and Dihydrido Carbonyl Clusters Obtained by - American Chemical

Article pubs.acs.org/Organometallics

Tetrahedral [HnPt4(CO)4(P∧P)2]n+ (n = 1, 2; P∧P = CH2C(PPh2)2) Cationic Mono- and Dihydrido Carbonyl Clusters Obtained by Protonation of the Neutral Pt4(CO)4(P∧P)2 Iacopo Ciabatti, Cristina Femoni, Maria Carmela Iapalucci, Giuliano Longoni, and Stefano Zacchini* Dipartimento di Chimica Industriale “Toso Montanari”, Università di Bologna, Viale Risorgimento 4, 40136 Bologna, Italy S Supporting Information *

ABSTRACT: The reaction of [Pt12(CO)24]2− with CH2C(PPh2)2 (P∧P) results in the neutral tetrahedral cluster Pt4(CO)4(P∧P)2. This reacts with strong acids such as HBF4 to afford, first, the [HPt4(CO)4(P∧P)2]+ monohydride monocation and, then, the [H2Pt4(CO)4(P∧P)2]2+ dihydride dication. The three clusters have been fully characterized in solution by means of IR and 1H and 31P NMR spectroscopy. Both Pt4(CO)4(P∧P)2 and [H2Pt4(CO)4(P∧P)2]2+ are static in solution, whereas [HPt4(CO)4(P∧P)2]+ displays a fluxional behavior of the unique hydride ligand. In addition, the molecular structures of all these clusters have been fully determined in the solid state via single-crystal X-ray diffraction, showing that all of them possess the same 56-electron tetrahedral Pt4(CO)4(P∧P)2 core to which the hydride ligands are added stepwise.

1. INTRODUCTION

short Pt−Pt interactions (2.752−2.790 Å), whereas the sixth Pt···Pt distance (3.543(8) Å) is nonbonding.3 The situation is not so clear in other reported 58-electron butterfly Pt carbonyl clusters, such as [Pt4(CO)3(PPh3)(dppm) 3 ] 2+ , [HPt 4 (CO) 2 (μ-dppm) 3 (η 1 -dppm)] + , and [Pt4(CO)3(μ-dpam)3(η1-dpam)]2+ (dppm = CH2(PPh2)2; dpam = CH2(AsPh2)2).4 In these cases, five Pt−Pt contacts are well below 3 Å and, thus, at bonding distances, whereas the sixth contact (3.068, 3.082, and 3.094 Å, respectively) may be or may be not considered as a bond. The covalent and van der Waals radius of Pt are 1.36 and 1.72 Å, respectively.7 Thus, contacts of ca. 3.1 Å are well below the sum of the van der Waals radii of Pt and, assuming a tolerance of 20% on the covalent radius, Pt−Pt distances up to ca. 3.24 Å might display some bonding interaction. In this respect, it is significant that the intertriangular Pt−Pt bonding contacts in the molecular clusters [Pt3n(CO)6n]2− (n = 2−6) are in the 3.02−3.10 Å range.8 In view of these considerations, it seems that there is not a clear-cut distinction between tetrahedral and butterfly geometries in the above tetranuclear clusters. Of course, it must also be considered that some short Pt−Pt contacts might be

The tetrahedral geometry is widely documented in metal cluster chemistry, with more than 1400 examples reported to date in the Cambridge Crystallographic Database.1 Nonetheless, tetrahedral Pt clusters are rather rare, and only two structures of Pt−CO clusters displaying a tetrahedral geometry are known: i.e., [HPt4(CO)7(PCy3)4]+ and Pt4(CO)2(PCy3)4(ReO4)2.2 More often, tetranuclear Pt carbonyl clusters show a butterfly or a square geometry.3−6 It must be remarked that one of the main differences among tetrahedral, butterfly, and square geometries is the number of Pt−Pt bonds: i.e., six, five, and four, respectively (Scheme 1). In this respect, it is noticeable that the 58-electron butterfly Pt4(CO)5(PPhMe2)4 cluster reported in 1969 by Dahl et al. displays, as expected, five Scheme 1

Received: July 23, 2013 Published: September 11, 2013 © 2013 American Chemical Society

5180

dx.doi.org/10.1021/om400723w | Organometallics 2013, 32, 5180−5189

Organometallics

Article

complex multiplet centered at δP 28.1 ppm (Figure 1). Coordination of P∧P to the cluster results in a considerable

due not to bonding interactions but to steric effects, especially in the presence of bidentate ligands. An electron count of 56 or 54 for tetranuclear Pt clusters in a tetrahedral geometry is predicted by theoretical studies on the basis of Pt(PH 3 ) 2 fragments. 9 The aforementioned [HPt4(CO)7(PCy3)4]2+ as well as the polyhydride cluster H8Pt4(PiPr2Ph)410 displays the expected tetrahedral geometry with an electron count of 56 cluster valence electrons (CVE). Conversely, Pt4(CO)2(PCy3)4(ReO4)22 and [H7Pt4(PBu3)4]+ 11 are tetrahedral with 54 CVE and also some examples of electron poorer tetrahedral Pt clusters are known: e.g., [H2Pt4(PBu3)4]2+ (48 CVE) and H2Pt4(PBu3)4 (50 CVE).11 Tetranuclear Pt clusters with 58 CVE usually display a butterfly metal core, even if some care may be taken, as described above, whereas a rectangular structure is expected in the case of 60 CVE, e.g., [H2Pt4(dppm)2(PPh2)2(μ-I)2]2+.5 Nonetheless, the deprotonated species Pt4(dppm)2(PPh2)2I2 displays a butterfly structure (sixth Pt···Pt contact 4.69 Å) despite its electron count of 56 CVE.5 All these data suggest that, despite their apparent simplicity, tetranuclear Pt clusters are far from simple and a more accurate interpretation is needed. Herein, we present the synthesis and structural characterization of the new tetrahedral 56 CVE Pt4(CO)4(P∧P)2 (P∧P = CH2C(PPh2)2) cluster, obtained from the reaction of [Pt12(CO)24]2− with the rigid P∧P ligand.12 This cluster is easily protonated by strong acids, resulting in the cationic clusters [HPt4(CO)4(P∧P)2]+ and [H2Pt4(CO)4(P∧P)2]2+, which retain the same tetrahedral structure and electron count. In addition, the reactions of [Pt12(CO)24]2− with other bidentate ligands are described.

Figure 1. 298 K.

P{1H} NMR spectrum of Pt4(CO)4(P∧P) in CD2Cl2 at

shift toward higher frequencies of the 31P resonance, since the free ligand shows a sharp singlet at −4.0 ppm. The four P atoms as well as the four Pt atoms of Pt4(CO)4(P∧P)2 are chemically equivalent but magnetically nonequivalent, giving a very complex second-order AA′A″A‴XX′X″X‴ system. In addition, the observed spectra are further complicated because of the 33% natural abundance of 195Pt, which gives rise to different isotopomers. Due to the low solubility of the cluster, the quality of the spectrum is not very high and, thus, it has been possible to assign only 1JPtP = 2712 Hz. This shows a typical value for a phosphine ligand directly bonded to a Pt cluster.4,5,6d,13−17 The 1H NMR spectrum shows, as expected, the resonances due to aromatic protons in the range 7.1−7.8 ppm (40H) and a broad multiplet at 5.65 ppm (4H) due to CH2. For comparison, the same olefinic protons show a multiplet at 6.35 ppm in the free P∧P ligand. The neutral cluster Pt4(CO)4(P∧P)2 (ν(CO) 1979 (s), 1954 (m) cm−1 in CH2Cl2) is protonated by strong acids such as HBF4·Et2O in CH2Cl2, resulting in, after the addition of 1 equiv of acid, the [HPt4(CO)4(P∧P)2]+ monohydride monocation (Scheme 2). This compound is completely soluble in CH2Cl2 and has been spectroscopically characterized (IR and 1H and 31 P NMR spectroscopy). Moreover, its structure has been fully determined by X-ray studies as [HPt4(CO)4(P∧P)2][BF4]· xCH2Cl2 (x = 1.47) crystals, obtained by slow diffusion of nhexane into a CH2Cl2 solution. It must be remarked that, in the attempt to crystallize this species, sometimes crystals of [HPt4(CO)4(P∧P)2][B2F7] have been obtained in minor amounts. This salt contains the same [HPt4(CO)4(P∧P)2]+ monohydride monocation as [HPt4 (CO)4 (P ∧ P) 2][BF 4]· xCH2Cl2 (x = 1.47), the only difference being the presence of the unusual [B2F7]− anion. This may be justified by partial decomposition of HBF4, as already reported in the literature.18 Both the 1H and 31P{1H} NMR spectra of [HPt4(CO)4(P∧P)2]+ recorded at 298 K in CD2Cl2 indicate that the compound is fluxional at this temperature. Thus, the 1 H NMR spectrum (Figure 2) shows a resonance centered at δ −2.40 ppm composed of several lines, due to the coupling of the hydride with four equivalent Pt atoms (avJPtH = 286 Hz) and four equivalent P atoms (avJPH = 37 Hz). This assignment has been corroborated by simulating the 1H NMR spectrum with

