back-π-donation effect, as with phosphite ligands).2 Within this prospect, the P(III) atom is generally made electron-deficient by bonding to neutral electronegative substituents, such as alkoxy,2c,e fluoroaryl,2a,b or imidazolyl groups.2d,f,g As α-cationic groups are among the most electronegative substituents, one more step has been taken with the study of α-cationic phosphanes.3 The blooming interest in α-cationic phosphines,3a or carbeniophosphines,3c is also fundamentally justified by the fact that they possess both intrinsic and extrinsic versatile coordination © XXXX American Chemical Society

chemistry features: they exhibit themselves a carbene− phosphenium character (Scheme 1),4 and, despite their electron deficiency, preserve a donor ability toward Lewis acids (LAs), ranging from a hard oxygen atom promoted in the singlet spin state to soft transition-metal centers, the successive coordination bonds defining a ternary C → P → LA coordination mode.3c The stabilization of the α-cationic phosphines currently used in coordination chemistry and catalysis is achieved by resonance of the formal positive charge from a P-αcarbenium center to two β- or γ-iminium ends. While the former case corresponds to generic amidiniophosphines or diaminocarbene−phosphenium adducts (mainly represented by imidazoliophosphines or NHC-phosphenium adducts), the latter is represented by bisaminocyclopropeniophosphines or bisaminocyclopropylidene (BAC 1)-phosphenium adducts (see Scheme 2). Since NHCs are weaker σ-donating carbenes than Received: July 1, 2016

A

DOI: 10.1021/acs.inorgchem.6b01524 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

Scheme 1. Resonance Forms of Carbene−Phosphenium Adducts (Top), Examples of Known Diimidazoliophosphines (DIMIOP Type A, Bottom Left), and Sole Known Example (2a) of Dicyclopropenio-phosphine (DICYPIOP Type B, Bottom Right)

Scheme 2. Preparation of the R-DCP Salts 2a (R = Ph) and 2b (R = tBu) from the Carbene 1 as the Source of the Cyclopropenylium Substituents, and PhPCl2 as the Source of the PPh Unit

report, 9a was phenyl-tetrakis(diisopropylamino)dicyclopropeniophosphine (Ph-DCP) 2a, as reported by Alcarazo et al. (Scheme 1):9b despite its electron deficiency, the P atom of 2a was found to retain donor ability toward electron-rich metal centers such as PtCl3− and AuCl. The 2a−AuCl complex was also shown to exhibit unprecedented π-acidic catalytic properties for the cyclo-isomerization of 2-ethynyl-1,1′-biaryls to sterically congested phenanthrenes. Likely because of the toohigh 2+/2+ electrostatic repulsion, two equivalents of 2a could not be coordinated at the same RhCl(CO) center. Nevertheless, the intrinsic coordinating properties of 2a can be correlated to its oxidation potential found of the same order of magnitude as that of a monocationic fluorinated pyridiniophosphine LF forming a stable complex [RhCl(CO)LF2][BF4]2.10 However, no coordinating properties could be evidenced for the tri-α-cationic hexakis(diisopropylamino)tricyclopropenylio-phosphine, where the phenyl group of 2a is replaced by a third cyclopropenylium susbtituent.11 As the phenyl P-substituent of 2a can be regarded as “neutral”, not only from the viewpoint of its formal charge, but also from the viewpoint of its σ,π-donating/withdrawing effects, the study of R-DCP ligands with noninnocent P-substituents R deserves natural attention. Considering the extreme inductive and hyper-conjugative electron-donating effects of the tert-butyl group as a potential balance to the converse electronwithdrawing effect of the cyclopropenio susbtitutents, the

BACs, the same trend applies to the global P-donating ability of the corresponding phosphenium adducts: while imidazoliophosphines are equivalent to trialkylphosphites,5 bisaminocyclopropeniophosphines are equivalent to triarylphosphines.6 In the absence of coordinating carbene, true phosphenium cationsalbeit in stabilized diaminophosphenium versions can also coordinate transition-metal centers.7 Similarly, an imidazolo-imidazolio-phenylphosphine and an imidazoliophosphonite, combining the electron-withdrawing effects of one α-carbenio and one imidazolo or two alkoxy substituents, were reported to preserve competitive Pcoordinating ability toward a Rh(I) center.4b One step beyond on the way to the P-coordinating limit of electron-deficient phosphanes consists of the P-substitution by a second αcarbenium moiety, giving rise to α-dicationic phosphines or dicarbeniophosphanes.4b,e If the carbenium is of the imidazolylium type, the diimidazoliophosphine family A (Scheme 1),8 can be divided between the P-acyclic representatives (ADIMIOPs = acyclic diimidazoliophosphines),8a,e,f and the P-cyclic ones, (BODIMIOPs = benzodiimidaziophosphines).8b−d However, their coordination chemistry is mainly limited to the hard promoted O atom (late transition metals at low oxidation degree possess a too-soft HSAB character to coordinate such very hard dicationic species).8c If the carbenium is of the cyclopropenylium type, the sole known representative of the dicyclopropeniophosphine family B (DICYPIOP, or R-DCP), until the ultimate revision of this B


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Inorganic Chemistry

Figure 1. ORTEP views of the X-ray crystal structures of the R-DCP salts 2a (R = Ph, left)9 and 2b (R = tBu, right), with thermal ellipsoids drawn at the 30% probability level (for the sake of clarity, the H atoms and the tetrafluoroborate anions are omitted). Selected bond distances for 2a: C1−P1, 1.808(3) Å; C16−P1, 1.804(3) Å; and C31−P1, 1.819(3) Å. Selected bond distances for 2b: C1−P1, 1.8099(19) Å; C16−P1, 1.8152(19) Å; and C31−P1, 1.8765(18) Å. Selected bond angles for 2a: C1−P1−C31, 102.14(13)°; C1−P1−C16, 98.46(13)°; and C16−P1−C31, 101.20(14)°. Selected bond angles for 2b: C1−P1−C31, 100.75(8)°; C1−P1−C16, 99.37(8)°; and C16−P1−C31, 107.07(8)°.

