J. Am. Chem. SOC.1991, 113, 5282-5292
5282
play an important role as dipolar templates for the activation of substrate molecules. Of particular interest will be reactions with H2 that may under certain conditions result in heterolytic cleavage of the H 2 bond and formation of the Mo(H)(O)(SH) hydridehydrosulfide units. In general M(H)(SR) units are rather rare. Notable exceptions include the one present in the [Mo(H)(ti~t)~(PMe,Ph),]complex4 (tipt = 2,4,6-SC6H2('Pr)3) and the Rh(H)(SR) units obtained by the reversible addition of H2 into the Rh-S bonds of the [(triph~s)Ru(p-S)~Rh(triphos)]~+com~lex.'~ If the Mo(H)(O)(SH) units can be generated, they should (46) Casewit, C. J.; Coons, D. E.; Wright, L. L.; Miller, W. K.; Rakowski DuBois, M.Organomerallics 1986, 5, 951. (47) Coons, D. E.; Laurie, J. C. V.; Haltiwanger. R. C.; Rakowski DuBois,
M. J. Am. Chem. Soc. 1987, 109, 283. (48) Burrow, T. E.; Lazarowych, N. J.; Moms, R. H.; Lane, J.; Richards, R. L. Polyhedron 1989,8, 1701.
(49) (a) Bianchini, C.; Mealli, C.; Meli, A.; Sabat, M.Inorg. Chem. 1986, 25, 4617. (b) Bianchini, C.; Meli, A. Inorg. Chem. 1987, 26, 4268.
be quite reactive, and some of their reactions with disulfides, thiophenes, and thiols may result in S-S or C-S bond cleavage with direct relevance to HDS c a t a l y s i ~ . ~ ~ ~ ~ ~ Acknowledgment. The support of this work by a grant from the National Science Foundation (CHE-90006069) is gratefully acknowledged. D.C. also acknowledges stimulating discussions with Prof. W. H. Pearson. Supplementary Material Available: Tables S 1 4 3 containing listings of positional parameters, thermal parameters, and selected distances and angles of [Ph4P][(C,H,)MO(O)(JL-S)~MO(O)(S~)~~ IV, (Ph4P)2[(s4)Mo(o)(r2-S)2Mo(o)(s)l, 1x9 and (Et4N14[[(S4)Mo(0)(p2-S),Mo(O)(S)12), X (20 pages); Tables S4-S6 listing structure factors for IV, IX, and X (43 pages). Crystalcomplex lographic data for the [(DMF),Mo(0)(p-S),Mo(O)(S2)] already has been deposited with a previous communication.20 Ordering information is given on any current masthead page.
Cluster Core Isomerization from Planar to Tetrahedral: Experimental and Theoretical Aspects. Steric Control by the Ligands of Cluster Geometry. Synthesis and Crystal Structure Pierre Braunstein,*it Claude de Meric de Bellefon,t Salah-Eddine Bouaoud,t Daniel Grandjean,g Jean-Franeois Halet,$ and Jean-Yves Saillard**$ Contribution from the Laboratoire de Chimie de Coordination, Associd au CNRS (UA 416), Uniuersitd Louis Pasteur, F-67070 Strasbourg Cddex, France, Ddpartement de Chimie, Universitd de Constantine, Route de Ain-el-Bey, Constantine, Algdrie, and Laboratoire de Cristallochimie, Associd au CNRS (VA 254), Universitd Rennes I, F-35042 Rennes Cddex, France. Received May 8, 1990
