Reactions of ditungsten hexaalkoxides with alkynylplatinum (II

J. Am. Chem. SOC. 1987, 109, 4552-4560

4552

Health Research Grant No. RR03 17 from the Biotechnology Resources Branch, Division of Research Resources.

F~(CO),MII(CO)~PP~~, 108563-06-0; [(~5-C5Me5)Fe(C0)2J2, 353441 1-7; [Mn(CO),] ,, 10170-69-1; [Mn(CO),PPh,],, 10170-70-4; CIMn(CO),PPh3, 14841-08-8;CIMn(C0)4P(OPh)3, 85362-16-9; (q5-C5H5)Registry No. (q5-C5H5)Fe(C0)2Mn(CO)s, 12088-73-2; (q5-C5Me5)35025-27-5; Fe(CO)&l, 12107-04-9; (~5-C5H5)Fe(CO)P(OPh),(C1), Fe(CO),Mn(CO),, 95421-00-4; (q5-5H5)Fe(C0)2Mn(CO)4P(OPh)3,Mn(C0)4(P(OPh)3)C1,85362-16-9;(qS-CsH5)FeMn(CO),,108563-07-1; 108563-04-8; [(q5-C,H,)Fe(C0),I2, 12154-95-9; [Mn(CO),P(OPh),],, (q5-C,Me5)FeMn(CO),, 108563-08-2; Mn(CO),CI, 14100-30-2; Mn215529-62-1;(q5-5H,)Fe(C0)2Mn(C0)4PPh3, 108563-05-9;(q5-C5Mes)(CO),,, 10170-69-1,

Reactions of Ditungsten Hexaalkoxides with Alkynylplatinum( 11) Complexes: Formation of Heterometallic Dicarbido Complexes in Competition with Products Derived from Alkyne Metathesis Reed J. Blau, Malcolm H. Chisholm,* Kirsten Folting, and Ruji J. Wang Contribution from the Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 4740.5. Received August 15, 1986

Abstract: In hydrocarbon solutions trans-Pt(G=CH),(PMe,Ph), (I) and W,(O-t-Bu), (11) react to give by successive eliminations of t-BuOH trans-Pt(C=CH)[C2W2(O-t-Bu),](PMe2Ph), (111) and tr~ns-Pt[C~W,(O-t-Bu)~]~(PMe~Ph), (IV). Compounds 111 and IV are shown to contain dicarbido(4-) ligands on the basis of 13CNMR studies and single-crystal X-ray crystallography. The PtC,W, units may also be classified as a-coordinated, dimetalla-substituted alkynes, {(p-PtC=CW,)=W,). (tBuO),W=CC=W(O-~-BU)~ (V) is also formed in the reaction between I with 11. Its proposed mechanism of formation includes alkyne metathesis, trans to cis isomerization about Pt(II), and intramolecular reductive elimination from Pt(I1). The complexes (quin)(t-BuO),W=CH and Pt(PMe,Ph), are formed in the reaction between I and I1 in the presence of excess quinuclidine and PMe,Ph, respectively, supporting the proposed mechanism. I and W2(O-i-Pr),(py), (11') yield products derived from alkyne metathesis, W,(O-i-Pr),(p-C,H,)(py),, and dicarbide formation, trans-Pt(C=CH) [C,W,(O-i-Pr),] (PMe2Ph), (VI) and ci~-Pt[C~W,(0-i-Pr),](PMe~Ph)~ (VII). VII, a cis complex, is unstable toward reductive elimination at ambient temperature, whereas IV, its bulkier trans analogue, is thermally stable to at least 7 5 OC. The reaction between 11' and trans-Pt(C= CMe),(PMe,Ph), (1') yields W,(fi~-O-i-Pr)~(O-i-Pr),(p~-CMe) as a product derived from C=C scission. The Pt-containing products formed in the reactions of both 11' with I and 11' with I' are unstable toward reductive elimination, and Pt(PMe,Ph), is eventually formed. Phosphine exchange in IV is very slow relative to that in 111 or I because of the steric bulk of the two -C2W2(0-t-Bu)5 ligands. Carbon monoxide adds across the W=W bonds of IV forming first trans-Pt[C,W,(O-tBu),] [C2W2(p-CO)(0-t-Bu),](PMe2Ph), (VIII) and then trans-Pt[C2W2(p-CO)(O-t-Bu)5]2(PMe2Ph)2 (IX).

add~cts,'~ and - ~p-C4R',-containing ~ compound^.^^^^^ W e anticipated that reactions employing metal-alkynyl complexes would provide an entry into heterometallic carbido chemistry in which the heterometal atom(s) and alkoxide-supported tungsten(s) would be coordinated to either a C4- or C2*-unit (x = 2, 3, 4, 5, or 6). Our initial efforts in this area were concentrated on reactions ~ P ~W2(O-t-Bu),l9 ),'~ between ~ ~ ~ ~ S - P ~ ( C = C H ) , ( P M(I)~ and (11). The choice of reactants was based on the well-defined coordination chemistry of Pt(I1) and the wealth of information that can be gleaned from coupling constants involving spin-active nuclei, 195Pt,I3C, ,lP, lS3W, and 'H as shown below. Small

W e are currently developing the organometallic chemistry of molybdenum and tungsten supported by alkoxide ligands with a view toward modeling the chemistry of the oxides of these elements.l Very few carbido clusters supported by alkoxide ligands are presently known,2 especially when compared to the large variety and vast number of such clusters supported by carbonyl ligand^.^.^ Alkoxy ligands, which are strong a-donors, are clearly very different from the carbonyl ligand, a neutral a-acceptor. Because of this, the physical properties and reactivity of the carbido centers in the two types of clusters may be very different. The reactions between W,(OR),(M=M) compounds and alkynes have yielded a variety of products including and bridging (p2'"9'I and y312J3)alkylidyne complexes, alkyne

(1 1) Cotton, F. A,; Schwotzer, W.; Shamshoun, E. S. Organometallics 1983, 2, 1340. (12) Chisholm, M. H.; Folting, K.; Heppert, J. A.; Hoffman, D. M.; Huffman, J. C. J . Am. Chem. SOC.1985, 107, 1234. (13) Chisholm, M. H.; Conroy, B. K.; Folting, K.; Hoffman, D. M.; Huffman, J. C. Organometallics 1986, 5, 2457. (14) Chisholm, M. H.; Folting, K.; Hoffman, D. M.; Huffman, J. C. J . Am. Chem. SOC.1984, 106, 6794. (15) Chisholm, M. H.; Conroy, B. K.; Huffman, J. C.; Marchant, N. S. Angew. Chem. Int. Ed. Engl. 1986, 25, 446.

H. J . Solid State Chem. 1985, 57, 120. (2) Chisholm, M. H.; Folting, K.; Huffman, J. C.; Leonelli, J.; Marchant, N. S.; Smith, C. A.; Taylor, L. C. E. J . Am. Chem. SOC.1985, 107, 3722. (3) Bradley, J. S. Adu. Organomer. Chem. 1983, 22, 1. (4) Tachikawa, M.; Muetterties, E. L. Prog. Inorg. Chem. 1981, 28, 203. (5) Schrock, R. R.; Listemann, M. L.; Sturgeoff, L. G. J . Am. Chem. SOC. 1982, 104, 4291. (6) Listemann, M. L.; Schrock, R. R. Organomerallics 1985, 4, 75. (7) Cotton, F. A,; Schwotzer, W.; Shamshoum, E. S. Organomerallics 1984, 3, 1770. (8) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. Inorg. Chem. 1983, 22, 2903. (9) Chisholm, M. H.; Conroy, B. K.; Huffman, J. C. Organometallics 1986, 5, 2384. (10) Cotton, F. A,; Schwotzer, W.; Shamshoun, E. S. Organometallics ( 1 ) Chisholm, M.

1983, 2,

(16) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. J . Am. Chem.

SOC.1984, 106, 6806.

(17) Chisholm, M. H.; Hoffman,D. M.; Huffman, J. C. Chem. SOC.Reu. 1985, 14, 69. (18) Bell, R. A,; Chisholm, M. H.; Couch, D. A,; Rankel, L. A. Inorg. Chem. 1977, 16, 677. (19) Akiyama, M.; Chisholm, M. H.; Cotton, F. A,; Extine, M. W.; Haitko, D. A.; Little, D.; Fanwick, P. E. Inorg. Chem. 1979, 18, 2266.

1167.

