Au-Ir and Hg-Ir Mixed-Metal Carbonyl Clusters. Synthesis

Nov 1, 1994 - Alessandro Ceriotti, Roberto Della Pergola, and Luigi Garlaschelli*. Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, vi...
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Organometallics 1995, 14, 186-193

186

Au-Ir and Hg-Ir Mixed-Metal Carbonyl Clusters. Synthesis, Characterization, and Solid State Structure of [Irs(co)idA~PPh3)21and [IrdCO)i4(HgC1)2l2Alessandro Ceriotti, Roberto Della Pergola, and Luigi Garlaschelli* Dipartimento di Chimica Inorganica, Metallorganica ed Analitica, via 'G. Venezian 21, 20133 Milano, Italy

Mario Manassero and Norbert0 Masciocchi* Istituto di Chimica Strutturistica Inorganica, via G. Venezian 21, 20133 Milano, Italy Received July 13, 1994@ The neutral cluster [Ir6(CO)15(AuPPh3)21has been obtained by reaction of [IrdC0)15I2with [AuPPh3]+. It crystallizes in the triclinic space group Pi with cell constants a = 13.160(2) b = 13.714(4) A, c = 18.266(3) a = 65.47(2)", /3 = 110.93(2)", y = 112.07(1)", V = 2699(2) Hi3, and 2 = 2. Data were collected at room temperature to a maximum 26' = 54". The final discrepancy indices were R = 0.032 and R, = 0.034 for 7217 independent reflections with I >30(I). The structure was solved by direct methods. The iridium atoms of the cluster define a n octahedral frame capped by one gold-phosphine group. The second AuPPh3 unit spans one Ir-Au edge. The metal skeleton of C1 symmetry is coordinated by twelve terminal and three edge-bridging carbonyl groups. The dianionic [IrdcO)14(Hgc1)21~has been prepared from [Irs(C0)15l2- and Hg2C12, HgC12 Hg, or HgClz in the presence of Na2C03. The salt [PPh4]2[Ir6(CO)14(HgC1)2] crystallizes in the monoclinic space group Cc with cell constants a = 10.257(2) b = 46.848(4) c = 14.639(3) A, /3 = 107.83(2)", V = 6696(4) A3, and 2 = 4. Data were collected at room temperature to a maximum 26' = 50". The final discrepancy indices were R = 0.037 and R, = 0.036 for 3619 independent reflections with I >30(1). The metallic framework forms a n octahedron of iridium atoms bearing, on four non-adjacent faces, two ,u3-HgC1fragments and two ,u3-C0 groups. The chemical shift of the lg9HgNMR was found at +1508 ppm, and suggests a n anomalous oxidation state.

A,

A,

+

A,

In recent papers we have described the syntheses and the chemical properties of mixed-metal clusters of formula [Ir6(C0)15ML]- [ML = CuNCMe ( l ) , lAuPPhs (2): and HgCl (3)2],obtained by the direct addition of electrophilic metal complexes t o [Irs(C0)1512-. These anions showed very similar behavior and structures, with face capping ML groups. The main difference between them is the arrangement of the three bridging carbonyls, which shows enhanced face-bridging character in the sequence 1, 2 and 3, increasing the molecular symmetry in the solid state from C3 to C3".ls2 These structural variations implied two different formal descriptions for the clusters: 1 and 2 were considered adducts of [Ir6(C0)15lZ-with ML+ fragments, retaining the ligand architecture of the parent dianion of D3 symmetry; 3 was envisaged as a structural analogue of Irg(COh (red isomer, Td point where one p3CO is replaced by one HgC1- group, formally acting as a two electron donor. Moreover, the synthetic studies and the multinuclear NMR measurements showed that other species were formed when an excess of the heteroatom complex was added; these data prompted us to investigate the Abstract published in Advance ACS Abstracts, November 1,1994. (1)Della Pergola, R.;Garlaschelli, L.; Demartin, F.; Manassero, M.; Masciocchi, N. J. Organometal. Chem., 1992,436,241. (2)Della Pergola, R.;Demartin, F.; Garlaschelli, L.; Manassero, M.; Martinengo, S.; Masciocchi, N.; Sansoni, M. Organometallics, 1991, 10,2239. (3)Garlaschelli, L.;Martinengo, S.; Bellon, P. L.; Demartin, F.; Manassero, M.; Chiang, M. Y.; Wei, C. Y.; Bau, R. J.Am. Chem. SOC., 1984,105,6664.

A,

systems further, resulting in the isolation of the new complexes [Ir6(C0)15(AuPPh3}~1(4) and [Ir6(C0)14(HgC1)212- (5) which showed remarkable differences in the behavior of Hg and Au, confirming that the previous formalism has substantial support. The adduct [Irs(C0)15{CuNCMe}2] (6) was obtained in solution, but was found to be too unstable t o be crystallized.

Results The addition of [Cu(NCMe)#, [AuPPh3]+ or HgCl2 to [Ir6(C0)15lZ-(molar ratio 1:l) in tetrahydrofuran (THF) at room temperature resulted in the fast formation of the monoanionic adducts [Ir6(CO)l5CuNCMe](l),[Irdc0)1&uPPh31- (2), and [ I ~ ~ ( C O ) I ~ H(31, ~C~]which showed strikingly similar spectroscopic, structural, and chemical properties.1!2 The same reactions were carried out with higher molar ratios between the monomeric complexes and the carbonyl cluster, searching for neutral derivatives. Synthesis and Spectroscopic Characterization of [Ir6(co)l6(cuNcMe)2].The reaction of [IrdC0)15l2with [Cu(NCMe)4]+(molar ratio 1:2) in CHzClz produced a new species which was easily identified as [ I I - ~ ( C O ) ~ ~ (CuNCMe)21,on the basis of the stoichiometry of reaction 1. The infrared spectrum of the product (vco in

+

-

[Ir6(C0)1512- 2[Cu(NCMe),I+ [Ir6(CO),5(C~CMe),] 6NCMe (1)