2. RESULTS AND DISCUSSION 2.1. Synthesis of [HnPt4(CO)4(P∧P)2]n+ (n = 0−2; P∧P = CH2C(PPh2)2). The neutral compound Pt4(CO)4(P∧P)2 (P∧P = CH2C(PPh2)2) can be obtained from the reaction of [Pt12(CO)24]2− with ca. 1.5 equiv of P∧P in acetone in accord with eq 1: 4[Pt12(CO)24 ]2 − + 6P∧P → 4[Pt 9(CO)18 ]2 − + 3Pt4(CO)4 (P∧P)2 + 12CO

31

(1)

Thus, after addition of P∧ P, the green solution of [Pt12(CO)24]2− turns red in agreement with formation of [Pt9(CO)18]2− and the scarcely soluble Pt4(CO)4(P∧P)2 starts to separate out as an orange microcrystalline solid. The reaction is complete after 2 days, and complete precipitation of Pt4(CO)4(P∧P)2 may be accomplished by addition of dmf to the acetone solution. Under these conditions, [Pt9(CO)18]2− remains in solution, as indicated by IR spectroscopy, and the two compounds can be easily separated by filtration. Conversely, crystals of Pt4(CO)4(P∧P)2 suitable for X-ray analyses can be obtained by slow diffusion of n-hexane into an acetone solution. Pt4(CO)4(P∧P)2 is almost insoluble in polar solvents such as CH3CN and dmf, scarcely soluble in less polar solvents such as acetone and thf, and partially soluble in CH2Cl2 (solubility 1.8 × 10−3 mol/L). Crystals of Pt4(CO)4(P∧P)2 display ν(CO) bands at 1979 (s) and 1954 (m) cm−1 in Nujol mull as well as CH2Cl2 solution, in agreement with the presence of only terminal CO ligands. The 31P{1H} NMR spectrum of Pt4(CO)4(P∧P)2 recorded at 298 K in CD2Cl2 displays a 5181


Organometallics

Article

Scheme 2

Figure 3. 31P{1H} NMR spectra of [HPt4(CO)4(P∧P)2]+ in CD2Cl2 at (a) 298 K and (b) 173 K.

Figure 2. 1H NMR spectra of [HPt4(CO)4(P∧P)2]+ in CD2Cl2 at (a) 298 K and (b) 173 K (* instrumental spike).

Scheme 3 the program gNMR 5.0.6.0 (Figure S.1 in the Supporting Information).19 The JPtH and JPH values are lower than those expected for a direct coupling, since the larger 1JPtH and 2JPH coupling constants are time-averaged with smaller multiplebond coupling constants.4,5,6d,13−17 Unfortunately, it has not been possible to freeze the fluxionality even at low temperature and, thus, to fully assign all the coupling constants of this AA′BB′MXX′YY′ system (A and B are P atoms, M is H, and X and Y are Pt atoms). Similarly, the 31P{1H} NMR spectrum recorded at 298 K displays a single resonance at 16.8 ppm with 1JPtP = 3010 Hz, whereas the other coupling constants could not be resolved (Figure 3). Coalescence in the 31P{1H} NMR spectrum is observed only at 183 K, and at 173 K two very broad resonances start to appear at δP 6.4 and 23.4 ppm. Conversely, the 1H NMR spectrum at 173 K is still fluxional and shows a pattern similar to that observed at 298 K, only much broader. Considering that both Pt4(CO)4(P∧P)2 and [H2Pt4(CO)4(P∧P)2]2+ (see below) are not fluxional, it is possible to conclude that the dynamic behavior observed for [HPt4(CO)4(P∧P)2]+ is due to the movement of the hydride ligand from one edge to the other of the tetrahedron without losing the Pt−P interaction (Scheme 3). In agreement with this, the JPtH and JPH values are averaged at 298 K as are the δP values, whereas 1JPtP seems not to be affected by the exchange. Further addition of HBF4·Et2O to [HPt4(CO)4(P∧P)2]+ results in the formation of the dihydride dication [H2Pt4(CO)4(P∧P)2]2+ (ν(CO) 2083 (s) cm−1 in CH2Cl2) (Scheme 1). As expected, the ν(CO) stretchings are moved toward higher wavenumbers after each protonation step, in

view of the increased positive charge. Complete formation of [H2Pt4(CO)4(P∧P)2]2+ requires 3−4 equiv of HBF4·Et2O/mol of the neutral precursor Pt4(CO)4(P∧P)2. In addition, the bisprotonated cluster is completely soluble in CH2Cl2 and has been fully characterized by means of IR and 1H and 31P NMR spectroscopy. Moreover, crystals of [H2Pt4(CO)4(P∧P)2][(BF4)2H]2 suitable for X-ray studies have been obtained by slow diffusion of n-hexane into a CH2Cl2 solution. The [(BF4)2H]− anion20 present in the solid state structure of [H2Pt4(CO)4(P∧P)2][(BF4)2H]2 is the result of the formation 5182


Organometallics

Article

of an adduct between BF4− and unreacted HBF4, in accord with eq 2:

and the two-bond Pt atoms (H−Pt−Pt ca. 90°).13−17 Conversely, the relatively large value of 2JPH (64 Hz) is in keeping with the nearly trans arrangement of the two atoms found in the solid-state structure (H−Pt−P ca. 160°).13−17 The 31P{1H} NMR spectrum in CD2Cl2 at 298 K displays a unique complex resonance at δP 4.6 with 1JPtP = 3178 Hz. Due to the complexity of the system and the poor resolution of the spectrum, it has not been possible to determine the smaller coupling constants. It is noteworthy that, difference from the case for [HPt4(CO)4(P∧P)2]+, both 1H and 31P{1H} NMR spectra of [H2Pt4(CO)4(P∧P)2]2+ are not fluxional, as was found also for the neutral Pt4(CO)4(P∧P)2. This suggests that the fluxionality observed for [HPt4(CO)4(P∧P)2]+ is due to its unsymmetrical structure. Finally, it must be noted that the 31P NMR chemical shift of the P∧P ligand coordinated to the cluster is shifted toward lower frequencies of ca. 12 ppm after each protonation step: i.e., Pt4(CO)4(P∧P)2, δP 28.1 ppm; [HPt4(CO)4(P∧P)2]+, δP 16.8 ppm (averaged resonance); [H2Pt4(CO)4(P∧P)2]2+, δP 4.6 ppm. Moreover, the low-temperature 31P NMR spectrum of [HPt4(CO)4(P∧P)2]+ shows two separate resonances at δP 23.4 and 6.4 ppm. In view of the chemical shifts shown by the neutral and dicationic clusters, the resonance at δP 6.4 ppm may be assigned to the P atoms bonded to the protonated Pt−Pt edge (see Scheme 1), whereas the resonance at δP 23.4 is attributable to the P atoms attached to the nonprotonated edge of the tetrahedron. 2.3. Crystal Structures of Pt4(CO)4(P∧P)2, [HPt4(CO)4(P∧P)2]+, and [H2Pt4(CO)4(P∧P)2]2+. The molecular structure of the Pt4(CO)4(P∧P)2 neutral cluster has been crystallographically determined (Figure 5 and Table 1). The asymmetric unit of the unit cell contains half of a cluster molecule located on a 2-fold axis.