0002-7863/87/1509-4552$01.50/0 , , I

0 1987 American Chemical Society -

J . Am. Chem. Soc., Vol. 109, No. 15, 1987 4553

Reactions of Ditungsten Hexaalkoxides Table I. Fractional Coordinates and Isotropic Thermal Parameters for the tran~-Pt[W~C~(O-t-Bu)~]~(PMe~Ph)~ Molecule“ atom I0 4 ~ 104~ 1042 IOB~,,,A2 0.6 Ob Ob 10 12 310.5 (3) -1976.3 (2) -1403.7 (4) -1772.0 (4) -3007.8 (2) -2470.1 (4) 13 -1 136 (6) -1062 ( I O ) 19 -476 (9) -1822 (5) -1697 (9) -1433 (8) 11 14 -958 (2) -644 ( I ) 1434 (2) -1620 (6) 18 1761 (10) -786 (9) 21 -418 (10) -101 (6) 3128 ( I O ) 19 -2654 (9) 845 ( I O ) -893 (6) -3422 ( I O ) -146 (11) 25 -1560 (6) 35 -1752 (7) -4689 (1 0) -560 (13) -5228 ( I O ) -22 (13) 33 -1301 (7) -4462 (1 1) 943 (12) 35 -616 (8) 1391 (11) 28 -422 (7) -3166 (11) 117 (7) 21 1288 (6) -2280 (4) 810 ( I O ) 23 1405 (11) -2976 (6) -181 (11) 32 858 (1 1) -3761 (7) 2796 (1 1) 1472 (13) 39 -2786 (8) 1832 (14) 43 -3015 (8) 786 (14) -2549 (6) 18 -1660 (4) 1282 (6) 1442 (10) -3657 ( I O ) 24 -2060 (6) -2155 (7) 324 ( I O ) -4909 ( I O ) 23 -1493 (7) 2628 (1 1) -3807 (12) 32 -3317 (11) 27 -2867 (7) 1592 (11) -2802 (6) 20 -2913 (4) -4197 (7) -4994 ( I O ) 22 -3408 (IO) -2413 (6) 27 -2486 ( I O ) -4856 (1 1) -1559 (7) 36 -3898 (12) -6452 (1 1) -2841 (8) 34 -4465 ( I O ) -4520 (13) -2390 (7) 18 -876 (6) -2122 (6) -3350 (4) 22 -761 (IO) -3166 ( I O ) -4020 (6) 34 -2800 (1 2) -629 (13) -4768 (7) 33 -4335 (11) -1938 (13) -4124 (7) 33 -3338 (12) -3750 (7) 522 (12) 20 -3956 (4) -1603 (6) -3218 (7) 28 -1941 (11) -4644 (6) -4217 (11) 56 -1116 (15) -5155 (8) -3672 (14) -5482 (12) -1714 (12) 34 -4320 (7) -3341 (14) -4598 (15) 53 -5112 (8) 4602 (1 4) 10027 ( I O ) 4375 (15) 52 (3) 9441 (14) 3712 (20) 3323 (22) 25 (4) 3533 (34) 9963 (21) 3470 (31) 57 (7) C(42) 2880 (13) 9723 (8) 2112 (14) 43 (3) Isotropic values for those atoms refined anisotropically are calculated by using the formula given by: Hamilton, W. C. Acta Crystallogr. 1959, 12, 609. bParameters marked by an asterisk (*) were not varied.

changes in the reactants, i-Pro vs. t-BuO and propynyl vs. ethynyl, altered the course of the reactions. Evidence for two types of reactions are described: C s C cleavage (eq la) and, for R’ = H, a proton transfer from the ethynyl to an alkoxide ligand yielding a dicarbido ligand and alcohol (eq lb). A preliminary finding was reported previously.20

Pt(CECR’),L, L,(R’CEC)PtCC,W,(OR),3

+

ROH

(lb)

R=t-Bu,n = O ;R=/-Pr, n = 2 R ‘ = H , M e ; L = PMe,Ph

Results and Discussion Reaction of tran~-Pt(C&cH),(PMe~Ph)~ with W2(O-t-Bu),.

This reaction has been monitored by ‘H, 13C, and 31PN M R spectroscopy. It proceeds very slowly, 5-6 days at 30 OC in toluene, yielding three observable metal-containing products. Two of these products, trans-Pt (C=CH) [C2W2(0-t-Bu) (PMe2Ph) (IV), are formed (111) and tran~-Pt[C~W,(O-t-Bu)~]~(PMe~Ph)~ (20) Blau, R. J.; Chisholm, M. H.; Folting, K.; Wang, R. J. J . Chem. Soc., Chem. Commun. 1985, 1582.

Table 11. Selected Bond Distances (A) and Bond Angles (deg) for IV Pt( 1)-P(6) W(2)-W(3) w (2)-O( 20) W(2)-C(5) W(3)-O(30) W(3)-C(5) P(6)-C(8) 0(15)-C(16) 0(25)-C(26) 0(35)-C(36) P( 6)-Pt ( 1)-P( 6’) C(4)-Pt( l)-C(4’) W(3)-W(2)-0(20) W(3)-W(Z)-C(5) O( 15)-W(Z)-C(4) 0(20)-W(2)-C(4) C(4)-W(2)-C(5) W(Z)-W(3)-0(30) W(Z)-W(3)-C(5) 0(25)-W(3)-0(35) 0(30)-W(3)-0(35) 0(35)-W(3)-C(5) Pt( l)-P(6)-C(8) C(7)-P(6)-C(8) C(S)-P(6)-C(9) W(2)-0(2O)-C(21) W(3)-0(30)-C(31) Pt( I)-C(4)-W(2) W(Z)-C( 4)-C( 5) W(Z)-C(5)-C(4)

Bond Distances 2.293 (3) Pt(l)-C(4) W(2)-O(15) 2.445 ( I ) 1.907 (6) W(2)-C(4) 2.121 (8) W(3)-O(25) 1.930 (6) W(3)-O(35) 2.054 (9) P(6)-C(7) 1.812 (g) P(6)-C(9) 0(20)-C(21) 1.463 (12) 1.443 (12) 0(30)-C(31) 1.429 (12) C(4)-C(5) Bond 180.0 180.0 115.6 (2) 52.9 (2) 117.0 (3) 112.9 (3) 37.3 (4) 99.1 (2) 55.4 (2) 90.6 (3) 101.5 (3) 162.8 (3) 116.3 (3) 101.2 (5) 104.7 (5) 136.0 (6) 129.2 (6) 140.8 (5) 74.2 (6) 68.5 (6)

2.050 (1) 1.883 ( 7 ) 2.052 (10) 1.912 (7) 1.897 (6) 1.809 (10) 1.830 ( I O ) 1.433 (11) 1.454 (12) 1.336 (13)

Angles P(6)-Pt(l)-C(4) w(3)-w(2)-0( 15) W(3)-W(Z)-C(4) 0(15)-W(2)-0(20) 0(15)-W(Z)-C(5) 0(20)-W(2)-C(5) W(2)-W(3)-0(25) W(Z)-W(3)-0(35) 0(25)-W(3)-0(30) 0(25)-W(3)-C(5) 0(30)-W(3)-C(5) Pt(l)-Pt(6)-C(7) Pt(l)-P(6)-C(9) C(7)-P(6)-C(9) W(2)-0(15)-C(16) W(3)-0(25)-C(26) W(3)-0(35)-C(36) Pt(l)-C(4)-C(5) W(Z)-C(5)-W(3) W(3)-C(5)-C(4)

92.2 (3) 113.1 (2) 90.2 (3) 107.6 (3) 127.3 (3) 124.4 (3) 119.7 (2) 108.7 (2) 133.1 (3) 92.6 (3) 88.5 (3) 115.6 (3) 114.1 (3) 103.1 (4) 143.8 (6) 146.6 (6) 154.9 (7) 143.9 (8) 71.7 (3) 140.2 (7)

A Figure 1. A ball and stick drawing of the trans-Pt(PMe2Ph),(C2W,(Ot-Bu),), molecule giving the atom numbering scheme used in the tables.

by two sequential “acid/base” reactions (eq 1b) yielding t-BuOH as an observable byproduct. The third, (t-BuO),W=CC=W(0-t-Bu), (V), is formed parallel to 111. When the stoichiometry of the reaction is 2.1 for 1I:I respectively, IV constitutes 75-85% of the final products with the remainder being V. A 1:l stoichiometry yields mixtures of I11 and IV (and V) suggesting that the two sequential acid/base reactions occur at comparable rates. The reaction was also followed between the I3C-labeled ethynyl P Mwhich ~ , P ~exists ) ~ in compound ~ ~ ~ ~ s - P ~ ( * C = * C H ) ~ ((I*) a variety of isotopomers resulting from its preparation employing commercially available (Merk, Sharp, and Dohme) H*C=*CH, where *C represents 92% g atom 13C. In these reactions the labeled I3C compounds III*, IV*, and V* are formed. Crystal Structure of trans -Pt[C2W2(0-t-Bu) PMe,Ph),] (IV) and the Properties of Its C,4- Units. Fractional coordinates and isotropic thermal parameters are given in Table I. Pertinent bond distances and angles are found in Table 11. The molecular structure of IV is centrosymmetric and is shown in Figure 1. A ball and stick view of the central PtP2(C2W205),skeleton is shown in Figure 2. The central PtP2C2unit is essentially square-planar,

4554 J. Am. Chem. SOC.,Vol. 109, No. 15, 1987

Blau et al.

n

A

Chart I. Structural Comparisons of Coordinated Alkynes Having

Y

Substituents in a Trans Configuration CHPh

//

I c'""u

A

cis')

C

dY Wt3'j

Figure 2. A ball and stick view of the central r r a n ~ - P t P ~ ( C ~ W , 0 ~ ) ~ moiety of the centrosymmetric trans-Pt(PMezPh)2(C2W2(O-f-Bu)512 molecule looking nearly down the P-Pt-P axis showing the planar Pt-

C2W2unit. Table 111. NMR Chemical Shifts (ppm) and Coupling Constants (Hz) for frans-Pt(C=CH),(PMe2Ph), and Derivatives Formed from Its Reactions with W,(OR),(py), (R = f-Bu, n = 0; R = i-Pr, n = 2)"

constant

W)

I

I11

IV

VI

VI1

-14.7 2447

-11.2 2591 100.5 941 235.2 802 97.1 259 302.1 78 132 122 19 36

-8.0 2176

-7.6 2757 94-100

-3.7

1J(195Pt-31P) 3171 na na 100.7 6(C,) 1J(195Pt-13C,) 947 na nd na 233.9 227.8 216.9 6(C,) na 1J(195pt-13C ,) na 801 814 983 na 94-100 na 6(C& 94.9 2J(l95pt-13C 8 ) na 266 nd na 302.0 284.3 282.3 6(C2) na 2 J ( 195pt-13c 2) na 76 86 115 1J(I83W-13C *) na 133 nd nd na 122 na I J(C,-Cd 122 -19 nd 19 IJ(C,-C2) na J(CPt C) 40 39 nd nd "Notations for carbon atoms are as follows: Pt-C,=C,H and Pt--(C,=C2W,(OR)5J; na = not applicable; nd = not determined.