0276-7333/95/2314-0186$09.OQIQ 0 1995 American Chemical Society

+

Au-Ir and Hg-Ir Mixed-Metal CO Clusters

Organometallics, Vol. 14, No. 1, 1995 187

c

+----G-.2000.0

2200.0

2200.0

2

0

CH-1

THF: 2075m, 2034vs, 1813m cm-l, Figure l a ) closely comparable results. The capping groups are rapidly displaced when an excess of halide salts is added to the resembles the spectrum of [Ir6(CO)15(AuPPh3)21 (see solution.2 later), and also that reported for [Ru6C(CO)l6(CuNCMe)2];4the coincidence of the infrared spectra strongly The infrared spectrum of [Ir6(C0)15(AuPPh3)21 shows suggests very similar architectures between the three bands at 2027m, 2036vs, 1978w, 1952w, 1819m cm-l, molecules. By analogy with [ R U ~ C ( C O ) ~ ~ ( C U N C M ~ )in ~ ITHF , ~ (Figure lb). The 31PNMR spectrum shows only the two copper atoms are most likely within bonding one signal at 66.2 ppm (CD2C12, room temperature), distance of each other. Unfortunately, the Ir-Cu which is slightly displaced to 64.9 ppm at -90 "C, cluster was too unstable to be crystallized, and the indicating that the two phosphines are equivalent on the NMR time scale, even a t low temperature. These characterization was limited to the IR data. Any attempt to grow crystals of 6 resulted in the transforfindings are in contrast t o the solid state structure, mation to Ir6(CO)1s3or 1, depending on the conditions where the two phosphorus atoms are in different used. This instability is not surprising considering the environments. The existence of several isomers is not efforts needed to obtain crystalline samples of 1. unlikely, since for [ R u ~ C ( C O ) ~ ~ ( A U Ptwo M ~difP~~)~~~ Synthesis and Spectroscopic Data of [Irs(CO)15ferent isomers in solution were observed by 31PNMR (AuPPh&l. The addition of two moles of [AuPPh31+ the isomer characterized by X-ray analysis showed two onto [Ir6(C0)15l2-occurs only when a large excess of the centrosymmetric edge-bridging gold atoms. However, cationic complex is used. Very similar results were 4 should be present in solution as a single isomer, obtained with solvent other than THF, such as 2-prodifferent from that observed in the solid state; more panol or CH2C12. In the alcoholic solvent, the soluble probably, the two capping gold atoms are rapidly potassium salt &[Ir6(c0)15]was employed, according exchanging their site, even at -90 "C; presumably, the to eq 2. The cluster 4 was obtained as a microcrystalline Auz(PPh3)~ group oscillates between two adjacent faces of the octahedral iridium framework, as previously suggested for [ R u s ( C O > ~ ~ B ~ A U ( P P ~ ~ > } ~ ~ . ~ Synthesis and Spectroscopic Data of [Ire(CO)l4(HgC1)2I2-. The addition of a large excess of HgCl2 to [Ir6(C0)15I2-does not change the products of the reacsolid, which was isolated by filtration. A very large tion, and the monoadduct 3 is the only product which excess of gold was needed to obtain complete conversion can always be detected. When a test reaction was even in CH2C12, where the [AuPPh31+is less stabilized carried out with EtHgC1, the formation of 3 was initially by solvation. The neutral cluster 4, once formed, is fairly stable and can be crystallized from THF, CH2Cl2, (5) Bunkall, S. R.; Holden, H. D.; Johnson, B. F. G.; Lewis, J.;Pain, or toluene, after precipitation with 2-propanol, with G. N.; Raithby, P. R.; Taylor, M. J. J. Chem. SOC.,Chem. Commun., (4) Bradley, J. S.; Pruett, R. L.; Hill, E.; Ansell, G. B.; Leonowicz, M. E.; Modrick, M. A. Organometallics, 1982, 1 , 748.

1984,25. (6) Housecroft, C. E.; Matthews, D. M.; Waller, A.; Edwards, A. J.; Rheingold, A. L. J. Chem. SOC.,Dalton Trans., 1993, 3057.

Ceriotti et al.

188 Organometallics, Vol. 14,No. 1, 1995 observed; however, after prolonged standing, small amounts of a more reduced species were formed. Eventually, this new cluster was isolated and was shown to be [Ir6(CO)14(HgC1)2I2-(5). The addition of the second Hg atom is thus accompanied by loss of CO and reduction of the cluster. Thereafter, three different successful methods of synthesis were devised, according t o eqs 3-5.

+ 2HgC1, + Na,CO, [Ir6(CO)14(HgC1),]2-+ 2 c 0 , + 2NaCl

Table 1. Selected Distances (A) and Angles (deg) in [ I ~ ~ ( C O ) I ~ ( A U P with P ~ ~ )Estimated ZI Standard Deviations (Esd’s) on the Last Figure in Parenthese@ Au(l)-Au(2) Au( 1)-Ir( 1) Au( 1)-Ir(4) Au( 1)-Ir(5) Au(2)-Ir( 1) h(1)-W) 1)-~4) ~ 1r)-1r(5) ( Wl)-W6)

Metal-Metal 2.8530(8) Ir(2)-Ir(3) 2.83 13(6) W)-W) 2.9347(5) Ir(2)-Ir(6) 2.8327(9) W3) -W4) 2.6569(6) W3)-W5) 2.760( 1) W)-Ir(6) 2.7849(7) Ir(4)-Ir(5) 2.9325(7) Ir(4)-Ir(6) 2.8422(5)

Ir(1)-C(11) Ir(l)-C(12) Ir(2)-C(21) Ir(2)-C(22) Ir(3)-C(3 1) Ir(3)-C(32)

1.90(1) 1.90(2) 1.91(2) 1.88(1) 1.87(1) 1.87(2)

Ir(3)-Cb( 1) Ir(5)-Cb( 1) Ir(2)-Cb(2)

