Organometallics 1995, 14, 2799-2805
2799
Mono(pentamethylcyclopentadieny1)thorium Chemistry. Formation and Structural Characterization of a Novel Triflate-Bridged Dimeric Thorium Complex Raymond J. Butcher,la David L. Clark,*Jb Steven K. Grumbine,lc and John G. Watkin*Jc Chemical Science and Technology Division (CST), Los Alamos National Laboratory, Los Alamos, New Mexico 87545 Received January 26, 1995@ Reaction of [(Me3Si)2Nl2Th[N(SiMe3)oiMe2CHz)](1) with 1 equiv of trifluoromethanesulfonic acid (HOTD produces the mono(triflate1 species Th[N(SiMe3)213(0Tf)(2), whereas the reaction of 1 with 2 equiv of HOTf yields both 2 and the tridtriflate) complex Th[N(SiMe3)21(0TD3(3)in approximately equal amounts. Heating a toluene solution of 2 with 1 equiv of Cp*H (Cp* = CsMes) leads to formation of the dimeric triflate-bridged complex I
I
Cp*[(Me3Si)2NlThCu2-OSO2CF3)3Th[N(SiMe3)(SiMe2CH2)lCp* (4). Reaction of 4 with 1 equiv of KN(SiMe3)2 produces the dimeric species { Cp*(TfD)Th[N(SiMe3)(SiMe2CH2)1}2 (5). Compounds 2-5 have been characterized by lH NMR and IR spectroscopy, elemental analysis, and, in the case of 4, by a single-crystal X-ray diffraction study. Compound 4 consists of two mono(pentamethylcyclopentadieny1)thoriummoieties (Th-Cp*centroid = 2.54 and 2.51 joined by means of three bridging triflate ligands. One thorium metal center while the other features a bears a bis(trimethylsily1)amide ligand (Th-N = 2.24(3) cyclometalated amide ligand (Th-N = 2.26(4) Th-C = 2.43(5) A tentative mechanism is proposed for the formation of 4. Crystal data for 4 a t -70 "C: monoclinic space group P21/n, a = 14.073(3) b = 23.242(5) c = 18.101(4) p = 105.70(3)",v = 5699.5 Hi3, dcalcd = 1.806 g ~ m - 2~ = , 4.
A)
A)
A,
A,
A,
Introduction The organometallic chemistry of the early actinide elements has been dominated by complexes containing Cp*& or C p h frameworks (Cp* = q-C5Mes, Cp = q-C5H5, An = Th, U)., Reports of actinide compounds containing mono~yclopentadienyl~ or mono(pentamethyl~yclopentadienyl)~ ancillary ligand sets are considerably less common, with many of these complexes being Abstract published in Advance ACS Abstracts, May 1, 1995. (1)(a) Current address: Department of Chemistry, Howard University, Washington, DC 20059.(b) LANL, Mail Stop G739.( c ) LANL, Mail Stop C346. (2)(a) Marks, T.J. In Comprehensive Organometallic Chemistry; Wilkinson. G.. Stone, F. G. A.. Abel, E. W., Eds.; Pergamon Press: Oxford, England, 1982;Vol. 3,p 211-223. (b) Ephritikhne, M. New J . Chem. 1992,16, 451. (3)See for example: (a) Cramer, R. E.; Bruck, M. A.; Gilje, J. W. Organometallics 1988,7, 1465.(b) Eigenbrot, C.W.; Raymond, K. N. Inorg. Chem. 1982,21,2653.(c) Ernst, R. D.; Kenelly, W. J.; Day, C. S.; Day, V. W.; Marks, T. J. J . Am. Chem. SOC.1979,101, 2656. (d) Bagnall, K. W.; Benetollo, F.; Bombieri, G.; de Paoli, G. J . Chem. SOC., Dalton Trans. 1984,67.(e) Bagnall, K. W.; Beheshti, A.; Heatley, F. J . Less-Common Met. 1978,61,63. (0 Delavaux-Nicot, B.;Ephritikhine, M. J . Organomet. Chem. 1990,399, 77. ( g ) Baudry, D.; Dorion, P.; (h) Baudry, D.; Ephritikhine, M. J . Organohet. Chem. 1988,356,165. Ephritikhine, M. J. Organomet. Chem. 1988,349,123.(i) Domingos, (i) Bagnall, A,; Marques, N.; Pires de Matos, A. Polyhedron 1990,9,69. K.W.; Edwards, J.;Tempest, A. C. J.Chem. SOC.,Dalton Trans. 1978, 295.(k) Bagnall, K. W.; Beheshti, A.; Edwards, J.;Heatley, F.; Tempest, A. C. J . Chem. SOC., Dalton Trans. 1979, 1241. (1) Baudin, C.; Ephritikhine, M. J . Organomet. Chem. 1989,364,C1. (m) Edelman, M. A,; Lappert, M. F.; Atwood, J. L.; Zhang, H. Inorg. Chim. Acta 1987, 139, 185.(n) Bombieri, G.; de Paoli, G.; Del Pra, A.; Bagnall, K. W. Inorg. Nucl. Chem. Lett. 1978,14,359.(0)Cramer, R. E.; Mori, A. L.; Maynard, R. B.; Gilje, J. W.; Tatsumi, K.; Nakamura, A. J. A m . Chem. Soc. 1984,106,5920.(p) Brianese, N.;Casellato, U.; Ossola, F.; Porchia, M.; Rossetto, G.; Zanella, P.; Graziani, R. J . Organomet. Chem. 1989, 365,223. (9) Rebizant, J.; Spirlet, M. R.; Apostolidis, A,; Kanellakopulos, B. Acta Cryst. 1992,48C, 452.