Abstract: The reaction of the phosphine ligands PCy,, P(i-Pr)3, PCyPh2, P ( ~ - T O I )P@-ToI)~ ~, and P(~-Bu)~, with the trinuclear complexes tran~-[Pt(M(Co)~Cpl~(PhCN),I (M = Mo, W; Cp = 7-C5H5or Cp' = q-C5H4CH3)affords the tetranuclear clusters [ P ~ ~ M ~ C P ~ ( C O ) ~(M ( P= R ~Mo, ) ~ R3 ] = Cy,, 1; M = Mo, R3 = Cy,, Cp = Cp', 2; M = W, R3 = Cy3, 3; M = Mo, R3 = (i-Pr)3, 4; M = W, R3 = (i-Pr)3, 5; M = Mo, R3 = CyPh2, 6; M = Mo, R3 = (m-T0l)3, 7; M = Mo, R3 = (p-Tol),, 8; M = Mo, R3 = ( ~ - B u )9). ~ , Solution studies using ,*P NMR spectroscopy have revealed that clusters 1-5 exist as mixtures of two isomers. The geometry of the metallic skeleton is planar triangulated rhombohedral (PTR) in isomers la-% like in clusters 6-9, whereas it is tetrahedral in isomers 1 M b . The isomerization process was shown to be reversible, and its thermodynamics has been determined for some of these clusters. The solution ratio of the two structural isomers (i.e., b:a) depends on the solvent used, the temperature, and the steric and electronic properties of the phosphine ligand. Solvents such as toluene and bulky and basic phosphine ligands (e.g., K y 3 ) favor the tetrahedral isomer b, whereas more polar solvents (e.&, dichloromethane) and small and/or less basic phosphine ligands (e.g., P ( ~ - T O ~P(i-Bu),) )~, point to the planar isomer a. Crystal data for 2b: monoclinic, space group P2,/n with Z = 4; u = 10.321 (3), b = 24.351 (8), c = 21.368 (6) A; B = 92.76 (4)O; V = 5364 A3; R = 0.042, R, = 0.052. Extended Hiickel molecular orbital calculations have been carried out on the model compound [Pt2M02Cp2(C0)6(PH3)2] in both PTR (a) and tetrahedral (b) geometries. The calculations have shown that, in isomer b, the Mo-Mo u* orbital is vacant and the Pt-Pt us one is occupied, while in isomer a Mo-Mo us is occupied and the LUMO has a strong Pt-Pt u* antibonding character. They confirmed the equilibrium measurements by revealing the existence of an avoided level crossing between isomers a and b, giving rise to an energy barrier and therefore to two isomers able to coexist in solution.
Introduction Polyhedral rearrangement is one of the most challenging problems in cluster chemistry.' Possible mechanisms for the framework reorganization or isomerization of boranes or carboran= have been proposed already 20 years ag+ but are still under current investigation.2b-c The conditions for the tetrahedral butterfly square-planar transformations of the 20e X2Y2Zintl ions have been recently investigated theoreti~ally.~Being more
-
-
'Dtpartement Laboratoire de Chimie de Coordination, Universitt Louis Pasteur. de Chimie, Universitt de Constantine. t
8 Laboratoire de
Cristallochimie. Universitt de Rennes 1.
0002-7863/91/1513-5282$02.50/0
recent, the chemistry of transition-metal clusters has provided only a few examples of skeletal i~omerism.~.~ This raises the question (1) For recent discussions, see: (a) Johnson. E. F. G. J. Chem. Soc., Chem. Commun. 1986,27. (b) Vahrenkamp, H. Ado. Organomet. Chem. 1983,22, 169. (c) King, R. B. Inorg. Chim. Acra 1986, 116, 99. (d) King, R. B. In Molecular Srrucrures and Energerics; Licbman, J. F.,Greensberg, J. A., Eds.; Verlag Chemic: Deerfield Beach, FL, 1986; s a also references cited therein. For a general review, sa:Johnson, B. F. G. In Transirfon Metal Clusrers; Johnson, 8. F. G., Ed.; Wiley: London, 1980. (2) (a) Lipscomb. W. N. Science (Washington, D.C.)1966,153, 373. (b) Gimarc, B. M.; Ott, J. J. Inorg. Chem. 1986, 25, 2708. (c) Wales, D. J.; Stone, A. J. Inorg. Chem. 1987, 26, 3845.