Pt4(CO)4 (P∧P)2 + 4HBF4 → [H 2Pt4(CO)4 (P∧P)2 ]2 + + 2[(BF4 )2 H]−

(2)

The 1H NMR spectrum of [H2Pt4(CO)4(P∧P)2]2+ shows the resonances of the P∧P ligands, as expected, at 7.1−8.1 ppm (40H, Ph) and 6.36 ppm (4H, CH2, broad multiplet). In addition, there is a broad resonance at δH 9.52 ppm attributable to the [(BF4)2H]− anion and a complex multiplet at −4.00 ppm due to the hydride ligands (1JPtH = 579 Hz; 2JPtH = 25 Hz; 2JPH = 64 Hz; 3JPH = 11 Hz) (Figure 4). The cluster contains four P

Figure 4. (a) 1 H and (b) 3 1 P{ 1 H} NMR spectra of [H2Pt4(CO)4(P∧P)2]2+ in CD2Cl2 at 298 K (* instrumental spike). Figure 5. Molecular structure of Pt4(CO)4(P∧P)2 (Pt, purple; P, orange; C, gray, O, red; H, white). H atoms bonded to Ph rings have been omitted for clarity.

atoms, two hydrides, and four Pt atoms which are chemically equivalent but not magnetically equivalent, resulting in a very complex AA′A″A‴MM′XX′X″X‴ second-order system (A = P, M = H, X = Pt). Simulation of the 1H NMR spectrum with the above parameters (Figure S.2 in the Supporting Information) supports the assignment of the coupling constants. Their values are in keeping with those reported for other Pt-containing clusters with bridging hydrides.6d,13,15−17,21 In particular, 1JPtH (579 Hz) displays the typical value for a direct H−Pt coupling in μ-H hydride clusters, whereas the lower value of 2JPtH (25 Hz) is in accord with the nearly cis arrangement of the hydride

The cluster consists of a tetrahedral Pt4 core elongated along its C2 axis. The two edges of the elongated tetrahedron perpendicular to the C2 axis are bridged by two P∧P ligands, and the coordination sphere of the cluster is completed by four terminal CO ligands, one for each Pt atom. The six Pt−Pt contacts are divided into three sets consisting of two bonds each. The shortest contacts are those bridged by the P∧P 5183


Organometallics

Article

Table 1. Main Bond Distances (Å) of Pt4(CO)4P∧P)2, [HPt4(CO)4(P∧P)2]+, and [H2Pt4(CO)4(P∧P)2]2+

Pt1−Pt2 Pt3−Pt4 Pt1−Pt4 Pt2−Pt3 Pt1−Pt3 Pt2−Pt4 Pt1−P1 Pt2−P2 Pt3−P3 Pt4−P4 Pt1−H1 Pt2−H1 Pt3−H2 Pt4−H2 Pt1−C1 Pt2−C2 Pt3−C3 Pt4−C4 C1−O1 C2−O2 C3−O3 C4−O4 C5−C6 C7−C8

Pt4(CO)4(P∧P)2

[HPt4(CO)4(P∧P)2]+

[H2Pt4(CO)4(P∧P)2]2+

2.6110(8) 2.6110(8) 2.5932(8) 2.5932(8) 3.0339(11) 3.0947(11) 2.259(3) 2.281(3) 2.259(3) 2.281(3)

2.8246(6) 2.6034(6) 2.5992(7) 2.6062(6) 3.0375(6) 3.0470(7) 2.265(3) 2.261(3) 2.278(3) 2.284(3) 1.64(4) 1.64(4)

1.838(16) 1.869(16) 1.838(16) 1.869(16) 1.159(17) 1.129(17) 1.159(17) 1.129(17) 1.328(18) 1.328(18)

1.878(13) 1.884(14) 1.852(14) 1.824(14) 1.157(12) 1.140(13) 1.135(13) 1.152(13) 1.332(13) 1.306(13)

2.8406(8) 2.8192(10) 2.5922(9) 2.6138(9) 3.1356(9) 3.0378(9) 2.272(3) 2.256(4) 2.270(4) 2.271(4) 1.67(7) 1.67(7) 1.63(7) 1.63(7) 1.901(18) 1.932(15) 1.941(17) 1.866(16) 1.159(19) 1.118(16) 1.114(18) 1.161(18) 1.32(2) 1.328(19)

[HPt 4 (CO) 4 (P ∧ P) 2 ][BF 4 ]·xCH 2 Cl 2 (x = 1.47) and [HPt4(CO)4(P∧P)2][B2F7] salts. Since the two salts contain exactly the same molecular cluster, only the structure of the latter will be discussed in detail (Figure 6 and Table 1), whereas the CIF file of [HPt4(CO)4(P∧P)2][BF4]·xCH2Cl2 (x = 1.47) has been deposited in the Supporting Information for completeness. The asymmetric unit of the unit cell of [HPt4(CO)4(P∧P)2][B2F7] contains one cluster cation and one [B2F7]− anion (all located on general positions). Some examples of the latter anion have been previously reported in the literature.18 [HPt4(CO)4(P∧P)2]+ mainly differs from the parent Pt4(CO)4(P∧P)2 cluster because of the presence of a μH bridging the Pt1−Pt2 edge, resulting in its elongation (2.8246(6) Å) in comparison to that in the neutral molecule (2.6110(8) Å). All of the other Pt−Pt contacts are almost unchanged in comparison to the neutral cluster (see Table 1), resulting in a significant asymmetry between Pt 1 −Pt 2 (2.8246(6) Å) and Pt3−Pt4 (2.6034(6) Å). Elongation of M−M bonds after addition of a μ-H ligand is normally found in polynuclear compounds and has been explained on the basis of theoretical considerations.22

ligands (Pt1−Pt4 and Pt2−Pt3 = 2.5932(8) Å) and perpendicular to the elongation axis. The two bonds almost parallel to the C2 axis (Pt1−Pt2 and Pt3−Pt4 = 2.6110(8) Å) have intermediate values. These are very important in order for an understanding of the structures of the protonated clusters, since the hydride ligands are added to these two edges. Conversely, the two diagonals of the elongated tetrahedron (Pt1−Pt3= 3.0339(11) Å; Pt2−Pt4 = 3.0947(11) Å) are the loosest Pt−Pt contacts. As discussed in the Introduction, these Pt−Pt contacts of ca. 3.03− 3.10 Å have been sometimes considered bonding in some of the literature reports and nonbonding in others.2−6,8 In our opinion, on the basis of the structures and bonding parameters of the clusters [Pt3n(CO)6n]2− (n = 2−8),8 they should be considered as chemical bonds, even if they are looser than those well below 3 Å and, thus, the Pt4(CO)4(P∧P)2 cluster contains six Pt−Pt bonds as expected for a tetrahedron. This is also in agreement with the fact that it possesses 56 CVE as predicted for a Pt4 tetrahedral cluster on the basis of theoretical considerations.9 The molecular structure of the monohydride monocationic cluster [HPt4(CO)4(P∧P)2]+ has been determined as its 5184


Organometallics

Article

In conclusion, by considering the molecular structures of the three [HnPt4(CO)4(P∧P)2]n+ (n = 0−2) clusters it is noteworthy that they possess the same Pt4(CO)4(P∧P)2 core, to which are then added the two hydride ligands without any major structural rearrangement. The bridging hydrides are added to the two Pt−Pt edges parallel to the C2 elongation axis of the Pt4 tetrahedron. As a result, these edges are elongated by ca. 0.2 Å after the addition of the hydrides, whereas all other bonding parameters remain almost unchanged. 2.3. Reactions of [Pt12(CO)24]2− with Other Diphosphines. The reaction of [Pt12(CO)24]2− in acetone with ca. 2 equiv of CH2(PPh2)2 (dppm) results in the formation of a dark red-purple precipitate of Pt6(CO)6(dppm)3 and a red solution containing [Pt9(CO)18]2−, in accord with eq 3: 2[Pt12(CO)24 ]2 − + 3dppm

Figure 6. Molecular structure of [HPt4(CO)4(P∧P)2]+ (Pt, purple; P, orange; C, gray, O, red; H, white). H atoms bonded to Ph rings have been omitted for clarity.