A).
A,
Lewis-base adducts of the CpAnX3 moiety (X= halide). The steric and electronic unsaturation of the monocyclopentadienyl actinide framework, relative to the Cp*2An or Cp& systems, makes it an attractive synthetic goal. Halide metathesis routes such as those shown in eqs 1-3 have been used to introduce a single q-CsMe5 or the related q-CsMe4Et ligand into the coordination sphere of an early actinide element.4a-c We report here an alternative synthetic route t o this most interesting class of compounds.
@
Q276-7333/95/2314-2799$09.Q~IQ
ThCl,(dma),
+ Li(C,Me,Et)
-
+ LiCl
(q-C,Me,Et)ThCl,(dma),
(1)
dma = MeCONMe, ThC1,
+ (C,Me,)MgCl.THF
-
+
(q-C5Me5)ThC13(THF), MgC1, (2)
+ (C,Me,)MgCl.THF (T~C,M~~)(~-C,H,)T~C~(THF), + MgC1, (3)
(rpC,H,)ThCl,(THF),
(4) (a) Mintz, E. A,; Moloy, K. G.; Marks, T. 3. J.Am. Chem. SOC. 1982,104,4692. (b) Gilbert, T. M.; Ryan, R. R.; Sattelberger, A. P. Organometallics 1989,8,857. (c) Bagnall, K. W.; Beheshti, A.; Heatley, F.; Tempest, A. C. J . Less-Common Met. 1979,64,267.(d) Schake, A. R.; Avens, L. R.; Burns, C. J.; Clark, D. L.; Sattelberger, A.P.; Smith, (e) Berthet, J. C.; Le Marechal, W. H. Organometallics 1993,12,1497. J. F.; Ephritikhine, M. J . Organomet. Chem. 1990, 393, '247. (0 Cymbaluk, T. H.; Ernst, R. D.; Day, V. W. Organometallics 1983,2, 963.(g) Ryan, R. R.; Salazar, K. V.; Sauer, N. N.; Ritchey, J. M. Inorg. Chim. Acta 1989,162, 221.
0 1995 American Chemical Society
2800 Organometallics, Vol. 14,No. 6, 1995
Butcher et al. Table 1. Summary of Crystallographic Data for Cp*[(Me&i)mTh@2-OS02CF3)3-
Results and Discussion Synthesis and Reactivity. Treatment of a hexane
~ [ N ( S i M e s ) ( S i M e z ~ H ~ ) l CC& p * (4)
r
solution of the thorium metallacycle [(MesSi)zNIzTh-
empirical formula color, habit cryst dimens, mm3 space group cell dimens a,A b, A
[NO(SiMezjCH2)l5 (1) with 1 equiv of a diethyl ether solution of trifluoromethanesulfonic acid (HOM at -40 "C resulted in the formation of the mono-triflate species Th[N(SiMe&I3(OTf)(21, which was isolated as a white crystalline solid in 55% yield as indicated in eq 4. Microanalytical data are consistent with the pro-
c,
vol, A3
H H
2 (molecules/cell)
1: C
\si
(Me3Si)2Ntt,,,,,, Th/ (Me3Si)2N0
\
A
A deg
.,%\\\
Me
' 'Me
fw Dcalcd, g c m 3 abs coeff, cm-l
1 HOTf
1(Mo Ka)
N
temp, "C 20 range, deg measd reflns unique intensities obsd reflns
Si Me3
OTf
R(FY RW(Flb goodness-of-fit
C~~HIXF~N~O~S~S~~T~Z colorless needle 0.30 x 0.10 x 0.08 P2l/n 14.073(3) 23.242(5) 18.101(4) 105.70(3) 5699.5 4 1549.6 1.806 54.83 0.710 73 -70 2.0-50.0 10 737 10 027 4902 (F > 3.0dF)) 0.0500 0.0651 1.95
a R(F)= XIIF01 - FcIlEIFo. RJF) = [X,~(lFol - IFcl)2E~lF~121"2; w = l/u2(lFol).
