Synthesis and skeletal isomerization of the phosphinidene acetylide cluster complexes [Ru4(CO)10(?4-PPh)(CCPh){WL(CO)}] where L = C5Me5 or C5H5

DAL

TON

FULL P

APER

J. Chem. Soc., Dalton Trans., 1998, Pages 1053–1056 1053

Synthesis and skeletal isomerization of the phosphinidene acetylide

cluster complexes [Ru

(CO)

(ì

-PPh)(CCPh){WL(CO)}] where

L

5 C

Me

or C

H

Wen-Cheng Tseng,

Yun Chi,*

†

Chi-Jung Su,

Arthur J. Carty,*

Shie-Ming Peng

and

Gene-Hsiang Lee

Department of Chemistry, National Tsing Hua University, Hsinchu 30043, Taiwan, R.O.C.

b

Steacie Institute for Molecular Sciences, National Research Council Canada, 100 Sussex Drive,

Ottawa, Ontario K1A 0R6, Canada

c

Department of Chemistry and Instrumentation Center, National Taiwan University,

Taipei 10764, Taiwan, R.O.C.

Reactions of the phosphinidene cluster [Ru4(CO)13(µ3-PPh)] with tungsten acetylide complexes [WL(CO)3(CCPh)]

(L= C5Me5 or C5H5) gave interconvertible isomers of formula [Ru4(CO)10(µ4-PPh)(CCPh){WL(CO)}]. The

structures of the two C5Me5 derivatives were determined by X-ray diffraction, showing a novel WRu4P octahedral

core arrangement, in which the acetylide ligand is co-ordinated to a WRu2 triangle with its C]C vector bridging

the Ru]Ru edge. For one isomer the phosphinidene ligand is located at the position trans to the W atom, while in the second isomer it is at the cis position. Possible mechanisms for this rare example of skeletal isomerization are suggested.

Facile addition of reactive organic and organometallic mole-cules to the phosphinidene cluster [Ru4(CO)13(µ3-PPh)]

pro-vides a convenient method to study the substrate–metal interaction between organic molecules and transition-metal atoms, and to obtain high-nuclearity metal cluster compounds.1

Recently, we reported the synthesis of a heterometallic cluster complex [Ru4(CO)10(µ4-PPh)(CCPh){W(C5Me5)O2}] 1 from the

reaction of [Ru4(CO)13(µ3-PPh)] with the high-oxidation-state

dioxo acetylide complex [W(C5Me5)O2(CCPh)] in which the

(C5Me5)WO2 fragment is linked to only one Ru metal atom

through the formation of a novel W]]O→Ru interaction.2 _The

W]]O→Ru bonding was retained, with no formation of an additional W]Ru bond, even under forcing conditions. This is due to the fact that all ligands on the (C5Me5)WO2(CCPh)

fragment are tightly bound to the W atom; therefore, the tungsten center acts as a well protected, saturated molecular entity.

In continuation of our investigation on the factors that in flu-ence mixed-metal cluster growth,3 _{we report here the reactions}

of [Ru4(CO)13(µ3-PPh)] with a low-oxidation-state acetylide

carbonyl complex [W(C5Me5)(CO)3(CCPh)]. In contrast to the

formation of 1, the products isolated from this reaction were two complexes with identical formula [Ru4(CO)11(µ4

-PPh)-(CCPh){W(C5Me5)}] each possessing a pentametallic

square-pyramidal core which is apparently obtained by removing CO ligands from the W atom. This study thus probes the properties of a low-oxidation-state transition-metal precursor, the ligands of which can dissociate in a stepwise manner. In addition, the rapid interchange between these WRu4 cluster compounds at

higher temperatures offered a challenging exploration of the mechanism for their skeletal isomerization.

