Organometallics 1995, 14, 2318-2324
2318
Dicarbonyl and Tricarbonyl Adducts of (W=W)6+-Containing Complexes. Preparation and Structures of W2(0CMe2CF3)6(C0)2 and W2(0CMe(CF3)2)4(NMe2)2(C0)3 Theodore A. Budzichowski, Malcolm H. Chisholm," Darin B. Tiedtke, John C. Huffman, and William E. Streib Department of Chemistry and Molecular Structure Center, Indiana University, Bloomington, Indiana 47405 Received September 26, 1994@ Carbon monoxide adds reversibly to W2(OR)6 compounds to give W2(0R)6(C0)2complexes
(R = SitBuMe2, 1;CMe2CF3, 2;2,6-Me&H3, 3)wherein the CO ligands bond to alternate tungsten atoms in a manner t h a t allows mixing of WW n and W d x to CO n* bonding. In contrast to the homoleptic alkoxides above, the mixed amido-alkoxide complex WdOCMe(CF3)2)4(NMe2)2(4),which also takes u p 2 equiv of CO, reacts further to give WAOCMe(CF3)2)4(NMe&(C0)3 (6), which has a n unusual structure wherein three CO ligands are bonded to a single tungsten atom and the W-W bond is supported by one NMe2 bridge. The formation of 6 is also reversible. 2 and 6 have been characterized by single-crystal X-ray crystallography, and all compounds have been characterized by lH and 13C{lH} NMR spectroscopy. The results are compared to earlier studies of the addition of CO to M2(OR)6 complexes such as W2(OtBu)6, which give bridged monocarbonyl adducts, and t h a t of Wolczanski et al. (Miller, R. L.; Wolczanski, P. T.; Rheingold, A. L. J.Am. Chem. SOC.1993, 115, 10422) wherein CO and WgCl2(silox)4 (silox = tB~3SiO)react reversibly t o give a bis(carbonyl) adduct with subsequent cleavage to give (silox)~(O)W~-C)W(silox)~Cl~. For 2, C26H36F1808W2, FW = 1186.2; a = 11.256(4), b = 18.496(6), C = 17.789(7) p = 97.97(1)"; monoclinic P21/n, 2 = 4. For 6, C23H24Fd207W2, FW = 1264.1; a = 14.053(3), b = 21.148(5), c = 12.789(3) a = 106.11(1),8, = 103.15(1), y = 86.81(1)"; triclinic Pi,2 = 4.
A;
A;
Introduction Prior work has established that carbon monoxide will add across the MEM bond in M2(OR)6 (M = Mo, W) complexes1 t o give M2(0R)s@-cO) compounds that exhibit extremely low C-0 stretching frequencies, e.g., v(C0) -1575 cm-l in W2(OtBu)6@-CO)and W2(OiPr)6(p-C0)(py)z.lc The electronic structure of the carbonyl adducts has been investigated by molecular orbital calculations employing the method of Fenske and Hall, and an understanding of the bonding has been obtained.2 They are inorganic analogues of cyclopropenones, and the C - 0 bond is thereby weakened relative to a simple ketone. The oxygen is nucleophilic, as is evidenced by the formation of the "dimer of dimers" [W2We were (OiPr)6@-C0)l2and [W2(OiPr)6@-CO)(py)12.1c,3 therefore most intrigued to learn that the related compound W2C12(silox)4, where silox = OSitBu3, reacts with carbon monoxide to form a bis(carbony1) adduct of proposed structure A which exhibits relatively high @Abstractpublished in Advance ACS Abstracts, March 1, 1995. (1)(a) Chisholm, M. H.; Cotton, F. A,; Extine, M. W.; Kelly, R. L. J . Am. Chem. SOC.1979,61,7645. (b) Chisholm, M.H.; Huffman, J . C.; Leonelli, J.; Rothwell, I. P. J . Am. Chem. SOC.1982,104,7030. ( c ) Chisholm, M. H.; Hoffman, D. M.; Huffman, J. C. Organometallics 1986,4 , 986. (2) Blower, P. J.; Chisholm, M. H.; Clark, D. L.; Eichorn, B. W. Organometallics 1986,5,2127. (3)Cotton, F.A,; Schwotzer, W. J . A m . Chem. SOC.1983,105,4955.
CI
R
0
/
I
\
0/
s
R
A
0 R
B
C - 0 stretching frequencies v(C0) = 2035 and 2010 ~ m - l .Furthermore, ~ upon heating W~Cl~(silox)4(CO)~ (l2Oo,CTD~), 1 equiv of CO was lost (reversibly) and the remaining carbonyl ligand was cleaved to give WZ@C)(O)2C12(silox)4having the structure depicted by B.4 This is an extremely rare example of the cleavage of C=O (D = 256 kcallmol) in coordination c h e m i ~ t r y . ~ Earlier attempts in this laboratory to prepare WZ(OSitBuMe2)6@-CO)by the addition of HOSitBuMe2 to Wz(OtBu)6@-CO)resulted in failure.6 Only W2(OSitwas isolated. The recent work by Wolczanski (4)Miller, R. L.;Wolczanski, P. T.; Rheingold, A. L. J . A m . Chem. SOC.1993,115,10422. (5)(a) Chisholm, M. H.; Hammond, C. E.; Johnston, V. J.; Streib, W. E.; Huffman, J. C. J . Am. Chem.Soc. 1992,114,7056.(b) Chisholm, M. H. J . Organomet. Chem. 1987, 334, 77. ( c ) Neithamer, D. R.; LaPointe, R. E.; Wheeler, R. A.; Richeson, D. S.; Van Duyne, G. D.; Wolczanski, P. T. J . A m . Chem. SOC.1989,111, 9056. (d) Evans, W. J.; Grate, J. W.; Hughs, L. A.; Zhang, H.; Atwood, J. L. J . Am. Chem. Soc. 1986,107,3728.(e) Tachikawa, M.; Muetterties, E. L. Prog. Inorg. Chem. 1981,28,203. (6)Dr. Cindy Cook, personal communication.