0 1991 American Chemical Society
Cluster Core Isomerization
J . Am. Chem. Soc., Vol. 113, No. 14, 1991 5283
Square
an n p x d w d r 3 .I removed
Buttwily
Tdgonal blpyramld
Tetrahedron
of the prediction of cluster skeleton geometries by using of the electron counting rules (ECR).6 Thus, different electron counts for tetranuclear clusters will be in general easily related to their butterfly, square, or tetrahedral skeletal geometries. A butterfly geometry (with five metal-metal bonds) is generally considered as an arachno structure, derived from a closo octahedron by removal of two adjacent vertices” and characterized by a total electron count (TEC) of 62 and the same number of skeletal electron pairs as the parent octahedron (S = 7). In principle, the square geometry can also be viewed as an octahedron-based arachno structure by removal of two opposite vertices. However, the T E C of such M4 organometallic clusters is generally larger (e.g.. 64 in O S ~ ( C O ) ~ ~The ) . ~tetrahedral structure is usually considered as a nido structure derived from a trigonal bipyramid (S= 6), by removal of an apical vertex. The literal application of ECR indicates a TEC of 60 for the tetrahedron, as well as for the other nido butterfly derived from the trigonal bipyramid, by removal of an equatorial vertex (see Scheme I). We know from the published data that this is valid for the tetrahedral but not for the butterfly complexes, which generally bear 62e (Note that the angle between the wings of a butterfly derived from a regular trigonal bipyramid (141.0°) is different from the one of the butterfly derived from an octahedron ( 109S0), but there is experimental evidence for the facile folding of butterfly skeletons*”). These examples illustrate the importance of skeletal shape and metal to metal connectivity when considering the geometries derived from a parent polyhedron according to the electron counting rules. Deviations from these rules have been encountered (3)Cave, R. J.; Davidson, E. R.; Sautet, P.; Canadell, E.; Eisenstein, 0. J. Am. Chem. Soc. 1989,111,8105. (4)For a good introduction to isomerism in transition-metal clusters, see: (a) MOller, M.;Schacht, H.-T.; Fischer, K.; Ensling, J.; GLitlich, P.; Vahrenkamp, H. Inorg. Chem. 1986,25,4032. (b) Sappa, E.; Tiripicchio, A.; Carty, A. J.; Toogood, G. E. Prog. Inorg. Chem. 1987,35,437. (5)For selected examples of cluster core isomerism, see: (a) Braunstein, P.; Jud, J.-M.; Tiripicchio, A,; Tiripicchio-Camellini, M.;Sappa, E. Angew. Chem., In?. Ed. Engl. 1982, 21. 307. (b) Williams, P. D.; Curtis, M. D.; Duffy, D. N.; Butler, W. M. Orgunometullics 1983,2, 165. (c) Bruce, M. I.; Nicholson, B. K. J. Orgunomet. Chem. 1983,250,627.(d) Briant, C. E.; Hall, K. P.; Mingos, D. M. P. J . Chem. Soc., Chem. Commun. 1984,290.(e) Fjare, D. E.;Gladfelter, W. L. J . Am. Chem. Soc. 1984, 106, 4799. (f) Bunkhall, S.R.; Holden, H. D.; Johnson, B. F. G.; Lewis, J.; Pain, G. N.; Raithby, P. R.; Taylor, M.J. J. Chem. Soc., Chem. Commun. 1984,25. (g) Braunstein, P.; Kervennal, J.; Richert, J.-L. Angew. Chem., In?. Ed. Engl. 1985,21. 768. (h) Bender, R.; Braunstein, P.; Tiripicchio, A.; TiripicchioCamellini, M. Angew. Chem., In?. Ed. Engl. 1985, 24,861. (i) Lang, H.; Huttner, G.; Sigwarth, B.; Weber, U.;Zsolnai, L.; Jibril, I.; Orama, 0. Z . Nuruflorsh. 1986, llB, 191. u) Huttner, 0.;Knoll, K. Angew. Chem., Int. Ed. Engl. 1907,26,743.(k) Wucherer, E.J.; Tasi. M.; Hansert, B.; Powell, A. K.; Garland, M. T.; Halet, J.-F.; Saillard, J.-Y.; Vahrenkamp, H. Inorg. Chem. 1989,28,3564. (1) Housecroft, C. E.; Shongwe, M.S.;Rheingold, A. L. Orgunometullics 1989,8, 2651. (m) Braunstein, P.; Richert, J.-L.; Dusausoy, Y . J. Chem. SOC.,Dalton Trans. 1990, 3801. (6)(a) Wade, K.Ado. Imrg. Chem. Rudiochem. 1976,18,1. (b) Lauher, J. W. J . Am. Chem. Soc. 1975,97,5034.(c) Mingos. D. M. P. Acc. Chem. Res. 1984, 17, 31 1. (7)(a) Johnston, V. J.; Einstein, F. W. B.; Pomeroy, R. K. J . Am. Chem. Sa.1987,109,81 1 1 . (b) Lauher, J. W. I n f . J . Quunfum Chem. 1988,22, 309.