2.07(1) 2.04(2) 2.01(1)

Ctem-Otermb Cb-Obb

1.14 1.16

w

[Ir6(C0),,I2-

(3)

2.7771(7) 2.7657(7) 2.8094(9) 2.8081(9) 2.7498(6) 2.7694(7) 2.8582(9) 2.7810(7)

Ir-Cterm Ir(4)-C(41) Ir(4)-C(42) Ir(5)-C(51) Ir(5)-C(52) Ir(6)-C(61) Ir(6)-C(62)

1.88(2) 1.90(1) 1.85(2) 1.91(1) 1.88(1) 1.87(2)

Ir(6)-Cb(2) Ir(4)-Cb(3) Ir(6)-Cb(3)

2.29(2) 2.01(1) 2.15(2)

Ir-Cb

All reactions are of a heterogeneous nature, since some of the reactants are insoluble in THF. Therefore they require more than 15 days to go to completeness, at room temperature; nevertheless they are very selective, and clean conversions to 5, as the only carbonylic product, are obtained. The reactions proceed via the very rapid intermediate formation of 3,which is then slowly transformed into the final product; in the case of reaction 4, the addition of the first HgCl+ group is allowed by the disproportionation of HgzC12, with formation of elemental Hg and C1-, which can be clearly detected in the reaction vessel as a greyish residue; the step which follows can be considered as a ligand substitution:

+

-

(PPh&Ir&CO)151 HgZC1, (PPh4)[Ir,(CO)15(HgCl)I Hg + (PPh4)C1( 6 ) (PPh4)[Ir,(CO),,(HgC1)1

+

+ Hg + (PPh4)C1-

(PPh~>,[Ir~(co)~~(HgC1),1 + CO (7) The sequence represented by steps 6 and 7 can be effected by the successive addition of HgClz and Hg (eq 5), with identical results. The infrared spectrum of 5 in THF shows bands at 2057w, 2013~5, 1972m, 1697m,br cm-l (Figure IC),the band a t lowest wavenumbers confirming the presence of face bridging carbonyls. The lg9HgNMR spectrum was recorded, in THF at -90 “C, and showed a single peak at +1590 ppm. The signal could also be observed at room temperature at 1508 ppm, and is well outside the usual range for this nucleus (+500, -3500 ppm).’ This chemical shift should be compared with the value of -1168 ppm found for 3,, and strongly supports the hypothesis of an anomalous oxidation state of Hg in the cluster (see Discussion). Solid State Structure of [Irs(CO)&-CO)a(AuPPhshI (4). The crystal structure of [Ir6(CO)l5(AuPPh3)d consists of discrete neutral molecules held together by van der Waals contacts. A list of the relevant bond distances and angles appears in Table 1. The metal skeleton of 4 is based on a Ir6 octahedron [av. Ir-Ir = 2.803 A (min 2.7498(6); max 2.9325(7) A, (7) Granger, P. in Transition Metal Nuclear Magnetic Resonance, Pregosin, P. S. (ed.), Amsterdam, Elsevier, 1991;p. 306-332.

Ir(l)-Au(l)-Au(2) Ir(4)-Au(l)-Au(2) Ir(4)-Au(l)-Ir( 1) k(5)-Au( l)-Au(2) Ir(5)-Au(l)-k(l) Ir(5)-Au(l)-Ir(4)

Other Distances Au( 1)-P( 1) Au(2)-P(2)

Angles 55.73(2) Ir(l)-Au(2)-A~(l) 111.09(2) Ir(1)-Au(1)-P(1) 57.73(2) Ir( l)-Au(2)-P(2) 75.92(2) Ir-Ctem-Otmb 62.36(2) Ir-Cb-Obb 59.38(2)

2.293(4) 2.272(3) 61.72(2) 157.69(9) 166.41(8) 176 138.5

Abbreviations for atoms in Tables 1-5: term = terminal; Ct = triple (face) bridging carbon; Ot = triple (face) bridging oxygen; Cb = double (edge) bridging carbon; Ob = double (edge) bridging oxygen. Average values.

r

Q8= 4.611, capped on a trian lar face by a p3-AuPPhs ligand [av Au(1)-Ir = 2.86 I; another AuPPh3 fragment brid es one of the Au-Ir edges [Au(l)-Au(2) = 2.8530(8) ;Au(2)-Ir(l) = 2.6569(1)AI. A set of twelve terminal (two on each iridium atom) and three edgebridging carbonyl ligands complete the molecule, which is fully depicted, with partial labeling scheme, in Figure 2. Average bonding values are: Ir-Ck, 1.88; Ctemob, 1.14; Ir-Cb, 2.10; Cbr-Obr 1.16 A; Ir-Ckm-Otem 176; Ir-Cbr-Obr 138”(term = terminal; br = bridging). The nature, and geometry, of the (AuPPh3)z ligand in 4 can be interpreted on the basis of the strong “aurophilic attraction”1° of two roughly linearly coordinating fragments [P(l)-Au(l)-Ir(l) = 157”; P(2)Au(2)-Ir(l) = 166O1, which, however, does not significantly affect the Au-P bond lengths [av. Au-P 2.28 A in 4; Au-P 2.272(3) in 21. Solid State Structure of (PPh&[Ire(CO)dp3C0)2(HgC1)21 (Sa). The crystal structure of [PPh412[Ir6(C0)14(HgCl)z]consists of an ionic packing of cluster anions 5 and PPh4+ cations; no anomalously short contacts are present. Relevant bond distances and angles are listed in Table 2. The metal cage of the

R

(8)The Q value meamres the deviations of the M-M edges from the average value; it was introduced in Della Pergola, R.; Garlaschelli, L.; Martinengo, S.; Demartin, F.; Manassero, M.; Masciocchi, N.; Bau, R.; Zhao, D. J. Organometal. Chem., 1990,396, 385. (9) A Fortran thermal-ellipsoid program for crystal structure illustration (Johnson, C. K. ORTEP; Oak Ridge National Laboratory: Oak Ridge, TN, 1971). (lO)PyykkO, P.; Zhao, Y. Angew. Chem. Int. Ed. Engl., 1991,30, 604 and references therein.