Experimental

General information and materials

Infrared spectra were recorded on a Perkin-Elmer 2000 FT-IR spectrometer, 1_{H and} 13_{C NMR spectra on either a Bruker}

† E-Mail: ychi@faculty.nthu.edu.tw

AM-400 or Varian Unity-400 instrument. The 1_{H and} 13_{C NMR}

chemical shifts are quoted with respect to the internal standard tetramethylsilane, 31_{P NMR chemical shifts with respect to the}

external standard 85% H3PO4. Mass spectra were obtained on a

JEOL HX110 instrument operating in fast atom bombardment (FAB) mode. All reactions were performed under a nitrogen atmosphere using deoxygenated solvents dried with an appropri-ate reagent. The phosphinidene complex [Ru4(CO)13(µ3-PPh)]

was prepared according to the literature procedure.4 _The

reac-tions were monitored by analytical thin-layer chromatography (5735 Kieselgel 60 F254, E. Merck) and the products were

separated on preparative thin-layer chromatographic plates (Kieselgel 60 F254, E. Merck). Elemental analyses were

per-formed at the NSC Regional Instrumentation Center at National Cheng Kung University, Tainan, Taiwan.

Preparation of phosphinidene acetylide clusters

To a reaction flask (100 cm3_{), [Ru}

4(CO)13(µ3-PPh)] (100 mg,

0.111 mmol), [W(C5Me5)(CO)3(CCPh)] (112 mg, 0.222 mmol)

and toluene (60 cm3_{) were added. The solution was then heated}

to reflux and heating continued for 50 min, during which time the mixture changed from dark red to black. The solution was allowed to cool to room temperature and the solvent removed under vacuum. The residue was separated by thin-layer chromatography (CH2Cl2–hexane 1 : 6), from which 31 mg of

green [Ru4(CO)10(µ4-PPh)(CCPh){W(C5Me5)(CO)}] 2a (0.025

mmol, 26%) and 70 mg of black [Ru4(CO)10(µ4

-PPh)(CCPh)-{W(C5Me5)(CO)}] 3a (0.057 mmol, 60%) were isolated as the

P Ph Ph W O O Ru C Ru Ru Ru C C5Me5 1

1054 J. Chem. Soc., Dalton Trans., 1998, Pages 1053–1056

major isolable products. Crystals of both complexes suitable for X-ray diffraction study were obtained from a mixture of CH2Cl2 and methanol at room temperature. Similarly, the

reaction of [Ru4(CO)13(µ3-PPh)] and [W(C5H5)(CO)3(CCPh)]

in refluxing toluene for 15 min afforded the corresponding complexes 2b and 3b in 55 and 36% yield, respectively.

Compound 2a: mass spectrum (FAB, 184_W, 102_{Ru) m/z 1244}

(M1); IR (C6H12) ν(CO) 2064m, 2025vs, 2002s, 1988w (sh), 1975m, 1964w (sh), 1946w (br) and 1834w (br) cm21; 1_{H NMR} (300 MHz, CD2Cl2, 293 K) δ 7.60–7.48 (m, 4 H), 7.35–7.25 (m, 6 H) and 2.11 (s, 15 H); 13_{C NMR (100 MHz, CD} 2Cl2, 293 K) δ 247.4 (JWC= 150), 205.7 (d, JPC= 34), 202.1 (d, JPC= 9, 3C), 199.4 (d, JPC= 3), 199.0, 198.2 (d, JPC= 37), 192.4 (JWC= 141, CCPh), 149.1 (d, JPC= 18, ipso-C of C6H5), 140.2 (ipso-C of C6H5), 133.8 (d, JPC= 15, 2C, o-C of C6H5), 131.9 (p-C of C6H5), 131.3 (2C, o-C of C6H5), 129.6 (2C, m-C of C6H5), 129.2 (p-C of C6H5), 128.6 (d, JPC= 12, 2C, m-C of C6H5), 119.0 (d, JPC= 7 Hz, CCPh), 106.8 (C5Me5) and 13.0 (C5Me5) (Found: C,

33.82; H, 2.13. Calc. for C35H25O11PRu4W: C, 33.88; H, 2.03%).