when dealing with clusters differing in their electron count while keeping the same overall skeletal geometry, as in [Nis(CO)121?which has a TEC of 76 instead of the expected one of 72.* Thew kinds of deviations have generally been rationalized by extended Hiickel molecular orbital calculation^.^ Subtle changes in the *-acceptor properties of ligands (CO vs CH2) have been invoked and substantiated by M O calculations to account for different geometries (butterfly and tetrahedral) for the isoelectronic 60e (L = CO and CH2, reclusters [PtOs3(p-H)2(CO)10(PCy3)(L)] spectively).I0 The question we would like to address concerns a new class of isomeric clusters that also have the same electron count but exhibit different skeletal geometries. In other words, do the current electron counting rules account for cluster skeletal isomerism within a family of closely related molecules characterized by the same TEC? As defined by Mingos in 1984, “skeletal isomers are compounds having the same stoichiometry but different skeletal geometries in the solid state”,5d as encountered, e.g., in [Pt3(p-PPh2)3Ph(PPh,),] ,5h [Os4S(CO)12(HC2Ph)],I1 [ R ~ A U ~ H ~ ( P M ~ ~ P ~ ) ~ (PPh3)3],12 [ F ~ , A u , ( C O ) , ~ L ~ B H(]L = p h o ~ p h i n e ) , ~ ’
[RU~CU~H~(CO)~~(P(~-P~)~}~I,~~ [R~~AU~C(CO)I~(PE~~)~ [Aug(P(C6H40Me-p)3}sl[NO313 9 % or [OsloAu,C(CO)24(PR3),Im ( M = Cu, Ag, Au; n = 1, m = 1; n = 2, m = O).I4 In these systems, each skeletal isomer has the same TEC as the other. In contrast, recent examples have been reported in which the change in geometry is accompanied by a change in the total electron count as in [Fe4(p-A)(C0)13]-(A = electrophilic fragment)15 and [ W R U ~ C ~ ( C O ) (Cp ~ ~ H=] C5H5or C5Me5).I6 Furthermore, clusters having the same skeletal geometry but that differ in the respective occupation of the vertices display an additional isomerism, a positional isomerism. This is particularly obvious when the atoms occupying the vertices are different in nature, as in [ F e R u 3 N (C O ) 12]-,Se [ Re2Au2H6(PMe2Ph)4(PPh3)21,I7 [M O ~ F ~ ~ S ~ C ~ ~ ( C[Hg(Fe2Rh(p3-COMe)(C0)7Cp)2] O)~] ,I9 or [FePdPt(C0)4(p-dppm)2].5g*m Note that, for these clusters, neither the overall geometry nor the electron count changes on going from one isomer to the other. Clusters exhibiting reversible core isomerism are of considerable interest and should provide two characteristic pieces of information. The first concerns the activation energy (a kinetic factor), which reflects the ease with which the core rearrangement takes place and thus provides information about the mechanism. The second useful piece of information concerns the energy difference between the isomers (a thermodynamic factor), which reflects the energy cost of changing the geometry and/or the relative positions of the metal atoms. The determination of such data is of fundamental importance because one would like, eventually, to correlate them with the electron counting rules and help predict the dynamic behavior of the skeleton. Furthermore, such quantitative data are of obvious relevance to the dynamic phenomena occurring on metal alloy surfaces or particles. ,5a9b718