-

and the bond distances and coupling constants to 195Pt(Table 111) establish this as formally Pt2+. The (W2C2)Pt(C2W2)'unit is also planar, and it forms a 62' angle with the PtP2C2plane. This deviation from 90' minimizes steric crowding between the PMe,Ph phenyls and the tert-butoxy methyls. The Pt(1)-C(4) and W(3)-C(5) distances in IV may be taken to represent Pt-C and W-C single bond distances and the C(4)-C(5) distance, 1.33 (1) A, and W(2)-W(3) distance, 2.445 (1) A, as C-C2' and W-WZ2 double bond distances, respectively. This allows the formal electron counting of each W as W(4') and the C2 units as C j - . The C2 units in IV may be classed as either dimetalla-substituted alkynes and thus related to normal alkynes in their modes of binding to transition metals, or they may also be described as peripheral dicarbido units, Cze, in a heterometallic cluster. Thus, comparisons with other dicarbido clusters prove useful. Pt( 1) and W(3) are bound to the C2 unit in IV through cr bonds forming a dimetalla-substituted alkyne which, in addition, is bound in a n fashion to W(2). This bonding mode is very similar to that found for the monometalla-substituted alkyne or acetylide unit (21) Kutchitsu, K. J . Chem. Phys. 1966, 44, 906. (22) Chisholm, M. H. Polyhedron 1983, 2, 681.

in Fe2(C0)6(v2-p-C=CPh)(p-PPh2)23 and those in other related where binuclear acetylides, M2(C0)4(L)2(v2-p-C=CR)(p-PPh2), M = Fe or Ru and R = alkyl or ary1.24,25As opposed to normal alkynes, R-CEC-R', where, upon coordination to a transition metal, the R and R' substituents bend away from the metal in a cis configuration relative to each other; in IV, W(3) and Pt(1) are found in a trans configuration (see Chart I). Such is also the case for the Feu and Ph substituents on the C=C unit of Fe2(CO)6(~2-p-C=CPh)(p-PPh2) in Chart I. The trans configuration of the substituents in IV and Fe2(C0),(v2-1-C=CPh)(P-PPh,) is caused by an interaction between W(3) and W(2) in the former and Feu and Fe, in the latter in addition to the normal M, to n-interactions observed for normal alkynes. A similar trans configuration of substituents about a transition-metal-bound In alkyne is observed in [OS(~~-P~C=CC=CHP~)(PM~~)~]+.~~ this case, the substituent bound to M, is C, instead of Mu. The coordination of normal alkynes gives rise to the lengthening of the C-C bond in addition to the bending of the C-R bonds away from the metal complex as was mentioned above. Both effects depend mainly on the n-back-donation from metal orbitals to an antibonding MO of the alkyne and can be taken as a measure of the reduction of triple-bond character upon coordination. In fact, a plot of C-C-R angles vs. length of the C - C bond has shown a good correlation between the two in a wide variety of coordinated alkynes.*' We report a similar trend in coordinated alkynes having trans-related substituents: as the C-C bond distances increase toward that of a double bond, the C-C-S (S = substrate) angles become less obtuse. In fact, the data listed in Chart I for IV, the Os complex, and the Fe2 dimer fit very well into the plot compiled by Gervasio et aL2' and span the range of C-C bond lengths and C-C-R bond angles observed for mononuclear complexes of the 02-type. When compared to C-C bond distances in alkyne complexes of ditungsten alkoxides, the C(4)-C(5) bond distance in IV, 1.34 (1) A, is intermediate between that of v2-alkynes, 1.29 (2)16 and 1.31 (1) A,28and the 1-perpendicular-type, 1.374 (1 5 ) A.14However, the C-C-S angles for both the v2- and @-per(23) Patel, H. A.; Fischer, R. G.; Carty, A. J.; Naik, D. V.; Palenik, G. J. J . Organomet. Chem. 1973,60, C49. (24) Carty, A. J. Pure Appl. Chem. 1973, 54, 113. (25) Smith, W. F.; Yule, J.; Taylor, N. J.; Paik, H. N.; Carty, A. J. Inorg. Chem. 1977, 16, 1593. (26) Gotzig, J.; Otto, H.; Werner, H. J . Organomef. Chem. 1985, 287, 247. (27) Gervasio, G.; Rossetti, R.; Stanghellini, P. L. Organometallics 1985,

4, 1612. (28) Chisholm, M. H.; Eichhorn, B. W.; Huffman, J. C. J . Chem. Soc., Chem. Commun. 1985, 861.

J. Am. Chem. SOC.,Vol. 109, No. 15, 1987 4555

Reactions of Ditungsten Hexaalkoxides Table IV. Elemental Analysis of trans-Pt(C2W,(O-t-Bu)5)2(PMezPh)2 (Cs0H112P2Pt010W.d C H P calcd obsd

c,, + 4 WC"

36.29 33.94 33.87

5.68 5.50 5.68

3.12 3.10 3.10

"This calculated elemental analysis assumes that only 56 of the total 60 carbons in IV are combustible and that the remaining four form tungsten carbide.

pendicular alkynes, 136 (3)01628and 133 ( l ) " , I 4 respectively, are less obtuse than those seen for IV, 142 (3)O. The C2 units in IV may very well be classified as dimetalla-substituted alkynes bound in an $-fashion to an additional metal center. The C2 unit in IV may also be classed as a peripheral4 dicarbido ligand, C24-.27Metal clusters containing such moieties are very rare at present with [ ~ ~ ~ ( ~ ~ ~ ~ ~ ) ( ~ L - C-C ~ ~ =) ~ ( ~ ~ ) g ( ~ ~ ~ ~ ) ] , 1.37 (2) being the only other reported example. In most dicarbido clusters where the two carbon atoms are within bonding distance, the C2 unit is encapsulated in a metal p o l y h e d r ~ n . ~ ~ - ~ ~ The C-C bond distances in these caged clusters are fairly long ranging from 1.38 ki3' in [Ni16(C0)23(C,)2]~-to 1.66 (6) in [ C O , , ( C ~ ) ( C O ) ~The ~ ] . bond distance in IV, 1.34 A, is shorter than all examples of dicarbido units listed above. This is due in part to bonding with fewer metals.32 One piece of evidence supporting the strong W-C interactions in the WzCzunits in IV comes from its elemental analysis which is listed in Table IV. Although the analyses for H and P are reasonable, the analysis for C is four carbons short (see Table IV). A plausible explanation for this discrepancy is that the four carbons in the CzW2units form 4 equiv of tungsten carbide upon combustion consistent with their carbidic nature in IV. 108 106 104 102 100 98 96 94 9 2 PPM The I3CNMR Characterization of I*, III*, and IV*. Although ~~~~S-P~(C~CH){C~W~(O(111) ~ -was B Unot )~ iso](PM~~P~)~ lated as a pure crystalline solid, it is well-characterized by N M R techniques. III* has 13Cresonances at 100.5 and 97.1 ppm similar to those corresponding to the CECH ligands in I* at 100.7 and 94.9 ppm, respectively. It also has 13C resonances at 235.2 and k 302.1 ppm similar to those attributed to the C, units in IV* at 233.9 and 302.0 ppm, respectively. In addition, the 19SPt-13C, Ig3W-J3C,and I3C-l3C coupling constants observed for the C=CH ligand in I* and the C2 unit in IV* parallel those observed for the corresponding C, units in III* (see Table 111). The coupling patterns for the I3C-labeled resonances of I* in Figure 3, HI*,and IV*,O are very complex. When only I3C-I3C couplings for the major isotopomer in each complex* are considered, AA'BB', ABMX, and AA'XX' coupling patterns are observed for I*, HI*,and IV*, respectively. In addition, every line in each of these C4 patterns is split into a triplet by the two equivalent 31Pnuclei. What adds further to the complexity of these spectra is the fact that the major isotopomer 13C4is found in 47% abundance in I*, and only 26% abundance in IV*. Ig5Pt Figure 3. The ')C NMR spectrum of the - G C H resonances of satellites, Ig3Wsatellites for H I * and IV*, and resonances due trans-Pt(C=CH),(PMe,Ph), with I3C at natural abundance (top) and to the various isotopomers I3C3are also observed. Despite their with a 92% g atom "C label at both acetylide carbon positions (middle): inherent complexity, the various resonances were simulated, e.g., A spectral simulation of the latter (bottom) is also shown. I* in Figure 3, and the coupling constants were determined (Table 111. For the Pt-CECH moiety, the values are 122 Hz whereas 111). those for the PtW,C2 unit are very small 18-19 Hz. For comPerhaps more noteworthy among the various coupling constants parison, IJ(I3C-I3C) in ethyne, ethylene, and ethane are 171.5, for I*, HI*,and IV* are the 1J(13C-13C)values listed in Table 67.6, and 34.6 Hz, respectively. The low value of J('3C-13C) in the PtC2W2unit is similar to values seen for W,(y-C,R,)-con(29) Gervasio, G.; Rossetti, R.; Stanghellini, P. L.; Bor, G. Inorg. Chem. taining compounds supported by alkoxide ligands where the central 1983, 23, 2073 and references therein. W2C2unit is best described as a dimeta1latetrahedra11e.l~Ap(30) (a) Ceriotti, A,; Longoni, G.;Manassero, M.; Masciocchi, N.; Giampiero, P.; Resconi, L.; Sansoni, M. J . Chem. SOC.,Chem. Commun. 1985, parently, bonding of such C2 units to the tungsten centers dra1402. (b) Arrigoni, A,; Ceriotti, A,; Pergola, R. D.; Longini, G.; Manassero, matically reduces the "sn character of the C-C bond. Other M.; Sansoni, M. J . Orgunomet. Chem. 1985, 296, 243. (c) Ceriotti, A,; couplings through the C-C bond of the PtC2W2unit are also Longoni, G.; Manassero, M.; Masciocchi, N.; Resconi, L.; Sansoni, M. J . reduced significantly relative to those observed for the Pt-C=CH Chem. SOC.,Chem. Commun. 1985, 181. (d) Arrigoni, A,; Ceriotti, A,; = 259 H z in I* vs. 2J(195Pt-13C2)= Pergola, R. D.; Longini, G.; Manassero, M.; Masciocchi, N.; Sansoni, M. moiety, e.g., 2J(195Pt-13Cp) Angew. Chem., Int. Ed. Engl. 1984, 23, 322. 78 Hz in III*. (31) Albano, V. G.; Braga, D.; Ciani, G.; Martinengo, S . J . Orgunomet. [(~-BUO)~W==L], (V) and Its Mechanism of Formation. One Chem. 1982, 213, 293. complex formed from the reaction of I and I1 was found to contain (32) See ref 27: the number of metal atoms to which an alkyne is bonded is one of the most important factors determining its C-C bond length. no platinum. There is evidence that it is [(~-BuO)~W=CC=W-