0276-733319512314-2318$09.00/0 0 1995 American Chemical Society
Carbonyl Adducts of (W=W)6+-Containing Complexes
Organometallics, Vol. 14,No. 5,1995 2319
et aL4 prompted us to reexamine the addition of CO to (WGW)~+ centers bearing less electron-donatingligands such as OSitBuMe2, OCMe2CF3, and 0(2,6-Me&&). We report here the results of these initial investigations and the first structural characterizations of bis- and tris(carbonyl) adducts of (W=W)6+-containingcompounds.
Results and Discussion Carbon monoxide ( 2 2 equiv) was added by vacuum transfer to NMR tubes containing W2(OR)6 compounds where R = SitBuMe2, CMe2CF3, and 2,6-Me&& in toluene-& (0.03 M, -196 to 23 "C). By 13CC1H}and lH NMR spectroscopies, a reversible reaction occurred which favored the formation of bis(carbony1) adducts, eq 1.
0193p I
c53
&
029 11
1,R = SitBuMe2 2, R = CMe,CF, 3,R = 2,6-Me2C,H, The l3C(lH} NMR spectra clearly showed the presence of terminal carbonyl ligands based on their chemical shift (6 217-241 ppm), 1J1s3~-13ccoupling constants (106-124 Hz), and magnitude of the observed satellites (14%, 183W;I = l/2, 14.3% natural abundance). Rather interestingly we have found no evidence for a monocarbony1 adduct @-CO)by NMR spectroscopy when R = SitBuMe2 or CMe2CF3. When R = 2,6-Me&H3, the formation of a bis(C0) adduct is favored (280% of the product mixture) when 2 equiv of CO is added, but there was clear evidence for the formation of a mono(carbony1) derivative. The latter apparently adopts a structure based analogous to that observed for [w2(oiPr)6(&co)]2 on the similarities of the spectroscopic data.lc The reversibility of CO binding impedes the isolation of these adducts, but crystals may be obtained upon cooling hexane or toluene solutions of 1 and 2 under an atmosphere of CO. For 2, the crystals were suitable for analysis by single-crystal X-ray diffraction (see Figure 1). The fractional atomic coordinates from this study appear in Table 1, and pertinent bond distances and angles are summarized in Table 2. The striking features of the structure are the eclipsed geometry, the syn arrangement of the two CO ligands (C-W-W-C torsion angle, 100') and the relatively small C-W-W angles of 81.7(6) and 84.4(5)". The W-W distance of 2.4498(13) implies some loss of M-M bonding due to the presence of the n-acceptor carbonyl ligands. Pictorially the bonding can be described by C wherein it becomes
C
readily apparent that the CO ligands are involved in bonding to different M-M n-bonding orbitals. A mixing of M-M and M-CO n bonding is implied by C,and this
Figure 1. ORTEP view of the Wz(OCMe2CF&(C0)2 molecule giving the atom number scheme (top) and a view of the central W206(C0>2core looking down the W-W bond (bottom). presumably is responsible for the acute C-W-W angles observed in the solid state. The observed structure cannot be favored by much over a structure where the two CO ligands are eclipsed and thus compete for the same M-M n-bonding orbital since only a t low temperatures is rotation about the W-W bond frozen out on the NMR time scale. On the basis of the observed coalescence temperature (Tc= -20 "C), we estimate AG* as -11 kcavmol. A comparison of the infrared v(C0)values for the two crystalline bis(carbony1)adducts reported here and that of Wolczanski's compound is given in Table 3. These numbers provide an indication of the electron density at the metal, with lower v(C0) values correlating with greater W dn to CO n* donation, and presumably with alkoxide pn to metal dn donation, as was observed by Caulton and co-workers for a series of Ru(H)(X)(CO)(PtBu2Me)2 ~omplexes.~ We attribute the observation of three CO stretches in the IR spectrum of 2 to the (7) Poulton, J. T.; Folting, K.; Streib, W. E.; Caulton, K. G. Inorg. Chem. 1992,31,3190.
Budzichowski et al.
2320 Organometallics, Vol. 14, No. 5, 1995 Table 1. Fractional Coordinates ( x 104) and Isotropic Thermal Parameters (x 10) for 2 atom
X
4'
Z
BLSO
9632(1) 7634(1) IO88 I( 10) 11276(18) l0686( 17) 11030(17) 1259315) 13124(IO) 12899(9) 13174(10) 9528( 10) l0428( 17) 10832(20) 11415(18) 9777(21) 10530(11) 9 2 9 3 11) 8878( 11) 10175(11) 11004(16) 11937(17) 11576(19) 10235(18) 10886(11) 9329(10) 9728(12) 8675(20) 8 171(12) 6571(11) 6307(17) 6411(17) 7077(18) 5006(17) 4572( 10) 4774( 10) 4285( 10) 6840( 11) 5688(15) 5 100(16) 4920( 17) 5928(18) 4925(11) 6547(10) 6612(11) 7946( 10) 7217(16) 7159( 18) 6010( 17) 7857(17) 8924(9) 7229( 10) 8074(11) 8287(19) 8664( 12)