→ 2[Pt 9(CO)18 ]2 − + Pt6(CO)6 (dppm)3 + 6CO

(3)

The nature of the two compounds has been confirmed by comparing their IR data with those reported in the literature.8,14 They may be separated by filtration and the solid dissolved in CH2Cl2, where it displays ν(CO) bands at 1836 (w), 1795 (s), and 1751 (m) cm − 1 , as previously reported for Pt6(CO)6(dppm)3.14 Since the structure of this neutral cluster was not reported before in the literature, crystals suitable for Xray analyses have been obtained by slow diffusion of n-hexane into a CH2Cl2 solution and the structure determined by X-ray crystallography (Figure 8 and Table 2). The crystals of

The molecular structure of the dihydride dicationic cluster [H2Pt4(CO)4(P∧P)2]2+ (Figure 7 and Table 1) has been

Figure 7. Molecular structure of [H2Pt4(CO)4(P∧P)2]2+ (Pt, purple; P, orange; C, gray, O, red; H, white). H atoms bonded to Ph rings have been omitted for clarity.

Figure 8. Molecular structure of Pt6(CO)6(dppm)3 (Pt, purple; P, orange; C, gray, O, red). H-atoms have been omitted for clarity.

determined as its [H2Pt4(CO)4(P∧P)2][(BF4)2H]2 salt. This contains the unusual [(BF4)2H]− H-bonded anion.20 The asymmetric unit of the unit cell contains one cluster cation and two [(BF4)2H]− anions (all located on general positions). The presence of two [(BF4)2H]− anions is clearly established by the short F···F distances (2.672(17) and 2.575(15) Å, respectively) between the two BF4− groups of each dimeric anion. A few other examples of the presence of this anion were identified by a search in the Cambridge Structural Database.20 The dihydride dicationic cluster [H2Pt4(CO)4(P∧P)2]2+ is obtained from the monohydride monocation by addition of a second μ-H ligand on Pt3−Pt4. This restores the symmetrical structure of the Pt4(CO)4(P∧P)2 parent neutral cluster, with the six Pt−Pt bonds equivalent two by two. With regard to the Pt− Pt contacts, the main difference in comparison to the neutral cluster is that both Pt1−Pt2 (2.8406(8) Å) and Pt3−Pt4 (2.8192(10) Å) are considerably elongated because of the presence of the bridging hydrides, whereas all other Pt−Pt bonds are almost unchanged.

Pt6(CO)6(dppm)3 display ν(CO) bands in Nujol mull at 1832 (w), 1787 (s), 1775 (m), and 1763 (m) cm−1. The crystal structure of Pt6(CO)6(dppm)3 fully confirms that proposed in the original paper,14 and the cluster is isostructural with the palladium analogue.23 It is composed of a Pt6 trigonal-prismatic core possessing D3h symmetry, to which are coordinated six μCO ligands bridging intratriangular Pt−Pt edges and three μdppm ligands bridging the six intertriangular edges of the prism. The structure of the cluster and the bonding parameters closely resemble those of [Pt6(CO)12]2−.8 The reaction of [Pt12(CO)24]2− in acetone with increasing amounts of o-C6H4(PPh2)2 (dppb) is apparently similar to that described above for dppm, but it results in different products. Thus, after the addition of a few equivalents of dppb, an orange precipitate starts to separate out and the solution turns from green to red, in agreement with the transformation of [Pt12(CO)24]2− into [Pt9(CO)18]2−. The reaction is fully accomplished after the addition of ca. 8−10 equiv of dppb. 5185


Organometallics

Article

Table 2. Main Bond Distances (Å) of Pt6(CO)6(dppm)3 in Comparison to Those of [Pt6(CO)12]2− Pt6(CO)6(dppm)3 [Pt6(CO)12]2− a a

Pt−Pt intratriangular

Pt−Pt intertriangulara

Pt−P

2.6427(5)−2.6945(5), av 2.6748(12) 2.644(7)−2.659(3), av 2.653(10)

3.0159(5)−3.1048(5), av 3.0567(9) 3.026(16)−3.049(17), av 3.03(3)

2.248(2)−-2.273(2), av 2.260(5)

From ref 8.

The solid was separated by filtration, dried under vacuum, and dissolved in CH2Cl2, where it surprisingly did not display any ν(CO) band. Thus, in order to shed some light on its nature, crystals suitable for X-ray analyses were grown by slow diffusion of n-hexane into a CH2Cl2 solution, showing that it consists of a tetrahedral Pt(dppb)2 complex (Figure 9 and Table 3). Its formation may be explained by eq 4.

cluster, affording the [Pt(dppb)2]2+ cation. The major product, [NBu4]2[Pt9(CO)18], has been identified by comparing its unit cell to that reported in the literature,8 whereas the structure of [Pt(dppb)2][Pt9(CO)18]·2CH3COCH3 has been fully determined by X-ray crystallography (Figure 10 and Table 3). The

Figure 9. Molecular structure of Pt(dppb)2 (Pt, purple; P, orange; C, gray, O, red). H atoms have been omitted for clarity.

Table 3. Main Bond Distances (Å) and Angles (deg) of Pt(dppb)2 and [Pt(dppb)2][Pt9(CO)18] (a) Pt(dppb)2 and the [Pt(dppb)2]2+ Cation of [Pt(dppb)2][Pt9(CO)18] Pt−P

dppb bite angle

2.2750(6)−2.3044(6), av 84.23(2) and 86.99(2), av 2.2870(12) 85.61(3) [Pt(dppb)2]2+ 2.325(8)−2.329(10), av 83.0(3)−83.5(3), av 2.33(2) 83.2(6) (b) [Pt9(CO)18]2− Anion of [Pt(dppb)2][Pt9(CO)18] Pt(dppb)2

Pt−Pt intratriangular [Pt9(CO)18]2−

2.642(2)−2.670(2), av 2.654(6)

2−

[Pt12(CO)24 ]

Figure 10. Molecular structures of (a) the [Pt(dppb)2]2+ cation and (b) the [Pt9(CO)18]2− anion present in the [Pt(dppb)2][Pt9(CO)18]· 2CH3COCH3 salt (Pt, purple; P, orange; C, gray, O, red). H atoms have been omitted for clarity.