Au-Ir and Hg-Ir Mixed-Metal CO Clusters

Organometallics, Vol.14,No. 1, 1995 189 A

Figure 2. ORTEP drawing and atom-labeling scheme for [Ir~(C0)15(AuPPh&l. Thermal ellipsoids are drawn at 30% probability. Carbonyl carbons are designated as the oxygens to which they are attached. Table 2. Selected Distances (A) and Angles (deg) in the Dianion [Ira(CO)~&IgCl)zl~with Estimated Standard Deviations (Esd's) on the Last Figure in Parentheses Metal-Metal W 1)-h(6) 2.808(2) 2.745(2) h(2)-~4) 2.787(1) ~ 2 ) - ~ 5 ) 2.768(2) W')-Ir(6) 2.788(2) W3)-W4) 2.777(2) M3)-M5) 2.804(2) W)-Ir(6) 2.874(2) W4)-M5) 2.85 l(2) W5)-W6)

2.754(2) 2.768(2) 2.748(2) 2.754(2) 2.899(2) 2.825(2) 2.846(2) 2.746(2) 2.947(2)

Ir-C,, 1.85(4) 1.73(3) 1.76(4) 1.83(4) 1.88(4) 1.7 l(3)

Ir(4)-C(41) Ir(4)-C(42) Ir(5)-C(5 1) Ir(5)-C(52) Ir(6)-C(61) Ir(6)-C(62)

1.96(3) 1.80(3) 1.89(4) 1.83(4) 1.85(3) 1.89(4)

Ir(2)-Ct(2) Ir(4)-Ct(2) Ir(5)-Ct(2)

2.33(3) 2.09(2) 2.13(3)

Ir-Ct 2.01(3) 2.29(3) 2.06( 3) 1.17 1.22 h(3)-Hg(l)-h(l) Ir(4)-Hg(l)-h(l) Ir(4)-Hg(l)-h(3) Ir(5)-Hg(2)-Ir(3)

Other Distances Hg( U-CK 1) Hg(2)-CW

Angles 62.33(5) h(6)-Hg(2)-Ir(3) 61.28(5) Ir(6)-Hg(2)-Ir(5) 63.20(4) Ir-Ctem-Otem" 61.13(5) Ir-Ct-Oto

2.444(7) 2.399(9) 61.76(5) 63.96(5) 171 131.5

* Average values.

[Ir~(CO)14(HgC1)212anion is also based on an octahedron of iridium atoms [av. Ir-Ir = 2.818 A (min 2.746(2); max 2.947(2)A, Q8 = 4.6)1, which is capped in meta(l,3)11positions by two pus-HgC1fragments [av HgIr = 2.779 A (min 2.768; max 2.808 A)]. Twelve

terminal (two on each iridium atom) and two facebridging carbonyl ligands complete the coordination around the metal cage. An ORTEPg drawing of the whole anion, with partial labeling scheme, is shown in Figure 3. Average bonding values are: Ir-Ck, 1.83; ckm-ok, 1.17; Ir-Cbr 2.15; Cbr-Obr 1.22 A; Ir-CkmOk, 171; Ir-Cbr-Obr 131" (term = terminal; br = bridging). Comparison of homologous bond distances in 3 and 5 is very informative. Ir-Hg interactions are shortened, whereas Hg-C1 interactions are loosened; the same trend is observed in Ir-C and C-0 distances, indicating (i) a stronger n back-donation effect in the dianion and (ii) the similar behavior of HgCl and CO in this context.2

Discussion In the following discussion, we want to correlate the different geometries found in mono- and bicapped octahedral clusters. Addition of a p3-MLn fragment t o an octahedral cluster frame (a in Scheme 1) generates a C3" metal skeleton (b); 1,2,and 3 are examples of this structure. A further addition of a second metallic fragment can formally occur in three different modes: on using the nomenclature developed in ref 11, trans(l,4) ( D 3 d , c), meta(l,3) (CzU,d), and cis(l,2) (CzU,e) isomers can be formed. Octanuclear carbonyl clusters possessing a trans bicapped octahedral core are exemplified by RUG(CO)18[CU(C7H8)]212and several carbido species of rhenium, such as [Re8C(C0)2412-,[Re7C(C0)21R(C4H7)lZ-, [Re7C(CO)2~Ir(CzH4XCO)lz-,[Re7C(C0)ziPd(CsHs)12-, and (11)Henly, T. J.; Shapley, J. R.; Rheingold, A. L. J. Organometal. Chem., 1966,310,55. (12)Ansell, G. B.; Modrick, M. A.; Bradley, J. S.;Acta Cryst., 1984, C40, 365.

190 Organometallics, Vol. 14, No. 1, 1995

Ceriotti et al.