Scheme 3. Oxidation of the R-DCP Dications of 2a (R = Ph) and 2b (R = tBu)

challenge is addressed below for the R-DCP 2b (R = tBu), by comparison to 2a (R = Ph).

pyramidalization of the P atom (301.8° for 2a, 307.2° for 2b) reveals the availability of a lone pair for possible coordination. In the DIMIOP series (type A, Scheme 1), the neutral Psubstituent R was shown to have a critical influence on the Pcoordinating and P-oxidative ability: for example, whereas no oxidation could be evidenced for the phenyl substituent (R = Ph), rapid P-oxidation was observed for strongly electrondonating substituents such as R = tBu and NiPr2.8b−d Therefore, similar investigations were undertaken in the R-DCP series, with the selected representatives 2a and 2b. Oxidation of the R-DCP salts (i.e., formal coordination of RDCPs to a promoted oxygen atom) was first envisaged. Treatment of 2a and 2b with m-CPBA in CH2Cl2 readily gave the corresponding phosphine oxides 5a and 5b in 92% yield (see Scheme 3). According to the general trend, the λ5−31P nuclei of the oxides (δP = −3.6 ppm for 5a, +20.7 ppm for 5b) are significantly deshielded (here, by ca. 40 ppm), with respect to the λ3−31P nuclei of the parent phosphines (δP = −48.6 ppm for 2a, δP = −16.5 ppm for 2b).14 The structure of the dicationic oxide salt 5b was determined by XRD analysis of white crystals deposited from a CH2Cl2/Et2O solvent mixture (see Figure 2).13 The P−O bond distance in the tBu-DCP oxide dication of 5b (1.478(6) Å) was found to be comparable to that occurring in the related dicationic tBu-BODIMIOP oxide (1.4768(15) Å; see Scheme 1).8c In contrast, many attempts to oxidize Ph-BODIMIOP failed,8c and the rapid Poxidation of 2a can be interpreted by invoking the stronger donor ability of BAC-type carbenes vs NHC-types carbenes toward the putative dicationic phosphenium oxide in the form of 6 (see Scheme 3).12,17

2. RESULTS AND DISCUSSION Both of the R-DCPs (2a and 2b) were prepared by a method alternative to the one previously employed for 2a (see Scheme 1).9b The BAC carbene 1 was thus first generated by deprotonation of the corresponding cyclopropenium salt with potassium(trimethylsilyl)amide,12 then reacted with 0.5 equiv of phenyl- or tert-butyl-dichlorophosphine. After metathesis of the chloride anions with tetrafluoroborate anions, the R-DCP salts 2a (R = Ph) and 2b (R = tBu) were isolated in 55% and 54% yield, respectively (Scheme 2). The identity of 2a was confirmed by classical analytical data (NMR, MS) fitting with those previously reported for the same complex prepared in 52% yield over two steps using PhPH2 as the PPh source.9b The 31 P NMR resonance of 2b occurs at lower field than that of 2a (δP = −16.5 ppm vs δP = −48.6 ppm).9b The “carbene method” , using PhPCl2 as the PPh source, produces the salts 2a and 2b, along with side products, as evidenced by deshielded singlet signals at δP = +97.9 ppm and +84.1 ppm. By comparison with previous reports in the DIMIOP series A (Scheme 1),8 these products could be assigned to the P-chloro(cyclopropenio)phosphine salts 3a and 3b, occurring as intermediates to 2a and 2b, respectively. Despite a possible simple associative electrostatic relaxation, with respect to the dicationic salts 2, the monocationic chloro-ylide salts 4 were not evidenced (the aromaticity of the cyclopropenium rings contributing to the stabilization of the dicationic form 2). The structure of the RDCP salts 2a and 2b was confirmed by X-ray diffraction (XRD) analysis of single crystals (Figure 1).13 In both cases, the C


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Inorganic Chemistry Scheme 4. Coordination of the tBu-DCP Salt 2b with Neutral or Anionic Electron-Rich Metal Centers

Figure 2. ORTEP views of the X-ray crystal structure of the phosphine oxide salt 5b (left,), and the Au(I) complex 7 (right, thermal ellipsoids drawn at the 30% probability level). For the sake of clarity, the H atoms and the tetrafluoroborate anions are omitted. Selected bond distances for 5b: C1− P1, 1.827(7) Å; C16−P1, 1.823(8) Å; C20−P1, 1.800(7) Å; and P1−O1, 1.478(6) Å. Selected bond distances for 7: C1−P1, 1.814(7); C16−P1, 1.786(9) Å; C31−P1, 1.840(9) Å; P1−Au1, 2.208(3); and Au1−Cl1, 2.261(3) Å. Selected bond angles for 5b: C1−P1−C20, 100.2(3)°; C1−P1− C16, 111.1(3)°; and C16−P1−C20, 108.1(3)°. Selected bond angles for 7: C1−P1−C31, 107.5(4)°; C1−P1−C16, 99.9(4)°; C16−P1−C31, 112.3(4)°; and P1−Au1−Cl1, 176.69(7)°.

Scheme 5. One-to-One Coordination Chemistry of the R-DCP Salts 2a and 2b with a PdCl2 Center

(2a)PtCl3−,9b was established by MS analysis (ESI+: m/z = 769.3): in both cases, the metalate negative charge is stabilized by the two vicinal cyclopropenium positive charges. Coordination of the Ph-DCP salt 2a was further investigated with the more electron-deficient Pd(II) center, PdCl2 (see Scheme 5). Upon treatment with a single equivalent of [PdCl2(MeCN)2], the 31P NMR spectrum of the reaction mixture displayed a new singlet signal at δP = −3.4 ppm, along with the signal of remaining free phosphine 2a (δP = −48.6 ppm). In order to achieve complete disappearance of the δP resonance of 2a, the use of 1.5 equiv of [PdCl2(MeCN)2] was required. MS analysis of the pure product 9a (ESI+: m/z: 843.3) was compatible a priori with a classical μ-Cl-bridged dimeric structure [(2a)PdCl2]2 (denoted as 9a′ in Scheme 5). However, XRD analysis of single crystals deposited at −20 °C from a CH2Cl2/EtO solvent mixture showed that the structure is indeed dinuclear, but not dimeric (i.e., not made of identical monomeric units only; see Figure 3):13 the (2a)PdCl2 units happen to be associated not in a direct way, but via a

Coordination of the R-DCP cations of 2a and 2b to transition-metal centers was then investigated. In the Ph-DCP series, Au(I) and Pt(II) complexes resulting from the reaction of 2a with (Me2S)AuCl and K2PtCl4, respectively, have been described.9b In a similar way, treatment of 2b with a stoichiometric amount of [(Me2S)AuCl] and [K2PdCl4] in CH2Cl2 afforded the Au(I) complex 7 and the Pd(II) complex 8, in 93% and 97% yield, respectively (see Scheme 4). Here again, in accordance with the general trend, the 31P NMR resonances of 7 and 8 occur at lower field (δP = +17.0 ppm for 7, +21.5 ppm for 8) than those of the ligand precursor 2b (δP = −16.5 ppm). The exact structure of 7 could be determined by XRD analysis of yellow crystals deposited from a CH2Cl2/Et2O solution mixture. The quasi-linear P−Au−Cl arrangement of the known analogous complex ion (2a)AuCl was thus observed in 7 (P1−Au1−Cl1 = 176.69(7)°; Figure 2).9b,14 The zwitterionic palladate structure of 8, reminiscent of the zwitterionic platinate structure of the known complex ion of D