Pt−Pt intertriangular 3.010(2)−3.066(3), av 3.042(6)

salt consists of a square-planar [Pt(dppb)2]2+ cation and a trigonal-prismatic [Pt9(CO)18]2− anion. The latter displays the same structure previously found in its [NR4]+ salts.8 With regard to the cation, this has not been reported before, but it presents a square-planar structure as found in several [Pt(LL)2]2+ complexes.28 The same structure has been found in other [M(dppb)2]n+ complexes containing d8 ions such as Rh+ and Ni2+.29

+ 6dppb

→ [Pt 9(CO)18 ]2 − + 3Pt(dppb)2 + 6CO

(4)

The Pt(dppb)2 complex shows a tetrahedral structure, as expected for a zerovalent Pt(LL)2 complex.24,25 The same structure has been previously found in other M(dppb)2 complexes containing d10 ions such as Ni(0), Cu(I), Ag(I), and Au(I).26,27 In agreement with eq 4, formation of Pt(dppb)2 requires 6 equiv of dppb. Since a slight excess of phosphine was added, in order to understand the fate of the dppb, we layered n-hexane into a red acetone solution of [Pt9(CO)18]2−. After slow diffusion, this resulted in the formation of crystals of [NBu4]2[Pt9(CO)18] (major product) and very few crystals of [Pt(dppb)2][Pt9(CO)18]·2CH3COCH3. Probably, the unreacted dppb remains in solution and, in conjunction with the presence of traces of air, it forces the partial oxidation of the

3. CONCLUSIONS In conclusion, we have reported the synthesis and crystal structure of a rare case of a tetrahedral Pt−CO cluster: i.e., Pt4(CO)4(P∧P)2. This neutral species is readily protonated by strong acids, affording cationic hydride clusters which retain the same tetrahedral geometry of the Pt 4 core: i.e., [HPt4(CO)4(P∧P)2]+ and [H2Pt4(CO)4(P∧P)2]2+. Cationic carbonyl clusters containing hydride ligands directly attached to metals are less well known as either/both the positive charge on the cluster increases or/and the size of the cluster 5186


Organometallics

Article

increases. 1 3 The structure and hydride nature of [HnPt4(CO)4(P∧P)2]n+ (n = 1, 2) has been corroborated by multinuclear NMR spectroscopy and directly confirmed by Xray crystallography, thanks to the limited nuclearity of these clusters.30,31 Pt 4 (CO) 4 (P ∧ P) 2 has been obtained by reacting [Pt12(CO)24]2− with the peculiar P∧P bidentate phosphine.12 The reaction is likely to proceed via the addition of P∧P to [Pt 1 2 (CO) 2 4 ] 2 − followed by elimination of some Pt3(CO)x(P∧P)y fragments that rapidly rearrange to give Pt4(CO)4(P∧P)2, which separates out, leaving the homoleptic anionic [Pt9(CO)18]2− cluster in solution. Competition between CO substitution and M−M bond cleavage is a general issue when carbonyl clusters are reacted with phosphines.32,33 Moreover, the reaction of [Pt3n(CO)6n]2− (n = 2−6) with the monodentate PPh3 has been recently discussed in detail,34 showing that up to three CO ligands may be replaced by PPh3, leading to the formation of miscellaneous [Pt3n(CO)6n−m(PPh3)m]2− (m = 1−3) clusters, before elimination of Pt3(CO)3(PPh3)3 occurs, leading to lower nuclearity [Pt3(n−1)(CO)6(n−1)]2− species. In the present paper, we have employed various bidentate phosphines and, even if they lead to different products, in all of the cases considered no substituted anionic clusters have been isolated. It seems, therefore, that bidentate phosphines favor the elimination of neutral Pt/CO/PP complexes or clusters with the concomitant formation of the homoleptic [Pt9(CO)18]2− anionic cluster. In addition, it seems that the use of the peculiar P∧P ligands is of paramount importance in order to obtain the tetrahedral cluster, since all other bidentate phosphines employed lead to completely different species. Finally, as pointed out in the Introduction and during the discussion of the structures of [HnPt4(CO)4(P∧P)2]n+ (n = 1, 2), some caution must be used when dealing with tetranuclear Pt clusters. [HnPt4(CO)4(P∧P)2]n+ (n = 1, 2) show the expected electron count for a Pt tetrahedron (56 CVE), but two Pt−Pt contacts display distances (3.03−3.10 Å) which have sometime been considered in the literature to be nonbonding.2−6,8,34 This is in contrast with the bonding Pt−Pt intratriangular contacts (3.02−3.10 Å) observed in several [Pt3n(CO)6n]2− (n = 2−8) clusters.8,34 If these distances are considered as (at least weak) bonds, the structures of some previously reported butterfly clusters (58 CVE) might be revised and considered as (at least incipient) tetrahedra. Even if they are apparently simple systems, tetranuclear Pt4 clusters seem to require further experimental and theoretical investigations in order to fully understand their structural and bonding properties.

H3PO4 (85% in D2O). Structure drawings have been performed with SCHAKAL99.35 4.2. Synthesis of Pt4(CO)4(P∧P)2. P∧P (0.095 g, 0.240 mmol) was added as a solid to a solution of [NBu4]2[Pt12(CO)24] (0.70 g, 0.200 mmol) in acetone (20 mL) and the mixture stirred at room temperature for 2 days. At this point, an orange precipitate of Pt4(CO)4(P∧P)2 started to form and the precipitation was completed by addition of dmf (20 mL). The solid was recovered by filtration, washed with CH3CN (2 × 20 mL), and dried under vacuum (yield 0.18 g, 18% based on Pt). Crystals of Pt4(CO)4(P∧P)2 suitable for Xray analyses have been obtained directly from the acetone solution by slow diffusion of n-hexane (40 mL). Anal. Calcd for C56H44O4P4Pt4 (1685.15): C, 39.91; H, 2.63; Pt, 46.31. Found: C, 39.74; H, 2.89; Pt, 46.05. IR (Nujol, 293 K): ν(CO) 1979 (s), 1954 (m) cm−1. IR (CH2Cl2, 293 K): ν(CO) 1979 (s), 1954 (m) cm−1. 1H NMR (CD2Cl2, 298 K): δ (ppm) 7.1−7.8 (m, 40H, Ph), 5.56 (m, 4H, CH2). 31P{1H} NMR (CD2Cl2, 298 K): δ (ppm) 28.1 (m, 1JPtP = 2406 Hz; 2JPtP = 696, 570, and 104 Hz; JPP = 25 and 60 Hz). 4.3. Synthesis of [HPt4(CO)4(P∧P)2][BF4]·xCH2Cl2 (x = 1.47). HBF4·Et2O (0.029 g, 0.179 mmol) was added to a solution of Pt4(CO)4(P∧P)2 (0.256 g, 0.152 mmol) in CH2Cl2 (20 mL), and the mixture was stirred at room temperature for 2 h. Then, the solution was filtered and the filtrate layered with n-hexane (40 mL), resulting in orange crystals of [HPt4(CO)4(P∧P)2][BF4]·xCH2Cl2 (x = 1.47) suitable for X-ray crystallography (yield 0.257 g, 89% based on Pt). It must be remarked that sometimes a few crystals of [HPt4(CO)4(P∧P)2][B2F7] were obtained as a side product due to the accidental formation of [B2F7]−. Anal. Calcd for C57.47H47.93BCl2.93F4O4P4Pt4 (1897.39): C, 36.38; H, 2.55; Pt, 41.12. Found: C, 36.65; H, 2.19; Pt, 41.46. IR (Nujol, 293 K): ν(CO) 2049 (w), 2044 (w), 2020 (s), 2009 (w) cm−1. IR (CH2Cl2, 293 K): ν(CO) 2057 (w), 2043 (w), 2030 (s), 2008 (w) cm−1. 1H NMR (CD2Cl2, 298 K): δ (ppm) 7.0−8.0 (m, 40H, Ph), 6.00 (m, 4H, CH2), −2.40 (m, 1H, avJPtH = 286 Hz, avJPH = 37 Hz, μ-H).31P{1H} NMR (CD2Cl2, 298 K): δ (ppm) 16.8 (m, 1JPtP = 3010 Hz). 31P{1H} NMR (CD2Cl2, 173 K): δ (ppm) 6.4 (br), 23.4 (br). 4.4. Synthesis of [H2Pt4(CO)4(P∧P)2][(BF4)2H]2. HBF4·Et2O (0.105 g, 0.651 mmol) was added to a solution of Pt4(CO)4(P∧P)2 (0.256 g, 0.152 mmol) in CH2Cl2 (20 mL) and the mixture stirred at room temperature for 2 h. Then, the solution was filtered and the filtrate layered with n-hexane (40 mL), resulting in orange crystals of [H2Pt4(CO)4(P∧P)2][(BF4)2H]2 suitable for X-ray crystallography (yield 0.282 g, 91% based on Pt). Anal. Calcd for C56H48B4F16O4P4Pt4 (2036.42): C, 33.03; H, 2.38; Pt, 38.32. Found: C, 32.89; H, 2.26; Pt, 38.48. IR (Nujol, 293 K): ν(CO) 2080 (sh), 2077 (s) cm−1. IR (CH2Cl2, 293 K): ν(CO) 2083 (s) cm−1. 1H NMR (CD2Cl2, 298 K): δ (ppm) 9.52 (br, 2H [(BF4)2H]−), 7.1−8.1 ppm (m, 40H, Ph), 6.36 ppm (m, 4H, CH2), −4.00 ppm (m, 2H, 1JPtH = 579 Hz, 2JPtH = 128 Hz, 2JPH = 64 Hz, 3JPH = 11 Hz, μ-H). 31P{1H} NMR (CD2Cl2, 298 K): δ (ppm) 4.6 (m, 1JPtP = 3178 Hz). 4.5. Synthesis of Pt6(CO)6(dppm)3. dppm (0.177 g, 0.460 mmol) was added to a solution of [NBu4]2[Pt12(CO)24] (0.70 g, 0.200 mmol) in acetone (20 mL) and the mixture stirred at room temperature for 2 h. At this point, an orange precipitate of Pt6(CO)6(dppm)3 started to form and the precipitation was completed by addition of dmf (20 mL). The solid was recovered by filtration, washed with CH3CN (2 × 20 mL), and dried under vacuum (yield 0.20 g, 20% based on Pt). Crystals of Pt6(CO)6(dppm)3 suitable for X-ray analyses have been obtained directly from the acetone solution by slow diffusion of nhexane (40 mL). Anal. Calcd for C81H66O6P6Pt6 (2491.70): C, 39.04; H, 2.67; Pt, 46.97. Found: C, 39.51; H, 2.97; Pt, 47.11. IR (Nujol, 293 K): ν(CO) 1832 (m), 1787 (s), 1775 (m), 1763 (m) cm−1. IR (CH2Cl2, 293 K): ν(CO) 1836 (w), 1795 (s), 1751 (m) cm−1. 4.6. Synthesis of Pt(dppb)2 and [Pt(dppb)2][Pt9(CO)18]· 2CH3COCH3. dppb (0.901 g, 2.02 mmol) was added to a solution of [NBu4]2[Pt12(CO)24] (0.70 g, 0.200 mmol) in acetone (20 mL) and the mixture stirred at room temperature for 2 h. At this point, an