Compound 2b: mass spectrum (FAB, 184_W, 102_{Ru) m/z 1174}

(M1); IR (C6H12) ν(CO) 2067m, 2030vs, 2006s, 1992w (sh), 1978m, 1967w (sh), 1952w (br) and 1869w (br) cm21; 1_{H NMR} (300 MHz, CDCl3, 293 K) δ 7.72–7.27 (m, 10 H) and 5.33 (s, 5 H); 13_{C NMR (75 MHz, CDCl} 3, 293 K) δ 237.6 (d, JPC= 2), 203.2 (d, JPC= 35), 200.2 (d, JPC= 12, 3C), 197.6 (d, JPC= 5), 197.4 (d, JPC= 6), 197.0 (d, JPC= 36), 186.5 (CCPh), 148.1 (d, JPC= 17, ipso-C of C6H5), 148.9 (ipso-C of C6H5), 132.4 (d, JPC= 14, 2C, o-C of C6H5), 131.2 (p-C of C6H5), 130.4 (2C, o-C of C6H5), 128.7 (2C, m-C of C6H5), 128.6 (p-C of C6H5), 127.8 (d, JPC= 12, 2C, m-C of C6H5), 118.8 (d, JPC= 7 Hz, CCPh) and

88.9 (C5H5) (Found: C, 30.14; H, 1.48. Calc. for C30H15O11

-PRu4W: C, 30.78; H, 1.29%).

Compound 3a: mass spectrum (FAB, 184_W, 102_{Ru) m/z 1244}

(M1); IR (C6H12) ν(CO) 2069vs, 2024vs, 2015vs, 2004s, 1985m, 1959m, 1933m and 1889w (br) cm21; 1_{H NMR (300 MHz,} CDCl3, 293 K) δ 7.49–7.12 (m, 10 H) and 2.12 (s, 15 H); 13C NMR (75 MHz, CD2Cl2, 293 K) δ 225.9 (d, JPC= 5, JWC= 165), 213.3 (d, JPC= 15), 206.2 (br, 3C), 205.1, 200.2, 196.7, 195.2 (d, JPC= 12, 3C), 187.6 (CCPh), 145.4 (d, JPC= 6 Hz, ipso-C of C6H5), 137.4 (ipso-C of C6H5), 133.5 (br, o-C of C6H5), 131.4 (br, o-C of C6H5), 131.2 (2C, o-C of C6H5), 130.7 (p-C of C6H5), 129.6 (p-C of C6H5), 129.5 (2C, m-C of C6H5), 128.9 (br, 2C, m-C of C6H5), 112.4 (CCPh), 106.1 (C5Me5) and 11.9 (C5Me5)

(Found: C, 33.85; H, 2.07. Calc. for C35H25O11PRu4W: C, 33.88;

H, 2.03%).

Compound 3b: mass spectrum (FAB, 184_W, 102_{Ru) m/z 1174}

(M1); IR (C6H12) ν(CO) 2071vs, 2028vs, 2016vs, 2006vs, 1988s, 1968m, 1952w, 1940m and 1918w (br) cm21; 1_{H NMR (300} MHz, CDCl3, 293 K) δ 7.45–7.23 (m, 10 H) and 5.51 (s, 5 H); 13_{C NMR (75 MHz, CD} 2Cl2, 293 K) δ 220.2 (d, JPC= 5), 212.9 (d, JPC= 14), 206.1, 203.5 (br, 3C), 201.4 (d, JPC= 3), 196.6, 195.2 (d, JPC= 13, 3C), 184.3 (CCPh), 149.0 (d, JPC= 10, ipso-C of C6H5), 137.1 (ipso-C of C6H5), 131.7 (d, JPC= 15, 2C, o-C of C6H5), 131.4 (2C, m-C of C6H5), 131.3 (p-C of C6H5), 129.8 (p-C of C6H5), 129.7 (d, JPC= 12, 2C, m-C of C6H5), 129.5 (2C, o-C of C6H5), 111.7 (d, JPC= 4 Hz, CCPh) and 92.6 (C5H5)

(Found: C, 30.53; H, 1.43. Calc. for C30H15O11PRu4W: C, 30.78;

H, 1.29%).