2
r
thorium complex Cp*[(Me3Si)zNlTh@z-OSO2CF&Th-
H H \ p
Si Me3
OTf
OTf
2
3
[ N O ( S i M e z t ) H z ) l C p *(4) as a white crystalline solid in 42% yield (eq 6). The lH NMR spectrum of 4 shows two Cp* resonances and a number of resonances between 0.12-1.39 ppm in a 9:3:3:1:1 ratio consistent with cyclometalation of one bis(trimethylsily1)amide ligand. The infrared spectrum shows vibrational features at 1332,1237, and 1219 cm-l, consistent with the presence of bridging OTf ligands.6 A single-crystal X-ray diffiaction study (vide infra) confirmed that one silylamide ligand had been activated to form a four-membered metallacyclic ring, as shown schematically in eq 6.
2
posed stoichiometry of 2. Use of 2 equiv of HOTf in an analogous reaction produces a mixture of the monotriflate complex (2) and the tris-triflate complex Th[N(SiMe&](OTf)3(3). The relative insolubility of 3 in common solvents results in straightforward separation of the two complexes, which may be isolated in 42% and 36% yields for 2 and 3, respectively (eq 5). Although some spectroscopic evidence exists for the transient formation of the expected bis-triflate product Th[N(SiMe&12(OTf)z,it appears that this species undergoes rapid ligand redistribution to form the isolated reaction products 2 and 3. Initial attempts to form mono(pentamethylcyc1opentadienyllthorium complexes through metathesis of 2 or 3 with KCp* were unsuccessful. Additionally, the reaction of metallacycle 1 with 1equiv of Cp*H was also unsuccessful, showing no reaction after heating at 110 "C in toluene for 3 days. However, reaction of Th[N(SiMe3)213(0Tf)(2) with Cp*H in a refluxing toluene solution for 8 days allows the isolation of a dinuclear (5) (a) Simpson, S. J.;Turner, H. W.; Andersen, R. A. J.Am. Chem. SOC.1979,101,7728. (b) Simpson, S. J.;Turner, H. W.; Andersen, R. A. Inorg. Chem. 1981,20, 2991.(c) Dormond, A,; El Bouadili, A. A,; Aaliti, A.; MoYse C. J . Orgunomet. Chem. 1986,288, C1.
2
Compound 4 reacts with 1 equiv of KN(SiMe& in a toluenePTHF solution to produce { Cp*(TfD)Th[N(SiMes)S C H 2 ) l ) z (5) in 50% yield (eq 7). The 'H NMR spectrum of 5 shows a single Cp* resonance, together with the distinctive pattern of resonances in a 9:3:3:2 ratio consistent with the presence of cyclometalated bis(trimethylsily1)amide ligands (we believe that the two (6) Lawrance, G. A. Chem. Rev. 1986,86, 17
Mono(pentamethylcyclopentadieny1)thorium Chemistry
diastereotopic Si-CHZ-Th methylene protons within the metallacycle are coincidentally overlapping). Infrared absorption bands at l324,1306,1258,.and 1240 cm-l in the solid-state IR spectrum of 5 suggest the presence of a bidentate triflate ligand.6 The dimeric structure shown in eq 7 is proposed on the basis of IR data, the comparable solubilities of 4 and 5, the expected steric unsaturation of a monomeric species, and the results of a solution molecular weight determination which found the degree of oligomerization in solution to be 2.3 (found 1555; calcd 676, for monomeric Cp*-
-
(TfO)Th[N(SiMe3)(SiMe2CH2)3). The two Cp* ligands in 5 are shown in a cis-orientation by analogy with that observed in the solid-state structure of 4 (vide infia).