______
~
~
(8)Longoni, G.;Chini, P.; Lower, L. D.; Dahl, L. F. J . Am. Chem. Soc. 1975,97,5034. (9) Johnston, R. L.; Mingos, D. M.P. J . Chem. Soc., Dulron Trans. 1987, 641. (IO) (a) Ewing, P.; Farrugia, L. J. New J. Chem. 1988,12, 409. (b) Ewing, P.; Farrugia, L. J. Organometallics 1989,8, 1665. (1 I) Adams, R. D.; Wang, S.J . Am. Chem. Soc. 1987, 109,924. (12)Sutherland, B. R.; Folting, K.; Streib, W. E.; Ho, D. M.;Huffman, J. C.; Caulton, K. G. J . Am. Chem. SOC.1987,109,3489. (13)Adatia, T.;McCarthy, P. J.; McPartlin, M.; Rizza, M.; Salter, I. D. J. Chem. SOC.,Chem. Commun. 1988, 1106. (14)Drake, S.R.;Johnson, B. F. G.; Lewis, J. J . Orgummet. Chem. 1988, 340, C31. ( 1 5 ) (a) Horwitz, C. P.; Holt, E.M.; Brock, C. P.; Shriver, D. F. J . Am. Chem. Soc. 1985,107,8136.(b) Horwitz, C. P.; Shriver, D.F. J. Am. Chem. SOC.1985,107,8147. (c) Wang, J.; Sabat, M.; Horwitz, C. P.; Shriver, D. F. Inorg. Chem. 1988, 27, 552. (16)Chi, Y.;Wu, F.-J.; Liu, B.-J.; Wang, C.-C.; Wang, S.-L. J . Chem. Soc., Chem. Commun. 1989,873. (17)Sutherland, B. R.;Ho, D. M.;Huffman, J. C.; Caulton, K. G. Angnv. Chem., Int. Ed. Engl. 1987, 26, 135. (18)Bogan, L.E., Jr.; Rauchfuss, T. B.; Rheingold, A. L. J . Am. Chem. SOC.1985, 107,3843. (19)Farrugia, L. J. J . Chem. Soc., Chem. Commun. 1987, 147.
Braunstein
5284 J . Am. Chem. Soc., Vol. 113, No. 14, 1991
Table 1. 31P(lHJNMR Dataa planar isomers
6 53.3 52.3 54.4 63.6 64.5 50.3 46.4 47.1 31.0
3J(PP) . .
6
[PtZMoZCpZ(C0)6(PCy3)2]
3J(PP) 102 101.5 98.5 102 99 111 108 107.5 93
11 42.5 10.5 ~PtZMo2C~’Z~C0~6~PC~3~~ (2b) 42.4 7.5 [Pt2WZC~Z(Co)6(PC~3)Z~ (3b) 57.2 11 ~ , 1 ~ ~ ~ z ~ ~ z ~ P z ~ ~ ~ ~ (4b) 6 l ~ ~ 53.5 ~ - ~ ~ ~ 3 ~ ~ ~ z ~ z ~ P z ~ ~ ~ ~ 6 l (Sb) ~ ~ ~ - ~ 68.6 ~ ~ 3 l z l6 ’Chemical shifts d (ppm), coupling constants J (Hz);spectra measured in CDC13 unless
(1b)
Following the first example of skeletal isomerism in transition-metal cluster chemistry with [Au,(P(C,H,OMe-p),l,][NO,], sd and the increasing, but still small, number of papers dealing with metal core i~omerism,4*~J’-~~ we wish to describe here our own results concerning this topic. Thus,we report in this paper (i) on the reactions of the readily available chain complex tr~ns-[Pt{M(C0)~Cp)~(PhCN)~] ( M = Mo, W; Cp = Cp or Cp’) with phosphine ligands (P(o-Tol),, PCy,, P(i-Pr),, P(m-Tol),, P(CyPh2), P(p-Tol),, and P(i-Bu), whose cone angles range from 194 to 1430M),which lead to new tetranuclear Pt2M02and Pt2W2 clusters; (ii) on the demonstration that steric hindrance is responsible for the folding of the tetranuclear cores of these clusters from a planar to a tetrahedral geometry; (iii) on the existence in solution of interconvertible isomeric clusters; (iv) on the X-ray characterization of the tetranuclear cluster [Pt2M02(VC5H4CH3)2(C0)6(PCy3)2] (2b);and finally (v) on a molecular orbital analysis of the planar and tetrahedral structures for this family of clusters.