w3'

Blau et al.

4556 J. Am. Chern. SOC., Vol. 109, No. 15, 1987 Table V. Major "C NMR-Active Isotopomers in V*, 50:50 V:V*, and 50:50 V:V* Scrambled % in % in scrambled isotopomer % in V* 50:50 V:V 5050 V:V* w*c*cw w*ccw *w*c*cw *wc*cw *wc*cw

62 11 21 2 2

31

16 37 3

5 10 1 1

6 6

Figure 5. The "C N M R central multiplet due to the 92% g atom I3Clabeled Pt-C=C carbons in trans-Pt[C,W,(O-t-Bu)5]z(PMe2Ph)z (right) where peaks due to the *C=*C-Pt-*C=C isotopomer (17% the intensity of the major isotopomer) are denoted by an asterisk. The left spectrum resulted from the reaction of 2 equiv of W,(O-t-Bu), with 0.5 equiv of trans-Pt(C=CH)z(PMe2Ph)2and 0.5 equiv of its "C-labeled analogue (see Figure 1). Peaks due to the above-mentioned isotopomer are enhanced in the left spectrum. This is consistent with the reversibility of reaction 2.

to stabilize (1-BuO) W s C H toward such decomposition. However, the reaction of I with 2 equiv of I1 in the presence of 6 equiv (~-BUO)~W=CC=W(O-~-BU (left) ) ~ and its spectral simulation (right) of quinuclidine produces detectable amounts of (quin)(tin which the alkylidyne carbons are labeled by 92% gatom I3C. The BuO),W=CH having the reported 'H N M R resonance at 5.15 central resonance is skirted by 183W( I = l/,, 14.3% natural abundance) ppm (2J(1S3W-1H) = 90 H z ) . ~Thus, ~ there is solid evidence for satellites due to three I3C isotopomers: *W*CCW (2% abundance, 1J('83W-13C) = 300 Hz), *WC*CW (2% abundance, 2J('83W-'3C) = (t-BuO),W=CH formation in alkyne metathesis steps such as 55 Hz), and *W*C*CW (the AA'X pattern, 21% abundance, 'J("C(2) and (3). I3C) = 44 Hz). Reaction 4, a trans to cis isomerization, and reaction 5, a reductive elimination, have precedence. For example, IV has a (0-t-Bu),] (V), a compound first reported by the Schrock group trans geometry. However, a less sterically demanding analogue in 1985.33 As reported earlier,33the complex can be isolated as prefers and is able to isomerize to a cis geometry, Le., cis-Ptdark red tablets, and it has a singlet in the 'H N M R at 1.57 ppm (C2W2(O-i-Pr)s),(PMe2Ph)2. This cis complex is unstable toward in C6D6. We observe a 13CN M R resonance at 268.5 ppm in C6D6 reductive elimination forming Pt(PMe,Ph), and other products which is 10 ppm upfield from the reported value of 278.6 ppm (discussed below). in CsD,N.33 It is known that pyridine coordinates to ( t We would expect that the - C = W ( O - ~ - B U ) ligands ~ in transB u O ) ~ W = C M at ~ a position trans to the W=C bond causing L,Pt(C=W(O-t-Bu),), would have a larger trans influence than a downfield shift in its 13CN M R resonance.33 Addition of 6 equiv either - C r C H or PMezPh and would much rather compete for of pyridine to V in toluene-d, does cause a downfield shift in the a-bonding orbitals with PMe,Ph than with themselves. Ther13Cresonance to 273.7 ppm. Thus, the disparity in the value for modynamically, the cis Pt(I1) isomer is therefore favored. Thus, the I3C chemical shift in V may be due to varying degrees of the trans to cis isomerization (4) should occur if it is sterically pyridine coordination. possible. Perhaps the best evidence that this product is V is the 13CN M R When excess PMe2Ph (4 equiv) is added to a reaction of I and of V*. Various isotopomers predicted for V* with its 92% g atom 2 equiv of 11, Pt(PMe,Ph)4 is formed, suggesting that a reductive 13Clabel are listed in Table V. Small doublets due to *W*CCW, elimination such as (5) is indeed occurring. Pt(PMe,Ph), for1J(1s3W-13C)= 300.3 Hz, and *WC*CW, 2J(1s3W-'3C) = 54.7 mation is not observed in the absence of added phosphine. ApHz, are observed as well as an AA'X pattern due to *W*C*CW, parently, Pt(PMe,Ph), ( n = 0-4) undergoes rapid phosphine 'J(13C-13C). All peaks are in their predicted ratios as shown in exchange under these conditions and its ,'P N M R peaks are Figure 4. A plausible mechanism for formation of V is as shown exchange-broadened beyond recognition. in eq 2-5 (L = PMe2Ph). Also there is evidence that reductive elimination steps such as (5) are intramolecular in nature. A reaction was conducted with I+IItrans-( HC=C)L,PtC=W ( 0 - t -Bu), + (~ - B u O ) ~ W = C H(2) 0.5 equiv of I, 0.5 equiv of I*, and 2 equiv of 11. If (5) is an intramolecular reductive elimination, peak ratios for W*C*CW I1 trans- ( H C r C ) L2PtC=W( 0-t-Bu) W*CCW, *W*C*CW, *W*CCW, and *WC*CW in the 13C trans-LzPt(C~W(O-t-Bu),J,+ (t-BuO),W=CH (3) N M R will remain essentially the same as they are in a reaction trans-LZPt(C=W(O-t-Bu),), ~ i s - L ~ P t ( C = W ( 0 - t - B u ) ~ ) ~ with only I* present. If, on the other hand, (5) is intermolecular, the relative intensities of peaks for *W*CCW and *WC*CW will (4) be much larger and those for *W*C*CW will be much smaller ~ i s - L ~ P t ( C ~ W ( 0 - t - B u ) ~Pt(L), }, + V ( n = 0-4) (5) than in the reaction with only I* present (see Table V). The former case was observed which is consistent with an intramo(~-BuO)~W=CH is not detected as a product of the reaction lecular reductive elimination. of I with 11. This is not surprising since it is thermally unstable The above-described crossover experiment provides evidence over the time scale of the reaction. For example, equilibrium that is consistent with the reversibility of reaction 2. The 13C mixtures containing W2(O-t-Bu),(fi-C2Hz)py and (~-BuO)~W= N M R peaks due to the W2*C=*C-Pt-*C=CW2 isotopomer CH decompose thermally over a 24-h period,17 which is compaof IV are enhanced in this experiment relative to their size in the rable to the rate at which V is formed. Even addition of excess reaction with only I* present (see Figure 5 ) . Such an enPMe2Ph to solutions of W2(0-t-Bu)6(fi-C,H,)py does not appear hancement could be caused by an intermolecular C2/C; or pcarbon scrambling resulting from the reversibility of reaction 2. (33) Listemann. M. L.; Schrock, R. R. Organometallics 1985, 4, 74. For example, trans- (H*C=* C)L,Pt * CE W (0-t- Bu) could react Figure 4. The 13C N M R spectrum due to the alkylidyne carbons of

+

-

-

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J. Am. Chem. SOC..Vol. 109, No. 15, I987