+ Me'
Si, Me
KN(SiMe3),
toluene -KOTf -HN(SiMe$Z
0 CF3
4
Me
5
Organometallics, Vol. 14,No.6,1995 2801
Table 2. Selected Atomic Coordinates and Equivalent Isotropic Displacement Coefficients for Cp*[Me3Si)zN1Th(lc2-OS02CF3)3-
-
~[N(S~M~S)(S~M~ZCHZ)ICP* C7HS (4) 1920.6(1) -1140.2(1) -882(7) 344(7) 1348(7) 1925(10) 995(9) -3511(8) -2869(9) 134(22) -1087(20) - 1404(21) 832(21) -337(17) 936(2 1) 1591(19) 349(19) 2058(21) 1631(24) -2694(27) 2223(34) -2717(30) 3810(28) 4000(33) 3674(29) 3305(35) 3395(32) -325(32) - 1334(31) -1614(26) -784(27) 3(29)
786.8(6) 2395.7(6) 809(4) 2097(4) 1828(4) -535(5) -219(5) 2108(5) 2013(5) 682( 11) 1325(12) 744(13) 15455(11) 2249(10) 2545( 12) 1494(11) 2063(11) 2226(12) -5815) 2187(12) lO(21) 2296(21) 1202(15) 708(19) 819(17) 1369(20) 1623(18) 3357(17) 3486(17) 3551(15) 3491(15) 3384(16)
3103(8) 3483.3(8) 3005(5) 2017(6) 4666(5) 3235(8) 1517(8) 2602(7) 4383(6) 3213( 14) 3341(17) 2251(17) 22438(15) 2474(15) 1900(16) 4093(15) 4397(13) 5084(15) 2476(19) 3518(19) 4032(26) 1956(21) 3808(21) 345(25) 2670(22) 2526(26) 3259(24) 4318(24) 4053(23) 3284(20) 3013(20) 3661(22)
481(5) 430(4) 480(33) 488(34) 464(33) 656(51) 612(46) 525(41) 560(43) 604(111 658(119 706(120 604(109 494(91) 645(112) 576(101) 524(98) 625(113) 600(135) 605(136) 776(200) 692(172) 478(87) 645(111) 537(91) 704(121) 615(106) 597(104) 58(10) 439(82) 439(82) 519(92)
Table 3. Selected Bond Distances (A) and Angles (deg) for C ~ * [ M ~ ~ S ~ ) Z N ~ T ~ ( ~ ~ Z - O S O ~
-
~h[N(SiMe3)(SiMe2~Hz)]Cp* C7& (4) Solid-state and Molecular Structure. Crystals of Th( 1)-0(1) 2.59(3) Th(2)-0(2) 2.50(3) 4 suitable for an X-ray diffraction study were grown by 'Th( 1)-O(4) 2.57(3) Th(2)-0(5) 2.42(3) Th(l)-0(7) 2.57(3) Th(2)-0(8) 2.42(2) cooling a concentrated toluene solution t o -40 "C, and Th( 1)-N( 1) 2.24(3) Th(2)-N(2) 2.26(4) the structure was determined from diffraction data Th(l)-Cp* (cent) 2.51(4) 2.54(4) Th(2)-Cp* (cent) collected at -70 "C. A summary of data collection and Th(l)-Cp* (av) 2.80(4) Th(2)-Cp* (av) 2.77(4) crystallographic parameters is given in Table 1. SeTh( 1)-C(4) 2.43(5) Th(S)-C(lO) 3.05(3) lected fractional coordinates are given in Table 2, and selected bond lengths and angles are given in Table 3. N(l)-Th(l)-C(4) 71.1(14) N(2)-Th(2)-C(10) 62.4(12) A ball-and-stick drawing giving the atom-numbering Th(l)-C(4)-Si(l) 90.5(18) Th(2)-C(lO)-Si(3) 82.1(12) Th(l)-N(l)-Si(l) 100.9(15) Th(2)-N(2)-Si(3) 112.9(20) scheme used in the tables is shown in Figure 1. The N(l)-Si(l)-C(4) 97.6(19) N(2)-Si(3)-C(10) 102.5(18) overall molecular structure of 4 consists of two mono(pentamethylcyclopentadieny1)thorium units joined by This may be due to the fact that Th(1) is more sterically means of three bridging triflate ligands. One thorium encumbered (formally six-coordinate) than Th(2) (formetal center bears a bis(trimethylsily1)amide ligand mally five-coordinate). A number of structurally charwhile the other features a cyclometalated amide ligand. acterized complexes have been found to contain bridging The Th-centroid distances compare favorably to those triflate ligands, although these have been predomiobserved in other examples of mono(pentamethylcyc1onantly in late transition metal complexes containing pentadieny1)thorium complexes. For example, the ThCu,' Hg,8and Ag.9 Structurally characterized examples ($*centroid distances of 2.54 and 2.51 A are very similar of metal centers bridged by two triflate ligands appear to those of 2.54 A seen in both Cp*Th(q-CsHs)ClzMg(tto be limited to the complexes { [Cp*Re(NO)(PPhs)l@while the Bu)(THF)~~ and Cp*Th(q-CsH~)[CH(SiMe3)21,4~ C ~ H ~ ~ Z ~ ~ R ~ ~ C and ~ [(q~ ~ average Th-C distances of 2.80 and 2.77 A are consisThe structure of 4 in which ~ H ~ ) C5H5)2Yb@-03SCF3)12.11 ~.~~ tent with that of 2.79 A seen in C ~ * T ~ ( C H Z C To the best of our knowledge, the three structures refer(7) See for example (a)Dedert, P. L.; Sorrell, T.; Marks, T. J.; Ibers, enced here represent the only previously reported J. A. Znorg. Chem. 1982,21, 3506. (b) Ferrara, J. D.; Tessier-Youngs, examples of structurally characterized mono(pentamC.; Youngs, W. J. Inorg. Chem. 1988,27,2201. ethylcyclopentadieny1)thorium complexes. (8) Balch, A. L.; Olmstead, M. M.; Rowley, S. P. Inorg. Chem. 1988, 27,2275. The bonding of the triflate ligands to thorium is (9)(a) Arif, A. M.; Richmond, T. G. J. Chem. SOC.,Chem. Commun. somewhat asymmetric with average Th-0 bond lengths 1990,871. (b) Gleiter, R.; Karcher, M.; Kratz, D.; Zeigler, M. L.; Nuber, B. Chem. Ber. 1990, 123, 1461. of 2.57(3) and 2.45(3)8, t o Th(1) and Th(2), respectively.