Results Synthesis. The reaction of the trinuclear complex trans-[Pt( M O ( C O ) ~ C ~ ) ~ ( P ~(Cp CN= ) ~&H5) ] with 1 equiv of PCy, (Cy = c-C6HlI)in refluxing tetrahydrofuran (THF) affords the (1) new heterometallic complexes [Pt2M02Cp2(C0)6(PCy3)2] (48%) and [PtCl(MoCp(CO),J(CO)(PCy,)] (ca. 5%)21 and ) ~ ~[Pt3(p-C0)3(PCy3)3](4%),2,which [ M o ( C O ) ~ C(~3]4~% ~and were separated by column chromatography (eq 1). Ph C N
I
CI
I
+
PhMozCPz(CO)dPCYdz 1; Cp Il l - C s H ~
+
I
Cy,P-PI-Mo(CO),Cp
(1)
I co
Replacing the C p group with Cp’ (Cp’ = a-CsH4CH3) has no influence on either the product distribution or the yields. However, the use cf C p instead of Cp’ facilitates the isolation of pure 1 by (20)Tolman, C. A. Chem. Reo. 1977,77, 313. (21) The chloride ligand in this heterodinuclear complex originates from the solvent (de MCric de Bellefon, C. T h k de 3tme Cycle. UnivenitE Louis Pasteur, Strasbourg, 1985). (22)Fischer, R. D.; Noack, K. J . Orgunomef. Chem. 1969, 16, 125. (23) (a) Albinati, A. Inorg. Chim. A m 1977, 22, L31. (b) Moor, A.; Piegosin, P. S.;Venanzi, L.M.Inorg. Chim.A m 1981,18, 153.
IJ(PtP) 4372 4416 4436 4364 4423 4436 4615 4617 4379
2J(PtP) -96 -99 -98 -97 -99 -107 -1 10 -111 -102
‘J(PtPt)
‘J(PtP) . .
2J(PtP) . .
‘J(PtPt) . .
186.5 190 193 185.5 193
1998
4855 4942 4796 4895 4840 otherwise stated.
et
al.
913 720 949 707
738 745 763
1977 1946 1920
CDCl3/CHZCIz. ‘In CDzCIz.
chromatography, whereas [Pt2M02Cp’2(CO)6(PCy3)2] (2) remains under the contaminated with [P~CI{MOC~’(CO),J(CO)(PC~~)]~~ same conditions (see Experimental Section). That the M q dimer, the trinuclear Pt3, and the tetranuclear Pt2M02clusters are all formed is consistent with a redox mechanism, probably involving radical intermediates, as already proposed for the formation of the closely related clusters [ M ’ 2 M z C p 2 ( C O ) 6 ( ~ ~ 3(M’ ) 2 ] = Pt, Pd; M = Cr, Mo, W; R = Me, Et, n-Bu, Ph). When tran~-[Pt(M(C0),Cp]~(PhCN)~] ( M = Mo, W) was reacted with P(i-Pr),, PCyPh2, P(m-Tol),, p(p-T~l)~, or P(i-Bu),, the only isolated products were [M(CO)3Cp]2( M = Mo, W) and the tetranuclear clusters [Pt2M2Cp2(C0)6(PR3)2] ( M = W, R3 = Cy3, 3 M = Mo, R3 = (i-Pr)3, 4; M = W, R, = (i-Pr),, 5; M = Mo, R3 = CyPh2, 6 M = Mo, R3 = (m-Tol),, 7; M = Mo, R, = @-Tal),, 8; M = Mo, R3 = (i-Bu),, 9 ) . However, with frans-[Pt(M0(CO),Cp)~(PhCN)~1 and P(o-Tol),, only decomposition occurred, yielding platinum metal and [Mo(CO),Cp12 (as evidenced by IR and 3’P(1HJN M R spectroscopies).22*2s It is noteworthy that the clusters containing trialkyl phosphines (Le., 1-5 and 9 ) are more soluble than their analogues with triaryland diarylalkylphosphines (i.e., 6, 7, and 8). This allows the use of chromatographic separation for the former, yielding red-brown microcrystalline powders, whereas the latter clusters are obtained as pure dark green microcrystals after recrystallization from CH2C12/n-hexane. Interestingly, when cluster 1 was recrystallized slowly from CH2C12/n-hexane, dark green, well-shaped crystals formed. They provided the same analytical results as red-brown 1. Spectroscopic Characterization. The analytical and IR