4. EXPERIMENTAL SECTION 4.1. General Procedures. All reactions and sample manipulations were carried out using standard Schlenk techniques under nitrogen and in dried solvents. All the reagents were commercial products (Aldrich) of the highest purity available and were used as received, except for [NBu4]2[Pt12(CO)24], which has been prepared according to the literature.8 The analysis of Pt was performed by atomic absorption on a Pye-Unicam instrument. Analyses of C, H, and N were obtained with a ThermoQuestFlashEA 1112NC instrument. IR spectra were recorded on a Perkin-Elmer SpectrumOne interferometer in CaF2 cells. 1H and 31P{1H} NMR measurements were performed on a Varian Mercury Plus 400 MHz instrument. The proton chemical shifts were referenced to the residual protons of the deuterated solvents, whereas the phosphorus chemical shifts were referenced to external 5187


Organometallics

Article

previously reported in the literature. Similar U restraints (su 0.01) were applied to the C atoms. The C and O atoms of the CO ligands, as well as some C atoms of the Ph groups of dppb, have been restrained to an isotropic-like behavior (ISOR line in SHELXL; su 0.01). The acetone molecules have been restrained to have similar geometries (SAME line in SHELXL; su 0.02). Restraints to bond distances were applied as follows (su 0.01): 1.51 Å for C−C and 1.21 Å for C−O in CH3COCH3.

orange precipitate of Pt(dppb)2 started to form and this was separated from the red solution by filtration. The acetone solution was layered with n-hexane (40 mL), resulting in a mixture of crystals of [NBu4]2[Pt9(CO)18] (major product) and [Pt(dppb)2][Pt9(CO)18]· 2CH3COCH3 (a few crystals). The solid was dissolved in CH2Cl2 (20 mL), and crystals of Pt(dppb)2 have been obtained after slow diffusion of n-hexane (yields 0.18 g, 7% based on Pt). 4.7. X-ray Crystallographic Study. Crystal data and collection details for Pt4(CO)4(P∧P)2, [HPt4(CO)4(P∧P)2][BF4]·xCH2Cl2 (x = 1.47), [HPt4(CO)4(P∧P)2][B2F7], [H2Pt4(CO)4(P∧P)2][(BF4)2H]2, Pt 6 (CO) 6 (dppm) 3 , Pt(dppb) 2 , and [Pt(dppb) 2 ][Pt 9 (CO) 18 ]· 2CH3COCH3 are reported in Table S.1 in the Supporting Information. The diffraction experiments were carried out on a Bruker APEX II diffractometer equipped with a CCD detector using Mo Kα radiation. Data were corrected for Lorentz−polarization and absorption effects (empirical absorption correction SADABS).36 Structures were solved by direct methods and refined by full-matrix least squares on the basis of all data using F2.37 Hydrogen atoms were fixed at calculated positions and refined by a riding model. All nonhydrogen atoms were refined with anisotropic displacement parameters, unless otherwise stated. Pt4(CO)4(P∧P)2. The asymmetric unit of the unit cell contains half of a cluster molecule located on a 2-fold axis. Similar U restraints (su 0.01) were applied to the C and O atoms. [HPt4(CO)4(P∧P)2][BF4]·xCH2Cl2 (x = 1.47). The asymmetric unit of the unit cell contains one cluster cation, one [BF4]− anion, and 1.47 CH2Cl2 molecules (all located on general positions). The CH2Cl2 molecules are highly disordered, and the disorder has been modeled as follows: part 1 includes a single CH2Cl2 molecule, whereas part 2 includes two independent CH2Cl2 molecules. One occupancy factor was used during the refinement, resulting in 1.47 CH2Cl2 molecules per cluster unit. Similar U restraints were applied to the C and O (su 0.01) and Cl (su 0.001) atoms. The O atoms were restrained to an isotropic-like behavior (ISOR line in SHELXL; su 0.01). The edgebridging hydride atom on the cluster cation was located in the Fourier map and refined isotropically with similar distance restraints to the two Pt atoms (SADI line in SHELXL; su 0.02). The [BF4]− anion was restrained to a tetrahedral geometry, applying appropriate SAME lines in SHELXL (su 0.02), and refined isotropically. The C−Cl bond distances in CH2Cl2 were restrained to 1.75 Å (su 0.01). [HPt4(CO)4(P∧P)2][B2F7]. The asymmetric unit of the unit cell contains one cluster cation and one [B2F7]− anion (all located on general positions). Similar U restraints (su 0.01) were applied to the C, O, and F atoms. The edge-bridging hydride atom on the cluster cation was located in the Fourier map and refined isotropically with similar distance restraints to the two Pt atoms (SADI line in SHELXL; su 0.02). [H2Pt4(CO)4(P∧P)2][(BF4)2H]2. The asymmetric unit of the unit cell contains one cluster cation and two [(BF4)2H]− anions (all located on general positions). Similar U restraints (su 0.005) were applied to the C and O atoms. The two edge-bridging hydride atoms on the cluster cation were located in the Fourier map and refined isotropically with similar distance restraints to the two Pt atoms (SADI line in SHELXL; su 0.02). The H atoms in the [(BF4)2H]− anions were initially located in the Fourier map and then refined using a riding model (AFIX 83 line in SHELXL). Their presence is corroborated by the very close F··· F contacts (see text), which are typical of the H-bonded [(BF4)2H]− anion.15 Pt6(CO)6(dppm)3. The asymmetric unit of the unit cell contains one cluster molecule located on a general position. Similar U restraints (su 0.01) were applied to the C and O atoms. Pt(dppb)2. The asymmetric unit of the unit cell contains one cluster molecule located on a general position. [Pt(dppb)2][Pt9(CO)18]·2CH3COCH3. The asymmetric unit of the unit cell contains one cluster anion, one [Pt(dppb)2]+ cation, and two acetone molecules (all located on general positions). The crystals are of very low quality, and the data have been, therefore, cut at θ = 21.97°. As a consequence, some Alert A’s are present in the Check CIF file. Nonetheless, the structures of the cluster anion and Pt(II) cation have been determined satisfactorily and compare well with those