~ P
2802 Organometallics, Vol. 14, No. 6, 1995
Butcher et al.
Figure 1. A ball and stick drawing of the solid-state structure of Cp*[(Me3Si)zNlTh@z-OSO2CF3)3Th[N(SiMe& (SiMezCHz)]Cp*(4) giving the atom-numbering scheme used in the tables. three triflate groups bridge two metal centers is only the second documented example of this structural motif.12 Furthermore, 4 appears to be the first crystallographically characterized example of an actinide triflate complex, with no other structures of these types being located in the Cambridge Structural Database. The Th-N distances of 2.24(3) and 2.26(4) A can be compared with the average Th-N distances of 2.34(1) A in (r-CsHs)Th[N(SiMe3)212,13a 2.32(2) A in (r3-BH4)Th[N(SiMe3)213,13band 2.31(1) A in Th[N(SiMe3)212( N M e p h ) ~ .The ~ ~ ~Th-C distance of 2.43(5) has a relatively large error associated with it but can be compared with the average Th-C distances of 2.58(1) A in Cp*Th(CH2CsH5)3,4"2.55(2)A in Th(CHzCsH&(MezPCH2CHzPMe2),14"2.51(2)A in [MezSi(Me4C&ITh(CH2The S i M e 3 ) ~ ,and l ~ ~2.49(1)A in [Cp*2Th(Me)(THF)z1+.l4" close contact of Th(2) to the methyl carbon of the trimethylsilyl group (Th(2)-C(10) = 3.05(3) A) is a further example of the y-agostic or /3-methyl interaction which is frequently observed in actinide and lanthanide structures containing bis(trimethylsily1)amide or bis(trimethylsilyllmethyl l i g a n d ~ . ~ ~ J ~ " J ~ (10)OConnor, J . M.; Uhrhammer, R.; Rheingold, A. L.; Staley, D. L. J . Am. Chem. SOC.1989,111, 7633. (11)Stehr, J.; Fischer, R. D. J . Organomet. Chem. 1992,430,C1. (12) Frankland, A. D.; Hitchcock, P. B.; Lappert, M. F.; Lawless, G. A. J. Chem. SOC.,Chem. Commun. 1994,2435. (13)(a) Gilbert, T. M.; Ryan, R. R.; Sattelberger, A. P. Organometallics 1988,7 , 2514. (b) Turner, H. W.; Andersen, R. A.; Zalkin, A,; Templeton, D. H. Inorg. Chem. 1979,18, 1221.(c) Barnhart, D. M.; Clark, D. L.; Grumbine, S. K.; Watkin, J. G. Inorg. Chem. 1996,34, 1695. (14)(a) Edwards, P.G.; Andersen, R. A.; Zalkin, A. Organometallics 1984,3,293.(b) Fendrick, C. M.; Mintz, E. A.; Schertz, L. D.; Marks, (c) Lin, 2.; Marechal, J.-L. L.; Sabat, T. J. Organometallics 1984,3,819. M.; Marks, T. J. J . Am. Chem. SOC.1987,109,4127. (15)(a) Tilley, T. D.; Andersen, R. A.; Zalkin, A. Inorg. Chem. 1984, 23,2271.(b) den Haan, K. H.; de Boer, J . L.; Teuben, J. H.; Spek, A. L.; Kojic-Prodic, B.; Hays, G. R.; Hues, R. Organometallics 1986,5, 1726.( c ) Schaverien, C. J.; Nesbitt, G. J. J . Chem. Soc., Dalton Trans. 1992,157.(d) Heeres, H. J.; Meetsma, A.; Teuben, J. H. J . Chem. SOC., Chem. Commun. 1988,962.(e) Tilley, T.D.; Andersen, R. A,; Zalkin, A. J . A m . Chem. SOC.1982, 104, 3725. (0 Jeske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann, H.; Marks, T. J . J . A m . Chem. SOC.1985,107,8091.(g) Clark, D. L.; Miller, M. M.; Watkin, J. G. Inorg. Chem. 1993,32, 772. (h) Barnhart, D. M.; Clark, D. L.; Gordon, J. C.; Huffman, J. C.; Watkin, J.G.; Zwick, B. D. J . Am. Chem. SOC. 1993, 115, 8461. (i) Van Der Sluys, W. G.; Burns, C. J.; Sattelberger, A. P. Organometallics 1989,8 , 855.