X-Ray crystallography

The X-ray diffraction measurements were carried out on a Nonius CAD-4 diffractometer. Lattice parameters were deter-mined from 25 randomly selected high-angle reflections. Three standard reflections were monitored every 3600 s. No signifi-cant change in intensities, due to crystal decay, was observed over the course of all data collection. Intensities of the diffrac-tion signals were corrected for Lorentz, polarizadiffrac-tion and absorption effects (ψ scans). The structure was solved by using the NRCC-SDP-VAX package.5 _{All the non-hydrogen atoms}

had anisotropic thermal parameters. The hydrogen atoms were placed at idealized positions with UH= UC1 0.1. The

crystal-lographic refinement parameters of complexes 2a and 3a are given in Table 1, while selected bond distances and angles are presented in Tables 2 and 3, respectively.

CCDC reference number 186/854.

See http://www.rsc.org/suppdata/dt/1998/1053/ for crystallo-graphic files in .cif format.

Results and Discussion

Synthesis and characterization

The generation of phosphinidene cluster complexes 2a and 3a was effected by the reaction of [Ru4(CO)13(µ3-PPh)] with

[W(C5Me5)(CO)3(CCPh)] in refluxing toluene solution (Scheme

1). Similarly, treatment of [Ru4(CO)13(µ3-PPh)] with [W(C5H5

)-(CO)3(CCPh)] afforded the corresponding pentametallic

complexes 2b and 3b in 55 and 36% yields, respectively. All

complexes were purified by routine thin-layer chromatography, followed by recrystallization. They were fully characterized using FAB mass spectrometry, IR, 1_{H and} 13_{C NMR}

spectro-scopies and single-crystal X-ray diffraction.

Complex 2a crystallizes in monoclinic space group P21/c with

two crystallographically independent, but structurally identical molecules in the unit cell. As indicated in Fig. 1 it possesses a square-pyramidal core arrangement with the W atom located at the apical position. In addition the metal skeleton is co-ordinated by 11 terminal CO ligands, one µ4-PPh fragment and

one µ3-η

2_{-CCPh fragment. The metal–metal distances are}

somewhat irregular, with the W]Ru distances [3.000(1)– 2.927(1) Å] being slightly longer than the Ru]Ru distances [2.958(1)–2.699(1) Å]. The acetylide ligand forms a σ bond to the W atom and two π interactions with Ru atoms in a bonding mode similar to that observed in the acetylide complexes [Ru2(CO)8(CCR)(WL)] (L= C5Me5 or C5H5; R= Ph, But, etc.6).

The phosphinidene ligand is found to link to four Ru atoms, and the Ru]P distances fall in the range 2.333(2)–2.380(2) Å which are in agreement with the structural data of other Ru5

phosphinidene complexes.7 _{If we consider that the µ} 4-PPh

ligand is a part of the cluster core, then the molecule appears to adopt a WRu4P octahedral geometry. This geometry has

also been observed in related cluster compounds containing a

Scheme 1 P Ph Ru _W(C 5Me5) Ru C Ru Ru Ru Ru P Ph Ru Ru Ph C Ph W(C5Me5) Ru C C Ph Ph W(C5Me5) Ru Ru Ru Ph–P C C Ru Ru Ru P Ru 2 3 4

J. Chem. Soc., Dalton Trans., 1998, Pages 1053–1056 1055

bridging sulfide ligand.8 _{Finally, assuming that the acetylide}

ligand serves as a five-electron donor, complex 2a contains a total of 74 valence electrons, which is compatible with the electron counting for pentametallic cluster compounds with eight M]M bonds.

An X-ray diffraction study of compound 3a was also under-taken in an attempt to compare its structure and bonding. As indicated in Fig. 2, the core arrangement is nominally similar to that of the previously discussed 2a, comprising a square-pyramidal WRu4 metal core and a µ3-η2-acetylide ligand

co-ordinated to the WRu2 triangle. A noteworthy distinction

between 2a and 3a is that the W atom now resides in a basal position, while the µ4-PPh phosphinidene ligand is co-ordinated Fig. 1 Molecular structure and atomic labelling scheme of the green complex [Ru4(CO)10(µ4-PPh)(CCPh){W(C5Me5)(CO)}] 2a with thermal

ellipsoids at the 30% probability level

Table 1 X-Ray structural data * for complexes 2a and 3a

Formula M Crystal system Space group a/Å b/Å c/Å β/8 U/Å3 Z Dc/g cm23 F(000) 2θmax/8 hkl Ranges Crystal size/mm µ(Mo-Kα)/cm21 Maximum, minimum transmission No. data in refinement