Reactions of Ditungsten Hexaalkoxides Table VI. Approximate Time“ Necessary for the Reactions of Ditungsten Hexaalkoxides with Alkynylplatinum(I1) Complexes To Reach 90% Completion at Ambient Temperature I‘ + I1 I’ + 11’ I + I1 reactns I + 11’ no reaction 1.5-2.5 h 4-6 davs time 3-8 min

with (t-BuO),W=CH to form I-l3C3and 11, Le., reaction -2. I-I3C3could then react with I1 by way of (lb) eventually forming the above-mentioned W2*C=*C-Pt-*C=CW2 isotopomer of IV-I3C3. Less conclusive N M R evidence exists for an enhancement in the W2C=C-Pt-C=*CW2 isotopomer of IV. Spectral simulations indicate that a total scrambling of @-carbonsdoes not occur suggesting that the reverse rate of (2) is not significantly faster than its forward rate or the rates of trans-(HC= C ) L2Pt.-C=W (0-t- Bu) 3 loss. Reactions of trans-Pt(=R),(PMe2Ph), (R = H, Me) with W2(O-i-Pr)6(py)z. The rates for reactions of ditungsten hexaalkoxides with alkynylplatinum( 11) complexes are very sensitive to the steric requirements of the accompanying ligands as shown in Table VI. For example, a reaction that takes days, Le., I 11, is retarded to the point that it is totally unfavorable even at elevated temperatures merely by replacing the acetylenic protons of I by the methyls of tr~ns-Pt(C=CMe)~(PMe,Ph),(I1).]* Because I’ does not react with 11, a less bulky dinuclear W(II1) compound, W2(O-i-Pr),(py), (II’),I9 was utilized. Here the reaction is complete in a few hours. As a further rate comparison, the reaction of I with 11’ occurs in a matter of minutes. The average volume of the cavities between the alkoxide ligands that have the potential for allowing substrates to react with the W=W centers is small especially in the case of 11. Thus, small changes in the size of the bulky substrates, I or 1’, cause a large change in reaction rates. The reaction of I’ with 11’ was investigated because the acidbase chemistry (eq lb) due to the acidic acetylenic protons in I is eliminated. The observed reaction sequence initiated by C=C bond cleavage (eq la) parallels that proposed in eq 2-5. The most conclusive evidence for alkyne metathesis is the formation of W3(pO-i-Pr)3(O-i-Pr)6(~3-CMe),’2 which is formed from the conproportionation of (i-PrO),W=CMe and W2(O-i-Pr)6(py)2. Pt(PMe2Ph)434the ultimate fate of the Pt-containing products of this metathesis, is readily characterized by its 31PN M R signal, b -34.2 (1J(’95Pt-3’P)= 3805 Hz). At least one of the major metastable species leading to Pt(PMe,Ph), has a cis geometry.35 Insufficient data are available at present to propose its exact structure or those of the remaining products since their N M R analysis is complicated by the fluxionality of 11’ and various W-containing products. However, alkyne metathesis, trans to cis isomerization about Pt, and reductive elimination appear to be essential features of the total reaction sequence. The reaction of I with 11’ occurs by both ( l a ) and (Ib) with is a major (la) predominating since W2(O-i-Pr)6(p-C2H2)(py)214 product. As in the reaction of I’ with II’, the Pt-containing products of metathesis are difficult to characterize by way of ‘H or 31PN M R . Further efforts in their characterization utilizing I* as a reactant were futile since broad, ill-defined I3C N M R resonances between 250 and 285 ppm and between 355 and 365 ppm result as the prime candidates attributable to P t - e W carbons. Whereas (t-BuO),W=CR are monomeric in solution,6 the isopropoxide analogues, e.g., [(HNMe2)(RC+(i-PrO),W( p 0 - i - P r ) l 2 (R = Et), can be dimeric both in solution36and in the solid state.9 The I3C N M R resonances for the alkylidyne carbons in these dimers are exchange-broadened due to fluxiona l i t ~and , ~ ~it becomes increasingly difficult to reach a slow-ex-

+

(34) Mann, B. E.; Musco, A. J . Chem. SOC.,Dalton Trans. 1980, 776. (35) Resonances for PMe,Ph and the ortho protons in PMe,Ph are split into triplets due to virtual coupling in trans-Pt complexes, but only into doublets in cis-Pt complexes. For the proposed cis complex resulting from the reaction of I’ with 11’: S(PMe,Ph) 2.23 (d, 2J(”P-’H) = 10.8 Hz, 3J(195Pt‘H) = 33 Hz), B(PMe,Ph, ortho-H) 7.87 (dd, ’J(”P-IH) = 12 Hz, )J(’H-IH) = 8.2 Hz, “J(’H-unassigned) = 1.8 Hz). For VI: b(PMe,Ph) 2.23 (d, ’J(”P-’H) = 10.5 Hz, 3J(’95Pt-’H) = 35 Hz), G(PMe,Ph, ortho H) 7.9 (dd). (36) Chisholm, M. H.; Conroy, B. K., unpublished results.

4557

change limit as the bulk of R C S increases. For example, this limit cannot be reached even at -70 “ C when R = Et.35 Thus, it is entirely possible that the Pt-C=W(O-i-Pr),-containing products resulting from the reaction of I with 11’ oligomerize and that the fluxionality of the resulting oligomers is the cause for the broad I3C resonances between 250 and 285 ppm. Again, Pt(PMe,Ph), is formed as the ultimate Pt-containing product. As it is formed, the above-described broad resonances are replaced by a mass of sharp singlets in the same general spectral ranges. Two products of the reaction of I with 11’ formed via (1 b) lend themselves to a more detailed characterization since they are neither oligomers nor are they fluxional. They have been characterized only as entities of a complex reaction mixture and are unstable toward reductive elimination forming Pt(PMe,Ph),. The initial product tran~-Pt(PMe~Ph)~(C=CH)(CzW,(o-i-Pr),) (VI) has a PtC2W2(OR), unit which is structurally very similar to that in IV. The ‘ H N M R of IV shows two OCMe3 resonances in a 3:2 ratio. That of VI shows two OCHMe2 septets in a 3:2 ratio and three OCHMe2 doublets in a 1:3:1 ratio since the two i-Pro groups on W(2) (compare Figure 2) are diastereotopic. The absence of bridging O R groups is noteworthy in 1V and VI because, as the oxidation state of similar ditungsten alkoxides increases, a tendency for formation of p O R groups becomes evident, e.g., in W2(g-O-i-Pr)2(0-i-Pr)4(p-C2H2)(py)214 and W2(1-O-tBu)~(O-~-BU),(~-CO).” Coupling constants and chemical shifts in Table 111 for VI* are very similar to those observed for III* and IV*. Complex VI is intermediate in the formation of cis-Pt(PMe2Ph),{C2W2(O-i-Pr),],(VII). The diversity and complexity of product spectra present in the ’HN M R when the concentration of the intermediate VI1 is maximum makes unequivocal assignment of its (0-i-Pr) N M R resonances almost impossible. However, several lines of evidence are in harmony with a cis geometry. In the ‘H N M R , PMe2Ph resonances indicative of a cis geometry about platinum35parallel the rise and fall of ,‘P and I3C resonances attributed to VII*. In the 3 i P and I3C N M R of VII*, an AA’MM’XX’ or ClC,’C2C,’PP’ pattern should be observed. The I3C N M R spectrum was simulated readily by such a coupling pattern although a satisfactory simulation of the ” P N M R was never achieved. A doublet coupling of 40.4 Hz assigned to (2J(,lP-I3C) 2J(31P-13C’)]is evident in both spectra and is further evidence for the cis geometry about Pt. Although the chemical shifts for VI1 and VII* in Table I11 parallel those observed for the trans derivatives 111, IV, and VI, the coupling constants to I9,Pt are considerably larger suggesting that both Pt-P and Pt-C bonding are stronger in the former. Obviously, the cis geometry in VI1 is thermodynamically more stable than the trans. This implies that the structurally related IV is kinetically stabilized toward the otherwise thermodynamically favored trans to cis isomerization by the steric bulk of its C2W2(O-t-Bu),ligands. This is also why IV is thermally stable to 75 “C: the cis geometry necessary for reductive elimination is sterically inaccessible. On the other hand, complexes containing smaller -CSW(OR)~ and/or -C2W2(0R)Sentities are kinetically labile forming a host of uncharacterized mono- or oligomeric products via sterically allowed trans to cis isomerizations. Reactivity of IV. Although H 2 0 and O2sensitive, this complex is thermally stable to at least 75 “C. Efforts have been initiated to probe the reactivity of the PtP2(C2W205),core of this molecule. Since the C2 unit is potentially nucleophilic, reactions with Lewis acids will be attempted. The reaction of IV with BC1, yielded a dark, insoluble precipitate and B C ~ , ( O - ~ - B U )in ~ -the , supernatant liquid. Iodine and related oxidizing reagents could either oxidize Pt(1I) or add to the C(4)-C(5) multiple bond or the W(2)-W(3) multiple bond. The reaction of I2 with IV produces a reddish brown precipitate that is totally insoluble in common organic solvents. The exact composition of this solid has not been investigated further. PMe2Ph lability in IV and its reaction with C O will now be discussed. Rates of PMe2Ph Exchange. Rates of PMe,Ph exchange in I, 111, and IV are retarded as the steric bulk of the ligands around Pt increases; Le., PMe2Ph exchange follows the order I > I11 >>