Discussion We were intrigued by the process in which the dinuclear species 4 is formed during the reaction between Th[N(SiMe3)213(0Tf)(2) and Cp*H, and therefore performed some additional experiments to probe the possible mechanistic pathway depicted in Scheme 1. The first step in the proposed mechanism is the cyclometalation of a bis(trimethylsily1)amide ligand in the mono(triflatel2 to produce the metallacyclic complex
-
[(M~~S~)ZNI(T~~)T~[N(S~M~~)(SIM~~CH~)I. Precedence for this type of reaction has been observed during the thermolysis of the closely related actinide mono(ary1oxide) complexes An[N(SiMes)zl3(OAr)(Ar = 2,6-t-BuzC&, An = Th, U)which lead to silylamide ligand activation and subsequent formation of a new metallacycle of formula (ArO)[(Me3Si)2N~[N(SiMe3)(SiMe2CH2)l.16 In an attempt to verify this initial step in the reaction scheme, complex 2 was heated in toluene for 7 days (100 "0, but only the starting complex and a small amount of an unidentified product were observed. This may indicate either that the first step in our preliminary mechanism is reversible or that it involves direct protonation of the Th-N bond by Cp*H to give the product of steps 1and 2 directly. Although an example of direct protonation of the metal-nitrogen bond in Zr(NEt214 and Hf(NMezI4by a substituted cyclopentadiene has been reported very recently,17 we feel that the significantly higher pKa of Cp*H compared with monosubstituted C5H5SiMe2X (X = NHPh, C5H5) makes a two-step pathway (metallacycle formation followed by Th-C protonation) more likely in the present case. The protonation reaction of the metallacyclic species
[(MesSi)2NI(TfO)~h[N(SiMes)(SiMe2~Hz)l with Cp*H to produce Cp*Th[N(SiMe3)212(0Tf)in the second step is favored based upon relative pKa values, although a pathway involving a a-bond metathesis process is (16)Berg, J. M.; Clark, D. L.; Huffman, J. C.; Morris, D. E.; Sattelberger, A. P.; Streib, W. E.; Van der Sluys, W. G.; Watkin, J. G.
J. A m Chem. SOC. 1992,114,10811. (17)Herrmann, W. A,; Morawietz, M. J. A,; Priermeier, T. Angew. Chem., Int. Ed. Engl. 1994,33,1946.
Mono(pentamethylcyclopentadieny1)thorium Chemistry
Organometallics, Vol. 14, No. 6, 1995 2803
Scheme 1
s
(Me3 i)2N\Th,oTf
(Me,Si),N\
A
I \ (Me3Si)zN N( SiMe3)z
-HN(SiMe3)2
2
*
,OTf Th
Me3SiN,s /
i/cH2 \
Me2
1
A -HN(SiMe3)2
“HOTP‘
+
’ N(SiMe&
incorporation of ‘12 equiv of triflic acid into 5 in order to facilitate the protonation of one metallacycle to an Si)2Nlz~h[N(SiMes)(SiMezCH2)1(1) has been shown to amide ligand and the concomitant introduction of the be unreactive toward Cp*H after 3 days at 110 “C (vide third bridging triflate ligand. We do indeed find that r when 5 is allowed t o react with l/2 equiv of triflic acid supra), the reduced steric bulk of [(MesSi)zNI(TfO)That -40 “C in toluene, the major product isolated is [N(SiMes)(SiMezCHdI compared with metallacycle 1 complex 4. The actual source of the triflic acid in the may allow the reaction to proceed more readily in this formation of 4 from Th[N(SiMe&]s(OTf)(2) and Cp*H case. is uncertain, but it could be a result of a small equilibAs mentioned above, the metallacycle formation prorium concentration of triflic acid arising from the posed in step 3 has precedence in the literature,16 and reverse of the reaction shown in eq 4. This postulate subsequent dimerization to form the independently was investigated by heating (NMR tube, 85 “ C , 18 h) synthesized complex ( C ~ * ( ~ ~ [ N ( S ~ M ~ ~ X S ~ M ~ complexes ~ C H ~ ) I2}and Z 5 together in benzene-de and observing in the lH NMR spectrum the formation of complexes 1 ( 5 ) seems logical based upon steric requirements. The and 4. last step in our proposed mechanism requires the formal perhaps more likely. Despite the fact that [(MesI
-
2804 Organometallics, Vol. 14, No. 6, 1995
Concluding Remarks
Butcher et al. Th[N(SiMe&l(OTf)s( 3 ) . A 50 mL hexane solution of the
metallacycle [(Me3Si)sNlz~h[N(SiMe3)(SiMez~H~)l(l) (3.00 g, 4.21 mmol) was cooled to -40 "C in the drybox. To this solution was added with stirring a cold (-40 "C) trifluoromethanesulfonic acid (1.29 g, 8.61 mmol) and diethyl ether (5 mL) solution over a 1 min period, resulting in a large amount of precipitation. The mixture was allowed to stir for 1 h, and the resulting white precipitate was isolated by vacuum filtration, washed with toluene (5 mL), and dried in vacuo to yield 1.30 g of 3 (36%). The precipitate is insoluble in toluene, diethyl ether, and methylene chloride. After concentrating and cooling the filtrate to -40 "C, 1.47 g of 2 was also isolated. IR (Nujol, cm-I): 1339 (m br), 7(42%) 1208 ( s br), 1036 (s), 846 (w), 641 (m). Anal. Calcd for complex C~*[(M~~S~)~N]T~(~~-OSO~CF~)~T~[N(SIM~~)CgHleF9NO&SizTh: C, 12.87; H, 2.16; N, 1.67. Found: C, (SiMezCHz)lCp* (41, formed from reaction of 2 with 12.66; H, 2.16; N, 1.17.