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Inorganic Chemistry

with a classical μ-Cl-bridged dimeric structure [(2b)PdCl2]2 (9b′), but according to the results obtained from 2a (leading to the complex 9a), the present product could be reasonably assigned to 9b, i.e., the pentachlorinated dinuclear complex [(2b)PdCl2]2Cl−. Nevertheless, many attempts at obtaining crystals of 9b suitable for X-ray crystallography failed. Although the product was obtained in a satisfactory purity according to 31 P and 1H NMR spectroscopy (see spectra in the Supporting Information) and to the relative sharpness of the melting point (mp 116−118 °C), elemental analysis of the solid did not allow confirmation of structure 9b (while being not compatible with 9b′ as well, likely because of incomplete combustion). However, assuming the analogy with 9a, 9b was inferred to be isolated in 85% yield. In the presence of an excess of [PdCl2(MeCN)2], the assumed complex 9b was found to evolve to a new complex, 10 (see Scheme 6), first characterized by a 31P NMR resonance at higher field (δP = −62.3 ppm). The structure of 10 was assigned by XRD analysis of orange crystals that had deposited from a CHCl3 solution (see Figure 4, as well as Table 1).13 The tetranuclear complex salt 10 (thus

Figure 3. ORTEP views of the X-ray crystal structure of the Pd(II) complex 9a, with thermal ellipsoids drawn at the 30% probability level (for the sake of clarity, the H atoms and the tetrafluoroborate anions are omitted). Selected bond distances are given as follows: C1−P1, 1.794(3) Å; C16−P1, 1.807(3) Å; P1−Pd1, 2.2053(7) Å; Cl1−Pd1, 2.4126(6) Å; Cl2−Pd1, 2.2980(7) Å; Cl3−Pd1, 2.3097(7) Å. Selected bond angles are given as follows: C1−P1−C16, 106.61(12)°; C1− P1−Pd1, 115.15(8)°; P1−Pd1−Cl1, 176.49(3)°; Cl2−Pd1−Cl3, 170.94(3)°; Pd1−Cl1−Pd2, 107.27(2)°.

supplementary bridging chloride anion in a pentachlorinated complex [(2a)PdCl2]2Cl−. This structure remains compatible with the recorded m/z value, instant dissociation of the Cl− bridge in the ionization chamber of the mass spectrometer releasing the same mononuclear monocationic fragments [(2b)PdCl2−BF4−]. The yield of formation of 9a from 2a was finally calculated to be 91%. The geometry of 9a consists in two quasi-square-planar PdPCl3 units, almost orthogonal to each other, and sharing an sp3-hybridized μ-Cl atom (Pd−Cl−Pd ≈ 107.3°) in trans position, with respect to the P ligands (Figure 3). As expected, the bridging Pd−Cl bonds are longer [2.4126(6) Å] than their terminal counterparts [2.2980(7), 2.3097(7) Å]. The driving force of the formation of 9a from 9a′ can be speculatively, but reasonably, attributed to an electrostatic screening of the repelling pairs of Ph-DCP positive charges in 9a′ by insertion of the negatively charged Cl− bridge: in the dimeric structure 9a′, these positive charges indeed repel each other more strongly. Coordination of the tBu-DCP salt 2b with the same PdCl2 center was then studied. Treatment of 2b with 1.5 equiv of [PdCl2(MeCN)2] afforded a single product, the 31P NMR spectrum of which displayed a singlet signal at δP = +22.6 ppm (as in the case of 2a, the use of a single equivalent of [PdCl2(MeCN)2] resulted in partial conversion of 2b, then evidenced by a resonance at δP = −16.5 ppm).15 ESI+ MS analysis of the product showed a peak at m/z = 823.3, corresponding to the (2b)PdCl2 fragment. This is compatible

Figure 4. ORTEP view of the X-ray crystal structure of the complex 10 (thermal ellipsoids drawn at the 30% probability level). For the sake of clarity, the H atoms and tetrafluoroborate anions are omitted.

isolated in 82% yield) is based on a centrosymmetric Pd4Cl82− core,16 acting as a bridge between two μ2−η1 α-dicationic dicyclopropeniophosphido ligands,17 resulting from the displacement of a tBu+ cation from 2b (see the discussion below). While the two P centers present a distorted tetrahedral configuration, each Pd atom resides in a quasi-square-planar PdPCl3 environment, where one of the Cl ligands is terminal [Pd−Cl = 2.2708(13) Å] and the two other are bridging [Pd− Cl = 2.3714(12) and 2.4147(11) Å]. The very large angles between bridged PdPCl3 mean planes (ca. 55.2°−55.6°) make

Scheme 6. One-to-Two “Reactive” Coordination Chemistry of the tBu-DCP Salt 2b with PdCl2 Centers

E


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Inorganic Chemistry

stoichiometry is tBu+ + BF4− + PdCl2(MeCN)2 → tBu-Cl + /2[PdCl(MeCN)2]2[BF4]2.21 In contrast to the assumed complex 9b, complex 9a was found to be stable in the presence of an excess of [PdCl2(MeCN)2], either in solution or in the solid state. As 9a and 9b should experience the same internal formal electrostatic constraints, their difference in reactivity is thus due to the much greater leaving group ability of tBu+ in 9b, with respect to Ph+ in 9a. Treatment of the tetranuclear DCP phosphido complex 10 with 2 equiv of HCl triggers dissociation to the dinuclear complex 11 in 88% yield (Scheme 6). The 31P NMR spectrum of 11 displays a resonance at higher field (δP = −75.6 ppm) than 10 (δP = −62.3 ppm), thus revealing an enhanced phosphido character of the DCP ligand. The exact structure of 11 was determined by XRD analysis of orange crystals deposited from a CH2Cl2/Et2O solvent mixture (Figure 5).13

Table 1. Selected Crystallographic Data, Bond Lengths, and Bond Angles from X-ray Diffraction (XRD) Analysis of the Tetranuclear Pd(II) Complex 10 parameter formula formula weight, Fw crystal system space group bond lengths (Å) C1−P1 C16−P1 P1−Pd1 P1−Pd2 Pd1−Cl1 Pd1−Cl2 Pd1−Cl4 Pd2−Cl1 Pd2−Cl3 Pd2−Cl5 bond angles (deg) C1−P1−C16 C1−P1−Pd1 C1−P1−Pd2 C16−P1−Pd2 Pd1−P1−Pd2 Cl1−Pd1−Cl4 P1−Pd1−Cl2 Pd1−Cl1−Pd2