+

4558 J. Am. Chem. Soc., Vol. 109, No. 15, 1987 Table VII. The iJ(i95Pt-3iP)Values (Hz) and IiP N M R Chemical Shifts (ppm) for Pt(I1) Complexes Containing -C,W,(OR), or -C,W,(p-CO)(OR), Ligands complex I 111 IV VI11 IX VI VI1 iJ(i95Pt-31P) 2447 2591 2776 2714 2672 2757 3171 G(PMe,Ph) -14.7 -11.2 -8.0 -8.4 -9.2 -7.6 -3.7

IV. N M R data supporting these relative rates can be derived from (a) Pt-C=CH resonances, (b) ortho-H resonances of PMezPh, and (c) PMezPh resonances. (i) The N M R spectra of solutions containing pure I show virtual coupling of the two 31Pnuclei in I to Pt-C=CH. After 18 h of the reaction of I with 11, this 31P coupling in I is not observed due to rapid phosphine exchange whereas the triplet nature of the Pt-CECH resonance in 111 is evident. Therefore, phosphine exchange in I is more rapid than in 111. In a similar reaction solution containing 4 equiv of PMe,Ph, the resonance in I11 has also reached the fast-exchange limit. (ii) Without PMezPh added, three separate ortho-H resonances can be observed in the ' H N M R for solutions containing I, 111, and IV. When 4 equiv of PMe,Ph are present, a separate resonance for IV and an exchange-averaged signal for PMe2Ph, I, and I11 are observed. Thus, phosphine exchange in IV is much slower than in I and 111. (iii) Solutions containing I, 111, and IV exhibit sharp 31PN M R signals for 111 and IV, but the I resonance is exchange-broaded. When 4 equiv of PMe2Ph are present, a sharp peak is observed again for IV, but the I, 111, and PMezPh resonances are exchange-averaged and centered at -39.5 ppm after 18 h, -43.4 ppm after 44 h, and -45.3 ppm after 90 h. The resonance for free PMezPh is at -45.7 ppm. The above data suggest that the Pt atom in IV is substitutionally inert. Ligand substitution in square-planar complexes is associative in nature in noncoordinating solvents and occurs via a five-coordinate intermediate. Formation of such an intermediate from IV is highly disfavored due to the steric bulk of the two -CzW2(O-t-Bu), ligands. This may also suggest that other bimolecular, Pt-centered reactions of IV will also be sluggish at best (e.g., oxidative additions). Reaction of IV with CO. The addition of 1 or 2 equiv of C O to IV forms two closely related complexes in a sequential manner. When I3CO is utilized, 13C N M R resonances for the initial product, 6(CO) 303.3 (1J(1g3W-13C)= 148 Hz), and final product, 6(CO) 303.1 (1J('*3W-13C)= 150 Hz), are readily observed. These chemical shifts and coupling constants are analogous to those found for W , ( p c o ) resonances of W2(0CH2CMe3),(py),(pCO) and related c ~ m p l e x e s . ' Apparently ~ CO adds to the W=W bonds of IV forming trans-Pt(PMe2Ph),(C,Wz(O-tBu),](C,W,(~-CO)(O-t-Bu),) (VIII) and trans-Pt(PMe,Ph),( C , W , ( ~ - C O ) ( O - ~ - B U(IX) ) ~ ) ~in successive steps. The doublet of triplets nature of the PMe2Ph ortho-hydrogen resonances is indicative of the trans geometry. The IJ('95Pt-31P) resonances of VIII, IX, and other related complexes readily show the relative cis influence37of the -CH, -C,W,(OR),, and -C2W2(p-CO)(O-t-Bu), ligands. See Table VII. The -C=CH ligand, which is isoelectronic with -CO, is a a-acceptor, and a-donation from Pt-centered orbitals such as d tends to weaken the C=C bond; e.g., v(C=C) in I is 1959 cg-l vs. 2140-2100 cm-l in R C E C H . The PMe,Ph ligands in I can also act as a-acceptors and compete with cis-oriented ligands for Pt d, orbital electron density. In the sequence I-111-IV, I J ( 195Pt-3;P)values increase signaling increasingly stronger Pt-P bonds.37 The -C,W,(O-t-Bu), ligand does not compete as readily with PMe,Ph for Pt a-electrons as does the -C=CH ligand: The W2 center is pumping electron density into the a*-orbitals of the C2 unit; thus it has a lower capacity to accept r-electron density from Pt. Since 1J('95Pt-31P)decreases in the series IV-VIII-IX, the -CZW2(pCO)(O-t-B~)5 !igand must have a larger cis influence than 4,W2(0-t-Bu),. This is reasonable: p C 0 is now competing with the C2 unit for a-electron density on the W2 center. Therefore, the C2 unit has a greater capacity to accept a-electron

Blau et al. density from Pt. The -C2W2(0-i-Pr), ligand has a smaller cis influence than the bulkier -C,W,(O-t-Bu), since the 1J(195Pt-31P) in VI is larger than that in the isostructural 111. The smaller 0-i-Pr ligands in the former allow stronger W,-C, bonding. The Cz unit, in turn, has a smaller capacity to accept a-electron density from Pt. From the above data, a cis influence scale can be created: -C=CH > -C~W,(/.L-CO)(O-~-BU), > -C,W,(O-t-Bu), > -C,W,(O-i-Pr),. It is unfortunate that insufficient data are present to add the -C=W(OR), moiety to this series. The consistent upfield shift in S(31P) with increasing 1J(195Pt-31P ) should also be noted. Projected Synthesis and Characterization of Acetylide and Carbide Clusters Supported by Alkoxides. The above results have opened new vistas for research. For example, acetylide complexes, (R'CzC)W2(0R),, similar in structure to a (PtC=C)W,(OR), unit in IV could possibly be synthesized by the reaction of LiCECR' with W2(OR),L,, yielding LiOR as a byproduct. The reaction could possibly proceed a step further for LiC=CH yielding an alkoxide-supporteddicarbido cluster of tungsten, LiOR, and ROH. Another potential route to carbido clusters may result from the use of Pt or Pd complexes such as I as templates for the formation small carbido clusters that might form larger clusters after reductive elimination has been induced. For example, conditions could possibly be optimized to form W,C,(OR),,, clusters from the controlled alcoholysis of IV by R O H where R = isopropyl, neopentyl, ethyl, etc. Similar reactions could be attempted for IX. Characterization of larger clusters becomes increasingly difficult. Introduction of a I3C label into these clusters by way of H*C=*CH would not be too arduous of a task. Another tool that may prove useful in their characterization is Ig3WNMR.38 This would be especially useful when crystals suitable for X-ray crystallography were not available. The lg3WNMR of 1V. The Ia3WN M R spectrum of IV shown in Figure 6 reveals two resonances where 6(W(2)) 4733 (,J(195Pt-'83W)= -41 Hz) and 6(W(1)) 4567. These resonances are very close to that of the parent W,(O-t-Bu),, 6 4408,39when the total chemical shift range for lg3WN M R of 11 000 ppm38 is considered. Each IS3Wresonance is skirted by Ig3Wsatellites with 1J(183W-'83W)= 252 Hz. The two sets of satellites are an AB quartet (b/a = 0.82); Le., each central resonance is at the center of mass and not the actual center of its pair of satellites. The former centers are displaced 6 Hz from the latter toward the center of the AB quartet. This, to our knowledge, is the first reported example of a one bond W-W coupling constant. Several two-bond W-0-W coupling constants have been reported.38 Work is in progress to obtain further 1J('83W-183W)as a function of W-W bond order. Experimental Section Reagents and General Techniques. General procedures and the preparations of W,(O-i-Pr),(py), and W,(O-t-Bu), have been described.I9 Quinuclidine was purchased from Lancaster Synthesis Ltd. and was used without further purification. Ethyne and carbon monoxide were purchased from Matheson and were used without further purification. Dry and oxygen-free hexane, toluene, tetrahydrofuran, and pyridine were used in all preparations. The elemental analysis was performed by Alfred Bernhardt Microanalytisches Laboratorium, West Germany. N M R samples were prepared by using dry and oxygen-free toluene-d, or benzene-& 'H and I3C N M R spectra were recorded on a Varian XL-300 instrument at 300 and 75.45 MHz, respectively. All 'H N M R chemical shifts are in parts per million relative to either the C6D5H singlet of C,D, set at 6 7.15 or the CHD, quintet of toluene-d8 set at 6 2.09. I3C N M R chemical shifts are in parts per million relative to the C,D, triplet at 6 128.0 or the C, heptet of toluene-d, at 20.4 ppm. The I3C N M R spectra were obtained for products derived from reactions using either the labeled truns-Pt(PMe2Ph),( 1,2-I3C2-C=CH)2 or "CCO. The 13C-labeled ethyne used in the synthesis of the former and the "C-labeled C O were purchased from MSD isotopes and used without ~~~

(37) Blau, Reed J.; Espenson, J. H. Inorg. Chem. 1986, 25, 878 and references therein.

~

~~

~~

~~

~

~

(38) Minelli, M.; Enemark, J. H.; Brownlee, R. T.; O'Connor, M. J.; Wedd, A. G. Coord. Chem. Reu. 1985, 68, 169. (39) Young, C. S.; Enemark, J. H.; Kober, E. Polyhedron 1987, 6, 255.