■

ASSOCIATED CONTENT

■

AUTHOR INFORMATION

S Supporting Information *

CIF files, giving X-ray crystallographic data for the structure determinations of Pt4(CO)4(P∧P)2, [HPt4(CO)4(P∧P)2][BF4]· xCH 2 Cl 2 (x = 1.47), [HPt 4 (CO) 4 (P ∧ P) 2 ][B 2 F 7 ], [H 2 Pt 4 (CO) 4 (P ∧ P) 2 ][(BF 4 ) 2 H] 2 , Pt 6 (CO) 6 (dppm) 3 , Pt(dppb)2, and [Pt(dppb)2][Pt9(CO)18]·2CH3COCH3, Table S.1, containing crystal data and collection details for the structures described in this paper, and Figures S.1 and S.2, giving 1H NMR spectral simulations for [HPt4(CO)4(P∧P)2]+ and [H2Pt4(CO)4(P∧P)2]2+. This material is available free of charge via the Internet at http://pubs.acs.org. Corresponding Author

*S.Z.: fax, +39 0512093690; e-mail, [email protected]. Notes

The authors declare no competing financial interest.

■

ACKNOWLEDGMENTS The financial support of the MIUR (PRIN2008) and the University of Bologna is gratefully acknowledged. Funding by Fondazione CARIPLO, Project No. 2011-0289, is heartily acknowledged.

■

REFERENCES

(1) Bruno, I. J.; Cole, J. C.; Edgington, P. R.; Kessler, M.; Macrae, C. F.; McCabe, P.; Pearson, J.; Taylor, R. ConQuest, new software for searching the Cambridge Structural Database and visualising crystal structures. Acta Crystallogr. 2002, B58, 389. (2) (a) Dahmen, K.-H.; Imhof, D.; Venanzi, L. M. Helv. Chim. Acta 1994, 77, 1029. (b) Hao, L.; Vittal, J. J.; Puddephatt, R. J.; ManojlovicMuir, Lj.; Muir, K. W. J. Chem. Soc., Chem. Commun. 1995, 2381. (3) Vranka, R. G.; Dahl, L. F.; Chini, P.; Chatt, J. J. Am. Chem. Soc. 1969, 91, 1574. (4) (a) Sterenberg, B. T.; Ramachandran, R.; Puddephatt, R. J. J. Cluster Sci. 2001, 12, 49. (b) Zhang, T.; Drouin, M.; Harvey, P. D. J. Cluster Sci. 1998, 9, 165. (5) Schuh, W.; Wachtler, H.; Laschober, G.; Kopacka, H.; Wurst, K.; Peringer, P. Chem. Commun. 2000, 1181. (6) (a) Imhof, D.; Venanzi, L. M. Chem. Soc. Rev. 1994, 185. (b) Frew, A. A.; Hill, R. H.; Manojlovic-Muir, Lj.; Mui, K. W.; Puddephatt. J. Chem. Soc., Chem. Commun. 1982, 198. (c) Douglas, G.; Manojlovic-Muir, Lj.; Muir, K. W.; Jennings, M. C.; Lloyd, B. R.; Rashidi, M.; Puddephatt, R. J. J. Chem. Soc., Chem. Commun. 1988, 149. (d) Douglas, G.; Manojlovic-Muir, Lj.; Muir, K. W.; Jennings, M. C.; Lloyd, B. R.; Rashidi, M.; Schoettel, G.; Puddephatt, R. J. Organometallics 1991, 10, 3927. (7) (a) Cordero, B.; Gómez, V.; Platero-Prats, A. E.; Revés, M.; Echevarría, J.; Cremades, E.; Barragán, F.; Alvarez, S. Dalton Trans. 2008, 2832. (b) Bondi, A. J. Phys. Chem. 1964, 68, 441. (8) (a) Longoni, G.; Chini, P. J. Am. Chem. Soc. 1976, 98, 7225. (b) Calabrese, J. C.; Dahl, L. F.; Chini, P.; Longoni, G.; Martinengo, S. J. Am. Chem. Soc. 1974, 96, 2614. (c) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Mehlstäubl, M.; Zacchini, S. Chem. Commun. 2005, 46, 5769. (d) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Mehlstäubl, M.; Zacchini, S.; Ceriotti, A. Angew.

5188


Organometallics

Article

Armaroli, N.; Seguy, I.; Navarro, J.; Destruel, P.; Nierengarten, J. −F. Chem. Commun. 2007, 3027. (27) (a) Igawa, S.; Hashimoto, M.; Kawata, I.; Hoshino, M.; Osawa, M. Inorg. Chem. 2012, 51, 5805. (b) Osawa, M.; Kawata, I.; Igawa, S.; Tsuboyama, A.; Hashizume, D.; Hoshino, M. Eur. J. Inorg. Chem. 2009, 3708. (28) (a) Engelhardt, L. M.; Patrick, J. M.; Raston, C. L.; Twiss, P.; White, A. H. Aust. J. Chem. 1984, 37, 2193. (b) Nagasawa, I.; Amita, H.; Kitagawa, H. Chem. Commun. 2009, 204. (c) Tirla, C.; Mezailles, N.; Ricard, L.; Matthey, F.; Le Floch, P. Inorg. Chem. 2002, 41, 6032. (29) (a) Marshall, W. J.; Aullon, G.; Alvarez, S.; Dobbs, K. D.; Grushin, V. V. Eur. J. Inorg. Chem. 2006, 3390. (b) Miedaner, A.; Haltiwanger, R. C.; DuBois, D. L. Inorg. Chem. 1991, 30, 417. (30) (a) Zacchini, S. Eur. J. Inorg. Chem. 2011, 4125. (b) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Ranuzzi, F.; Zacchini, S.; Zanello, P.; Fedi, S. Chem. Eur. J. 2008, 14, 1924. (c) Bernardi, A.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Dalton Trans. 2009, 4245. (31) (a) Collini, D.; Fabrizi de Biani, F.; Dolznikov, D. S.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Tiozzo, C.; Zacchini, S.; Zanello, P. Inorg. Chem. 2011, 50, 2790. (b) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S.; Fedi, S.; Fabrizi de Biani, F. Eur. J. Inorg. Chem. 2012, 2243. (c) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Zacchini, S.; Fedi, S.; Fabrizi de Biani, F. Dalton Trans. 2012, 41, 4649. (32) (a) Schmid, G. , Ed. Clusters and Colloids; Wiley-VCH: New York, 1994. (b) Braunstein, P., Oro, L. A., Raithby, P. R., Eds. Metal Clusters in Chemistry; Wiley-VCH: New York, 1999. (c) Vargas, M. D.; Nicholls, J. N. Adv. Inorg. Chem. Radiochem. 1986, 30, 123. (d) Chini, P. J. Organomet. Chem. 1980, 200, 37. (e) Adams, R. D.; Captain, B. Acc. Chem. Res. 2009, 42, 409. (33) (a) Adams, R. D., Cotton, F. A., Eds. Catalysis by Di- and Polynuclear Metal Cluster Complexes; Wiley-VCH: New York, 1998. (b) Gates, B. C., Guczi, L., Knözinger, H., Eds. Metal Clusters in Catalysis; Elsevier: Amsterdam, 1986. (c) Shriver, D. F., Kaesz, H. D., Adams, R. D., Eds. The Chemistry of Metal Cluster Complexes, VCH: New York, 1990. (34) Ciabatti, I.; Femoni, C.; Iapalucci, M. C.; Longoni, G.; Lovato, T.; Zacchini, S. Inorg. Chem. 2013, 52, 4384. (35) Keller, E. SCHAKAL99; University of Freiburg, Freiburg, Germany, 1999. (36) Sheldrick, G. M. SADABS, Program for empirical absorption correction; University of Göttingen, Göttingen, Germany, 1996. (37) Sheldrick, G. M. SHELX97, Program for crystal structure determination; University of Göttingen, Göttingen, Germany, 1997.