1

value C60H112B2Cl8F8N8P2Pd4 1890.38 orthorhombic Pca21 1.766(5) 1.806(5) 2.1955(12) 2.2026(11) 2.3714(12) 2.4147(11) 2.2708(13) 2.3671(11) 2.4046(11) 2.2841(12) 107.1(2) 115.81(17) 114.21(16) 112.69(16) 90.87(4) 172.18(4) 171.59(4) 82.80(4)

the shortest Pd···Pd distance (ca. 3.13 Å) definitely nonbonding. The two BF4− anions are noncoordinating, and the shortest BF···HC distance (unambigously assigned because of the secondary character of the involved isopropyl CH center: BF···HCMe2N ≈ 2.72 Å) is close to the sum of the van der Waals radii. The most striking structural feature of 10 is the quasi-planarity of the eight-membered ring spanned by the four Pd and P1, P2, Cl2, and Cl3 atoms, the Pd4P2Cl2 mean plane forming an angle of ca. 38.6° with each PdPCl3 mean plane. Finally, short contacts between each pair of closest out-of-plane Cl atoms and a carbenium center indicate the occurrence of a type of electrostatic pincers Clδ−···C+···Clδ− (ca. 3.24 ± 0.03 Å, vs a sum of van der Waals radii of 1.68 + 1.84 = 3.52 Å).18 The two μ2-P(BAC+)2 bridging units of 10 are actually “dicationic phosphido ligands”, making the structural type of the tetranuclear complex unprecedented. Indeed, while the chemistry of phosphido ligands has been extensively investigated,19 it is noteworthy that only one example of cationic representative has been previously reported.17 The stoichiometry of the global transformation 2b → 10 requires the release of tBuBF4, i.e. tBu+ + BF4− (Scheme 6). The driving force of the formation of 10 can be attributed to the combination of both electrostatic and steric constraints occurring in the likely intermediate complexes 9b′/9b (see Scheme 5 and discussion above):20 removal of the tBu+ groups indeed results not only in a steric relaxation, but also in a compensation by a palladate negative charge of the local +/+ electrostatic repulsion between the cyclopropenium rings. From the standpoint of stoichiometry, the process requires the elimination of tBu+ + BF4− (or equivalently Me2C = CH2 + HBF4, and in the absence of a sufficiently basic agent, tBu-F + BF3). In the presence of the excess of PdCl2(MeCN)2; however, chloride anions are available and the most likely

Figure 5. ORTEP view of the X-ray crystal structure of the Pd(II) complex 11 with thermal ellipsoids drawn at the 30% probability level (for the sake of clarity, the H atoms are omitted). Selected bond distances for 11: C1−P1, 1.779(3) Å; C16−P1, 1.780(3) Å; P1−Pd1, 2.2133(8) Å; P1−Pd2, 2.2106(8) Å; Cl1−Pd1, 2.3630(7) Å; Cl2− Pd1, 2.2808(7) Å; and Cl3−Pd1, 2.3586(9) Å. Selected bond angles (deg) for 11: C1−P1−C16, 106.16(14)°; C1−P1−Pd1, 116.75(11)°; P1−Pd1−Cl1, 79.81(3)°; Cl1−Pd1−Cl2, 172.48(3)°; and Pd1−Cl1− Pd2, 86.30(2)°.

While the P atom of 11 is thus found in a tetrahedral configuration (as in 10), the two palladate centers reside in quasi-square-planar environments, tilted by ca. 47.3°, with respect to each other. The PdCl5 core involves one bridging Cl ligand [Pd−Cl: 2.3631(7) Å] and four terminal ones [Pd−Cl: 2.2808(7), 2.3586(9) Å]. As in the tetranuclear complex 10, the structure of 11 is also characterized by the absence of any Pd− Pd interaction (Pd···Pd ≈ 3.23 Å) and by the occurrence of a Clδ−···C+···Clδ− electrostatic pincer between two terminal Cl atoms and one of the α-carbenium centers [C+···Clδ− ≈ 3.22 and 3.30 Å < 3.52 Å for the sum of van der Waals radii).18 These features provide the complex 11 with the status of a unique example of doubly zwitterionic organometallate.22

3. CONCLUSION Within the context of the ascendant concern for the chemistry of carbeniophosphanes, the presented results provide a generalized knowledge of both the extrinsic and intrinsic reactivity of the R-DCP α-dicationic phosphines. The generalF