J . Am. Chem. SOC.,Vol. 109, No. 15, 1987

Reactions of Ditungsten Hexaalkoxides

I,

The "C,-labeled complex was synthesized similarly by using 230 mg of cis-PtCI2(PMe2Ph),, a 30% excess of n-butyllithium, and only a 50% excess l3C-labeled ethyne. The reaction yielded -140 mg of pure product. N M R data are for I and I* in C6D6. 'H NMR: 6(=CH) 2.38 (t, 2 H, 3J('95Pt-1H) = 45 Hz, 4J(3'P-'H) = 2.3 Hz); G(PMe) 1.81 (t, 12 H, 3J('95Pt-'H) = 33 Hz, 4J(31P-1H)= 7.8 Hz), G(PPh-ortho H ) 7.82 (dt, 4 H , 3J('H-'H) = 6 Hz, 'J("P-'H) = 6.0 Hz). 31PNMR: 6(PMe2Ph) -14.7 (s, 1J(195Pt-31P)= 2447 Hz). "C NMR for H C p C,-Pt-C,'EC,": 6(C,) 100.7 (t, 'J(195Pt-'3C,) = 948 Hz, ,J(I3C,-'H) = 42 Hz, 2J(3'P-'3C,) = 15.0 Hz); 6(Cp) 94.9 (s, 2J(195Pt13C,) = 266 Hz, 'J('3CB-1H) = 224 Hz). I3C NMR for I*: ' J ('3C,-'3Cp) = 122 Hz, 3J('3C,-'3Cp') = 10.5 Hz, *J(I3C,-l3C,') = 40 Hz). trsns-Pt(PMe2Ph)2(C=CH)(C2W2(O-t-Bu)5}. The reaction of a 1:l stoichiometry of I with I1 in toluene yields ultimately a mixture containing I, 111, IV, and V. After the solvent was stripped, unreacted I can be separated from the products by extraction of the products into hexanes leaving the insoluble I as a residue. Although 111 is less soluble than IV or V in hexanes, it was never isolated as a pure crystalline solid. N M R data are for 111 and III* in C6D6. 'H NMR: 6(=CH) 2.40 (t, 1 H, 3J(195Pt-lH) = 43 Hz, 2J 4J(31P-'H) = 4.3 Hz); 6(PMe) 1.79 (t, 12 H, 3J('95Pt-'H) = 32 Hz, ' J 4J(31P-1H)= 7.2 Hz); 6(O-t-Bu) 1.56 (s, 36 H); 6(0-t-Bu') 1.53 (s, 54 H); G(PPh-ortho H ) 7.9 (dt, H, 3J(1H-1H) = 6.4 Hz, 'J("P-'H) = 5 Hz). 31PNMR: G(PMe,Ph) -1 1.2 (s, 1J(195Pt-31P) = 2591 Hz). I3C NMR for HCpC,-Pt-C,=C,: 6(C,) 100.5 (t, 'J('95Pt-'3C,) = 941 Hz, 2J(31P-13C,)= 16.0 Hz) G(C0) 97.12 ( s , 2J(195Pt-'3CB)= 259 Hz); 6(Cl) 235.2 (t, 'J(195Pt-13Cl) = 802 Hz; 2J(31P-'3CI) = 11.5 Hz); 6(CJ 302.1 (t, 2J('95Pt-'3C2)= 78.2 Hz, ' J (183w(1)-13c2) = 132 HZ, 3~(31~-13c,)= 2 HZ). 13cNMR of HI*: 1J('3C,-13C9) = 122.2 Hz, 2J(13C,-'3Cl) = 36.2 Hz, 3J(13C,-13C2)= 3.3 Hz, 1J("Cl-13C2) = 18.5 Hz, 3J(13Cl-'3CB) = 12.0 H z . traran~-Pt(PMe~Ph)~(C,W~(O-t-Bu),),. W,(O-t-Bu), (1.0 g, 1.24 mmol) and ~ ~ O ~ ~ - P ~ ( P M ~ ~ P ~ )(0.32 , ( C =g,C0.62 H ) ~mmol) were added to a 30-mL Schlenk reaction vessel followed by 10 mL of toluene. The burgundy solution turns slowly to a golden brown. After 5 days of reaction at 30 OC, the toluene volume was reduced 50% and the resulting solution was cooled to -15 'C overnight. This procedure yielded 0.58 g of crystalline IV (brown crystals) contaminated with -10% of amorphous V. A further recrystallization in hexanes of solids from the supernatant liquid yielded an additional 0.32 g of solid with comparable purity. IV may be depleted of V by a careful crystallization of V from solutions of IV and V in toluene by slowly cooling. The elemental analysis is reported in Table IV. NMR data are for IV and IV* in C6D6. ' H NMR: 6(PMe) 1.77 (t, 12 H, 3J('95Pt-'H) = 30 Hz, ' J + 4J(3'P-'H) = 6.9 Hz); 6 ( 0 - t - B ~ 1.51 ) (s, 36 H); 6(0-t-Bu) 1.48 (s, 54 H ) ; 6(PPh-ortho H) 8.0 (dt, 4 H, 3J('H-1H) = 7 Hz, 3J(3'P-1H)= 6 Hz). 31PNMR: 6(PMe2Ph) -8.0 (s, 1J(195Pt-31P)2776 Hz). "C N M R for C,'=Cl'-Pt-Cl=C2: 6(CJ = 50.5 Hz, 2J(31P233.9 (t, 1J(195Pt-'3Cl)= 801 Hz, 'J(183W(2)-13Cl) I3Cl) = 12.5 Hz); 6(CJ 302.1 (t, 'J('83W(1)-13C2) = 133 Hz, 2J(195Pt-'3C2)= 76.3 Hz, 3J(3'P-13Cz)= 2.2 Hz). 13C NMR for IV*: AA'LL'XX' pattern where N = ' J 3J(13Cl-'3C2)= 21.6 Hz. Reasonable simulation of the central resonances may be obtained for IJ('3Cl-'3CJ = 18.5 Hz, 3J('3CI-'3Ci) = 3.1 Hz, 2J(13Cl-13Cl')= 39.4 Hz. 195Pt('H} NMR: 6(Pt) -4565 (t). I8'W NMR: 6 W(1) 4567 (s, 1 ~ ( 1 8 3 ~ ( 1 ) - 1 8 3 ~ ( 2=) )252 HZ); 6 w(2) 4733 (s, 2~(195pt-'83~(2)) = 41 Hz). IR (cm-I): in Nujol, 1255 w, 1230 m, 1170 s, 1100 w, 1020 m, 995 m, 957 s, 947 s, 930 m, 842 w, 790 m, 737 m, 720 w, 480 w; in Fluorolube, 2982 s, 2910 m, 1383 m, 1358 s. [(t-BuO),W=C],. This complex is a minor product in the synthesis of IV described above. It can be isolated from the reaction mixture in toluene by slowly cooling the solution. Pure reddish brown tablets can be isolated. NMR data are for V and V* in C6D6. 'H NMR: 6(0-t-Bu) 1.57 (s). 13C NMR of V*: 6(W=C) 268.5 (s, 'J('83W-'3C) = 300.3 Hz, ,J(183W-'3C)= 54.7, 'J('3C-'3C') = 44.5 Hz). Reactions in Sealed NMR Tubes. Reactions were often followed in sealed NMR tubes especially in earlier stages of product characterization and in reactions involving I3C-labeled materials. In the case of very complicated reactions, e.g., I' 11' and I + II', serious attempts at product isolation have not been made, and the products have only been characterized as entities of a complex reaction mixture by N M R techniques. Typically, 60-120 mg (0.070-0.150 mmol) of [W(III)IZwere added to 20-40 mg (0.035-0.070 mmol) of Pt(I1) in a 5-mm NMR tube with a 4 in. long, 5 mm (outer diameter), Pyrex glass extension. Approximately 0.6 mL of deuteriated solvent was added, the solution was frozen to -196 'C, and the NMR tube was evacuated and sealed. Facile re-

+

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n

I/

1

_ _ r _ _ l ' ' ' ' / ' ' ' r l ' ' ' ' I ' ' ' ' l ' Y7YS '1790 Li735 Y730 Y725

.

'1720

PPM

Figure 6. The Ig3W N M R signals for truns-Pt[C2W2(0-t-Bu)5](PMe,Ph),. One resonance is flanked by distorted 195Ptsatellites (,J(195Pt-183W(2))N 41 Hz) (bottom) and is assigned to W(2) in Figure 1. Each resonance is accompanied by a set of Ig3Wsatellites indicated by an asterisk that are barely visible above the noise level. The two pairs = 252 of lS3Wsatellites are an AB quartet where 1J(183W(1)-183W(2)) Hz. further purification. 31PNMR spectra were recorded on a Varian XL100 at 40.5 MHz. "P chemical shifts are reported relative to 85% H3P04. Infrared spectra were recorded on a Perkin-Elmer 283 spectrophotometer as Nujol or Fluorolube mulls between NaCl plates. "C NMR Simulations. 13C N M R simulations were conducted on a Nicolet NT-360 360-MHz spectrometer using the accompanying NMCSIM software. Coupling patterns for the major isotopomers (>5% abundance) of I*, HI*, and IV* were calculated separately and added individually to a composite spectrum as the appropriate fraction of the total spectrum. Comparisons between experimental and calculated spectra were visual in nature. Ig3WNMR of IV. A 0.9-g sample of IV and 2.5 mL of C6D6were sealed in a 10-mm N M R tube. The solid was not totally dissolved at ambient temperature; thus spectra were taken at 35 OC yielding a solution -0.2 M in IV. Chemical shifts are in parts per million relative to Na2W04. Spectra were taken on a Nicolet N T 360-MHz spectrometer at 15.11 MHz. Initial spectra were taken with a very large window, flO000 Hz. Additional spectra were accumulated with a smaller window to improve resolution and to verify that the resonances were not "folded over". Preliminary spectra were accumulated overnight. The final spectrum was accumulated for -64 h with 28 810 scans. The pulse width was 40 f i s followed by a 5-s delay. The sweep width was 12500 Hz with the spectrometer frequency at 15.112877 MHz and an offset of 69 732 Hz from NaZWO4. trans-Pt(PMe2Ph),(C=CH),. This complex was synthesized from the reaction of cis-PtCI2(PMe2Ph),and L i C E C H according to the literatureI8 with the exception that a 30% rather than a 60-100% excess of n-butyllithium is utilized in the in situ formation of L i C E C H from ethyne.