We have shown that the reaction of an actinide amide complex, such as Th[N(SiMe3)213(0Tf)(21, with Cp*H can provide an alternative t o the traditional halide metathesis routes to mono(pentamethylcyc1opentadienyllactinide species. As reported recently for the Group IV metals,17 this synthetic method can offer distinct advantages over halide metathesis procedures, most notably by eliminating the problem of salt retention by the actinide product.4b The X-ray crystal structure of the dinuclear actinide
Cp*H, has been determined and reveals an unusual molecular geometry in which three v2-triflate ligands bridge the two thorium metal centers. We have proposed a mechanism to explain the formation of 4 and have shown that several of the proposed mechanistic steps may be verified in independent reactions. Further studies of the reactivity and catalytic properties of mono-Cp* thorium complexes with alkoxide and alkyl supporting ligands are currently underway.
Cp*[(Me~i)zN1Th~~OsozCF~~~~~~SiMe~~~S Cp* (4). In a Schlenk reaction vessel, toluene (40 mL), pentamethylcyclopentadiene (0.46 g, 3.2 mmol), and 2 (2.40 g, 2.78 mmol) were combined and refluxed under argon for 8 days. All volatiles were removed in vacuo and the residue was extracted with hexane (3 x 10 mL), leaving a white microcrystalline powder (0.73 g). Upon cooling the solution to -40 "C more microcrystalline powder formed. Total yield: 0.94 g (43%). 'H NMR (300 MHz, C6D6,22 "C): 6 0.12 (s, 9 H, SiMes), 0.16 ( s , 9 H, SiMes), 0.36 ( s , 9 H, SiMes), 0.53 ( s , 3 H, SiMe), 0.54 (s, 3 H, SiMe), 1.34 ( s , 1 H, ThCHz), 1.39 (s, 1H, ThCHd, Experimental Section 2.08 ( s , 15 H, CbMes), 2.35 ( s , 15 H, C5Me5). IR (Nujol, cm-'): 1332 (m), 1237 ( s ) , 1219 (s), 1196 (m), 1183 (m), 1142 (w), 1030 General Procedures and Techniques. All manipula(SI, 1014 (SI, 964 (m), 857 (m), 831 (m), 802 (w), 772 (w), 759 tions were carried out under an inert atmosphere of oxygen(w), 727 (w), 693 (w), 640 (m), 629 ( ~ 1 , 6 0 (w), 1 506 (w). Anal. free UHP grade argon using standard Schlenk techniques Calcd for C35H65F9N20gS3Si4Th~0.5C7H8: C, 29.88; H, 4.49; or under oxygen-free helium in a Vacuum Atmospheres I N, 1.81. Found: C, 29.74; H, 4.29; N, 1.45. glovebox. The metallacyclic complex [(MesSi)nN]zTh[N{Cp*(TfO)Th[N(SiMe3)(SiMezCH2)l)z (5). A toluene so(SiMe3)(SiMezCHz)l (1) was prepared as described previlution (5 mL) of KN(SiMe& (0.079 g, 0.40 mmol) was added o ~ s l y . ~Trifluoromethanesulfonic ~'~ acid and pentamethylcyto a toluene(20 mL)/THF(5 mL) solution of 4 (0.63 g, 0.40 clopentadiene were obtained from Aldrich and degassed prior mmol), and the solution was stirred for 4 h. All volatiles to use. Solvents were degassed and distilled from Na or N d were removed under vacuum, and the solid was extracted with benzophenone ketyl under nitrogen. Benzene-d6 was dried toluene (2 x 10 mL) and filtered through Celite. Upon cooling with Nahenzophenone ketyl and then trap-to-trap distilled to -40 "C, a white powder was deposited (65 mg). The filtrate before use. Solvents were taken into the glovebox, and small was pumped dry and washed with hexane, leaving a second amounts were tested with a solution of sodium benzophenone crop of the white powder. Total yield: 0.28 g (50%). 'H NMR in THF. Solvents that failed to maintain a purple coloration (300 MHz, C6&, 22 "C) 6 0.29 (s, 3 H, SiMe), 0.34 (s, 9 H, from this test were not used. SiMes), 0.40 ( s , 3 H, SiMe), 0.58 ( s , 2 H, ThCHz), 2.32 ( s , 15 NMR spectra were recorded at 22 "C on a Bruker WM 300 H, C5Me5). IR (Nujol, cm-I): 1324 (w), 1306 ( s ) ,1258 (s), 1240 spectrometer in benzene-ds solution. All 'H NMR chemical (s), 1201 (m), 964 (w), 857 (m), 828 (m), 804 (w), 770 (w), shifts are reported in ppm relative to the 'H impurity in 634 (s), 625 ( s ) , 602 ( s ) , 548 (w), 515 (w). Anal. Calcd for benzene-ds set a t 6 7.15. Infrared