2464.5(4) 2310.9(4) 1895(6) 1470(10) 735(10) 1885(9) 1412(10) lOlO(7) 1072(6) 2033(6) 1828(6) 1632(9) 873( 1 I ) 2164( 12) 1611(11) 1458(7) 2263(6) 1137(6) 3336(6) 3930( IO) 387 1( 10) 3934( 11) 4599( 10) 5200(6) 4634(6) 4628(6) 3166( 11) 3522(7) 1702(6) 1320(10) 1820(10) 645(10) 1137( 10) 745(6) 737(5) 1715(6) 3 182(6) 3508(9) 3581(11) 3087( 11) 4245( 10) 462 l(6) 4232(6) 4657( 6) 1590(5) 1191(9) 415(11) 1512(11) 1247(9) 915(6) 942(6) 1931(6) 3029(9) 3370(7)
665.6(4) IO4 1.4(4) 1230(6) 1872(IO) 181l(11) 2583(9) 1882(IO) 2472(6) 1252(6) 1910(6) -191(6) -650( 10) -446( 11) -599( 12) - 1478(1 1) - 1959(6) -1679(6) -1573(6) 1159(6) 1126(ll) 185I ( 11) 419(11) 1182(11) 1153(6) 606(6) 1816(7) - 14I( 12) -596(7) 393(7) -304( IO) -981(9) -304( 11) -333( 11) -945(6) 282(6) -327(7) 659(6) 662(10) - 160(IO) 1127(11) 986( 11) 1031(7) 1696(6) 581(7) 1809(6) 2252(9) 1985(10) 223 1(11) 3074( IO) 3157(5) 3566(6) 3293(6) 1950(11) 2451(8)
10 9 10 19 17 16 16 29 24 25 11
18 20 21 29 26 29 12 15 22 23 16 19 25 26 23 22
Bond Distances (A) 2.4498(13) W(1)-0(19) 1.896(11) W(2)-0(37) l.921(1I ) 1.925(11) W(I)-C(27) 2.115(21) W(2)-0(45) 1.906(10) 1.917(1I ) W(2)-O(29) 1.910(11) W(2)-C(53) 2.141(23) Bond Angles (deg)
W(I)-C(27)-0(28) W(I)-W(2)-0(29) W(l)-W(2)-0(37) W(I)-W(2)-0(45) W(l)-W(2)-C(53) cis L-w-L
177.1(16) 115.2(4) 101.9(4) 101.1(4) 84.4(5) 87.9 av
W(2)-C(53)-0(54) W(Z)-W(1)-0(3) W(2)-W(l)-O(ll) W(2)-W(1)-0(19) W(2)-W(l)-C(27) trans L-W-L
RO,, RO '. -W-W
/OR
Me,N
\"OR NMe2
/
R = CMeICFJ),
0 C
OR
15
26 25 27 31 30 28 13 17 19 24 19 29 26 32 24 23 18 17 16 20 19 28 21 26 14 13
Table 2. Selected Bond Distances and Angles for Wz(0CMezCFddC0)z (2) W(l)-W(2) W(1)-0(3) W(1)-0(11)
Scheme 1
175.7(15) 115.2(3) 100.9(4) 102.8(4) 81.7(6) 156.1 av
presence of rotamers in the Nujol mull at room temperature. Two absorptions may be readily assigned t o the symmetric and asymmetric modes of the syn rotamer (C2 symmetry), which was structurally characterized by single-crystal X-ray diffraction. Another rotamer with an anti 1,2-C0 structure ( C 2 h symmetry) is
Table 3. Comparison of v(C0) Values in Bis(carbony1) Adducts of WP-Containing Compounds compound
v(C0)(cm-')
ref
%'2(0SiMez'Bu)6(C0)? W2(0CMe2CFMCO)z W2C12( silox)&O)?)
2029, 1995 2081,2064,2050 2055,2035
this work this work 4
postulated t o account for the third absorption. For this species the symmetric (4) stretch is IR inactive, and only the asymmetric (B,) stretch is observed. The addition of a large excess of (CF3)2MeCOHto W2(NMez)s does not lead to complete replacement of all of the amido ligands, and W2(0CMe(CF3)2)4(NMe2)2(4) is formed instead. This is presumably the result of a combination of steric and electronic factors. Partial replacement of the amido ligands by the more weakly n-donating hexafluoro-tert-butoxide ligands results in a significant strengthening of the remaining W-NMe2 bonds due to enhanced N pn t o W dn bonding, which renders this linkage less susceptible to attack by electrophiles. Partial replacement of amido groups for the more sterically demanding hexafluoro-tert-butoxide ligands also makes these linkages less accessible on steric grounds. Similar results have been observed by Cotton et al. for the reaction of Moz(NMe2)swith HOC(CF3)3.8 Addition of CO to 4 leads to the formation of a bis(CO) adduct W2(0CMe(CF3)2)4(NMe2)2(C0)2(5). This complex also possesses terminally bound CO ligands on alternate W atoms, and these apparently are trans to each of the remaining amido ligands. Unlike the other bis(C0) adducts, however, 5 slowly reacts in a reversible manner with additional CO to form the tris(C0) adduct Wz(OCMe(CF3)2)4(NMe2)2(C0)3(6)as shownin Scheme 1. This complex was initially believed to be a carbamoyl derivative, as had been previously observed in the reaction between W~Clz(NMe2)4and C0.9 In the I3C{lH} NMR spectrum, there are three resonances arising from 13C0 at 6 231, 211, and 197 ppm and each is flanked by satellites due to lg3W coupling that indicate a terminal, rather than bridging mode of bonding. The low-field resonance appears as a doublet, and the highfield resonance is notably broader than the others. We propose that these signals are coupled with the highfield resonance, exhibiting si@cant quadrupolar broadening due to its proximity to 14N(I= l),which obscures (8) Abbott, R. G.; Cotton, F. A,; Falvello, L. R. Polyhedron 1990,9, 1821. (9)Ahmed, K. J.; Chisholm, M. H. Organometallics 1986,5,185.