Article

Inorganic Chemistry

of the solvent under vacuum, the solid residue was washed with Et2O (3 × 10 mL). Recrystallization from CH2Cl2/Et2O at −20 °C gave 2b as yellow crystals (133 mg, 54%). Melting point (Mp) of 234−236 °C. 1 H NMR (CD3CN, 25 °C): δ = 1.30 (d, J = 6.8 Hz, 12H, CH3), 1.36 (d, J = 7.2 Hz, 12H, CH3), 1.43 (t, J = 6.0 Hz, 24H, CH3), 1.49 (d, J = 16.4 Hz, 9H, CH3), 4.14 (sept, J = 6.8 Hz, 4H, CH), 4.27 (m, 4H, CH). 13C NMR (CD3CN, 25 °C): δ = 21.04 (CH3), 21.32 (CH3), 21.34 (CH3), 21.51 (CH3), 28.82 (d, JCP = 14.9 Hz, CH3), 35.10 (d, JCP = 13.9 Hz, C), 53.80 (CH), 98.60 (d, JCP = 72.5 Hz, C), 139.98 (C). 31P NMR (CD3CN, 25 °C): δ = −16.5 ppm. IR (ATR): 576, 645, 684, 732, 1029, 1046, 1152, 1360, 1374, 1457, 1546, 1847, 2978 cm−1. MS (ES+): m/z: 647.5 [M − BF4]+. HRMS (ES+): calcd for C34H65N4BF4P, 646.5012; found, 646.5018. 2,3-Bis[bis(propan-2-yl)amino]-1-({bis[bis(propan-2-yl)amino]cycloprop-2-en-1-ylium-1-yl}(phenyl)phosphoryl)cycloprop-2-en-1ylium (Ph-DCP oxide salt) (5a). To a solution of 2a (43 mg, 0.06 mmol) in CH2Cl2 (3 mL) at rt was added m-CPBA (9 mg, 0.06 mmol). The solution was then stirred for 2 h. Evaporation of the solvent under vacuum, and recrystallization from CH2Cl2/Et2O afforded 5a as an orange solid (42 mg, 92%). Mp = 95−98 °C. 1 H NMR (CD2Cl2, 25 °C): δ = 1.26 (d, J = 6.8 Hz, 12H, CH3), 1.35 (d, J = 6.8 Hz, 12H, CH3), 1.46 (d, J = 6.8 Hz, 12H, CH3), 1.47 (d, J = 6.8 Hz, 12H, CH3), 3.78 (sept, J = 6.8 Hz, 4H, CH), 4.26 (sept, J = 6.8 Hz, 4H, CH), 7.80−7.84 (m, 3H, Har), 8.08−8.14 (m, 2H, Har). 13C NMR (CD2Cl2, 25 °C): δ = 20.18 (CH3), 20.37 (CH3), 20.90 (CH3), 21.05 (CH3), 54.31 (CH), 55.38 (CH), 95.42 (d, JCP = 117.3 Hz, C), 127.61 (d, JCP = 129.4 Hz, Car), 130.60 (d, JCP = 15.3 Hz, CHar), 131.50 (d, JCP = 12.9 Hz, CHar), 135.70 (d, JCP = 2.9 Hz, CHar), 137.25 (d, JCP = 6.5 Hz, C). 31P NMR (CD2Cl2, 25 °C): δ = −3.6 ppm. IR (ATR): 597, 696, 725, 892, 1054, 1351, 1458, 1567, 1706, 1867, 2259, 2978, 3124 cm−1. MS (ES+): m/z: 683.5 [M − BF4]+. HRMS (ES+): calcd for C36H61N4BF4PO, 682.4648; found, 682.4650. 2,3-Bis[bis(propan-2-yl)amino]-1-({bis[bis(propan-2-yl)amino]cycloprop-2-en-1-ylium-1-yl}(tert-butyl)phosphoryl)cycloprop-2-en1-ylium (tBu-DCP oxide salt) (5b). To a solution of 2b (100 mg, 0.14 mmol) in CH2Cl2 (5 mL) at rt was added m-CPBA (24 mg, 0.14 mmol). The solution was then stirred for 2 h. Evaporation of the solvent under vacuum afforded 5b as a white solid (94 mg, 92%). Recrystallization from CH2Cl2/Et2O gave 5b as white crystals. Mp = 195−198 °C. 1 H NMR (CD3CN, 25 °C): δ = 1.37 (d, J = 6.8 Hz, 12H, CH3), 1.40 (d, J = 7.2 Hz, 12H, CH3), 1.44 (d, J = 7.2 Hz, 12H, CH3), 1.47 (d, J = 7.2 Hz, 12H, CH3), 1.48 (d, J = 20.0 Hz, 9H, CH3), 4.18 (sept, J = 6.8 Hz, 4H, CH), 4.30 (m, 4H, CH). 13C NMR (CD3CN, 25 °C): δ = 19.72 (CH3), 20.28 (CH3), 20.57 (CH3), 20.81 (CH3), 23.26 (CH3), 36.77 (d, JCP = 81.2 Hz, C), 54.50 (brs, CH), 94.32 (d, JCP = 89.2 Hz, C), 137.89 (d, JCP = 6.9 Hz, C). 31P NMR (CD3CN, 25 °C): δ = +20.7 ppm. IR (ATR): 596, 686, 806, 894, 1048, 1150, 1358, 1464, 1564, 1846, 2980 cm−1. MS (ES+): m/z: 663.5 [M − BF4]+. HRMS (ES+): calcd for C34H65N4BF4PO, 662.4961; found, 662.4967. t Bu-DCP-AuCl Complex Salt (7). [AuCl(SMe2)] (32 mg, 0.11 mmol) was added to a solution of 2b (80 mg, 0.11 mmol) in CH2Cl2 (3 mL) at −20 °C. The solution was slowly warmed to rt and stirred for 2 h. After evaporation of the solvent under vacuum, 7 was isolated as a yellow solid (89 mg, 93%). Recrystallization from CH2Cl2/Et2O at −20 °C gave 7 as yellow crystals. Mp = 185−188 °C. 1 H NMR (CD3CN, 25 °C): δ = 1.43 (d, J = 6.9 Hz, 12H, CH3), 1.46 (d, J = 6.9 Hz, 12H, CH3), 1.47 (d, J = 6.9 Hz, 12H, CH3), 1.55 (d, J = 6.9 Hz, 12H, CH3), 1.63 (d, J = 22.2 Hz, 9H, CH3), 4.20 (sept, J = 6.9 Hz, 4H, CH), 4.35 (m, 4H, CH). 13C NMR (CD3CN, 25 °C): δ = 21.02 (CH3), 21.19 (CH3), 21.56 (CH3), 27.37 (d, JCP = 7.8 Hz, CH3), 39.42 (d, JCP = 29.9 Hz, C), 53.95 (CH), 56.37 (CH), 89.67 (d, JCP = 37.2 Hz, C), 139.85 (d, JCP = 7.1 Hz, C). 31P NMR (CD3CN, 25 °C): δ = +17.0 ppm. IR (ATR): 578, 651, 682, 892, 1032, 1050, 1149, 1376, 1454, 1555, 1845, 2939, 2978 cm−1. MS (ES+): m/z: 879.4 [M − BF4]+. HRMS (ES+): calcd for C34H65AuClBF4N4P, 879.4336; found, 879.4356. t Bu-DCP-PdCl3− Complex Salt (8). [K2PdCl4] (32 mg, 0.098 mmol) was added to a solution of 2b (72 mg, 0.098 mmol) in CH2Cl2 (6 mL) at −20 °C. The solution was slowly warmed to rt and stirred for 12 h.

ization addresses not only the variation of the neutral R substituent, from R = Ph to R = tBu, but also the extension of the set of compatible Lewis acids, including the promoted oxygen atom and two types of Pd(II) centers. Whereas the anionic PdCl3− center leads to a stable one-to-one complex, the neutral PdCl2 center gives rise to a versatile coordination chemistry, where the electrostatic factors play a dominant role, and where the nature of the R group is pivotal. In the presence of an excess of [(MeCN)2PdCl2], the Ph-DCP ligand remains intrinsically stable, but the tBu-DCP ligand undergoes a P−tBu bond cleavage, leading to a dicationic phosphido ligand bridging two hemipalladate centers in the tetranuclear complex 10, or two true palladate centers in the doubly zwitterionic dinuclear complex 11. From a more general standpoint, the disclosed results illustrate the ambivalence between the phosphenium and phosphido characters of PRR′ ligands: while the PR(BAC+) moiety of the R-DCP salts 2a and 2b (i.e., [PR(BAC+)2][BF4]2, R = Ph and tBu) are invoked to possess a partial phosphenium character,23 the P(BAC+)2 moieties in complexes 10 and 11 are definitely μ2-phosphido ligands (of the LX type in the Green formalism).24 The growing diversity in the family of carbeniophosphane complexes should promote future developments, in particular in the field of catalysis as recently initiated.9

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EXPERIMENTAL SECTION

General Remarks. Tetrahydrofuran (THF), diethyl ether, and toluene were dried and distilled over sodium/benzophenone, pentane, dichloromethane (DCM), and acetonitrile over CaH. All other reagents were used as commercially available. All reactions were carried out under an argon atmosphere, using Schlenk and vacuum line techniques. The following analytical instruments were used: for 1H, 13 C, and 31P NMR, Bruker DPX 300, Avance 400, and Avance 500 equipment was used. NMR chemical shifts (δ) are given in ppm, with positive values to high frequency relative to the tetramethylsilane (TMS) reference for 1H and 13C, and to the H3PO4 reference for 31P; coupling constants J are given in Hz. Mass spectra were obtained on a PerkinElmer Sciex spectrometer (tandem mass spectroscopy (MS/ MS), Model API-365). The bis(diisopropylamino)cyclopropenylidene (BAC) (1) was prepared according to a previously described procedure.12 2,3-Bis[bis(propan-2-yl)amino]-1-({bis[bis(propan-2-yl)amino]cycloprop-2-en-1-ylium-1-yl}(phenyl)phosphanyl)cycloprop-2-en-1ylium (Ph-DCP salt) (2a). To a solution of bis(diisopropylamino)cyclopropenylidene 1 (185 mg, 0.78 mmol) in THF (10 mL), cooled to −78 °C, was added dichlorophenylphosphine (30 μL, 0.39 mmol). The solution was slowly warmed to room temperature (rt) and stirred for 4 h. After evaporation of the solvent under vacuum, the residue was dissolved in CH2Cl2 (10 mL), and an aqueous saturated solution of NaBF4 (10 mL) was added. The mixture was then stirred for 30 min. After the addition of CH2Cl2 (10 mL), the organic phase was extracted and dried over Na2SO4. After evaporation of the solvent under vacuum, the solid residue was washed with Et2O (3 × 10 mL). Recrystallization at −20 °C from CH2Cl2/Et2O gave 2a as colorless crystals (315 mg, 55%). The Ph-DCP salt 2a was first prepared by Alcarazo et al., following a different procedure.9 2,3-Bis[bis(propan-2-yl)amino]-1-({bis[bis(propan-2-yl)amino]cycloprop-2-en-1-ylium-1-yl}(tert-butyl)phosphanyl)cycloprop-2en-1-ylium ( t Bu-DCP salt) (2b). To a solution of bis(diisopropylamino)cyclopropenylidene 1 (80 mg, 0.34 mmol) in THF (10 mL), cooled to −78 °C, was added tert-butyldichlorophosphine (27 mg, 0.17 mmol). The solution was slowly warmed to rt and stirred for 4 h. After evaporation of the solvent under vacuum, the residue was dissolved in CH2Cl2 (10 mL), and an aqueous saturated solution of NaBF4 (10 mL) was added. The mixture was then stirred for 30 min. After the addition of CH2Cl2 (10 mL), the organic layer was extracted and dried over Na2SO4. After evaporation G