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4560 J . Am. Chem. SOC.,Vol. 109, No. 15, 1987

Blau et al.

IV in an N M R tube. A septum was secured on the top of the tube, the sample was cooled to -78 OC, and the proper amount of C O or I3C-labeled C O was injected into the tube via a gas-tight syringe. After C O addition, the septum and top of the tube were wrapped with parafilm and the tube was shaken vigorously. The solution was kept near -78 "C until it was analyzed by ambient- or low-temperature NMR. N M R data for products characterized in this fashion follow. ~raran~-Pt(PMe~Ph)~(C,W,(O-t-Bu)~){C~W~(p-C0)(0-f-B~)~} (VIII). This complex is formed from the reaction of 1 equiv of C O with IV at temperatures above 0 OC. In the absence of excess CO, this product appears to be thermally stable at ambient temperature. N M R data are for VIII in toluene-d,. 'H NMR: 6(PPh-ortho H) 8.13 (dt, 4 H, 'J('H-'H) = 6.8 Hz, 3J(31P-1H)= 6 Hz); 6(0-t-Bu) 1.503 (s, 18 H); 6(0-t-Bu) 1.426 (s, 27 H); t-BuO ligands on the -C2W2(pCO)(O-t-Bu), unit appear to be fluxional at room temperature. "P NMR: 6(PMe2Ph) -8.4 ('J(195Pt-31P)= 2714 Hz). "C NMR: 6(pCO) 303.3 (1J('83W-13C)= 148 Hz). tran~-Pt(PMe~Pb)~{C~W~(p-C0)(0-t-Bu)~)~ (IX). This complex is formed from the reaction of 2 equiv of C O with IV at temperatures above 10 'C. Reaction of IV with more than 2 equiv of C O forms W(CO), and other uncharacterized products. N M R data are for IX in toluene-d,. 'H NMR: G(PPh-ortho H) 8.36 (dt, 4 H, 3J(1H-'H) = 6.5, 3J(3'P-1H) = 6.6 Hz); G(PMe) 1.135 (t, 12 H); r-BuO ligands appear to be fluxional at ambient temperature. 3 i P N M R : 6(PMe2Ph) -9.2 (IJ(195Pt-3'P) = 2672 Hz). "C NMR: 6 ( p CO) 303.1 (1J('83W-13C)= 150 Hz). Crystallographic Study of IV. General operating facilities and listings of programs have been given previously.@ Crystal data for IV are found in Table VIII. A suitable small crystal obtained by recrystallization from hexanes was selected and transferred to the goniostat, where it was cooled to -1 55 "C for characterization and data collection. A systematic search of a limited hemisphere of reciprocal space yielded a set of reflections which exhibited no symmetry or extinctions. The choice of the triclinic space group P1 bar was confirmed by successful solution and refinement of the structure. The structure was solved by a combination of direct methods and heavy-atom Fourier techniques. All non-hydrogen atoms were located and refined by using anisotropic thermal parameters. Hydrogen atoms were included in fixed calculated positions in the final cycles of refinement. The unit cell contains a molecule of n-hexane disordered around actions were followed by using low temperature N M R techniques. N M R a center of symmetry (atoms C(40), C(41), C(41'), and C(42)). The data for new complexes characterized in this manner without isolation solvent atoms were refined by using isotropic thermal parameters. No are presented below. absorption correction was carried out. ~~~S-P~(PM~~P~)~(CL=CH){C~W~(O-~-P~)~). This product is formed The final difference map was essentially featureless except for a refrom the reaction of trans-Pt(PMe2Ph),(C=CH), with W2(O-i-Pr),(py)2 sidual of 2 e/A3 at the Pt position. at temperatures above 5 "C. In the presence of excess 11', it rapidly ( t l j 2 The molecule possesses a crystallographic center of symmetry. 20 min) undergoes further reaction(s) at ambient temperature. N M R data are for VI and VI* in toluene-d,. 'H NMR: G(PPh-xtho Acknowledgment. We thank the National Science Foundation, H ) 7.82 (dt, 4 H); G(OCHMe,) 5.27 (septet, 2 H, 3J('H-'H) = 6 Hz), the donors of the Petroleum Research Fund, administered by the 4.87 (septet, 3 H, 3J('H-1H) = 6 Hz); 6(0CHMe2) 1.48 (d, 6 H), 1.32 American Chemical Society, and the Wrubel Computing Center (d, 18 H), 1.19 (d, 6 H). 31PNMR: 6(PMe2Ph) -7.6 (s, 1J(19sPt-3'P) for support. The Varian 300 N M R was purchased in part by a = 2757). I3C N M R for VI*; HC+2,-Pt-Cl=C2: 6(Cl) 227.8 grant (PHS-S10-RR-1882-01) from the National Institutes of ('J('9sPt-"C1) = 814 Hz); G(C2) 284.3 (2J('9sPt-'3C2) = 86 Hz); 6(C, Health. Thanks are also extended to the Indiana University NMR and C,) 94-100 ('J('3C,-'3C$ = 122 Hz). C~S-P~(PM~,P~)~{C~W~(O-I-P~)~)~. This product is formed from the Laboratory staff especially for their assistance with Is3W N M R . reaction of I with 211' where t l / , N 20 min at ambient temperature. It Finally, we acknowledge helpful comments from Professors A. decomposes thermally in solution in a matter of hours. J. Carty of the University of Waterloo and Helmut Werner of N M R data are for VI1 and VII* in toluene-d8. 'H NMR: G(PPhthe University of Wurzburg. ortho H ) 7.9 (dd, 4 H, )J("P-'H) = 11.7 Hz, 3J(1H-'H) = 6.9 Hz); 6(PMe) 2.23 (d, 12 H , 3J('9sPt-'H) = 35 Hz). N M R : 6(PMe2Ph) Supplementary Material Available: Complete listings of bond G(CJ -3.7 (s, 1J('9sPt-31P) = 3171. I3C N M R for VII* (Pt-Cl=C2): lengths and bond angles and anisotropic thermal parameters (4 216.9 ('J('95Pt-'3C) = 983 Hz, {2J(3'P-CI) 2J(31P-C,')} = 40.4 Hz); pages); listings of F, and F, values (12 pages). Ordering infor6(C,) 282.3 (2J(19sPt-13C)= 115 Hz, IJ(CI-C2) = 19 Hz). Reasonable mation is given on any current masthead page. The complete simulation of C l and C, may be obtained by using 2J(13CI-'3C1') = 7.4 structural report is available from the Indiana University ChemHz, 2J(3'P-"P) = 16.6 Hz, 2J(3'P-'3CI) = 25.8 Hz, 2J(31P-"C2) = 15.5 istry Library, in microfiche form only. Request MSC Report No. Hz. Although simulation of the I I P multiplet (ddd) of VII* was un(C=C) W2(OC(CH3)3)J 2. 85074 for Pt [ (P(CH3)2C6H5) satisfactory, couplings of 40, 17, and 7 H z appear to be present. Reactions of CO with IV in NMR Tubes. The analysis of reactions of C O with IV are only at a preliminary stage at present. Typically, (40) Chisholm, M . H.; Huffman, J. C.; Kirkpatrick, C. C. Inorg. Chern. 1984, 23, 1021. -0.6 mL of toluene-d8 was added to 50-80 mg (0.025-0.04 mmol) of

Table VIII. Summary of Crystallographic Data for IV

fw space group

1985.98 pi 11.983 (5) a, A 17.413 (9) b, A 10.574 (4) c, A a,deg 92.31 (2) 107.87 (2) 0, deg 108.59 (2) 7,deg z 1 v,A3 1966.89 dcaled, 4cm-I 1.677 linear abs coeff, cm-' 78.269 temp, "C -155 sample to source dist, cm 23.5 takeoff angle, deg 2.0 scan width, deg 1.8 0.692 tan 8 28 range, deg 6-45 data collected 6696 total unique data with 4544 F, > 2.33a(F0) cryst size, mm 0.10 x 0.10 x 0.10 reddish brown cryst color Mo K a (A = 0.71069 A), graphite radiatn monochromator instrument Picker four-circle diffractometer locally modified and interfaced detector aperture 3.0 mm wide X 4.0 mm high, 22.5 cm from crystal scan speed, deg/min 4.0 bkgd counts, s, at each 10 end of scan unique data 5162 0.0353 R(0 0.0360 RJF) 0.914 goodness of fit 0.05 largest A l a

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