Organometallics, Vol. 14, No. 5, 1995 2321
Carbonyl Adducts of (W=W)6+-Containing Complexes
Table 4. Fractional Coordinates ( x lo4) and Isotropic Thermal Parameters ( x 10) for 6 Y Z Bm atom X Y
atom
X
W(1)A W(W N3)A C(4)A C(5)A N(6)A C(7)A C(8)A C(9)A O(10)A C( 1l)A O(12)A C(13)A O(14)A O(15)A C( 16)A C(17)A C( 18)A F(19)A F(20)A F(21)A C(22)A F(23)A F(24)A F(25)A O(26)A C(27)A C(28)A C(29)A F(30)A F(31)A F(32)A C(33)A F(34)A F(35)A F(36)A O(37)A C(38)A C(39)A C(40)A F(41)A F(42)A F(43)A C(W.4 F(45)A F(46)A F(47)A O(48)A C(49)A C(50)A C(5 l)A F(52)A F(53)A F(54)A C(55)A F(56)A F(57)A F(58)A
3116.1(5) 2194.8(5) 1520(9) 1124(12) 830(12) 1672(11) 1728(12) 1025(13) 3555(13) 3922(9) 3639(13) 3951(8) 4592( 15) 54 35(9) 2950(8) 3374( 15) 4543( 15) 2929( 14) 2935( 10) 2023(9) 3407(10) 3220(20) 2305(12) 3551(13) 3747( 11) 2622(7) 2898( 12) 3944( 12) 2234( 13) 1269(7) 2317(9) 2367(8) 276 1(12) 2948(8) 3386(9) 1867(8) 3059(8) 3817(12) 4796( 15) 3574(16) 3460(8) 4278(8) 2744(9) 3922(12 46 16(8) 3098(8) 4151(8) 1449(7) 966( 11) 896( 12) -68(13) -644(8) -494(8) -84(7) 1538(13) 1030(9) 1779(7) 2372(8)
874.2(3) 1624.8(3) 1081(7) 1378(9) 528(8) 1159(7) 470(9) 1567(9) 741(8) 639(6) 1818(9) 2327(6) 688(8) 627(7) 821(5) 1005(8) 1195(16) 1642(10) 2 109(6) 1540(7) 1877(7) 4 13(17) 271(7) 594(8) -92(6) -77(5) -722(8) -809(8) -1043(8) -994(5) -794(6) - 1703(5) - 1044(9) -1681(5) -745(5) -958(5) 222 l(6) 2479(9) 2152(9) 2323( 10) 1679(6) 2514(6) 26 1O(6) 3210(9) 3488(5) 354 l(6) 3340(5) 2328(5) 2926(7) 3238(8) 2820(9) 3332(6) 2315(6) 2649(5) 3373(8) 3907(5) 3076(5) 3591(5)
1830(1) 665(1) 1407(11) 2411(15) 735( 15) -802( 12) - 1530(14) - 1472(14) 380(18) -359(10) 2593( 14) 3004(9) 2187(16) 2306( 12) 3353(8) 4449( 16) 4753( 15) 5071( 14) 4607( 11) 51 18(11) 615 1(11) 4916( 18) 47 19(11) 6076( 11) 4547( 11) 1339(9) 1181(13) 1739(15) 1640(15) 1154(10) 2706(9) 1472(10) -122(16) -351(9) -502(9) -667(8) 470(9) 152(14) 533( 18) -1105(17) - 1563(9) -1500(10) - 1466(10) 734(15) 436( 11) 475( 11) 1841(10) 1358(8) 1491(14) 562(15) 1617(15) 1588(10) 762(9) 2557(8) 2622( 16) 2985(11) 3410(9) 247 5( 10)
13 12 17 24 21 21 24 22 28 29 22 22 30 37 15 30 71 30 53 54 59 70 62 72 56 13 16 22 24 33 40 37 27 37 38 30 22 23 36 35 37 42 43 25 45 44 40 14 15 21 25 39 36 26 25 43 32 38
the weak J 1 3 c - q coupling of -7 Hz. The lH NMR spectrum at low temperature (-40 "C, C7Dd showed that this complex was asymmetric and exhibited unique resonances for each of the four alkoxide ligands and two resonances for each amido group. Single crystals were grown from toluene solution under an atmosphere of CO and a single-crystal X-ray diffraction study was performed. Fractional atomic coordinates appear in Table 4, and pertinent bond distances and angles are summarized in Table 5. There were two unique molecules in the asymmetric unit, and these have been labeled A and B for convenience in comparing the metrical parameters for each. As is readily apparent, the two differ very little in structure. The molecular structure as determined from this experiment is shown in Figure 2,
W1)B W(2P N3)B C(4)B C(5)B N6)B C(7)B CWB C(9)B O(10)B C( 1l)B O( 12)B C(13)B O(14)B O(15)B C(16)B C(17)B C( 18)B F(19)B F(20)B F(21)B C(22)B F(23)B F(24)B F(25)B O(26)B C(27)B C(28)B C(29)B F(30)B F(31)B F(32)B C(33)B F(34)B F(35)B F(36)B O(37)B C(38)B C(39)B C(40)B F(41)B F(42)B F(43)B C(44)B F(45)B F(46)B F(47)B O(48)B C(49)B C(50)B C(51)B F(52)B F(53)B F(54)B C(55)B F(56)B F(57)B F(58)B
6867.9(4) 8010.2(4) 7599(9) 8290(12) 7002( 11) 7348(9) 6321(110 8026(12) 6337(11) 5962(8) 8083(11) 8734(7) 6 185(12) 5857(9) 7055(7) 7260(13) 6539(24) 8288(16) 8905(9) 8414(12) 8534(11) 7017( 14) 7118(8) 6137(7) 7619(7) 5682(8) 4709( 11) 4374( 12) 4495( 14) 4789(8) 5014(9) 3564(7) 4095(13) 3 13l(7) 4261(8) 429 l(8) 8427(8) 8375(12) 7679( 14) 8035(14) 7123(8) 8023(10) 8575(9) 9415( 14) 9403(9) 10025(8) 9765( 10) 9336(7) 10304(11) 10683(14) 10457(13) 11367(8) 9828(9) 10286(8) l0858( 12) 11803(8) 10507(8) 10796(8)
3463.4(3) 3299.9(3) 4217(7) 4636(9) 4669(8) 3381(6) 3410(8) 3363(9) 2810(7) 2418(6) 2979(8) 2690(5) 2734(8) 2274(6) 4095(5) 4207(9) 4779( 11) 441 1(11) 40 19(7) 5024(7) 4517(8) 3620( 10) 3694(6) 3378(6) 3095(5) 4033(5) 4094(8) 3803( 10) 4847(9) 5143(5) 5132(6) 4994(5) 3782( 10) 3849(7) 3132(6) 3998(8) 2400(5) 1722(8) 1408(9) 1534(8) 1752(6) 889(5) 1805(5) 1463(10) 784(6) 1595(6) 1673(7) 3599(5) 3642(8) 3087( 10) 4291(9) 4357(6) 4297(7) 4822(6) 3656(9) 3789(7) 4 105(7) 3083(7)