c12

02 1

:p

Figure 3. ORTEP drawing and atom-labeling scheme for [Ir6(C0)14(HgC1)2]2-.Thermal ellipsoids are drawn at 30% probability. Carbonyl carbons are designated as the oxygens to which they are attached. of the two AuPPhs groups in 4,evidenced by 31PNMR, [ R ~ ~ C ( C O ) Z ~ ( A U P Ptrigonal ~ ~ ) ~prisms ~ - ; ~bicapped ~,~~ on triangular faces are present in the [Rh6C(C0)15(MZ)zI this cluster can be conceived as having an average Cpv family ( M = Ag,L = CH3CN; M = Cu, Ag, Au, L = structure, i.e. (e) or even (g),where a formal Auz(PPh3)a PPh31.I4 moiety bridges an Ir-Ir edge. This latter description The m e t a ( l , 3 ) bicapping process ideally leads to would raise a strong analogy between the black (Du) products possessing a metal skeleton of Cpv symmetry isomer of Ir6(CO)16,3 possessing four symmetricallyedge(d), such as those found in Pt3Ru5C(C0)14(COD)z,15[Ossbridging carbonyls, and compound 4, in which the twoelectron donor Auz(PPh3)~fragment formally substitutes Ptz(C0)17(COD)~l,’~ Pd8(CO)8(PMe3)7,17and in the [ ~ S ~ ( ~ ~ ) [hIr(co)2313Z Z ~ ~ - , ~ l9 ~and [Ir6(Co)i4(H&1>~1~- one p-CO of the homoleptic cluster. anions. Products of cis(l,2) addition or clusters containFinally, compounds 3 and 5 can also be correlated ing the metal cores (e) in Scheme 1, are still unknown; with the simple Td geometry of the red isomer of 11-6however, after a slight distortion the two capping metals (CO)IS;as a matter of fact, substitution of p3-carbonyls can be shifted to within bonding distance of each other, of the latter with one or two [HgClI- fragments leads leading t o the metallic framework of [Rh&(CO)13to the structures of 3 and 5, respectively. In order to (AuPPh3)2I2Oand [Ru~H(CO)~~B(AUPP~~)~].~ With difavoid a high separation of formal charge, [ I I - ~ ( C O ) ~ ~ ferent deformations the solid state structures (0 of (HgCl)zI-, as 3,should be better considered as an Ir6[RU&(CO)I~(CUL)~~~ and [ I ~ ~ ( C O ) ~ ~ ( A Ucan P P ~be~ ) Z I (CO)16 analogue, rather than as an adduct of two HgCl+ attained, without breaking the M-M bond between the fragments to the (unknown) [Ir6(C0)14I4-. heterometal atoms. Considering the fluxional behavior Both views agree with electron-counting theories: according to the latter description, each [HgClI+capping (13) (a) Ma, L.; Wilson, S. R.; Shapley, J. R. Inorg. Chem., 1990,29, group adds 12 electrons to the total number of CvE’s 5133. (b) Henly, T. J.; Shapley, J. R.; Rheingold, A. L.; G i b , S. J. (cluster valence electrons), but does not increase the Organometallics, 1988,7,441.(c) Henly, T. J.; Wilson, S. R.; Shapley, J. R. Inorg. Chem., 1988, 27, 2551. (d) Henly, T. J.; Shapley, J. R. number of filled skeletal orbitals, as required by the Organometallics, 1989, 8, 2729. capping principle.21 In the second case, the [HgClI(14) (a)Albano, V. G.;Braga, D; Martinengo, S.; Chini, P.;Sansoni, M; Strumolo,D. J.Chem. SOC.,Dalton Trans.,1980,52. (b)Fumagalli, groups can be considered as nonconventional ligands A.; Martinengo, S; Albano, V. G.; Braga, D. J. Chem. SOC.,Dalton donating two electrons each to the “Irg(CO)14))fragment. Trans., 1988, 1237. Indeed, EHMO calculations show that HgC1- and CO (15)Adams, R.; Wu, W. J. Cluster Sci., 1991,2, 271. (16)Couture, C.; Farrar, D. H.; Goudsmit, R. J. Inorg. Chim. Acta, groups are isolobal fragments, having a filled u orbital l984,89, L29. and two empty x orbitals (suitable for back-donation) (17) Bochmann, M.; Hawkins, I.; Hursthouse, M. B.; Short, R. L. Polyhedron, 198’7, 6, 1987. at comparable energy levels.22 Moreover, the ability of (18)Jackson, P.F.; Johnson, B. F. G.; Lewis, J.; Raithby, P. R. J. Hg atoms to act as simple ligands in osmium carbonyl Chem. SOC.,Chem. Commun., 1980, 60. (19) Ma, L.; Wilson, S. R.; Shapley, J. R. J.Am. Chem. SOC.,1994, 116, 787. (20)Fumagalli, A.; Martinengo, S.; Albano, V. G.; Braga, D.; Grepioni, F. J. Chem. SOC.,Dalton Trans., 1989, 2343.

(21) (a) D. M. P. Mingos, ACC.Chem. Res., 1984, 17, 311. (b) D. M. P. Mingos, D. J. Wales, Introduction to Cluster Chemistry; PrenticeHall International: Englewood Cliffs, NJ 1990.

Au-Ir a n d Hg-Ir Mixed-Metal CO Clusters

Organometallics, Vol. 14,No. 1, 1995 191

Scheme 1. Symmetry of Mono- and Bicapped Octahedra C3" monocapped octahedron

o h octahedron

.!

L

I V

bicapped octahedra cis (1,2)

meta (1.3)

trans ( 1 , 4 )

(d) czv

distortion of the capping atoms

I

I

I

V

V

n

clusters was recently invoked in order to rationalize their fluxional behavior.23 Unfortunately, very little data are known for the chemical shift of Hg bound to large clusters, and the value found for 5 cannot therefore be attributed great significance in supporting our p r ~ p o s a l .For ~ sake of comparison, it should be noted that the chemical shift of HgCl groups bound to iridium in mononuclear organometallic compounds typically are in the negative range (-2000 to -3000 ppmh7 Experimental Section All the solvents were purified and dried by conventional methods and stored under nitrogen. All the reactions were carried out under an oxygen-free nitrogen atmosphere using the Schlenk-tube technique.24 [IrdC0)1612-,26 [Cu(NCMe)d (22) CACAO, Mealli, C.; Proserpio, D. M. J. Chem. Ed., 1990, 67, 399. (23) Gade, L. H. Angew. Chem. Int. Ed. Engl., 1993,32,24.