Article

Inorganic Chemistry After filtration, and evaporation of the solvent under vacuum, 8 was isolated as an orange solid (90 mg, 97%). Mp = 117−119 °C. 1 H NMR (CD2Cl2, 25 °C): δ = 1.52 (d, J = 6.9 Hz, 12H, CH3), 1.53 (d, J = 7.2 Hz, 12H, CH3), 1.57 (d, J = 6.9 Hz, 24H, CH3), 1.74 (d, J = 19.8 Hz, 9H, CH3), 4.35 (sept, J = 6.9 Hz, 4H, CH), 4.94 (sept, J = 6.9 Hz, 4H, CH). 13C NMR (CD2Cl2, 25 °C): δ = 21.98 (CH3), 22.31 (CH3), 22.39 (CH3), 22.49 (CH3), 30.79 (d, JCP = 4.75 Hz, CH3), 40.16 (d, JCP = 20.99 Hz, C), 54.21 (CH), 58.29 (CH), 95.02 (d, JCP = 16.5 Hz, C), 139.85 (d, JCP = 8.4 Hz, C). 31P NMR (CD2Cl2, 25 °C): δ = +21.5 ppm. IR (ATR): 582, 678, 729, 886, 1034, 1111, 1266, 1374, 1452, 1541, 1840, 2925. MS (ES+): m/z: 771.3 [M+]. HRMS (ES+): calcd for C34H65Cl3N4PPd, 769.3053; found 769.3046. Dinuclear Ph-DCP-PdCl2 Complex Salt (9a). [Pd(MeCN)2Cl2] (43 mg, 0.16 mmol) was added to a solution of 2a (80 mg, 0.11 mmol) in CH2Cl2 (3 mL) at −20 °C. The solution was slowly warmed to rt and stirred for 2 h. After filtration, and evaporation of the solvent under vacuum, 9a was isolated as an orange solid (181 mg, 91%). Recrystallization from CH3CN/Et2O at rt gave 9a as orange crystals. Mp = 85−88 °C. 1 H NMR (CD2Cl2, 25 °C): δ = 1.15 (d, J = 6.4 Hz, 24H, CH3), 1.26 (d, J = 6.4 Hz, 24H, CH3), 1.41 (d, J = 6.8 Hz, 48H, CH3), 4.31 (m, 16H, CH), 7.77−7.86 (m, 6H, Har), 8.37−8.43 (m, 4H, Har). 13C NMR (CD2Cl2, 25 °C): δ = 20.35 (CH3), 20.87 (CH3), 21.01 (CH3), 54.00 (CH), 56.66 (CH), 130.37 (d, JCP = 13.0 Hz, CHar), 135.71 (brs, CHar), 137.23 (d, JCP = 13.5 Hz, CHar), 137.59 (brs, C), the quaternary C atom in α-position of the P-center is not observed. 31P NMR (CD2Cl2, 25 °C): δ = −3.4 ppm. IR (ATR): 576, 694, 732, 893, 1034, 1147, 1268, 1376, 1454, 1559, 1851, 2930 cm−1. MS (ES+): m/z: 843.3 [M − BF4]+. HRMS (ES+): calcd for C36H61Cl2BF4N4PPd, 843.3075; found, 843.3184. Dinculear tBu-DCP-PdCl2 Complex Salt (9b). [Pd(MeCN)2Cl2] (43 mg, 0.16 mmol) was added to a solution of 2b (82 mg, 0.11 mmol) in CH2Cl2 (3 mL) at −20 °C. The solution was then stirred for 2 h at −20 °C. After filtration, and evaporation of the solvent under vacuum, the product, attributed to the structure 9b by analogy with 9a (but without crystallographic confirmation in this case) was isolated as an orange solid (165 mg, 85%). Recrystallization from CH2Cl2/Et2O at −20 °C afforded orange crystals, which proved to be nonsuitable for XRD analysis. Mp = 116−118 °C. 1 H NMR (CD2Cl2, 25 °C): δ = 1.52−1.59 (m, 96H, CH3), 1.75 (d, J = 15.9 Hz, 18H, CH3), 4.38 (m, 8H, CH), 4.78 (m, 8H, CH). 13C NMR (CD2Cl2, 25 °C): δ = 21.88 (CH3), 22.14 (CH3), 22.21 (CH3), 30.61 (d, JCP = 4.7 Hz, CH3), 41.90 (d, JCP = 32.19 Hz, C), 54.85 (CH), 58.54 (CH), 91.85 (d, JCP = 69.6 Hz, C), 139.75 (d, JCP = 17.8 Hz, C). 31P NMR (CD2Cl2, 25 °C): δ = +22.6 ppm. IR (ATR): 582, 679, 732, 893, 1051, 1148, 1269, 1376, 1454, 1546, 1843, 2980 cm−1. MS (ES+): m/z: 823.3 [M − BF4]+. HRMS (ES+): calcd for C34H65Cl2BF4N4PPd, 823.3400; found, 823.3405. Tetranuclear DCP Phosphido Complex Salt (10). [Pd(MeCN)2Cl2] (113 mg, 0.44 mmol) was added to a solution of 2b (80 mg, 0.11 mmol) in CH2Cl2 (3 mL) at −20 °C. The solution was slowly warmed to rt and stirred for 12 h. After filtration, and evaporation of the solvent under vacuum, 10 was isolated as an orange solid (680 mg, 82%). Recrystallization from CHCl3 at rt gave 10 as orange crystals. Mp = 207−209 °C. 1 H NMR (CD3CN, 25 °C): δ = 1.42 (d, J = 7.2 Hz, 48H, CH3), 1.60 (d, J = 6.8 Hz, 48H, CH3), 4.26−4.31 (m, 8H, CH), 5.09 (m, 8H, CH). 13C NMR (CD3CN, 25 °C): δ = 21.04 (brs, CH3), 53.32 (brs, CH), 56.02 (brs, CH), 137.38 (d, JCP = 10.6 Hz, C), the quaternary C atom in α-position of the P-center is not observed. 31P NMR (CD2Cl2, 25 °C): δ = − 62.3 ppm. IR (ATR): 578, 680, 733, 802, 893, 1027, 1146, 1262, 1342, 1454, 1510, 1560, 1850, 2329, 2974, 3002 cm−1. MS (ES+): m/z: 855.1 [M+]. HRMS (ES+): calcd for C30H56Cl4N4PPd2, 855.1071; found, 855.1090. Dinuclear DCP Phosphido Complex (11). HCl (8.4 μL, 0.280 mmol) was added to 10 (264 mg, 0.140 mmol) in CH2Cl2 (3 mL), and the solution was stirred at rt for 12 h. After filtration, and evaporation of the solvent under vacuum, 11 was obtained as an orange solid (110 mg, 88%). Recrystallization from CH2Cl2/Et2O at −20 °C gave 11 as orange crystals. Mp = 172−175 °C.