~~
Z
6903(1) 5556(1) 6418( 11) 7399( 14) 5834(14) 4149( 10) 351 1(13) 3415(14) 5454( 15) 4675( 10) 75 15(14) 7828(9) 7233(13) 7334( 10) 8480(8) 96 13(15) 10108(16) 10092(19) 9640( 12) 9937( 11) 11214(11) 9945( 15) 11032(9) 9465(9) 9646(8) 6619(9) 6635( 15) 7468( 17) 6915( 16) 6253( 11) 7952( 10) 6915( 10) 5467( 18) 5412(10) 5228( 12) 4677(9) 5129(9) 475 1(14) 5220( 17) 3493(16) 3169(9) 3022(9) 2984(9) 5079( 16) 4819(12) 4508( 11) 6136( 11) 6256(9) 6235( 14) 5422(18) 5973( 19) 5865( 12) 5014( 12) 6743(12) 7412( 15) 7603( 10) 8210(10) 7638( 10)
&so
11 11 16 25 17 13 15 20 18 24 18 17 19 28 15 24 71 41 51 63 66 29 36 38 26 20 21 33 28 40 46 36 35 52 56 54 20 18 29 28 40 44 40 33 53 47 58 18 20 35 32 49 55 50 25 49 50 46
where a single molecule is shown for clarity. Quite remarkably there are three carbonyl ligands bonded to a single tungsten atom, two of which appear to be semibridging in the solid state. Note the acute W(2)W(l)-C(9) and W(2)-W(l)-C(ll) angles (68.0(5) and 72.2(5)", respectively, for molecule A shown), as well as the long W(2)-C(9) and W(2)-C(ll) distances (2.611(15) and 2.761(15) A, respectively). There is also one bridging NMez ligand which completes a distorted octahedral coordination geometry about the metal centers. It is evident from the disposition of the ligands that a valence disproportionation has occurred. Previously it was observed that, in the reaction of MdORh compounds with excess CO, M(CO)6 is often formed (M = Mo, W),l and Cotton and co-workers isolated and structurally
Budzichowski et al.
2322 Organometallics, Vol. 14, No. 5, 1995 Table 5. Selected Bond Distances and Angles for WZ(OC(CF~)ZM~)~(NM~Z)Z(CO)~ (6) Bond Distances (A)
W(l)-W(2) W(I)-C(13) W(l)-C(9) W(1)-C(I1) W(1)-0(15)
2.5734110) 2.061(21) 2.027(22) 2.057(18) 2.047(9)
W(l)-W(2) W(l)-C(13) W(l)-C(9) W(1)-C(11) W(1)-0(15)
2.5551(10) 2.047(17) 1.991(17) 2.054(15) 2.056(10)
Molecule A W(1)-0(26) 2.043(10) W(l)-N(3) 2.233(13) W(2)-N(3) 2.064(12) W(2)-N(6) 1.860114)
W(2)-0(37) 1.900(11) W(2)-0(48) 1.901(10) W(2)-C(9) 2.611(15) W(2)-C(ll) 2.761(15)
Molecule B W(1)-O(26) 2.026(11) W(l)-N(3) 2.235(12) W(2)-N(3) 2.071(14) W(2)-N(6) 1.877(13)
W(2)-0(37) 1.926(10) W(2)-O(48) 1.931(10) W(2)-C(9) 2.584(15) W(2)-C(ll) 2.751(15)
W(2)-W(l)-C(9) W(2)-W( 1)-C( 11) W(l)-C(9)-0(10) W(1)-C(l1)-O(l2)
Bond Angles (deg) Molecule A W(l)-C(13)-0(14) 68.0(5) 72.2(5) C(9)-W( 1)-C( 11) 170.4(16) C(9)-W(l)-C(13) 178.0(16) C(ll)-W(l)-C(l3)
172.0(16) 98.0(6) 74.1(8) 80.3(7)
W(2)-W(l)-C(9) W(2)-W( 1)-C( 11) W(l)-C(9)-0( 10) W(l)-C(l1)-0(12)
Molecule B 68.0(4) W(1)-C(13)-0(14) 72.4(5) C(9)-W( 1)-C( 11) 172.8(14) C(9)-W(l)-C(l3) 177.3(14) C(ll)-W(l)-C(l3)
172.0(14) 100.9(6) 72.3(7) 81.2(7)
characterized (zPr0)4W~-OiPr)2W(C0)4,a complex (shown schematically in D) with a W(CO)4-& moiety R
0
R='Pr
D
C(5)
Figure 2. ORTEP view of the WZ(OCM~(CF~)Z)~(NM~Z)Zbridged to W(OiPr)6-d0 center that lacked a W-W bond.1° The formation of a tricarbonyl compound with a structure related to that shown in Figure 2 for WZ(OCM~(CF~)Z)~(NM~Z)Z(CO)~ may be a precursor to (iPr0)4W@-OiPr)zW(C0)4shown in D. While 6 clearly exhibits valence disproportionation, this process also is completely reversible, and complex 4 may be obtained simply by applying a vacuum to samples of 6. Also, in contrast to the reactions of aliphatic Wz6+ alkoxide complexes with excess CO, which rapidly result in valence disproportionation, formation of the tris(C0) complex 6 from the bis(C0) complex 5 takes nearly 1 week to proceed to completion. We also note that the NMR spectroscopic data for 6 are consistent with the maintenance of the solid state structure in toluene solution at low temperature. Since changing the electronic characteristics of the alkoxide ligands favored the formation of bis(C0) derivatives similar to W~(Cl)~(silox)4(CO)z, we were eager to thermolyze these new adducts to see if reductive cleavage of the C s O bond would occur. To date all of these efforts have failed. If the bis(C0) adducts 1 and 2 are dissolved in toluene-& at low temperature and then heated in a sealed NMR tube, the only reaction that occurs involves the reversible dissociation of the carbonyl ligands even after prolonged heating (looo,12 h or more). When W Z ( O C M ~ Z CisF ~ pressurized )~ with (10)Cotton, F.A.; Schwotzer,W. J.Am. Chem. Soc. 1993,105,5639.