[I_{> 2σ(I)}] No. atoms and

parameters Weight modifier, g Maximum _{∆/σ ratio} R, R9 Goodness of _fit Maximum, minimum electron density peaks/e Å23 2a C35H25O11PRu4W 1240.67 Monoclinic P21/c 32.487(4) 10.295(3) 22.624(2) 96.06(1) 7524(3) 8 2.190 4652 45.0 234 to 34, 0–11, 0–24 0.05 × 0.10 × 0.55 47.51 1.000, 0.816 7136 154, 938 0.000 02 0.004 0.027, 0.024 1.32 0.69, 20.61 3a C35H25O11PRu4W 1240.67 Orthorhombic P212121 10.856(2) 16.522(1) 20.453(2) 3668.2(8) 4 2.247 2326 55.0 0–14, 0–21, 0–26 0.10 × 0.15 × 0.40 48.73 1.000, 0.778 3674 77, 470 0.000 01 0.009 0.030, 0.030 1.08 0.67, 20.74

* Common features: λ(Mo-Kα) = 0.7107 Å; function minimized Σ(w|Fo2 Fc|

2_{), weighting scheme w}21_{= σ}2_(F o)1 |g|Fo

2_{; goodness of}

fit =[Σw|Fo2 Fc|2/(No2 Nv)]¹² (No= number of observations, Nv=

number of variables).

to the WRu3 square face with W]P and Ru]P distances in

the range 2.447(3)–2.380(3) Å, analogous to those of W]Ru heterometallic phosphinidene cluster compounds.9 _Compound 3a is hence related to 2a by moving the W atom from the apical

vertex to the basal position. Associated with this change of the cluster skeleton, a unique CO(2) ligand, which spans the Ru(1)]Ru(3) edge and adopts a semibridging mode with Ru(1)]C(2)]O(2) 151.6(9) and Ru(3)]C(2)]O(2) 126.4(8)8, was observed together with 10 other terminal CO ligands.

Skeletal isomerization

A delicate equilibrium between compounds 2a and 3a at higher temperature is implicated because heating a toluene solution of

2a provided a mixture of both complexes. Similarly, the

isomer-ization is established from the opposite direction by heating a

Fig. 2 Molecular structure and atomic labelling scheme of the black complex [Ru4(CO)10(µ4-PPh)(CCPh){W(C5Me5)(CO)}] 3a with thermal

ellipsoids at the 30% probability level

Table 2 Selected bond distances (Å) and angles (8) of complex 2a with estimated standard deviations (e.s.d.s) in parentheses

W_]Ru(1) W]Ru(3) Ru(1)_]Ru(2) Ru(1)]Ru(4) Ru(1)_]P Ru(3)]P W_]C(12) Ru(4)]C(12) Ru(4)_]C(13) W_]C(12)]C(13) W]C(1)]O(1) 3.000(1) 2.966(1) 2.930(1) 2.699(1) 2.333(2) 2.380(2) 1.898(8) 2.164(7) 2.173(7) 160.5(6) 160.8(7) W_]Ru(2) W]Ru(4) Ru(2)_]Ru(3) Ru(3)]Ru(4) Ru(2)_]P Ru(4)]P Ru(1)_]C(12) Ru(1)]C(13) C(12)_]C(13) C(12)_]C(13)]C(14) 2.927(1) 2.993(1) 2.845(1) 2.958(1) 2.341(2) 2.361(2) 2.180(7) 2.119(7) 1.37(1) 136.1(7)