H NMR (CD3CN, 25 °C): δ = 1.41 (d, J = 7.2 Hz, 24H, CH3), 1.60 (d, J = 6.8 Hz, 24H, CH3), 4.27 (m, 4H, CH), 5.17 (m, 4H, CH). 13 C NMR (CD3CN, 25 °C): δ = 20.97 (CH3), 21.08 (CH3), 52.98 (CH), 55.82 (CH), 95.52 (brs, C), 137.53 (d, JCP = 10.9 Hz, C). 31P NMR (CD2Cl2, 25 °C): δ = −75.6 ppm. IR (ATR): 570, 679, 731, 798, 893, 1031, 1109, 1145, 1260, 1375, 1452, 1549, 1850, 2931, 2970 cm−1. MS (ES+): m/z: 785.2 [M − Cl2−Cl]+. HRMS (ES+): calcd for C30H56Cl2N4PPd22+; 785.1699, found; 785.1746. Crystal Structure Determination of 2a,9 2b, 5b, 7, 9a, 10, and 11. XRD data for the crystals were collected at low temperature on an Agilent Gemini diffractometer or a Bruker Apex2 diffractometer using Mo Kα (or Cu Kα radiation source for 2a). Multiscan absorption corrections were applied. The structures were solved using SUPERFLIP25 or direct methods (SIR9226 and SHELXS8627) and refined by means of least-squares procedures using the programs of the PC version of CRYSTALS.28 Atomic scattering factors were taken from the international tables for X-ray crystallography.29 When possible, all non-hydrogen atoms were refined anisotropically. 5b was weakly diffracting and only isotropic thermal parameters were refined. For structures of 2a, 7, 10, 9a, and 11, it was not possible to resolve diffuse electron-density residuals (enclosed solvent molecules). Treatment with the SQUEEZE facility from PLATON (Spek, 1990) resulted in a smooth refinement. Hydrogen atoms were refined with riding constraints. Crystal Data for 2a. An X-ray crystal structure of 2a was previously resolved in the Pbcn space group (orthorhombic);9 an “allotropic version” has been here resolved in the C2/c space group (monoclinic), giving similar molecular geometrical data: C36H61B2F8N4P, M = 754.49 g mol−1, monoclinic, a = 55.3030(12) Å, b = 16.0098(4) Å, c = 20.5714(5) Å, β = 100.312(2)°, V = 17919.5(7) Å3, T = 100 K, space group C2/c, Z = 16, μ(Cu Kα) = 1.064 mm−1, 134 736 reflections measured, 17 227 unique (Rint = 0.086), 902 parameters, refinement on F, 11 169 reflections used in the calculations [I > 3σ(I)], R1 = 0.0665, wR2 = 0.0734. Crystal Data for 2b. C35H67B2Cl2F8N4P, M = 819.43 g mol−1, monoclinic, a = 15.3856(4) Å, b = 15.1946(4) Å, c = 19.7008(6) Å, β = 104.455(3)°, V = 4459.8(2) Å3, T = 100 K, space group P21/n, Z = 4, μ(Mo Kα) = 0.243 mm−1, 67 743 reflections measured, 11 147 unique (Rint = 0.060), 469 parameters, refinement on F, 7096 reflections used in the calculations [I > 3σ(I)], R1 = 0.0486, wR2 = 0.0567. Crystal Data for 5b. C35H67B2Cl2F8N4OP, M = 835.43 g mol−1, orthorhombic, a = 9.6469(4) Å, b = 12.0148(7) Å, c = 37.576(2) Å, V = 4355.3(4) Å3, T = 100 K, space group P212121, Z = 4, μ(Mo Kα) = 0.252 mm−1, 27 178 reflections measured, 5320 unique (Rint = 0.061), 256 parameters, refinement on F, 4135 reflections used in the calculations [I > 3σ(I)], R1 = 0.0990, wR2 = 0.1091. Crystal Data for 7. C34H65AuB2ClF8N4P, M = 966.92 g mol−1, monoclinic, a = 19.9147(9) Å, b = 11.9581(6) Å, c = 22.5379(10) Å, β = 105.692(2)°, V = 5167.2(4) Å3, T = 100 K, space group P21/n, Z = 4, μ(Mo Kα) = 2.982 mm−1, 95 159 reflections measured, 5487 unique (Rint = 0.050), 439 parameters, refinement on F, 4525 reflections used in the calculations [I > 3σ(I)], R1 = 0.0502, wR2 = 0.0421. Crystal Data for 9a. C72H122B3Cl5F12N8P2Pd2, M = 1812.23 g mol−1, monoclinic, a = 16.1147(3) Å, b = 19.4263(2) Å, c = 32.2555(8) Å, β = 96.968(2)°, V = 10023.0(3) Å3, T = 120 K, space group P21/n, Z = 4, μ(Mo Kα) = 0.584 mm−1, 174 439 reflections measured, 25 695 unique (Rint = 0.035), 925 parameters, refinement on F, 20 699 reflections used in the calculations [I > 3σ(I)], R1 = 0.0525, wR2 = 0.0542. Crystal Data for 10. C60H112B2Cl8F8N8P2Pd4, M = 1890.38 g mol−1, orthorhombic, a = 26.1981(16) Å, b = 10.9270(6) Å, c = 36.837(2) Å, V = 10545.1(10) Å3, T = 100 K, space group Pca21, Z = 4, μ(Mo Kα) = 0.949 mm−1, 65 386 reflections measured, 27 502 unique (Rint = 0.035), 830 parameters, refinement on F, 21 188 reflections used in the calculations [I > 3σ(I)], R1 = 0.0454, wR2 = 0.0492. Crystal Data for 11. C30H56Cl5N4PPd2, M = 893.84 g mol−1, triclinic, a = 11.1830(4) Å, b = 11.2218(4) Å, c = 11.6073(4) Å, α = 67.5830(10)°, β = 74.7270(10)°, γ = 76.5760(10)°, V = 1284.76(8) 1

H


Article

Inorganic Chemistry Å3, T = 100 K, space group P1, Z = 1, μ(Mo Kα) = 1.010 mm−1, 48 759 reflections measured, 16 906 unique (Rint = 0.018), 338 parameters, refinement on F, 15 028 reflections used in the calculations [I > 3σ(I)], R1 = 0.0358, wR2 = 0.0389.