(Cola molecule giving the atom number scheme (top) and a view of the central WzNz04(C0)3core showing the local geometry about each W atom (bottom). Two independent molecules were present in the asymmetric unit of the unit cell, but only one is shown for clarity. CO (large excess) and heated, a valence disproportionation reaction is apparent, as evidenced by the formation of W(CO)6. The other tungsten-containing species have not been identified, but we are confident that a carbido cluster is not produced from reactions employing 13C0 which were monitored by 13C(lH} NMR spectrosCOPY*
Concluding Remarks In summary, the following points are worthy of note. 1. The bis(carbony1)complexes Wz(OR)6(C0)21,2, and 3 are thermodynamically favored relative to W2(OR)6+-CO) compounds, which are preferred when R = tBu and iPr. 2. The bis(carbony1)compounds reported here are likely to be directly analogous to Wolczanski's compound W~Clz(silox)4(CO)~, and though carbonyl binding is reversible, we have yet to observe any C=O cleavage products even at elevated temperatures. We can only postulate that steric factors account for this disparity. When the extremely bulky OSitBu3 ligand is a spectator, steric pressure may force the two tungsten centers apart and provide an additional thermo-
Carbonyl Adducts of W=WY+-Containing Complexes dynamic impetus (ground state destabilization of WzCl2(siloxk) for CEO cleavage. I t is quite clear that the electronic properties which favor reversible formation of bis(C0) adducts and inhibit valence disproportionation are similar to Wz(OSitBuMe2)6,Wz(oCMezCF3)6, Wz(NMe2)2(0CMe(CF3)2)4,and W2Clz(OSitBu&. Subtle electronic differences that enable the latter to reductively cleave C z O are not easily identifiable. 3. The tris(carbony1) compound Wz(OCMe(CF3)2)4(NMe2)2(CO)~ adopts a remarkable structure in the solid state and provides insight into the redox reactions that have been noted previously in the reaction between CO and M2(OR)6 complexes wherein M(CO)s is one of the ultimate products. In the presence of the less electrondonating groups CMe(CF3)2, OCMezCF3, and OS?BuMe2, the formation of W(CO)s is suppressed. A critical factor may be the inability of these ligands to stabilize the high oxidation state product which would be formed concomitantly. Steric factors may also play a role since bulky alkoxide(si1oxide) ligands are less likely to occupy bridging sites and are therefore harder to transfer from one metal to the other as required for the valence disproportionation process (cf. the structure of 6, Figure 2). At this point it is worth mentioning that the corresponding molybdenum complexes have been prepared and their reactions with CO investigated. Adduct formation was not detected even at low temperatures for Mo2(0SitBuMe2)6,Mo2(0CMe2CF3)6,or Moz(NMe2)z(OCMe(CF3)2)4,consistent with the lower Lewis acidity of Mo versus W.ll Collectively these results provide further evidence of the rich chemistry associated with the central (WZW)~+ moiety that may be modified subtly or quite dramatically by the attendant ligands. Further studies are in progress.
Organometallics, Vol. 14,No. 5, 1995 2323
Preparation of W2(0Si'BuMe2)&0)2 (1). Wz(OSitBuMe2)6 (25 mg, 0.0216 mmol) was dissolved in 0.6 mL of toluene-& in an NMR tube equipped with a J. Young valve. One atmosphere of CO was added with the aid of a calibrated gas manifold at -196 "C. Upon thawing the solution, a reaction is evident based on the observation of a color change from deep burgundy to brownish black. The reaction was then monitored by NMR spectroscopy, which showed that the yield of 1 was >90% at -20 "C or lower but that the carbonyl ligands reversibly dissociated upon warming. Due to the lability of this complex, analytically pure samples have not been obtained and elemental analysis was not attempted. Crystalline material has been obtained from hexanes at -35 "C, but the crystals have thus far been unsuitable for study by X-ray diffraction. This material was used for analysis by IR spectroscopy by working quickly since the material loses CO even in the solid state. 'H NMR (300 MHz, C&, -60 "C): 6 1.18(s, 18H), 1.07 (s, 18H),0.89 (s, 18H), 0.48 (5, 6H), 0.42 (s, 12H), 0.41 (s, 6H), 0.39 (s, 6H), 0.26 (s, 6H). 