spectra were recorded as C ~ ~ H ~ Z F ~ N O C, ~ S30.22; S ~ ~H, T~ 4.77; : N, 2.07. Found: C, Nujol mulls or hexane solutions (KBr)on a Perkin-Elmer 1500 30.59; H, 4.42; N, 1.42. spectrophotometer interfaced with a 1502 central processor. Crystallographic Studies. Cp*[(MesSi)zN]Th(pzElemental analyses were performed on a Perkin-Elmer 2400 I 1 CHN analyzer. Elemental analysis samples were prepared OSOzCF3)3Th[N(SiMe3)(SiMe2CH2)lCp** C,Hs (4). The and sealed in tin capsules in the glovebox prior to combustion. clear, well-formed crystals were examined in mineral oil under Th[N(SiMe3)213(OTO(2). A 50 mL hexane solution of an argon stream. A suitable crystal measuring 0.30 x 0.10 x 0.083 mm3 was affixed to the end of a glass fiber using Apiezon [(Me3Si)zNl~~h[N(SiMe3)(SiMez~Hz)1(4.00 g, 5.62 mmol) was grease. The crystal was then transferred to the goniostat of cooled to -40 "C in the drybox. To this solution was added an Enraf-Nonius CAD4 diffractometer and cooled t o -70 "C with stirring a cold (-40 "C) trifluoromethanesulfonic acid for characterization and data collection. Unit cell parameters (0.76 g, 5.1 mmol) and diethyl ether (10 mL) solution over a 5 were determined from the least-squares refinement of (sin 0/,1)2 min period, resulting in a small amount of precipitation. The values for 25 accurately centered reflections with a 20 range mixture was stirred for 14 h, and the solvent was removed in between 16" and 32". Three reflections were chosen as vacuo. The resulting white solid was extracted into hexane intensity standards and were measured every 3600 s of X-ray (60 mL), filtered through Celite, and cooled t o -40 "C. After exposure time. 18 h, a crop of colorless crystals had formed, which were The data were reduced using the Structure Determination isolated by vacuum filtration inside the glovebox. Yield: 2.66 Package provided by Enraf-Nonius, and corrected for absorpg (55%). 'H NMR (300 MHz, C6D6, 22 "C): 6 0.36 (s, 54 H, tion empirically using the high-X pscans. All data were SiMe3). IR (hexane, cm-'1: 1367 (m), 1256 ( s ) ,1238 (m), 1200 corrected for Lorentz and polarization effects, and equivalent (s), 1162 (m), 972 (m), 917 ( s ) , 896 (m sh), 852 ( s ) , 772 (m), data were averaged to a unique set of intensities and associ656 (w),633 (m), 613 (m). Anal. Calcd for C19H54F3N303SSi6ated ds in the usual manner. The structure was solved by Th: C, 26.47; H, 6.31; N, 4.87. Found: C, 26.53; H, 6.01; N, Patterson and Fourier techniques and refined by full matrix 4.82.
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Organometallics,Vol. 14,No.6, 1995 2805
Mono(pentamethylcyclopentadieny1)thorium Chemistry least squares. All non-hydrogen atoms were treated anisotropically except for the ring carbons of the pentamethylcyclopentadienyl ligands and the toluene of crystallization ((236C39). All hydrogen atoms were placed in fixed, idealized positions in the final cycle of refinement. A final difference Fourier contained some residual electron density around the thorium, the largest peak being 2.58 el@. All data solution calculations were performed using the Siemens SHELXTL PLUS computing package (Siemens Analytical X-ray Instruments, Inc, Madison, WI, 1990).
Acknowledgment. This work was performed under the auspices of the Laboratory Directed Research and Development Program. Los Alamos National Labora-
tory is operated by the University of California for the U.S.Department of Energy under Contract W-7405-
ENG-36. SupplementaryMaterial Available: Tables of fractional atomic coordinates, bond lengths and angles, anisotropic thermal parameters, hydrogen atom coordinates, and an I
ORTEP drawing for C~*[(M~~S~)~N]T~(,U~-OSO~CF~)~ (SiMe3)(SiMez~Hz)lCp* * C7Hs (4) (11pages). Ordering information is given on any current masthead page. Structure factor tables are available from the authors upon request. OM950072C