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T. Resolution and Characterization of 2,2′-Bis(Diphenylphosphino)1,1′-Bibenzimidazole (BIMIP): The First Chiral Atropisomeric Diphosphine Ligand with Hindered Rotation around a N−N Bond. Phosphorus, Sulfur Silicon Relat. Elem. 1999, 144, 405−408. (g) Benincori, T.; Brenna, E.; Sannicolo, F.; Trimarco, L.; Antognazza, P.; Cesarotti, E.; Demartin, F.; Pilati, T.; Zotti, G. Chiral atropisomeric five-membered biheteroaromatic diphosphines: New ligands of the bibenzimidazole and biindole series. J. Organomet. Chem. 1997, 529, 445−453. (3) (a) Alcarazo, M. Synthesis, Structure, and Applications of αCationic Phosphines. Acc. Chem. Res. 2016, 49, 1797−1805. (b) Alcarazo, M. α-Cationic Phosphines: Synthesis and Applications. Chem.Eur. J. 2014, 20, 7868−7877. (c) Gaillard, S.; Renaud, J. L. When phosphorus and NHC (N-heterocyclic carbene) meet each other. Dalton Trans. 2013, 42, 7255−7270. (d) Canac, Y.; Maaliki, C.; Abdellah, I.; Chauvin, R. Carbeniophosphanes and their carbon → phosphorus → metal ternary complexes. New J. Chem. 2012, 36, 17− 27. (4) For truly cationic imidazoliophosphines as diaminocarbenephosphenium adducts, see, for example: (a) Lepetit, C.; Maraval, V.; Canac, Y.; Chauvin, R. On the nature of the dative bond: Coordination to metals and beyond. The carbon case. Coord. Chem. Rev. 2016, 308, 59−75. (b) Maaliki, C.; Lepetit, C.; Canac, Y.; Bijani, C.; Duhayon, C.; Chauvin, R. On the P-Coordinating Limit of NHC-Phosphenium Cations toward RhI Centers. Chem.Eur. J. 2012, 18, 7705−7714. (c) Abdellah, I.; Lepetit, C.; Canac, Y.; Duhayon, C.; Chauvin, R. Imidazoliophosphines are True N-Heterocyclic Carbene (NHC)− Phosphenium Adducts. Chem.Eur. J. 2010, 16, 13095−13108. (d) Ellis, B. D.; Ragogna, P. J.; Macdonald, C. L. B. Computational Insights into the Acceptor Chemistry of Phosphenium Cations. Inorg. Chem. 2004, 43, 7857−7867. For an imidazol-2-ylidene tribromophosphorane condensed form, and a α-dicationic dimeric derivative, see: (e) Waters, J. B.; Everitt, T. A.; Myers, W. K.; Goicoechea, J. M. N-heterocyclic carbene induced reductive coupling of phosphorus tribromide. Isolation of a bromine bridged P−P bond and its subsequent reactivity. Chem. Sci. 2016, DOI: 10.1039/c6sc02343f. For zwitterionic imidazoliophosphides as diaminocarbene−phosphidene adducts, see, as a recent example: (f) Pal, K.; Hemming, O. B.; Day, B. M.; Pugh, T.; Evans, D. J.; Layfield, R. A. Iron- and CobaltCatalyzed Synthesis of Carbene Phosphinidenes. Angew. Chem., Int. Ed. 2016, 55, 1690−1693. (5) (a) Canac, Y.; Debono, N.; Vendier, L.; Chauvin, R. NHCDerived Bis(amidiniophosphine) Ligands of Rh(I) Complexes: Versatile cis−trans Chelation Driven by an Interplay of Electrostatic and Orbital Effects. Inorg. Chem. 2009, 48, 5562−5568. (b) Azouri, M.; Andrieu, J.; Picquet, M.; Richard, P.; Hanquet, B.; Tkatchenko, I. Straightforward Synthesis of Donor-Stabilised Phosphenium Adducts from Imidazolium-2-carboxylate and Their Electronic Properties. Eur. J. Inorg. Chem. 2007, 31, 4877−4883. (6) (a) Kozma, A.; Deden, T.; Carreras, J.; Wille, C.; Petuskova, J.; Rust, J.; Alcarazo, M. Coordination Chemistry of CyclopropenylideneStabilized Phosphenium Cations: Synthesis and Reactivity of Pd and Pt Complexes. Chem.Eur. J. 2014, 20, 2208−2214. (b) Petuskova, J.; Bruns, H.; Alcarazo, M. Cyclopropenylylidene-Stabilized Diaryl and Dialkyl Phosphenium Cations: Applications in Homogeneous Gold Catalysis. Angew. Chem., Int. Ed. 2011, 50, 3799−3802. (7) (a) Nakazawa, H. Transition Metal Complexes Bearing a Phosphenium Ligand. Adv. Organomet. Chem. 2004, 50, 107−143. (b) Gudat, D. Cationic low coordinated phosphorus compounds as ligands: Recent developments. Coord. Chem. Rev. 1997, 163, 71−106. (c) Sanchez, M.; Mazières, M. R.; Lamande, L.; Wolf, R. In Multiple Bonds and Low Coordination in Phosphorus Chemistry; Regitz, M., Scherer, O., Eds.; G. Thieme Verlag: Stuttgart, Germany, 1990; 129. (d) Cowley, A. H.; Kemp, R. A. Synthesis and reaction chemistry of stable two-coordinate phosphorus cations (phosphenium ions). Chem. Rev. 1985, 85, 367−382. (8) (a) Henne, F. D.; Dickschat, A. T.; Hennersdorf, F.; Feldmann, K. O.; Weigand, J. J. Synthesis of Selected Cationic Pnictanes [LnPnX3−n]n+ (L = Imidazolium-2-yl; Pn = P, As; n = 1−3) and

ASSOCIATED CONTENT

S Supporting Information *

The Supporting Information is available free of charge on the ACS Publications website at DOI: 10.1021/acs.inorgchem.6b01524. 31 P and 1H NMR spectra of 2a, 2b, 5a, 5b, 7, 8, 9a, 9b, 10, and 11 (PDF) Crystallographic data for 2a, 2b, 5b, 7, 9a, 10, and 11 (ZIP)

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AUTHOR INFORMATION

Corresponding Author

*Fax: (+33)5 61 55 30 03. E-mail: [email protected]. Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS The authors thank the Centre National de la Recherche Scientifique (CNRS) for research facilities and for half a teaching sabbatical for R.C. in 2015−2016. The Gabonese Agency of Scholarships is acknowledged for the doctoral fellowship (No. 762241D) of C.D.M. Dr. Valérie Maraval is also acknowledged for the proper conduct of the work.

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REFERENCES

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