13C{1H}NMR (75 MHz, C7D8, -60 "C): 6 240.2 (CO, Jw-c = 103 Hz, 14%), 27.30, 26.83, 26.63 (1:l:l for C(CH&), 0.69, -1.21, -1.59, -1.96, -2.54 (2:l:l: 1:l for Si(CH3)z);SiC(CH3)3 not observed. Preparation of W2(0CMe2CF3)e(C0)2 (2). W2(0CMezCF3)6 (25 mg, 0.0221 mmol) was dissolved in 0.6 mL of toluene& in an NMR tube equipped with a J. Young valve. One atmosphere of CO was added with the aid of a calibrated gas manifold at -196 "C. Upon thawing, a reaction is clearly evident based on the observation of a color change from deep burgundy to brownish black. Analysis by NMR spectroscopy shows that the yield of 2 at -20 "C exceeds 95%, but the complex dissociates upon warming. Due to the lability of this complex, analytically pure samples have not been obtained and elemental analysis was not attempted. Crystalline material may be obtained from toluene at -35 "C. This material was used for analysis by IR spectroscopy by working quickly since the material loses CO even in the solid state. 'H NMR (300 MHz, C7D8, -40 "C): 6 1.91, 1.88, 1.34, 1.22, 1.05,0.96 (s, 6H). 13C{'H} NMR (75 MHz, C7D8, -40 "C): 6 217.6 (CO, Jw-c = 110 Hz, 13%). Preparation of W2(0-2,6-Me~CsH3)s(C0)2(3). wz(0-2,6MezCsH3)a (25 mg, 0.0229 mmol) was dissolved in 0.6 mL of toluene-& in an NMR tube equipped with a J. Young valve. Experimental Section One atmosphere of CO was added with the aid of a calibrated All operations were carried out in an inert atmosphere gas manifold. The yield from NMR spectroscopy at -20 "C is (nitrogen) using standard Schlenk and vacuum techniques. -80%. 'H NMR (300 MHz, C7D8, -40 "C): 6 2.36, 2.27, 1.97 Aromatic and aliphatic hydrocarbon solvents were dried and (s, 12H), 7.0-6.4 br m's (18H total). 13C{lH}NMR (75 MHz, distilled from sodium diphenyl ketyl and stored over 4 A C&, -40 "C): 6 228.6 (CO, Jw-c = 124 Hz, 14%). The molecular sieves. The NMR solvent, toluene-&, was degassed 'H remainder (-20%) is mostly [W~(O-2,6-MezC6H3)6(C0)]~. with dry nitrogen and stored over 4 A sieves. The fluoro NMR (300 MHz, C7D8, -40 "C): 6 2.90, 1.85, 1.72, 1.61 (6:12: alcohols were purchased from PCR Chemical Co., distilled, 12:6 for CH3), 7.0-6.5 br m's (18H). 13C{1H)NMR (75 MHz, degassed with dry nitrogen, and dried over 4 A sieves. The CvDa, -40 "C): 6 320.1 (Jw-c = 198, 157 Hz, 26.5% total silanol was purchased from Aldrich Chemical Co., degassed satellite intensity). Crystalline samples of either species have with dry nitrogen, and dried over 4 A sieves. wz(NMe~)6,'~~ not yet been obtained. In this case, it is quite apparent that the reaction proceeds beyond addition of 2 equiv of CO under W2(OSitB~Me~)6,12b and W2(0-2,6-Me~CsH3)6~~~ were prepared according to the literature procedures. Wz(OCMe2CF3)6 was mild conditions: W(CO)6 is observed after 1 day under an atmosphere of CO at room temperature. prepared by the alcoholysis of Wz(NMe2)6in a manner similar to the preparation O f Wz(OSitBfiez)6. In this case, the product Preparation of W2(0C(CF3)2Me)dNMe2)2(4). W2(NMe& is initially isolated as a blackhrown bis(HNMe2) adduct, but (2.20 g, 3.48 mmol) was dissolved in 25 mL of hexanes. The the ammine ligands are liberated upon heating in uacuo (50 fluoro alcohol (4.3 g, 23.6 mmol) was then added to the solution "C, 0.01 Torr). Red powdery Wz(OCMezCF3)6produced in this with a syringe and the reaction stirred for several hours. An manner may be recrystallized from toluene (75 to -34 "C). instantaneous reaction is evident based on the observation of IH and I3C NMR spectra were recorded on a Varian XLa color change to a deep red and red microcrystals of the 300. Infrared spectra were recorded on a Perkin-Elmer 283 sparingly soluble product deposit over the course of the spectrometer working quickly with a Nujol mull between NaCl reaction. At the conclusion the solvent was evaporated in plates. uucuo (23 "C, 0.01 Torr), and 2.49 g of 4 (61% yield) was crystallized from hexanes (65 to -35 "C). The crystalline material was dried in uacuo (23 "C, 2 h, 0.01 Torr) prior t o (11)Budzichowski, T. A.; Chisholm, M. H. Polyhedron 1994, 13, use. IH NMR (300 MHz, C7D8, 23 "C): 6 4.22, 2.47, 1.54 ( 6 : 2035, and references therein. (12) (a) Chisholm, M. H.; Cotton, F. A.; Extine, M.; Stults, B. R. J . 6:12 for anti rotamer), 4.30, 2.34, 2.07, 1.21 (septet, JH-F = Am. Chem. SOC.1976,98,4477. (b) Chisholm, M. H.; Cook, C. M.; 1.5 Hz) (6:6:6:6 for gauche rotamer). I3C{lH} NMR (75 MHz, Huffman, J. C.; Streib, W. E. J . Chem. SOC.,Dalton Trans. 1991,929. C7D8,23 "C): 6 82.36,60.42, 39.37, 19.42 (s, for anti rotamer), (c) Latham, I. A,; Sita, L. R.; Schrock, R. R. Organometallics 1986,5, 82.60, 82.13,60.11,40.04,20.24,19.57 (s forgauche rotamer). 1508.
2324 Organometallics, Vol. 14,No.5, 1995
Budzichowski et al.