P F s , and ~ ~ AuPPh&lZ7 were prepared by the published methods. Infrared spectra (IR)were recorded on a Perkin-Elmer 781 grating spectrophotometer using calcium fluoride cells previously purged with N2. Samples for mass spectra were suspended in a matrix of m-nitrobenzyl alcohol and bombarded with a beam of Xe atoms at 70 keV with a VG Micromass machine and compared with computed theoretical isotope patterns; mass peaks refer to the most abundant isotopomers. Elemental analyses were carried out by the staff of Laboratorio di Analisi of the Dipartimento di Chimica Inorganica, Metallorganica e Analitica. 31Pand lg9HgNMR spectra were recorded on a Bruker AC200 spectrometer, operating at 81.0 MHz for phosphorus and at 35.76 MHz for mercury and are reported in ppm downfield from the (24) D. F. Shriver, M. A. Drezdzon, in The Manipulation of Airsensitive Compounds, 2nd ed.; Wiley: New York, 1986. (25) Angoletta, M.; Malatesta, L.; Caglio, G. J.Orgunometal. Chem., 1976, 94, 99. (26) Kubas, G. J. Znorg. Synth., 1979,19, 311. (27) Bruce, M. I.; Nicholson, B. EL;Shawkataly, 0. B. Inorg. Synth,, 1989,26, 325.

192 Organometallics, Vol. 14, No. 1, 1995

Ceriotti et al.

Table 3. Crystal Data and Data Collection Parameters compd formula fw cryst syst space group a, A b, A

4

Sa

c5iH3chzIr6015Pz

C6zbC1zHgzIr601& 2696.2 monoclinic

2491.9 hi_clinic P1 13.160(2) 13.714(4) 18.266(3) 65.47(2) 110.93(2) 112.07(1) 2699(2) 2 3.066 202.06 0.70

Table 4. Fractional Atomic Coordinates for [IrdCO)14AuPPhdd (4) (Esd’s in Parentheses) atom

Au 1 Au2 CC IIl 10.257(2) Ir2 46.848(4) Ir3 14.639(3) c, A Ir4 90 a, deg Ir5 107.83(2) B, deg Ir6 90 Y,deg P1 6696(4) v, A3 P2 4 Z Ob1 2.674 Dcdcdr g Cm-3 Ob2 165.85 p(Mo Ka), cm-l Ob3 0.22 min. transm. fact. 0 11 scan mode w 0 012 w-scan width, deg 1.2 0.35 tan e 1.2 0.35 tan e 0 21 &range, deg 3-27 3-25 022 octants of reciprocal fh,fk,l fh,k,l 0 31 space explored 032 measd reflns 12197 6182 0 41 unique obsd reflns with 7217 3619 042 I 3u(I) 0 51 final R and Rwa 0.032, 0.034 0.037,0.036 052 505 41 1 no.of variables 0 61 - klFcl)Z/C~Fo2]L”. 062 Cbl Cb2 external standard (85%H3P04 in DzO for phosphorus and neat Cb3 MezHg for mercury).2 c11 Preparation of [I~~(CO)IS(CUNCM~)ZI. (PPh4)2[Ir6(co)161 c12 (90 mg; 40 pmol), CHzClz (5 mL), [Cu(NCMe)4]PF6 (30 mg; 80 c 21 pmol) were placed in a Schlenk tube under nitrogen; infrared c22 spectra showed complete conversion afier 10 min stirring; C3 1 cyclohexane (5 mL) was added and the colourless precipitate C32 C4 1 of (PPh)PF6 was eliminated by filtration. The red solution C42 was layered with cyclohexane. On standing overnight, well C5 1 shaped orange crystals of Ir6(CO)16and Cu metal were formed. C52 Preparation of [Ir&O)l~(AuPPha)zl in .%Propanol. C6 1 AuPPh&1(490 mg; 0.98 mmol) and THF (10 mL) were placed C62 in a Schlenk tube. When the solid was dissolved, AgBF4 (185 Clll mg; 0.95 mmol) was added, causing the precipitation of AgCl c112 which was allowed t o settle for 10 min. K2[Irg(co)15] was C113 dissolved with 2-propanol (30 mL) and filtered; the salt could C114 C115 not be weighed, since there were too large amounts of KC1 C116 present; it was estimated 350 mg (0.21 mmol). Small portions c121 (2 mL each) of the solution of [AuPPhs]BF4 were added, while c122 monitoring the disappearance of [Ir6(CO)16]2- by infrared. C123 When the reaction was complete, about one half of the solvent C124 was evaporated in vacuo. The black solid was filtered, washed C125 with 2-propanol (5 mL), and dried. It was then extracted with C126 CHzClz and layered with 2-propanol. C131 Preparation of [ I r d C O ) l d A u P P ~ ) z in l CHZClz. A soluC132 C133 tion of [AuPPh31BF4 was prepared in a Schlenk tube under C134 nitrogen with AuPPh&1(900 mg; 1.81mmol), CHzClz (15 mL) C135 and AgBF4 (336 mg; 1.71 “01). (NEt4)2[Ir6(C0)16](350 mg; C136 0.19 mmol) was dissolved in CHzClz (15 mL), and small c211 fractions of the first solution were added, monitoring the c212 reaction by infrared. Total conversion was achieved after C213 addition of 12 mL (molar ratio Ir6:Au = 1:7). The initially C214 brown solution became red and, eventually, green. Addition C215 of cyclohexane (15 mL) caused precipitation of colourless NEbC216 BF4, which was eliminated by filtration. The solution was c221 c222 dried, and the residue was dissolved in CHzClz and layered C223 with 2-propanol. Yield 58%. C224 Anal. Calcd for Ca~Ha&~zIrsOlsPz: c , 24.2; H, 1.2. C225 Found: C, 24.26; H, 1.37. C226 FAB-MS (negative ions) m / z : 2037 [ I ~ ~ ( C O ) ~ & I P P ~ ~ ] - ;C23 1 2037 28x (2 = 1-51 [Ir6(C0)16.&hPPh&; the parent peak C232 was never observed, either with electron impact or in the C233 positive FAB region. C234 Preparation of CIr&O)d€gC1)d2- &om HgCls (PPh4hC235 C236 [Ir6(c0)161(460mg; 0.204 mmol), THF (20 mL), HgClz (98 mg;

+

’