data of these tetranuclear PtzM2 clusters are consistent with their belonging to the family of structurally fully characterized and closely related clusters [M’2M2Cp2(C0)6(PR3)2](M’ = Pt, Pd; M = Cr, Mo, W; R = Me, Et, n-Bu, Ph).24 Thus, the v(C0) frequencies found between 1728 and 1802 cm-’ are typical for only bridging carbonyl ligands being present. The 3’P(1HJN M R spectra clearly indicate the presence of a P-Pt-Pt-P arrangement, which is characterized by the superimposition of the spectra of the three isotopomers (relative abundance) P-Pt-Pt-P (44%), P-19’Pt-Pt-P (44.7%),and P-195PtIs5Pt-P (1 1.3%). Such systems have been analyzed previously.xb The 31P{1H) N M R data for clusters 6-9 agree well with the planar triangulated rhombohedral (PTR) structures previously encountered in clusters [Pt2M02(cp)2(co)6(PR3)2] (R = Me, Et, n-Bu). Indeed, these PtzMoz clusters possess typical ‘J(PtP), 2J(PtP), and ,J(PP) coupling constants in the range of 4350 to 4620, -96 to - 1 1 1 , and 91 to 107.5 Hz, respectively (see Table I). In contrast, the spectra of complexes 1-5 reveal a mixture of two (24)(a) Bender, R.;Braunstein, P.; Jud, J.-M.; Dusausoy, Y . Inorg, Chem. 1983,22, 3394. (b) Bender, R.;Braunstein, P.; Jud, J.-M.; Dusausoy, Y . Inorg. Chem. 1984,23, 4489. (25) Pinnell, R. P.; Megerle, C. A.; Manatt, S.L.;Kroon, P. A. J . Am. Chem. Soc. 1973,95, 977.
J. Am. Chem. SOC..Vol. 113, No. 14, 1991 5285
Cluster Core Isomerization A
Table 11. Selected Interatomic Distances in 2b bond bond length (A)6 bond” bond“ length (A)6 3.126 (1) 2.992 (1) Mo( l)-M0(2) Pt(1)-Pt(2) 2.76 (1) 2.755 (1) Mo( I)C(50) Pt(1)-Mo(1) 2.02 (1) 2.884 (1) Mo( 1 ) C ( 5 2 ) Pt(1)-Mo(2) 1.997 (8) 2.870 (1) Mo(l)C(53) Pt(Z)-Mo(l) 2.342 (9) 2.727 (1) Mo( 1 ) C ( 5 4 ) Pt(2)-M0(2) 2.299 (2) Pt(1)-P(1) M o ( l ) C p [C(43)C(47)1 1.99 (2) 2.022 (9) 2.291 (2) Mo( 2 ) C ( 49) Pt(2)-P(2) 2.00 (1) Pt(l)C(51) 1.97 (1) Mo(2)C(50) 2.42 (1) 2.53 (1) M o ( 2 ) C ( 5 1) Pt(l)-C(52) 2.70 (1) 2.225 (9) M o ( 2 ) C ( 52) Pt(l)C(53) 2.183 (9) Pt(2)-C(49) M0(2)-CP [C(37)C(41)1 1.98 (2) 2.50 (1) Pt(2)-C(5O) 1.939 (9) Pt(2)-C(54) “Atoms are labeled in agreement with Figure 1. bNumbers in parentheses are estimated standard deviations in the least significant digit. ~~
The planar triangulated rhombohedral (PTR) structure
The tetrahedral structure
spectroscopically different compounds a and b, each having a P-Pt-Pt-P arrangement. The coupling constants and chemical shifts are in the expected range (‘J(PtP) ca. 4OOO Hz).One family of clusters (i.e., la-Sa) possesses a PTR core structure (2J(PtP) and 3J(PP) criterion), whereas the other (lb-5b) should have a different geometry, since it presents a positive 2J(PtP) (185-190 Hz)and a surprisingly small 3J(PP) coupling (ca. 10 Hz).The ‘H N M R spectra of 1-5 also confirm the presence of two forms in solution, although the signals for isomers a and b sometimes overlap, precluding a definitive attribution. The situation is different with phosphines having a cone angle smaller than that of P(bPr)3 (165’): Only the planar form a is observed for the trialkylphosphines PMe3 and P ( ~ - B u (cone ) ~ angle