Table 6. Summary of Crystallographic Data
W2(0CMe&Fs)s(C0)2. Crystals suitable for study by single-crystal X-ray diffraction were grown by cooling a toluene solution of 2 to -35 "C under an atmosphere of CO for several empirical formula C26H3608F18W2 C23H24hN207W2 days. Working quickly at room temperature, a small wellformula wt 1264.12 1186.24 formed crystal was cleaved from a larger specimen, affixed to color; habit dark brown black the end of a glass fiber with silicone grease, and transferred 0.25 x 0.35 x 0.35 0.12 x 0.12 x 0.28 cryst size (mm) to the goniostat where it was cooled to -172 "C for characspace roup P2dn P1 terization and data collection. A systematic search of a limited a( 1 11.256(4) 14.053(3) hemisphere of reciprocal space located a set of reflections with 18.496(6) 21.148(5) b (A) 17.789(7) 12.789(3) monoclinic symmetry and systematic absences corresponding cA 106.11 (1) a (de@ to the unique space group P21/n. Data were collected using a 97.97( 1) 103.131) P (deg) standard moving crystal, moving detector technique with fixed 86.81( 1) b (deg) background counts at each extreme of the scan. The data were temp ("C) -172 -169 corrected for Lorentz and polarization effects, and equivalent vol(A3) 3668.01 3555.60 data were averaged. The structure was solved by direct 4 4 methods (SHEIX-86) and Fourier techniques. Hydrogen 2.148 2.362 Dcalcd k3/cm3) atoms were not located but were placed in fixed idealized radiation Mo K a (0.710 69) Mo K a (0.710 69) scan range (w, deg) 2.0 plus dispersion 2.0 plus dispersion positions for the final cycles of refinement. 8.0 scan speed (deg/min) 6.0 W Z ( ~ C M ~ ( C F ~ ) ~ ) ~ ( N M ~Crystals ~ ) ~ ( C suitable O ) S . for study 65.336 abs coeff (mm-I) 67.701 by single-crystal X-ray diffraction were grown by cooling a 6-45 28 range (deg) 6-45 toluene solution of 6 t o -35 "C under an atmosphere of CO no. of reflctns collected 5110 11 317 for several days. Working quickly at room temperature, a no. of independent reflctns 4782 [Rjnt = 3.10%) 9325 (Rint = 4.70%) small well-formed crystal was selected under an inert atmono. of obsd reflctns 3946 ( F > 2.33uF) 7677 ( F > 3 . 0 ~ 0 sphere in a glovebag and affixed t o the end of a glass fiber 0.0615 0.0599 R(F) 0.0612 0.0535 with silicone grease. It was then transferred to the goniostat, RW(R goodness of fit 2.346 1.383 where it was cooled to -169 "C for characterization and data 0.015 largest A/u 0.23 collection. A systematic search of a limited hemisphere of reciprocal space revealed no symlretry among the observed "F('H} NMR (340 MHz, C7D8, 23 "C): 6 -78.75 (9, JF-F= 10 intensities. An initial choice of P1 was later proven correct Hz), -79.59 (9, JF-F= 10Hz) (anti rotamer), -78.87 (9, 6F, by the successful solution of the structure. Data were collected JF-F= 9 Hz), -79.04 (s, 12F), -79.96 (9, 6F, JF-F= 9Hz) using a standard moving crystal, moving detector technique (gauche rotamer). with fEed background counts at each extreme of the scan. The Preparation of WZ(~C(CF~)ZM~)~(NM~Z)Z(CO)Z (5). data were corrected for Lorentz and polarization effects, and W2(0C(CF3)2Me)4(NMe2)z(25 mg, 0.0251 mmol) was dissolved equivalent data were averaged. The structure was solved by in 0.6 mL of toluene-& in an NMR tube equipped with a J. initially locating the positions of the tungsten atoms from a Young valve. One atmosphere of CO was added with the aid Patterson map (SHELX-86). The positions of the remaining of a calibrated gas manifold at -196 "C. Upon thawing, a non-hydrogen atoms were obtained from subsequent iterations reaction is clearly evident based on the observation of a color of least-squared refinement and difference Fourier calculachange from deep burgundy to brownish black. The yield from tions. Hydrogen atoms were not located but were placed in NMR spectroscopy at -20 "C exceeds 90%, with the major fixed idealized positions for the final cycles of refinement with contaminant (-10%) being 6. Due to the lability of this thermal parameters fixed at 1plus the thermal parameter of complex, analytically pure samples have not been obtained and the atom t o which they were bonded. All non-hydrogen atoms elemental analysis was not attempted. 'H NMR (300 MHz, were refined anisotropically. There are two molecules of the C7&, -40 "C): 6 4.01, 1.99, 1.47, 1.41 (6:6:6:6). 13C{'H} NMR complex in the asymmetric unit which were labeled A and B (75 MHz, C7D8, -40 "C): 6 208.6 (CO, Jw-c = 123 Hz, 14%). t o facilitate comparison of the metrical parameters. The final Preparation of W ~ ( ~ C ( C F ~ ) Z M ~ ) ~ ( N M ~(6). ~ ) ZIf( C O )difference ~ map was somewhat noisier than usual possibly due the NMR tube equipped with a J. Young valve containing 5 to some disorder and/or thermal motion of the CH3 and CF3 and 1 atm of CO remains at -35 "C for 1week, 6 is produced groups. The largest difference peak was 2.9 elA3 near the in greater than 90% yield by NMR spectroscopy. Crystalline C(17)B methyl group and the deepest hole was -2.0 e/A3. material was obtained by reducing the volume of solvent in uucuo (0 "C, 0.01 Torr), pressurizing with an atmosphere of Acknowledgment. We thank the Department of CO, and cooling to -35 "C for 1week. This material was used Energy, Office of Basic Science, Chemistry Division for for analysis by IR spectroscopy by working quickly since the support of this work. material loses CO even in the solid state. Due to the lability of this complex, analytically pure samples have not yet been obtained and elemental analysis was not attempted. 'H NMR SupplementaryMaterial Available: Complete tables of (300 MHz, C7D8, -20 "c): 6 4.27, 4.07, 3.48, 2.92, 1.54, 1.50, H-atom coordinates, bond distances and angles, and anisotro1.38, 1.25 (3:3:3:3:3:3:3:3). 13C{'H} NMR (75 MHz, C7D8, -20 pic thermal parameters and VERSORT/ORTEP drawings for "C): 6 230.46 (d, CO, Jc-c = 7 Hz, Jw-c = 133 Hz, 14%),211.36 2 and 6 (MSC report numbers 93251 and 94017, respectively) (CO, Jw-c = 131 Hz, 14%), 196.65 (br s, CO, JW-C= 105 Hz, (30 pages). Ordering information is given on any current 14%). IR (Nujol, KBr plates): v(C0) = 2064, 1964, 1875 cm-'. masthead page. Crystal Structure Analyses. Crystal data for 2 and 6 appear in Table 6. OM940743R 2
1
6