-

+

xla

-0.3 1720(4) -0.21608(4j -0.08140(4) 0.01660(4) -0.05317(4) -0.15521(4) -0.21007(4) 0.07365(4) -0.4943(2) -0.2936(3) -0.1758(9) 0.2513(7) 0.0018(8) 0.0806(9) -0.1260(9) 0.0956(8) 0.000(1) -0.151(1) 0.1424(9) -0.198(1) -0.3474(8) -0.263( 1) -0.4430(8) 0.2756(8) 0.1397(9) -0.157( 1) 0.164(1) -0.022( 1) 0.021(1) -0.115(1) 0.072(1) O.O07(1) -0.1 15(1) 0.069(1) -0.185( 1) -0.276(1) -0.247( 1) -0.359( 1) 0.199( 1) 0.1 14(1) -0.604( 1) -0.574( 1) -0.654( 1) -0.759( 1) -0.787(1) -0.7 10(1) -0.4995(9) -0.593( 1) -0.595( 1) -0.506( 1) -0.409( 1) -0.408( 1) -0.543 l(9) -0.618( 1) -0.641(1) -0.588( 1) -0.5 10(1) -0.491( 1) -0.432( 1) -0.460(1) -0.566( 1) -0.640( 1) -0.611(1) -0.507( 1) -0.31 l(1) -0.406( 1) -0.415(1) -0.331(1) -0.236( 1) -0.227( 1) -0.206( 1) -0.1 18(1) -0.061( 1) -0.085( 1) -0.171(1) -0.230( 1)

Ylb 0.49610(4) 0.3 18~ ( 4 j 0.52205(4) 0.55182(4) 0.74338(4) 0.71233(4) 0.54477(4) 0.72841(4) 0.4568(3) 0.13 16(3) 0.6135(9) 0.5968(8) 0.9462(7) 0.3837(9) 0.520(1) 0.5828(9) 0.3056(8) 0.9384(8) 0.848(1) 0.737( 1) 0.8111(9) 0.3268(8) 0.58 1(1) 0.9097(8) 0.716(1) 0.628(1) 0.606(1) 0.848(1) 0.435( 1) 0.520(1) 0.574(1) 0.399(1) 0.863(1) 0.808( 1) 0.725(1) 0.773( 1) 0.407(1) 0.563(1) 0.841(1) 0.7 17(1) 0.344(1) 0.296(1) 0.207(1) 0.169( 1) 0.218(1) 0.312(1) 0.417(1) 0.416(1) 0.378(1) 0.344(1) 0.350(1) 0.385(1) 0.582(1) 0.598(1) 0.703(1) 0.788(1) 0.769(1) 0.669(1) 0.080(1) 0.147(1) 0.108(1) 0.007(1) -0.053( 1) -0.017( 1) 0.085(1) 0.095(1) 0.074(1) 0.038(1) 0.026(1) 0.046(1) 0.056(1) 0.114(1) 0.048(1) -0.067( 1) -0.123( 1) -0.061( 1)

dc

0.25443(3) 0.3 1209(4j 0.30067(3) 0.17956(3) 0.07945(3) 0.20160(3) 0.12888(3) 0.23976(3) 0.2716(2) 0.3417(2) -0.0418(6) 0.2894(7) 0.1775(8) 0.4 106(7) 0.4516(7) 0.0313(7) 0.2412(9) -0.0278(7) -0.0014(8) 0.3445(7) 0.0745(7) 0.1033(8) 0.0403(7) 0.1850(7) 0.4189(7) 0.0209(9) 0.2542(9) 0.192(1) 0.3706(9) 0.3944(8) 0.0890(9) 0.218(1) 0.012(1) 0.030(1) 0.290(1) 0.1251(9) 0.1 170(9) 0.076(1) 0.2045(8) 0.3513(9) 0.2345(9) 0.1947(9) 0.170(1) 0.185(1) 0.224(1) 0.2478(9) 0.3801(8) 0.3995(9) 0.484(1) 0.545(1) 0.525(1) 0.442(1) 0.2168(8) 0.1396(9) 0.094(1) 0.130(1) 0.2088(9) 0.2483(9) 0.3634(9) 0.391 l(9) 0.411(1) 0.404(1) 0.377(1) 0.3551(9) 0.2571(9) 0.1906(9) 0.120(1) 0.1 14(1) 0.181(1) 0.256(1) 0.4330(9) 0.484( 1) 0.558(1) 0.583(1) 0.532( 1) 0.459(1)

Au-Ir and Hg-Ir Mixed-Metal CO Clusters

Organometallics, Vol. 14, No. 1, 1995 193

Table 5. Fractional Atomic Coordinates for the Anion [Ir6(CO)~~(HgC1)~l2(5) (Esd's in Parentheses) atom

xla

ylb

dC

Hg 1

0.0 0.2484(2) 0.0426(2) 0.3139(2) 0.1 177(2) 0.2663(2) 0.3905(1) 0.1623(2) -0.1217(8) 0.2913(9) 0.074(2) 0.574(2) -0.019(3) -0.239(3) 0.3 14(2) 0.525(3) 0.208(2) -0.155(3) 0.345(2) 0.263(2) 0.508(2) 0.632(3) -0.092(2) 0.309(2) 0.107(3) 0.460(3) 0.015(3) -0.123(3) 0.316(4) 0.452(4) 0.176(3) -0.035(3) 0.317(3) 0.266(2) 0.463(3) 0.536(4) 0.011(3) 0.258(4)

0.14913(3) 0.05208(3) 0.14359(3) 0.14387(3) 0.09953(3) 0.15307(3) 0.10363(3) 0.09430(3) 0.1637(2) 0.0017(2) 0.1384(5) 0.1572(5) 0.2057(6) 0.1232(6) 0.2029(6) 0.1205(6) 0.0801(5) 0.0733(7) 0.1506(5) 0.2149(5) 0.091 l(5) 0.0762(6) 0.0602(5) 0.0671(5) 0.1321(7) 0.1467(6) 0.1825(8) 0.1304(7) 0.1798(9) 0.133(1) 0.0892(8) 0.0819(7) 0.1536(7) 0.1915(6) 0.0939(7) 0.0852(9) 0.0709(7) 0.0750(9)