Chem., Int. Ed. 2006, 45, 2060. (e) Femoni, C.; Kaswalder, F.; Iapalucci, M. C.; Longoni, G.; Zacchini, S. Eur. J. Inorg. Chem. 2007, 1483. (f) Femoni, C.; Iapalucci, M. C.; Longoni, G.; Lovato, T.; Stagni, S.; Zacchini, S. Inorg. Chem. 2010, 49, 5992. (9) (a) Mingos, D. M. P. Introduction to Cluster Chemistry; Prentice Hall: Englewood Cliffs, NJ, 1990. (b) Evans, D. G.; Mingos, D. M. P. J. Organomet. Chem. 1982, 240, 321. (c) Evans, D. G. J. Organomet. Chem. 1987, 319, 265. (10) Frost, P. W.; Howard, J. A. K.; Spencer, J. L.; Turner, D. G.; Gregson, D. J. Chem. Soc., Chem. Commun. 1981, 1104. (11) Goodfellow, R. J.; Hamon, E. M.; Howard, J. A. K.; Spencer, J. L.; Turner, D. G. J. Chem. Soc., Chem. Commun. 1984, 1604. (12) (a) Schmidbaur, H.; Herr, R.; Müller, G.; Riede, J. Organometallics 1985, 4, 1208. (b) Mayer, T.; Parsa, E.; Böttcher, H.-C. J. Organomet. Chem. 2011, 696, 3415. (13) Heaton, B. T.; Iggo, J. A.; Podkorytov, I. S.; Ponomarenko, V. I.; Selivanov, S. I.; Tunik, S. P. Inorg. Chim. Acta 2010, 363, 549. (14) Hao, L.; Spivak, G. J.; Xao, J.; Vittal, J. J.; Puddephatt, R. J. J. Am. Chem. Soc. 1995, 117, 7011. (15) (a) Ara, I.; Falvello, L. R.; Forniés, J.; Lalinde, E.; Martı ́n, A.; Martínez, F.; Moreno, M. T. Organometallics 1997, 16, 5392. (b) Ramachandran, R.; Yang, D.-S.; Payne, N. C.; Puddephatt, R. J. Inorg. Chem. 1992, 31, 4236. (c) Feguson, G.; Lloyd, B. R.; Puddephatt, R. J. Organometallics 1986, 5, 344. (16) (a) Béni, Z.; Ros, R.; Tassan, A.; Scopelliti, R.; Roulet, R. Inorg. Chim. Acta 2005, 358, 497. (b) Minghetti, G.; Bandini, A. L.; Banditelli, G.; Bonati, F.; Szostak, R.; Strouse, C. E.; Knobler, C. B.; Kaesz, H. D. Inorg. Chem. 1983, 22, 2332. (c) Beringhelli, T.; Ceriotti, A.; D’Alfonso, G.; Della Pergola, R.; Ciani, G.; Moret, M.; Sironi, A. Organometallics 1990, 4, 1053. (17) Pregosin, P. S.; Kunz, R. W. 3P and 13C NMR of Transition Metal Phosphine Complexes. In NMR Basic Principles and Progress; Diehl, P., Fluck, E., Kosfeld, R., Eds.; Springer-Verlag: Berlin, 1979; Vol. 16. (18) (a) Akiba, K.; Yamashita, M.; Yamamoto, Y.; Nagase, S. J. Am. Chem. Soc. 1999, 121, 10644. (b) Yamashita, M.; Yamamoto, Y.; Akiba, K.; Hashizume, D.; Iwasaki, F.; Takagi, N.; Nagase, S. J. Am. Chem. Soc. 2005, 127, 4354. (c) Fawcett, J.; Harding, D. A. J.; Hope, E. G.; Singh, K.; Solan, G. A. Dalton Trans. 2009, 6861. (d) Sellmann, D.; Hein, K.; Heinemann, F. W. Eur. J. Inorg. Chem. 2004, 3136. (e) Coleman, K. S.; Fawcett, J.; Harding, D. A. J.; Hope, E. G.; Singh, K.; Solan, G. A. Eur. J. Inorg. Chem. 2010, 4130. (19) Budzelaar, P. H. M. gNMR for Windows (5.0.6.0). NMR Simulation Program; IvorySoft, 2006. (20) (a) Clark, G. R.; O’Neale, T. R.; Roper, W. R.; Tonei, D. M.; Wright, L. J. Organometallics 2009, 28, 567. (b) Kokatam, S.; Weyhermüller, T.; Bothe, E.; Chaudhuri, P.; Wieghardt, K. Inorg. Chem. 2005, 44, 3709. (c) Goodfellow, R. G.; Hamon, E. M.; Howard, J. A. K.; Spencer, J. L.; Turner, D. G. J. Chem. Soc., Chem. Commun. 1984, 1604. (21) Davies, D. L.; Jeffery, J. C.; Miguel, D.; Sherwood, P.; Stone, F. G. A. J. Organomet. Chem. 1990, 383, 463. (22) (a) Chini, P. J. Organomet. Chem. 1980, 200, 37. (b) Bau, R.; Drabnis, M. H. Inorg. Chim. Acta 1997, 259, 27. (c) Teller, R. G.; Bau, R. Struct. Bonding (Berlin) 1981, 41, 1. (23) Holah, D. G.; Hughes, A. N.; Krysa, E.; Magnuson, V. R. Organometallics 1993, 12, 4721. (24) (a) Miedaner, A.; Raebiger, J. W.; Curtis, C. J.; Miller, S. M.; DuBois, D. L. Organometallics 2004, 23, 2670. (b) Asker, K. A.; Hitchcock, P. B.; Moulding, R. P.; Seddon, K. R. Inorg. Chem. 1990, 29, 4146. (25) (a) Baker, M. J.; Harrison, K. N.; Orpen, A. G.; Pringle, P. G.; Shaw, G. J. Chem. Soc., Chem. Commun. 1991, 803. (b) Tominaga, H.; Sakai, K.; Tsubomura, T. Chem. Commun. 1995, 2273. (c) Berning, D. E.; Noll, B. C.; DuBois, D. L. J. Am. Chem. Soc. 1999, 121, 11432. (26) (a) Spek, A. L.; Zijlstra, R. W. L.; Bouwman, E. Private Communication to CSD, CCDC-158198, 2001. (b) Moudam, O.; Kaeser, A.; Delavaux-Nicot, B.; Duhayon, C.; Holler, M.; Accorsi, G.; 5189


and Dihydrido Carbonyl Clusters Obtained by - American Chemical

Recommend Documents