Table 3 Selected bond distances (Å) and angles (8) of complex 3a with e.s.d.s in parentheses W_]Ru(1) W]Ru(3) Ru(1)_]Ru(3) Ru(2)]Ru(3) Ru(3)_]Ru(4) Ru(2)]P W_]C(12) Ru(3)]C(12) Ru(3)_]C(13) Ru(1)]C(2) W]C(12)]C(13) W_]C(1)]O(1) Ru(3)]C(2)]O(2) 2.929(1) 2.988(1) 2.820(1) 2.699(1) 2.879(1) 2.399(3) 1.959(9) 2.199(9) 2.186(9) 1.96(1) 158.5(7) 167.5(8) 126.4(8) W_]Ru(2) W]P Ru(1)_]Ru(4) Ru(2)]Ru(4) Ru(1)_]P Ru(4)]P Ru(2)_]C(12) Ru(2)]C(13) C(12)_]C(13) Ru(3)]C(2) C(12)]C(13)]C(14) Ru(1)_]C(2)]O(2) 2.950(1) 2.447(3) 2.897(1) 2.782(1) 2.380(3) 2.403(3) 2.188(9) 2.182(9) 1.31(1) 2.32(1) 140.0(9) 151.6(9)

1056 J. Chem. Soc., Dalton Trans., 1998, Pages 1053–1056

pure sample of 3a in refluxing toluene under nitrogen. In add-ition, no retardation of the relative rate of isomerization was observed when the reactions were conducted under an atmos-phere of carbon monoxide. Based on these experimental find-ings, the involvement of CO dissociation as the initial step is eliminated, which leaves the intramolecular process as the most likely reaction pathway.

Among the many possibilities, two mechanisms have been proposed to account for these skeletal isomerization reactions. The first involves a direct twisting of a Ru2P face with respect to

the opposite WRu2 metal triangle which is capped by the

acetyl-ide ligand (Scheme 1). In this case an intermediate possessing a trigonal-prismatic core structure (4) is envisioned. It is interest-ing that this formally contains only six M]M bonds; therefore, it is electron deficient and some partial bonding interactions between the non-bonded metal atoms are required to stabilize it. Alternatively, the isomerization may proceed through a combination of the diamond–square–diamond (DSD) re-arrangement10 _{and concomitant phosphinidene migration. One}

possible pathway is shown in Scheme 2, in which the direction of motion for the metal atoms is shown by the arrows, the chemical bond being broken is indicated by the dashed line, and the WRu2 face supporting the acetylide ligand is shown by the

solid triangle. The transformation from compound 2 to 3 may be accomplished via the first DSD process to give a trigonal-bipyramidal intermediate with the phosphinidene ligand moved to a Ru3 triangle. The transformation of the phosphinidene

ligand from the µ4 to the µ3 mode is energetically feasible, and

this is supported by the isolation of many µ3-phosphinidene

cluster compounds.11 _{After the phosphinidene ligand further}

migrates to a nearby WRu2 triangle, the application of a second

DSD process, but in a reverse direction, would lead to the formation of 3 with the phosphinidene ligand co-ordinated cis to the W atom. Interestingly, the trigonal-bipyramidal inter-mediates proposed in this DSD process contain nine instead of the eight M]M bonds which are associated with the square-pyramidal structures of both 2 and 3. Hence, the activation energy for phosphinidene migration may be lowered by the increase in electron density through the formation of this extra M]M bond in the trigonal-bipyramidal intermediates.

Finally, extensive heating of the corresponding C5H5

deriva-tive 3b in toluene at reflux afforded the isomeric complex 2b in 93% yield, while heating a toluene solution of 2b under similar conditions failed to regenerate 3b in significant quantity. This observation suggests that the isomer 3 with a cis arrangement of the W and the µ4-PPh fragment could be the initial product

Scheme 2 Ru Ru W P Ru Ru W Ru Ru Ru P Ru Ru P Ru P W Ru Ru Ru W Ru Ru Ru cis-3 trans-2 DSD DSD P-migration

of these cluster-growth reactions. Moreover, the trans arrange-ment is a thermodynamically more favorable structure for the C5H5 derivatives. Unfortunately, the preference of the metal

framework, caused by changing the ancillary ligand on the W atom, is not clear at present. Thus, further examination is required before we can delineate an unambiguous explanation for such selectivity.

Acknowledgements

We thank the National Science Council of the Republic of China for financial support (Grant No. NSC 87-2113-M007-047).

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