0.0 0.1863(1) 0.1980(1) 0.3188(1) 0.0870(1) 0.1245(1) 0.2085(1) 0.2879(1) -0.1644(5) 0.1887(6) 0.408(1) 0.2431) 0.214(2) 0.150(2) 0.387(2) 0.49 l(2) -0.083(2) 0.023(2) -0.064(2) 0.143(2) 0.043(2) 0.35 l(2) 0.257(2) 0.478(2) 0.337(2) 0.224(2) 0.205(2) 0.168(2) 0.355(2) 0.426(3) -0.019(2) 0.047(2) 0.006(2) 0.129(2) 0.108(2) 0.292(3) 0.264(2) 0.403(3)

Hg2 Irl Ir2 Ir3 Ir4 Ir5 Ir6 c11 c12 Otl Ot2 011 012 0 21 022 0 31 032 0 41 042 0 51 052 0 61 062 Ct2 Ct2 c11 c12 c 21 c22 C3 1 C32 C41 C42 C5 1 C52 C6 1 C62

0.36mmol) and NazC03.10HzO (77mg; 0.27mmol) were placed in a Schlenk tube under nitrogen. The reaction mixture was stirred vigorously for 12 days at room temperature. A black insoluble residue was slowly formed, while the colour of the clear solution turned red. Small amounts of HgClz and NazCO3 were then added, and the stirring continued for 5 more days. The disappearance of [Ir6(CO)16Hgcl]-could be followed by monitoring the infrared band of the bridging carbonyls at 1765 cm-l. When the reaction was complete, the solution was cautiously filtered and dried in vacuo. The red residue was dissolved in CHzClz and layered with cyclohexane. Yield: 425 mg, 78%. The cluster is well soluble in THF, CHZC12, and acetone. It decomposes when exposed to protic solvents, such as alcohols or water. Anal. Calcd for C ~ Z & O C ~ Z H ~ Z Ic, ~ ~27.6; P Z ~H, I ~1.5. : Found: C, 28.2;H, 1.46.The compound is always impure with uncharacterized thin, colorless, needles. The FAB-MS immediately recorded showed a broad, unresolved signal at m l z = 2008,corresponding to the parent peak. However, fast decomposition of the cluster with the matrix did not permit the recording of satisfactory spectra. Preparationof [Ira(CO>~&SgCl)zl~from HgzCh. (Pfih[Ir6(co)U] (493 mg; 0.219 mmol), THF (20mL), and HgzClz

(103 mg; 0.219 mmol) were placed in a Schlenk tube under nitrogen. A grey insoluble residue immediately formed, while the colour of the clear solution turned red. The reaction mixture was stirred vigorously for 15 days at room temperature. The product was treated as above described, with comparable yields (420mg; 71%) and higher purity. Anal. Calcd for C ~ Z H ~ O C ~ Z H ~c,Z 27.6; I ~ ~ H, P Z1.5. ~~~: Found: C, 27.33;H, 1.66. X-Ray Collections and Structural Refinements. A summary of crystal data parameters and some experimental details are collected in Table 3. Crystals of the two compounds were mounted in arbitrary orientation on the tip of a glass fibre mounted onto a goniometer head. Diffraction data were collected on a n Enraf-Nonius CAD4 automated diffractometer using Mo Ka radiation (1 = 0.710 73 A), equipped with a pyrolitic graphite crystal monochromator in the incident beam. Cell dimensions were obtained by the least-squares method on the setting angles of 25 intense reflections, randomly distributed in the reciprocal space, having 9 < 8 < 11". Periodic measurements of three standard reflections revealed a crystal decay, on X-ray exposure, which was evaluated as null for 4 and 22% for 5a (on I) at the end of data collection. Lorentz, polarization, decay and absorption corrections were applied, the latter performed with the empirical method described in ref 28. The structures were solved by Direct Methods (MULTAN),29 which succeeded in locating the metal atoms; the coordinates of the remaining non-hydrogen atoms were determined by successive least-squares refinements and difference Fourier maps. The refinements were carried out by full-matrix least squares with anisotropic temperature factors for Ir, Hg, Au, C1, P and, for 4, also for carbonyl atoms. Individual weights were given as: w =N[uz(F,) BFO21,withA = 1.3353,1.0646 and B = 0.000 572, 0.000824 for 4 and Sa, respectively. Scattering factors, corrected for real and imaginary anomalous dispersion terms, were taken from ref 30;the contribution of the hydrogen atoms to the scattering factors was neglected. The absolute structure of the crystal of Sa was tested by refining two inverted models; tabulated values refer to that having the lowest agreement discrepancy. All computations were performed on a Silicon Graphics Indigo computer, running IRM 4.1,using SHELX31 The positional parameters for 4 and 5a are listed in Tables 4 and 5 , respectively.

+

Acknowledgment. We acknowledge the Minister0 della Ricerca Scientifica for funding and the Consiglio Nazionale delle Ricerche for use of NMR equipments. Supplementary Material Available: Tables of fractional atomic coordinates and isotropic thermal parameters and of all bond distances and angles for 4a and 5a (11 pages). Ordering information is given on any current masthead page.

OM940557L (28) North, A. C. T.; Phillips, D. C.; Mathews, F. S.; Acta Cryst., Sect.A.: Cryst. Phys. D e .Theor., Gen. Crystallogr. 1968, A24, 351. (29) Germain, G.; Main, P.; Woolfson M. M. MULTAN, a system of computer programs for the automatic solution of crystal structures from X-ray diffraction data. Acta Crystallogr., 1971, A27, 368. (30) International Tables for X-Ray Crystallography; Kynoch Press: Birmingham, England, 1974; Vol. 4. (31) Sheldrick, G. M. SHELX76, A program for crystal structure determination, University of Cambridge, 1976.